Inkjet printer

Abstract

To provide an inkjet printer capable of reducing ink dot coalescence while improving print resolution during printing on a non-horizontal surface.SOLUTION: An inkjet head 21 includes a nozzle row 26 constituted by a plurality of arrayed nozzles 27 for ejecting ink, and prints by ejecting ink from the nozzles 27 of the nozzle row 26 for each line along the vertical direction of an image onto a print surface of a print medium, the print surface being a vertical plane. The nozzle row 26 is inclined so that the nozzles 27 on the upstream side in a conveying direction of the print medium are arranged at lower positions.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to inkjet printing devices. [Background technology]

[0002] BACKGROUND ART Inkjet printing devices are known that eject ink in a horizontal direction to print on a vertical printing surface of a printing medium (see Patent Document 1).

[0003] Furthermore, in inkjet printing devices, a technique is known in which the nozzle pitch is reduced and printing resolution is increased by arranging the inkjet head at an angle relative to a direction perpendicular to the direction of movement of the printing medium (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-86350 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-167802 Summary of the Invention [Problem to be solved by the invention]

[0005] In the inkjet printing device that prints on the above-mentioned vertical printing surface, the ink that lands on the printing surface moves downward due to the influence of gravity before settling on the printing surface. This downward movement of the ink can cause multiple ink dots to coalesce. The coalesced ink dots are more susceptible to the influence of gravity, which can cause ink drips on the printing surface and degrade print quality.

[0006] In particular, in an inkjet printing device that prints on a vertical printing surface, if the inkjet head is configured to be tilted diagonally relative to the vertical direction perpendicular to the direction of movement of the printing medium to increase printing resolution, the distance between dots becomes smaller, making it more likely that the ink dots will merge as described above.

[0007] The printing surface is not limited to a vertical surface, and even if the surface is non-horizontal, the ink dots may move due to the influence of gravity, causing the ink dots to coalesce, which may result in a deterioration in print quality.

[0008] SUMMARY OF THE INVENTION The present invention has been made in view of the above, and has as its object to provide an inkjet printing apparatus that can reduce ink dot coalescence while increasing print resolution when printing on a non-horizontal surface. [Means for solving the problem]

[0009] In order to achieve the above object, an inkjet printing device of the present invention comprises an inkjet head having a nozzle array formed by an arrangement of multiple nozzles that eject ink, which moves relative to a printing medium and ejects ink from the nozzles of the nozzle array in lines along a direction perpendicular to the relative movement direction of an image onto a printing surface of the printing medium that is non-horizontal and parallel to the direction of relative movement, and which is characterized in that the nozzle array is inclined so that the nozzles that are more upstream in the direction of relative movement of the printing medium as viewed from the inkjet head are positioned at a lower position. [Effects of the Invention]

[0010] The inkjet printing apparatus of the present invention can reduce ink dot coalescence while increasing print resolution when printing on a non-horizontal surface. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a block diagram showing a configuration of an inkjet printing apparatus according to an embodiment; [Figure 2]2 is a schematic diagram of a transport unit and a head bar of the inkjet printing apparatus shown in FIG. 1. FIG. [Figure 3] FIG. 2 is a schematic diagram illustrating the configuration of an inkjet head of a head bar of the inkjet printing apparatus shown in FIG. [Figure 4] 2 is a diagram for explaining the behavior of ink that has been ejected from an inkjet head and landed on a printing surface in the inkjet printing apparatus shown in FIG. 1. FIG. [Figure 5] 10A and 10B are diagrams for explaining the behavior of ink that has been ejected from an inkjet head of a comparative example and landed on a printing surface. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same or equivalent parts and components are designated by the same or equivalent reference numerals throughout the drawings.

[0013] The following embodiments are examples of devices that embody the technical idea of the present invention, and the technical idea of the present invention does not limit the materials, shapes, structures, arrangements, etc. of each component to those described below. The technical idea of the present invention can be modified in various ways within the scope of the claims.

[0014] FIG. 1 is a block diagram showing the configuration of an inkjet printing apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing the configuration of a transport unit and a head bar of the inkjet printing apparatus shown in FIG. 1. FIG. 3 is a schematic diagram showing the configuration of an inkjet head of a head bar. In the following description, the direction perpendicular to the plane of FIG. 2 is referred to as the front-to-rear direction, and the front side of the plane of the paper is referred to as the forward direction. The up-down, left-to-right, and up-down, indicated by arrows in FIG. 2 are referred to as the left-to-right and up-to-down, left-to-right directions. The up-down direction is the vertical direction, and the left-to-right and front-to-rear directions are mutually orthogonal, and are all orthogonal to the up-down direction and parallel to the horizontal direction.

[0015] As shown in FIG. 1, the inkjet printing apparatus 1 according to this embodiment includes a transport unit 2, four head bars 3, and a control unit 4.

[0016] The transport unit 2 transports the print medium 11. The transport direction of the print medium 11 by the transport unit 2 is from right to left, parallel to the horizontal direction. The print medium 11 is, for example, a cardboard box. The print medium 11 has a print surface 11a that is printed by the head bar 3. In this embodiment, the print surface 11a is a vertical surface that is perpendicular to the front-to-back direction.

[0017] The head bars 3 perform printing by ejecting ink onto the printing surface 11a of the print medium 11. Each of the four head bars 3 ejects ink of a different color (for example, black, cyan, magenta, and yellow). The four head bars 3 are arranged side by side in the transport direction (left-right direction) of the print medium 11. The head bars 3 are arranged in front of the area where the print medium 11 is transported in the front-to-back direction. The four head bars 3 have the same configuration, except that they eject different colors of ink.

[0018] The head bar 3 includes a plurality of inkjet heads 21, a head holder 22, and an angle adjustment unit (corresponding to an adjustment unit) 23.

[0019] As shown in Fig. 3, the inkjet head 21 has a nozzle row 26. The nozzle row 26 is formed by arranging a plurality of nozzles 27 in a straight line along the longitudinal direction of the inkjet head 21. The nozzles 27 open in a nozzle surface 21a, which is the vertical surface of the inkjet head 21 that faces the printing surface 11a of the printing medium 11 being transported, and eject ink horizontally toward the printing surface 11a. Note that Fig. 3 is a view of the inkjet head 21 as seen from the rear side (the printing medium 11 side).

[0020] The inkjet head 21 is disposed at an incline relative to the up-down direction (vertical direction) so that the more upstream in the transport direction of the print medium 11 the head is positioned, the lower it becomes. As a result, the nozzle row 26 is inclined so that the nozzles 27 on the more upstream side are positioned at a lower position.

[0021] The nozzle row 26 of the inkjet head 21 prints by ejecting ink from the nozzles 27 for each line along the up-down direction (vertical direction) of the image onto the printing surface 11a. Because the nozzle row 26 is inclined with respect to the up-down direction, the nozzle pitch in the up-down direction can be made smaller than in a nozzle row that is parallel to the up-down direction, and printing resolution can be improved.

[0022] The inkjet heads 21 are arranged in a tilted state along the vertical direction as described above. The inkjet heads 21 are arranged such that the vertical distance between the lowermost nozzle 27 of the upper inkjet head 21 and the uppermost nozzle 27 of the lower inkjet head 21 is the same as the vertical nozzle pitch of the inkjet heads 21.

[0023] The head holder 22 holds each inkjet head 21 .

[0024] The angle adjustment unit 23 rotates each inkjet head 21 around a rotation axis parallel to the front-to-rear direction, thereby adjusting the angle of inclination of each inkjet head 21, i.e., the angle of inclination of each nozzle row 26. Furthermore, in accordance with the adjustment of the angle of inclination of each inkjet head 21, the angle adjustment unit 23 adjusts the vertical spacing of each inkjet head 21 so that the vertical spacing between the lowermost nozzle 27 of the upper inkjet head 21 and the uppermost nozzle 27 of the lower inkjet head 21, of two inkjet heads 21 adjacent to each other in the vertical direction, is the same as the vertical nozzle pitch of the inkjet heads 21.

[0025] The control unit 4 controls the operation of each unit of the inkjet printing device 1. The control unit 4 is configured with a CPU, RAM, ROM, a hard disk, and the like.

[0026] Next, the operation of the inkjet printing apparatus 1 will be described.

[0027] When a print job is input, the control unit 4 acquires the type of print medium 11 from the setting information included in the print job. Then, the control unit 4 controls the angle adjustment unit 23 of each head bar 3 to adjust the angle of inclination of each inkjet head 21 (the angle of inclination of each nozzle row 26) according to the type of print medium 11.

[0028] As will be described later, ink ejected from the nozzles 27 and landing on the printing surface 11a of the printing medium 11 penetrates into the printing surface 11a and evaporates to become fixed there. During this process, the ink that has landed on the printing surface 11a moves downward due to the influence of gravity before it becomes fixed, which can cause multiple ink dots to coalesce. Because the coalesced ink dots are more susceptible to the influence of gravity, ink drips onto the printing surface 11a, potentially degrading print quality.

[0029] The above-described movement of ink on the printing surface 11a is more likely to occur when the printing medium 11 is of a type with poor wettability.

[0030] Furthermore, the likelihood of ink movement on the printing surface 11a described above varies depending on the characteristics of the ink. Specifically, the higher the ink density, the more susceptible the ink is to gravity, making it more likely to move. Furthermore, the higher the ink's dynamic surface tension, the slower the ink's penetration into the printing surface 11a, making it more likely to move. Furthermore, the lower the ink's viscosity, the more likely the ink is to move on the printing surface 11a.

[0031] Furthermore, the greater the angle of inclination of the nozzle row 26 relative to the vertical direction, the smaller the nozzle pitch in the vertical direction, making it easier for multiple ink dots to coalesce.

[0032] Therefore, in the inkjet printing device 1, for each head bar 3, the angle of inclination of the nozzle row 26 relative to the vertical direction is set according to the density, dynamic surface tension, and viscosity at standard temperature of the ink used in that head bar 3 for each type of printing medium 11. The angle of inclination of the nozzle row 26 relative to the vertical direction is set to a smaller angle as the type of printing medium 11 has poorer wettability.

[0033] The control unit 4 controls the angle adjustment unit 23 to adjust the angle of inclination of each inkjet head 21 (the angle of inclination of each nozzle row 26) in each head bar 3 so that the angle of inclination of each nozzle row 26 becomes the angle set according to the type of printing medium 11 as described above.

[0034] In addition, the control unit 4 controls the angle adjustment unit 23 to adjust the vertical spacing of each inkjet head 21 in accordance with the adjustment of the inclination angle of each inkjet head 21 so that the vertical spacing between the lowest nozzle 27 of the upper inkjet head 21 and the highest nozzle 27 of the lower inkjet head 21 of two inkjet heads 21 adjacent to each other in the vertical direction is the same as the vertical nozzle pitch of the inkjet heads 21.

[0035] The density, dynamic surface tension, and viscosity of ink change depending on the temperature of the ink. Therefore, an ink temperature detection unit (not shown) that detects the temperature of the ink may be provided in each head bar 3, and the control unit 4 may adjust the angle of inclination of the nozzle rows 26 in each head bar 3, which is set according to the type of print medium 11, based on the temperature of the ink detected by the ink temperature detection unit in each head bar 3.

[0036] After adjusting the angle of inclination of each nozzle row 26 (each inkjet head 21) of each head bar 3, the control unit 4 starts executing the print job. Specifically, the control unit 4 controls the inkjet heads 21 of each head bar 3 to eject ink and print an image on the printing surface 11a of the printing medium 11 while transporting the printing medium 11 using the transport unit 2.

[0037] Here, ink is ejected for each line along the up-down direction (vertical direction) of the image to print from the nozzles 27 of the nozzle row 26 of the inkjet head 21. The nozzle row 26 is inclined so that the nozzles 27 on the more upstream side are positioned lower, so that ink is ejected from the nozzles 27 of the nozzle row 26 in order from bottom to top along the same up-down line.

[0038] When printing based on the print job is completed, the series of operations is completed.

[0039] Next, the behavior of ink ejected from the inkjet head 21 in the inkjet printing apparatus 1 and landing on the printing surface 11a will be described with reference to FIG.

[0040] 4 shows the behavior of ink ejected from three consecutive nozzles 27 in the nozzle row 26. Here, the three consecutive nozzles 27 are designated as nozzles 27A, 27B, and 27C from the bottom (upstream side).

[0041] Ink is sequentially ejected in the same line from nozzles 27A, 27B, and 27C, thereby forming ink dots 31A, 31B, and 31C sequentially from the bottom up, as shown in Fig. 4. The ink dots 31A to 31C are formed when ink ejected from nozzles 27A to 27C, respectively, lands on the printing surface 11a.

[0042] Here, the ink that has landed on the printing surface 11a is fixed to the printing surface 11a by penetrating into the printing surface 11a and evaporating, but before it is fixed, it moves downward due to the influence of gravity.

[0043] Therefore, after the ink ejected from nozzle 27A lands, when the ink ejected from nozzle 27B lands, the ink in ink dot 31A formed by the ink ejected from nozzle 27A moves downward. Similarly, after the ink ejected from nozzle 27B lands, when the ink ejected from nozzle 27C lands, the ink in ink dot 31B formed by the ink ejected from nozzle 27B moves downward.

[0044] In contrast, as shown in Figure 4, the ink ejected from nozzle 27B lands above ink dot 31A, making it difficult for ink dot 31B from nozzle 27B to coalesce with ink dot 31A. Similarly, the ink ejected from nozzle 27C lands above ink dot 31B, making it difficult for ink dot 31C from nozzle 27C to coalesce with ink dot 31B. In the example of Figure 4, the ink dots do not coalesce, and ink dots 31A to 31C are fixed on printing surface 11a.

[0045] In this way, in the inkjet printing device 1, the coalescence of ink dots and the resulting ink dripping are less likely to occur.

[0046] Next, the behavior of ink ejected from the inkjet head of the comparative example and landing on the printing surface 11a will be described with reference to FIG.

[0047] 5 has a nozzle row 42. The nozzle row 42 is formed by arranging a plurality of nozzles 43 in a straight line along the longitudinal direction of the inkjet head 41.

[0048] Unlike the inkjet head 21 of the present embodiment, the inkjet head 41 is disposed at an incline with respect to the up-down direction (vertical direction) so that it is higher on the upstream side in the transport direction of the print medium 11. As a result, the nozzle row 42 is inclined so that the nozzles 43 on the upstream side are disposed at a higher position.

[0049] Since the nozzle row 42 is inclined as described above, ink is ejected from the nozzles 43 of the nozzle row 42 in order from top to bottom along the same vertical line.

[0050] 5 shows the behavior of ink ejected from three consecutive nozzles 43 in the nozzle row 42. Here, the three consecutive nozzles 43 are designated as nozzles 43A, 43B, and 43C from the top (upstream side).

[0051] Ink is sequentially ejected in the same line from the nozzles 43A, 43B, and 43C, thereby forming ink dots 51A, 51B, and 51C sequentially from the top, as shown in Fig. 5. The ink dots 51A to 51C are formed when the ink ejected from the nozzles 43A to 43C, respectively, lands on the printing surface 11a.

[0052] 5, in this comparative example, ink dot 51A formed by ink ejected from nozzle 43A moves downward due to the influence of gravity, while ink ejected from nozzle 43B lands below ink dot 51A. This makes it easier for ink dot 51B formed by ink ejected from nozzle 43B to coalesce with ink dot 51A. The coalesced ink dots are more susceptible to the influence of gravity, making ink more likely to drip.

[0053] 5, ink dots 51A and 51B coalesce, causing ink dripping. The dripping ink then reaches ink dot 51C, and ink dots 51A to 51C are fixed on printing surface 11a in an indistinguishable shape.

[0054] In a configuration like this comparative example, where the nozzle row is inclined so that the nozzles on the more upstream side are positioned at a higher position, the ink dots are more likely to coalesce and the resulting ink drips, which can easily lead to a deterioration in print quality.

[0055] As described above, in the inkjet printing device 1, the nozzle row 26 is tilted so that the nozzles 27 on the more upstream side are positioned lower. This allows ink to be ejected from the nozzles 27 of the nozzle row 26 in order from bottom to top along the same vertical line. For this reason, even if ink that has landed on the printing surface 11a moves downward due to the influence of gravity, coalescence of the ink dots is unlikely to occur. Therefore, when printing on the printing surface 11a, which is a vertical surface, the inkjet printing device 1 can reduce coalescence of ink dots while increasing printing resolution by tilting the nozzle row 26.

[0056] Furthermore, in the inkjet printing device 1, the control unit 4 controls the angle adjustment unit 23 of each head bar 3 to adjust the angle of inclination of each nozzle row 26 according to the type of print medium 11. As a result, while the likelihood of ink movement differs depending on the type of print medium 11, by adjusting the angle of inclination of the nozzle row 26 and adjusting the nozzle pitch in the vertical direction, it is possible to increase printing resolution while further reducing the coalescence of ink dots.

[0057] It is also possible to omit the angle adjustment unit 23 and set the angle of inclination of the nozzle row 26 to a fixed angle.

[0058] Furthermore, in the above-described embodiment, a line-type inkjet printing device 1 that prints while moving the print medium 11 has been described, but the present invention is not limited to this and can also be applied to a serial-type inkjet printing device that prints on the print medium while moving the inkjet head. Any inkjet printing device may be used as long as the inkjet head having a nozzle row prints on the print medium while moving relative to the print medium, and the nozzle row is inclined so that the nozzles that are more upstream in the direction of relative movement of the print medium as viewed from the inkjet head are positioned lower.

[0059] Furthermore, in the above-described embodiment, an inkjet printing device 1 that prints by ejecting ink horizontally onto a printing surface 11a that is a vertical surface has been described. However, the present invention is not limited to vertical surfaces, and can be applied to inkjet printing devices that print on non-horizontal printing surfaces that are parallel to the relative movement direction between the inkjet head and the printing medium.

[0060] The present invention is not limited to the above-described embodiments, and the components can be modified and embodied in practice without departing from the spirit of the invention. Furthermore, various inventions can be created by appropriately combining multiple components disclosed in the above-described embodiments. For example, some components may be omitted from all the components shown in the embodiments.

[0061] [Note] The present application discloses the following inventions.

[0062] (Appendix 1) an inkjet head having a nozzle row formed by arranging a plurality of nozzles that eject ink, which moves relative to a print medium and ejects ink from the nozzles of the nozzle row line by line along a direction perpendicular to the relative movement direction of an image onto a printing surface of the print medium that is non-horizontal and parallel to the direction of relative movement; an inkjet printing device, wherein the nozzle row is inclined so that the nozzles located at a lower position are located at a more upstream side in the direction of relative movement of the print medium as viewed from the inkjet head;

[0063] (Appendix 2) an adjustment unit that adjusts the angle of inclination of the nozzle row; a control unit that controls the adjustment unit to adjust the angle of inclination of the nozzle row according to the type of print medium; 2. The inkjet printing apparatus according to claim 1, further comprising: [Explanation of symbols]

[0064] 1. Inkjet printing device 2. Conveyor section 3 Head Bar 4. Control Unit 11 Print media 11a Print side 21,41 Inkjet head 21a Nozzle surface 22 Head holder 23 Angle adjustment section 26,42 nozzle rows 27, 27A, 27B, 27C, 43, 43A, 43B, 43C nozzles

Claims

1. an inkjet head having a nozzle row formed by arranging a plurality of nozzles that eject ink, which moves relative to a print medium and ejects ink from the nozzles of the nozzle row line by line along a direction perpendicular to the relative movement direction of an image onto a printing surface of the print medium that is non-horizontal and parallel to the direction of relative movement; an inkjet printing device, wherein the nozzle row is inclined so that the nozzles located at a lower position are located at a more upstream side in the direction of relative movement of the print medium as viewed from the inkjet head;

2. an adjustment unit that adjusts the angle of inclination of the nozzle row; a control unit that controls the adjustment unit to adjust the angle of inclination of the nozzle row according to the type of print medium; The inkjet printing apparatus of claim 1 further comprising:

Images