Electrohydrodynamic printing head having an ink pinning

Abstract

The electrohydrodynamic printhead includes a nozzle carrier (6) on which a number of nozzles (4) are disposed. A number of electrodes (38, 40, 42) associated with the nozzles (4) are disposed on a front surface of the nozzles (4). A support structure (8) for supporting the electrodes (38, 40, 42) is disposed on the nozzle carrier (6) and includes a number of support elements (76, 78) disposed between the nozzles (4). An ink retainer (66) is disposed between the nozzles (4) and the support elements (76, 78). A front surface (68) of the ink retainer (66) is disposed behind a front end (70) of the nozzles (4) to prevent the nozzles (4) from submerging in the ink. A guard electrode (42) may be provided between the ejection electrode (38) and the ink retainer (66) to reduce the electric field in the ink retainer (66), thereby improving the efficiency of the ink retainer (66) in retaining the ink. A suction duct (16) surrounding each nozzle (4) makes it possible to remove ink from the nozzles (5).

Description

Technical Field

[0001] The present invention relates to an electrohydrodynamic printing head and a method of operating the electrohydrodynamic printing head.

Background Art

[0002] Patent Document 1 describes an electrohydrodynamic printing head having a nozzle carrier including a plurality of nozzles. The electrohydrodynamic printing head is designed to eject ink along an ejection direction. The nozzles form protrusions extending along this ejection direction. The ejection electrodes are associated with the nozzles and are disposed on the target side of the nozzles.

[0003] In the printing head of this design, the ink can form a "pool" that "submerges" the nozzles and can interfere with the operation of the printing head.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0005] Therefore, the problem to be solved by the present invention is to provide a printing head and a method of operating the printing head that enable more reliable printing.

Means for Solving the Problems

[0006] This problem is solved, in a first aspect of the invention, by the print head of the first independent claim.

[0007] Thus, the print head may comprise at least the following elements. - Nozzle carrier: This is a substrate on which nozzles are arranged.

[0008] - A plurality of nozzles arranged on the carrier: Each of the nozzles forms a protrusion (i.e., a projecting portion) on the "front side" of the nozzle carrier, which is the side facing the printing target during operation. The nozzles extend along the ejection direction of the print head, i.e., along the direction in which the print head is designed to eject ink. The nozzles may extend parallel to the ejection direction or at a small angle, in particular at an angle less than 45° with respect to the ejection direction.

[0009] - A plurality of ejection electrodes associated with the nozzles and arranged on the front side of the nozzles: The ejection electrodes are used, for example, to individually eject ink from the nozzles associated with the ejection electrodes.

[0010] - A support structure for supporting the ejection electrodes on the nozzle carrier. This support structure comprises a plurality of support elements arranged between the nozzles.

[0011] - A plurality of ink holding parts arranged between the nozzles and the support elements: The ink holding parts prevent the ink from reaching the support elements and wetting them, i.e., the ink holding parts "retain" the ink pool within a defined boundary. In a given nozzle, the nearest ink holding part is arranged away from the nozzle.

[0012] The ink holding parts prevent the ink from reaching the support elements. If the ink reaches the support elements, the ink wets the support elements and forms an ink pool that may immerse the nozzles, thereby preventing the proper formation of the electric field used for droplet ejection.

[0013] Preferably, along the ejection direction, the front surface of the ink holding portion is disposed behind the front end of the nozzle (i.e., closer to the nozzle carrier). In other words, along the ejection direction, the ink holding portion is set to be rearward with respect to the front end of the nozzle. Since the holding portion is disposed closer to the nozzle carrier than the front end of the nozzle, the nozzle extends forward from any ink pool that may be formed between the nozzle and the holding portion, that is, the nozzle does not "sink" into the ink pool. However, it should be noted that the vertical wall of the nozzle can be wetted by the ink.

[0014] Each ink holding portion preferably forms a ledge portion facing opposite to the nozzle closest to the respective ink holding portion, thereby assisting the fastening process.

[0015] In a particularly preferred embodiment, the print head comprises a plurality of guard electrodes for the purpose of guarding the ink holding portion from the electric field generated by the ejection electrode. At a given nozzle, the guard electrode associated with the nozzle is disposed between the ejection electrode associated with the nozzle and the ink holding portion associated with the same nozzle. Since the electric field of the ejection electrode tends to reduce the surface tension of the ink, this design reduces the risk of the periphery of the ink holding portion being wetted.

[0016] In particular, the print head may comprise a voltage supply configured to set the potential of the guard electrode to be closer to the potential of the ink holding portion than the (maximum) potential of the ejection electrode.

[0017] The print head may further comprise a plurality of ink supply ducts for the nozzles. The ink supply ducts are at least partially disposed in the nozzle carrier. Preferably, at least one ink supply duct ends at each nozzle. The ink supply ducts are configured to supply ink to the nozzles.

[0018] In that case, in a given nozzle, the closest ink holding part surrounds the nozzle and the end part of the supply duct. Thereby, the ink coming from the supply duct can be held.

[0019] In a second aspect of the present invention, the present invention relates to an electrohydrodynamic printing head comprising at least the following parts. - Nozzle carrier: This is a substrate on which nozzles are arranged.

[0020] - A plurality of nozzles arranged on the carrier: Each of the nozzles forms a protrusion (i.e., a projecting part) on the "front side" of the nozzle carrier, which is the side facing the printing target during operation. The nozzles extend along the ejection direction of the printing head, that is, along the direction in which the printing head is designed to eject ink. The nozzles can extend parallel to the ejection direction or at a small angle, particularly at an angle less than 45° with respect to the ejection direction.

[0021] - A plurality of ejection electrodes associated with the nozzles and arranged on the front side of the nozzles: The ejection electrodes are used, for example, to individually eject ink from the nozzles associated with the ejection electrodes.

[0022] - A plurality of ink supply ducts for the nozzles: At least one ink supply duct ends at each nozzle and supplies ink to each nozzle.

[0023] - A plurality of ink suction ducts: At least one ink suction duct ends at each nozzle.

[0024] The ink suction duct is configured to supply ink from the nozzle. Thereby, an excessive amount of ink can be prevented in a given nozzle.

[0025] Same as the first aspect, thereby confining the ink in the area around a given nozzle, thereby preventing the nozzle from sinking into the ink pool.

[0026] The ink supply duct and the suction duct can be arranged at least partially on the nozzle carrier.

[0027] Same as the first aspect of the present invention, the print head preferably comprises a support structure that supports the ejection electrodes on the nozzle carrier. This support structure comprises a plurality of support elements arranged between the nozzles. The suction duct can be used to prevent ink from reaching the support elements.

[0028] This second aspect is preferably combined with the first aspect, i.e., the print head has, at a given nozzle, at least one suction duct and at least one ink holding portion, both of which can cooperate to hold ink.

[0029] At a given nozzle, the closest ink holding portion preferably surrounds not only the end portions of the nozzle and the supply duct but also the end portion of the suction duct. Thus, the two ducts can be used to maintain a pool of fresh ink within the area surrounded by the ink holding portion.

[0030] In a preferred design, the nozzle carrier comprises at least the following parts. - Front layer: The nozzles are attached to the front side of the front layer.

[0031] - A backing layer arranged on the rear side of the front layer.

[0032] The electrical vias connected to the ejection electrodes extend through the front layer and the backing layer. The electrical vias supply voltage to the ejection electrodes.

[0033] In addition, the ink supply duct is arranged in (at least) the front layer.

[0034] In particular, the print head may comprise, in the front layer, an interconnecting portion for the ink that extends transversely, in particular perpendicularly, to the ejection direction. This makes it possible to interconnect the supply ducts for the nozzles and / or to interconnect the suction ducts for the nozzles, reducing (or eliminating) the number of ink ducts passing through the backing layer.

[0035] Preferably, both the front layer and the backing layer are dielectric layers. This design is based on the understanding that electrical vias need to be guided through these layers and that the electrical vias need to be insulated from each other and accompanied by high voltages. Alternatively, the layer may also be made of a composition of a dielectric material and a non-dielectric material, for example, a silicon wafer covered in certain regions by a thick layer of thermal silicon dioxide. However, since the silicon dioxide layer may not be manufacturable with sufficient thickness, this technology may only operate for limited voltage ranges.

[0036] Most preferably, the backing layer is made of glass, which provides both electrical insulation and mechanical stability.

[0037] The front layer is preferably made of a plurality of photoactive polymer layers, for example, an epoxy-based dry film laminate that can be easily formed into any form of vertical and horizontal duct structures. Alternatively, the horizontal ducts may also be formed by bonding several structured glass layers to each other.

[0038] The invention also relates to a method of operating a print head, in which ink is confined in the region around a given nozzle by using the ink holding portion (66) and / or by sucking ink from the nozzle by using a suction duct. In both cases, by controlling and confining the ink, it is possible to prevent the formation of a pool where the ink can reach the surrounding support elements and submerge the nozzles.

[0039] In a particularly important embodiment, the method includes generating an electric field at the front end of at least one of the nozzles, thereby ejecting ink from the front end. However, at the same time, the electric field in the ink holding portion is maintained at less than 50%, particularly less than 10%, of the intensity of the electric field at the front end of the nozzle.

[0040] Considering the following detailed description of the present invention, the present invention will be more fully understood and other objects than those described above will become apparent. The description refers to the accompanying drawings.

Brief Description of the Drawings

[0041]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

Figure 21

[0042] Note: The injection direction X in Figure 1 points downward, and the target is located below the print head. However, the injection direction X in all other figures showing vertical cross-sections points upward. That is, Figure 1 is rotated 180° with respect to all other figures showing cross-sections parallel to the injection direction. Rather, the directions in those figures are based on the way the manufacturing proceeds, i.e., the lower layer is manufactured before the upper layer.

Best Mode for Carrying Out the Invention

[0043] Definitions "Front" defines the direction in which the print head is designed to eject ink. For example, the injection electrode is in front of the nozzle.

[0044] "Rear" defines the opposite direction. For example, the nozzle is located behind the injection electrode.

[0045] "Forward" and "backward" are understood to indicate the height positions in front of or behind something else.

[0046] "Front" and "rear" refer to the front side and the back side.

[0047] The feature "with a given nozzle" is preferably understood as a feature that applies to the majority, in particular at least 90% of the nozzles. For example, in the case of "with a given nozzle, the guard electrode is arranged between the ejection electrode and the ink holding part", this preferably means that it applies to the majority of the nozzles, in particular at least 90% of the nozzles. For example, there may be some nozzles that do not have an ejection electrode and / or a guard electrode, such as the nozzles at the edge of the print head and / or unused nozzles.

[0048] The ejection direction X of the print head defines the "vertical" upward direction, that is, the print head is designed by definition to eject ink upward. (Of course, during operation, it may be at an angle less than any angle with respect to the direction of gravity.) Therefore, definitions such as "above" and "below" should be understood with reference to this definition of "vertical".

[0049] "Horizontal" is any direction perpendicular to the vertical direction.

[0050] "Sideways" indicates a direction that is horizontal when viewed from something else.

[0051] Print head FIG. 1 shows a schematic cross-sectional view of an embodiment of a print head 1. It is depicted above a target 2 and is configured to eject ink onto the target along the ejection direction X.

[0052] The print head includes a plurality of nozzles 4 arranged on the front surface of a nozzle carrier 6. The nozzles 4 can be arranged in a one- or two-dimensional array.

[0053] The printing head has a plurality of ejection electrodes (not shown in FIG. 1) for ejecting ink from nozzles 4 and an optional further electrode arranged on a support structure 8, the design of which is described in more detail below. The further electrode can be provided in electrical contact with the ink in order to set the ink to a defined electrical potential.

[0054] The nozzle carrier 6 comprises a front layer 10, and the nozzles 4 are attached to the front face of the front layer 10 and form protrusions thereon. It also comprises a backing layer 12 arranged on the rear side of the front layer 10.

[0055] The internal structure of the front layer 10 is not shown in FIG. 1 but is described in more detail below. It can be, for example, a dielectric, in particular a polymer.

[0056] The backing layer 12 can be, for example, an insulating semiconductor material or it can be a dielectric. Preferably, the backing layer 12 is at least partially glass.

[0057] The electrical via 14 is connected to the ejection electrode and extends through the front layer 10 and the backing layer 12 to connect the ejection electrode to a voltage supply 17. Preferably, there is at least one via 14 for each nozzle 4. Further vias can be provided to connect other electrodes to the voltage supply 17.

[0058] The ink ducts 15, 16 supply ink to the nozzles 4 and (optionally) return ink from the nozzles 4 for reuse. They are partially arranged in the front layer 10 and they extend through the peripheral region of the backing layer 12. Their design is described in more detail below.

[0059] FIG. 1 shows an embodiment of a printing head having an ink supply duct 15 and a suction duct 16.

[0060] If there is a suction duct to supply ink to the supply duct 15, at least one pump 18 and / or another pressure source or vacuum source is provided to recover ink from the suction duct 16.

[0061] Preferably, the print head comprises a first pressure control 20 that generates a first regulated pressure p1 at an input of the supply duct 15, for example in a storage tank 22.

[0062] The ink is supplied to the nozzles 4 through an optional filter 24 and the supply duct 15.

[0063] If there is a suction duct 16, the suction duct 16 is connected to a suction system that may comprise a second pressure control 26 that generates a second regulated pressure p2 at an outlet of the suction duct 16, for example in a suction tank 28. The suction system may also comprise a pump. This may in particular be the pump 18 as described above, in which case the pump 18 functions as a circulation pump.

[0064] A suitable pump design is shown, for example, in Patent Document 2.

[0065] As further shown in FIG. 1, the print head may comprise a circuit carrier 30, such as a PCB, disposed on a rear side of the nozzle carrier 6.

[0066] An optional intervening layer 32 may be provided between the circuit carrier 30 and the nozzle carrier 6 to match the finer resolution of the vias 14 to the resolution of the circuits of the circuit carrier 30. The intervening layer is used, for example, in a flip chip design in which semiconductor chips are mounted on a PCB.

[0067] The circuit carrier 30 supports a control circuit 33, which may implement, for example, at least a part of the voltage supply 17, such as a driver stage of the voltage supply, and connects a voltage source to each electrode of the print head.

[0068] In the illustrated embodiment, the ink ducts 15, 16 extend through the intervening layer 32 (if present) and the circuit carrier 30.

[0069] If the vias 14 have a sufficiently large mutual spacing (e.g., greater than 0.4 mm), the vias 14 can interface directly with the circuit carrier 30 without the intervening layer 32.

[0070] Preferably, the target 2 is arranged on an acceleration electrode connected to the voltage supply 17 to generate an acceleration electric field between the print head 1 and the target 2.

[0071] The pressure controls 20, 26 can be used to maintain the pressure as described below in the section on operation of the print head. Preferably, they can adjust the pressure in the supply duct 15 and the pressure duct 16 separately.

[0072] Nozzle design 1 Figures 2 to 8 show a first embodiment of the nozzle 4 and the surrounding elements. (As described above, in contrast to Figure 1, the ejection direction X in Figure 2 points upwards.)

[0073] As can be seen from Figure 2, the nozzle 4 forms a protrusion on the front face 36 of the nozzle carrier 6, for example on the front side of its front layer 10. It is arranged in the outlet passage 5 through which the ink can be ejected towards the target 2.

[0074] Figure 2 also shows various electrodes that can be associated with the nozzle 4.

[0075] The ejection electrode 38 is arranged on the front side of the nozzle 4. In the embodiments of Figures 2 and 7, it is annular with a central opening 39 for the passage of the ink. It is connected to one of the vias 14 that extend through the support structure 8 and the nozzle carrier 6.

[0076] Figures 3 and 4 show two possible implementations of via 14. On the right side, below reference numeral 14, a hollow implementation is shown, where the via is formed as a metal coating 14a within a dielectric tube 14b that extends along the injection direction and surrounds a central duct 14c, and the central duct 14c can also be used as a ventilation duct for supplying gas to / from the region between the print head and the target. This type of structure can be formed, for example, a) forming the tube 14b together with a honeycomb structure as described below, and b) formed, for example, by forming the metal coating 14a within the tube 14b by sputtering.

[0077] The alternative design shown below reference numeral 14’ comprises a solid metal core 14’a within a dielectric tube 14’b. Again, the tube 14’b can be formed together with a honeycomb structure as described below, and the metal core 14’a can be formed, for example, by electroplating.

[0078] The alternative via designs 14, 14’ are also shown in Figure 17. The hollow via design 14 is depicted for connecting the shielding electrode 40, while the filled via design 14’ is depicted for the injection electrode 38 (not visible in Figure 17). Note: Only the metal parts are shown as hatched areas in Figure 17, while the other cross-sectional parts are not hatched.

[0079] Normally, a single print head uses only vias of one design, and two different types are shown in Figures 3, 4, and 17 for illustrative purposes only.

[0080] Referring to Figures 2 and 8, the shielding electrode 40 can be arranged remotely on the front side of the injection electrode 38, i.e., with respect to the nozzle carrier 6, the injection electrode 38 is closer than the shielding electrode 40. Preferably, there is one continuous shielding electrode 40 extending in front of the print head 1, although several such shielding electrodes can also be present.

[0081] When several shielding electrodes are used, they can be applied at different potentials, for example, by applying a voltage gradient, for example, by means of a voltage divider that enables the ink to be gradually deflected in the cross-section of the print head.

[0082] The shielding electrode 40 is provided to control the field between the print head 1 and the target 2. For each nozzle 4, the opening 41 in the shielding electrode 40 allows the ink to pass through.

[0083] As shown in FIGS. 2 and 5, the guard electrode 42 can be arranged at a distance behind the ejection electrode 38, but can also be arranged at a distance in front of the nozzle carrier 6. Again, as shown in FIGS. 2 and 5, it can be annular. Alternatively, it may also extend across several nozzles.

[0084] The opening 43 in the guard electrode 42 above the nozzle 4 allows the ink to pass through.

[0085] The function of the guard electrode 42 is described below.

[0086] The nozzle 4 of the present embodiment includes a tip portion 46, a shaft portion 48, and base portions 50, 52. The tip portion 46 is arranged in front of the shaft portion 48, and the base portions 50, 52 (FIGS. 2, 3) are arranged behind the shaft portion 48.

[0087] The illustrated nozzle design relies on the ink wetting the lateral surface of the nozzle 4 (as known, for example, from Patent Document 5) and does not rely on the ink passing through the central flow path of the nozzle 4, but the latter can also be used.

[0088] When the nozzle 4 has a central flow path, for example, when the outlet duct 60 extends throughout to the tip of the nozzle, preferably, the nozzle 4 is still operated such that the ink wets not only above the nozzle but also the outer side thereof. Certainly, by covering the outside of all the nozzles with ink, all the nozzles give the same ink profile to the ejection electrodes, thereby enabling more uniform ink ejection across the entire print head.

[0089] To promote the desired flow of ink along the nozzle 4 in the ejection direction X, preferably, the nozzle 4 has at least one groove extending along the ejection direction X on its lateral surface, that is, on the surface extending along the ejection direction X. This groove extends along at least a part of the length of the nozzle 4.

[0090] This can be seen, for example, in FIG. 5, where the tip portion 46 is shown in a cross-sectional shape (with four recesses 46a formed between the cross-shaped arms), and the shaft portion 48 forms two grooves 48a.

[0091] FIG. 6 shows an alternative design of the tip portion 46. (a) is the tip portion 46 having a convex lateral surface and being, for example, a cylinder without a groove, (b) is the tip portion 46 having formed two lateral grooves 46a, (c) is the tip portion having formed an axial tube 46c.

[0092] The base portions 50, 52 connect the tip portion 46 and the shaft portion 48 to the nozzle carrier 6. It also includes ducts for supplying ink to the nozzles. This can be best seen in FIGS. 2, 3, and 4.

[0093] In particular, in the illustrated embodiment, the base portions 50, 52 comprise a bottom sub-layer 52 and an upper sub-layer 50. The bottom sub-layer 52 has a central opening 54 that communicates with an end of a supply duct portion 15a that supplies ink to the nozzle 4. One or more radial transverse outlet ducts 56 extend outwardly from the central opening 54 transversely to the injection direction X and toward a first annular duct 58.

[0094] In FIG. 2, the flow of ink in the duct is depicted by the arrows.

[0095] The upper sub-layer 50 may also form an axial outlet duct 60 that extends toward the tip of the nozzle and connects the supply duct portion 15a to a groove 48a (FIG. 5) in the shaft portion 48, thereby guiding the ink directly upward toward the tip portion 46.

[0096] The upper sub-layer 50 may be surrounded by a second annular duct 62 that is aligned with the first annular duct 58 surrounding the nozzle 4.

[0097] The nozzle 4 is surrounded by an ink holding portion 66 for the purpose of holding the ink laterally. The annular duct 62 is disposed radially between the ink holding portion 66 and the nozzle 4 and thereby communicates with a region 64 between the nozzle 4 and the ink holding portion 66.

[0098] The front face 68 of the ink holding portion 66 (i.e., the face facing forward most closely to the injection electrode 38) is set rearward along the injection direction X with respect to the front end 70 of the nozzle 4. Thus, when ink is present in the region 64, the surface of the ink forms an upward slope toward the tip of the nozzle 4 as indicated by the dashed line, ensuring that the tip is at the position closest to the injection electrode 38, thereby forming a regulated point for ejecting the ink.

[0099] The main function of the ink holding portion 66 is to hold the ink, that is, to prevent the ink from approaching the vertical portion of the support structure 8, that is, to prevent the ink from rising and forming a pool that can submerge the nozzles.

[0100] This function is implemented by one or more combinations of the following features. a) The ink holding portion 66 is provided with a hydrophobic and / or oleophobic surface, for example, by a hydrophobic and / or oleophobic coating 73 shown as a thick black line in FIG. 2. For example, the surface can be formed at least partially of Teflon (registered trademark) and / or PTFE, which is hydrophobic and oleophobic. Depending on the range of inks used, the surface can also be only hydrophobic (e.g., HMDS, that is, bis(trimethylsilyl)amine) or only oleophobic (e.g., polymer-based). In particular, the surface of the ink 66 holding portion is preferably more hydrophobic and / or oleophobic than the surface of the nozzle 4.

[0101] b) The ink holding portion 66 forms a ledge portion 66a directed away from the nearest nozzle 4, thereby making it difficult for the ink to advance around it. In other words, when viewed from the nozzle, the ledge portion extends outward and forms an "undercut" 66b.

[0102] c) The ink holding portion 66 is arranged in a region with a low electric field. Since a strong electric field tends to reduce the surface tension of the ink, this design reduces the risk of the area around the ink holding portion being wetted by the ink. In the illustrated embodiment, the guard electrode 42 associated with the nozzle 4 is arranged between the injection electrode 38 and the ink holding portion 66. In this context, "between" preferably means that the guard electrode 42 crosses, preferably divides into two, the volume of the space between the injection electrode 38 and the ink holding portion 66.

[0103] Note that the ink holding part 66 is not the only means of holding the ink horizontally, i.e., preventing the ink from reaching the nearest support element. Alternatively, or in addition thereto, the ink suction duct 16 can be used to remove any ink that may reach the support element. This is described in more detail in the section on the operation of the print head.

[0104] The guard electrode 42 is connected to the voltage supply 17, for example, by vias 14' or 14, which can be set to a potential closer to the potential of the ink holding part 66 (i.e., the ink) than the (maximum) potential of the ejection electrode during operation. In particular, the voltage supply 17 can be configured to maintain the guard electrode 42 at the same potential as the ink holding part 66. This can keep the electric field in the ink holding part 66 very low.

[0105] As shown in FIG. 2, the guard electrode 42 is preferably arranged at the same "height" (the vertical direction is defined by the ejection direction X) as the front end 70 of the nozzle 4, for example, within an accuracy of 25% of the vertical distance d between the ejection electrode 38 and the front end 70 of the nozzle 4. This still provides a desirable shielding of the ink below the tip of the nozzle 4 while significantly exposing the tip with respect to the field of the ejection electrode 38.

[0106] As can be seen in FIG. 2, there is an air-filled cavity 71 that forms a gap between the guard electrode 42 and the ink holding part 66, which prevents the ink from reaching the guard electrode 42.

[0107] To hold the ink horizontally within the region 64, the ink holding part 66 is preferably arranged on and protrudes from the front surface 36 of the nozzle carrier 6. In the embodiments of FIGS. 2 to 4, it comprises a first ring 72 attached to the front surface 36 of the nozzle carrier 6 and a second ring 74 attached to the front side of the first ring 72. The second ring 74 forms the above-mentioned ledge portion 66a.

[0108] Ink suction As described above, in the embodiments of FIGS. 1 and 2, the suction duct 16 is provided to collect ink from the nozzle 4. Thereby, in a given nozzle, a fresh ink flow can be maintained.

[0109] In that case, in a given nozzle, the nearest ink holding part 66 preferably surrounds not only the nozzle 4 and the end part 15a of the supply duct, but also the end of the end part 16a of the suction duct 16. Thus, the two ducts can be used to control the flow of ink towards and back from the nozzle.

[0110] The pressures in the supply duct 15 and the suction duct 16 are adjusted to maintain the ink, for example, somewhere within the region 64 between the upper height 64a and the lower height 64b as shown in FIG. 2. Preferably, the ink is maintained at the lower height 64b, as described in more detail in the section "Operation of the print head" below.

[0111] For the desired lateral confinement of the ink, each nozzle 4 is preferably surrounded by one or more openings or openings of the suction duct. This can be, for example, a single annular opening (such as formed by the annular opening 62 in FIG. 2), or it can be a series of annular suction openings. This opening or these openings are arranged between the nozzle and the adjacent support element 78.

[0112] Support structure As described, the support structure 8 is provided to connect the different electrodes 38, 40, 42 to the nozzle carrier 6 respectively. It is arranged on the front surface 36 of the nozzle carrier 6.

[0113] The support structure 8 includes a plurality of support elements 76, 78 arranged between the nozzles 4.

[0114] The ink holding part 66 is preferably designed to prevent the ink from reaching these support elements 76, 78 and to prevent the ink from wetting them, thereby reducing the tendency of the ink to submerge the nozzles.

[0115] The support structure 8 preferably comprises at least one electrode carrier layer. In the embodiment of FIG. 2, there are three such layers 80, 82, 84. Each of the electrode carrier layers comprises at least one electrode 38, 40, 42 and can extend parallel to the upper surface 36.

[0116] Normally, the electrodes 38, 40, 42 are embedded in their electrode carrier layers 80, 82, 84 and are covered by at least one dielectric sublayer 80a, 80b, or 82a, 82b, or 84a, 84b on their front and rear sides.

[0117] At least a part of the support elements is formed by the vertical walls 76 forming the honeycomb structure with reference to FIG. 3. Each of the honeycomb structures is used in various parts of the print head and is part of a multilayer structure described in more detail below.

[0118] In addition to or alternatively to the walls 76 forming the honeycomb structure, in the illustrated embodiment, the support elements comprise vertical walls 78 surrounding the outlet passages 5 of each nozzle 4. The walls 78 can be, for example, cylindrical walls, but they can also be, for example, polygonal. Preferably, it is centered on the nozzle 4.

[0119] In another embodiment, the wall 78 can also be omitted, and the walls around the outlet passage 5 can be formed by the walls 76 of the honeycomb structure. In this case, it is necessary to align the honeycomb structure with the nozzles.

[0120] In yet another embodiment, several nozzles can be surrounded by a single wall 78.

[0121] In the embodiments shown here, the support elements 76 and / or 78 are provided between each of the electrode carrier layers 80, 82, 84 and between the last electrode carrier layer 80a and the nozzle carrier 6. However, they can also be provided only between a subset of these structures.

[0122] As best seen from FIG. 2, there is a first recess disposed between the nozzle 4 and its ink reservoir 66, which is formed by the annular first and second annular ducts 58, 62. It provides a volume for receiving at least a portion of the ink pool 64. Along the injection direction X, the bottom of the first recesses 58, 62 is behind the front face 68 of the ink reservoir 66 (i.e., closer to the nozzle carrier 6 than to the front face 68).

[0123] In the illustrated embodiment, there is a second recess 86 disposed between the ink reservoir 66 and the nearest support element 78. It provides space for the ledge portion 66a and / or makes it more difficult for ink to reach the support element 78. Along the injection direction X, the bottom of the recess 86 is behind the front face 68 of the ink reservoir 66 (i.e., closer to the nozzle carrier 6 than the front face 68).

[0124] Nozzle Design 2 FIGS. 9 and 10 show a second embodiment of the nozzle design. It mainly differs from the first one in that there is only an ink supply duct 15 for the nozzle (the end portion 15a of which is shown in FIG. 10) and there is no suction duct.

[0125] Furthermore, there is no recess between the nozzle 4 and the ink reservoir 66. Rather, the ink reservoir 66 is disposed laterally over the nozzle 4, and its front face 68 is away from the front end (tip) 70 of the nozzle 4.

[0126] In other words, its front face 68 is set behind the front end 70 of the nozzle 4 to form an upward slope with respect to the ink within the region 64 to reduce the risk of submerging the nozzle.

[0127] Preferably, the ink holding portion 66 is mounted "low" on the nozzle 4 in order to reduce the possibility of submerging the nozzle. In particular, the front surface 68 of the ink holding portion 66 is closer to the front size 36 of the nozzle carrier 6 than to the front end 70 of the nozzle 4.

[0128] As can be seen, in this embodiment, the ink holding portion 66 is formed by the sub-layer 52 of the base portion of the nozzle 4.

[0129] Nozzle design 3 FIG. 11 shows a third embodiment of the nozzle design. It mainly differs from the second one in that it does not have a guard electrode. In order to keep the electric field low at the position of the ink holding portion 66, the ink holding portion 66 is disposed far behind.

[0130] In particular, as shown in FIG. 11, the distance d' along the ejection direction X between the front surface 68 of the ink holding portion 66 and the front end 70 of the nozzle 4 is large.

[0131] Quantitatively, when d represents the distance along the ejection direction X between the ejection electrode 38 and the front end 70 of the nozzle 4, preferably, the following condition is maintained: d' > k·d k is at least 0.5, particularly at least 1.0.

[0132] Nozzle design without ink holding portion In the embodiments illustrated so far, the nozzle 4 has been surrounded by an ink holding portion 66 that protrudes upward from the upper surface 36 of the nozzle carrier 6. However, by using an ink suction portion, the ink holding portion can be omitted. This is shown in FIG. 21, which basically corresponds to that of FIG. 2 but shows an embodiment without an ink holding portion. Therefore, the layers forming the base portions 50, 52 of the embodiment of FIG. 2 can be omitted.

[0133] In this embodiment, the ink is held around the nozzle 4 by being sucked into the end portion 16a of the ink suction duct 16 surrounding the nozzle.

[0134] In one embodiment, a single annular (or, for example, hexagonal or otherwise closed-loop) end portion 16a of the suction duct 16 can be arranged around the nozzle 4.

[0135] In another embodiment, a plurality of individual end portions 16a are provided surrounding the nozzle 4 at close intervals and can be arranged, for example, along a circle or another closed loop.

[0136] In this embodiment, the guard electrode 42 can still be useful to reduce the tendency of the ink to spread along the surface 36 of the nozzle carrier 6.

[0137] In the illustrated embodiment, the outlet duct 60 extends over the entire area up to above the nozzle 70. Therefore, the ink flows axially through the nozzle. Preferably, the pressure in the outlet duct 60 is selected such that the ink overflows from the nozzle and flows downward along its side walls. From there, the ink reaches the end portion 16a of the suction duct 16 and is removed. This provides continuous ink exchange within the nozzle.

[0138] In another embodiment, the ink can be guided upward along the outer surface of the nozzle, for example, in a groove as shown in the embodiments of FIGS. 2 to 5, and the ink can be sucked from the end portion 16a through, for example, an axial opening in the nozzle.

[0139] However, optionally, the design of this section can also be combined with, for example, a simple ink holding portion 66 (as shown by the dotted line) surrounding the end portion 16a of the suction duct 16.

[0140] Nozzle carrier Figures 12 to 16 show a possible design of the nozzle carrier 6. Figures 13 to 15 are shown at a reduced scale compared to Figure 12 to show how adjacent nozzles can be interconnected by supply ducts and suction ducts, and it should be noted that Figure 16 is shown at an even more reduced scale showing the entire cross-section of the print head at the height of the backing layer 12.

[0141] These figures show the nozzles of Figure 2, but a similar nozzle carrier can be used in various nozzle designs such as the designs of Figures 9 and 11.

[0142] As described above, the nozzle carrier 6 includes a front layer 10, the nozzle 4 is attached to its front surface 36, and further, the backing layer 12 is disposed on the rear side of the front layer 10. Then, the front layer 10 and the backing layer 12 can be a multilayer structure.

[0143] They are described in more detail below.

[0144] The front layer 10 is composed of several sub-layers 10a to 10d and forms at least a part of the ducts 15, 16 that supply ink to the nozzles and, where applicable, supply ink from the nozzles.

[0145] In the embodiment of Figure 12, the front layer 10 includes sub-layers 10a, 10b, 10c, and 10d that form ducts in order from front to back.

[0146] The sub-layer 10a forms the front surface 36 and includes openings 15a, 16a for the supply duct and (where necessary) the suction duct, respectively.

[0147] The sub-layer 10b forms the horizontal portion 16b of the suction duct and the vertical portion 15b of the supply duct (where necessary).

[0148] As can be best seen in FIG. 13, the horizontal portion 16b of the suction duct is interconnected with all of the nozzles 4 or at least a plurality of the nozzles 4. Additionally, between the ducts, the sub-layer 10b comprises vertical walls 90 that form a honeycomb pattern similar to that of the support structure 8. The area of the honeycomb pattern can be separated from the ducts 16b and / or 15b by vertical separation walls 92.

[0149] FIG. 13 also shows vias 14, 14' that extend along the injection direction X through all of the front layer 10.

[0150] The vertical portion 15b of the supply duct is connected to the vertical portion 15c of the supply duct within the sub-layer 10c, with reference to FIG. 14.

[0151] As shown in FIG. 15, the sub-layer 10d forms a horizontal portion 15d of the supply duct that is interconnected with adjacent nozzles.

[0152] Again, the sub-layer 10d can comprise vertical walls 94 that form a honeycomb pattern similar to that of the support structure 8. The area of the honeycomb pattern can be separated from the ducts 15 by vertical separation walls 96.

[0153] FIG. 15 also shows vias 14, 14' that extend along the injection direction X through all of the front layer 10.

[0154] FIG. 16 shows a possible arrangement for the electrical vias 14 (and 14'), supply ducts 15, and suction ducts 16 at the height of the backing layer 12. Since the horizontal distribution of the ink ducts 15 , 16 is implemented in the front layer 10 above the backing layer 12, it is possible to supply ink through one or several, possibly large, ink ducts that are arranged outside the convex hull 96 of a regular array of the electrical vias 14, which simplifies the design of the backing layer 12, i.e., the ink ducts do not extend through the backing layer 12 within the convex hull 96.

[0155] Instead of using a honeycomb structure within the sub-layers 10b and / or 10d, for example, a solid layer of glass can be used.

[0156] Honeycomb multi-layer structure As described above, the print head shown here preferably uses one or more honeycomb multi-layer structures. One such multi-layer structure 109 is shown in FIGS. 18 and 19. It has a bottom layer 110, an upper layer 112, and at least one intermediate layer 114 between the bottom layer 110 and the upper layer 102. The intermediate layer 114 forms a wall 116 that extends between the bottom layer 110 and the upper layer 112. These walls form at least part of the walls of a plurality of cavities 118 in the intermediate layer 114 between the bottom layer 110 and the upper layer 112.

[0157] The wall 114 preferably forms a honeycomb pattern.

[0158] In particular, when the bottom layer 110 or the upper layer 112 is a material different from the intermediate layer 114, and / or when it is disposed near or adjacent to another layer that is a material different from the intermediate layer 114, the structure has been found to reduce mechanical stress.

[0159] Examples of the honeycomb multi-layer structure in the above examples are as follows. - In FIGS. 2, 11, and 12: The front layer 10 or the sub-layer 10a is the "bottom layer" 110, the layer 80 of the support structure 8 is the "upper layer" 112, and the wall 76 between them forms the "intermediate layer" 114.

[0160] - In FIGS. 2, 11, and 12: The layer 80 of the support structure is the "bottom layer" 110, the layer 82 of the support structure 8 is the "upper layer" 112, and the wall 76 between them forms the "intermediate layer" 114.

[0161] - In FIGS. 2, 11, and 12: The layer 82 of the support structure is the "bottom layer" 110, the layer 84 of the support structure 8 is the "upper layer" 102, and the wall 76 between them forms the "intermediate layer" 114.

[0162] - In FIGS. 12 and 13: The sub-layer 10c is the "bottom layer" 110, the sub-layer 10a is the "upper layer" 112, and the wall 90 of the sub-layer 10b therebetween forms the "intermediate layer" 114.

[0163] - In FIGS. 12 and 15: The lining layer 12 is the "bottom layer" 110, the sub-layer 10c is the "upper layer" 112, and the wall 94 of the sub-layer 10d therebetween forms the "intermediate layer" 114.

[0164] In the first three examples, the support structure 8 comprises at least the intermediate layer 114 of the multilayer structure.

[0165] In the last two examples, the nozzle carrier 6 comprises at least the intermediate layer 114 of the multilayer structure.

[0166] When the thickness t of the intermediate layer 114 (see FIG. 18) is relatively large, the stress reduction achieved by the multilayer structure is particularly obvious. Preferably, the thickness t is greater than 1 μm, particularly greater than 10 μm.

[0167] Preferably, the intermediate layer 114 is, for example, a polymer layer formed from a structured SU-8 layer. This type of layer can be easily manufactured and structured (see the following manufacturing information), and when using it in the multilayer structure as shown, it reduces stress compared to the solid layer of the material.

[0168] Therefore, preferably, the print head comprises at least one layer of a material different from the intermediate layer, particularly a semiconductor or glass layer.

[0169] The cavity 118 is preferably a closed cavity, that is, the cavity 118 does not form part of the ink duct portion 15b or 16d in FIGS. 15 and 13, and the cavity 118 does not communicate with the surrounding atmosphere.

[0170] When the wall 116 forms a regular repeating pattern, the uniformity is improved and the stress can be further reduced.

[0171] Preferably, the wall 116 has a thickness m of less than 25% of the minimum diameter M of the cavity (see FIG. 19). This leads to a low content of solid material in the intermediate layer and further reduces mechanical stress. In this context, the thickness m is the extent of the wall 116 perpendicular to the surface of the wall 116. The diameter M of the cavity is the extent of the cavity 118 in a direction parallel to the bottom layer and the upper layer 110, 114.

[0172] To optimally remove strain, the minimum diameter M of the cavity 118 is preferably greater than the thickness t of the intermediate layer 114, i.e., M > t. The smaller the cavity extending through the intermediate layer 114, the higher the mechanical stress generated in the intermediate layer.

[0173] The wall 116 preferably extends perpendicular to the bottom layer 110 and the upper layer 112. This not only improves the mechanical stability against forces acting perpendicular to the layer, but also enables the formation of the wall by anisotropic material removal techniques, particularly by photolithography of photoactive polymers.

[0174] Note that the upper and bottom layers of the multilayer structure are parallel to each other.

[0175] The closed cavity 118 is not in communication with the ink duct, i.e., the closed cavity 118 is not used to guide the ink passing through the print head. If the print head has ventilation ducts, the closed cavity 118 is not in communication with these ventilation ducts either.

[0176] The closed cavity 118 can be filled with air. Alternatively, the closed cavity 118 can be evacuated. Or, the closed cavity 118 can be filled with a gas such as nitrogen. Preferably, the closed cavity 118 can be filled with a gas having a high breakdown voltage such as SF6 or C4F8. The gas can be introduced by performing each manufacturing step (see below) within a working space having a desired gas composition.

[0177] Electrode Design The print head is designed to withstand the high electric fields that occur during operation with minimal structural damage.

[0178] For this purpose, the electrodes 38, 40, 42 are arranged between the solid dielectric layers 80a, 80b, 82a, 82b, 84a, 84b that form the boundaries with the cavities. In the illustrated embodiment, the cavities are formed, for example, by the cavities 71, 71', 71'' below the electrode carrier layers 80, 82, 84 and / or by the cavity 118 formed by the wall 116.

[0179] At least a part of the cavity can be a closed cavity (i.e., surrounded by walls on all sides like the cavity 118).

[0180] At least a part of the cavity can be an open cavity, particularly a cavity that is adjacent to and communicates with the outlet passage 5 of the nozzle 4, such as the cavities 71, 71', 71'' in the above embodiment.

[0181] In this design, the solid dielectric layer around the electrode can usually withstand a higher field than the gas in the cavity, also has a higher relative permittivity ε, and thus prevents overall breakdown. At the same time, since there is no fixed molecular or atomic structure in the cavity, the cavity is less susceptible to permanent damage caused by a large electric field. Therefore, this design improves the ability of the print head to withstand the influence of the electric field of the electrode even during long-term operation.

[0182] As can be seen in the embodiments illustrated herein, there are solid support structures, such as walls 76 and 78, that extend vertically between adjacent electrode carrier layers 80, 82, 84. However, preferably, there is no such solid support structure that extends directly between adjacent electrodes. In other words, any straight line extending between two adjacent electrodes extends through at least one of the cavities 71, 71', 71'', or 118. This condition should be met when some or especially all of the adjacent electrodes of the print head are associated with substantially different potentials, especially potentials that differ by at least 100 V of voltage, during operation.

[0183] This condition can be met, for example, by not arranging a solid support structure to extend vertically between the electrodes at the position of the contact lead 38b in FIG. 7 and / or by locally removing a portion of the support structure.

[0184] In yet another embodiment, the electric field strength can be reduced by designing the electric track to be very narrow at positions where there are no cavities between the electrodes. In that case, the track preferably has a width that is less than or equal to half the height of the wall structures 76, 78. For example, if the wall structure has a height of 5 μm, the track should have a width of 2.5 μm or less.

[0185] Preferably, the lateral offset between the electrode and the adjacent (i.e., closest) support structure should be at least 25% of the vertical distance between two adjacent electrodes for at least one of the two adjacent electrodes.

[0186] Preferably, at least one of the dielectric layers that protect the electrodes has a high relative permittivity ε. Thus, the field is weakened therein, and the major voltage drop shifts to the layer with a lower permittivity, especially the cavity. Thereby, the structure can be more fully protected from dielectric breakdown.

[0187] In this regard, a high relative dielectric constant ε is preferably at least 5. Suitable materials are, for example, Si3N4 (having a relative dielectric constant ε of 9.5 to 10.5) or Al2O3 (having an ε of 9.3 to 11.5).

[0188] Preferably, as shown in FIG. 20, some dielectric layers are provided between the cavity 120 and the electrode 122. (The cavity 120 in FIG. 20 represents, for example, the cavity 118 or 71, 71', 71'' of the above example, and the electrode 122 represents one of the electrodes 38, 40, 42 of the above example, particularly the injection electrode 38.)

[0189] In the illustrated embodiment, the electrode 122 is surrounded by the first dielectric layers 124a, 124b, and then the first dielectric layers 124a, 124b are surrounded by the second dielectric layer 126.

[0190] The first dielectric layers 124a, 124b are preferably polymer layers formed of, for example, patterned SU-8 (see the following manufacturing process). The polymer layer has a low relative dielectric constant of, for example, 2.5 to 3.0. It corresponds to, for example, the sub-layers 80a, 80b, 82a, 82b, 84a, 84b of the above-described electrode carrier layers 80, 82, 84 and can be manufactured at least partially using a lamination technique (see below).

[0191] The second dielectric layer 126 is an inorganic layer having a higher dielectric breakdown threshold than the first dielectric layers 124a, 124b. It preferably has a relative dielectric constant higher than that of the first dielectric layers 124a, 124b, particularly twice as high. It can be, for example, Si3N4 or Al2O3 for the reasons described above. It has the highest breakdown resistance among all components between the two electrodes and usually prevents dielectric breakdown.

[0192] Disposing the first dielectric layers 124a, 124b between the electrode 122 and the second dielectric layer 126 has, for example, the advantage that the peak electric field strength at the edge of the electrode 122 is within the first dielectric layer, and thus increases the ability of the second dielectric layer 126 to prevent breakdown.

[0193] Thus, in a preferred embodiment, at least a portion of the cavity 120 is disposed between some different electrodes of the print head or between an electrode of the print head and the ink holding portion 66 of the print head.

[0194] Preferably, the different electrodes 38, 40, 42, 122 are separated from the cavity or cavities 120 by one or more solid dielectric layers 124a, 124b, 126.

[0195] In particular, the one or more solid dielectric layers 124a, 124b, 126 preferably comprise polymer layers 124a, 124 and / or an inorganic layer 126. Preferably, the polymer layers 124a, 124 are disposed between the electrode 122 and the inorganic layer 126.

[0196] Operation of the print head During operation, i.e., during printing, ink is supplied to the print head by the supply duct 15. This ink is restricted to the region 64 between the nozzle 4 and the ink holding portion 66.

[0197] To eject an ink droplet, the voltage at the desired ejection electrode (with respect to the voltage of the ink) is temporarily increased. For example, a voltage pulse of 400 V can be generated. While not printing, the voltage at the ejection electrode is maintained at a level where no ink is ejected. Preferably, it is not zero, but for example, 200 V.

[0198] As described above, the electric field in the ink holding section 66 is preferably low, for example, maintained at less than 50%, particularly less than 10% of the electric field strength at the front end 70 of the nozzle. Since a high electric field strength reduces the surface tension of the ink, this procedure reduces the tendency of the ink to wet and cross the ink holding section.

[0199] The suction duct 16, if present, is used to recover ink from the nozzle. Preferably, the printing method includes the following steps. - Supplying ink to the nozzles individually using the supply duct 15 in the nozzle carrier 6, and - Suctioning ink from the nozzles individually using the suction duct 16 in the nozzle carrier 6.

[0200] Thereby, a fresh ink reservoir can be maintained at the nozzle.

[0201] During operation, the pressure px at the end of the suction duct 16 at a given nozzle is preferably maintained such that the ink is not brought close to the ink holding section 66, for example, at the height 64b in FIG. 2. Preferably, px should not be too low to prevent air from being sucked into the suction duct 16. A suitable pressure can be calculated from the radial width w of the annular duct 62. For an ink having a surface tension of water and w = 5 μm, the Young-Laplace equation results in a pressure difference dp of 144 mbar (about 14.4 kPa). For a liquid having the surface tension of an alkane, the pressure difference dp is 40 mbar (about 4 kPa). Thus, by maintaining the pressure px below dp with respect to the ambient pressure, the surface 64b can be maintained and air is not sucked in.

[0202] If, instead of the annular duct 62, for example, several circular openings with a diameter of 5 μm are used, dp becomes twice as large.

[0203] When the difference between the ambient pressure and px is less than dp, the height of the liquid rises, for example, to line 64a in FIG. 2. There, the curvature is much lower than that of line 64b. In a simplified example, assuming the curvature is 10 times lower, the corresponding pressure difference is 14 mbar (about 1.4 kPa for water). Thus, for example, by maintaining the pressure px 50 mbar (about 5 kPa) lower than the atmospheric pressure, it is possible to prevent the ink from reaching a height similar to that of line 64a.

[0204] On the other hand, the pressure py at the end of the supply duct 15 in a given nozzle can be adjusted to maintain a desired ink flow through the nozzle. Also, as described above, the ink flow through the outlet ducts 56 and 60 can be adjusted by selecting a suitable diameter in these ducts.

[0205] In yet another embodiment, the pressure difference (lower than the ambient pressure) at the end portion 16a of the suction duct 16 can be selected to be greater than dp at the lower height 64b. Thus, air is sucked into the suction duct 16.

[0206] In that case, when the ink returning through the suction duct 16 is reused, a separation device can be used to separate the ink and air before the ink is supplied to the recirculation pump 18.

[0207] Manufacture This printing head can be manufactured, for example, using techniques known from, for example, semiconductor manufacturing and packaging as described in Patent Documents 3 to 5.

[0208] Preferably, at least a part of the layers of the printing head, in particular the intermediate layer 114 of the multilayer structure used therein of the type shown in FIGS. 18 and 19, is a polymer layer.

[0209] The manufacture of the multilayer structure preferably includes the following steps. 1. The step of providing the bottom layer 110. This can be, for example, the upper layer formed by a previous manufacturing step.

[0210] 2. Step of adding a material layer on the bottom layer 110. This material layer forms the intermediate layer 114.

[0211] 3. Step of adding the upper layer 112 above the material layer.

[0212] The material layers deposited in steps 2 and 3 can be added using various techniques such as lamination, spin coating, sputtering, or evaporation.

[0213] In particular, lamination is particularly preferred for adding the upper layer 112. In lamination, the layer is added as a sheet material and is connected to the underlying structure using, for example, heat and pressure. Thereby, the cavity can be easily bridged and / or an overhanging structure can be created.

[0214] The material layer in step 2 is preferably a photoresist such as SU-8, whereby the material layer can be easily structured. In this case, step 2 includes at least the following sub-steps. 2a: Sub-step of irradiating the material layer with collimated light through a mask, thereby defining an irradiated area and a non-irradiated area in the material layer.

[0215] 2b: Sub-step of selectively removing the irradiated area or the non-irradiated area from the material layer depending on whether a positive or negative photoresist is used.

[0216] Alternatively, the upper layer 112 can also be formed from a solid material, such as a glass wafer, which is bonded to the intermediate layer 114 by, for example, adhesive bonding, fusion bonding, eutectic bonding, etc.

[0217] The inorganic dielectric layer 126 (FIG. 20) can be manufactured, for example, by atomic layer deposition in which it is deposited on the polymer dielectric layers 124a, 124b.

[0218] Note In most of the embodiments illustrated heretofore, each nozzle is surrounded by an ink holding portion that defines a restricted area where ink can flow from the nozzle.

[0219] In an example, each nozzle is surrounded by its own ink holding portion. Alternatively, some nozzles may be surrounded by a common ink holding portion, i.e., one ink holding portion may surround several nozzles.

[0220] Alternatively, or in addition thereto, each support element of the support structure 8 may be surrounded by an ink holding portion that defines an ink-free area around the support element and prevents ink from reaching the support element. This may be particularly preferred when the support elements form individual isolated pillars.

[0221] As can be seen in the embodiments illustrated above, the guard electrode 42 is preferably close to the axis of the nozzle. This is shown, for example, in FIG. 12.

[0222] Here, the central axis 100 of the nozzle 4 extending along the ejection direction X is shown by a dashed line. x1 is the distance between the guard electrode 42 and the nozzle axis 100. x2 is the distance between the ink holding portion 66 and the nozzle axis 100. x3 is the distance between the closest support element 78 and the nozzle axis 100 and the support element 78 is an element adjacent to the nozzle carrier 6.

[0223] The following relationships are preferred. x1 < x2, particularly x1 < 0.8·x2: By disposing the guard electrode 42 closer to the nozzle axis 100 than the ink holding portion 66, more sufficient shielding of the ink holding portion 66 is achieved.

[0224] x1 < x3, particularly x1 < 0.8·x3, particularly x1 < 0.5·x3: Again, by disposing the closest support element 78 further away from the axis 100 than the guard electrode 42, the support element is similarly shielded.

[0225] In addition or alternatively, the difference x2 - x1 is preferably at least 50% of the vertical distance d' between the guard electrode 42 and the ink holding portion 66.

[0226] In particular, x3 should be greater than x2 by at least 1 μm, in particular by at least 5 μm.

[0227] Therefore, the following relationships are preferred, either alone or in any combination. - The distance x1 between the guard electrode 42 and the nozzle axis 100 is smaller than the distance x2 between the ink holding portion 66 and the nozzle axis 100.

[0228] - The distance x1 between the guard electrode 42 and the nozzle axis 100 is smaller than the distance x3 between the axis 100 and the support element 78 adjacent to the nozzle carrier 6 and closest to the nozzle axis 100.

[0229] - The difference x2 - x1 (between the distance x1 between the guard electrode 42 and the nozzle axis 100 and the distance x2 between the ink holding portion 66 and the nozzle axis 100) is at least 50% of the vertical distance between the guard electrode 42 and the ink holding portion 66.

[0230] - The distance x3 (between the axis 100 and the support element 78 adjacent to the nozzle carrier 6) is greater than the distance x2 between the ink holding portion 66 and the nozzle axis 100 by at least 1 μm, in particular by at least 5 μm.

[0231] - The difference x2 - x1 (between the distance x1 between the guard electrode 42 and the nozzle axis 100 and the distance x2 between the ink holding portion 66 and the nozzle axis 100) is preferably at least 50% of the vertical distance between the guard electrode 42 and the ink holding portion 66.

[0232] As described above, the print head may also include a gas duct for supplying gas to and / or recovering gas from the area between the print head and the target. The gas duct supply may also include horizontal portions, such as interconnecting portions, in the front layer 10 and / or the backing layer 12 and / or the intervening layer 32, similar to the ink ducts shown in FIGS. 13 and 15.

[0233] In the embodiments described so far, three electrodes at three different vertical heights have been described, namely the ejection electrode, the guard electrode, and the shielding electrode. However, it should be noted that other electrodes may exist as follows. - The electrode may be provided in the nozzle carrier 6, for example, in the supply duct 15 and / or the suction duct 16, and / or in the nozzle and / or the ink holding portion, to define the potential of the ink. The electrode can, for example, keep the ink at the same or a similar potential as the guard electrode 42. Preferably, the electrode is platinum and / or gold.

[0234] - A further electrode (e.g., between the ejection electrode 38 and the shielding electrode 40 in FIG. 2) may be provided when nozzles of different sizes are present in the print head. This is particularly useful for nozzles where the distance between the ejection electrode and the nozzle is significantly smaller than the distance between the shielding electrode and the ejection electrode.

[0235] Although the presently preferred embodiments of the present invention have been illustrated and described, it should be clearly understood that the present invention is not limited thereto and may be variously embodied and implemented in other ways within the scope of the following claims. Note that there are the following embodiments of the present invention. [Embodiment 1] An electrohydrodynamic printing head, a nozzle carrier (6), a plurality of nozzles (4) disposed on the nozzle carrier (6), each nozzle (4) forming a protrusion disposed on the front surface (36) of the nozzle carrier (6) and extending in the ejection direction (X) of the printing head, the plurality of nozzles (4); a plurality of ejection electrodes (38) associated with the nozzles (4) and disposed on the front side of the nozzles (4); a support structure (8) that supports the ejection electrodes (38) on the nozzle carrier (6), the support structure (8) including a plurality of support elements (76, 78) disposed between the nozzles (4), the support structure (8); a plurality of ink holding portions (66) disposed between the nozzles (4) and the support elements, in a given nozzle (4), the nearest ink holding portion (66) being disposed away from the nozzle (4), the plurality of ink holding portions (66); An electrohydrodynamic printing head comprising the above. [Embodiment 2] The printing head according to Embodiment 1, wherein along the ejection direction (X), the front surface (68) of the ink holding portion (66) is disposed behind the front end (70) of the nozzle (4). [Embodiment 3] The printing head according to Embodiment 1 or 2, wherein each ink holding portion (66) forms a ledge portion (66a) facing away from the nearest nozzle (4) to the respective ink holding portion (66). [Embodiment 4] The printing head according to any one of Embodiments 1 to 3, wherein the ink holding portion (66) is disposed protruding from the front surface (36) of the nozzle carrier (6). [Embodiment 5] The printing head according to any one of Embodiments 1 to 4, wherein each nozzle (4) is surrounded by the ink holding portion (66). [Embodiment 6] The printing head according to any one of Embodiments 1 to 5, wherein each support element (76, 78) is surrounded by the ink holding portion (66). [Embodiment 7] The printing head according to any one of aspects 1 to 6, wherein, in a given nozzle (4), the surface of the ink holding portion (66) is more hydrophobic and / or oleophobic than the surface of the nozzle (4). [Aspect 8] There is a first recess (58, 62) disposed between the given nozzle (4) and the ink holding portion (66) between the given nozzle (4) and a support element (78) adjacent to the nozzle carrier (6) closest to the nozzle (4), and / or there is a second recess (86) disposed between the ink holding portion (66) and the closest support element (78). In particular, along the injection direction (X), the bottom of the first and / or second recess is behind the front surface (68) of the ink holding portion (66). The printing head according to any one of aspects 1 to 7. [Aspect 9] The ink holding portion (66) is disposed laterally on the nozzle (4) away from the front end (70) of the nozzle (4). In particular, the front surface (68) of the ink holding portion (66) is closer to the front surface (36) of the nozzle carrier (6) than the front end (70) of the nozzle (4). The printing head according to any one of aspects 1 to 8. [Aspect 10] Comprising a guard electrode (42), in a given nozzle (4), the guard electrode (42) is disposed between the injection electrode (38) and the ink holding portion (66). In particular, in a given nozzle (4), the guard electrode (42) is disposed in front of the ink holding portion (66), and the injection electrode (38) is disposed in front of the guard electrode (42). The printing head according to any one of aspects 1 to 9. [Aspect 11] The electrical potential of the guard electrode (42) is configured to be closer to the electrical potential of the ink holding portion (66) than the electrical potential of the injection electrode (38). In particular, the voltage supply (17) is further provided, and the potential of the guard electrode (42) is configured to be set to the same potential as the ink holding portion (66). The printing head according to aspect 10. [Aspect 12] In a given nozzle (4), there is a cavity (71) formed between the guard electrode and the ink holding portion (66). The printing head according to any one of aspects 10 or 11. [Aspect 13] The guard electrode (42) is attached to the support structure (8), the print head according to any one of aspects 10 to 12. [Aspect 14] For a given nozzle (4), the nozzle (4) has a central nozzle axis (100) extending along the ejection direction (X), and the guard electrode (42) has a distance x1 from the nozzle axis (100), the distance x1 is smaller than the distance x2 between the ink holding portion (66) and the nozzle axis (100), in particular, x1 < 0.8·x2, and / or the distance x1 is smaller than the distance x3 between the nozzle axis (100) and the support element (78) adjacent to the nozzle carrier (6) closest to the nozzle axis (100), in particular, x1 < 0.8·x3, in particular, x1 < 0.5·x3, and / or the difference x2 - x1 between the distance x1 and the distance x2 between the ink holding portion (66) and the nozzle axis (100) is at least 50% of the vertical distance (d') between the guard electrode (42) and the ink holding portion (66), the print head according to any one of aspects 10 to 13. [Aspect 15] In the nozzle carrier (6), further comprising a plurality of ink supply ducts (15) for the nozzle (4), in particular, at least one ink supply duct (15) ends at each nozzle (4), the print head according to any one of aspects 1 to 14. [Aspect 16] In a given nozzle (4), the closest ink holding portion (66) surrounds the nozzle (4) and the end portion (15a) of the supply duct (15), the print head according to aspects 5 and 15. [Aspect 17] In a given nozzle (4), the supply duct (15) appears at the base portion (50, 52) of the nozzle (4), the print head according to aspect 16. [Aspect 18] The supply duct (15) is connected to at least one transverse outlet duct (56), in particular a plurality of transverse outlet ducts (56) extending transversely to the ejection direction (X), the print head according to aspect 17. [Aspect 19] An electrohydrodynamic print head, in particular, the print head according to any one of aspects 1 to 18, a nozzle carrier (6), A plurality of nozzles (4) arranged on the nozzle carrier (6), each nozzle (4) being arranged on the front surface (36) of the nozzle carrier (6) and forming a protrusion extending in the ejection direction (X) of the print head, said plurality of nozzles (4); A plurality of ejection electrodes (38) associated with the nozzles (4) and arranged on the front side of the nozzles (4); A plurality of ink supply ducts (15) for the nozzles (4), at least one ink supply duct (15) ending at each nozzle (4), said plurality of ink supply ducts (15); A plurality of ink suction ducts (16), at least one ink suction duct (16) ending at each nozzle (4), said plurality of ink suction ducts (16); An electrohydrodynamic print head comprising the above. [Aspect 20] The print head according to any of Aspects 17 or 18 and Aspect 19, wherein in a given nozzle (4), the closest ink holding portion (66) surrounds the end portion (16a) of the suction duct (16). [Aspect 21] The print head according to Aspect 19 or 20, further comprising at least one pump (18) connected to the supply duct (15) and / or the suction duct (16). [Aspect 22] In a given nozzle (4), The supply duct (15) is connected to at least one transverse outlet duct (56), particularly a plurality of transverse outlet ducts (56), extending transversely to the ejection direction (X), and in addition, The supply duct (15) is connected to an axial outlet duct (60) extending towards the tip of the nozzle (4), the print head according to any of Aspects 19 to 21. [Aspect 23] For a given nozzle (4), the nozzle is surrounded by the opening or openings (16a) of one or more suction ducts (16), said opening or openings being arranged between the nozzle (4) and the adjacent support element (78) of the nozzle (4), the print head according to any of Aspects 19 to 22. [Aspect 24] The nozzle carrier (6) comprises A front layer (10) to which the nozzles (4) are attached on the front surface (36) of the front layer (10), said front layer (10); A backing layer (12) arranged on the rear side of the front layer (10); Comprising the above. The electrical via (14) connected to the injection electrode (38) extends through the front layer (10) and the backing layer (12), The ink ducts (14, 16) are arranged in the front layer (10), the print head according to any one of aspects 1 to 23. [Aspect 25] The front layer (10) is a dielectric layer, and / or The backing layer (12) is a dielectric layer, in particular a glass layer, the print head according to aspect 24. [Aspect 26] In the front layer (10), it has interconnecting portions (15d, 16b) for the ink that extend transversely, in particular perpendicularly, to the injection direction (X), any one of aspects 16 to 23, and the print head according to any one of aspects 24 to 25. [Aspect 27] A plurality of said vias (14) are arranged in an array in the backing layer (12), The ink ducts (15, 16) do not extend through the backing layer (12) within the convex hull (96) of the array, the print head according to aspect 26. [Aspect 28] A method of operating a print head according to any one of aspects 1 to 27, comprising the step of confining the ink by using the ink holding portion (66) and / or by sucking ink from the nozzle (4) by using a suction duct (15) in a region around a given nozzle (4). [Aspect 29] Generating an electric field at at least one front end (70) of the nozzles (4), and by said generation, ejecting the ink from the front end (70) while maintaining the electric field in the ink holding portion (66) at less than 50%, in particular less than 10%, of the intensity of the electric field at the front end (70) of the nozzles (4), the method according to aspect 28. [Aspect 30] Individually supplying ink to the nozzles (4) using an ink supply duct (15) within the nozzle carrier (6), Individually sucking ink from the nozzles (4) using an ink suction duct (16) within the nozzle carrier (6), Including, the method according to any one of aspects 28 or 29.

Claims

1. An electrohydrodynamic printing head, comprising: a nozzle carrier (6); a plurality of nozzles (4) disposed on the nozzle carrier (6), each nozzle (4) being disposed on the front surface (36) of the nozzle carrier (6) and forming a protrusion extending in the ejection direction (X) of the electrohydrodynamic printing head; a plurality of ejection electrodes (38) associated with the nozzles (4) and disposed on the front side of the nozzles (4); a support structure (8) for supporting the ejection electrodes (38) on the nozzle carrier (6), the support structure (8) comprising a plurality of support elements (76, 78) disposed between the nozzles (4); a plurality of ink holding portions (66) disposed between the nozzles (4) and the support elements, in a given nozzle (4), the nearest ink holding portion (66) being disposed away from the nozzle (4); An electrohydrodynamic printing head comprising the above components.

2. The printing head according to claim 1, wherein along the ejection direction (X), the front surface (68) of the ink holding portion (66) is disposed behind the front end (70) of the nozzle (4).

3. The printing head according to claim 1 or 2, wherein each ink holding portion (66) forms a ledge portion (66a) facing away from the nearest nozzle (4) to the respective ink holding portion (66).

4. The printing head according to any one of claims 1 to 3, wherein the ink holding portion (66) is disposed protruding from the front surface (36) of the nozzle carrier (6).

5. The printing head according to any one of claims 1 to 4, wherein each nozzle (4) is surrounded by the ink holding portion (66).

6. The printing head according to any one of claims 1 to 5, wherein each support element (76, 78) is surrounded by the ink holding portion (66).

7. The printing head according to any one of claims 1 to 6, wherein in a given nozzle (4), the surface of the ink holding portion (66) is more hydrophobic and / or oleophobic than the surface of the nozzle (4).

8. Between a given nozzle (4) and a support element (78) adjacent to the nozzle carrier (6) closest to the nozzle (4), there is a first recess (58, 62) arranged between the nozzle (4) and the ink holding part (66), and / or there is a second recess (86) arranged between the ink holding part (66) and the closest support element (78). In particular, along the injection direction (X), the bottom of the first and / or second recess is behind the front surface (68) of the ink holding part (66). The print head according to any one of claims 1 to 7.

9. The ink holding part (66) is arranged horizontally on the nozzle (4) away from the front end (70) of the nozzle (4). In particular, the front surface (68) of the ink holding part (66) is closer to the front surface (36) of the nozzle carrier (6) than the front end (70) of the nozzle (4). The print head according to any one of claims 1 to 8.

10. Comprising a guard electrode (42), in a given nozzle (4), the guard electrode (42) is arranged between the injection electrode (38) and the ink holding part (66). In particular, in a given nozzle (4), the guard electrode (42) is arranged in front of the ink holding part (66), and the injection electrode (38) is arranged in front of the guard electrode (42). The print head according to any one of claims 1 to 9.

11. The electrical potential of the guard electrode (42) is configured to be closer to the electrical potential of the ink holding part (66) than the electrical potential of the injection electrode (38). In particular, the electrical potential of the guard electrode (42) is configured to be set to the same potential as the ink holding part (66). Further comprising a voltage supply (17). The print head according to claim 10.

12. In a given nozzle (4), there is a cavity (71) formed between the guard electrode and the ink holding part (66). The print head according to any one of claims 10 or 11.

13. The guard electrode (42) is attached to the support structure (8). The print head according to any one of claims 10 to 12.

14. For a given nozzle (4), the nozzle (4) has a central nozzle axis (100) extending along the injection direction (X), and the guard electrode (42) has a distance x1 from the central nozzle axis (100), the distance x1 is smaller than the distance x2 between the ink holding part (66) and the central nozzle axis (100), in particular, x1 < 0.8 · x2, and / or the distance x1 is smaller than the distance x3 between the central nozzle axis (100) and the support element (78) adjacent to the nozzle carrier (6) closest to the central nozzle axis (100), in particular, x1 < 0.8 · x3, especially x1 < 0.5 · x3, and / or the difference x2 - x1 between the distance x1 and the distance x2 between the ink holding part (66) and the central nozzle axis (100) is at least 50% of the vertical distance (d') between the guard electrode (42) and the ink holding part (66), the print head according to any one of claims 10 to 13.

15. In the nozzle carrier (6), further comprising a plurality of ink supply ducts (15) for the nozzle (4), in particular, at least one ink supply duct (15) ends at each nozzle (4), the print head according to any one of claims 1 to 14.

16. In the nozzle carrier (6), further comprising a plurality of ink supply ducts (15) for the nozzle (4), in particular, at least one ink supply duct (15) ends at each nozzle (4), In a given nozzle (4), the closest ink holding part (66) surrounds the nozzle (4) and the end portion (15a) of the ink supply duct (15), the print head according to claim 5.

17. In a given nozzle (4), the ink supply duct (15) appears at the base portion (50, 52) of the nozzle (4), the print head according to claim 16.

18. The ink supply duct (15) is connected to at least one transverse outlet duct (56), in particular a plurality of transverse outlet ducts (56), extending transversely to the injection direction (X), the print head according to claim 17.

19. An electrohydrodynamic print head, a nozzle carrier (6), A plurality of nozzles (4) arranged on the nozzle carrier (6), each nozzle (4) being arranged on the front surface (36) of the nozzle carrier (6) and having a protrusion extending in the ejection direction (X) of the electrohydrodynamic printing head, said plurality of nozzles (4); A plurality of ejection electrodes (38) associated with the nozzles (4) and arranged on the front side of the nozzles (4); A plurality of ink supply ducts (15) for the nozzles (4), at least one ink supply duct (15) ending at each nozzle (4), said plurality of ink supply ducts (15); A plurality of ink suction ducts (16), at least one ink suction duct (16) ending at each nozzle (4), said plurality of ink suction ducts (16); An electrohydrodynamic printing head comprising the above.

20. A support structure (8) for supporting the ejection electrodes (38) on the nozzle carrier (6), said support structure (8) comprising a plurality of support elements (76, 78) arranged between the nozzles (4), said support structure (8); A plurality of ink holding portions (66) arranged between the nozzles (4) and the support elements, in a given nozzle (4), the nearest ink holding portion (66) being arranged away from the nozzle (4), said plurality of ink holding portions (66); In a given nozzle (4), the ink supply duct (15) appears at the base portions (50, 52) of the nozzle (4); In a given nozzle (4), the nearest ink holding portion (66) surrounds the end portion (16a) of the ink suction duct (16). The printing head according to claim 19.

21. The printing head according to claim 20, wherein the ink supply duct (15) is connected to at least one transverse outlet duct (56), in particular a plurality of transverse outlet ducts (56), extending transversely to the ejection direction (X).

22. The printing head according to any one of claims 19 to 21, further comprising at least one pump (18) connected to the ink supply duct (15) and / or the ink suction duct (16).

23. In a given nozzle (4) The ink supply duct (15) is connected to at least one transverse outlet duct (56), in particular a plurality of transverse outlet ducts (56), which extends transversely to the injection direction (X), and in addition, The ink supply duct (15) is connected to an axial outlet duct (60) extending towards the tip of the nozzle (4), the print head according to any one of claims 19 to 22.

24. For a given nozzle (4), the nozzle is surrounded by an opening or openings (16a) of one or more ink suction ducts (16), the opening or openings being arranged between the nozzle (4) and a support element (78) adjacent to the nozzle (4), the print head according to any one of claims 19 to 23.

25. The nozzle carrier (6) is a front layer (10), the nozzle (4) being attached to the front side of the front layer (10), the front layer (10) and a backing layer (12) arranged on the rear side of the front layer (10), comprising the electrical vias (14) connected to the injection electrodes (38) extend through the front layer (10) and the backing layer (12), the ink ducts (15, 16) are arranged in the front layer (10), the print head according to any one of claims 1 to 24.

26. The front layer (10) is a dielectric layer and / or the backing layer (12) is a dielectric layer, in particular a glass layer, the print head according to claim 25.

27. In the front layer (10), there are provided interconnecting portions (15d, 16b) for the ink that extend transversely, in particular perpendicularly, to the injection direction (X), the print head according to any one of claims 25 to 26.

28. A plurality of the electrical vias (14) are arranged in an array in the backing layer (12), the ink ducts (15, 16) do not extend through the backing layer (12) within the convex hull (96) of the array, the print head according to claim 27.

29. A method of operating a print head according to any one of claims 1 to 28, comprising the step of confining ink by using an ink holding portion (66) and / or by sucking ink from the nozzle (4) by using an ink suction duct (16) in a region around a given nozzle (4).

30. generating an electric field at at least one front end (70) of the nozzle (4), and by the generation, while ejecting ink from the front end (70), maintaining the electric field in the ink holding part (66) at less than 50%, particularly less than 10%, of the intensity of the electric field at the front end (70) of the nozzle (4), the method according to claim 29

31. individually supplying ink to the nozzle (4) using an ink supply duct (15) within the nozzle carrier (6); individually sucking ink from the nozzle (4) using an ink suction duct (16) within the nozzle carrier (6); The method according to any one of claims 29 or 30, comprising:

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