Inkjet printer

Abstract

To provide an inkjet printer capable of reducing degradation of print quality caused by ink dripping during printing on a non-horizontal surface.SOLUTION: Inkjet heads 21A and 21B are disposed spaced apart from each other in a conveying direction of a print medium 11, and each have a nozzle row constituted by a plurality of arrayed nozzles, wherein ink is ejected from nozzles of the nozzle rows onto a print surface 11a of the print medium 11. A control unit 4 regulates the conveying speed of the print medium 11 by a conveying unit 2 so that the time from landing of ink ejected from the inkjet head 21A on the print surface 11a to landing of ink ejected from the inkjet head 21B on the same region as the ink ejected from the inkjet head 21A is equal to or longer than the time from landing of ink ejected from the inkjet head 21A on the print surface 11a to permeation into the print surface 11a.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] 2. Description of the Related Art Inkjet printing devices are known that print by ejecting ink horizontally onto a vertical printing surface of a print medium being transported.

[0003] In such inkjet printing devices, if ink ejected from an inkjet head lands on the printing surface before it has fully penetrated, and ink ejected from another inkjet head lands in the same area, the printing medium may not be able to absorb all the ink, causing ink to drip onto the printing surface, resulting in a deterioration in print quality.

[0004] In this regard, Patent Document 1 discloses a technique for suppressing ink dripping by using ink containing water, a coloring material, a resin, two or more types of organic solvents, and a surfactant. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2023-86350 Summary of the Invention [Problem to be solved by the invention]

[0006] However, even when the technology of Patent Document 1 is used, if the printing medium is transported at a high speed, and ink is ejected from multiple inkjet heads onto the same area in a short period of time, there is a risk that ink dripping will cause a deterioration in print quality.

[0007] The printing surface is not limited to a vertical surface, and even if the printing surface is a non-horizontal surface, there is a risk of the print quality being degraded due to ink dripping as described above.

[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 degradation of print quality due to ink dripping 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 a plurality of ejection units arranged at a distance from each other in a relative movement direction between the printing medium and the plurality of ejection units, and which eject ink onto a printing surface of the printing medium that is non-horizontal and parallel to the direction of relative movement while moving relative to the printing medium; and a control unit that adjusts at least one of the relative movement speed between the printing medium and the plurality of ejection units and the distance between each of the plurality of ejection units, so that, for each of the ejection units other than the most upstream ejection unit in the relative movement direction of the printing medium as viewed from the plurality of ejection units, the time from when ink ejected by the ejection unit adjacent to the upstream side of the ejection unit lands on the printing surface to when ink ejected by the ejection unit adjacent to the upstream side of the ejection unit lands on the printing surface is equal to or longer than the time from when ink ejected by the ejection unit adjacent to the upstream side lands on the printing surface to when it penetrates into the printing surface. [Effects of the Invention]

[0010] According to the inkjet printing apparatus of the present invention, degradation of print quality due to ink dripping can be reduced when printing on a non-horizontal surface. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic configuration diagram of an inkjet printing apparatus according to an embodiment; [Figure 2] FIG. 2 is a schematic configuration diagram of a head module of the inkjet printing apparatus shown in FIG. [Figure 3] FIG. 10 is a diagram showing changes in the dynamic surface tension of ink. [Figure 4] 10A and 10B are explanatory diagrams illustrating ink ejection onto a pixel to which two colors of ink are ejected in an overlapping manner. [Figure 5]10A and 10B are explanatory diagrams illustrating ink ejection onto a pixel to which two colors of ink are ejected in an overlapping manner. [Figure 6] 10A and 10B are explanatory diagrams illustrating ink ejection onto a pixel to which two colors of ink are ejected in an overlapping manner. [Figure 7] FIG. 10 is a schematic configuration diagram of a head module according to a modified example. 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 schematic diagram of an inkjet printing apparatus according to an embodiment of the present invention. Fig. 2 is a schematic diagram of a head module of the inkjet printing apparatus shown in Fig. 1. In the following description, the up / down, left / right, front / rear directions indicated by arrows in Fig. 1 are referred to as up / down, left / right, front / rear directions. The up / down direction is the vertical direction, and the left / right and front / rear directions are mutually orthogonal, and are all directions 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, a printing unit 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 a direction parallel to the horizontal direction, from back to front. The print medium 11 is, for example, a cardboard box. The print medium 11 has a print surface 11a that is printed by the printing unit 3. The print surface 11a is a vertical surface that is perpendicular to the left-right direction.

[0017] The printing unit 3 performs printing by ejecting ink onto the printing surface 11a of the printing medium 11. The printing unit 3 is equipped with inkjet heads 21A and 21B. The inkjet heads 21A and 21B eject ink of different colors (types). The inkjet heads 21A and 21B are arranged parallel to each other and spaced apart in the transport direction (front-to-back direction) of the printing medium 11. The inkjet heads 21A and 21B have the same configuration except for the different colors (types) of ink they eject. Note that the alphabetical subscripts in the reference numerals of the inkjet heads 21A and 21B may be omitted to refer to them collectively.

[0018] The inkjet head 21 includes a plurality of head modules 22. In this embodiment, the inkjet head 21 includes six head modules 22.

[0019] In the inkjet head 21, the six head modules 22 are arranged in a staggered pattern along the up-down direction. That is, in the inkjet head 21, the six head modules 22 arranged along the up-down direction are arranged with their positions alternately shifted in the front-rear direction.

[0020] As shown in FIG. 2, the head module 22 has a nozzle row (corresponding to an ejection section) 24 formed by arranging a plurality of nozzles 23 that eject ink in a straight line along the vertical direction.

[0021] The nozzles 23 open to a nozzle surface 22a, which is a vertical surface of the head module 22 that faces the printing surface 11a of the print medium 11. The nozzles 23 eject ink in a direction perpendicular to the nozzle surface 22a. In other words, the nozzles 23 eject ink in a horizontal direction toward the printing surface 11a of the print medium 11. In this embodiment, the head module 22 can selectively eject ink droplets of two sizes, large droplets and small droplets, from the nozzles 23.

[0022] 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.

[0023] Specifically, the control unit 4 controls the inkjet heads 21A and 21B to eject ink onto the printing surface 11a of the printing medium 11 while transporting the printing medium 11 using the transport unit 2. For pixels where two colors of ink are ejected in an overlapping manner, the control unit 4 ejects ink from the nozzles 23 of the downstream inkjet head 21B onto the same region as the ink ejected from the nozzles 23 of the upstream inkjet head 21A and landed on the printing surface 11a.

[0024] Here, the control unit 4 adjusts the transport speed v of the print medium 11 by the transport unit 2 so that the impact time interval ti is equal to or greater than the penetration time tp.

[0025] The landing time interval ti is the time from when the ink ejected by inkjet head 21A lands on the printing surface 11a to when the ink ejected by inkjet head 21B lands in the same region (same pixel) as the ink ejected by inkjet head 21A.

[0026] The penetration time tp is the time from when the ink ejected from inkjet head 21A lands on the printing surface 11a until it penetrates into the printing surface 11a (printing medium 11). More specifically, the penetration time tp is the time from when the large droplets of ink ejected from inkjet head 21A lands on the printing surface 11a until the large droplets of ink ejected from inkjet head 21A penetrate into the printing surface 11a (printing medium 11) to such an extent that, even if large droplets of ink ejected from inkjet head 21B subsequently lands in the same area as the large droplets of ink ejected from inkjet head 21A, ink dripping does not occur or, if it does occur, it is within an acceptable range.

[0027] Furthermore, the control unit 4 sets the ink ejection speed of the inkjet head 21A in accordance with the relaxation time τ of the dynamic surface tension σ(t) of the ink ejected by the inkjet head 21A.

[0028] When ink ejected from the nozzles 23 lands on the printing surface 11a, it collides with the printing surface 11a and enters a non-equilibrium (dynamic) state. At this time, the ink has high surface tension and does not easily penetrate into the printing surface 11a.

[0029] The dynamic surface tension σ(t) of ink decreases over time t and reaches an equilibrium state, as shown in Figure 3. The relaxation time τ is a value that characterizes the decrease in dynamic surface tension σ(t), and is a value that satisfies the following equation (1).

[0030] σ(t)=σs+σ0-σs / (1+(t / τ) n ) …(1) where σs is the static surface tension of the ink, σ0 is the surface tension of the ink solvent, and n is a constant.

[0031] The relaxation time τ is determined by the type of ink. The smaller the relaxation time τ, the more quickly the surface tension of the ink decreases. In other words, the shorter the relaxation time τ, the more quickly the surface tension of the ink decreases, and the more easily the ink penetrates into the printing surface 11a. Therefore, ink with a relatively long relaxation time τ decreases its surface tension relatively slowly, and therefore does not penetrate into the printing surface 11a easily.

[0032] Incidentally, by reducing the kinetic energy of the ink when it lands on the printing surface 11a, the dynamic surface tension σ(t) at the time of landing can be reduced. Therefore, by reducing the kinetic energy of the ink ejected from the inkjet head 21A, it is possible to reduce the penetration time tp. The kinetic energy of the ink ejected from the inkjet head 21A can be reduced by reducing the ejection speed of the ink from the inkjet head 21A.

[0033] The shorter the penetration time tp, the shorter the impact time interval ti can be, and therefore the faster the transport speed v of the print medium 11 by the transport unit 2 can be. The faster the transport speed v, the more the productivity of printed matter produced by the inkjet printing device 1 can be improved.

[0034] Therefore, in order to reduce the penetration time tp, the control unit 4 sets the ink ejection speed of the inkjet head 21A in accordance with the relaxation time τ of the dynamic surface tension σ(t) of the ink ejected from the inkjet head 21A, as described above. Here, the control unit 4 sets the ink ejection speed to be smaller as the relaxation time τ of the dynamic surface tension σ(t) of the ink ejected from the inkjet head 21A is longer.

[0035] The above-described adjustment of the transport speed v uses the permeation time tp that corresponds to the ink ejection speed of the inkjet head 21A set as described above.

[0036] Furthermore, the permeation time tp varies depending on the type of printing medium 11. For this reason, the control unit 4 sets the transport speed v according to the permeation time tp for each type of printing medium 11. The permeation time tp for each type of printing medium 11 is determined by experimentation or simulation.

[0037] Here, the nozzle row distance, which is the distance in the transport direction (front-to-back direction) of the print medium 11 between the nozzle row 24 of the head module 22 of inkjet head 21A and the nozzle row 24 of the head module 22 of inkjet head 21B, is defined as d (see FIG. 4). In this embodiment, the ink ejection speed of ink jet head 21B is set to the same speed as the ink ejection speed of ink jet head 21A. Then, since the impact time interval ti=d / v, a transport speed v for each type of print medium 11 that satisfies the permeation time tp≦d / v is determined in advance. The control unit 4 stores this transport speed v for each type of print medium 11.

[0038] Next, the operation of the inkjet printing apparatus 1 will be described.

[0039] 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 causes the conveying unit 2 to convey the print medium 11 at a conveying speed v according to the type of print medium 11.

[0040] Then, the control unit 4 controls the inkjet heads 21A and 21B so that ink is ejected from the head modules 22 thereof to print on the printing surface 11a of the print medium 11 being transported by the transport unit 2, based on the print job.

[0041] Here, for pixels where two colors of ink are to be ejected in an overlapping manner, ink 31 is first ejected from the nozzles 23 of the head module 22 of the inkjet head 21A, as shown in Fig. 4. The ejected ink 31 lands on the printing surface 11a of the printing medium 11, and begins to permeate into the printing surface 11a (printing medium 11), as shown in Fig. 5.

[0042] After the ink 31 is ejected from the inkjet head 21A, as shown in FIG. 5, ink 32 is ejected from the nozzles 23 of the head module 22 of the inkjet head 21B.

[0043] 5, when the ink 31 from inkjet head 21A lands and begins to permeate the printing surface 11a, ink 32 is being ejected from inkjet head 21B. However, depending on the distance d between the nozzle rows, etc., there are cases where ink 32 has not yet started to be ejected from inkjet head 21B when the ink 31 lands and begins to permeate the printing surface 11a.

[0044] The ink 32 ejected from inkjet head 21B lands at the same position as the ink 31, as shown in FIG. 6, after a landing time interval ti from when the ink 31 from inkjet head 21A lands.

[0045] As described above, the transport speed v is set so that the impact time interval ti is equal to or greater than the penetration time tp. Therefore, by the time the ink 32 from inkjet head 21B impacts the printing surface 11a, the ink 31 from inkjet head 21A has already penetrated the printing surface 11a, thereby preventing ink dripping.

[0046] When printing based on the print job is completed, the series of operations is completed.

[0047] As described above, in the inkjet printing device 1, the control unit 4 adjusts the transport speed v of the print medium 11 by the transport unit 2 so that the impact time interval ti is equal to or greater than the penetration time tp. This prevents ink ejected by inkjet head 21A from landing in the same area on the printing surface 11a before the ink ejected by inkjet head 21B has penetrated into the same area. As a result, degradation of print quality due to ink dripping can be reduced when printing on the vertical printing surface 11a.

[0048] Furthermore, in the inkjet printing apparatus 1, the control unit 4 sets the ink ejection speed to be slower as the relaxation time τ of the dynamic surface tension σ(t) of the ink ejected from the inkjet head 21A becomes longer. This makes it possible to shorten the penetration time tp and increase the transport speed v. As a result, the productivity of printed matter in the inkjet printing apparatus 1 can be improved.

[0049] In the above-described embodiment, the inkjet heads 21A and 21B are configured to eject ink of different colors (types). However, an inkjet head having two nozzle rows that eject ink of different colors (types) may be used.

[0050] For example, the inkjet heads 21A and 21B of the inkjet printing apparatus 1 described above may be replaced with an inkjet head in which a plurality of head modules 41 shown in FIG. 7 are arranged in a staggered pattern along the vertical direction.

[0051] The head module 41 has two nozzle rows 43, each of which has a plurality of nozzles 42 arranged linearly in the vertical direction. The head module 41 also has two ink chambers (not shown) that store ink of different colors (types) corresponding to the two nozzle rows 43. The two nozzle rows 43 eject ink from the nozzles 42 in the ink chambers that correspond to them.

[0052] In the case of a configuration using this head module 41, the distance between the two nozzle rows 43 in the transport direction (front-rear direction) of the print medium 11 is the nozzle row distance d.

[0053] Furthermore, in the above-described embodiment, the ink ejection speed of the inkjet head 21A is set in accordance with the relaxation time τ of the dynamic surface tension σ(t) of the ink ejected by the inkjet head 21A, but this may be omitted.

[0054] In the above-described embodiment, the transport speed v is adjusted so that the landing time interval ti is equal to or greater than the penetration time tp. However, a mechanism for adjusting the distance between the inkjet heads 21A and 21B may be provided, and the distance between the inkjet heads 21A and 21B may be adjusted to adjust the distance d between the nozzle rows so that the landing time interval ti is equal to or greater than the penetration time tp. Alternatively, both the transport speed v and the distance d between the nozzle rows may be adjusted. It is sufficient that at least one of the transport speed v and the distance d between the nozzle rows is adjusted.

[0055] In the above-described embodiment, the inkjet printing device 1 is described as printing using two colors (two types) of ink. However, the present invention is also applicable to an inkjet printing device that prints using three or more different colors (types) of ink, ejecting the ink from three or more nozzle rows that eject each ink.

[0056] For example, if there are three nozzle rows arranged in parallel in the transport direction of the printing medium, and the penetration times of the ink ejected by the two upstream nozzle rows are different from each other, the transport speed cannot be changed midway, so the transport speed can be adjusted so that the impact time interval between the nozzle row ejecting the ink with the longer penetration time of the two upstream nozzle rows and the nozzle row adjacent to that nozzle row downstream is equal to or greater than the penetration time.

[0057] In the above-described embodiment, a line-type inkjet printing device 1 that prints while moving the print medium 11 has been described. However, the present invention can be applied to any inkjet printing device that prints while moving a nozzle row relative to the print medium. For example, the present invention can also be applied to a serial-type inkjet printing device that prints while moving an inkjet head having a nozzle row.

[0058] That is, it is sufficient to adjust at least one of the relative movement speed between the printing medium and the multiple ejection units and the distance between each of the multiple ejection units so that the time from when ink ejected by an ejection unit adjacent to the upstream side of each ejection unit lands on the printing surface to when ink ejected by an ejection unit adjacent to the upstream side of each ejection unit lands on the printing surface until ink ejected in the same area as ink ejected by an ejection unit adjacent to the upstream side of the ejection unit lands on the printing surface is equal to or longer than the time from when ink ejected by the adjacent upstream ejection unit lands on the printing surface to when ink penetrates into the printing surface. Furthermore, for each ejection unit other than the downstreammost ejection unit in the relative movement direction of the printing medium as viewed from the multiple ejection units, the ink ejection speed may be reduced as the relaxation time of the dynamic surface tension of the ejected ink becomes longer.

[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) a plurality of ejection units that are arranged spaced apart from one another in a direction of relative movement with respect to the printing medium, and that eject ink onto a printing surface of the printing medium that is non-horizontal and parallel to the direction of relative movement while moving relative to the printing medium; a control unit that adjusts at least one of the relative movement speed between the printing medium and the plurality of ejection units and the distance between each of the plurality of ejection units, so that, for each of the ejection units other than the most upstream ejection unit in the relative movement direction of the printing medium as viewed from the plurality of ejection units, a time from when ink ejected by an ejection unit adjacent to the upstream side of the ejection unit lands on the printing surface until ink ejected by the ejection unit adjacent to the upstream side of the ejection unit lands in the same region as ink ejected by the ejection unit adjacent to the upstream side of the ejection unit lands on the printing surface is equal to or longer than a time from when ink ejected by the ejection unit adjacent to the upstream side lands on the printing surface until it penetrates into the printing surface; An inkjet printing apparatus comprising:

[0063] (Appendix 2) The inkjet printing device described in Appendix 1 is characterized in that the control unit reduces the ink ejection speed for each ejection unit other than the most downstream ejection unit in the relative movement direction of the printing medium as seen from the multiple ejection units, as the relaxation time of the dynamic surface tension of the ejected ink becomes longer. [Explanation of symbols]

[0064] 1. Inkjet printing device 2. Conveyor section 3 Printing Department 4. Control Unit 11 Print media 11a Print side 21, 21A, 21B Inkjet head 22,41 Head module 23,42 nozzle 24,43 nozzle row

Claims

1. a plurality of ejection units that are arranged spaced apart from one another in a direction of relative movement with respect to the printing medium, and that eject ink onto a printing surface of the printing medium that is non-horizontal and parallel to the direction of relative movement while moving relative to the printing medium; a control unit that adjusts at least one of the relative movement speed between the printing medium and the plurality of ejection units and the distance between each of the plurality of ejection units, so that, for each of the ejection units other than the most upstream ejection unit in the relative movement direction of the printing medium as viewed from the plurality of ejection units, a time from when ink ejected by an ejection unit adjacent to the upstream side of the ejection unit lands on the printing surface until ink ejected by the ejection unit adjacent to the upstream side of the ejection unit lands in the same region as ink ejected by the ejection unit adjacent to the upstream side of the ejection unit lands on the printing surface is equal to or longer than a time from when ink ejected by the ejection unit adjacent to the upstream side lands on the printing surface until it penetrates into the printing surface; An inkjet printing apparatus comprising:

2. 2. The inkjet printing device according to claim 1, wherein the control unit reduces the ink ejection speed for each ejection unit other than the ejection unit furthest downstream in the relative movement direction of the printing medium as viewed from the plurality of ejection units, the longer the relaxation time of the dynamic surface tension of the ejected ink.

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