Image forming device

Abstract

To cause air taken in from an air supply duct to pass for each of discharge wires in a corona charger, while effectively discharge ozone.SOLUTION: An air supply duct 224 is formed with a center partition wall part 253 that partitions the inside of the air supply duct 224 into a first air channel 251 for passing air toward a first discharge wire 2221 and a second air channel 252 for passing air toward a second discharge wire 2222. An opening 270 is formed between the center partition wall part 253 and a center partition plate 2215, a first center shield plate 2212, and a second center shield plate 2214, but the opening 270 is closed by an elastic sheet 259. The elastic sheet 259 closes the opening 270 to prevent the generation of airflow from the second air channel 252 to the first air channel 251, thereby preventing a relative reduction in the volume of air flowing in the second air channel 252. Thus, even if air flows to a corner area of the second air channel 252, ozone can be effectively discharged.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus using electrophotographic technology, such as a printer, a copying machine, a facsimile machine, or a multifunction machine. [Background technology]

[0002] Electrophotographic image forming apparatuses use corona chargers to uniformly charge the surface of a photosensitive drum. The corona charger is positioned away from the surface of the photosensitive drum, with a gap between them, and the photosensitive drum is charged by ions generated by the corona charger. When a corona charger is used, corona discharge can generate discharge products such as ozone, which can corrode the discharge wire, grid electrode plate, and other components. Therefore, an air intake duct is provided in the corona charger, forming an air flow path leading from the air intake duct to the corona charger, allowing ozone to be discharged from the corona charger (see Patent Document 1). The ozone discharged from the corona charger is exhausted to the outside through a suction duct located downstream of the corona charger in the direction of rotation of the photosensitive drum. The device described in Patent Document 1, which relates to a corona charger with multiple discharge wires, includes a rectifying member in the air intake duct to form an air path (referred to as a second air path) that supplies clean air to the discharge wire side farther from the suction duct. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-91327 Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional device described in Patent Document 1, a straightening member is disposed with a gap between it and the corona charger to form an air passage (called a first air passage) in the air supply duct that supplies air to the discharge wire side closer to the suction duct. However, because air flows from the second air passage to the first air passage through the gap between the straightening member and the corona charger, the volume of air flowing through the second air passage is relatively small. This makes it difficult for air to flow through the second air passage, particularly toward the upstream corners, which can lead to ineffective ozone discharge.

[0005] To provide an image forming apparatus capable of passing air through a corona charger so as to effectively discharge ozone when air taken in from an air supply duct is divided and passed through each discharge wire in the corona charger. [Means for solving the problem]

[0006] An image forming apparatus according to one embodiment of the present invention is an image forming apparatus including: a rotating photosensitive drum; a corona charger disposed with a gap from the surface of the photosensitive drum and charging the surface of the photosensitive drum; an air intake duct that supplies air from the opposite side of the photosensitive drum, passes it through the corona charger, and discharges it toward the photosensitive drum; and an exhaust duct that is disposed downstream of the corona charger in the rotation direction of the photosensitive drum and exhausts air that is discharged from the corona charger and flows along the photosensitive drum, wherein the corona charger includes, in the rotation direction, a first discharge wire that charges the surface of the photosensitive drum; a second discharge wire that is upstream of the first discharge wire and charges the surface of the photosensitive drum; a first shield plate disposed downstream of the first discharge wire; a second shield plate disposed upstream of the second discharge wire; and a shield plate that is disposed downstream of the first discharge wire. and a central shield portion arranged to separate the first discharge wire and the second discharge wire, and holding portions at both ends of the photosensitive drum in the direction of the rotation axis that hold the first discharge wire, the second discharge wire, the first shield plate, the second shield plate, and the central shield portion, wherein the air intake duct has a first wall portion connected to the first shield plate, a second wall portion connected to the second shield plate, and a central partition portion formed between the first wall portion and the second wall portion in the direction of the rotation axis and dividing the inside of the air intake duct into a first air passage for passing air toward the first discharge wire side and a second air passage for passing air toward the second discharge wire side, wherein a gap is provided between the central partition portion and the central shield portion, and the air intake duct is provided with a flexible sheet member that closes the gap between the central partition portion and the central shield portion. [Effects of the Invention]

[0007] According to the present invention, when a corona charger having multiple discharge wires is used, when the air taken in from the air supply duct is divided and passed through each discharge wire in the corona charger, the air can be passed through the corona charger so as to effectively discharge ozone. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram illustrating an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is an external perspective view showing a corona charger and an air supply duct. [Figure 3] FIG. [Figure 4] FIG. [Figure 5] FIG. [Figure 6] FIG. [Figure 7] FIG. 4 is a cross-sectional view showing the configuration of a flow dividing plate relative to an air intake duct. [Figure 8] 1A is a graph showing the wind speed distribution in a space in this embodiment, and FIG. 1B is a graph showing the wind speed distribution in a space in a comparative example. [Figure 9] 1A is a graph showing the air volume in this embodiment, and FIG. 1B is a graph showing the air volume in a comparative example. [Figure 10] FIG. 10 is a cross-sectional view illustrating the retraction of the sealing member. [Figure 11] FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Image forming device> The present embodiment will be described below. First, the image forming apparatus of the present embodiment will be described with reference to Fig. 1. The image forming apparatus 100 shown in Fig. 1 is an intermediate transfer tandem type full-color printer in which yellow, magenta, cyan, and black image forming units Pa, Pb, Pc, and Pd are arranged along an intermediate transfer belt 20. Examples of recording materials S that can be used with the image forming apparatus 100 include plain paper, cardboard, rough paper, textured paper, and coated paper.

[0010] The recording material conveyance process of the image forming apparatus 100 will be described. The recording material S is stored in a stacked form in a paper feed cassette 10, and is fed out of the paper feed cassette 10 by a paper feed roller 13 in accordance with the image formation timing. The recording material S fed out by the paper feed roller 13 is conveyed to a registration roller 12 arranged midway along a conveyance path 414. Then, after the registration roller 12 performs skew correction and timing correction on the recording material S, the recording material S is sent to a secondary transfer portion T2. ​​The secondary transfer portion T2 is a transfer nip portion formed by an inner secondary transfer roller 21 and an outer secondary transfer roller 11, and a toner image is transferred onto the recording material in response to, for example, the application of a secondary transfer voltage to the outer secondary transfer roller 11.

[0011] The image forming process for the recording material S being conveyed to the secondary transfer station T2 at the same timing as the process for conveying the recording material S to the secondary transfer station T2 described above will now be described. First, the image forming stations Pa, Pb, Pc, and Pd for each color are configured in almost the same way except that the toner colors used in the developing devices 1a, 1b, 1c, and 1d are yellow, magenta, cyan, and black, respectively. Therefore, the following description will be given of the yellow image forming station Pa as a representative, and descriptions of the other image forming stations Pb, Pc, and Pd will be omitted.

[0012] The image forming unit Pa is mainly composed of a developing device 1a, a charging device 2a, a photosensitive drum 3a, a photosensitive drum cleaner 4a, and an exposure device 5a. The photosensitive drum 3a is rotated in the direction of arrow R1 in the figure by a drive motor (not shown) or the like. The surface of the photosensitive drum 3a is uniformly charged in advance by the charging device 2a, and then an electrostatic latent image is formed on it by the exposure device 5a, which is driven based on a signal for image information. In this embodiment, the charging device 2a is a corona charger. The charging device 2a will be described in detail later.

[0013] The electrostatic latent image formed on the photosensitive drum 3a is developed into a toner image using a developer by the developing device 1a. Then, the toner image formed on the photosensitive drum 3a is primarily transferred onto the intermediate transfer belt 20 in response to the application of a primary transfer voltage to a primary transfer roller 6a disposed across the image forming unit Pa and the intermediate transfer belt 20. The primary transfer residual toner remaining on the photosensitive drum 3a is collected by a photosensitive drum cleaner 4a.

[0014] The intermediate transfer belt 20 is tensioned by an inner secondary transfer roller 21, a tension roller 22, and a tension roller 23, and is driven in the direction of arrow R2 in the figure. The image formation processes for each color, which are processed in parallel by the image forming units Pa to Pd, are performed at a timing such that the image is sequentially superimposed on the toner image of the upstream color that has been primarily transferred onto the intermediate transfer belt 20. As a result, a full-color toner image is finally formed on the intermediate transfer belt 20 and is transported to the secondary transfer unit T2. Note that the residual toner after passing through the secondary transfer unit T2 is collected by a belt cleaner device 30.

[0015] Through the conveying process and image creation process described above, the timing of the recording material S and the full-color toner image are synchronized at the secondary transfer portion T2, and secondary transfer is performed. The recording material S is then conveyed to the fixing device 50, where a predetermined pressure and heat are applied, thereby fixing the toner image on the recording material. In the single-sided print mode, the recording material S with the fixed toner image is sandwiched between discharge rollers 14a and 14b and delivered directly onto the discharge tray 420. In the case of double-sided image formation, the conveying path is switched by a switching flapper 410 from the path leading to the discharge tray 420 to a double-sided conveying path 411, and the recording material S sandwiched and conveyed between the discharge rollers 14a and 14b is delivered to the double-sided conveying path 411. The leading and trailing ends of the recording material S are then swapped by reversing rollers 412, and the recording material is again delivered to the conveying path 414 via the double-sided conveying path 413. The subsequent conveying and the image creation process for the back side (second side) are the same as those described above, and therefore will not be described here.

[0016] <Charging device> Next, the charging devices 2a to 2d will be described with reference to Figures 2 and 3. However, since the charging devices 2a to 2d have the same configuration, the charging device 2a will be described as a representative example in Figures 2 and 3. To make the description easier to understand, the illustration of a flow dividing plate (see Figures 4 and 5), which will be described later, has been omitted in Figure 3.

[0017] 2, the charging device 2a is detachably mounted on the image forming apparatus 100 along a charging rail 223 as a rail member so as to be positioned opposite the photosensitive drum 3a along the rotation axis direction (also referred to as the longitudinal direction) of the photosensitive drum 3a. The charging device 2a has a front block 219 disposed on the front side in the insertion direction (arrow X direction) of the charging device 2a, and a rear block 220 disposed on the rear side in the insertion direction.

[0018] 3, the charging device 2a has, along the rotation direction (direction of arrow R1) of the photosensitive drum 3a, a first charging portion 2a1 arranged downstream, a second charging portion 2a2 arranged upstream, and a central partition plate 2215 arranged between the first charging portion 2a1 and the second charging portion 2a2. The first charging portion 2a1, the second charging portion 2a2, and the central partition plate 2215 are held at both ends in the longitudinal direction by the front block 219 and the rear block 220, which serve as the above-mentioned holding portions. In the following description, unless otherwise specified, upstream and downstream refer to the upstream and downstream in the rotation direction of the photosensitive drum 3a.

[0019] The first charging unit 2a1 has a first shield plate 2211, a first central shield plate 2212, a first discharge wire 2221, and a first grid electrode plate 2223. The second charging unit 2a2 has a second shield plate 2213, a second central shield plate 2214, a second discharge wire 2222, and a second grid electrode plate 2224. The second discharge wire 2222 charges the surface of the photosensitive drum 3a upstream of the first discharge wire 2221. The first shield plate 2211 is disposed downstream of the first discharge wire 2221, and the second shield plate 2213 is disposed upstream of the second discharge wire 2222. A central shield unit composed of a central partition plate 2215, a first central shield plate 2212, and a second central shield plate 2214 is provided to separate the first discharge wire 2221 and the second discharge wire 2222.

[0020] In this embodiment, the first charging unit 2a1 and the second charging unit 2a2 have the same configuration, so the following description will be given taking the first charging unit 2a1 as an example. The first shield plate 2211 and the first central shield plate 2212 are a pair of shield electrodes and are formed into plates using, for example, stainless steel (SUS). The first shield plate 2211 and the first central shield plate 2212 are arranged to face each other with a gap (for example, 30 mm) between them in the rotation direction of the photosensitive drum 3a.

[0021] <Discharge wire> The charging device 2a has a first discharge wire 2221 which is a discharge electrode, and a first grid electrode plate 2223 which is a control electrode. The first discharge wire 2221 is disposed between a first shield plate 2211 and a first central shield plate 2212. A corona discharge occurs in the first discharge wire 2221 when a charging voltage is applied from a high-voltage power supply (not shown). The first discharge wire 2221 is made of, for example, stainless steel, nickel, molybdenum, or tungsten, and is formed into a wire shape with a diameter of, for example, 40 μm to 100 μm.

[0022] <Grid electrode plate> The first grid electrode plate 2223 is disposed between the photosensitive drum 3a and the first discharge wire 2221 so as to be in close proximity to the surface of the photosensitive drum 3a. The first grid electrode plate 2223 controls the amount of current flowing toward the photosensitive drum 3a when a high voltage is applied from a high-voltage power supply (not shown). This controls the amount of charge on the surface of the photosensitive drum 3a. Bringing the first grid electrode plate 2223 closer to the surface of the photosensitive drum 3a can improve the effect of uniformly charging the surface of the photosensitive drum 3a. In this embodiment, the closest distance between the first grid electrode plate 2223 and the photosensitive drum 3a, as well as the central shield opening 2217 (described later), are set to 1.3±0.3 mm. The closest distance between the first grid electrode plate 2223 and the first discharge wire 2221 is set to, for example, 8 mm.

[0023] The first grid electrode plate 2223 is a so-called etching grid, which has a mesh portion with numerous through-holes formed by etching a thin metal plate substrate, for example, with a thickness of 1 mm or less. In this embodiment, a thin plate made of austenitic stainless steel (SUS304) with a thickness of approximately 0.1 mm is used as the substrate. Other substrate materials, such as martensitic stainless steel or ferritic stainless steel, may also be used. It is preferable that the surface of the first grid electrode plate 2223 be subjected to a surface treatment to improve corrosion resistance, forming a protective layer with anti-rust properties. For example, the protective layer is formed using tetrahedral amorphous carbon (ta-C), a material that is highly chemically inert to discharge products generated by corona discharge. In addition to ozone, discharge products include ammonium nitrate, which is generated by the combination of ozone with nitrogen and moisture in the air.

[0024] The front block 219 and the rear block 220 (see FIG. 2) suspend the first discharge wire 2221 in the longitudinal direction via a support member (not shown), and also hold a first shield plate 2211, a first central shield plate 2212, and a first grid electrode plate 2223. The support member (not shown) supports both ends of the first discharge wire 2221 outside the maximum image forming area of ​​the recording material S on which an image can be formed in the longitudinal direction, so as not to interfere with charging the surface of the photosensitive drum 3a by the first discharge wire 2221. The first shield plate 2211, the first central shield plate 2212, and the first grid electrode plate 2223 are held by the front block 219 and the rear block 220 to form a housing with an open, approximately U-shaped cross section. A first charging area 2225 is formed inside the housing.

[0025] For example, a voltage of approximately −7 kV is applied to the first discharge wire 2221, and a voltage of approximately −1 kV is applied to each of the first grid electrode plate 2223, the first shield plate 2211, and the first central shield plate 2212. As a result, the first charging unit 2a1 controls the charge amount in the first charging region 2225 to charge the surface of the photosensitive drum 3a. The second charging unit 2a2 controls the charge amount in the second charging region 2226 to charge the surface of the photosensitive drum 3a. The front block 219, the rear block 220, and the central partition plate 2215 are made of electrically insulating materials so that the charge amounts in the first charging region 2225 and the second charging region 2226 can be controlled independently. In this embodiment, the longitudinal lengths of the first charging region 2225 and the second charging region 2226 are 350 mm, which is approximately 10% larger than the maximum image formation area of ​​the recording material S on the photosensitive drum 3a.

[0026] <Air supply duct and exhaust duct> The charging device 2a ionizes the air around the first discharge wire 2221 and the second discharge wire 2222 by corona discharge to generate ions, which then charge the photosensitive drum 3a. To generate ions by corona discharge, it is necessary to supply air to the charging device 2a.

[0027] Furthermore, the charging device 2a generates not only ions but also ozone during corona discharge. Ozone corrodes the first discharge wire 2221, the second discharge wire 2222, the first grid electrode plate 2223, and the second grid electrode plate 2224 of the charging device 2a, potentially reducing the charging function of the charging device 2a. Therefore, as shown in FIGS. 2 and 3, an air intake duct 224 is provided in the charging device 2a to supply air from the opposite side of the photosensitive drum 3a. Furthermore, as shown in FIG. 3, an exhaust duct 230 is provided downstream of the photosensitive drum 3a from the charging device 2a to exhaust ozone and other contaminants from the charging device 2a using air supplied from the air intake duct 224 and then collect the exhausted ozone and other contaminants.

[0028] 2, air intake duct 224 forms an air passage for guiding air to charging device 2a, and air intake fan 225 is disposed on the air intake port 2241 side of air intake duct 224. Air intake fan 225 forms an air passage for taking air into air intake duct 224 and guiding it to charging device 2a. Air intake duct 224 is connected to charging device 2a on the air outlet 2242 side to guide the taken-in air to charging device 2a. Air intake duct 224 has air outlet 2242 opened in the longitudinal direction to blow air across the longitudinal direction of charging device 2a.

[0029] 3, the air outlet of air supply duct 224 is divided into first air passage outlet 257 and second air passage outlet 258 by central partition wall 253 (described later), and opens in a rectangular shape along the longitudinal direction of charging device 2a. Therefore, air taken in from air supply port 2241 by air supply fan 225 is blown out from first air passage outlet 257 and second air passage outlet 258 to charging device 2a.

[0030] The air intake duct 224 is disposed above the charging rail 223, with a downstream first wall portion 224a connected to the first shield plate 2211 and an upstream second wall portion 224b connected to the second shield plate 2213. The air intake fan 225 is disposed at the front end of the air intake duct 224 to take in air from the front of the main body of the image forming apparatus 100. That is, the air intake fan 225 and the air intake duct 224 are disposed above the charging device 2a so as to avoid other components of the image forming unit Pa, and the air intake port 2241 of the air intake fan 225 is disposed at the front of the main body of the image forming apparatus 100. The air intake duct 224 is formed in a curved shape as shown in the figure so that the air taken in from the front and flowing along the longitudinal direction can be blown toward the charging device 2a in the radial direction of the photosensitive drum 3a (a direction intersecting the rotation axis direction).

[0031] The air discharged from the charging device 2a, specifically the first charging portion 2a1 and the second charging portion 2a2, toward the photosensitive drum 3a travels from upstream to downstream on the surface of the rotating photosensitive drum 3a and is guided to the exhaust duct 230 through the gap (first shield opening 2216) between the first shield plate 2211 and the photosensitive drum 3a. An ozone filter (not shown) is disposed in the exhaust duct 230, and the air containing ozone discharged from the charging device 2a passes through the ozone filter. In this way, the air from which the ozone has been removed is discharged from the exhaust duct 230 to the outside of the main body of the image forming apparatus 100.

[0032] A flexible sealing sheet 256 is provided in the gap between the second shield plate 2213 and the photosensitive drum 3a to close the gap. The sealing sheet 256 as a sealing member prevents the air containing ozone from flowing out toward the photosensitive drum cleaner 4a (see FIG. 1) arranged upstream, and also makes it easier for the air containing ozone to flow toward the exhaust duct 230 as the photosensitive drum 3a rotates.

[0033] Generally, air vortices are likely to occur in air intake duct 224, where the cross-sectional shape changes between air intake port 2241 and first air passage outlet 257 and second air passage outlet 258, and this tends to cause turbulence in the air flow. Therefore, conventionally, even if air intake fan 225 takes in air at a uniform wind speed through air intake port 2241, the wind speed of the air blown out from first air passage outlet 257 and second air passage outlet 258 tends to be non-uniform. Furthermore, air intake duct 224 is bent so that the direction of air flow from air intake port 2241 to first air passage outlet 257 and second air passage outlet 258 changes from longitudinal direction B to the radial direction of charging device 2a. Therefore, the wind speed of the air blown out from first air passage outlet 257 and second air passage outlet 258 tends to be non-uniform in the longitudinal direction.

[0034] As described above, when an air vortex occurs in the air supply duct 224, toner on the surface of the photosensitive drum 3a and external additives such as silica added to the toner are likely to adhere to the discharge wires (2221, 2222) and grid electrode plates (2223, 2224). In addition, the wind speed of the air blown out of the air supply duct 224 becomes uneven, ozone is not properly discharged, and uneven corrosion may occur in the discharge wires (2221, 2222) and grid electrode plates (2223, 2224). This is undesirable because it becomes difficult to uniformly charge the surface of the photosensitive drum 3a.

[0035] <Flow divider plate> In view of the above, in this embodiment, the air is rectified so as not to generate vortexes in the air intake duct 224, so that air is blown out from the air intake duct 224 at a uniform wind speed in the longitudinal direction. The configuration for achieving this will be described below with reference to Figures 4 to 7.

[0036] 4 and 5, in the air supply duct 224 of this embodiment, a plurality of (here, 53) flow dividing plates 3101 to 3153 are arranged along the longitudinal direction B. These flow dividing plates 3101 to 3153 are provided to extend in the vertical direction C, which is the radial direction of the photosensitive drum.

[0037] 6, the flow diverting plates 3101-3153 are arranged at flow diverting plate interval Db1 along the longitudinal direction B. The lower ends of the flow diverting plates 3101-3153 are located at the same position in the vertical direction C, while the upper ends 3301-3353 of the flow diverting plates 3101-3153 are arranged so as to be separated by a flow diverting plate tip distance Dc1 along the vertical direction C. The farther the flow diverting plates 3101-3153 are located from the air intake port 2241 in the longitudinal direction B, the farther their upper ends 3301-3353 are located from the first air passage outlet 257 and the second air passage outlet 258. In other words, of the flow diverting plates 3101-3153, the height of the downstream side flow diverting plate in the direction in which the air flows before being diverted is higher than the height of the adjacent upstream side flow diverting plate. In this way, the vertical lengths of adjacent flow dividing plates 3101 to 3153 differ by the flow dividing plate tip distance Dc1.

[0038] In this embodiment, backflow of air is prevented by equally dividing the air taken in through air supply port 2241 into each air passage formed between adjacent air flow dividing plates 3101-3153 and blowing it out from first air passage outlet 257 and second air passage outlet 258. That is, of the multiple air flow dividing plates 3101-3153, air flow dividing plate 3101 located most upstream in the direction of air flow from air supply port 2241 (direction of arrow Z) divides the air taken in through air supply port 2241 into air to be flowed toward first blowing area 3201 and air to be flowed toward blowing areas 3202-3254 downstream of first blowing area 3201, so that a portion of the air taken in through air supply port 2241 turns and flows toward first blowing area 3201. Similarly, the other airflow dividing plates 3102 to 3153 divide the air taken in from the air supply port 2241 so as to redirect the air toward the corresponding blowing areas 3202 to 3254, respectively.

[0039] It is preferable that the flow dividing plate tip distance Dc1 be set to the same value for adjacent flow dividing plates 3101-3153. This is because the air taken in from the air supply port 2241 can be divided in the same way in each of the blowing areas 3201-3254. For example, if it is desired to divide the air equally among the blowing areas 3201-3254, the flow dividing plate tip distance Dc1 is preferably set to "L0 (air path width) / n (number of flow dividing plates) = flow dividing plate tip distance Dc1." However, this is not a limitation, and some or all of the flow dividing plate tip distances Dc1 may be set to be different.

[0040] In this embodiment, by making the distances Db1 between the flow diverting plates 3101-3153 equal, backflow of air is less likely to occur in the blowing areas 3201-3254, and the average wind speed of the air blown out from the blowing areas 3201-3254 is therefore approximately the same. That is, the first air passage outlet 257 and the second air passage outlet 258 of the air supply duct 224 are equally divided into a plurality of flow diverting areas along the longitudinal direction B by the flow diverting plates 3101-3153. In this case, the air diverted by the flow diverting plates 3101-3153 flows through the corresponding flow diverting areas divided in the longitudinal direction B at the first air passage outlet 257 and the second air passage outlet 258, making it easier to make the wind speed of the blown out air more uniform in the longitudinal direction. In this way, in this embodiment, the wind speed of the air blown out from the first air passage outlet 257 and the second air passage outlet 258 is made uniform in the longitudinal direction.

[0041] It is preferable that the flow divider plates 3101 to 3153 have the following relationships between the flow divider plate spacing Db1 (mm) and the flow divider plate length (mm) in the vertical direction C: "when 3.0≦flow divider plate spacing≦5.5, then the flow divider plate length in the vertical direction C≧flow divider plate spacing×0.1", "when 5.5≦flow divider plate spacing≦6.5, then the flow divider plate length in the vertical direction C≧flow divider plate spacing×0.1", "when 6.5≦flow divider plate spacing≦9.0, then the flow divider plate length in the vertical direction C≧flow divider plate spacing×0.46−2.34", "when 9.0≦flow divider plate spacing≦13.0, then the flow divider plate length in the vertical direction C≧flow divider plate spacing×0.53−2.93", and "when 13.0≦flow divider plate spacing≦28.0, then the flow divider plate length≧flow divider plate spacing×7.21−89.79".

[0042] However, if the inter-plate spacing Db1 (see FIG. 6 ) of the above-described air divider plates 3101-3153 is too wide, air vortices are generated in the air outlet regions 3201-3254, causing the air speed of the air blown out from the first air passage outlet 257 and the second air passage outlet 258 to become uneven in the longitudinal direction B. Therefore, it is desirable to narrow the inter-plate spacing Db1 as much as possible. However, the air supply duct 224 is often manufactured using a resin injection molding die. Therefore, as the inter-plate spacing Db1 is narrowed, the shape of the die used to mold the air supply duct 224 with the air divider plates may become more complex and narrower, which may result in the die being unable to withstand the molding pressure. In other words, as the inter-plate spacing Db1 is narrowed and the number of air divider plates increases, it becomes more difficult to mold the air supply duct 224 with the air divider plates from resin.

[0043] In view of the above, in this embodiment, as shown in Fig. 7, air supply duct 224 is configured to be formed by combining two members, upper member 224-1 and lower member 224-2, which are located above and below in vertical direction C. Of flow dividing plates 3101 to 3153, odd-numbered flow dividing plates (3101, 3103, ...) are provided on lower member 224-2, and even-numbered flow dividing plates (3102, 3104, ...) are provided on upper member 224-1, in order of arrangement from the downstream side in the direction of air flow from air supply port 2241 (direction of arrow Z). Lower member 224-2 and upper member 224-1, which include these flow dividing plates, are each molded using resin using separate injection molding dies.

[0044] By combining the upper member 224-1 and the lower member 224-2, one air supply duct 224 is formed in which odd-numbered flow dividing plates (3101, 3103, ...) and even-numbered flow dividing plates (3102, 3104, ...) are arranged alternately in the longitudinal direction B. This makes it possible to narrow the flow dividing plate spacing Db1 while still making it possible to mold the plates from resin.

[0045] 3, air taken in through the air supply duct 224 is divided into a first air passage 251 on the downstream side and a second air passage 252 on the upstream side with respect to the rotation direction of the photosensitive drum 3a (the direction of arrow R1). To achieve this, the interior of the air supply duct 224 is divided along the longitudinal direction by a central partition wall 253. The first air passage 251 is connected to a first charging region 2225 of the charging device 2a, and the second air passage 252 is connected to a second charging region 2226 of the charging device 2a. In other words, the first air passage 251 and the first charging region 2225 form a single air passage, and the second air passage 252 and the second charging region 2226 form a single air passage.

[0046] In this embodiment, the central partition wall portion 253 is not connected to the central partition plate 2215, the first central shield plate 2212, or the second central shield plate 2214. In other words, an opening 270, which is a gap, is formed between the central partition wall portion 253 and them.

[0047] However, if the opening 270 is formed, as in a comparative example shown in Fig. 8(b) described in detail later, air flows between the first air passage 251 and the second air passage 252 via the opening 270 (see opening Q in Fig. 8(b)). In this case, almost no air flows in the corner area between the photosensitive drum 3a and the second shield plate 2213 in the second air passage 252, and ozone cannot be effectively discharged through the second air passage 252 according to the air flow.

[0048] Therefore, in air supply duct 224, elastic sheet 259 is provided as a sheet member that closes opening 270 so as to prevent air from flowing between first air passage 251 and second air passage 252. Elastic sheet 259 is formed of a flexible member such as a thin urethane sheet or a thin PET sheet, and has one end fixed to central partition wall portion 253 and the other end provided so as to be movable toward and away from second central shield plate 2214.

[0049] In this way, elastic sheet 259 that closes opening 270 is provided so as to be able to come into contact with and separate from second central shield plate 2214, in other words, so as to come into contact with and separate from second air passage 252 on the side. This is to prevent elastic sheet 259 from entering into first air passage 251 due to air passing through second air passage 252. In other words, if elastic sheet 259 enters into first air passage 251, some of the air will flow from second air passage 252 to first air passage 251, making it difficult for air to reach the corner region. Therefore, even if elastic sheet 259 is pushed toward first air passage 251 by air passing through second air passage 252, elastic sheet 259 comes into contact with second central shield plate 2214, so that elastic sheet 259 does not enter into first air passage 251 and is maintained in a state of closing opening 270.

[0050] In this embodiment, the central shield section is configured by the central partition plate 2215, the first central shield plate 2212, and the second central shield plate 2214, but this is not limited to this. For example, without providing the central partition plate 2215, the first central shield plate 2212 and the second central shield plate 2214 may be used as a single common shield plate, and this common shield plate may be the central shield section.

[0051] As described above, the effect of closing opening 270 with elastic sheet 259 and separating the spaces within air supply duct 224 so as to prevent airflow between first air passage 251 and second air passage 252 will be described using Figures 8(a) and 8(b). Figures 8(a) and 8(b) are graphs showing the wind speed distribution within the space when air is sent only to second air passage 252, obtained by computer simulation.

[0052] Fig. 8(a) shows this embodiment, in which opening 270 is blocked by elastic sheet 259 to separate the space within air supply duct 224, preventing airflow between first air passage 251 and second air passage 252. Fig. 8(b) shows a comparative example, in which airflow can occur between first air passage 251 and second air passage 252 from opening Q formed between central partition wall portion 253e and first central shield plate 2212e (second central shield plate 2214e). In Figs. 8(a) and 8(b), darker colored areas indicate faster airflow (flow velocity), and lighter colored areas indicate slower airflow (flow velocity).

[0053] 8(b), almost no air flows in the corner area between the photosensitive drum 3a, indicated by the dashed-dotted ellipse in the figure, and the second shield plate 2213. This is because air flows between the first air passage 251 and the second air passage 252 through the opening Q formed in the lower part of the central partition wall portion 253e, and a wind speed vector is generated pointing in the direction of the first air passage 251, making it difficult for air to reach the corner area.

[0054] 8(a), air is distributed even in the corner areas where almost no air flow occurred in the comparative example, which are indicated by the dashed-dotted ovals in the figure, and air flows. In other words, the corner areas where no air flow occurs in second air passage 252 are reduced compared to the comparative example. In this way, in the present embodiment, the area where air flows in second air passage 252 can be widened, and ozone can be effectively discharged from second air passage 252 in accordance with the air flow.

[0055] Generally, the volume of air passing through an air duct is determined by the pressure loss in the air duct, and the pressure loss in the air duct increases in proportion to the square of the air speed. The air speed is greatest at the point in the air duct where the air passing area is the smallest. In other words, the point in the air duct with the smallest passing area has a large contribution to the pressure loss of the air duct and has a large effect on the volume of air passing through the air duct.

[0056] 3, air taken into air supply duct 224 is diverted to first air passage 251 through first air passage opening 254 and to second air passage 252 through second air passage opening 255. As described above, first air passage 251 and second air passage 252 are partitioned by central partition wall 253 and elastic sheet 259, and are connected to first charging area 2225 and second charging area 2226, respectively. In the present embodiment, the distance between central partition wall 253 and first wall portion 224a is narrowest at the tip end that forms an air inlet into first air passage 251 together with first wall portion 224a, and the distance between central partition wall 253 and second wall portion 224b is wider than the gap between central partition plate 2215 and photosensitive drum 3a.

[0057] In this embodiment, the volume of air passing through the first air passage 251 and the second air passage 252 varies depending on the ratio of the opening areas of the first air passage opening 254 and the second air passage opening 255 on the tip end side of the central partition wall portion 253. It is preferable that the opening area of ​​the first air passage opening 254, which has the smallest area through which air passes in the first air passage 251 and the second air passage 252, is approximately the same as the opening area of ​​the central shield opening 2217, which is the gap between the central partition plate 2215 and the photosensitive drum 3a. This makes it possible to equalize the pressure loss in the first air passage 251 and the second air passage 252, preventing more air from flowing in one direction than the other. In other words, the same volume of air can pass through the first air passage 251 and the second air passage 252. The opening area of ​​the central shield opening 2217 is determined by the gap between the central partition plate 2215 and the photosensitive drum 3a and the length of the corona charger in the direction of the rotation axis.

[0058] 9(a) and 9(b) are graphs showing the airflow rate through first air passage 251 (air passage 1), the airflow rate through second air passage 252 (air passage 2), and the total airflow rate (total airflow rate) obtained by computer simulation. The unit of airflow rate is "m 3 / min".

[0059] 9(a) shows the present embodiment, in which the opening area of ​​the first air passage opening 254 and the opening area of ​​the central shield opening 2217 are set to be approximately the same. Here, the longitudinal lengths of the first air passage opening 254 and the central shield opening 2217 are approximately the same, and the heights are the same at 2.5 mm, so that the opening areas are the same. FIG. 9(b) shows a comparative example, in which the opening area of ​​the first air passage opening 254 and the opening area of ​​the central shield opening 2217 are set to be different. Here, the longitudinal lengths of the first air passage opening 254 and the central shield opening 2217 are the same as in the present embodiment, and the heights are set to 2.5 mm and 3.5 mm, respectively, so that the opening areas are different.

[0060] 9(b), the opening areas are different, resulting in a difference between the airflow rate (0.15) through first air passage 251 and the airflow rate (0.25) through second air passage 252. To generate a larger airflow rate in first air passage 251, which has a relatively smaller airflow rate, while keeping the opening area the same, it is necessary to increase the total airflow rate. To achieve this, it is necessary to increase the size of air supply fan 225.

[0061] 9(a), there is also a difference between the airflow rate (0.17) through first air passage 251 and the airflow rate (0.21) through second air passage 252. However, this difference is smaller than in the comparative example, and it can be said that the difference is approximately equal compared to the comparative example. Furthermore, the airflow rate through first air passage 251 can be increased with a total airflow rate (0.38) that is less than the total airflow rate (0.40) in the comparative example. That is, in the case of this embodiment, the airflow rate through first air passage 251 can be increased and the difference between the airflow rate through second air passage 252 can be reduced so that the same airflow rate passes through first air passage 251 and second air passage 252 using inexpensive air supply fan 225.

[0062] In addition, when the amount of ozone generated per unit time in the first charging area 2225 and the second charging area 2226 is different from "α1" and "α2," it is preferable to set the air volume ratio between the first air passage 251 and the second air passage 252 to "α1:α2," as this allows ozone to be effectively discharged. In other words, if the first air passage 251 and the second air passage 252 are regarded as parallel pipes, the ratio of the air volumes of the respective air passages is equal to the ratio of the squares of the cross-sectional areas of the respective air passages. Therefore, in order to set the air volume ratio between the first air passage 251 and the second air passage 252 to "α1:α2," the ratio of the opening area of ​​the first air passage opening 254 to the opening area of ​​the central shield opening 2217 should be set to "α1 2 :α2 2 " is a good idea.

[0063] As described above, in air supply duct 224 of the present embodiment, opening 270 is formed between central partition wall portion 253 and central partition plate 2215, and opening 270 is closed by flexible elastic sheet 259. Here, opening 270 is formed between central partition wall portion 253 and central partition plate 2215 for the following reason.

[0064] When the charging device 2a is a corona charger, discharge products such as ozone generated by corona discharge, as well as toner and toner additives, adhere to the discharge wires (2221, 2222) and grid electrode plates (2223, 2224). The deposits on the discharge wires and grid electrode plates can cause rust and other problems on the discharge wires and grid electrode plates. Rust on the discharge wires and grid electrode plates makes it difficult to uniformly charge the photosensitive drum 3a to a predetermined potential, making charging unevenness more likely to occur. Therefore, the charging device 2a is provided with a cleaning unit that cleans the discharge wires and grid electrode plates to remove deposits from the discharge wires and grid electrode plates. The cleaning unit will be described with reference to FIG. 10.

[0065] As shown in FIG. 10 , the cleaning unit 600 includes a first wire cleaning member 520 that cleans the first discharge wire 2221 and a second wire cleaning member 521 that cleans the second discharge wire 2222. The cleaning unit 600 also includes a first grid cleaning member 510 that cleans the first grid electrode plate 2223 and a second grid cleaning member 511 that cleans the second grid electrode plate 2224. The cleaning unit 600 also includes a cleaning carriage 512. The cleaning members (510, 511, 520, 521) are held by the cleaning carriage 512 and, as the cleaning carriage 512 reciprocates in the longitudinal direction, rub against and clean the discharge wires (2221, 2222) and grid electrode plates (2223, 2224). When the cleaning unit 600 is not in operation (for example, during image formation), it waits at a standby position that is longitudinally outboard of the corona charger (2a) and elastic sheet 259.

[0066] As described above, to clean the discharge wires (2221, 2222) and the grid electrode plates (2223, 2224), the cleaning unit 600 needs to be operated by a motor (not shown) or the like to reciprocate in the longitudinal direction. However, if the central partition wall 253 is connected to the central partition plate 2215, the cleaning carriage 512 will come into contact with the central partition wall 253, preventing the cleaning unit 600 from moving. It is conceivable to separate the cleaning unit 600 into a unit that cleans the first discharge wire 2221 and first grid electrode plate 2223 on the first air passage 251 side and a unit that cleans the second discharge wire 2222 and second grid electrode plate 2224 on the second air passage 252 side, and move each of these units separately. However, this would complicate the configuration and increase costs, making it difficult to adopt.

[0067] Therefore, in the air supply duct 224 of this embodiment, an opening 270 is formed between the central partition wall 253 and the central divider plate 2215 so that the movement of the cleaning unit 600 is not hindered by the central partition wall 253. As described above, the elastic sheet 259 blocks the opening 270. In this embodiment, as shown in FIG. 10 , the elastic sheet 259 is retracted by the cleaning carriage 512 so as to enter the second air passage 252 side by the cleaning carriage 512 so that the moving cleaning carriage 512 can pass through. In other words, the cleaning unit 600 moves in the longitudinal direction while the cleaning carriage 512 retracts the elastic sheet 259 in a flip-over manner.

[0068] To retract the elastic sheet 259 during movement, the cleaning unit 600 is provided with a rubbing portion 590 on the cleaning carriage 512 that rubs against the elastic sheet 259, as shown in FIG. 11 . When the cleaning carriage 512 moves toward the rear in the longitudinal direction, the rubbing portion 590 retracts the other end of the elastic sheet 259 in a direction away from the second central shield plate 2214 (in the direction of arrow E). To do so, the rubbing portion 590 has a rubbing surface 590a that abuts and rubs against the elastic sheet 259. This rubbing surface 590a is formed in a shape that is inclined from downstream to upstream in the movement direction of the cleaning carriage 512 (from front to rear) in a direction away from the second central shield plate 2214 (in the direction of arrow E). As the cleaning unit 600 moves back to the standby position (from rear to front), the retracted elastic sheet 259 returns to its original position blocking the opening 270 due to the flexibility of the elastic sheet 259 itself.

[0069] As described above, the air supply duct 224 is formed with a central partition wall portion 253 that separates the interior of the air supply duct 224 into a first air passage 251 that passes air toward the first discharge wire 2221 side and a second air passage 252 that passes air toward the second discharge wire 2222 side. In this embodiment, an opening 270 is formed between the central partition wall portion 253 and the central partition plate 2215, the first central shield plate 2212, and the second central shield plate 2214, and the opening 270 is blocked by an elastic sheet 259. Blocking the opening 270 with the elastic sheet 259 in this manner prevents air from flowing from the second air passage 252 to the first air passage 251, and therefore the volume of air flowing through the second air passage 252 does not become relatively small. Therefore, air also flows into the corner regions of the second air passage 252, enabling ozone to be effectively discharged. Therefore, in this embodiment, when the air taken in from the air supply duct 224 is divided and passed through each discharge wire in the corona charger, the air can be passed through the corona charger so as to effectively discharge ozone. [Explanation of symbols]

[0070] 2a... corona charger (charging device), 3a... photosensitive drum, 219... holding portion (front block), 220... holding portion (rear block), 223... rail member (charging rail), 224... air supply duct, 224a... first wall portion, 224b... second wall portion, 230... exhaust duct, 253... central partition wall portion, 256... sealing member (seal sheet), 259... sheet member (elastic sheet), 590... sliding portion, 590a... sliding surface, 600... cleaning unit, 2211... first shield plate, 2212... central shield portion (first central shield plate), 2213... second shield plate, 2214... central shield portion (second central shield plate), 2215... central shield portion (central partition plate), 2221... first discharge wire, 2222... second discharge wire, 3101 to 3153... flow dividing plates

Claims

1. an air supply duct that supplies air from the opposite side of the photosensitive drum, passes the air through the corona charger, and discharges the air toward the photosensitive drum; and an exhaust duct that is disposed downstream of the corona charger in the rotation direction of the photosensitive drum, and exhausts the air that is discharged from the corona charger and flows along the photosensitive drum, the corona charger includes: a first discharge wire that charges the surface of the photosensitive drum in the rotation direction; a second discharge wire that charges the surface of the photosensitive drum upstream of the first discharge wire; a first shield plate arranged downstream of the first discharge wire; a second shield plate arranged upstream of the second discharge wire; a central shield portion arranged to separate the first discharge wire and the second discharge wire; and holding portions that hold the first discharge wire, the second discharge wire, the first shield plate, the second shield plate, and the central shield portion at both ends of the rotation axis of the photosensitive drum, the air supply duct has a first wall portion connected to the first shield plate, a second wall portion connected to the second shield plate, and a central partition portion formed in the rotational direction between the first wall portion and the second wall portion along the rotational axis, the central partition portion dividing the interior of the air supply duct into a first air passage for passing air toward the first discharge wire side and a second air passage for passing air toward the second discharge wire side, the central partition wall portion is provided with a gap between it and the central shield portion, a flexible sheet member is provided in the air supply duct so as to close the gap between the central partition wall portion and the central shield portion; An image forming apparatus characterized by:

2. The sheet member has one end fixed to the central partition wall portion and the other end movable toward and away from the central shield portion in a direction intersecting the rotation axis direction.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. a rail member that detachably holds the corona charger and guides the corona charger to the air supply duct along the rotation axis direction; the sheet member is rubbed by the corona charger that moves along the rail member, and the corona charger moves away from the central shield portion so as to be able to pass through a gap between the central partition wall portion and the central shield portion; 3. The image forming apparatus according to claim 2, wherein the image forming apparatus is a recording medium.

4. a cleaning unit that cleans the inside of the corona charger while moving along the rotation axis direction; the sheet member is moved away from the central shield portion as the cleaning unit slides against the sheet member while the sheet member is moving, allowing the cleaning unit to pass through a gap between the central partition wall and the central shield portion.

3. The image forming apparatus according to claim 2, wherein the image forming apparatus is a recording medium.

5. the cleaning unit has a sliding portion that slides against the sheet member, The sliding portion is formed in a shape such that a sliding surface that slides against the sheet member is inclined away from the central shield portion from the downstream side to the upstream side in the movement direction.

5. The image forming apparatus according to claim 4.

6. The central partition is formed so that the distance between the first wall portion and the first wall portion at a first tip portion that forms an air inlet into the first air duct with the first wall portion is shorter than the distance between the second wall portion and the second wall portion at a second tip portion that forms an air inlet into the second air duct with the second wall portion.

6. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

7. The central partition portion is formed so that when the distance between the central partition portion and the first wall portion is narrowest at a first tip portion that forms an air inlet into the first air passage between the central partition portion and the first wall portion and the distance between the central partition portion and the second wall portion is wider at a second tip portion that forms an air inlet into the second air passage between the central partition portion and the second wall portion, the area of ​​the inlet into the first air passage is approximately the same as the area determined by the distance of the gap and the length of the corona charger in the direction of the rotation axis.

6. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

8. The second shield plate is provided with a sealing member that closes a gap between the second shield plate and the photosensitive drum.

8. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

9. The air supply duct has a plurality of diverter plates arranged in the direction of the rotation axis, which diverge the air flowing in the direction of the rotation axis into a plurality of flows in a direction intersecting the direction of the rotation axis and supply the flows to the corona charger, The height of an upper end of the downstream flow dividing plate in the direction in which the air before being divided flows is higher than the height of an upper end of the adjacent upstream flow dividing plate.

9. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

Images