Image forming apparatus

Abstract

To provide an image forming apparatus that prevents an image defect caused by electric discharge generated between a transfer material and an intermediate transfer belt.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 transfer material at the transfer nip part; a static eliminating unit 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 transfer material; and a transfer voltage application unit that applies a transfer voltage to the transfer member. The static eliminating unit is arranged to eliminate 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] A known electrophotographic color image forming apparatus has an independent image forming unit for each color, and images are transferred sequentially from the image forming unit for each color to an intermediate transfer belt, which then transfers the images all at once to a recording material. The toner images developed on the photosensitive drums of the image forming units for each color are primarily transferred to the intermediate transfer belt. The toner images primarily transferred to the intermediate transfer belt are then secondarily transferred to the recording material at the transfer position.

[0003] In image forming devices that use an intermediate transfer belt, if a gap occurs between the transfer material and the intermediate transfer belt immediately before the transfer section, there is a problem of discharge causing image defects due to the transfer of the toner image. Therefore, to prevent image defects from occurring in the area where discharge occurs, measures are needed to suppress abnormal discharge in the gap formed between the intermediate transfer belt and the transfer material upstream of the transfer nip. In this case, if the transfer material is brought into contact with the surface of the intermediate transfer belt upstream of the transfer section in the transfer material transport direction while entering the transfer nip, which is the contact point between the intermediate transfer belt and the secondary transfer member, abnormal discharge occurring in the transfer section can be suppressed, resulting in good transferability.

[0004] Patent Document 1 describes a method of suppressing abnormal discharge by supporting the transfer material from behind the printing surface before secondary transfer and adjusting the pressure on the transfer material to ensure an appropriate penetration angle. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-204642 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the configuration of Patent Document 1 had the following problems: Abnormal discharge at the transfer section becomes more pronounced when the transfer material is too rigid to contact the intermediate transfer belt, when it is glossy paper with high resistance, or when the transfer material is used in a low-humidity environment where it is prone to charging. Therefore, a technique is needed to bring the transfer material into closer contact with the intermediate transfer belt than with ordinary transfer materials used in a room-temperature, normal-pressure environment. The operation of pressing the transfer material against the intermediate transfer belt requires a fairly complex configuration and space for the mechanism and its control, which increases the size of the image forming device and leads to higher manufacturing costs due to the more complex configuration and increased number of parts.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an image forming apparatus that suppresses image defects caused by discharge occurring in the transfer section. [Means for solving the problem]

[0008] The image forming apparatus of the present invention is characterized by comprising 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 the transfer material, a de-electrifying member that de-electrifies 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 transfer material, a transfer voltage application portion that applies a transfer voltage to the transfer member, and the de-electrifying member is arranged so as to de-electrify the surface of the transfer member at the opposing portion when the transfer voltage is applied to the transfer member. [Effects of the Invention]

[0009] According to the present invention, it is possible to suppress image defects caused by discharge occurring in the transfer portion. [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] FIG. 2 is a diagram for explaining an experimental system for confirming a phenomenon according to the first embodiment. [Figure 4] 4 is a schematic diagram illustrating the static elimination effect according to Example 1. FIG. [Figure 5] FIG. 2 is a control block diagram according to the first embodiment. [Figure 6] FIG. 3 is a diagram illustrating the configuration of a pre-transfer static elimination needle according to the first embodiment. [Figure 7] 4 is a diagram illustrating the positional relationship between a pre-transfer static elimination needle and a secondary transfer roller according to the first embodiment. FIG. [Figure 8] 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. [Example]

[0012] [Image forming equipment] 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 11, 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 60 (FIG. 5) 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 60 serving as a motor, rotates (moves) the intermediate transfer belt 8 in the direction indicated by arrow Z 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 60 may have a drive unit for the secondary transfer opposing roller 12 separate from the photosensitive drum 2.

[0019] 5, 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. 5. 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 assist roller 11 regulates the angle of the intermediate transfer belt 8 with respect to the conveyance path of the transfer material S (dotted line L in FIG. 1) so that the transfer material S can enter the secondary transfer nip SN while contacting the intermediate transfer belt 8.

[0023] The assist roller 11, secondary transfer opposing roller 12 (opposing member), and tension roller 13 are each grounded via a resistive element with the same resistance value. In this embodiment, three types of resistive elements are used: 1 GΩ, 100 MΩ, and 10 MΩ. The resistance of each rubber layer of the assist roller 11 and secondary transfer opposing roller 12 is sufficiently smaller than 1 GΩ, 100 MΩ, and 10 MΩ, so electrical influences can be ignored.

[0024] 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. 5. 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.

[0025] 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 9 The volume resistivity of the secondary transfer roller 15 is set to 10 Ω·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. Therefore, 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.

[0026] Line L 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 T, 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 placed 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 hits 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, and then, in synchronization with the movement of the leading edge of the toner image on intermediate transfer belt 8 to secondary transfer unit T, the pair of registration rollers 19 conveys transfer material S to secondary transfer unit T. Then, the toner image on intermediate transfer belt 8 is transferred to transfer material S.

[0027] 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.

[0028] 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.

[0029] [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. 5 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. 5.

[0030] The control unit 502 includes a CPU 32 as a processing means, which is a central element for performing various arithmetic operations, and main memory, such as a RAM 33, a ROM 34, and a nonvolatile memory (NVRAM) 35, which are memory elements for storing information. The CPU 32 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 memory, and stores programs and various data used by the CPU 32 to control the image forming apparatus 500. The RAM 33 is a readable / writable memory, and data stored in the ROM 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 powered 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 32 and used to control the image forming section 1 and the like.

[0031] 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 issue operation commands to the various process devices.

[0032] 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.

[0033] 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 60, etc.

[0034] The drive unit 60 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.

[0035] 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.

[0036] [Image formation operation] When image formation begins, the photosensitive drum 2, intermediate transfer belt 8, etc., are driven by the drive unit 60 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 is uniformly charged to a surface potential of approximately -450 V due to discharge between the photosensitive drum 2 and the charging roller 3, to which a predetermined charging voltage (approximately -1000 V) is applied by the charging power supply 71. 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] [Pre-transfer static eliminator] In this embodiment, a pre-transfer charge eliminating needle 30 is disposed upstream of the secondary transfer nip SN in the conveyance direction of the transfer material S and upstream of the rotation direction of the secondary transfer roller 15 as a charge eliminating means for eliminating charge on the surface of the secondary transfer roller 15. In this embodiment, the pre-transfer charge eliminating member 30 is a charge eliminating needle. The pre-transfer charge eliminating needle 30 is disposed upstream of the rotation direction of the secondary transfer roller 15, with the tip 30a of the needle facing the surface of the secondary transfer roller 15 near the upstream side of the secondary transfer nip SN. In other words, the tip of the needle faces the surface of the secondary transfer roller 15 near the upstream side of the secondary transfer nip SN. When the transfer voltage applied to the secondary transfer roller 15 reaches a predetermined transfer voltage, an ionic current is generated due to the potential difference between the tip 30a of the pre-transfer charge eliminating needle 30 and the surface of the secondary transfer roller 15 at the closest position. This eliminates charge on the surface of the secondary transfer roller 15 near the upstream side of the secondary transfer nip SN. As a result, the electric field generated upstream of the secondary transfer nip portion SN is reduced, and even if a transfer voltage that would previously cause image defects due to discharge is applied to the secondary transfer roller 15, the discharge phenomenon upstream of the secondary transfer nip portion SN is suppressed, resulting in good image quality. The pre-transfer static elimination needle 30 will be described in detail below with reference to FIG.

[0041] As shown in FIG. 6, the pre-transfer static elimination needle 30 is a static elimination needle with a sawtooth tip made from a 0.1 mm thick SUS304 thin plate. The pitch C between adjacent sawtooth teeth is 3.5 mm, the length D of the sawtooth teeth is 2 mm, and the tip angle E of the sawtooth teeth is 18.9°. If the sawtooth pitch C is too wide, some areas will not be neutralized, while 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. The pre-transfer static elimination needle 30 is positioned at a height that does not contact the conveyed transfer material S, with the tip 30a of the sawtooth facing the surface of the secondary transfer roller 15 near the secondary transfer nip SN. The pre-transfer static elimination needle 30 is supported by a support member 31 and is grounded by a circuit (not shown). The tip 30a of the sawtooth of the pre-transfer static elimination needle 30 is positioned so that it does not contact the secondary transfer roller 15. That is, the tip 30a of the pre-transfer static elimination needle 30 is disposed at a position facing the surface of the secondary transfer roller 15, forming a facing portion.

[0042] The tip 30a of the pre-transfer static elimination needle 30 is positioned facing the secondary transfer roller 15 in a non-contact state with a gap of 3 mm between it and the secondary transfer roller 15. This allows ionic current to concentrate at the tip of the pre-transfer static elimination needle 30 when the secondary transfer voltage is applied. This causes corona discharge between the pre-transfer static elimination needle 30 and static elimination position B', lowering the potential on the surface of the secondary transfer roller 15 and thereby suppressing image defects. The static elimination position B is the position on the surface of the secondary transfer roller 15 that is closest to the pre-transfer static elimination needle 30. As shown in Figure 7, the line B-B' is perpendicular to the tangent to the surface of the secondary transfer roller 15. The distance between the line B-B' is defined as the distance between the secondary transfer roller 15 and the tip of the pre-transfer static elimination needle 30.

[0043] The greater the current generated by this corona discharge, the lower the potential at the charge removal position B', thereby enhancing the discharge suppression effect. Therefore, the distance between the pre-transfer charge removal needle 30 and the charge removal position B' must be closer than the corona discharge initiation distance between the pre-transfer charge removal needle 30 and the charge removal position B'. Furthermore, to achieve sufficient image degradation suppression, the current flowing due to corona discharge between the pre-transfer charge removal needle 30 and the charge removal position B' should be equal to or greater than the transfer current flowing through the transfer nip SN. The distance between the secondary transfer roller 15 and the tip of the pre-transfer charge removal needle 30 is preferably 1 mm to 10 mm. The angle of the sawtooth relative to the secondary transfer roller 15 is most effective when the tip of the sawtooth faces the center of rotation of the secondary transfer roller 15. The closer the sawtooth is to the secondary transfer nip SN, the greater the effect. However, the effect can be confirmed if the tip of the sawtooth is positioned upstream of the secondary transfer nip SN in the transport direction of the transfer material S. Therefore, the angle and position may be adjusted as needed depending on the configuration of the image forming apparatus 500.

[0044] The configuration around the pre-transfer charge elimination needle 30 will be described in detail with reference to FIG. 2. FIG. 2 is an enlarged view showing the vicinity of the secondary transfer portion T in FIG. 1, which is formed by the intermediate transfer belt 8 and the secondary transfer roller 15 as the transfer material S moves toward the secondary transfer portion T. The intermediate transfer belt 8 is stretched by an assist roller 11, a secondary transfer opposing roller 12 that also serves to drive the intermediate transfer belt 8, and a tension roller 13 (not shown). The secondary transfer nip SN is formed by the secondary transfer roller 15, which faces and presses against the secondary transfer opposing roller 12 via the intermediate transfer belt 8. 19a denotes a transport path for the transfer material S transported from the pair of registration rollers 19 to the secondary transfer nip SN. The surface of the intermediate transfer belt 8 moves in the direction of arrow Z, and the secondary transfer roller 15 rotates in the direction of arrow Y. The transfer material S obtains the charge required for secondary transfer from the secondary transfer roller 15 at the transfer nip SN, and the toner on the intermediate transfer belt 8 is transferred to the transfer material S. The pre-transfer static elimination needles 30 are arranged in the area W1 where the secondary transfer roller 15 is arranged, out of the areas W1 and W2 divided by the tangent line W between the secondary transfer roller 15 and the intermediate transfer belt 8.

[0045] A discharge region H is formed by the transfer voltage applied to the secondary transfer roller 15 in the gap immediately before the transfer material S enters the secondary transfer nip SN, which is the sandwiched portion between the intermediate transfer belt 8 and the secondary transfer roller 15. When the transfer material S enters the discharge region H, the discharge region formed between the secondary transfer roller 15 and the transfer material S is designated as Ha, and the discharge region formed between the transfer material S and the intermediate transfer belt 8 is designated as Hb. When the volume resistance of the secondary transfer roller 15 increases, such as in a low-temperature, low-humidity environment or during the latter half of use of the image forming apparatus 500, the transfer voltage applied to the transfer roller must be increased in order for the transfer material S to acquire the charge necessary for secondary transfer. When the transfer voltage applied to the secondary transfer roller 15 increases, the electric field in the discharge region H becomes stronger. When the transfer material S is transported in this state, the back surface of the transfer material S becomes highly charged in the discharge region Ha. Then, in the discharge region Hb, an abnormal discharge occurs between the front surface of the transfer material S and the intermediate transfer belt 8, disrupting the potential of the toner on the intermediate transfer belt 8 and resulting in a defective image. In this embodiment, in order to suppress the above-mentioned image defects, the pre-transfer charge elimination needles 30 form an opposing portion B-B' upstream in the rotation direction of the secondary transfer roller 15 from the region H where discharge occurs between the secondary transfer roller 15 and the intermediate transfer belt 8.

[0046] Therefore, in this embodiment, the sawtooth tip 30a of the pre-transfer static elimination needle 30 is positioned so that it faces the surface of the secondary transfer roller 15 near the secondary transfer nip SN. This eliminates static from the surface of the secondary transfer roller 15 before it reaches the secondary transfer nip SN. When the surface of the secondary transfer roller 15 is neutralized, the electric field in the discharge region H is reduced, suppressing abnormal discharge in the discharge region Hb and reducing image defects. Meanwhile, the transfer voltage applied to the secondary transfer roller 15 ensures the current necessary for transfer. While this embodiment employs a non-contact static elimination needle as the static elimination member, a similar effect can be achieved by, for example, pressing an electrically grounded metal plate against the transfer member. In contrast, when the static elimination member is a non-contact static elimination needle, as in the configuration of this embodiment, the pre-transfer static elimination needle 30 exhibits its static elimination effect only when the transfer voltage applied to the secondary transfer roller 15 is relatively high. When the transfer voltage is low, the potential difference between the pre-transfer charge elimination needles 30 and the surface of the secondary transfer roller 15 is also small, and no charge elimination current flows. In other words, in environments where the transfer voltage required for secondary transfer is low and image defects due to upstream discharge at the secondary transfer nip SN do not occur, such as room temperature or high-temperature / humidity environments, no charge elimination current needs to flow. Therefore, by changing the transfer conditions according to the environment, the load on the transfer high-voltage output can be reduced, and charge elimination can be effectively achieved under the required conditions. That is, when the transfer voltage during image formation is high enough to cause discharge with the pre-transfer charge elimination needles 30, current can be passed through the pre-transfer charge elimination unit 30. Furthermore, charge elimination may also be performed during non-image formation operations if the conditions are such that discharge occurs. Examples of non-image formation operations include pre-rotation operations performed before image formation operations, post-rotation operations performed after image formation operations, and sheet-to-sheet operations performed between image formation operations.

[0047] [Confirmation of the phenomenon through experiments] Next, we present the results of an experiment conducted to verify the effectiveness of the pre-transfer static eliminator needles 30 of this embodiment. The experiment confirmed that the pre-transfer static eliminator needles 30 neutralize the surface potential of the secondary transfer roller 15. Figure 3 shows the vicinity of the secondary transfer zone T formed by the intermediate transfer belt 8 and secondary transfer roller 15 used in the experiment. A high-voltage power supply K is positioned so that it can apply a transfer voltage to the transfer roller 15 via the core metal 15b of the secondary transfer roller 15. In an environment with a room temperature of 15°C and a humidity of 10%, the transfer voltage applied to the secondary transfer roller 15 by the high-voltage power supply K was monitored, and the current (transfer current TAI) flowing from the transfer roller 15 to ground via the secondary transfer counter roller 12 was measured using an ammeter TA. A surface potential measurement probe 50 (Trek Corporation, Model 341B surface potential meter) was positioned upstream of the secondary transfer nip SN, and the surface potential of the transfer roller 15 upstream of the secondary transfer nip SN was measured. The pre-transfer static elimination needle 30 is grounded via an ammeter JA, which monitors the current (static elimination current JAI) flowing through the pre-transfer static elimination needle 30. The transfer voltage applied to the secondary transfer roller 15 was changed, and the resulting change in the surface potential of the secondary transfer roller 15, as well as the values ​​of the transfer current TA and static elimination current JA, were plotted depending on whether or not the pre-transfer static elimination needle 30 was present. The results are shown in Table 1.

[0048] [Table 1]

[0049] The mechanism of this phenomenon, along with the reasons for the above results, is illustrated using Figure 4. Figure 4 is a cross-sectional view of the vicinity of the secondary transfer portion T during image formation, and is a schematic diagram of the timing during this experiment when the pre-transfer charge elimination needle 30 discharges the surface of the secondary transfer roller 15. A charge elimination current (ion flow) J is generated from the tip of the pre-transfer charge elimination needle 30 toward the secondary transfer roller 15. This discharges the surface of the transfer roller 15, and the discharged area (the solid dotted area in Figure 4) is the charge elimination area G. The surface potential of the charge elimination area G is lowest (the absolute value of the potential is small) directly below the pre-transfer charge elimination needle 30. As one moves in the direction of arrow F (away from the pre-transfer charge elimination needle 30 and toward the secondary transfer nip SN), the potential gradually recovers and eventually returns to the previous potential. The charge elimination area G extends to the position of the discharge area Ha. The lower potential on the surface of the secondary transfer roller 15 in the discharge area Ha reduces the electric field in the discharge area Ha. In this experiment, the potential was restored by the time the secondary transfer nip portion SN was reached, and the potential difference formed between the core metal 15b of the secondary transfer roller 15 and the secondary transfer nip portion SN was maintained, and the current required for transfer was maintained.

[0050] It is not necessary to set the discharge area G up to the point just before the secondary transfer nip portion SN. For example, even if the discharge area G is located within the secondary transfer nip portion SN, the range of the discharge area G can be adjusted as appropriate depending on the configuration of the image forming apparatus 500, such as by adjusting the applied voltage so that it becomes the voltage required for transfer.

[0051] In this experiment, as shown in Table 1, when the pre-transfer static eliminator needle 30 was installed, current was observed to flow through the pre-transfer static eliminator needle 30 when the transfer voltage reached 3.0 kV. It was also found that the surface potential of the secondary transfer roller 15 was lower than when the pre-transfer static eliminator needle 30 was not installed. This indicates that when a transfer voltage of 3.0 kV or higher is required, the pre-transfer static eliminator needle 30 can eliminate static electricity from the surface of the secondary transfer roller 15, thereby suppressing discharge upstream of the transfer roller. On the other hand, when a transfer voltage of 2.0 kV or lower can be selected and there is little concern about image defects due to discharge upstream of the transfer roller, it is possible to prevent the discharge current from flowing. Furthermore, the transfer current TAI exhibited the same correlation between transfer voltage and transfer current, regardless of whether the pre-transfer static eliminator needle 30 was installed or not. This indicates that by installing the pre-transfer static eliminator needle 30 upstream of the transfer roller, the surface potential upstream of the secondary transfer roller 15 can be reduced while maintaining the necessary transfer current.

[0052] [Confirmation of effectiveness through experiments] Next, in order to confirm the actual discharge suppression effect of this embodiment, the transfer material S was passed through in an environment of room temperature 15° C. and humidity 10%, and it was confirmed whether or not discharge image defects occurred.

[0053] The transfer voltage was varied between 1.0 kV and 5.0 kV, and the margins for image defects due to insufficient transfer voltage and image defects due to discharge upstream of transfer were confirmed. As a comparative example, an image forming apparatus without a pre-transfer static elimination needle 30 was prepared, and a comparison between the example and the comparative example was conducted. In order to confirm the effect more accurately, conditions for the transfer material S were prepared that simulated normal use (Experiment i) and conditions that were more severe than normal use (Experiment ii), and the effects of Example 1 and the comparative example were compared.

[0054] <Experimental condition i: Conditions assuming normal use> The paper used as transfer material S is 80 g / cm 2 (GFC-081 (Canon Inc.), paper size A4) was left in the above environment for 48 hours, and the moisture content was 3.3% (measured with a paper moisture meter Moistrex MX8000).

[0055] <Experimental Conditions II: Harsh Conditions> The paper used as transfer material S is 163 g / cm 2 (Xerox 163, paper size LTR) was left in the above environment for one week, and the moisture content was 2.9% (measured with a paper moisture meter Moistrex MX8000).

[0056] The occurrence of image defects was evaluated visually. "Occurred" in the table indicates that image defects have occurred, "Slight" indicates that image defects have occurred but that they do not pose a problem in practical use. "None" indicates that image defects have not occurred. The evaluation results are shown below. The results of Experiment I are shown in Table 2, and the results of Experiment II are shown in Table 3.

[0057] [Table 2]

[0058] [Table 3]

[0059] Based on the above results, we first discuss the case where a frequently used paper type was left in a low-temperature, low-humidity environment, as in Experiment i. As shown in Table 2, in the comparative example configuration without the pre-transfer static eliminator needles 30, when a high transfer voltage (3.0 kV or higher) was selected to suppress image defects due to insufficient transfer voltage, a discharge image upstream of the transfer occurred at 5.0 kV. This is because, as shown in Figures 2 to 4, as the transfer voltage applied to the transfer roller 15 increases, the electric field in the discharge region H becomes stronger. When the transfer material S is transported under this condition, the back surface of the transfer material S becomes highly charged in the discharge region Ha. Then, in the discharge region Hb, an abnormal discharge occurs between the front surface of the transfer material S and the intermediate transfer belt 8, disrupting the potential of the toner on the intermediate transfer belt 8 and resulting in image defects. In contrast, in the configuration of this embodiment, no discharge image upstream of the transfer occurred even at 5.0 kV. This is because the pre-transfer static eliminator needles 30 are positioned upstream of the transfer roller 15, ensuring the transfer current required for transfer while lowering the surface potential upstream of the transfer roller 15. In the configuration of the first embodiment, even if a high transfer voltage is selected depending on the state of the transfer roller 15 and the resistance of the paper as the transfer material S, a good image state can be maintained.

[0060] Next, we will discuss the case where the transfer material S was used under harsh conditions, such as in Experiment ii. The transfer material S left under the conditions of Experiment ii was dry, so the resistance of the transfer material S increased, and the transfer current required for transfer increased, making it more susceptible to discharge. Furthermore, if the basis weight of the transfer material S is large, the paper is thick and stiff, making it more likely to have gaps between it and the intermediate transfer belt 8. Therefore, the gaps make it easier for discharge to occur, which can easily result in poor images.

[0061] As shown in Table 3, in the comparative example configuration without the pre-transfer static elimination needles 30, when a high transfer voltage (3.0 kV or higher) is selected to suppress image defects due to insufficient transfer voltage, upstream discharge images begin to occur. Therefore, the comparative example configuration does not provide a satisfactory image margin under the above conditions. On the other hand, in the configuration of this embodiment with the pre-transfer static elimination needles 30, a satisfactory margin is obtained where neither image defects due to insufficient transfer voltage nor upstream discharge image defects occur at transfer voltages of 3.0 kV to 4.0 kV. Even under conditions such as those in Experiment ii, the configuration of Example 1 allows the surface potential upstream of the secondary transfer roller 15 to be reduced while ensuring the transfer current required for transfer.

[0062] As described above, in the configuration of this embodiment, the pre-transfer static elimination needles 30 eliminate the surface potential upstream of the rotation direction of the secondary transfer roller 15, thereby achieving the following effects. That is, even when a high transfer voltage must be selected, such as in a low-temperature, low-humidity environment or when using high-resistivity paper, the electric field formed upstream of the secondary transfer nip SN can be reduced, thereby suppressing image defects due to discharge occurring upstream of the secondary transfer nip SN. On the other hand, under conditions where a low transfer voltage can be selected and there is no concern about image defects due to discharge upstream of the secondary transfer nip SN, such as in a room temperature environment or a high-temperature, high-humidity environment, it is possible to adjust the static elimination current so that it does not occur.

[0063] The configuration of the first embodiment has the following features. An image forming apparatus capable of performing an image forming operation to form an image on a transfer material S includes an intermediate transfer belt 8 having a movable surface. A rotatable secondary transfer roller 15 contacts the surface of the intermediate transfer belt 8 to form a secondary transfer nip SN, and transfers toner 90 supplied to the surface of the intermediate transfer belt 8 at the secondary transfer nip SN to the transfer material S. A pre-transfer charge eliminating needle 30 is provided upstream of the secondary transfer nip SN in the rotation direction of the secondary transfer roller 15 and at an opposing portion facing the surface of the secondary transfer roller 15 upstream of the secondary transfer nip SN in the movement direction of the transfer material S, for eliminating charge from the surface of the secondary transfer roller 15. The apparatus includes a secondary transfer power source 74 that applies a transfer voltage to the secondary transfer roller 15, a drive unit 60 that drives the intermediate transfer belt 8, and a control unit 502 that controls the secondary transfer power source 74 and the drive unit 60. During image formation, the control unit 502 controls the application of a transfer voltage to the secondary transfer roller 15 while driving the intermediate transfer belt 8 and rotating the secondary transfer roller 15. During image formation, the pre-transfer static elimination needles 30 are arranged so that the absolute value of the surface potential of the secondary transfer roller 15 at the opposing portion is smaller than the absolute value of the surface potential of the secondary transfer roller 15 at the secondary transfer nip portion SN. The pre-transfer static elimination needles 30 are also arranged in contact with the inner surface of the intermediate transfer belt 8 and facing the secondary transfer roller 15, and the secondary transfer nip portion SN is formed by the intermediate transfer belt 8, the secondary transfer roller 15, and the opposing member. 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 pre-transfer static elimination needles 30 are arranged in the region where the secondary transfer roller 15 is located, among the regions divided by the tangents to the secondary transfer roller 15 and the intermediate transfer belt 8. The pre-transfer static elimination needles 30 are positioned so as not to come into contact with the secondary transfer roller 15. The transfer voltage during the image forming operation is of a magnitude that causes discharge with the pre-transfer static elimination needles 30. The pre-transfer static elimination needles 30 are positioned so as not to come into contact with the transfer material S. The pre-transfer static elimination needles 30 form an opposing portion upstream in the rotation direction of the secondary transfer roller 15 from the area where discharge occurs between the secondary transfer roller 15 and the intermediate transfer belt 8. The control unit 502 controls the image forming operation and also the non-image forming operation in which no image is formed on the transfer material S so as to be executable.In the non-image forming operation, the intermediate transfer belt 8 is driven to rotate the secondary transfer roller 15, and a transfer voltage is applied to the secondary transfer roller 15. The pre-transfer static elimination needles 30 are arranged so that the absolute value of the surface potential of the secondary transfer roller 15 at the opposing portion is smaller than the absolute value of the surface potential of the secondary transfer roller 15 at the secondary transfer nip portion SN. Here, the non-image forming operation is a pre-rotation operation performed before the image forming operation. Alternatively, the non-image forming operation may be a post-rotation operation performed after the image forming operation. When a first image forming operation and a second image forming operation, which is an image forming operation performed after the first image forming operation, are performed consecutively, the non-image forming operation may be an inter-sheet operation performed between the first image forming operation and the second image forming operation.

[0064] In this embodiment, the distance between the pre-transfer charge eliminator needles 30 and the secondary transfer roller 15 is 3 mm. However, this distance can be adjusted depending on the configuration and characteristics of the secondary transfer roller 15. If the surface potential of the secondary transfer roller 15 is to be further reduced, the distance may be reduced. For example, if the intermediate transfer belt 8 is suspended on two axes as shown in FIG. 8 rather than the three-axis configuration shown in this embodiment, the gap between the transfer material S and the intermediate transfer belt 8 is likely to be large, and strong discharge is likely to occur upstream of the secondary transfer nip SN. Therefore, in such a configuration, it is more effective to reduce the distance between the pre-transfer charge eliminator needles 30 and the secondary transfer roller 15. Therefore, as shown in FIG. 8, this configuration is also applicable to a two-axis configuration in which the intermediate transfer belt 8 is suspended by the secondary transfer opposing roller 12 and the tension roller 13 without using the assist roller 11. On the other hand, if the surface potential of the secondary transfer roller 15 is to be prevented from being reduced more than necessary, the distance may be reduced by less than 3 mm.

[0065] In a configuration in which the transfer material S is transported to the secondary transfer nip portion SN along the intermediate transfer belt 8, the configuration in FIG. 8 is more susceptible to image defects due to discharge than the configuration in FIG. 1. Even in such a configuration as in FIG. 8, the configuration of this embodiment has a special effect. In other words, even in the configuration as in FIG. 8, it is possible to suppress image defects due to discharge occurring at the secondary transfer portion T.

[0066] Furthermore, the effects of the present invention are not limited to color image forming apparatus configurations; similar effects can be obtained in direct transfer configurations, such as monochrome, by eliminating the surface potential upstream of the transfer member. Therefore, the present invention can also be applied to relationships such as between a photosensitive drum and a transfer roller. Furthermore, as long as the pre-transfer static elimination member 30 is non-contact, the shape of the static elimination needle is not critical, and static elimination brushes, static elimination cloths, and other options can be used.

[0067] The disclosure of the embodiments of the present invention includes the following configurations.

[0068] (Configuration 1) an image carrier; a rotatable transfer member that contacts the surface of the image carrier to form a transfer nip portion and transfers the toner supplied to the surface of the image carrier to the transfer material at the transfer nip portion; 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 transfer material; a transfer voltage applying section that applies a transfer voltage to the transfer member; The image forming apparatus is characterized in that the charge removing member is disposed in the opposing portion so as to remove charge from the surface of the transfer member while the transfer voltage is applied to the transfer member.

[0069] (Configuration 2) a drive unit that drives the image carrier; a control unit that controls the transfer voltage application unit and the drive unit, the control unit controls the image carrier to be driven and the transfer member to be rotated in an image forming operation for forming an image on a transfer material, and applies the transfer voltage to the transfer member in a state where the transfer member is rotated; The image forming apparatus according to configuration 1, characterized in that, when the image forming operation is performed, the charge removal member is arranged so that the absolute value of the surface potential of the transfer member at the opposing portion is smaller than the absolute value of the surface potential of the transfer member at the transfer nip portion.

[0070] (Configuration 3) 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.

[0071] (Configuration 4) 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.

[0072] (Configuration 5) 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.

[0073] (Configuration 6) 2. The image forming apparatus according to claim 1, wherein the charge removing member is disposed at a position where it does not come into contact with the transfer member.

[0074] (Configuration 7) 2. The image forming apparatus according to claim 1, wherein the neutralizing member is a neutralizing needle.

[0075] (Configuration 8) 2. The image forming apparatus according to claim 1, wherein the transfer voltage in the image forming operation is large enough to discharge the transfer voltage to the charge removing member.

[0076] (Configuration 9) 2. The image forming apparatus according to claim 1, wherein the charge removing member is disposed at a position where it does not come into contact with the transfer material.

[0077] (Configuration 10) 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.

[0078] (Configuration 11) the control unit controls the image forming operation and a non-image forming operation in which the image is not formed on the transfer material, The image forming apparatus according to configuration 1, characterized in that in the non-image forming operation, the image carrier is driven to control the application of the transfer voltage to the transfer member while the transfer member is rotating, and the charge removal member is arranged so that the absolute value of the surface potential of the transfer member at the opposing portion is smaller than the absolute value of the surface potential of the transfer member at the transfer nip portion.

[0079] (Configuration 12) 12. The image forming apparatus according to claim 11, wherein the non-image forming operation is a pre-rotation operation that is executed before the image forming operation.

[0080] (Configuration 13) 12. The image forming apparatus according to claim 11, wherein the non-image forming operation is a post-rotation operation that is executed after the image forming operation.

[0081] (Configuration 14) When a first image forming operation and a second image forming operation that is an image forming operation that is executed after the first image forming operation are executed consecutively, 12. The image forming apparatus according to configuration 11, wherein the non-image forming operation is an inter-sheet operation that is executed between the first image forming operation and the second image forming operation.

[0082] (Configuration 15) The image forming apparatus according to Configuration 1, wherein the image carrier is an intermediate transfer belt.

[0083] (Configuration 16) The image forming apparatus according to Configuration 1, wherein the image carrier is a photosensitive drum. [Explanation of symbols]

[0084] 2 Photosensitive drum 8 Intermediate transfer belt 15 Secondary transfer roller 30 Pre-transfer static elimination needle 60 Drive unit 74 Secondary transfer voltage application unit 502 control section

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 transfer 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 transfer material; a transfer voltage applying section that applies a transfer voltage to the transfer member; The image forming apparatus is characterized in that the charge removing member is disposed in the opposing portion so as to remove charge from the surface of the transfer member while the transfer voltage is applied to the transfer member.

2. a drive unit that drives the image carrier; a control unit that controls the transfer voltage application unit and the drive unit, the control unit controls the image carrier to be driven and the transfer voltage to be applied to the transfer member in a state where the transfer member is rotated during an image forming operation for forming an image on a transfer material, 2. The image forming apparatus according to claim 1, wherein the charge removal member is arranged so that, when the image forming operation is performed, the absolute value of the surface potential of the transfer member at the opposing portion is smaller than the absolute value of the surface potential of the transfer member at the transfer nip portion.

3. 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.

4. 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.

5. 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.

6. 2. The image forming apparatus according to claim 1, wherein the charge removing member is disposed at a position where it does not come into contact with the transfer member.

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

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

9. 2. The image forming apparatus according to claim 1, wherein the charge removing member is disposed at a position where it does not come into contact with the transfer material.

10. 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.

11. the control unit controls the image forming operation and a non-image forming operation in which no image is formed on the transfer material, 3. The image forming apparatus according to claim 2, wherein, in the non-image forming operation, the image carrier is driven to apply the transfer voltage to the transfer member while the transfer member is rotating, and the charge removal member is arranged so that the absolute value of the surface potential of the transfer member at the opposing portion is smaller than the absolute value of the surface potential of the transfer member at the transfer nip portion.

12. 12. The image forming apparatus according to claim 11, wherein the non-image forming operation is a pre-rotation operation that is performed before the image forming operation.

13. 12. The image forming apparatus according to claim 11, wherein the non-image forming operation is a post-rotation operation that is executed after the image forming operation.

14. When a first image forming operation and a second image forming operation that is an image forming operation that is executed after the first image forming operation are executed consecutively, 12. The image forming apparatus according to claim 11, wherein the non-image forming operation is an inter-sheet operation that is executed between the first image forming operation and the second image forming operation.

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

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

Images