Printing method and printing apparatus

Abstract

To provide technique for suppressing the occurrence of color streaks when printing is performed using a printing apparatus.SOLUTION: When a dot line group is formed in a high duty mode, edge correction processing for reducing the amount of ink droplets ejected from at least one of a plurality of right end side nozzles 42Rs and a plurality of left end side nozzles 42Ls is performed.SELECTED DRAWING: Figure 15

Description

[Technical field]

[0001] The present invention relates to a printing method and a printing device. [Background technology]

[0002] A known printing device includes an inkjet head having a plurality of head units, and a transport mechanism that transports a recording medium in a transport direction. The plurality of head units are arranged in a staggered pattern. In detail, the plurality of head units form two rows of head units aligned in the transport direction, and each head unit row extends in a longitudinal direction perpendicular to the transport direction. In two head units adjacent in the longitudinal direction, an end nozzle of the used nozzle of one head unit and an end nozzle of the used nozzle of the other head unit are adjacent in the longitudinal direction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2008-074065 A Summary of the Invention [Problem to be solved by the invention]

[0004] In two head units adjacent to each other in the longitudinal direction of an inkjet head of a known printing device, the range in which ink droplets ejected from multiple end nozzles located at one end in the longitudinal direction of the used nozzles of the head unit upstream in the transport direction land, and the range in which ink droplets ejected from multiple nozzles located at the other end in the longitudinal direction of the used nozzles of the head unit downstream in the transport direction land, partially overlap in the longitudinal direction.

[0005] In the above known printing device, ink ejected from the end nozzle of the upstream head unit wets and spreads over time, but this wet spreading becomes more pronounced when the amount of ink is large. Therefore, when ink is ejected from the end nozzle of the downstream head unit, the ink may penetrate to just below the end nozzle due to wet spreading. If ink is ejected from the end nozzle of the downstream head unit in this state, it will land on top of the ink that has penetrated, and this may result in areas with a high density (so-called color streaks).

[0006] An object of the present invention is to provide a technique for suppressing the occurrence of color streaks when printing is performed using a printing device. [Means for solving the problem]

[0007] According to an aspect of the present invention, there is provided a printing method using a printing device, comprising the steps of: The printing device includes: a head bar having a first head and a second head aligned along a first direction and arranged at positions shifted from each other in a second direction perpendicular to the first direction; a conveying mechanism configured to convey the recording medium from the upstream side to the downstream side along the second direction, the first head and the second head each have a nozzle region in which a plurality of nozzles are arranged at a pitch P along the first direction, and an end portion of the nozzle region of the first head on one side in the first direction and an end portion of the nozzle region of the second head on the other side in the first direction overlap in the first direction, The printing method includes: determining the nozzles in use of the first head and the nozzles in use of the second head such that a distance in the first direction between a first nozzle located at an end on one side in the first direction among the nozzles in use of the first head and a second nozzle located at an end on the other side in the first direction among the nozzles in use of the second head is equal to or less than the pitch P; and performing printing by repeatedly ejecting droplets from the active nozzles of the first head and the active nozzles of the second head while transporting the recording medium along the second direction, When the first droplets are ejected from both the first nozzle and the second nozzle, if color streaks occur at positions on the recording medium where the first droplets ejected from the first nozzle and the second nozzle land, A printing method is provided, which includes: when forming a dot line formed on the recording medium by droplets ejected by the first nozzle and the second nozzle, the dot line being formed by a plurality of droplets along the second direction, changing the size of a droplet ejected from at least one of the first nozzle and the second nozzle for any of the plurality of droplets so that the size is smaller than the size of the first droplet. Effect of the Invention

[0008] In the above configuration, when forming dot lines in high duty mode, the amount of droplets ejected from at least one of the multiple nozzles on one end side and the multiple nozzles on the other end side is reduced, thereby making it possible to suppress the occurrence of color streaks. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a plan view showing an outline of a printing device 1. As shown in FIG. [Diagram 2] FIG. 2 is a schematic diagram showing an outline of the printing device 1. As shown in FIG. [Diagram 3] FIG. 3 is a schematic diagram for explaining the arrangement of the heads 11 included in the head group 20. As shown in FIG. [Figure 4] FIG. 4 is a schematic diagram for explaining the inside of the flow passage unit 40. As shown in FIG. [Diagram 5] FIG. 5 is a schematic explanatory diagram for explaining a state in which head 11A and head 11B are ideally aligned. [Figure 6]FIG. 6 is a schematic diagram for explaining a case where 100% of the ink is ejected from the right end nozzle 42R and the left end nozzle 42L when the overlap of the printing areas is 0.5px. [Figure 7] FIG. 7 is a schematic diagram for explaining a case where the overlap of the print areas is 0.5px and the right end nozzle 42R and the left end nozzle 42L each eject 75% of the ink amount. [Figure 8] Figure 8(a) is a schematic diagram to explain printing data when the overlap of printing areas is 0 μm (0 px), Figure 8(b) is a schematic diagram to explain printing data when the overlap of printing areas is 6 μm (approximately 0.28 px), Figure 8(c) is a schematic diagram to explain printing data when the overlap of printing areas is 11 μm (approximately 0.52 px), and Figure 8(d) is a schematic diagram to explain printing data when the overlap of printing areas is 18 μm (approximately 0.85 px). [Figure 9] FIG. 9 is a flowchart illustrating the printing process. [Figure 10] FIG. 10 is a sequence diagram of printing. [Figure 11] FIG. 11 is a flowchart for explaining correction of print data according to the thinning rate. [Figure 12] Figure 12(a) is an explanatory diagram for explaining a state in which the ink concentration is low and there are gaps where no ink droplets have landed, Figure 12(b) is an explanatory diagram for explaining a state in which there are few gaps where no ink droplets have landed, and Figure 12(c) is an explanatory diagram for explaining a state in which ink droplets land on top of ink droplets that have already landed. [Figure 13] FIG. 13(a) is an explanatory diagram to explain printing in high duty mode, and FIG. 13(b) is an explanatory diagram to explain that when printing in high duty mode, the ink density becomes higher in the overlapping area between the printing area of ​​head 11A and the printing area of ​​head 11B. [Figure 14] FIG. 14 is an explanatory diagram for explaining the right end nozzle 42Rs and the left end nozzle 42Ls. [Figure 15] FIG. 15 is an explanatory diagram for explaining an example of edge processing. [Figure 16] FIG. 16 is an explanatory diagram for explaining another example of edge processing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] A printing device 1 according to an embodiment of the present invention will be described below with reference to the drawings. In Fig. 1, the transport direction of the recording medium 4 corresponds to the front-rear direction of the printing device 1. The width direction of the recording medium 4 corresponds to the left-right direction of the printing device 1. A direction perpendicular to the front-rear direction and left-right direction, i.e., a direction perpendicular to the paper surface in Fig. 1, corresponds to the up-down direction of the printing device 1. The left-right direction is an example of a first direction in the present invention, and the front-rear direction and the transport direction are examples of a second direction in the present invention.

[0011] 1 and 2, the printing device 1 includes a platen 3 housed in a housing 2, three head bars 10, two transport rollers 5A and 5B, an arch frame 6, a controller 7, and three ink reservoirs 8. Note that in Figs. 1 and 2, only one ink reservoir 8 is shown in order to simplify the drawings.

[0012] As shown in Figures 1 and 2, the recording medium 4 passes over the upper surface of the platen 3. The three head bars 10 are positioned above the platen 3 so as to face the platen 3. Ink is supplied to each head bar 10 from an ink reservoir 8. The structure of the head bars 10 will be explained later. The three head bars 10 are fixed to the arch frame 6 while being aligned in the front-rear direction (the conveying direction of the recording medium 4). As shown in Figure 2, the arch frame 6 has an arch shape, and the three head bars 10 are inclined at different angles with respect to the horizontal plane.

[0013] As shown in FIGS. 1 and 2, the two transport rollers 5A and 5B are located behind and in front of the platen 3, respectively. The two transport rollers 5A and 5B are driven by a motor (not shown). As shown in FIG. 2, the recording medium 4 is fed from a feed roll 4A wound in a roll shape and taken up by a take-up roll 4B. For example, the recording medium 4 is a roll paper. Rotary shafts 4C and 4D rotated by a motor (not shown) are fixed to the feed roll 4A and the take-up roll 4B, respectively. These two rotary shafts 4C and 4D and the two transport rollers 5A and 5B work together to feed the recording medium 4 from the feed roll 4A, transport it downstream (forward) in the transport direction so as to pass over the platen 3, and take it up by the take-up roll 4B. The two rotary shafts 4C and 4D and the two transport rollers 5A and 5B are an example of a transport mechanism of the present invention.

[0014] As shown in FIG. 3, each head bar 10 includes a head group 20 having a plurality of heads 11 (for example, 12 heads 11). In FIG. 1, the number of heads 11 is reduced to simplify the drawing. As shown in FIG. 3, the plurality of heads 11 constitute two head rows arranged in the front-rear direction. Each head row includes six heads 11 arranged in the left-right direction. The six heads 11 arranged in the left-right direction in one head row have the same front-rear position. However, in the following description, the same position does not mean that the positions are exactly the same, but that the positions are the same within the range of manufacturing error and installation error. The left-right positions of the heads 11 included in the two head rows are shifted from each other. In other words, the 12 heads 11 of the head group 20 are positioned in a staggered manner.

[0015] The lower surface of each head 11 is a nozzle surface 41b (see FIG. 4) in which a plurality of nozzles 42 are formed. In the following description, the area of ​​the nozzle surface 41b in which the nozzles 42 are formed is called a nozzle area (see, for example, FIG. 5). In addition, not all of the nozzles 42 of the head 11 are used for printing, and among the nozzles 42 of the head 11, the nozzles from which the ink is ejected and used for printing are called used nozzles. In this embodiment, as shown in FIG. 3, the head 11 has two nozzle rows, but this is merely an example, and the head 11 may have two or more nozzle rows. In addition, in FIG. 3, the number of nozzles 42 included in each nozzle row is reduced for the sake of simplicity of the drawing, but the number of nozzles 42 included in each nozzle row can be any number. For example, each nozzle row may have 1000 or more nozzles 42. In addition, a flow path in the head is formed inside the head 11, and the shape of the flow path in the head will be described later.

[0016] As described above, the twelve heads 11 of each head bar 10 (head group 20) form two head rows, and each head 11 has two rows of nozzles. The twelve heads 11 of the head bar 10 located at the rearmost position (most upstream in the transport direction) are supplied with yellow ink from one of the three ink reservoirs 8. The twelve heads 11 of the head bar 10 located second from the rear (second from the upstream in the transport direction) are supplied with magenta ink from one of the three ink reservoirs 8. The twelve heads 11 of the head bar 10 located at the frontmost position (most downstream in the transport direction) are supplied with cyan ink from one of the three ink reservoirs 8. In this manner, in this embodiment, light-colored to dark-colored inks are ejected from the three head bars 10 aligned in the transport direction in order from upstream to downstream in the transport direction. In this embodiment, the printing device 1 has three head bars 10, but may have two more head bars 10. White ink and black ink may be ejected, respectively, from the two head bars 10. Note that the white ink, yellow ink, magenta ink, cyan ink, and black ink are all, for example, UV curable inks.

[0017] 3 and 4, the flow passage unit 40 and the actuator unit 50 constituting each head 11 will be described. Note that since the structures of the flow passage unit 40 and the actuator unit 50 are common to all 12 heads 11, the flow passage unit 40 and the actuator unit 50 in one head 11 will be described.

[0018] As shown in Fig. 4, the flow path unit 40 is formed by a plurality of metal plates stacked in the vertical direction and a nozzle plate 41. In the plurality of metal plates, ink flow paths such as individual flow paths 12 including pressure chambers 12a, a supply manifold 13a, and a return manifold 13b are formed by etching. The nozzle plate 41 is formed from a polymer synthetic resin material such as polyimide, and is bonded to the lower surfaces of the stacked metal plates with an adhesive. The lower surface of the nozzle plate 41 is the nozzle surface 41b described above. The nozzle plate 41 may also be formed from a metal material such as stainless steel.

[0019] As shown in FIG. 4, inside the flow path unit 40, the individual flow paths 12 communicating with each nozzle 42, and the supply manifold 13a and the return manifold 13b communicating with the individual flow paths 12 are formed. Although not shown in the figure, the supply manifold 13a and the return manifold 13b extend in the left-right direction (the direction perpendicular to the paper surface in FIG. 4). The supply manifold 13a is connected to a tank 400 located outside the head 11 via an ink supply port (not shown) formed in the flow path unit 40. The return manifold 13b is connected to a tank 400 (see FIG. 2) located outside the head 11 via an ink discharge port (not shown) formed in the flow path unit 40. This forms an ink circulation path in which the ink discharged from the tank 400 returns to the tank 400 through the supply manifold 13a, the individual flow paths 12, and the return manifold 13b.

[0020] Although not shown, in the flow passage unit 40, the individual flow passages 12 corresponding to the nozzles 42 are positioned to form two rows of individual flow passages extending in the left-right direction, in response to the nozzles 42 being positioned to form two rows of individual flow passages extending in the left-right direction as described above. The flow passage unit 40 is formed with 12 supply manifolds 13a and 12 return manifolds 13b, and each supply manifold 13a and each return manifold 13b communicates with the individual flow passages 12 constituting the two rows of individual flow passages. As a result, inside the flow passage unit 40, a plurality of ink flow passages are formed, which run from the supply manifold 13a through the pressure chambers 12a of the individual flow passages 12 to the nozzles 42 and the return manifold 13b. The number of the supply manifolds 13a and the return manifolds 13b formed in the flow passage unit 40 is adjusted according to the number of the nozzles 42. In addition, the number of individual flow passages 12 communicating with each supply manifold 13 a and each return manifold 13 b is adjusted according to the number of nozzles 42 .

[0021] As shown in FIG. 4, a pressure chamber 12a is formed in each individual flow path 12, and an actuator unit 50 is located above the pressure chamber 12a. The actuator unit 50 includes a vibration plate 51 located on the upper surface of the flow path unit 40 so as to cover all the pressure chambers 12a, a plurality of piezoelectric bodies 52 located on the upper surface of the vibration plate 51 at positions facing the pressure chambers 12a, and a plurality of individual electrodes 53 located on the upper surfaces of the plurality of piezoelectric bodies 52. As described later, the vibration plate 51 functions as a common electrode. The vibration plate 51 as a common electrode, the individual electrode 53, and the piezoelectric body 52 form one driving element 55. In other words, the actuator unit 50 includes a plurality of driving elements 55 corresponding to the plurality of nozzles 42, respectively.

[0022] The diaphragm 51 is a metal plate having a substantially rectangular shape in a plan view, and is made of, for example, an iron-based alloy such as stainless steel, a copper-based alloy, a nickel-based alloy, or a titanium-based alloy. The upper surface of the conductive diaphragm 51 is located below the piezoelectric body 52. ​​Therefore, the upper surface of the diaphragm 51 can also serve as a common electrode. The diaphragm 51 as a common electrode is connected to the ground wiring of a driver IC (not shown) that drives the actuator unit 50, and is always kept at a ground potential. Note that the diaphragm 51 does not necessarily have to be a metal plate, and may be made of, for example, the same piezoelectric material as the piezoelectric body 52, and a metal film as a common electrode may be formed on the upper surface of the diaphragm 51.

[0023] The piezoelectric body 52 is formed of a piezoelectric material mainly composed of lead zirconate titanate (PZT), which is a solid solution of lead titanate and lead zirconate and a ferroelectric. The piezoelectric body 52 is polarized in the thickness direction (vertical direction) at least in the region (portion sandwiched between the individual electrode 53 and the vibration plate 51) facing the pressure chamber 12a. In this embodiment, there are a plurality of piezoelectric bodies 52 corresponding to the plurality of pressure chambers 12a, but the piezoelectric body 52 may be a layer (piezoelectric layer) of a piezoelectric body continuously formed across the plurality of pressure chambers 12a on the upper surface of the vibration plate 51. In this case, the vibration plate 51 as a common electrode, the individual electrode 53, and the portion of the piezoelectric body 52 sandwiched between the individual electrode 53 and the vibration plate 51 form one driving element 55.

[0024] Next, the operation of the driving element 55 of the actuator unit 50 during ink ejection will be described. When a predetermined driving potential is applied to an individual electrode 53 from a driver IC (not shown), a potential difference occurs between the individual electrode 53 to which this driving potential is applied and the vibration plate 51 as a common electrode held at ground potential. As a result, an electric field acts in the thickness direction on the piezoelectric body 52 sandwiched between the individual electrode 53 and the vibration plate 51. The direction of this electric field is parallel to the polarization direction of the piezoelectric body 52. ​​Therefore, the piezoelectric body 52 in the area (active area) facing the individual electrode 53 contracts in a planar direction perpendicular to the thickness direction. Here, the vibration plate 51 below the piezoelectric body 52 is fixed to the flow path unit 40. Therefore, as the piezoelectric body 52 located on the upper surface of this vibration plate 51 contracts in the planar direction, the part of the vibration plate 51 covering the pressure chamber 12a deforms so as to be convex toward the pressure chamber 12a (unimorph deformation, see FIG. 4). At this time, the volume inside the pressure chamber 12a decreases, so that the ink pressure inside the pressure chamber 12a increases, and ink is ejected from the nozzle 42 that communicates with this pressure chamber 12a.

[0025] The controller 7 includes a main controller 7A that controls each part of the printing device 1 except the head bar 10, and a plurality of head controllers 7B that control the head bar 10 (see FIG. 1). The main controller 7A is connected to an external device 9 (see FIG. 1) such as a PC so as to be able to perform data communication, and controls each part of the printing device 1 based on print data sent from the external device 9. The head controllers 7B are provided corresponding to each head bar 10. The controller 7 (main controller 7A and head controller 7B) includes an FPGA (Field Programmable Gate Array), an EEPROM (Electrically Erasable Programmable Read-Only Memory), a RAM (Random Access Memory), etc. The controller 7 may include a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), etc.

[0026] The main controller 7A controls the motors that drive the rotating shafts 4C and 4D and the motors that drive the transport rollers 5A and 5B to cause the two transport rollers 5A and 5B to transport the recording medium 4 in the transport direction. In addition, the head controller 7B controls the three head bars 10 to eject ink from the nozzles 42 toward the recording medium 4. As a result, an image is printed on the recording medium 4.

[0027] <Head Bar 10 Structure> As shown in Fig. 3, the head bar 10 has a plurality of heads 11 arranged in a staggered pattern. Hereinafter, focusing on two heads 11 adjacent to each other in the left-right direction and shifted in the front-rear direction, the head 11 located on the left side will be referred to as head 11A, and the head 11 located on the right side will be referred to as head 11B. As shown in Fig. 14, the right region located on the right end side of the nozzle region of the nozzle surface 41b of head 11A and the left region located on the left end of the nozzle region of the nozzle surface 41b of head 11B overlap each other in the left-right direction.

[0028] As shown in Fig. 5, it is ideal to align the heads 11A and 11B so that the nozzle 42 located at the right end of the head 11A and the nozzle 42 located at the left end of the nozzles 42 of the head 11B are completely equal in the left-right direction. In this case, the nozzles to be used by the heads 11A and 11B are determined so that the nozzle 42 at the right end of the head 11A is the nozzle located at the rightmost position among the used nozzles of the head 11A, and the nozzle 42 second from the left end of the head 11B is the nozzle located at the leftmost position among the used nozzles of the head 11B. In this case, the distance in the left-right direction between the nozzle 42 located at the rightmost position among the used nozzles of the head 11A and the nozzle 42 located at the leftmost position among the used nozzles of the head 11B is equal to the pitch P, so that the heads 11A and 11B can be treated as one long head. However, due to manufacturing errors of the heads 11A and 11B and mounting errors on the head bar 10, it is very difficult to completely match the left-right positions of the rightmost nozzle 42 of the head 11A and the leftmost nozzle 42 of the head 11B. Even if the rightmost nozzle 42 of the head 11A and the leftmost nozzle 42 of the head 11B are aligned to completely match the left-right positions of the heads 11A and 11B, the rightmost nozzle 42 of the head 11A and the leftmost nozzle 42 of the head 11B may be misaligned in the left-right direction due to manufacturing errors of the heads 11A and 11B and mounting errors on the head bar 10. In this case, even if the nozzles to be used of the heads 11A and 11B are determined as described above, the distance in the left-right direction between the rightmost nozzle 42 of the used nozzles of the head 11A and the leftmost nozzle 42 of the used nozzles of the head 11B (the second nozzle 42 from the left end of the head 11B) may be greater than the pitch P. In such a case, the landing positions of the ink droplets ejected from the rightmost nozzle 42 of the used nozzles of head 11A and the leftmost nozzle 42 of the used nozzles of head 11B will be farther apart in the left-right direction than when the left-right positions of the rightmost nozzle 42 of head 11A and the leftmost nozzle 42 of head 11B are perfectly aligned. When the ink landing positions are farther apart in the left-right direction, so-called white streaks will occur.Users looking at a printed document can easily notice even the slightest white streaks, so it is necessary to completely prevent the occurrence of white streaks.

[0029] In this way, when the nozzle 42 at the right end of the head 11A and the nozzle 42 at the left end of the head 11B are aligned to completely match the left-right positions, the distance between the right end nozzle 42 of the used nozzles of the head 11A and the left end nozzle 42 of the used nozzles of the head 11B in the left-right direction may become larger than the pitch P due to manufacturing errors of the heads 11A and 11B and mounting errors on the head bar 10, and white stripes may occur. Therefore, in this embodiment, in order to reliably suppress the occurrence of white stripes, the right end side of the nozzle region of the nozzle surface 41b of the head 11A and the left end side of the nozzle region of the nozzle surface 41b of the head 11B are made to overlap each other in the left-right direction as shown in FIG. 6. Then, among the nozzles 42 at the left end side of the nozzle region of the head 11B, the nozzle 42 whose left-right distance from the nozzle 42 located at the right end of the head 11A is equal to or smaller than the pitch P is identified, and the used nozzle of the head 11B is determined so that the identified nozzle 42 becomes the left end nozzle of the used nozzles. In other words, for the head 11A, the nozzle to be used is determined so that the nozzle 42 at the right end of the head 11A is the rightmost nozzle of the nozzles to be used, and for the head 11B, the nozzle 42 whose left-right distance from the nozzle 42 at the right end of the head 11A is equal to or less than the pitch P is determined to be the leftmost nozzle of the nozzles to be used. In the following description, the rightmost nozzle of the nozzles to be used of the head 11A is called the rightmost nozzle 42R, and the leftmost nozzle of the nozzles to be used of the head 11B is called the leftmost nozzle 42L. The rightmost nozzle 42R is an example of the first nozzle of the present invention, and the leftmost nozzle 42L is an example of the second nozzle of the present invention. Note that, in this embodiment, among the nozzles 42 of the head 11B, not all of the nozzles 42 overlapping with the nozzle region of the head 11A are used for printing, and the nozzles located to the left of the leftmost nozzle 42L are not used nozzles. In this embodiment, when using a nozzle 42 that is not the used nozzle, i.e., a nozzle 42 located to the left of the leftmost nozzle 42L of head 11B, a so-called shingling technique is used to form a single dot using nozzle 42 of head 11A and nozzle 42 of head 11B in cooperation.To perform such control, the controller 7 needs to create print data for shingling, which makes the control complicated. In the heads 11A and 11B of this embodiment, the controller 7 does not need to create such print data for shingling.

[0030] When the resolution of the heads 11A and 11B is 1200 dpi, the width of one pixel (1px) is 21.16 μm, and the pitch P of the nozzles 42 is also 21.16 μm. When the horizontal distance between the right-end nozzle 42R and the left-end nozzle 42L is equal to the pitch P (corresponding to 1px), the overlap between the print area of ​​the head 11A and the print area of ​​the head 11B is 0px, and the width of the print area of ​​the two nozzles 42R and 42L is 2px. In contrast, when the horizontal distance between the right-end nozzle 42R and the left-end nozzle 42L is 50% of the pitch P (corresponding to 0.5px), for example, the overlap between the print area of ​​the head 11A and the print area of ​​the head 11B is 0.5px, and the width of the print area of ​​the two nozzles 42R and 42L is 1.5px. In the following description, the overlap between the print area of ​​head 11A and the print area of ​​head 11B will simply be referred to as "overlap of print areas."

[0031] Consider the case where ink droplets of the same size are continuously ejected from the right end nozzle 42R and the left end nozzle 42L when the overlap of the print areas is 0px. If the amount of ink ejected from either the right end nozzle 42R or the left end nozzle 42L is 100%, then 200% of the ink will land on the print area of ​​width 2.0px. In contrast, consider the case where 100% of the ink is ejected from the right end nozzle 42R and the left end nozzle 42L when the overlap of the print areas is 0.5px (see FIG. 6). In this case, 200% of the ink will land on the print area of ​​width 1.5px. Therefore, the ink density (amount of ink that lands on the print area of ​​a unit width) will be greater than when the overlap of the print areas is 0px, and there is a high possibility of color streaks occurring.

[0032] Consider the case where the overlap of the print areas is 0.5px, and 75% of the ink is ejected from the right-end nozzle 42R and the left-end nozzle 42L (see Figure 7). In this case, 150% of the ink will land on a print area that is 1.5px wide. In this case, it is possible to achieve the same ink density as when the overlap of the print areas is 0px, and the occurrence of color streaks can be suppressed.

[0033] For example, when the overlap of the print areas is 6 μm (approximately 0.28 px), the ink density can be achieved to the same extent as when the overlap of the print areas is 0 px by reducing the amount of ink ejected from the right end nozzle 42R and the left end nozzle 42L by approximately 14% each (see FIG. 8(b)). When the overlap of the print areas is 11 μm (approximately 0.52 px), the ink density can be achieved to the same extent as when the overlap of the print areas is 0 px by reducing the amount of ink ejected from the right end nozzle 42R and the left end nozzle 42L by approximately 26% each (see FIG. 8(c)). When the overlap of the print areas is 18 μm (approximately 0.85 px), the ink density can be achieved to the same extent as when the overlap of the print areas is 0 px by reducing the amount of ink ejected from the right end nozzle 42R and the left end nozzle 42L by approximately 43% each (see FIG. 8(d)). In this manner, in this embodiment, the amount of ink ejected from the right-end nozzle 42R and the left-end nozzle 42L is adjusted according to the overlap of the printing areas so as to achieve an ink density similar to that when the overlap of the printing areas is 0px.

[0034] It is also possible that for each combination of two heads 11, the head controller 7B determines the size of ink droplets to be ejected from the right end nozzle 42R and the left end nozzle 42L in accordance with the overlap of the printing areas, and constantly ejects ink droplets of that size from the right end nozzle 42R and the left end nozzle 42L, thereby reducing the amount of ink ejected from the right end nozzle 42R and the left end nozzle 42L. For example, in the above example, if it is desired to reduce the amount of ink ejected from the right end nozzle 42R and the left end nozzle 42L by approximately 26%, respectively, the head controller 7B may set the size of ink droplets ejected from the right end nozzle 42R and the left end nozzle 42L to be approximately 26% smaller than the size of ink droplets ejected from the other nozzles 42. Also, if it is desired to reduce the amount of ink ejected from the right end nozzle 42R and the left end nozzle 42L by approximately 43%, respectively, the head controller 7B may set the size of ink droplets ejected from the right end nozzle 42R and the left end nozzle 42L to be approximately 43% smaller than the size of ink droplets ejected from the other nozzles 42. However, the size of the ink droplets ejected from the head 11 is usually limited to several predetermined sizes. For example, the head 11 of this embodiment can eject ink droplets of three sizes: small (DS1), medium (DS2), and large (DS3). For example, for a certain ink among white ink, yellow ink, magenta ink, cyan ink, and black ink, the large ink droplet is 3.2 pl, the medium ink droplet is 2.8 pl, and the small ink droplet is 2.0 pl. In addition, it is very difficult to eject ink droplets of sizes according to the overlap of the printing areas from the right end nozzle 42R and the left end nozzle 42L for each head 11. This is because the above-mentioned three types of ink droplet size settings, large, medium, and small, are not sufficient, and more ink droplet size settings must be prepared in order to eject multiple ink droplets of different sizes according to the overlap of the printing areas.

[0035] Therefore, in this embodiment, a correction is performed to reduce the amount of ink ejected from the right end nozzle 42R and the left end nozzle 42L by adjusting the ratio of large, medium, small, and non-ejection when forming a dot line formed by multiple dots that are continuous in the transport direction according to the overlap of the print area, so as to realize an ink density equivalent to that when the overlap of the print area is 0px, according to the following procedure. Such a correction performed on the right end nozzle 42R and the left end nozzle 42L is hereinafter called stitch correction. Hereinafter, stitch correction will be described with reference to the flowchart shown in FIG. 9 and the printing sequence diagram shown in FIG. 10. In the following description, the main control is performed by the head controller 7B.

[0036] As shown in FIG. 9, for each of two heads 11 adjacent in the left-right direction, the nozzles to be used of the head 11 located on the left side and the nozzles to be used of the head 11 located on the right side are determined (S11). Hereinafter, the head 11 located on the left side is referred to as head 11A, and the head 11 located on the right side is referred to as head 11B. As described above, the nozzles to be used of the head 11A are determined so that the nozzle 42 at the right end becomes the nozzle at the right end of the nozzles to be used. For the head 11B, the nozzles to be used are determined so that the nozzle 42 at the left end of the nozzles to be used of the head 11B becomes the nozzle at the left end of the nozzles to be used of the head 11B, the nozzle 42 at the left end of which is ... which is the nozzle at the left end of the nozzles to be used of the head 11B, which is the nozzle at the left end of the nozzles to be used of the head 11B, which is the nozzle at the left end of the nozzles to be used of the head 11B. Then, the landing position of the ink ejected from the right end nozzle 42R located at the right end of the nozzles to be used of the head 11A and the landing position of the ink ejected from the left end nozzle 42L located at the left end of the nozzles to be used of the head 11B are measured. As a result, the distance in the left-right direction between the right-end nozzle 42R and the left-end nozzle 42L is calculated, and the overlap between the printing area of ​​the head 11A and the printing area of ​​the head 11B is determined (S12). Then, based on the overlap of the printing areas, the thinning rate of the ink droplets, that is, the extent to which the amount of ink ejected from the right-end nozzle 42R and the left-end nozzle 42L is reduced relative to the amount of ink ejected from the other nozzles 42, is set (S13). Note that the processes up to this point are performed by the manufacturer or user of the printing device 1 before the start of printing. For example, after the printing device 1 is brought in and installed, these processes can be performed to store information about the nozzles used for each head 11 and information about the thinning rate of the ink droplets in the EEPROM of the main controller 7A or the head controller 7B. Note that the measurement of the landing position of the ink ejected from the right-end nozzle 42R of the head 11A and the landing position of the ink ejected from the left-end nozzle 42L of the head 11B may be performed, for example, by the following procedure. First, the manufacturer or user of the printing device 1 prints a test pattern using the printing device 1 and reads the test pattern with a scanner connected to the printing device 1. Then, based on the scan results, the main controller 7A measures the landing position of ink ejected from the rightmost nozzle 42R of the active nozzles of head 11A and the landing position of ink ejected from the leftmost nozzle 42L of the active nozzles of head 11B.Then, the main controller 7A calculates the left-right distance between the rightmost nozzle 42R and the leftmost nozzle 42L from the measured landing positions, and further determines the overlap between the printing area of ​​head 11A and the printing area of ​​head 11B.

[0037] Next, the printing process will be described. As shown in Fig. 10, when a print start instruction is input from the user of the printer 1 to the main controller 7A (S301), the main controller 7A transmits a print command to each head controller 7B (S302). The head controller 7B, which has received the print instruction, requests the main controller 7A to transmit print data (S303) and receives the print data (S304). When the head controller 7B receives the print data, it corrects the print data according to the set thinning rate (S305). Then, it transmits the corrected print data to the head 11 (S306). The printer 1 repeats the processes from S302 to S306 until printing is completed.

[0038] Next, the correction of print data according to the thinning ratio in the process of S305 described above will be described with reference to FIG. 11. First, the head controller 7B calculates the total amount of ink droplets required to form a dot line of 12 large dots (DS3) (S401). The dot line of 12 dots is a dot line of 12 dots that continues in the conveying direction of the recording medium 4. Next, the head controller 7B acquires data of each ink droplet of the large (DS3), medium (DS2), and small (DS1) from the EEPROM of the main controller 7A or the head controller 7B (S402). Furthermore, the head controller 7B acquires information regarding the thinning ratio from the EEPROM of the main controller 7A or the head controller 7B (S403). This information regarding the thinning ratio is information regarding the thinning ratio of ink droplets set in the above-mentioned step of S13, and is information stored in the EEPROM of the main controller 7A or the head controller 7B. The processes from S401 to S403 may be performed before or after the process (S304) in which the head controller 7B receives the print data.

[0039] The head controller 7B acquires print data for 12px to be printed next from the print data acquired in the process of S304 (S404). The head controller 7B calculates the amount of ink droplets required to print 12px from the print data for 12px (S405). The head controller 7B calculates the amount of ink droplets to be reduced based on the information on the thinning rate acquired in the process of S403, creates print data in which the amount of ink droplets has been reduced by that amount, and sends it to the head 11 (S406). At that time, if the same ejection pattern is repeated, that part may stand out more than other parts. Therefore, the head controller 7B can create print data for each of 12px so that the ejection pattern of the dot line of 12 dots in a certain area (first area) of the recording medium 4 and the ejection pattern of the dot line of 12 dots in a second area located downstream of the first area of ​​the recording medium 4 in the transport direction are different from each other. For example, the head controller 7B can create print data for 12px each so that the ejection pattern of the first 12-dot dot line and the ejection pattern of the tenth 12-dot dot line are different. For example, when the overlap of the print area is 6 μm (about 0.28px), as described above, the head controller 7B reduces the amount of ink droplets ejected from the right end nozzle 42R and the left end nozzle 42L by about 14%, respectively, thereby achieving ink density equivalent to that when the overlap of the print area is 0px (see FIG. 8(b)). In the example of FIG. 8(b), of the total of 24 dots (12 dots x 2 nozzles (right end nozzle 42R and left end nozzle 42L), 23 dots are medium dots (DS2) and 1 dot is small dot (DS1). The head controller 7B can then create print data for each 12px so that the appearance position of one small ball (DS1) in the ejection pattern of a first 12-dot dot line (whether it is ejected from either the right-most nozzle 42R or the left-most nozzle 42L, or which of the 12 dots ejected in succession by one nozzle) is different from the appearance position of one small ball (DS1) in the ejection pattern of a tenth 12-dot dot line.In this way, the head controller 7B creates print data for each of 12 px so that the ejection pattern of the 12 dot dot line in the first region and the ejection pattern of the 12 dot dot line in the second region are different, which is also effective in the edge correction process described below. After sending the print data to the head 11, the head controller 7B judges whether there is print data for the next 12 px (S407), and if there is print data for the next 12 px, returns to the process of S404 to obtain print data for the next 12 px. If there is no print data for the next 12 px, the head controller 7B ends printing.

[0040] In the process of S406, the head controller 7B first performs a process of reducing the amount of ink droplets by changing the large ball (DS3) to a medium ball (DS2). If changing the large ball (DS3) to a medium ball (DS2) does not reduce the amount of ink droplets by the required amount, then the head controller 7B performs a process of reducing the amount of ink droplets by changing the medium ball (DS2) to a small ball (DS1). If changing the medium ball (DS2) to a small ball (DS1) does not reduce the amount of ink droplets by the required amount, then the head controller 7B performs a process of reducing the amount of ink droplets by changing the small ball (DS1) to non-ejection (Null). If non-ejection occurs continuously, there is a risk that the parts where ink has not landed will be noticeable to the naked eye. Therefore, if non-ejection (Null) occurs for 2 px in a row, the head controller 7B does not perform a process of changing the small ball (DS1) to non-ejection (Null). However, since it is originally desired to make the small droplet (DS1) non-ejecting (Null) and lower the ink density, if the small droplet (DS1) is not changed to non-ejecting (Null), there is a risk that the ink density will not be reduced to the target ink density, that is, the ink density will not be reduced to the same level as when the overlap of the print areas is 0px. Therefore, if the small droplet (DS1) is not changed to non-ejecting (Null), it is preferable to change the small droplet (DS1) to non-ejecting (Null) in other dots instead. When performing a process to change the small droplet (DS1) to non-ejecting (Null) in other dots, it is preferable for the head controller 7B to change the small droplet (DS1) to non-ejecting (Null) for nozzles 42 that are not non-ejecting (Null) adjacent to the nozzles in the left and right directions and the transport direction. Note that if non-ejecting (Null) continues for 2px in the transport direction, not performing the process to change the small droplet (DS1) to non-ejecting (Null) is also effective in the edge correction process described later. In addition, since the right end nozzle 42R and the left end nozzle 42L are adjacent nozzles in the left-right direction, even if both nozzles are non-ejecting (Null) at the same time, there is a risk that the areas where ink has not landed will be noticeable to the naked eye. Therefore, in the process of S406, the head controller 7B can perform a process to reduce the amount of ink droplets so that the right end nozzle 42R and the left end nozzle 42L do not become non-ejecting (Null) at the same time.In the case where non-ejection (Null) continues for 2px in the left-right direction, the head controller 7B does not perform the process of changing the small droplet (DS1) to non-ejection (Null), which is also effective in the edge correction process described later. Among the nozzles used by the head 11A, the nozzle 42 to the left of the right-end nozzle 42R is called the first adjacent nozzle, and among the nozzles used by the head 11B, the nozzle 42 to the right of the left-end nozzle 42L is called the second adjacent nozzle. Consider a case where the first adjacent nozzle and the second adjacent nozzle, which are the nozzles adjacent to the right-end nozzle 42R and the left-end nozzle 42L in the left-right direction, are non-ejection (Null), such as when an image formed by dots of ink ejected from the two nozzles 42, the right-end nozzle 42R and the left-end nozzle 42L, is a thin line. In this case, as described above, if a correction (stitch correction) is performed to reduce the amount of ink ejected from the right end nozzle 42R and the left end nozzle 42L, the drop in ink density of the dot line formed by the ink droplets ejected by the right end nozzle 42R and the left end nozzle 42L may be noticeable. Therefore, if the first adjacent nozzle and the second adjacent nozzle, which are the nozzles on both sides of the right end nozzle 42R and the left end nozzle 42L in the left and right direction, are non-ejecting (Null), the head controller 7B may not perform the stitch correction described above. This makes it possible to prevent the drop in ink density of the dot line from being noticeable and causing a decrease in print quality.

[0041] 8(a) to 8(d) show examples of print data corrected by the above procedure. The numbers arranged horizontally indicate the size of ink droplets ejected from each nozzle 42, and the numbers 3, 2, and 1 indicate that large ink droplets (DS3), medium ink droplets (DS2), and small ink droplets (DS1) are ejected from the nozzles 42, respectively. The number 0 indicates non-ejection (null). The vertical arrangement indicates that the data is 12 px worth of continuous data. FIG. 8(a) is an example of print data when the overlap of the print areas is 0 μm (0 px). FIG. 8(b) is an example of print data when the overlap of the print areas is 6 μm (approximately 0.28 px), and the amount of ink ejected from the rightmost nozzle 42R and the leftmost nozzle 42L is corrected to be reduced by approximately 14% each. FIG. 8(c) is an example of print data when the overlap of the print areas is 11 μm (approximately 0.52 px), and the amount of ink ejected from the right end nozzle 42R and the left end nozzle 42L is corrected to be reduced by approximately 26% each. FIG. 8(d) is an example of print data when the overlap of the print areas is 18 μm (approximately 0.85 px), and the amount of ink ejected from the right end nozzle 42R and the left end nozzle 42L is corrected to be reduced by approximately 43% each. By performing such correction, ink density is achieved that is approximately the same as when the overlap of the print areas is 0 px. In this way, the head controller 7B sets the size of the ink droplets ejected from the right end nozzle 42R and the left end nozzle 42L in the print data for 12 px consecutive in the transport direction to one of four types: large, medium, small, or non-ejection. As a result, although only one of the four types listed above can be selected at 1px, when looking at the entire 12px area, the amount of ink ejected from the rightmost nozzle 42R and the leftmost nozzle 42L can be adjusted so that the ink density corresponds to the overlap of the printing areas.

[0042] Next, the occurrence of color streaks when ink is ejected at a high duty will be described, and a process for suppressing the occurrence of such color streaks (hereinafter, referred to as edge correction process) will be described.

[0043] As described above, the heads 11 are arranged in a staggered pattern on the head bar 10. Therefore, two heads 11 adjacent in the left-right direction are offset from each other in the front-rear direction. In the following description, it is assumed that, of the two heads 11 adjacent in the left-right direction, the head 11A located on the left side is located upstream in the transport direction, and the head 11B located on the right side is located downstream in the transport direction.

[0044] As shown in FIG. 12(a), when the density of the ejected ink is low due to a low frequency of ejecting ink droplets and / or a small size of the ink droplets ejected from the head 11, gaps where no ink droplets have landed are observed between the dots formed by the landed ink droplets. As shown in FIG. 12(b), when the density of the ejected ink is increased by increasing the frequency of ejecting ink droplets and / or by increasing the size of the ink droplets, the gaps where no ink droplets have landed between the dots formed by the ink droplets are reduced. As shown in FIG. 12(c), when the density of the ejected ink is increased by further increasing the frequency of ejecting ink droplets and / or by further increasing the size of the ink droplets, the gaps where no ink droplets have landed between the dots formed by the ink droplets are eliminated, and a state occurs in which further ink droplets land on the landed ink droplets. A mode in which printing is performed at a high ink density in which ink droplets land on top of already landed ink droplets, as shown in Figure 12(c), is an example of a high duty mode of the present invention, and a mode in which printing is performed at a lower ink density, as shown in Figures 12(a) and 12(b), is an example of a low duty mode of the present invention.

[0045] As shown in FIG. 13(a), when printing is performed in high duty mode, ink droplets that land on top of the ink droplets that have already landed tend to wet and spread outward. On the other hand, the ink tends to stay on the outer edge of the area where the ink has landed due to the effect of surface tension, so as not to wet and spread outward too much. Therefore, the outer edge of the area where the ink has landed has a higher ink concentration than the inner area. Note that the heads 11 in this embodiment are arranged in a staggered pattern, and the head 11A is located upstream of the head 11B in the transport direction. As described above, the printing area of ​​the head 11A and the printing area of ​​the head 11B partially overlap. Therefore, as shown in FIG. 13(b), in the overlapping area between the printing area of ​​the head 11A and the printing area of ​​the head 11B, after the printing area where the ink droplets ejected from the head 11A land are formed, the ink droplets ejected from the head 11B will land on top of the printing area. (Note that in FIG. 13(b), to make the drawing easier to see, heads 11A and 11B are shown to be at different vertical positions, but in reality heads 11A and 11B are at the same vertical positions.) In particular, when printing is performed in high duty mode, the outer edge of the printing area of ​​head 11A has a high ink density, and this is further overlapped by the outer edge of the printing area of ​​head 11B. Therefore, when printing is performed in high duty mode, the ink density is higher in the overlapping area between the printing areas of head 11A and head 11B and in the vicinity thereof than in other areas. Due to this, when printing is performed in high duty mode, color streaks may occur in the overlapping area between the printing areas of head 11A and head 11B and in the vicinity thereof.

[0046] In this embodiment, when printing is performed in high duty mode, the head controller 7B performs a process (edge ​​correction process) to reduce the amount of ink droplets ejected from the other nozzles 42, not only for the right end nozzle 42R of the head 11A and the left end nozzle 42L of the head 11B, but also for a plurality of nozzles 42 counted from the right end of the head 11A's nozzles (hereinafter referred to as the right end nozzles 42Rs. See FIG. 14) and a plurality of nozzles 42 counted from the left end of the head 11B's nozzles (hereinafter referred to as the left end nozzles 42Ls. See FIG. 14). When printing is performed in low duty mode, the head controller 7B does not need to perform edge correction process. Therefore, when printing is performed in low duty mode, the head controller 7B may perform only the above-mentioned stitch correction process without performing edge correction process. Furthermore, the head controller 7B may not perform edge correction process for nozzles 42 located near the left and right ends of the head 11 that do not overlap with other heads 11, even if the nozzles 42 are located near the left and right ends of the head 11. In the edge correction process, similarly to the stitch correction process described above, the head controller 7B adjusts the ratio of large, medium, small, and non-ejection when forming a dot line formed by a plurality of dots consecutive in the transport direction, thereby adjusting the amount of ink droplets ejected from the right end nozzle 42Rs and / or the left end nozzle 42Ls to be less than the amount of ink droplets ejected from the other nozzles 42. However, the head controller 7B can adjust the ratio of large, medium, small, and non-ejection independently for the stitch correction process and the edge correction process. In other words, when forming a dot line group in the high duty mode, the head controller 7B can make the ejection pattern in which ink droplets of different sizes (e.g., large and medium) are ejected from the right end nozzle 42R and the ejection pattern in which ink droplets of different sizes (e.g., large and medium) are ejected from the nozzles 42 other than the right end nozzle 42R among the plurality of right end nozzles 42Rs different from each other.Note that color streaks occurring in the overlapping portion between the print area of ​​the head 11A and the print area of ​​the head 11B and in the vicinity thereof do not necessarily occur on both sides of the overlapping portion, but may occur only on one side. Therefore, the head controller 7B performs a process to reduce the amount of ink droplets ejected from at least one of the multiple right-end nozzles 42Rs and the multiple left-end nozzles 42Ls, depending on the location where the color streaks occur, compared to the amount of ink droplets ejected from the other nozzles 42. For example, the head controller 7B may perform edge correction processing only on the left-end nozzles 42Ls of the head 11B located downstream in the transport direction, without performing edge correction processing on the right-end nozzles 42Rs of the head 11A located upstream in the transport direction. When ink droplets are ejected from the head 11B, ink droplets have already been ejected from the head 11A located upstream, so if ink lands on the recording medium 4 wet with ink from the head 11B located further downstream, the ink may not be easily fixed on the recording medium, and color streaks may occur. In such a case, it is effective to perform edge correction processing on the head 11B located on the downstream side.

[0047] Hereinafter, a case will be considered as an example in which the head controller 7B performs processing to make the amount of ink droplets ejected from the multiple right-end nozzles 42Rs of the head 11A less than the amount of ink droplets ejected from the other nozzles 42 in the high duty mode. As shown in FIG. 15, the amount of ink droplets ejected from the multiple right-end nozzles 42Rs can be made the same. Alternatively, as shown in FIG. 13, the amount of ink droplets ejected from the nozzles 42 located at both ends of the multiple right-end nozzles 42Rs can be made less than the amount of ink droplets ejected from the nozzles 42 located inside. In the case of color streaks that occur in the high duty mode, the color of the center part may be particularly dark, and this is particularly effective in suppressing the occurrence of such color streaks.

[0048] <Effects of the embodiment> In the above embodiment, the head bar 10 of the printing device 1 has heads 11A and 11B arranged side by side in the left-right direction and spaced apart in the transport direction. The printing device 1 further has transport rollers 5A and 5B configured to transport the recording medium 4 from the upstream side to the downstream side along the transport direction. The head 11A is located upstream of the head 11B in the transport direction. The heads 11A and 11B each have a nozzle region in which a plurality of nozzles 42 arranged at a pitch P along the left-right direction are arranged, and the right end of the nozzle region of the head 11A and the left end of the nozzle region of the head 11B overlap in the left-right direction. The nozzles in use of the head 11A include a plurality of right-end nozzles 42Rs located on the right end side in the left-right direction. The nozzles in use of the head 11B include a plurality of left-end nozzles 42Ls located on the left end side. The left-right distance between the right end nozzle 42R located at the right end of the multiple right end nozzles 42Rs and the left end nozzle 42L located at the left end of the left end nozzles 42Ls is equal to or less than the pitch P.

[0049] The printing device 1 is configured to execute a low duty mode for forming a dot line group of a first density and a high duty mode for forming a dot line group of a second density higher than the first density when forming a dot line group formed by ink droplets ejected by the right end nozzle 42Rs along the transport direction. The printing method according to the present embodiment includes performing printing by repeatedly ejecting ink droplets from the used nozzles of the head 11A and the used nozzles of the head 11B while transporting the recording medium 4 along the transport direction, and performing edge correction processing. The edge correction processing refers to reducing the amount of ink droplets ejected from at least one of the multiple right end nozzles 42Rs and the multiple left end nozzles 42Ls when forming a dot line group in the high duty mode by ink droplets ejected by the multiple right end nozzles 42Rs and the multiple left end nozzles 42Ls.

[0050] When forming dot lines in high duty mode, edge correction processing is performed to reduce the amount of ink droplets ejected from at least one of the right-end nozzles 42Rs and the left-end nozzles 42Ls, thereby making it possible to suppress the occurrence of color streaks in high duty mode.

[0051] In the above embodiment, when forming a dot line group in high duty mode, the ejection pattern of ejecting ink droplets of different sizes (e.g., large and medium) from the right end nozzle 42R is different from the ejection pattern of ejecting ink droplets of different sizes (e.g., large and medium) from the nozzles 42 other than the right end nozzle 42R among the multiple right end nozzles 42Rs. Alternatively, when forming a dot line group in high duty mode, the ejection pattern of ejecting ink droplets of different sizes (e.g., large and medium) from the left end nozzle 42L is different from the ejection pattern of ejecting ink droplets of different sizes (e.g., large and medium) from the nozzles 42 other than the left end nozzle 42L among the multiple left end nozzles 42Ls. For example, the above-mentioned stitch correction process can be performed on the left end nozzle 42L and the right end nozzle 42R, and edge correction process can be performed on the other nozzles. Color streaks that can be suppressed by stitch correction and color streaks that can be suppressed by edge correction have different causes, so it is preferable to perform correction processes appropriate for each.

[0052] When forming a dot line group in high duty mode, edge correction can be performed so that ink droplets ejected from the nozzle 42 located between the two nozzles located at both ends in the left-right direction among the right end nozzles 42Rs are smaller than ink droplets ejected from the two nozzles located at both ends in the left-right direction among the right end nozzles 42Rs. Alternatively, when forming a dot line group in high duty mode, edge correction can be performed so that ink droplets ejected from the nozzle 42 located between the two nozzles located at both ends in the left-right direction are smaller than ink droplets ejected from the two nozzles located at both ends in the right end nozzles 42Rs. Color streaks that occur in high duty mode may have a particularly dark color in the center, and this is particularly effective in suppressing the occurrence of such color streaks.

[0053] When forming a dot line group in high duty mode, edge correction can be performed so that ink droplets of a certain size and ink droplets smaller than that (for example, large ink droplets and medium ink droplets) land at positions separated in the transport direction. In other words, when forming a dot line group, edge correction can be performed so that ink droplets of the same size do not land consecutively in the transport direction. In this case, the occurrence of color streaks can be effectively suppressed while suppressing the total amount of ink droplets.

[0054] When forming a dot line group in a certain area (first area) of the recording medium 4 in a high duty mode, the ejection pattern ejecting ink droplets of a predetermined size (e.g., large droplets) and smaller ink droplets (e.g., medium droplets) from the right end nozzle 42Rs and the left end nozzle 42Ls can be made different from the ejection pattern when forming a dot line group by ejecting a plurality of ink droplets from the right end nozzle 42Rs and the left end nozzle 42Ls in a second area located downstream of the first area of ​​the recording medium 4 in the transport direction. For example, the ejection patterns can be controlled to be different between the first line and the 1000th line. When the same ejection pattern is repeated, that part may stand out more than other parts, but by controlling the ejection patterns to be different as described above, it is possible to suppress a decrease in print quality due to the repetition of the same ejection pattern.

[0055] In the above embodiment, the size of the ink droplets ejected from at least one of the right end nozzle 42Rs and the left end nozzle 42Ls can be changed so that the size of the ink droplets ejected from the right end nozzle 42Rs is not continuously zero (Null) when forming a dot line group in the high duty mode, and the size of the ink droplets ejected from the left end nozzle 42Ls is not continuously zero (Null). Alternatively, the size of the ink droplets ejected from at least one of the right end nozzle 42Rs and the left end nozzle 42Ls can be changed so that the size of the ink droplets ejected simultaneously from two nozzles 42 adjacent in the left-right direction among the right end nozzle 42Rs and the left end nozzle 42Ls is not zero (Null) when forming a dot line group in the high duty mode. If the non-ejection of ink droplets continues, there is a risk that the part where the ink has not landed will be noticeable visually. As described above, by controlling the non-ejection to prevent two consecutive dots in the left-right direction or the transport direction from occurring consecutively, it is possible to prevent areas where ink has not landed from becoming noticeable and thereby prevent a decrease in print quality.

[0056] When forming a dot line group in high duty mode, edge correction processing is not performed on the right end nozzle 42Rs of the head 11A located on the upstream side in the transport direction, and edge correction processing can be performed only on the left end nozzle 42Ls of the head 11B located on the downstream side in the transport direction. When ink droplets are ejected from the head 11B, ink droplets have already been ejected from the head 11A located on the upstream side. In other words, the recording medium 4 may already be wet with ink in the overlapping area. If more ink lands on the recording medium 4 wet with ink, the ink may not be easily fixed on the recording medium, and color streaks may occur. In such a case, it is effective to perform edge correction processing on the head 11B located on the downstream side.

[0057] In the above embodiment, when forming dot lines in low duty mode, it is possible to avoid performing edge correction processing. In this case, since there is no need to perform edge correction processing, it becomes easier to control the right end nozzles 42Rs and the left end nozzles 42Ls.

[0058] In the above embodiment, edge correction processing does not need to be performed on nozzles 42 that do not overlap with other heads 42, even if the nozzles 42 are located near the left and right ends of the head 11. In this case, since there is no need to perform edge correction processing, control of the nozzles 42 that do not overlap with other heads 42 becomes easier.

[0059] The embodiments disclosed herein are illustrative in all respects and are not restrictive. Not all of the configurations shown in the above embodiments are essential, and the configurations can be changed or omitted as necessary.

[0060] In the above embodiment, the number of head bars 10 is three. However, the present invention is not limited to such an embodiment, and the number and positions of the head bars 10 may be changed as appropriate. Similarly, the number and positions of the heads 11 included in one head group 20 may be changed as appropriate. Furthermore, the number and positions of the nozzles 42 included in each head 11 may also be changed as appropriate.

[0061] In the above embodiment, a recording medium wound in a roll (e.g., roll paper) is used as the recording medium 4. However, the present invention is not limited to such an embodiment, and a recording medium 4 of an appropriate shape and material can be used as necessary. The printing device 1 in the above embodiment has three head bars 10 and is configured to eject five colors of ink: white ink, cyan ink, magenta ink, yellow ink, and black ink. The present invention is not limited to such an embodiment, and the printing device 1 can be configured to eject ink of an appropriate color. Also, in the present embodiment, UV curable ink is used. However, the present invention is not limited to such an embodiment, and ink other than UV curable ink (e.g., water-based ink, pigment ink, etc.) can be used.

[0062] In addition, the present invention is not necessarily limited to a head bar including a line head, but can be widely applied to a head bar including a plurality of heads. In addition, the present invention is not limited to an inkjet type printing device that ejects ink. In addition, the present teachings can be applied to printing devices used for various purposes other than printing images, etc. For example, the present teachings can be applied to a printing device that ejects a conductive liquid onto a substrate to form a conductive pattern on the substrate surface. The scope of the present invention is intended to include all modifications within the scope of the claims and equivalents to the scope of the claims. [Explanation of symbols]

[0063] 1 Printing device 10 Head Bar 11 Head 42 Nozzle 42L Left end nozzle 42Ls Left end nozzle 42R Right end nozzle 42Rs Right end nozzle

Claims

1. A printing method using a printing device, comprising: The printing device includes: a head bar including a first head and a second head aligned along a first direction and spaced apart from each other in a second direction perpendicular to the first direction; a conveying mechanism configured to convey a recording medium from an upstream side to a downstream side along the second direction, the first head is located upstream of the second head in the second direction, the first head and the second head each have a nozzle region in which a plurality of nozzles are arranged at a pitch P along the first direction, and an end portion on one end side of the nozzle region of the first head in the first direction and an end portion on the other end side of the nozzle region of the second head in the first direction overlap with each other in the first direction, the nozzles in use of the first head include a plurality of one-end nozzles located on the one end side in the first direction, the nozzles in use of the second head include a plurality of other-end nozzles located on the other end side in the first direction, and a distance in the first direction between a first nozzle located at an end on the one end side in the first direction among the plurality of one-end nozzles and a second nozzle located at an end on the other end side in the first direction among the plurality of other-end nozzles is equal to or less than the pitch P, the printing device is configured to execute a low duty mode for forming a dot line group having a first density and a high duty mode for forming a dot line group having a second density higher than the first density when forming a dot line group formed by droplets ejected from the plurality of one end nozzles along the second direction, The printing method includes: performing printing by repeatedly ejecting droplets from the active nozzles of the first head and the active nozzles of the second head while transporting the recording medium along the second direction; When the dot line group is formed in the high duty mode by the droplets ejected from the plurality of one end nozzles, reducing a volume of droplets ejected from at least one of the plurality of one end nozzles and the plurality of other end nozzles.

2. When forming the dot line group in the high duty mode, an ejection pattern for ejecting the first droplet and a droplet smaller than the first droplet from the first nozzle is different from an ejection pattern for ejecting the first droplet and a droplet smaller than the first droplet from a nozzle other than the first nozzle among the plurality of one end side nozzles; Or, 2. The printing method according to claim 1, wherein an ejection pattern for ejecting the first droplet and a droplet smaller than the first droplet from the second nozzle is different from an ejection pattern for ejecting the first droplet and a droplet smaller than the first droplet from nozzles other than the second nozzle among the plurality of other end side nozzles.

3. When forming the dot line group in the high duty mode, 2. A printing method as described in claim 1, wherein the amount of droplets ejected from at least one of the multiple one-end side nozzles and the multiple other-end side nozzles is reduced so that droplets ejected from a nozzle between the two one-end side nozzles are smaller than droplets ejected from the two nozzles located at both ends in the first direction, or so that droplets ejected from a nozzle between the two other-end side nozzles are smaller than droplets ejected from the two other-end side nozzles located at both ends in the first direction.

4. When forming the dot line group in the high duty mode, 2. The printing method according to claim 1, wherein the first droplet and a droplet smaller than the first droplet are ejected from a nozzle included in the plurality of one-end side nozzles or a nozzle included in the plurality of other-end side nozzles so that the first droplet and a droplet smaller than the first droplet land at positions separated in the second direction.

5. 2. The printing method according to claim 1, wherein an ejection pattern for ejecting first droplets and droplets smaller than the first droplets from at least one of the plurality of one-end side nozzles and the plurality of other-end side nozzles when forming the dot line group in the first region of the recording medium in the high duty mode is different from an ejection pattern for ejecting first droplets and droplets smaller than the first droplets from at least one of the plurality of one-end side nozzles and the plurality of other-end side nozzles when forming the dot line group in the high duty mode in a second region of the recording medium located downstream in the transport direction from the first region.

6. 2. A printing method as described in claim 1, wherein when forming the dot line group in the high duty mode, the amount of droplets ejected from at least one of the plurality of one-end side nozzles and the plurality of other-end side nozzles is reduced so that the size of droplets ejected from nozzles included in the plurality of one-end side nozzles is not continuously zero and the size of droplets ejected from nozzles included in the plurality of one-end side nozzles is not continuously zero.

7. 2. A printing method as described in claim 1, wherein when forming the dot line group in the high duty mode, the amount of droplets ejected from at least one of the plurality of one-end side nozzles and the plurality of other-end side nozzles is reduced so that the size of droplets ejected simultaneously from two nozzles adjacent to each other in the first direction among the plurality of one-end side nozzles, or two nozzles adjacent to each other in the first direction among the plurality of other-end side nozzles, is not zero.

8. 2. A printing method according to claim 1, wherein when forming the dot line group in the high duty mode, the amount of droplets ejected from the plurality of one end nozzles is not reduced, but the amount of droplets ejected from the plurality of other end nozzles is reduced.

9. When forming the dot line group in the low duty mode, Reducing the amount of droplets ejected from at least one of the first nozzle and the second nozzle; 2. A printing method as described in claim 1, wherein the amount of droplets ejected from the plurality of one-end side nozzles other than the first nozzle is not reduced, and the amount of droplets ejected from the plurality of other-end side nozzles other than the second nozzle is not reduced.

10. the head bar has a plurality of heads including the first head and the second head, the first head being located at an end of the plurality of heads on the other side in the first direction; the use nozzles of the first head include a plurality of third end nozzles located at the end on the other side in the first direction, the plurality of third end nozzles do not overlap with the plurality of heads in the first direction, The printing method according to claim 1 , wherein when forming the dot line group in the high duty mode, the amount of droplets ejected from the third end nozzles is not reduced.

11. a head bar including a first head and a second head aligned along a first direction and shifted from each other in a second direction perpendicular to the first direction; a transport mechanism configured to transport the recording medium along the second direction; a controller for controlling the head bar and the transport mechanism, the first head is located upstream of the second head in the second direction, the first head and the second head each have a nozzle region in which a plurality of nozzles are arranged at a pitch P along the first direction, and an end portion of the nozzle region of the first head on one side in the first direction and an end portion of the nozzle region of the second head on the other side in the first direction overlap in the first direction, the nozzles in use of the first head include a plurality of one-end nozzles located at the end on one side in the first direction, and the nozzles in use of the second head include a plurality of other-end nozzles located at the end on the other side in the first direction, and a distance in the first direction between a first nozzle located at the end on the one side in the first direction among the plurality of one-end nozzles and a second nozzle located at the end on the other side in the first direction among the plurality of other-end nozzles is equal to or less than the pitch P, The controller controls the head bar and the transport mechanism. a low duty mode for forming a dot line group having a first density at a first ejection frequency and a high duty mode for forming a dot line group having a second density higher than the first density at a second ejection frequency higher than the first ejection frequency when forming a dot line group formed by droplets ejected by the plurality of one end side nozzles and the plurality of other end side nozzles along the second direction; performing printing by repeatedly ejecting droplets from active nozzles including the first nozzles of the first head and active nozzles including the second nozzles of the second head while transporting the recording medium along the second direction; When forming the dot line group in the high duty mode, reducing an amount of droplets ejected from at least one of the plurality of one end nozzles and the plurality of other end nozzles; 23. A printing device configured to:

Images