Printing device and printing method

Abstract

To discharge a large amount of white ink onto a print medium without requiring a high-performance discharge unit.SOLUTION: Each of discharge heads 3wu, 3wd discharges white ink dots onto a web 10. The discharge heads 3wu, 3wd are controlled so as to share the discharge of white ink onto the web 10. As a result of such control, in the X direction, an ink dot discharged from the discharge head 3wd onto the web 10 is interposed between two ink dots discharged continuously from a nozzle 31 of the discharge head 3wu onto the web 10, and in the X direction, an ink dot discharged from the discharge head 3wu onto the web 10 is interposed between two ink dots discharged continuously from the nozzle 31 of the discharge head 3wd onto the web 10. Therefore, each of the discharge head 3wu and the discharge head 3wd only needs to continuously discharge ink in the cycle being the two times of the cycle Tcy, and the need of discharging ink continuously in a short period of time is not necessary.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a technique for printing an image on a printing medium by ejecting ink from nozzles using an inkjet method. [Background technology]

[0002] A color image can be printed on a print medium by ejecting ink of a color such as cyan, magenta, yellow, or black from nozzles onto the print medium using the inkjet method. Also, a white background image can be printed on the print medium by ejecting white ink from nozzles onto the print medium. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5754537 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, in order to improve the contrast between a color image and a background image (in other words, the visibility of the color image), it is necessary to eject a large amount of ink of a specific color (white) used in the background image without any gaps. However, the amount of ink that can be ejected per unit time is limited by the performance of the ejection unit that ejects the ink. Therefore, in order to eject a large amount of ink of a specific color, it is necessary to prepare a high-performance ejection unit.

[0005] The present invention has been made in consideration of the above-mentioned problems, and has an object to make it possible to eject a large amount of ink of a specific color onto a printing medium without requiring a high-performance ejection section. [Means for solving the problem]

[0006] The printing device according to the present invention comprises a transport means for transporting a printing medium in a transport direction, a first ejection unit having a plurality of first nozzles arranged at a predetermined arrangement pitch in an arrangement direction intersecting the transport direction and forming ink dots on the printing medium with ink ejected from the first nozzles, a second ejection unit having a plurality of second nozzles arranged at the arrangement pitch in the arrangement direction and forming ink dots on the printing medium with ink ejected from the second nozzles, a third ejection unit having a plurality of third nozzles arranged at the arrangement pitch in the arrangement direction and forming ink dots on the printing medium with ink ejected from the third nozzles, and a control unit for controlling the first ejection unit, the second ejection unit and the third ejection unit, wherein the first ejection unit, the second ejection unit and the third ejection unit are arranged in the transport direction, The color of ink ejected from the second nozzle by the second ejection unit and the color of ink ejected from the third nozzle by the third ejection unit are the same specific color, and the color of ink ejected from the first nozzle by the first ejection unit is different from the specific color, and the control unit controls the timing at which each of the second ejection unit and the third ejection unit ejects ink droplets so that, in the transport direction, one ink dot formed on the printing medium by ink ejected from the third nozzle is interposed between two ink dots formed on the printing medium by ink ejected from the second nozzle, and so that one ink dot formed on the printing medium by ink ejected from the second nozzle is interposed between two ink dots formed on the printing medium by ink ejected from the third nozzle.

[0007] The printing method according to the present invention includes the steps of: transporting a print medium in a transport direction; controlling the timing at which a first ejection section having a plurality of first nozzles arranged at a predetermined arrangement pitch in an arrangement direction intersecting the transport direction ejects ink from the first nozzles onto the print medium; controlling the timing at which a second ejection section having a plurality of second nozzles arranged at the arrangement pitch in the arrangement direction ejects ink from the second nozzles onto the print medium; and controlling the timing at which a third ejection section having a plurality of third nozzles arranged at the arrangement pitch in the arrangement direction ejects ink from the third nozzles onto the print medium, wherein the first ejection section, the second ejection section and the third ejection section are arranged in the transport direction, and the second ejection section controls the timing at which the ink ejected from the second nozzles by the second ejection section is ejected from the third nozzles onto the print medium. the color of the ink ejected from the third nozzle by the third ejection unit is the same specific color, and the color of the ink ejected from the first nozzle by the first ejection unit is different from the specific color, and the timing at which each of the second ejection unit and the third ejection unit ejects ink is controlled so that, in the transport direction, one ink dot formed on the printing medium by ink ejected from the third nozzle is interposed between two ink dots formed on the printing medium by ink ejected from the second nozzle, and one ink dot formed on the printing medium by ink ejected from the second nozzle is interposed between two ink dots formed on the printing medium by ink ejected from the third nozzle.

[0008] In the present invention (printing device and printing method) configured in this way, the second ejection section that ejects ink from the second nozzle and the third ejection section that ejects ink from the third nozzle each eject ink of a specific color onto the printing medium. In particular, the second ejection section and the third ejection section share the role of ejecting ink of a specific color onto the printing medium. That is, the timing at which each of the second ejection section and the third ejection section ejects ink is controlled so that one ink dot formed on the printing medium by the ink ejected from the third nozzle is interposed between two ink dots formed on the printing medium by two inks ejected from the second nozzle onto the printing medium, and one ink dot formed on the printing medium by the ink ejected from the second nozzle onto the printing medium is interposed between two ink dots formed on the printing medium by two inks ejected from the third nozzle onto the printing medium. Therefore, each of the second ejection section and the third ejection section does not necessarily need to be able to eject ink continuously in a short period of time. As a result, it is possible to eject a large amount of ink of a specific color onto the print medium without requiring a high-performance ejection section.

[0009] The printing device may be configured such that the control unit controls the timing at which the first ejection unit ejects ink in the transport direction so that ink of a color different from the specific color is ejected onto the printing medium at a predetermined resolution, and the control unit controls the timing at which the second ejection unit and the third ejection unit eject ink in the transport direction so that ink of the specific color is ejected onto the printing medium at the resolution. In this configuration, the timing at which the first ejection unit ejects ink and the timing at which the second ejection unit and the third ejection unit eject ink can be controlled based on the same resolution. This reduces the load on the control unit required to control the timing at which ink is ejected.

[0010] The printing device may be configured so that the maximum amount of ink per ink dot ejected from the second nozzle by the second ejection unit and the maximum amount of ink per ink dot ejected from the third nozzle by the third ejection unit are greater than the maximum amount of ink per ink dot ejected from the first nozzle by the first ejection unit. In this configuration, by ejecting the maximum amount of ink from each of the second nozzle and the third nozzle, it is possible to eject a large amount of ink of a specific color onto the printing medium.

[0011] In particular, in Patent Document 1, the amount of white ink ejected onto the printing medium was ensured by ejecting white ink at a higher resolution than color inks. Therefore, image processing at different resolutions was required, which made the control more complicated, and the amount of data required to control the ejection of white ink was large, which placed a heavy load on the control unit. In response to this, as described above, the maximum amount of ink ejected per ink dot by the second and third ejection units is greater than the maximum amount of ink ejected per ink dot by the first ejection unit, and the maximum amount of ink ejected per ink dot by the second and third ejection units is greater than the maximum amount of ink ejected per ink dot by the first ejection unit, thereby reducing the load on the control unit that controls the ejection of ink and ejecting a large amount of ink of a specific color onto the printing medium.

[0012] However, if the maximum amount of ink ejected per ink dot by the second and third ejection units is made greater than the maximum amount of ink ejected per ink dot by the first ejection unit, the following situation may occur: In other words, if a line constituting a specific target image having a specific color, specifically a line drawing or character, is thicker than a predetermined width, the second and third ejection units may eject their respective maximum amounts of ink to print the line. However, because the maximum amounts of ink ejected by the second and third ejection units are set to be large, there is a possibility that the lines constituting the target image may become too thick.

[0013] In view of this, the printing device may be configured to further include a control unit that generates a first control signal for controlling the ejection of ink from the first nozzle of the first ejection unit, a second control signal for controlling the ejection of ink from the second nozzle of the second ejection unit, and a third control signal for controlling the ejection of ink from the third nozzle of the third ejection unit from image data representing an image to be printed on a printing medium, the first ejection unit ejects ink from the first nozzle at a timing indicated by the first control signal, the second ejection unit ejects ink from the second nozzle at a timing indicated by the second control signal, and the third ejection unit ejects ink from the third nozzle at a timing indicated by the second control signal, and the control unit executes an ink amount adjustment process for reducing the amount of ink per ink dot ejected onto a target image including at least one of a line drawing and a character to be formed with ink of a specific color among the images represented by the image data, to generate the second control signal and the third control signal. This makes it possible to prevent the lines constituting the target image from becoming too thick.

[0014] Specifically, the control unit may configure the printing device to execute, as the ink amount adjustment process, image processing that narrows the width of the target image indicated by the image data. Alternatively, the control unit may configure the printing device to execute, as the ink amount adjustment process, image processing that limits the range of the target image into which ink is ejected by executing a halftone process on the target image indicated by the image data. With this configuration, it is possible to prevent the lines that make up the target image from becoming too thick.

[0015] The control unit may be configured to control the timing at which the second and third ejection units eject ink so that the ink dots formed on the printing medium by the ink ejected from the second nozzles and the ink dots formed on the printing medium by the ink ejected from the third nozzles are arranged alternately in the transport direction on the printing medium. With this configuration, it is possible to eject a large amount of ink of a specific color onto the printing medium without requiring a high-performance ejection unit.

[0016] In addition, various patterns in the arrangement direction of the ink dots formed on the printing medium by the ink ejected from the second nozzles and the third nozzles are assumed. In other words, the control unit may be configured to configure the printing device so that the second ejection unit and the third ejection unit each control the timing at which the ink is ejected so that the ink dots formed on the printing medium by the ink ejected from the second nozzles and the ink dots formed on the printing medium by the ink ejected from the third nozzles are alternately arranged in the arrangement direction on the printing medium. Alternatively, the control unit may be configured to configure the printing device so that the second ejection unit and the third ejection unit each control the timing at which the ink is ejected so that the ink dots formed on the printing medium by the ink ejected from different second nozzles are aligned in a line in the arrangement direction, and the ink dots formed on the printing medium by the ink ejected from different third nozzles are aligned in a line in the arrangement direction. Effect of the Invention

[0017] As described above, according to the present invention, it is possible to eject a large amount of ink of a specific color onto a print medium without requiring a high-performance ejection section. [Brief description of the drawings]

[0018] [Figure 1A] FIG. 1 is a diagram illustrating a first example of a basic configuration of a printing device according to the present invention. [Figure 1B] FIG. 1B is a diagram illustrating printing performed by the printing device of FIG. 1A. [Figure 2A] FIG. 2 is a diagram illustrating a second example of the basic configuration of a printing device according to the present invention. [Figure 2B] FIG. 2B is a diagram showing a schematic diagram of printing performed by the printing apparatus of FIG. 2A. [Figure 3A] FIG. 2 is a plan view illustrating a basic configuration of a discharge head. [Figure 3B] FIG. 2 is a cross-sectional view illustrating a basic configuration of a discharge head. [Figure 3C] FIG. 4 is a diagram showing a schematic relationship between the amounts of ink droplets of each color. [Figure 4] FIG. 2 is a diagram illustrating an electrical configuration of the printing apparatus. [Diagram 5] FIG. 4 is a plan view showing a first example of the range in which each of the two ejection heads that eject white ink ejects ink. [Figure 6] 6 is a timing chart showing a schematic timing of applying drive signals to two ejection heads that eject white ink to perform the operation shown in FIG. 5; [Figure 7] FIG. 11 is a plan view showing a second example of the range in which each of the two ejection heads that eject white ink ejects ink. [Figure 8] 11 is a flowchart showing a first example of target image correction control. [Figure 9] 10 is a flowchart showing a second example of target image correction control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] FIG. 1A is a diagram showing a first example of the basic configuration of a printing device according to the present invention, and FIG. 1B is a diagram showing printing performed by the printing device of FIG. 1A. The printing device 1 prints an image on the web 10, which is a printing medium, by ejecting ink onto the web 10 using an inkjet method. For example, the web 10 may be made of a transparent film, or a non-transparent film or paper. Of both sides of the web 10, the surface that is visible to humans is called the front surface 10a, and the surface opposite to the front surface 10a is called the back surface 10b (see the "Web 10" column in FIG. 1B). In FIG. 1A and the following figures, the X direction, which is the transport direction of the web 10 in the printing device 1, the Y direction, which is the width direction of the web 10, and the Z direction, which is the vertical direction, are appropriately shown. Here, the X direction and the Y direction are orthogonal to each other. Also, in FIG. 1B, the direction that is visible to humans is shown by an arrow.

[0020] The printing device 1 includes a transport section 2 that transports the web 10. The transport section 2 has a feed roller 21 that pays out the web 10 and a take-up roller 22 that takes up the web 10 paid out from the feed roller 21, and transports the web 10 in the X direction from the feed roller 21 to the take-up roller 22 in a roll-to-roll manner. The transport section 2 transports the web 10 at a predetermined transport speed V while facing the surface 10a of the web 10 upward. Note that in FIG. 1A, the transport section 2 is shown diagrammatically, and the transport section 2 has other rollers between the feed roller 21 and the take-up roller 22, which are not shown. In addition, the transport path of the web 10 curves appropriately in response to the winding of the web 10 by the other rollers.

[0021] The printing device 1 also includes two ejection heads 3w, one ejection head 3k, one ejection head 3c, one ejection head 3m, and one ejection head 3y arranged in the X direction, which is the transport direction of the web 10. In other words, the number of ejection heads 3w (2) is greater than the number of each of the ejection heads 3k, 3c, 3m, and 3y (1).

[0022] Each of the two ejection heads 3w faces the surface 10a of the web 10 from above and ejects white ink onto the surface 10a. The ejection head 3k faces the surface 10a of the web 10 from above downstream of the two ejection heads 3w in the X direction and ejects black ink onto the surface 10a. The ejection head 3c faces the surface 10a of the web 10 from above downstream of the ejection head 3k in the X direction and ejects cyan ink onto the surface 10a. The ejection head 3m faces the surface 10a of the web 10 from above downstream of the ejection head 3c in the X direction and ejects magenta ink onto the surface 10a. The ejection head 3y faces the surface 10a of the web 10 from above downstream of the ejection head 3m in the X direction and ejects yellow ink onto the surface 10a.

[0023] The two ejection heads 3w eject white ink onto the front surface 10a of the web 10, which is being transported by the transport unit 2 at a transport speed V, thereby printing a background image Ib on the front surface 10a (see the "After White Ink Ejection" section of FIG. 1B). The specific operation of the two ejection heads 3w that print the background image Ib will be described later. The front surface 10a of the web 10, on which the background image Ib has been printed, is transported toward the ejection heads 3k, 3c, 3m, and 3y downstream in the X direction from the two ejection heads 3w. The ejection heads 3k, 3c, 3m, and 3y then eject black, cyan, magenta, and yellow inks (color inks) onto the front surface 10a of the web 10, which has been transported at the transport speed V, thereby printing a color image Ic (design image) on the front surface 10a (see the "After Color Ink Ejection" section of FIG. 1B).

[0024] The printing device 1 also includes a white fixing unit 4w and a color fixing unit 4c. The white fixing unit 4w is provided downstream of the two ejection heads 3w in the X direction and is located between the ejection heads 3w and 3k. The white fixing unit 4w performs a process of fixing the white ink ejected from the two ejection heads 3w onto the surface 10a of the web 10 onto the surface 10a. The color fixing unit 4c is provided downstream of the ejection heads 3k, 3c, 3m, and 3y in the X direction. The color fixing unit 4c performs a process of fixing the black, cyan, magenta, and yellow ink ejected from the ejection heads 3k, 3c, 3m, and 3y onto the surface 10a of the web 10. If the ink is water-based ink, the white fixing unit 4w and the color fixing unit 4c perform a process of heating and drying the ink, and if the ink is UV (Ultra Violet) ink, the white fixing unit 4w and the color fixing unit 4c perform a process of irradiating the ink with UV light to harden the ink.

[0025] FIG. 2A is a diagram showing a second example of the basic configuration of a printing device according to the present invention, and FIG. 2B is a diagram showing printing performed by the printing device of FIG. 2A. The difference from the first example is that color inks are ejected onto the back surface 10b of the web 10 before white ink is ejected. Therefore, the following mainly describes the differences from the first example, and the common points are given the corresponding reference numerals and will not be described. In the second example, a web 10 made of a transparent film is used as the web 10. Also, in FIG. 2B, the direction in which a person views is indicated by an arrow.

[0026] The transport unit 2 of the second example transports the web 10 at a predetermined transport speed V while facing the back surface 10b of the web 10 upward. Meanwhile, the ejection heads 3k, 3c, 3m, and 3y eject black, cyan, magenta, and yellow inks (color inks) onto the back surface 10b of the web 10 transported by the transport unit 2 at the transport speed V, respectively, to print a color image Ic (design image) onto the back surface 10b (see the "After ejection of color ink" section of FIG. 2B). The back surface 10b of the web 10 on which the color image Ic has been printed is transported toward two ejection heads 3w downstream in the X direction from the ejection heads 3k, 3c, 3m, and 3y. The two ejection heads 3w then eject white ink onto the back surface 10b of the transported web 10, to print a background image Ib onto the back surface 10b (see the "After ejection of white ink" section of FIG. 2B).

[0027] The color fixing unit 4c is provided downstream in the X direction from the ejection heads 3k, 3c, 3m, and 3y, and performs a process of fixing the black, cyan, magenta, and yellow inks ejected from the ejection heads 3k, 3c, 3m, and 3y onto the surface 10a of the web 10. The white fixing unit 4w is provided downstream in the X direction from the two ejection heads 3w, and performs a process of fixing the white ink ejected from the two ejection heads 3w onto the surface 10a of the web 10.

[0028] Fig. 3A is a plan view showing the basic configuration of the discharge head, and Fig. 3B is a cross-sectional view showing the basic configuration of the discharge head. Note that, since the discharge heads 3w, 3k, 3c, 3m, and 3y all have the same basic configuration, they will be referred to as discharge head 3 without distinction here.

[0029] The ejection head 3 has a housing 30 and a plurality of nozzles 31 that open at the bottom surface of the housing 30. In Fig. 3A, the nozzles 31 are shown by dashed lines through the housing 30. The plurality of nozzles 31 are arranged in the Y direction and open at different positions in the Y direction. The arrangement of the nozzles 31 is not limited to a linear arrangement as shown in Fig. 3A, and may be a staggered arrangement.

[0030] The housing 30 is provided therein with a plurality of cavities 32 each communicating with a plurality of nozzles 31, and an ink supply chamber 33 communicating with the plurality of cavities 32, and ink supplied from the ink supply chamber 33 is stored in the cavities 32. Each cavity 32 is provided with a piezoelectric element 34, and the piezoelectric element 34 is displaced in response to a drive signal S (electrical signal), thereby applying a pressure fluctuation to the ink in the cavity 32. This pressure fluctuation pushes the ink out of the cavity 32, and the ink is ejected as ink droplets from the nozzle 31 communicating with the cavity 32. The ink droplets ejected from the nozzle 31 in this manner land on the web 10, forming ink dots on the web 10.

[0031] There are three types of drive signals Ss, Sm, and Sl as the drive signal S that drives the piezoelectric element 34. The drive signal Sm has a larger amplitude than the drive signal Ss, and the amount Qm of ink droplets ejected by driving the piezoelectric element 34 with the drive signal Sm is larger than the amount Qs of ink droplets ejected by driving the piezoelectric element 34 with the drive signal Ss. In addition, the drive signal Sl has a larger amplitude than the drive signal Sm, and the amount Ql of ink droplets ejected by driving the piezoelectric element 34 with the drive signal Sl is larger than the amount Qm of ink droplets ejected by driving the piezoelectric element 34 with the drive signal Sm.

[0032] The above is the basic configuration common to the ejection heads 3w, 3k, 3c, 3m, and 3y. On the other hand, the ejection head 3w is different from the ejection heads 3k, 3c, 3m, and 3y in the volume of the cavity 32. In other words, the volume of the cavity 32 of the ejection head 3w is larger than the volume of the cavity 32 of each of the ejection heads 3k, 3c, 3m, and 3y. Therefore, compared to the ejection heads 3k, 3c, 3m, and 3y, the ejection head 3w can eject a larger amount of ink at one time to form ink dots.

[0033] Therefore, there is a magnitude relationship shown in Fig. 3C between the amount of white ink droplets ejected from nozzles 31 by ejection head 3w and the amount of color ink (black, cyan, magenta or yellow ink) droplets ejected from nozzles 31 by ejection heads 3k, 3c, 3m or 3y. Here, Fig. 3C is a diagram showing a schematic relationship between the amount of ink droplets for each color. In other words, the amount Qs (Qsw) of ink droplets ejected by the nozzles 31 of ejection head 3w is greater than the amount Qs (Qsc) of ink droplets ejected by the nozzles 31 of ejection heads 3k, 3c, 3m or 3y, the amount Qm (Qmw) of ink droplets ejected by the nozzles 31 of ejection head 3w is greater than the amount Qm (Qmc) of ink droplets ejected by the nozzles 31 of ejection heads 3k, 3c, 3m or 3y, and the amount Ql (Qlw) of ink droplets ejected by the nozzles 31 of ejection head 3w is greater than the amount Ql (Qlc) of ink droplets ejected by the nozzles 31 of ejection heads 3k, 3c, 3m or 3y.

[0034] In this example, black, cyan, magenta, and yellow inks are collectively referred to as color inks, and the amounts of color inks are expressed as Qsc, Qmc, and Qlc, respectively. However, this does not mean that the amounts of black, cyan, magenta, and yellow ink droplets are equal, and there may be differences in the amounts of ink droplets between these colors.

[0035] 4 is a diagram showing a schematic diagram of an electrical configuration of the printing device. The printing device 1 includes a controller 9 that performs overall control of the printing device 1. The controller 9 is configured, for example, with a processor such as a CPU (Central Processing Unit) or an FPGA (Field Programmable Gate Array). The controller 9 includes a transport control unit 91 that controls the transport unit 2. The transport control unit 91 controls the transport unit 2 so that the web 10 is transported in the X direction at a transport speed V. Furthermore, the controller 9 includes a data acquisition unit 92, a RIP (Raster Image Processor) 93, a halftone processing unit 94, and a head control unit 95.

[0036] The data acquisition unit 92 acquires vector data Dv (manuscript data) indicating an image to be printed by the printing device 1 from, for example, an external computer. The RIP 93 converts the vector data Dv received from the data acquisition unit 92 into bitmap data Dbk, Dbc, Dvm, Dby, and Dbw of each color by rasterizing the vector data Dv received from the data acquisition unit 92. Here, the bitmap data Dbk is black bitmap data, the bitmap data Dbc is cyan bitmap data, the bitmap data Dbm is magenta bitmap data, the bitmap data Dby is yellow bitmap data, and the bitmap data Dbw is white bitmap data.

[0037] The halftone processor 94 executes halftone processing on each of the bitmap data Dbk, Dbc, Dvm, Dby, and Dbw, using a threshold matrix to binarize the gradation value indicated for each pixel in the bitmap data generated by the RIP 93. Through this halftone processing, the bitmap data Dbk is converted into black halftone image data Dhk, the bitmap data Dbc is converted into cyan halftone image data Dhc, the bitmap data Dbm is converted into magenta halftone image data Dhm, the bitmap data Dby is converted into yellow halftone image data Dhy, and the bitmap data Dbw is converted into white halftone image data Dhw.

[0038] The head control unit 95 controls each of the multiple piezoelectric elements 34 of the ejection head 3 based on the halftone image data Dhk, Dhc, Dhm, Dhy, and Dhw. The control of the piezoelectric elements 34 is performed by providing a drive signal S to the piezoelectric elements 34 and driving the piezoelectric elements 34 with the drive signal S. As described above, there are three types of drive signals Ss, Sm, and Sl. Therefore, the head control unit 95 determines the drive signal S to be provided to each piezoelectric element 34 of the ejection head 3 from among the drive signals Ss, Sm, and Sl based on the halftone image data Dhk, Dhc, Dhm, Dhy, and Dhw.

[0039] That is, the drive signal S to be provided to each piezoelectric element 34 of the ejection head 3k is determined based on the halftone image data Dhk, and the piezoelectric elements 34 of the ejection head 3k are driven by the drive signal S. The drive signal S to be provided to each piezoelectric element 34 of the ejection head 3c is determined based on the halftone image data Dhc, and the piezoelectric elements 34 of the ejection head 3c are driven by the drive signal S. The drive signal S to be provided to each piezoelectric element 34 of the ejection head 3m is determined based on the halftone image data Dhm, and the piezoelectric elements 34 of the ejection head 3m are driven by the drive signal S. The drive signal S to be provided to each piezoelectric element 34 of the ejection head 3y is determined based on the halftone image data Dhy, and the piezoelectric elements 34 of the ejection head 3y are driven by the drive signal S.

[0040] Similarly, based on the halftone image data Dhw, a drive signal S to be given to each piezoelectric element 34 of the ejection head 3w is determined, and the piezoelectric element 34 of the ejection head 3w is driven by the drive signal S. In particular, when the ejection head 3w is made to eject white ink to print the background image Ib as described above, it is determined that a drive signal Sl is given to each piezoelectric element 34 of the ejection head 3w. That is, the background image Ib is printed by ejecting white ink droplets of an amount Qlw. Furthermore, two ejection heads 3w that eject white ink are provided. Therefore, the head control unit 95 generates drive signals Sl for each of the two ejection heads 3w from the halftone image data Dhw and gives them to the piezoelectric elements 34 of each ejection head 3w. As a result, the two ejection heads 3w share the task of printing the white background image Ib indicated by the halftone image data Dhw.

[0041] This point will be explained using Figures 5 and 6. Figure 5 is a plan view showing a first example of the range in which each of the two ejection heads that eject white ink ejects ink, and Figure 6 is a timing chart showing a timing diagram of the timing of providing drive signals to the two ejection heads that eject white ink to perform the operation of Figure 5. Here, of the two ejection heads 3w, the ejection head 3w on the upstream side in the X direction will be appropriately distinguished as ejection head 3wu, and the ejection head 3w on the downstream side will be distinguished as ejection head 3wd.

[0042] As shown in FIG. 5, a plurality of pixels PX arranged in a matrix in the X and Y directions are set on the web 10. In the Y direction, the pixels PX are arranged at an arrangement pitch of the nozzles 31 of the ejection head 3w. In the X direction, the pixels PX are arranged at an arrangement pitch Rx according to the resolution of the image. The nozzles 31 of the ejection head 3w eject ink droplets onto the pixels PX arranged at the same positions as the nozzles 31 in the Y direction. That is, the nozzles 31 eject ink droplets onto a pixel row Cp consisting of pixels PX arranged in parallel in the X direction. In addition, the nozzles 31 of the ejection heads 3wu and 3wd, which are arranged at the same positions as each other in the Y direction, eject ink droplets onto the pixel row Cp arranged at the same positions as the nozzles 31 in the Y direction.

[0043] At this time, the nozzles 31 of the ejection head 3wu and the nozzles 31 of the ejection head 3wd eject ink droplets onto different pixels PX in one pixel row Cp, thereby sharing the task of ejecting ink droplets onto the pixel row Cp. That is, as shown in Fig. 5, in the pixel row Cp, pixels PX onto which the ejection head 3wu ejects ink droplets (pixels PX with dot hatching) and pixels PX onto which the ejection head 3wd ejects ink droplets (pixels PX with diagonal hatching) are arranged alternately in the X direction.

[0044] In order to execute such sharing, a drive signal S is provided to the nozzles 31 of each of the ejection heads 3wu and 3wd at the timing shown in the timing chart of Fig. 6. Here, the period Tcy shown in Fig. 6 is a value obtained by dividing the arrangement pitch Rx of the pixels PX in the X direction by the transport speed V, and corresponds to the time required for the web 10 to move the arrangement pitch Rx in the X direction. The ejection of ink droplets from the nozzles 31 of each of the ejection heads 3k, 3c, 3m, and 3y other than the ejection head 3w is executed in synchronization with the period Tcy. In contrast, the ejection of ink droplets from the ejection heads 3wu and 3wd is executed in synchronization with a period twice the period Tcy.

[0045] In other words, at time Tu1, a drive signal Sl is given to the nozzle 31 of the ejection head 3wu, causing the nozzle 31 to eject an amount of white ink Qlw, at time Tu2, which is twice the period Tcy after time Tu1, a drive signal Sl is given to the nozzle 31 of the ejection head 3wu, causing the nozzle 31 to eject an amount of white ink Qlw, and at time Tu3, which is twice the period Tcy after time Tu2, a drive signal Sl is given to the nozzle 31 of the ejection head 3wu, causing the nozzle 31 to eject an amount of white ink Qlw, and such operations are repeated.

[0046] Similarly, at time Td1, a drive signal Sl is given to the nozzle 31 of the ejection head 3wd, causing the nozzle 31 to eject an amount of white ink Qlw, at time Td2, which is twice the period Tcy since time Td1, a drive signal Sl is given to the nozzle 31 of the ejection head 3wd, causing the nozzle 31 to eject an amount of white ink Qlw, and at time Td3, which is twice the period Tcy since time Td2, a drive signal Sl is given to the nozzle 31 of the ejection head 3wd, causing the nozzle 31 to eject an amount of white ink Qlw, and such operations are repeated.

[0047] 5, the ink dots ejected from the ejection head 3wu and the ink dots ejected from the ejection head 3wd are arranged alternately in the X direction on the web 10. In the Y direction, the ink dots ejected from the multiple nozzles 31 of the ejection head 3wu are arranged in a line on the web 10, and the ink dots ejected from the multiple nozzles 31 of the ejection head 3wd are arranged in a line on the web 10. In other words, the range from which the ejection head 3wu ejects ink and the range from which the ejection head 3wd ejects ink are arranged in an interlaced manner.

[0048] In the embodiment described above, each of the ejection head 3wu (second ejection section) that ejects ink from the nozzle 31 (second nozzle) and the ejection head 3wd (third ejection section) that ejects ink from the nozzle 31 (third nozzle) ejects white (specific color) ink dots onto the web 10. In particular, the ejection head 3wu and the ejection head 3wd are controlled to share the ejection of white ink onto the web 10, as shown in FIG. 5. As a result of such control, in the X direction, an ink dot ejected from the ejection head 3wd onto the web 10 is interposed between two ink dots ejected consecutively from the nozzle 31 of the ejection head 3wu onto the web 10. Also, in the X direction, an ink dot ejected from the ejection head 3wu onto the web 10 is interposed between two ink dots ejected consecutively from the nozzle 31 of the ejection head 3wd onto the web 10. In other words, each of the ejection heads 3wu and 3wd only needs to be able to eject ink continuously at a period twice the period Tcy, and does not necessarily need to be able to eject ink continuously in a short period (period Tcy). As a result, it is possible to eject a large amount of white ink onto the web 10 without requiring a high-performance ejection head 3w (ejection unit).

[0049] Moreover, the controller 9 (controller) controls the timing at which the ejection heads 3k, 3c, 3m, or 3y (first ejection unit) eject ink in the X direction (transport direction) so that the color ink is ejected onto the web 10 at a predetermined resolution (resolution corresponding to the arrangement pitch Rx). The controller 9 also controls the timing at which the ejection heads 3wu and 3wd eject ink in the X direction so that the white ink is ejected onto the web 10 at a resolution (resolution corresponding to the arrangement pitch Rx). In this configuration, the timing at which the ejection heads 3k, 3c, 3m, or 3y eject ink and the timing at which the ejection heads 3wu and 3wd eject ink can be controlled based on the same resolution (resolution corresponding to the arrangement pitch Rx). Specifically, the above rasterization and halftone processing can be performed at a common resolution for colors (black, cyan, magenta, yellow) and white. Therefore, the load on the controller 9 required for controlling the ink ejection timing can be reduced.

[0050] Furthermore, the maximum value Qlw of the amount of ink per ink dot ejected from the nozzles 31 of the ejection heads 3wu and 3wd is greater than the maximum value Qlc of the amount of ink per ink dot ejected from the nozzles 31 of the ejection heads 3k, 3c, 3m, and 3y (first ejection units). With this configuration, by ejecting white ink in an amount equal to the maximum value Qlw per ink dot from the nozzles 31 of each of the ejection heads 3wu and 3wd, a large amount of white ink can be ejected onto the web 10.

[0051] In particular, in Patent Document 1, the amount of white ink ejected onto the web 10 was ensured by ejecting white ink at a higher resolution than color inks. This required image processing at different resolutions, which made control more complex, and the amount of data required to control the ejection of white ink was large, placing a heavy load on the control unit. In response to this, as described above, by making the maximum value Qlw of the amount of ink ejected from the nozzles 31 of the ejection heads 3wu and 3wd greater than the maximum value Qlc of the amount of ink ejected from the nozzles 31 of the ejection heads 3k, 3c, 3m, and 3y (first ejection unit), it is possible to eject a large amount of white ink onto the web 10 while reducing the load on the controller 9 that controls the ejection of ink.

[0052] Furthermore, the controller 9 controls the timing at which the ejection heads 3wu and 3wd eject ink, so that the ink dots ejected from the nozzles 31 of the ejection heads 3wu and the ink dots ejected from the nozzles 31 of the ejection heads 3wd are arranged alternately in the X direction on the web 10. With this configuration, it is possible to eject a large amount of white ink onto the web 10 without requiring a high-performance ejection head 3w.

[0053] Fig. 7 is a plan view showing a second example of the range in which each of two ejection heads ejecting white ink ejects ink. In the second example of Fig. 7, as in the first example of Fig. 5, in the pixel row Cp, pixels PX (pixels PX with dot hatching) to which the ejection head 3wu ejects ink droplets and pixels PX (pixels PX with diagonal hatching) to which the ejection head 3wd ejects ink droplets are arranged alternately one by one in the X direction. However, the phase in which the pixels PX to which the ejection head 3wu ejects ink droplets and the pixels PX to which the ejection head 3wd ejects ink droplets are arranged differs by 180 degrees between adjacent pixel rows Cp. The only difference from the first example of Fig. 5 is the phase of the arrangement, and the other points are the same as the first example of Fig. 5.

[0054] 7, the ink dots ejected from the ejection head 3wu and the ink dots ejected from the ejection head 3wd are arranged alternately one by one in the X direction on the web 10. Furthermore, the ink dots ejected from the ejection head 3wu and the ink dots ejected from the ejection head 3wd are arranged alternately one by one in the Y direction on the web 10. In other words, the range from which the ejection head 3wu ejects ink and the range from which the ejection head 3wd ejects ink are arranged in a checkered flag shape.

[0055] In the embodiment described above, each of the ejection head 3wu (second ejection section) that ejects ink from the nozzle 31 (second nozzle) and the ejection head 3wd (third ejection section) that ejects ink from the nozzle 31 (third nozzle) ejects white (specific color) ink dots onto the web 10. In particular, the ejection head 3wu and the ejection head 3wd are controlled to share the ejection of white ink onto the web 10, as shown in FIG. 7. As a result of such control, in the X direction, an ink dot ejected from the ejection head 3wd onto the web 10 is interposed between two ink dots ejected consecutively from the nozzle 31 of the ejection head 3wu onto the web 10. Also, in the X direction, an ink dot ejected from the ejection head 3wu onto the web 10 is interposed between two ink dots ejected consecutively from the nozzle 31 of the ejection head 3wd onto the web 10. In other words, each of the ejection heads 3wu and 3wd only needs to be able to eject ink continuously at a period twice the period Tcy, and does not necessarily need to be able to eject ink continuously in a short period (period Tcy). As a result, it is possible to eject a large amount of white ink onto the web 10 without requiring a high-performance ejection head 3w (ejection unit).

[0056] Furthermore, since each of the ejection heads 3wu and 3wd only needs to eject white ink at long intervals, there is also the following advantage. That is, in order to properly eject ink from the nozzle 31 using the inkjet method, the stability of the meniscus formed at the interface between the ink and air in the nozzle 31 is important. However, after the ink is ejected, residual vibration occurs in the meniscus. Therefore, it is required to eject the ink after the residual vibration of the meniscus has settled. In particular, with white ink, such residual vibration is large, and it takes a long time for the residual vibration to settle. In contrast, in the above embodiment, the ejection interval of the white ink can be set long, so that the white ink can be stably ejected after the residual vibration has settled.

[0057] Furthermore, the controller 9 controls the timing at which the ejection heads 3wu and 3wd eject ink, so that the ink dots ejected from the nozzles 31 of the ejection heads 3wu and the ink dots ejected from the nozzles 31 of the ejection heads 3wd are arranged alternately in the X direction on the web 10. With this configuration, it is possible to eject a large amount of white ink onto the web 10 without requiring a high-performance ejection head 3w.

[0058] However, if the maximum value Qlw of the ink amount per ink dot ejected by the ejection heads 3wu and 3wd is made larger than the maximum value Qlc of the ink amount per ink dot ejected by the ejection heads 3k, 3c, 3m, and 3y, the following situation may occur. That is, if a line constituting a predetermined target image having white, specifically a line drawing (ruled line, etc.) or a character (alphabet, kanji, etc.), is thicker than a predetermined width, the ejection heads 3wu and 3wd may eject ink in an amount equal to the maximum value Qlw to print the line. However, since the maximum value Qlw of the ink ejection amount of each of the ejection heads 3wu and 3wd is set large, the line constituting the target image may become too thick. Therefore, the target image correction control shown in the following FIG. 8 or FIG. 9 may be executed.

[0059] Fig. 8 is a flow chart showing a first example of the target image correction control. The target image correction control in Fig. 8 is executed by the data acquisition unit 92 of the controller 9. That is, when the data acquisition unit 92 acquires vector data Dv (step S101), it determines whether or not the target image (line drawing or text) is included in the white image indicated by the vector data Dv (step S102). If the target image is not included ("NO" in step S102), the data acquisition unit 92 outputs the acquired vector data Dv to the RIP 93 (step S104). As a result, the RIP 93 executes rasterization on the vector data Dv.

[0060] If the white image represented by the vector data Dv contains a target image (line drawing or text) ("YES" in step S102), the data acquisition unit 92 modifies the vector data Dv by performing image processing on the vector data Dv to reduce the width of the lines that make up the target image (step S103). The data acquisition unit 92 then outputs the vector data Dv modified in step S103 to the RIP 93. As a result, the RIP 93 rasterizes the modified vector data Dv. Subsequent processing by the halftone processing unit 94 and head control unit 95 is as described above.

[0061] That is, the controller 9 generates a drive signal S (first control signal) for controlling the ejection of ink from the nozzles 31 of the ejection heads 3k, 3c, 3m, and 3y (first ejection section), a drive signal S (second control signal) for controlling the ejection of ink from the nozzles 31 (second nozzles) of the ejection head 3wu (second ejection section), and a drive signal S (third control signal) for controlling the ejection of ink from the nozzles 31 (third nozzles) of the ejection head 3wd (third ejection section) from the vector data Dv (image data). In addition, the controller 9 executes the process of step S103 (ink amount adjustment process) for reducing the amount of ink ejected onto a target image including at least one of a line drawing and a character to be formed with white ink among the images indicated by the vector data Dv, and generates the drive signal S for the ejection heads 3wu and 3wd. This makes it possible to prevent the lines constituting the target image from becoming too thick.

[0062] Specifically, the controller 9 executes image processing to narrow the width of the target image represented by the vector data Dv (step S103), thereby preventing the lines constituting the target image from becoming too thick.

[0063] FIG. 9 is a flow chart showing a second example of the target image correction control. The target image correction control in FIG. 9 is executed by the halftone processing unit 94 of the controller 9. That is, when the halftone processing unit 94 acquires white bitmap data Dbw (step S201), it judges whether or not the target image (line drawing or text) is included in the white image indicated by the bitmap data Dbw (step S202). If the target image is not included (if "NO" in step S202), the halftone processing unit 94 executes halftone processing using a normal threshold matrix on the acquired bitmap data Dbw to generate halftone image data Dhw (step S203). This halftone processing is the same as that described above. Then, this halftone image data Dhw is output to the head control unit 95 (step S205).

[0064] If the white image indicated by the bitmap data Dbw contains a target image (line drawing or text) (YES in step S202), the halftone processing unit 94 executes halftone processing using a special threshold matrix on the acquired bitmap data Dbw to generate halftone image data Dhw (step S204). This special threshold matrix limits the range in which ink is ejected onto the target image more than the normal threshold matrix. In other words, the range in which ink is ejected onto the target image in the halftone image data Dhw obtained when halftone processing using the special threshold matrix is ​​executed on the bitmap data Dbw is more limited than the range in which ink is ejected onto the target image in the halftone image data Dhw obtained when halftone processing using the normal threshold matrix is ​​executed on the bitmap data Dbw. Then, this halftone image data Dhw is output to the head control unit 95 (step S205).

[0065] That is, the controller 9 generates a drive signal S (first control signal) for controlling the ejection of ink from the nozzles 31 of the ejection heads 3k, 3c, 3m, and 3y (first ejection section), a drive signal S (second control signal) for controlling the ejection of ink from the nozzles 31 (second nozzles) of the ejection head 3wu (second ejection section), and a drive signal S (third control signal) for controlling the ejection of ink from the nozzles 31 (third nozzles) of the ejection head 3wd (third ejection section) from the bitmap data Dbk, Dbc, Dbm, Dby, and Dbw (image data). In addition, the controller 9 executes the process (ink amount adjustment process) of step S204 for reducing the amount of ink ejected to the target image including at least one of a line drawing and a character to be formed with white ink among the images indicated by the bitmap data Dbw, and generates the drive signal S for the ejection heads 3wu and 3wd. This makes it possible to prevent the lines constituting the target image from becoming too thick.

[0066] Specifically, the controller 9 executes image processing that limits the range where ink is ejected from the target image by performing halftone processing on the target image indicated by the bitmap data Db2 (step S204). This can suppress the lines that make up the target image from becoming too thick.

[0067] In the embodiment described above, the printing apparatus 1 corresponds to an example of the "printing apparatus" of the present invention, the web 10 corresponds to an example of the "printing medium" of the present invention, the conveyance unit 2 corresponds to an example of the "conveyance means" of the present invention, each of the ejection heads 3k, 3c, 3m, 3y corresponds to an example of the "first ejection unit" of the present invention, each nozzle 31 of the ejection heads 3k, 3c, 3m, 3y corresponds to an example of the "first nozzle" of the present invention, the ejection head 3wu corresponds to an example of the "second ejection unit" of the present invention, the nozzle 31 of the ejection head 3wu corresponds to an example of the "second nozzle" of the present invention, the ejection head 3wd corresponds to an example of the "third ejection unit" of the present invention, the nozzle 31 of the ejection head 3wd corresponds to an example of the "third nozzle" of the present invention, the controller 9 corresponds to an example of the "control unit" of the present invention, the drive signal S for each of the ejection heads 3k, 3c, 3m, 3y corresponds to an example of the "first control signal" of the present invention, the drive signal S for the ejection head 3wu corresponds to an example of the "second control signal" of the present invention, the drive signal S for the ejection head 3wd corresponds to an example of the "third control signal" of the present invention, the X direction corresponds to an example of the "conveyance direction" of the present invention, and the Y direction corresponds to an example of the "array direction" of the present invention.

[0068] Note that the present invention is not limited to the above-described embodiment, and various modifications can be made other than those described above without departing from the spirit thereof. For example, among the inequalities regarding the ejection amounts of the white ink shown in the above example, Qsc < Qsw and Qmc < Qmw do not necessarily have to be satisfied. That is, the amount Qsc and the amount Qsw may be set to be about the same, or the amount Qmc and the amount Qmw may be set to be about the same. Specifically, such a setting is possible by adjusting the amplitudes of the drive signals Ss and Sm applied to the ejection head 3w.

[0069] Further, the volume of the cavity 32 of the ejection head 3w may be equal to the volume of the cavity 32 of the ejection heads 3k, 3c, 3m, and 3y. In this case, by adjusting the amplitude of the drive signal Sl applied to the ejection head 3w, control may be performed such that the inequality Qlc < Qlw is satisfied.

[0070] Further, the color (specific color) of the background image Ib is not limited to white and may be a color other than white.

[0071] Further, the number of ejection heads 3w that eject white ink is not limited to two and may be three or more.

[0072] Further, the number of ejection heads 3 that eject color ink is not limited to the above four and may be one or more.

[0073] Further, the mechanism for ejecting ink by the inkjet method is not limited to the mechanism using the piezoelectric element 34 described above, and a mechanism for ejecting ink by heating may also be used.

Industrial Applicability

[0074] The present invention is applicable to the entire technology of printing an image on a printing medium by ejecting ink from a nozzle by an inkjet method.

Explanation of Signs

[0075] 1... Printing apparatus 10... Web (printing medium) 2... Conveying unit (conveying means) 3k, 3c, 3m, 3y... Ejection heads (first ejection unit) 3w... Ejection head (second ejection unit, third ejection unit) 31... Nozzles (first nozzle, second nozzle, third nozzle) 9... Controller (control unit) S... Drive signal (first control signal, second control signal, third control signal) X... X direction (conveying direction) Y... Y direction (array direction)

Claims

1. A transport means for transporting the print medium in a transport direction; a first ejection unit that has a plurality of first nozzles arranged at a predetermined arrangement pitch in an arrangement direction intersecting the transport direction, and that forms ink dots on the print medium by ink ejected from the first nozzles; a second ejection section that has a plurality of second nozzles arranged at the arrangement pitch in the arrangement direction and that forms ink dots on the print medium by ink ejected from the second nozzles; a third ejection unit that has a plurality of third nozzles arranged at the arrangement pitch in the arrangement direction and that forms ink dots on the print medium by ink ejected from the third nozzles; a control unit that controls the first discharge unit, the second discharge unit, and the third discharge unit; Equipped with the first discharge portion, the second discharge portion, and the third discharge portion are arranged in the transport direction, a color of ink ejected from the second nozzle by the second ejection unit and a color of ink ejected from the third nozzle by the third ejection unit are the same specific color; the color of the ink ejected from the first nozzle by the first ejection unit is different from the specific color; The control unit controls the timing at which each of the second and third ejection units ejects ink droplets so that, in the transport direction, one ink dot formed on the printing medium by ink ejected from the third nozzle is interposed between two ink dots formed on the printing medium by ink ejected from the second nozzle in succession, and so that one ink dot formed on the printing medium by ink ejected from the second nozzle is interposed between two ink dots formed on the printing medium by ink ejected from the third nozzle.

2. the control unit controls a timing at which the first ejection unit ejects ink in the transport direction so that ink of a color different from the specific color is ejected onto the print medium at a predetermined resolution; The printing device according to claim 1 , wherein the control unit controls the timing at which the second ejection unit and the third ejection unit eject ink in the transport direction so that ink of the specific color is ejected onto the printing medium at the resolution.

3. 3. A printing device according to claim 2, wherein the maximum amount of ink per ink dot ejected from the second nozzle by the second ejection unit and the maximum amount of ink per ink dot ejected from the third nozzle by the third ejection unit are greater than the maximum amount of ink per ink dot ejected from the first nozzle by the first ejection unit.

4. a control unit that generates a first control signal that controls the ejection of ink from the first nozzle of the first ejection unit, a second control signal that controls the ejection of ink from the second nozzle of the second ejection unit, and a third control signal that controls the ejection of ink from the third nozzle of the third ejection unit, from image data that represents an image to be printed on the printing medium; the first ejection unit ejects ink from the first nozzle at a timing indicated by the first control signal; the second ejection unit ejects ink from the second nozzle at a timing indicated by the second control signal; the third ejection unit ejects ink from the third nozzle at a timing indicated by the second control signal; The printing device described in claim 3, wherein the control unit performs an ink amount adjustment process to reduce the amount of ink per ink dot ejected onto a target image represented by the image data, the target image including at least one of a line drawing and a character to be formed with ink of the specific color, and generates the second control signal and the third control signal.

5. The printing apparatus according to claim 4 , wherein the control unit executes image processing for narrowing a width of the target image indicated by the image data as the ink amount adjustment processing.

6. The printing device according to claim 4 , wherein the control unit performs image processing as the ink amount adjustment processing, which limits the range of the target image into which ink is ejected by performing halftone processing on the target image indicated by the image data.

7. 7. A printing device as described in any one of claims 1 to 6, wherein the control unit controls the timing at which the second ejection unit and the third ejection unit eject ink so that ink dots formed on the printing medium by ink ejected from the second nozzles and ink dots formed on the printing medium by ink ejected from the third nozzles are arranged alternately in the transport direction on the printing medium.

8. 8. The printing device according to claim 7, wherein the control unit controls the timing at which the second ejection unit and the third ejection unit eject ink so that the ink dots formed on the printing medium by the ink ejected from the second nozzles and the ink dots formed on the printing medium by the ink ejected from the third nozzles are arranged alternately in the arrangement direction on the printing medium.

9. 8. The printing device according to claim 7, wherein the control unit controls the timing at which the second ejection unit and the third ejection unit eject ink so that ink dots formed on the printing medium by ink ejected from the second nozzles which are different from each other are aligned in a line in the arrangement direction, and ink dots formed on the printing medium by ink ejected from the third nozzles which are different from each other are aligned in a line in the arrangement direction.

10. A step of transporting the print medium in a transport direction; a step of controlling a timing at which a first ejection unit having a plurality of first nozzles arranged at a predetermined arrangement pitch in an arrangement direction intersecting the transport direction ejects ink from the first nozzles onto the print medium; a step of controlling a timing at which a second ejection unit having a plurality of second nozzles arranged at the arrangement pitch in the arrangement direction ejects ink from the second nozzles onto the print medium; a step of controlling a timing at which a third ejection unit having a plurality of third nozzles arranged at the arrangement pitch in the arrangement direction ejects ink from the third nozzles onto the print medium; Equipped with the first discharge portion, the second discharge portion, and the third discharge portion are arranged in the transport direction, a color of ink ejected from the second nozzle by the second ejection unit and a color of ink ejected from the third nozzle by the third ejection unit are the same specific color; the color of the ink ejected from the first nozzle by the first ejection unit is different from the specific color; A printing method in which the timing at which each of the second and third ejection units ejects ink is controlled so that, in the transport direction, one ink dot formed on the printing medium by ink ejected from the third nozzle is interposed between two ink dots formed on the printing medium by ink ejected from the second nozzle, and one ink dot formed on the printing medium by ink ejected from the second nozzle is interposed between two ink dots formed on the printing medium by ink ejected from the third nozzle.

Images