Image forming apparatus

Abstract

To provide an image forming apparatus that can ensure a sufficient image quality level even if the image forming apparatus employs a two-component developing system using an amorphous silicon photoreceptor in which carrier development easily occurs.SOLUTION: An image forming apparatus comprises an image carrier, a charging device, an exposure device, a developing device, and a developing voltage power supply. The image carrier has an amorphous silicon photoreceptor layer formed on its surface. The developing device has a developer carrier carrying a two-component developer including toner and a carrier, and supplies the toner in the developer carried on the developer carrier to the image carrier to develop an electrostatic latent image into a toner image. The developing voltage power supply applies, to the developer carrier, a developing voltage in which AC voltage is superimposed on DC voltage. When a white ground part potential of the image carrier is defined as V0 [V], the DC voltage as Vdc [V], a peak-to-peak value of the AC voltage Vac as Vpp [kV], and the gap between the image carrier and the developer carrier as Ds [mm], 10≤V0-Vdc≤90 and 1.2≤Vpp / Ds≤3.5 are satisfied.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine including an image carrier, and more particularly to an image forming apparatus using a two-component development system with an amorphous silicon photoreceptor as the image carrier.

Background Art

[0002] In an image forming apparatus, an electrostatic latent image formed on an image carrier made of a photoreceptor or the like is developed by a developing device and visualized as a toner image. As one of such developing devices, a two-component development system using a two-component developer is adopted.

[0003] When adopting the two-component development system in an image forming apparatus with a high process line speed, there is a problem that carrier transfer (carrier development) from the developing device to the photoreceptor drum easily occurs. Carrier development is particularly likely to occur when using an amorphous silicon (a-Si) photoreceptor having a high dielectric constant and a large carrier adhesion force.

[0004] In order to solve the above problems, for example, Patent Document 1 discloses an image forming apparatus that suppresses carrier development by reducing the adhesion force between the carrier and the photoreceptor by defining the surface roughness of the photoreceptor surface or the carrier surface.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the method of Patent Document 1, in the case of an image forming apparatus using a resin intermediate transfer belt that has a great influence on the image quality of carrier development, there has been a problem that carrier development cannot be suppressed to a sufficient image quality level.

[0007] In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of obtaining a sufficient image quality level even in a configuration where carrier development easily affects the image quality, in a two-component development type image forming apparatus using an amorphous silicon photoreceptor.

Means for Solving the Problems

[0008] A first configuration of the present invention for achieving the above object is an image forming apparatus including an image carrier, a charging device, an exposure device, a developing device, and a developing voltage power source. An amorphous silicon photosensitive layer is formed on the surface of the image carrier. The charging device charges the surface of the image carrier. The exposure device exposes the surface of the image carrier charged by the charging device to form an electrostatic latent image in which the charge is attenuated. The developing device has a developer carrier that carries a two-component developer including toner and a carrier, and supplies the toner in the developer carried on the developer carrier to the image carrier to develop the electrostatic latent image into a toner image. The developing voltage power source applies a developing voltage obtained by superimposing an AC voltage on a DC voltage to the developer carrier. When the potential of the non-image area of the image carrier is V0 [V], the DC voltage is Vdc [V], the peak-to-peak value of the AC voltage Vac is Vpp [kV], and the gap between the image carrier and the developer carrier is Ds [mm], the following formulas (1) and (2) are satisfied. 10 ≦ V0 - Vdc ≦ 90 ···(1) 1.2 ≦ Vpp / Ds ≦ 3.5 ···(2)

Effects of the Invention

[0009] According to the first configuration of the present invention, it is possible to suppress carrier development that easily occurs when using an image carrier having an amorphous silicon photosensitive layer and the occurrence of leak color dots to a level that does not affect the image quality, and also to suppress the occurrence of image fog and image density unevenness.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a color printer 100 according to an embodiment of the present invention. FIG. 2 is an enlarged view of the vicinity of the image forming unit Pa in FIG. 1. Note that the image forming units Pb to Pd have basically the same configuration, so the description thereof will be omitted.

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

[0013] In these image forming units Pa to Pd, photosensitive drums 1a, 1b, 1c, and 1d for carrying visible images (toner images) of respective colors are disposed. Further, an intermediate transfer belt 8 that rotates in the counterclockwise direction in FIG. 1 is provided adjacent to each of the image forming units Pa to Pd. The intermediate transfer belt 8 is wound around a downstream driving roller 10 and an upstream tension roller 11. A belt cleaning device 30 that faces the tension roller 11 with the intermediate transfer belt 8 interposed therebetween is disposed upstream of the image forming unit Pa with respect to the rotation direction of the intermediate transfer belt 8.

[0014] As shown in FIG. 2, around the photosensitive drum 1a, a charging device 2a, a developing device 3a, a cleaning device 7a, and a discharging device 20 are disposed along the drum rotation direction (clockwise direction in FIG. 2), and a primary transfer roller 6a is disposed with the intermediate transfer belt 8 interposed therebetween.

[0015] The photosensitive drums 1a to 1d are each 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 amorphous silicon photosensitive drum in which an amorphous silicon (a-Si) photosensitive layer is laminated as the photosensitive layer 19b on the surface of a cylindrical conductive substrate 19a made of aluminum is used.

[0016] The charging devices 2a to 2d each include a charging roller 21 that contacts the photosensitive drums 1a to 1d and applies a charging voltage (DC voltage + AC voltage) to the drum surface, and a charging cleaning roller 22 for cleaning the charging roller 21.

[0017] The developing devices 3a to 3d are of a two-component development type having a developing roller 23, a stirring and conveying screw 43, and a supply and conveying screw 44, and are filled with a predetermined amount of a two-component developer containing toner of each color of yellow, magenta, cyan, and black and a magnetic carrier. A magnetic brush is formed on the surface of the developing roller 23 using the two-component developer, and the magnetic brush is brought into contact with the surface of the photosensitive drum 1a while applying a developing voltage having the same polarity (here, positive polarity) as the toner to the developing roller 23 to attach the toner and form a toner image. When the ratio of the toner in the two-component developer filled in each of the developing devices 3a to 3d falls below a specified value due to the formation of the toner image, toner is replenished from the toner containers 4a to 4d to each of the developing devices 3a to 3d.

[0018] The cleaning devices 7a to 7d have a cleaning blade 31 and a recovery screw 33. The cleaning blade 31 removes toner and the like remaining on the surfaces of the photosensitive drums 1a to 1d. The recovery screw 33 discharges the toner and the like removed by the cleaning blade 31 to the outside of the cleaning devices 7a to 7d and recovers them in a waste toner recovery container (not shown). The charge removing device 20 irradiates the surfaces of the photosensitive drums 1a to 1d with charge removing light to remove residual charges.

[0019] When image data is input from a host device such as a personal computer, first, the rotation of the photosensitive drums 1a to 1d is started by a main motor 40 (see FIG. 3). Also, the rotation drive of the intermediate transfer belt 8 is started by a belt drive motor 41 (see FIG. 3). Next, the surfaces of the photosensitive drums 1a to 1d are uniformly charged to the same polarity (here, positive polarity) as the toner by the charging devices 2a to 2d. Then, light irradiation is performed according to the image data by the exposure device 5 to form an electrostatic latent image in which the charge is attenuated according to the image data on each of the photosensitive drums 1a to 1d.

[0020] The developing devices 3a to 3d are filled with a two-component developer (hereinafter also simply referred to as a developer) containing toners of yellow, magenta, cyan, and black colors by toner containers 4a to 4d in a predetermined amount. The toners in the developer are supplied onto the photoreceptor drums 1a to 1d by the developing devices 3a to 3d and electrostatically adhere thereto. Thereby, a toner image corresponding to the electrostatic latent image formed by the exposure from the exposure device 5 is formed.

[0021] Then, an electric field is applied at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photoreceptor drums 1a to 1d by the primary transfer rollers 6a to 6d, and the yellow, magenta, cyan, and black toner images on the photoreceptor drums 1a to 1d are primarily transferred onto the intermediate transfer belt 8. Toner and the like remaining on the surfaces of the photoreceptor drums 1a to 1d after the primary transfer are removed by the cleaning devices 7a to 7d. Residual charges remaining on the surfaces of the photoreceptor drums 1a to 1d after the primary transfer are removed by the charge removing device 20.

[0022] The transfer paper P onto which the toner image is to be transferred is housed in a paper cassette 16 disposed at the lower part inside the color printer 100, and the transfer paper P is conveyed to the nip portion (secondary transfer nip portion) between the secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8 and the intermediate transfer belt 8 at a predetermined timing via the paper feed roller 12a and the registration roller pair 12b. The transfer paper P onto which the toner image has been secondarily transferred is conveyed to the fixing unit 13.

[0023] The transfer paper P conveyed to the fixing unit 13 is heated and pressurized by the fixing roller pair 13a so that the toner image is fixed on the surface of the transfer paper P, and a predetermined full-color image is formed. The transfer paper P on which the full-color image has been formed is discharged to the discharge tray 17 by the discharge roller pair 15 (either as it is or after being branched to the reverse conveyance path 18 by the branching unit 14 and images are formed on both sides).

[0024] FIG. 3 is a side cross-sectional view showing the configuration of the developing device 3a mounted on the color printer 100. In FIG. 3, the configuration and operation of the developing device 3a corresponding to the photosensitive drum 1a shown in FIG. 1 will be described. However, since the configurations and operations of the developing devices 3b to 3d are the same as those of the developing device 3a, the description thereof will be omitted.

[0025] As shown in FIG. 3, the developing device 3a includes a developing container 24 in which a two-component developer (hereinafter also simply referred to as a developer) containing a magnetic carrier and toner is stored. The developing container 24 is partitioned into a stirring and conveying chamber 24b and a supply and conveying chamber 24c by a partition wall 24a. In the stirring and conveying chamber 24b and the supply and conveying chamber 24c, a stirring and conveying screw 43 and a supply and conveying screw 44 for mixing, stirring, and charging the toner supplied from the toner container 4a (see FIG. 1) with the magnetic carrier are rotatably disposed, respectively.

[0026] Then, the developer is stirred by the stirring and conveying screw 43 and the supply and conveying screw 44 and conveyed in the axial direction (the direction perpendicular to the plane of FIG. 3), and circulates between the stirring and conveying chamber 24b and the supply and conveying chamber 24c through a communication portion (not shown) formed at both ends of the partition wall 24a. That is, a circulation path of the developer is formed in the developing container 24 by the stirring and conveying chamber 24b, the supply and conveying chamber 24c, and the communication portion.

[0027] The developing container 24 extends obliquely upward to the right in FIG. 3, and a developing roller 23 is disposed obliquely upward to the right of the supply and conveying screw 44 in the developing container 24. A part of the outer peripheral surface of the developing roller 23 is exposed from the opening of the developing container 24 and faces the photosensitive drum 1a with a predetermined interval (developing gap Ds) therebetween, forming a developing region. The developing roller 23 rotates in the counterclockwise direction in FIG. 3 (trailing rotation at the position facing the photosensitive drum 1a).

[0028] The developing roller 23 is composed of a developing sleeve 23a and a magnet 23b. The developing sleeve 23a is cylindrical and rotates counterclockwise in FIG. 3. As the developing sleeve 23a, those with a knurled surface, those with a large number of concave shapes (dimples) formed on the surface, those with a blasted surface, and further, those with a blasted surface in addition to knurling or forming a concave shape, or those with a plating treatment can be used.

[0029] The magnet 23b is non-rotatably fixed inside the developing sleeve 23a. The magnet 23b has a five-pole configuration including a main pole S1 arranged in the facing area (developing area) with the photoreceptor drum 1a, and a regulating pole (pick-up pole) N1, conveying poles S2, N2, and peeling pole N3 arranged in the facing area (regulating portion) with the regulating blade 27. When a driving force is input to the developing device 3a, the developing sleeve 23a rotates, but the magnet 23b does not rotate. A developing voltage composed of a DC voltage Vdc and an AC voltage Vac is applied to the developing roller 23 by a developing voltage power supply 53 (see FIG. 4).

[0030] Also, a regulating blade 27 is attached to the developing container 24. More specifically, the regulating blade 27 is attached along the longitudinal direction of the developing roller 23 (the direction perpendicular to the paper surface of FIG. 3) via a blade support plate 28. A slight gap (regulating gap) is provided between the tip of the regulating blade 27 and the outer peripheral surface of the developing roller 23, forming a regulating portion. In this embodiment, a magnetic blade made of stainless steel (SUS430) is used as the regulating blade 27.

[0031] A magnetic field in the attracting direction is generated between the regulating pole N1 of the magnet 23b and the regulating blade 27, thereby forming a magnetic brush in which the developer is continuous between the regulating blade 27 and the developing roller 23. When the magnetic brush passes through the regulating blade 27 (regulating portion), the layer thickness is regulated to a desired height. Then, when the developing sleeve 23a rotates in the counterclockwise direction, the magnetic brush moves to the developing region. And a magnetic field in the attracting direction is applied between the photosensitive drum 1a by the main pole S1, and the magnetic brush contacts the surface of the photosensitive drum 1a to develop the electrostatic latent image.

[0032] Furthermore, when the developing sleeve 23a rotates in the counterclockwise direction, a magnetic field in the direction along the outer peripheral surface of the developing sleeve 23a is applied by the conveying poles N2 and S2 this time, and the developer not used for forming the toner image is recovered onto the developing sleeve 23a together with the magnetic brush. Further, the magnetic brush detaches from the developing roller 23 at the peeling pole N3 having a different polarity from the conveying pole S2 and falls into the supply and conveyance chamber 24c. Then, after being agitated and conveyed by the supply and conveyance screw 44, a magnetic brush is formed again on the developing sleeve 23a by the magnetic field of the regulating pole N1.

[0033] FIG. 4 is a block diagram showing an example of a control path used in the color printer 100. In using the color printer 100, various controls of each part of the color printer 100 are performed, so the control path of the entire color printer 100 becomes complicated. Therefore, here, the parts necessary for the implementation of the present invention in the control path will be mainly described.

[0034] The charging voltage power supply 52 applies a charging voltage to the charging roller 21 in the charging devices 2a to 2d. The developing voltage power supply 53 applies a developing voltage obtained by superimposing an AC voltage Vac on a DC voltage Vdc to the developing roller 23 in the developing devices 3a to 3d. The transfer voltage power supply 54 applies a predetermined primary transfer voltage and a secondary transfer voltage to the primary transfer rollers 6a to 6d and the secondary transfer roller 9, respectively. The voltage control circuit 55 is connected to the charging voltage power supply 52, the developing voltage power supply 53, and the transfer voltage power supply 54, and operates these power supplies according to the output signal from the control unit 90.

[0035] The image input unit 60 is a receiving unit that receives image data transmitted from a personal computer or the like to the color printer 100. The image signal input from the image input unit 60 is converted into a digital signal and then sent to the temporary storage unit 94.

[0036] The operation unit 70 is provided with a liquid crystal display unit 71 and an LED 72. The liquid crystal display unit 71 displays the operating state of the color printer 100, the image formation status, the number of printed copies, etc. The LED 72 displays various states and errors of the color printer 100. Various settings of the color printer 100 are made from the printer driver of the personal computer.

[0037] In addition, the operation unit 70 is provided with a start button for the user to instruct to start image formation, a stop / clear button used when aborting image formation, a reset button used when setting various settings of the color printer 100 to the default state, and the like.

[0038] The in-machine temperature and humidity sensor 80 detects the temperature and humidity inside the color printer 100, particularly the temperature and humidity around the image forming units Pa to Pd, and is arranged near the image forming units Pa to Pd.

[0039] The control unit 90 includes at least a CPU (Central Processing Unit) 91 as a central processing unit, a ROM (Read Only Memory) 92 which is a read-only storage unit, a RAM (Random Access Memory) 93 which is a read-write storage unit, a temporary storage unit 94 that temporarily stores image data and the like, a counter 95, and a plurality (here two) of I / F (interfaces) 96 that transmit control signals to each device in the color printer 100 and receive input signals from the operation unit 50. The control unit 90 can be arranged at any location inside the color printer 100 main body.

[0040] The ROM 92 stores data such as the control program for the color printer 100 and numerical values necessary for control, which will not be changed during the use of the color printer 100. The RAM 93 stores necessary data generated during the control of the color printer 100 and data temporarily required for the control of the color printer 100. The temporary storage unit 94 temporarily stores the image signal input from the image input unit 60 and converted into a digital signal. The counter 95 accumulatively counts the number of printed sheets.

[0041] Also, the control unit 90 transmits a control signal to each part and device in the color printer 100 from the CPU 91 through the I / F 96. Also, a signal indicating its state and an input signal are transmitted from each part and device to the CPU 91 through the I / F 96. Examples of the parts and devices controlled by the control unit 90 include, for example, the image forming units Pa to Pd, the exposure device 5, the intermediate transfer belt 8, the secondary transfer roller 9, the fixing unit 13, the voltage control circuit 55, the image input unit 60, the operation unit 70, the in-machine temperature and humidity sensor 80, and the like.

[0042] In the color printer 100 of the two-component development system of the present embodiment, when an amorphous silicon photoreceptor drum is used as the photoreceptor drums 1a to 1d, image defects are suppressed by appropriately setting the development conditions. Hereinafter, the setting of the potential V0 of the blank part (background part) of the photoreceptor drums 1a to 1d, the development voltage (DC voltage Vdc, AC voltage Vac), and the gap (development gap) Ds between the photoreceptor drums 1a to 1d and the development roller 23 will be described in detail.

[0043] In the present embodiment, the potential difference (development potential difference) V0 - Vdc [V] between the potential V0 [V] of the blank part and the DC voltage Vdc [V] of the development voltage is set to satisfy the following formula (1). 10 ≦ V0 - Vdc ≦ 90 ···(1)

[0044] In addition, the peak-to-peak value Vpp [kV] of the alternating current voltage Vac of the developing voltage and the developing gap Ds [mm] are set so as to satisfy the following formula (2). The conditions of formulas (1) and (2) are set in a considerably lower region compared to the developing conditions of the normal two-component developing method. 1.2 ≦ Vpp / Ds ≦ 3.5 ···(2)

[0045] FIG. 5 is a diagram showing the occurrence status of image defects when V0 - Vdc and Vpp / Ds are changed. As shown in FIG. 5, in the region where V0 - Vdc is less than 10 [V] (the left hatched region in FIG. 5), since V0 - Vdc is too small, image fogging occurs. On the other hand, in the region where V0 - Vdc exceeds 90 [V] (the right hatched region in FIG. 5), since V0 - Vdc is too large, carrier development at a visually confirmable level occurs.

[0046] Also, in the region where Vpp / Ds is less than 1.2 (the lower dotted hatched region in FIG. 5), image density unevenness occurs. On the other hand, in the region where Vpp / Ds exceeds 3.5 (the upper dotted hatched region in FIG. 5), color spots due to leakage between the photoreceptor drums 1a to 1d and the developing roller 23 occur.

[0047] From the above, by setting the developing conditions (the white area in FIG. 5) such that V0 - Vdc and Vpp / Ds satisfy formulas (1) and (2), it is possible to suppress carrier development and the occurrence of leakage color spots, which are likely to occur when using an amorphous silicon photoreceptor, to a level that does not affect the image quality. Furthermore, it is possible to suppress the occurrence of image fogging and image density unevenness as well.

[0048] Note that in the region where V0 - Vdc is 60 to 90 [V] (the broken line region in FIG. 5), carrier development is measured but not visually confirmed, and it is at a level that causes no practical problems. Therefore, by setting the developing potential difference V0 - Vdc [V] so as to satisfy the following formula (3), it is possible to obtain higher image quality. 10 ≦ V0 - Vdc ≦ 60 ···(3)

[0049] Next, the setting of the frequency f of the alternating voltage Vac of the developing voltage will be described. Table 1 shows the relationship between the frequency f, image fogging, and image density unevenness. In Table 1, when there is no image fogging and no image density unevenness, it is marked as ○; when they occur but are not visible to the naked eye and there are no practical problems, it is marked as △; when image fogging and image density unevenness are significantly occurring and pose practical problems, it is marked as ×.

[0050]

Table 1

[0051] As shown in Table 1, when the frequency f is less than 10 [kHz], image fogging occurred. On the other hand, when the frequency f exceeds 15 [kHz], image density unevenness occurred. Therefore, the frequency f [kHz] is set to satisfy the following formula (4). Thereby, while suppressing the level of image fogging that is likely to occur when V0 - Vdc and Vpp / Ds are set to satisfy formulas (1) and (2), the occurrence of image density unevenness can be suppressed. 10 ≦ f ≦ 15 ···(4)

[0052] Note that in the range where the frequency f is from 10 to 12 [kHz], image fogging occurs but is not confirmed visually and is at a level with no practical problems. Therefore, by setting the frequency f [kHz] to satisfy the following formula (5), it becomes possible to obtain higher image quality. 12 ≦ f ≦ 15 ···(5)

[0053] Also, by setting the white background potential V0 [V] of the photoreceptor drums 1a to 1d to satisfy the following formula (6), the variation in the surface potential of the photoreceptor drums 1a to 1d can be suppressed. As a result, it becomes possible to control V0 - Vdc within a narrow range that satisfies formulas (1) and (3). 100 ≦ V0 ≦ 250 ···(6)

[0054] Furthermore, in the present embodiment, the half-value width (the angle at which the magnetic force is 1 / 2 or more of the peak value) of the regulating pole N1 of the developing roller 23 is set to 50° or more, and the regulating blade 27 and the blade support plate 28 are made of a magnetic material, and the regulating blade 27 is attached with a step provided so as to protrude in a direction approaching the developing roller 23 more than the blade support plate 28.

[0055] FIG. 6 is a simulation diagram showing a state in which a magnetic brush is formed at the tip of the regulating blade 27. As shown in FIG. 6, by providing a step d between the tip of the regulating blade 27 and the tip of the blade support plate 28, a sufficient magnetic brush is formed between the developing roller 23 (developing sleeve 23a), the regulating blade 27, and the blade support plate 28. Therefore, it becomes possible to obtain a stable magnetic brush conveyance amount on the outer peripheral surface of the developing roller 23, and it becomes possible to stably ensure the image quality under the developing conditions as described above.

[0056] In addition, the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention. For example, in the above-described embodiment, the color printer 100 of the intermediate transfer type that primarily transfers the toner images formed on the photosensitive drums 1a to 1d to the intermediate transfer belt 8 and then secondarily transfers them to the transfer paper P has been described, but the present invention is not limited thereto, and the present invention is also applicable to a color printer of the direct transfer type that directly transfers the toner images formed on the photosensitive drums 1a to 1d to the transfer paper P.

[0057] However, in the intermediate transfer type, when carrier development occurs, a primary transfer failure occurs due to the interposition of the carrier between the photosensitive drums 1a to 1d and the intermediate transfer belt 8, and thus the carrier development easily affects the image quality. Therefore, the configuration of the present embodiment is effective in an image forming apparatus of the intermediate transfer type, and is particularly effective in a configuration using a resin belt in which a primary transfer failure due to carrier development easily occurs as the intermediate transfer belt 8.

[0058] In the above-described embodiment, a tandem-type color printer 100 has been described as an example of the image forming apparatus. However, the present invention can of course also be applied to other image forming apparatuses using a two-component development system, such as color copiers, color multifunction printers, monochrome printers, and monochrome multifunction printers.

Industrial Applicability

[0059] The present invention can be used in an image forming apparatus including a developing device using a two-component development system with an amorphous silicon photoreceptor as an image carrier. By using the present invention, it is possible to provide an image forming apparatus capable of obtaining a sufficient image quality level even in a configuration where carrier development is likely to affect the image quality.

Explanation of Signs

[0060] Pa~Pd Image forming unit 1a~1d Photoconductor drum (image carrier) 2a~2d Charging device 23 Developing roller (developer carrier) 23a Developing sleeve 23b Magnet 27 Regulation blade 28 Blade support plate 3a~3d Developing device 5 Exposure device 6a~6d Primary transfer roller 7a~7d Cleaning device 8 Intermediate transfer belt 9 Secondary transfer roller 19a Conductive substrate 19b Photosensitive layer 29 Developing roller (developer carrier) 52 Charging voltage power supply 53 Developing voltage power supply 54 Transfer voltage power supply 90 Control unit 100 Color printer (image forming apparatus)

Claims

1. An image carrier having an amorphous silicon photosensitive layer formed on its surface, a charging device for charging the surface of the image carrier, an exposure device for exposing the surface of the image carrier charged by the charging device to form an electrostatic latent image with attenuated charge, a developing device having a developer carrier for carrying a two-component developer containing toner and carrier, and supplying the toner in the developer carried on the developer carrier to the image carrier to develop the electrostatic latent image into a toner image, a developing voltage power source for applying a developing voltage obtained by superimposing an alternating voltage on a direct current voltage to the developer carrier, In an image forming apparatus provided with: When the potential of the non-image area of the image carrier is V0 [V], the direct current voltage is Vdc [V], the peak-to-peak value of the alternating voltage Vac is Vpp [kV], and the gap between the image carrier and the developer carrier is Ds [mm], the image forming apparatus is characterized by satisfying the following formulas (1) and (2). 10 ≦ V0 - Vdc ≦ 90... (1) 1.2 ≦ Vpp / Ds ≦ 3.5... (2)

2. The image forming apparatus according to claim 1, characterized by satisfying the following formula (3). 10 ≦ V0 - Vdc ≦ 60... (3)

3. The image forming apparatus according to claim 1, characterized in that the frequency f [kHz] of the alternating voltage Vac satisfies the following formula (4). 10 ≦ f ≦ 15... (4)

4. The image forming apparatus according to claim 3, characterized by satisfying the following formula (5). 12 ≦ f ≦ 15... (5)

5. The image forming apparatus according to claim 1, characterized in that the potential V0 [V] of the non-image area satisfies the following formula (6). 100 ≦ V0 ≦ 250... (6)

6. The developing device has a regulating blade that is disposed opposite to the outer peripheral surface of the developer carrier and regulates the layer thickness of the magnetic brush formed on the developer carrier by the two-component developer, and a blade support plate that is disposed on the upstream side of the regulating blade with respect to the rotation direction of the developer carrier and to which the regulating blade is fixed, and the developer carrier has a rotatable developing sleeve, and a magnet that is non-rotatably fixed inside the developing sleeve and has a plurality of magnetic poles including a main pole facing the image carrier and a regulating pole facing the regulating plate. and The image forming apparatus according to claim 1, wherein the half-value width of the regulating electrode is 50° or more, and the regulating blade is provided with a step in a direction approaching the developing sleeve and is attached to the blade support plate.

7. The image forming apparatus according to any one of claims 1 to 6, further comprising an intermediate transfer belt disposed opposite to the image carrier, on which the toner image formed on the image carrier is primarily transferred.

8. The image forming apparatus according to claim 7, wherein the intermediate transfer belt is a resin belt.

Images