EP4613491A1

EP4613491A1 - Image forming apparatus, density adjustment method, and recording medium

Info

Publication number: EP4613491A1
Application number: EP25161233.9A
Authority: EP
Inventors: Shinya Tokutake; Takuya Ishigai; Keishi Suzuki
Original assignee: Konica Minolta Inc
Current assignee: Konica Minolta Inc
Priority date: 2024-03-04
Filing date: 2025-03-03
Publication date: 2025-09-10
Also published as: JP2025134320A

Abstract

Provided are an image forming apparatus, a density adjustment method, and a program each capable of determining the amount of a pretreatment agent appropriately and adjusting the density of a formed image. The image forming apparatus (1) includes: a first inkjet head (262) that ejects a pretreatment agent; a second inkjet head (242) that ejects an ink; and a controller (40) that controls ejection by the first inkjet head and the second inkjet head. The controller causes an adjustment image to be formed on a recording medium (P), where the adjustment image includes the pretreatment agent and the ink and has a plurality of patterns in which an amount of the pretreatment agent is changed stepwise, and determines the amount of the pretreatment agent based on respective densities of the plurality of patterns in the adjustment image.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to an image forming apparatus, a density adjustment method, and a recording medium.

2. Description of Related Art

In the related art, there is known an image forming apparatus of an inkjet type (hereinafter referred to as "inkjet image forming apparatus" as appropriate) that forms an image on a recording medium such as cloth or sheet by ejecting ink onto the recording medium. In the inkjet image forming apparatus, the degree of ink permeability varies depending on the type of a recording medium on which printing is performed, and an image defect such as bleeding or a void caused by banding or other irregularities may occur.
In order to suppress such an image defect, a pretreatment agent such as a coagulant for adjusting ink permeability is applied. However, when the pretreatment agent is applied, the ink density changes. For this reason, an image having a quality desired by the user may not be obtained.
Accordingly, in recent years, it has been proposed to adjust the amount of a pretreatment agent appropriately so as to obtain an image having a desired quality. For example, Japanese Patent Publication Laid-Open No. 2014-050968 (hereinafter referred to as "Patent Literature 1") discloses a printing apparatus that acquires in advance information on a recording medium to be used, such as the material of the recording medium and the way of folding the recording medium, and determines the amount of a pretreatment agent based on the information on the recording medium.
However, although the printing apparatus described in Patent Literature 1 uses the pretreatment agent in the amount determined based on the information on the recording medium, the printing apparatus may actually involve an occurrence of an image defect due to a factor(s) contributing to permeability other than information included in the information on the recording medium. For this reason, there has been a problem in that an image having a quality desired by the user may not be obtained.

SUMMARY OF THE INVENTION

An object of the present disclosure is to provide an image forming apparatus, a density adjustment method, and a recording medium each capable of determining the amount of a pretreatment agent appropriately and adjusting the density of a formed image.
In order to achieve at least one of the above-described objects, an image forming apparatus reflecting one aspect of the present disclosure includes:

a first inkjet head that ejects a pretreatment agent;
a second inkjet head that ejects an ink; and
a controller that controls ejection by the first inkjet head and the second inkjet head, and
the controller
- causes an adjustment image to be formed on a recording medium, where the adjustment image includes the pretreatment agent and the ink and has a plurality of patterns in which an amount of the pretreatment agent is changed stepwise, and
- determines the amount of the pretreatment agent based on respective densities of the plurality of patterns in the adjustment image.

In order to achieve at least one of the above-described objects, a density adjustment method reflecting one aspect of the present disclosure includes:

forming, on a recording medium, an adjustment image including a pretreatment agent and an ink and having a plurality of patterns in which an amount of the pretreatment agent is changed stepwise; and
determining an amount of the pretreatment agent based on respective densities of the plurality of patterns in the adjustment image.

In order to achieve at least one of the above-described objects, a recording medium reflecting one aspect of the present disclosure accommodates a program that causes a computer to execute the above-described density adjustment method.

BRIEF DESCRIPTION OF DRAWING

The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention:

Fig. 1 is a schematic diagram illustrating an example of the configuration of an inkjet image forming apparatus according to the present embodiment;
Fig. 2 is a schematic diagram illustrating an example of the configuration of an ink head unit 24;
Fig. 3 is a block diagram illustrating a main functional configuration of an image forming apparatus 1;
Fig. 4 is a schematic diagram illustrating a first example of an adjustment image used in density adjustment processing;
Fig. 5 is a schematic diagram illustrating a second example of the adjustment image used in the density adjustment processing;
Fig. 6 is a schematic diagram illustrating a third example of the adjustment image used in the density adjustment processing;
Fig. 7 is a schematic diagram illustrating an example of a region in which an adjustment image is formed;
Fig. 8 is a schematic diagram illustrating another example of the region in which an adjustment image is formed; and
Fig. 9 is a flowchart illustrating an example of the flow of the density adjustment processing according to the present embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments.
Further, in the drawings, components denoted by the same reference signs are the same or equivalent components, and this is commonly applied throughout the specification in its entirety.

[Configuration of Inkjet Image Forming Apparatus 1]

Hereinafter, the present embodiment will be described with reference to the accompanying drawings. Fig. 1 is a schematic view illustrating an example of the configuration of an inkjet image forming apparatus 1 according to the present embodiment. As illustrated in Fig. 1, the inkjet image forming apparatus (hereinafter simply referred to as the "image forming apparatus") 1 includes a supply section 10, an image forming section 20, a discharge section 30, and a control section (controller) 40 (see Fig. 3).
The image forming apparatus 1 conveys a recording medium P, which has been accommodated in the supply section 10, to the image forming section 20 under the control of the control section 40. Then, the image forming apparatus 1 forms an image on the recording medium P at the image forming section 20, and conveys the recording medium P, on which the image has been formed, to the discharge section 30. As the recording medium P, for example, fabric is used. Note that, the recording medium P is not limited to this, and in addition to paper such as a plain paper or a coated paper, it is possible to use various media, such as sheet-like resin, on which ink having landed on the surface can be fixed.
The supply section 10 includes an accommodation section 11 that accommodates the recording medium P, and a medium supply section 12 that conveys and supplies the recording medium P from the accommodation section 11 to the image forming section 20. The medium supply section 12 includes a belt having a ring shape whose inner side is supported by two rollers, and rotates the rollers in a state in which the recording medium P is placed on the belt to convey the recording medium P from the accommodation section 11 to the image forming section 20.
The image forming section 20 includes a conveyance section 21, a transfer unit 22, a heating section 23, an ink head unit 24, a pretreatment agent head unit 26, a drying section 25, and a delivery section 28.
The conveyance section 21 holds the recording medium P placed on a conveyance surface 211a (placement surface) of a conveyance drum 211 having a cylindrical shape. Further, the conveyance section 21 performs a conveyance operation in which the recording medium P on the conveyance drum 211 is conveyed in the conveyance direction (the Y direction) as the conveyance drum 211 rotates and circulates around a rotation axis (cylindrical axis) extending in the X direction (the direction perpendicular to the paper face in Fig. 1).
The conveyance drum 211 includes a claw section (not illustrated) and a suction section (not illustrated) for holding the recording medium P on the conveyance surface 211a thereof. The recording medium P is held on the conveyance surface 211a by being pressed at its end portion by the claw section and by being sucked to the conveyance surface 211a by the suction section. The conveyance section 21 is connected to a conveyance drum motor (not illustrated) for rotating the conveyance drum 211. The conveyance drum 211 rotates just by an angle proportional to the amount of rotation of the conveyance drum motor.
The transfer unit 22 transfers the recording medium P, which has been conveyed by the medium supply section 12 of the supply section 10, to the conveyance section 21. The transfer unit 22 is disposed in a position between the medium supply section 12 of the supply section 10 and the conveyance section 21. The transfer unit 22 holds one end of the recording medium P, which has been conveyed from the medium supply section 12, with a swing arm section 221 to pick the recording medium P up, and then transfers the recording medium P to the conveyance section 21 via a transfer drum 222.
The heating section 23 is disposed between the disposition position of the transfer drum 222 and the disposition position of the ink head unit 24. The heating section 23 heats the recording medium P such that the recording medium P, which is conveyed by the conveyance section 21, has a temperature within a predetermined temperature range. The heating section 23 includes, for example, an infrared heater or the like, and energizes the infrared heater based on a control signal supplied from the control section 40 (see Fig. 3) to cause the infrared heater to generate heat.
The ink head unit 24 ejects ink onto the recording medium P held on the conveyance drum 211 to form an image. Specifically, the ink head unit 24 ejects ink onto the recording medium P from ink ejection ports formed in a nozzle surface 245 (see Fig. 2) facing the conveyance surface 211a of the conveyance drum 211 at an appropriate timing according to the rotation of the conveyance drum 211. The ink head unit 24 is disposed such that the ink ejection ports and the conveyance surface 211a are separated from each other by a predetermined distance.
In the image forming apparatus 1 according to the present embodiment, four ink head units 24 corresponding to four colors of ink: yellow (Y), magenta (M), cyan (C), and black (K), respectively, are arranged. Specifically, for example, the four ink head units 24 are arranged at predetermined intervals in the order of Y, M, C, and K from the upstream side in the conveyance direction of the recording medium P.
Fig. 2 is a schematic diagram illustrating an example of the configuration of the ink head unit 24. Here, nozzle surfaces of the ink head unit 24, which face the conveyance surface 211a of the conveyance drum 211, are illustrated.
The ink head unit 24 includes four inkjet heads 242 attached to an attachment member 244. In each of the inkjet heads 242, a plurality of image forming elements (recording elements) each including a pressure chamber for storing ink, a piezoelectric element disposed on a wall surface of the pressure chamber, and nozzles 243 is formed. In the image forming element, when a driving signal for deforming and operating the piezoelectric element is inputted, the deformation of the piezoelectric element deforms the pressure chamber to change the pressure in the pressure chamber, thereby ejecting ink from the nozzles 243 communicating with the pressure chamber.
In the inkjet head 242, two nozzle arrays each including the nozzles 243 arranged at equal intervals in a direction intersecting the conveyance direction of the recording medium P (in the present embodiment, a direction orthogonal to the conveyance direction, that is, the X direction) are formed in the nozzle surface 245. These two nozzle arrays are arranged such that the positions of the nozzles 243 are shifted from each other in the X direction by a half of the disposition interval of the nozzles 243 in each nozzle array.
The four inkjet heads 242 are disposed in a hounds-tooth check pattern such that the disposition range of the nozzle arrays in the X direction is connected without a break. The disposition range of the nozzles 243 included in the ink head unit 24 in the X direction covers the X-direction width of a region, in which an image is formed, in the recording medium P that is conveyed by the conveyance section 21. At this time, the ink head unit 24 is used in a fixed position with respect to the rotation axis of the conveyance drum 211 during image formation. That is, the ink head unit 24 includes a line head capable of ejecting ink over an image formable width in the X direction with respect to the recording medium P, and the image forming apparatus 1 is an image forming apparatus of a single-pass type.
Note that, the number of nozzle arrays included in the inkjet head 242 may not be two, but may be one or may be three or more. In addition, the number of the inkjet heads 242 included in the head unit 24 may not be four, but may be three or less or may be five or more. In addition, the inkjet head 242 corresponds to the "second inkjet head" of the present disclosure.
Fig. 1 will be described again. The pretreatment agent head unit 26 ejects a pretreatment agent onto the recording medium P held on the conveyance drum 211 to perform pretreatment on the recording medium P. Specifically, the pretreatment-agent head unit 26 ejects the pretreatment agent onto the recording medium P from pretreatment agent ejection ports formed in a nozzle surface (not illustrated) facing the conveyance surface 211a of the conveyance drum 211 at an appropriate timing according to the rotation of the conveyance drum 211.
The pretreatment agent head unit 26 is disposed on the upstream side of the ink head unit 24 in the conveyance direction. More specifically, the pretreatment agent head unit 26 is disposed between the disposition position of the heating section 23 and the disposition position of the ink head unit 24. In addition, the pretreatment agent head unit 26 is disposed such that the pretreatment agent ejection ports and the conveyance surface 211a are separated from each other by a predetermined distance.
Note that, the configuration of the pretreatment agent head unit 26 is similar to that of the ink head unit 24 illustrated in Fig. 2, and includes inkjet heads 262, nozzles 263, an attachment member 264, and nozzle surfaces 265. The inkjet head 262 corresponds to the "first inkjet head" of the present disclosure.
In the present embodiment, for example, a coagulant is used as the pretreatment agent. The coagulant is used for adjusting ink permeability. Mixing the coagulant with ink causes the ink to be coagulated to suppress bleeding or the like on the recording medium P.
A density measurement section (density measurer) 27 measures the density of an image formed on the recording medium P. The density measurement section 27 is configured to include, for example, a light emitting section (light emitter) and a light receiving sensor, and detects light, which has been emitted from the light emitting section and has been reflected by an image, with the light receiving sensor. Then, the density measurement section 27 measures the density of the image based on the received light amount of the detected light. The density measuring section 27 supplies the measurement result to the control section 40.
The drying section 25 includes a heat source section, such as a heater, and an air blowing section, such as a fan, and blows hot air onto the image forming surface (upper surface) of the recording medium P placed on the conveyance section 21, thereby drying the ink on the recording medium P. The drying section 25 is disposed to face the conveyance surface 211a between the disposition position of the ink head unit 24 and the disposition position of a transfer drum 281 of the delivery section 28 in the conveyance direction.
Note that, although the drying section 25 has been described as being integrally formed inside the image forming section 20 in this example, the present disclosure is not limited thereto, and the drying section 25 may be formed separately from the image forming section 20. In a case where the drying section 25 is configured separately from the image forming section, the drying section 25 is disposed, for example, between the image forming section 20 and the discharge section 30.
The delivery section 28 includes the transfer drum 281 having a cylindrical shape, which transfers the recording medium P from the conveyance section 21 to a belt loop 282, and the belt loop 282, which includes a belt having a ring shape whose inner side is supported by two rollers. The delivery section 28 conveys the recording medium P, which has been transferred from the conveyance section 21 onto the belt loop 282 by the transfer drum 281, with the belt loop 282, and delivers the recording medium P to the ejection section 30.
The ejection section 30 includes a placement section 31 on which the recording medium P, which has been delivered from the image forming section 20 by the delivery section 28, is placed.
Fig. 3 is a block diagram illustrating a main functional configuration of the image forming apparatus 1. As illustrated in Fig. 3, the image forming apparatus 1 includes the heating section 23, a head driving section 241, the inkjet head 242, a head driving section 261, the inkjet head 262, the drying section 25, the control section 40, a conveyance driving section 51, an operation display section 52, and an input/output interface 53.
The head driving section 241 supplies a driving signal for deforming and operating the piezoelectric element to the image forming element of the inkjet head 242 at an appropriate timing according to image data. Thus, the head driving section 241 causes the nozzles 243 of the inkjet head 242 to eject ink in an amount corresponding to the pixel value of the image data.
The head driving section 261 supplies a driving signal for deforming and operating the piezoelectric element to the image forming element of the inkjet head 262 at an appropriate timing according to image data. Thus, the head driving section 261 causes the nozzles 263 of the inkjet head 262 to eject a predetermined amount of the pretreatment agent.
The control section 40 controls the image forming apparatus 1 in its entirety. In particular, in the present embodiment, the control section 40 controls the head driving section 241 of the ink head unit 24 and the head driving section 261 of the pretreatment agent head unit 26. Thus, density adjustment processing for adjusting the density of ink is performed. Details of the density adjustment processing will be described later.
The control section 40 includes a central processing unit (CPU) 41, a random access memory (RAM) 42, a read only memory (ROM) 43, and a storage section (storage) 44.
The CPU 41 reads programs and setting data for various controls stored in the ROM 43, stores the read programs and data in the RAM 42, and executes the programs to perform various arithmetic processing. Further, the CPU 41 performs integrated control of the entire operation of the image forming apparatus 1.
The RAM 42 provides a working memory space to the CPU 41 and temporarily stores data. The RAM 42 may include a non-volatile memory.
The ROM 43 accommodates programs and setting data for various controls to be executed by the CPU 41, and the like. Note that, a rewritable non-volatile memory such as an electrically erasable programmable read only memory (EEPROM) or a flash memory may be used instead of the ROM 43.
The storage section 44 stores a print job (image forming instruction) inputted from an external apparatus 2 via the input/output interface 53, image data related to the print job, and the like. Among those mentioned above, the print job includes information designating image data on an image to be formed, as well as information on the type of the recording medium P on which the image is formed (for example, the type, size, thickness, and/or the like of the recording medium P). As the storage section 44, for example, a hard disk drive (HDD) is used, and a dynamic random access memory (DRAM) or the like may also be used in combination.
Further, the storage section 44 stores various information required for the control section 40 to control each section. For example, in the present embodiment, the storage section 44 stores information indicating a relationship between a condition(s) related to the recording medium P, such as the type, thickness, and/or the like of the recording medium P, and the amount of the pretreatment agent and the density in the density adjustment processing to be described later. This information is used in the density adjustment processing in a case where the condition(s) such as the type, thickness, and/or the like of the recording medium P is/are the same.
The conveyance driving section 51 supplies a driving signal to the conveyance drum motor of the conveyance drum 211 based on a control signal supplied from the control section 40 to rotate the conveyance drum 211 at predetermined rate and timing.
Further, the conveyance driving section 51 supplies driving signals to motors for operating the medium supply section 12, the transfer unit 22, and the delivery section 28, based on a control signal supplied from the control section 40. Thus, the conveyance driving section 51 causes the recording medium P to be supplied to the conveyance section 21 and to be discharged from the conveyance section 21.
The operation display section 52 includes a display apparatus, such as a liquid crystal display or an organic EL display, and an input apparatus, such as an operation key or a touch screen disposed in an overlapping manner on a screen of the display apparatus. The operation display section 52 causes the display apparatus to display various information, converts the user's input operation on the input apparatus into an operation signal, and outputs the operation signal to the control section 40.
The input/output interface 53 mediates transmission and reception of data between the external apparatus 2 and the control section 40. The input/output interface 53 is constituted by, for example, one of various serial interfaces and various parallel interfaces, or a combination thereof.
The external apparatus 2 is, for example, a personal computer and supplies a print job, image data, and/or the like to the control section 40 via the input/output interface 53.

[Adjustment of Ink Density]

Fig. 4 is a schematic diagram illustrating a first example of an adjustment image used in density adjustment processing. Here, a case where a coagulant is used as the pretreatment agent and the density is adjusted by using ink of one color of Y, M, C, and K will be described as an example.
In the density adjustment processing, an adjustment image is first formed on the recording medium P as illustrated in Fig. 4. The adjustment image is an image formed for adjusting the density of an image when an actual image is formed.
The adjustment image is, for example, a test pattern in which ink of the same density is printed on a plurality of coagulant patterns which has been printed while the amount of the coagulant is changed stepwise within a predetermined range. That is, the adjustment image is an image including a plurality of patterns having different amounts of the coagulant. In this example, the adjustment image is formed such that the amount of the coagulant increases stepwise toward the direction opposite to the conveyance direction.
In the thus formed adjustment image, each pattern included in the adjustment image is a mixture of the coagulant and the ink. Since the density of the ink is the same in one adjustment image, the respective densities of the patterns included in the adjustment image vary depending on the amount of the coagulant.
Accordingly, the respective densities of the patterns included in the adjustment image are measured, and a pattern having a density desired by the user is selected from the measurement results, whereby the amount of the coagulant to be used is determined. Then, the determined amount of the coagulant is set to the image forming apparatus 1, so that the density at the time of forming an actual image is adjusted.
In this way, by using the adjustment image in which the amount of the coagulant is changed stepwise, it is possible to determine the amount of the pretreatment agent for achieving the density desired by the user appropriately and to adjust the density of a formed image.
Note that, in a case where the density adjustment processing is performed, when the condition(s) such as the type, thickness, and/or the like of the recording medium P is/are the same as the condition(s) when the density adjustment processing was performed in the past, the information stored in the storage section 44 may be used so that the density adjustment processing may be omitted. Thus, the time required for image formation can be shortened, and productivity can be improved.
In addition, in this example, it has been described that the density of a formed image is adjusted with the same ink density of the adjustment image, but the present disclosure is not limited thereto, and the density of a formed image may be adjusted by changing the ink density stepwise as well in addition to changing the amount of the coagulant stepwise.
Fig. 5 is a schematic diagram illustrating a second example of the adjustment image used in the density adjustment processing. In the density adjustment processing in this case, as illustrated in Fig. 5, a plurality of adjustment images including a first adjustment image using ink with a predetermined density and a second adjustment image using ink with a different density are formed on the recording medium P. In this example, the adjustment images are formed side by side in the conveyance direction of the recording medium P such that the ink density becomes higher toward the direction opposite to the conveyance direction.
In the plurality of adjustment images formed in this way, the respective densities of the patterns vary depending on the ink density and the amount of the coagulant. Accordingly, the respective densities of the patterns included in the adjustment images are measured, and a pattern having a density desired by the user is selected from the measurement results, whereby the amount of the coagulant to be used is determined. Then, the determined amount of the coagulant is set to the image forming apparatus 1, so that the density at the time of forming an actual image is adjusted.
In this way, as both the ink density and the amount of the coagulant are optimized, it is possible to set the density of the actual image with higher precision.
In addition, in this example, it has been described that the amount of the coagulant is determined using the ink of a single color, but the present disclosure is not limited thereto, and the corresponding amounts of the coagulant may be determined for a plurality of colors, respectively.
Fig. 6 is a schematic diagram illustrating a third example of the adjustment image used in the density adjustment processing. In the density adjustment processing in this case, as illustrated in Fig. 6, a plurality of adjustment images using inks of different colors is formed on the recording medium P. In this example, the adjustment images are formed side by side in the conveyance direction of the recording medium P such that the colors of inks are Y, M, C, and K in the order from the left side in the conveyance direction.
In the plurality of adjustment images formed in this way, the densities of the patterns for each color vary depending on the ink density and the amount of the coagulant. Accordingly, the respective densities of the patterns included in the adjustment images are measured, and a pattern having a density desired by the user is selected for each color from the measurement results, whereby the amount of the coagulant to be used is determined. Then, the determined amount of the coagulant is set to the image forming apparatus 1, so that the density at the time of forming an actual image is adjusted.
In this way, as the coagulant for each color of ink is optimized, it is possible to set the density of each color of ink appropriately.

(Determination of Amount of Coagulant)

Here, the amount of the coagulant required for coagulating ink varies depending on the solid content concentration of the ink, and the amount of the coagulant required for coagulating ink is larger for ink having a higher solid content concentration of a pigment or the like. The solid content concentration varies depending on the color of ink.
For this reason, in a case where the amount of the coagulant is determined, it is preferable to determine the amount of the coagulant according to an ink having the highest solid content concentration among a plurality of inks. Accordingly, in a case where the amount of the coagulant is determined, for example, it is satisfactory to form an adjustment image by using, among a plurality of inks, an ink of a color having the highest solid content concentration and perform the density adjustment processing.
In this way, by determining the amount of the coagulant for ink of a color that requires the largest amount of the coagulant, it is possible to suppress the time required for adjustment of the inks of the other colors as well as the inks required when the density adjustment processing is performed.
In addition, the amount of the coagulant required for coagulating ink greatly varies depending on the type and thickness of the recording medium P. Accordingly, the range of the amount of the coagulant to be changed stepwise when an adjustment image is formed may be changed according to the type and thickness of the recording medium P. As a result, it is possible to improve the accuracy when determining the amount of the coagulant.
Note that, particularly in a case where the recording medium P is fabric, the range of an appropriate amount of the coagulant is large depending on the fabric type, the fabric thickness, the way of folding, and the like, as compared with a case where the recording medium P is paper. For this reason, the amount of the coagulant when an adjustment image is formed is preferably about 10 to 40 g/m², for example. This is because when the amount of the coagulant is too large, it becomes excessive when ink is coagulated, and when the amount of the coagulant is too small, the effect of coagulating ink cannot be obtained.
Incidentally, a coagulant is used for coagulating ink used in image formation. For this reason, it is satisfactory to adjust the amount of the coagulant after the density of ink to be used is determined.
At this time, when the recording medium P on which an image is actually formed is fabric, the ink density is determined by using paper as the recording medium P. Then, the amount of the coagulant, which is greatly affected by the type and thickness of the recording medium P, may be determined by using the fabric that is actually used.

(Regarding Execution Timing of Density Adjustment Processing)

As described above, the optimal amount of the coagulant greatly varies depending on the type and thickness of the recording medium P. For this reason, the density adjustment processing is preferably performed using the recording medium P on which an actual image is printed. Accordingly, it is satisfactory to perform the density adjustment processing, for example, when the recording medium P is replaced with a recording medium to be used when an image is actually printed, and before the image is formed.
Further, the density adjustment processing may be performed at the time of activation of the image forming apparatus 1 so as not to affect the productivity thereafter.
Further, when the use environment of the image forming apparatus 1, such as temperature and humidity, changes, even in a case where the image forming apparatus 1 is used for the same type and thickness, the optimum amount of the coagulant for a desired density of a formed image may change. Accordingly, in the case of determining the optimum amount of the coagulant, the density adjustment processing may be performed according to a change in the use environment.
In this case, for example, the image forming apparatus 1 is provided with a temperature and humidity sensor, and when the temperature and/or humidity detected by the temperature and humidity sensor change(s), the density adjustment processing is performed. Accordingly, it is possible to reduce an error in the amount of the coagulant due to a change in the use environment of the image forming apparatus 1 and to more surely obtain a desired density.

(Regarding Adjustment Image Forming Region)

An adjustment image is formed, for example, in a non-image forming region excluding an image forming region, in which an actual image is formed, on the recording medium P.
Fig. 7 is a schematic diagram illustrating an example of a region in which an adjustment image is formed. Fig. 8 is a schematic diagram illustrating another example of a region in which an adjustment image is formed. In the example illustrated in Fig. 7, the adjustment image is formed, for example, in an end portion of the recording medium P.
Further, in the example illustrated in Fig. 8, the adjustment image is formed, for example, between a plurality of jobs for forming an image on the recording medium P. That is, the adjustment image is formed, for example, in a non-image forming region between an image forming region for an image formed by a first job and an image forming region for an image formed by a second job.

[Density Adjustment Processing]

Fig. 9 is a flowchart illustrating an example of the flow of the density adjustment processing according to the present embodiment. In this example, a case where a coagulant is used as the pretreatment agent and the density is adjusted using ink of one color of Y, M, C, and K will be described as an example.
In step S1, the control section 40 causes an adjustment image to be formed on the recording medium P. Specifically, the control section 40 first causes a coagulant, which is a pretreatment agent, to be ejected onto the recording medium P to form coagulant patterns.
The coagulant patterns are formed, for example, by ejecting the coagulant from the nozzles 263 of the pretreatment agent head unit 26 while the recording medium P is conveyed. At this time, the control section 40 controls the head driving unit 261 of the pretreatment agent head unit 26 such that the amount of the coagulant to be ejected changes at a predetermined timing.
Next, the control section 40 causes ink to be ejected from the nozzles 243 of the ink head unit 24 onto the coagulant patterns while the recording medium P is conveyed. Thus, an adjustment image having different densities for each pattern is formed on the recording medium P.
In step S2, the control section 40 causes the densities to be measured for each pattern of the adjustment image. The control section 40 causes the densities of each pattern to be measured based on the light amount of light emitted from the light emitting section of the density measurement section 27 and reflected by the adjustment image.
In step S3, the control section 40 determines the amount of the coagulant desired by the user, based on the measured densities for each pattern. For example, the control section 40 converts the densities for each pattern into numerical values based on the measurement results, and selects, among the respective densities of the patterns, a pattern having a density corresponding to a value included in a predetermined range.
Then, in step S4, the control section 40 sets the amount of the coagulant of the selected pattern as the optimum amount of the coagulant when the recording medium P is used this time. The amount of the coagulant set in this way is the optimal amount of the coagulant when forming an image having a quality desired by the user.
As described above, the image forming apparatus 1 according to the present embodiment forms, on the recording medium P, an adjustment image having a plurality of patterns in which the amount of the coagulant is changed stepwise, and determines the amount of the coagulant based on the respective densities of the patterns in the adjustment image. Accordingly, since the amount of the coagulant is determined according to the recording medium P, it is possible to appropriately set the density of an image which is actually formed.
Further, in the present embodiment, the amount of the coagulant is determined using the recording medium P on which an actual image is formed. For this reason, even when the recording medium P to be used is an unknown recording medium P for which the necessary amount of the coagulant is unknown, the amount of the coagulant can be optimized.
Although an embodiment has been described above, the present disclosure is not limited to the above-described embodiment, and various modifications and applications are possible without departing from the spirit and scope of the present disclosure. For example, although a case where the image forming apparatus 1 is of a single-pass type has been described in the present embodiment, the present disclosure is not limited thereto, and for example, the image forming apparatus 1 may be of a scanning type.
In a case where the image forming apparatus 1 is of a scanning type, it is possible to change the amount of the coagulant stepwise in one scan, and thus, the time required for forming an adjustment image is shortened. For this time, the time required for one density adjustment processing can be shortened.
Although embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for purpose of illustration and example only and not limitation. The scope of the present invention should be interpreted by terms of the appended claims.

Claims

An image forming apparatus (1), comprising:
a first inkjet head (262) that ejects a pretreatment agent;

a second inkjet head (242) that ejects an ink; and

a controller (40) that controls ejection by the first inkjet head (262) and the second inkjet head (242), wherein the controller (40)
causes an adjustment image to be formed on a recording medium (P), the adjustment image including the pretreatment agent and the ink and having a plurality of patterns in which an amount of the pretreatment agent is changed stepwise, and

determines the amount of the pretreatment agent based on respective densities of the plurality of patterns in the adjustment image.
The image forming apparatus (1) according to claim 1, wherein
the controller (40) causes the adjustment image to be formed on the recording medium (P), the adjustment image being an image in which the amount of the pretreatment agent and a density of the ink are changed.
The image forming apparatus (1) according to claim 1, wherein
the controller (40)
causes the adjustment image to be formed on the recording medium (P) for each of colors of a plurality of the inks, and

determines the amount of the pretreatment agent for each of the colors of the plurality of inks.
The image forming apparatus (1) according to claim 1, wherein
the controller (40) causes the adjustment image to be formed by using, among a plurality of the inks, an ink of a color having a highest solid content concentration.
The image forming apparatus (1) according to claim 1, wherein
the controller (40) determines a range of the amount of the pretreatment agent according to a type of the recording medium (P) and a thickness of the recording medium (P), the amount of the predetermined agent being changed stepwise.
The image forming apparatus (1) according to claim 5, wherein
the amount of the pretreatment agent is 10 to 40 g/m².
The image forming apparatus (1) according to claim 1, wherein
the controller (40) causes the adjustment image to be formed after determining an amount of the ink when the adjustment image is formed.
The image forming apparatus (1) according to claim 7, wherein
in a case where the recording medium (P) is fabric, the controller (40) determines a density of the ink by using paper, and determines the amount of the pretreatment agent by using the recording medium (P).
The image forming apparatus (1) according to claim 1, wherein
the controller (40) causes the adjustment image to be formed, when the recording medium (P) is replaced and before an actual image is formed.
The image forming apparatus (1) according to claim 1, wherein
the controller (40) causes the adjustment image to be formed at a time of activation of the image forming apparatus (1).
The image forming apparatus (1) according to claim 1, further comprising a temperature and humidity sensor that detects a temperature and a humidity in the image forming apparatus (1), wherein
the controller (40) causes the adjustment image to be formed based on a detection result by the temperature and humidity sensor.
The image forming apparatus (1) according to claim 1, wherein
the controller (40) causes the adjustment image to be formed in a non-image forming region excluding an image forming region on the recording medium (P), the image forming region being a region in which an actual image is formed.
The image forming apparatus (1) according to claim 12, wherein
the non-image forming region is an end portion of the recording medium (P).
The image forming apparatus (1) according to claim 12, wherein
the non-image forming region is a region between respective images formed by a plurality of jobs.
The image forming apparatus (1) according to claim 1, further comprising a density measurer (27) that includes:
a light emitter that emits light to the adjustment image; and

a light receiving sensor that detects the light reflected by the adjustment image, and
measures the respective densities of the plurality of patterns in the adjustment image based on a received light amount of the light having been reflected.
The image forming apparatus (1) according to claim 1, further comprising a storage (44) that stores information indicating a relationship between a condition related to the recording medium (P) and the amount of the pretreatment agent and the densities.
A density adjustment method, comprising:
forming, on a recording medium (P), an adjustment image including a pretreatment agent and an ink and having a plurality of patterns in which an amount of the pretreatment agent is changed stepwise; and

determining the amount of the pretreatment agent based on respective densities of the plurality of patterns in the adjustment image.
A recording medium, accommodating a program that causes a computer to execute the density adjustment method according to claim 17.