Image forming apparatus

Abstract

An image forming apparatus includes an image carrier, a charging device, an exposure device, a developing device, a driving unit, a developing voltage power supply, and a control unit. The developing device includes a developer carrier that carries a two-component developer including a toner and a carrier, and develops an electrostatic latent image into a toner image by supplying the toner in the developer carried by the developer carrier to an image carrier. The drive unit drives the image carrier to rotate at a predetermined linear speed. The developing voltage power supply applies a developing voltage obtained by superimposing an alternating-current voltage on a direct-current voltage to the developer carrier. The image forming apparatus has a first printing mode in which an image carrier is driven by a drive unit to rotate at a linear speed of 250 [mm / sec] or more. The image carrier has a single organic photosensitive layer as a photosensitive layer, and the thickness of the photosensitive layer at the start of use is 40 [mu] m or more.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a copier, printer, facsimile machine, and a multifunction machine thereof having an image carrier, and in particular to an image forming apparatus having a developing device of a two-component developing method using a two-component developer. Background Art

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

[0003] When a two-component developing method is used in an image forming apparatus with a high processing line speed, in order to suppress the carrier from moving from the developing device to the photosensitive drum (carrier development), the electric field intensity of the photosensitive drum is preferably weak. Specifically, an organic photosensitive body (OPC) is more preferred than an amorphous silicon (a-Si) photosensitive body, and as a photosensitive layer of the organic photosensitive body, a single layer is more preferred than a laminated layer.

[0004] On the other hand, from the viewpoint of extending the life of the image forming apparatus, it is necessary to use a thicker photosensitive drum whose photosensitive layer has a thickness of a certain thickness or more at the beginning of use. However, when a thicker organic photosensitive body is used in an image forming apparatus of a two-component development method with a fast processing line speed, the setting margin (operation window) of the surface potential of the photosensitive body and the DC voltage of the development voltage is narrow, and image defects such as uneven discharge and drum ghosting are easily generated. Summary of the invention

[0005] An object of the present invention is to provide an image forming apparatus which can achieve a longer life and ensure a setting range of development conditions in an image forming apparatus of a two-component development method with a high processing line speed.

[0006] An image forming device of a first structure of the present invention comprises: an image carrier having a photosensitive layer formed on the 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 charge decay; a developing device having a developer carrier carrying a two-component developer including a colorant and a carrier, supplying the colorant in the developer carried by the developer carrier to the image carrier to develop the electrostatic latent image into a colorant image; a driving unit for driving the image carrier to rotate at a predetermined linear speed; a developing voltage power supply for applying a developing voltage obtained by superimposing an AC voltage on a DC voltage to the developer carrier; and a control unit for controlling the driving unit and the developing voltage power supply, wherein the image forming device has a first printing mode in which the image carrier is driven by the driving unit to rotate at a linear speed of 250 [mm / sec] or more, wherein the image carrier has a single-layer organic photosensitive layer as the photosensitive layer, and the thickness of the photosensitive layer at the beginning of use is 40 [μm] or more.

[0007] According to the first structure of the present invention, in an image forming device of a two-component development method having a first printing mode for driving an image carrier to rotate at a linear speed of more than 250 [mm / sec], by using an image carrier having a single-layer organic photosensitive layer with a layer thickness of 40 [μm] as a photosensitive layer, it is possible to achieve a high processing linear speed and a long life of the image carrier by optimizing the development conditions, and it is possible to fully ensure the settable area (operating window) of the development voltage and the surface potential of the image carrier. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a schematic diagram of the structure of a color printer 100 according to one embodiment of the present invention. Figure 2 yes Figure 1 An enlarged view of the vicinity of the image forming portion Pa in FIG. Figure 3 2 is a block diagram showing an example of a control path for the color printer 100 . Figure 4 This is a graph showing the relationship between the thickness of the photosensitive layer 19 b of the photosensitive drums 1 a to 1 d and the number of printable sheets when the photosensitive layer 19 b is a single-layer organic photosensitive layer. Figure 5 This is a graph showing the relationship between the process linear speed and the high-speed responsiveness in the two-component development type color printer 100 using an organic photosensitive layer as the photosensitive layer 19 b . Figure 6 This is a graph showing the relationship between the process linear speed, the surface potential, and image failure in a two-component development type color printer 100 using a single organic photosensitive layer as the photosensitive layer 19 b . Figure 7 This is a graph showing the relationship between the process linear speed, the surface potential, the development voltage, and image defects in a two-component development-type color printer 100 using a single organic photosensitive layer as the photosensitive layer 19 b . Figure 8 1 is a graph showing the relationship between the development frequency and the drum ghost in the two-component development method color printer 100 using a single organic photosensitive layer as the photosensitive layer 19 b . DETAILED DESCRIPTION

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figure 1 This is a schematic cross-sectional view of a color printer 100 according to an embodiment of the present invention. Figure 2 yes Figure 1 1 is an enlarged view of the vicinity of the image forming section Pa in FIG. The image forming sections Pb to Pd also have basically the same configuration, and thus their description is omitted.

[0010] In the main body of the color printer 100, from the upstream side in the conveying direction (at Figure 1 The left side in the center) is provided with four image forming units Pa, Pb, Pc and Pd in ​​sequence. The image forming units Pa to Pd are provided to correspond to images of four different colors (yellow, magenta, cyan and black), and form yellow, magenta, cyan and black images in sequence through the processes of charging, exposure, development and transfer.

[0011] The image forming units Pa to Pd are provided with photosensitive drums 1a, 1b, 1c and 1d for carrying visible images (toner images) of respective colors. Figure 1 In the image forming unit, an intermediate transfer belt 8 is provided adjacent to each image forming unit Pa to Pd and rotates counterclockwise. The intermediate transfer belt 8 is wound around a driving roller 10 on the downstream side and a tension roller 11 on the upstream side, and a belt cleaning device 30 is provided on the upstream side of the image forming unit Pa along the rotation direction of the intermediate transfer belt 8 and is opposed to the tension roller 11 across the intermediate transfer belt 8.

[0012] like Figure 2 As shown, around the photosensitive drum 1a, along the drum rotation direction ( Figure 2 In the clockwise direction of FIG. 1 , a charging device 2a, a developing device 3a, a cleaning device 7a and a neutralizing device 20 are arranged, and a primary transfer roller 6a is arranged across the intermediate transfer belt 8.

[0013] The photosensitive 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 this embodiment, a single organic photosensitive layer is laminated on the surface of a cylindrical conductive substrate 19a made of aluminum as the photosensitive layer 19b.

[0014] The charging devices 2 a to 2 d include a charging roller 21 that contacts the photosensitive drums 1 a to 1 d and applies a charging voltage (DC voltage+AC voltage) to the drum surface, and a charging cleaning roller 24 for cleaning the charging roller 21 .

[0015] The developing devices 3a to 3d are two-component developing devices having a developing roller 29 and two spiral stirring conveyors 25, and are respectively filled with a predetermined amount of two-component developer containing toner and magnetic carrier, and the toner is toner of each color of yellow, magenta, cyan and black. A magnetic brush is formed on the surface of the developing roller 29 using the two-component developer, and when a developing voltage of the same polarity as the toner (positive polarity in this case) is applied to the developing roller 29, the magnetic brush is brought into contact with the surface of the photosensitive drum 1a, so that the toner adheres to the surface of the photosensitive drum 1a, forming a toner image. In addition, when the proportion of the toner in the two-component developer filled in each developing device 3a to 3d is lower than a specified value due to the formation of the toner image, the toner is replenished from the toner container 4a to 4d to each developing device 3a to 3d.

[0016] The cleaning devices 7a to 7d include a cleaning blade 31 and a spiral recovery device 33. The cleaning blade 31 removes the toner and the like remaining on the surface of the photosensitive drums 1a to 1d. The spiral recovery device 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 it into a waste toner recovery container (not shown). The static elimination device 20 irradiates the surface of the photosensitive drums 1a to 1d with static elimination light to remove the residual charge.

[0017] When image data is input from a higher-level device such as a computer, the main motor 40 (see Figure 3 ) causes the photosensitive drums 1a to 1d to start rotating. In addition, the belt drive motor 41 (see Figure 3 ) and the rotation drive of the intermediate transfer belt 8 is started. Then, the surfaces of the photosensitive drums 1a to 1d are uniformly charged with the same polarity as the toner (positive polarity in this case) by the charging devices 2a to 2d. Then, light is irradiated according to the image data by the exposure device 5, and an electrostatic latent image is formed on each photosensitive drum 1a to 1d to attenuate the charging according to the image data.

[0018] A two-component developer (hereinafter referred to as developer) containing toners of various colors, yellow, magenta, cyan and black, is filled in the developing devices 3a to 3d in a predetermined amount through the toner containers 4a to 4d, and the toners in the developer are supplied to the photosensitive drums 1a to 1d through the developing devices 3a to 3d and electrostatically attached to the photosensitive drums 1a to 1d. Thus, a toner image corresponding to the electrostatic latent image formed by the exposure from the exposure device 5 is formed.

[0019] Then, an electric field is applied between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d at a predetermined transfer voltage by the primary transfer rollers 6a to 6d, and the yellow, magenta, cyan and black toner images on the photosensitive drums 1a to 1d are primarily transferred to the intermediate transfer belt 8. The toner and the like remaining on the surfaces of the photosensitive drums 1a to 1d after the primary transfer are removed by the cleaning devices 7a to 7d. The residual charge remaining on the surfaces of the photosensitive drums 1a to 1d after the primary transfer is removed by the charge removing device 20.

[0020] The transfer paper P to which the toner image is transferred is stored in a paper cassette 16 disposed at the lower part of the color printer 100, and the transfer paper P is conveyed to a nip portion (secondary transfer nip portion) between a secondary transfer roller 9 and an intermediate transfer belt 8 at a predetermined timing by a paper feed roller 12a and a registration roller pair 12b, and the secondary transfer roller 9 is disposed adjacent to the intermediate transfer belt 8. The transfer paper P to which the toner image is secondarily transferred is conveyed to a fixing unit 13.

[0021] The transfer paper P conveyed to the fixing section 13 is heated and pressed by the fixing roller pair 13a, and the toner image is fixed to the surface of the transfer paper P, thereby forming a predetermined full-color image. The transfer paper P with the full-color image formed thereon is discharged to the discharge tray 17 by the discharge roller pair 15 directly (or after being distributed to the reversing conveying path 18 by the branch section 14 and having images formed on both sides).

[0022] Figure 3 1 is a block diagram showing an example of a control path for the color printer 100. In addition, since various controls are performed on various parts of the color printer 100 based on the use of the color printer 100, the control path of the entire color printer 100 becomes complicated. Therefore, the part of the control path that is necessary for the implementation of the present invention is mainly described here.

[0023] The charging voltage power supply 52 applies a charging voltage to the charging roller 21 in the charging device 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 29 in the developing device 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 the above-mentioned power supplies through an output signal from the control unit 90.

[0024] The image input unit 60 is a receiving unit that receives image data sent from a 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.

[0025] The operation unit 70 includes 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 forming status, the number of copies, etc. The LED 72 displays various states and errors of the color printer 100. Various settings of the color printer 100 are performed according to the printer driver of the computer.

[0026] The operation unit 70 also includes a start button for the user to instruct the start of image formation, a stop / clear button for suspending image formation, and a reset button for returning various settings of the color printer 100 to default.

[0027] The internal 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 disposed near the image forming units Pa to Pd.

[0028] 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 storage unit, a RAM (Random Access Memory) 93 as a readable and writable storage unit, a temporary storage unit 94 for temporarily storing image data, etc., a counter 95, and a plurality of (here, two) I / Fs (interfaces) 96 for sending control signals to various devices in the color printer 100 or receiving input signals from the operation unit 70. The control unit 90 can be arranged at any position inside the main body of the color printer 100.

[0029] The ROM 92 stores a control program for the color printer 100, numerical values ​​required for control, and data that does not change during use of the color printer 100. The RAM 93 stores necessary data generated during the control of the color printer 100, data temporarily required for the control of the color printer 100, and the like. The temporary storage unit 94 temporarily stores an image signal input from the image input unit 60 and converted into a digital signal. The counter 95 accumulates and counts the number of printed sheets.

[0030] In addition, the control unit 90 sends control signals from the CPU 91 to various parts and devices in the color printer 100 through the I / F 96. In addition, signals indicating the status and input signals are sent from each part and device to the CPU 91 through the I / F 96. As the various parts and devices controlled by the control unit 90, for example, image forming units Pa to Pd, exposure device 5, intermediate transfer belt 8, secondary transfer roller 9, fixing unit 13, voltage control circuit 55, image input unit 60, operation unit 70, and internal temperature and humidity sensor 80 can be listed.

[0031] When the two-component development method is adopted in the color printer 100 with a fast process linear speed (250 [mm / sec] or more), the electric field intensity between the developing roller 29 and the photosensitive drums 1a to 1d is preferably weak in order to suppress the development of the carrier. The process linear speed is the printing process speed (transfer speed of the transfer paper P) in the color printer 100, and is the same as the rotation speed of the photosensitive drums 1a to 1d.

[0032] For example, the relative dielectric constant ε of an amorphous silicon (a-Si) photosensitive layer is ε = 10, and the relative dielectric constant ε of an organic photosensitive layer (OPC) is ε = 3. Therefore, in a color printer 100 of a two-component development method with a fast processing line speed, an organic photosensitive layer is more advantageous than an a-Si photosensitive layer.

[0033] Figure 4 1 is a graph showing the relationship between the thickness of the photosensitive layer 19b of the photosensitive drums 1a to 1d and the number of printable sheets (durable life) when the photosensitive layer 19b is a single-layer organic photosensitive layer. Figure 4 As shown, when the photosensitive layer 19 b is a single-layer organic photosensitive layer, in order to achieve a long life with a printable number of 300k or more sheets, the layer thickness of the photosensitive layer 19 b needs to be set to 40 [μm] or more.

[0034] Figure 5 This is a graph showing the relationship between the processing line speed and the high-speed responsiveness in a two-component development method color printer 100 using an organic photosensitive layer as the photosensitive layer 19b. The high-speed responsiveness refers to the degree of decrease in the surface potential of the photosensitive drums 1a to 1d when the photosensitive drums 1a to 1d charged to a predetermined surface potential are exposed by the exposure device 5. Figure 5 In the figure, the potential of the exposed part (image part) after exposure by the exposure device 5 when the process line speed is changed in the stacked organic photosensitive layer (data series of ○ in the figure) with a layer thickness of 40 [μm] and the single-layer organic photosensitive layer (data series of △ in the figure) is compared. That is, it can be said that the lower the potential of the exposed part, the better the responsiveness, and the higher the potential of the exposed part, the worse the responsiveness.

[0035] like Figure 5 As shown, when the thickness of the photosensitive layer 19b is 40 [μm], the responsiveness of the stacked organic photosensitive layers is particularly reduced in the linear velocity region above 250 [mm / sec], so a single-layer organic photosensitive layer is advantageous. Figure 5 It is known that when a two-component development method is adopted in a color printer 100 in which the linear speed of the photosensitive drums 1a to 1d is 250 [mm / sec] or more, a single-layer organic photosensitive layer with a thickness of 40 [μm] or more is preferably used as the photosensitive layer 19b.

[0036] However, when a two-component developing method is adopted in a color printer 100 with a fast processing line speed, if a single-layer organic photosensitive layer with a layer thickness of more than 40 [μm] is used as the photosensitive layer 19b of the photosensitive drum 1a~1d, image defects such as image unevenness and drum ghosting are likely to occur.

[0037] Therefore, in the two-component development method color printer 100 of the present embodiment, when the processing linear speed is 250 [mm / sec] or more and a single-layer organic photosensitive layer with a layer thickness of 40 [μm] or more is used as the photosensitive layer 19b of the photosensitive drums 1a to 1d, the above-mentioned image defects can be suppressed by appropriately setting the development conditions. The setting of the development conditions will be described in detail below.

[0038] [Development voltage setting under different process line speed conditions] Figure 6 1 is a graph showing the relationship between the processing linear speed, the surface potential and the image failure in a two-component development method color printer 100 using a single organic photosensitive layer as the photosensitive layer 19b. Figure 6 In FIG. 1 , the horizontal axis represents the process linear velocity and the vertical axis represents the surface potential V0 of the photosensitive drums 1a to 1d, and the image evaluation results are shown when two layer thicknesses of 40 [μm] and 20 [μm] are used as the layer thickness of the photosensitive layer 19b. Figure 6 In FIG. 1 , solid lines A and B indicate the upper and lower limits of the surface potential V0 when the layer thickness is 40 μm, and dashed lines C and D indicate the upper and lower limits of the surface potential V0 when the layer thickness is 20 μm.

[0039] like Figure 6 As shown, in the area with high surface potential V0, an uneven discharge image is generated due to the high charging voltage applied to the photosensitive drums 1a to 1d. In addition, when the thickness of the photosensitive layer 19b is 40 [μm], compared with the case where the thickness is 20 [μm], in order to charge the photosensitive drums 1a to 1d to the desired surface potential, the required charging voltage becomes higher, and uneven discharge is more likely to occur. That is, the upper limit value of the surface potential is lower when the thickness is 40 [μm] than when the thickness is 20 [μm].

[0040] On the other hand, in the area where the surface potential V0 is low, it is easily affected by the primary transfer electric field to the intermediate transfer belt 8 and other potential unevenness, resulting in image unevenness and drum ghosting. In addition, when the thickness of the photosensitive layer 19b is 40 [μm], it is more difficult to eliminate the reverse charge injected during the primary transfer than when the thickness is 20 [μm], and drum ghosting is more likely to occur. That is, the lower limit value of the surface potential is higher when the thickness is 40 [μm] than when the thickness is 20 [μm].

[0041] Due to the above reasons, the settable range of the surface potential V0 (the interval between the solid lines A and B) of the photosensitive drums 1a to 1d using the photosensitive layer 19b having a thicker layer thickness (40 [μm]) is narrower than the settable range of the surface potential V0 (the interval between the dotted lines C and D) of the photosensitive drums 1a to 1d using the photosensitive layer 19b having a thinner layer thickness (20 [μm]).

[0042] Figure 7 1 is a graph showing the relationship between the processing linear speed, the surface potential, the developing voltage and image defects in a two-component developing color printer 100 using a single organic photosensitive layer as the photosensitive layer 19b. Figure 7 In the figure, the horizontal axis is the processing linear velocity, the left vertical axis is the developing voltage (DC voltage Vdc), and the right vertical axis is the surface potential V0. In the two-component developing method, in order to avoid fogging images and carrier development, the difference V0-Vdc (developing potential difference) between the DC voltage Vdc and the surface potential V0 needs to be set to a fixed value, and V0-Vdc is set to 150 [V] here.

[0043] exist Figure 7 In the figure, the carrier resistance is 10 9 [Ω·cm] and 10 11 Image evaluation results of two carriers [Ω·cm] as carriers of a two-component developer. Figure 7 In FIG. 1 , the solid line A indicates the upper limit value of the DC voltage Vdc at which discharge unevenness does not occur, and the solid line B indicates the lower limit value of the DC voltage Vdc at which drum ghosting and image unevenness do not occur.

[0044] like Figure 7 As shown, the carrier resistance is 10 9 In the case of [Ω·cm] (data series indicated by “○” in the figure), the range of change of the developing voltage when considering density adjustment and deviation due to calibration is in a region (between solid lines A and B) where image defects do not occur even when the process linear speed changes.

[0045] On the other hand, when a high-resistance carrier is used, the developing property decreases, especially when the processing linear velocity is in the high-speed region. Therefore, in order to ensure the image density when the processing linear velocity is in the high-speed region, it is necessary to set the developing voltage high and to set the surface potential V0 of the photosensitive drums 1a to 1d high in accordance with the developing voltage. As a result, when the carrier resistance is 10 11 [Ω·cm] (data series of △ in the figure), when the process linear speed is in the high speed region (200 [mm / sec] or more), it becomes the region where image defects occur (region above the solid line A).

[0046] Therefore, in the color printer 100 of the two-component development method using a single-layer organic photosensitive layer as the photosensitive layer 19b, by using a carrier with a resistance of 10 9 Such a low-resistance carrier of [Ω·cm] can improve the developability in a high process linear speed region and reduce the amount of change in the required developing voltage between different process linear speeds.

[0047] As described above, when using photosensitive drums 1a to 1d with a photosensitive layer 19b having a thickness of 40 [μm], the setting range of the surface potential V0 is narrow, so a low-resistance carrier is required to reduce the difference in the developing voltage between different linear velocities. Specifically, in a two-component developing color printer 100, in order to maintain image quality, the change in the developing voltage when the processing linear velocity difference is 180 [mm / sec] needs to be suppressed to less than 40 [V]. The two-component developing color printer 100 has a Figure 6 , Figure 7 The process line speed used in the evaluation was 250 [mm / sec] or higher, and a single-layer organic photosensitive layer with a thickness of 40 [μm] or higher was used as the photosensitive layer 19b.

[0048] As a countermeasure for this, for example, by using a carrier resistor having a value of 10 9 [Ω·cm] or less, so that the change in the developing voltage of the photosensitive drum 1a~1d having a single-layer organic photosensitive layer with a layer thickness of 40 [μm] at the beginning of use can be suppressed to less than 40 [V] when it is used in a printing mode with a processing line speed of 270 [mm / sec] (first printing mode) and in a printing mode with a processing line speed of 90 [mm / sec] (second printing mode) (the processing line speed difference is 180 [mm / sec]).

[0049] In addition, Figure 7 In the example shown, the variation of the developing voltage when the process linear velocity difference is 180 [mm / sec] is suppressed to 40 [V] or less in consideration of density adjustment and variation due to calibration. However, as long as the variation of the surface potential V0 of the photosensitive drums 1a to 1d can be suppressed, there is no risk of image defects such as discharge unevenness and drum ghosting. Therefore, it is not necessary to suppress the variation of the developing voltage to 40 [V] or less.

[0050] [Setting of the development frequency for suppressing drum ghosting] Figure 8 1 is a graph showing the relationship between the development frequency and the drum ghost in a two-component development method color printer 100 using a single organic photosensitive layer as the photosensitive layer 19b. Figure 8In the figure, the horizontal axis is the frequency of the AC voltage Vac of the development voltage (hereinafter referred to as the development frequency), and the vertical axis is the image density difference ΔE, which shows the image evaluation results when the processing line speed is set to 270 [mm / sec] and two layer thicknesses of 40 [μm] and 20 [μm] are used as the layer thickness of the photosensitive layer 19b. Figure 8 In FIG. 1 , the dotted line indicates the density difference ΔE (=1.5) that can be visually recognized as a drum ghost.

[0051] like Figure 8 As shown in the figure, the ΔE when the thickness of the photosensitive layer 19b is 40 [μm] (the data series of △ in the figure) is larger than the ΔE when the thickness is 20 [μm] (the data series of ○ in the figure). This is because the thicker the photosensitive layer 19b is, the more difficult it is to charge. Therefore, when using the photosensitive drums 1a to 1d with a thick photosensitive layer 19b of 40 [μm], it is necessary to suppress drum ghosting.

[0052] In addition, by Figure 8 It can be seen that as the development frequency increases, ΔE also increases. This is because as the development frequency increases, the toner becomes easier to move from the developing roller 29 to the photosensitive drums 1a to 1d, showing a tendency to improve the development performance, and the image contrast becomes larger, and ΔE increases. Figure 8 It is found that when a single-layer organic photosensitive layer of 40 [μm] is used in a printing mode with a process linear speed of 270 [mm / sec], the development frequency needs to be set to 4 [kHz] or less.

[0053] According to the present embodiment, in a two-component development method color printer 100 using photosensitive drums 1a to 1d having a single-layer organic photosensitive layer having a layer thickness of 40 [μm] or more at the beginning of use as the photosensitive layer 19b, by optimizing the development conditions, it is possible to achieve a high processing line speed, a long life of the photosensitive drums 1a to 1d, and ensure a settable range (operation window) for the development voltage and the surface potential V0. As a result, it is possible to suppress the occurrence of image defects and maintain appropriate image quality.

[0054] Specifically, in two printing modes with a process linear velocity difference of 180 [mm / sec] or more, by suppressing the variation of the developing voltage (DC voltage Vdc) to 40 [V] or less, it is possible to set the DC voltage Vdc and the surface potential V0 that do not cause discharge unevenness, drum ghosting, and image unevenness. As a method for suppressing the variation of the developing voltage (DC voltage Vdc) to 40 [V] or less, for example, using a carrier having a resistance of 10 9 Two-component developer with a carrier of [Ω·cm] or less.

[0055] In addition, by setting the development frequency to 4 [kHz] or less, it is possible to suppress the occurrence of drum ghosting in a printing mode in which the processing line speed is 250 [mm / sec] or more. In addition, if the development frequency is reduced, the occurrence of drum ghosting can be suppressed, but on the other hand, a foggy image is easily generated. Therefore, in a printing mode (second printing mode) in which the processing line speed is 90 [mm / sec] and drum ghosting is difficult to occur, it is preferable to set the development frequency to be greater than 4 [kHz].

[0056] In addition, the present invention is not limited to the above-mentioned embodiment, and various changes can be made within the scope of the main purpose of the present invention. For example, in the above-mentioned embodiment, the color printer 100 of the intermediate transfer method in which the toner image formed on the photosensitive drums 1a to 1d is transferred to the intermediate transfer belt 8 and then transferred to the transfer paper P is described, but it is not limited to this, and it can also be applied to the color printer of the direct transfer method in which the toner image formed on the photosensitive drums 1a to 1d is directly transferred to the transfer paper P.

[0057] In addition, in the above-mentioned embodiment, a serial color printer 100 is illustrated as an example of an image forming device, but the present invention can of course also be applied to other image forming devices of a two-component development method such as a color copier, a color multifunction peripheral, a black and white printer, and a black and white multifunction peripheral.

[0058] The present invention can be used in an image forming apparatus having a developing device of a two-component developing method. By using the present invention, when a single-layer organic photosensitive body is used in an image forming apparatus with a fast processing line speed, an image forming apparatus can be provided that can achieve a long life and can suppress image defects such as carrier development and drum ghosting.

Claims

1. An image forming device comprising: Image carrier, with a photosensitive layer formed on the 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 charge decay; A developing device having a developer carrier carrying a two-component developer including a toner and a carrier, and supplying the toner in the developer carried by the developer carrier to the image carrier to develop the electrostatic latent image into a toner image; A driving unit, driving the image carrier to rotate at a predetermined linear speed; A developing voltage power supply, for applying a developing voltage obtained by superimposing a DC voltage on an AC voltage to the developer carrier; as well as a control unit that controls the driving unit and the developing voltage power supply, The image forming apparatus has a first printing mode in which the drive unit drives the image carrier to rotate at a linear speed of 250 [mm / sec] or more. The image forming apparatus is characterized in that The image carrier has a single-layer organic photosensitive layer as the photosensitive layer, and the thickness of the photosensitive layer at the beginning of use is 40 [μm] or more.

2. The image forming apparatus according to claim 1, wherein: The control unit can switch between a plurality of printing modes including the first printing mode and a second printing mode, wherein a linear speed of the second printing mode is lower than a linear speed of the first printing mode, and a linear speed difference between the second printing mode and the first printing mode is greater than 180 [mm / sec], The amount of change in the DC voltage of the development voltage in the first printing mode and the second printing mode is 40 [V] or less.

3. The image forming apparatus according to claim 1, wherein: The resistance value of the carrier in the developer is 10 9 [Ω·cm] or less.

4. The image forming apparatus according to any one of claims 1 to 3, wherein: The frequency of the AC voltage used in the first printing mode is 4 [kHz] or less.

Images