Printing apparatus

Abstract

To provide an inkjet printing device that performs printing on a printing medium by discharging ink thereto, which can enhance a quality of a printed matter.SOLUTION: First, a correction region that is a region to which second ink (typically white ink) should be discharged of regions on a base material is determined (S10). Subsequently, density data are corrected so that the second ink is discharged to the correction region (S20). Then, actual printing on the base material is started (S30). Then, the second ink is discharged to the correction region (S40), and first ink (typically color ink) is discharged onto the second ink discharged onto the base material in the correction region (S50).SELECTED DRAWING: Figure 28

Description

Technical Field

[0001] The present invention relates to a printing apparatus having an ink ejection head (printing head) provided with a large number of nozzles for ejecting ink, and a printing method using the same.

Background Art

[0002] Conventionally, an inkjet printing apparatus (hereinafter simply referred to as "inkjet printer") that performs printing by ejecting ink onto a substrate (such as printing paper) has been known. In an inkjet printing apparatus, generally, printing is performed using aqueous ink. However, in recent years, for example, for label printing, the development of an inkjet printing apparatus that performs printing using UV ink (ultraviolet curable ink) has been progressing. In an inkjet printing apparatus using UV ink, in order to fix the UV ink ejected from the ink ejection head onto the substrate, irradiation of UV light (ultraviolet rays) onto the UV ink is performed.

[0003] By the way, regarding an inkjet printing apparatus, there are individual differences in the nozzles provided in the ink ejection head. Therefore, even when ink is ejected from a large number of nozzles provided in the ink ejection head based on the same drive signal, there are variations in the amount of ink ejected from those large number of nozzles. When printing is executed in such a state, a high-quality printed matter cannot be obtained. Therefore, density equalization correction for correcting the density of print data is performed so that ink is ejected from all nozzles in the same manner.

[0004] Furthermore, in inkjet printing devices, ink ejection failures can occur due to factors such as ink solidification from prolonged disuse. When ink ejection failures occur, dots corresponding to the defective nozzle (hereinafter referred to as the "defective nozzle") are missing in the printed image. Therefore, nozzle missing correction is performed to correct the density of the print data so that the ink that should be ejected from the defective nozzle is ejected from other nozzles (typically nozzles adjacent to the defective nozzle). An example of nozzle missing correction is disclosed in Japanese Patent Application Publication No. 2014-188785.

[0005] Referring to Figure 29, density uniformity correction and nozzle defect correction will be explained further. Here, we focus on five pixel sections 9(1) to 9(5) corresponding to five nozzles. We assume that single-color printing is performed in the five pixel sections 9(1) to 9(5) using ink of the same color ejected from the five nozzles. Furthermore, we assume that in the print data generated by the RIP process, the density (screen percentage) of the five pixel sections 9(1) to 9(5) is all 50, as shown in the section labeled 91. Density uniformity correction corrects the density of the five pixel sections 9(1) to 9(5), for example, as shown in the section labeled 92. In this example, based on the same drive signal, the nozzle corresponding to pixel section 9(1) ejects (5 / 4) times more ink than the nozzle corresponding to pixel section 9(2), so the density of pixel section 9(1) is corrected to 40, which is (4 / 5) times 50. Furthermore, based on the same drive signal, the nozzle corresponding to pixel 9(4) ejects (5 / 6) times more ink than the nozzle corresponding to pixel 9(2), so the density of pixel 9(4) is corrected to 60, which is (6 / 5) times 50. In this example, of the five nozzles, the nozzle corresponding to pixel 9(3) is a defective nozzle. Therefore, nozzle defect correction is applied to the data shown in the part labeled 92. As a result, the densities of the five pixel parts 9(1) to 9(5) are corrected as shown in the part labeled 93. In this regard, since the density of pixel 9(3) before nozzle defect correction is 40, 20 is added to the density of pixel 9(2) and 20 is added to the density of pixel 9(4). That is, the density of pixel 9(2) is corrected to 70 and the density of pixel 9(4) is corrected to 80.

[0006] Through the density uniformity correction and nozzle defect correction described above, the occurrence of unevenness in printed images caused by individual differences between nozzles and the presence of defective nozzles is suppressed. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2014-188785 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, when a defective nozzle occurs, even if the amount of ink that should have been ejected from that defective nozzle is ejected from other nozzles through nozzle defect correction, a printed product with the defect satisfactoryly resolved may not be obtained. In particular, when a defect occurs in a nozzle corresponding to an area where single-color, high-density printing is performed, the dot size of the ink ejected from other nozzles is often insufficient to resolve the defect. Thus, depending on the image being printed, conventional nozzle defect correction may not produce a printed product of sufficient quality.

[0009] Furthermore, while ink ejection heads generally contain multiple head modules, color unevenness can occur in areas where ink ejection by one head module overlaps with ink ejection by an adjacent head module. Additionally, there is a strong demand from users for improved print quality of solid-color images.

[0010] In view of the above circumstances, the present invention aims to realize an inkjet printing apparatus (a printing apparatus that performs printing by ejecting ink onto a printing medium) that enables high-quality printing of printed materials. [Means for solving the problem]

[0011] The first invention is a printing apparatus that performs printing by ejecting ink onto a printing medium, A transport unit for transporting the aforementioned printing medium, The printing medium that is transported by the transport unit It is an ultraviolet-curing ink. A first ink ejection head including multiple ink ejection ports for ejecting a first ink, The transport unit is positioned upstream of the first ink ejection head in the direction in which the printing medium is transported by the transport unit, and the transport unit is positioned upstream of the first ink ejection head in the direction in which the printing medium is transported by the transport unit. It is an ultraviolet-curing ink.A second ink ejection head, which ejects a second ink, includes multiple ink ejection ports, A correction region determination unit that determines a correction region which is a region on the printing medium where the second ink should be ejected, An ink ejection control unit controls the ejection of the second ink from the second ink ejection head so that the second ink is ejected into the correction region before the first ink is ejected into the correction region. 、 A first ultraviolet irradiation unit that cures the first ink ejected from the first ink ejection head onto the printing medium by ultraviolet irradiation, A second ultraviolet irradiation unit for curing the second ink ejected from the second ink ejection head onto the printing medium by ultraviolet irradiation, A UV irradiation control unit that controls UV irradiation by the second UV irradiation unit and Equipped with, The wetting area of ​​the first ink on the printing medium is larger when the first ink is dispensed onto the second ink dispensed on the printing medium than when the first ink is dispensed directly onto the printing medium. Ku, The correction region determination unit determines the correction region based on the position of a defective ink ejection port, which is one of the plurality of ink ejection ports included in the first ink ejection head and has an ejection defect, such that the second ink is ejected from an ink ejection port that corresponds to an ink ejection port adjacent to the defective ejection port and is included in the second ink ejection head. When the second ink is ejected into the correction region, the ultraviolet irradiation control unit stops the ultraviolet irradiation by the second ultraviolet irradiation unit, or reduces the intensity of the ultraviolet irradiation by the second ultraviolet irradiation unit. The first ink ejection head consists of multiple ink ejection heads, each corresponding to a different color, which eject color inks of different colors from one another. The ink ejection control unit controls the ejection of the second ink from the second ink ejection head such that the closer the distance from the ink ejection head corresponding to the color ink ejected as the first ink onto the second ink in the correction region of the plurality of ink ejection heads is to the first ultraviolet irradiation unit, the larger the size of the second ink ejected from the second ink ejection head. It is characterized by the following:

[0014] The 2 The invention is the first 1 In the invention, The correction area determination unit determines the correction area based on print data consisting of density data for each of the multiple colors of ink, such that the correction area includes only the area where printing is performed using a single color ink that should be ejected from the defect ejection port and has a density equal to or greater than a predetermined value.

[0015] The 3 The invention is the first 1 In the invention, The correction region determination unit is characterized in that it determines the correction region such that one pixel on which the second ink is ejected and one pixel on which the second ink is not ejected appear alternately in the direction in which the printing medium is transported by the transport unit.

[0016] The 4 invention of this 1 is, in the invention of this characterized in that the correction area determination unit determines the correction area such that two pixels where the second ink is ejected and two pixels where the second ink is not ejected appear alternately in the direction in which the print medium is conveyed by the conveyance unit.

Effect of the Invention

[0031] According to the first invention described above, the printing apparatus is provided with a first ink ejection head that ejects a first ink and a second ink ejection head that ejects a second ink and is disposed upstream of the first ink ejection head in the conveyance direction of the print medium. Then, when printing is performed on the correction area determined by the correction area determination unit, the second ink is ejected before the first ink is ejected. The correction area is determined when a defective nozzle is detected in the first ink ejection head, taking into consideration the position of the defective nozzle. Here, the wetting spread range of the first ink on the print medium is larger when the first ink is ejected onto the second ink ejected onto the print medium than when the first ink is directly ejected onto the print medium. Therefore, in the correction area, the dot size of the first ink becomes larger than normal. Furthermore, since the wetting range of the second ink becomes larger than it should be, the wetting range of the first ink ejected onto the second ink also effectively increases. Moreover, regardless of which of the multiple ink ejection heads ejecting different colored inks is used to eject the colored ink onto the second ink, the wetting range of the colored ink becomes within a suitable range. As a result, the occurrence of unevenness caused by the presence of defective ejection ports is effectively suppressed. It becomes possible to improve the print quality compared to the prior art. As described above, a printing apparatus (a printing apparatus that performs printing by ejecting ink onto a print medium) that enables high-quality printing is realized. UV curing type

[0034] According to the 2 invention described above, since only the area where the unevenness due to the presence of the defective ejection port is conspicuous is defined as the correction area, wasteful consumption of the second ink is suppressed.

[0035] According to the 3 invention described above, the same effect as that of the 1 invention described above can be obtained.

[0036] According to the 4 invention described above, the same effect as that of the 1 invention described above can be obtained. [Brief explanation of the drawing]

[0051] [Figure 1] This is an overall configuration diagram of a printing system according to the first embodiment of the present invention. [Figure 2] This is a schematic diagram showing one example of the configuration of the inkjet printing apparatus in the first embodiment described above. [Figure 3] This is a schematic plan view showing the configuration of the recording unit in the first embodiment described above. [Figure 4] This is a plan view showing one example of the configuration of the ink ejection surface of one ink ejection head in the first embodiment described above. [Figure 5] This is a diagram illustrating the arrangement of nozzles in the head module in the first embodiment described above. [Figure 6] This is a block diagram showing the hardware configuration of the print control device in the first embodiment described above. [Figure 7] This is a diagram illustrating the outline of white correction in the first embodiment described above. [Figure 8] This figure illustrates the ink ejection in the region where white correction is performed in the first embodiment described above. [Figure 9] This figure shows an example of experimental results regarding the wetting and spreading of colored inks on a film substrate. [Figure 10] This is a block diagram showing the detailed functional configuration of the density correction processing unit in the first embodiment described above. [Figure 11] This figure shows an example of a template for white correction in the first embodiment described above. [Figure 12] This is a diagram illustrating the creation of a correction pattern in the first embodiment described above. [Figure 13] This is a diagram illustrating the creation of a correction pattern in the first embodiment described above. [Figure 14] This figure shows an example of a template for white correction in the first embodiment described above. [Figure 15] This figure shows an example of a template for white correction in the first embodiment described above. [Figure 16] This figure shows an example of a template for white correction in the first embodiment described above. [Figure 17] This is a flowchart illustrating the procedure for concentration correction in the first embodiment described above. [Figure 18] This is a diagram illustrating the overview of transparency correction in the first modified example of the first embodiment described above. [Figure 19] This figure illustrates the ink ejection in the region where transparency correction is performed in the first modified example of the first embodiment described above. [Figure 20] This figure illustrates the outline of yellow correction in a second modified example of the first embodiment described above. [Figure 21] This figure illustrates the ink ejection in the region where yellow correction is performed in a second modified example of the first embodiment described above. [Figure 22] This is a diagram illustrating the outline of a second embodiment of the present invention. [Figure 23] This block diagram shows the detailed functional configuration of the density correction processing unit in the second embodiment described above. [Figure 24] This figure shows an example of a template for white correction in the second embodiment described above. [Figure 25] This is a flowchart illustrating the procedure for concentration correction in the second embodiment described above. [Figure 26] This is a block diagram showing the detailed functional configuration of the concentration correction processing unit in the third embodiment of the present invention. [Figure 27] This is a diagram illustrating the identification of the nozzle to be corrected in the third embodiment described above. [Figure 28] This flowchart outlines the general procedure in the concept encompassing the first to third embodiments described above. [Figure 29]This diagram illustrates concentration uniformity correction and nozzle chipping correction in relation to a conventional example. [Modes for carrying out the invention]

[0052] Embodiments of the present invention will be described below with reference to the attached drawings.

[0053] <1. First Embodiment> <1.1 Overall Configuration of the Printing System> Figure 1 is an overall configuration diagram of a printing system according to the first embodiment of the present invention. This printing system consists of an inkjet printing device 10 and a print data generation device 30. The inkjet printing device 10 and the print data generation device 30 are connected to each other by a communication line 4. The print data generation device 30 generates print data by performing RIP processing on input data such as PDF files. The print data consists of density data for each of multiple colors of ink. The print data generated by the print data generation device 30 is transmitted to the inkjet printing device 10 via the communication line 4. The inkjet printing device 10 performs printing without using a printing plate by ejecting ink onto a substrate that serves as a printing medium, such as film or printing paper, based on the print data transmitted from the print data generation device 30. In this embodiment, UV ink (ultraviolet-curing ink) is used as the ink for printing. The inkjet printing device 10 consists of a printing machine body 100 and a print control device 200 that controls the operation of the printing machine body 100.

[0054] <1.2 Configuration of an inkjet printing device> Figure 2 is a schematic diagram showing one example configuration of an inkjet printing apparatus 10. As described above, this inkjet printing apparatus 10 is composed of a printing press body 100 and a printing control device 200. The printing press body 100 includes a substrate delivery unit 11 for supplying a substrate 12, a first drive roller 13 for transporting the substrate 12 into the printing mechanism, a plurality of support rollers 14 for transporting the substrate 12 inside the printing mechanism, a recording unit 15 for recording an image on the substrate 12 by ejecting ink onto the substrate 12 and curing the ink ejected onto the substrate 12, an imaging unit 16 for capturing a printed image (substrate 12 after printing), a second drive roller 17 for outputting the substrate 12 from inside the printing mechanism, and a substrate winding unit 18 for winding up the substrate 12 after printing. As will be described later, the recording unit 15 includes an ink ejection head for ejecting ink and a UV-LED (light-emitting diode that emits ultraviolet light) for curing the ink. The printing control device 200 controls the operation of the printing press body 100 having the configuration described above. The transport section is realized by the first drive roller 13, a plurality of support rollers 14, and the second drive roller 17.

[0055] In this embodiment, before printing to obtain the desired printed material, an inspection chart is printed to check the condition of the nozzles in the ink ejection head. The printed image obtained from printing the inspection chart is captured by the imaging unit 16, and the resulting image data is sent to the print control device 200. Then, the print control device 200 performs density correction, which will be described later, based on the image data.

[0056] Figure 3 is a schematic plan view showing the configuration of the recording unit 15 in this embodiment. The recording unit 15 includes a plurality of ink ejection heads 150 for ejecting ink and a plurality of UV-LEDs 159 for curing the ink ejected onto the substrate 12 by ultraviolet irradiation. More specifically, the recording unit 15 includes an ink ejection head 150(W) for ejecting white ink, a UV-LED 159(b) for curing the white ink ejected onto the substrate 12 by ultraviolet irradiation, an ink ejection head 150(B) for ejecting blue ink, an ink ejection head 150(O) for ejecting orange ink, an ink ejection head 150(C) for ejecting cyan ink, an ink ejection head 150(M) for ejecting magenta ink, and an ink ejection head 150( The system consists of an ink ejection head 150(W) for ejecting black ink, a UV-LED 159(c) for curing the color inks (blue ink, orange ink, cyan ink, magenta ink, yellow ink, and black ink) ejected onto the substrate 12 by ultraviolet irradiation, a spare ink ejection head 150(E), and a UV-LED 159(a) for curing the ink ejected from the ink ejection head 150(E) onto the substrate 12 by ultraviolet irradiation. With respect to the transport direction of the substrate 12, the ink ejection head 150(W) for white ink is located upstream of the ink ejection heads 150(B), 150(O), 150(C), 150(M), 150(Y), and 150(K) for color inks. In this embodiment, it is assumed that the ink ejection head 150(E) and UV-LED 159(a) are not used.

[0057] Since the substrate 12 is transported from bottom to top in Figure 3, first, white ink is dispensed onto the substrate 12, and the white ink is cured by the UV-LED 159(b). Then, blue ink, orange ink, cyan ink, magenta ink, yellow ink, and black ink are dispensed onto the substrate 12 in order, and the blue ink, orange ink, cyan ink, magenta ink, yellow ink, and black ink are cured by the UV-LED 159(c). However, if white correction is performed as described later, and white ink is dispensed onto the substrate 12, the white ink will not be cured by the UV-LED 159(b). Therefore, if white correction is performed, the color inks will be dispensed on top of the uncured white ink.

[0058] In this embodiment, a first ink ejection head is realized by ink ejection heads 150(B), 150(O), 150(C), 150(M), 150(Y), and 150(K); a second ink ejection head is realized by ink ejection head 150(W); a first ultraviolet irradiation unit is realized by UV-LED 159(c); and a second ultraviolet irradiation unit is realized by UV-LED 159(b).

[0059] Note that the configuration of the recording unit 15 shown in Figure 3 is just one example, and the present invention is not limited thereto. For example, a recording unit 15 can be adopted in a configuration that does not include an ink ejection head 150(B) for ejecting blue ink or an ink ejection head 150(O) for ejecting orange ink.

[0060] Figure 4 is a plan view showing one example of the configuration of the ink ejection surface of a single ink ejection head 150. The ink ejection head 150 is composed of a single rectangular head module 151. The head module 151 has a number of nozzles 152 that serve as ink ejection ports. In the example shown in Figure 4, the shape of the head module 151 is a single rectangle, but it is not limited to this, and various configurations can be adopted, such as being composed of multiple parallelogram-shaped head modules or multiple trapezoidal head modules. Note that the nozzles correspond to the ink ejection ports, and the defective nozzles mentioned above correspond to the defective ejection ports.

[0061] Figure 5 is a diagram illustrating the arrangement of nozzles 152 in the head module 151. Typically, the head module 151 includes multiple rows of nozzles, each consisting of multiple nozzles arranged in the main scanning direction. In the example shown in Figure 5, the head module 151 includes four rows of nozzles. The parts labeled 41 in Figure 5 schematically show the landing positions of the ink ejected from each nozzle 152 on the substrate 12. The multiple nozzles 152 in the head module 151 are arranged such that the landing positions of the ink ejected from the nozzles 152 in the first row of nozzles, the second row of nozzles, the third row of nozzles, and the fourth row of nozzles are all different from each other. For example, the landing position of the ink ejected from each nozzle 152 in the first row of nozzles is between the landing position of the ink ejected from the nozzle 152 in the third row of nozzles and the landing position of the ink ejected from the nozzle 152 in the fourth row of nozzles.

[0062] In the example shown in Figure 5, the ink impact point 42 ejected from the nozzle labeled 152(p) and the ink impact point 43 ejected from the nozzle labeled 152(q) are adjacent. In this specification, two nozzles whose ink impact points are adjacent in this manner are treated as "adjacent nozzles". In the above example, the nozzle labeled 152(p) and the nozzle labeled 152(q) are treated as adjacent nozzles.

[0063] In the following, if any color is named "Z", the nozzle that ejects Z ink (the nozzle included in the Z ink ejection head 150) may be referred to as the "Z ink ejection nozzle". For example, the nozzle that ejects cyan ink (the nozzle included in the cyan ink ejection head 150(C)) may be referred to as the "cyan ink ejection nozzle".

[0064] <1.3 Hardware configuration of the print control device> Figure 6 is a block diagram showing the hardware configuration of the print control device 200. As shown in Figure 6, the print control device 200 includes a main unit 210, an auxiliary storage device 221, an optical disc drive 222, a display unit 223, a keyboard 224, and a mouse 225. The main unit 210 includes a CPU (processor) 211, memory 212, a first disk interface unit 213, a second disk interface unit 214, a display control unit 215, an input interface unit 216, and a communication interface unit 217. The CPU 211, memory 212, first disk interface unit 213, second disk interface unit 214, display control unit 215, input interface unit 216, and communication interface unit 217 are connected to each other via a system bus. The auxiliary storage device 221 is connected to the first disk interface unit 213. The optical disc drive 222 is connected to the second disk interface unit 214. The display unit (display device) 223 is connected to the display control unit 215. The input interface unit 216 is connected to a keyboard 224 and a mouse 225. The communication interface unit 217 is connected to the printer body 100 via a communication cable. The communication interface unit 217 is also connected to a communication line 4. The auxiliary storage device 221 is a magnetic disk drive or the like. An optical disk 29, such as a CD-ROM or DVD-ROM, is inserted into the optical disk drive 222, which is a computer-readable recording medium. The display unit 223 is a liquid crystal display or the like. The display unit 223 is used to display information desired by the operator. The keyboard 224 and mouse 225 are used by the operator to input instructions to this print control device 200.

[0065] The auxiliary storage device 221 stores a print control program (a program for controlling the execution of printing processes by the printing press 100) P. The CPU 211 reads the print control program P stored in the auxiliary storage device 221 into the memory 212 and executes it, thereby realizing various functions of the print control device 200. The memory 212 includes RAM and ROM. The memory 212 functions as a work area for the CPU 211 to execute the print control program P stored in the auxiliary storage device 221. The print control program P is provided stored on the above-mentioned computer-readable recording medium (non-transient recording medium). That is, for example, the user purchases an optical disc 29 as a recording medium for the print control program P, inserts it into the optical disc drive 222, reads the print control program P from the optical disc 29, and installs it into the auxiliary storage device 221.

[0066] <1.4 White Correction> In this embodiment, when the nozzle defect correction described above is performed, a process is carried out to correct the density data included in the print data so that white ink is ejected from the white ink ejection nozzle corresponding to the nozzle adjacent to the defective nozzle (hereinafter referred to as the "defect-adjacent nozzle" for convenience). Hereinafter, this process will be referred to as "white correction".

[0067] Figure 7 is a diagram illustrating the overview of white correction. For the sake of explanation, Figure 7 shows multiple nozzles arranged in a single row in each ink ejection head 150. Also, the UV-LED 159 is omitted in Figure 7. Here, we assume that the nozzle labeled 51 among the multiple nozzles included in the ink ejection head 150(C) for cyan ink is a defective nozzle. In this case, when the above-mentioned nozzle defect correction is performed, a larger amount of cyan ink than originally intended is ejected from the nozzles adjacent to the defective nozzle (the nozzles labeled 52 and 53). Also, when white correction is performed, white ink is ejected from the nozzles corresponding to the nozzles adjacent to the defective nozzle (the nozzles labeled 54 and 55). In this example, cyan ink corresponds to the first ink, and white ink corresponds to the second ink.

[0068] In this embodiment, white correction is performed only in areas where printing is performed with a single-color ink that should be ejected from a defective nozzle and has a density equal to or greater than a predetermined value. Therefore, if the ink ejection head 150(C) for cyan ink contains a defective nozzle as described above, white correction is performed only in areas where printing of a high-density single-color cyan ink, for example, with a density of 80% or more, is performed. However, white correction may also be performed in areas where mixed-color printing is performed.

[0069] When white correction is performed, in the example above, during printing, white ink is first ejected onto the substrate 12 from the white ink ejection nozzle corresponding to the nozzle adjacent to the defect. Then, cyan ink is ejected from the nozzle adjacent to the defect. In other words, in the area where white correction has been performed, cyan ink 6(C) is ejected on top of the white ink 6(W) ejected onto the substrate 12, schematically as shown in Figure 8.

[0070] Incidentally, the wetting spread range of the color ink (cyan ink in the above example) on the substrate 12 is larger when the color ink is dispensed on top of white ink dispensed on the substrate 12 than when the color ink is dispensed directly onto the substrate 12. An example of the results of an experiment related to this is shown in Figure 9. In Figure 9, the part labeled 61 shows the dot size (of the ink) obtained when the color ink was dispensed directly onto a certain film substrate, and the part labeled 62 shows the dot size (of the ink) obtained when the color ink was dispensed after white ink was dispensed onto the same substrate. It can be seen that for both color inks, dispensing white ink onto the substrate beforehand increases the wetting spread range (effectively increases the dot size of the color ink). In view of the above, by dispensing white ink beforehand at the position (on the substrate 12) where the color ink is dispensed from the nozzle adjacent to the defect, the color ink dispensed from the nozzle adjacent to the defect spreads sufficiently on the substrate 12, and the effect of nozzle chipping correction (the effect of eliminating defects and suppressing the occurrence of unevenness) is enhanced.

[0071] Furthermore, while normally the white ink is cured by ultraviolet irradiation after it is dispensed, in this embodiment, when white correction is performed to dispense the white ink onto the target area, the ultraviolet irradiation of the white ink by UV-LED 159(b) is stopped. By stopping the ultraviolet irradiation of the white ink in this way, the wetting spread area of ​​the white ink is increased, and the wetting spread area of ​​the color ink dispensed on the white ink is also effectively increased.

[0072] <1.5 Density correction> In the inkjet printing apparatus 10 according to this embodiment, in addition to the conventional density uniformity correction and nozzle defect correction, the above-described white correction is performed. In this specification, the series of processes including density uniformity correction, nozzle defect correction, and white correction are referred to as "density correction." When the print control program P is executed in the print control device 200, a density correction processing unit, which is a functional component for performing density correction, is realized.

[0073] <1.5.1 Functional Configuration> Figure 10 is a block diagram showing the detailed functional configuration of the density correction processing unit 24 in this embodiment. As shown in Figure 10, the density correction processing unit 24 includes a correction coefficient calculation unit 241, a defective nozzle detection unit 242, a substrate determination unit 243, a print data holding unit (image memory) 244, a white correction determination unit 245, a correction target nozzle identification unit 246, a correction pattern creation unit 247, an ink ejection control unit 248, and a UV-LED setting unit 249. The ink ejection control unit 248 includes a first correction processing unit 2481 and a second correction processing unit 2482.

[0074] The correction coefficient calculation unit 241 calculates a correction coefficient 71 for performing density uniformity correction based on the imaging data 70 obtained by the imaging unit 16 capturing the printed image of the inspection chart described above. For example, when focusing on a certain nozzle, if the density obtained by the ink ejected from that nozzle is (4 / 5) times the original density, the correction coefficient 71 corresponding to that nozzle is set to 1.25.

[0075] The defective nozzle detection unit 242 detects defective nozzles, which are nozzles in a discharge malfunction state, from among the many nozzles contained in the ink discharge head 150 for color ink, based on the imaging data 70. Then, defective nozzle information 72 that identifies the defective nozzle is output from the defective nozzle detection unit 242. If no defective nozzles are detected at all, only density uniformity correction is performed by the first correction processing unit 2481 in the ink discharge control unit 248.

[0076] The substrate determination unit 243 determines the substrate to be used for printing as a printing medium, for example, based on pre-set printing conditions. Then, substrate information 73 that identifies the substrate is output from the substrate determination unit 243.

[0077] The print data holding unit 244 temporarily holds the print data (RIP processed data) 74 transmitted from the print data generation device 30. The print data holding unit 244 is implemented by a hardware memory 212 (see Figure 6).

[0078] The white correction determination unit 245 determines whether or not to perform white correction based on the defective nozzle information 72, the substrate information 73, and the print data 74. The determination result 75 is then output from the white correction determination unit 245. In this embodiment, based on the substrate information 73, if the substrate used for printing is not a white substrate, it is determined that white correction will not be performed. Also, based on the defective nozzle information 72 and the print data 74, if a defective nozzle exists and the area from which ink is ejected from the defective nozzle and its vicinity includes an area where single-color high-density printing is performed using ink of the color that should be ejected from the defective nozzle, it is determined that white correction will be performed. In other words, even if a defective nozzle exists, if the area from which ink is ejected from the defective nozzle and its vicinity does not include an area where single-color high-density printing is performed using ink of the color that should be output from the defective nozzle, it is determined that white correction will not be performed. In this way, white correction is performed only in areas where unevenness due to the presence of a defective nozzle is noticeable, thus suppressing the wasteful consumption of white ink.

[0079] If the determination result 75 output from the white correction determination unit 245 indicates that white correction should be performed, the nozzle identification unit 246 identifies the nozzle that ejects white ink for white correction (hereinafter referred to as the "nozzle to be corrected") from among the many nozzles included in the ink ejection head 150(W) for white ink, based on the defective nozzle information 72 and the print data 74. Then, the nozzle identification unit 246 outputs nozzle identification information 76 that identifies the nozzle to be corrected.

[0080] In this embodiment, a template is provided that defines the pattern in which white ink will be ejected to the pixels within the printing area by white correction. This template is referenced by the correction target nozzle identification unit 246 and the correction pattern creation unit 247. For example, a template like the one shown in Figure 11 is provided. In Figure 11, the pixels in the column denoted by reference numeral 64 correspond to defective nozzles, and the shaded pixels are the pixels to which white ink will be ejected. With respect to the main scanning direction, each nozzle corresponds to one pixel. In the example shown in Figure 11, the columns denoted by reference numeral 64L and the columns denoted by reference numeral 64R include shaded pixels. Therefore, among the many nozzles included in the ink ejection head 150(W) for white ink, the nozzles that eject ink to the pixels in the column denoted by reference numeral 64L and the nozzles that eject ink to the pixels in the column denoted by reference numeral 64R are identified as correction target nozzles by the correction target nozzle identification unit 246.

[0081] The correction pattern creation unit 247 creates a correction pattern 77 that represents a pattern as shown in the template above for the entire printing area, based on the correction target nozzle information 76 and the print data 74. In this embodiment, the area where white ink should be ejected based on this correction pattern 77 is treated as the correction area. Therefore, creating the correction pattern 77 is equivalent to determining the correction area.

[0082] As described above, in this embodiment, white correction is performed only in the area where single-color high-density printing is performed. Here, for example, let's assume that there is a defect in the cyan ink ejection nozzle that ejects ink in the dotted line area labeled 57 in Figure 12, and that single-color high-density printing with cyan ink is performed in the rectangular area labeled 58. In this case, the correction pattern 77 created by the correction pattern creation unit 247 so that white correction is performed only in the area where single-color high-density printing with cyan ink is performed will be as shown in Figure 13.

[0083] The ink ejection control unit 248 corrects the density data contained in the print data 74 and controls the ejection of ink from each ink ejection head 150 based on the corrected density data 78. As described above, the ink ejection control unit 248 includes a first correction processing unit 2481 and a second correction processing unit 2482. If the determination result 75 output from the white correction determination unit 245 indicates that white correction should not be performed, the first correction processing unit 2481 performs the process of correcting the density data contained in the print data 74. If the determination result 75 indicates that white correction should be performed, the second correction processing unit 2482 performs the process of correcting the density data contained in the print data 74.

[0084] The first correction processing unit 2481 performs density uniformity correction and nozzle defect correction based on the correction coefficient 71, defective nozzle information 72, and print data 74. As a result, the density data included in the print data 74 is corrected, and density data 78 is generated to control the ejection of ink from each ink ejection head 150.

[0085] The second correction processing unit 2482 performs density uniformity correction, nozzle defect correction, and white correction based on the correction coefficient 71, defective nozzle information 72, correction pattern 77, and print data 74. As a result, the density data included in the print data 74 is corrected, and density data 78 is generated to control the ejection of ink from each ink ejection head 150.

[0086] Incidentally, each ink ejection head 150, including the ink ejection head 150(W) for white ink, is configured to eject ink in multiple sizes. Specifically, a piezoelectric element is provided corresponding to each nozzle in the ink ejection head 150, and the size of the ink ejected from the nozzle can be changed by changing the voltage waveform of the drive signal supplied to the piezoelectric element. In this embodiment, the density data is corrected by the second correction processing unit 2482 so that white ink is ejected in the correction region in the smallest size among the multiple sizes. That is, the ink ejection control unit 248 controls the ejection of white ink from the ink ejection head 150(W) so that white ink is ejected in the correction region in the smallest size among the multiple sizes. This prevents white ink from being consumed more than necessary to widen the wetting spread range of the color ink. However, white ink may be ejected in sizes other than the smallest size for the correction region.

[0087] The time it takes for the color ink to harden from the ink ejection head 150 onto the substrate 12 until it is cured by ultraviolet irradiation from the UV-LED 159(c) varies depending on the color of the ink. Referring to Figure 3, for example, it can be seen that the time it takes for the black ink to harden from the ink ejection head 150(K) onto the substrate 12 is significantly shorter than the time it takes for the blue ink to harden from the ink ejection head 150(B) onto the substrate 12. Therefore, with regard to white correction, if the size of the white ink ejected from the ink ejection head 150(W) is kept constant, it is conceivable that the wetting spread area of ​​the black ink will be smaller than the wetting spread area of ​​the blue ink. Therefore, the ejection of white ink from the ink ejection head 150(W) may be controlled such that the size of the white ink increases as the distance from the ink ejection head 150 to the UV-LED 159(c) corresponding to the color ink ejected onto the white ink in the correction area decreases.

[0088] The UV-LED setting unit 249 controls the ultraviolet irradiation by the UV-LED 159(b) for white ink by providing an ultraviolet irradiation control signal 79 to the UV-LED 159(b) based on the determination result 75 output from the white correction determination unit 245. Specifically, if the determination result 75 indicates that white correction should be performed, the UV-LED setting unit 249 stops the ultraviolet irradiation by the UV-LED 159(b). Therefore, when white correction is performed, the white ink ejected from the ink ejection head 150(W) onto the substrate 12 is not irradiated with ultraviolet light from the UV-LED 159(b) during printing. If the determination result 75 indicates that white correction should not be performed, the UV-LED setting unit 249 maintains the ultraviolet irradiation by the UV-LED 159(b). In the case where the determination result 75 indicates that white correction should be performed, the UV-LED setting unit 249 may reduce the intensity of the ultraviolet irradiation by the UV-LED 159(b). In other words, if the wetting area of ​​the colored ink is sufficiently wide when the colored ink is ejected onto the white ink, it is not necessarily required to stop the UV-LED159(b) from irradiating the white ink with ultraviolet light.

[0089] In this embodiment, the calculation of the correction coefficient 71 by the correction coefficient calculation unit 241 and the identification of defective nozzles by the defective nozzle detection unit 242 are performed based on the imaging data 70, but the present invention is not limited thereto. If an inkjet printing apparatus 10 without an imaging unit 16 is used, the calculation of the correction coefficient 71 and the identification of defective nozzles may be performed by an operator visually checking the printed image of the inspection chart.

[0090] Alternatively, instead of the substrate determination unit 243, a configuration may be adopted that includes a component that receives input of substrate information 73 from an operator, and the white correction determination unit 245 performs processing (processing to determine whether or not to perform white correction) based on the substrate information 73 received by the component.

[0091] In this embodiment, the correction pattern creation unit 247 realizes the correction region determination unit, and the UV-LED setting unit 249 realizes the ultraviolet irradiation control unit.

[0092] <1.5.2 Correction Pattern Template> In the above explanation, it was assumed that the template shown in Figure 11 is provided as the template that will serve as the basis for the correction pattern 77 created by the correction pattern creation unit 247. However, the templates that can be used are not limited to the template shown in Figure 11. For example, templates such as the template shown in Figure 14, the template shown in Figure 15, and the template shown in Figure 16 can also be used. Furthermore, templates other than those shown in Figures 11, 14 to 16 can also be used.

[0093] If the template shown in Figure 11 or Figure 15 is adopted, the nozzles that eject ink to the pixels in the row labeled 64L and the nozzles that eject ink to the pixels in the row labeled 64R are identified as nozzles to be corrected from among the many nozzles included in the ink ejection head 150(W) for white ink. If the template shown in Figure 14 or Figure 16 is adopted, the nozzles that eject ink to the pixels in the row labeled 64, the nozzles that eject ink to the pixels in the row labeled 64L1, the nozzles that eject ink to the pixels in the row labeled 64R1, the nozzles that eject ink to the pixels in the row labeled 64L2 and the nozzles that eject ink to the pixels in the row labeled 64R2 are identified as nozzles to be corrected from among the many nozzles included in the ink ejection head 150(W) for white ink.

[0094] Furthermore, focusing on the transport direction of the substrate 12 with respect to the pixel areas where white ink is ejected, if the template shown in Figure 11 or Figure 14 is used, one pixel area where white ink is ejected and one pixel area where white ink is not ejected will appear alternately. If the template shown in Figure 15 or Figure 16 is used, two pixel areas where white ink is ejected and two pixel areas where white ink is not ejected will appear alternately.

[0095] <1.5.3 Procedure> The procedure for density correction in this embodiment will be described below with reference to Figure 17. It is assumed that the print data 74 to be processed is already held in the print data holding unit 244 (see Figure 10).

[0096] After density correction begins, the recording unit 15 first prints an inspection chart to check the condition of the nozzles in the ink ejection heads 150 for the color inks (specifically, the ink ejection head 150(B) for blue ink, the ink ejection head 150(O) for orange ink, the ink ejection head 150(C) for cyan ink, the ink ejection head 150(M) for magenta ink, the ink ejection head 150(Y) for yellow ink, and the ink ejection head 150(K) for black ink) (step S110). Then, the printed image obtained from printing the inspection chart is captured by the imaging unit 16 (step S112). As a result, imaging data 70 is output from the imaging unit 16.

[0097] Subsequently, the correction coefficient calculation unit 241 calculates a correction coefficient 71 for performing density uniformity correction based on the imaging data 70 (step S114). Next, the defective nozzle detection unit 242 detects defective nozzles among the many nozzles contained in the ink ejection head 150 for color ink based on the imaging data 70 (step S116).

[0098] After detecting a defective nozzle, the substrate determination unit 243 determines the substrate (printing medium) to be used for printing (step S118). Then, the white correction determination unit 245 determines whether or not the substrate used for printing is a white substrate (step S120). As a result, if the substrate used for printing is a white substrate, the process proceeds to step S121; otherwise, the process proceeds to step S130.

[0099] In step S121, the white correction determination unit 245 further determines whether or not white correction is necessary based on the print data 74 and the information on defective nozzles detected in step S116 (the defective nozzle information 72). If white correction is necessary, the process proceeds to step S122; otherwise, the process proceeds to step S130.

[0100] In step S122, the nozzle identification unit 246 identifies the nozzle to be corrected based on the print data 74 and the information on the defective nozzle detected in step S116 (the defective nozzle information 72).

[0101] Next, the correction pattern creation unit 247 creates the correction pattern 77 based on the print data 74 and the information of the nozzles to be corrected identified in step S122 (the above-mentioned correction target nozzle information 76) (step S124). In other words, a correction area is determined, which is the area on the substrate 12 where white ink should be ejected in order to widen the wetting spread range of the color ink.

[0102] After the correction pattern 77 is created, the ultraviolet irradiation from the UV-LED 159(b) for the white ink is stopped based on the control by the UV-LED setting unit 249 (step S126). As a result, as described above, when white correction is performed, the white ink ejected from the ink ejection head 150(W) onto the substrate 12 is not irradiated with ultraviolet light from the UV-LED 159(b).

[0103] After ultraviolet irradiation from UV-LED 159(b) is stopped, the second correction processing unit 2482 performs density uniformity correction, nozzle chipping correction, and white correction based on the correction coefficient 71 calculated in step S114, the defective nozzle information detected in step S116 (defective nozzle information 72), the correction pattern 77 created in step S124, and the print data 74 (step S128).

[0104] In step S130, the first correction processing unit 2481 performs density uniformity correction and nozzle chipping correction based on the correction coefficient 71 calculated in step S114, the defective nozzle information (defective nozzle information 72) detected in step S116, and the print data 74.

[0105] This concentration correction is completed when the process in step S128 or step S130 is finished.

[0106] After density correction is performed using the procedure described above, the ink ejection control unit 248 controls the ejection of ink from each ink ejection head 150 based on the density data 78 obtained from the density correction, thereby performing actual printing on the substrate 12. At that time, as can be seen from Figure 3, the ink is ejected onto the substrate 12 in the order of white ink, blue ink, orange ink, cyan ink, magenta ink, yellow ink, and black ink. Now, if we consider, for example, the case in which a defect is detected in the cyan ink ejection nozzle, in the correction region, white ink is ejected onto the substrate 12 first, and then cyan ink is ejected on top of the white ink.

[0107] <1.6 Effects> According to this embodiment, when a defective nozzle is detected in the ink ejection head 150 for color ink, white correction is performed to correct the density data so that white ink is ejected from the white ink ejection nozzle corresponding to the nozzle adjacent to the defect in the area where single-color high-density printing is performed using the ink of the color that should be ejected from the defective nozzle (the area on the substrate 12) where ink is ejected from the defective nozzle and the nozzles in its vicinity. Here, the wetting spread range of the color ink on the substrate 12 is larger when the color ink is ejected on top of white ink ejected on the substrate 12 than when the color ink is ejected directly onto the substrate 12. Therefore, by ejecting ink from each ink ejection head 150 based on the density data after white correction, the color ink spreads sufficiently on the substrate 12 in the area targeted for white correction, and the effect of nozzle defect correction (the effect of eliminating defects and suppressing the occurrence of unevenness) is enhanced compared to the conventional method. In other words, even if a defect occurs in the nozzle corresponding to the area where single-color high-density printing is performed, the occurrence of unevenness in the printed image caused by the presence of the defective nozzle is effectively suppressed. Furthermore, the color of the ink (white ink) used to widen the wetting range of the color ink is the same as the color of the substrate 12. Therefore, the color of the ink ejected onto the substrate 12 to widen the wetting range of the color ink does not stand out in the printed image. As described above, this embodiment realizes an inkjet printing apparatus 10 that enables high-quality printed materials. In addition, since the occurrence of unevenness caused by the presence of defective nozzles is effectively suppressed, the need for reprinting is reduced compared to conventional methods, and the consumption of substrate and ink can be reduced. In this way, it can contribute to achieving the SDGs (Sustainable Development Goals).

[0108] <1.7 Variation> In the first embodiment, in order to increase the wetting spread area of ​​the color ink on the substrate 12 by performing nozzle chipping correction, white ink was ejected onto the substrate 12 before the color ink was ejected onto the substrate 12 in the target area. However, the present invention is not limited to this. Therefore, an example of using an ink other than white ink to increase the wetting spread area of ​​the color ink will be described below as a modification of the first embodiment. Note that the first and second modifications described here can also be applied to the second and third embodiments described later.

[0109] <1.7.1 First variation> In this modified example, printing is performed on a transparent substrate for labels. Instead of the white ink used in the first embodiment, transparent ink is used. To achieve this, the ink ejection head 150(E) provided in the recording unit 15 (Figure 3) is used as an ink ejection head that ejects transparent ink. Furthermore, instead of the white correction in the first embodiment, a process is performed to correct the density data so that transparent ink is ejected from the ink ejection head 150(E) in order to increase the wetting spread range of the color ink (hereinafter, this process is referred to as "transparency correction").

[0110] Here, we assume that the nozzle labeled 511 in Figure 18 is a defective nozzle among the multiple nozzles included in the cyan ink ejection head 150(C). In this case, due to the nozzle chipping correction described above, a larger amount of cyan ink than originally intended is ejected from the nozzles adjacent to the defective nozzle (the nozzle labeled 512 and the nozzle labeled 513). In addition, due to the transparency correction, transparent ink is ejected from the transparent ink ejection nozzles corresponding to the nozzles adjacent to the defective nozzle (the nozzle labeled 514 and the nozzle labeled 515).

[0111] When transparency correction is performed, in the example above, during printing, transparent ink is first ejected onto the substrate (transparent substrate) 12 from the transparent ink ejection nozzle corresponding to the nozzle adjacent to the defect. Subsequently, cyan ink is ejected from the nozzle adjacent to the defect. That is, in the area where transparency correction has been performed, cyan ink 6(C) is ejected on top of the transparent ink 6(T) ejected onto the substrate (transparent substrate) 12, schematically as shown in Figure 19.

[0112] <1.7.2 Second variation> In this modified example, when a defect occurs in the black ink ejection nozzle, in order to enhance the effect of nozzle chipping correction, yellow ink with a higher brightness value than black ink is ejected onto the substrate 12 in the target area before black ink is ejected onto the substrate 12. In addition, instead of the white correction in the first embodiment, a process is performed to correct the density data so that yellow ink with a higher brightness value than black ink is ejected from the ink ejection head 150(Y) so that the wetting spread range of the black ink is increased (hereinafter this process is referred to as "yellow correction").

[0113] Furthermore, to enhance the effect of nozzle chipping correction, the area in which yellow ink is ejected is limited to areas other than those in which yellow ink is ejected to form the printed image. By limiting the area in which yellow ink is ejected in this way, a decrease in print quality caused by using yellow ink to increase the wetting spread area of ​​black ink is prevented.

[0114] Here, we assume that the nozzle labeled 521 in Figure 20 is a defective nozzle among the multiple nozzles included in the black ink ejection head 150(K). In this case, due to the nozzle chipping correction described above, a larger amount of black ink than intended is ejected from the nozzles adjacent to the defective nozzle (the nozzles labeled 522 and 523). In addition, due to the yellow correction, yellow ink is ejected from the yellow ink ejection nozzles corresponding to the nozzles adjacent to the defective nozzle (the nozzles labeled 524 and 525).

[0115] When yellow correction is performed, during printing, yellow ink is first ejected onto the substrate 12 from the yellow ink ejection nozzle corresponding to the nozzle adjacent to the defect. Subsequently, black ink is ejected from the nozzle adjacent to the defect. In other words, in the area where yellow correction has been performed, black ink 6(K) is ejected on top of the yellow ink 6(Y) ejected onto the substrate 12, schematically as shown in Figure 21.

[0116] As another example, when a defect occurs in the black ink ejection nozzle, in order to enhance the effect of nozzle chipping correction, blue ink with little color difference from the black ink may be ejected onto the substrate 12 in the target area before the black ink is ejected onto the substrate 12. In such a case, instead of the white correction in the first embodiment, a process to correct the density data (hereinafter referred to as "blue correction") may be performed so that blue ink with little color difference from the black ink is ejected from the ink ejection head 150(B) so that the wetting spread range of the black ink is increased, and ejection control may be performed in the same way as in the case of yellow correction.

[0117] In this modified version, white ink and transparent ink are not used. Therefore, even in an inkjet printing apparatus that prints using only process color inks, adopting the configuration of this modified version makes it possible to effectively suppress the occurrence of unevenness in the printed image caused by the presence of defective nozzles in the black ink ejection nozzle.

[0118] <2. Second Embodiment> <2.1 Overview> Generally, the ink ejection heads 150(W) for ejecting white ink, 150(B) for ejecting blue ink, 150(O) for ejecting orange ink, 150(C) for ejecting cyan ink, 150(M) for ejecting magenta ink, 150(Y) for ejecting yellow ink, and 150(K) for ejecting black ink, which constitute the recording unit 15, each consist of multiple ink ejection heads 150. For example, the ink ejection heads 150(W), 150(B), 150(O), 150(C), 150(M), 150(Y), and 150(K) are each composed of multiple ink ejection heads 150 arranged in a staggered pattern, as shown in Figure 22. Therefore, color unevenness may occur in areas where ink is ejected by one ink ejection head 150 and areas where ink is ejected by an adjacent ink ejection head 150 overlap (hereinafter referred to as the "head connection area"). For example, color unevenness may occur in areas where ink is ejected from nozzles included in the area labeled 66 in Figure 22 and areas where ink is ejected from nozzles included in the area labeled 67 in Figure 22. Therefore, in this embodiment, unlike the first embodiment, white correction is performed to suppress such a decrease in print quality caused by the ejection of ink from multiple ink ejection heads 150 to the same area (an area on the substrate 12).

[0119] The overall configuration of the printing system (see Figure 1), the configuration of the inkjet printing device 10 (see Figure 2), the configuration of the recording unit 15 (see Figure 3), the configuration of the ink ejection surface of the ink ejection head 150 (see Figure 4), the arrangement of the nozzles 152 in the head module 151 (see Figure 5), and the hardware configuration of the print control device 200 (see Figure 6) are the same as in the first embodiment.

[0120] <2.2 Density correction> The following describes the concentration correction in this embodiment.

[0121] <2.2.1 Functional Configuration> Figure 23 is a block diagram showing the detailed functional configuration of the density correction processing unit 24 in this embodiment. As can be seen from Figures 23 and 10, the density correction processing unit 24 in this embodiment includes a white correction candidate area acquisition unit 251 in addition to the components in the first embodiment. The correction coefficient calculation unit 241, defect nozzle detection unit 242, substrate determination unit 243, print data holding unit 244, correction pattern creation unit 247, ink ejection control unit 248, and UV-LED setting unit 249 operate in the same manner as in the first embodiment.

[0122] The white correction candidate area acquisition unit 251 determines a white correction candidate area 81, which is a candidate area for white correction, based on head information 80 that includes information about the position of the head module 151 within the ink ejection head 150. In this embodiment, for example, the head connection area, such as the area where ink is ejected from the nozzles included in the parts labeled 66 and 67 in Figure 22, is designated as the white correction candidate area 81.

[0123] The white correction determination unit 245 determines whether or not to perform white correction based on the substrate information 73, the white correction candidate area 81, and the print data 74. The determination result 75 is then output from the white correction determination unit 245. In this embodiment, similar to the first embodiment, based on the substrate information 73, a determination is made not to perform white correction if the substrate used for printing is not a white substrate. Also, based on the white correction candidate area 81 and the print data 74, a determination is made to perform white correction if the white correction candidate area 81 includes an area where single-color printing is performed. In this way, white correction is performed only in areas where color unevenness is noticeable, thus suppressing the wasteful consumption of white ink. In this embodiment, white correction is performed only in areas where single-color printing is performed, but white correction may also be performed in areas where mixed-color printing is performed.

[0124] If the determination result 75 output from the white correction determination unit 245 indicates that white correction should be performed, the correction target nozzle identification unit 246 identifies the correction target nozzle from among the many white ink ejection nozzles included in the ink ejection head 150(W) for white ink, based on the white correction candidate area 81 and the print data 74. Then, correction target nozzle information 76 identifying the correction target nozzle is output from the correction target nozzle identification unit 246. Since the head module portion corresponding to the white correction candidate area 81 contains many nozzles, typically a larger number of white ink ejection nozzles are identified as correction target nozzles compared to the first embodiment. Therefore, the correction pattern creation unit 247 creates a correction pattern 77 such that the area to be ejected with white ink (correction area) is wider than in the first embodiment.

[0125] In this embodiment, multiple templates are prepared in advance as templates for which the correction pattern 77 is based, and the template to be adopted is determined based on the print density obtained from the print data 74. For example, the template shown in Figure 14 and the template shown in Figure 24 are prepared in advance, and if the print density is higher than a predetermined threshold, the template shown in Figure 14 is adopted, and if the print density is below the predetermined threshold, the template shown in Figure 24 is adopted. When the template shown in Figure 24 is adopted, as in the case when the template shown in Figure 14 is adopted, the nozzles that eject ink to the pixels in the column labeled with reference numeral 64, the nozzles that eject ink to the pixels in the column labeled with reference numeral 64L1, the nozzles that eject ink to the pixels in the column labeled with reference numeral 64R1, the nozzles that eject ink to the pixels in the column labeled with reference numeral 64L2, and the nozzles that eject ink to the pixels in the column labeled with reference numeral 64R2 are identified as nozzles to be corrected from among the many nozzles included in the ink ejection head 150(W) for white ink. Furthermore, focusing on the transport direction of the substrate 12 with respect to the pixel area where white ink is ejected, if the template shown in Figure 24 is used, one pixel area where white ink is ejected and three pixel areas where white ink is not ejected will appear alternately.

[0126] <2.2.2 Procedure> The procedure for density correction in this embodiment will now be described with reference to Figure 25. The processing in steps S210 to S216 is the same as the processing in steps S110 to S116 in the first embodiment (see Figure 17).

[0127] In step S217, the white correction candidate area acquisition unit 251 determines the white correction candidate area 81 described above. The processing in steps S218 to S220 is the same as the processing in steps S118 to S120 in the first embodiment.

[0128] In step S221, the white correction determination unit 245 determines whether or not white correction is necessary based on the print data 74 and the white correction candidate area 81 determined in step S217. If white correction is necessary, the process proceeds to step S222; otherwise, the process proceeds to step S230. Note that if the white correction candidate area 81 includes an area where single-color printing is performed, the determination that white correction is necessary is made.

[0129] In step S222, the nozzle identification unit 246 identifies the nozzle to be corrected based on the print data 74 and the white correction candidate area 81 determined in step S217.

[0130] The processing in steps S224 to S230 is the same as the processing in steps S124 to S130 in the first embodiment.

[0131] <2.3 Effects> According to this embodiment, white correction is performed to correct the density data so that white ink is ejected from white ink ejection nozzles identified based on a predetermined pattern in the area of ​​the head connection region where single-color printing is performed. As described above, the wetting spread range of the color ink on the substrate 12 is larger when the color ink is ejected on top of white ink ejected on the substrate 12 than when the color ink is ejected directly onto the substrate 12. Therefore, by ejecting ink from each ink ejection head 150 based on the density data after white correction, the color ink spreads sufficiently on the substrate 12 in the area subject to white correction, and the occurrence of color unevenness in the head connection region is effectively suppressed. Thus, an inkjet printing apparatus 10 that enables high-quality printed materials is realized. Furthermore, since the occurrence of color unevenness in the head connection region is effectively suppressed, the need for reprinting is reduced compared to conventional methods, and the consumption of substrate and ink can be reduced. In this way, it can contribute to achieving the SDGs.

[0132] <3. Third Embodiment> <3.1 Overview> When printing solid images using an inkjet printer, depending on the printing conditions and the substrate used, the dot size of the ink ejected from the nozzle may be insufficient, resulting in unsatisfactory print quality for the user. Therefore, in this embodiment, white correction is performed to improve the print quality of solid images.

[0133] The overall configuration of the printing system (see Figure 1), the configuration of the inkjet printing device 10 (see Figure 2), the configuration of the recording unit 15 (see Figure 3), the configuration of the ink ejection surface of the ink ejection head 150 (see Figure 4), the arrangement of the nozzles 152 in the head module 151 (see Figure 5), and the hardware configuration of the print control device 200 (see Figure 6) are the same as in the first embodiment.

[0134] <3.2 Density correction> The following describes the concentration correction in this embodiment.

[0135] <3.2.1 Functional Configuration> Figure 26 is a block diagram showing the detailed functional configuration of the density correction processing unit 24 in this embodiment. As can be seen from Figures 26 and 10, the density correction processing unit 24 in this embodiment includes the same components as the density correction processing unit 24 in the first embodiment. The correction coefficient calculation unit 241, the defective nozzle detection unit 242, the substrate determination unit 243, the print data holding unit 244, the correction pattern creation unit 247, the ink ejection control unit 248, and the UV-LED setting unit 249 operate in the same way as in the first embodiment, but the white correction determination unit 245 and the correction target nozzle identification unit 246 operate differently from the first embodiment.

[0136] The white correction determination unit 245 determines whether or not to perform white correction based on the substrate information 73 and the print data 74. The determination result 75 is then output from the white correction determination unit 245. In this embodiment, similar to the first embodiment, based on the substrate information 73, a determination is made not to perform white correction if the substrate used for printing is not a white substrate. Also, based on the print data 74, a determination is made to perform white correction if there is an area within the print area that forms a solid image (an area where the density of color ink is 100%). Therefore, if the substrate used for printing is a white substrate and there is an area within the print area that forms a solid image, a determination is made to perform white correction.

[0137] If the determination result 75 output from the white correction determination unit 245 indicates that white correction should be performed, the correction target nozzle identification unit 246 identifies the correction target nozzle from among the many white ink ejection nozzles included in the ink ejection head 150(W) for white ink, based on the print data 74. Then, correction target nozzle information 76 that identifies the correction target nozzle is output from the correction target nozzle identification unit 246. In this embodiment, the correction target nozzle is identified based on the color that forms the solid image and the region (range) that forms the solid image. For example, according to the print data 74, it is assumed that the shaded area labeled 85 in Figure 27 is the region that forms a cyan solid image, the shaded area labeled 86 in Figure 27 is the region that forms a magenta solid image, and the shaded area labeled 87 in Figure 27 is the region that forms a yellow solid image. In this case, for example, based on a white correction template as shown in Figure 14, a correction target nozzle that ejects white ink to the shaded area 85 is identified from among a plurality of white ink ejection nozzles corresponding to the shaded area 85, a correction target nozzle that ejects white ink to the shaded area 86 is identified from among a plurality of white ink ejection nozzles corresponding to the shaded area 86, and a correction target nozzle that ejects white ink to the shaded area 87 is identified from among a plurality of white ink ejection nozzles corresponding to the shaded area 87. Note that, normally, the area that forms a solid image corresponds to a large number of nozzles, so, as in the second embodiment, a larger number of white ink ejection nozzles are identified as correction target nozzles compared to the first embodiment. Accordingly, the correction pattern creation unit 247 creates a correction pattern 77 such that the area to which white ink is ejected (correction area) is wider than in the first embodiment.

[0138] <3.2.2 Procedure> The procedure for concentration correction in this embodiment will be explained with reference to the flowchart shown in Figure 17. The processes in steps S110 to S120 and steps S124 to S130 are the same as in the first embodiment.

[0139] In step S121, the white correction determination unit 245 determines, based on the print data 74, whether or not white correction needs to be performed. If white correction is deemed necessary, the process proceeds to step S122; otherwise, the process proceeds to step S130. In this embodiment, the determination that white correction needs to be performed is made when there is an area within the print area where a solid image is to be formed.

[0140] In step S122, the nozzle identification unit 246 identifies the nozzles to be corrected based on the print data 74. At this time, the nozzles to be corrected are identified from among a plurality of white ink ejection nozzles corresponding to the area forming the solid image, based on a white correction template.

[0141] <3.3 Effects> According to this embodiment, white correction is performed to correct the density data so that white ink is ejected from white ink ejection nozzles identified based on a predetermined pattern in the area where a solid image is printed. As described above, the wetting spread range of the color ink on the substrate 12 is larger when the color ink is ejected on top of white ink ejected on the substrate 12 than when the color ink is ejected directly onto the substrate 12. Therefore, by ejecting ink from each ink ejection head 150 based on the density data after white correction, the color ink spreads sufficiently on the substrate 12 in the area where the solid image is printed, and the dot size of the color ink becomes larger than in the conventional method. As a result, the print quality of the solid image is improved. Thus, an inkjet printing apparatus 10 that enables high-quality printed materials is realized.

[0142] <4. Summary> To summarize the first to third embodiments, the process is generally carried out according to the procedure shown in Figure 28. First, a correction area is determined, which is the area on the substrate 12 where the second ink (typically white ink) should be ejected (step S10). Next, a process is performed to correct the density data for controlling the ejection of ink from the ink ejection head 150 for the second ink so that the second ink is ejected into the correction area determined in step S10 (step S20). After that, actual printing on the substrate 12 is started (step S30). Then, the second ink is ejected into the correction area (step S40). Next, in the correction area, the first ink (typically color ink) is ejected on top of the second ink ejected on the substrate 12 (step S50). Note that step S10 corresponds to the correction area determination step, step S40 corresponds to the second ink ejection step, and step S50 corresponds to the first ink ejection step.

[0143] <5. Others> The present invention is not limited to the above embodiments (including modifications), and can be implemented in various modified forms without departing from the spirit of the invention. For example, although the above embodiments illustrate an inkjet printing apparatus 10 that performs printing using UV ink, the present invention can also be applied to an inkjet printing apparatus that performs printing using ink that hardens upon irradiation with radiation other than ultraviolet light.

[0144] <6. Addendum> Based on the above disclosures, a printing apparatus with the following configuration is also conceivable.

[0145] A printing apparatus that performs printing by ejecting ink onto a printing medium, A transport unit for transporting the aforementioned printing medium, A first ink ejection head, which includes a plurality of ink ejection ports, ejects a first ink onto the printing medium being transported by the transport unit, A second ink ejection head, which includes a plurality of ink ejection ports, is positioned upstream of the first ink ejection head in the direction in which the printing medium is transported by the transport unit, and ejects a second ink onto the printing medium being transported by the transport unit. Processor and The memory that stores the program and Equipped with, The wetting area of ​​the first ink on the printing medium is larger when the first ink is dispensed onto the second ink dispensed on the printing medium than when the first ink is dispensed directly onto the printing medium. A printing apparatus characterized in that, when the program stored in the memory is executed by the processor, the program causes the processor to perform the following operations (A) and (B): (A) Determine the correction region, which is the region on the printing medium where the second ink should be ejected. (B) The ejection of the second ink from the second ink ejection head is controlled so that the second ink is ejected into the correction region before the first ink is ejected into the correction region. [Explanation of Symbols]

[0146] 10… Inkjet printing equipment 15…Records Department 16…IMAGING Department 24...Density Correction Processing Unit 100... Printer body 150... Ink ejection head 151... Head Module 152…Nozzle 159…UV-LED 200…Printing control device 241...Correction coefficient calculation unit 242...Defective nozzle detection unit 243...Base material determination section 244...Print data storage unit 245... White correction judgment unit 246... Nozzle identification part to be corrected 247... Correction pattern creation unit 248... Ink ejection control unit 249…UV-LED setting section 251... White correction candidate area acquisition unit 2481...First correction processing unit 2482...Second correction processing unit

Claims

1. A printing apparatus that performs printing by ejecting ink onto a printing medium, A transport unit for transporting the aforementioned printing medium, A first ink ejection head, which includes a plurality of ink ejection ports, ejects a first ink, which is an ultraviolet-curable ink, onto the printing medium being transported by the transport unit, A second ink ejection head, which includes a plurality of ink ejection ports, is positioned upstream of the first ink ejection head in the direction in which the printing medium is transported by the transport unit, and ejects a second ink, which is an ultraviolet-curable ink, onto the printing medium being transported by the transport unit. A correction region determination unit that determines a correction region which is a region on the printing medium where the second ink should be ejected, An ink ejection control unit controls the ejection of the second ink from the second ink ejection head so that the second ink is ejected into the correction region before the first ink is ejected into the correction region. A first ultraviolet irradiation unit that cures the first ink ejected from the first ink ejection head onto the printing medium by ultraviolet irradiation, A second ultraviolet irradiation unit for curing the second ink ejected from the second ink ejection head onto the printing medium by ultraviolet irradiation, The ultraviolet irradiation control unit controls the ultraviolet irradiation by the second ultraviolet irradiation unit, and Equipped with, The wetting area of ​​the first ink on the printing medium is larger when the first ink is dispensed onto the second ink dispensed on the printing medium than when the first ink is dispensed directly onto the printing medium. The correction region determination unit determines the correction region based on the position of a defective ink ejection port, which is one of the plurality of ink ejection ports included in the first ink ejection head and has an ejection defect, such that the second ink is ejected from an ink ejection port included in the second ink ejection head that corresponds to an ink ejection port adjacent to the defective ejection port. When the second ink is ejected into the correction region, the ultraviolet irradiation control unit stops the ultraviolet irradiation by the second ultraviolet irradiation unit, or reduces the intensity of the ultraviolet irradiation by the second ultraviolet irradiation unit. The first ink ejection head consists of multiple ink ejection heads, each corresponding to a different color, which eject color inks of different colors from one another. A printing apparatus characterized in that the ink ejection control unit controls the ejection of the second ink from the second ink ejection head such that the closer the distance from the ink ejection head corresponding to the color ink ejected as the first ink onto the second ink in the correction region of the plurality of ink ejection heads is to the first ultraviolet irradiation unit, the larger the size of the second ink ejected from the second ink ejection head.

2. The printing apparatus according to claim 1, characterized in that the correction area determination unit determines the correction area based on printing data consisting of density data of each of a plurality of colored inks, such that only areas where printing is performed with a single color ink that is to be ejected from the defect ejection port and has a density equal to or greater than a predetermined value are included in the correction area.

3. The printing apparatus according to claim 1, characterized in that the correction area determination unit determines the correction area such that one pixel on which the second ink is ejected and one pixel on which the second ink is not ejected appear alternately with respect to the direction in which the printing medium is transported by the transport unit.

4. The printing apparatus according to claim 1, characterized in that the correction region determination unit determines the correction region such that two pixels on which the second ink is ejected and two pixels on which the second ink is not ejected appear alternately with respect to the direction in which the printing medium is transported by the transport unit.

Images