Electrohydrodynamic printhead with ink pinning - Patent Application 20070123633

Abstract

The electrohydrodynamic print head comprises a nozzle carrier (6) on which a plurality of nozzles (4) are disposed. A plurality of ejection electrodes (38) are associated with the nozzles (4). The print head further comprises at least one multi-layer structure (109) having a bottom layer (110), a top layer (112), and at least one intermediate layer (114) between the bottom layer (110) and the top layer (112). The intermediate layer (114) forms walls (116) extending between the bottom layer (110) and the top layer (112) arranged in a honeycomb pattern. A plurality of cavities (118) are disposed in the intermediate layer (114), which is a polymeric material and may have a substantial thickness.

Description

[Technical field]

[0001] The present invention relates to an electrohydrodynamic printhead and a method for manufacturing the electrohydrodynamic printhead. [Background technology]

[0002] US Patent No. 5,399,633 describes an electrohydrodynamic printhead having a nozzle carrier with a number of nozzles. The electrohydrodynamic printhead is designed to eject ink along an ejection direction. The nozzles form projections extending along this ejection direction. An ejection electrode is associated with the nozzle and is arranged on the target side of the nozzle. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 6,631,983 [Patent Document 2] International Publication No. 2013 / 000558 [Patent Document 3] International Publication No. 2016 / 120381 [Patent Document 4] International Publication No. 2016 / 169956 Summary of the Invention [Problem to be solved by the invention]

[0004] The problem to be solved by the present invention is to provide a specific printhead of this type and a method for its manufacture. [Means for solving the problem]

[0005] This problem is solved by a print head according to claim 1.

[0006] Thus, the print head may comprise at least the following elements: Nozzle carrier: This is the substrate on which the nozzles are arranged.

[0007] a plurality of nozzles disposed on the carrier, the nozzles defining the locations from which ink is ejected;

[0008] - A number of ejection electrodes associated with the nozzles and arranged in front of the nozzles: the ejection electrodes are used, for example, to eject ink individually from the nozzles associated with them.

[0009] The printhead comprises at least one multi-layer structure having a bottom layer, a top layer, and at least one intermediate layer between the bottom layer and the top layer, the intermediate layer forming a wall extending between the bottom layer and the top layer, and a plurality of cavities disposed in the intermediate layer between the bottom layer and the top layer.

[0010] The wall may form at least a part of a wall of the cavity.

[0011] Preferably, at least some of the cavities, in particular the majority of the cavities, are closed cavities, i.e. they are closed on all sides, in particular by walls and by bottom and top layers. This aspect of the invention is based on the understanding that the cavities have applications other than as ducts. In particular, they can be used to reduce mechanical stresses and / or to shape electric fields.

[0012] In one embodiment, the walls form a honeycomb structure, i.e., a hexagonal pattern, between the bottom and top layers, which has been found to reduce mechanical stress.

[0013] In an important aspect of the invention, at least a portion of the cavity is located between different electrodes of the printhead, or between an electrode and an ink retaining portion of the printhead. In this context, "different electrodes" are preferably electrodes that may be subject to different voltages during operation of the printhead. This design improves the ability of the printhead to withstand the effects of electric fields.

[0014] Preferably, each different electrode is separated from the cavity or cavities by one or more solid dielectric layers, which serve to prevent electrical breakdown between the electrodes.

[0015] The electrodes may be attached to a bottom layer and / or a top layer of a multi-layer structure, in particular, some electrodes are attached to the bottom layer and other electrodes are attached to the top layer.

[0016] Preferably, the electrodes are embedded in the bottom and / or top layers, the bottom and / or top layers forming a dielectric solid layer covering the electrodes from the bottom and top sides.

[0017] The print head may further comprise a guard electrode arranged at a height behind the ejection electrodes, in the present context "at a height behind the ejection electrodes" indicating that the guard electrode is closer to the nozzle carrier than the ejection electrodes, which may be used to reduce the electric field strength behind it, for example to reduce fields in structures that hold (retain) ink.

[0018] In this case, for a given nozzle, at least a portion of the cavity may be located between the guard electrode and the ejection electrode, thereby reducing the risk of electrical breakdown between the ejection electrode and the guard electrode.

[0019] The print head may further comprise at least one shield electrode arranged at a level in front of the ejection electrodes, which in the present context indicates that the ejection electrodes are closer to the nozzle carrier than the shield electrode, which may be used to control the electric field between the print head and the target.

[0020] In this case, for a given nozzle, at least a portion of the cavity may be located between the ejection electrode and the shielding electrode, thereby reducing the risk of electrical breakdown between the ejection electrode and the shielding electrode.

[0021] As stated, the print head has a nozzle carrier with nozzles attached to it, in one embodiment the nozzle carrier may comprise the multi-layer structure described above (or at least one of several such multi-layer structures, if present).

[0022] In a preferred design, the nozzle carrier comprises at least the following parts: - Front layer: The nozzle is attached to the front side of the front layer.

[0023] - A lining layer placed behind the front layer.

[0024] Electrical vias connected to the ejection electrodes may extend through the front layer and the backing layer, the electrical vias providing a voltage to the ejection electrodes.

[0025] In addition, the ink supply ducts are located (at least) in the front layer.

[0026] In this case, the front layer may comprise the intermediate layer (or at least one of the layers, if several such multi-layer structures are present), which allows the formation of thick ink ducts without creating excessive mechanical strain in the printhead.

[0027] The print head may comprise a support structure supporting the ejection electrodes on the nozzle carrier, the support structure comprising a plurality of support elements arranged between the nozzles, in which case the support structure preferably comprises at least an intermediate layer of the multi-layer structure (or at least one of them, if several such multi-layer structures are present).

[0028] In this case, the print head may further comprise a number of ink retainers arranged between the nozzles and the support element, the ink retainers preventing ink from reaching and wetting the support element, the front faces of the ink retainers being arranged at a height behind the front ends of the nozzles (i.e. closer to the nozzle carrier) along the jetting direction, i.e. the ink retainers are set rearward relative to the protrusions along the jetting direction.

[0029] The method of manufacturing the printhead preferably comprises at least the following steps. - adding a layer of material on top of said bottom layer, which will later form at least part of the intermediate layer, said material can be for example a permanent photoresist such as SU8.

[0030] - Removing part of the layer of material: this leaves the wall in place and forms the cavity.

[0031] - Adding a top layer above the layer of material.

[0032] The invention will be better understood and other objects than those set forth above will become apparent from a consideration of the following detailed description thereof, which description makes reference to the accompanying drawings, in which: [Brief description of the drawings]

[0033] [Figure 1] FIG. 1 shows a partial cross-sectional view of a print head and target. [Diagram 2] FIG. 2 is a vertical cross-section through a first embodiment of a nozzle. [Diagram 3] FIG. 3 is a horizontal cross-sectional view taken along line AA in FIG. [Figure 4] FIG. 4 is a horizontal cross-sectional view taken along line BB in FIG. [Diagram 5] FIG. 5 is a horizontal cross-sectional view taken along line CC in FIG. [Figure 6] FIG. 6 shows several alternative nozzle tip designs in addition to the cross-sectional design of FIG. [Figure 7] FIG. 7 is a horizontal cross-sectional view taken along line DD in FIG. [Figure 8] FIG. 8 is a horizontal cross-sectional view taken along line EE in FIG. [Figure 9] FIG. 9 is a vertical cross-section through a second embodiment of a nozzle. [Figure 10] FIG. 10 is a horizontal cross-sectional view taken along line AA in FIG. [Figure 11] FIG. 11 is a vertical cross-section through a third embodiment of a nozzle. [Figure 12] FIG. 12 is a vertical section through a fourth embodiment of a nozzle, which basically corresponds to the first embodiment, but shows the design of the nozzle support. [Figure 13] FIG. 13 is a horizontal cross-sectional view taken along line AA in FIG. [Figure 14] FIG. 14 is a horizontal cross-sectional view taken along line BB in FIG. [Figure 15] FIG. 15 is a horizontal cross-sectional view taken along line CC in FIG. [Figure 16] FIG. 16 is a horizontal cross-sectional view taken along line DD in FIG. [Figure 17] FIG. 17 is a vertical cross section showing two possible via designs for electrode routing. [Figure 18] FIG. 18 shows a multi-layer honeycomb structure. [Figure 19] FIG. 19 shows the inter-story wall design. [Figure 20] FIG. 20 shows a vertical cross-sectional view of an electrode with an embodiment of a dielectric layer surrounding the electrode. [Figure 21] FIG. 21 is a vertical cross-sectional view of an embodiment without an ink retainer.

[0034] Note: while the jetting direction X in Fig. 1 points downwards and the target is located below the print head, the jetting direction X in all other figures showing vertical cross sections points upwards, i.e. Fig. 1 is rotated 180° with respect to all other figures showing cross sections parallel to the jetting direction. Rather, the orientation in those figures is based on the way the manufacturing proceeds, i.e. lower layers are manufactured before upper layers. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] definition "Front" defines the direction that the printhead is designed to eject ink, e.g., the ejection electrodes are in front of the nozzles.

[0036] "Behind" defines the opposite direction, e.g., the nozzle is located behind the ejection electrode.

[0037] "In front of" and "in rear of" are understood to indicate a position at a height in front of or behind something else.

[0038] "Front" and "rear" mean the front and rear.

[0039] The property "for a given nozzle" is preferably understood as a property that applies to the majority, in particular at least 90% of the nozzles. For example, when it says "for a given nozzle, the guard electrode is located between the ejection electrode and the ink retainer", this preferably means that it applies to the majority, in particular at least 90% of the nozzles. For example, this may be some nozzles that do not have ejection electrodes and / or guard electrodes, such as nozzles at the edge of the print head and / or unused nozzles.

[0040] The printhead jetting direction X defines a "vertical" upward direction, i.e. the printhead is, by definition, designed to jet ink upward (which, of course, in operation may be less than any angle relative to the direction of gravity). Thus, definitions such as "upward" and "downward" should be understood with reference to this definition of "vertical".

[0041] "Horizontal" is any direction perpendicular to the vertical direction.

[0042] "Horizontal" indicates something horizontal from something else.

[0043] Print head Figure 1 shows a schematic cross-sectional view of an embodiment of a print head 1. It is depicted above a target 2, which is configured to eject ink along an ejection direction X at the target.

[0044] The print head comprises a plurality of nozzles 4 arranged on the forward side of a nozzle carrier 6. The nozzles 4 may be arranged in a one or two dimensional array.

[0045] The print head comprises a number of ejection electrodes (not shown in FIG. 1) which eject ink from nozzles 4, and optional further electrodes disposed on a support structure 8, the design of which is described in more detail below. The further electrodes may be provided in electrical contact with the ink to set the ink at a defined electrical potential.

[0046] The nozzle carrier 6 comprises a front layer 10, on whose front side the nozzles 4 are attached and form projections thereon. It also comprises a backing layer 12 arranged on the rear side of the front layer 10.

[0047] The internal structure of the front layer 10 is not shown in Figure 1 but will be described in more detail below. It may for example be a dielectric, in particular a polymer.

[0048] The lining layer 12 may be, for example, an insulating semiconducting material, or it may be a dielectric. Preferably, the lining layer 12 is at least partially glass.

[0049] Electrical vias 14 are connected to the ejection electrodes and extend through the front layer 10 and backing layer 12 to connect the ejection electrodes to a voltage supply 17. Preferably, there is at least one via 14 for each nozzle 4. Further vias may be provided to connect other electrodes to the voltage supply 17.

[0050] Ink ducts 15, 16 supply ink to the nozzles 4 and (optionally) return and recycle ink from the nozzles 4. They are partly arranged in the front layer 10 and they extend through the peripheral area of ​​the backing layer 12. Their design will be described in more detail below.

[0051] FIG. 1 shows an embodiment of a printhead having a supply duct 15 and a suction duct 16 for ink.

[0052] To supply ink to the supply duct 15, at least one pump 18 and / or another pressure or vacuum source is provided to withdraw ink from the suction duct 16, if one is present.

[0053] Preferably, the print head comprises a first pressure control 20 which generates a first defined pressure p1 at the input of the supply duct 15, for example a reservoir tank 22.

[0054] Ink is supplied to the nozzles 4 through an optional filter 24 and a supply duct 15 .

[0055] If the suction duct 16 is present, it is connected to a suction system which may comprise a second pressure control 26 generating a second defined pressure p2 at the outlet of the suction duct 16, for example a suction tank 28. The suction system may also comprise a pump, which may in particular be the pump 18 as described above, in which case the pump 18 functions as a circulation pump.

[0056] A suitable pump design is shown, for example, in US Pat. No. 5,399,633.

[0057] As further shown in FIG. 1, the printhead may include a circuit carrier 30, such as a PCB, located on the rear side of the nozzle carrier 6.

[0058] An optional interposer 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 circuitry of the circuit carrier 30. Such an interposer layer is used, for example, in flip-chip designs where a semiconductor chip is added to a PCB.

[0059] The circuit carrier 30 supports a control circuit 33 which may for example implement at least a part of the voltage supply 17, for example a driver stage of said voltage supply, connecting the voltage source to the respective electrodes of the print head.

[0060] In the illustrated embodiment, the ink ducts 15 , 16 extend through the interposer layer 32 (if present) and through the circuit carrier 30 .

[0061] If the vias 14 have a sufficiently large mutual spacing (eg, greater than 0.4 mm), the vias 14 may interface directly with the circuit carrier 30 without the intervening layer 32 .

[0062] Preferably, the target 2 is arranged on an accelerating electrode which is connected to a voltage supply 17 to generate an accelerating electric field between the print head 1 and the target 2 .

[0063] Pressure controls 20, 26 may be used to maintain the pressure as described below in the section on print head operation. Preferably, they are capable of adjusting the pressure in the supply duct 15 and the pressure duct 16 separately.

[0064] Nozzle Design 1 Figures 2 to 8 show a first embodiment of a nozzle 4 and surrounding elements (as mentioned above, in contrast to Figure 1, the jet direction X in Figure 2 points upwards).

[0065] As can be seen in figure 2, the nozzle 4 forms a protrusion on the front side 36 of the nozzle carrier 6, for example on the front side of its front layer 10. It is arranged in an outlet passage 5 through which ink can be ejected towards the target 2.

[0066] FIG. 2 also illustrates various electrodes that may be associated with the nozzle 4.

[0067] An ejection electrode 38 is arranged on the front side of the nozzle 4. In the embodiment of Figures 2 and 7 it is annular with a central opening 39 for the passage of ink. It is connected to one of the vias 14 which extend through the support structure 8 and the nozzle carrier 6.

[0068] Figures 3 and 4 show two possible implementations of the vias 14. On the right, under reference number 14, a hollow implementation is shown, where the vias are formed as a metal coating 14a in a dielectric tube 14b that extends along the jetting direction and surrounds a central duct 14c, which can also be used as a ventilation duct to supply gas to / from the region between the print head and the target. This type of structure can be used, for example, in a) forming tube 14b with a honeycomb structure as described below; and b) It may be formed by forming a metal coating 14a within the tube 14b, for example by sputtering.

[0069] An alternative design, shown under reference numeral 14', includes a solid metal core 14'a within a dielectric tube 14'b. Again, the tube 14'b may be formed with a honeycomb structure as described below, and the metal core 14'a may be formed, for example, by electroplating.

[0070] Alternative via designs 14, 14' are also shown in Figure 17. Hollow via design 14 is depicted for connecting shield electrode 40, while filled via design 14' is depicted for injection electrode 38 (not visible in Figure 17). Note: Only metal portions are shown as hatched areas in Figure 17, while other cross-sectional portions are not hatched.

[0071] Typically a single printhead will only use vias of one design, and for illustrative purposes only, two different types are shown in Figures 3, 4 and 17.

[0072] 2 and 8, the shield electrode 40 may be located away in front of the ejection electrode 38, i.e. closer to the nozzle carrier 6 than the shield electrode 40. Preferably, there is one continuous shield electrode 40 extending in front of the print head 1, but there may be several such shield electrodes.

[0073] If several shielding electrodes are used, they can be applied to different potentials, for example by applying a voltage gradient, for example by a voltage divider, which makes it possible to gradually deflect the ink in a cross section of the print head.

[0074] A shield electrode 40 is provided to control the field between the print head 1 and the target 2. For each nozzle 4, an opening 41 in the shield electrode 40 allows the passage of ink.

[0075] As shown in Figures 2 and 5, the guard electrode 42 may be spaced behind the ejector electrode 38, but may be spaced forward of the nozzle carrier 6. Again, as shown in Figures 2 and 5, it may be annular. Alternatively, it may also extend across several nozzles.

[0076] An opening 43 in the guard electrode 42 above the nozzle 4 allows ink to pass through.

[0077] The function of the guard electrode 42 is described below.

[0078] The nozzle 4 in this embodiment comprises a tip portion 46, a shaft portion 48, and base portions 50, 52, with the tip portion 46 being positioned in front of the shaft portion 48 and the base portions 50, 52 (Figures 2 and 3) being positioned behind the shaft portion 48.

[0079] The nozzle design shown relies on ink wetting the lateral surfaces of the nozzle 4 and not on ink passing through a central flow path of the nozzle 4 (as is known, for example, from U.S. Pat. No. 5,393,363), although the latter could be used as well.

[0080] Where the nozzle 4 has a central flow passage, for example where the exit duct 60 extends all the way to the tip of the nozzle, the nozzle 4 is preferably still operated so that the ink wets not only the top of the nozzle but also the outside to the side of it. By ensuring that ink covers the outside of all nozzles, all nozzles present the same ink profile to the ejection electrodes, which can result in more uniform ink ejection across the printhead.

[0081] To facilitate a desired flow of ink along the nozzle 4 in the jetting direction X, the nozzle 4 preferably has, in its lateral surface, i.e. in the surface extending along the jetting direction X, at least one groove extending along the jetting direction X. This groove extends along at least a part of the length of the nozzle 4.

[0082] This can be seen, for example, in FIG. 5, where tip portion 46 is shown in cross-sectional shape (with four recesses 46a formed between the arms of the cross) and shaft portion 48 defines two grooves 48a.

[0083] FIG. 6 shows an alternative design for tip portion 46 . (a) is a tip portion 46 having a convex lateral surface and being, for example, a cylinder without grooves - this is the presently preferred design because it creates the desired meniscus for the ejected ink; (b) shows the tip portion 46 having two lateral grooves 46a formed therein; (c) is the tip portion where the axial tube 46c is formed.

[0084] Base portions 50, 52 connect the tip portion 46 and shaft portion 48 to the nozzle carrier 6. It also contains the ducts which supply ink to the nozzles. This can be best seen in Figures 2, 3 and 4.

[0085] In particular, in the illustrated embodiment, the base portion 50, 52 comprises a bottom sub-layer 52 and a top sub-layer 50. The bottom sub-layer 52 has a central opening 54 which opens into the end of the feed duct portion 15a which supplies ink to the nozzles 4. One or more radial transverse outlet ducts 56 extend outwardly from the central opening 54 transversely to the jetting direction X towards a first annular duct 58.

[0086] In FIG. 2, the flow of ink in the ducts is depicted by arrows.

[0087] The upper sub-layer 50 may also form an axial outlet duct 60 that extends towards the tip of the nozzle and connects the supply duct portion 15a to a groove 48a in the shaft portion 48 (FIG. 5), thereby guiding ink directly up towards the tip portion 46.

[0088] The upper sublayer 50 may be surrounded by a second annular duct 62 aligned with the first annular duct 58 surrounding the nozzle 4 .

[0089] The nozzle 4 is surrounded by an ink retaining portion 66, the purpose of which is to retain the ink laterally. An annular duct 62 is disposed radially between the ink retaining portion 66 and the nozzle 4, thereby communicating with the area 64 between the nozzle 4 and the ink retaining portion 66.

[0090] A front surface 68 of the ink retaining portion 66 (i.e., the forward-facing surface closest to the ejection electrode 38) is set aft along the ejection direction X relative to a forward end 70 of the nozzle 4. Thus, when ink is present in the region 64, the surface of the ink forms an upward slope, as shown by the dashed and dotted line, towards the tip of the nozzle 4, ensuring that the tip is closest to the ejection electrode 38, thereby forming a defined point for ink delivery.

[0091] The main function of the ink retaining portion 66 is to retain ink, i.e., to keep ink away from the vertical parts of the support structure 8, i.e., to prevent ink from rising and forming a pool that could submerge the nozzle.

[0092] This functionality is implemented by a combination of one or more of the following features: a) The ink retaining portion 66 is provided with a hydrophobic and / or oleophobic surface, for example by a hydrophobic and / or oleophobic coating 73, shown in Fig. 2 by a thick black line. For example, the surface may be made at least in part of Teflon and / or PTFE, which are hydrophobic and oleophobic. Depending on the range of inks used, the surface may also be only hydrophobic (for example HMDS, i.e. bis(trimethylsilyl)amine) or only oleophobic (for example polymer-based). In particular, the surface of the ink 66 retaining portion is preferably more hydrophobic and / or oleophobic than the surface of the nozzle 4.

[0093] b) the ink retaining portion 66 forms a ledge portion 66a that faces away from the nozzle 4 closest to it, making it difficult for ink to move around it; in other words, as viewed from the nozzle, the ledge extends outwards forming an "undercut" 66b.

[0094] c) the ink retaining portion 66 is located in an area of ​​low electric field. Strong electric fields tend to lower the surface tension of the ink, so this design reduces the risk of ink wetting around the ink retaining portion. In the illustrated embodiment, the guard electrode 42 associated with the nozzle 4 is located between the ejection electrode 38 and the ink retaining portion 66. In this context, "between" preferably means that the guard electrode 42 traverses, and preferably bisects, the volume of space between the ejection electrode 38 and the ink retaining portion 66.

[0095] It should be noted that the ink retainer 66 is not the only means of laterally retaining ink, i.e. preventing it from reaching the nearest support element. Alternatively, or in addition, 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 entitled Operation of the Printhead.

[0096] The guard electrode 42 is connected, for example by vias 14' or 14, to a voltage supply 17, which, during operation, may be set to a potential closer to the potential of the ink retainer 66 (i.e., of the ink) than the (maximum) potential of the ejection electrodes. In particular, the voltage supply 17 may be configured to maintain the guard electrode 42 at the same potential as the ink retainer 66. This allows the electric field at the ink retainer 66 to be kept very low.

[0097] 2, the guard electrode 42 is preferably positioned at the same "height" as the forward end 70 of the nozzle 4 (the vertical direction being defined by the ejection direction X), for example within an accuracy of 25% of the vertical distance d between the ejection electrode 38 and the forward end 70 of the nozzle 4. This provides desirable shielding of the ink below the tip of the nozzle 4 whilst still leaving the tip significantly exposed to the field of the ejection electrode 38.

[0098] As can be seen in FIG. 2, there is an air-filled cavity 71 forming a gap between the guard electrode 42 and the ink retaining portion 66 , which prevents ink from reaching the guard electrode 42 .

[0099] To retain ink laterally within region 64, ink retaining portion 66 is preferably located on and projects from the front side 36 of nozzle carrier 6. In the embodiment of Figures 2-4 it comprises a first ring 72 attached to the front face 36 of nozzle carrier 6 and a second ring 74 attached to the front side of first ring 72. Second ring 74 forms the ledge portion 66a mentioned above.

[0100] Ink suction As mentioned above, in the embodiment of figures 1 and 2, a suction duct 16 is provided to withdraw ink from the nozzles 4, thereby making it possible to maintain a flow of fresh ink at a given nozzle.

[0101] In that case, for a given nozzle, the nearest ink holder 66 preferably surrounds not only the nozzle 4 and the end portion 15a of the supply duct, but also the end of the end portion 16a of the suction duct 16. Thus, two ducts can be used to control the flow of ink to and from the nozzle.

[0102] The pressure in the supply duct 15 and the suction duct 16 is adjusted to maintain the ink within a region 64 somewhere between an upper level 64a and a lower level 64b, for example as shown in Figure 2. Preferably, the ink is maintained at the lower level 64b, as described in more detail in the section "Operation of the Printhead" below.

[0103] For the desired lateral restriction of the ink, each nozzle 4 is preferably surrounded by one or more suction duct openings or openings. This can be, for example, a single annular opening (as formed by the annular opening 62 in FIG. 2) or it can be an annular series of suction openings. This opening or these openings are arranged between the nozzle and the support element 78 next to it.

[0104] support structure As mentioned, the support structure 8 is provided for connecting the different electrodes 38, 40, 42 to the nozzle carrier 6. It is located on the front side 36 of the nozzle carrier 6.

[0105] The support structure 8 comprises a number of support elements 76 , 78 disposed between the nozzles 4 .

[0106] The ink retainer 66 is preferably designed to prevent ink from reaching these support elements 76, 78 and to prevent ink from wetting them, thereby reducing the tendency of ink to submerge the nozzles.

[0107] The support structure 8 preferably comprises at least one electrode carrier layer. In the embodiment of Figure 2, there are three such layers 80, 82, 84. Each of the electrode carrier layers may comprise at least one electrode 38, 40, 42 and extend parallel to the upper surface 36.

[0108] Typically, the electrodes 38, 40, 42 are embedded in their electrode carrier layers 80, 82, 84 and are covered on their front and rear sides by at least one dielectric sub-layer 80a, 80b or 82a, 82b or 84a, 84b.

[0109] At least a portion of the support element is formed by vertical walls 76 forming honeycomb structures, see Figure 3. Each of the honeycomb structures is part of a multi-layer structure that is used in various portions of the printhead and is described in more detail below.

[0110] In addition to or as an alternative to the honeycomb-structured wall 76, in the illustrated embodiment the support element comprises a vertical wall 78 surrounding the outlet passage 5 of each nozzle 4. The wall 78 may for example be a cylindrical wall, but it may also for example be polygonal. Preferably, it is centred on the nozzle 4.

[0111] In an alternative embodiment, the wall 78 may also be omitted and the peripheral wall of the outlet passage 5 may be formed by the honeycomb structure wall 76. In this case, it is necessary to align the honeycomb structure with the nozzle.

[0112] In yet another embodiment, several nozzles may be surrounded by a single wall 78 .

[0113] In the embodiment shown here, support elements 76 and / or 78 are provided between each of the electrode carrier layers 80, 82, 84, and between the rearmost electrode carrier layer 80a and the nozzle carrier 6. However, they may also be provided only between a subset of these structures.

[0114] As can be best seen in Figure 2, there is a first recess located between the nozzle 4 and its ink carrier 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 jetting direction X, the bottom of the first recess 58, 62 is rearward with respect to the front face 68 of the ink carrier 66 (i.e. closer to the nozzle carrier 6 than to the front face 68).

[0115] In the illustrated embodiment, there is a second recess 86 located between the ink retainer 66 and the nearest support element 78, which provides space for the ledge portion 66a and / or makes it more difficult for ink to reach the support element 78. Along the jetting direction X, the bottom of the recess 86 is rearward relative to the front face 68 of the ink retainer 66 (i.e., closer to the nozzle carrier 6 than the front face 68).

[0116] Nozzle Design 2 Figures 9 and 10 show a second embodiment of a nozzle design, which differs from the first one mainly in that there is only an ink supply duct 15 to the nozzle (its end portion 15a is shown in Figure 10), but no suction duct.

[0117] Furthermore, there is no recess between the nozzle 4 and the ink retaining portion 66. Rather, the ink retaining portion 66 is disposed laterally over the nozzle 4 such that its forward face 68 is spaced from the forward end (tip) 70 of the nozzle 4.

[0118] In other words, the front face 68 is set back relative to the front end 70 of the nozzle 4 to provide an upward slope for the ink in the region 64 and reduce the risk of submerging the nozzle.

[0119] Preferably, the ink retainer 66 is mounted "low" on the nozzle 4 to reduce the possibility of submerging the nozzle. In particular, the forward face 68 of the ink retainer 66 is closer to the forward end 70 of the nozzle 4 than the forward edge 36 of the nozzle carrier 6.

[0120] As can be seen, in this embodiment, the ink retaining portion 66 is formed by the sub-layer 52 at the base of the nozzle 4 .

[0121] Nozzle Design 3 Figure 11 shows a third embodiment of the nozzle design. It differs from the second one mainly in that it does not have a guard electrode. In order to keep the electric field at the ink holder 66 low, the ink holder 66 is placed far back.

[0122] In particular, as shown in FIG. 11, the distance d' along the jetting direction X between the front face 68 of the ink retaining portion 66 and the front end 70 of the nozzle 4 is large.

[0123] Quantitatively, if d denotes 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 holds: d'>k·d k is at least 0.5, in particular at least 1.0.

[0124] Nozzle design with no ink holder In the embodiments shown so far, the nozzles 4 are surrounded by an ink retaining portion 66 which projects above the upper surface 36 of the nozzle carrier 6. However, by using an ink suction portion, said ink retaining portion can be omitted. This is shown in Figure 21, which shows an embodiment which basically corresponds to that of Figure 2, but without the ink retaining portion. Thus, the layers forming the base portions 50, 52 of the embodiment of Figure 2 can be omitted.

[0125] In this embodiment, ink is retained around the nozzle 4 by being sucked into an end portion 16a of an ink suction duct 16 which surrounds the nozzle.

[0126] In one embodiment, a single annular (or, for example, hexagonal or otherwise closed loop) end portion 16 a of the suction duct 16 may be disposed around the nozzle 4 .

[0127] In another embodiment, a plurality of individual end portions 16a may be provided, closely spaced and surrounding the nozzle 4, for example arranged along a circle or other closed loop.

[0128] In this embodiment, the guard electrode 42 may still be useful because it reduces the tendency of ink to spread along the face 36 of the nozzle carrier 6.

[0129] In the embodiment shown, the outlet duct 60 extends all the way up to the top 70 of the nozzle. The ink therefore flows axially through the nozzle. Preferably, the pressure in the outlet duct 60 is selected so that the ink overflows the nozzle and flows down along its lateral side walls. From there, the ink reaches the end portion 16a of the suction duct 16 to be removed. This provides a continuous exchange of ink in the nozzle.

[0130] In another embodiment, the ink may be guided up along the outer surface of the nozzle, for example in a groove as shown in the embodiment of Figures 2-5, and the ink may be aspirated from end portion 16a, for example through an axial opening in the nozzle.

[0131] Optionally, however, the design of this section may also be combined with a simple ink holder 66 (as shown by the dotted line), for example surrounding the end portion 16a of the suction duct 16.

[0132] Nozzle Carrier Figures 12 to 16 show possible designs of the nozzle carrier 6. It should be noted that Figures 13 to 15 are on a reduced scale compared to Figure 12 in order to show how adjacent nozzles can be interconnected by supply and suction ducts, and Figure 16 is on an even reduced scale showing the entire cross section of the printhead at the level of the backing layer 12.

[0133] Although these figures show the nozzle of FIG. 2, similar nozzle carriers can be used with a variety of nozzle designs, such as the designs of FIGS.

[0134] As mentioned above, the nozzle carrier 6 comprises a front layer 10, with the nozzle 4 attached to its front side 36, and furthermore, a backing layer 12 disposed on the rear side of the front layer 10. The front layer 10 and the backing layer 12 may then be a multi-layer structure.

[0135] They are described in more detail below.

[0136] The front layer 10 is made up of several sub-layers 10a to 10d and forms at least part of the ducts 15, 16 which feed the ink to the nozzles and, if applicable, feed the ink from the nozzles.

[0137] In the embodiment of Figure 12, the front layer 10 comprises, in order from front to rear, sub-layers 10a, 10b, 10c and 10d which form ducts.

[0138] Sub-layer 10a is the front surface 36 and is provided with openings 15a, 16a for the supply duct and (if necessary) the suction duct, respectively.

[0139] The sub-layer 10b forms (if necessary) the horizontal portion 16b of the suction duct and the vertical portion 15b of the supply duct.

[0140] 13, horizontal portions 16b of the suction ducts interconnect all or at least a number of nozzles 4. In addition, between the ducts, sublayer 10b includes vertical walls 90 forming a honeycomb pattern similar to that of support structure 8. The honeycomb patterned areas may be separated from ducts 16b and / or 15b by vertical separation walls 92.

[0141] FIG. 13 also shows vias 14 , 14 ′ extending along the jetting direction X through all of the forward layer 10 .

[0142] Vertical portion 15b of the supply duct is connected to vertical portion 15c of the supply duct in sublayer 10c, see FIG.

[0143] As shown in FIG. 15, sub-layer 10d forms a horizontal portion 15d of a supply duct interconnecting adjacent nozzles.

[0144] Again, sub-layer 10d may include vertical walls 94 forming a honeycomb pattern similar to that of support structure 8. The honeycomb patterned areas are separated by vertical separating walls 96. 15 It can be separated from

[0145] FIG. 15 also shows vias 14, 14' that extend along the jetting direction X through all of the front layer 10.

[0146] Figure 16 shows a possible arrangement for the electrical vias 14 (and 14') at the level of the lining layer 12, the supply ducts 15 and the suction ducts 16. Ink ducts 15 , 16 is implemented in the front layer 10 above the lining layer 12, it is possible to supply ink through one or several, possibly large, ink ducts arranged outside the convex hull 96 of the regular array of electrical vias 14, which simplifies the design of the lining layer 12, i.e. a design in which the ink ducts do not extend through the lining layer 12 within the convex hull 96.

[0147] Instead of using a honeycomb structure in sub-layers 10b and / or 10d, for example, a solid layer of glass may be used.

[0148] Honeycomb multi-layer structure As will be seen from the above, the printheads illustrated herein preferably use one or more honeycomb multi-layer structures. One such multi-layer structure 109 is shown in Figures 18 and 19. It has a bottom layer 110, a top layer 112, and at least one intermediate layer 114 between the bottom layer 110 and the top layer 112. The intermediate layer 114 forms walls 116 extending between the bottom layer 110 and the top layer 112. These walls form at least a portion of the walls of a plurality of cavities 118 in the intermediate layer 114 between the bottom layer 110 and the top layer 112.

[0149] The walls 114 preferably form a honeycomb pattern.

[0150] In particular, when the bottom layer 110 or the top layer 112 is a different material than the middle layer 114 and / or is located near or adjacent to another layer that is a different material than the middle layer 114, the structure has been found to reduce mechanical stress.

[0151] An example of the honeycomb multi-layer structure in the above example is as follows. 2, 11 and 12: the front layer 10 or sub-layer 10a is the "bottom layer" 110, the layer 80 of the support structure 8 is the "top layer" 112, and the wall 76 therebetween forms the "middle layer" 114.

[0152] 2, 11 and 12: layer 80 of the support structure is the “bottom layer” 110, layer 82 of the support structure 8 is the “top layer” 112 and the wall 76 therebetween forms the “middle layer” 114.

[0153] 2, 11 and 12: layer 82 of the support structure is the “bottom layer” 110, layer 84 of the support structure 8 is the “top layer” 102 and the wall 76 therebetween forms the “middle layer” 114.

[0154] 12, 13: sub-layer 10c is the "bottom layer" 110, sub-layer 10a is the "top layer" 112, and the wall 90 of sub-layer 10b between them forms the "middle layer" 114.

[0155] 12, 15: backing layer 12 is the "bottom layer" 110, sub-layer 10c is the "top layer" 112, and wall 94 of sub-layer 10d between them forms the "middle layer" 114.

[0156] In the first three examples, the support structure 8 comprises at least an intermediate layer 114 of the multi-layer structure.

[0157] In the last two examples, the nozzle carrier 6 comprises at least an intermediate layer 114 of a multi-layer structure.

[0158] The stress reduction achieved by the multi-layer structure is particularly evident when the thickness t (see FIG. 18) of the intermediate layer 114 is relatively large. Preferably, the thickness t is greater than 1 μm, in particular greater than 10 μm.

[0159] Preferably, the intermediate layer 114 is a polymer layer formed, for example, from a structuring SU-8 layer. This type of layer can be easily manufactured and structured (see manufacturing information below) and reduces stresses when used in a multi-layer structure as shown, compared to a solid layer of that material.

[0160] Preferably therefore the print head comprises at least one layer of a material different from the intermediate layer, in particular a layer of semiconductor or glass.

[0161] Cavity 118 is preferably a closed cavity, ie, cavity 118 does not form part of ink duct portions 15b or 16d of Figures 15 and 13, nor does cavity 118 communicate with the surrounding atmosphere.

[0162] If the walls 116 form a regular repeating pattern, uniformity may be improved and stress may be further reduced.

[0163] Preferably, the wall 116 has a thickness m 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 middle layer, further reducing mechanical stresses. In the present context, the thickness m is the extent of the wall 116 perpendicular to the plane of the wall 116. The cavity diameter M is the extent of the cavity 118 in a direction parallel to the bottom and top layers 110, 114.

[0164] For optimal strain relief, 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 stresses generated in the intermediate layer.

[0165] The walls 116 preferably extend perpendicular to the bottom layer 110 and the top layer 112. This not only improves mechanical stability against forces acting perpendicular to the layers, but also allows the walls to be formed by anisotropic material removal techniques, in particular by photolithography of photoactive polymers.

[0166] Note that the top and bottom layers of the multi-layer structure are parallel to each other.

[0167] The closed cavity 118 does not communicate with any ink ducts, i.e., the closed cavity 118 is not used to guide ink through the printhead, and if the printhead has ventilation ducts, the closed cavity 118 does not communicate with these ventilation ducts either.

[0168] The closed cavity 118 may be filled with air. Alternatively, the closed cavity 118 may be evacuated. Or, the closed cavity 118 may be filled with a gas, such as nitrogen. Preferably, the closed cavity 118 may be filled with a gas having a high breakdown voltage, such as SF6 or C4F8. The gas may be introduced by performing the respective manufacturing step (see below) in a working space having the desired gas composition.

[0169] electrode design The printhead is designed to withstand the high electric fields encountered during operation with minimal structural damage.

[0170] To this end, the electrodes 38, 40, 42 are arranged between solid dielectric layers 80a, 80b, 82a, 82b, 84a, 84b which border a cavity, in the illustrated embodiment, formed for example by a cavity 71, 71', 71'' below the electrode carrier layers 80, 82, 84 and / or by a cavity 118 formed by a wall 116.

[0171] At least some of the cavities may be closed cavities (ie, surrounded by walls on all sides, such as cavity 118).

[0172] At least some of the cavities may be open cavities, in particular cavities adjacent to and communicating with the outlet passage 5 of the nozzle 4, such as cavities 71, 71', 71'' in the above embodiment.

[0173] In this design, the solid dielectric layer around the electrodes is typically able to withstand higher fields than the gas in the cavity and also has a higher dielectric constant ε, thus preventing total destruction. At the same time, since no fixed molecular or atomic structures exist within the cavity, the cavity is less susceptible to permanent damage caused by large electric fields. Thus, this design improves the printhead's ability to withstand the effects of the electric fields of the electrodes even during long-term operation.

[0174] As can be seen in the embodiment illustrated here, there are solid support structures, such as walls 76 and 78, extending vertically between adjacent electrode carrier layers 80, 82, 84. However, preferably, there are no such solid support structures extending directly between adjacent electrodes. In other words, any straight line extending between two adjacent electrodes extends through at least one of 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, in operation, with substantially different electrical potentials, especially with potentials differing by a voltage of at least 100V.

[0175] This condition may be met, for example, by not placing a solid support structure extending vertically between the electrodes at the location of contact lead 38b in FIG. 7, and / or by locally removing portions of the support structure.

[0176] In yet another embodiment, the strength of the electric field can be reduced by designing the electrical tracks very narrow at locations where there is no cavity between the electrodes, in which case the tracks are preferably no wider than half the height of the wall structures 76, 78. For example, if the wall structures have a height of 5 μm, the tracks should be no wider than 2.5 μm.

[0177] Preferably, the lateral offset between an electrode and an adjacent (i.e., nearest) support structure should be at least 25% of the vertical distance between the two adjacent electrodes for at least one of the two adjacent electrodes.

[0178] Preferably, at least one of the dielectric layers protecting the electrodes has a high relative dielectric constant ε, so that the field is weakened therein and the main voltage drop is shifted to the layers with lower dielectric constants, in particular to the cavities, which allows the structure to be better protected from electrical breakdown.

[0179] In this connection, the high relative dielectric constant ε is preferably at least 5. Suitable materials are for example Si3N4 (with a relative dielectric constant ε of 9.5 to 10.5) or Al2O3 (with an ε of 9.3 to 11.5).

[0180] Preferably, several dielectric layers are provided between the cavity 120 and the electrode 122, as shown in Figure 20. (The cavity 120 in Figure 20 represents, for example, the cavity 118 or 71, 71', 71'' in the above example, and the electrode 122 represents one of the electrodes 38, 40, 42 in the above example, in particular the ejection electrode 38.

[0181] In the illustrated embodiment, the electrode 122 is surrounded by a first dielectric layer 124 a , 124 b , which in turn is surrounded by a second dielectric layer 126 .

[0182] The first dielectric layer 124a, 124b is preferably a polymer layer, for example made of patterned SU-8 (see manufacturing process below), having a low relative dielectric constant, for example between 2.5 and 3.0. It corresponds, for example, to the sub-layers 80a, 80b, 82a, 82b, 84a, 84b of the electrode carrier layers 80, 82, 84 described above and may be manufactured, at least in part, using lamination techniques (see below).

[0183] The second dielectric layer 126 is an inorganic layer that has a higher threshold of electrical breakdown than the first dielectric layers 124a, 124b. It preferably has a higher relative dielectric constant than the first dielectric layers 124a, 124b, in particular twice as high. It can be, for example, Si3N4 or Al2O3 for the reasons mentioned above. It has the highest breakdown resistance of all the components between the two electrodes and generally prevents electrical breakdown.

[0184] Disposing the first dielectric layer 124a, 124b between the electrode 122 and the second dielectric layer 126 has the advantage that, for example, the peak electric field strength at the edge of the electrode 122 is within the first dielectric layer, thus increasing the ability of the second dielectric layer 126 to prevent breakdown.

[0185] Thus, in a preferred embodiment, at least a portion of the cavity 120 is located between several different electrodes of the printhead, or between an electrode of the printhead and the ink-retaining portion 66 of the printhead.

[0186] Preferably, the different electrodes 38 , 40 , 42 , 122 are separated from the cavity or cavities 120 by one or more solid dielectric layers 124 a , 124 b , 126 .

[0187] In particular, the one or more solid dielectric layers 124a, 124b, 126 preferably comprise a polymer layer 124a, 124 and / or an inorganic layer 126. Preferably, the polymer layer 124a, 124 is disposed between the electrode 122 and the inorganic layer 126.

[0188] Print Head Operation In operation, i.e. during printing, ink is supplied to the printhead by the supply duct 15. This ink is confined to the area 64 between the nozzles 4 and the ink reservoir 66.

[0189] To eject an ink droplet, the voltage on the desired ejection electrode (relative to the voltage of the ink) is temporarily increased. For example, a voltage pulse of 400V can be generated. During periods of not printing, the voltage on the ejection electrode is maintained at a level at which no ink is being ejected. Preferably, it is not zero, but is, for example, 200V.

[0190] As mentioned above, the electric field at the ink retainer 66 is preferably kept low, for example less than 50%, and especially less than 10%, of the strength of the electric field at the nozzle front end 70. Because 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 retainer.

[0191] A suction duct 16, if present, is used to withdraw ink from the nozzles. Preferably, the printing method comprises the following steps: - supplying the nozzles with ink individually using supply ducts 15 in the nozzle carrier 6, and - sucking the ink out of the nozzles individually using the suction ducts 16 in the nozzle carrier 6.

[0192] This helps maintain a reservoir of fresh ink in the nozzles.

[0193] In operation, the pressure px at the end of the suction duct 16 at a given nozzle is preferably maintained at a level such as 64b in FIG. 2 to keep ink away from the ink retainer 66. 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 w=5 μm and ink with the surface tension of water, the Young-Laplace equation gives a pressure difference dp of 144 mbar (about 14.4 kPa). For a liquid with the surface tension of an alkane, the pressure difference dp is 40 mbar (about 4 kPa). Thus, by maintaining the pressure px at or below dp below the ambient pressure, the surface 64b can be maintained and air is not sucked in.

[0194] If instead of the annular duct 62 several circular openings of, for example, 5 μm diameter are used, dp becomes twice as large.

[0195] If the difference between the ambient pressure and px is less than dp, the liquid height will rise, for example to line 64a in FIG. 2, where the curvature is much lower than line 64b. In a simplified example, if we assume that the curvature is 10 times lower, the corresponding pressure difference is 14 mbar (about 1.4 kPa) (for water). Thus, for example, by keeping the pressure px 50 mbar (about 5 kPa) lower than atmospheric pressure, the ink can be prevented from reaching a height similar to that of line 64a.

[0196] On the other hand, the pressure py at the end of the supply duct 15 at a given nozzle can be adjusted to maintain a desired ink flow through the nozzle, and, as mentioned above, the ink flow through the outlet ducts 56 and 60 can be adjusted by selecting suitable diameters in these ducts.

[0197] 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.

[0198] In that case, when the ink returning through the suction duct 16 is recycled, a separation device may be used to separate the ink and air before the ink is supplied to the recirculation pump 18 .

[0199] manufacturing The printhead may be manufactured using techniques known, for example, from semiconductor manufacturing and packaging, as described, for example, in US Pat. No. 5,399,633; US Pat. No. 5,499,625; and US Pat. No. 5,599,635.

[0200] Preferably, at least some of the layers of the printhead, and in particular the intermediate layer 114 of the multi-layer structure used therein of the type of FIGS. 18 and 19, are polymer layers.

[0201] The manufacture of the multi-layer structure preferably comprises the following steps: 1. Providing a bottom layer 110. This may be, for example, a top layer formed by a previous manufacturing step.

[0202] 2. Adding a layer of material over the bottom layer 110. This layer of material forms the middle layer 114.

[0203] 3. Adding a top layer 112 above the layer of material.

[0204] The material layers deposited in steps 2 and 3 may be applied using a variety of techniques, such as lamination, spin coating, sputtering, or evaporation.

[0205] In particular, lamination is particularly preferred for applying the top layer 112. In lamination, the layer is applied as a sheet material and connected to the underlying structure using, for example, heat and pressure, which can facilitate bridging cavities and / or creating overhanging structures.

[0206] The material layer of step 2 is preferably a photoresist, such as SU-8, which allows easy structuring of said material layer. In this case, step 2 comprises at least the following sub-steps: 2a: Sub-step of irradiating the material layer with collimated light through a mask, thereby defining irradiated and non-irradiated areas in the material layer.

[0207] 2b: Substep of selectively removing irradiated or non-irradiated areas from the material layer, depending on whether a positive or negative photoresist is used.

[0208] Alternatively, the top layer 112 can also be formed from a solid material, such as a glass wafer, that is bonded to the middle layer 114, for example, by adhesive bonding, fusion bonding, eutectic bonding, or the like.

[0209] The inorganic dielectric layer 126 (Figure 20) may be fabricated, for example, by an atomic layer deposition process that deposits it on the polymer dielectric layers 124a, 124b.

[0210] Note In most of the embodiments illustrated heretofore, each nozzle is surrounded by an ink holding portion that defines a restricted area through which ink can flow from the nozzle.

[0211] 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.

[0212] 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.

[0213] 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.

[0214] 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 nearest support element 78 and the nozzle axis 100 and the support element 78 is an element adjacent to the nozzle carrier 6.

[0215] 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.

[0216] x1 < x3, particularly x1 < 0.8·x3, particularly x1 < 0.5·x3: Again, by disposing the nearest support element 78 further away from the axis 100 than the guard electrode 42, the support element is similarly shielded.

[0217] Additionally 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.

[0218] In particular, x3 should be greater than x2 by at least 1 μm, in particular by at least 5 μm.

[0219] Therefore, the following relationships, either alone or in any combination, are preferred: 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.

[0220] 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 adjacent support element 78 of the nozzle carrier 6 which is closest to the nozzle axis 100;

[0221] - 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.

[0222] 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 holder 66 and the nozzle axis 100 by at least 1 μm, in particular by at least 5 μm.

[0223] - 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.

[0224] As mentioned, the print head may also comprise gas ducts for supplying gas to and / or withdrawing gas from the region between the print head and the target, said gas duct supply may also comprise horizontal portions, such as interconnecting portions, for example in the front layer 10 and / or backing layer 12 and / or intermediate layer 32, similar to the ink ducts shown in Figures 13 and 15.

[0225] In the embodiments described so far, three electrodes at three different vertical heights are described: an ejection electrode, a guard electrode, and a shield electrode. However, it should be noted that other electrodes may also be present, such as: - electrodes may be provided in the nozzle carrier 6, for example in the supply duct 15 and / or in the suction duct 16 and / or in the nozzle and / or ink holder, in order to establish the potential of the ink. Said electrodes make it possible, for example, to maintain the ink at a similar or the same potential as the guard electrode 42. Preferably, said electrodes are platinum and / or gold.

[0226] - Additional electrodes (e.g. between the ejection electrode 38 and the shield electrode 40 in Figure 2) may be provided if nozzles of different sizes are present in the printhead. This is particularly useful for nozzles where the distance between the ejection electrode and the nozzle is significantly smaller than the distance between the shield electrode and the ejection electrode.

[0227] While presently preferred embodiments of the invention have been illustrated and described, it is to be clearly understood that the invention is not limited thereto and may be otherwise embodied and carried out within the scope of the following claims. The following are some embodiments of the present invention. [Aspect 1] 1. An electrohydrodynamic print head comprising: A nozzle carrier (6); A plurality of nozzles (4) arranged on the nozzle carrier (6); a plurality of ejection electrodes (38) associated with the nozzles (4) and disposed in front of the nozzles (4); Equipped with the printhead comprises at least one multi-layer structure (109) having a bottom layer (110), a top layer (112), and at least one intermediate layer (114) between the bottom layer (110) and the top layer (112), the intermediate layer (114) forming a wall (116) extending between the bottom layer (110) and the top layer (112); An electrohydrodynamic printhead, wherein a plurality of cavities (118, 120) are disposed in the middle layer (114) between the bottom layer (110) and the top layer (112). [Aspect 2] 2. The print head of claim 1, wherein at least a portion of the cavities (118), in particular a majority of the cavities (118), are closed cavities. [Aspect 3] The print head of any one of aspects 1 to 2, wherein at least some of the cavities (118) form a repeating regular pattern. [Aspect 4] The print head according to any one of the preceding aspects, wherein the wall (116) forms a honeycomb structure between the bottom layer (110) and the top layer (112). [Aspect 5] The print head of any one of aspects 1 to 4, wherein the wall (116) has a thickness (M) that is less than 25% of the minimum diameter (M) of the cavity (118). [Aspect 6] The print head of any one of aspects 1 to 5, wherein a minimum diameter (M) of the cavity (118) is greater than a thickness (t) of the intermediate layer (114). [Aspect 7] The print head of any one of aspects 1 to 6, wherein the wall (116) extends perpendicular to the bottom layer (110) and the top layer (112). [Aspect 8] A print head according to any one of aspects 1 to 7, wherein at least a portion of the cavity (71, 71', 71'', 120) is in communication with and adjacent to an outlet passage (5) disposed in the nozzle (4). [Aspect 9] At least a portion of the cavity (71) is disposed between different electrodes (38, 40, 42, 122) of the print head; A print head according to any one of aspects 1 to 8, in particular, any straight line extending between two adjacent electrodes (38, 40, 42, 122) extends through at least one of the cavities (71, 71', 71''). [Aspect 10] The print head according to any one of aspects 1 to 9, wherein at least a portion of the cavity (71', 71'') is disposed between an electrode (38, 42, 122) of the print head and an ink retaining portion (66) of the print head. [Aspect 11] 11. The print head of any of aspects 9 or 10, wherein the different electrodes (38, 40, 42, 122) are separated from the cavity or cavities (118, 120) by one or more solid dielectric layers (124a, 124b, 126). [Aspect 12] A print head according to any of aspects 10 or 11, wherein the electrodes (38, 40, 42, 122) are attached to the bottom layer (110) and / or the top layer (112) of the multi-layer structure (109). [Aspect 13] A print head as described in aspect 12, wherein the electrodes (38, 40, 42, 122) are embedded within the bottom layer (110) and / or the top layer (112) of the multilayer structure (109), and the bottom layer (110) and / or the top layer (112) form a dielectric solid layer covering the electrodes (38, 40, 42, 122) from the bottom side and the top side. [Aspect 14] A print head according to any one of aspects 11 to 13, wherein the one or more solid dielectric layers (124a, 124b, 126) comprise a polymer layer (124a, 124b) and / or an inorganic layer (126), and in particular, the polymer layer (124a, 124) is disposed between the electrode (122) and the inorganic layer (126). [Aspect 15] A print head according to any one of aspects 10 to 14, further comprising a guard electrode (42) arranged at a height behind the ejection electrodes (38), and at least a portion of the cavity (71') being arranged between at least one of the ejection electrodes (38) and at least one of the guard electrodes (42). [Aspect 16] A print head as described in any one of aspects 10 to 15, further comprising at least one shield electrode (40) arranged at a height forward of the ejection electrodes (38), and at least a portion of the cavity (71'') being arranged between at least one of the ejection electrodes (38) and the shield electrode (42). [Aspect 17] A print head according to any one of aspects 1 to 16, wherein the nozzle carrier (6) comprises at least the intermediate layer (114) of the multi-layer structure (109). [Aspect 18] The nozzle carrier (6) is a front layer (10), said nozzle (4) being attached to the front side (36) of said front layer (10); - a backing layer (12) arranged on the rear side of the front layer (10); an electrical via (14) connected to the ejection electrode (38) and extending through the front layer (10) and the backing layer (12); - ink supply ducts (15, 16) arranged in said front layer (10); Equipped with The front layer (10) comprises at least the intermediate layer (114), The print head according to any one of the preceding embodiments, in particular, wherein there is a closed cavity (118) that does not communicate with the ink ducts (15, 16). [Aspect 19] a support structure (8) for supporting the ejection electrode (38) on the nozzle carrier (6), the support structure (8) comprising a plurality of support elements (76, 78) arranged between the nozzles (4); The print head according to any one of the preceding aspects, wherein the support structure (8) comprises at least the intermediate layer (114) of the multi-layer structure (109). [Aspect 20] A print head as described in embodiment 19, further comprising a plurality of ink retaining portions (66) arranged between the nozzles (4) and the support elements (76, 78), and a front surface (68) of the ink retaining portion (66) is arranged at a height behind a front end (70) of the nozzles (4) along the ejection direction (X) of the print head. [Aspect 21] The print head according to any of the preceding embodiments, wherein the thickness (t) of the intermediate layer (114) is at least 1 μm, in particular at least 10 μm. [Aspect 22] The print head of any one of the preceding aspects, wherein the intermediate layer (114) is a polymer layer. [Aspect 23] The print head according to any of the preceding aspects, comprising at least one material layer of a material different from the intermediate layer (114), in particular a semiconductor or glass layer. [Aspect 24] A method of manufacturing a print head according to any one of aspects 1 to 23, comprising the steps of: adding a layer of material over the bottom layer (110); removing a portion of the layer of material that defines the cavity (118); adding said top layer (112) above said layer of material; A method comprising: [Aspect 25] The layer of material is a photoresist, in particular SU-8, and the method comprises: illuminating the layer of material with collimated light through a mask, the illumination defining illuminated and non-illuminated areas in the layer of material; selectively removing the irradiated or non-irradiated areas from the material layer; 25. The method of embodiment 24, comprising: [Aspect 26] 26. The method of any one of aspects 24 or 25, comprising applying the top layer (112) over the layer of material using lamination.

Claims

1. 1. An electrohydrodynamic print head comprising: A nozzle carrier (6); a plurality of nozzles (4) arranged on the nozzle carrier (6); a plurality of ejection electrodes (38) associated with the nozzles (4) and disposed in front of the nozzles (4); Equipped with the printhead comprises at least one multi-layer structure (109) having a bottom layer (110), a top layer (112), and at least one intermediate layer (114) between the bottom layer (110) and the top layer (112), the intermediate layer (114) forming a wall (116) extending between the bottom layer (110) and the top layer (112); A plurality of cavities (118, 120) are disposed in the middle layer (114) between the bottom layer (110) and the top layer (112); An electrohydrodynamic printhead, wherein at least some of the cavities (118) are closed cavities.

2. The printhead of claim 1 , wherein at least a portion of the plurality of cavities (118) form a repeating regular pattern.

3. The printhead of claim 1 or 2, wherein the wall (116) forms a honeycomb structure between the bottom layer (110) and the top layer (112).

4. The printhead of any one of claims 1 to 3, wherein the wall (116) has a thickness (M) that is less than 25% of a minimum diameter (M) of the plurality of cavities (118).

5. The printhead of any one of claims 1 to 4, wherein a minimum diameter (M) of the plurality of cavities (118) is greater than a thickness (t) of the intermediate layer (114).

6. The printhead of any one of claims 1 to 5, wherein the wall (116) extends perpendicular to the bottom layer (110) and the top layer (112).

7. A printhead as claimed in any one of claims 1 to 6, wherein at least some of the cavities (71, 71', 71'', 120) are in communication with and adjacent to an outlet passage (5) arranged in the nozzle (4).

8. A printhead according to any one of the preceding claims, wherein at least some of the cavities (71) are arranged between different electrodes (38, 40, 42, 122) of the printhead.

9. The print head of any one of claims 1 to 8, wherein at least some of the cavities (71', 71'') are disposed between an electrode (38, 42, 122) of the print head and an ink retaining portion (66) of the print head.

10. 9. The printhead of claim 8, wherein the different electrodes (38, 40, 42, 122) are separated from one or more of the plurality of cavities (118, 120) by one or more solid dielectric layers (124a, 124b, 126).

11. The printhead of any one of claims 9 or 10, wherein the electrodes (38, 40, 42, 122) are attached to the bottom layer (110) and / or the top layer (112) of the multi-layer structure (109).

12. 12. The print head of claim 11, wherein the electrodes (38, 40, 42, 122) are embedded in the bottom layer (110) and / or the top layer (112) of the multilayer structure (109), the bottom layer (110) and / or the top layer (112) forming a dielectric solid layer covering the electrodes (38, 40, 42, 122) from the bottom side and from the top side.

13. The printhead of claim 10, wherein the one or more solid dielectric layers (124a, 124b, 126) comprise a polymer layer (124a, 124b) and / or an inorganic layer (126).

14. A print head as claimed in any one of claims 9 to 13, further comprising a guard electrode (42) arranged at a height behind the ejection electrodes (38), and at least some of the cavities (71') are arranged between at least one of the ejection electrodes (38) and at least one of the guard electrodes (42).

15. A print head according to any one of claims 9 to 14, further comprising at least one shield electrode (40) arranged at a height in front of the ejection electrodes (38), and at least some of the cavities (71'') being arranged between at least one of the ejection electrodes (38) and the shield electrode (42).

16. A printhead according to any one of the preceding claims, wherein the nozzle carrier (6) comprises at least the intermediate layer (114) of the multi-layer structure (109).

17. The nozzle carrier (6) is a front layer (10), said nozzle (4) being attached to the front side (36) of said front layer (10); a backing layer (12) arranged on the rear side of said front layer (10); - an electrical via (14) connected to said ejection electrode (38) and extending through said front layer (10) and said backing layer (12); - ink supply ducts (15, 16) arranged in said front layer (10); Equipped with A printhead according to any one of the preceding claims, wherein the front layer (10) comprises at least the intermediate layer (114).

18. a support structure (8) for supporting the ejection electrode (38) on the nozzle carrier (6), the support structure (8) comprising a plurality of support elements (76, 78) arranged between the nozzles (4); The printhead according to any one of the preceding claims, wherein the support structure (8) comprises at least the intermediate layer (114) of the multi-layer structure (109).

19. 19. The printhead of claim 18, further comprising a plurality of ink retaining portions (66) arranged between the nozzles (4) and the support element (76, 78), and along the jetting direction (X) of the printhead, a front surface (68) of the ink retaining portion (66) is arranged at a height behind a front end (70) of the nozzles (4).

20. The printhead of any one of the preceding claims, wherein the thickness (t) of the intermediate layer (114) is at least 1 μm.

21. The printhead of any one of the preceding claims, wherein the intermediate layer (114) is a polymer layer.

22. A printhead according to any one of the preceding claims, comprising at least one layer of material of a different material than the intermediate layer (114).

23. An electrohydrodynamic printhead comprising: A nozzle carrier (6); a plurality of nozzles (4) arranged on the nozzle carrier (6); a plurality of ejection electrodes (38) associated with the nozzles (4) and disposed in front of the nozzles (4); Equipped with the printhead comprises at least one multi-layer structure (109) having a bottom layer (110), a top layer (112), and at least one intermediate layer (114) between the bottom layer (110) and the top layer (112), the intermediate layer (114) forming a wall (116) extending between the bottom layer (110) and the top layer (112); A plurality of cavities (118, 120) are disposed in the middle layer (114) between the bottom layer (110) and the top layer (112); The wall (116) forms a honeycomb structure between the bottom layer (110) and the top layer (112).

24. A method for manufacturing a printhead according to any one of claims 1 to 23, comprising the steps of: adding a layer of material over the bottom layer (110); removing portions of the layer of material that form the plurality of cavities (118); adding said top layer (112) above said layer of material; A method comprising:

25. the layer of material is a photoresist, and the method comprises: illuminating the layer of material with collimated light through a mask, the illumination defining illuminated and non-illuminated areas in the layer of material; selectively removing the irradiated or non-irradiated areas from the material layer; 25. The method of claim 24, comprising:

26. 26. The method of any one of claims 24 or 25, comprising applying the top layer (112) over the layer of material using lamination.

27. The printhead of claim 1 , wherein a majority of the plurality of cavities are closed cavities.

28. 9. The printhead of claim 8, wherein any straight line extending between two adjacent electrodes (38, 40, 42, 122) extends through at least one of the plurality of cavities (71, 71', 71'').

29. The printhead of claim 13, wherein the polymer layer (124a, 124) is disposed between the electrode (122) and the inorganic layer (126).

30. 18. A printhead according to claim 17, in which there is a closed cavity (118) that does not communicate with the ink supply ducts (15, 16).

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