JP2018159851A - Image forming apparatus and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus and a program that can increase the range of adjustment of the amount of toner to be used compared with a case where one image forming part forms a toner image in a specific color.SOLUTION: An image forming apparatus comprises: first image forming parts that form first toner images with toner in specific colors; second image forming parts that are arranged downstream of the first image forming parts and form second toner images with the toner in specific colors; transfer parts that transfer the formed toner images to a recording medium; and a control part that, when forming the images on the recording medium with the toner in specific colors, forms the first toner images with the first image forming parts on the basis of first image data obtained from image information and form the second toner images with the second image forming parts on the basis of second image data obtained from the image information, and controls image formation performed by the first image forming parts, second image forming parts, and transfer parts such that the formed first toner images and second toner images are transferred to the recording medium in an overlapping manner.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an image forming apparatus and a program.

  In Patent Document 1, a transfer body that transfers an image, a transfer body that conveys the image, and a toner containing a metal pigment are attached by electrostatic force to form a first image, and the first image is transferred to the transfer body at a transfer position. A first object to be transferred to the first object and a charge having a polarity opposite to that of the toner adhering to the first object after the first image is transferred to the first object. A first removal unit that removes an image history on an object to be formed, and a toner that does not contain a metal pigment and is attached by electrostatic force are disposed downstream of the transfer position in the transport direction of the transfer body to form a second image. A second object on which the second image is transferred to the transfer member, and a charge having a polarity opposite to that of the toner adhering to the second object after the second image is transferred. A second removing unit that is applied to the two formed bodies and removes an image history on the second formed body; When the first image is transferred to the transfer body, the output of at least one of the first removal section and the second removal section is reduced as compared with the case where the first image is not transferred to the transfer body. An image forming apparatus including a control unit is disclosed.

Japanese Patent Laid-Open No. 2006-153828

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus and program capable of increasing the range of adjustment of the amount of toner used compared to the case where there is one image forming unit that forms a toner image of a specific color. is there.

  In order to achieve the above-mentioned object, the invention according to claim 1 is arranged on the downstream side of the first image forming unit, the first image forming unit for forming a first toner image with a specific color toner, and the specific image forming unit. A second image forming unit that forms a second toner image with a color toner, a transfer unit that transfers the formed toner image to a recording medium, and an image formed on the recording medium with the specific color toner. Forming a first toner image by the first image forming unit based on the first image data obtained from the image information and forming the second image based on the second image data obtained from the image information. Forming a second toner image by the unit, and forming the first image forming unit and the second image forming unit so that the formed first toner image and the second toner image are transferred to the recording medium in an overlapping manner. And control for controlling image formation by the transfer unit. And parts, which is an image forming apparatus equipped with.

  A second aspect of the present invention is the image forming apparatus according to the first aspect, wherein the specific color toner is a white toner.

  According to a third aspect of the present invention, when the toner amount per unit area obtained from the image information exceeds the first upper limit threshold, the control unit sets the first toner amount to the first upper limit threshold. Image data and second image data having a toner amount per unit area exceeding the first upper limit threshold value are generated, and a first toner image is generated by the first image forming unit based on the first image data. The image forming apparatus according to claim 1, wherein the image formation is controlled so that a second toner image is generated by the second image forming unit based on the second image data.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the first upper limit threshold value is an upper limit value of a toner amount per unit area obtained by the first image forming unit.

  According to a fifth aspect of the invention, the first upper limit threshold is a value at which a residual toner amount remaining in the first image forming unit after the transfer of the first toner image is less than a second upper limit threshold. 3. The image forming apparatus according to 3.

  According to a sixth aspect of the present invention, in a case where the concealing property is prioritized, the control unit sets the toner amount per unit area to the target amount with the first upper limit threshold of the toner amount per unit area as the target amount. First image data and second image data having a toner amount per unit area larger than 0 and equal to or less than the target amount are generated by the first image forming unit based on the first image data. 2. The image forming apparatus according to claim 1, wherein the image formation is controlled so that a toner image is generated and a second toner image is generated by the second image forming unit based on the second image data.

  According to a seventh aspect of the present invention, when the control unit is configured to prioritize image quality, the toner amount per unit area obtained from the image information is set as a target amount, and the toner amount per unit area is the target amount. First image data and second image data in which the amount of toner per unit area is the remainder of the target amount is generated, and the first image forming unit generates the first image data based on the first image data. 2. The image forming apparatus according to claim 1, wherein the image formation is controlled such that one toner image is generated and the second image forming unit generates a second toner image based on the second image data. .

  According to an eighth aspect of the present invention, in the control unit, the remaining amount of toner in one of the first image forming unit and the second image forming unit is the other of the first image forming unit and the second image forming unit. The ratio between the part and the remaining part is changed so that the amount of toner consumed by the one of the first image forming unit and the second image forming unit increases when the remaining amount of toner exceeds the remaining amount of toner. The image forming apparatus described in the above.

  According to a ninth aspect of the present invention, the control unit, when the image is a solid image, the first image data for forming a halftone dot image having a lower halftone dot area ratio than the solid image; The image forming apparatus according to claim 7, wherein the second image data for forming the solid image is generated based on image information.

  A tenth aspect of the present invention is a program for causing a computer to function as a control unit of the image forming apparatus according to any one of the first to ninth aspects.

  According to the first and tenth aspects of the present invention, it is possible to increase the range of adjustment of the amount of toner used compared to the case where there is one image forming unit that forms a toner image of a specific color.

  According to the second aspect of the present invention, the number of types of toner to be adjusted can be reduced as compared with the case where the toner is not white.

  According to the third and fourth aspects of the invention, the amount of toner per unit area can be increased as compared with the case where the number of image forming portions that form a specific color toner image is one.

  According to the fifth aspect of the present invention, it is possible to reduce the residual toner dropout compared to the case where the first upper limit threshold is not limited.

  According to the sixth aspect of the present invention, it is possible to realize a high concealment rate as compared with the case where there is one image forming unit that forms a toner image of a specific color.

  According to the seventh aspect of the present invention, the image quality of the formed image is improved as compared with the case where an image is formed on one of the first image forming unit and the second image forming unit.

  According to the eighth aspect of the invention, as compared with the case where the ratio is not changed, the deviation of the toner consumption amount between the first image forming unit and the second image forming unit is corrected.

  According to the ninth aspect of the present invention, the gloss of the image can be reduced as compared with the case where the halftone image is not formed.

1 is a schematic diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a schematic diagram illustrating an example of a configuration of a toner image forming unit provided in the image forming apparatus according to the embodiment of the present invention. 1 is a block diagram illustrating an example of an electrical configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 6 is a schematic diagram illustrating an example of a setting screen displayed on an operation display unit of the image forming apparatus according to the embodiment of the present invention. It is a schematic diagram which shows another example of the setting screen displayed on the operation display part of the image forming apparatus which concerns on embodiment of this invention. 6 is a flowchart illustrating an example of a procedure of “white image forming processing” executed by the control unit of the image forming apparatus according to the embodiment of the present invention. It is a flowchart which shows an example of the procedure of an "image superimposition process." It is a flowchart which shows an example of the procedure of the "image data generation process" in an image superimposition process. 6 is a graph showing the relationship between toner dropout and the amount of toner in the transport direction per image size A3. It is a flowchart which shows an example of the procedure of the "image data generation process" in a concealment mode process. It is a graph which shows the relationship between a concealment rate and TMA. 12 is a flowchart illustrating an example of a procedure of “image data generation processing” in image quality priority mode processing. 12 is a flowchart illustrating another example of the procedure of “image data generation processing” in image quality priority mode processing. 6 is a chart showing a relationship between a difference in remaining toner amount and a TMA ratio. (A) And (B) is a graph which shows the relationship between the toner remaining amount of each image formation part, and image formation amount. It is a flowchart which shows another example of the procedure of the "image data generation process" in the gloss suppression mode process. It is a graph which shows an example of the relationship between gross and TMA. It is a schematic diagram which shows an example of a structure of a superimposed image.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

<Image forming apparatus>
First, the configuration of the image forming apparatus will be described.
FIG. 1 is a schematic diagram showing an example of the configuration of an image forming apparatus according to an embodiment of the present invention. As shown in FIG. 1, the image forming apparatus 10 includes an image forming unit 12 that forms an image on a sheet-like recording medium P by an electrophotographic method, and a transport device 50 that transports the recording medium P. Yes.

(Image forming part)
The image forming unit 12 includes a toner image forming unit 20 that forms a toner image, a transfer device 30 that transfers the toner image formed by the toner image forming unit 20 to the recording medium P, and a toner image transferred to the recording medium P. And a fixing device 40 for fixing the image to the recording medium P.

  A plurality of toner image forming units 20 are provided so as to form a toner image for each color. In this embodiment, a toner image forming unit for a total of six colors of first special color (V), second special color (W), yellow (Y), magenta (M), cyan (C), and black (K). 20 is provided. (V), (W), (Y), (M), (C), and (K) shown in FIG. 1 indicate the colors described above. As the first special color (V) and the second special color (W), any color that the user of the image forming apparatus 10 wants to use is used.

  In the present embodiment, white of white toner containing a white pigment is used as the first special color (V) and the second special color (W). In the illustrated example, the toner image forming unit 20V of the first special color (V) is provided on the upstream side of the toner image forming units 20Y to 20K for each color of YMCK. The second special color (W) toner image forming unit 20W is provided on the downstream side of the YMCK toner image forming units 20Y to 20K.

  In this embodiment, the case where there are two image forming units 20 that form a white toner image is described. However, the purpose is to increase the range of adjustment of the amount of toner used, and overlapping colors are used. Is not limited to white. Two image forming units 20 for forming a toner image of a specific color are sufficient. For example, two image forming units 20 that form toner images of each color of YMCK may be provided. When adjusting the toner amount of each color of YMCK, the toner amount of all colors of YMCK is adjusted in order to maintain the ratio of four colors. Alternatively, the K color may be replaced with three YMC colors, and two YMC toner image forming units 20 may be provided. In this case, in order to maintain the ratio of the three colors, the toner amounts of all YMC colors are adjusted. On the other hand, when adjusting the amount of white toner, only the amount of white toner needs to be adjusted.

  The transfer device 30 transfers the superimposed toner image onto the recording medium P at the transfer nip NT from the transfer belt 31 on which the toner images of the respective colors are primarily transferred. When a white image is formed, each of the toner images formed by the toner image forming unit 20V and the toner image forming unit 20W is primarily transferred onto the transfer belt 31 and the superimposed toner image is recorded. Transferred to the medium P.

(Toner image forming unit)
Here, a detailed configuration of the toner image forming unit will be described.
FIG. 2 is a schematic diagram illustrating an example of a configuration of a toner image forming unit provided in the image forming apparatus according to the embodiment of the present invention. The toner image forming unit 20 for each color is basically configured in the same manner except for the toner to be used. Therefore, hereinafter, the toner image forming unit 20 of each color will be described without particular distinction. As shown in FIG. 2, the toner image forming unit 20 includes a photosensitive drum 21, a charger 22, an exposure device 23, a developing device 24, a charge applying device 26, and a cleaning device 25. ing.

  The photosensitive drum 21 is formed in a cylindrical shape and grounded, and is driven to rotate around its own axis by a driving unit (not shown). As an example, a photosensitive layer having a negative charging polarity is formed on the surface of the photosensitive drum 21. As shown in FIG. 1, the photosensitive drums 21 of the respective colors are arranged in a straight line along the apparatus width direction when viewed from the front.

  As shown in FIG. 2, the charger 22 charges the surface (photosensitive layer) of the photosensitive drum 21 to a negative polarity. In this embodiment, the charger 22 is a corona discharge type (non-contact charging type) scorotron charger.

  The exposure device 23 forms an electrostatic latent image on the surface of the photosensitive drum 21. Specifically, the surface of the photosensitive drum 21 charged by the charger 22 is irradiated with the modulated exposure light L in accordance with the image data received from the control unit 70. The portion irradiated with the exposure light L by the exposure device 23 exhibits positive polarity, and an electrostatic latent image is formed on the surface of the photosensitive drum 21.

  The developing device 24 holds the toner (developer) with the developing roll 241, and develops the electrostatic latent image formed on the surface of the photosensitive drum 21 with the toner held with the developing roll 241, whereby the photosensitive drum A toner image is formed on the surface 21. Specifically, the toner held by the developing roll 241 is attached to the photosensitive drum 21 by electrostatic force to form a toner image. In other words, the negative toner adheres to the positive electrostatic latent image and is developed.

  The charge applying device 26 applies charge to the photosensitive drum 21 after transfer, and removes the image history on the photosensitive drum 21. Specifically, by applying a negative charge to the photosensitive drum 21, the history of the electrostatic latent image exhibiting the positive polarity is removed. As the charge applying device 26, for example, a corona discharge type (non-contact charging type) corotron is used.

  As shown in FIG. 2, the cleaning device 25 includes a brush 251 that removes residual toner remaining on the surface of the photosensitive drum 21 after the transfer of the toner image to the transfer device 30, and the residual toner on the photosensitive drum 21. A blade 252 that scrapes off the surface. Further, the cleaning device 25 includes a seal member 253 disposed on the upstream side (downward side) of the photosensitive drum 21 in the rotation direction with respect to the brush 251.

  The seal member 253 has an upper end (downstream end) in contact with the photosensitive drum 21 and a lower end (upstream end) separated from the photosensitive drum 21. The seal member 253 guides the toner so that the toner scraped off by the blade 252 and the toner removed by the brush 251 are dropped into the housing 254 (left side in FIG. 2).

(Transfer device)
The transfer device 30 performs primary transfer by superimposing a toner image of the photosensitive drum 21 of each color on a transfer belt 31 (intermediate transfer member) as an example of a transfer member, and transferring the superimposed toner image onto a recording medium P. Next transfer is to be done. This will be specifically described below.

  As shown in FIG. 1, the transfer belt 31 has an endless shape and is wound around a plurality of rolls 32 to determine the posture. In this embodiment, the transfer belt 31 has an inverted obtuse triangular posture that is long in the apparatus width direction when viewed from the front. Among the plurality of rolls 32, the roll 32D shown in FIG. 1 functions as a drive roll that rotates the transfer belt 31 in the arrow A direction by the power of a motor (not shown).

  The transfer belt 31 circulates in the direction of the arrow A, thereby conveying the primary transferred image to the transfer nip NT (secondary transfer position).

  Of the plurality of rolls 32, the roll 32 </ b> T illustrated in FIG. 1 functions as a tension applying roll that applies tension to the transfer belt 31. Among the plurality of rolls 32, the roll 32B illustrated in FIG. 1 functions as a counter roll of a secondary transfer roll 34 described later. As described above, the top of the lower end side forming the obtuse angle of the transfer belt 31 in the inverted obtuse triangular shape is wound around the roll 32B. The transfer belt 31 is in contact with the photosensitive drum 21 of each color from below at the upper side extending in the apparatus width direction in the above-described posture.

  Inside the transfer belt 31, a primary transfer roll 33 (an example of a transfer member) that transfers the toner image of each photosensitive drum 21 to the transfer belt 31 is disposed. Each primary transfer roll 33 is disposed opposite to the corresponding photosensitive drum 21 with the transfer belt 31 in between. The primary transfer roll 33 is applied with a transfer voltage having a polarity opposite to the toner polarity by the power feeding unit 72. By applying this transfer voltage, the toner image formed on the photosensitive drum 21 is transferred to the transfer belt 31.

  Further, the transfer device 30 includes a secondary transfer roll 34 that transfers the toner image superimposed on the transfer belt 31 to the recording medium P. The secondary transfer roll 34 is arranged so that the transfer belt 31 is sandwiched between the secondary transfer roll 34 and the roll 32 </ b> B, and a transfer nip NT is formed between the secondary transfer roll 34 and the transfer belt 31. A recording medium P is supplied to the transfer nip NT from the medium supply unit 52 in a timely manner. The secondary transfer roll 34 is applied with a transfer voltage having a polarity opposite to the toner polarity by the power feeding unit 72. By applying the transfer voltage, the toner image is transferred from the transfer belt 31 to the recording medium P passing through the transfer nip NT.

  Furthermore, the transfer device 30 includes a cleaning device 35 that cleans the transfer belt 31 after the secondary transfer. The cleaning device 35 is disposed downstream of the portion where the secondary transfer is performed (transfer nip NT) and upstream of the portion where the primary transfer is performed in the circumferential direction of the transfer belt 31. The cleaning device 35 includes a blade 351 that scrapes off toner remaining on the surface of the transfer belt 31 from the surface of the transfer belt 31.

(Fixing device)
The fixing device 40 fixes the toner image on the recording medium P onto which the toner image has been transferred by the transfer device 30. Specifically, the fixing device 40 is configured to fix the toner image on the recording medium P by heating and pressing the toner image at the fixing nip NF by the heating roll 41 and the pressure roll 42. .

(Transport device)
As illustrated in FIG. 1, the transport device 50 includes a medium supply unit 52, an intermediate transport unit 58, and a downstream transport unit 54.

  The medium supply unit 52 includes a container 521 in which the recording medium P is stacked and stored. A medium supply path 52P is formed from the container 521 to the transfer nip NT that is the secondary transfer position by a plurality of conveying roll pairs 522, a guide (not shown), and the like.

  In addition, on the upper side of the container 521, a delivery roll 523 for feeding the uppermost recording medium P loaded in the container 521 is disposed. Among the plurality of transport roll pairs 522, the transport roll pair 522S on the uppermost stream side in the transport direction of the recording medium P separates the recording media P sent from the container 521 by the delivery roll 523 one by one. Act as a role. Further, among the plurality of conveyance roll pairs 522, the conveyance roll pair 522R located immediately upstream of the transfer nip NT in the conveyance direction of the recording medium P is a movement timing of the toner image on the transfer belt 31 and a conveyance timing of the recording medium P. It is designed to work together.

  As shown in FIG. 1, the intermediate conveyance unit 58 includes an endless conveyance belt that is disposed between the transfer nip NT of the transfer device 30 and the fixing nip NF of the fixing device 40 and is wound around a roll. A plurality of belt conveying members 581 are provided.

  While the air is sucked from the inside of the belt conveying member 581 (negative pressure suction) and the recording medium P is sucked onto the surface of the conveying belt, the conveying belt circulates and conveys the recording medium P.

  As shown in FIG. 1, the downstream side conveyance unit 54 includes a belt conveyance member 541 that is disposed on the downstream side of the fixing device 40 and includes an endless conveyance belt wound around a roll. The belt conveying member 541 conveys the recording medium P on which the toner image has been fixed by the fixing device 40 toward a discharge unit (not shown) that accommodates the recording medium P.

<Electrical Configuration of Image Forming Apparatus>
Next, the electrical configuration of the image forming apparatus will be described.
FIG. 3 is a block diagram showing an example of the electrical configuration of the image forming apparatus according to the embodiment of the present invention. As shown in FIG. 3, the control unit 70 is configured as a computer that controls the entire apparatus and performs various calculations. That is, the control unit 70 includes a CPU (Central Processing Unit) 70A, a ROM (Read Only Memory) 70B, a RAM (Random Access Memory) 70C, a nonvolatile memory 70D, and an input / output interface (I / O). 70E. In the present embodiment, a program for executing a “white image forming process” to be described later is stored in the ROM 70B.

  The CPU 70A, ROM 70B, RAM 70C, memory 70D, and I / O 70E are connected to each other via a bus 70F. The CPU 70A reads the program stored in the ROM 70B and executes the program using the RAM 70C as a work area. The I / O 70E of the control unit 70 is connected to the image forming unit 12, the conveyance device 50, the power feeding unit 72, the operation display unit 100, the communication unit 102, and the storage unit 104. The control unit 70 controls these units.

  The operation display unit 100 includes various buttons such as a start button and a numeric keypad, and a touch panel for displaying various screens such as a setting screen. With the above configuration, the operation display unit 100 accepts user operations and displays various information to the users.

  The communication unit 102 is an interface for communicating with an external device via a wired or wireless communication line. For example, it functions as an interface for communicating with a computer connected to a network such as a LAN (Local Area Network). The storage unit 104 includes a storage device such as a hard disk. The storage unit 104 stores various data such as log data.

  The image information may be acquired from an image reading device (not shown) in the image forming apparatus, or may be acquired from an external device via the communication unit 102. The image formation instruction and setting information may be acquired from the operation display unit 100 or may be acquired from an external device via the communication unit 102. Here, “setting information” is information relating to image forming conditions set by the user. Various programs may also be acquired from an external device via the communication unit 102.

  Various drives may be connected to the control unit 70. The various drives are devices that read data from a computer-readable portable recording medium such as a magneto-optical disk, a CD-ROM, and a USB (Universal Serial Bus) memory, and write data to the recording medium. When various drives are provided, the program may be recorded on a portable recording medium and read and executed by the corresponding drive.

<Operation of Image Forming Apparatus>
Next, the operation of the image forming apparatus will be described.
(White toner and colored toner)
In the present embodiment, white is used as the first special color (V) and the second special color (W) in addition to the four colors of YMCK. The white toner includes a white pigment, a binder resin, and various additives. The color toner of each color of YMCK includes each color pigment, a binder resin, and various additives. Here, “colored” means not transparent or white. These toners are used as a developer by combining with a carrier.

  Each of the white toner and the colored toner may have a center particle size in the range of 3 μm to 9 μm and a specific gravity in the range of 1 to 1.7. For example, white toner having a center particle diameter of 6 μm and a specific gravity of 1.4 may be used. In order to increase the concealment ratio with the white toner, a white toner having a larger center particle diameter than the colored toner may be used.

(Image formation mode)
4 and 5 are schematic diagrams illustrating an example of a setting screen displayed on the operation display unit of the image forming apparatus according to the embodiment of the present invention. As shown in FIG. 4, in this embodiment, a normal mode, a white background mode, and a white image mode are prepared as options for the image forming mode. The user operates the setting screen 106 shown in FIG. 4 to select one of the modes and set it as an image forming mode.

  The normal mode is an aspect in which, for example, a colored image is formed with colored toner on a white recording medium. A white image may be formed with white toner together with a colored image. The white background mode is an aspect in which, for example, a white solid image is formed as a background with a white toner on a colored recording medium. A colored image may be formed on the white solid image with colored toner.

  The white image mode is an aspect in which a white image is formed based on white image data. In the present embodiment, a superimposed image in which another white image is further superimposed on the white image formed on the recording medium is formed according to the image information and the setting information. In this embodiment, an example in which a superimposed image is formed in the white image mode will be described. However, a superimposed image of a white image may be formed in other modes.

  The white image formed on the recording medium (hereinafter referred to as “second white image”) is obtained by transferring and fixing the toner image formed by the toner image forming unit 20W onto the recording medium P (FIG. 1). reference). The other white image formed on the second white image (hereinafter referred to as “first white image”) is obtained by transferring and fixing the toner image formed by the toner image forming unit 20V onto the recording medium P. Yes (see FIG. 1). FIG. 18 is a schematic diagram illustrating an example of a configuration of a superimposed image. As shown in FIG. 18, a superimposed image is formed by superimposing the first white image on the second white image formed on the recording medium. In the following, for convenience, it is expressed that a white image is formed by the toner image forming unit 20.

  When the white image mode is selected, a setting screen for setting a mode (white overlap mode) for further overlapping the white image is displayed. As shown in FIG. 5, in the present embodiment, there are prepared no mode setting, a concealment mode, an image quality priority mode, and a gloss suppression mode as options for the white overlay mode. The user operates the setting screen 108 shown in FIG. 5 to select one of the modes, and sets it as the white overlap mode.

  The control unit 70 generates image data of each color for image formation from the acquired image information. For white image data, first, one image data is generated. When a white image is formed using only the toner image forming unit 20V, this one image data is used.

  As will be described later, when a superimposed image of a white image is formed, first image data for the toner image forming unit 20V (first white image) and a second image for the toner image forming unit 20W (second white image). Image data. For example, each of the first white image and the second white image has the same pixel distribution as that of the original white image, and an image in which the toner amount per unit area (hereinafter referred to as “TMA”) is different from that of the original white image. It is.

Here, the toner amount per unit area obtained from the previously generated white image data is referred to as “TMA ₀ based on image data”. Since the particle size of the white toner is larger than the particle size of the colored toner, the TMA of the white toner is larger than the TMA of the colored toner. For example, the TMA of the colored toner is in the range of 2.5 g / m ² to 5.0 g / m ² , and the TMA of the white toner is in the range of 5.0 g / m ² to 10.0 g / m ² . In this example, the TMA of the white toner is more than twice that of the colored toner.

No mode setting is a mode in which when the TMA ₀ based on the image data exceeds the upper threshold, the first white image is formed by the toner image forming unit 20V and the second white image is formed by the toner image forming unit 20W. is there. When TMA ₀ based on the image data is equal to or less than the upper threshold, only the first white image is formed by the toner image forming unit 20V.

  The concealment mode is an aspect in which the toner image forming unit 20V forms the first white image and the toner image forming unit 20W forms the second white image so that the TMA of the superimposed image exceeds the upper limit threshold.

In the image quality priority mode, the TMA of the superimposed image becomes the above-mentioned “TMA ₀ based on image data”, and the first white image is displayed by the toner image forming unit 20V so that the ratio of TMA ₁ by the first white image is high. In this embodiment, the second white image is formed by the toner image forming unit 20W.

  In the gloss suppression mode, when the white image is a solid image, the toner image forming unit 20V forms a halftone dot image as the first white image, and the toner image forming unit 20W forms a solid image as the second white image. is there.

(Image formation procedure)
Next, an image forming procedure in each mode will be described with reference to FIGS. The procedure of each mode is started when an image formation in a mode set by the user is instructed. When starting the procedure, it is assumed that the acquired image information is converted into image data (raster data) of each color for image formation.

-Normal mode image formation procedure-
When the normal mode is selected, the control unit 70 instructs each unit of the image forming unit 12 and the conveyance device 50 including the YMCK toner image forming units 20Y to 20K and the white toner image forming unit 20V. Image formation is controlled so that a colored image and a white image are formed on the recording medium P. The white toner image forming unit 20W is not used.

  As shown in FIG. 1, the YMCK color toner image forming units 20Y to 20K, the white toner image forming unit 20V, the transfer device 30, and the fixing device 40 are operated. As a result, as shown in FIG. 2, the photosensitive drum 21 of each color toner image forming unit 20 and the developing roll 241 of the developing device 24 are rotated, and the transfer belt 31 is circulated. Further, the pressure roll 42 is rotated and the heating roll 41 is rotated. Further, in synchronization with these operations, the control unit 70 operates the transport device 50 and the like.

  The photosensitive drums 21 of the respective colors are charged by the charger 22 while being rotated. Further, the control unit 70 passes the image data to each exposure device 23. Each exposure device 23 emits each exposure light L according to the image data and exposes each charged photosensitive drum 21. Then, an electrostatic latent image is formed on the surface of each photosensitive drum 21. The electrostatic latent image formed on each photoconductor drum 21 is developed by the developer supplied from the developing device 24. As a result, YMCK and white toner images are formed on the photosensitive drums 21 of the respective colors.

  The toner images of the respective colors formed on the photosensitive drums 21 of the respective colors are sequentially transferred onto the rotating transfer belt 31 by applying a transfer voltage to the primary transfer roll 33 of each color. As a result, a superimposed toner image in which the toner images of the respective colors are superimposed is formed on the transfer belt 31. This superimposed toner image is conveyed to the transfer nip NT by the rotation of the transfer belt 31.

  As shown in FIG. 1, the recording medium P is supplied to the transfer nip NT in synchronization with the conveyance of the superimposed toner image by the conveyance roller pair 522 </ b> R of the medium supply unit 52. The superimposed toner image is transferred from the transfer belt 31 to the recording medium P by applying a transfer voltage at the transfer nip NT.

  The recording medium P onto which the toner image has been transferred is conveyed by the intermediate conveyance unit 58 from the transfer nip NT toward the fixing nip NF. The fixing device 40 applies heat and pressure to the recording medium P that passes through the fixing nip NF. As a result, the toner image transferred to the recording medium P is fixed. The recording medium P discharged from the fixing device 40 is transported toward a discharge unit (not shown) by the belt transport member 541 of the downstream transport unit 54.

-Image formation procedure in white background mode-
When the white background mode is selected, the control unit 70 generates white solid image data for forming a white solid image with white toner. Subsequently, the control unit 70 instructs each unit of the image forming unit 12 and the conveying device 50 including the toner image forming units 20Y to 20K for each color of YMCK and the white toner image forming unit 20V, and prints white on the recording medium P. Image formation is controlled so that the solid image and the colored image are formed to overlap each other. The white toner image forming unit 20W is not used.

  Using the white solid image data, an image is formed on the recording medium P in the same manner as in the normal mode except that the white toner image forming unit 20V forms a white solid toner image on the photosensitive drum 21V. . The recording medium P on which the white solid image and the colored image are formed in an overlapping manner is conveyed toward a discharge unit (not shown).

-Image formation procedure in white image mode-
When the white image mode is selected, the control unit 70 executes “white image forming process”. That is, the CPU 70A of the control unit 70 reads a program for executing the “white image forming process” from the ROM 70B, and executes the program using the RAM 70C as a work area.

  FIG. 6 is a flowchart showing an example of the procedure of “white image forming processing” executed by the control unit of the image forming apparatus according to the embodiment of the present invention. As described above, the “white image formation process” is started when an image formation in a mode set by the user is instructed. When the “white image forming process” is started, the control unit 70 instructs each unit of the white toner image forming unit 20V, the white toner image forming unit 20W, the transfer device 30, the fixing device 40, and the conveying device 50. Then, image formation is controlled.

First, in step 100, TMA (TMA ₀ based on image data) is acquired from white image data. Next, in step 102, it is determined whether TMA ₀ based on the image data exceeds an upper limit threshold value. Here, the “upper limit threshold” is an upper limit value (TMA _MAX ) of TMA that can be formed by the toner image forming unit 20V. If TMA ₀ based on the image data exceeds the upper threshold, the process proceeds to step 104. In step 104, “image superimposition processing” is executed and the routine is terminated. On the other hand, if TMA ₀ based on the image data is less than or equal to the upper threshold, the process proceeds to step 106.

  Next, in step 106, it is determined whether or not a concealment mode is set. If the concealment mode is set, the process proceeds to step 108. In step 108, “concealment mode processing” is executed and the routine is terminated. On the other hand, if the concealment mode is not set, the process proceeds to step 110.

  Next, in step 110, it is determined whether the image quality priority mode is set. If the image quality priority mode is set, the process proceeds to step 112. In step 112, "image quality priority mode processing" is executed and the routine is terminated. On the other hand, if the image quality priority mode is not set, the process proceeds to step 114.

  Next, in step 114, it is determined whether or not the gloss suppression mode is set. If the gloss suppression mode is set, the process proceeds to step 116. In step 116, “gross suppression mode processing” is executed and the routine is terminated. On the other hand, if the gloss suppression mode is not set, the routine is terminated. In this case, only the first white image is formed by the toner image forming unit 20V.

(Image superimposition processing)
Next, “image superimposition processing” will be described.
FIG. 7 is a flowchart illustrating an example of the procedure of “image superimposition processing”. FIG. 8 is a flowchart showing an example of the procedure of “image data generation processing” in the image superimposition processing.

  First, in step 200 in FIG. 7, first image data for the toner image forming unit 20V (first white image) and second image data for the toner image forming unit 20W (second white image) are generated. "Image data generation process" is executed.

In the “image data generation process” in the image superimposition process, TMA ₀ based on the image data exceeds the upper limit value (TMA _MAX ) of TMA that can be formed by the toner image forming unit 20V. The upper limit value TMA _MAX is an upper limit value of TMA that can be placed on the recording medium. For this reason, the white image whose TMA is “TMA ₀ ” cannot be formed only by the toner image forming unit 20V. Therefore, a white image is formed by the toner image forming unit 20V and the toner image forming unit 20W. The TMA ₀ based on the image data is not more than twice the upper limit value TMA _MAX .

Here, the “image data generation process” will be described in detail with reference to FIG. In step 300, first image data for the first white image is generated so that TMA _{1 of} the first white image formed by the toner image forming unit 20V becomes the upper limit value TMA _MAX . In the subsequent step 302, the second image data for the second white image is generated so that the TMA _{2 of} the second white image formed by the toner image forming unit 20W becomes the remaining TMA (= TMA ₀ -TMA ₁ ). Then, the routine ends.

  When the “image data generation process” in step 200 in FIG. 7 ends, the process proceeds to step 202. In step 202, the toner image forming unit 20V is instructed to form the first white toner based on the first image data. In the following step 204, the toner image forming unit 20W is instructed to form a second white toner image based on the second image data.

  Next, in Step 206, the first white toner image and the second white toner image are transferred onto the recording medium P so that the transferred superimposed toner image is fixed, and the transfer device 30, the fixing device 40, Then, each part of the transfer device 50 is instructed to end the routine.

In the above description, the upper limit value TMA _MAX is the upper limit value of TMA that can be placed on the recording medium. However, the upper limit value TMA _MAX may be another value. For example, TMA that does not cause a dropout in the toner image forming unit 20V may be used as the upper limit value TMA _MAX . The upper limit value TMA _MAX may be set in advance or may be set for each image formation.

  Here, with reference to FIG. 2, the “blurring drop” that occurs in the toner image forming unit 20V will be described. The white toner held on the developing roll 241 of the developing device 24V of the toner image forming unit 20V is charged negatively. The white toner transferred to the transfer belt 31 after adhering to the photosensitive drum 21V is charged with positive polarity by injecting positive charge at the time of transfer. The white toner remaining on the photosensitive drum 21V without being transferred to the transfer belt 31 is also charged to the positive polarity like the transferred white toner.

  The white toner remaining on the photosensitive drum 21V is negatively charged from the charge applying device 26V and becomes zero charged (a state in which neither the negative polarity nor the positive polarity is charged). The zero charge white toner has a low electrostatic adhesion to the photosensitive drum 21V. As a result, the zero-charged white toner cannot pass through the seal member 253 and stays in the seal member 253 (see P1 in FIG. 2). Then, the staying white toner falls on the charge applying device 26V (see P2 in FIG. 2).

  FIG. 9 is a graph showing the relationship between toner dropout and the amount of toner in the transport direction per image size A3. The toner amount in the transport direction per image size A3 is the toner amount when an image is formed on a recording medium having the width and length of the image size A3. The length direction of the image size A3 is the “conveying direction”, and the width direction of the image size A3 is the “crossing direction” that intersects the “conveying direction”. For example, when a long image is formed in the transport direction, the toner amount in the transport direction increases.

As shown in FIG. 9, when the toner amount in the transport direction exceeds the reference amount C, white toner falls off. As the amount of toner in the transport direction increases, the amount of drop also increases. This is presumed that as the amount of toner in the transport direction increases, the amount of white toner (residual toner amount) adhering to the photosensitive drum 21V increases, and the amount of staying and dropping at the seal member 253 also increases. Is done. Here, if it is assumed that the residual toner amount is equal to or greater than the threshold value and “blurring” occurs, the TMA value at which the residual toner amount is less than the threshold value may be set as the TMA upper limit value TMA _MAX . For example, the reference amount C shown in FIG. 9 may be set to the upper limit value TMA _MAX .

  In the above description, the “blurring drop” that occurs in the toner image forming unit 20V has been described. However, in the toner image forming unit 20 on the downstream side of the toner image forming unit 20V, such as the toner image forming unit 20W and the toner image forming unit 20Y, Dropping caused by white toner occurs. This is because the white toner transferred to the transfer belt 31 adheres to the photosensitive drum 21 of the toner image forming unit 20 on the downstream side of the toner image forming unit 20V and becomes residual toner.

(Hidden mode processing)
Next, the “concealment mode process” will be described.
FIG. 10 is a flowchart showing an example of the procedure of “image data generation processing” in the concealment mode processing. Note that the procedure of the “hiding mode process” is the same as the procedure of the “image superimposition process” except for the “image data generation process”, and thus illustration is omitted.

In the “image data generation process” in the concealment mode process, the upper limit of the TMA that can form a white image with the toner image forming unit 20V and the toner image forming unit 20W and place it on the recording medium with the toner image forming unit 20V. A TMA greater than the value TMA _MAX is obtained.

Here, the “image data generation process” will be described in detail with reference to FIG. In step 400, first image data for the first white image is generated so that TMA _{1 of} the first white image formed by the toner image forming unit 20V becomes the upper limit value TMA _MAX . In the subsequent step 402, second image data for the second white image is generated so that the TMA _{2 of} the second white image formed by the toner image forming unit 20W becomes the upper limit value TMA _MAX, and the routine is ended. .

FIG. 11 is a graph showing the relationship between the concealment rate and TMA. Here, the unit of TMA is [g / m ² ]. As shown in FIG. 11, as the TMA increases, the concealment rate of the recording medium increases. That is, the white image formed on the recording medium with the white toner becomes whiter as the TMA becomes larger.

  When the “image data generation process” is completed, each unit is instructed similarly to the “image superimposition process” to form a first white toner image based on the first image data, and a second white color based on the second image data. A toner image is formed, and the first white toner image and the second white toner image are transferred onto the recording medium P, and the transferred superimposed toner image is fixed.

In the above example, in the superimposed image in which the first white image and the second white image are superimposed, the TMA is twice the upper limit value TMA _MAX , the color of the recording medium is difficult to see through, and the high concealment rate Is realized.

(Image quality priority mode processing)
Next, “image quality priority mode processing” will be described.
FIG. 12 is a flowchart showing an example of the procedure of “image data generation processing” in the image quality priority mode processing. The procedure of the “image quality priority mode process” is the same as the procedure of the “image superimposition process” except for the “image data generation process”, and thus illustration is omitted.

In the “image data generation process” in the image quality priority mode process, the toner image forming unit 20V and the toner image forming unit 20W form a white image and obtain TMA ₀ based on the image data.

Here, the “image data generation process” will be described in detail with reference to FIG. In step 500, first image data for the first white image is generated so that TMA _{1 of} the first white image formed by toner image forming unit 20V is 0.7 times TMA ₀ based on the image data. To do. In the subsequent step 502, the second image data for the second white image is changed so that the TMA _{2 of} the second white image formed by the toner image forming unit 20W is 0.3 times the TMA ₀ based on the image data. Generate and exit the routine.

  When the “image data generation process” is completed, each unit is instructed similarly to the “image superimposition process” to form a first white toner image based on the first image data, and a second white color based on the second image data. A toner image is formed, and the first white toner image and the second white toner image are transferred onto the recording medium P, and the transferred superimposed toner image is fixed.

  The toner image forming unit 20V is disposed upstream of the toner image forming unit 20W in the image forming direction. Therefore, in the toner image forming unit 20V, the white toner attached to the transfer belt 31 is transferred to the downstream primary transfer unit (TY, TM, TC, TK, TW in FIG. 1) before being actually transferred to the recording medium P. ), Positive charge is injected (blank transfer) over a plurality of times. The number of empty transfers of the toner image forming unit 20V is larger than the number of empty transfers of the toner image forming unit 20W. Accordingly, the white toner that is secondarily transferred via the toner image forming portion 20V is charged more than the white toner that is secondarily transferred via the toner image forming portion 20W.

  The toner with low charge is scattered forward and backward in the conveyance direction of the recording medium due to applied pressure and charge fluctuation on the back surface of the recording medium during the secondary transfer. In the image quality priority mode, the first white toner image is superimposed on the second white toner image during the secondary transfer. The white toner constituting the first white toner image has a higher charge than the white toner constituting the second white toner image. The white toner with high charge is placed on the white toner with low charge, and the scattering of the toner is reduced.

In the above example, the ratio of TMA ₁ of the first white image and TMA ₂ of the second white image is (0.7: 0.3). However, during the secondary transfer, the second white toner image (low The first white toner image (high charge) may be superimposed on the (charge), and is not limited to the above ratio. For example, the ratio of TMA ₁ and TMA ₂ may be changed so that there is no bias in toner consumption between the toner image forming unit 20V and the toner image forming unit 20W.

FIG. 13 is a flowchart showing another example of the “image data generation process” in the image quality priority mode process. In this example, when the remaining amount of toner in the toner image forming unit 20V is smaller than the remaining amount of toner in the toner image forming unit 20W, the TMA ₁ is decreased and the TMA ₂ is increased, thereby correcting the bias in toner consumption. To do.

  First, in step 600, the remaining amount of toner in the toner image forming unit 20V is obtained. In the subsequent step 602, the remaining amount of toner in the toner image forming unit 20W is obtained. The developing device 24 of each toner image forming unit 20 replenishes toner as a developer by replacing the toner cartridge. The remaining amount of toner in each toner image forming unit 20 is the remaining amount of toner in the toner cartridge used in the developing device 24. The remaining amount of toner in the toner cartridge can be obtained by referring to the use history stored in the storage unit 104 or the like and subtracting the toner use amount from the toner amount at the start of use.

  Next, in step 604, a difference between the remaining amount of toner in the toner image forming unit 20V and the remaining amount of toner in the toner image forming unit 20W is obtained. Before correcting the unevenness of the toner consumption amount, the toner consumption amount of the toner image forming unit 20V is larger than the toner consumption amount of the toner image forming unit 20W. Therefore, a value obtained by subtracting the remaining amount of toner in the toner image forming unit 20V from the remaining amount of toner in the toner image forming unit 20W is the “difference in remaining toner amount”.

Next, in step 606, the ratio of TMA ₁ and TMA ₂ corresponding to the difference in the remaining amount of toner is determined. FIG. 14 is a chart showing the relationship between the difference in the remaining amount of toner and the TMA ratio. The relationship between the difference in the remaining amount of toner and the TMA ratio (X: Y) is stored in the memory 70D of the control unit 70 in the table format shown in FIG. 14, for example. In the illustrated example, the TMA ratio when the difference in the remaining amount of toner is less than A is (0.7: 0.3), and the TMA ratio when the difference in the remaining amount of toner is A or more and less than B is (0.5: 0.5), the TMA ratio when the difference in the remaining amount of toner is B or more is (0.3: 0.7). B is larger than A.

Next, in step 608, the first image data for the first white image is changed so that TMA _{1 of} the first white image formed by the toner image forming unit 20V is X times TMA ₀ based on the image data. Generate. In subsequent Step 610, second image data for the second white image is generated so that TMA _{2 of} the second white image formed by toner image forming unit 20W is Y times TMA ₀ based on the image data. To complete the routine.

  FIGS. 15A and 15B are graphs showing the relationship between the remaining amount of toner in each image forming unit and the image forming amount. The vertical axis represents the remaining amount of toner, and the horizontal axis represents the image formation amount. The unit of the remaining amount of toner is [kg]. The image forming amount is represented by the number of PV (Print Volume), that is, the number of A4 size recording media on which an image is formed. kPV represents a unit of 1000 sheets. The solid line represents the remaining amount of toner in the toner image forming unit 20V, and the alternate long and short dash line represents the remaining amount of toner in the toner image forming unit 20W. The dotted line represents the remaining amount of toner in the toner image forming units 20Y to 20K for each color of YMCK.

  As shown in FIG. 15A, before the deviation of the toner consumption is corrected, the toner remaining amount decreasing rate of the toner image forming unit 20V is faster than the toner remaining amount decreasing rate of the toner image forming unit 20W. . Further, since the TMA of the white toner is larger than the TMA of the colored toner, the decrease rate of the remaining amount of toner in the toner image forming unit 20V is faster than the decrease rate of the remaining amount of toner in the toner image forming units 20Y to 20K of YMCK colors. . Therefore, in the toner image forming unit 20V, the toner cartridge replacement time comes before the other toner image forming units 20.

  As shown in FIG. 15B, when the deviation of the toner consumption is corrected, the decrease rate of the remaining amount of toner in the toner image forming unit 20V after correction becomes slower than the decrease rate before correction. The replacement timing of the toner cartridge of the toner image forming unit 20V is also delayed. For example, as illustrated, the toner cartridges for YMCK color toner image forming units 20Y to 20K, the white toner image forming unit 20W, and the white toner image forming unit 20V may be replaced at the same time. You may correct the bias in consumption. This shortens the period during which image formation is stopped for replacement of a toner cartridge that is a consumable item.

(Gloss suppression mode processing)
Next, the “gloss suppression mode process” will be described.
FIG. 16 is a flowchart illustrating an example of a procedure of “image data generation processing” in the gloss suppression mode processing. The procedure of the “image quality priority mode process” is the same as the procedure of the “image superimposition process” except for the “image data generation process”, and thus illustration is omitted.

  In the “image data generation process” in the gloss suppression mode process, the original white image is a solid image. On the second white image (white solid image) formed by the toner image forming unit 20W, the first white image (halftone dot image) is formed by the toner image forming unit 20V to reduce the gloss of the white image.

  In step 700, first image data for the first white image is generated so that a halftone image is formed by the toner image forming unit 20V. The halftone dot image is an image having a predetermined halftone dot area ratio. For example, the dot area ratio may be 20%. In the following step 702, the original white image data is used as the second image data for the second white image, and the routine is ended.

  When the “image data generation process” is completed, each unit is instructed similarly to the “image superimposition process” to form a first white toner image based on the first image data, and a second white color based on the second image data. A toner image is formed, and the first white toner image and the second white toner image are transferred onto the recording medium P, and the transferred superimposed toner image is fixed.

  When a solid image is formed with white toner, the white solid image has a higher gloss because the TMA of the white toner is larger than the TMA of the colored toner. Further, since the gloss of the white solid image is higher than that of the surrounding area, a “gloss level difference” in which the difference in the gloss with the surrounding area is conspicuous occurs in the plane. In the above example, the halftone image is superimposed on the white solid image, and irregularities are formed on the surface of the white image that is the superimposed image. Thereby, the gloss of a white image falls and a gloss level difference is also eliminated.

FIG. 17 is a graph showing an example of the relationship between gross and TMA. The vertical axis represents 60% gloss and the horizontal axis represents TMA. The unit of TMA is [g / m ² ]. The gloss (glossiness) is measured using a gloss measuring machine. The 60% gloss is gloss measured at an incident angle of 60 ° in the specular gloss measurement method (JIS Z 87411).

  A solid line represents a relationship when only a white solid image is formed, and a dotted line represents a relationship when a white solid image and a halftone image are formed. As shown by a solid line in FIG. 17, the larger the TMA, the higher the gloss. In a region with a large TMA such as a white solid image, when a halftone image is formed on the white solid image, the gloss is reduced as compared with the case where only the white solid image is formed.

<Modification>
Note that the configurations of the image forming apparatus and the program described in the above embodiment are merely examples, and it goes without saying that the configurations may be changed without departing from the gist of the present invention.

  In the above, an example (see FIG. 1) in which the toner image forming unit 20W is arranged on the downstream side of the YMCK color toner image forming units 20Y to 20K has been described. However, the toner image forming unit 20W is the same as the toner image forming unit 20V. What is necessary is just to be arrange | positioned in the downstream, and it is not limited to said arrangement | positioning. For example, the toner image forming unit 20W may be disposed next to the toner image forming unit 20V.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Image forming part 20 Toner image forming part 21 Photoconductor drum 22 Charger 23 Exposure apparatus 24 Developing apparatus 25 Cleaning apparatus 26 Charge application apparatus 30 Transfer apparatus 31 Transfer belt 32 Roll 33 Primary transfer roll 34 Secondary transfer roll 35 Cleaning Device 40 Fixing Device 41 Heating Roll 42 Pressure Roller 50 Conveying Device 52 Medium Supplying Unit 54 Downstream Conveying Unit 58 Intermediate Conveying Unit 70 Control Unit 72 Power Supply Unit 100 Operation Display Unit 102 Communication Unit 104 Storage Unit 106 Setting Screen 108 Setting Screen 241 Developing roll 251 Brush 252 Blade 253 Seal member 254 Housing NF Fixing nip NT Transfer nip P Recording medium

Claims (10)

A first image forming unit that forms a first toner image with toner of a specific color;
A second image forming unit disposed downstream of the first image forming unit and forming a second toner image with the specific color toner;
A transfer portion for transferring the formed toner image to a recording medium;
When an image is formed on the recording medium with the specific color toner,
The first image forming unit forms a first toner image based on the first image data obtained from the image information, and the second image forming unit forms the first toner image based on the second image data obtained from the image information. Forming a second toner image, and transferring the formed first toner image and the second toner image to the recording medium in an overlapping manner, the first image forming unit, the second image forming unit, And a control unit for controlling image formation by the transfer unit;
An image forming apparatus.   The image forming apparatus according to claim 1, wherein the specific color toner is a white toner. The controller is
When the toner amount per unit area obtained from the image information exceeds the first upper limit threshold,
Generating first image data having a toner amount per unit area exceeding a first upper limit threshold, and second image data having a toner amount per unit area exceeding the first upper limit threshold;
The first image forming unit generates a first toner image based on the first image data, and the second image forming unit generates a second toner image based on the second image data. Control formation,
The image forming apparatus according to claim 1.   The image forming apparatus according to claim 3, wherein the first upper limit threshold is an upper limit value of a toner amount per unit area obtained by the first image forming unit.   4. The image forming apparatus according to claim 3, wherein the first upper limit threshold is a value at which a residual toner amount remaining in the first image forming unit after the transfer of the first toner image is less than a second upper limit threshold. The controller is
For settings that prioritize concealment,
The first upper limit threshold of the toner amount per unit area as a target amount, the first image data in which the toner amount per unit area is the target amount, and the toner amount per unit area is greater than 0 and less than the target amount Generating second image data;
The first image forming unit generates a first toner image based on the first image data, and the second image forming unit generates a second toner image based on the second image data. Control formation,
The image forming apparatus according to claim 1. The controller is
If priority is given to image quality,
First image data in which the toner amount per unit area obtained from the image information is a target amount, and the toner amount per unit area is a part of the target amount, and the toner amount per unit area is the remainder of the target amount And second image data to be
The first image forming unit generates a first toner image based on the first image data, and the second image forming unit generates a second toner image based on the second image data. Control formation,
The image forming apparatus according to claim 1. The controller is
If the remaining amount of toner in one of the first image forming unit and the second image forming unit is greater than the remaining amount of toner in the other of the first image forming unit and the second image forming unit, the first image forming unit The ratio between the part and the remaining part is changed so that the amount of toner consumed by the one of the first and second image forming units increases.
The image forming apparatus according to claim 7. The controller is
If the image is a solid image,
Generating the first image data for forming a halftone dot image having a lower halftone dot area ratio than the solid image, and the second image data for forming the solid image based on the image information;
The image forming apparatus according to claim 7 or 8. Computer
The program for functioning as a control part of the image forming apparatus of any one of Claim 1-9.