JP2016206535A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which: in an image forming apparatus including contact parts that are not rotated and in contact with a moving transfer belt, an unexpected discharge current may be generated from a power supply member.SOLUTION: Transfer means comprises: raising part 6α that is not rotated with respect to a moving transfer belt 10 and in contact with the inner peripheral surface of the transfer belt 10; and a power supply target part 6γ that is not in contact with the inner peripheral surface of the transfer belt 10 and supplied with a power from a power supply member 63. The transfer belt 10 is arranged between the power supply target part 6γ and a photoreceptor 1 and includes a reinforcement tape 10t that has a higher resistance than that of the transfer belt 10.SELECTED DRAWING: Figure 10

Description

  The present invention relates to an electrophotographic image forming apparatus.

  Conventionally, as an image forming apparatus such as a copying machine or a printer using an electrophotographic system, there is a system using an intermediate transfer member. In an intermediate transfer body type image forming apparatus, a full-color image is formed through a primary transfer process and a secondary transfer process. In the primary transfer process, the toner image formed on the surface of the photoreceptor is transferred to an intermediate transfer belt. By repeating this process for a plurality of color toner images, a plurality of color toner images are formed on the intermediate transfer belt. In the secondary transfer process, the plurality of color toner images are collectively transferred onto the surface of a transfer material such as paper. The toner image transferred onto the transfer material is then fixed by fixing means. Thereby, a full color image is obtained.

  As the primary transfer member of the image forming apparatus, a transfer member such as a roller shape, a blade shape, or a brush shape is used. These transfer members are in contact with the back surface of the intermediate transfer belt at positions facing the photoconductor, and are used by applying a primary transfer voltage. In particular, the brush-like transfer member is formed of a group of conductive fibers, and each of the fibers can contact the intermediate transfer belt independently. Therefore, contact unevenness that occurs when a roller-like or blade-like transfer member is used is improved, and a more uniform contact property with respect to the intermediate transfer belt is obtained. As a result, image defects such as density unevenness that occur in the primary transfer step are satisfactorily suppressed. Patent Document 1 discloses a configuration in which a conductive fiber capable of supplying voltage as a primary transfer member is brought into sliding contact with an intermediate transfer belt.

  Patent Document 2 discloses a method in which a metal holder is fixed to a fiber portion of a conductive fiber with a conductive adhesive or a conductive tape, and a voltage is supplied to the conductive fiber through the metal holder.

JP-A-5-127546 JP2011-248385A

  However, if a power supply member for supplying a voltage to the conductive fiber that contacts the transfer belt that does not rotate with respect to the transfer belt that moves, such as an intermediate transfer belt, is disposed opposite to the transfer belt, the power supply member expects it. There is a risk of generating a discharge current. This problem may occur not only in conductive fibers but also in transfer means including a contact portion that contacts the moving transfer belt without rotating.

  SUMMARY An advantage of some aspects of the invention is that in an image forming apparatus including a contact portion that contacts a moving transfer belt without rotating, generation of an unexpected discharge current from a power supply member is suppressed.

  The object is to contact a photosensitive member carrying a toner image, an endlessly movable transfer belt for transferring a toner image from the photosensitive member to a transfer material, and an inner peripheral surface of the transfer belt. A transfer unit for transferring a toner image from a photoreceptor to the transfer belt, a transfer power source for applying a voltage to the transfer unit, and a power supply member for supplying a voltage from the transfer power source to the transfer unit; In the image forming apparatus, the transfer unit has a contact portion that contacts the inner peripheral surface of the transfer belt without rotating with respect to the moving transfer belt, and a width direction orthogonal to the moving direction of the transfer belt. A power-supplied part that is arranged outside the contact part and that is fed from the power-feeding member without contacting the inner peripheral surface of the transfer belt, and the transfer belt includes the power-supplied part and the photoconductor Between Are arranged, it is achieved by an image forming apparatus, comprising a high regulating member resistance than the transfer belt.

  According to the present invention, it is possible to suppress the occurrence of an unexpected discharge current from the power supply member.

1 is a diagram illustrating an outline of a configuration of an image forming apparatus according to a first embodiment. Control block diagram for controlling operation of image forming apparatus FIG. 2 is a schematic diagram illustrating an appearance of an intermediate transfer belt according to the first embodiment. The figure explaining the whole primary transfer member composition in Embodiment 1. The figure explaining the whole structure of the primary transfer member in a comparative example Diagram explaining the relationship between transfer voltage and primary transfer current (A) Cross-sectional view viewed from the moving direction of the intermediate transfer belt for explaining the discharge generated between the power supply member and the intermediate transfer belt in Embodiment 1. (b) A graph showing the relationship between the curvature and the threshold voltage at which the discharge current is generated. FIG. 5 is a graph showing a relationship between a primary transfer voltage and a primary transfer current when a discharge current is generated in the first embodiment. (A) Cross-sectional view for explaining the positional relationship between the primary transfer member and each member in the width direction of the intermediate transfer belt (b) An enlarged cross-sectional view for explaining the positional relationship between the feeding member and the reinforcing tape 10 in (a) Schematic explaining the positional relationship of each member in the width direction of the intermediate transfer belt Explanatory drawing explaining the movement of charges during the image forming process Explanatory drawing explaining the electric potential change of area | region (i), (ii), (iii) in Embodiment 1. FIG. Sectional drawing of the primary transfer part in the width direction of the intermediate transfer belt in Embodiment 2 Sectional drawing of the primary transfer part in the width direction of the intermediate transfer belt in Embodiment 3

  DETAILED DESCRIPTION Exemplary embodiments for carrying out the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. That is, the scope of the present invention is not intended to be limited to the following embodiments.

(Embodiment 1)
[Description of Image Forming Apparatus]
First, the configuration of each embodiment of an image forming apparatus having a primary transfer configuration according to the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of a color image forming apparatus. The image forming apparatus according to the present embodiment includes first to fourth image forming stations. Specifically, the first station a is an image forming station for forming a yellow toner image, the second station b is magenta, the third station c is cyan, and the fourth station d is a black toner image. This image forming apparatus has a plurality of photosensitive drums 1 (1a, 1b, 1c, 1d) as photosensitive members, and each is rotated by a motor (not shown) in the direction of the arrow. When the diameter of the photosensitive drum 1 is the center value, a full-color image is formed by sequentially performing primary transfer on the intermediate transfer belt 10 as the second image carrier while rotating the surface speed to be 100 mm / sec. An inline printer.

  Hereinafter, for convenience of explanation, an image forming operation in the first station (a) will be described. The other stations have the same configuration. The photosensitive drum 1a is uniformly charged to a negative polarity by a charging roller 2a that is a charging member. Next, a laser beam is irradiated by the exposure means 3a. Hereinafter, the laser beam irradiation direction is referred to as a main scanning direction, and the direction orthogonal to the irradiation direction is referred to as a sub-scanning direction. Thereby, an electrostatic latent image corresponding to the yellow color image is formed. Next, the electrostatic latent image is developed at the developing position by the first developing device (yellow developing device) 4a, and the yellow toner image is visualized. The yellow toner image formed on the photosensitive drum 1a is primarily transferred onto the intermediate transfer member in the process of passing through a primary transfer portion that is a contact portion between the photosensitive drum 1a and the intermediate transfer member. At that time, a primary transfer voltage having a positive polarity is applied to a primary transfer brush 6a which is a primary transfer member by a high voltage power supply 7a for primary transfer. A process in which a toner image is primarily transferred from each photosensitive drum 1 to an intermediate transfer belt 10 as an intermediate transfer member is referred to as a primary transfer process. Residual toner remaining on the photosensitive drum 1a is cleaned by the cleaning means 5a. When printing is continued, the process returns to the image forming process after charging again. In the same manner, a magenta toner image of the second color, a cyan toner image of the third color, and a black toner image of the fourth color are formed and sequentially transferred onto the intermediate transfer belt 10 to transfer the color toner image. obtain. The four color toner images on the intermediate transfer belt 10 are secondarily transferred onto the surface of the recording material P fed by the paper feeding means 50. A process in which the toner image is secondarily transferred from the intermediate transfer belt 10 to the recording material P is referred to as a secondary transfer process. A secondary transfer portion that is a contact portion with the intermediate transfer belt 10 is formed by a secondary transfer roller 20 that is a secondary transfer member, and a secondary transfer voltage is applied by a high-voltage power supply 21 for secondary transfer.

  Thereafter, the recording material P carrying the four color toner images is conveyed to the fixing device 30 where the four color toners are melted and mixed and fixed to the recording material P by being heated and pressurized there. A full color image is formed by the above operation. On the other hand, the residual toner of the positive polarity toner and the negative polarity toner is mixed on the intermediate transfer belt 10 after the secondary transfer. The residual toner is uniformly scattered and charged by the conductive brush 16. By applying a positive voltage from the brush high-voltage power supply 80 to the conductive brush 16, the residual toner is charged to a positive polarity. Further, by applying a positive voltage to the conductive roller 17 by the roller high-voltage power supply 70, the residual toner is further charged to a positive polarity. The residual toner charged to the positive polarity is transferred to the photosensitive drum 1 and collected by the cleaning device 5 disposed on the photosensitive drum 1.

[Explanation of control block diagram]
Next, the control block will be described.

  FIG. 2 is a control block diagram for controlling the operation of the image forming apparatus. The PC 271 serving as the host computer issues a print command to the formatter 273 inside the image forming apparatus 1 and transmits the image data of the print image to the formatter 273. The formatter 273 converts the image data from the PC 271 into exposure data and transfers it to the exposure control unit 277 in the DC controller 274. The exposure control unit 277 controls the exposure unit by controlling on / off of exposure data according to an instruction from the CPU 276. When the CPU 276 receives a print command from the formatter 273, the CPU 276 starts an image forming sequence. The DC controller 274 is equipped with a CPU 276, a memory 275, and the like, and performs preprogrammed operations. The CPU 276 performs image formation by controlling charging high voltage, development high voltage, and transfer high voltage to control formation of an electrostatic latent image, transfer of a developed toner image, and the like. The CPU 276 also performs processing related to primary transfer control. In the primary transfer control, the primary transfer voltage is determined by detecting the current value with respect to the voltage applied to the primary transfer member 6 a, and the current value at each voltage is stored in the memory 275. After completion of the primary transfer control, calculation is performed via the CPU 276 to determine the primary transfer voltage. Details will be described later.

[Description of intermediate transfer belt]
Next, the intermediate transfer belt 10 will be described as a transfer belt.

The intermediate transfer belt 10 is made of an endless polyimide resin having a thickness of 70 μm and a width of 250 mm, and having a volume resistivity adjusted to 10 ⁸ Ωcm by applying a conductive agent. The intermediate transfer belt 10 has a peripheral length of 650 mm as a center value, and can be stretched and moved by a plurality of stretching members. The plurality of stretching members are a driving roller 11, a tension roller 12, and a secondary transfer counter roller 13. The intermediate transfer belt 10 is rotationally driven by rotating the driving roller 11 with the same motor as the motor that rotationally drives the photosensitive drum 1. The intermediate transfer belt 10 is set to have a surface speed of 100 mm / sec when the diameter of the driving roller 11 is the center value. In the width direction, which is a direction orthogonal to the moving direction of the intermediate transfer belt 10, reinforcing members for reinforcing the end side are provided on both end surfaces of the intermediate transfer belt 10. In the present embodiment, a tape-like reinforcing tape 10 t is attached as a reinforcing member over one circumference of the intermediate transfer belt 10.

  FIG. 3 is a schematic view showing the appearance of the intermediate transfer belt 10. As shown in FIG. 3, the reinforcing tape 10t is attached to the outer peripheral surfaces of both ends of the intermediate transfer belt 10 over a width of 8 mm. The reinforcing tape 10t only needs to be electrically insulated, and in this embodiment, a polyester adhesive tape is used (manufactured by Nitto Denko: polyester adhesive tape 31B). Further, in view of the strength of the intermediate transfer belt 10, it may be pasted one or more times in the circumferential direction, and may be pasted over two or more belts.

[Description of primary transfer member]
Next, the overall configuration of the primary transfer brush 6 that is a primary transfer member will be described.

  FIG. 4 is a perspective view of the primary transfer brush 6. The primary transfer brush 6 includes a raised portion 6α that is a contact portion that contacts an inner peripheral surface (back surface) of the intermediate transfer belt 10 and a base fabric portion 6β. An insulating double-sided tape 64 that is electrically insulated is attached to the back surface of the base fabric portion 6β and adhered to the support member 61. (The insulating tape 64 will be described with reference to FIG. 5.) The raised portion 6α is supported by the base fabric portion 6β, and the raised portion 6α and the base fabric portion 6β constitute a brush portion.

  The raised portion 6α has a length of 3 mm in the moving direction (R3 direction) of the intermediate transfer belt 10, and the width of the base cloth portion 6β is 5 mm in the moving direction (R3 direction) of the intermediate transfer belt 10. . The width of the raised portion 6α corresponding to the width direction of the intermediate transfer belt 10 is 230 mm, and the width of the base fabric portion 6β is 250 mm. Further, a welding portion 6γ is formed on one end side in the width direction of the intermediate transfer belt 10 over a width of 8 mm. The welded portion 6γ is a region having a thickness of about 100 μm formed by welding the raised portion 6α, and has a resistivity substantially equal to that of the raised portion 6α.

The raised portion 6α is a collection of a plurality of conductive fibers made of conductive nylon fibers in which carbon powder is dispersed. The conductive fibers have a single yarn fineness of 2 to 15 dtex [detx indicates mass (unit of gram) per 10,000 m of single fiber], a diameter of 10 to 40 μm, and a dry strength of 1 to 3 cN / dtex. Is preferred. The fiber resistivity ρfiber is preferably in the range of 10 to 10 ⁸ Ωcm. The resistivity ρfiber is measured by the following method. A bundle of 50 fibers is brought into contact with a metal probe on the surface of the bundle with an interval of about 1 cm. Then, using a high resistance meter Advantest R8340A or the like, the resistance value Rfiber is measured under an applied voltage of 100 V, and the resistivity ρfiber is calculated by the following equation.

ρfiber = Rfiber × (fiber diameter / 2) ² × 3.14 × 50 ÷ 1.0
In the present embodiment, the fiber length d of the primary transfer brush 6 is 1.5 mm. Here, the fiber length d is a length from the base fabric portion 6β to the free end of the conductive fiber in a state where the primary transfer brush 6 is not in contact with the intermediate transfer belt 10.

  Next, the pressurizing configuration will be described. As shown in FIG. 4, the support member 61 is pressed by a pressure spring 62 that is an urging member so that the primary transfer brush 6 is brought into contact with the intermediate transfer belt 10. The pressure spring 62 causes the primary transfer brush 6 to contact the back surface of the intermediate transfer belt 10 facing the photosensitive drum 1 with a pressurizing force of 2N via the support member 61. At this time, the raised portions 6α of the primary transfer brush 6 are deformed and come into contact with the intermediate transfer belt 10 in a state where the restoring force and the pressure applied by the pressure spring 62 are balanced.

  Incidentally, since the intermediate transfer belt 10 is rotationally driven, the primary transfer brush 6 is slid against the intermediate transfer belt 10 under pressure. Further, when a voltage is applied to the primary transfer brush 6, the primary transfer brush 6 and the intermediate transfer belt 10 are electrostatically adsorbed in addition to the pressure applied by the pressure spring 62. growing. For this reason, sufficient adhesive force is provided between the base fabric portion 6β and the support member 61 so that the raised portions 6α are not peeled off from the support member 61 in consideration of the applied pressure and electrostatic adsorption. is necessary.

  FIG. 5 is a perspective view illustrating the configuration of the primary transfer brush 60 of the comparative example. Since the basic configuration of the primary transfer brush 60 of the comparative example is substantially the same as that of the primary transfer brush 6, the description of the same configuration is omitted. In the comparative example of FIG. 5, a conductive double-sided tape 6 δ is used as a bonding means between the base fabric portion 6 β and the support member 61. In the comparative example, a part of the double-sided tape 6δ protrudes from the base cloth portion 6β, and power is supplied to the protruding region. Since the double-sided tape 6δ has a conductive component such as carbon having no adhesive force dispersed in the adhesive layer, the adhesiveness tends to be lower than that of the insulating double-sided tape. Therefore, in the configuration of the comparative example, the base cloth portion 6β may be peeled off by sliding with the intermediate transfer belt 10.

  Therefore, in the present embodiment, the base cloth portion 6β and the support member 61 use an insulating double-sided tape 64, and a power supply member for supplying a voltage to the primary transfer brush 6 on the welding portion 6γ side of the primary transfer brush 6. 63 is arranged.

  Next, a method for supplying power to the primary transfer brush 6 of this embodiment will be described. In the present embodiment, as shown in FIG. 4, a weld portion 6γ is formed on one end side in the longitudinal direction. The welded portion 6γ is formed by thermally aggregating the conductive fibers of the raised portion 6α. The welded portion 6γ is a region having conductivity because the conductive fiber is melted. A metal power supply member 63 made of stainless steel is in contact with the welded portion 6γ. The power feeding member 63 has a clip shape as shown in FIG. 7 to be described later, and one end thereof is in contact with the welded portion 6γ. (Therefore, the welded portion 6γ is a power-supplied portion fed from the power feeding member 63.) The other end of the power feeding member 63 is in contact with the back surface side of the support member 61, and the power feeding member 63 is supported by the welded portion 6γ. The member 61 is held together. The power supply member 63 is pressed by a pressure spring 62, and a transfer voltage is applied to the pressure spring 62 by the transfer high-voltage power supply 7. Therefore, the power supply member 63 is a member for supplying (applying) a voltage from the transfer high-voltage power supply to the primary transfer member 6.

  As described above, in this embodiment, instead of using the insulating double-sided tape 64 for bonding the base fabric portion 6β and the support member 61, the power supply member 63 is used as the power supply member. It has a configuration capable of supplying power while having a sufficient adhesive force with the support member 61.

[Explanation of primary transfer control]
Next, the primary transfer control method will be described. In the primary transfer control, transfer voltage adjustment (ATVC (Auto Transfer Voltage Control) control) is performed before image formation in order to determine a voltage to be applied to the primary transfer brush 6. The ATVC control is a control for determining the primary transfer voltage value Vg so that the target current It can be obtained at the time of image formation even if the resistance of the intermediate transfer belt 10 fluctuates. In this embodiment, the ATVC control in the first station (a) will be described as a representative, but the same applies to other stations.

  Details of the ATVC control will be described. In FIG. 6, the horizontal axis indicates the transfer voltage (V), and the vertical axis indicates the transfer current (μA). During the ATVC control, a negative voltage is applied to the charging roller 2a, and the surface potential of the photosensitive drum 9a is adjusted to be equal to that during image formation. The transfer voltage control unit 281 controls the primary transfer power source 7a to apply three kinds of voltages of predetermined primary transfer voltages (Vt1, Vt2, Vt3) to the primary transfer brush 6a, and the current values (It1, It2, It3) is detected by the current detector in the transfer voltage controller 281. The transfer voltage control unit 281 calculates a primary transfer voltage value Vg corresponding to the target transfer current It via the CPU 276. The calculated primary transfer voltage value Vg is stored in the memory 275 of the engine control unit 272.

[Discharge current from power supply member 63]
Next, a discharge current generated from the power supply member 63 toward the intermediate transfer belt 10 will be described. A potential is formed in the power supply member 63, and therefore, a discharge may occur between the intermediate transfer belt 10 and the power supply member 63. FIG. 7A is a cross-sectional view seen from the moving direction of the intermediate transfer belt 10 for explaining the discharge generated between the power supply member 63 and the intermediate transfer belt 10. As shown in FIG. 7A, the electric charge concentrates at the edge portion H which is the end portion of the power supply member 63, so that the electric field is locally dense around the edge portion.

  As a result, depending on the potential difference between the potential of the power supply member 63 and the potential of the intermediate transfer belt 10, a discharge current may be generated from the edge portion H toward the intermediate transfer belt 10. FIG. 7B is a graph showing the relationship between the curvature and the threshold voltage at which the discharge current is generated. The horizontal axis represents the radius of curvature, and the vertical axis represents the absolute value of the discharge occurrence threshold voltage. As shown in FIG. 7B, the threshold voltage decreases as the radius of curvature decreases.

  FIG. 8 is a graph showing the relationship between the primary transfer voltage and the primary transfer current when a discharge current is generated during ATVC control. In the present embodiment, a case where a discharge current is generated at Vt2 or more will be described. When a discharge current is generated at Vt2 or higher, the primary transfer current that flows when Vt3 is applied is obtained by adding the current It3 that flows through the raised portion 6α of the primary transfer brush 6 and the discharge current Id from the edge portion H of the power supply member 63. It3 + Id flows. As the primary transfer voltage, a voltage value that becomes It is calculated by a current value (It1, It2, It3 + Id) with respect to the primary transfer voltage (Vt1, Vt2, Vt3). For this reason, Vgd lower than the primary transfer voltage Vg to be originally applied is determined as the primary transfer voltage. As a result, a primary transfer voltage lower than the desired primary transfer voltage is applied, so that the toner image on the photosensitive drum 1 is not partially transferred due to a current shortage, which may result in an image defect such as a low image density. There is. Further, when the discharge current Id is large, not only the ATVC control is affected, but the intermediate transfer belt 10 may break.

  Therefore, in order to prevent the occurrence of the discharge current, it is necessary to make the potential difference between the edge portion H of the power supply member 63 and the intermediate transfer belt 10 smaller than the potential difference between the base cloth portion 6β and the intermediate transfer belt 10. is there.

[Features of this embodiment]
In the present embodiment, the power feeding member 63 is arranged so that the edge portion H of the power feeding member 63 is directly below the reinforcing tape 10t. The positional relationship of each member in this embodiment will be described. FIG. 9A is a cross-sectional view illustrating the positional relationship between the primary transfer member 6 and each member in the width direction of the intermediate transfer belt 10. FIG. 9B is an enlarged cross-sectional view for explaining the positional relationship between the power feeding member 63 and the reinforcing tape 10t in FIG.

  As shown in FIG. 9A, the primary transfer brush 6 and the intermediate transfer belt 10 are arranged so that the intermediate transfer belt 10 and the center line of the raised portion 6α are aligned. As shown in FIGS. 9A and 9B, a welded portion 6γ is formed over a width of 8 mm from the right end portion of the raised portion 6α. Further, the reinforcing tape 10t is attached to both ends of the intermediate transfer belt 10 over a width of 8 mm, and the welded portion 6γ is arranged over 6 mm directly below the reinforcing tape 10t. The reinforcing tape 10t at both ends of the intermediate transfer belt 10 is a regulating member having higher resistance than the intermediate transfer belt 10, and as described above, an insulating member is used in this embodiment. Further, the power supply member 63 is arranged so that the edge portion H is directly below the reinforcing tape 10t.

  FIG. 10 is a schematic diagram illustrating the positional relationship among the charging roller 2, the photosensitive drum 1, the intermediate transfer belt 10, the reinforcing tape 10 t, and the power supply member 63 in the width direction of the intermediate transfer belt 10. As shown in FIG. 10, the power supply member 63 is disposed such that the edge portion H is located at a position away from the end of the reinforcing tape 10 t by Δa. In this embodiment, Δa is 2 mm. Δc is the distance from the end of the reinforcing tape 10t to the end of the charging roller 2a. In this embodiment, Δc is 5 mm. For this reason, the edge portion H of the power supply member 63 is located in a region where the reinforcing tape 10 is provided in the width direction of the intermediate transfer belt 10 and overlaps the region where the charging roller 2a is charged. .

[Operation of this embodiment]
Next, the movement of charges during the image forming process will be described with reference to FIG. For simplicity, a case where a toner image is not formed will be described. Since all the image forming stations have the same configuration, description will be made by omitting the symbols a, b, c, and d from each member.

  First, since a positive voltage is applied to the primary transfer brush 6 from the power source 7, positive charges are injected into the intermediate transfer belt 10 via the primary transfer brush 6a (arrow L1 in FIG. 11). The injected positive charge moves with the rotational movement of the intermediate transfer belt 10 (arrow L2 in FIG. 11). On the other hand, a negative voltage is applied to the charging roller 2, and the surface of the photosensitive drum 1a is negatively charged by the discharge from the charging roller 2, and moves with the rotation of the photosensitive drum 1 (arrow in FIG. 11). L3). As a result, a discharge current is generated between the surface of the intermediate transfer belt 10 and the photosensitive drum 1 (arrow L4 in FIG. 11). Since the magnitude of the discharge current is determined by the potential difference between the potential of the surface of the photosensitive drum 1 and the potential of the intermediate transfer belt 10, it increases as the voltage applied to the primary transfer brush 6 increases.

  Next, the movement of electric charges in each region in the cross section in the sub-scanning direction of the primary transfer portion will be described with reference to FIGS. A region (i) in FIG. 10 is a region where the raised portion 6α of the primary transfer brush 6a is in contact with the intermediate transfer belt 10, and a region (ii) is a position corresponding to the welded portion 6γ of the primary transfer brush 6. The region without the reinforcing tape 10t. The region (iii) is a region where the reinforcing tape 10t is attached. In FIG. 12, the horizontal axis represents the distance, and the vertical axis represents the potential, and the potential change in the regions (i), (ii), and (iii) is described.

  S1 in FIG. 12 is a graph showing changes in the potential of the region (i). First, a point ia in FIG. 12 is the surface of the photosensitive drum 1 and is a negative potential. In the area (i), since a current flows from the primary transfer brush 6a to the photosensitive drum 1a, the potential is attenuated in the intermediate transfer belt 10, and a positive potential is shown on the back surface of the intermediate transfer belt 10 as indicated by a point i-b. It becomes. Further, the potential is attenuated from the raised portion 6α to the base fabric portion 6β of the primary transfer brush 6a to reach the point ic. The point i-c is substantially the same as the potential supplied by the power source 7a.

  In the region (ii), since there is a space between the intermediate transfer belt 10 and the base cloth portion 6β of the primary transfer brush 6a, a potential difference is generated between the intermediate transfer belt 10 and the base cloth portion 6β. S2 in FIG. 12 is a graph showing the transition of the potential in the region (ii). A point ii-a is the surface potential of the photosensitive drum 6 and is negative like the region (i). Then, it is attenuated by the intermediate belt 10 and becomes the potential indicated by point ii-b at the back surface of the intermediate transfer belt 10.

  At the point ib, in addition to the potential attenuation according to the dielectric constant of the intermediate transfer belt 10, the potential is attenuated by the positive charge injection from the raised portion 6α of the primary transfer brush 6, whereas the point ii- b is only potential attenuation according to the dielectric constant of the intermediate transfer belt 10. For this reason, the point ii-b has a lower potential than the point ib. Next, the point ii-c is the potential of the weld 6β, which is the same as the potential supplied by the power source 7.

  That is, the potentials at the points ii-c and ic are equal. In the region (ii), a potential difference S (ii) is generated between the point ii-b that is the potential of the back surface of the intermediate transfer belt 10 and the point ii-c that is the potential of the welded portion 6β.

  S3 in FIG. 12 is a graph showing the transition of the potential in the direction of arrow L3 in FIG. 10 in the region (iii). Point iii-a is the surface potential of the photosensitive drum 6a and is negative as in the region (i). Next, the point iii-α is the potential of the back surface portion of the reinforcing tape 10t. The absolute value of the point iii-α is smaller than that of the point iii-a due to the potential attenuation in the reinforcing tape 10t. Further, at the point iii-b, the absolute value becomes smaller than the potential at the point iii-b due to the potential attenuation in the intermediate transfer belt 10. The point iii-c is the potential of the power feeding member 63 and is the same as the potential supplied by the power source 7a.

  From the above, it is assumed that the potential difference between the points ii-b and ii-c in the region (ii) is S (ii), and the potential difference between the points iii-b and iii-c in the region (iii) is S (iii). , S (iii) <S (ii). Therefore, the potential difference between the power supply member 63 and the intermediate transfer belt 10 is smaller in the region (iii) than in the region (ii), and the discharge current from the edge portion H of the power supply member 63 is suppressed. .

  As described above, in the present embodiment, the position of the edge portion H of the power supply member 63 is reinforced in the width direction of the intermediate transfer belt 10 in order to suppress the generation of the discharge current from the edge portion H of the power supply member 63. It arrange | positioned so that it might become in the area | region corresponding to 10t.

  In order to suppress the occurrence of a discharge current from the edge portion H of the power supply member 63, a configuration in which the edge portion of the power supply member 63 is covered with an insulating member instead of the reinforcing tape 10t may be employed. However, in the configuration in which the edge portion of the power supply member 63 is covered with the insulating member, a partial discharge current is generated when a leak point occurs. On the other hand, in the configuration of the present embodiment, the reinforcing tape 10t is attached over the entire circumference of the intermediate transfer belt 10. For this reason, even if the reinforcing tape is worn or broken due to a change with time or the like and a leak point is partially generated, the leak point is not fixed because the reinforcing tape 10t is rotated together with the intermediate transfer belt 10. That is, in the configuration of the present embodiment, it is possible to prevent a situation in which electric field concentration is constantly generated between the leak point and the power supply member 63. For this reason, there exists a merit that the generation | occurrence | production risk of discharge current is reduced.

  In the present embodiment, the power feeding member 63 is disposed so that the edge portion H of the power feeding member 63 is directly below the reinforcing tape 10t and directly below the charging roller 2a. However, when the arrangement space is allowed, the edge portion H of the power supply member 63 may be located outside the edge of the charging roller 2a. In this case, since the photosensitive drum 1a is not charged by the charging roller 2a, a discharge current is hardly generated between the photosensitive drum 1a and the reinforcing tape 10t. Therefore, since the potential difference between the intermediate transfer belt 10 and the power supply member 63 becomes smaller, the discharge current from the edge portion H of the power supply member 63 is further suppressed.

  In the present embodiment, an example in which a conductive brush is used as the primary transfer configuration has been described. However, since the same effect can be obtained with a primary transfer member that slides with respect to the intermediate transfer belt 10, for example, A member such as a conductive sheet may be used.

  In this embodiment, the image forming apparatus that uses the intermediate transfer belt 10 as a transfer belt has been described. However, the same applies to an image forming apparatus that uses a conveyance belt that adsorbs and conveys media such as paper and cardboard. effective. The same effect can be obtained even in a system in which a single photosensitive drum is used instead of a plurality of photosensitive drums.

  Furthermore, in this embodiment, independent power sources are connected to the plurality of primary transfer members, but a configuration in which a common power source is used for some or all of the primary transfer members. Also good.

(Embodiment 2)
The second embodiment is different from the first embodiment in that a regulating member is attached to the back end portion of the intermediate transfer belt 10 instead of the reinforcing tape 10t. Since other configurations are the same as those of the image forming apparatus of the first embodiment, the same portions are described with the same reference numerals. In the second embodiment, another configuration capable of obtaining the same effect as that of the first embodiment will be described.

  In the present embodiment, an insulating member as a regulating member is attached to the back surface end portion (inner peripheral surface end portion) of the intermediate transfer belt 10, and the power supply member 63 is positioned so that the edge portion H of the power supply member 63 is located directly below the insulating member. It is characterized by arranging.

  FIG. 13 is a cross-sectional view of the primary transfer portion in the width direction of the intermediate transfer belt 10 in the present embodiment. As a regulating member, an insulating rib 10 r is attached to the entire circumference of the back surface of the intermediate transfer belt 10. The insulating rib 10r is a movement restricting member that restricts the movement of the intermediate transfer belt 10 when the intermediate transfer belt 10 approaches the width direction. The insulating rib 10r has an effect of stably rotating the intermediate transfer belt 10 along the guide members disposed at the end portions of the driving roller 11, the tension roller 12, and the secondary transfer counter roller 13. The insulating rib 10r is an electrically insulating foamed urethane material (INOAC Corporation: Polon HH48), and has a thickness of 100 μm and a width of 8 mm. Also in the present embodiment, the distance Δa between the edge portion H of the insulating rib 10γ and the edge portion H of the power feeding member 63 is 2 mm. The insulating rib 10r may be another insulating member in view of the running property of the intermediate transfer belt 10 and the required durability.

  Similar to the first embodiment, the present embodiment also has an effect of suppressing the generation of a discharge current from the edge portion H of the power supply member 63 by the insulating rib 10r that is a restricting member.

(Embodiment 3)
The third embodiment is different from the first embodiment in that the edge portion H of the reinforcing member 63 is bent with respect to the first embodiment. Since other configurations are the same as those of the image forming apparatus of the first embodiment, the same portions are described with the same reference numerals.

  The present embodiment is characterized in that the power supply member 63 is bent at the contact end where it contacts the welded portion 6γ, and has a curvature at a portion closest to the region (ii). FIG. 14 is a cross-sectional view of the primary transfer portion in the width direction of the intermediate transfer belt 10 in the present embodiment. As shown in FIG. 14, in this embodiment, the edge portion H is separated from the end portion of the reinforcing tape 10 t by Δb by bending the end portion of the conductive power supply member 63. In the present embodiment, Δb is 5 mm.

  As a result, the distance from the intermediate transfer belt 10 and the edge portion H of the power supply member 63 in the region (ii) is increased. Therefore, the electric field acting between the intermediate transfer belt 10 and the edge portion H of the power supply member 63 is weaker than that in the first embodiment, and the possibility of occurrence of a discharge current can be further suppressed. In addition, since the edge part H of the electric power feeding member 63 can suppress possibility that a discharge current generate | occur | produces, so that it is far from the area | region (ii), not only the structure of this embodiment but the distance (DELTA) b from the edge part of the reinforcement tape 10t more It is good also as a big structure.

1a, 1b, 1c, 1d Photosensitive drum 10 Intermediate transfer belt 6a, 6b, 6c, 6d Primary transfer member 10t, 10r Restricting member 63 Power supply member 80 Charging member 6γ Power-supplied part

Claims (12)

A photosensitive member carrying a toner image; a transfer belt that is endlessly movable and transfers the toner image from the photosensitive member to a transfer material; and an inner peripheral surface of the transfer belt that contacts the inner peripheral surface of the transfer belt. Image forming comprising transfer means for transferring a toner image toward a transfer belt, a transfer power supply for applying a voltage to the transfer means, and a power supply member for supplying a voltage from the transfer power supply to the transfer means In the device
The transfer means is disposed outside the contact portion in a width direction perpendicular to the moving direction of the transfer belt, and a contact portion that contacts the inner peripheral surface of the transfer belt without rotating with respect to the moving transfer belt And a power-supplied part that is fed from the power feeding member without contacting the inner peripheral surface of the transfer belt,
The image forming apparatus, wherein the transfer belt includes a regulating member that is disposed between the power-supplied portion and the photosensitive member and has a higher resistance than the transfer belt.   The image forming apparatus according to claim 1, wherein the regulating member is a reinforcing tape that is provided on an outer peripheral surface of the transfer belt and reinforces an end portion side in the width direction of the transfer belt.   2. The movement restricting member that is provided on an inner peripheral surface of the transfer belt, and that restricts movement of the transfer belt when the transfer belt approaches the width direction. The image forming apparatus described.   4. The image according to claim 1, wherein the regulating member is attached to the transfer belt over at least one turn in a circumferential direction of the transfer belt. 5. Forming equipment.   The contact portion is composed of a plurality of conductive fibers, and the power-supplied portion is a welded portion formed by welding the plurality of conductive fibers. 5. The image forming apparatus according to claim 4.   The transfer means includes a support member that supports the contact portion and the weld portion, and the contact portion and the weld portion are bonded to the support member by a double-sided tape not provided with a conductive agent. The image forming apparatus according to claim 5.   The image forming apparatus according to claim 6, wherein the power supply member has a shape that sandwiches the support member and the welded portion.   The image forming apparatus according to claim 1, wherein the power supply member is a metal.   The image forming apparatus according to claim 1, wherein the regulating member is an electrically insulating member.   The image forming apparatus according to claim 1, wherein an end portion of the regulating member is bent.   11. The image forming apparatus according to claim 1, wherein the transfer belt is an intermediate transfer belt on which a toner image is primarily transferred from the photoconductor. The image forming apparatus according to claim 1, wherein the transfer belt is a conveyance belt that conveys a transfer material onto which a toner image is transferred from the photoconductor.

Images