Image formation device and cartridge

Abstract

This image formation device forms an image on a recording material, and comprises: a photoconductor drum that carries a toner image; a frame body that rotatably supports the photoconductor drum; a sheet member, one end of which is secured to the frame body such that the other end is a free end; and a transfer roller that comes into contact with the photoconductor drum to form a transfer nip, and transfers the toner image to the recording material when the recording material is conveyed and passes through the transfer nip. The sheet member includes a conductive layer and an insulating layer, and is provided on the downstream side of the transfer nip in the conveyance direction of the recording material. When viewed from the thickness direction of the sheet member, the conductive layer and the insulating layer at least partially overlap, and the insulating layer is disposed so as to face the surface of the photoconductor drum.

Description

Image forming apparatus and cartridge

[0001] The present invention relates to an image forming apparatus and a cartridge for forming an image on a recording material.

[0002] 2. Description of the Related Art Image forming apparatuses are widely used in which a toner image is transferred onto a recording material by passing the recording material through a transfer section so as to be superimposed on a toner image carried on an image carrier such as a photosensitive drum.

[0003] When a toner image is transferred to a recording material, the conveyed paper as the recording material may be electrostatically attracted to the surface depending on the configuration of the photosensitive drum, which is an image carrier, and its surroundings. For this reason, Patent Document 1 discloses a configuration in which a separation claw, which is a separating means, is brought into contact with the surface of the photosensitive drum, and the conveyed paper is mechanically separated from the photosensitive drum.

[0004] JP 2009-175283 A

[0005] SUMMARY OF THE INVENTION An object of the present invention is to provide a new embodiment of an image forming apparatus.

[0006] One aspect of the present invention is an image forming device that forms an image on a recording material, comprising: a photosensitive drum that carries a toner image; a frame that rotatably supports the photosensitive drum; a sheet member that has one end fixed to the frame and one end that is a free end; and a transfer roller that contacts the photosensitive drum to form a transfer nip and transfers the toner image to the recording material as the recording material is transported and passes through the transfer nip, wherein the sheet member includes a conductive layer and an insulating layer and is located downstream in the transport direction of the recording material in the transfer nip, and when viewed in the thickness direction of the sheet member, the conductive layer and the insulating layer overlap at least in part, and the insulating layer is closer to the photosensitive drum than the conductive layer and is arranged so as to face the surface of the photosensitive drum.

[0007] According to the present invention, a new embodiment of an image forming apparatus can be provided.

[0008] Cross-sectional view of an image forming apparatusCross-sectional view of a developing unit of the present inventionPerspective view of a developing unit of the present inventionCross-sectional view of a developing unit attached to a photosensitive unitPerspective view of a process cartridge of the present inventionPerspective view of a developing unit and a photosensitive unit of the present inventionEnlarged cross-sectional view of an imaging section of a process cartridgeEnlarged cross-sectional view of an imaging section of a process cartridgeSchematic view of a conductive sheetSchematic view of a conductive sheetSchematic view of a conductive sheetSchematic view of a conductive sheetEnlarged cross-sectional view of an imaging section of a process cartridgeEnlarged cross-sectional view of an imaging section of a process cartridge

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0010] [First Embodiment] An image forming apparatus according to a first embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0011] In the following description, directions are defined based on the user using the image forming apparatus 1. That is, the front side of the image forming apparatus 1 is referred to as the "front," the back side as the "rear," the top side as the "upper," and the bottom side as the "lower." Furthermore, the left side of the image forming apparatus 1 when viewed from the front side is referred to as the "left," and the right side as the "right." Directions in each drawing are defined by arrows shown on the drawing.

[0012] The front-to-rear, up-down, and left-to-right directions indicated by the arrows are mutually orthogonal. These directions are the same in all drawings. The up-to-down direction is parallel to the vertical direction, and the left-to-right and front-to-rear directions are parallel to the horizontal direction. The left-to-right directions are parallel to the rotational axis of the photosensitive drum 61 and the rotational axis of the developing roller 71, respectively. The developing unit (developing cartridge) 7 mounted integrally with the photosensitive unit (drum cartridge) 6 is referred to as a process cartridge (cartridge) 5. This process cartridge 5 is inserted in the direction of arrow S1 in the figure (mounting direction) when mounted into the apparatus main body 2, and is removed in the direction of arrow S2 in the figure.

[0013] 1, an image forming apparatus 1 that forms an image on a recording material mainly includes a paper feed unit 3 for supplying paper S (recording material) into an apparatus main body 2, an exposure device 4, a process cartridge 5 that transfers toner as a developer onto the paper S as a toner image, and a fixing device 8 that thermally fixes the toner image transferred onto the paper S. The paper feed unit 3 is provided in the lower part of the apparatus main body 2, and mainly includes a paper feed tray 31 and a paper feed mechanism 32.

[0014] The exposure device 4 is disposed in the upper part of the device main body 2, and includes a laser emitting unit (not shown), a polygon mirror (shown without reference numerals), a lens, a reflecting mirror, etc. In the exposure device 4, the laser light based on image data emitted from the laser emitting unit is scanned at high speed over the surface of the photosensitive drum 61, thereby exposing the surface of the photosensitive drum 61.

[0015] The process cartridge 5 is disposed below the exposure device 4. It is configured to be inserted into the device main body 2 in the direction of arrow S1 through an opening formed when a door (opening / closing member) 21 provided on the device main body 2 is opened (shown by a two-dot chain line in FIG. 1 ) and then attached to the device main body 2. When removing the process cartridge 5 from the device main body 2, the process cartridge 5 is moved in the direction of arrow S2 and removed. In this way, the process cartridge 5 is configured to be detachable from the device main body 2 of the image forming apparatus 1.

[0016] This process cartridge 5 mainly includes a photosensitive unit 6 and a developing unit 7. The photosensitive unit 6 mainly includes a photosensitive drum 61, a charging roller 62, and a transfer roller 63. The developing unit 7 is configured to be detachably attached to the photosensitive unit 6. The developing unit 7 includes a developing roller 71, a supply roller 72, a layer thickness regulating blade 73, a toner storage section (developer storage section) 74 that stores toner (developer), and a first stirring member 75A and a second stirring member 75B provided in the toner storage section 74.

[0017] <Configuration of Process Cartridge> Next, a description will be given of each unit of the process cartridge 5. The process cartridge 5 includes a photosensitive unit 6 and a developing unit 7 that is detachable from the photosensitive unit 6.

[0018] First, the configuration of the developing unit 7 will be described using Figures 2, 3, 7A, and 7B. Figure 2 is a cross-sectional view of the developing unit 7, taken along line A-A in Figure 3, which will be described later. Figure 3 is a perspective view of the developing unit 7 as seen from above. Figure 4 is a cross-sectional view of the developing unit 7 attached to the photosensitive unit 6, with the cross section parallel to the up-down and front-rear directions.

[0019] 2, the developing unit 7 has a grip portion 701 that is gripped by a user at the front of a housing (second frame) 700 serving as a developing frame, and a developing roller 71 is rotatably supported at the rear. Hereinafter, the configuration of the developing unit 7 will be described with the direction of the rotational axis of the developing roller 71 being referred to as the axial direction.

[0020] 2 and 3, the developing unit 7 is electrically connected to the developing roller 71. The developing unit 7 is also electrically connected to a first electrical contact 720A to which a voltage is applied to the developing roller 71, and to the supply roller 72. The developing unit 7 is further provided with a second contact 720B to which a voltage is applied to the supply roller 72. These electrical contacts come into contact with power supply contacts (not shown) provided in the apparatus main body 2, thereby supplying power to the developing roller 71 and the supply roller 72.

[0021] In conjunction with the closing operation of the door 21 provided in the apparatus main body 2, a developing drive transmission member (not shown) provided in the apparatus main body 2 moves to a position where it engages with a developing coupling (not shown). Conversely, in conjunction with the opening operation of the door 21, the developing drive transmission member moves to a position where it disengages from the developing coupling (not shown). In this way, a drive transmission mechanism is configured from the apparatus main body 2 to the process cartridge 5 via the developing unit 7.

[0022] The developing unit 7 employs two agitating members, a first agitating member 75A and a second agitating member 75B, to agitate the toner in the toner storage section 74. The first agitating member 75A includes an agitating rod 78A and an agitating sheet 79A. The second agitating member 75B includes an agitating rod 78B and an agitating sheet 79B. The second agitating member 75B supplies the toner in the toner storage section 74 to the first agitating member 75A side. The toner near the first agitating member 75A in the toner storage section 74 is agitated by the first agitating member 75A, then supplied to the supply roller 72 side, and further supplied to the developing roller 71 by the supply roller 72.

[0023] Next, the detailed configuration of the photosensitive unit 6 will be described with reference to Figures 4, 5 and 6. Figure 5 is a perspective view of the process cartridge 5. Figure 6 is a perspective view of the developing unit 7 and the photosensitive unit 6.

[0024] As shown in FIG. 4 , the photosensitive unit 6 mainly includes a photosensitive drum 61, a charging roller 62, and a transfer roller 63. As shown in FIGS. 5 and 6 , the photosensitive unit 6 mainly includes a frame (first frame) 610 having a pair of left and right walls 611 and 612, and a photosensitive drum 61 rotatably supported at the rear of the frame 610. In this embodiment, the diameter of the photosensitive drum 61 is 30 mm. The front of the frame 610 is provided with a mounting portion 615 into which the developing unit 7 can be mounted, a gripping portion 617 with which the user grips the photosensitive unit 6, a pressing member 640 that presses the developing unit 7, and a lifting member (moving member) 642 that lifts the developing unit 7. The lifting member 642 lifts the developing unit 7 mounted in the mounting portion 615. The toner storage portion 74 of the developing unit 7 mounted in the mounting portion 615 is located between the left and right walls 611 and 612 in the left-right direction.

[0025] 6, a photosensitive gear 65 and a transfer gear 66 are fixed to the left end of the photosensitive drum 61 and are configured to rotate integrally with the photosensitive drum 61. When the process cartridge 5 is mounted in the apparatus main body 2, a drive gear (not shown) of the apparatus main body 2 meshes with the photosensitive gear 65, transmitting a driving force to the photosensitive drum 61 and the transfer gear 66, enabling them to rotate. Furthermore, the transfer gear 66 meshes with a transfer roller gear 67 fixed to the left end of the transfer roller 63, enabling the transfer roller 63 to rotate as well.

[0026] The photosensitive drum 61 has a support and a photosensitive layer. The support is a conductive support having electrical conductivity, and in this embodiment, an aluminum support is used.

[0027] The lifespan of the developing unit 7, which is determined by the amount of toner stored in the developing unit 7, is set to be shorter than the lifespan of the photosensitive unit 6. Therefore, it is necessary to replace only the developing unit 7 that has reached the end of its life, separately from the photosensitive unit 6. In this case, the door 21 is opened, the process cartridge 5 is removed from inside the apparatus main body 2, the developing unit 7 that has reached the end of its life is removed from the photosensitive unit 6, and another developing unit 7 is attached to the photosensitive unit 6 as shown in the attachment direction AD in Figure 6. Thereafter, the photosensitive unit 6 with the attached developing unit 7 is attached to the apparatus main body 2 as a process cartridge 5.

[0028] <Image Forming Process> Next, the image forming process will be described with reference to Figures 1, 4, and 7A. Figure 7A is an enlarged cross-sectional view of the image forming section of the process cartridge for explaining this embodiment.

[0029] The photosensitive drum 61 is rotated during the image forming process. First, the surface of the photosensitive drum 61 is uniformly charged by a charging roller 62, which is a charging member, and then the surface is exposed to laser light corresponding to image data emitted from the exposure device 4, thereby forming an electrostatic latent image corresponding to the image data on the photosensitive drum 61. In this embodiment, the voltage applied to the charging roller 62 is positive, and the surface of the photosensitive drum 61 is positively charged.

[0030] The toner in the toner storage section 74 is agitated by the second agitating member 75B and the first agitating member 75A, and then supplied to the developing roller 71 via the supply roller 72. The toner supplied to the developing roller 71 then enters between the developing roller 71 and the layer thickness regulating blade 73 and is carried on the developing roller 71 as a thin layer of a constant thickness. In this way, the developing roller 71 functions as a developer carrier that carries the toner, which is the developer.

[0031] The toner carried on the developing roller 71 is supplied to the electrostatic latent image formed on the photosensitive drum 61. As a result, the toner adheres to the electrostatic latent image, making it visible, and a toner image is formed on the photosensitive drum 61.

[0032] Meanwhile, paper S stored in paper feed tray 31 is fed by paper feed mechanism 32 and guided by transport rollers 33 to a transport path formed by the frame of photosensitive unit 6 and the frame of developing unit 7. The transport path is indicated by dashed line P in Figure 4. Paper S passes through transport path P and is transported between photosensitive drum 61 and transfer roller 63 (transfer nip N).

[0033] A desired transfer voltage is applied to the transfer roller 63, which is a transfer member, by a voltage application means (not shown), and the toner image (developer image) on the photosensitive drum 61 is transferred onto the sheet S at the transfer nip N. A separation claw 34 that mechanically separates the sheet S from the photosensitive drum 61 is disposed downstream of the transfer nip N in the paper transport direction. The configuration of this separation claw 34 is unique to this embodiment, and will be described in detail later with reference to Figures 8A and 8B. In this embodiment, the voltage applied to the transfer roller 63 is negative.

[0034] After transfer, the paper S is transported to the fixing device 8, which is disposed behind the process cartridge 5. The fixing device 8 is equipped with a heating roller 92 and a pressure roller 91, which are fixing members. The paper S, onto which the toner image has been transferred, passes through the fixing device 8, during which the paper S is heated and pressurized between the heating roller 92 and the pressure roller 91, and the toner image is fixed onto the paper S. After passing through the fixing device 8, the paper S is discharged onto the paper output tray 22.

[0035] Next, a cleaning unit 200 that mainly removes foreign matter from the surface 61 a of the photosensitive drum 61 will be described with reference to FIGS. 7A and 7B . The cleaning unit 200 is fixed to the frame 610 of the photosensitive unit 6. The cleaning unit 200 has a cleaning roller (cleaning member) 210 as a first collection member that rotates in contact with the surface 61 a of the photosensitive drum 61 to collect foreign matter from the surface of the photosensitive drum 61. The cleaning unit 200 also has a collection roller 220 as a second collection member that rotates in contact with the surface of the cleaning roller 210 to collect foreign matter collected by the cleaning roller 210 from the cleaning roller 210. The cleaning unit 200 further has a scraping member 230 that is disposed so as to be able to slide against the rotating collection roller 220 and scrapes foreign matter from the collection roller 220. The cleaning unit 200 also has a foreign matter collection section 241 that serves as a storage section that forms a storage space for storing foreign matter, and the foreign matter scraped by the scraping member 230 is stored in the foreign matter storage section 241.

[0036] On the other hand, most of the untransferred toner remaining on the photosensitive drum 61 passes through the contact point between the photosensitive drum 61 and the cleaning unit 200, is collected by the developing roller 71, and is returned to the developing unit 7 again.

[0037] <Configuration Unique to This Embodiment> Next, the configuration unique to this embodiment will be described in detail with reference to FIGS. 7A, 7B, 8A, and 8B.

[0038] Fig. 7B is a detailed view of the main components in the vicinity of the transfer nip in Fig. 7A to explain the leading edge position of the conductive sheet (sheet member) 34. Fig. 8A is a cross-sectional view of the conductive sheet 34, and Fig. 8B is a cross-sectional view of the conductive sheet 34 taken along the line A-A.

[0039] The conductive sheet 34 is composed of a resin sheet 341, which is an elastic sheet and an insulating layer, and a metal film 343, which is a conductive layer, and the resin sheet 341 side is attached to the lower surface 610b of the frame 610 with double-sided tape. Separation claws 342, which are protrusions that make point contact with the surface 61a of the photosensitive drum 61, are provided in multiple locations on the front side of the resin sheet 341. As shown in Fig. 7B, these separation claws 342, which are also elastic bodies, are pressed against and come into contact with the surface 61a of the photosensitive drum 61, thereby mechanically peeling the paper S from the surface 61a of the photosensitive drum 61. In other words, one end of the conductive sheet 34 is fixed to the frame 610 so that the other end remains free.

[0040] Here, the resin sheet 341 is a polyester (PET) sheet having a thickness of 80 μm, and the metal film 343 is an aluminum vapor-deposited film having a thickness of approximately 0.2 μm. It is preferable that the thickness of the polyester (PET) sheet is 40 μm or more and 200 μm or less, and the thickness of the aluminum vapor-deposited film is 0.1 μm or more and 0.5 μm or less. Thus, in this embodiment, when viewed from the thickness direction, the conductive sheet 34 can be said to have at least a partial overlap of the aluminum vapor-deposited film, which is the conductive layer, and the polyester sheet, which is the insulating layer.

[0041] The leading edge of the conductive sheet 34 is located within an area Sa that is covered by dashed line L2 (first imaginary line), dashed line L3 (second imaginary line), and the outer periphery of the surface 61a of the photosensitive drum 61. Here, dashed line L2 is a tangent to the photosensitive drum 61 at the downstream end (downstream end point) Na of the transfer nip. Also, dashed line L3 is a perpendicular to dashed line L2 on the downstream side of the transfer nip and is also a tangent to the photosensitive drum 61.

[0042] Furthermore, the metal film 343 as a conductive layer is electrically connected to the support of the photosensitive drum 61 of the photosensitive unit 6 and is configured to have the same potential as the support of the photosensitive drum 61. In this configuration, a cylindrical aluminum cylinder is used for the support of the photosensitive drum 61. Furthermore, when the process cartridge is mounted in the apparatus main body 2, the support of the photosensitive drum 61 is electrically grounded to the apparatus main body 2.

[0043] During the transfer process, a negative transfer voltage is applied by the transfer roller 63 to the sheet S transported through the transfer nip N, causing the sheet S to become negatively charged. Meanwhile, the surface 61a of the photosensitive drum 61 is positively charged, and downstream of the transfer nip N, the sheet S is attracted to the photosensitive drum 61 due to the potential difference between the negatively charged sheet S and the positively charged photosensitive drum surface 61a. To prevent the sheet S ejected from the transfer nip from coming into contact with the frame 610, the leading edge of the conductive sheet 34 must be positioned at least above the dashed line L2. Furthermore, the leading edge of the conductive sheet 34 must be positioned closer to the photosensitive drum 61a than the dashed line L3, which is the area where the electric field from the photosensitive drum 61 affects the sheet S.

[0044] Therefore, in order to stably transport the paper while reducing the electrostatic force between the paper and the photosensitive drum 61, the leading edge of the conductive sheet 34 is located within a neighborhood area Sa of the photosensitive drum surface 61a, which is closer to the photosensitive drum surface 61a than the dashed line L2 and closer to the photosensitive drum surface 61a than the dashed line L3. In this case, when viewed from the direction of the rotation axis of the photosensitive drum 61, at least a portion of the conductive layer overlaps with the neighborhood area Sa.

[0045] As described above, the present invention has a conductive sheet 34 disposed near the photosensitive drum surface 61a, and its potential is the same as that of the support of the photosensitive drum 61. When the potential difference between the negatively charged paper S and the positively charged surface 61a of the photosensitive drum 61 is compared with the potential difference between the negatively charged paper S and the metal film 343, which is the potential between the negatively charged paper S and the support of the photosensitive drum 61, the latter is smaller, and therefore the electric field is weaker. Therefore, the electrostatic force acting on the paper S is weakened, and problems such as the printed surface of the paper S coming into contact with the waste container, which disrupts the toner image on the paper S, and the toner contamination of components downstream of the photosensitive unit can be prevented.

[0046] An experiment was conducted to verify the effectiveness of this embodiment. Resin sheets with and without the conductive layer 343 were prepared, and each was attached to a photoconductor unit to prepare two photoconductor units. Canon CS-052 A4 size paper was used for evaluation, and a paper feed test was conducted in an environment with a temperature of 15°C and humidity of 10%. The evaluation paper was selected because it has low stiffness and tends to be relatively attracted to the photoconductor drum. The evaluation pattern consisted of thin lines approximately 0.1 mm wide printed across the entire surface in the left-right direction (in the direction of the photoconductor rotation axis) at 10 mm intervals, and image distortion due to friction with the underside of the photoconductor unit was confirmed. Furthermore, an external power source was used to output images at a transfer voltage ranging from 1 kV to 3 kV in 0.5 kV increments.

[0047] The evaluation ranks are: A - no image distortion, B - 2 or less lines of image rubbing, C - 5 or less lines, D - 15 or less lines, and E - 16 or more lines of image rubbing. The results of image distortion are shown in Table 1.

[0048]

[0049] As shown in Table 1, in the comparative example without the conductive layer 343, increasing the transfer voltage tends to worsen image distortion. This tendency is due to the fact that the amount of charge on the paper increases with the increase in transfer voltage, and the increased charge causes the paper to be subjected to a greater electrostatic force, making it more likely to be attracted to the photosensitive drum 61.

[0050] Furthermore, when the conductive layer 343 of this embodiment is present, the static electricity applied to the paper is weakened by the effect of this embodiment, so that image distortion does not occur.

[0051] Here, the material of the resin sheet 341 is not limited to polyester, but may include elastic resin sheets such as polyethylene naphthalate resin, polycarbonate, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polystyrene, polyamide, polyarylate polyethylene naphthalate, polybutylene naphthalate, and thermoplastic polyimide.

[0052] On the other hand, if the resin sheet 341 is made of an insulator, a memory image may occur due to friction with the photosensitive drum 61. This occurs when the resin sheet 341 becomes excessively charged due to friction with the photosensitive drum 61, and the charge is discharged from the resin sheet 341 to the photosensitive drum 61. Adjusting the resistance value of the resin sheet 341 by its material is an effective countermeasure against memory images. For example, it is possible to prevent memory images by dispersing carbon black as an electrical resistance adjuster to form a high-resistivity sheet with a volume resistivity of 10^8 Ω cm or more.

[0053] The conductive layer 343 is not limited to aluminum, and any conductive metal film may be used. Although the manufacturing method has been described using vapor deposition as an example, it is not limited to this, and sputtering or CVD may also be used.

[0054] Furthermore, the conductive layer as a conductor can be expected to be effective if it has a medium to low surface resistivity of 1.00 x 10^6 Ω / sq or less. As long as this medium to low resistivity resistance value is met, the metal coating may be thin. Alternatively, the conductive layer 343 may be formed by coating a curable resin containing a conductive filler such as carbon black, as described above.

[0055] The cleaning unit 200 must collect foreign matter throughout the life of the photosensitive unit 6. Because the amount of foreign matter collected varies depending on the life setting of the photosensitive unit 6, if the life of the photosensitive unit 6 is set longer, the capacity of the foreign matter storage compartment 241 must be increased accordingly. Expanding the foreign matter storage compartment 241 rearward in the front-to-rear direction may further increase the size of the photosensitive unit 6 rearward, potentially lengthening the transport path between the transfer and fixing stages. This affects the transportable paper size and the size of the device main body 2. Furthermore, expanding the foreign matter storage compartment 241 downward in the vertical direction would bring the downstream transfer side lower portion 610a of the frame 610 of the photosensitive unit 6 closer to the transport path, increasing the risk of image distortion due to contact with the downstream transfer side lower portion 610a. For these reasons, the configuration of this embodiment is particularly effective for photosensitive units with long lifespans.

[0056] 8A, the conductive sheet 34 has three contact positions in the longitudinal direction, but this is not limited to this. Also, although the method of fixing the conductive sheet 34 to the photosensitive unit 6 is described in this embodiment using double-sided tape, this is not limited to this.

[0057] 8A, in the range where the conductive sheet 34 is provided along the direction of the rotation axis of the photosensitive drum, it can be said that the conductive sheet 34 is in contact with the surface of the photosensitive drum at the first position, which is the contact position, and that the conductive sheet 34 is not in contact with the surface of the photosensitive drum at the second position, which is the non-contact position.

[0058] Furthermore, instead of the sponge 230, a blade made of an elastic material such as rubber may be used as the scraping member.

[0059] In this embodiment, the positioning of the leading edge of the conductive sheet 34 has been described, but there is also a desirable arrangement for parts other than the leading edge. That is, in the region from the dashed line L3 toward the photosensitive drum 61, parts other than the leading edge of the conductive sheet 34 should be arranged above the dashed line L2, which reduces the risk of contact between the paper S and the conductive sheet 34.

[0060] The above describes a desirable form for locating the leading edge of the conductive sheet 34, and this region Sa begins from the downstream end Na of the transfer nip N. In this embodiment, in which the frame 610 of the photosensitive unit 6 supports the transfer roller 63, it is possible to reduce the positional variation of the downstream end Na of the transfer nip on the photosensitive drum. This increases the degree of freedom in locating the conductive sheet 34 in the desired region Sa. Of course, in a configuration in which the transfer roller is provided in the device main body, the degree of freedom in locating the conductive sheet 34 is reduced, but it goes without saying that the same effect can be obtained by locating the conductive sheet 34 in the region Sa.

[0061] As described above, after the conveyed paper is mechanically separated from the photosensitive drum, an electrostatic force acts on the conveyed paper, attracting it to the photosensitive drum and preventing it from passing near the photosensitive drum. This is particularly effective for thin paper, which is easily attracted to the photosensitive drum. It is also suitable for the photosensitive drum downstream of the transfer section to have a recovery unit for recovering residual toner and foreign matter, as well as a recovery container for storing the recovered toner. This effectively prevents the printed surface of the conveyed paper ejected from the transfer section coming into contact with the recovery container near the photosensitive drum, which can disrupt the toner image on the conveyed paper and contaminate components downstream of the photosensitive drum with toner.

[0062] Because the area that comes into contact with the photosensitive drum is insulating, there is no uneven charging, which would occur if a conductive object came into contact with the photosensitive drum. Uneven charging can lead to uneven recharging in the charging process, which is a later step in the image formation process. This can also result in image abnormalities, such as memory images. However, this embodiment can effectively prevent such a phenomenon.

[0063] Even if the transported paper electrostatically adheres to the surface of the photosensitive drum, which is the image carrier, the leading edge of the conductive sheet is in contact with the photosensitive drum, so it can be separated reliably without slipping through the gap between the conductive sheet and the photosensitive drum. In addition, because the metal film is located close to the photosensitive drum, the electrostatic force that attracts the paper to the photosensitive drum after separation is weakened.

[0064] Therefore, in this embodiment, it is possible to mechanically separate the transported paper from the photosensitive drum while weakening the electrostatic force that attracts the transported paper to the photosensitive drum, thereby preventing problems such as the transported paper being attracted by electrostatic force and the printed surface coming into contact with the collection container, which disrupts the toner image on the paper and causes toner contamination of components downstream of the photosensitive drum.

[0065] [Second Embodiment] A second embodiment will be described using Figures 9A to 9C. Figures 9A to 9C illustrate the conductive sheet 34, which is a conductive member and separation claw that characterizes this embodiment. Figure 9A is a view of the conductive sheet from below, and Figure 9B is a cross-sectional view taken along dashed line A-A in Figure 9A. Figure 9C is a detailed view of the main components near the transfer nip to explain the vicinity of the leading edge of the conductive sheet 34.

[0066] In this embodiment, the resin portion 341 of the conductive sheet 34 is rubbed and worn away as the photosensitive unit 6 is used, thereby preventing the conductive layer 343 from coming into contact with the drum.

[0067] The separation claw, which is the tip of the conductive sheet 34 that contacts and rubs against the surface 61a of the photosensitive drum 61, undergoes resin wear with use. In the shape of the first embodiment shown in Figures 8A and 8B, wear progresses and the conductive layer 343 comes into contact with the photosensitive drum 61, which can cause the charged charge on the surface of the photosensitive drum 61 to leak to the photosensitive drum substrate via the conductive layer 343. This can cause charging unevenness between the area where the conductive sheet 34, which is the separation claw, contacts the photosensitive drum 61 and the area where it does not. If this charging unevenness causes the image to be non-uniformly recharged in the subsequent charging process, image abnormalities will become apparent as memory images.

[0068] In this embodiment, by providing an exposed portion 344 of the resin sheet as shown in Figures 9A to 9C, the purpose is to prevent contact of the conductive layer 343 with the photosensitive drum 61 and to prevent leakage of electric charge from the conductive layer 343 to the photosensitive drum 61, which causes memory images.

[0069] An example of this exposed portion 344 will be described in detail using Figures 9B and 9C. Figure 9C shows the case where the photosensitive drum has been removed from the photosensitive unit of this embodiment, with the surface of the imaginary photosensitive drum indicated by the dashed line 61b. Since there is no photosensitive drum for the conductive sheet 34 to abut, the conductive sheet 34 penetrates straight into the imaginary photosensitive drum. Here, the distance by which the conductive sheet 34 penetrates into the photosensitive drum surface 61b is defined as an intrusion amount D1. Meanwhile, as shown in Figure 9B, the distance from the tip of the exposed portion 344 to the conductive layer 343 is defined as D2, and the relationship between the distance D1 and the distance D2 is set as shown in Equation 1 below. D1>D2 (Equation 1)

[0070] This prevents the conductive layer 343 from coming into contact with the surface of the photosensitive drum even when the resin sheet 341 is worn, thereby preventing the occurrence of image memory. This configuration is particularly effective for photosensitive units with long life specifications.

[0071] Furthermore, it goes without saying that the conductive sheet 34 is positioned so that the end of the conductive layer 343 of the conductive sheet 34 on the photosensitive drum side is included within the area Sa covered by the dashed line L2, the dashed line L3, and the surface 61a of the photosensitive drum 61, and by doing so, the same effect as in Example 1 is achieved.

[0072] Although the configuration of this embodiment has been described using the relationship of Equation 1 as an example, it is not necessary to necessarily satisfy Equation 1. For example, the distance D2 of the conductive sheet 34 may be set based on the amount of wear of the conductive sheet 34 and the cartridge lifespan, and the distance D2 may be set to be equal to or less than the penetration amount D1.

[0073] The conductive layer 343 in FIG. 9B may be attached to the lower surface 610 b of the frame 610 .

[0074] Since the exposed portion 344 of the resin sheet is provided, it is not the conductive layer 343 but the exposed portion 344 of the resin sheet that comes into contact with the photosensitive drum surface 61b.

[0075] In this case, when the image forming device is viewed from the direction of gravity, the resin sheet overlaps the conductive layer on the downstream side of the conveying direction of the recording material at the transfer nip of the conductive sheet, and the resin sheet does not overlap the conductive layer on the upstream side.

[0076] [Third Embodiment] Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings. A third example will be described with reference to Fig. 10. Fig. 10 shows a configuration in which the conductive sheet 34 is extended rearward from the lower surface of the photosensitive unit.

[0077] The lower surface 610a of the photosensitive unit may become charged. The source of the charge that causes the charge may be foreign matter or toner in the foreign matter collection container 241. The charge on the lower surface 610a of the photosensitive unit due to these factors is more unstable than the charge on the photosensitive drum 61, and in some cases may increase the potential difference with the paper, causing the paper to be strongly attracted.

[0078] To address this issue, it is effective to extend the conductive sheet 34 rearward from the underside of the photosensitive unit. The area of ​​the rearward extension is preferably an area that includes the rearmost end of the foreign matter storage section 241, which is the source of the charge that causes charging. By limiting the area to the rearmost end of the foreign matter storage section 241, the amount of conductive sheet 34 used is not increased more than necessary, and costs can be kept to a minimum.

[0079] Furthermore, the effect can be achieved even if the conductive sheet 34 is not grounded to the support of the photosensitive drum 61 as in Example 1. This is because the charged potential of the lower surface 610a of the photosensitive unit 6 varies depending on the position, and the conductive sheet 34 averages out the uneven surface potential.

[0080] While the first and second embodiments specify the position of the conductive sheet 34 on the photosensitive drum side, this embodiment describes the position in the rear direction. Even in the configurations of the first and second embodiments, if the rear of the conductive sheet 34 overlaps the lower surface 610a of the photosensitive unit, the conductive sheet 34 is effective even if it is not grounded to the support body of the photosensitive drum 61.

[0081] In this embodiment, the conductive sheet 34 is described as an integrated sheet extending rearward, but it may be a plurality of sheets with separate functions for the separation claws and the remaining rear portion.

[0082] 11A and 11B, a fourth embodiment will be described. In this embodiment, a conductive plate such as a metal plate is disposed as a conductive member near the photosensitive drum in a non-contact manner.

[0083] 11A shows the state in which the metal plate 35 is disposed near the photosensitive drum 61. The conductive sheet 35 has the same configuration as in Example 1. The aluminum vapor deposition film provided on the conductive sheet 35 is electrically connected to the support of the photosensitive drum 61. This resin sheet 35 is disposed longitudinally in the direction of the rotation axis of the photosensitive drum 61, i.e., across the left-right direction of the device main body 2. Because the conductive sheet 35 is not in contact with the photosensitive drum surface 61a, it does not have the function of mechanically peeling off the paper S, but the paper S is peeled off from the photosensitive drum surface 61a due to the curvature of the photosensitive drum.

[0084] Here, the aluminum vapor deposition film of the conductive sheet 35 has the same potential as the support of the photosensitive drum 61, and can reduce the electrostatic force acting on the paper S, as in the first embodiment. Therefore, the electrostatic force acting on the paper is weakened, which stabilizes the paper transport and prevents image distortion and other problems.

[0085] FIG. 11B is a diagram illustrating the main components in the vicinity of the transfer nip in FIG. 11A in order to explain the leading edge position of the conductive sheet 35. In FIG.

[0086] The leading edge of the conductive sheet 35 near the photosensitive drum 61 is located within an area Sa covered by the dashed lines L2 and L3 and the surface 61a of the photosensitive drum 61. Here, the dashed line L2 is a tangent to the photosensitive drum 61 at the downstream end Na of the transfer nip. The dashed line L3 is a tangent to the photosensitive drum 61 that is perpendicular to the dashed line L2 on the downstream side of the transfer nip.

[0087] By positioning the leading edge of the conductive sheet 35 at least above the dashed line L2, transport failures caused by the paper getting caught between the conductive sheet 35 and the photosensitive drum 61 are prevented. In order to reduce the electrostatic force between the paper and the photosensitive drum 61, the leading edge of the conductive sheet 35 is positioned at least closer to the photosensitive drum surface 61a than the dashed line L3, thereby preventing image distortion and transport path contamination.

[0088] The unique effect of this embodiment is that the conductive layer is arranged in a non-contact manner with the photosensitive drum, thereby preventing scratches on the surface of the photosensitive drum due to friction and preventing memory images.

[0089] The above describes a desirable form for positioning the leading edge of the conductive sheet 35, and this area Sa begins at the downstream end Na of the transfer nip N. In this embodiment, in which the frame 610 of the photosensitive unit 6 supports the transfer roller 63, it is possible to reduce the positional variation of the downstream end Na of the transfer nip on the photosensitive drum. This improves the accuracy with which the conductive sheet 35 is forced into the desired area Sa. Needless to say, the same effect can be obtained by forcing the metal plate 35 into the area Sa even in a configuration in which the transfer roller is provided in the device main body.

[0090] The conductive sheet 35 is an insulating resin sheet 341 having a metal film 343 on one surface.

[0091] The conductive sheet 35 is disposed so that the resin sheet 341 faces the surface of the photosensitive drum 61. The metal film 343 is formed on the surface of the resin sheet 341 opposite to the side where the photosensitive drum 61 is located. In this way, the conductive sheet 35 is configured as a two-layer structure with the resin sheet 341 and the metal film 343 provided.

[0092] Suppose the leading edge of the conductive sheet 35 comes into contact with the photosensitive drum 61. In such a case, the contact of the metal film 343 causes the charge on the photosensitive drum 61 to leak at the contact point, resulting in uneven surface potential of the photosensitive drum 61. If this unevenness is not eliminated in the charging process, it is conceivable that a problem such as drum ghosts becoming apparent in the printed image may occur.

[0093] However, by adopting the configuration of this embodiment, even if the tip of the conductive sheet 35 happens to come into contact with the photosensitive drum 61, the contact will be with the insulating resin sheet 341, thereby preventing the above-mentioned problems.

[0094] The present invention is not limited to the above-described embodiments, and various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to apprise the public of the scope of the present invention.

[0095] This application claims priority based on Japanese Patent Application No. 2023-173991, filed on October 6, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. An image forming apparatus for forming an image on a recording material, comprising: a photosensitive drum for carrying a toner image; a frame for rotatably supporting the photosensitive drum; a sheet member having one end fixed to the frame while the other end is a free end; and a transfer roller for contacting the photosensitive drum to form a transfer nip and transferring the toner image to the recording material as the recording material is transported and passes through the transfer nip; wherein the sheet member includes a conductive layer and an insulating layer, and is provided downstream in the transport direction of the recording material at the transfer nip, wherein when viewed in the thickness direction of the sheet member, the conductive layer and the insulating layer overlap at least in part, and the insulating layer is closer to the photosensitive drum than the conductive layer and is positioned so as to face the surface of the photosensitive drum.

2. The image forming apparatus according to claim 1, wherein the one end is an end of the insulating layer and abuts against the surface of the photosensitive drum.

3. The image forming apparatus according to claim 1, wherein said conductive layer is electrically grounded.

4. The image forming apparatus according to claim 1, characterized in that the photosensitive drum has a cylindrical conductive support and a photosensitive layer supported by the support and formed on the surface of the support, and the support and the conductive layer are electrically connected.

5. The image forming apparatus according to claim 1, wherein the insulating layer is fixed to the frame, and the conductive layer is provided on the opposite side of the insulating layer to the side that contacts the photosensitive drum.

6. The image forming apparatus according to claim 1, characterized in that the conductive layer is fixed to the frame, the insulating layer is provided on the opposite side of the conductive layer from the side that contacts the photosensitive drum, and when viewed from the direction of gravity, the insulating layer overlaps the conductive layer on the downstream side of the transfer nip of the sheet member in the conveying direction of the recording material, and the insulating layer does not overlap the conductive layer on the upstream side.

7. The image forming apparatus according to claim 1, further comprising a cleaning member that collects and cleans toner that has not been transferred to the recording material from the photosensitive drum, and a storage section that stores the toner collected by the cleaning member, wherein when viewed from the direction of gravity, the other end overlaps with the storage section.

8. The image forming apparatus according to claim 1, characterized in that the material of the conductive layer includes either a metal or carbon black, and the material of the insulating layer includes either polyester, polyethylene naphthalate, polycarbonate, polyvinylidene fluoride, polyethylene, polypropylene, polystyrene, polyamide, polyarylate polyethylene naphthalate, polybutylene naphthalate, or thermoplastic polyimide.

9. The image forming apparatus according to claim 1, further comprising: an apparatus main body; and a cartridge configured to be detachably attached to the apparatus main body, the cartridge comprising the photosensitive drum, the frame, and the sheet member.

10. The image forming apparatus according to claim 9, further comprising: a cleaning member that collects and cleans toner that has not been transferred to the recording material from the photosensitive drum; and a storage section that stores the toner collected by the cleaning member, wherein the transfer roller, the cleaning member, and the storage section are integrally supported by the frame body and are provided in the cartridge.

11. The image forming apparatus according to claim 1, characterized in that the surface resistivity of the conductive layer is 1.0 x 10^6 Ω / sq or less, and the volume resistivity of the insulating layer is 1.0 x 10^8 Ω·cm or more.

12. The image forming apparatus according to claim 1, wherein the conductive layer has a thickness of 0.1 μm or more and 0.5 μm or less, and the insulating layer has a thickness of 40 μm or more and 200 μm or less.

13. An image forming apparatus as described in claim 1, characterized in that, in a range in which the sheet member is provided in the direction of the rotation axis of the photosensitive drum, at a first position the sheet member abuts against the surface of the photosensitive drum, and at a second position the sheet member does not abut against the surface of the photosensitive drum.

14. The image forming apparatus of claim 1, characterized in that, when viewed from the direction of the rotation axis of the photosensitive drum, a tangent line that passes through the downstream end point of the transfer nip and touches the outer periphery of the photosensitive drum in the paper transport direction at the transfer nip is defined as a first imaginary line, and a tangent line that is perpendicular to the first imaginary line and touches the outer periphery of the photosensitive drum and is downstream in the paper transport direction at the transfer nip is defined as a second imaginary line, at least a portion of the conductive layer overlaps with an area surrounded by the first imaginary line, the second imaginary line, and the outer periphery.

15. A drum cartridge configured to be detachably attached to an image forming device that forms an image on a recording material, comprising: a photosensitive drum that carries a toner image; a frame that rotatably supports the photosensitive drum; a sheet member having one end fixed to the frame while the other end is a free end; and a transfer roller that contacts the photosensitive drum to form a transfer nip and transfers the toner image to the recording material when the recording material passes through the transfer nip, wherein the sheet member includes a conductive layer and an insulating layer, and is provided downstream in the transport direction of the recording material at the transfer nip, when viewed in the thickness direction of the sheet member, the conductive layer and the insulating layer at least partially overlap, and the insulating layer is positioned so as to face the surface of the photosensitive drum.

16. The drum cartridge according to claim 15, characterized in that, when the frame body is a first frame body, a developing cartridge including a developing roller for developing an electrostatic latent image on the photosensitive drum, and a second frame body for rotatably supporting the developing roller is configured to be detachably attached.

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