Image forming apparatus

Abstract

To provide an image forming apparatus that can achieve both miniaturization and transferability.SOLUTION: An image forming apparatus has: an image carrier; a rotatable transfer member that is in contact with a surface of the image carrier to form a transfer nip part and transfers a toner supplied to the surface of the image carrier to a recording material at the transfer nip part; a static eliminating member that eliminates static electricity from a surface of the transfer member at a facing part that faces the surface of the transfer member on the upstream side of the transfer nip part in the direction of rotation of the transfer member and on the upstream side of the transfer nip part in the direction of movement of the recording material; a guide member that is in contact with a surface of the recording material opposite to a surface to which the toner is transferred, to guide conveyance of the recording material to the transfer nip part; and a transfer voltage application unit that applies a transfer voltage to the transfer member. The guide member and the static eliminating member are grounded via the same current suppression circuit. The static eliminating member eliminates static electricity from the surface of the transfer member at the facing part, while the transfer voltage is applied to the transfer member.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Conventionally, some electrophotographic image forming apparatuses use an endless belt that rotates while carrying a toner image. For example, in an intermediate transfer image forming apparatus, a toner image is primarily transferred from a photosensitive member to an intermediate transfer belt, which is an intermediate transfer member formed of an endless belt, at a primary transfer section. The toner image primarily transferred to the intermediate transfer belt is then transferred to a recording material at a secondary transfer nip by a transfer voltage applied to a secondary transfer roller.

[0003] In image forming devices using such intermediate transfer belts, abnormal discharge occurs between the recording material and the intermediate transfer belt in the discharge area formed just before the secondary transfer nip, causing image defects (whiteouts) in which the toner image in the abnormally discharged area is not transferred and is missing.

[0004] One proposed method for suppressing this image defect is to contact a grounded charge removal unit with the surface of the secondary transfer roller immediately before the secondary transfer unit, thereby lowering the potential on the surface of the secondary transfer roller and weakening the electric field in the discharge area (Patent Document 1). Patent Document 1 also describes a configuration in which a transport guide is placed before the transfer nip as a guide means for stably guiding the recording material to the transfer nip. If such a transport guide is not electrically grounded, a charged potential may be generated due to friction with the recording material in a low-humidity environment, and this potential may interfere with transfer efficiency. Therefore, a common configuration is to ground the transport guide to allow the charged potential to escape. However, if the transport guide is directly grounded without a resistor, when a toner image is transferred to a recording material whose resistance has decreased due to moisture absorption, transfer current may flow through the recording material to the transport guide, resulting in transfer defects. Patent Document 2 proposes a method for suppressing this transfer defect by grounding the transport guide through a high-resistance resistor element. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-197114 [Patent Document 2] Japanese Patent Application Publication No. 59-34570 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the configurations of Cited Documents 1 and 2 have the following problems: In particular, if the conveying guide and the static eliminator are grounded by separate conductive paths, the configuration of the conductive path itself and the configuration for electrically connecting the conductive path to the conveying guide and the control electrode are required in the limited space before transfer, which results in a problem of an increase in the size of the image forming apparatus.

[0007] SUMMARY OF THE INVENTION The object of the present invention is to solve the above problems and to provide an image forming apparatus that is both compact and has good transferability. [Means for solving the problem]

[0008] The image forming apparatus of the present invention comprises an image carrier, a rotatable transfer member that abuts against the surface of the image carrier to form a transfer nip portion and transfers toner supplied to the surface of the image carrier at the transfer nip portion to a recording material, a discharge member that discharges the surface of the transfer member at an opposing portion that is upstream of the transfer nip portion in the rotation direction of the transfer member and faces the surface of the transfer member upstream of the transfer nip portion in the movement direction of the recording material, a guide member that guides the transport of the recording material to the transfer nip portion by contacting the surface of the recording material opposite to the surface to which the toner is transferred, and a transfer voltage application portion that applies a transfer voltage to the transfer member, wherein the guide member and the discharge member are grounded via the same current suppression circuit, and the discharge member discharges the surface of the transfer member at the opposing portion while the transfer voltage is applied to the transfer member. [Effects of the Invention]

[0009] According to the present invention, it is possible to achieve both miniaturization of the image forming apparatus and transferability. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram for explaining an image forming apparatus according to a first embodiment. [Figure 2] FIG. 3 is an enlarged view of a secondary transfer portion according to the first embodiment. [Figure 3] 1 is a schematic diagram of a current suppression circuit according to first and second embodiments. [Figure 4] 10A and 10B are enlarged views of secondary transfer portions according to Comparative Example 1, Modification Example 1, and Modification Example 2. [Figure 5] FIG. 10 is an enlarged view of a secondary transfer portion according to a third embodiment. [Figure 6] FIG. 10 is a schematic diagram of a current suppression circuit according to a fourth embodiment. [Figure 7] FIG. 10 is a schematic diagram of a current suppression circuit according to another embodiment. [Figure 8] FIG. 2 is a control block diagram according to the first embodiment. [Figure 9] FIG. 10 is a diagram for explaining an image forming apparatus according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] The following describes in detail exemplary embodiments of the present invention with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the embodiments may be changed as appropriate depending on the configuration of the device to which the invention is applied and various conditions, and the scope of the present invention is not limited to the following embodiments.

[0012] [Example 1] <Overall Configuration and Operation of Image Forming Apparatus> An image forming apparatus 500 according to this embodiment shown in FIG. 1 is a tandem type full-color image forming apparatus that uses an intermediate transfer member as an image carrier, and the figure is a cross-sectional view showing the schematic configuration thereof.

[0013] In the image forming apparatus 500 of the first embodiment, four image forming units, i.e., image forming units 1a, 1b, 1c, and 1d, which respectively form toner images of yellow (Y), magenta (M), cyan (C), and black (Bk), are arranged from upstream to downstream. These four image forming units are arranged in a line (side by side) at regular intervals. The four image forming units are image forming unit 1a, which forms yellow images, image forming unit 1b, which forms magenta images, image forming unit 1c, which forms cyan images, and image forming unit 1d, which forms black images. When the image forming apparatus 500 is installed, an intermediate transfer belt 8, which is an intermediate transfer member stretched over rollers 12 and 13, is disposed below the image forming units 1a, 1b, 1c, and 1d in the direction of gravity.

[0014] Each image forming unit 1a, 1b, 1c, and 1d is provided with a photosensitive drum 2a, 2b, 2c, and 2d, respectively, as an image carrier. In this embodiment, the photosensitive drums 2a, 2b, 2c, and 2d are negatively charged organic photosensitive members having a photosensitive layer on a drum substrate made of aluminum or the like, and are driven to rotate at a predetermined process speed by a drive unit 160 (FIG. 8) as a drive device. In this embodiment, the process speed was set to 100 mm / sec.

[0015] Developing devices 5a, 5b, 5c, and 5d are arranged around the photosensitive drums 2a, 2b, 2c, and 2d, respectively, and include charging rollers 3a, 3b, 3c, and 3d, which serve as charging members, and developing rollers 4a, 4b, 4c, and 4d, which serve as developing members and developer carriers. Developing devices 5a, 5b, 5c, and 5d contain toners 90a, 90b, 90c, and 90d, respectively, corresponding to yellow (Y), magenta (M), cyan (C), and black (Bk). Non-magnetic, single-component polymerized toners with a charge of -20 to -50 μC / mg were used for the toners 90a, 90b, 90c, and 90d. The normal charge polarity of the toners 90a, 90b, 90c, and 90d is negative. This image forming apparatus 500 employs a reverse development system. Furthermore, cleaning devices 6a, 6b, 6c, and 6d having cleaning blades 7a, 7b, 7c, and 7d as cleaning members are installed around each of the photosensitive drums 2a, 2b, 2c, and 2d. The cleaning blades 7a, 7b, 7c, and 7d scrape off foreign matter such as toner, paper dust, and fillers remaining on the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d, and collect the remaining foreign matter inside the cleaning devices 6a, 6b, 6c, and 6d. Furthermore, exposure devices 9a, 9b, 9c, and 9d are installed above each of the photosensitive drums 2a, 2b, 2c, and 2d in the direction of gravity.

[0016] Here, the configuration and operation of each image forming unit 1 are essentially the same except for the different colors of toner used. Therefore, unless a particular distinction is required in the following description, the suffixes a, b, c, and d given to the reference numerals in FIG. 1 will be omitted to indicate that the element is provided for one of the colors, and the description will be generalized. Also, in this embodiment, four image forming units 1 will be described, but this is not limited to this, and multiple image forming units 1 may be provided. Also, as will be described later, it is possible to use a monochrome printer having a single image forming unit 1.

[0017] A rotatable, endless intermediate transfer belt 8 is installed as an intermediate transfer body at positions facing the image forming units 1a, 1b, 1c, and 1d. Primary transfer rollers 41a, 41b, 41c, and 41d are arranged to transfer the toner images formed on the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d onto the surface of the intermediate transfer belt 8. The intermediate transfer belt 8 is stretched by a secondary transfer opposing roller 12 and a tension roller 13, which also serve as tensioning members and drive the intermediate transfer belt 8. The secondary transfer opposing roller 12, which is connected to a drive unit 160 serving as a motor, rotates (moves) the intermediate transfer belt 8 in the direction of arrow Z shown in FIG. 1 (counterclockwise in FIG. 1). As shown in FIG. 1, four image forming units 1 and four primary transfer rollers 41 are arranged in parallel along the rotational direction of the intermediate transfer belt 8. Hereinafter, the rotational direction of the intermediate transfer belt 8 will be referred to as the circumferential direction of the intermediate transfer belt 8. The thickness of the intermediate transfer belt 8 is preferably 50 μm to 200 μm, because if it is too thin, the belt strength weakens, and if it is too thick, it loses elasticity and becomes difficult to bend. Furthermore, the thickness affects the electrostatic capacitance of the intermediate transfer belt 8. If it is too thin, the electrostatic capacitance increases and it is prone to charging. In consideration of this, in this embodiment, the thickness of the intermediate transfer belt 8 is set to 80 μm. Materials commonly used for the intermediate transfer belt 8 include PI, PET, PEN, and PVDF, but PI was used for its strength. The resistance of the intermediate transfer belt 8 must be adjusted by adding a conductive agent to achieve the desired electrical resistance. In this embodiment, carbon black is used as the conductive agent. Generally, the conductive mechanism of carbon black is electronic conductivity, which has little environmental dependency but high voltage dependency. On the other hand, ionic conductive agents have little voltage dependency but high environmental dependency. In this embodiment, the resistance increase of the intermediate transfer belt 8 in a low-humidity environment is suppressed, and abnormal discharge during secondary transfer is suppressed by lowering the secondary transfer voltage required for secondary transfer. In addition, the addition of a small amount of carbon black makes it possible to adjust the electrical resistance, and it is preferable because it can be produced at low cost. 8 ~10 14 The range is Ω·cm. 10 8If the resistivity is less than Ω·cm, the charge of the toner transferred onto the intermediate transfer belt 8 will flow out onto the intermediate transfer belt 8, which will cause the toner image to become distorted. 14 If it exceeds Ω·cm, the voltage required for secondary transfer becomes large, making abnormal discharge more likely to occur.

[0018] The drive unit 160 may have a drive unit for the secondary transfer opposing roller 12 separate from the photosensitive drum 2.

[0019] 8, a transfer voltage (bias) of positive polarity opposite to the normal polarity of toner 90 is applied to primary transfer roller 41. The transfer voltage (bias) is constant voltage or constant current controlled from primary transfer power source 73 as a primary transfer voltage application unit shown in FIG. 8. Then, the toner image formed on photosensitive drum 2 is transferred onto intermediate transfer belt 8.

[0020] Secondary transfer roller 15, which serves as a secondary transfer member, transfers the toner image formed on intermediate transfer belt 8 to transfer material S, which serves as a recording material. In this embodiment, a secondary transfer roller having a diameter of 18 mm is used, which is made by covering a metal core having a diameter of 8 mm with an NBR foam sponge body. A constant voltage or constant current controlled positive voltage is applied to secondary transfer roller 15 from secondary transfer power source 74, which serves as a secondary transfer voltage application unit shown in FIG.

[0021] The secondary transfer opposing roller 12 is provided with a high friction rubber layer on the surface to drive the intermediate transfer belt 8. This rubber layer has a volume resistivity of 10 5 It has a conductivity of Ω·cm or less. It also abuts against a secondary transfer roller 15, which serves as a secondary transfer member, via the intermediate transfer belt 8, to form a secondary transfer section SN. Here, the secondary transfer roller 15 is disposed so as to abut against the intermediate transfer belt 8, and forms a secondary transfer nip SN between it and the intermediate transfer belt 8, as shown in FIG. 1. The tension roller 13 applies a total tension of approximately 60 N to the intermediate transfer belt 8, and rotates in accordance with the intermediate transfer belt 8.

[0022] The secondary transfer opposing roller 12 (opposing member) and the tension roller 13 are each grounded via a resistive element having the same resistance value. In this embodiment, three types of resistive elements are used: 100 MΩ, 10 MΩ, and 10 MΩ. The resistance of the rubber layer of the secondary transfer opposing roller 12 is sufficiently smaller than 100 MΩ and 10 MΩ, so electrical influences can be ignored.

[0023] The secondary transfer roller 15 has a volume resistivity of 10 7 ~10 9 An elastic roller with a resistance of Ωcm and a rubber hardness of 30° (Asker C hardness scale) was used. The transfer roller 15 was configured to press the secondary transfer opposing roller 12 with a total pressure of approximately 39.2 N via the intermediate transfer belt 8. The secondary transfer roller 15 rotates in accordance with the rotation of the intermediate transfer belt 8. A secondary transfer voltage of -2.0 to 7.0 kV can be applied to the transfer roller 15 from a secondary transfer voltage application unit 74, which serves as a secondary transfer (high-voltage) power source shown in FIG. 8. The secondary transfer roller 15 corresponds to the transfer member, and the secondary transfer roller 15 and the secondary transfer power source 74 correspond to the secondary transfer means. A belt cleaning device 75 having a belt cleaning blade 80 as a belt cleaning member for removing and collecting residual toner remaining on the surface of the intermediate transfer belt 8 is installed on the outer periphery of the intermediate transfer belt 8.

[0024] As shown in FIG. 2, the secondary transfer roller 15 has a cylindrical core 15b and a cylindrical elastic layer 15a that covers the outer circumferential surface of the core 15b. The outer diameter of the core 15b is 6 mm, and the outer diameter of the elastic layer 15a is 16 mm. The core 15b is made of a highly rigid conductive material, and in this embodiment, iron is used. The elastic layer 15a is made of commonly used acrylonitrile butadiene rubber (NBR) ion conductive rubber that has been foamed into a sponge-like shape. The volume resistivity of the elastic layer 15a in this embodiment is 10 7 ~10 9Ω·cm. If the volume resistivity of the secondary transfer roller 15 is too low, the resistance of the transfer material S will have a large effect on the transferability, which may result in unstable transferability depending on the environment. Conversely, if the volume resistivity is too high, the voltage required for secondary transfer will increase, making it more likely that abnormal discharge will occur. For this reason, the volume resistivity of the elastic layer 15a is set to 10 5 ~10 11 A hardness in the Ω·cm range is desirable. If the hardness of the secondary transfer roller 15 is too soft, the width of the transfer nip portion SN will increase, which will increase the torque of the driven secondary transfer roller 15. If the hardness is too hard, the nip width of the transfer nip portion SN will narrow, which may result in poor transfer. Therefore, the hardness of the secondary transfer roller 15 is preferably 20° to 40° when using an Asker C hardness tester with a 500g load. The secondary transfer roller 15 used had a hardness of 30° when using an Asker C hardness tester with a 500g load.

[0025] Line W in FIG. 1 is a conveyance line indicating the conveyance path along which transfer material S is conveyed when an image is formed on the first surface (front surface) of transfer material S. The paper feed unit feeds and conveys transfer material S to secondary transfer unit SN, and multiple transfer materials S are stored in paper feed cassette 16. During image formation, a pickup roller 17 (a half-moon roller) picks up the top transfer material S stacked on paper feed cassette 16, and a pair of paper feed rollers 18 conveys the transfer material S to a pair of registration rollers 19, which are conveyance rollers. The leading edge of transfer material S strikes the pair of registration rollers 19 and stops temporarily. A toner image formed by image forming unit 1 is transferred to intermediate transfer belt 8. At this time, the transfer material S is conveyed to secondary transfer unit SN by registration roller pair 19, while being regulated by regulating portion A, which serves as a guide portion of conveyance guide 32, which serves as a guide member, in synchronization with the leading edge of the toner image on intermediate transfer belt 8 moving to secondary transfer unit SN. Then, the toner image on intermediate transfer belt 8 is transferred to transfer material S.

[0026] A downstream charge elimination needle 40 is disposed downstream in the conveyance direction of the transfer material S to eliminate charge formed on the transfer material S. The downstream charge elimination needle 40 is a 0.1 mm-thick SUS304 thin plate processed into a sawtooth shape, with a pitch of 1 mm between adjacent sawtooth teeth. The downstream charge elimination needle 40 is installed at a height that does not contact the conveyed transfer material S, with the tip of the sawtooth facing the second surface (back surface) of the transfer material S. By eliminating the charge on the transfer material S downstream in the conveyance direction of the transfer material S that has passed through the secondary transfer unit T, the electrostatic attraction force to the intermediate transfer belt 8 is reduced, improving the separation of the transfer material S. In this embodiment, the distance between the tip of the downstream charge elimination needle 40 and the secondary transfer roller 15 is 3 mm.

[0027] The fixing member 20, which serves as a fixing unit, fixes the multicolor toner image transferred to the transfer material S. The heating member 21 on the print surface side is composed of a ceramic heater 21a (hereinafter referred to as the heater), a ceramic plate-shaped heating element, a holder member 21b for holding the heater, and a fixing film 21c of the heating member that completely encases the heater and holder member. A thermistor is located behind the heater 21 to control the heater temperature. A pressure roller 22 applies pressure from the opposing side, forming a fixing nip. This heats and presses the print surface side with the heating member 21 and the non-print surface side with the pressure roller 22, melting and fixing the toner image to the transfer material S. A pair of paper discharge rollers 23 is located downstream of the fixing member 20 in the conveyance direction of the transfer material S, and discharges the transfer material S to a paper discharge tray 24 of the device main body.

[0028] <Control unit> Reference numeral 502 in Fig. 1 denotes a control unit of the image forming apparatus 500. The control unit 502 controls the operations of the image forming unit 1 and the like. Fig. 8 is a block diagram showing the control configuration of the main parts of the image forming apparatus 500 of this embodiment. The control unit 502 will be described in further detail with reference to Fig. 8.

[0029] The control unit 502 includes a CPU 31 as a central processing unit that performs various arithmetic operations, and main memory such as a RAM 33, a ROM 34, and a nonvolatile memory (NVRAM) 35 that store information. The CPU 31 is connected to the exposure unit 9 as well as the RAM 33, the ROM 34, and the nonvolatile memory NVRAM 35. The ROM 34 is a read-only storage unit (memory) that stores programs and various data used by the CPU 31 to control the image forming apparatus 500. The RAM 33 is a readable / writable memory, and data stored in the RAM 34 is expanded and various data is saved therein. The NVRAM 35 is a readable / writable memory that retains its contents even when the image forming apparatus is turned off. The RAM 33 temporarily stores sensor detection results, counter count results, calculation results, and the like. The ROM 34 also stores a control program and data tables obtained in advance through experiments, etc. The NVRAM 35 also stores counter count results, various setting information, sensor results, and the like. The environment sensor 36 is made up of a temperature sensor and a relative humidity sensor, and temperature information and relative humidity information inside the engine section 501 are taken into the CPU 31 and used to control the image forming section 1 and the like.

[0030] Signals indicating various types of information are input to and output from the control unit 502 via the electrical connections. The control unit 502 processes signals input from various process devices and sensors, and processes signals output to instruct the various process devices to operate.

[0031] The control unit 502 is connected to each control target, sensor, counter, etc. in the image forming apparatus 500. The control unit 502 controls the input and output of various signals, the timing of driving each unit, etc., and controls a predetermined image formation sequence.

[0032] The control unit 502 controls, for example, a charging power supply 71 as a charging voltage application unit for applying a charging voltage to the charging roller 3, and a developing power supply 72 as a developing voltage application unit for applying a developing voltage to the developing roller 4. In addition, the control unit 502 controls the exposure device 9, a primary transfer power supply 73 as a primary transfer voltage application unit, a secondary transfer power supply 74 as a secondary transfer voltage application unit, the fixing unit 20, the drive unit 160, etc.

[0033] The drive unit 160 is configured to include a drive motor as a drive source, a drive transmission member, etc. The drive sources that drive the rotating members such as the photosensitive drum 2 and the developing roller 4 may be provided independently, or at least a portion may be shared. The drive sources that drive the elements for each color may be provided independently, or at least a portion may be shared.

[0034] Here, the image forming apparatus 500 executes an image forming operation (print job), which is a series of operations initiated by a single start command to form and output an image on one or more transfer materials S. The image forming operation generally includes an image forming process, a pre-process (pre-rotation process, pre-printing operation), an inter-sheet process when forming images on multiple transfer materials S, and a post-process (post-rotation process, post-printing operation). The image forming process is a period during which an electrostatic latent image of the image to be actually formed and output on the transfer material S is formed, a toner image is formed, the toner image is primarily transferred, and the toner image is fixed. This period is referred to as the image formation time. More specifically, the timing of the image formation time varies depending on the position where each of the processes of charging, exposure, development, primary transfer, secondary transfer, and fixing is performed. The pre-process, which is a pre-rotation operation, is a period from when a start command is input until the actual start of image formation, during which preparatory operations are performed before the image forming process. The inter-sheet process, which is an inter-sheet operation, is a period corresponding to the interval between transfer materials S when image formation is continuously performed on multiple transfer materials S (continuous image formation). The post-rotation process, which is a post-rotation operation, is a period in which a rearrangement operation (preparation operation) is performed after the image forming process. The non-image formation time is a period other than the image formation time, and includes the pre-process, the inter-sheet process, the post-process, and further the pre-multiple rotation process, which is a preparatory operation when the image forming apparatus 500 is turned on or when it returns from a sleep state.

[0035] <Image formation operation> When image formation begins, the photosensitive drum 2, intermediate transfer belt 8, etc., are driven by the drive unit 160 at a predetermined process speed (100 mm / sec in this example) and begin to rotate in the direction of the arrow. The photosensitive drum 2 discharges between itself and the charging roller 3, to which a predetermined charging voltage (approximately -1000 V) is applied by the charging power supply 71, and is uniformly charged to a surface potential of approximately -450 V. This surface potential of approximately -450 V is referred to as the dark potential Vd. An electrostatic latent image based on the output image data is then formed by the scanning beam from the exposure device 9. When the solid electrostatic latent image is formed, the surface potential of the photosensitive drum is approximately -100 V. This surface potential of approximately -100 V is referred to as the light potential Vl.

[0036] At this time, the electrostatic latent images of each color are formed at a predetermined timing so that the four colors will later be superimposed on the intermediate transfer belt 8 to form a full-color image. As the exposed photosensitive drum 2 continues to rotate, the electrostatic latent images on the photosensitive drum 2 are visualized (developed) by the developing roller 4, to which a developing voltage of approximately -300 V is applied by the developing power supply 72. The developing roller 4 rotates in the forward direction relative to the rotation direction of the photosensitive drum 2. Then, toner images of Y, M, C, and Bk are formed on the photosensitive drum 2, respectively. As the toner images on the photosensitive drum 2 continue to rotate, the toner images are transferred onto the intermediate transfer belt 8 by the primary transfer roller 41, to which a primary transfer voltage of approximately +800 V is applied by the primary transfer power supply 73.

[0037] The transfer material S loaded in the paper feed cassette 16 is fed by a crescent-shaped pickup roller / paper feed roller 17, separated into individual sheets by a separation roller / paper feed roller 18, and conveyed to a registration roller 19, where it is temporarily stopped. The stopped transfer material S is supplied to the secondary transfer nip SN by the registration roller 19 in synchronization with the timing at which the four-color toner image formed on the intermediate transfer belt 8 reaches the secondary transfer nip SN. Then, a secondary transfer voltage is applied by a secondary transfer power supply 74, and the toner image on the intermediate transfer belt 8 is transferred onto the transfer material S.

[0038] The transfer material S onto which the toner image has been transferred is separated from the intermediate transfer belt 8 and sent to the fixing device 20. Here, the print side is heated and pressed by a heating member 21, and the non-print side is heated and pressed by a pressure roller 22, melting the toner image and fixing it to the transfer material S. Downstream of the fixing member 20 in the conveyance direction of the transfer material S, there is a pair of discharge rollers 23, which discharge the transfer material S onto a discharge tray 24 of the device main body. Residual toner remaining on the surface of the intermediate transfer belt 8 is collected by a belt cleaning device 75 having a belt cleaning blade 80 as a belt cleaning member.

[0039] <Configuration of the secondary transfer unit> In this embodiment, the transport guide 32 having the restricting portion A as a guide portion and the contact electrode 29 as a static eliminator having the static eliminator B are electrically connected and are grounded via a current suppression circuit 60. The detailed configuration of the transport guide 32 in this embodiment will be described below with reference to FIG.

[0040] The conveyance guide 32 is made of a 1.0 mm thick iron sheet metal and has a restricting portion A protruding toward the secondary transfer opposing roller 12. The contact electrode 29 is also made of a 1.0 mm thick iron sheet metal and contacts the secondary transfer roller 15 at the charge removal portion B. The conveyance guide 32 and the contact electrode 29 are connected via a conductive path 61. In this embodiment, the distance α between the restricting portion A and the entrance SNa of the nip SN is set to 5 mm. The shorter this distance α, the more stable the leading edge of the recording material S can be guided into the nip SN. The distance β between the charge removal portion B and the entrance SNa of the nip SN is set to 5 mm. The shorter this distance β, the lower the potential on the surface of the secondary transfer roller 15 in the discharge region 6, thereby effectively suppressing whiteout. Whiteout refers to an image defect in which abnormal discharge occurs between the recording material S and the intermediate transfer belt 8 in the discharge region H formed immediately before the secondary transfer nip SN, resulting in a missing toner image in the abnormal discharge area being transferred.

[0041] Furthermore, the transport guide 32 is grounded via a current suppression circuit 60. Specifically, the transport guide 32 is connected to the current suppression circuit 60 via a conductive path 60a, and the current suppression circuit 60 is connected to ground via a conductive path 60b. In this manner, by grounding the transport guide 32 and the contact electrode 29 to ground via the same conductive path 60a rather than via separate conductive paths, it is possible to reduce the number of conductive paths grounded to ground and increase the flexibility in the layout of the conductive paths. This allows the transport guide 32, the contact electrode 29, and the conductive paths grounding them to ground to be compactly arranged in the limited space immediately before the secondary transfer nip SN, thereby achieving a more compact image forming apparatus.

[0042] A static elimination unit B is formed at the tip of the conveyance guide 32. As shown in Fig. 2, the static elimination unit B is disposed on the side of the region L1 where the secondary transfer roller 15 is disposed, out of the regions L1 and L2 divided by the tangent line L between the secondary transfer roller 15 and the intermediate transfer belt 8.

[0043] In this embodiment, the regulating portion A of the conveyance guide 32 is positioned in an area L2 on the opposite side of the secondary transfer roller 15 (the side of the secondary transfer opposing roller 12) from the straight line L connecting the entrance SNa and exit SNb of the transfer nip SN. By positioning the regulating portion A in this manner, the conveyance path of the recording material S regulated by the regulating portion A approaches the intermediate transfer belt 8 at the discharge portion H, which is the discharge area. The short distance between the recording material S and the intermediate transfer belt 8 at the discharge portion H makes it less likely for abnormal discharge to occur, further reducing whiteout. In addition, the toner image printing range on the recording material S of the image forming apparatus 500 in this embodiment is up to 5 mm from the trailing edge of the recording material S, with the 5 mm remaining at the trailing edge of the recording material S being left blank. By setting the distance α to be equal to or less than the length of the blank, as in this embodiment, blankouts in the toner image near the trailing edge of the recording material S can also be reduced.

[0044] In this embodiment, as shown in FIG. 3(b), a single medium resistance element 603 having a resistance between the high resistance element 602 and the low resistance element 601 in FIG. 3(a), which will be described in detail in Example 2, is used. The configuration shown in FIG. 3(b) contributes to the miniaturization of the entire device, while also being able to accommodate both low-humidity and high-humidity environments to some extent. In other words, it can be used without problems under conditions where white spots and transfer defects are unlikely to occur. In this embodiment, the resistance range of the medium resistance element 603 is preferably in the range of 100 MΩ to 1 GΩ. The resistance of the medium resistance element 603 in Example 1 was set to 600 MΩ.

[0045] <Evaluation test> To confirm the effects of this embodiment, evaluations were conducted on white spots and transfer defects. Two types of image forming apparatuses were prepared for evaluation: Example 1 shown in FIG. 3(b) and Comparative Example 1 as a conventional technique. The configuration of Comparative Example 1 was changed from Example 1 in that the conductive path for grounding the conveyance guide 32 and the contact electrode 29, and the configuration of the electrical suppression circuit 60 were modified.

[0046] Comparative Example 1 will be described with reference to FIG. 4(a). In the image forming apparatus of Comparative Example 1, the conveying guide 32 and the contact electrode 29 are grounded to ground via separate conductive paths. Specifically, the conveying guide 32 is grounded to ground via a high-resistance element 602 connected by a conductive path 602a, and the contact electrode 29 is grounded to ground via a low-resistance element 601 connected by a conductive path 601a. ​​The resistance values ​​of the high-resistance element 602 and the low-resistance element 601 are the same as those in Example 1. In this configuration, the conductive path 601a must be positioned at a sufficient distance from the conveying guide 32 and the conductive path 602a to prevent electrical shorts or discharges between them. Therefore, the image forming apparatus may become larger depending on the space required for arranging the conductive path 601a.

[0047] The evaluation methods for white spots and transfer spots are as follows.

[0048] Evaluation method for white spots: The recording material S is 75 g / m 2Using unopened paper (Vitality (Xerox), paper size LTR), 10 sheets of all-black images were printed in an environment with a room temperature of 15°C and humidity of 10%. The voltage applied to the secondary transfer roller 15 was 3500V (the transfer current flowing from the secondary transfer roller 15 to the recording material S was targeted to be 10μA), which is the optimum level for the transfer efficiency of the toner to the recording material S. If there were no visible white spots in the printed toner image, it was judged as OK, and if even one sheet had white spots, it was judged as NG.

[0049] Evaluation method for transfer defects: The recording material S is 75 g / m 2 Using unopened paper (Vitality (Xerox), paper size LTR), 10 sheets of all-black images were printed in an environment with a room temperature of 30°C and humidity of 80%. The voltage applied to the secondary transfer roller 15 was set to 700V (the transfer current flowing from the secondary transfer roller 15 to the recording material S was targeted to be 10μA), which is the optimum voltage for transferring the toner to the recording material S. If there were no visible transfer gaps in the printed toner image, it was judged as OK, and if even one sheet was missing, it was judged as NG.

[0050] The evaluation results and whether the configuration is suitable for miniaturization are shown in Table 1. Configurations that are suitable for miniaturization of image forming devices are marked as OK, and configurations that are not suitable for miniaturization of image forming devices are marked as NG.

[0051] For Comparative Example 1, the current value flowing through the low resistance element 601 during secondary transfer for evaluation of white spots and the current value flowing through the high resistance element 602 during secondary transfer for evaluation of transfer spots were measured and shown in parentheses, respectively. Also, for Example 1, the current value flowing through the current suppression circuit 60 during secondary transfer was measured and shown in parentheses.

[0052] [Table 1]

[0053] As shown in Table 1, both white spots and transfer defects were OK in Comparative Example 1. This is because the contact electrode 29 and the transport guide 32 were grounded via appropriate resistances. However, as mentioned above, miniaturization was not possible.

[0054] On the other hand, in Example 1, both the conveyance guide 32 and the contact electrode 29 are grounded via the current suppression circuit 60, which allows for miniaturization while preventing both white voids and transfer defects. This is because, by setting the resistance value of the current suppression circuit 60 to a medium resistance band so as to be able to handle transfer onto a high-resistance recording material S in a low-humidity environment, it is possible to release some of the transfer current from the static elimination unit B. In addition, by setting the resistance value of the current suppression circuit 60 to a medium resistance band so as to be able to handle transfer onto a low-resistance recording material S in a high-humidity environment, it is possible to suppress some of the outflow of the transfer current via the conveyance guide 32.

[0055] The configuration of the first embodiment has the following features.

[0056] The device includes an intermediate transfer belt 8 and a rotatable secondary transfer roller 15 that contacts the surface of the intermediate transfer belt 8 to form a secondary transfer nip portion SN and transfers toner 90 supplied to the surface of the intermediate transfer belt 8 to the recording material S at the secondary transfer nip portion SN. A contact electrode 29 is provided at an opposing portion that is located upstream of the secondary transfer nip portion SN in the rotation direction of the secondary transfer roller 15 and that faces the surface of the secondary transfer roller 15 upstream of the secondary transfer nip portion SN in the movement direction of the recording material S. A conveyance guide 32 is provided that contacts the surface of the recording material S opposite to the surface onto which the toner 90 is transferred, thereby guiding conveyance of the recording material S to the secondary transfer nip portion SN. A secondary transfer voltage application unit 74 is provided that applies a transfer voltage to the secondary transfer roller 15. The conveying guide 32 and the contact electrode 29 are grounded via a resistor 603 that serves as the same current suppression circuit 60. The contact electrode 29 neutralizes the surface of the secondary transfer roller 15 at the opposing portion when a transfer voltage is applied to the secondary transfer roller 15. The contact electrode 29 contacts the secondary transfer roller 15 at the opposing portion B-B'. The secondary transfer opposing roller 12 contacts the inner surface of the intermediate transfer belt 8 and faces the secondary transfer roller 15. The transfer nip portion SN is formed by the intermediate transfer belt 8, the secondary transfer roller 15, and the secondary transfer opposing roller 12. The normal polarity of the toner 90 is opposite to the polarity of the transfer voltage. In a cross section perpendicular to the rotation axis of the secondary transfer roller 15, the contact electrode 29 is located in the region L1, where the secondary transfer roller 15 is located, of the regions L1 and L2 divided by the tangent to the secondary transfer roller 15 and the intermediate transfer belt 8. The transfer voltage is of a magnitude that discharges the contact electrode 29. The contact electrode 29 forms an opposing portion BB' upstream in the rotation direction of the secondary transfer roller 15 from an area H where discharge occurs between the secondary transfer roller 15 and the intermediate transfer belt 8.

[0057] As described above, in the embodiment, it is possible to achieve both the effect of suppressing white spots and the effect of suppressing transfer defects while reducing the size of the image forming apparatus.

[0058] [Example 2] Next, a second embodiment will be described. In the second embodiment, both the conveying guide 32 and the contact electrode 29 are grounded via a current suppression circuit 60, which is configured differently from the first embodiment, and the transfer current is released from the secondary transfer roller 15 to the charge removal unit B by discharging. Therefore, compared to the first embodiment, it is possible to suppress image damage caused by transfer even in an environment where blank areas or transfer defects are likely to occur, while still ensuring a smaller size. The rest of the configuration is the same as that of the first embodiment. Therefore, elements having the same or equivalent functions and configurations as those of the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

[0059] <Configuration of the secondary transfer unit> 3(a), the current suppression circuit 60 of this embodiment is configured so that the resistance connected to ground can be switched between a low resistance element 601 and a high resistance element 602 by a relay switch 60c controllable by the control unit 502. In this embodiment, the control unit 502 reads the detection result of the temperature and humidity sensor 36 serving as an environmental sensor, and determines that a high humidity environment is present when the humidity is 50% or higher, or a low humidity environment when the humidity is below 50%, and switches the relay switch 60c accordingly. The temperature and humidity sensor 36 serving as an environmental sensor may be a humidity sensor that can detect only humidity.

[0060] In a low-humidity environment, the recording material S dries and its electrical resistance increases. This requires a higher transfer voltage to be applied to the secondary transfer roller 15 to transfer the toner to the recording material S, which increases the likelihood of blank spots occurring. Therefore, in a low-humidity environment, the relay switch 60c of the current suppression circuit 60 is switched to the low-resistance element 601, which has low resistance, to facilitate the escape of a portion of the transfer current from the surface of the secondary transfer roller 15 to ground via the charge removal unit B. This locally reduces (eliminates) the potential on the surface of the secondary transfer roller 15 near the charge removal unit B, thereby reducing the electric field in the discharge area H. This suppresses abnormal discharge between the transfer material S and the intermediate transfer belt 8 in the discharge area H, thereby reducing blank spots. The resistance value of the low-resistance element 601 must be set to a value sufficient to ensure a sufficient current flow from the charge removal unit B to ground to suppress blank spots, preferably between 0 Ω and 300 MΩ. In this embodiment, the resistance value of the low-resistance element 601 was set to 100 MΩ.

[0061] In a high-humidity environment, the recording material S absorbs moisture and its electrical resistance decreases, which can lead to the transfer current leaking through the recording material S, resulting in transfer defects. Therefore, in a high-humidity environment, the relay switch 60c of the current suppression circuit 60 is switched to the high-resistance element 602, which has high resistance, to prevent current from flowing from the charge removal unit B to ground. This prevents the transfer current from leaking through the recording material S and the regulating unit A, even when the recording material S absorbs moisture and its electrical resistance decreases. Regarding whiteout, the transfer voltage when transferring toner to the recording material S, which has low electrical resistance, is low, so whiteout is unlikely to occur even if the current from the charge removal unit B to ground is less likely to flow. The resistance value of the high-resistance element 602 must be set to a value that can limit the amount of current from the regulating unit A to ground to a level that prevents transfer defects due to the leaking of the transfer current. A value of approximately 400 MΩ to 5 GΩ is desirable. In this embodiment, the resistance value of the high-resistance element 602 was set to 1 GΩ.

[0062] <Evaluation test> To confirm the effects of this embodiment, evaluations were conducted on white spots and transfer defects. Three types of image forming apparatuses were prepared for evaluation: Example 2 and Modifications 1 and 2. For reference, the configuration of Example 1 is also shown. Modifications 1 and 2 differ from Example 2 in the configurations of the conveyance guide 32, the conduction path for grounding the contact electrode 29, and the configuration of the electrical suppression circuit 60.

[0063] Modification 1 will be described with reference to FIG. 4(b) and Modification 2 with reference to FIG. 4(c). In the image forming apparatus of Modification 1, the transport guide 32 and the contact electrode 29 are connected by a conductive path 61, and the transport guide 32 is grounded to ground via a high-resistance element 602 connected by a conductive path 602a. In this configuration, the transport guide 32 and the contact electrode 29 are grounded to ground via the same conductive path 602a as in Example 1, and this configuration is suitable for reducing the size of the image forming apparatus, as in Examples 1 and 2. In the image forming apparatus of Modification 2, the transport guide 32 and the contact electrode 29 are connected by a conductive path 61, and the transport guide 32 is grounded to ground via a low-resistance element 601 connected by a conductive path 601a. ​​In this configuration, the transport guide 32 and the contact electrode 29 are grounded to ground via the same conductive path 601a as in Example 1, and this configuration is suitable for reducing the size of the image forming apparatus, as in Example 1. Therefore, Modifications 1 and 2 are evaluated solely by comparison with Example 2 under the following conditions, and there is no problem in use under the above conditions similar to those of Example 1.

[0064] The evaluation method for white spots and transfer defects is as follows: The conditions are such that image defects are more likely to occur than in the evaluations carried out in Example 1 and Comparative Example 1.

[0065] Evaluation method for white spots: Recording material S is 75 g / m 2 The paper used was Vitality (Xerox), paper size LTR, which had been left to dry for one week at a room temperature of 15°C and a humidity of 10%. The moisture content was 2.9% (measured with a Moistrex MX8000 paper moisture meter), which is prone to white spots. Ten full-black images were printed in the above environment.

[0066] The voltage applied to the secondary transfer roller 15 was set to 4000V (the transfer current flowing from the secondary transfer roller 15 to the recording material S was targeted to be 10μA), which is the voltage that optimizes the transfer efficiency of the toner to the recording material S. If there were no visible white spots in the printed toner image, it was judged as OK, and if even one sheet had white spots, it was judged as NG.

[0067] Evaluation method for transfer defects: Recording material S is 75 g / m 2 We used Vitality (Xerox), paper size LTR, paper that had been left in an environment of 30°C room temperature and 80% humidity for one week to absorb moisture. Then, using paper with a moisture content of 9.2% (measured with a Moistrex MX8000 paper moisture meter), which is prone to transfer defects, we printed 10 all-black images under the above environment. The voltage applied to the secondary transfer roller 15 was 500V (the transfer current flowing from the secondary transfer roller 15 to the recording material S was targeted at 10μA), which optimizes the transfer efficiency of the toner to the recording material S. If there were no visible transfer defects in the printed toner image, it was considered OK, and if even one sheet had any, it was considered NG.

[0068] The evaluation results and whether the configuration is suitable for miniaturization are shown in Table 2. Configurations that are suitable for miniaturization of image forming devices are marked as OK, and configurations that are not suitable for miniaturization of image forming devices are marked as NG.

[0069] For Modification 1, the current values ​​flowing through the high resistance element 602 during secondary transfer for the evaluation of white spots and transfer voids are shown in parentheses. For Modification 2, the current values ​​flowing through the low resistance element 601 during secondary transfer for the evaluation of white spots and transfer voids are measured and shown in parentheses. For Examples 1 and 2, the current values ​​flowing through the current suppression circuit 60 during secondary transfer are measured and shown in parentheses.

[0070] [Table 2]

[0071] As shown in Table 2, in Modification 1, the white spots were not recognized as acceptable. This is because the contact electrode 29 was connected to the ground via the high-resistance element 602, and the current flowing from the contact electrode 29 to the ground was insufficient to suppress the white spots.

[0072] In Modification 2, the transfer defects were not acceptable. This is because the transport guide 32 is grounded via the low-resistance element 601, and a large amount of transfer current flows from the transport guide 32 to ground through the recording material S. In other words, if the transport guide 32 and the contact electrode 29 are grounded via the same resistance element, it is possible to reduce the size of the image forming apparatus. However, depending on the conditions, it may not be possible to achieve both the effect of suppressing white defects and the effect of suppressing transfer defects. Therefore, when using Modifications 1 and 2, it is important to note that it may be necessary to design the system taking the above-mentioned cases into consideration.

[0073] On the other hand, in Example 1, the conditions were changed to ones that made it easier for white spots and transfer defects to occur, and a slight deterioration in both phenomena was observed, but the image quality was still within an acceptable range.

[0074] In the second embodiment, both the conveyance guide 32 and the contact electrode 29 are grounded via the current suppression circuit 60, thereby enabling miniaturization and achieving even better levels of both white voids and transfer defects than in the first embodiment. When transferring a high-resistance recording material S in a low-humidity environment, the resistance value of the current suppression circuit 60 is reduced to allow the transfer current to escape sufficiently from the charge removal unit B. When transferring a low-resistance recording material S in a high-humidity environment, the resistance value of the current suppression circuit 60 is increased to suppress the outflow of the transfer current via the conveyance guide 32. Because both environments are addressed, the second embodiment can achieve both the effects of suppressing white voids and transfer defects.

[0075] The configuration of the second embodiment has the following features.

[0076] The device includes an environmental sensor 36 as a humidity detection unit that detects information related to humidity, and a control unit 502 that controls a current suppression circuit 60 based on the detection result of the environmental sensor 36. The current suppression circuit 60 is a variable resistance circuit, and the control unit 502 controls the resistance value of the variable resistance circuit based on the detection result by a relay switch 60c so as to switch the resistance connected to ground between a low resistance element 601 and a high resistance element 602. The amount of current in the current suppression circuit 60 is configured to be suppressed more when a toner image on the intermediate transfer belt 8 is transferred to a second recording material S, which has a lower resistance than that of the first recording material S, than when a toner image on the intermediate transfer belt 8 is transferred to a first recording material S.

[0077] As described above, in the embodiment, it is possible to reduce the size of the image forming apparatus while simultaneously achieving both the effect of suppressing white spots and the effect of suppressing transfer defects.

[0078] [Example 3] The configuration of the image forming apparatus to which Example 3 is applied is the same as that of Example 2, except that the static eliminator B is not in contact with the secondary transfer roller 15, and the transfer current is released from the secondary transfer roller 15 to the static eliminator B by discharging. Therefore, elements having the same or corresponding functions and configurations as those in Example 2 are denoted by the same reference numerals, and detailed explanations thereof will be omitted.

[0079] FIG. 5(a) is an enlarged view showing the vicinity of the secondary transfer portion formed by the intermediate transfer belt 8 and the secondary transfer roller 15 in this embodiment, and FIG. 5(b) is a schematic view of the non-contact electrode 28 in this embodiment as viewed from the direction of arrow X shown in FIG. 5(a).

[0080] In this embodiment, a non-contact electrode 28 is used as the static eliminator in place of the contact electrode 29 in the second embodiment. The non-contact electrode 28 is formed from a 1.0 mm thick iron sheet metal. As shown in FIG. 5(b), the end of the secondary transfer roller 15 side is a static eliminator needle processed into a sawtooth shape as static eliminator B, with the pitch C of adjacent sawtooth teeth being 3.5 mm, the length D of the sawtooth teeth being 2 mm, and the tip angle E of the sawtooth teeth being 18.9°. The tip of static eliminator B is polished to a thickness of 0.1 mm. If the sawtooth pitch C is too wide, there will be areas where static elimination is not performed, and if it is too narrow, the effect of tip discharge will be reduced. Therefore, a pitch C of approximately 0.5 mm to 8.0 mm is preferable.

[0081] The tip of the static elimination needle serving as static elimination unit B is positioned so that it faces the secondary transfer roller 15 while remaining in non-contact with the secondary transfer roller 15 via a 1 mm gap. Furthermore, static elimination unit B forms an opposing area B-B' upstream of area H, where discharge occurs between the secondary transfer roller 15 and the intermediate transfer belt 8, in the direction of rotation of the secondary transfer roller 15. Furthermore, the non-contact electrode 28 is connected to the conveyance guide 32 via a conductive path 61, and the non-contact electrode 28 and the conveyance guide 32 are grounded via a current suppression circuit 60 connected by the same conductive path 60a. With this configuration, when the secondary transfer voltage is applied, ion current concentrates at the tip of the static elimination needle of static elimination unit B, causing a corona discharge between static elimination unit B and static elimination position B'. This lowers the potential on the surface of the secondary transfer roller 15, thereby suppressing whiteout. The discharge position B' is the position on the surface of the secondary transfer roller 15 closest to the discharge unit B, and as shown in FIG. 5A, the line B-B' is perpendicular to the tangent to the surface of the secondary transfer roller 15. The larger the current amount due to this corona discharge, the lower the potential at the discharge position B', and the greater the white blemish effect. Therefore, the distance between the discharge unit B and the discharge position B' must be closer than the corona discharge initiation distance between the discharge unit B and the discharge position B'. Furthermore, to achieve a sufficient white blemish suppression effect, it is desirable that the current amount flowing due to corona discharge between the discharge unit B and the discharge position B' be equal to or greater than the transfer current flowing through the transfer nip SN.

[0082] In this way, by configuring the conveyance guide 32 and the non-contact electrode 28 to be grounded via the same conductive path 60a rather than via separate conductive paths, it is possible to reduce the number of conductive paths grounded to ground and increase the degree of freedom in arranging the conductive paths. This allows the conveyance guide 32, the non-contact electrode 28, and the conductive paths grounding them to ground to be compactly arranged in the limited space immediately before the transfer nip SN, thereby achieving a more compact image forming apparatus.

[0083] Furthermore, by using a non-contact static eliminator such as a static eliminator needle as the static eliminator B in this embodiment, the transfer current is released to the static eliminator B without contacting the secondary transfer roller 15, which is more advantageous than the configuration of Example 1 in terms of durability of the secondary transfer roller 15. However, the configuration of this embodiment requires a gap to be provided between the static eliminator B and the secondary transfer roller 15, which may reduce the degree of freedom in design. Therefore, the static eliminator B can be selected to be contact or non-contact depending on the characteristics required by the image forming apparatus.

[0084] <Evaluation test> In order to confirm the effect of this embodiment, the white spots and transfer defects were evaluated. The evaluation method for the white spots and transferability was the same as that described in Example 2.

[0085] Table 3 shows the evaluation results and whether the configuration is suitable for miniaturization.

[0086] If the configuration is suitable for downsizing the image forming device, it is marked as OK, and if the configuration is not suitable for downsizing the image forming device, it is marked as NG. In addition, the current value flowing through the current suppression circuit 60 during secondary transfer was measured and recorded in parentheses.

[0087] [Table 3]

[0088] As can be seen from Table 3, in Example 3, both the conveyance guide 32 and the non-contact electrode 28 are grounded via the current suppression circuit 60, which allows for miniaturization, as in Examples 1 and 2, while also preventing both whiteout and transfer defects. This is because, when transferring a high-resistance recording material S in a low-humidity environment, the resistance value of the current suppression circuit 60 is lowered to allow the transfer current to sufficiently escape from the discharge unit B. Furthermore, when transferring a low-resistance recording material S in a high-humidity environment, the resistance value of the current suppression circuit 60 is increased to suppress the outflow of transfer current via the conveyance guide 32. Furthermore, as described above, this example is also advantageous for miniaturization.

[0089] As described above, in the configuration of this embodiment, even in the case of using the non-contact electrode 28 that does not contact the secondary transfer roller 15, it is possible to achieve both the effect of suppressing white spots and the effect of suppressing transfer spots while reducing the size of the image forming apparatus.

[0090] In this embodiment, the non-contact electrode 28 is configured to be thin only in the vicinity of the static elimination unit B, but the present invention is not limited to this configuration. For example, the thickness of the static elimination unit B may be left at 1.0 mm, but in that case, the discharge between the static elimination unit B and the secondary transfer roller becomes unstable, and the effect of suppressing white voids is slightly inferior to the configuration of this embodiment. Furthermore, as long as the static elimination member is non-contact, it is not necessary to be a static elimination needle; a static elimination brush or static elimination cloth can be selected as long as it can eliminate static on the surface of the secondary transfer roller 15.

[0091] [Example 4] The configuration of the image forming apparatus to which Example 4 is applied is the same as that of Example 3 except for the configuration of the current suppression circuit 60, so elements having the same or equivalent functions and configurations as those of Example 3 are given the same symbols and detailed explanations are omitted.

[0092] FIG. 6 is a diagram illustrating a current suppression circuit 60 according to this embodiment. The current suppression circuit 60 according to this embodiment is configured to be grounded via a Zener diode 60c serving as a constant voltage element. The Zener diode 60c is an element that maintains a predetermined voltage (hereinafter referred to as the breakdown voltage) when a current flows through it. According to the configuration of this embodiment, one end (anode side) of the Zener diode 60c is grounded, and the positive end (cathode side) is connected to the transport guide 32 via a conductive path 60a. Therefore, when a current greater than a certain level flows through the Zener diode 60c, the transport guide 32 is maintained at the breakdown voltage of the Zener diode 60c.

[0093] The breakdown voltage of the Zener diode 60c is preferably set to approximately the same as the transfer voltage applied to the secondary transfer roller 15 under conditions where transfer defects are likely to occur (for example, when a low-resistivity recording material S is being secondary-transferred). This setting allows the potential of the transport guide 32 to be maintained at the same potential as the transfer voltage when a low-resistivity recording material S is being secondary-transferred. This also prevents transfer defects from occurring when the transfer current from the secondary transfer roller 15 flows through the recording material S to the transport guide 32. If the breakdown voltage of the Zener diode 60c is too low, the transfer current will begin to flow through the recording material S to the transport guide 32, causing transfer defects. Conversely, if the breakdown voltage of the Zener diode 60c is too high, current will flow from the transport guide 32 through the recording material S to the transfer nip SN, reducing transfer efficiency. Therefore, the breakdown voltage of the Zener diode 60c is preferably set to ±100 V of the transfer voltage under conditions where transfer defects are likely to occur. In this embodiment, the breakdown voltage of the Zener diode 60c is set to 500V.

[0094] Even in the configuration of this embodiment, under conditions where blank spots are likely to occur, it is possible to pass a sufficient current through the current suppression circuit 60 to suppress blank spots. Even when performing secondary transfer on a high-resistance recording material S that is prone to blank spots, the conveyance guide 32 is maintained at a potential of 500 V. Therefore, the charge-eliminating portion B of the non-contact electrode 28 connected to the conveyance guide 32 by the conductive path 61 is also maintained at a potential of 500 V. When performing secondary transfer on a high-resistance recording material S that is prone to blank spots, a transfer voltage higher than that applied to the non-contact electrode 28 is applied to the secondary transfer roller 15. Therefore, the charge-eliminating portion B can lower the potential on the surface of the secondary transfer roller 15.

[0095] In this way, the configuration of this embodiment does not require components such as the temperature and humidity sensor 36 and relay switch 60c as in Examples 1, 2, and 3, and it is possible to achieve both white voids and transfer voids while miniaturizing the image forming apparatus with a simple, low-cost configuration.

[0096] <Evaluation test> In order to confirm the effect of this example, the white spots and the transfer voids were evaluated. The evaluation method for the white spots and the transfer voids was the same as that described in Example 3.

[0097] The evaluation results and whether the configuration is suitable for miniaturization are shown in Table 4. Configurations suitable for miniaturization of image forming devices are marked as "OK," while configurations not suitable for miniaturization of image forming devices are marked as "NG." Additionally, the current value flowing through the current suppression circuit 60 during secondary transfer was measured and recorded in parentheses.

[0098] [Table 4]

[0099] As can be seen from Table 4, in Example 4, by grounding both the conveyance guide 32 and the non-contact electrode 28 via the current suppression circuit 60 consisting of a constant voltage element, both white voids and transfer voids are acceptable while enabling miniaturization, as in Example 3. This is because the current suppression circuit 60 allows the transfer current to escape sufficiently from the discharge unit B when transferring a high-resistance recording material S, and the current suppression circuit 60 can suppress the outflow of the transfer current via the conveyance guide 32 when transferring a low-resistance recording material S.

[0100] As described above, in the embodiment, it is possible to achieve both the effect of suppressing white spots and the effect of suppressing transfer defects while reducing the size of the image forming apparatus.

[0101] Even when the contact electrode 29 as in the first embodiment is used instead of the non-contact electrode 28 of this embodiment, the image forming apparatus can be made smaller by using the current suppression circuit 60 made of a constant voltage element as in this embodiment. Furthermore, it is possible to achieve both the effect of suppressing white voids and the effect of suppressing transfer voids.

[0102] The current suppression circuit 60 of the present invention is not limited to a configuration using a single constant-voltage element, as in this embodiment. Any configuration is acceptable as long as it can maintain the potential of the conductive path 60a approximately equal to the transfer voltage under conditions where transfer defects are likely to occur. For example, a configuration in which a capacitor 60d is arranged in parallel with the constant-voltage element, as shown in FIG. 6(b), is also acceptable. In this configuration, if high-frequency noise flows in through the recording material S, the capacitor 60d can reduce voltage fluctuations caused by this noise. Alternatively, a configuration in which a low-resistance element 601 is arranged in series with the constant-voltage element, as shown in FIG. 6(c), is also acceptable. This configuration allows for appropriate adjustment of the amount of transfer current released from the static eliminator B. Alternatively, a configuration combining the configurations of FIGS. 6(b) and 6(c), as shown in FIG. 6(d), is also acceptable. While this embodiment uses a Zener diode 60c as the constant-voltage element, an avalanche diode or a varistor may also be used as an element capable of achieving the same effect as the Zener diode 60c. Also, as shown in FIG. 6(e), the constant voltage element may be replaced with a high voltage power supply 60d, and a voltage may be applied directly to the conductive path 60a.

[0103] In Examples 1 to 4, the transport guide 32, the contact electrode 29, and the non-contact electrode 28 are formed from iron sheet metal, but the present invention is not limited to such a structure as long as they are conductive. For example, the transport guide 32, the contact electrode 29, and the non-contact electrode 28 may be formed from a conductive resin.

[0104] In the first to fourth embodiments, the contact electrode 29 or the non-contact electrode 28 has the charge eliminating section B, but the transport guide 32 may have the charge eliminating section B. For example, as shown in FIG. 7( a), the transport guide 32 may have the charge eliminating section B that comes into contact with the secondary transfer roller 15 to eliminate charge on the surface of the secondary transfer roller 15, and the transport guide 32 may be grounded via a current suppression circuit 60. Alternatively, as shown in FIG. 7( b), the transport guide 32 may have the charge eliminating section B that does not come into contact with the secondary transfer roller 15 to eliminate charge on the surface of the secondary transfer roller 15, and the transport guide 32 may be grounded via a current suppression circuit 60. These configurations eliminate the need for the contact electrode 29, the non-contact electrode 28, and the conductive path 61, enabling further miniaturization.

[0105] Furthermore, the intermediate transfer belt 8 in the configuration of this embodiment is stretched by a secondary transfer opposing roller 12 and a tension roller 13, which serve as tensioning members and also serve to drive the intermediate transfer belt 8. However, as shown in Fig. 9, a configuration in which the intermediate transfer belt 8 is stretched by a three-axis configuration using a tension roller 11 is also applicable.

[0106] The effects of the present invention are not limited to image forming apparatuses that use an intermediate transfer belt, but similar effects can also be obtained in configurations such as monochrome image forming apparatuses in which toner is transferred directly from a photosensitive drum to a recording material.

[0107] The disclosure of the embodiments of the present invention includes the following configurations.

[0108] (Configuration 1) an image carrier; a rotatable transfer member that contacts the surface of the image carrier to form a transfer nip and transfers the toner supplied to the surface of the image carrier to a recording material at the transfer nip; a charge removing member that removes charge from the surface of the transfer member at an opposing portion that faces the surface of the transfer member upstream of the transfer nip portion in the rotation direction of the transfer member and upstream of the transfer nip portion in the movement direction of the recording material; and a guide member that contacts a surface of the recording material opposite to a surface onto which the toner is transferred, thereby guiding the recording material to be conveyed to the transfer nip portion; a transfer voltage application unit that applies a transfer voltage to the transfer member, the guide member and the charge removing member are grounded via the same current suppression circuit, The image forming apparatus is characterized in that the charge removing member removes electricity from the surface of the transfer member at the opposing portion while the transfer voltage is applied to the transfer member.

[0109] (Configuration 2) 2. The image forming apparatus according to claim 1, wherein the charge removing member contacts the transfer member at the opposing portion.

[0110] (Configuration 3) 2. The image forming apparatus according to claim 1, wherein the charge removing member is not in contact with the transfer member at the opposing portion.

[0111] (Configuration 4) 4. The image forming apparatus according to any one of the first to third aspects, wherein the current suppressing circuit is a variable resistance circuit.

[0112] (Configuration 5) humidity detection means for detecting information relating to humidity; a control unit that controls the current suppression circuit based on the detection result of the humidity detection means, The image forming apparatus according to configuration 4, wherein the current suppression circuit is a variable resistance circuit, and the control unit controls the variable resistance circuit to change its resistance value based on the detection result.

[0113] (Configuration 6) 4. The image forming apparatus according to any one of the first to third aspects, wherein the current suppression circuit is a constant voltage element.

[0114] (Configuration 7) 7. The image forming apparatus according to configuration 6, wherein the constant voltage element is a Zener diode.

[0115] (Configuration 8) The image forming apparatus according to configuration 1, characterized in that the amount of current of the current suppression circuit is configured to be suppressed more when the toner image on the image carrier is transferred to a second recording material having a lower resistance than the first recording material than when the toner image on the image carrier is transferred to a first recording material.

[0116] (Configuration 9) 2. The image forming apparatus according to claim 1, wherein the guide member also serves as the charge removing member.

[0117] (Configuration 10) a facing member that contacts the inner surface of the image carrier and faces the transfer member; 2. The image forming apparatus according to claim 1, wherein the transfer nip portion is formed by the image carrier, the transfer member, and the opposing member.

[0118] (Configuration 11) 2. The image forming apparatus according to claim 1, wherein the normal polarity of the toner and the polarity of the transfer voltage are opposite to each other.

[0119] (Configuration 12) The image forming apparatus according to configuration 1, characterized in that in a cross section perpendicular to the rotation axis of the transfer member, the charge removal member is arranged in the area where the transfer member is arranged among the areas divided by tangents to the transfer member and the image carrier.

[0120] (Configuration 13) 2. The image forming apparatus according to claim 1, wherein the neutralizing member is a neutralizing needle.

[0121] (Configuration 14) 3. The image forming apparatus according to claim 2, wherein the transfer voltage is large enough to discharge the transfer voltage to the charge removing member.

[0122] (Configuration 15) The image forming apparatus according to configuration 1, wherein the neutralization member forms the opposing portion upstream in the rotation direction of the transfer member from an area where discharge occurs between the transfer member and the image carrier.

[0123] (Configuration 16) The image forming apparatus according to Configuration 1, wherein the image carrier is an intermediate transfer belt.

[0124] (Configuration 17) The image forming apparatus according to Configuration 1, wherein the image carrier is a photosensitive drum. [Explanation of symbols]

[0125] 2 Photosensitive drum 8 Intermediate transfer belt 15 Secondary transfer roller 28 Non-contact electrode 29 Contact electrode 32 Transport guide 60 Current suppression circuit 74 Secondary transfer voltage application unit

Claims

1. an image carrier; a rotatable transfer member that contacts the surface of the image carrier to form a transfer nip and transfers the toner supplied to the surface of the image carrier to a recording material at the transfer nip; a charge removing member that removes charge from the surface of the transfer member at an opposing portion that faces the surface of the transfer member upstream of the transfer nip portion in the rotation direction of the transfer member and upstream of the transfer nip portion in the movement direction of the recording material; a guide member that contacts a surface of the recording material opposite to a surface onto which the toner is transferred, thereby guiding the recording material to be conveyed to the transfer nip portion; a transfer voltage application unit that applies a transfer voltage to the transfer member, the guide member and the charge removing member are grounded via the same current suppression circuit, The image forming apparatus is characterized in that the charge removing member removes electricity from the surface of the transfer member at the opposing portion while the transfer voltage is applied to the transfer member.

2. 2. The image forming apparatus according to claim 1, wherein the charge removing member contacts the transfer member at the facing portion.

3. 2. The image forming apparatus according to claim 1, wherein the charge removing member is not in contact with the transfer member at the facing portion.

4. 4. The image forming apparatus according to claim 1, wherein the current suppressing circuit is a variable resistance circuit.

5. humidity detection means for detecting information relating to humidity; a control unit that controls the current suppression circuit based on the detection result of the humidity detection means, 5. The image forming apparatus according to claim 4, wherein the control unit controls the variable resistor circuit to change its resistance value based on the detection result.

6. 4. The image forming apparatus according to claim 1, wherein the current suppressing circuit is a constant voltage element.

7. 7. The image forming apparatus according to claim 6, wherein the constant voltage element is a Zener diode.

8. 2. The image forming apparatus according to claim 1, wherein the amount of current of the current suppression circuit is configured to be suppressed when transferring the toner image on the image carrier to a second recording material having a lower resistance than that of the first recording material, more than when transferring the toner image on the image carrier to a first recording material.

9. 2. The image forming apparatus according to claim 1, wherein the guide member also serves as the charge removing member.

10. a facing member that contacts the inner surface of the image carrier and faces the transfer member; 2. The image forming apparatus according to claim 1, wherein the transfer nip portion is formed by the image carrier, the transfer member, and the opposing member.

11. 2. The image forming apparatus according to claim 1, wherein the normal polarity of the toner and the polarity of the transfer voltage are opposite to each other.

12. 2. The image forming apparatus according to claim 1, wherein, in a cross section perpendicular to the rotation axis of the transfer member, the charge removal member is arranged in an area where the transfer member is arranged among areas divided by tangents to the transfer member and the image carrier.

13. 2. The image forming apparatus according to claim 1, wherein the charge eliminating member is a charge eliminating needle.

14. 3. The image forming apparatus according to claim 2, wherein the transfer voltage is a voltage that discharges the charge from the charge removing member.

15. 2. The image forming apparatus according to claim 1, wherein the neutralization member forms the opposing portion upstream in the rotation direction of the transfer member from a region where discharge occurs between the transfer member and the image carrier.

16. 2. The image forming apparatus according to claim 1, wherein the image carrier is an intermediate transfer belt.

17. 2. The image forming apparatus according to claim 1, wherein the image carrier is a photosensitive drum.

Images