JP2025169727A - Image forming device - Google Patents

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

The present invention relates to image forming devices such as printers, copiers, facsimile machines, and multifunction devices that use electrophotographic or electrostatic recording methods.

Conventionally, some electrophotographic image forming devices use an endless belt that rotates while carrying a toner image. For example, in an intermediate transfer image forming device, a toner image is primarily transferred from a photosensitive element to an intermediate transfer belt, an intermediate transfer member made of an endless belt, at a primary transfer unit. 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.

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 immediately before the secondary transfer nip, causing image defects (blank areas) where the toner image in the abnormally discharged area is not transferred and is missing.

One proposed method for suppressing this image degradation is to contact a grounded charge removal unit with the surface of the secondary transfer roller immediately prior to 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, friction with the recording material in a low-humidity environment can generate a charged potential, which can interfere with transfer efficiency. For this reason, a common configuration is to ground the transport guide to allow the charged potential to escape. However, if the transport guide is grounded directly 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 transfer defects by grounding the transport guide through a high-resistance resistor element, thereby suppressing the outflow of transfer current.

Japanese Patent Application Laid-Open No. 2019-197114 Japanese Unexamined Patent Publication No. 59-34570

However, the configurations described in Cited Documents 1 and 2 have the following problems. In particular, if the conveyance guide and the static eliminator are grounded via separate conductive paths, the limited space before transfer requires the construction of the conductive path itself and a structure for electrically connecting the conductive path to the conveyance guide and control electrode, which results in an increase in the size of the image forming apparatus.

The purpose of the invention of this application is to address these problems and provide an image forming apparatus that is both compact and has good transferability.

The image forming apparatus of the present invention comprises an image carrier; a rotatable transfer member that contacts the surface of the image carrier to form a transfer nip and transfers toner supplied to the surface of the image carrier at the transfer nip 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 in the rotation direction of the transfer member and faces the surface of the transfer member upstream of the transfer nip in the direction of movement of the recording material; a guide member that contacts the surface of the recording material opposite to the surface to which the toner is transferred to guide the recording material as it is transported to the transfer nip; and a transfer voltage application unit that applies a transfer voltage to the transfer member. 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.

This invention makes it possible to achieve both compactness and transferability in image forming devices.

FIG. 1 is a diagram illustrating an image forming apparatus according to a first embodiment. FIG. 2 is an enlarged view of a secondary transfer portion according to the first embodiment. FIG. 2 is a schematic diagram of a current suppression circuit according to the first and second embodiments. 10A and 10B are enlarged views of secondary transfer portions according to Comparative Example 1, Modification Example 1, and Modification Example 2. FIG. 10 is an enlarged view of a secondary transfer portion according to a third embodiment. FIG. 10 is a schematic diagram of a current suppression circuit according to a fourth embodiment. FIG. 10 is a schematic diagram of a current suppression circuit according to another embodiment. FIG. 2 is a control block diagram according to the first embodiment. FIG. 10 is a diagram for explaining an image forming apparatus according to another embodiment.

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

[Example 1]
<Overall Configuration and Operation of Image Forming Apparatus>
The 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.

In the image forming apparatus 500 of Example 1, four image forming units, namely, image forming units 1a, 1b, 1c, and 1d, which form toner images of the colors yellow (Y), magenta (M), cyan (C), and black (Bk), respectively, are arranged from upstream to downstream. These four image forming units are arranged in a row (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 body stretched over rollers 12 and 13, is disposed below the image forming units 1a, 1b, 1c, and 1d in the direction of gravity.

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 bodies 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 (Figure 8) as a drive device. The process speed in this embodiment was set to 100 mm/sec.

Developing devices 5a, 5b, 5c, and 5d are arranged around each photosensitive drum 2a, 2b, 2c, and 2d, which serves as an image carrier. These devices 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). Toners 90a, 90b, 90c, and 90d are non-magnetic, single-component polymerized toners with a charge of -20 to -50 μC/mg. The normal charge polarity of toners 90a, 90b, 90c, and 90d is negative. This image forming device 500 employs a reversal development system. Additionally, cleaning devices 6a, 6b, 6c, and 6d having cleaning blades 7a, 7b, 7c, and 7d as cleaning members are installed around each photosensitive drum 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 them inside the cleaning devices 6a, 6b, 6c, and 6d. Furthermore, exposure devices 9a, 9b, 9c, and 9d are installed above each photosensitive drum 2a, 2b, 2c, and 2d in the direction of gravity.

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 distinction is required in the following explanation, the suffixes a, b, c, and d added to the reference numerals in Figure 1 will be omitted to indicate that the element is provided for one of the colors, and the explanation will be general. 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. Furthermore, as will be described later, it is also possible to use a monochrome printer with a single image forming unit 1.

A rotatable, endless intermediate transfer belt 8 is disposed opposite each of the image forming units 1a, 1b, 1c, and 1d as an intermediate transfer member. Primary transfer rollers 41a, 41b, 41c, and 41d are disposed on the surface of the intermediate transfer belt 8 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 tensioned 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. Drive of 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 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 becomes 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. Furthermore, carbon black is preferable because the electrical resistance can be adjusted by adding a small amount, and it can be manufactured inexpensively. In this embodiment, the volume resistivity is set to a range of 10 ⁸ to 10 ¹⁴ Ω·cm. If it is less than 10 ⁸ Ω·cm, the charge of the toner transferred onto the intermediate transfer belt 8 will leak onto the intermediate transfer belt 8, making the toner image more likely to be distorted. Conversely, if it exceeds 10 ¹⁴ Ω·cm, the voltage required for secondary transfer will increase, making it more likely to cause abnormal discharge.

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

A positive transfer voltage (bias) of opposite polarity to the normal polarity of the toner 90 is applied to the primary transfer roller 41 from the primary transfer power supply 73 (shown in Figure 8) as the primary transfer voltage application unit. The voltage is controlled by a constant voltage or constant current. The toner image formed on the photosensitive drum 2 is then transferred onto the intermediate transfer belt 8.

The secondary transfer roller 15, which serves as a secondary transfer member, transfers the toner image formed on the intermediate transfer belt 8 to the transfer material S, which serves as the recording material. In this embodiment, a secondary transfer roller having a diameter of 18 mm was used, with a metal core of 8 mm covered with an NBR foam sponge. A constant voltage or constant current controlled positive voltage is applied to the secondary transfer roller 15 from the secondary transfer power supply 74, which serves as the secondary transfer voltage application unit shown in Figure 8.

The secondary transfer opposing roller 12 has a high-friction rubber layer on its surface to drive the intermediate transfer belt 8, and this rubber layer has conductivity with a volume resistivity of 10 ⁵ 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. 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.

The 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: 100 MΩ, 10 MΩ, and 10 MΩ. The resistance of the rubber layer of the secondary transfer opposing roller 12 is sufficiently small compared to 100 MΩ and 10 MΩ, so any electrical influence can be ignored.

The secondary transfer roller 15 is an elastic roller with a volume resistivity of 10 ⁷ to 10 ⁹ Ωcm and a rubber hardness of 30° (Asker C hardness scale). The transfer roller 15 is configured to press against the secondary transfer opposing roller 12 via the intermediate transfer belt 8 with a total pressure of approximately 39.2 N. 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.

As shown in FIG. 2, the secondary transfer roller 15 includes a cylindrical core 15b and a cylindrical elastic layer 15a covering the outer surface of the core 15b. The core 15b has an outer diameter of 6 mm, and the elastic layer 15a has an outer diameter of 16 mm. The core 15b is made of a highly rigid conductive material, iron in this embodiment. The elastic layer 15a is made of a commonly used acrylonitrile butadiene rubber (NBR) ion conductive rubber foamed into a sponge-like shape. In this embodiment, the volume resistivity of the elastic layer 15a was set to 10 ⁷ to 10 ⁹ 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 significant effect on the transferability, resulting in unstable transferability depending on the environment. Conversely, if the volume resistivity is too high, the voltage required for secondary transfer will be high, making abnormal discharge more likely. Therefore, a volume resistivity of the elastic layer 15a in the range of 10 ⁵ to 10 ¹¹ Ω·cm 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 result in an increase in the torque of the driven secondary transfer roller 15. Also, if the hardness is too hard, the nip width of the transfer nip portion SN will become narrow, which may lead to poor transfer. Therefore, the hardness of the secondary transfer roller 15 is preferably 20° to 40° under a 500 g load on an Asker C hardness scale. The secondary transfer roller 15 used had a hardness of 30° under a 500 g load on an Asker C hardness scale.

Line W in Figure 1 is a transport line indicating the transport path along which transfer material S is transported when an image is formed on the first side (front surface) of transfer material S. The paper feed unit feeds and transports transfer material S to secondary transfer unit SN, with multiple transfer materials S 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 transports the transfer material S to a pair of registration rollers 19, which are transport rollers. The leading edge of the transfer material S strikes the pair of registration rollers 19 and stops temporarily. The toner image formed by image forming unit 1 is transferred to intermediate transfer belt 8. At this time, in synchronization with the movement of the leading edge of the toner image on intermediate transfer belt 8 to secondary transfer unit SN, the transfer material S is transported to secondary transfer unit SN by the pair of registration rollers 19, while being regulated by a regulating portion A, which serves as a guide portion of a transport guide 32, which serves as a guide member. The toner image on the intermediate transfer belt 8 is then transferred to the transfer material S.

A downstream charge elimination needle 40 is positioned downstream in the transport direction of the transfer material S to eliminate any charge formed on the transfer material S. The downstream charge elimination needle 40 is made of 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 transported 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 transport 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 was 3 mm.

The fixing member 20, which serves as a fixing unit, fixes the multi-color toner image transferred to the transfer material S. The heating member 21 on the print surface side consists of a ceramic heater 21a (hereafter referred to as the heater), a ceramic plate-shaped heating element, a holder member 21b for holding it, and a fixing film 21c of the heating member that completely encases the heater and holder member. A thermistor is mounted on the back of the heater 21 to control and regulate the heater temperature. Pressure is applied from the opposing side by a pressure roller 22, 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. Downstream of the fixing member 20 in the transport direction of the transfer material S, a pair of discharge rollers 23 discharges the transfer material S to a paper output tray 24 of the device main body.

<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.

The control unit 502 includes a CPU 31, which serves as a central processing unit that performs various arithmetic operations, and main memory, such as RAM 33, ROM 34, and NVRAM 35 (non-volatile memory), which serve as storage units for storing information. In addition to the exposure unit 9, the RAM 33, ROM 34, and non-volatile NVRAM 35 are connected to the CPU 31. ROM 34 is a read-only storage unit (memory) into which programs and various data used by the CPU 31 to control the image forming device 500 are written. RAM 33 is a readable/writable memory into which data in ROM 34 is expanded and various data is saved. NVRAM 35 is a readable/writable memory whose contents are retained even when the image forming device is powered off. RAM 33 temporarily stores sensor detection results, counter count results, calculation results, and the like. ROM 34 also stores control programs and data tables obtained in advance through experiments. Additionally, NVRAM 35 stores counter count results, various setting information, sensor results, etc. The environmental sensor 36 consists of a temperature sensor and a relative humidity sensor, and temperature information and relative humidity information inside the engine unit 501 are taken into the CPU 31 and used to control the image forming unit 1, etc.

Signals indicating various types of information are input to and output from the control unit 502 via electrical connections. The control unit 502 processes signals input from various process devices and sensors, and signals output to issue operational commands to the various process devices.

The control unit 502 is connected to each control target, sensor, counter, etc. in the image forming device 500. The control unit 502 controls the input and output of various signals and the timing of driving each unit, and controls the specified image formation sequence, etc.

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

The drive unit 160 is also configured to include a drive motor as a drive source, drive transmission members, 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 some of them may be shared. The drive sources that drive the elements for each color may also be provided independently, or at least some of them may be shared.

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. An image forming operation generally includes an image formation process, a pre-process (pre-rotation process, pre-printing operation), a paper-to-paper process when forming images on multiple transfer materials S, and a post-process (post-rotation process, post-printing operation). The image formation process is the 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 image formation time. More specifically, the timing of image formation varies depending on the location where the charging, exposure, development, primary transfer, secondary transfer, and fixing processes are performed. The pre-process, which is a pre-rotation operation, is the period from when a start command is input until the actual start of image formation, during which preparatory operations are performed before the image formation process. The paper-to-paper process, which is a paper-to-paper operation, is the period corresponding to the interval between transfer materials S when image formation is performed continuously on multiple transfer materials S (continuous image formation). The post-rotation process, which is a post-rotation operation, is a period during which a sorting operation (preparatory operation) is performed after the image formation process. Non-image formation time refers to periods other than image formation, and includes the pre-process, between-sheet process, and post-process, as well as 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.

<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 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. Subsequently, an electrostatic latent image based on the output image data is formed by a scanning beam from the exposure device 9. When the electrostatic latent image of a solid 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.

At this time, the electrostatic latent images for 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 development power supply 72. The developing roller 4 rotates in the forward direction relative to the rotation of the photosensitive drum 2. Then, toner images of Y, M, C, and Bk are formed on the photosensitive drum 2. As the toner image on the photosensitive drum 2 continues to rotate, the toner image is 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.

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

The transfer material S with the transferred toner image is separated from the intermediate transfer belt 8 and sent to the fixing device 20. Here, the printed side is heated and pressurized by a heating member 21, and the non-printed side is heated and pressurized 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 transport direction of the transfer material S, there is a pair of discharge rollers 23, which discharge the transfer material S into 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, which has a belt cleaning blade 80 as a belt cleaning member.

<Configuration of 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 charge removing member having the charge removing portion 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.

The transport guide 32 is made of iron and molded from a 1.0 mm thick metal plate, and has a regulating portion A that protrudes toward the secondary transfer opposing roller 12. The contact electrode 29 is also made of iron and molded from a 1.0 mm thick metal plate, and contacts the secondary transfer roller 15 at a discharge portion B. The transport guide 32 and contact electrode 29 are connected via a conductive path 61. In this embodiment, the distance α from the regulating portion A to the entrance SNa of the nip portion SN is set to 5 mm. The shorter this distance α, the more stably the leading edge of the recording material S can be guided into the nip portion SN. The distance β from the discharge portion B to the entrance SNa of the nip portion 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 area 6, thereby increasing the effect of suppressing whiteout. White spots are an image defect that occurs when abnormal discharge occurs between the recording material S and the intermediate transfer belt 8 in the discharge area H formed immediately before the secondary transfer nip SN, resulting in the toner image in the abnormal discharge area not being transferred and being missing.

The transport guide 32 is also 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 way, 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 placement 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 placed in the limited space immediately before the secondary transfer nip SN, thereby achieving a more compact image forming apparatus.

A static eliminator B is formed at the tip of the conveying guide 32. As shown in Figure 2, static eliminator B is located on the side of area L1, where the secondary transfer roller 15 is located, of areas L1 and L2 divided by a tangent line L between the secondary transfer roller 15 and the intermediate transfer belt 8.

In this embodiment, the regulating portion A of the conveying guide 32 is positioned in region L2, which is 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 conveying 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. This 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 margin at the trailing edge of the recording material S. By setting the distance α to be equal to or less than the length of the margin, as in this embodiment, whiteout in the toner image near the trailing edge of the recording material S can also be reduced.

In this embodiment, as shown in Figure 3(b), a single medium resistance element 603 is used, which has a resistance between the high resistance element 602 and the low resistance element 601 in Figure 3(a), which will be described in detail in Example 2. The configuration shown in Figure 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 whiteouts 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.

<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. 3B and Comparative Example 1 as a conventional technique. The configuration of Comparative Example 1 was changed from Example 1 in the configuration of the conveyance guide 32, the conduction path for grounding the contact electrode 29, and the configuration of the electrical suppression circuit 60.

Comparative Example 1 will be described using Figure 4(a). In the image forming device of Comparative Example 1, the transport guide 32 and contact electrode 29 are grounded to ground via separate conductive paths. Specifically, the transport 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 in Example 1. In this configuration, the conductive path 601a must be positioned at a sufficient distance from the transport guide 32 and the conductive path 602a to prevent electrical shorts or discharges between them. Therefore, the image forming device may become larger depending on the space required for the conductive path 601a.

The evaluation method for white spots and transfer defects is as follows:

Evaluation method for white spots:
The recording material S was unopened paper of 75 g/ ^m2 (Vitality (Xerox), paper size LTR), and 10 sheets were printed with an all-black image at room temperature of 15°C and humidity of 10%. The voltage applied to the secondary transfer roller 15 was 3500 V (the transfer current flowing from the secondary transfer roller 15 to the recording material S was targeted to be 10 μA), which 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.

Evaluation method for transfer defects:
The recording material S was unopened paper of 75 g/ ^m2 (Vitality (Xerox), paper size LTR), and 10 sheets were printed with an all-black image at room temperature of 30°C and humidity of 80%. The voltage applied to the secondary transfer roller 15 was 700 V (the transfer current flowing from the secondary transfer roller 15 to the recording material S was targeted to be 10 μA), 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 judged as OK, and if even one sheet was missing, it was judged as NG.

Table 1 shows the evaluation results and whether the configuration is suitable for miniaturization. Configurations that are suitable for miniaturization of image forming devices are marked OK, and configurations that are not suitable for miniaturization of image forming devices are marked NG.

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 are shown in parentheses. For Example 1, the current value flowing through the current suppression circuit 60 during secondary transfer was measured and are shown in parentheses.

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

In contrast, in Example 1, both the transport guide 32 and the contact electrode 29 are grounded via the current suppression circuit 60, enabling miniaturization while preventing both whiteout and transfer defects. This is because, by setting the resistance value of the current suppression circuit 60 to the medium resistance band, it is possible to allow some of the transfer current to escape from the discharge section B so that it can handle transfer onto high-resistance recording material S in a low-humidity environment. In addition, by setting the resistance value of the current suppression circuit 60 to the medium resistance band, it is possible to prevent some of the transfer current from leaking out via the transport guide 32 so that it can handle transfer onto low-resistance recording material S in a high-humidity environment.

The configuration of Example 1 has the following features:

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 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 SN. A contact electrode 29 is provided at an opposing portion that is located upstream of the secondary transfer nip SN in the direction of rotation of the secondary transfer roller 15 and that faces the surface of the secondary transfer roller 15 upstream of the secondary transfer nip SN in the direction of movement of the recording material S, thereby discharging the surface of the secondary transfer roller 15. A transport 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 the transport of the recording material S to the secondary transfer nip 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 discharges 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 and the polarity of the transfer voltage are opposite. 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 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.

As described above, this embodiment makes it 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.

[Example 2]
Next, Example 2 will be described. In Example 2, both the conveying guide 32 and the contact electrode 29 are grounded via a current suppression circuit 60, which is configured differently from Example 1, and the transfer current is released from the secondary transfer roller 15 to the charge removal unit B by discharge. Therefore, compared to the configuration of Example 1, it is possible to suppress image damage caused by transfer even in environments where white spots or transfer defects are likely to occur, while ensuring compactness. The configuration other than the above is the same as that of Example 1. Therefore, elements having the same or equivalent functions and configurations as those of Example 1 are designated by the same reference numerals, and detailed description thereof will be omitted.

<Configuration of Secondary Transfer Unit>
3A, 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 results 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.

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, making blank areas more likely to occur. 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 discharge unit B. This locally reduces (discharges) the potential on the surface of the secondary transfer roller 15 near the discharge 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 that occurs in the discharge area H, thereby suppressing blank areas. The resistance value of this low-resistance element 601 must be a value that ensures a sufficient amount of current from the discharge unit B to ground to suppress blank areas, and is preferably approximately 0 Ω to 300 MΩ. In this embodiment, the resistance value of the low-resistance element 601 was set to 100 MΩ.

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 discharge 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, however, the transfer voltage is low when transferring toner to the recording material S, which has low electrical resistance. Therefore, whiteout is unlikely to occur even if the current from the discharge unit B to ground is less likely to flow. The resistance value of this 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 transfer current. A resistance 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.

<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.

Variation 1 will be described using Figure 4(b) and Variation 2 will be described using Figure 4(c). In the image forming apparatus of Variation 1, the transport guide 32 and 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 contact electrode 29 are grounded to ground via the same conductive path 602a as in Example 1, and like Examples 1 and 2, this configuration is suitable for reducing the size of the image forming apparatus. In the image forming apparatus of Variation 2, the transport guide 32 and 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 contact electrode 29 are grounded to ground via the same conductive path 601a as in Example 1, and like Variation 1, this configuration is suitable for reducing the size of the image forming apparatus. Therefore, variants 1 and 2 were evaluated solely in comparison with example 2, which has the following conditions, and there are no problems with use if the above conditions are the same as those of example 1.

The evaluation method for white spots and transfer defects is as follows. These conditions make image defects more likely to occur than the evaluations conducted in Example 1 and Comparative Example 1.

Evaluation method for white spots:
The recording material S used was 75 g/ ^m2 (Vitality (Xerox), paper size LTR) paper that had been left to dry for one week in an environment with a room temperature of 15°C and a humidity of 10%. The moisture content was 2.9% (measured with a paper moisture meter, Moistrex MX8000), which is prone to white voids. Ten full-black images were printed in the above environment.

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

Evaluation method for transfer defects:
The recording material S used was 75 g/ ^m2 (Vitality (Xerox), paper size LTR) paper, which had been left for one week at a room temperature of 30°C and a humidity of 80% to absorb moisture. The moisture content was 9.2% (measured with a Moistrex MX8000 paper moisture meter), which is prone to transfer defects, and 10 full-black images were printed in the above environment. The voltage applied to the secondary transfer roller 15 was 500 V (the transfer current flowing from the secondary transfer roller 15 to the recording material S was targeted to be 10 μA), 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, the result was OK; if even one sheet had any, the result was NG.

Table 2 shows the evaluation results and whether the configuration is suitable for miniaturization. Configurations that are suitable for miniaturization of image forming devices are marked OK, and configurations that are not suitable for miniaturization of image forming devices are marked NG.

For variant 1, the current values flowing through the high resistance element 602 during secondary transfer for the white void evaluation and transfer void evaluation are each shown in parentheses. Furthermore, for variant 2, the current values flowing through the low resistance element 601 during secondary transfer for the white void evaluation and transfer void evaluation were measured and shown in parentheses. Furthermore, for examples 1 and 2, the current values flowing through the current suppression circuit 60 during secondary transfer were measured and shown in parentheses.

As shown in Table 2, in variant 1, the white spots were not visible. This is because the contact electrode 29 was grounded 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.

In variant 2, transfer defects were not observed. This is because the transport guide 32 is grounded via the low-resistance element 601, resulting in a large amount of transfer current flowing from the transport guide 32 to ground through the recording material S. In other words, if the transport guide 32 and contact electrode 29 are grounded via the same resistance element, it is possible to reduce the size of the image forming device. 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 variants 1 and 2, please note that it may be necessary to design the system taking the above cases into consideration.

On the other hand, in Example 1, the conditions changed to one that made white spots and transfer defects more likely to occur, and there was a slight tendency for both phenomena to worsen. However, the image quality was still within an acceptable range.

In Example 2, both the conveying guide 32 and the contact electrode 29 are grounded via the current suppression circuit 60, enabling miniaturization while achieving even better levels of both white voids and transfer defects than in Example 1. When transferring 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 escape sufficiently from the discharge section B. When transferring 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 conveying guide 32. Because both environments are accommodated, Example 2 can further achieve both white void suppression and transfer defect suppression effects.

The configuration of Example 2 has the following features:

The device includes an environmental sensor 36 as a humidity detection means for detecting humidity-related information, and a control unit 502 that controls a current suppression circuit 60 based on the detection results of the environmental sensor 36. The current suppression circuit 60 is a variable resistance circuit, and the control unit 502 controls the resistance of the variable resistance circuit based on the detection results, using a relay switch 60c to switch the resistance between the variable resistance circuit and 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 transferring a toner image on the intermediate transfer belt 8 to a second recording material S, which has a lower resistance than the first recording material S, than when transferring a toner image on the intermediate transfer belt 8 to a first recording material S.

As described above, this embodiment makes it possible to reduce the size of the image forming apparatus while also achieving both the effects of suppressing white spots and transfer defects.

[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.

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

In this embodiment, a non-contact electrode 28 is used as the static elimination member in place of the contact electrode 29 in Example 2. The non-contact electrode 28 is formed from a 1.0 mm thick iron sheet metal. As shown in Figure 5(b), the end on the secondary transfer roller 15 side is a static elimination needle processed into a sawtooth shape as static elimination section B, with the pitch C of adjacent sawtooth teeth being 3.5 mm, the length D of the sawtooth being 2 mm, and the tip angle E of the sawtooth being 18.9°. In addition, the tip of static elimination section B is polished to a thickness of 0.1 mm. If the sawtooth pitch C is too wide, there will be areas that are not neutralized, 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.

The tip of the static elimination needle serving as static elimination unit B is positioned so that it faces the secondary transfer roller 15, with a gap of 1 mm between it and the secondary transfer roller 15. Furthermore, static elimination unit B forms an opposing area B-B' upstream in the direction of rotation of the secondary transfer roller 15 from area H, where discharge occurs between the secondary transfer roller 15 and the intermediate transfer belt 8. The non-contact electrode 28 is connected to the transport guide 32 via a conductive path 61, and the non-contact electrode 28 and the transport 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, ionic 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. Discharge position B' is the position on the surface of secondary transfer roller 15 closest to discharge unit B, and as shown in Figure 5(a), the line B-B' is perpendicular to the tangent to the surface of secondary transfer roller 15. The greater the current amount due to this corona discharge, the lower the potential at discharge position B', and the greater the white void effect. Therefore, the distance between discharge unit B and discharge position B' must be closer than the corona discharge initiation distance between discharge unit B and discharge position B'. Furthermore, to achieve sufficient white void suppression effect, it is desirable that the amount of current flowing due to corona discharge between discharge unit B and discharge position B' be equal to or greater than the transfer current flowing through transfer nip SN.

In this way, by configuring the transport guide 32 and 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 flexibility in arranging the conductive paths. This allows the transport guide 32, 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, making it possible to achieve a more compact image forming device.

Furthermore, by using a non-contact static eliminator such as a static eliminator needle as static eliminator B in this embodiment, the transfer current is released to static eliminator B without contacting the secondary transfer roller 15, which is advantageous in terms of durability of the secondary transfer roller 15 compared to the configuration of Example 1. However, the configuration of this embodiment requires a gap between static eliminator B and the secondary transfer roller 15, which may reduce design freedom. Therefore, it is possible to select whether static eliminator B is contact or non-contact depending on the characteristics required by the image forming device.

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

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

If the configuration is suitable for miniaturizing the image forming device, it is marked as OK, and if the configuration is not suitable for miniaturizing 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.

As can be seen from Table 3, in Example 3, both the transport guide 32 and the non-contact electrode 28 are grounded via the current suppression circuit 60, which, like Examples 1 and 2, allows for miniaturization while also allowing for both blank areas and transfer defects. This is because, when transferring 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 section B. Furthermore, when transferring 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 transport guide 32. Furthermore, as mentioned above, this example is also advantageous for miniaturization.

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

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

[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 in Example 3 are given the same symbols and detailed explanations are omitted.

Figure 6 shows the current suppression circuit 60 in this embodiment. The current suppression circuit 60 in this embodiment is configured to be grounded via a Zener diode 60c 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. In this configuration, 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 the conduction path 60a. Therefore, when a current above a certain level flows through the Zener diode 60c, the transport guide 32 is maintained at the breakdown voltage of the Zener diode 60c.

It is desirable to set the breakdown voltage of the Zener diode 60c to approximately the same level as the transfer voltage applied to the secondary transfer roller 15 under conditions where transfer defects are likely to occur (e.g., 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, resulting in 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, it is desirable to set the breakdown voltage of the Zener diode 60c to ±100V of the transfer voltage under conditions where transfer defects are likely to occur. In this example, the breakdown voltage of the Zener diode 60c was set to 500V.

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

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

<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.

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

As can be seen from Table 4, in Example 4, by grounding both the transport guide 32 and the non-contact electrode 28 via a current suppression circuit 60 consisting of a constant voltage element, both whiteout and transfer voids are possible while still allowing for miniaturization, just like in Example 3. This is because when transferring high-resistance recording material S, the current suppression circuit 60 allows the transfer current to escape sufficiently from the discharge section B, and when transferring low-resistance recording material S, the current suppression circuit 60 is able to suppress the outflow of transfer current via the transport guide 32.

As described above, this embodiment makes it 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.

Even if the contact electrode 29 of Example 1 is used instead of the non-contact electrode 28 of this example, the image forming apparatus can be made smaller by using a current suppression circuit 60 made of a constant voltage element as in this example. Furthermore, it is possible to achieve both the effect of suppressing white spots and the effect of suppressing transfer defects.

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 Figure 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 Figure 6(c), is also acceptable. This configuration allows for appropriate adjustment of the amount of transfer current released from the charge removal unit B. A configuration combining Figures 6(b) and 6(c), as shown in Figure 6(d), is also acceptable. In this embodiment, a Zener diode 60c is used as the constant-voltage element, but an avalanche diode, varistor, or other element capable of achieving the same effect as the Zener diode 60c, may also be used. Alternatively, as shown in Figure 6(e), the constant voltage element may be replaced with a high-voltage power supply 60d, and voltage may be applied directly to the conduction path 60a.

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

In Examples 1 to 4, the contact electrode 29 or the non-contact electrode 28 has the charge removal section B, but the transport guide 32 may also have the charge removal section B. For example, as shown in FIG. 7(a), the transport guide 32 may have a charge removal section B that contacts the secondary transfer roller 15 to remove charge from 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 a charge removal section B that does not contact the secondary transfer roller 15 to remove charge from 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, non-contact electrode 28, and conductive path 61, enabling further miniaturization.

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

The effects of this invention are not limited to image forming devices that use an intermediate transfer belt; similar effects can also be obtained in configurations such as monochrome image forming devices, in which toner is transferred directly from a photosensitive drum to a recording material.

The disclosure of embodiments of the present invention includes the following configurations:

(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 the 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.

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

(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.

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

(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,
5. The image forming apparatus according to claim 4, wherein the current suppression circuit is a variable resistance circuit, and the control unit controls the variable resistance circuit to change a resistance value based on the detection result.

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

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

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

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

(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.

(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.

(Configuration 12)
The image forming apparatus described in 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.

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

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

(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.

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

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

2 Photosensitive drum 8 Intermediate transfer belt 15 Secondary transfer roller 28 Non-contact electrode 29 Contact electrode 32 Conveyance guide 60 Current suppression circuit 74 Secondary transfer voltage application section

Claims (17)

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 the 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. An image forming apparatus according to claim 1, wherein the charge removal member contacts the transfer member at the opposing portion. An image forming apparatus according to claim 1, wherein the charge removal member is not in contact with the transfer member at the opposing portion. An image forming apparatus according to any one of claims 1 to 3, wherein the current suppression circuit is a variable resistance circuit. 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. An image forming apparatus according to any one of claims 1 to 3, wherein the current suppression circuit is a constant voltage element. The image forming apparatus of claim 6, wherein the constant voltage element is a Zener diode. The image forming apparatus of claim 1, wherein the amount of current in 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. The image forming apparatus according to claim 1, wherein the guide member also serves as the charge removal member. 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. The image forming apparatus of claim 1, wherein the normal polarity of the toner and the polarity of the transfer voltage are opposite. The image forming apparatus of claim 1, wherein, in a cross section perpendicular to the rotation axis of the transfer member, the charge removal member is disposed in the area where the transfer member is disposed, among the areas divided by tangents to the transfer member and the image carrier. The image forming apparatus according to claim 1, wherein the static elimination member is a static elimination needle. An image forming apparatus according to claim 2, characterized in that the transfer voltage is of a magnitude that discharges with the charge removal member. An image forming apparatus according to claim 1, wherein the neutralization member forms the opposing portion upstream in the direction of rotation of the transfer member from the area where discharge occurs between the transfer member and the image carrier. The image forming apparatus of claim 1, wherein the image carrier is an intermediate transfer belt. 2. The image forming apparatus according to claim 1, wherein the image carrier is a photosensitive drum.