Droplet ejector and method for producing printed matter

Abstract

Provided are a droplet ejector which continues to satisfactorily eject any ink and a method for producing printed matter. The droplet ejector comprises: a droplet ejection head for ejecting a liquid; a relative-movement mechanism which moves a base and the droplet ejection head relatively to each other; and a control unit which makes the base and the droplet ejection head move relatively to each other and makes the droplet ejection head eject the liquid, thereby printing an image on the base. The space between the droplet ejection head and the base is vacuum. The droplet ejection head is equipped with circulation passages for circulating the liquid. The control unit makes the droplet ejection head circulate the liquid at least during printing.

Description

Droplet ejection device and method for manufacturing printed matter

[0001] The present invention relates to a droplet ejection device and a method for producing a printed matter, and more particularly to a technique for stabilizing the ejection state.

[0002] In order to expand the range of applications of inkjet technology, there is a need to be able to land droplets on a substrate without being strongly affected by air resistance, even when the distance between the inkjet head and the substrate is large.

[0003] In response to this problem, Patent Document 1 discloses a printing system that performs printing using an inkjet method, and that includes an inkjet head having nozzles that eject droplets of curable ink that harden in response to external energy onto a medium, an ultraviolet ray irradiation unit that is a curing energy generation unit that generates energy to harden the ink that has landed on the medium, a decompression chamber that houses at least the inkjet head and the medium, a pump that is a pressure reduction means that reduces the air pressure in the decompression chamber to a pressure lower than atmospheric pressure, and a water cooling device that is a cooling means that cools the ultraviolet ray irradiation unit via a refrigerant that has a higher specific heat than the air in the decompressed decompression chamber.

[0004] Japanese Patent No. 5738513 Japanese Patent Application Laid-Open No. 2017-65159

[0005] However, the printing system described in Patent Document 1 has a problem in that there are limitations on the inks that can be used. For example, depending on the type of ink, there is a problem in that the solvent components in the ink evaporate, causing a deterioration in the ejection state.

[0006] The present invention has been made in view of the above circumstances, and has as its object to provide a droplet ejection device that maintains a good ejection state even in a reduced pressure environment, and a method for producing a printed matter.

[0007] To achieve the above object, a droplet discharge device according to a first aspect of the present disclosure includes a droplet discharge head that discharges liquid, a relative movement mechanism that moves a substrate and the droplet discharge head relative to each other, and a control device that prints an image on the substrate by moving the substrate and the droplet discharge head relative to each other and discharging liquid from the droplet discharge head, wherein a vacuum is created between the droplet discharge head and the substrate, the droplet discharge head has a circulation flow path inside the droplet discharge head, and the control device circulates the liquid through the circulation flow path at least during printing. According to this aspect, a good discharge state can be maintained.

[0008] A droplet ejection device according to a second aspect of the present disclosure is a droplet ejection device according to the first aspect, wherein the droplet ejection head has an ejection element including a nozzle, a pressure chamber, and an ejection energy generating element, and the circulation flow path preferably includes a supply flow path that supplies liquid to the ejection element and a recovery flow path that recovers liquid from the ejection element.

[0009] A droplet ejection device according to a third aspect of the present disclosure is the droplet ejection device according to the first or second aspect, and preferably includes a first liquid tank for storing liquid and a second liquid tank, and the control device supplies liquid from the first liquid tank to the droplet ejection head by a head difference, and recovers liquid from the droplet ejection head to the second liquid tank by a head difference.

[0010] A droplet ejection device according to a fourth aspect of the present disclosure is the droplet ejection device according to the third aspect, further comprising a chamber that houses a droplet ejection head, a relative movement mechanism, a first liquid tank, and a second liquid tank, and an exhaust mechanism that evacuates the inside of the chamber, and it is preferable that the basis for the head difference is the pressure inside the chamber.

[0011] A droplet ejection device according to a fifth aspect of the present disclosure is the droplet ejection device according to the fourth aspect, further comprising a liquid delivery mechanism that supplies liquid from the second liquid tank to the first liquid tank, and it is preferable that the liquid delivery mechanism be arranged outside the chamber.

[0012] A droplet ejection device according to a sixth aspect of the present disclosure is a droplet ejection device according to any one of the first to fifth aspects, wherein the control device preferably makes the amount of liquid circulated during printing greater than the amount of liquid circulated during non-printing.

[0013] A droplet ejection device according to a seventh aspect of the present disclosure is the droplet ejection device according to any one of the first to sixth aspects, wherein the control device preferably stops circulation of the liquid when not printing.

[0014] A droplet ejection device according to an eighth aspect of the present disclosure is a droplet ejection device according to any one of the first to seventh aspects, wherein the control device preferably applies vibration to non-ejecting nozzles during printing to an extent that droplets are not ejected.

[0015] A droplet ejection device according to a ninth aspect of the present disclosure is a droplet ejection device according to any one of the first to eighth aspects, wherein the liquid contains a solvent, and the device is provided with a concentration measuring device that measures the concentration of the circulated liquid, and it is preferable that the control device adds an amount of solvent to the liquid to compensate for evaporation of the solvent.

[0016] A droplet ejection device according to a tenth aspect of the present disclosure is the droplet ejection device according to the fourth aspect, wherein the liquid preferably contains a solvent, and the solvent is disposed in an open state inside the chamber.

[0017] A droplet ejection device according to an eleventh aspect of the present disclosure is a droplet ejection device according to the fourth or tenth aspect, which is provided with a circuit element for driving the droplet ejection head, and the circuit element is preferably arranged outside the chamber.

[0018] A droplet ejection device according to a twelfth aspect of the present disclosure is the droplet ejection device according to any one of the first to eleventh aspects, wherein the vacuum is preferably 0.5 atmospheres to 0.01 atmospheres.

[0019] A droplet ejection device according to a thirteenth aspect of the present disclosure is the droplet ejection device according to any one of the first to twelfth aspects, wherein the liquid is preferably an aqueous ink containing water as a solvent.

[0020] To achieve the above object, a method for producing a printed matter according to a fourteenth aspect of the present disclosure is a method for producing a printed matter, which includes: creating a vacuum between a droplet ejection head and a substrate, moving the substrate and the droplet ejection head relative to each other, and ejecting liquid from the droplet ejection head to print an image on the substrate; and circulating the liquid through a circulation flow path of the droplet ejection head at least during printing. According to this aspect, a good ejection state can be maintained.

[0021] According to the present invention, a good ejection state can be maintained even in a reduced pressure environment.

[0022] FIG. 1 is a side view showing an outline of a printing apparatus. FIG. 2 is a plan view showing an outline of a printing apparatus. FIG. 3 is a perspective view of a droplet ejection head. FIG. 4 is a plan view perspective view showing an example of the structure of a silicon die. FIG. 5 is a cross-sectional view taken along line 5-5 of FIG. 4. FIG. 6 is a cross-sectional view taken along line 5-5 of FIG. 4 according to a modified example. FIG. 7 is a schematic diagram showing an example of the configuration of a vacuum environment and ink circulation in a printing apparatus. FIG. 8 is a schematic diagram showing an example of the configuration of a printing apparatus according to a second embodiment. FIG. 9 is a schematic diagram showing an example of the configuration of a printing apparatus according to a third embodiment. FIG. 10 is a schematic diagram showing an example of the configuration of a printing apparatus according to a fourth embodiment. FIG. 11 is a schematic diagram showing an example of the configuration of a printing apparatus according to a fifth embodiment. FIG. 12 is a schematic diagram showing an example of the configuration of a printing apparatus according to a sixth embodiment. FIG. 13 is a block diagram showing the electrical configuration of a printing apparatus.

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the description of each embodiment, illustration and description of parts common to other embodiments will be omitted as appropriate.

[0024] <Outline of Printing Apparatus: First Embodiment> Fig. 1 is a side view showing an outline of a printing apparatus 10, and Fig. 2 is a plan view showing an outline of the printing apparatus 10. The printing apparatus 10 is a droplet ejection device that prints an image on a substrate 1.

[0025] The printing device 10 includes a transport device 12 and a droplet ejection head 14. The transport device 12 is a relative movement mechanism that moves the substrate 1 relative to the droplet ejection head 14 by transporting the substrate 1 in the horizontal Y direction. The droplet ejection head 14 is an inkjet head that ejects droplets I of aqueous ink (an example of a "liquid") containing water as a solvent using an inkjet method.

[0026] The printing device 10 forms an image by ejecting ink droplets I from a droplet ejection head 14 onto a recording surface of a substrate 1 transported in the Y direction by a transport device 12. The substrate 1 is, for example, a printed circuit board, and the ink is, for example, a conductive ink containing a conductive material. The printing device 10 may also include a head carriage that moves the droplet ejection head 14 in the X direction.

[0027] In the printing device 10, at least the space S between the droplet ejection head 14 and the substrate 1 is at a low vacuum (negative pressure) that is relatively lower than atmospheric pressure. Atmospheric pressure refers to the pressure of the atmosphere in the printing device 10, and may be 1 atmosphere. Furthermore, negative pressure refers to, but is not limited to, approximately 0.5 atmospheres to 0.01 atmospheres at room temperature. The negative pressure is a value measured using a vacuum gauge (for example, an EA106B manufactured by ESCO Corporation).

[0028] By creating a low vacuum in the space S, it is possible to reduce the air resistance to the droplets I. As a result, the printing device 10 can maintain a good ejection state and accurately land the droplets I on the substrate 1 even when the distance between the droplet ejection head 14 and the substrate 1 is relatively wide, such as 5 mm to 30 mm. In a typical printing device, the distance between the droplet ejection head and the substrate to accurately land the droplets I is about 0.5 mm to 2 mm.

[0029] [Configuration of droplet ejection head] There is a concern that the ejection may deteriorate due to evaporation of the ink solvent if the space S is made low vacuum. In this embodiment, a droplet ejection head that circulates ink to the periphery of the nozzles is used to stabilize the ejection state even if evaporation of the ink solvent occurs.

[0030] 3 is a perspective view of the droplet ejection head 14. The droplet ejection head 14 includes an L-shaped bracket 16, a silicon die 24, an ink supply path 18, an ink recovery path 20, and a filter housing 22.

[0031] The L-shaped bracket 16 is a member for fixing the droplet ejection head 14 to a head support member (not shown).

[0032] The ink supply path 18 is connected to the upper ink tank 32 (see FIG. 7). The ink supply path 18 supplies ink from the upper ink tank 32 to the droplet ejection head 14. The ink recovery path 20 is connected to the lower ink tank 34 (see FIG. 7). The ink recovery path 20 recovers the ink supplied to the droplet ejection head 14 into the lower ink tank 34.

[0033] The filter housing 22 houses a filter for removing foreign matter and the like contained in the ink inside the droplet ejection head 14 .

[0034] The silicon die 24 has a nozzle surface 200 (see FIG. 5) that faces the substrate 1 transported by the transport device 12. Fig. 4 is a plan perspective view showing an example of the structure of the silicon die 24, and Fig. 5 is a cross-sectional view taken along line 5-5 in Fig. 4.

[0035] The silicon die 24 includes a nozzle plate 230 in which nozzles 202, which are ink droplet ejection ports, are formed, and a flow path plate 232 in which ink flow paths are formed. The nozzle plate 230 and the flow path plate 232 are laminated and bonded together. The flow path plate 232 has a structure in which one or more substrates are laminated. The nozzle plate 230 and the flow path plate 232 are made of silicon and can be processed into the required shape using a semiconductor manufacturing process.

[0036] The silicon die 24 has a plurality of nozzles 202 on its bottom surface, the nozzle surface 200. A plurality of ink chamber units 206, each consisting of a pressure chamber 204 and the like provided corresponding to each nozzle 202, are arranged two-dimensionally in a fixed array pattern. This achieves a high density of the effective nozzle spacing projected as being aligned along the X direction.

[0037] The pressure chambers 204 are connected to supply tributaries 210 via supply restrictors 208, and each supply tributary 210 is connected to a common flow path 212. In addition, a descender 214 connected to each pressure chamber 204 is connected to an ink circulation path 216 and a common circulation path 220 via a recovery tributary 218. The silicon die 24 is provided with an ink supply port 18A and an ink discharge port 20A. The ink supply path 18 (see FIG. 3) is connected to the ink supply port 18A. The ink discharge port 20A is connected to the ink recovery path 20 (see FIG. 3).

[0038] In this way, the ink supply port 18A and ink discharge port 20A of the silicon die 24 are connected via the common flow path 212, the supply tributary 210, the supply restrictor 208, the pressure chamber 204, the descender 214, the ink circulation path 216, the recovery tributary 218, and the circulation common flow path 220.

[0039] Therefore, the ink supplied from the ink supply path 18 to the ink supply port 18A flows through the common flow path 212, the supply tributary 210, the supply restrictor 208, the pressure chamber 204, and the descender 214, and a portion of the ink is ejected from each nozzle 202, while the remaining ink is discharged from the ink discharge port 20A to the ink recovery path 20 via the ink circulation path 216, the recovery tributary 218, and the circulation common flow path 220.

[0040] Furthermore, a piezoelectric actuator 228 equipped with an individual electrode (not shown) is joined to a vibration plate 226 that forms the top surface of the pressure chamber 204 and also serves as a common electrode. When a predetermined voltage is applied to the individual electrode, the piezoelectric actuator 228 deforms in a direction that contracts the pressure chamber 204. This causes ink to be ejected from the nozzle 202. The piezoelectric actuator 228 then deforms in a direction that expands the pressure chamber 204. This causes new ink to be supplied to the pressure chamber 204 from the common flow path 212 through the supply tributary 210 and the supply orifice 208.

[0041] Here, a piezo actuator 228 is used as the ejection energy generating element for ejecting ink from the nozzle 202, but it is also possible to apply a thermal method in which a heater is provided inside the pressure chamber 204 and ink is ejected using the pressure of film boiling caused by heating by the heater.

[0042] As such, the droplet ejection head 14 has an ejection element 222 that includes a nozzle 202, a pressure chamber 204, and a piezoelectric actuator 228. The droplet ejection head 14 also includes a supply tributary 210 (an example of a "supply flow path") that supplies ink to the ejection element 222, and a recovery tributary 218 (an example of a "recovery flow path") that recovers ink from the ejection element 222. The supply tributary 210 and the recovery tributary 218 together form a "circulation flow path."

[0043] The ink circulation path 216 is preferably configured to be provided around the nozzle 202. Here, the ink circulation path 216 is provided in a region that communicates with the descender 214 and is in contact with the nozzle plate 230 of the flow path plate 232. This allows the ink to circulate near the nozzle 202, preventing the ink inside the nozzle 202 from thickening and enabling stable ejection.

[0044] Figure 6 is a cross-sectional view of a modified example taken along line 5-5 of Figure 4. In the modified example shown in Figure 6, the ink circulation path 216 is provided in an area that communicates with the descender 214 and is in contact with the vibration plate 226. Even with this configuration, the effect is less than that of the ink chamber unit 206 shown in Figure 5, but ink circulates near the nozzle 202, enabling stable ejection.

[0045] [Control of Droplet Ejection Head] By using a droplet ejection head 14 in which ink is circulated, new ink is continuously supplied to the ink chamber unit 206, even though the ink solvent evaporates from the nozzles 202. This makes it possible to maintain the ejection state even in a vacuum environment. In particular, water has a high vapor pressure and evaporates easily, making it difficult to use aqueous ink in a printing device that uses a vacuum, but ink circulation makes it possible to use aqueous ink. Furthermore, as will be described later, ink circulation allows the heat generated by the droplet ejection head 14 to be extracted to the outside through the ink, in response to insufficient heat dissipation from the droplet ejection head 14 due to reduced thermal conductivity in a vacuum.

[0046] It is desirable to change the amount of ink circulation when the printing device 10 is printing and when it is not printing. When printing, this includes at least a state in which the droplet ejection head 14 and the substrate 1 are facing each other. The printing device 10 prints by applying ink using the droplet ejection head 14 while the substrate 1 is transported by the transport device 12. In this embodiment, the printing period is from when the substrate 1 reaches a position facing the droplet ejection head 14 until it has completely passed the position facing the droplet ejection head 14, and the rest of the time is when it is not printing.

[0047] During printing, it is desirable to always have fresh ink flowing into the ink chamber unit 206, so the ink circulation volume is increased as much as possible. For the same ink, it is desirable to circulate the ink at a volume at least twice as large as the general ink circulation volume of 1,000 pL / sec to 10,000 pL / sec per nozzle, more desirably at least three times as large, and even more desirably at least five times as large.

[0048] On the other hand, when not printing, it is desirable to minimize ink evaporation, so it is desirable to reduce the amount of ink circulation compared to when printing, to a level that does not cause the nozzles 202 to solidify due to ink evaporation. For example, at around 0.1 atmospheres, even aqueous ink will not clog the nozzles 202 for several minutes, so in that case, stopping the ink circulation for only a short time can be selected as a method for suppressing solvent evaporation. In other words, when not printing, the cycle of stopping circulation → a few minutes later → circulation → a few minutes later → stopping circulation... can be repeated. In this way, by stopping the ink circulation at unnecessary times or reducing the amount of ink circulation, unnecessary ink evaporation can be reduced.

[0049] Furthermore, in order to suppress the adverse effects of ink solvent evaporation on ejection, it is desirable to apply vibrations (so-called meniscus shaking) from the piezo actuator 228 to non-ejecting nozzles that do not eject ink during printing, to the extent that they do not eject ink. By combining this with ink circulation, fresh ink can be sent to the nozzles 202, which further suppresses an increase in ink viscosity in the nozzles 202 and achieves more stable ejection.

[0050] 7 is a schematic diagram showing an example of the vacuum environment and ink circulation configuration of the printing device 10. The printing device 10 includes a chamber 30, an exhaust mechanism 31, an upper ink tank 32, a lower ink tank 34, a return flow path 36, and an ink pump 38.

[0051] The chamber 30 houses the transport device 12 (not shown in FIG. 7 ), the droplet ejection head 14, the upper ink tank 32, the lower ink tank 34, the return flow path 36, and the ink pump 38. The chamber 30 is provided with an exhaust port (not shown). The pressure inside the chamber 30 is reduced by an exhaust mechanism 31 such as a vacuum pump via the exhaust port. Here, the inside of the chamber 30 is maintained at a low vacuum atmosphere of 0.1 atmospheres. That is, the space S between the droplet ejection head 14 and the substrate 1 is a low vacuum of 0.1 atmospheres.

[0052] The upper ink tank 32 (an example of a "first liquid tank") is a container for storing ink to be supplied to the droplet ejection head 14. The upper ink tank 32 is in communication with the droplet ejection head 14 via the ink supply path 18. The interior of the upper ink tank 32 is open to the atmosphere inside the chamber 30. The upper ink tank 32 is supported by a first up-and-down movement mechanism 72 (see FIG. 13) that is movable in the vertical direction (Z direction), and is positioned at a height that provides the desired head difference.

[0053] The lower ink tank 34 (an example of a "second liquid tank") is a container for storing ink recovered from the droplet ejection head 14. The lower ink tank 34 is in communication with the droplet ejection head 14 via the ink recovery path 20. The interior of the lower ink tank 34 is open to the atmosphere inside the chamber 30. The lower ink tank 34 is supported by a second up-and-down movement mechanism 74 (see FIG. 13) that is movable in the vertical direction, and is positioned at a height that provides the desired head difference.

[0054] The return flow path 36 connects the upper ink tank 32 and the lower ink tank 34. An ink pump 38, which is a liquid delivery mechanism, is provided in the return flow path 36 and delivers ink from the lower ink tank 34 to the upper ink tank 32.

[0055] In this way, the printing device 10 has the droplet ejection head 14 disposed between the upper ink tank 32 and the lower ink tank 34. The upper ink tank 32 and the lower ink tank 34 have a mechanism for causing ink to flow to the droplet ejection head 14 by a head difference using gravity with the pressure inside the chamber 30 as the reference. This results in a simple ink circulation configuration, and also makes it easier to control as there is no need to provide a mechanism to follow pressure changes within the low vacuum region.

[0056] Of course, ink may be circulated by controlling the pressure with a pump based on atmospheric pressure as described in Patent Document 2. However, the method shown in Figure 7 is simple and easy to control.

[0057] The amount of circulated ink can be controlled by the first vertical movement mechanism 72 and the second vertical movement mechanism 74. To minimize the effect on ejection, it is desirable to move the upper ink tank 32 and the lower ink tank 34 up and down when ink is not being ejected from the droplet ejection head 14.

[0058] <Ink Pump Placement: Second Embodiment> It is preferable not to install the ink pump 38 within the low vacuum region. Although there are pumps that can be used in low vacuum regions, these are expensive and there is also the risk of the grease in the ink pump 38 evaporating. Therefore, the ink pump 38 is installed outside the low vacuum region.

[0059] 8 is a schematic diagram showing an example of the configuration of a printing apparatus 10A according to the second embodiment. In the example shown in FIG. 8, the ink pump 38 is disposed outside the chamber 30.

[0060] In this way, by providing the ink pump 38 in an atmospheric pressure region, it is possible to operate the ink pump 38 in an environment where it is easy to operate. If it is confirmed from the detection result of the first liquid level sensor 76 (see FIG. 13) provided in the upper ink tank 32 that the amount of ink stored in the upper ink tank 32 is decreasing, and if the detection result of the second liquid level sensor 78 (see FIG. 13) provided in the lower ink tank 34 indicates that there is a sufficient amount of ink stored in the lower ink tank 34, the ink pump 38 can be operated to pump ink from the lower ink tank 34 to the upper ink tank 32.

[0061] The tube of the return flow path 36 arranged in the atmospheric pressure region needs to be a hard tube or pipe so that it will not be crushed by external pressure when ink in a negative pressure state flows through it.

[0062] Similarly, the tube of the return flow path 36, which is located in the low vacuum region, is also subject to pressure changes, so it is desirable that the tube be made of a hard material. Meanwhile, a Cableveyor (registered trademark) (not shown) is used for the tube of the return flow path 36 to facilitate handling of the tube in accordance with the operation of the droplet ejection head 14. Therefore, it is desirable that the tube of the return flow path 36 be hard enough to withstand the movement of the Cableveyor (registered trademark). For example, it is desirable to use Novatec (registered trademark) LD-LA320 manufactured by Japan Polyethylene Corporation.

[0063] <Ink Refill: Third Embodiment> Furthermore, it is desirable to perform ink refill from outside the low vacuum region. Fig. 9 is a schematic diagram showing an example of the configuration of a printing apparatus 10B according to a third embodiment.

[0064] The printing device 10B includes a first ink pump 38A, a first valve 40, a refill ink tank 42, a refill flow path 44, a second ink pump 46, and a second valve 48.

[0065] The first ink pump 38A is disposed outside the chamber 30. The first valve 40 is provided in the return flow path 36 outside the chamber 30. The first valve 40 switches between allowing and blocking the passage of ink through the return flow path 36 under the control of a control device 70 (see FIG. 13 ).

[0066] The refill ink tank 42 is provided outside the chamber 30. The refill ink tank 42 is a container for storing ink to refill the lower ink tank 34. The refill ink tank 42 communicates with the return flow path 36 via a refill flow path 44. The inside of the refill ink tank 42 is open to the atmosphere at atmospheric pressure outside the chamber 30.

[0067] A second ink pump 46 and a second valve 48 are provided in the refill flow path 44. The second ink pump 46 sends ink from the refill ink tank 42 to the upper ink tank 32. The second valve 48 switches between allowing and blocking the passage of ink through the refill flow path 44 under the control of the control device 70 (see FIG. 13 ).

[0068] In the printing device 10B configured in this manner, when ink in the upper ink tank 32 and the lower ink tank 34 runs low, printing is carried out up to an appropriate interval and then the interior of the chamber 30 is opened to the atmosphere. Then, by opening the second valve 48 and driving the first ink pump 38A and the second ink pump 46, ink stored in the refill ink tank 42 can be sent to the upper ink tank 32. When sending ink to the lower ink tank 34, the first valve 40 and the second valve 48 are opened and the second ink pump 46 is driven, so that ink stored in the refill ink tank 42 can be sent to the lower ink tank 34.

[0069] Although it is not desirable, if you want to replenish the upper ink tank 32 with ink stored in the refill ink tank 42 during printing, you can open the second valve 48 and then slowly drive the first ink pump 38A and the second ink pump 46.

[0070] Furthermore, because the solvent evaporates quickly in the low vacuum region, the amount of solvent in the ink gradually decreases even though the ink is circulating. Therefore, by extracting ink from an ink extraction location (not shown) in the atmospheric pressure region and evaluating the ink components using a concentration sensor 80 (see FIG. 13, an example of a "concentration measuring device"), it is possible to determine whether the ink is in an appropriate state. Furthermore, by adding insufficient solvent to the ink using a solvent adding device 82 (see FIG. 13), the ink can be adjusted to an appropriate concentration.

[0071] If it becomes clear that the amount of solvent in the ink has decreased significantly, the thickened ink may be extracted from the ink tube (not shown) and disposed of, and new ink may be supplied from the refill ink tank 42.

[0072] <Prevention of Solvent Evaporation: Fourth Embodiment> In order to prevent evaporation of the ink solvent from the liquid surface of the upper ink tank 32 and the lower ink tank 34, a film or beads may be floated on the liquid surface to reduce the exposed surface area.

[0073] Furthermore, the upper ink tank 32 and the lower ink tank 34 may be closed with a soft material such as a damper membrane that can follow changes in external pressure, rather than being open to the atmosphere inside the chamber 30. The upper ink tank 32 and the lower ink tank 34 may be configured as a pouch or other material that can be deformed as a whole.

[0074] Furthermore, to prevent solvent evaporation from the nozzles 202 of the droplet ejection head 14, only the solvent may be added to the chamber 30 in advance. FIG. 10 is a schematic diagram showing an example configuration of a printing apparatus 10C according to a fourth embodiment. The printing apparatus 10C includes a container 50 inside the chamber 30. The container 50 is positioned vertically below the droplet ejection head 14. The container 50 contains the ink solvent (water in this case), and the solvent is open to the space inside the chamber 30. Therefore, the solvent inside the container 50 evaporates naturally. Although this slightly reduces the degree of vacuum inside the chamber 30, it is possible to increase the partial pressure of the solvent and prevent ink evaporation from the nozzles 202.

[0075] <Heat Generation in Droplet Discharge Head: Fifth Embodiment> When a droplet discharge head is used in a low vacuum region, there is a concern that the droplet discharge head itself may generate heat. In the case of an inkjet head using a piezoelectric actuator, the piezoelectric actuator itself generates heat, as does the ASIC (Application Specific Integrated Circuit) that outputs the drive voltage for controlling the piezoelectric actuator. Of course, the substrate that supplies power and transmits signals to the inkjet head also generates heat.

[0076] It is naturally desirable that the substrate be located outside the low vacuum area. Also, it is desirable that the ASIC is not mounted on the inkjet head itself, but is located at a position away from the inkjet head, outside the low vacuum area.

[0077] 11 is a schematic diagram showing an example of the configuration of a printing device 10D according to the fifth embodiment. The printing device 10D includes a control board 52, an ASIC 54, and a flexible cable 56.

[0078] The control board 52 sends control signals to the ASIC 54 for controlling the droplet ejection head 14. The ASIC 54 (an example of a "circuit element") distributes the signals received from the control board 52 to the multiple piezo actuators 228 and outputs drive voltages. The flexible cable 56 is wiring that transmits signals and drive voltages between the control board 52, the ASIC 54, and the droplet ejection head 14.

[0079] The control board 52 is disposed at the end of the flexible cable 56, and the ASIC 54 is disposed at a position between both ends of the flexible cable 56. The control board 52 and the ASIC 54 are disposed outside the chamber 30. By disposing the heat source outside the chamber 30 in this way, heat can be dissipated outside the chamber 30, and a temperature rise in the low vacuum region inside the chamber 30 can be prevented.

[0080] Naturally, circulating the ink also has the effect of dissipating heat from the droplet ejection head 14. Ink circulation is effective against both the tendency for ink to evaporate and the deterioration of thermal conductivity, which occur in low vacuum regions.

[0081] It is desirable to use cooled ink to minimize evaporation of the ink. The ink can be cooled by providing an ink cooling mechanism 84 (see FIG. 13) to the ink supply path 18, the ink recovery path 20, the upper ink tank 32, the lower ink tank 34, etc. The ink cooling mechanism 84 can use a chiller or a Peltier element that flows cooling water. The ink cooling mechanism 84 cools the ink to, for example, 20°C. If the viscosity of the cooled ink increases, the voltage waveform applied to the piezo actuator 228 of the droplet ejection head 14 can be increased.

[0082] 12 is a schematic diagram showing an example of the configuration of a printing apparatus 10E according to a sixth embodiment. The chamber 30 of the printing apparatus 10E includes an inlet slit 60A, an outlet slit 60B, and a first shutter 64A, a second shutter 64B, a third shutter 64C, and a fourth shutter 64D that can be opened and closed, respectively.

[0083] The loading slit 60A is a slit-shaped opening for loading the substrate 1 from the outside to the inside of the chamber 30. The unloading slit 60B is a slit-shaped opening for unloading the substrate 1 from the inside to the outside of the chamber 30.

[0084] The first shutter 64A, the second shutter 64B, the third shutter 64C, and the fourth shutter 64D are each disposed on a transport path of the substrate 1 by the transport device 12. The first shutter 64A is disposed in the carry-in slit 60A and opens and closes the carry-in slit 60A. The fourth shutter 64D is disposed in the carry-out slit 60B and opens and closes the carry-out slit 60B.

[0085] The chamber 30 has a first pressure adjustment chamber 66A between the first shutter 64A and the second shutter 64B, which is a space that is relatively narrow compared to the low vacuum region inside the chamber 30 where the droplet ejection head 14 and the like are disposed. The chamber 30 also has a second pressure adjustment chamber 66B between the third shutter 64C and the fourth shutter 64D, which is a space that is relatively narrow compared to the low vacuum region inside the chamber 30. The first pressure adjustment chamber 66A and the second pressure adjustment chamber 66B each include a vacuum pump (not shown).

[0086] The second shutter 64B switches between opening and closing the first pressure adjustment chamber 66A and the low vacuum region, and the third shutter 64C switches between opening and closing the low vacuum region and the second pressure adjustment chamber 66B.

[0087] When transferring the substrate 1 from outside the chamber 30 into the chamber 30, the first shutter 64A is first opened, the transfer device 12 transfers the substrate 1 into the first pressure adjustment chamber 66A, and the first shutter 64A is closed. Next, the vacuum pump creates a low vacuum state (e.g., 0.1 atmospheres) inside the first pressure adjustment chamber 66A, the second shutter 64B is opened, the transfer device 12 transfers the substrate 1 into the low vacuum region of the chamber 30, and the second shutter 64B is closed.

[0088] Furthermore, when the substrate 1 inside the chamber 30 is transported to the outside of the chamber 30, the inside of the first pressure adjustment chamber 66A is first put into a low vacuum state by the vacuum pump. Then, the third shutter 64C is opened, the substrate 1 is transported into the second pressure adjustment chamber 66B by the transport device 12, and the third shutter 64C is closed. Next, the fourth shutter 64D is opened, the substrate 1 is transported out of the chamber 30 by the transport device 12, and the fourth shutter 64D is closed. Then, the inside of the second pressure adjustment chamber 66B is put into a low vacuum state.

[0089] By transporting the substrate 1 in the above manner, the substrate 1 can be carried into the low vacuum region where the droplet discharge head 14 is located without introducing a large amount of air into the low vacuum region.

[0090] 13 is a block diagram showing the electrical configuration of the printing devices 10, 10A, 10B, 10C, 10D, and 10E. The printing devices 10, 10A, 10B, 10C, 10D, and 10E each include a control device 70. The control device 70 includes a processor 70A and a memory 70B.

[0091] The processor 70A executes instructions stored in the memory 70B. The hardware configuration of the processor 70A is the following various processors. The various processors include a CPU (Central Processing Unit), which is a general-purpose processor that executes software (programs) and functions as various functional units, a GPU (Graphics Processing Unit), which is a processor specialized for image processing, a PLD (Programmable Logic Device), which is a processor whose circuit configuration can be changed after manufacture such as an FPGA (Field Programmable Gate Array), and a dedicated electrical circuit, such as an ASIC (Application Specific Integrated Circuit), which is a processor having a circuit configuration designed specifically for executing specific processing.

[0092] A single processing unit may be configured with one of these various processors, or may be configured with two or more processors of the same or different types (e.g., multiple FPGAs, a combination of a CPU and an FPGA, or a combination of a CPU and a GPU). Multiple functional units may also be configured with a single processor. Examples of multiple functional units configured with a single processor include: a first configuration, as typified by a client or server computer, in which a single processor is configured with a combination of one or more CPUs and software, and this processor operates as multiple functional units; and a second configuration, as typified by a SoC (System on Chip), in which a processor is used to realize the functions of an entire system including multiple functional units on a single IC (Integrated Circuit) chip. In this way, the various functional units are configured with one or more of the above-mentioned various processors as a hardware structure.

[0093] Furthermore, the hardware structure of these various processors is, more specifically, an electric circuit made up of a combination of circuit elements such as semiconductor elements.

[0094] The memory 70B stores instructions to be executed by the processor 70A. The memory 70B includes a random access memory (RAM) and a read-only memory (ROM). The processor 70A uses the RAM as a working area, executes software using various programs and parameters stored in the ROM, and executes various processes for controlling the printing devices 10, 10A, 10B, 10C, 10D, and 10E by using parameters stored in the ROM, etc.

[0095] The control device 70 controls the exhaust mechanism 31. That is, the control device 70 reduces the pressure inside the chamber 30 using the exhaust mechanism 31, and maintains the inside of the chamber 30 at a low vacuum atmosphere of, for example, 0.1 atmospheres. Furthermore, when the substrate 1 is carried in and out, the control device 70 reduces the pressure inside the first pressure adjustment chamber 66A and the second pressure adjustment chamber 66B using a vacuum pump (not shown) to create a low vacuum state.

[0096] The control device 70 controls the droplet ejection head 14. That is, the control device 70 ejects ink droplets I from the nozzles 202 of the droplet ejection head 14 to form an image on the substrate 1. Furthermore, during printing, the control device 70 vibrates the meniscus of the non-ejecting nozzles 202 by applying vibrations to the piezoelectric actuators 228 of the non-ejecting nozzles 202 to an extent that does not eject ink.

[0097] The control device 70 controls the transport device 12, the first shutter 64A, the second shutter 64B, the third shutter 64C, and the fourth shutter 64D. That is, the control device 70 transports the substrate 1 in the Y direction using the transport device 12. Furthermore, when the substrate 1 is transported into the chamber 30, the control device 70 opens and closes the first shutter 64A and the second shutter 64B in sequence to prevent a large amount of air from entering the low vacuum region inside the chamber 30. Furthermore, when the substrate 1 is transported out of the chamber 30, the control device 70 opens and closes the third shutter 64C and the fourth shutter 64D in sequence to prevent a large amount of air from entering the low vacuum region inside the chamber 30.

[0098] The control device 70 controls the ink pump 38. That is, the control device 70 causes the ink pump 38 to pump ink from the lower ink tank 34 to the upper ink tank 32.

[0099] The control device 70 controls the first ink pump 38A, the second ink pump 46, the first valve 40, and the second valve 48. That is, the control device 70 opens the first valve 40 to drive the first ink pump 38A and send ink from the lower ink tank 34 to the upper ink tank 32. The control device 70 also opens the second valve 48 to drive the first ink pump 38A and the second ink pump 46 and send ink from the refill ink tank 42 to the upper ink tank 32. The control device 70 also opens the first valve 40 and the second valve 48 to drive the second ink pump 46 and send ink from the refill ink tank 42 to the lower ink tank 34.

[0100] The control device 70 controls the first up-down movement mechanism 72 and the second up-down movement mechanism 74. That is, the control device 70 adjusts the vertical position of the upper ink tank 32 using the first up-down movement mechanism 72 to adjust the head difference between the upper ink tank 32 and the droplet ejection head 14, and adjusts the vertical position of the lower ink tank 34 using the second up-down movement mechanism 74 to adjust the head difference between the droplet ejection head 14 and the lower ink tank 34, thereby controlling the circulation of ink in the droplet ejection head 14.

[0101] The control device 70 makes the amount of ink circulated during printing by the droplet ejection head 14 greater than the amount of ink circulated during non-printing. The control device 70 stops the circulation of ink during non-printing.

[0102] The control device 70 obtains the detection results from the first liquid level sensor 76 and the second liquid level sensor 78. That is, the control device 70 confirms the amount of ink stored in the upper ink tank 32 from the detection result of the first liquid level sensor 76. The control device 70 also confirms the amount of ink stored in the lower ink tank 34 from the detection result of the second liquid level sensor 78.

[0103] The control device 70 obtains the detection result from the concentration sensor 80. That is, the control device 70 confirms the amount of solvent in the ink from the detection result of the concentration sensor 80.

[0104] The control device 70 controls the solvent adding device 82. That is, the control device 70 adds an amount of solvent to the ink according to the detection result of the concentration sensor 80, and adjusts the concentration of the solvent in the ink.

[0105] The control device 70 controls the ink cooling mechanism 84. That is, the control device 70 causes the ink cooling mechanism 84 to cool the ink to a desired temperature.

[0106] The printing devices 10, 10A, 10B, 10C, 10D, and 10E configured as described above can implement a method for manufacturing a printed matter, which includes creating a low vacuum in the space S between the droplet ejection head 14 and the substrate 1, circulating ink through the droplet ejection head 14, and printing on the substrate 1 by moving the substrate 1 and the droplet ejection head 14 relative to each other using the conveying device 12 and ejecting ink from the droplet ejection head 14.

[0107] According to the printing devices 10, 10A, 10B, 10C, 10D, and 10E, the space S between the droplet ejection head 14 and the substrate 1 is at a low vacuum, which reduces air resistance to the droplets I. Furthermore, by circulating the ink through the droplet ejection head 14, the ejection state can be stabilized even if the solvent evaporates from the ink.

[0108] <Others> Here, a printing device that applies conductive ink to a printed circuit board has been described as the droplet ejection device, but the substrate and ink are not limited to this. The droplet ejection device can be applied to substrates with uneven surfaces, such as paper, cloth, leather, metal, resin, glass, and wood. The substrate is not limited to one that fits entirely within the chamber, but may be a long piece that extends inside and outside the chamber.

[0109] The droplet ejection device can use inks such as color inks containing coloring materials, ultraviolet curable inks that are cured by ultraviolet irradiation, insulating inks that have insulating properties, etc. The droplet ejection device can use the number of droplet ejection heads according to the type of ink, and multiple droplet ejection heads may be arranged in one chamber, or a chamber may be provided for each droplet ejection head.

[0110] The technical scope of the present invention is not limited to the scope described in the above embodiments. The configurations and the like in each embodiment can be appropriately combined with each other within the scope that does not deviate from the spirit of the present invention.

[0111] 1...Substrate 10...Printing device 10A...Printing device 10B...Printing device 10C...Printing device 10D...Printing device 10E...Printing device 12...Transportation device 14...Droplet ejection head 16...L-shaped bracket 18...Ink supply path 18A...Ink supply port 20...Ink recovery path 20A...Ink discharge port 22...Filter housing 24...Silicon die 30...Chamber 31...Exhaust mechanism 32...Upper ink tank 34...Lower ink tank 36...Return flow path 38...Ink pump 38A...First ink pump 40...First valve 42...Refill ink tank 44...Refill flow path 46...Second ink pump 48...Second valve 50...Container 52...Control board 54...ASIC 56...Flexible cable 60A...Inlet slit 60B...Exit slit 64A...First shutter 64B...Second shutter 64C...Third shutter 64D...Fourth shutter 66A...First pressure adjustment chamber 66B...Second pressure adjustment chamber 70...Control device 70A...Processor 70B...Memory 72...First up-down movement mechanism 74...Second up-down movement mechanism 76...First liquid level sensor 78...Second liquid level sensor 80...Concentration sensor 82...Solvent addition device 84...Ink cooling mechanism 200...Nozzle surface 202...Nozzle 204...Pressure chamber 206...Ink chamber unit 210...Supply branch 212...Common flow path 214...Descender 216...Ink circulation path 218...Recovery branch 220...Circulation common flow path 222...Ejection element 226...Vibration plate 228...Piezoelectric actuator 230...Nozzle plate 232...Flow path plate I...Liquid droplet S...Space

Claims

1. A droplet ejection head that ejects liquid; a relative movement mechanism for moving the substrate and the droplet discharge head relative to each other; a control device that prints an image on the substrate by moving the substrate and the droplet ejection head relative to each other and ejecting liquid from the droplet ejection head; Equipped with A vacuum is provided between the droplet ejection head and the substrate, the droplet discharge head includes a circulation flow path therein, The control device circulates liquid through the circulation flow path at least during printing. Droplet ejection device.

2. the droplet ejection head has an ejection element including a nozzle, a pressure chamber, and an ejection energy generating element; the circulation flow path includes a supply flow path that supplies liquid to the ejection element, and a recovery flow path that recovers liquid from the ejection element. The droplet ejection device according to claim 1 .

3. The liquid supply device includes a first liquid tank and a second liquid tank for storing liquid, the control device supplies liquid from the first liquid tank to the droplet discharge head by a head difference, and recovers liquid from the droplet discharge head to the second liquid tank by a head difference; The droplet ejection device according to claim 1 .

4. a chamber that accommodates therein the droplet ejection head, the relative movement mechanism, the first liquid tank, and the second liquid tank; an exhaust mechanism for creating a vacuum inside the chamber; Equipped with the head difference is based on the pressure inside the chamber; The droplet ejection device according to claim 3 .

5. a liquid supply mechanism that supplies liquid from the second liquid tank to the first liquid tank, The liquid delivery mechanism is disposed outside the chamber. The droplet ejection device according to claim 4 .

6. the control device makes the amount of circulation of the liquid during printing greater than the amount of circulation of the liquid during non-printing; The droplet ejection device according to claim 1 .

7. The control device stops the circulation of the liquid when printing is not being performed. The droplet ejection device according to claim 1 .

8. the control device applies vibration to non-ejecting nozzles during printing to a degree that prevents droplets from being ejected; The droplet ejection device according to claim 1 .

9. the liquid comprises a solvent; A concentration measuring device for measuring the concentration of the circulated liquid is provided, The control device adds an amount of solvent to the liquid to compensate for evaporation of the solvent. The droplet ejection device according to claim 1 .

10. A chamber that accommodates the droplet ejection head and the relative movement mechanism therein; an exhaust mechanism for creating a vacuum inside the chamber; Equipped with the liquid comprises a solvent; placing the solvent in an open state within the chamber; The droplet ejection device according to claim 1 .

11. A chamber that accommodates the droplet ejection head and the relative movement mechanism therein; an exhaust mechanism for creating a vacuum inside the chamber; A circuit element for driving the droplet ejection head; Equipped with the circuit element is disposed outside the chamber; The droplet ejection device according to claim 1 .

12. The vacuum is between 0.5 atmospheres and 0.01 atmospheres. The droplet ejection device according to claim 1 .

13. Equipped with a cooling mechanism for cooling the liquid. The droplet ejection device according to claim 1 .

14. The liquid is an aqueous ink containing water as a solvent. The droplet ejection device according to claim 1 .

15. creating a vacuum between the droplet ejection head and the substrate, and relatively moving the substrate and the droplet ejection head to eject liquid from the droplet ejection head, thereby printing an image on the substrate; circulating liquid through a circulation flow path of the droplet ejection head at least during printing; A method for producing a printed matter comprising the steps of: