JP6225968B2 - Image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming method.

2. Description of the Related Art There is known an image forming apparatus that records an image or a character by ejecting a liquid such as ink from a nozzle provided in a head unit and landing a droplet (ink dot) on a medium. In some image forming apparatuses, ultraviolet curable ink (UV ink) that cures when irradiated with ultraviolet (UV) light
There is something that erupts. When an image is formed by ejecting UV ink, the UV ink dot gradually spreads over time from when the UV ink dot lands on the medium until it is cured by being irradiated with UV. Is getting bigger.

A method of forming an image while adjusting the dot diameter and print density of UV ink using such properties is known. For example, a serial printing printer that performs UV irradiation from two UV irradiation units arranged at both ends of the head unit while ejecting UV ink while reciprocating the head unit in the main scanning direction perpendicular to the medium conveyance direction There is. There has been proposed a method for adjusting the size and density of UV ink dots by adjusting the time until the UV ink is cured by irradiating UV while controlling the UV irradiation timing using such a printer. (For example, patent document 1).

JP 2004-167864 A

In connection with the method of Patent Document 1, if only one UV irradiation unit is provided on one side in the main scanning direction of the head unit and UV irradiation is performed using the UV irradiation unit, the weight of the apparatus and the UV light source It is possible to adjust the size and density of the UV ink dots while suppressing the cost of the ink. However, in such a printer, when the head portion moves in one direction, it is possible to irradiate UV immediately after the UV ink ejection, but when the head portion moves in the other direction, the UV immediately after the UV ink ejection. It is impossible to irradiate. That is, when the head portion moves forward and backward, UV
Since the timing from when the ink dots land on the medium until the UV is irradiated is different, U
It is difficult to accurately adjust the size and density of the V ink dots.

In the present invention, the UV ink is ejected while the head portion moves in the main scanning direction.
UV ink is ejected by a serial printing type printer that performs printing by main scanning that irradiates V ink and main scanning that discharges UV ink while the head portion moves in the main scanning direction and does not irradiate UV ink during the movement. When forming an image using this method, it is an object to accurately adjust the size and density of UV ink dots.

The main invention for achieving the above object is as follows: (A) a head part that ejects liquid that is cured by light irradiation from a nozzle to a medium; and (B) the head part is mounted and intersects the sub-scanning direction. A carriage section that moves in the main scanning direction; (C) an irradiation section that is provided in the main scanning direction of the head of the carriage section and that irradiates the light; and (D) the head while moving the carriage section. A controller that ejects the liquid from a portion and irradiates the light from the irradiating portion, wherein the liquid is ejected from the head portion while moving the carriage portion in the main scanning direction. A first liquid curing method of irradiating light from the irradiation unit during movement of the carriage unit after the main scanning without irradiating the ejected liquid with light from the irradiation unit in the main scanning Second liquid curing in which, in the main scanning in which the liquid is ejected from the head unit while moving the carriage unit in the main scanning direction, the ejected liquid is irradiated with light from the irradiation unit in the main scanning. And a control unit for performing the image forming, wherein the amount of liquid ejected during the second liquid curing method is greater than the amount of liquid ejected during the first liquid curing method. Device.

  Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

1 is a block diagram illustrating an overall configuration of a printer. FIG. 2A is a diagram illustrating the configuration of the printer 1 according to the present embodiment. FIG. 2B is a side view illustrating the configuration of the printer 1 of the present embodiment. It is sectional drawing explaining the structure of a head. It is explanatory drawing of the nozzle Nz provided in the head. FIG. 6 is a diagram illustrating a flow of image processing by a printer driver. It is a figure showing the flow for demonstrating the flow of a halftone process. It is a figure which shows an example of a dot production rate table (LUT). It is a figure which shows the mode of the dot ON / OFF determination by a dither method. 9A and 9B are diagrams for explaining the dot forming operation in the UV ink curing method 2. It is a figure explaining the difference between LUT1 and LUT2.

  At least the following matters will become clear from the description of the present specification and the accompanying drawings.

(A) a head portion that ejects liquid that is cured by irradiation of light from a nozzle to a medium; (B) a carriage portion that is mounted with the head portion and moves in a main scanning direction that intersects the sub-scanning direction; C) an irradiation unit that is provided in the main scanning direction of the head of the carriage unit and irradiates the light; and (D) the liquid is ejected from the head unit while moving the carriage unit, and the irradiation unit A control unit that irradiates the light from the head, and in the main scanning to eject the liquid from the head unit while moving the carriage unit in the main scanning direction, the irradiation is performed in the main scanning. A first liquid curing method of irradiating light from the irradiation unit in the movement of the carriage unit after the main scanning without irradiating light from the unit, and the carriage unit in the main scanning direction A second liquid curing method for irradiating the ejected liquid with light from the irradiating unit in the main scanning at the time of main scanning for ejecting the liquid from the head unit while moving the control unit; And an image forming apparatus having a larger amount of liquid ejected during the second liquid curing method than an amount of liquid ejected during the first liquid curing method.

According to such an apparatus, the head portion ejects UV ink while moving in the main scanning direction,
The main scanning that irradiates the UV ink during the movement, and the UV while the head portion moves in the main scanning direction
Adjusting the size and density of UV ink dots with high accuracy when forming an image using UV ink with a serial printing printer that discharges ink and performs printing by main scanning without UV ink irradiation during the movement can do.

In this image forming apparatus, the ejection amount of the liquid ejected corresponding to predetermined data of the image data input to the image forming apparatus is greater than that in the first liquid curing method. It is desirable to have more during the liquid curing method.
According to such an image forming apparatus, even when an image is printed using the same data, an image with good image quality is formed by ejecting an optimal amount of UV ink according to the difference in the liquid curing method. It becomes possible to do.

The image forming apparatus includes a storage unit that stores a data conversion table used for creating print data, and the control unit creates print data from the image data input to the image forming apparatus by the control unit, When image formation is performed using the created print data and the liquid is ejected, print data is created using different data conversion tables for the first liquid curing method and the second liquid curing method. , The second than the first liquid curing method.
It is desirable to eject a larger amount of liquid during the liquid curing method.
According to such an image forming apparatus, by selecting an appropriate table from the registered data conversion tables, it is possible to wait until UV ink dots are formed on the medium until they are cured by receiving UV irradiation. In the first liquid curing method that takes a long time, the ink ejection amount can be easily adjusted, and an image with good image quality can be formed.

In this image forming apparatus, it is preferable that the data conversion table is a table that defines the amount of ink ejected per unit area of the medium.
According to such an image forming apparatus, by selecting an appropriate table from the registered dot generation rate tables, it is possible to easily adjust the amount of ink applied to the medium, and to achieve a good image quality. An image can be formed.

In this image forming apparatus, it is desirable that the liquid has a viscosity at 20 ° C. of 7 mPa · S or more.
According to such an image forming apparatus, since it is easy to maintain a spherical shape without collapsing the UV ink dots until they are cured by receiving UV irradiation, color mixing or the like that occurs due to the ink dots spreading wet. It is possible to suppress and form an image with good image quality.

In this image forming apparatus, the liquid is represented by the following general formula (1).
_{^{CH 2 = CR 1 -COOR 2 -O}} -CH = CH-R 3 ··· (1)
Wherein R ¹ is a hydrogen atom or a methyl group, R ² is a divalent organic residue having 2 to 20 carbon atoms, and R ³ is a monovalent organic residue having 1 to 11 carbon atoms. .)
It is desirable to contain the component represented by these.
According to such an image forming apparatus, by using a UV ink having higher curability,
Ink dots can be easily cured, and UV ink dots can be prevented from spreading.

In such an image forming apparatus, when a plurality of types of liquids having different viscosities are ejected and a liquid having a low viscosity among the plurality of types of liquids is ejected in the first liquid curing method, the viscosity is low. It is desirable to reduce the amount of the liquid ejected from the head unit, rather than ejecting a high liquid.
According to such an image forming apparatus, it is possible to appropriately control the amount of ink applied according to the viscosity of the UV ink, and it is possible to form a good image in terms of color mixing and density.

In addition, (A) main scanning in which a liquid that is cured by receiving light from a head unit mounted on the carriage unit is ejected to a medium while moving the carriage unit in a main scanning direction that intersects the sub-scanning direction. Irradiating the light from the irradiating unit in the movement of the carriage unit after the main scanning without irradiating the ejected liquid from the irradiating unit in the main scanning, and (B ) In the main scan in which the liquid is ejected from the head unit to the medium while moving the carriage unit in the main scan direction, the ejected liquid is irradiated with the light from the irradiation unit in the main scan. (C) the main scanning (
The image forming method in which the amount of liquid ejection is larger in the main scanning (B) than in the case of A) becomes clear.

=== Basic Configuration of Image Forming Apparatus ===
As an embodiment of the image forming apparatus for carrying out the invention, an ink jet printer (printer 1) will be described as an example.

<Configuration of Printer 1>
The printer 1 is a form of an image forming apparatus that records an image by ejecting a liquid such as ink toward a medium such as paper, cloth, or film sheet. In this embodiment, ultraviolet rays (hereinafter referred to as U
An image is recorded on the medium by ejecting ultraviolet curable ink (hereinafter referred to as UV ink) that is cured by irradiation with V). The UV ink is an ink containing an ultraviolet curable resin, and is cured by undergoing a photopolymerization reaction in the ultraviolet curable resin when irradiated with UV. Details of the UV ink will be described later. Note that the printer 1 of the present embodiment has a U
As V ink, black (K), cyan (C), magenta (M), and yellow (Y)
An image is recorded using the four color inks.

FIG. 1 is a block diagram showing the overall structure of the printer 1. The printer 1 includes a transport unit 10, a carriage unit 20, a head unit 30, an irradiation unit 40, a detector group 50, and a controller 60. The controller 60 uses the head unit 30 and the irradiation unit 4 based on print data received from the computer 110 which is an external device.
It is a control part which controls each unit, such as 0. The situation in the printer 1 is monitored by the detector group 50, and the detector group 50 outputs the detection result to the controller 60. The controller 60 controls each unit based on the detection result output from the detector group 50.

<Computer 110>
The printer 1 is communicably connected to a computer 110 that is an external device.
A printer driver is installed in the computer 110. The printer driver is a program for displaying a user interface on a display device and converting image data output from an application program into print data (image formation data). This printer driver is a flexible disk FD or CD-RO.
It is recorded on a recording medium (computer-readable recording medium) such as M. Also, the printer driver can be downloaded to the computer 110 via the Internet. In addition, this program is comprised from the code | cord | chord for implement | achieving various functions. Image processing by the printer driver will be described later.

The computer 110 outputs print data corresponding to the image to be printed to the printer 1 in order to cause the printer 1 to print an image. The print data is data in a format that can be interpreted by the printer 1 and includes various command data and pixel data. The command data is data for instructing the printer 1 to execute a specific operation. The command data includes, for example, command data for instructing medium supply, command data indicating the transport amount of the medium, and command data for instructing medium ejection. The pixel data is data related to pixels of an image to be printed.

Here, a pixel is a unit element constituting an image, and is a unit element of recording defined by recording resolution. An image is formed by two-dimensionally arranging the pixels. The pixel data in the print data is data (for example, gradation values) related to dots formed on a medium (for example, a medium). The pixel data is composed of, for example, 2-bit data for each pixel.
The 2-bit pixel data is data that can express one pixel with four gradations.

<Transport unit 10>
FIG. 2A is a bird's-eye view showing the configuration of the printer 1 of this embodiment, and FIG. 2B is a side view showing the configuration of the printer 1.

The transport unit 10 is for transporting a medium in a predetermined direction (hereinafter referred to as a transport direction or a sub-scanning direction). The transport unit 10 includes a medium supply roller 11, a transport motor 12, a transport roller 13, a platen 14, and a medium discharge roller 15 (FIGS. 2A and 2B).

The medium supply roller 11 is a roller for supplying the medium inserted into the medium insertion opening into the printer 1. The transport roller 13 is a roller that transports the medium supplied by the medium supply roller 11 to a printable area, and is driven by the transport motor 12. The operation of the transport motor 12 is controlled by a controller 60 on the printer side. The platen 14 is a member that supports the medium being printed from the back side. The medium discharge roller 15
This roller discharges the medium to the outside of the printer, and is provided on the downstream side in the transport direction with respect to the printable area.

Note that in the sub-scanning in which the head and the medium are relatively moved in the sub-scanning direction, sub-scanning in which the medium is transported in the transporting direction (sub-scanning direction) with respect to the head may be performed. Sub-scanning may be performed in the transport direction (sub-scanning direction).

<Carriage unit 20>
The carriage unit 20 is for moving the carriage 21 to which the head unit 30 is attached in a direction crossing the sub-scanning direction (also referred to as “scanning”). Hereinafter, this moving direction is also referred to as a main scanning direction. The carriage unit 20 includes a carriage 21 and
It has a carriage motor 22 (also called a CR motor) (FIGS. 2A and 2B).

The carriage 21 can reciprocate in the main scanning direction and is driven by a carriage motor 22. The operation of the carriage motor 22 is controlled by a controller 60 on the printer side. Further, the carriage 21 detachably holds an ink cartridge that stores ink.

<Head unit 30>
The head unit 30 is for ejecting ink onto the medium. Head unit 3
0 includes a head 31 having a plurality of nozzles. The head 31 is provided on the carriage 21, and when the carriage 21 moves in the main scanning direction, the head 31 also moves in the main scanning direction. Then, when the head 31 moves in the main scanning direction, ink is intermittently ejected from the nozzles, thereby forming a dot line (raster line) along the main scanning direction on the medium.

FIG. 3 is a cross-sectional view showing the structure of the head 31. The head 31 includes a case 311, a flow path unit 312, and a piezo element group PZT. Case 311 is a piezo element group PZ.
T is accommodated, and the flow path unit 312 is joined to the lower surface of the case 311. The flow path unit 312 includes a flow path forming plate 312a, an elastic plate 312b, and a nozzle plate 312c. The flow path forming plate 312a is formed with a groove portion serving as the pressure chamber 312d, a through hole serving as the nozzle communication port 312e, a through port serving as the common ink chamber 312f, and a groove portion serving as the ink supply path 312g. The elastic plate 312b has an island portion 312h to which the tip of the piezo element PZT is joined. An elastic region is formed by an elastic film 312i around the island portion 312h. The ink stored in the ink cartridge is supplied to the pressure chamber 312d corresponding to each nozzle Nz via the common ink chamber 312f. The nozzle plate 312c is a plate on which the nozzles Nz are formed.

On the nozzle surface, a yellow nozzle row Y that ejects yellow ink as a color ink ejection nozzle row that forms an image, a magenta nozzle row M that ejects magenta ink, a cyan nozzle row C that ejects cyan ink, and black ink. A black nozzle row K for jetting is provided.

FIG. 4 is an explanatory diagram of the nozzle Nz provided in the head 31. FIG. 4 is a view of the nozzle virtually seen from the upper surface side. As shown in FIG. 4, each nozzle row is configured by nozzles Nz serving as ejection ports for ejecting ink of each color being arranged at intervals of 180 dpi in the transport direction. In each nozzle row, 360 nozzles N1 to # 360 N
z is provided. In addition, the number of nozzles per row is arbitrary, and it is not necessarily required to be 360. For example, the number of nozzles per row may be 180 or 240.

The piezo element group includes a plurality of comb-like piezo elements PZT (drive elements), and is provided in a number corresponding to the nozzles Nz. A drive signal is applied to the piezo element PZT by a flexible cable (not shown) which is a wiring board, and the piezo element expands and contracts in the vertical direction according to the potential of the drive signal. When the piezo element PZT expands and contracts, the island portion 312 shown in FIG.
h is pushed toward the pressure chamber 312d or pulled in the opposite direction. At this time, the elastic film 312i around the island portion 312h is deformed, and the pressure in the pressure chamber 312d rises and falls, thereby ejecting ink droplets (dots) from the nozzle.

<Irradiation unit 40>
The irradiation unit 40 irradiates UV toward the ink dots that have landed on the medium. The dots formed on the medium are cured by receiving UV irradiation from the irradiation unit 40. The irradiation unit 40 of this embodiment includes an irradiation unit 41.

The irradiation unit 41 is mounted on one end of the carriage 21 and is disposed adjacent to each KCMY nozzle row arranged in the main scanning direction. The irradiation unit 41 moves in the main scanning direction integrally with the head 31 as the carriage 21 moves. And it is comprised so that UV can be irradiated with respect to the UV ink dot ejected while the head 31 scanned from one end side to the other end side. That is, when the nozzle row of each color of the head 31 moves in the main scanning direction,
The irradiation unit 41 irradiates UV while moving while maintaining the relative position to the nozzle row of each color. For example, in FIG. 4, when the head 31 moves from the right side to the left side in the main scanning direction (forward movement of the reciprocating operation), the same scanning is performed on the UV ink dots ejected from each nozzle row (KCMY). Then, UV is irradiated from the irradiation unit 41. Thereby, the UV ink dot immediately after landing on the medium can be cured immediately. On the other hand, when the head 31 moves from the left side to the right side in the main scanning direction (reverse movement of the reciprocating operation), the irradiation unit 41 is closer to the moving direction than the nozzle row. Accordingly, it is impossible to irradiate UV ink dots ejected from the nozzle rows during the backward movement in the same scanning. In this case, the UV ink dots ejected during the backward movement are cured by the UV irradiation during the next forward movement.

The length of the irradiation unit 41 in the transport direction is longer on the downstream side than the length of each nozzle row provided in the head 31 in the transport direction. And it is provided so that it may extend to the downstream of a conveyance direction rather than this nozzle row (refer FIG. 4). At the time of the above-described backward movement, the ink dots ejected by the nozzles on the most downstream side in the transport direction of each nozzle row (# 360 nozzle in FIG. 4) are the U dots at the next forward movement.
Cured by V irradiation. Between the backward movement and the next forward movement, the medium is transported by a predetermined amount in the transport direction, so that the ink dot is further UV positioned at a position downstream of the nozzle row in the transport direction.
Will receive irradiation. Therefore, the irradiation unit 41 is provided so as to be longer on the downstream side in the transport direction than each nozzle row.

In this embodiment, the irradiation unit 41 is a light emitting diode (LED: LED) as a light source for UV irradiation.
Light Emitting Diode). The wavelength peak of the LED is preferably 360-420 nm
Those having an emission peak wavelength are used. The LED can easily change the irradiation energy by controlling the magnitude of the input current. In this embodiment, the UV ink dots are cured to an optimum hardness by controlling the UV irradiation intensity by changing the irradiation energy preferably in the range of 150 to 300 mJ / cm ² . The light source of the irradiation unit 41 is isolated from the head 31 by being accommodated in the irradiation unit 41. As a result, UV light emitted from the light source is prevented from leaking to the lower surface of the head 31, thereby preventing the UV ink from being cured (nozzle clogging) in the vicinity of the opening of each nozzle formed on the lower surface. doing.

Note that the irradiation unit 41 is not limited to being mounted only on one end of the carriage 21, and the irradiation unit 41 is mounted on both ends of the carriage 21, and one of the irradiation units is irradiated. By stopping the irradiation of the other irradiation section, when the head 31 moves forward, the ink ejected by the forward movement is irradiated by the forward movement, and when the head 31 moves backward, The ink ejected by the backward movement may not be irradiated by the backward movement.

<Detector group 50>
The detector group 50 is for monitoring the status of the printer 1. The detector group 50 includes a linear encoder 51, a rotary encoder 52, a medium detection sensor 53, an optical sensor 54, and the like (FIGS. 2A and 2B).

The linear encoder 51 detects the position of the carriage 21 in the moving direction. The rotary encoder 52 detects the rotation amount of the transport roller 13. The medium detection sensor 53 detects the position of the front end of the medium being supplied. The optical sensor 54 detects the presence / absence of the medium at the opposed position by the light emitting unit and the light receiving unit attached to the carriage 31, for example, detects the position of the end of the medium while moving in the scanning direction, and detects the medium width. Can be detected. Further, the optical sensor 54 is a front end of the medium (an end on the downstream side in the transport direction, also referred to as an upper end) depending on the situation.
-The rear end (the end on the upstream side in the transport direction and also called the lower end) can be detected.

<Controller 60>
The controller 60 is a control unit (control unit) for controlling the printer. The controller 60 includes an interface unit 61, a CPU 62, a memory 63,
And a unit control circuit 64 (FIG. 1).

The interface unit 61 transmits and receives data between the computer 110 that is an external device and the printer 1. The CPU 62 is an arithmetic processing device for performing overall control of the printer 1. The memory 63 is a storage unit for securing an area for storing a program of the CPU 62, a work area, and the like, and includes a storage element such as a RAM or an EEPROM. Then, the CPU 62 controls each unit such as the transport unit 10 via the unit control circuit 64 in accordance with a program stored in the memory 63.

<Image forming operation>
An image forming operation by the printer 1 will be briefly described. The controller 60 receives a print command from the computer 110 via the interface unit 61 and controls each unit to perform medium supply processing, dot formation processing, transport processing, and the like.

The medium supply process is a process of supplying a medium to be printed into the printer and positioning the medium at a print start position (also referred to as a cue position). The controller 60 rotates the medium supply roller 11 and sends the medium to be printed to the transport roller 13. Subsequently, the transport roller 1
3 is rotated, and the medium sent from the medium supply roller 11 is positioned at the print start position.

In the dot formation process, the head 3 mounted on the carriage 21 that moves along the main scanning direction.
In this process, ink is ejected intermittently from 1 to form dots on the medium. The controller 60 moves the carriage 21 in the main scanning direction, and ejects ink from the head 31 based on the print data while the carriage 21 is moving. When the ejected ink droplets land on the medium, dots are formed on the medium, and a dot line composed of a plurality of dots along the moving direction is formed on the medium. The irradiation unit 41 of the irradiation unit 40 is formed on the formed dots.
The dots are cured by irradiating with UV. However, as described above, in the printer 1, since the irradiation unit 41 is mounted only on one side of the carriage 21 (head 31) in the main scanning direction, the ejection of ink dots and the UV irradiation can be performed in the same scanning. Is only while the carriage 21 moves in one direction of the main scanning direction.

The transport process is a process of moving the medium relative to the head along the transport direction.
The controller 60 rotates the transport roller 13 to transport the medium in the transport direction. By this carrying process, the head 31 can form a dot line at a position different from the position of the dot line formed by the previous dot formation process.

In this embodiment, the distance transported in one transport process is the distance in the medium transport direction of nozzles used for nozzle array printing (distance between nozzles of head 31 (180 dpi) × (for nozzle array printing). The printing method (so-called interlace method) in which a raster line that is not recorded is sandwiched between raster lines that are recorded while the carriage 21 is moved once in the main scanning direction. It is possible to perform printing with a printing method in which dots are formed by a plurality of main scans for one raster line, and in the case of these printing methods, pixels of recording units defined by the recording resolution are recorded. Among them, the possibility of forming dots in the same main scanning in the pixels adjacent in the vertical direction or the horizontal direction is low, or the amount of ink to be shot in one main scanning is small. In order, it preferred Nari less bleeding between adjacent dots.

The controller 60 alternately repeats the dot formation process and the conveyance process until there is no more data to be printed, and gradually prints an image composed of dot lines on the medium. When there is no more data to be printed, the medium discharge roller 15 is rotated to discharge the printed medium. Note that the determination of whether or not to discharge the medium may be based on a discharge command included in the print data.
The same process is repeated when the next printing is performed, and the printing operation is terminated when the next printing is not performed.

=== About image processing by printer driver ===
The printer driver inputs image data from an application program, converts it into image formation data (print data) in a format that can be interpreted by the printer 1, and outputs the image formation data to the printer. When converting image data into recording data from an application program, the printer driver performs resolution conversion processing, color conversion processing, halftone processing, rasterization processing, command addition processing, and the like. Various processes performed by the printer driver will be described below. The printer driver may be installed in the controller 60 of the printer 1 and image processing may be performed by the printer 1 itself.

FIG. 5 shows a flow of image processing by the printer driver. In this embodiment,
The image processing is performed by executing each processing of S101 to S106.

First, the computer 110 and the printer 1 are connected (see FIG. 1), and a printer driver is installed in the computer 110 to prepare for printing. When printing is started by the user instructing printing from the application program, the printer driver is called, and image data (original image data) to be printed is received from the application program (S101). Each process (S described below)
102 to S106) are sequentially executed.

The resolution conversion process (S102) is a process for converting image data (text data, image data, etc.) output from the application program into a resolution (recording resolution) for recording on a medium. For example, if the recording resolution is specified as 720 × 720 dpi, the image data in the vector format received from the application program is stored in 720 ×
The image data is converted into bitmap format image data having a resolution of 720 dpi.
Each pixel data of the image data after the resolution conversion process is RGB data of each gradation (for example, 256 gradations) represented by the RGB color space.

The color conversion process (S103) is a process for converting RGB data into data in the KCMY color space. The image data in the KCMY color space is data corresponding to the ink color of the printer. This color conversion processing is performed based on a table (color conversion lookup table LUT) in which the gradation values of RGB data and the gradation values of KCMY data are associated with each other.
The pixel data after the color conversion process is 256-bit 8-bit KCMY data represented by the KCMY color space.

The halftone process (S104) is a process for converting high gradation number data into gradation number data that can be formed by the printer. For example, data representing 256 gradations is converted into 1-bit data representing 2 gradations or 2-bit data representing 4 gradations by halftone processing.
In the halftone process, a dither method, a γ correction, an error diffusion method, or the like is used. The halftone processed data has a resolution equivalent to the recording resolution (for example, 720 × 720 dpi). In this embodiment, the image data after halftone processing corresponds to pixel data of 2 bits for each pixel, and this pixel data indicates the dot formation status (large dot, medium dot,
Any small dot is formed or no dot is formed). Details of the halftone process will be described later.

The rasterizing process (S105) rearranges the pixel data arranged in a matrix for each pixel data in the order of data to be transferred to the printer 1. For example, the pixel data is rearranged according to the arrangement order of the nozzles in each nozzle row.
The command addition process (S106) is a process for adding command data corresponding to the recording method to the rasterized data. The command data includes, for example, conveyance data indicating the medium conveyance speed.

The image formation data generated through these processes is transmitted to the printer 1 by the printer driver.

<Details of halftone processing>
FIG. 6 is a flowchart for explaining the flow of halftone processing. The halftone process of this embodiment is a halftone process using a dither method. However, the present invention is not limited to this. For example, an error diffusion method may be used.

The printer driver uses the image data (Y image data, M after the color conversion processing (S103)).
Image data, C image data, and K image data) are acquired (S201 in FIG. 6). 4 Y,
The same halftone process is performed for all of the M, C, and K image data. Therefore, for the sake of simplicity, the halftone process for K image data will be described below. For all the pixel data (K pixel data) included in the K image data, the processing from step S202 to step S212 in FIG. 6 is executed while sequentially changing the K pixel data to be processed. As a result, all the K pixel data included in the K image data is “No dot formation [00
], “Small dot formation [01]”, “Medium dot formation [10]”, “Large dot formation [11]
Is converted into dot identification data (2-bit data) indicating any of the above.

FIG. 7 is a diagram illustrating an example of a dot generation rate table (LUT) that defines the dot generation rate. In the figure, the horizontal axis represents the gradation value (0 to 255) indicated by the pixel data, and the left vertical axis represents the dot generation rate (%
), The vertical axis on the right side indicates level data (0 to 255). A profile SD indicated by a broken line in the figure indicates a generation rate of small dots, a profile MD indicated by a solid line indicates a generation rate of medium dots, and a profile LD indicated by a one-dot chain line indicates a generation rate of large dots. ing.

Note that “dot generation rate” means the proportion of pixels in which dots are formed among the pixels belonging to a unit region when the gradation value indicated by all the pixels belonging to the unit region on the medium is constant. To do. For example, it is assumed that the unit area is composed of 16 pixels × 16 pixels, the gradation values of all the pixel data in the unit area are constant, and n dots are formed in the unit area. In this case, the dot generation rate at the constant gradation value is {n / (16 × 16)} × 100 (%). The level data refers to data obtained by converting the dot generation rate into numerical values 0 to 255 in 256 levels.

That is, the dot generation rate table is a data conversion table used for creating print data from image data, and specifically, a table that defines the amount of ink ejected per unit area of the medium.

The dot generation rate table (LUT) is stored in the memory 63 which is a storage unit. When performing the image forming operation, the printer driver first reads the level data LVL corresponding to the gradation value indicated by the K pixel data to be processed from the profile LD for large dots (the dashed line in FIG. 7) (FIG. 6). S202). For example, as shown in FIG. 7, if the gradation value of the K pixel data to be processed is gr, the level data LVL for large dots is obtained as 1d based on the profile LD for large dots.

FIG. 8 is a diagram showing a state of dot on / off determination by the dither method. In this embodiment, dot on / off determination is performed using a dither mask by the dither method. The dither mask is composed of a plurality of threshold values arranged two-dimensionally, and a dither mask is set for each dot size. The printer driver obtains the level data LVL related to the large dot, and then the dither mask threshold value THL corresponding to the K pixel data to be processed in the large dot dither mask.
The level data LVL and the threshold value THL are compared with each other (S203). For example, S20
When the level data 1d regarding the large dot obtained in 2 is larger than the threshold value THL (
The printer driver converts the K pixel data to be processed into dot identification data [11] indicating large dot creation (S211).

On the other hand, when the level data LVL is equal to or less than the threshold value THL (S203 → NO), the printer driver sets the medium dot level data LVM (S204). The medium dot level data LVM is read from the medium dot profile MD (solid line in FIG. 7) according to the gradation value indicated by the K pixel data to be processed. For example, if the gradation value of the K pixel data is gr, the level data LVM is obtained as 2d. The printer driver then uses the dither mask threshold T corresponding to the K pixel data to be processed in the medium dot dither mask.
The level data 2d and the threshold value THM are compared with reference to the HM (S205). If the level data LVM is larger than the threshold THM (S205 → YES), the printer driver converts the K pixel data to be processed into dot identification data [10] indicating medium dot creation (S210).

When the level data LVM is equal to or less than the threshold value THM (S205 → NO), the printer driver sets the small dot level data LVS (S206). The small dot level data LVS is read from the small dot profile SD (broken line in FIG. 7) according to the gradation value indicated by the K pixel data to be processed. Then, the printer driver refers to the threshold value THS of the dither mask corresponding to the K pixel data to be processed in the dither mask for small dots, and compares the level data LVS with the threshold value THS (S207). When the level data LVS is larger than the threshold value THS (S207 → YES), the printer driver converts the K pixel data to be processed into dot identification data [01] indicating small dot creation (S209).
). When the level data LVS is equal to or less than the threshold value THS (S207 → NO), the printer driver converts the K pixel data to be processed into dot identification data [00] indicating no dot (S208).

Thus, after the K pixel data to be processed has been changed to any of the four dot identification data (S208 to S211), the printer driver determines whether or not the processing for all the K pixel data has been completed ( S212). The printer driver ends the halftone processing of the K image data when the processing for all the K pixel data has been completed (S
212 → YES), if not completed, the processing target is moved to unprocessed K pixel data, and the process returns to step S202. Similarly, halftone processing is executed for image data of other colors.

=== About liquid ===
The liquid used for forming an image in this embodiment will be described. The liquid can be, for example, UV ink. The UV ink used in this embodiment is composed of a polymerizable compound and, if necessary, a photopolymerization initiator and other additives. The UV ink preferably has a viscosity at 20 ° C. of 7 mPa · S or more, and more preferably 7 mPa · S or more and 25 mPa · S or less. When the viscosity is within the above range, the spread of the ink can be reduced, and further, the heating of the ink can be reduced. The UV ink preferably has a surface tension of 35 mN / m or more, more preferably 35 to 45 mN / m. Within this range, it is possible to form dots with a uniform dot spread.

A polymerizable compound is a compound capable of undergoing a polymerization reaction when irradiated with light. Specific examples of the polymerizable compound include various (meth) acrylate monomers, various (meth) acrylate oligomers, various vinyl monomers, various vinyl ether monomers, and the like. The content of the polymerizable compound in the liquid is preferably 60 to 95% by mass.

By using the monomer A represented by the following general formula (1) as the polymerizable compound, a UV ink having good curability and low viscosity can be obtained.
_{^{CH 2 = CR 1 -COOR 2 -O}} -CH = CH-R 3 ··· (1)
Wherein R ¹ is a hydrogen atom or a methyl group, R ² is a divalent organic residue having 2 to 20 carbon atoms, and R ³ is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms. Group.)

In the above general formula (1), the divalent organic residue having 2 to 20 carbon atoms represented by R ² is a linear, branched or cyclic substituted having 2 to 20 carbon atoms. An alkylene group that may be substituted, an alkylene group that has an oxygen atom by an ether bond and / or an ester bond in the structure, an optionally substituted alkylene group that has 2 to 20 carbon atoms, and an optionally substituted divalent that has 6 to 11 carbon atoms Aromatic groups are preferred. Among these, ethylene group, n-propylene group, isopropylene group,
And an alkylene group having 2 to 6 carbon atoms such as a butylene group, an oxyethylene group, an oxy n-propylene group, an oxyisopropylene group, and an oxybutylene group having an oxygen atom due to an ether bond in the structure of 2 to 9 carbon atoms Are preferably used.

In the general formula (1), the monovalent organic residue having 1 to 11 carbon atoms represented by R ³ is a linear, branched or cyclic substituted group having 1 to 10 carbon atoms. Suitable alkyl groups and optionally substituted aromatic groups having 6 to 11 carbon atoms are preferred. Among these, 6 or more carbon atoms such as an alkyl group having 1 or 2 carbon atoms that is a methyl group or an ethyl group, a phenyl group, and a benzyl group
˜8 aromatic groups are preferably used.

When each of the organic residues is an optionally substituted group, the substituent is divided into a group containing a carbon atom and a group not containing a carbon atom. First, when the substituent is a group containing a carbon atom, the carbon atom is counted in the carbon number of the organic residue. As a group containing a carbon atom,
Although not limited to the following, examples thereof include a carboxyl group and an alkoxy group. Next, examples of the group not containing a carbon atom include, but are not limited to, a hydroxyl group and a halo group. Although content in the liquid of the monomer A is not specifically limited, 10 mass% or more is preferable and 10 mass%-70 mass% are especially preferable.

The UV ink may contain a photopolymerization initiator as necessary. The photopolymerization initiator is a compound having a function of efficiently initiating polymerization of a polymerizable compound when irradiated with light. Specific examples of the photoinitiator include alkylphenone initiators, acylphosphine initiators, titanocene initiators, thioxanthone initiators, and the like. The content of the photopolymerization initiator in the UV ink is preferably 5 to 15% by mass. The UV ink may further contain a solvent, a surfactant, a polymerization inhibitor, a polymerization accelerator, a coloring material such as a pigment or a dye, and the like as other additives as necessary.

=== Embodiment ===
<Description of ink>
Table 1 shows the composition components of four types of UV inks (ink numbers 1 to 4) used in the following description. The inks 1 to 4 are color UV inks containing a cyan or magenta pigment. In the following embodiments, inks containing cyan as a pigment among the inks 1 to 4 are denoted as 1C, 2C, 3C, and 4C, respectively, and inks containing magenta as a pigment are each 1M.
, 2M, 3M, 4M. The UV ink may contain a pigment (for example, yellow) other than cyan and magenta.

In Table 1, the polymerizable compound VEEA corresponds to the monomer A described above.

VEEA: 2- (2-vinyloxyethoxy) ethyl acrylate (manufactured by Nippon Shokubai Co., Ltd.)
・ DEGDA: Diethylene glycol diacrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.)
・ TMPTA: Trimethylolpropane triacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.)
・ IBXA: Isobornyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.)
2-MTA: 2-methoxyethyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.)
EBECRYL 600: Bisphenol A type epoxy acrylate (manufactured by Daicel Cytec) 819: IRGACURE 819 (manufactured by BASF)
-TPO: DAROCUR TPO (BASF)
・ DETX-S: KAYACURE DETX-S (manufactured by Nippon Kayaku Co., Ltd.)
Pigment: PIGMENT BLUE 15: 4 (manufactured by DIC)
Leveling agent: BYK-UV3500 (manufactured by BYK)
-Polymerization inhibitor: MEHQ (manufactured by Kanto Chemical)

<Ink characteristic evaluation>
Further, regarding the ink characteristics, the viscosity and curability described below are evaluated.
Table 1 shows the evaluation contents for inks 1 to 4.

(1) Viscosity evaluation The viscosity of the ink at 20 ° C. is measured using a rheometer (MCR-300, manufactured by Physica). The evaluation criteria are as follows.
1: Less than 7 (mPa · s)
2: 7 to less than 15 (mPa · s)
3: 15 to 30 (mPa · s)
Over 4:30 (mPa · s)

(2) Curability evaluation “Curability” refers to whether the ink dots are cured to such an extent that the image is not disturbed even when the user touches the surface of the formed image (this state is also referred to as “tack-free”). Show. The evaluation of curability is a resolution of 720 × 720 dpi, a film thickness of 10 μm (thickness after curing), 1 cm × 1
A solid print is made in the area of cm, the printed ink is irradiated with UV, and the surface is swabbed (for example,
Johnson &Johnson's Johnson swab) is irradiated with irradiation energy until it reaches tack-free (no ink adheres to the swab and the ink cured product formed on the medium is not scratched). to decide. The number of rubbing is 10 reciprocations, and the rubbing strength is 100 g load. Irradiation uses an LED having an emission peak wavelength of 395 nm, and an irradiation intensity of 800 mW / cm.
^This is done by changing the irradiation time. The evaluation criteria are as follows.
A: Accumulated UV irradiation energy at tack free ≦ 200 mJ / cm ² or less B: 200 mJ / cm ² <Accumulated UV irradiation energy at tack free

=== Evaluation of formed image ===
The UV ink dots forming the image are subjected to various evaluations while changing the printing conditions, thereby verifying the conditions under which a good image can be formed. Specifically, a test pattern is formed for each of the inks (inks 1 to 4) to be used, and each of the three items “curability”, “color mixing”, and “density” is evaluated. The test pattern is the above cyan ink 1
Using C to 4C (or magenta inks 1M to 4M), a solid printing is performed on a region of 10 μm (maximum value) and 1 cm × 1 cm with a resolution of 720 × 720 dpi. In addition, when a heating mechanism is attached to the head of an ink jet printer and ink having a high ink viscosity is used, the ink is heated so that the ink viscosity is about 10 mPa · s.
As a discharge. In addition, the recording medium carried into the ink jet printer is not heated. Further, LE used in the above-described viscosity evaluation for the carriage part of the ink jet printer.
The same thing as D was attached, and irradiation energy was made into the energy amount which makes each ink tack-free.
Hereinafter, each evaluation item will be described.

(1) About Color Mixing “Color mixing” indicates whether or not ink dots of different colors are blurred and mixed in the formed image.
First, the principle of color mixing will be described. The color mixture occurs when ink dots of different colors are adjacent to each other and mixed by contacting each other before the dots are cured (before receiving UV irradiation), and the color is blurred. In particular, when a large amount of ink is ejected and a large dot is formed, adjacent dots are likely to come into contact with each other, so that color mixing is likely to occur. It is also affected by the viscosity of the ink itself. That is, the dot is easy to maintain a spherical shape in the ink with high viscosity (for example, ink 1). Therefore, the dot diameter is kept small. On the other hand, in a low viscosity ink (for example, ink 4), the dots are crushed and spread, tend to be a disk shape, and the dot diameter is also increased. When ink dots of different colors are adjacent to each other, the larger the diameter of the adjacent ink dots, the easier it is for the dots to come into contact with each other, resulting in color mixing.

In this embodiment, the test pattern is formed with magenta color ink so as to be adjacent to the test pattern formed with cyan color ink. Then, it is checked with the naked eye whether or not color mixing has occurred at the boundary between both test patterns. Adjacent test patterns are formed using the same type of ink. For example, the test pattern of ink 1M is formed adjacent to the test pattern of ink 1C, and the test pattern of ink 1C and the test patterns of inks 2M to 4M are not formed adjacent to each other. This is because, in actual printing, an image is formed using color inks of the same component, so that the possibility that color ink dots of different components are formed adjacent to each other is extremely low. The evaluation criteria are as follows.
○: Mixed color is not confirmed at the boundary part ×: Mixed color is confirmed at the boundary part

(2) Density Indicates whether the density of the color indicated in the original image data is reproduced as instructed by the data. The density is evaluated by measuring the optical density (OD value) of the test pattern using a colorimeter (for example, Spectrolino, manufactured by DretagMacbeth). The optical density indicates how much light is not transmitted or reflected. When the light transmittance is 100%, the optical density becomes zero, and the optical density increases as the transmittance decreases.

In the present embodiment, a reference optical density (reference density) is measured in advance for each of the inks 1 to 4. The reference density is a density of an image to be reproduced on a medium based on image data input to the image forming apparatus. Then, density evaluation is performed by comparing the difference with the optical density measured when an image is formed by changing the conditions (ink ejection amount, UV irradiation method, etc.). The evaluation criteria are as follows.
AA: Difference between reference concentration and measured concentration ≦ 0.1
A: 0.1 <difference between reference concentration and measured concentration ≦ 0.3
B: 0.3 <difference between reference concentration and measured concentration

=== Reference Example ===
First, as a reference example, an evaluation example when the above-described test pattern is formed with inks 1 to 4 will be described. In the following example, a PET film (for example, Lumirror 125E20 manufactured by Panasonic Corporation) is used as the medium.

Table 2 shows test pattern formation conditions and various evaluation data in the reference example.

In Table 2, “UV ink curing method 1” means that the head 31 moves while moving in the main scanning direction.
This is an ink curing method in which when the ink dots are ejected, the ink dots are cured by irradiating UV from the irradiation unit 41 in the same scanning. That is, in the UV ink curing method 1, UV is irradiated immediately after ink dot ejection. Note that the LED wavelength peak during UV irradiation in the reference example is 395 nm as described above. The time from when the ejected ink has landed on the medium until the start of UV irradiation is about 0.3 seconds.
“Used LUT1” is a dot generation rate table used as a reference in halftone processing, and in this reference example, the LUT shown in FIG. 7 is used.

In any of the reference examples 1 to 4, the evaluation of the color mixing property is ◯, and no color mixing occurs. Further, the optical density values measured for the reference examples 1 to 4 are the reference densities of the inks 1 to 4, respectively.

=== Example ===
In the present embodiment, when the head 31 moves in the main scanning direction from one side to the other side (assuming forward movement), UV ink dots are ejected. The UV ink dots formed during the forward movement are cured by irradiating UV when the head 31 moves in the main scanning direction from the other side to the one side (reverse movement).

Table 3 shows data on various evaluations when an image (test pattern) is formed while changing the ink used and the printing conditions by the method of the present embodiment.

In Table 3, “UV ink curing method 2” means that the carriage 21 moves in the main scanning direction in one direction when the irradiation unit 41 is mounted on one direction side of the carriage 21 in the main scanning direction. UV ink dots are ejected from the head 31 during main scanning (during forward movement). At this time, U
V is not irradiated. Then, after the main scanning, the ink curing method is such that the ink dots are cured by irradiating UV from the irradiation unit 41 when the carriage 21 moves in the main scanning direction to another direction (reverse movement). In other words, ink dots are ejected at the time of forward movement but are not irradiated with UV, and are irradiated with UV at the time of backward movement, thereby curing the ink dots formed at the time of forward movement. That is, in the ink curing method 2, UV is irradiated after a predetermined time has elapsed from the ejection of the ink dots, and the dots are cured.

9A and 9B are diagrams for explaining the dot forming operation in the UV ink curing method 2. FIG. FIG. 9A shows the operation at the time of forward movement, and FIG. 9B shows the operation at the time of backward movement.

At the time of forward movement (FIG. 9A), the controller 60 moves a head 31 (carriage 21) from the left side to the right side (one direction) in the main scanning direction, while transferring a predetermined amount of UV ink from each nozzle row to the medium. A dot is ejected. Thereby, dot lines arranged in the main scanning direction are formed. At this time, since the irradiation unit 41 does not emit UV, the dot line is in an uncured state.

Next, at the time of backward movement (FIG. 9B), the head 31 (carriage 21) is moved from the right side to the left side in the main scanning direction (in the other direction) while irradiating UV from the irradiation unit 41 to move forward The dot lines that are sometimes formed are cured. Thereby, an image composed of a plurality of dot lines is formed.

In addition, UV may be irradiated from the irradiation unit 41 while ejecting ink from each nozzle row of the head 31 during the backward movement. That is, the dot line can be formed while the head 31 reciprocates in the main scanning direction. In this case, it is necessary to transport the medium by a predetermined amount in the transport direction before shifting from the forward movement to the backward movement (the above-described transport process).

In the present embodiment, the time from when the head 31 starts moving (scanning) in one direction of the main scanning direction to finishing moving (scanning) in the other direction is about 7 seconds. That is, it takes 7 seconds for the carriage 21 to reciprocate once in the main scanning direction.

In this embodiment, the time required for the dots formed during the forward movement to be cured by receiving the UV irradiation during the backward movement is longer than in the case of the reference example described above. For this reason, if the amount of ink dots ejected at the time of forward movement is large, the ink dots spread before being cured, and there is a risk of color mixing or the like between uncured dots. Therefore, by reducing the amount of ink ejected per unit area (unit area) during forward movement, such color mixing is suppressed. In other words, printer 1
The amount of the UV ink ejected corresponding to the predetermined data of the image data input to is larger in the case of the UV ink curing method 1 than in the case of the UV ink curing method 2. Details will be described later.

LUTs 2 to 4 shown in “Used LUT” in Table 3 are LUT 1 (LUT used in the reference example).
The dot generation rate table is changed so that the dot generation rate is less than that in (1). FIG. 10 is a diagram illustrating the difference between LUT1 and LUT2. The dotted line in the figure represents the dot occurrence rate in LUT1, and the solid line represents the dot occurrence rate in LUT2. As shown in the figure, in the case of data showing the same gradation value, LUT2 is lower than LUT1 for all dot generation rates of large dots (LD), medium dots (MD), and small dots (SD). Yes. That is, when printing is performed based on the same print data, the amount of ink applied per unit area of the medium is smaller when the LUT 2 is used than when the LUT 1 is used.

Similarly, LUT3 is set to have a smaller dot generation rate than LUT2, and LUT4 is set to LUT4.
The dot generation rate is set to be smaller than 3. In other words, the dot generation rate decreases as the LUT has a larger number.

In the UV ink curing method 2, when the UV ink is ejected, the above-described UV ink curing method 1 is used.
Print data is created using a different data conversion table. Then, an amount of UV ink that is smaller than the amount of UV ink ejected by the UV ink curing method 1 is ejected, so that the generation rate of dots formed during forward movement is adjusted to be small.

<Results of Examples>
In Example 1, ink 1 (see Table 1) is used, and a test pattern is formed using LUT2. Since the LUT 2 having a smaller ink ejection amount per unit area than the LUT 1 is used, the UV ink curing method 2 can also obtain a good color mixing test result (◯). As described above, in the UV ink curing method 2, a predetermined time is required from the time when dots are formed during forward movement to the time when they are cured by UV irradiation during backward movement. If dots are formed with a normal ink ejection amount using the LUT 1, the dots may wet and spread in a large amount before being cured, and color mixing may occur. However, by using the LUT 2 with a small amount of ink shot per unit area, the number of dots generated during forward movement is reduced, so that the dots are prevented from spreading in a large amount before being cured and color mixing can be suppressed. .

Compared with the reference example 1, the concentration test also gives a better result (AA). By using LUT2 to reduce the amount of ink shot per unit area, the absolute number of dots formed on the image surface is reduced, but color development similar to the reference density (density of reference example 1) can be obtained. It is shown that.

On the other hand, since ink 1 is used in Example 1, the result of the curability test is B as shown in Table 1. Therefore, in order to sufficiently cure the dots, it is necessary to increase the UV irradiation output or lengthen the UV irradiation time. In the former case, it is necessary to take measures such as changing the light source of the irradiation unit 41 to a high-performance one or increasing the power consumption, which increases the cost.
In the latter case, it is necessary to slow down the moving speed of the carriage 21 to increase the irradiation time, and the printing speed is slowed down.

Thus, in Example 1, curability is inferior. That is, in this embodiment, VE
A UV ink containing no EA is disadvantageous in terms of curability.

Example 2 is an example in which the test pattern is formed using the LUT 2 using the ink 2. As in the first embodiment, since the LUT 2 with a small ink ejection amount per unit area is used, a good color mixing test result (◯) can be obtained even with the UV ink curing method 2. Compared with the reference example 2, the density test also gives a better result (AA).
In Example 2, unlike ink 1 of Example 1, ink 2 containing 10% of VEEA is used, and therefore a good result (A) is obtained in the curability test (see Table 1). .

Example 3 is an example in which the test pattern is formed using the ink 3 and using the LUT 3. Since ink 3 contains 70% VEEA, the curability becomes high as described above,
Good results (A) are obtained for the curability test. On the other hand, ink 3 has a low ink viscosity (see Table 1). When the viscosity of the ink is low, the ink dot is crushed before it is cured by being irradiated with UV, and the spherical shape cannot be maintained. As a result, color mixing may occur and image quality may be deteriorated.
In order to suppress such wetting and spreading, in the third embodiment, the dot generation amount is adjusted by using the LUT 3 having a smaller ink ejection amount per unit area than in the second embodiment. By appropriately selecting the LUT to be used, wetting and spreading of the ink dots are suppressed, and good results are obtained in both the color mixing test (◯) and the density test (A).

Example 4 is an example in which the ink 4 is used and a test pattern is formed using the LUT 3. Ink 4 has a different ink composition than inks 1 to 3, and as shown in Table 1, 2-
Since the MTA content is 60% by mass, the ink viscosity is low, and the ink viscosity at 20 ° C. is less than 7 MPa · s. As a result, a good result (A) is obtained for the density test, but the result of the color mixing test is x. This is because the viscosity of the ink is too low, and the dots are crushed before the dots are hardened and spread easily, so that color mixing occurs between the cyan ink dots and the magenta ink dots.
Therefore, it can be said that when the ink 4 is used, the LUT 3 has too much ink ejection amount.

In the fifth embodiment, therefore, the ink 4 is used, and the test pattern is formed by using the LUT 4 having a smaller ink ejection amount per unit area than the LUT 3. In Example 5, a favorable evaluation result (◯) is obtained for the color mixing test. This is because the use of the LUT 4 prevents an amount of dots that cause color mixing from being formed on the medium.
However, in Example 5, the result of the density test is B, and the density of the formed image is greatly deteriorated. It can be seen that if the amount of ink shot is reduced to such an extent that no color mixing occurs, the density decreases, and the image quality cannot be satisfied.
That is, in this embodiment, if the ink viscosity at 20 ° C. is less than 7 mPa · S, an image that satisfies both the color mixing property and the density cannot be formed even if the use LUT is appropriately selected.

Example 6 is an example in which a test pattern is formed using LUT 1 using ink 2. Conditions other than the used LUT are the same as in the second embodiment. As described above, since the viscosity of the ink 2 is appropriate and the VEEA content is also appropriate, good evaluation can be obtained for the concentration test and the curable test (see Tables 1 and 2). However, in Example 6, the evaluation of the color mixture test is ×
become. Since the LUT 1 having a larger ink placement amount than in the second embodiment is used, the amount of ink dots becomes too large, and in the UV ink curing method 2, the ink dots spread out before the ink dots are cured and color mixing occurs. I understand that.
That is, even when UV ink having an appropriate viscosity and VEEA content is used, an image with good image quality cannot be obtained if the LUT used is selected incorrectly.

From the above, in the image forming method of the present embodiment (the above-described UV ink curing method 2), 2
Printing is preferably performed using UV ink having an ink viscosity of 7 or more (mPa · S) at 0 ° C. Further, among a plurality of types of ink having different viscosities, an LUT that generates an appropriate amount of dots according to the viscosity of the ink is selected and used. Specifically, an LUT is selected such that the dot generation rate decreases as the viscosity decreases. As a result, when ink with low viscosity is ejected, the amount of ink ejected per unit area is smaller than when ink with high viscosity is ejected, which is good in terms of color mixing, density, and curability. An image can be formed.

When using ink with high viscosity, the ink in the head is heated to lower the viscosity of the ink and discharged, but since the medium is not heated, the ink ejected from the head is The temperature drops and drops to near the viscosity of the ink at room temperature. In addition, when the ink viscosity at 20 ° C. exceeds 30 mPa · S, it is necessary to increase the heating temperature in order to lower the ink viscosity, which is not preferable in terms of power saving and durability of the printer.

=== Other Embodiments ===
Although a printer or the like as one embodiment has been described, the above embodiment is for facilitating the understanding of the present invention, and is not intended to limit the present invention. The present invention
Needless to say, the present invention includes equivalents thereof without departing from the spirit of the invention. In particular, the embodiments described below are also included in the present invention.

<About image forming apparatus>
In each of the embodiments described above, a printer has been described as an example of an image forming apparatus, but the present invention is not limited to this. For example, color filter manufacturing apparatus, dyeing apparatus, fine processing apparatus, semiconductor manufacturing apparatus, surface processing apparatus, three-dimensional molding machine, liquid vaporizer, organic EL manufacturing apparatus (especially polymer EL manufacturing apparatus), display manufacturing apparatus, film formation The same technique as that of the present embodiment may be applied to various image forming apparatuses to which inkjet technology such as an apparatus and a DNA chip manufacturing apparatus is applied.

<About liquid ejection amount>
In each of the above-described embodiments, the image forming apparatus creates print data from the input image data using a data conversion table, and ejects liquid using the created print data, thereby corresponding to the image data. Spout liquid. In the above-described embodiment, by changing the LUT used in the halftone process, the amount of liquid ejected to one pixel corresponding to predetermined data of the image data is, for example, in the case of the first liquid curing method. Is a medium dot and is a large dot in the second liquid curing method, and the second curing method has a larger total amount of liquid ejected per unit area of the recording medium than the first curing method. I was trying to be. The liquid ejection amount when the liquid ejection amount is larger in the second liquid ejection method than in the first liquid curing method is the total liquid ejected per predetermined unit area of the recording medium. Amount. For example, when the image data corresponding to each pixel included in the unit area composed of 10 × 10 pixels has a predetermined value, the image data is ejected to the unit area composed of 10 × 10 pixels corresponding to the image data. It is assumed that the total amount of the liquid is larger in the second liquid curing method than in the first liquid curing method. Note that the amount of liquid ejected to one pixel is not limited to three types and is 1
There may be four types or more, and there may be pixels in which the amount of liquid ejected to one pixel is zero (no liquid is ejected). The step of reducing the amount of ink ejected per unit area is not limited to the above example, and may be performed in any step of generating print data for finally ejecting dots from image data. For example, it may be performed in a color conversion process for converting RGB data into data in the KCMY color space. Similarly, the data conversion table used when creating the print data from the image data is not limited to the LUT used in the halftone process, and is a table used in any process until the print data is created from the image data. Also good.

<About ink>
In the above-described embodiment, ink that is cured by being irradiated with ultraviolet rays (UV) (U
V ink) was discharged from the nozzles. However, the liquid to be ejected is not limited to such an ink, and may be cured by receiving irradiation of electromagnetic waves other than UV.

<About nozzle row>
In the above-described embodiment, an example in which an image is formed using four colors of KCMY and clear ink has been described. However, the present invention is not limited to this. For example, an image may be recorded using inks of colors other than KCMY, such as light cyan, light magenta, and white.

The order of arrangement of the nozzle rows in the head portion is also arbitrary. For example, the order of the nozzle rows for K and C may be switched, or the number of nozzle rows for K ink may be greater than the number of nozzle rows for other inks.

<About piezo elements>
In each of the above-described embodiments, the piezo element PZ is used as an element that performs an operation for ejecting liquid.
Although T is illustrated, other elements may be used. For example, a heating element or an electrostatic actuator may be used.

<About the printer driver>
In each of the embodiments described above, the printer driver process is performed by the computer 110 (PC).
However, the printer driver may be installed in the controller 60 and the printer driver may be processed by the printer itself.

DESCRIPTION OF SYMBOLS 1 Printer 10 Conveyance unit, 11 Medium supply roller, 12 Conveyance motor, 1
3 transport roller, 14 platen, 15 medium discharge roller, 20 carriage unit, 21 carriage, 22 carriage motor, 30 head unit, 31 head, 311 case, 312 flow path unit, 312a flow path forming plate, 312b elastic plate, 312c nozzle Plate, 312d Pressure chamber, 312e Nozzle communication port, 312f
Common ink chamber, 312g ink supply path, 312h island part, 312i elastic film,
40 irradiation unit, 41 irradiation unit, 50 detector group, 51 linear encoder, 52
Rotary encoder, 53 Paper detection sensor, 54 Optical sensor, 60 Controller, 61 Interface unit, 62 CPU, 63 Memory, 64 Unit control circuit, 110 Computer

Claims (7)

An image forming method performed on a medium,
While moving the carriage section provided with the irradiation section in the main scanning direction that intersects the sub-scanning direction, the liquid cured by receiving light irradiation from the head section mounted on the carriage section to one medium During the main scan to eject the nozzle,
In the main scanning, the liquid ejected to the medium 1 is not irradiated with the light from the irradiation unit, and the light is irradiated from the irradiation unit in the movement of the carriage unit after the main scanning. (A) and
Main scanning (B) for irradiating the light from the irradiating unit in the main scanning to the liquid ejected to the one medium;
The amount of liquid ejection is greater during the main scanning (B) than during the main scanning (A),
The image forming method, wherein the liquid has a viscosity at 20 ° C. of 7 mPa · S or more. The image forming method according to claim 1,
Image formation in which the amount of ejection of the liquid ejected corresponding to predetermined data of image data input to the image forming apparatus is larger in the main scanning (B) than in the main scanning (A) Method. The image forming method according to claim 1 or 2,
An image forming apparatus including the carriage includes a storage unit that stores a data conversion table used for creating print data, and a control unit.
The controller is
Create print data using the data conversion table from the image data input to the image forming apparatus, perform image formation using the created print data,
When ejecting the liquid, print data is created using different data conversion tables for the main scan (A) and the main scan (B),
An image forming method in which a larger amount of liquid is ejected during the main scanning (B) than during the main scanning (A).   4. The image forming method according to claim 3, wherein the data conversion table is a table that defines an amount of ink ejected per unit region of the one body.   The image forming method according to claim 1, wherein the irradiation unit includes a light emitting diode. In any one of Claims 1-5,
The image forming method, wherein the liquid has a viscosity at 20 ° C. of 7 mPa · S or more and 30 mPa · S or less. In any one of Claims 1-6,
Multiple types of liquids with different viscosities are ejected,
The controller is
In the main scanning (A), when the liquid having a low viscosity among the plurality of kinds of liquids is ejected, the liquid ejected from the head unit is ejected more than when the liquid having a high viscosity is ejected. An image forming method that reduces the amount.

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