JP2008158050A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that if a quantity of toner attached to the surface of a recording material is decreased, the color reproducibility of a high density area decreases. <P>SOLUTION: The image forming apparatus independently incorporates developing means using toners of the identical color hue but of different quantities of coloring material contained in the toners and hence different color densities. The image forming apparatus has a first image formation mode in which images are formed using only the developing device having the toner of the lowest concentration among the developing means, and a second image formation mode in which images are formed using only the developing device having the highest density toner among the developing means. The speed of the image formation in the second image formation mode is higher than that in the first image formation mode. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile machine that forms an image on a recording material by using an electrophotographic system or an electrostatic recording system and outputs an image formed product.

  An example of a conventional full-color image forming apparatus will be described with reference to FIG. This image forming apparatus is a full-color laser beam printer of an electrophotographic system or an intermediate transfer belt system.

  Reference numeral 101 denotes an electrophotographic photosensitive member (photosensitive drum) as an image carrier, which is driven to rotate at a predetermined speed in the counterclockwise direction of an arrow. Around the photosensitive drum 101, a pre-exposure lamp 102, a corona charger (charging means) 103, and an exposure means 104 that is a laser exposure optical system are arranged. In addition, a potential sensor 105, a movable body (development rotary) 106 that is a rotary developer holding unit, an intermediate transfer belt device 107, and a photosensitive drum cleaner 108 are disposed.

  The developing rotary 106 is equipped with four color toner developing devices, a magenta toner developing device 106M, a cyan toner developing device 106C, a yellow toner developing device 106Y, and a black toner developing device 106K. Then, by sequentially controlling the rotation of the rotary developing device holding unit 106, the developing device that operates to face the photosensitive drum 101 is sequentially switched.

  The intermediate transfer belt device 107 uses a flexible endless belt-shaped intermediate transfer belt 107a as an intermediate transfer member. The intermediate transfer belt 107a is suspended by four first to fourth parallel belt suspension rollers 107b to 107e suspended. A primary transfer roller 107f is disposed inside the intermediate transfer belt 107a and presses the photosensitive drum 101 with the intermediate transfer belt 107a interposed therebetween. The secondary transfer roller 107g presses the fourth belt suspension roller 107e with the intermediate transfer belt 107a interposed therebetween. In addition, a cleaning device 107h is provided in contact with the first belt suspension roller 107b with the intermediate transfer belt 107a interposed therebetween.

  The first belt suspension roller 107b is a drive roller, and rotates the intermediate transfer belt 107a in a clockwise direction indicated by an arrow at a predetermined speed. The second belt suspension roller 107c is a driven roller, the third belt suspension roller 107d is a tension roller, and the fourth belt suspension roller 107e is a roller facing the secondary transfer roller.

  The secondary transfer roller 107g and the cleaning device 107h can be retracted with respect to the intermediate transfer belt 107a.

  In the exposure unit 104, the input image signal is converted into an image signal of 0 to 255 (FFh) level for each color of CMYK by an image processor (not shown). The image signal is converted into an optical signal by the laser output unit, and the laser beam converted into the optical signal is reflected by the polygon mirror, and is irradiated onto the surface of the photosensitive drum 101 through the lens and the reflecting mirror.

  At the time of image formation, the photosensitive drum 101 is rotated, and the photosensitive drum 101 after being neutralized by the pre-exposure lamp 102 is uniformly charged by the charger 103. Then, the exposure unit 104 performs exposure E corresponding to each color to form an electrostatic latent image on the photosensitive drum 101.

  Next, the developing rotary 106 is rotated to move predetermined developing units 106M, 106C, 106Y, and 106K to the developing unit. Then, a bias is applied to the developing device to reversely develop the electrostatic latent image on the photosensitive drum 101 to form a developer image (toner image) using a resin and a pigment as a base on the photosensitive drum 101.

  The toner image on the photosensitive drum 101 is transferred to the intermediate transfer belt 107a by applying a primary transfer bias to the primary transfer roller 107f. The transfer residual toner on the surface of the photosensitive drum 101 is removed by the cleaning device 108.

  In the case of a full color image, four toner images of a magenta toner image, a cyan toner image, a yellow toner image, and a black toner image are sequentially superimposed on the intermediate transfer belt 107a to form a full color toner image.

  On the other hand, the secondary transfer roller 107g is moved at a predetermined control timing so as to contact the fourth belt suspension roller 107e with the intermediate transfer belt 107a interposed therebetween, thereby forming a secondary transfer portion T2. The recording material is conveyed to the secondary transfer portion T2, and a transfer bias is applied to the secondary transfer roller 107g, whereby the full color toner image on the intermediate transfer belt 107a is transferred to the recording material P.

  Then, the recording material onto which the toner image has been transferred is conveyed to the fixing device 109, and the toner image is fixed on the recording material.

The transfer residual toner on the intermediate transfer belt 107a after the transfer material is separated is cleaned by the cleaning device 107h.
In fixing a full-color toner image, the amount of applied toner and productivity are greatly related. For example, as in Japanese Patent Application Laid-Open No. H11-260260, when the toner application amount is small because the toner application amount on the recording material in the case of a six-color image is smaller than the toner application amount on the recording material in the case of a four-color image. It is described that productivity can be increased.

In order to increase the productivity of a four-color image, a configuration such as that of Patent Document 2 can be given. An image decimation unit is provided that thins out the repetition cycle of image formation in the main scanning direction when the conveyance speed of the paper conveyance unit is increased by the sub operation speed switching unit. In this way, the amount of applied toner on the recording material is reduced.
JP-A-2005-003925 JP 05-221025 A

  However, as disclosed in Patent Document 2, if the amount of applied toner on the recording material is reduced in order to increase productivity, there arises a problem that the maximum density that can be output is reduced by the amount of reduction of the amount of applied toner. Therefore, there is a demand for an image forming apparatus that can increase the productivity by reducing the amount of toner on the recording material without reducing the maximum density.

  As means for solving the above problems, at least one image carrier, a first image forming mode for forming an image on a recording material with only four color toners of yellow, magenta, cyan and black, yellow, magenta and cyan At least one of the black colors uses a toner having the same hue and density as the color used in the first image forming mode, and an image on the recording material with only four color toners. A maximum image amount formed in the second image formation mode is smaller than a maximum image amount formed in the first image formation mode. The maximum density of the image formed in the second image forming mode is substantially the same as the maximum density of the image formed in the first image forming mode. Forming the number may be greater than the image formation per unit time first image formation mode.

  According to the present invention, productivity can be increased without reducing the concentration in the high concentration region.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings. Note that the dimensions, materials, shapes, relative positions, and the like of the components of the image forming apparatus are not intended to limit the scope of the present invention only to those unless otherwise specified.

[Example 1]
FIG. 1 is a schematic sectional view of a full-color image forming apparatus according to an embodiment of the present invention. This example includes a reader unit 300 that is an image reading unit in the upper part and a printer unit 100 that is an image forming unit in the lower part.

  In the reader unit 300, the original 230 on the original platen glass 231 is exposed and scanned by an optical moving system 232 including an exposure lamp and a mirror. Then, the reflected light image is condensed on the full color CCD sensor 234 by the lens 232 to obtain a color separation image signal. The color-separated image signal is processed by a video processing unit (not shown) through an amplification circuit (not shown) and sent to the control unit of the printer unit 100 via an image memory (not shown).

  In addition to the signal from the reader unit 300, the image signal from the computer and the image signal from the FAX are input to the control unit of the printer unit 100.

  Next, the printer unit 100 will be described. FIG. 2 is an enlarged view of the printer unit 100.

  The printer unit 100 according to the present embodiment is roughly provided with two image forming units. That is, the first image forming unit Sa including the first photosensitive drum 1 a and the second image forming unit Sb including the second photosensitive drum 1 b are arranged with respect to the intermediate transfer belt (intermediate transfer member) device 57. Yes. The first and second image forming portions Sa and Sb have substantially the same configuration (shape). Specifically, the photosensitive drum and the cleaning device have the same configuration.

  The two photosensitive drums as the image carrier, that is, the first photosensitive drum 1a and the second photosensitive drum 1b are each rotatable in the direction of the arrow in FIG. Around each of the photosensitive drums 1a and 1b, pre-exposure lamps 11a and 11b, corona chargers (charging means) 2a and 2b, a first laser exposure optical system 3a and a second laser exposure optical system 3b which are exposure means. Is provided. Further, potential sensors 12a and 12b for detecting the potential on the photosensitive drum are provided. Further, four developing devices (developing means) 41 to 44 and 45 to 48, each containing developer of different colors, are accommodated in the developing rotary. Further, primary transfer rollers 5a and 5b, which are primary transfer units, and cleaning units 6a and 6b are arranged.

  Each of the developing devices 41 to 44 is filled with magenta, cyan, yellow, and black toners having a lower density, and each of the developing devices 45 to 48 is filled with magenta, cyan, yellow, and black toners having a higher density. Has been.

  Here, the low density toner and the high density toner are prepared by changing the content of the pigment having the same spectral characteristics. That is, toners having the same hue and different densities are obtained.

In Example 1, each color toner having a lower density has a reflection density of 1.6 when the density per unit area on the paper is 0.55 [mg / cm ² ]. Further, each color toner having a higher density has a reflection density of 1.6 when the density per unit area on the paper is 0.30 [mg / cm ² ]. At this time, the colorant content of each color toner having a higher density is about twice that of the toner having a lower density. Hereinafter, the toner having the lower density is referred to as “normal toner”, and the toner having the higher density is referred to as “dark toner”.

  In this embodiment, the developing devices 41 to 48 are filled with the two-component developer used by mixing the toner and the carrier, but there is no problem even with the one-component developer composed only of the toner.

  In the laser exposure optical systems 3a and 3b, the image signal from the reader unit 300 reflects the laser beam E from a laser output unit (not shown) by the polygon mirror 235. Then, the photosensitive drums 1a and 1b charged by the charger are irradiated through an optical system including a lens 236 and a reflection mirror 237.

  A voltage is applied to the sleeve (toner carrying member) of the developing means based on the electrostatic latent image formed by exposure, and a developer image (toner image) having a resin and a pigment as a base on the photosensitive drums 1a and 1b. ) Is formed.

  Further, as shown in FIG. 1, the toner in the developing devices 41 to 48 is kept at a predetermined timing so as to keep the toner ratio from the toner storage portions (hoppers) 61 to 68 for the respective colors to the carrier in the developing device constant. To be replenished from time to time.

  The intermediate transfer belt device 57 uses a flexible endless belt-shaped intermediate transfer belt 5 as an intermediate transfer member. The intermediate transfer belt 5 is stretched around four first to fourth parallel belt suspension rollers 51 to 54. The primary transfer rollers 5a and 5b are disposed inside the intermediate transfer belt 5 and press the photosensitive drums 1a and 1b with the intermediate transfer belt interposed therebetween. Further, the secondary transfer roller 55 presses against the fourth belt suspension roller 54 with the intermediate transfer belt 5 interposed therebetween. The belt cleaning device 50 presses the first belt suspension roller 51 with the intermediate transfer belt 5 interposed therebetween. The intermediate transfer belt 5 is driven to rotate at a predetermined speed in the direction of the arrow by the driving force of the first belt suspension roller 51 as a driving roller. The second roller 52 is a driven roller, the third roller 53 is a tension roller, and the fourth roller 54 is a secondary transfer counter roller. The secondary transfer roller 55 is in contact with the secondary transfer counter roller 54 that is the fourth roller with the intermediate transfer belt 5 interposed therebetween to form a secondary transfer portion T2.

  The toner images formed on the respective photosensitive drums 1a and 1b of the first and second image forming portions Sa and Sb are transferred onto the intermediate transfer belt 5 by the primary transfer rollers 5a and 5b at the primary transfer portions T1a and T1b. The primary transfer is sequentially performed so that the images are formed in an overlapping manner. At this time, a primary transfer bias is applied to the primary transfer rollers 5a and 5b. As a result, the respective toner images are sequentially superimposed on the intermediate transfer belt 5 to form a full color toner image.

  Thereafter, the toner image on the intermediate transfer belt 5 is secondarily transferred to the recording material at the secondary transfer portion T2 by applying a voltage to the secondary transfer roller.

  In addition, a sensor 56 that detects the positional deviation and density of the images transferred from the respective drums 1 a and 1 b is disposed so as to face the driven roller 52. The sensor 56 controls the first and second image forming units Sa and Sb to correct the image density, the toner supply amount, the image writing timing, the image writing start position, and the like as needed.

  Further, the transfer cleaning device 50 facing the drive roller 51 starts to contact so as to press the drive roller 51 via the intermediate transfer belt 5 after transfer to the recording material. The transfer cleaning device 50 cleans residual toner on the intermediate transfer belt 5 after being transferred to the transfer material P. After cleaning, the transfer cleaning device 50 is separated from the intermediate transfer belt 5 in preparation for the next image formation.

  On the other hand, the recording material P is conveyed one by one from the first to third storage units 71, 72, 73 or the manual feed tray 74 by the respective paper feeding means 81, 82, 83, 84. Then, the skew is corrected by the registration roller 85, and the secondary transfer roller 55 and the intermediate transfer belt 5 which are secondary transfer means for transferring the toner image on the intermediate transfer belt 5 to the transfer material at a desired timing. In the meantime, it is conveyed to the secondary transfer portion T2.

  The recording material P onto which the toner image has been transferred at the secondary transfer portion T2 passes through the conveyance portion 86, and the toner image is fixed to the recording material by heat at the heat roller fixing device 9. Thereafter, the recording material P is discharged to a paper discharge tray 89 or a paper post-processing device (not shown).

  When images are formed on both surfaces of the transfer material, the recording material P passes through the fixing device 9 and then the conveyance path switching guide 91 is driven. The recording material is conveyed to the reverse path 76 via the conveyance vertical path 75. The Then, by reverse rotation of the reversing roller 87, the rear end at the time of feeding is set at the top, the sheet is moved away from the feeding direction, and is sent to the duplex conveyance path 77. After that, the paper passes through the double-sided conveyance path, skew correction and timing are performed by the double-sided conveyance roller 88, and are conveyed to the registration roller 85 at a desired timing, and an image is formed on the other side again by the image forming process described above. The

  The image forming apparatus includes two image forming modes, a “normal speed image forming mode” (= first image forming mode) and a “high speed image forming mode” (= second image forming mode). At the time of normal image formation, the normal speed image formation mode is set, and the high speed image formation mode can be changed by the operation of the operator. In other words, the high-speed image forming mode is effective when it is desired to output as many high density images as possible in a short time.

  FIG. 3 shows a flowchart of mode control. When the image forming signal is input and the image forming is started (S1), the control unit determines which of the above-described image forming modes (S2). When the “normal speed image forming mode” is selected in step S2 (S3), only the first image forming unit Sa using the normal toner among the first and second image forming units Sa and Sb is used. Image formation (S4) is executed. That is, an image using only normal toner is output (S7). On the other hand, when the “high speed image forming mode” is selected in step S2 (S5), the second image forming unit using dark toner among the first and second image forming units Sa and Sb. Image formation by only Sb (S6) is executed. That is, an image using only dark toner is output (S7).

  In this embodiment, the color image forming speed in the “normal speed image forming mode” is A4 size 30 sheets / minute, and the image forming speed in the “high speed image forming mode” is A4 size 50 sheets / minute.

  FIG. 4 shows the characteristics of the amount of applied toner on the recording material (hereinafter referred to as “on-paper M / S”) with respect to the image signal value when an image is formed in each of the first and second image forming modes in the first embodiment. . As an example, FIG. 5 shows the reflection density characteristics of the formed image with respect to the image signal value when an image is formed using only cyan toner. From FIGS. 4 and 5, by using “dark toner” having a sufficiently high density (in Example 1, approximately twice the colorant content) as in the first embodiment, a high density is obtained. It can be seen that high-speed image formation can be realized without deteriorating the color gamut reproducibility on the side.

  That is, it can be seen that the maximum density in the first image forming mode and the maximum density in the second image forming mode are substantially equal to the input maximum signal value of 1.6.

  Referring to FIG. 5, it can be seen that when dark toner is used, the reproducibility from the low density region to the intermediate density region is lower than that of the normal toner. The reason is as follows. In image formation with dark toner, the M / S on paper is halved compared to image formation with normal toner. For this reason, in an image in a low density region, an image with dark toner has a higher degree of exposure of the recording material than an image with normal toner, and the sensitivity of density change to toner M / S change is lowered. Therefore, the density change ratio with respect to the signal becomes small. When the toner is in a density area that covers the recording material to some extent, the exposure of the recording material becomes small and does not affect the density change. Therefore, in the image formation with the dark toner, the color gamut reproducibility on the high density side is maintained at the same level as the image formation with the normal toner.

[Example 2]
In the second embodiment, the black toner has high density black and low density black. Therefore, when outputting a full-color image, a normal density toner is used to prioritize image quality. In a monochrome image, only black toner having a high density is used when giving priority to image output speed over image quality, and only black toner having a normal density is used when giving priority to image quality.

  FIG. 8 shows a schematic cross-sectional view of a full-color image forming apparatus in Embodiment 2 of the present invention.

  In this embodiment, the developing devices 41 to 44 are filled with magenta, cyan, yellow, and black toners, respectively, and the developing device 48 is filled with black toner having a higher density than the black toner of the developing device 44. .

In this embodiment, each of the magenta, cyan and yellow colors, and the black toner having the lower density has a reflection density of 1.6 when the density per unit area on the paper is 0.55 [mg / cm ² ]. . Further, the black toner having a high density has a reflection density of 1.6 when the density per unit area on the paper is 0.30 [mg / cm ² ]. At this time, the colorant content of the black toner having the higher density is about twice that of the black toner having the lower density. Hereinafter, the black toner having the lower density is referred to as “normal black toner”, and the toner having the higher density is referred to as “dark black toner”.

  This image forming apparatus has two image forming modes, a “monochrome image forming mode” and a “full color image forming mode”. Further, when “monochrome image forming mode” is selected, two modes, “normal speed image forming mode” (= first image forming mode) and “high speed image forming mode” (= second image forming mode), are selected. An image forming mode is provided and can be selected by an operator's operation.

  FIG. 9 is a flowchart of the mode control of this embodiment. When an image formation signal is input and image formation is started (S11), an image control unit (not shown) determines which mode is “monochrome image formation mode” or “full color image formation mode” (S12). . When the “monochrome image quality formation mode” is selected in step S12, it is further determined whether the mode is “normal speed image formation mode” or “high speed image formation mode” (S13). When “normal speed image forming mode” is selected in step S13 (S14), image formation is performed only by the developing device 44 filled with normal black toner out of the two developing devices 44 and 48 filled with black toner ( S15) is executed. That is, an image using only normal black toner is output (S19). On the other hand, when the “high speed image forming mode” is selected in step S13 (S16), only the developing device 48 filled with dark black toner out of the two developing devices 44 and 48 filled with black toner is used. Image formation (S17) is executed. That is, an image using only dark black toner is output (S19). When the “full color image quality formation mode” is selected in step S12, image formation (S18) is executed using magenta, cyan, yellow toners and normal black toner, and a full color image is output (S19).

  In this embodiment, the color image forming mode speed in the “normal speed image forming mode” is A4 size 30 sheets / min. In the “normal speed image formation mode” of the “monochrome image formation mode”, the image formation speed is A4 size 40 sheets / minute, and in the “high speed image formation mode”, the image formation speed is 60 sheets / minute A4 size. Can do.

[Example 3]
Embodiment 3 shows a developing device configuration different from those of Embodiments 1 and 2 for realizing the method of the present invention in a color image forming apparatus.

  FIG. 6 illustrates the configuration of the developing device according to the third embodiment. The developing device 300 according to the third exemplary embodiment includes two developer accommodating portions 301 and 302 illustrated in FIG. Reference numerals 303 to 306 denote developer agitating and mixing members (= screws), and reference numerals 307 and 308 denote developer carriers (= developing sleeves), which are configured to realize two-color development separately with one developing device.

  The developing device 300 has a developing device rotating shaft 309 and a developing device rotation driving means (not shown) at the center, and the developing device 300 rotates around the rotating shaft 309. At that time, the developing device moving means (not shown) is rotated away from the developing portion. When the developing device 300 is rotationally driven, any one of the developing sleeves 307 and 308 is moved to the toner flying portion close to the photosensitive drum 310, thereby forming an image with one of the two color toners filled in the developing device. Is called.

  In a single developing device, normal toner and dark toner of the same color are accommodated in the two developer accommodating portions. When the “normal speed image forming mode” is selected by the user, the developing device is rotationally driven so that the developing sleeve carrying the normal toner is opposed to the photosensitive drum. When the “high speed image forming mode” is selected, the developing sleeve carrying the dark toner is opposed to the photosensitive drum by the same operation. Then, a toner image is formed on the drum by the opposing developing device.

  FIG. 7 shows an example of the configuration of a full-color image forming apparatus using the developing device of Example 3. As shown in FIG. 7, developing devices 401 to 404 are provided in yellow, magenta, cyan, and black colors, and are arranged on the intermediate transfer belt 405. With this configuration, the method of the present invention can be realized without the image forming apparatus main body becoming excessively large.

[Others]
1) Each of the above embodiments is a color image forming apparatus, but the present invention selectively selects a normal speed image forming mode using normal toner and a high speed image forming mode using dark toner in a monochromatic image forming apparatus (for example, monochrome). The present invention can also be effectively applied to an image forming apparatus to be executed in the first place.

  2) In the above embodiments, the first and second image forming modes each have a dedicated image carrier. However, a normal toner developer and a dark toner developer are arranged around one image carrier. It is possible to realize the present invention even by a method of arranging in the above.

  The image formation on the recording material is not limited to the transfer method, and may be image formation by a direct method.

  3) The image formation principle / process of the toner image of the image forming apparatus is not limited to electrophotography, and is arbitrary such as a transfer method, a direct electrostatic recording method, and a magnetic recording method.

  4) The colorant contained in the normal toner and the dark toner is not limited to the pigment.

1 is a schematic configuration diagram of an image forming apparatus according to a first exemplary embodiment. FIG. 3 is a partially enlarged view of a printer unit. 3 is a flowchart of an image forming mode according to the first exemplary embodiment. 6 is a graph illustrating the amount of applied toner on a transfer material with respect to an image signal value when an image is formed with normal toner and dark toner in Example 1. 6 is a graph illustrating toner reflection density on a transfer material with respect to an image signal value when an image is formed with normal toner and dark toner of Example 1. 10 is a schematic diagram illustrating a configuration of a developing device in Embodiment 3. FIG. 6 is a schematic diagram illustrating a configuration of an image forming apparatus in Embodiment 3. FIG. 6 is a schematic configuration diagram of an image forming apparatus in Embodiment 2. FIG. 6 is a flowchart illustrating an image forming mode according to the second exemplary embodiment. It is a schematic explanatory drawing of the conventional image forming apparatus.

Explanation of symbols

1a First photosensitive drum (image carrier)
1b Second photosensitive drum (image carrier)
3a, 3b Laser exposure optical system 4a First developing rotary 4b Second developing rotary 5 Intermediate transfer belt (intermediate transfer member)
41 to 48 Developing device Sa First image forming unit Sb Second image forming unit

Claims (3)

A first image forming mode in which an image is formed on a recording material with only at least one image carrier and four color toners of yellow, magenta, cyan, and black; and at least one of yellow, magenta, cyan, and black colors A second image forming mode in which an image is formed on a recording material with only four color toners using a toner of a color having the same hue and a dark color as compared with the color used in the first image forming mode; In an image forming apparatus having
The maximum applied amount of the image formed in the second image forming mode is smaller than the maximum applied amount of the image formed in the first image forming mode, and the maximum density of the image formed in the second image forming mode is the first image. It is substantially the same as the maximum density of the image formed by the formation mode, and the number of image formations per unit time in the second image formation mode is larger than the number of image formations per unit time in the first image formation mode. A featured image forming apparatus.   In the second image forming mode, the respective color toners for forming toner images of dark yellow, dark magenta, dark cyan, and dark black having the same hue as each of the yellow, magenta, cyan, and black colors and a dark color. 2. The image forming apparatus according to claim 1, wherein a toner image is formed on the recording material by a plurality of dark toner developing means for developing the toner. At least one image carrier, a plurality of developing means for developing with each color toner of yellow, magenta, cyan, and black for forming an image on the recording material; and the yellow for forming an image on the recording material And at least one dark toner developing means for developing with toner having the same hue and dark color with respect to at least one of magenta, cyan, and black, and having a plurality of image forming modes In
An image forming apparatus comprising: selecting a developing unit to be used in accordance with an image forming mode from a developing unit for toner having the same hue and high density and a developing unit for toner having the same hue and a low density.

Images