Image forming apparatus

Abstract

To reproduce a suitable hue in a wide color gamut image forming mode.SOLUTION: A control unit performs control so that it can execute a first mode in which a developer carrier rotates relative to an image carrier at a first peripheral speed ratio, and a second mode in which the developer carrier rotates relative to the image carrier at a second peripheral speed ratio larger than the first peripheral speed ratio. In a case where an image forming operation is executed in the second mode, when image data for output is formed only of a first pattern formed of a first gradation, the control unit performs control to apply, to a recording material, a first transfer voltage so as to transfer a toner image formed of the first pattern, and when the image data for output is formed of the first pattern and a second pattern formed of a second gradation having a lower density than the first gradation, performs control to apply, to the recording material, a second transfer voltage having a smaller absolute value than the first transfer voltage so as to transfer a toner image formed of the first pattern and the second pattern.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image forming apparatus.

Background Art

[0002] In an electrophotographic color image forming apparatus, there is one having a wide color gamut image forming mode for expanding the color gamut, in addition to the normal image forming mode. In order to realize a wide color gamut, a method of increasing the amount of developer (toner) placed on the recording material more than usual is adopted. For example, in Patent Document 1, a method is proposed in which the amount of toner supplied to the photosensitive drum is increased by changing the peripheral speed ratio between the photosensitive drum and the developing roller, and the color gamut of the toner image formed particularly when two or more kinds of toners are overlapped, such as secondary colors, is expanded.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the configuration of Patent Document 1 has the following problems. In the wide color gamut image forming mode, a transfer setting with a higher transfer strength than in the normal image forming mode is made so that even if the amount of toner loaded on the entire recording material is larger than that in the normal image forming mode, it can be appropriately transferred to the recording material. On the other hand, in the market, there are demands such as accurately reproducing corporate colors such as corporate logos. In this case, as shown in FIG. 8, the corporate logo is often placed at a single point in a very small part of the document. And even if most of the remaining areas are low-density halftone images with a small amount of toner loaded, in the configuration of Patent Document 1, it is necessary to select the wide color gamut image forming mode.

[0005] In such a case, for the halftone image in most areas on the recording material, the transfer intensity becomes excessive, and abnormal discharge images may occur in a wide area on the recording material, significantly degrading the image quality.

[0006] In view of the above situation, an object of the present invention is to provide an image forming apparatus capable of reproducing a suitable color tone in a wide color gamut image forming mode.

Means for Solving the Problems

[0007] In order to achieve the above object, in an image forming apparatus capable of executing an image forming operation for forming an image on a recording material, a rotatable image carrier, an exposure unit that forms an electrostatic latent image on the surface of the image carrier based on output image data, a rotatable developer carrier that supplies a developer to the surface of the image carrier and develops the electrostatic latent image formed on the surface of the image carrier to form a toner image, an intermediate transfer member that forms a transfer portion in contact with the surface of the image carrier and transfers the toner image formed on the surface of the image carrier in the transfer portion, a transfer member that transfers the toner image transferred to the surface of the intermediate transfer member to the recording material, a driving unit that drives the image carrier and the developer carrier, a transfer voltage applying unit that applies a transfer voltage to the transfer member, an acquisition unit that acquires information regarding the output image data, and a control unit that controls the driving unit and the transfer voltage applying unit, wherein the control unit is capable of controlling to execute a first mode in which the developer carrier rotates at a first peripheral speed ratio with respect to the image carrier and a second mode in which the developer carrier rotates at a second peripheral speed ratio greater than the first peripheral speed ratio with respect to the image carrier, and when the image forming operation is executed in the second mode, i) when the acquisition unit acquires that the output image data is composed only of a first pattern composed of a first gradation, controls to apply a first transfer voltage to transfer the toner image composed of the first pattern to the recording material, and ii) when the acquisition unit acquires that the output image data is composed of the first pattern composed of the first gradation and a second pattern composed of a second gradation having a lower density than the first gradation, controls to apply a second transfer voltage having an absolute value smaller than that of the first transfer voltage to transfer the toner image composed of the first pattern and the second pattern to the recording material.

Effect of the Invention

[0008] As described above, in the wide color gamut image forming mode, it becomes possible to reproduce a suitable color tone.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0010] 〔First Embodiment〕 Hereinafter, the image forming apparatus according to the present invention will be described in detail. However, the dimensions, materials, shapes, relative arrangements, etc. of the component parts described in this embodiment are not intended to limit the scope of the present invention only to these, unless otherwise specifically described.

[0011] [Image Forming Apparatus] The image forming apparatus 500 according to the present embodiment shown in FIG. 1 is an intermediate transfer type tandem full-color image forming apparatus using an intermediate transfer body as an image carrier, and the figure is a longitudinal sectional view showing its schematic configuration.

[0012] The engine unit 501 arranges four image forming units, namely, the image forming units 100Y, 100M, 100C, and 100Bk that form toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (Bk), in series from upstream to downstream. In a state where the image forming apparatus 500 is installed, below the image forming units 100Y, 100M, 100C, and 100Bk in the gravitational direction, an intermediate transfer belt 14, which is an intermediate transfer member spanned over rollers 13, 19, and 23, is disposed.

[0013] As the intermediate transfer member of this embodiment, the intermediate transfer belt 14 uses a resin belt mainly composed of PEN (polyethylene naphthalate) with a thickness of 100 μm and a volume resistivity of 10E10 Ω·cm. This volume resistivity is the result of measurement using a high resistance meter High Resista UP MCP-HT450 type manufactured by Dain Instruments Co., Ltd. and a measurement probe UR-100 manufactured by the same company under the conditions of applying 250 V for 30 seconds in an environment of 23°C and 50% RH.

[0014] Note that as the intermediate transfer belt 14, resin materials such as PVdF (polyvinylidene fluoride), polyamide, PET (polyethylene terephthalate), and polycarbonate with a thickness of 50 to 200 μm and a volume resistivity of about 10E9 to 10E16 Ω·cm may be used. Furthermore, if necessary, conductive fillers such as carbon, ZnO, SnO2, and TiO2 may be dispersed in these materials to adjust the volume resistivity to about 10E7 to 10E11 Ω·cm.

[0015] Each of the image forming units 100Y, 100M, 100C, and 100Bk includes an integrated process cartridge composed of drum units 10Y, 10M, 10C, and 10Bk and developing units 8Y, 8M, 8C, and 8Bk as developing apparatuses. Among these, the drum units 10Y, 10M, 10C, and 10Bk each have photosensitive drums 1Y, 1M, 1C, and 1Bk having OPC (organic photoconductor) photosensitive layers. And each includes cleaning blades 9Y, 9M, 9C, and 9Bk made of elastic rubber and charging rollers 2Y, 2M, 2C, and 2Bk.

[0016] Further, the developing units 8Y, 8M, 8C, and 8Bk have developing rollers 5Y, 5M, 5C, and 5Bk as developer carriers. They each include toners 3Y, 3M, 3C, and 3Bk as developers, toner application rollers 6Y, 6M, 6C, and 6Bk as supply rollers, and toner regulating blades 7Y, 7M, 7C, and 7Bk as regulating members. As the toners 3Y, 3M, 3C, and 3Bk, non-magnetic one-component polymer toners with a charge amount of -20 to -50 μC / mg were used. The normal charging polarities of the toners 3Y, 3M, 3C, and 3Bk are set to a negative (minus) polarity. Note that this image forming apparatus 500 employs a reversal development method.

[0017] Above each of the image forming units 100Y, 100M, 100C, and 100Bk, there are exposure devices 11Y, 11M, 11C, and 11Bk, which are exposure units composed of scanner units that scan laser light with a polygon mirror. The exposure devices 11Y, 11M, 11C, and 11Bk irradiate modulated scanning beams 12Y, 12M, 12C, and 12Bk based on image data onto photosensitive drums 1Y, 1M, 1C, and 1Bk as image carriers to form electrostatic latent images. The spot diameters of the scanning beams 12Y, 12M, 12C, and 12Bk are each approximately 60 μm on the photosensitive drums 1Y, 1M, 1C, and 1Bk, and image formation is possible at a resolution of 600 dpi in both the main scanning direction and the sub-scanning direction. In this embodiment, the image data is 8-bit data for each color, that is, represented at 256 levels from 00h to FFh (h means hexadecimal representation). The image data FFh represents a solid image. As the image data decreases, the image density decreases, and at 00h, it becomes a non-image (solid white image). The image data may sometimes be expressed as a ratio with FFh as 100% and 00h as 0% hereinafter. The FFh side is the high-tone side, and the 00h side is the low-tone side. Also, the image data may sometimes be represented with dec attached in decimal notation. For example, FFh of the solid image as the first pattern is 255dec, and 80h of the halftone image as the second pattern is 128dec, which will be described later.

[0018] Inside the intermediate transfer belt 14, primary transfer rollers 4Y, 4M, 4C, and 4Bk are disposed as primary transfer members that press the intermediate transfer belt 14 against the photosensitive drums 1Y, 1M, 1C, and 1Bk from below.

[0019] These primary transfer rollers 4Y, 4M, 4C, and 4Bk transfer the toner images on the photosensitive drums 1Y, 1M, 1C, and 1Bk onto the intermediate transfer belt 14. In this embodiment, a primary transfer roller having a metal core bar with a diameter of φ6 covered with an NBR foamed sponge body to a diameter of φ8 was used. The resistance value of this primary transfer roller is 10E6Ω. The measurement of the resistance value R is performed by measuring the voltage V in the environment of 23°C and 50%RH by the method shown in FIG. 7. That is, the roller 701 to be measured is brought into contact with an aluminum cylinder 702 with a diameter of φ30 under a total pressure of 9.8N (1kgf) and rotated at 30rpm, and the current when a voltage of +1000V is applied from the power supply 703 is measured. The current is obtained by measuring the terminal voltage Vr of a 100Ω resistor 704 with a voltmeter 705. And the roller resistance R is obtained by the following formula. Roller resistance R = applied voltage × 100 / Vr To these primary transfer rollers 4Y, 4M, 4C, and 4Bk, a transfer voltage (bias) of positive (P) polarity opposite to the normal polarity of the toner 3 controlled by constant voltage or constant current is applied from a primary transfer power supply 73 as the primary transfer voltage application unit shown in FIG. 9. Then, the toner images formed on the photosensitive drums 1Y, 1M, 1C, and 1Bk are transferred onto the intermediate transfer belt 14.

[0020] A secondary transfer roller 20 as a secondary transfer member transfers the toner image formed on the intermediate transfer belt 14 to the recording material P. In this embodiment, a secondary transfer roller having a metal core bar with a diameter of φ8 covered with an NBR foamed sponge body to a diameter of φ18 was used. The resistance value of this secondary transfer roller is 10E7Ω measured by the aforementioned roller resistance measurement method. A voltage of positive polarity controlled by constant voltage or constant current is applied to the secondary transfer roller 20 from a secondary transfer power supply 74 as the secondary transfer voltage application unit shown in FIG. 9.

[0021] Of the three rollers 13, 19, and 23 that support the intermediate transfer belt 14, 13 is a driving roller and a secondary transfer opposing roller. While driving and conveying the intermediate transfer belt 14 in the direction of arrow R14, it forms a transfer portion as a secondary transfer nip with the secondary transfer roller 20 via the recording material P. Roller 23 is an auxiliary roller that keeps the surface of the recording material P near the secondary transfer nip and the intermediate transfer belt 14 at a predetermined angle to suppress abnormal discharge between the recording material P and the toner image on the intermediate transfer belt 14. 19 is a tension roller for stretching the intermediate transfer belt 14 with a predetermined tension.

[0022] Downstream of roller 13, a cleaning member 22 composed of an elastic blade for cleaning the toner 3 remaining on the intermediate transfer belt 14 without being transferred to the recording material P at the secondary transfer nip is arranged.

[0023] 21 is a fixing device composed of a fixing roller 21a and a pressure roller 21b for melting and fixing the toner image formed on the recording material P.

[0024] [Control Unit] 502 in FIG. 1 shows the control unit of the image forming apparatus 500. The control unit 502 can communicate with the image processing unit 504 described later, and controls the operation of the engine unit 501 according to an instruction from the image processing unit 504.

[0025] Connected to the CPU 32 are, in addition to the exposure devices 11Y, 11M, 11C, and 11Bk, a RAM 33, a ROM 34, and a non-volatile memory NVRAM 35. The ROM 34 is a read-only storage means (memory) in which programs and various data for the CPU 32 to control the image forming apparatus 500 are written. The RAM 33 is a readable and writable memory in which the data in the ROM 34 is expanded and various data are stored. The NVRAM 35 is a readable and writable memory that retains the recorded content even when the power of the image forming apparatus is turned off. The environment sensor 36 consists of a temperature sensor and a relative humidity sensor, and the temperature information and relative humidity information inside the engine unit 501 are taken into the CPU 32 and used for the control of the engine unit 501. Further connected to the CPU 32, which is a control means, is an operation panel 31 for the user to make various settings and instructions and for the user to be informed of information.

[0026] FIG. 9 is a block diagram showing the control configuration of the main part of the image forming apparatus 500 of the present embodiment. Using FIG. 9, the control unit 502 will be described in more detail. Through electrical connections, signals indicating various types of information are input to and output from the control unit 502. The control unit 502 performs processing of signals input from various process devices and sensors and processing of signals output to give operation commands to various process devices. The image processing unit 504 provided in the image forming apparatus 500 inputs and outputs various signals to and from an external device (host device) 503 and inputs and outputs various signals to and from the control unit 502. The control unit 502 comprehensively controls the operation of the image forming apparatus 500 according to instructions from the image processing unit 504 in accordance with a predetermined control program and a reference table.

[0027] The control unit 502 includes a CPU 32 as arithmetic processing means, which is a central element for performing various arithmetic processes, and main memories such as a RAM 33, a ROM 34, and an NVRAM 35 (non-volatile memory), which are storage elements as storage means for storing information. In the RAM 33, the detection results of sensors, the count results of counters, arithmetic results, etc. are temporarily stored. In the ROM 34, control programs, data tables obtained in advance through experiments, etc. are stored. In the NVRAM 35, the count results of counters, various setting information, the results of sensors, etc. are stored. To the control unit 502, each control target, sensor, counter, etc. in the image forming apparatus 500 are connected. The control unit 502 controls the input / output of various signals, the driving timings of each part, etc., and performs control of a predetermined image forming sequence.

[0028] The control unit 502 performs control of, for example, a charging power source 71 as a charging voltage application unit, a developing power source 72 as a developing voltage application unit, a supply power source 75, a regulation power source 76, an exposure device 11, a primary transfer power source 73, a secondary transfer power source 74, a driving unit 60, etc.

[0029] Also, the driving unit 60 includes a driving motor as a driving source, a driving transmission member, etc. The driving sources for driving rotating members such as the photosensitive drum 1 and the developing roller 5 may be provided independently of each other, or at least a part of them may be shared. Also, the driving sources for driving elements for each color may be provided independently of each other, or at least a part of them may be shared.

[0030] Here, the image forming apparatus 500 executes an image forming operation (print job), which is a series of operations for forming and outputting an image on one or more recording materials P started by one start instruction. The image forming operation generally includes an image forming process, a pre-process (pre-rotation process, pre-print operation), an intersheet process when forming an image on a plurality of recording materials P, and a post-process (post-rotation process, post-print operation). The image forming process is a period during which an electrostatic latent image of the image to be actually formed and output on the recording material P is formed, a toner image is formed, the toner image is primarily transferred, and fixing is performed. When referring to image formation, it means this period. More specifically, the timings during image formation are different at the positions where the processes of charging, exposure, development, primary transfer, secondary transfer, and fixing are performed. The pre-process is a period during which preparatory operations before the image forming process are performed from when a start instruction is input until actual image formation begins. The intersheet process is a period corresponding to between the recording materials P when continuously forming images on a plurality of recording materials P (continuous image formation). The post-rotation process is a period during which sorting operations (preparatory operations) after the image forming process are performed. When not forming an image, it is a period other than during image formation, and includes the above-mentioned pre-process, intersheet process, post-process, and further a pre-multi-rotation process, which is a preparatory operation when the image forming apparatus 500 is powered on or resumes from a sleep state.

[0031] [Image Processing Unit] The image forming apparatus 500 is connected to a host computer 503 either stand-alone or via a network. An image created by application software or the like in the host computer 503 is output as print information through a printer driver 201 and sent to an image processing unit 504. As this print information, a printer description language called PDL (Page Description Language), which is composed of drawing commands such as characters, graphics, and images, is used.

[0032] The image processing unit 504 is composed of an image generation unit 41, a color processing unit 42, an image analysis unit 43, and an image buffer 44. The printing information sent to the image processing unit 504 is analyzed by the image generation unit 41 and rasterized, and then expanded into bitmap image data of each color of red (R), green (G), and blue (B) at 600 dpi according to the resolution of the image forming apparatus and the size of the printed image. Then, it is sent to the color processing unit 42.

[0033] The color processing unit 42 is composed of a color conversion unit 45, a gradation correction unit 46, and a halftoning unit 47. The R, G, and B bitmap image data sent to the color processing unit 42 is color-converted as follows. In the color conversion unit 45, it is color-converted into Y, M, C, and Bk image data using a data conversion table that defines the correspondence between R, G, and B image data (referred to as a color table) and Y, M, C, and Bk image data. Furthermore, gradation correction is performed on the image data in the gradation correction unit 46 so that the image data and the density of the image output by the engine unit are in a predetermined relationship. This gradation correction is performed using a lookup table (LUT) that represents the correspondence between the input image data and the output image data. The gradation-corrected image data is further subjected to gradation expression processing such as dithering in the halftoning unit 47 to generate output image data. After the configuration of the image data is analyzed by the image analysis unit 43, the output image data is stored in the image buffer 44 and sent to the control unit 502 at a predetermined timing.

[0034] [Normal Image Formation Mode] In the normal image forming mode as the first mode, when image formation starts, the photosensitive drums 1Y, 1M, 1C, 1Bk, the intermediate transfer belt 14, etc. are driven by the driving unit 60 at a predetermined process speed (here 160 mm / s) and start to rotate in the direction of the arrow. The photosensitive drums 1Y, 1M, 1C, 1Bk generate discharge with the charging rollers 2Y, 2M, 2C, 2Bk to which a predetermined charging voltage (about -1000 V) is applied by the charging power source 71, and are uniformly charged to a surface potential of about -450 V. This surface potential of about -450 V at this time is called the dark part potential Vd. Subsequently, an electrostatic latent image based on the output image data is formed by the scanning beams 12Y, 12M, 12C, 12Bk from the exposure devices 11Y, 11M, 11C, 11Bk. The surface potential of the photosensitive drum when the electrostatic latent image of a solid image is formed is about -100 V. This surface potential of about -100 V at this time is called the bright part potential Vl.

[0035] At this time, the electrostatic latent images of each color are formed at predetermined timings of each color so that the four colors are later superimposed on the intermediate transfer belt 14 to form a full-color image. When the exposed photosensitive drums 1Y, 1M, 1C, 1Bk further rotate, the electrostatic latent images on the photosensitive drums 1Y, 1M, 1C, 1Bk are visualized (developed) by the developing rollers 5Y, 5M, 5C, 5Bk to which a developing voltage of about -300 V is applied by the developing power source 72. The developing rollers 5Y, 5M, 5C, 5Bk rotate in the forward direction with respect to the direction of the arrow, that is, the rotation direction of the photosensitive drums 1Y, 1M, 1C, 1Bk. Then, toner images of Y, M, C, Bk are respectively formed on the photosensitive drums 1Y, 1M, 1C, 1Bk. When the toner image on the photosensitive drum 1Y further rotates, the toner image is transferred onto the intermediate transfer belt 14 by the primary transfer roller 4Y to which a primary transfer voltage of about +800 V is applied by the primary transfer power source 73. And in synchronization with the conveyance of the intermediate transfer belt 14, the toner images of M, C, Bk are sequentially transferred onto the intermediate transfer belt 14 by the primary transfer rollers 4M, 4C, 4Bk to which primary transfer voltages of about +850 V, +900 V, +950 V are applied. Then, a toner image composed of four colors is formed on the intermediate transfer belt 14.

[0036] The recording material P loaded in the paper feed cassette 15 is fed by the semi-circular paper feed roller 16, separated into single sheets by the separation roller 17, conveyed to the registration roller 18, and temporarily stopped. The temporarily stopped recording material P is supplied to the secondary transfer nip by the registration roller 18 in synchronization with the timing when the four-color toner images formed on the intermediate transfer belt 14 reach the secondary transfer nip. Then, a secondary transfer voltage of about +1.5 kV to +3.5 kV is applied by the secondary transfer power supply 74, and the toner images on the intermediate transfer belt 14 are transferred onto the recording material P. In this embodiment, the secondary transfer voltage is set to +2.5 kV.

[0037] The recording material P onto which the toner image has been transferred is separated from the intermediate transfer belt 14 and sent to the fixing device 21. Then, it is heated and pressed by the fixing roller 21a and the pressure roller 21b, and the toner image is melted and fixed on the surface of the recording material P. The fixed recording material P is discharged onto the paper discharge tray 25 by the paper discharge roller pair 24.

[0038] In the primary transfer, the transfer residual toner remaining on the photosensitive drums 1Y, 1M, 1C, 1Bk without being transferred to the intermediate transfer belt 14 is removed by the cleaning blades 9Y, 9M, 9C, 9Bk.

[0039] In the secondary transfer, the transfer residual toner remaining on the intermediate transfer belt 14 without being transferred to the recording material P is removed at the cleaning nip, which is the contact portion between the edge portion of the cleaning blade 22 and the intermediate transfer belt 14, and collected in the waste toner container 28.

[0040] [Wide Color Gamut Image Formation Mode] The wide color gamut image forming mode as the second mode will be described. When changing the peripheral speed ratio Vd / Vdr, which is the ratio of the peripheral speed Vd of the developing roller 5 to the peripheral speed Vdr of the photosensitive drum 1, the result of measuring the toner loading amount per unit area developed on the photosensitive drum 1 is shown in the graph of FIG. 2. Here, the peripheral speed ratio Vd / Vdr is defined as the developing peripheral speed ratio. Also, hereinafter, "toner loading amount" will refer to "toner loading amount per unit area". Further, the "toner loading amount" used hereinafter is substantially the same on the photosensitive drum 1, on the intermediate transfer body 14, and on the recording material P. The potential setting of the photosensitive drum 1, the developing voltage, the toner charge amount, etc. are set as appropriate. In this embodiment, the developing contrast, which is the potential difference between the developing voltage and the highlight potential in the wide color gamut image forming mode, is set to 250 V. That is, the highlight potential Vl in the wide color gamut image forming mode is set to -50 V, and the developing contrast is made larger than the developing contrast in the normal image forming mode as the first mode. As a means of increasing the developing contrast, in this embodiment, the exposure amount by the exposure unit 11 is increased to cope with it. However, alternatively, the developing voltage may be changed or the charging voltage may be changed. As the developing peripheral speed ratio Vd / Vdr increases from 100%, the amount of toner developed (moved from the developing roller 5 and loaded on the photosensitive drum 1) on the photosensitive drum 1 increases, so the toner loading amount increases. And in the wide color gamut image forming mode, the toner loading amount is saturated at a peripheral speed ratio of about 280%.

[0041] FIG. 3 is a graph showing the relationship between the toner loading amount per unit area on the recording material P and the reflection density, which is measured after transferring and fixing the toner image developed on the photosensitive drum 1 onto the recording material P. The reflection density was measured using a reflection density measuring instrument model RD-918 manufactured by Macbeth. FIG. 3 shows an example of the M toner as an example among Y, M, C, and Bk. As the toner loading amount on the recording material P increases, the reflection density increases, and the reflection density is saturated when the toner loading amount on the recording material P is about 8E-03 [kg / m^2].

[0042] From the above results, in this embodiment, the normal image formation mode and the wide color gamut image formation mode were set as follows. As the normal image formation mode, for general office documents and the like, a reflection density of about 1.45 is sufficient. Therefore, the development peripheral speed ratio between the photosensitive drum 1 and the developing roller 5 was set to ΔV1 = 140%, and the maximum toner loading amount on the recording material P was set to about 4.0E-03 [kg / m^2] in monochrome. Hereinafter, the loading amount in the normal image formation mode is referred to as the first toner loading amount. As the wide color gamut image formation mode, the development peripheral speed ratio between the photosensitive drum 1 and the developing roller 5 was set to ΔV2 = 280%, and the maximum toner loading amount on the recording material P was set to about 8.0E-03 [kg / m^2] in monochrome. Hereinafter, the loading amount in the wide color gamut image formation mode is referred to as the second toner loading amount.

[0043] When the development peripheral speed ratio of the photosensitive drum 1 and the developing roller 5 in the normal image formation mode is 140%, as a means to increase the development peripheral speed ratio of the photosensitive drum 1 and the developing roller 5 in the wide color gamut image formation mode to 280%, the following was done. When the process speed in the normal image formation mode was set to 1 / 1 speed, in the wide color gamut image formation mode, the process speed was set to 1 / 2 speed, the peripheral speed (rotation speed) of the photosensitive drum 1 was set to half of that in the normal image formation mode, and the peripheral speed (rotation speed) of the developing roller 5 was set to the same as that in the normal image formation mode. For example, the peripheral speed of the developing roller 5 was fixed at 0.28 [m / s], and the peripheral speed of the photosensitive drum 1 was set to 0.2 [m / s] in the normal image formation mode and 0.1 [m / s] in the wide color gamut image formation mode. As a result, in the wide color gamut image formation mode compared to the normal image formation mode, the amount of toner developed from the toner coated on the developing roller 5 onto the photosensitive drum 1 increases. That is, by increasing the rotational peripheral speed ratio between the photosensitive drum 1 and the developing roller 5, the amount of toner supplied from the developing roller 5 per unit area of the photosensitive drum 1 increases. Due to these two effects, the amount of toner on the recording material P can be increased, enabling the printing of high-density and wide color gamut images.

[0044] Alternatively, the process speed may remain at 1 / 1 speed, and the circumferential speed (rotation speed) of the developing roller may be increased approximately twofold to increase the circumferential speed ratio between the photosensitive drum 1 and the developing roller 5 to 280%. In this case, the load on the drive motor 60, which is the drive source of the developing roller 5, increases, and it is necessary to increase the fixing ability by raising the fixing temperature, for example. However, the image formation time can be shortened with respect to a process speed of 1 / 2 speed. On the other hand, when the process speed is 1 / 2 speed, an excessive load is not applied to the drive motor 60 of the developing roller 5, and appropriate fixing can be achieved without raising the fixing temperature. Therefore, in this embodiment, a setting to lower the process speed is selected in the wide color gamut image formation mode. Of course, the circumferential speed of the developing roller 5 and the circumferential speed of the photosensitive drum 1 may be changed together to be set to the developing circumferential speed ratio as in this embodiment.

[0045] At this time, a transfer setting higher than the transfer voltage (transfer strength) required to transfer an image with the maximum toner loading amount in the normal image formation mode to the recording material P is required so that a wide color gamut image can be appropriately transferred to the recording material P for all image data. Therefore, the target current of the constant current control of the secondary transfer voltage for the wide color gamut image formation mode is set as transfer setting 1.

[0046] [Image formation operation] Hereinafter, the image formation operation of the image forming apparatus 500 of this embodiment will be described using the flowchart of FIG. 4.

[0047] First, print information is input from the host computer 503 to the image forming apparatus 500 together with an instruction of the print mode (normal image formation mode or wide color gamut image formation mode) by the start operation (S400) (S401). Then, the image processing unit 504 generates output image data corresponding to the print mode (S402) and sends it to the image analysis unit 43.

[0048] The image analysis unit 43 determines the printing mode (S403). If it is the normal image formation mode, it is directly sent to the image buffer 44, and image formation is performed in the normal image formation mode (S404). On the other hand, if it is the wide color gamut image formation mode, the image analysis unit 43 analyzes the configuration of the output image data (S405).

[0049] The output image data in this embodiment is configured as shown in FIG. 5. P(x, y) represents one pixel at the position coordinates (x, y) in the output image data, and P(x, y) is composed of the respective image data P_Y(x, y), P_M(x, y), P_Y(x, y), P_Bk(x, y) of Y, M, C, and Bk. In this embodiment, S(x, y) is provided as identification information representing the configuration of the pixel P(x, y).

[0050] In the image forming apparatus 500 of this embodiment, for each color, the toner loading amount is increased for 80% (CDh) or more of the output image data compared to the first toner loading amount so as to achieve the effect of the wide color gamut image formation mode. Therefore, a pixel in which there is one or more of the output image data of Y, M, C, and Bk of each pixel P(x, y) that is CDh (=205 dec) or more is determined as a wide color gamut image, and S(x, y) is set to 1 (identification number of the wide color gamut image).

[0051] On the other hand, as a result of the authors' study, it was found that compared with the high-tone-side image as the first pattern represented by the solid image, the halftone image as the second pattern on the low-tone side is more likely to generate an abnormal discharge image due to an increased transfer electric field. As a halftone image that is likely to generate an abnormal discharge image, the total number of pixels of each color of Y, M, C, and Bk is 1% or more and 40% or less (for example, Y: 0%, M: 20%, C: 20%, Bk: 0%). This is an image with a toner loading amount of about half or less of the first toner loading amount per color. Since 40% of the image data is 102dec, for pixels that satisfy P_Y(x,y)+P_M(x,y)+P_Y(x,y)+P_Bk(x,y)≦102dec, S(x,y) is set to 2 (the identification number of the halftone image that is likely to generate an abnormal discharge image). For pixels that are a combination of image data where S(x,y) does not correspond to 1 or 2, S(x,y) is set to 0 (the identification number of images other than the above). Therefore, in this embodiment, with 102dec as the boundary, 102dec or more is defined as high tone, and less than 102dec is defined as low tone. Among them, 205dec or more is defined as a wide color gamut image. For example, when a halftone image of 102dec or more is mixed in an area of 205dec or more, it goes without saying that the former is the high-tone pattern and the latter is the low-tone pattern. That is, when two image patterns with different tones are mixed, the configuration of this embodiment is very effective.

[0052] Perform the above operations on all pixels of the output image data (S406), and then calculate the following S, HT, and W (S407). S: The total number of pixels where S(x,y) is 1 HT: The total number of pixels where S(x,y) is 2 W: The total number of pixels where S(x,y) is 0 And then, HT / (W + S + HT) ≥ 0.3 ··· (Equation 1) S / (W + S + HT) ≤ 0.1 ··· (Equation 2) When the condition is satisfied, it is determined that a configuration exists in which a very small part of the output image data is a wide-color gamut image, and a halftone image, which is an image in which abnormal discharge images are likely to occur, exists with a certain area in the remaining area. Note that (W + S + HT) represents the total number of pixels in the output image data and corresponds to the area of the output image. In other words, the first ratio occupied by the halftone image with respect to one sheet of recording material P is 30% or more, and the second ratio occupied by the solid image with respect to one sheet of recording material P is 10% or less. That is, it is to determine whether the ratio of the solid image as an example of the first pattern is 10% or less with respect to the whole, and the ratio of the halftone image as the second pattern is 30% or more with respect to the whole. Also, depending on the conditions, the transfer control conditions may be determined from only Equation 1, or the transfer control conditions may be determined from only Equation 2.

[0053] Also, Equations 1 and 2 may be calculated from the ratio occupied by images other than the halftone image and the ratio occupied by images other than the solid image. In that case, it becomes as follows in Equations 3 and 4 below. (W + S) / (W + S + HT) ≤ 0.7 ··· (Equation 3) (W + HT) / (W + S + HT) ≥ 0.9 ··· (Equation 4) In the case of Equations 3 and 4, the third ratio occupied by areas other than the halftone image with respect to one sheet of recording material P is 70% or less, and the fourth ratio occupied by areas other than the solid image with respect to one sheet of recording material P is 90% or more. That is, it is to determine whether the ratio of areas other than the solid image as an example of the first pattern is 90% or more with respect to the whole, and the ratio of areas other than the halftone image as the second pattern is 70% or less with respect to the whole.

[0054] And at this time, the transfer setting 2 in which the transfer strength of the secondary transfer voltage is lower than the transfer setting 1 for the wide-color gamut image formation mode is selected (S408), and image formation is performed in the wide-color gamut image formation mode (S410).

[0055] The transfer setting 2 was determined through the following considerations. Assuming a recording material P of A4 size, an image data Y: 100%, M: 100% Red image and a halftone image with C: 40% as shown in Fig. 6(a) were prepared. Using the full-surface Y: 100%, M: 100% Red images (b) as shown in Fig. 6(a) and Fig. 6(b), the image was confirmed while changing the secondary transfer voltage setting (target current of constant current control) in the wide color gamut image formation mode under the environment of 15°C / 10%RH. For the halftone, a dither-processed image of about 166 lines was used. Here, Fig. 6(a) satisfies the relationships of Equation 1 and Equation 2, and Fig. 6(b) is an image that does not satisfy the relationships of Equation 1 and Equation 2.

[0056] The results were as shown in Table 1. The target current and the average voltage indicate the amount of decrease from Ref (transfer setting 1). That is, the target current of setting a was 15.5 μA, and the average transfer voltage at this time was +2.7 kV.

[0057] The image was confirmed by the level of abnormal discharge images generated in the halftone image (HT) part for each target current and the color difference (ΔE) between the □30 Red and full-surface Red images at each target current with respect to transfer setting 1. Each Red image was measured under the measurement illumination condition M2 using eXact of X-Rite, and the CIE (International Commission on Illumination)-defined L*a*b* (CIE / L*a*b*) was output under the condition of D50 light source and 2-degree field of view, and ΔE was obtained using the CIE1976 color difference calculation formula.

[0058]

Table 1

[0059] By lowering the target current, the generation of abnormal discharge images disappears, but if it is lowered too much, the color difference of the Red image becomes large. That is, the color tone changes. However, the change in the color difference of □30 Red was gentler compared to the full-surface Red. This tendency could be confirmed until S / (W+S+HT) reached 0.1, and since the change in the color difference was small from exceeding 0.1 to about 0.2, the numerical value of Equation (2) could be set to 0.2.

[0060] In this embodiment, the target current for constant current control is set to setting c, which reduces the current by 3 μA from transfer setting 1 for the normal wide color gamut image formation mode, based on the occurrence status of abnormal discharge images and the degree of change in the color difference of □30Red. This condition is regarded as transfer setting 2. At this time, the average voltage (transfer intensity) of the transfer voltage decreased by about 600 V. In this embodiment, the transfer current is described, and although the transfer setting of the secondary transfer voltage was the target current for constant current control, it may also be the target voltage for constant voltage control.

[0061] On the other hand, for images that do not satisfy the conditions of Equation 1 and Equation 2, transfer setting 1 is selected (S409), and image formation is performed in the wide color gamut image formation mode (S410).

[0062] If S is 0 in S407, it means there is no data for the wide color gamut image, so transfer setting 3 as setting d in Table 1 can also be selected. The conditions of this transfer setting 3 are settings higher than the transfer setting in the normal image formation mode as the first mode, and it is preferably a setting with a weaker transfer intensity than transfer setting 2. This case is considered to occur when the user has selected the high color gamut image formation mode once, but there are normal images mixed in the subsequent continuous jobs described later. In that case, by providing transfer setting 3, it becomes possible for users who have selected the high color gamut image formation mode to output both normal images and high color gamut images suitably. In this embodiment, the target current at transfer setting 3 is 12.5 μA, and the average transfer voltage at this time is +2.25 kV. Note that for the transfer setting in the normal image formation mode, since the process speed is 1 / 1 speed, the target current is 20.5 μA, and the average transfer voltage at this time is +2.5 kV.

[0063] After image formation is performed in the normal image formation mode (S404) or image formation is performed in the wide color gamut image formation mode (S410), it is checked whether there is a subsequent job (S411). If there is a subsequent job, the process returns to S403 again to determine whether that job is specified for the wide color gamut image formation mode. If there is no subsequent job, the image formation operation is terminated (S412).

[0064] In S403, it is determined whether the user himself / herself has selected the wide color gamut image forming mode, but it may be controlled to automatically perform switching discrimination from the image pattern. That is, when continuously forming an image on the recording material P, the user may select the mode one by one, or the mode may be automatically selected according to the image. For example, in the case of a user who forms images on the recording material P continuously for two sheets, if the first sheet is a high color gamut image and the second sheet is a normal image, the control may be switched in units of one sheet. Also, if both the first sheet and the second sheet are high color gamut images, and the first sheet satisfies the conditions of S407, transfer setting 2 is selected, and if the second sheet does not satisfy S407, transfer setting 1 is selected. In this embodiment, it is desirable to switch the control for each sheet of the recording material P so as not to cause disadvantage to the user.

[0065] In the conventional wide color gamut image forming mode, the secondary transfer voltage was set so that the toner image could be appropriately transferred even when the area of the image in which a plurality of colors exceeded the first toner loading amount corresponded to the entire surface of the recording material P (transfer setting 1 in this embodiment). However, in the wide color gamut image forming mode, as the area of the region of the image exceeding the first toner loading amount becomes smaller, an excessive secondary transfer voltage is applied to the region of the image below the first toner loading amount. Furthermore, when the region of the image below the first toner loading amount becomes a halftone image with a small toner loading amount, the secondary transfer voltage becomes excessive and abnormal discharge images are likely to occur.

[0066] Therefore, by setting the secondary transfer voltage as described above, it becomes possible to output a wide color gamut image without generating abnormal discharge images regardless of the configuration of the output image data.

[0067] The configuration of Example 1 has the following characteristics.

[0068] In an image forming apparatus 500 capable of performing an image forming operation for forming an image on a recording material P, there is a photosensitive drum 1 as a rotatable photosensitive drum 1. An exposure unit 11 is provided on the surface of the photosensitive drum 1 for forming an electrostatic latent image based on output image data. There is a developing roller 5 as a rotatable developer carrier for supplying toner 3 as a developer to the surface of the photosensitive drum 1 to develop the electrostatic latent image formed on the surface of the photosensitive drum 1 and form a toner image. An intermediate transfer member 14 is provided in contact with the surface of the photosensitive drum 1 to form a transfer portion, and the toner image formed on the surface of the photosensitive drum 1 is transferred at the transfer portion. There is a secondary transfer roller 20 as a secondary transfer member for transferring the toner image transferred to the surface of the intermediate transfer member 14 to the recording material. It has a drive unit 60 for driving the photosensitive drum 1 and the developing roller 5, a secondary transfer voltage applying unit 74 for applying a secondary transfer voltage to the secondary transfer roller 20, and an image analysis unit 43 which is an acquisition unit for acquiring information regarding output image data. It has a control unit 502 for controlling the drive unit 60 and the secondary transfer voltage applying unit 74.

[0069] The control unit 502 is controllable to execute a first mode which is a normal image forming mode in which the developing roller 5 rotates with respect to the photosensitive drum 1 at a first peripheral speed ratio. Also, it is controllable to execute a second mode which is a wide color gamut image forming mode in which the developing roller 5 rotates with respect to the photosensitive drum 1 at a second peripheral speed ratio greater than the first peripheral speed ratio. When the image forming operation is performed in the second mode, the control unit 502 controls as follows. i) When it is acquired by the image analysis unit 43 that the output image data is composed only of a first pattern composed of first gradations, it controls to apply a first transfer voltage in order to transfer a toner image composed of the first pattern to the recording material P. ii) When it is acquired that it is composed of the first pattern and a second pattern composed of second gradations having a lower density than the first gradations, it controls to apply a second transfer voltage having an absolute value smaller than that of the first transfer voltage.

[0070] The first transfer voltage and the second transfer voltage are voltages having polarities opposite to the normal charging polarity of the toner 3.

[0071] Also, of course, control may be performed based on the transfer current instead of the control based on the transfer voltage. That is, iii) When it is acquired by the image analysis unit 43 that the output image data is composed only of a first pattern composed of a first gradation, control is performed so that a first transfer current flows to transfer a toner image composed of the first pattern to the recording material P. iv) When it is acquired that the image is composed of a first pattern and a second pattern composed of a second gradation having a lower density than the first gradation, control is performed so that a second transfer current having an absolute value smaller than that of the first transfer current flows.

[0072] Also, when the image forming operation is executed in the second mode and two recording materials are continuously output, the control unit 502 performs control as follows. v) When the first output image data on one of the two recording materials P, the first recording material P, is composed only of a first pattern composed of a first gradation, control is performed to apply a first transfer voltage when transferring a toner image composed of the first pattern to the first recording material P. vi) When the second output image data on the other second recording material P is composed of a first pattern and a second pattern composed of a second gradation having a lower density than the first gradation, control is performed to apply a second transfer voltage having an absolute value smaller than that of the first transfer voltage.

[0073] Typically, the first pattern is a solid image, and the second pattern is a halftone image. When the ratio of the first pattern to one sheet of the recording material P in the output image data exceeds the first ratio, the control unit 502 performs control to apply the first transfer voltage. When the ratio of the second pattern to one sheet of the recording material P in the output image data is less than the second ratio, the control unit 502 performs control to apply the first transfer voltage. In the present embodiment, for example, the first ratio is 30%, and the second ratio is 10%.

[0074] Further, when the ratio of the area of the region where the toner loading amount exceeds a predetermined amount to the area of the output image data is equal to or greater than a predetermined value among the output image data, the control unit 502 may control so that the first transfer voltage is applied. When the ratio is equal to or less than the predetermined value for the output image data, the control unit 502 may control so that the second transfer voltage is applied.

[0075] By having the configuration and features as described above, it becomes possible to reproduce a suitable color tone in the wide color gamut image forming mode.

[0076] 〔Example 2〕 Hereinafter, the image forming apparatus according to Example 2 will be described. Note that components and operations similar to those in Example 1 are denoted by the same reference numerals and description thereof will be omitted.

[0077] Abnormal discharge images are likely to occur when the secondary transfer voltage becomes high. That is, they are likely to occur in a low humidity environment where the resistance of the recording material and various members increases. On the other hand, they are less likely to occur in a high humidity environment where the intensity of the secondary transfer voltage is low.

[0078] Therefore, in this embodiment, the absolute moisture content is used to determine the implementation of setting the secondary transfer voltage in the wide color gamut image forming mode.

[0079] That is, the environment where the image forming apparatus 500 is installed is determined using the environmental sensor 36 shown in FIG. 1. The determination is made based on the absolute moisture content calculated using the temperature information and the relative humidity information, and when it is 0.002 [kg / kg'] or less, the implementation of setting the secondary transfer voltage in the wide color gamut image forming mode is determined. The implementation of setting the secondary transfer voltage may be determined from only the temperature information or only the relative humidity information. That is, when the temperature or humidity detected by the environmental sensor 36 as the detection unit crosses a threshold value, the control unit 502 may control as follows. When the output image data is a first pattern composed of a first gradation and a second pattern composed of a second gradation having a lower density than the first gradation, the second transfer voltage is applied.

[0080] As a result, it is possible to set an appropriate secondary transfer voltage only for an environment in which abnormal discharge images are likely to occur.

[0081] [Others] As described above, the present invention has been described with reference to specific embodiments, but the present invention is not limited to the above-described embodiments.

[0082] In the above-described embodiment, the photoreceptor is not limited to a drum-shaped member, and may be a belt-shaped member or the like.

[0083] Also, the primary transfer member is not limited to a roller shape, and may be a brush-shaped member, a sheet-shaped member, or the like.

[0084] In addition, dimensions, materials, shapes, relative arrangements, etc. of the components described in the above embodiments should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. That is, the scope of the present invention is not intended to be limited to the above-described embodiments.

[0085] Vdr, Vd, ΔV1, and ΔV2 can be other than those described above according to the actual situation of the image forming apparatus 500.

[0086] The numerical values used in Formula 1 and Formula 2 may be other than these according to the actual situation of the image forming apparatus 500.

[0087] In addition, although a configuration in which a toner image is transferred to the surface of the belt once, such as the intermediate transfer belt 14, is adopted, a configuration in which a recording material conveyance belt is adopted and transferred to the recording material P conveyed from the photosensitive drum 1 to the recording material conveyance belt may also be used.

[0088] The disclosure of the embodiments of the present invention includes the following configurations.

[0089] (Configuration 1) In an image forming apparatus capable of executing an image forming operation for forming an image on a recording material, a rotatable image carrier, and An exposure unit that forms an electrostatic latent image on the surface of the image carrier based on output image data; A rotatable developer carrier that supplies a developer to the surface of the image carrier and develops the electrostatic latent image formed on the surface of the image carrier to form a toner image; An intermediate transfer member that forms a transfer portion in contact with the surface of the image carrier and transfers the toner image formed on the surface of the image carrier in the transfer portion; A transfer member that transfers the toner image transferred to the surface of the intermediate transfer member to a recording material; A drive unit that drives the image carrier and the developer carrier; A transfer voltage application unit that applies a transfer voltage to the transfer member; An acquisition unit that acquires information regarding the output image data; A control unit that controls the drive unit and the transfer voltage application unit, the image forming apparatus comprising: The control unit is capable of controlling to execute a first mode in which the developer carrier rotates at a first peripheral speed ratio with respect to the image carrier, and a second mode in which the developer carrier rotates at a second peripheral speed ratio greater than the first peripheral speed ratio with respect to the image carrier. When the image forming operation is executed in the second mode, i) When it is acquired by the acquisition unit that the output image data is composed only of a first pattern composed of a first gradation, control is performed to apply a first transfer voltage in order to transfer the toner image composed of the first pattern to a recording material; ii) When it is acquired by the acquisition unit that the output image data is composed of the first pattern and a second pattern composed of a second gradation having a lower density than the first gradation, control is performed to apply a second transfer voltage having an absolute value smaller than that of the first transfer voltage in order to transfer the toner image composed of the first pattern and the second pattern to a recording material. An image forming apparatus characterized by the above.

[0090] (Configuration 2) In an image forming apparatus capable of executing an image forming operation for forming an image on a recording material, A rotatable image carrier; An exposure unit that forms an electrostatic latent image on the surface of the image carrier based on output image data; A rotatable developer carrier that supplies a developer to the surface of the image carrier and develops the electrostatic latent image formed on the surface of the image carrier to form a toner image; An intermediate transfer member that forms a transfer portion in contact with the surface of the image carrier and transfers the toner image formed on the surface of the image carrier in the transfer portion; A transfer member that transfers the toner image transferred to the surface of the intermediate transfer member to a recording material; A drive unit that drives the image carrier and the developer carrier; A transfer voltage application unit that applies a transfer voltage to the transfer member; A control unit that controls the drive unit and the transfer voltage application unit; The control unit is capable of controlling to execute a first mode in which the developer carrier rotates at a first peripheral speed ratio with respect to the image carrier and a second mode in which the developer carrier rotates at a second peripheral speed ratio greater than the first peripheral speed ratio with respect to the image carrier. When the image forming operation is executed in the second mode and two sheets of recording materials are continuously output, i) When the first output image data on one of the two sheets of recording materials, the first recording material, is composed only of a first pattern composed of a first gradation, and the toner image composed of the first pattern is transferred to the first recording material, control is performed to apply a first transfer voltage; ii) When the second output image data on the other of the two sheets of recording materials, the second recording material, is composed of the first pattern and a second pattern composed of a second gradation having a lower density than the first gradation, and the toner image composed of the first pattern and the second pattern is transferred to the second recording material, control is performed to apply a second transfer voltage having an absolute value smaller than that of the first transfer voltage. An image forming apparatus characterized by this.

[0091] (Configuration 3) The image forming apparatus according to Configuration 1 or 2, characterized in that the first pattern is a solid image and the second pattern is a halftone image.

[0092] (Configuration 4) The control unit controls to apply the first transfer voltage when the ratio of the first pattern to the recording material in one sheet of the recording material exceeds a first ratio in the output image data, according to the image forming apparatus described in Configuration 1.

[0093] (Configuration 5) The control unit controls to apply the first transfer voltage when the ratio of the second pattern to the recording material in one sheet of the recording material is less than a second ratio in the output image data, according to the image forming apparatus described in Configuration 1 or 4.

[0094] (Configuration 6) The first ratio is 30%, according to the image forming apparatus described in Configuration 4.

[0095] (Configuration 7) The second ratio is 10%, according to the image forming apparatus described in Configuration 5.

[0096] (Configuration 8) Having a detection unit that detects at least one of temperature and humidity, When the control unit executes an image forming operation in the second mode, when the temperature or the humidity detected by the detection unit crosses a threshold value, and when it is acquired that the output image data is composed of the first pattern composed of the first gradation and the second pattern composed of a second gradation having a lower density than the first gradation, the control unit controls to apply the second transfer voltage to transfer the toner image composed of the first pattern and the second pattern to the recording material, according to the image forming apparatus described in Configuration 1.

[0097] (Configuration 9) The control unit controls the first transfer voltage and the second transfer voltage to be voltages having polarities opposite to the normal charging polarity of the developer, according to the image forming apparatus described in Configuration 1 or 2.

[0098] (Configuration 10) The image forming apparatus according to Configuration 1 or 2, characterized in that the amount of toner loaded on the recording material per unit area in the first pattern is larger than the amount of toner loaded on the recording material per unit area in the second pattern.

[0099] (Configuration 11) The control unit controls such that when the ratio of the area of the region where the amount of toner loaded exceeds a predetermined amount to the area of the output image data among the output image data becomes a predetermined value or more, the first transfer voltage is applied, and when the output image data has the ratio below the predetermined value, the second transfer voltage is applied. The image forming apparatus according to Configuration 10.

Explanation of Signs

[0100] 1 Photosensitive drum 2 Charging roller 5 Developing roller 11 Exposure device 14 Intermediate transfer belt 20 Secondary transfer roller 60 Driving unit 74 Secondary transfer power supply 500 Image forming apparatus 502 Control unit

Claims

1. In an image forming apparatus capable of performing an image forming operation for forming an image on a recording material, a rotatable image carrier; an exposure unit that forms an electrostatic latent image on the surface of the image carrier based on output image data; a rotatable developer carrier that supplies a developer to the surface of the image carrier and develops the electrostatic latent image formed on the surface of the image carrier to form a toner image; an intermediate transfer body that forms a transfer portion in contact with the surface of the image carrier and transfers the toner image formed on the surface of the image carrier in the transfer portion; a transfer member that transfers the toner image transferred to the surface of the intermediate transfer body to the recording material; a driving unit that drives the image carrier and the developer carrier; a transfer voltage applying unit that applies a transfer voltage to the transfer member; an acquisition unit that acquires information regarding the output image data; a control unit that controls the driving unit and the transfer voltage applying unit, wherein the control unit is capable of controlling to execute a first mode in which the developer carrier rotates at a first peripheral speed ratio with respect to the image carrier and a second mode in which the developer carrier rotates at a second peripheral speed ratio greater than the first peripheral speed ratio with respect to the image carrier, and when the image forming operation is executed in the second mode, i) when it is acquired by the acquisition unit that the output image data is composed only of a first pattern composed of a first gradation, controls to apply a first transfer voltage to transfer the toner image composed of the first pattern to the recording material; ii) when it is acquired by the acquisition unit that the output image data is composed of the first pattern and a second pattern composed of a second gradation having a lower density than the first gradation, controls to apply a second transfer voltage having an absolute value smaller than that of the first transfer voltage to transfer the toner image composed of the first pattern and the second pattern to the recording material. An image forming apparatus characterized by this.

2. In an image forming apparatus capable of performing an image forming operation for forming an image on a recording material, a rotatable image carrier; an exposure unit that forms an electrostatic latent image on the surface of the image carrier based on output image data; a rotatable developer carrier that supplies a developer to the surface of the image carrier and develops the electrostatic latent image formed on the surface of the image carrier to form a toner image; An intermediate transfer member that forms a transfer portion in contact with the surface of the image carrier and transfers the toner image formed on the surface of the image carrier in the transfer portion; A transfer member that transfers the toner image transferred onto the surface of the intermediate transfer member to a recording material; A driving unit that drives the image carrier and the developer carrier; A transfer voltage applying unit that applies a transfer voltage to the transfer member; A control unit that controls the driving unit and the transfer voltage applying unit; The control unit is controllable to execute a first mode in which the developer carrier rotates at a first peripheral speed ratio with respect to the image carrier, and a second mode in which the developer carrier rotates at a second peripheral speed ratio greater than the first peripheral speed ratio with respect to the image carrier. When the image forming operation is executed in the second mode and two sheets of recording materials are continuously output, i) When the first output image data on one of the two sheets of recording materials, the first recording material, is composed only of a first pattern composed of a first gradation, and the toner image composed of the first pattern is transferred to the first recording material, control is performed to apply a first transfer voltage. ii) When the second output image data on the other of the two sheets of recording materials, the second recording material, is composed of the first pattern and a second pattern composed of a second gradation having a lower density than the first gradation, and the toner image composed of the first pattern and the second pattern is transferred to the second recording material, control is performed to apply a second transfer voltage having an absolute value smaller than that of the first transfer voltage. An image forming apparatus characterized by this.

3. The image forming apparatus according to claim 1 or 2, wherein the first pattern is a solid image and the second pattern is a halftone image.

4. The control unit is configured to control to apply the first transfer voltage when the ratio of the first pattern to the one sheet of recording material in the output image data exceeds a first ratio. The image forming apparatus according to claim 1.

5. The control unit is configured to control to apply the first transfer voltage when the ratio of the second pattern to the one sheet of recording material in the output image data is less than a second ratio. The image forming apparatus according to claim 1 or 4.

6. The image forming apparatus according to claim 4, wherein the first ratio is 30%.

7. The image forming apparatus according to claim 5, wherein the second ratio is 10%.

8. comprising a detection unit that detects at least one of temperature and humidity, when the control unit executes an image forming operation in the second mode, when the temperature or the humidity detected by the detection unit crosses a threshold value, and when the acquisition unit acquires that the output image data is composed of the first pattern composed of the first gradation and the second pattern composed of a second gradation having a lower density than the first gradation, the control unit controls to apply the second transfer voltage to transfer the toner image composed of the first pattern and the second pattern to a recording material. The image forming apparatus according to claim 1, characterized in that.

9. The image forming apparatus according to claim 1 or 2, wherein the control unit controls the first transfer voltage and the second transfer voltage to be voltages having polarities opposite to the normal charging polarity of the developer.

10. The image forming apparatus according to claim 1 or 2, wherein the amount of toner loaded on the recording material per unit area in the first pattern is larger than the amount of toner loaded on the recording material per unit area in the second pattern.

11. When the ratio of the area of the region where the amount of toner loaded in the output image data exceeds a predetermined amount to the area of the output image data becomes a predetermined value or more, the control unit applies the first transfer voltage, and when the ratio is less than the predetermined value for the output image data, the control unit controls to apply the second transfer voltage. The image forming apparatus according to claim 10, characterized in that.

Images