Intermediate transfer unit and image forming apparatus equipped therewith

Abstract

To provide an intermediate transfer unit that can effectively solve defects in transfer images at primary transfer units with a simple configuration, and an image forming apparatus including the same.SOLUTION: An intermediate transfer unit comprises: an endless intermediate transfer belt on which toner images formed on image carriers are sequentially laminated; a drive roller that is arranged in contact with an inner peripheral surface of the intermediate transfer belt and drives to rotate the intermediate transfer belt; a tension roller that rotates following the intermediate transfer belt and applies a predetermined tension to the intermediate transfer belt; primary transfer members that are brought into pressure contact with the image carriers with the intermediate transfer belt therebetween; and a transfer voltage power supply. The transfer voltage power supply applies, to the primary transfer members, primary transfer voltage having a polarity opposite to the toner images. The intermediate transfer belt has a surface resistivity of 109.5 to 1010.5 [Ω / sq.] and a volume resistivity of 1010 [Ω cm] or less. The primary transfer members have a resistance value of 106.3 to 107.3 [Ω]. The transfer voltage power supply is in constant current control.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an intermediate transfer unit for transferring a toner image formed on an image carrier such as a photoreceptor drum onto an intermediate transfer belt, and to an image forming apparatus equipped therewith. [Background technology]

[0002] Conventionally, an image forming apparatus using an intermediate transfer method is known, which comprises an endless intermediate transfer belt that rotates in a predetermined direction and a plurality of image forming units provided along the intermediate transfer belt, in which toner images of each color are sequentially superimposed on the intermediate transfer belt by each image forming unit for primary transfer, and then the toner images are secondaryly transferred onto a recording medium such as paper by a secondary transfer roller.

[0003] In image forming apparatuses using an intermediate transfer method, the surface potential of the photoreceptor drum decreases in the next rotation due to the influence of the primary transfer electric field, and this effect appears in the transferred image, a phenomenon known as ghosting (transfer history). This is more likely to occur when the resistance of the intermediate transfer belt or primary transfer roller is low. Also, when the transfer voltage is high, discharge occurs between the intermediate transfer belt and the photoreceptor drum, resulting in a spotted image. This is more likely to occur when the resistance of the intermediate transfer belt or primary transfer member is high.

[0004] Patent Document 1 discloses an intermediate transfer unit in which the resistance of the primary transfer member and the intermediate transfer belt are defined in order to stabilize the transfer performance in the primary transfer section. Specifically, the resistance value of the primary transfer member is set to 10 6 ~10 8 [Ω], the surface resistance of the intermediate transfer belt is 10 8 ~10 12 [Ω / □], volume resistivity is 10 8 ~10 12 The impedance is set to [Ωcm], and when the impedance of the primary transfer section is large, the high-voltage power supply is controlled by constant current, and when the impedance is small, the high-voltage power supply is controlled by constant voltage. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Laid-Open No. 10-240042 [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] However, in the method of Patent Document 1, since the control of the high-voltage power supply is switched between constant voltage control and constant current control according to the impedance of the primary transfer unit, a high-voltage power supply capable of switching between constant voltage control and constant current control is required, resulting in high costs and complex control.

[0007] In view of the above problems, an object of the present invention is to provide an intermediate transfer unit and an image forming apparatus including the same that can effectively eliminate defects in a transferred image in a primary transfer unit with a simple configuration. [Means for Solving the Problems]

[0008] A first configuration of the present invention for achieving the above object is an intermediate transfer unit including an intermediate transfer belt, a driving roller, a tension roller, a primary transfer member, and a transfer voltage power supply. The intermediate transfer belt is endless, and toner images formed on an image carrier are sequentially laminated thereon. The driving roller is disposed in contact with the inner peripheral surface of the intermediate transfer belt and rotationally drives the intermediate transfer belt. The tension roller rotates following the intermediate transfer belt and applies a predetermined tension to the intermediate transfer belt. The primary transfer member is pressed against the image carrier via the intermediate transfer belt. The transfer voltage power supply applies a primary transfer voltage having a polarity opposite to that of the toner image to the primary transfer member. The surface resistivity of the intermediate transfer belt is 10 9.5 ~10 10.5 [Ω / sq], the volume resistivity is 10 10 [Ω·cm] or less, the resistance value of the primary transfer member is 10 6.3 ~10 7.3 [Ω], and the transfer voltage power supply is constant current control. [Effects of the Invention]

[0009] According to the first configuration of the present invention, by defining the range of resistance values ​​of the primary transfer member, the volume resistivity and surface resistivity of the intermediate transfer belt, ghosting, spotted images, and transferability can be kept within acceptable limits regardless of the installation environment of the image forming apparatus. Furthermore, by using constant current control for the transfer voltage power supply, it becomes easier to maintain a constant primary transfer current, and a good primary transfer image can be obtained. In addition, the control path of the transfer voltage power supply is also simplified. [Brief explanation of the drawing]

[0010] [Figure 1] A schematic cross-sectional view showing the overall configuration of an image forming apparatus 100 according to one embodiment of the present invention. [Figure 2] Figure 1 shows a magnified view of the area around the image forming section Pa. [Figure 3] Side cross-sectional view of the intermediate transfer unit 30 mounted on the image forming apparatus 100. [Figure 4] Block diagram showing an example of the control path of the image forming apparatus 100. [Figure 5] This graph shows the relationship between the surface resistivity of the intermediate transfer belt 8 and the primary transfer current in a normal temperature and humidity environment (RR environment). [Figure 6] This graph shows the relationship between the surface resistivity of the intermediate transfer belt 8 and the primary transfer current in a low-temperature, low-humidity environment (LL environment). [Figure 7] This graph shows the relationship between the surface resistivity of the intermediate transfer belt 8 and the primary transfer current in a high-temperature, high-humidity environment (HH environment). [Figure 8] Graph showing the relationship between the resistance values ​​of primary transfer rollers 6a-6d and the primary transfer current in a low-temperature, low-humidity environment (LL environment). [Modes for carrying out the invention]

[0011] The embodiments of the present invention will now be described in detail with reference to the drawings. Figure 1 is a schematic diagram showing the configuration of an image forming apparatus 100 according to one embodiment of the present invention, and Figure 2 is an enlarged view of the area around the image forming section Pa in Figure 1. The image forming sections Pb to Pd have basically the same configuration, so their description will be omitted.

[0012] Inside the main body of the image forming apparatus 100 (here, a color printer), four image forming units Pa, Pb, Pc, and Pd are arranged in order from the upstream side in the conveyance direction (the left side in FIG. 1). These image forming units Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and form cyan, magenta, yellow, and black images sequentially through the steps of charging, exposure, development, and transfer respectively.

[0013] Photoconductor drums 1a, 1b, 1c, and 1d for carrying visible images (toner images) of each color are respectively arranged in these image forming units Pa to Pd. Further, an intermediate transfer belt 8 that is wound around a plurality of rollers including a driving roller 10 and a tension roller 11 and rotates in the counterclockwise direction in FIG. 1 is provided adjacent to each of the image forming units Pa to Pd. As shown in FIG. 2, around the photoconductor drum 1a, a charging device 2a, a developing device 3a, a cleaning device 7a, and a discharging lamp 20 are arranged along the drum rotation direction (clockwise direction in FIG. 2), and a primary transfer roller 6a is arranged across the intermediate transfer belt 8.

[0014] The photoconductor drums 1a to 1d are composed of a conductive substrate 19a and a photosensitive layer 19b formed on the surface of the conductive substrate 19a. In the present embodiment, an organic photosensitive layer is laminated as the photosensitive layer 19b on the surface of a cylindrical conductive substrate 19a made of aluminum.

[0015] The charging devices 2a to 2d have a charging roller 21 that contacts the photoconductor drum 1a and applies a charging voltage (DC voltage) to the drum surface, and a charging cleaning roller 24 for cleaning the charging roller 21. In the present invention, in order to reduce the amount of generated ozone and the cost of the charging voltage power supply 52 (see FIG. 4), a charging voltage consisting only of a DC voltage is applied to the charging roller 21.

[0016] Each developing unit 3a to 3d is a two-component developing type, each having two agitation and transport screws 25 and a developing roller 29. Each unit is filled with a predetermined amount of two-component developer containing cyan, magenta, yellow, and black toners and a magnetic carrier. A magnetic brush is formed on the surface of the developing roller 29 using the two-component developer, and while applying a developing voltage of the same polarity as the toner (positive polarity in this case) to the developing roller 29, the magnetic brush is brought into contact with the surface of the photoreceptor drum 1a to deposit toner and form a toner image. If the proportion of toner in the two-component developer filled in each developing unit 3a to 3d falls below a specified value due to the formation of the toner image, toner is replenished from toner containers 4a to 4d into each developing unit 3a to 3d.

[0017] When image data is input from a higher-level device such as a personal computer, the main motor 40 (see Figure 4) first starts rotating the photoreceptor drums 1a to 1d. The belt drive motor 41 (see Figure 4) also starts rotating the intermediate transfer belt 8. Next, the charging devices 2a to 2d uniformly charge the surfaces of the photoreceptor drums 1a to 1d with the same polarity as the toner (positive polarity in this case). Then, the exposure device 5 irradiates the drums with light according to the image data, forming an electrostatic latent image on each photoreceptor drum 1a to 1d with the charge attenuated according to the image data. Finally, the developing devices 3a to 3d supply toner onto the photoreceptor drums 1a to 1d, and by electrostatic adhesion, a toner image corresponding to the electrostatic latent image is formed.

[0018] Then, by applying a predetermined primary transfer electric field between the primary transfer rollers 6a to 6d and the photoreceptor drums 1a to 1d using the primary transfer rollers 6a to 6d, the yellow, cyan, magenta, and black toner images on the photoreceptor drums 1a to 1d are primary transferred onto the intermediate transfer belt 8. After the primary transfer, any toner remaining on the surface of the photoreceptor drums 1a to 1d is removed by the cleaning devices 7a to 7d. Any residual charge remaining on the surface of the photoreceptor drums 1a to 1d after the primary transfer is removed by the static elimination lamp 20.

[0019] The transfer paper S onto which the toner image is transferred is housed in a paper cassette 16 located at the bottom of the image forming apparatus 100. The transfer paper S is transported via the paper feed roller 12a and the registration roller pair 12b to the secondary transfer roller 9 and the nip portion (secondary transfer nip portion) of the intermediate transfer belt 8, which are located adjacent to the intermediate transfer belt 8, at a predetermined timing. The transfer paper S onto which the toner image on the intermediate transfer belt 8 has been secondarily transferred by the secondary transfer roller 9 is transported to the fixing unit 13.

[0020] The transfer paper S, transported to the fixing unit 13, is heated and pressurized by the fixing roller pair 13a, fixing the toner image to the surface of the transfer paper S and forming a predetermined full-color image. The transfer paper S, on which the full-color image has been formed, is then discharged into the discharge tray 17 by the discharge roller pair 15 (or is diverted to the inversion transport path 18 by the branching unit 14, after which images have been formed on both sides).

[0021] Figure 3 is a side cross-sectional view of an intermediate transfer unit 30 mounted on an image forming apparatus 100. As shown in Figure 3, the intermediate transfer unit 30 includes an intermediate transfer belt 8 stretched between a drive roller 10 and a tension roller 11, primary transfer rollers 6a to 6d that contact the photoreceptor drums 1a to 1d via the intermediate transfer belt 8, and a pressure switching roller 34.

[0022] The drive roller 10 and tension roller 11 are positioned downstream and upstream, respectively, of the transport surface (bottom surface) of the intermediate transfer belt 8 with respect to the direction of travel. A belt cleaning unit 37 for removing toner remaining on the surface of the intermediate transfer belt 8 is positioned opposite the tension roller 11. The secondary transfer roller 9 is mounted and pressed against the drive roller 10 via the intermediate transfer belt 8, forming a secondary transfer nip section N.

[0023] The intermediate transfer unit 30 includes a roller contact / separation mechanism 35 which has a pair of support members (not shown) that rotatably support both ends of the rotation axes of the primary transfer rollers 6a to 6d and the pressure switching roller 34 and move perpendicular to the direction of travel of the intermediate transfer belt 8 (up and down direction in Figure 3), and a driving means (not shown) that reciprocates the primary transfer rollers 6a to 6d and the pressure switching roller 34 in the up and down direction. The roller contact / separation mechanism 35 can be switched between a color mode in which the four primary transfer rollers 6a to 6d are pressed against the photoreceptor drums 1a to 1d (see Figure 1) via the intermediate transfer belt 8, a monochrome mode in which only the primary transfer roller 6d is pressed against the photoreceptor drum 1d via the intermediate transfer belt 8, and a retraction mode in which all four primary transfer rollers 6a to 6d are separated from the photoreceptor drums 1a to 1d.

[0024] Next, the control path of the image forming apparatus 100 of the present invention will be described. Figure 4 is a block diagram showing an example of a control path used in the image forming apparatus 100 of the present invention. Since various controls are performed on each part of the image forming apparatus 100 when it is in use, the overall control path of the image forming apparatus 100 is complex. Therefore, here we will focus on explaining the parts of the control path that are necessary for implementing the present invention.

[0025] The control unit 90 includes at least a CPU (Central Processing Unit) 91 as a central processing unit, a ROM (Read Only Memory) 92 as a read-only memory, a RAM (Random Access Memory) 93 as a read-write memory, a temporary memory 94 for temporarily storing image data, etc., a counter 95 for accumulating and counting the number of printed pages, and multiple (in this case, two) I / F (interfaces) 96 for transmitting control signals to each device within the image forming apparatus 100 and receiving input signals from the operation unit 60. Furthermore, the control unit 90 can be placed anywhere inside the main body of the image forming apparatus 100.

[0026] ROM92 stores control programs for the image forming apparatus 100, necessary control values, and other data that should not be changed during use of the image forming apparatus 100. RAM93 stores necessary data generated during the control of the image forming apparatus 100, as well as data temporarily required for the control of the image forming apparatus 100.

[0027] Furthermore, the control unit 90 transmits control signals from the CPU 91 to each part and device of the image forming apparatus 100 via the I / F 96. In addition, signals indicating their status and input signals are transmitted from each part and device to the CPU 91 via the I / F 96. Examples of parts and devices controlled by the control unit 90 include the image forming units Pa to Pd, the exposure apparatus 4, the primary transfer rollers 6a to 6d, the secondary transfer roller 9, the main motor 40, the belt drive motor 41, the image input unit 50, the voltage control circuit 51, and the operation unit 60.

[0028] The image input unit 50 is a receiving unit that receives image data transmitted from a personal computer or the like to the image forming apparatus 100. The image signal input from the image input unit 50 is converted into a digital signal and then sent to the temporary storage unit 94 via the I / F 96.

[0029] The voltage control circuit 51 is connected to the charging voltage power supply 52, the developing voltage power supply 53, and the transfer voltage power supply 54, and operates each of these power supplies by output signals from the control unit 90. Each of these power supplies operates according to the control signals from the voltage control circuit 51. The charging voltage power supply 52 applies a charging voltage to the charging rollers 21 in the charging devices 2a to 2d. The developing voltage power supply 53 applies a developing voltage to the developing rollers 29 in the developing devices 3a to 3d, which is a development voltage obtained by superimposing a development AC voltage on a development DC voltage. The transfer voltage power supply 54 applies predetermined primary transfer voltages and secondary transfer voltages to the primary transfer rollers 6a to 6d and the secondary transfer roller 9, respectively.

[0030] The charging voltage applied to the charging roller 21 from the charging voltage power supply 52 is preferably a DC voltage. When the charging voltage is a DC voltage, the amount of discharge from the charging roller 21 to the photoreceptor drums 1a to 1d is less compared to when it is a superimposed voltage of a DC voltage and an AC voltage, and the amount of wear on the photoreceptor layer 19b of the photoreceptor drums 1a to 1d can be reduced.

[0031] The control unit 60 is equipped with a liquid crystal display 61 and LEDs 62 that indicate various statuses. The user can stop image formation by operating the stop / clear button on the control unit 60, and reset the various settings of the image forming apparatus 100 to their default state by operating the reset button. The liquid crystal display 61 is designed to show the status of the image forming apparatus 100, as well as the image formation status and the number of copies to be printed. Various settings of the image forming apparatus 100 are made from the printer driver on a personal computer.

[0032] Next, the primary transfer rollers 6a to 6d and the intermediate transfer belt 8 provided in the intermediate transfer unit 30 will be described. As mentioned above, ghosts and spotted images are likely to occur due to the resistance of the primary transfer rollers 6a to 6b or the intermediate transfer belt 8. Therefore, in this embodiment, the range of resistance values ​​of the primary transfer rollers 6a to 6d, the volume resistivity and surface resistivity of the intermediate transfer belt 8 are defined, and the transfer voltage power supply 54 that applies the transfer voltage to the primary transfer rollers 6a to 6d is controlled by constant current, thereby suppressing defects in the transferred image during primary transfer.

[0033] The stability of the transferred image during primary transfer (primary transfer performance) depends on the primary transfer current flowing from the primary transfer rollers 6a to 6d through the intermediate transfer belt 8 to the photoreceptor drums 1a to 1d. Therefore, maintaining a constant primary transfer current is important to improve primary transfer performance. By using constant current control for the transfer voltage power supply 54, as in this embodiment, it becomes easier to maintain a constant primary transfer current compared to constant voltage control. Consequently, a better primary transfer image can be obtained. Furthermore, since there is no need to switch between constant current control and constant voltage control, the control path of the transfer voltage power supply 54 is also simplified.

[0034] Figures 5 to 7 are graphs showing the relationship between the surface resistivity of the intermediate transfer belt 8 and the primary transfer current in a normal temperature and humidity environment (RR environment, 25°C, 50%RH), a low temperature and low humidity environment (LL environment, 10°C, 10%RH), and a high temperature and high humidity environment (HH environment, 32.5°C, 80%RH), respectively. In Figures 5 to 7, L1, L2, and L3 indicate boundaries where ghosting, spotting, and transferability exceed acceptable limits, respectively. Specifically, in the region above boundary line L1 (hatched area), ghosting exceeds the acceptable limit. Similarly, in the region above boundary line L2 (dotted area), spotting exceeds the acceptable limit. In the region below boundary line L3 (vertical hatched area), transferability exceeds the acceptable limit.

[0035] The area enclosed by boundary lines L1 to L3 (the white area in Figures 5 to 7) represents the OW (operation window, designable range) of the surface resistivity of the intermediate transfer belt 8 in each environment. As shown in Figures 5 to 7, the OW of the intermediate transfer belt 8 differs slightly in each environment, but as shown in the area R1 enclosed by the dashed line in Figures 5 to 7, the surface resistivity of the intermediate transfer belt 8 is set to 10 9.5 ~10 10.5 By setting the value to [Ω / □] and controlling the constant current so that the primary transfer current is 9-11 [μA] in an RR environment, 8-10 [μA] in an LL environment, and 11-13 [μA] in an HH environment, the value can be kept within the OW range in all environments.

[0036] Furthermore, in Figures 5 to 7, the volume resistivity of the intermediate transfer belt 8 is set to 10. 10 The volume resistivity of the intermediate transfer belt 8 is set to be less than [Ωcm]. 10 When the value exceeds [Ωcm], ghosting and spotting in the image will exceed the acceptable range.

[0037] Figure 8 is a graph showing the relationship between the resistance values ​​of primary transfer rollers 6a-6d and the primary transfer current in a low-temperature, low-humidity environment (LL environment, 10°C, 10%RH). In Figure 8, L4 indicates the boundary line where the mass productivity of primary transfer rollers 6a-6d exceeds the acceptable range. Specifically, in the region to the left of boundary line L4 (horizontal hatching region), the mass productivity exceeds the acceptable range. Boundaries L1-L3 are the same as in Figures 5-7.

[0038] As shown in the dashed area R2 in Figure 8, the resistance values ​​of the primary transfer rollers 6a to 6d are set to 10 6.3 ~10 7.3 By setting the resistance to [Ω] and controlling the constant current so that the primary transfer current is 9~11[μA], it can be kept within the OW. Note that although the OW of primary transfer rollers 6a~6d in the LL environment has been described here, the OW is narrowest in the LL environment, so the resistance value of primary transfer rollers 6a~6d should be set to 10 6.3 ~10 7.3 By setting it to [Ω], it can be kept within the OW (Overhead View) in both RR (Relative Load) and HH (High Heat) environments.

[0039] The primary transfer rollers 6a to 6d are elastic rollers in which an elastic layer with carbon added as a conductive material is laminated on the outer surface of the core metal (shaft). As the material of the elastic layer, an ion-conductive rubber such as ECO (epichlorohydrin rubber) is used. Considering the transfer properties, the Asker C hardness of the elastic layer is preferably 37 to 47°.

[0040] Furthermore, simply specifying the resistance values ​​of the primary transfer rollers 6a to 6d is insufficient, as interference between the image forming sections Pa to Pd occurs when the surface resistivity of the intermediate transfer belt 8 is low, causing the primary transfer current to flow into adjacent primary transfer rollers 6a to 6d via the intermediate transfer belt 8. Also, simply specifying the surface resistivity of the intermediate transfer belt 8 is insufficient, as ghosting becomes more pronounced when the resistance values ​​of the primary transfer rollers 6a to 6d are low. Therefore, it is necessary to specify the resistance values ​​of the primary transfer rollers 6a to 6d, as well as the volume resistivity and surface resistivity of the intermediate transfer belt 8.

[0041] Next, other primary transfer conditions in this embodiment will be described. The primary transfer conditions in the RR environment, LL environment, and HH environment are shown in Tables 1 to 3.

[0042] [Table 1]

[0043] [Table 2]

[0044] [Table 3]

[0045] The offset amounts [mm] in Tables 1 to 3 represent the amount of displacement of the primary transfer rollers 6a to 6d downstream in the belt movement direction relative to the photoreceptor drums 1a to 1d. As shown in Tables 1 to 3, in all RR, LL, and HH environments, a speckled image is likely to occur when the offset amount is 4.745 [mm] or more. Also, ghosting occurs when the offset amount is 3.225 [mm] or less. Therefore, in this embodiment, the offset amount is set to 4 ± 0.725 [mm].

[0046] As shown in Table 1, in an RR environment, a toner charge of 35 [μC / g] or higher is a condition that makes spotted images and ghosting more likely to occur. Therefore, in an RR environment, the toner charge is set to 25-35 [μC / g]. Similarly, in an LL environment, a toner charge of 40 [μC / g] or higher is a condition that makes spotted images and ghosting more likely to occur, and in an HH environment, a toner charge of 30 [μC / g] or higher is a condition that makes spotted images and ghosting more likely to occur. Therefore, in an LL environment, the toner charge is set to 30-40 [μC / g], and in an HH environment, the toner charge is set to 20-30 [μC / g].

[0047] As shown in Table 1, in an RR environment, when the surface potential of the photoreceptor drums 1a to 1d falls below 350[V], spotted images and ghosting are likely to occur. Therefore, in an RR environment, the surface potential is set to 350 to 450[V]. Similarly, in an LL environment, when the surface potential falls below 400[V], and in an HH environment, when the surface potential falls below 300[V], spotted images and ghosting are likely to occur. Therefore, in an LL environment, the surface potential is set to 400 to 500[V], and in an HH environment, the surface potential is set to 300 to 400[V]. In addition, the charging capacity (degree of increase in surface potential with respect to incoming current) of the photoreceptor drums 1a to 1d is preferably 8 to 12[V / μA].

[0048] The primary transfer pressure load [N / cm] in Tables 1 to 3 indicates the pressure load of the primary transfer rollers 6a to 6d on the photoreceptor drums 1a to 1d. If the primary transfer pressure load is less than 0.11 [N / cm], gaps will occur in the primary transfer image. On the other hand, if the pressure load exceeds 0.13 [N / cm], transfer unevenness is likely to occur. Therefore, in this embodiment, the primary transfer pressure load is set to 0.11 to 0.13 [N / cm].

[0049] Based on the above, the offset amount of the primary transfer rollers 6a to 6d relative to the photoreceptor drums 1a to 1d is set to 4 [mm], the contact load of the primary transfer rollers 6a to 6d relative to the photoreceptor drums 1a to 1d is set to 0.11 to 0.13 [N / cm], the charging capacity of the photoreceptor drums 1a to 1d is set to 8 to 12 [V / μA], the surface potential is set to 300 to 500 [V], and a two-component developing system 3a to 3d using a two-component developer containing toner and carrier is used, with the toner charge amount set to 20 to 40 [μC / g]. This makes it possible to suppress the occurrence of gaps in the image during primary transfer while ensuring the transferability of the toner and effectively suppressing the occurrence of image defects such as ghosts and spotted images.

[0050] Furthermore, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. For example, the present invention is not limited to the tandem-type color printer shown in Figure 1, but can be applied to various image forming devices that use an intermediate transfer unit to transfer a toner image formed on a photoreceptor drum onto an intermediate transfer belt, such as color copiers and color multifunction printers. [Industrial applicability]

[0051] The present invention can be used in an intermediate transfer unit that transfers a toner image formed on an image carrier such as a photoreceptor drum onto an intermediate transfer belt. By using the present invention, it is possible to provide an intermediate transfer unit that can effectively resolve defects in the transferred image in the primary transfer section with a simple configuration, and an image forming apparatus equipped therewith. [Explanation of symbols]

[0052] Pa~Pd Image Forming Unit 1a~1d Photoreceptor drum (image carrier) 2a~2d Charging device 3a~3d developing device 5. Exposure apparatus 6a~6d Primary transfer roller (primary transfer member) 8. Intermediate transfer belt 9. Secondary transfer roller (secondary transfer member) 10 Drive rollers 11 Tension Roller 19a Conductive substrate 19b Photosensitive layer 30 Intermediate Transfer Unit 100 Image forming apparatus

Claims

1. An image carrier having a photosensitive layer formed on its surface, A charging device for charging the surface of the image carrier, An exposure apparatus that exposes the surface of the image carrier, which has been charged by the charging device, to form an electrostatic latent image on the surface of the image carrier, A developing apparatus having a developer carrier that carries a developer containing toner, and developing the electrostatic latent image formed on the surface of the image carrier into a toner image, An endless intermediate transfer belt on which toner images formed on the image carrier are sequentially layered, A drive roller is positioned in contact with the inner circumferential surface of the intermediate transfer belt and rotates the intermediate transfer belt, A tension roller that rotates in conjunction with the intermediate transfer belt and applies a predetermined tension to the intermediate transfer belt, A primary transfer member is pressed against the image carrier via the intermediate transfer belt, A transfer voltage power supply that applies a primary transfer voltage with the opposite polarity to the toner image to the primary transfer member, An intermediate transfer unit comprising, which first transfers the toner image developed by the developing device onto the intermediate transfer belt, A secondary transfer member that transfers the toner image, which has been primary transferred onto the intermediate transfer belt, onto a recording medium, Equipped with, The surface resistivity of the intermediate transfer belt is 10 9.5 ~10 10.5 [Ω / □], volume resistivity is 10 10 [Ω・cm] or less, the resistance value of the primary transfer member is 10 6.3 ~10 7.3 [Ω], and the transfer voltage power supply is constant current controlled, The primary transfer member is an elastic roller in which an elastic layer containing carbon as a conductive material is laminated on the outer surface of a core metal. The primary transfer member has an Asker C hardness of 37 to 47 [°] in the elastic layer. The image forming apparatus is characterized in that the primary transfer member has a pressure load of 0.11 to 0.13 [N / cm] on the image carrier and an offset amount of 4 ± 0.725 [mm] on the image carrier.

2. The image forming apparatus according to Claim 1, characterized in that the image carrier has a photosensitive layer with a charging capacity of 8 to 12 [V / μA], and the surface potential of the image carrier charged by the charging device is 300 to 500 [V].

3. The developing apparatus is a two-component developing method using a two-component developer containing the toner and a carrier, and the charge amount of the toner is 20 to 40 [μC / g], characterized in that the image forming apparatus is as described in Claim 1 or Claim 2.

Images