Droplet ejection device and liquid delivery method

Abstract

Provided are a liquid droplet ejection device and a liquid feeding method capable of effectively suppressing occurrence of a problem due to air bubbles while suppressing an increase in pressure loss. This liquid droplet ejection device is provided with: a liquid droplet ejection head having a nozzle that ejects a liquid, a supply flow path through which the liquid to be supplied to the nozzle passes, a discharge flow path that communicates with the supply flow path and through which a liquid to be discharged without being ejected from the nozzle passes, a filter that is provided in the supply flow path and through which the liquid that is to pass through the supply flow path passes, and a communication flow path that branches off from an upstream side of the filter in a liquid feeding direction of the liquid in the supply flow path and communicates with the discharge flow path; and a liquid feeding unit that performs a liquid feeding operation to cause the liquids of the supply flow path and the discharge flow path to flow in the liquid feeding direction. The mesh diameter of the filter is smaller than the opening diameter of the nozzle. The liquid feeding unit performs the liquid feeding operation in a mode in which pressure loss in the filter becomes smaller than a first meniscus break pressure at which meniscus of the liquid breaks in the filter.

Description

[Technical field]

[0001] The present invention relates to a droplet ejection device and a liquid delivery method. [Background technology]

[0002] Conventionally, there are droplet ejection devices that eject liquid such as ink from nozzles provided in a droplet ejection head and land the liquid at desired positions on a recording medium to form images, etc. The droplet ejection head of the droplet ejection device has a channel (pressure chamber) that communicates with the nozzle, and ejects droplets of the liquid from the nozzle by varying the pressure of the liquid in the channel.

[0003] If there are air bubbles in the channel, pressure will not be applied normally to the liquid in the channel, causing poor ejection of the liquid from the nozzle and degrading image quality. In response to this, there is a technique for suppressing defects caused by air bubbles by providing a degassing device that removes air bubbles and dissolved gases in the liquid and supplying the degassed liquid to the channel (for example, Patent Document 1). There is also a technique in which a degassing path is branched off midway through a supply flow path for liquid to a nozzle, and air bubbles in the liquid are discharged from the degassing path to the outside of the droplet ejection head (for example, Patent Document 2).

[0004] In recent years, in response to demands for higher image resolution and improved productivity, the number of nozzles in droplet ejection heads has increased and their driving speeds have increased, which has resulted in an increase in the amount of droplets ejected from the nozzles. In a droplet ejection head that ejects a large amount of droplets, if the flow path resistance of the liquid flow path is high, the pressure fluctuation during ejection becomes large, making it impossible to perform stable ejection. For this reason, there is a demand for a design that reduces the flow path resistance, i.e., a design that reduces the pressure loss in the droplet ejection head. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6098264 [Patent Document 2] Patent No. 5531872 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in a configuration in which a degassing device is provided as in Patent Document 1, a large pressure loss occurs due to the high flow resistance of the degassing device. Furthermore, in a configuration in which a degassing path is provided as in Patent Document 2, it is necessary to increase the amount of liquid flowing into the droplet ejection head in order to generate a flow in the degassing path that will expel air bubbles, resulting in large pressure losses in the droplet ejection head. As described above, the conventional techniques have the problem that it is difficult to effectively prevent problems caused by air bubbles while suppressing an increase in pressure loss.

[0007] An object of the present invention is to provide a droplet ejection device and a liquid delivery method that can effectively prevent problems caused by air bubbles while suppressing an increase in pressure loss. [Means for solving the problem]

[0008] In order to achieve the above object, the invention of the droplet ejection device described in claim 1 is as follows: A nozzle for discharging a liquid; a supply flow path through which liquid is supplied to the nozzle; a discharge flow path that communicates with the supply flow path and through which liquid that is discharged without being ejected from the nozzle passes; a filter provided in the supply flow path and through which the liquid passing through the supply flow path passes The filter is provided to capture at least air bubbles larger than the mesh size of the filter. and, a communication flow path that branches off from the supply flow path at an upstream side of the filter in a liquid sending direction and communicates with the discharge flow path; A droplet ejection head having a liquid sending unit that performs a liquid sending operation to cause the liquid in the supply flow path and the discharge flow path to flow in the liquid sending direction; Equipped with The filter The aboveThe mesh diameter is smaller than the opening diameter of the nozzle, The liquid delivery section is configured such that a pressure loss in the filter is The liquid surface of the air bubbles The liquid delivery operation is performed in a mode in which the pressure is smaller than a first meniscus break pressure at which the meniscus breaks.

[0009] The invention described in claim 2 is the droplet ejection device described in claim 1, When a flow rate of the liquid in the supply flow path corresponds to a maximum amount of the liquid discharged from the nozzle per unit time, the maximum discharge flow rate is defined as: The pressure loss caused in the filter by the maximum discharge flow rate of liquid is less than a second meniscus break pressure at which a meniscus of the liquid breaks in the nozzle.

[0010] The invention described in claim 3 is the droplet ejection device described in claim 1 or 2, the supply flow path has a downward portion in which the liquid sending direction has a vertical downward component, The liquid delivery section performs the liquid delivery operation in such a manner that the vertical downward component of the liquid velocity in the descending portion is greater than the speed at which bubbles smaller than the opening diameter of the nozzle rise due to buoyancy.

[0011] The invention described in claim 4 is the droplet ejection device described in any one of claims 1 to 3, The nozzle has a tapered portion in which the cross-sectional area perpendicular to the liquid ejection direction becomes smaller toward the nozzle opening.

[0012] The invention described in claim 5 is the droplet ejection device described in any one of claims 1 to 4, The liquid is a water-based ink.

[0013] In order to achieve the above object, the invention of the liquid delivery method described in claim 6 comprises: a nozzle for ejecting a liquid; a supply flow path through which the liquid to be supplied to the nozzle passes; a discharge flow path that is connected to the supply flow path and through which the liquid that is not ejected from the nozzle passes; and a filter that is provided in the supply flow path and through which the liquid passing through the supply flow path passes. The filter is provided to capture at least air bubbles larger than the mesh size of the filter. and a communication flow path that branches off from the supply flow path at an upstream side of the filter in a liquid delivery direction and communicates with the discharge flow path, The above A liquid delivery method for a droplet ejection device, the mesh diameter of which is smaller than the opening diameter of the nozzle, comprising: a liquid sending step of causing the liquid in the supply flow path and the discharge flow path to flow in the liquid sending direction, In the liquid sending step, the pressure loss in the filter is The liquid surface of the air bubbles The liquid is caused to flow in a manner that is less than a first meniscus break pressure at which the meniscus breaks. Effect of the Invention

[0014] According to the present invention, it is possible to effectively suppress the occurrence of problems due to air bubbles while suppressing an increase in pressure loss. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a droplet ejection device. [Diagram 2] FIG. 2 is a schematic diagram illustrating a configuration of a head unit. [Diagram 3] FIG. 2 is a perspective view of a droplet ejection head. [Figure 4] 2 is a cross-sectional perspective view of the inside of a main body of a liquid storage tank, as viewed from the bottom side. FIG. [Figure 5A] FIG. 2 is a cross-sectional view illustrating an ink flow path of the droplet ejection head. [Figure 5B] FIG. 2 is a cross-sectional view illustrating an ink flow path of the droplet ejection head. [Figure 6A] FIG. 2 is a cross-sectional view illustrating an ink flow path of the droplet ejection head. [Figure 6B] FIG. 2 is a cross-sectional view illustrating an ink flow path of the droplet ejection head. [Figure 6C] FIG. 2 is a cross-sectional view illustrating an ink flow path of the droplet ejection head. [Figure 6D] FIG. 2 is a cross-sectional view illustrating an ink flow path of the droplet ejection head. [Figure 6E] FIG. 2 is a cross-sectional view illustrating an ink flow path of the droplet ejection head. [Figure 7] FIG. 6C is an enlarged view of the vicinity of the nozzle in FIG. 6B. [Figure 8] FIG. 2 is a schematic diagram illustrating a configuration of an ink circulation mechanism. [Figure 9] 2 is a block diagram showing a main functional configuration of the droplet ejection device. FIG. [Figure 10] FIG. 2 is a diagram illustrating a schematic diagram of an ink flow path in a droplet ejection head. [Figure 11] 11A and 11B are diagrams illustrating the contents and results of an experiment for confirming the effects of the embodiment. [Figure 12] 10 is a cross-sectional view illustrating an ink flow path of a droplet ejection head according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a droplet ejection device and a liquid delivery method according to the present invention will be described with reference to the drawings.

[0017] <Configuration of Droplet Discharge Device> FIG. 1 is a diagram showing a schematic configuration of a droplet ejection device 1. As shown in FIG. The droplet ejection device 1 includes a transport section 2 and a head unit 3. The droplet ejection device 1 of this embodiment is an inkjet recording device that ejects droplets of ink as a liquid onto a recording medium M to form an image.

[0018] The transport unit 2 includes two transport rollers 2a and 2b that rotate around a rotation axis extending in the Y direction in Fig. 1, and a ring-shaped transport belt 2c whose inner side is supported by these transport rollers 2a and 2b. In the transport unit 2, with the recording medium M placed on the transport surface of the transport belt 2c, the transport roller 2a rotates in response to the operation of a transport motor (not shown), causing the transport belt 2c to move in a circular motion, thereby transporting the recording medium M in the moving direction of the transport belt 2c (transport direction; X direction in Fig. 1).

[0019] The recording medium M may be a sheet of paper cut to a certain size. The recording medium M is supplied onto a conveyor belt 2c by a paper feeder (not shown), and after an image is recorded by ejecting ink from the head unit 3, the recording medium M is discharged from the conveyor belt 2c to a predetermined paper discharge section. Roll paper may be used as the recording medium M. In addition to paper such as plain paper or coated paper, various media capable of fixing ink that has landed on the surface, such as fabric or sheet-like resin, may be used as the recording medium M.

[0020] The head units 3 eject ink at appropriate timing based on image data onto the recording medium M transported by the transport section 2 to record an image. In the droplet ejection device 1 of this embodiment, four head units 3 corresponding respectively to the four colors of ink, yellow (Y), magenta (M), cyan (C), and black (K), are arranged at predetermined intervals in the order of Y, M, C, and K from the upstream side in the transport direction of the recording medium M. The number of head units 3 may be three or less, or five or more.

[0021] 2 is a schematic diagram showing the configuration of the head unit 3, and is a plan view of the head unit 3 seen from the side facing the conveyance surface of the conveyor belt 2c. The head unit 3 has a plate-shaped support portion 3a and a plurality of (eight in this case) droplet ejection heads 100 fixed to the support portion 3a in a state where they are fitted into through holes provided in the support portion 3a. The droplet ejection heads 100 are fixed to the support portion 3a in a state where a nozzle opening surface 100a where the openings of the nozzles N are provided is exposed in the -Z direction from the through holes of the support portion 3a.

[0022] In the droplet ejection head 100, a plurality of nozzles N are arranged at equal intervals in a direction intersecting the transport direction of the recording medium M (in this embodiment, the width direction perpendicular to the transport direction, i.e., the Y direction). In this embodiment, each droplet ejection head 100 has four rows (nozzle rows) of nozzles N arranged one-dimensionally at equal intervals in the Y direction. These four nozzle rows are arranged such that their positions in the Y direction are shifted from each other so that the positions of the nozzles N do not overlap. The number of nozzle rows in the droplet ejection head 100 is not limited to four, and may be three or less, or five or more.

[0023] The eight droplet ejection heads 100 in the head unit 3 are arranged in a staggered pattern so that the arrangement range of the nozzles N in the Y direction is continuous. The arrangement range in the Y direction of the nozzles N included in the head unit 3 covers the width in the Y direction of an area on the recording medium M transported by the transport belt 2c on which an image can be recorded. The head unit 3 is used in a fixed position when recording an image, and ejects ink from the nozzles N to each position at predetermined intervals in the transport direction (transport direction intervals) in accordance with the transport of the recording medium M, thereby recording an image by a single pass method.

[0024] In this embodiment, aqueous ink is used as the ink ejected from the droplet ejection head 100. The aqueous ink contains, for example, water as a dispersion medium and a pigment or dye as a colorant, and may also contain various water-soluble organic solvents, hydrophobic polymers, and the like. The ink ejected from the droplet ejection head 100 is not limited to aqueous ink, and may be solvent ink using an organic solvent as a dispersion medium, ultraviolet curable ink that is cured by exposure to ultraviolet light, or the like.

[0025] FIG. 3 is a perspective view of the droplet ejection head 100. As shown in FIG. The droplet ejection head 100 includes an ejection operation unit 10, a liquid storage tank 20, a cover member 30, and the like.

[0026] The discharge operation unit 10 has nozzles N, and its bottom surface side (-Z direction side) is a nozzle opening surface 100a where the openings of the nozzles N are arranged. The discharge operation unit 10 discharges liquid, here ink, supplied from a liquid storage tank 20 from the nozzles N. The discharge operation unit 10 can also discharge the supplied ink that has not been discharged from the nozzles N into the liquid storage tank 20. The discharge operation unit 10 further includes ink channels 151 (see FIG. 5B) communicating with each nozzle N, and pressure fluctuation means for applying pressure fluctuations to the ink in the ink channels 151.

[0027] The cover member 30 is fitted to the discharge operation unit 10 and houses therein a circuit section for supplying a drive signal to the pressure varying means of the discharge operation unit 10 and the like.

[0028] The liquid storage tank 20 is attached at a position covering a part of the outside of the cover member 30 on the opposite side (+Z direction side) to the nozzle opening surface 100a side (ejection surface side) of the ejection operation unit 10. The liquid storage tank 20 has a supply port 21 (inlet) for ink supplied from an external ink tank or the like, a main body portion 20a provided with a liquid storage portion 23 (see FIG. 4) that stores (retains) the supplied ink (liquid), an outlet 25 that allows ink to flow from the liquid storage portion 23 to the ejection operation unit 10, an inlet 26 through which ink discharged from the ejection operation unit 10 flows in, and an outlet 28 (outlet) that discharges the discharged ink to the outside.

[0029] Inside the liquid storage tank 20, there are provided an ink flow path that connects from the supply port 21 through the liquid storage section 23 to the outlet 25 and passes ink to be supplied to the ejection section 10, and an ink flow path that connects from the inlet 26 to the outlet 28 and passes ink to be discharged from the ejection section 10. The outlet 25 is connected to the ink inlet 11 of the ejection section 10, and the inlet 26 is connected to the ink outlet 17 of the ejection section 10. As a result, in the droplet ejection head 100, the ink flow path (liquid flow path) from the supply port 21 to the outlet 28 of the liquid storage tank 20 is continuous. The outlet 25 and the inlet 26 are provided in legs protruding from the main body section 20a. The liquid storage tank 20 is removably fixed by screwing these legs to the ejection section 10 with screws S.

[0030] The liquid storage tank 20 is long in the Y direction and thin in the X direction when viewed from the top side (the side overlooking the supply port 21 and the discharge port 28), that is, in a plan view (viewed from the +Z direction) here. The supply port 21 and the discharge port 28 are arranged separately near both ends in the longitudinal direction (Y direction) of the liquid storage tank 20. Similarly, the outlet 25 and the inlet 26 are arranged separately near both ends in the longitudinal direction (Y direction) of the liquid storage tank 20. Hereinafter, the upper part and the upper end mean the highest position in the +Z direction (the position with the largest Z coordinate), and the lower part and the lower end mean the lowest position in the +Z direction (the position with the smallest Z coordinate).

[0031] FIG. 4 is a cross-sectional perspective view of the inside of the main body 20a of the liquid storage tank 20 as viewed from the bottom side. Also, FIGS. 5A, 5B, 6A to 6E, and 7 are cross-sectional views for explaining the ink flow paths of the droplet ejection head 100. FIGS. 5A and 5B are cross-sectional views in a plane parallel to the YZ plane, and in FIG. 5A, the cross-section is taken along a plane including the liquid storage portion 23 (rear chamber 23b), while in FIG. 5B, the cross-section is taken along a plane including the supply port 21, the discharge port 28, and the nozzle N. FIGS. 6A to 6E are cross-sectional views in a plane parallel to the XZ plane at the positions of the cross-sectional lines AA to EE in FIGS. 5A and 5B, respectively. FIG. 7 is an enlarged view showing the vicinity of the nozzle N in FIG. 6B.

[0032] The liquid storage section 23, which is provided in the main body 20a of the liquid storage tank 20 and stores ink, is divided into a front chamber 23a and a rear chamber 23b by a filter 231 provided therein (FIGS. 4, 6B, and 6C). The filter 231 captures air bubbles and foreign matter (impurities) in the ink that flows from the front chamber 23a to the rear chamber 23b. Here, the filter 231 is provided in a plane parallel to the YZ plane, i.e., perpendicular to the horizontal plane, and extends in the longitudinal direction.

[0033] The filter 231 may be, for example, a plate-like member made of resin or metal with many fine through-holes that allow ink to pass through (hereinafter referred to as a "through-hole filter"), or a filter having three-dimensional fine internal flow paths through which liquid can pass (hereinafter referred to as a "porous plate filter"). Examples of the porous plate filter include filters in which metal fibers are woven three-dimensionally, and porous members produced by sintering resin particles such as polyethylene resin.

[0034] In this embodiment, the filter 231 has a mesh diameter smaller than the opening diameter of the nozzle N (the diameter of the circle formed by the opening of the nozzle N). When filter 231 is a through-hole filter, the mesh size of filter 231 is the diameter of the through-holes. When filter 231 is a porous plate filter, the mesh size of filter 231 is the particle size indicated as the absolute filtration accuracy of filter 231 (if no indication is given, the particle size corresponding to the absolute filtration accuracy). Here, the absolute filtration accuracy is the minimum value of X that satisfies the condition that filter 231 can capture 99.9% or more of particles of particle size X.

[0035] The supply port 21 and the front chamber 23a are connected by a first supply path 22 (FIGS. 4, 5A, 5B, 6A), and ink supplied from the outside flows into the front chamber 23a. An opening end 232 where the first supply path 22 connects to the front chamber 23a is provided at the bottom of the end of the front chamber 23a that is closer to the supply port 21 in the Y direction (FIGS. 4, 5A). The rear chamber 23b and the outlet 25 are connected by a second supply path 24 (FIGS. 4, 5A, 5B, 6A, 6C), and ink supplied from the rear chamber 23b to the ejection section 10 flows out. An opening end 233 where the second supply path 24 connects to the rear chamber 23b is provided at the top of the end of the rear chamber 23b that is closer to the discharge port 28 (discharge path 27) in the Y direction (FIGS. 5A, 6C).

[0036] Opening end 232 and opening end 233 are provided at diagonal positions in liquid storage section 23 (FIG. 5A). This allows ink flowing in from opening end 232 to easily pass through filter 231 over a wide range of liquid storage section 23, preventing ink from stagnating in the remaining portion. A diagonal position here means that the opening is provided so as to include a diagonal vertex, and the opening may be provided on any of the three faces that make up that vertex (it may span more than one of these three faces).

[0037] Here, the supply port 21 and the outlet 25 are provided on the same side in the Y direction, opposite to the inlet 26 and the outlet 28 (discharge path 27) (here, the +Y side), and the opening end 233 is provided on the opposite side in the Y direction from the supply port 21 and the outlet 25 (FIGS. 5A, 6B). The opening end 233 (the connection end to the rear chamber 23b) is provided across the width of the rear chamber 23b in the direction perpendicular to the Y direction (X direction) in the XY plane (i.e., the plane parallel to the discharge surface) (FIG. 6C). The second supply path 24 extends from the opening end 233 above the rear chamber 23b (+Z direction side) in the Y direction, then bends downward, and enters below the first supply path (-Z direction side) to be connected to the outlet 25 (FIGS. 5A, 5B, 6A). At this time, the second supply path 24 and the common ink chamber 12 are determined to have an appropriate diameter so as to obtain a flow speed that can advance the air bubbles in the downward ink flow direction against buoyancy in the portion where the ink flows downward.

[0038] The inlet 26 and the outlet 28 are located on the same side in the Y direction, opposite the supply port 21 and the outlet 25 (here, the -Y side), and the inlet 26 and the outlet 28 are connected by a discharge path 27 extending in the Z direction (Figures 5A, 5B, and 6E).

[0039] A plurality of inlets 26 (two in this example) are provided to match the plurality of ink outlets 17a, 17b (FIG. 6E). Ink discharge paths 27a, 27b connected to the two inlets 26a, 26b respectively join together inside the liquid storage tank 20 and communicate with a single discharge port 28.

[0040] A check valve 271 is provided between the junction of the discharge paths 27a and 27b in the discharge path 27 and the discharge port 28 (Figures 5B and 6E) to prevent ink from flowing back from the discharge port 28 into the ejection section 10.

[0041] The front chamber 23a and the discharge channel 27 are connected by a communication channel 29 (FIGS. 5A, 5B, 6C, and 6D). That is, the communication channel 29 branches from the upstream side (front chamber 23a) of the filter 231 in the ink sending direction in the liquid storage section 23 and communicates with the discharge channel 27. The communication channel 29 functions as a deaeration channel that guides air bubbles (air) that do not pass through the filter 231 from the front chamber 23a to the discharge channel 27 and discharges them. The communication channel 29 extends in the -Y direction from the opening end 234 of the front chamber 23a, and then bends in the +Z direction, X direction, and -Y direction in this order to reach the discharge channel 27. Here, the opening of the communication channel 29 on the discharge channel 27 side is between the inlet 26 and the check valve 271. The opening end 234 of the communication channel 29 on the front chamber 23a side is provided at the upper part of the front chamber 23a, at the end closer to the discharge channel 27 in the Y direction. This makes it easier for air bubbles to flow into the communication flow path 29 due to buoyancy.

[0042] The ejection operation unit 10 comprises an ink manifold 16 having an ink inlet 11 and an ink outlet 17 (17a, 17b), and a head chip 15 fixed to the lower surface (the surface on the -Z direction side) of the ink manifold 16 (Figures 5A and 5B).

[0043] The ink manifold 16 is provided with a common ink chamber 12 that communicates with the ink inlet 11 and the ink outlet 17a (FIGS. 5B and 6E). The common ink chamber 12 is provided parallel to the nozzle opening surface 100a and extends in the Y direction. In other words, the common ink chamber 12 extends parallel to the longitudinal direction of the liquid storage section 23. The ink inlet 11 and the common ink chamber 12 are connected by a common supply flow path 13, and the common ink chamber 12 and the ink outlet 17a are connected by a first common discharge flow path 14.

[0044] The ink manifold 16 is also provided with a second common discharge flow path 18 separated from the common ink chamber 12 (FIGS. 6B to 6E, 7). The second common discharge flow path 18 is provided parallel to the nozzle opening surface 100a and extends in the Y direction. That is, the second common discharge flow path 18 extends parallel to the common ink chamber 12. The second common discharge flow path 18 is bent in the +Z direction at the end on the ink outlet 17 side (-Y direction side) of the ejection operation section 10, and the end becomes an ink outlet 17b (FIG. 6E). This ink outlet 17b is connected to the ink inlet 26b described above.

[0045] Head chip 15 includes nozzles N, ink channels 151 communicating with nozzles N, and individual discharge channels 152 branching off from ink channels 151 (FIGS. 5A, 5B, 6B, and 7). The configuration of head chip 15 will be described below with reference to FIG. 7.

[0046] The head chip 15 has a configuration in which a nozzle plate 15a, a flow path substrate 15b, and a pressure chamber substrate 15c are laminated in the Z direction. The nozzle plate 15a is a plate-like member having through holes that become nozzles N. The nozzles N in this embodiment have a straight portion Ns and a tapered portion Nt. The straight portion Ns is a cylindrical, i.e. straight-shaped portion that is provided within a predetermined range in the Z direction from the opening (ejection port) of the nozzle N. The tapered portion Nt is connected to the end of the straight portion Ns on the +Z direction side, and the cross-sectional area perpendicular to the ink ejection direction (Z direction) becomes smaller the closer it is to the opening of the nozzle N (i.e., the closer it is to the straight portion Ns).

[0047] The meniscus m (liquid surface) of the ink inside the nozzle N (straight portion Ns in this case) is slightly pulled inward toward the inside of the nozzle N, i.e., is convex upward in FIG. 7. This is because the pressure inside the nozzle N is adjusted to be slightly negative relative to atmospheric pressure. This prevents ink from dripping unintentionally when ink is not being ejected. Hereinafter, the pressure obtained by subtracting the pressure inside the nozzle N from the atmospheric pressure will be referred to as the meniscus pressure of the nozzle. As the pressure inside nozzle N is reduced, the meniscus m breaks at a certain pressure, and air bubbles get into the nozzle N. The meniscus pressure of the nozzle when the meniscus m breaks is referred to as the second meniscus break pressure (meniscus break pressure of nozzle N). If the second meniscus break pressure is P2 [Pa], the opening diameter of nozzle N is dn [m], and the surface tension of the ink is σ [N / m], then the relationship P2 = 4σ / dn holds.

[0048] In the flow path substrate 15b and the pressure chamber substrate 15c, ink channels 151 and individual discharge flow paths 152 are formed. One ink channel 151 is provided for each nozzle N. The ink channel 151 penetrates the flow path substrate 15b and the pressure chamber substrate 15c in the Z direction, with an upper end communicating with the lower surface of the common ink chamber 12 and a lower end communicating with one nozzle N. Ink supplied to the common ink chamber 12 is supplied to the nozzle N via this ink channel 151.

[0049] The material of the pressure chamber substrate 15c constituting a part of the wall surface of the ink channel 151 is a ceramic piezoelectric body (a member that deforms in response to the application of a voltage). Examples of such piezoelectric bodies include PZT (lead zirconate titanate), lithium niobate, barium titanate, lead titanate, lead metaniobate, and the like. In addition, a driving electrode (not shown) is provided on the inner wall surface of the pressure chamber substrate 15c. In response to the application of a driving signal from the above-mentioned circuit unit to the driving electrode, the side wall separating the adjacent ink channels 151 undergoes a shear mode type displacement, and the pressure of the ink in the ink channel 151 fluctuates. In response to this pressure fluctuation, the ink in the ink channel 151 is ejected from the nozzle N. In this way, the droplet ejection head 100 of this embodiment ejects ink in a shear mode type. The side wall of the ink channel 151 and the driving electrode constitute the above-mentioned pressure fluctuation means. 5B, air chambers without an ink inflow path may be provided instead of the ink channels 151 at positions where every other ink channel 151 is formed in the Y direction. With this configuration, when the partition wall of an ink channel 151 is deformed, the deformation does not affect other ink channels 151.

[0050] The individual discharge flow path 152 has a horizontal portion 152a that branches off from the end of the ink channel 151 on the nozzle N side and extends in the -X direction, and a vertical portion 152b that bends in the +Z direction from the end of the horizontal portion 152a and communicates with the second common discharge flow path 18. One individual discharge flow path 152 is provided for one ink channel 151. The horizontal portion 152a of the individual discharge flow path 152 is a groove provided on the surface on the -Z direction side of the plate-shaped flow path substrate 15b, and the vertical portion 152b is a through hole provided in the flow path substrate 15b and the pressure chamber substrate 15c. The horizontal portion 152a of the individual discharge flow path 152 is not limited to a groove provided in the flow path substrate 15b, and may penetrate the flow path substrate 15b, or may be a groove provided in the nozzle plate 15a. In addition, the connection position of the individual discharge flow path 152 in the ink channel 151 is not limited to the end on the nozzle N side, and the individual discharge flow path 152 can branch off from any position of the ink channel 151.

[0051] The individual discharge flow paths 152 guide the ink that has been supplied to the ink channels 151 but has not been ejected from the nozzles N to the second common discharge flow path 18. This flow of ink also ejects minute air bubbles 62 and foreign matter in the ink channels 151 to the second common discharge flow path 18. The ink ejected to the second common discharge flow path 18 passes through the ink outlet 17b, the ink inlet 26b, and the discharge path 27, and is then ejected from the discharge port 28.

[0052] Of the components of the droplet ejection head 100 described above, the supply port 21, the first supply path 22, the liquid storage section 23, the second supply path 24, the common supply flow path 13, the common ink chamber 12, and the ink channel 151 form a supply flow path 101 (see FIG. 10) through which ink passes to be supplied to the nozzle. Therefore, the ink passing through this supply flow path 101 passes through the filter 231. Further, a discharge flow path 102 (see FIG. 10) through which ink that is discharged without being ejected from the nozzle passes is configured by the first common discharge flow path 14, the individual discharge flow paths 152, the second common discharge flow path 18, the discharge paths 27 (27a, 27b), and the discharge ports 28. The communication flow path 29 communicates the supply flow path 101 and the discharge flow path 102.

[0053] The ink flow from the supply port 21 of the droplet ejection head 100 through the supply flow path 101 and the discharge flow path 102 to the discharge port 28 can be generated by an ink circulation mechanism 9 that the droplet ejection device 1 has.

[0054] FIG. 8 is a schematic diagram showing the configuration of the ink circulation mechanism 9. As shown in FIG. The ink circulation mechanism 9 includes a supply sub-tank 91, a return sub-tank 92, a main tank 93, ink flow paths 94 to 97, pumps 98 and 99, and the like. The supply sub-tank 91 stores ink to be supplied to the droplet ejection head 100. The supply sub-tank 91 is connected to the supply port 21 by an ink flow path 94. The reflux sub-tank 92 is connected to the discharge port 28 by an ink flow path 95, and stores the ink discharged from the discharge port 28. The supply sub-tank 91 and the return sub-tank 92 are connected by an ink flow path 96. Ink can be returned from the return sub-tank 92 to the supply sub-tank 91 by a pump 98 provided in the ink flow path 96. The main tank 93 stores ink to be supplied to the supply subtank 91. The main tank 93 is connected to the supply subtank 91 by an ink flow path 97. In addition, ink is supplied from the main tank 93 to the supply subtank 91 by a pump 99 provided in the ink flow path 97.

[0055] The supply sub-tank 91 is provided at a position where its liquid level is higher than the nozzle opening surface 100a of the ejection operation unit 10 by a height H1. The return sub-tank 92 is provided at a position where its liquid level is lower than the nozzle opening surface 100a by a height H2. As a result, when the pressure inside the nozzle N (≈atmospheric pressure) is taken as the reference pressure, the pressure at the supply port 21 is a positive pressure Pin with respect to the reference pressure due to the head difference, and the pressure at the discharge port 28 is a negative pressure Pout with respect to the reference pressure due to the head difference. Due to the pressure difference between the pressure Pin and the pressure Pout, a flow of ink is generated from the supply port 21 through the supply flow path 101 and the discharge flow path 102 toward the discharge port 28. By changing the position of the liquid level in each sub-tank, the pressure Pin and the pressure Pout can be adjusted, and the flow rate of ink can be adjusted. The ink circulation mechanism 9 corresponds to a "liquid delivery section." Moreover, the operation of the ink circulation mechanism 9 for moving the ink through the supply flow path 101 and the discharge flow path 102 corresponds to a "liquid delivery operation." Here, the liquid delivery operation includes the operation of pumping up the ink by the pumps 98 and 99.

[0056] FIG. 9 is a block diagram showing the main functional configuration of the droplet ejection device 1. As shown in FIG. The droplet ejection device 1 includes the head unit 3, a control unit 40, a transport drive unit 51, a communication unit 52, and the like, and these units are connected via a bus 53. Of these, the head unit 3 includes a head drive unit 200 and a droplet ejection head 100. In addition, the control unit 40 includes a CPU 41 (Central Processing Unit), a RAM 42 (Random Access Memory), a ROM 43 (Read Only Memory), and a storage unit 44.

[0057] The CPU 41 reads out various control programs and setting data stored in the ROM 43, stores them in the RAM 42, and executes the programs to perform various arithmetic processing. The CPU 41 also performs overall control of the overall operation of the droplet ejection device 1.

[0058] The RAM 42 provides a working memory space for the CPU 41 and stores temporary data. The RAM 42 may include a non-volatile memory.

[0059] The ROM 43 stores various control programs and setting data executed by the CPU 41. Note that the ROM 43 may be replaced with a rewritable non-volatile memory such as an EEPROM (Electrically Erasable Programmable Read Only Memory) or a flash memory.

[0060] The storage unit 44 stores a print job and image data related to the print job input from an external device via the communication unit 52. As the storage unit 44, for example, a HDD (Hard Disk Drive) or the like is used.

[0061] The head driving unit 200 supplies various control signals and image data to the circuit unit of the droplet ejection head 100 at appropriate timing based on a control signal from the control unit 40 .

[0062] The ink circulation mechanism 9 operates the pumps 98 and 99 based on a control signal from the control unit 40 to perform the above-mentioned liquid delivery operation.

[0063] Based on a control signal supplied from the CPU 41, the transport drive unit 51 supplies a drive signal to a motor that drives the transport rollers 2a, 2b of the transport unit 2, causing the transport rollers 2a, 2b to rotate at a predetermined speed and timing, and causing the transport belt 2c to move in a circular motion.

[0064] The communication unit 52 is a communication interface that controls communication operations with external devices. The communication interface may include one or more interfaces that support various communication protocols, such as a LAN board or a LAN card. The communication unit 52 acquires image data to be recorded and setting data (job data) related to image recording from the external device under the control of the control unit 40, and also transmits status information and the like to the external device.

[0065] <Operation of the droplet ejection device> Next, the operation of the droplet ejection device 1 will be described, focusing on the operation related to the circulation of ink. FIG. 10 is a diagram showing a schematic diagram of the ink flow path in the droplet ejection head 100. As shown in FIG. 10, a pressure difference between the pressure Pin of the supply port 21 and the pressure Pout of the discharge port 28 causes an ink flow from the supply port 21 through the front chamber 23a, the rear chamber 23b, the second supply path 24, the common supply flow path 13, the common ink chamber 12, the first common discharge flow path 14, and the discharge path 27 to the discharge port 28. The above pressure difference also causes an ink flow from the common ink chamber 12 through the ink channel 151, the individual discharge flow paths 152, and the second common discharge flow path 18 to the discharge path 27. The above pressure difference also causes an ink flow from the front chamber 23a of the liquid storage unit 23 through the communicating flow path 29 to the discharge path 27.

[0066] Among these, the flow rate of ink that flows through the first common discharge flow path 14, the second common discharge flow path 18, and the communicating flow path 29 into the discharge path 27 and is discharged from the discharge port 28 is referred to as the circulating flow rate hereinafter. The circulating flow rate is constant regardless of the ink discharge status (discharge amount) from the nozzle N.

[0067] The amount of ink discharged from the nozzle N increases or decreases depending on the content of the image to be formed. In response to the ink discharged from the nozzle N, the amount of ink discharged is supplied to the common ink chamber 12. Therefore, the greater the amount of ink discharged per unit time from the nozzle N, the greater the flow rate of ink in the supply flow path 101, i.e., the flow rate of ink passing through the filter 231. Hereinafter, of the ink flow rates in the supply flow path 101, the flow rate equivalent to the maximum amount of ink discharged from the nozzle N per unit time is referred to as the maximum discharge flow rate. Therefore, the maximum flow rate of ink passing through the supply flow path 101 is the sum of the maximum discharge flow rate and the circulation flow rate.

[0068] In general, the flow rate of ink flowing through a channel is Q [m 3 / s], the pressure difference (differential pressure) between both ends of the flow path is ΔP [Pa], and the flow path resistance is R [Pa s / m3 ], the relationship Q = ΔP / R holds. Also, if the flow path is a circular pipe and the ink flow is laminar, the following Hagen-Poiseuille equation holds. R = (128 μ L) / (π d 4 ) Here, μ [Pa s] is the viscosity of the ink, L [m] is the length of the flow path, and d [m] is the diameter of the flow path.

[0069] In the front chamber 23a, air bubbles 61 larger than the mesh diameter of the filter 231 are captured and retained by the filter 231. These air bubbles 61 may include those that flow in from the supply port 21, as well as those that are formed when gas dissolved in the ink turns into bubbles due to pressure changes, temperature changes, etc. The air bubbles 61 are guided to the discharge path 27 through the communicating flow path 29 together with the ink, and are discharged from the discharge port 28.

[0070] When the pressure loss in the filter 231, i.e., the pressure difference between the front chamber 23a and the rear chamber 23b, exceeds a certain pressure, the liquid surface (meniscus) of the air bubble 61 breaks and breaks into smaller bubbles. The pressure difference at this time is referred to as the first meniscus break pressure (meniscus break pressure of the filter). When the filter 231 is a through-hole filter, the first meniscus break pressure P1 [Pa] can be calculated using the relation P1=4σ / dt, where dt [m] is the opening diameter of the through-hole of the filter 231 and σ [N / m] is the surface tension of the ink. Furthermore, when the filter 231 is a porous plate filter, the first meniscus break pressure P1 [Pa] can be found from the relational expression P1=4σ / da, where da is the value of the absolute filtration accuracy. Alternatively, the first meniscus break pressure can be found experimentally as follows. That is, when the rear chamber 23b of the filter 231 is filled with liquid and the front chamber 23a is filled with air, and the front chamber 23a is pressurized, the pressure in the front chamber 23a at which the filter 231 breaks into a meniscus is measured, and the result is determined as the first meniscus break pressure. Here, the meniscus break of the filter 231 refers to the start of air bubbles penetrating (passing) into the rear chamber 23b.

[0071] In the phenomenon in which an air bubble 61 trapped by the filter 231 undergoes meniscus break (is broken) and passes through the filter 231, the air bubble after passing through the filter 231 may become larger than the mesh diameter of the filter 231. This is because, in this phenomenon, an air bubble larger than the mesh diameter deforms and passes through the mesh of the filter 231, or multiple air bubbles coalesce after passing through the filter 231. If an air bubble larger than the mesh diameter after passing through the filter 231 enters the ink channel 151 from the rear chamber 23b, this may cause ink ejection problems. Therefore, the ink circulation mechanism 9 as the liquid sending section of this embodiment performs the liquid sending operation in a manner that satisfies the condition that the air bubble 61 does not break in the filter 231. In other words, the ink circulation mechanism 9 performs the liquid sending operation in a manner that satisfies the condition that "the pressure loss in the filter 231 is smaller than the first meniscus break pressure at which the meniscus of the liquid breaks in the filter 231" (hereinafter referred to as the first condition). The pressure Pin of the supply port 21 and the pressure Pout of the discharge port 28 are adjusted so that such a first condition is satisfied. As a result, the air bubble 61 remains in the front chamber 23a without breaking, and is discharged from the communication flow path 29. Note that the first condition may be satisfied by adjusting the circulating flow rate of the ink instead of (or in addition to) adjusting the pressures Pin and Pout. The circulating flow rate of the ink can be adjusted by the shape of the flow path, the area of ​​the filter 231, etc.

[0072] Furthermore, when the increase or decrease in pressure loss in the filter 231 becomes equal to or greater than the second meniscus break pressure, a pressure fluctuation equivalent to the increase or decrease occurs in the meniscus m of the nozzle N, causing the meniscus m to break and air bubbles to flow into the nozzle N. Here, the increase or decrease in pressure loss that can occur in the filter 231 corresponds to the difference between the pressure loss when the amount of ink ejected per unit time from the nozzle N is 0 and the pressure loss when the amount of ink ejected per unit time is maximum. Therefore, the increase or decrease in pressure loss in the filter 231 is equal to the pressure loss occurring in the filter 231 due to the ink at the maximum ejection flow rate described above. Therefore, the droplet ejection device 1 of this embodiment is configured to satisfy the condition that "the pressure loss caused in the filter 231 by the ink at the maximum ejection flow rate is smaller than the second meniscus break pressure" (hereinafter referred to as the second condition). That is, the area and mesh diameter of the filter 231 are determined so that the second condition is satisfied. Moreover, the ink circulation mechanism 9 performs the liquid delivery operation in such a manner that the second condition is satisfied.

[0073] Incidentally, some of the air bubbles present in the front chamber 23a are originally smaller than the mesh diameter of the filter 231. Air bubbles 62 of this size can pass through the filter 231 and can flow into the rear chamber 23b, as shown in Fig. 10. Some of the air bubbles 62 that flow into the rear chamber 23b are discharged from the discharge port 28 together with the ink via the second supply path 24, the common supply flow path 13, the common ink chamber 12, the first common discharge flow path 14, and the discharge path 27. The remaining part of the air bubbles 62 flows from the common ink chamber 12 into the ink channel 151, and then flows into the discharge path 27 via the individual discharge flow paths 152 and the second common discharge flow path 18.

[0074] 7, in the ink channel 151, the ink flows vertically downward (in the -Z direction). That is, the ink channel 151, which is part of the supply flow path 101, corresponds to a descending portion in which the liquid sending direction has a vertically downward component. The ink circulation mechanism 9 performs a liquid sending operation in such a manner that the vertically downward component of the ink velocity in the ink channel 151 is greater than the velocity at which the air bubble 62 rises due to buoyancy. This causes the air bubble 62 to flow downward in the ink channel 151. 5A, the portion of the second supply path 24 where the ink flows downward also corresponds to the above-mentioned descending portion. The ink circulation mechanism 9 performs the liquid sending operation in such a manner that the vertically downward component of the ink velocity in that portion is greater than the velocity at which the air bubbles 62 rise due to buoyancy, so that the air bubbles 62 flow downward in that portion of the second supply path 24. As a result, the air bubbles 62 flow downward in the above-mentioned portion of the second supply path 24. The descending portion is not limited to one extending in the vertical direction, but includes any portion in which the liquid transfer direction has a vertically downward component.

[0075] 7, the flow path of the air bubble 62 includes the ink channel 151, but even if an air bubble 62 large enough to pass through the filter 231 flows into the ink channel 151, it is unlikely to lead to poor ink ejection from the nozzle N. This is because the mesh diameter of the filter 231 is smaller than the opening diameter of the nozzle N, and therefore the air bubble 62 is smaller than the opening diameter of the nozzle N. Generally, air bubbles in the ink channel 151 cause ejection defects because the air bubbles absorb the pressure waves generated in the ink channel 151 by the pressure fluctuation means. Here, the smaller the opening diameter of the nozzle N, the greater the energy required to eject ink, and so small air bubbles are more likely to lead to ejection defects. More specifically, simulation results show that ejection defects occur when the size of the air bubbles is equal to or larger than the opening diameter of the nozzle N, and ejection defects are unlikely to occur when the air bubbles are smaller than the opening diameter of the nozzle N.

[0076] Thus, in the droplet ejection head 100 of this embodiment, even if an air bubble 62 smaller than the opening diameter of the nozzle N flows into the ink channel 151, ejection defects due to the air bubble 62 are unlikely to occur. By utilizing this, it is possible to reduce the pressure loss of the entire droplet ejection head 100 while suppressing the occurrence of ejection defects by increasing the mesh diameter of the filter 231 to a certain extent. From this perspective, the mesh diameter of the filter 231 is preferably, for example, ⅓ or more of the opening diameter of the nozzle N, and more preferably ½ or more of the opening diameter of the nozzle N.

[0077] <Effects> As described above, the droplet ejection device 1 according to this embodiment includes the droplet ejection head 100 and the ink circulation mechanism 9 as a liquid sending section. The droplet ejection head 100 includes a nozzle N for ejecting ink, a supply flow path 101 through which ink supplied to the nozzle N passes, a discharge flow path 102 that communicates with the supply flow path 101 and through which ink that is not ejected from the nozzle N but is discharged passes, a filter 231 that is provided in the supply flow path 101 and through which the ink passing through the supply flow path 101 passes, and a communication flow path 29 that branches off from the upstream side of the filter 231 in the ink sending direction of the supply flow path 101 and communicates with the discharge flow path 102. The mesh diameter of the filter 231 is smaller than the opening diameter of the nozzle N, and the ink circulation mechanism 9 performs a liquid sending operation in a mode in which the pressure loss in the filter 231 is smaller than a first meniscus break pressure at which the meniscus of the ink breaks in the filter 231. This allows air bubbles having a size at least equal to or larger than the opening diameter of the nozzle N to be captured by the filter 231, and allows the air bubbles to be discharged to the outside via the communication flow path 29 and the discharge flow path . In addition, because the pressure loss in the filter 231 can be made smaller than the first meniscus break pressure, the air bubbles trapped in the filter 231 are less likely to break. Therefore, the trapped air bubbles can be efficiently discharged from the communication flow path 29, and ink ejection defects caused by air bubbles breaking and flowing into the ink channel 151 can be suppressed. Also, by allowing some of the bubbles smaller than the opening diameter of the nozzle N (bubbles 62 smaller than the mesh diameter of the filter 231) to pass through the filter 231, it is possible to reduce the flow path resistance of the supply flow path 101. This makes it possible to suppress the pressure loss of the entire droplet ejection head 100, i.e., the difference between the ink pressure at the supply port 21 and the ink pressure at the nozzle N, while suppressing large bubbles (bubbles larger than the opening diameter of the nozzle N) that may lead to ejection defects from flowing into the ink channel 151 and discharging them to the outside.

[0078] Furthermore, when the flow rate of ink in the supply flow path 101 is defined as the flow rate equivalent to the maximum amount of ink ejected from the nozzle N per unit time, the pressure loss caused in the filter 231 by the ink at the maximum ejection flow rate is smaller than the second meniscus break pressure at which the ink meniscus breaks in the nozzle N. As a result, even if the amount of ink discharged from the nozzle N varies, it is possible to prevent the meniscus m of the nozzle N from being destroyed due to the variation. Therefore, it is possible to prevent discharge defects caused by air bubbles flowing in from the nozzle N.

[0079] In addition, the supply flow path 101 has an ink channel 151 as a descending portion in which the liquid transport direction has a vertical downward component, and the ink circulation mechanism 9 performs a liquid transport operation in such a manner that the vertical downward component of the ink velocity in the ink channel 151 is greater than the speed at which an air bubble 62 smaller than the opening diameter of the nozzle N rises due to buoyancy. This allows the air bubbles in the ink channel 151 to flow downward against buoyancy and be discharged from the individual discharge flow path 152.

[0080] Further, the nozzle N has a tapered portion Nt whose cross-sectional area perpendicular to the ink ejection direction becomes smaller as it approaches the opening of the nozzle N. By providing the tapered portion Nt in the nozzle N, it is possible to reduce the energy required for ejecting ink, thereby making it possible to make ejection defects caused by the inflow of air bubbles into the ink channel 151 less likely to occur.

[0081] Moreover, in this embodiment, water-based ink is used. Water-based ink has a tendency for dissolved gas to turn into bubbles at high pressure compared to solvent ink, and air bubbles are easily generated by cavitation (a negative pressure state in the ink channel 151 after ink is ejected). For this reason, when water-based ink is applied to the droplet ejection device 1 of this embodiment, the occurrence of problems due to air bubbles can be effectively suppressed.

[0082] In addition, the liquid feed direction in this embodiment includes a liquid feed step in which the ink in the supply flow path 101 and the discharge flow path 102 is caused to flow in the liquid feed direction, and in this liquid feed step, the ink is caused to flow in such a manner that the pressure loss in the filter 231 is smaller than the first meniscus break pressure at which the ink meniscus breaks in the filter 231. This makes it possible to suppress large air bubbles that may lead to ejection defects from entering the ink channel 151 and to expel them to the outside, while keeping the pressure loss in the entire droplet ejection head 100 small.

[0083] <Example> Next, an experiment conducted to confirm the effects of the above embodiment will be described. FIG. 11 shows the details and results of the experiment. A total of 11 types of experiments were conducted: Experiment 1 to Experiment 11. In each experiment, at least some of the mesh diameter, opening rate, and area of ​​the filter 231, the opening diameter of the nozzle N, and the maximum discharge flow rate were made different from one another. Among these, the mesh diameter, opening rate, and area of ​​the filter 231 were changed to adjust the levels of the filter's flow resistance, pressure loss (a1), pressure loss (a2), and first meniscus break pressure (b) (referred to as "MB pressure" in the table). Here, the pressure loss (a1) is the pressure loss caused by ink at the maximum flow rate, which is the sum of the circulation flow rate and the maximum ejection flow rate, and the pressure loss (a2) is the pressure loss caused by ink at the maximum ejection flow rate among these. The pressure losses (a1) and (a2) were calculated from the calculated values ​​of the flow resistance. In addition, a porous plate filter was used as the filter 231, and the first meniscus break pressure (b) was calculated by calculation. In addition, the opening diameter of the nozzle N was changed between two levels, 40 [μm] and 20 [μm], to adjust the level of the second meniscus break pressure (c). In addition, the ink circulation flow rate was set to two levels, 90 [ml / min] and 20 [ml / min], and the maximum ejection flow rate was set to two levels, 80 and 60 [ml / min].By combining these, the maximum flow rate, which is the combined circulation flow rate and maximum ejection flow rate, was set to three levels, 170 [ml / min], 150 [ml / min], and 80 [ml / min]. The parameters common to Experiments 1 to 11 are as follows. Filter thickness: 100[μm] Ink viscosity: 0.01 [Pa s] Ink surface tension: 30 [mN / m] Taper angle of nozzle N: 8 degrees Ink type: Water-based ink

[0084] In each experiment, continuous ejection was performed for 10 minutes at the maximum ejection amount from nozzle N, and the presence or absence of a missing defect due to non-ejection of ink from nozzle N was determined. In the "Continuous ejection evaluation results" in Fig. 11, "○" indicates that a missing defect did not occur, and "×" indicates that a missing defect occurred. Missing defects in the continuous ejection evaluation are mainly caused by air bubbles 61 in the front chamber 23a breaking and small air bubbles 62 flowing into the ink channel 151.

[0085] In each experiment, intermittent ejection was performed for 10 minutes by switching the ejection volume from nozzle N between minimum (OFF) and maximum (ON) at 0.5 second intervals, and the presence or absence of a defect due to non-ejection of ink from nozzle N was determined. In the "Intermittent ejection evaluation results" in Figure 11, "○" indicates that no defect occurred, and "×" indicates that a defect occurred. Defects due to the intermittent ejection evaluation are mainly caused by the destruction of the meniscus m of nozzle N due to fluctuations in pressure loss.

[0086] As a result of the experiment, in Experiments 2 to 4, 6, 7, and 9 to 11, which satisfied the condition that "the pressure loss (a1) of the filter 231 is smaller than the first meniscus break pressure (b)" (corresponding to the first condition described above), the continuous discharge evaluation result was "○". In addition, in Experiments 1, 5, and 8, which did not satisfy the first condition, the continuous discharge evaluation result was "×". In addition, in Experiments 2 to 4, 6, 7, 10, and 11, which satisfied the condition that "the pressure loss (a2) caused in the filter 231 by the ink at the maximum discharge flow rate is smaller than the second meniscus break pressure (c)" (corresponding to the second condition described above), the intermittent discharge evaluation result was "○". In Experiments 1, 5, 8, and 9, which did not satisfy the second condition, the intermittent discharge evaluation result was "×".

[0087] <Modification> Next, a modification of the droplet ejection device 1 will be described. FIG. 12 is a cross-sectional view illustrating an ink flow path of a droplet ejection head 100 according to a modified example. In the droplet ejection head 100 of this modified example, the common ink chamber 12 has an upper layer 12a and a lower layer 12b located on the -Z direction side of the upper layer 12a. The upper layer 12a and the lower layer 12b are separated by a filter 231 parallel to the XY plane. In this manner, the filter 231 may be provided outside the liquid storage tank 20.

[0088] The upper layer 12a is connected to the first common discharge flow passage 14, the inlet 26a, and the discharge passage 27a. The lower layer 12b is connected to an inlet 26c provided separately from the inlets 26a and 26b, and is connected to a discharge passage 27c provided separately from the discharge passages 27a and 27b. The discharge passage 27c merges with the discharge passages 27a and 27b and is connected to a discharge port 28.

[0089] The ink that has passed through the common supply flow path 13 from the ink inlet 11 first flows into the upper layer 12a of the common ink chamber 12. A portion of the ink in the upper layer 12a, together with air bubbles and foreign matter, passes through the first common discharge flow path 14, the ink inlet 26a, and the discharge path 27a and is discharged from the discharge port 28. In this modification, the section from the first common discharge flow path 14 to the discharge path 27a corresponds to a "communicating flow path" and functions as a deaeration path.

[0090] Also, a portion of the ink in the upper layer 12a passes through the filter 231 and flows into the lower layer 12b. A portion of the ink in the lower layer 12b flows into the ink channel 151, a portion of which is ejected from the nozzle N, and the remainder passes through the individual discharge flow path 152, the second common discharge flow path 18, the inlet 26b, and the discharge path 27b and is discharged from the discharge port 28. Also, the ink in the lower layer 12b that does not flow into the ink channel 151 passes through the inlet 26c and the discharge path 27c and is discharged from the discharge port 28.

[0091] With the configuration of this modified example as well, it is possible to suppress the pressure loss in the entire droplet ejection head 100, while suppressing large air bubbles that may lead to ejection defects from entering the ink channel 151 and discharging them to the outside.

[0092] <Other> The present invention is not limited to the above-described embodiment and modifications, and various changes are possible. For example, the droplet ejection head 100 may eject a liquid other than ink, such as a functional liquid for forming a circuit pattern or the like on a recording medium.

[0093] In addition to the communication flow path 29 branching off from the front chamber 23a, a communication flow path branching off from the rear chamber 23b and communicating with the discharge path 27 may be further provided.

[0094] Also, although a shear mode droplet ejection head 100 has been exemplified, the present invention is not limited to this. For example, a vent mode droplet ejection head 100 may be used, in which ink is ejected by varying the pressure of the ink in the pressure chamber by deforming a piezoelectric element (pressure varying means) fixed to the wall surface of a pressure chamber communicating with a nozzle. In this case, the individual ejection flow paths can be branched from any position in the range from the pressure chamber to the nozzle.

[0095] In addition, the discharge flow path 102 is exemplified as having an individual discharge flow path 152 branching off from the ink channel 151, and a second common discharge flow path 18 communicating with the individual discharge flow path 152, but is not limited to this, and the individual discharge flow path 152 and the second common discharge flow path 18 may be omitted.

[0096] Furthermore, the single-pass type droplet ejection device 1 has been described as an example, but the present invention may also be applied to a droplet ejection device that records an image while scanning a head unit or a droplet ejection head.

[0097] Although an example in which the recording medium M is transported by the transport belt 2c has been described, the present invention is not limited to this. For example, the recording medium M may be held and transported on the outer circumferential surface of a rotating transport drum.

[0098] Although several embodiments of the present invention have been described, the scope of the present invention is not limited to the above-described embodiments, but includes the scope of the invention described in the claims and its equivalents. [Industrial Applicability]

[0099] The present invention can be used in a droplet ejection device and a liquid delivery method. [Explanation of symbols]

[0100] 1 Droplet discharge device 2. Conveyor section 3 Head Unit 9 Ink Circulation Mechanism 10 Discharge operation part 11 Ink inlet 12 Common ink chamber 13 Common supply channel 14 First common exhaust flow path 15 Ink Channel 15a Nozzle plate 15b Flow path substrate 15c Pressure chamber substrate 151 Ink Channel 152 Individual exhaust flow path 16 Ink manifold 17, 17a, 17b Ink outlet 18 Second common exhaust flow path 20 Liquid storage tank 20a Main body 21 Supply port 22 1st supply route 23 Liquid storage section 23a Antechamber 23b Posterior chamber 231 Filters 232, 233, 234 Open end 24 2nd supply route 25 Outlet 26, 26a~26c inlet 27, 27a~27c discharge path 271 Check valve 28 Outlet 29 Connecting flow path 30 Cover member 40 Control section 61, 62 Bubbles 100 Droplet ejection head 100a Nozzle opening surface 101 Supply channel 102 Exhaust flow path M Recording medium N Nozzle Ns Straight section Nt Tapered section m Meniscus

Claims

1. A nozzle for discharging a liquid; a supply flow path through which liquid is supplied to the nozzle; a discharge flow path that communicates with the supply flow path and through which liquid that is discharged without being ejected from the nozzle passes; a filter provided in the supply flow path and through which a liquid passing through the supply flow path passes, the filter being provided to capture at least air bubbles larger than a mesh diameter of the filter; a communication flow path that branches off from the supply flow path at an upstream side of the filter in a liquid sending direction and communicates with the discharge flow path; A droplet ejection head having a liquid sending unit that performs a liquid sending operation to cause the liquid in the supply flow path and the discharge flow path to flow in the liquid sending direction; Equipped with the mesh diameter of the filter is smaller than the opening diameter of the nozzle, The liquid delivery section performs the liquid delivery operation in such a manner that a pressure loss in the filter is smaller than a first meniscus break pressure at which a meniscus, which is a liquid surface of the air bubble, breaks in the filter.

2. When a flow rate of the liquid in the supply flow path corresponds to a maximum amount of the liquid discharged from the nozzle per unit time, the maximum discharge flow rate is defined as: The droplet ejection device of claim 1 , wherein a pressure loss caused in the filter by the maximum ejection flow rate of liquid is less than a second meniscus break pressure at which a meniscus of liquid breaks in the nozzle.

3. the supply flow path has a downward portion in which the liquid sending direction has a vertical downward component, The droplet ejection device according to claim 1 or 2, wherein the liquid delivery section performs the liquid delivery operation in such a manner that the vertical downward component of the liquid velocity in the descending portion is greater than the speed at which a bubble smaller than the opening diameter of the nozzle rises due to buoyancy.

4. 4. The droplet ejection device according to claim 1, wherein the nozzle has a tapered portion in which a cross-sectional area perpendicular to a liquid ejection direction becomes smaller toward the nozzle opening.

5. 5. The droplet ejection device according to claim 1, wherein the liquid is a water-based ink.

6. a liquid ejection unit including a nozzle that ejects liquid, a supply flow path through which liquid supplied to the nozzle passes, a discharge flow path that is connected to the supply flow path and through which liquid that is discharged without being ejected from the nozzle passes, a filter that is provided in the supply flow path and through which liquid passing through the supply flow path passes, the filter being provided for capturing at least air bubbles larger than a mesh diameter of the filter, and a communicating flow path that branches off from the supply flow path upstream of the filter in a liquid sending direction and communicates with the discharge flow path, the mesh diameter of the filter being smaller than an opening diameter of the nozzle, a liquid sending step of causing the liquid in the supply flow path and the discharge flow path to flow in the liquid sending direction, The liquid transport method, in the liquid transport step, comprises causing the liquid to flow in such a manner that a pressure loss in the filter is smaller than a first meniscus break pressure at which a meniscus, which is the liquid surface of the air bubbles, breaks in the filter.

Images