Electrohydrodynamic printer with fluid extractor.

Abstract

Electrohydrodynamic printers have a fluid extractor. A flow of liquid or carrier fluid at a different electrical potential compared to the printing fluid passes past the extraction port for extracting the printing fluid from the extraction port. The flow of liquid can be a continuous flow, a uniform flow of droplets, or a non-uniform flow of droplets. The extracted printing fluid can merge with the extraction fluid to be carried to the printing surface for deposition. The flow of extraction fluid can be intermittently charged to intermittently extract the printing fluid such that select portions of the flow do not extract the printing fluid.

Description

[Technical field]

[0001] Technical Field FIELD OF THE DISCLOSURE This disclosure relates generally to printing, and more particularly to electrohydrodynamic printing. [Background technology]

[0002] background Electrohydrodynamic printing, also known as e-jet printing, is a printing technique that relies on an electric field to extract a charged or polarized printing fluid from a printing nozzle for deposition onto a printing surface. E-jet printing is capable of very high resolution printing compared to other drop-on-demand or flow printing methods with droplet sizes and spatial precision on the submicron or nanometer scale. Initially, e-jet printing was limited to electrically conductive printing surfaces, since the printing surface was one of multiple electrodes between which an electric field was created. There were also problems with alignment to the electric field, as the deposited ink would cause interference to the electric field as the print progressed. U.S. Patent No. 9,415,590 by Barton et al. addressed these and other issues with an ingenious ink extraction and directing technique that does not rely on a conductive printing surface. Summary of the Invention [Problem to be solved by the invention]

[0003] overview According to various embodiments, an electrohydrodynamic printer includes a fluid extractor.

[0004] In various embodiments, the extractor is a stream of carrier fluid that meets the extracted printing fluid and carries the printing fluid towards the printing surface.

[0005] In various embodiments, the extractor is a stream of liquid that is at a different electrical potential compared to the printing fluid extracted from the extraction port of the printing fluid supply.

[0006] In various embodiments, the extractor is a continuous flow of liquid. In various embodiments, the extractor is a uniform stream of droplets.

[0007] In various embodiments, each of the first portions of the droplet extracts a droplet of printing fluid and each of the second portions of the droplet does not extract a droplet of printing fluid.

[0008] In various embodiments, a first portion of the droplet carries the extracted printing fluid and is directed toward the printing surface, and a second portion of the droplet is not directed toward the printing surface.

[0009] In various embodiments, the extractor is a non-uniform stream of droplets. According to various embodiments, the printer includes a first nozzle and a second nozzle. The first nozzle is configured to direct a flow of carrier fluid toward the printing surface and the second nozzle is configured to provide a printing fluid at an extraction port. The flow of carrier fluid passes through the extraction port as it flows toward the printing surface. A potential difference between the carrier fluid and the printing fluid causes the printing fluid to be extracted from the second nozzle.

[0010] In various embodiments, the extracted printing fluid merges with a flow of carrier fluid for transport towards the printing surface.

[0011] In various embodiments, the carrier fluid is uniformly pressurized within the first nozzle to provide a continuous flow of carrier fluid.

[0012] In various embodiments, the pressure of the carrier fluid at the first nozzle is varied at a constant frequency to break the carrier fluid stream into a uniform stream of droplets.

[0013] In various embodiments, the printer includes a piezoelectric element configured to deform at a certain frequency to vary the pressure of the carrier fluid at the first nozzle.

[0014] In various embodiments, the printer includes an electrode located external to the first nozzle, the stream of carrier fluid being charged by the electrode to provide at least a portion of the potential difference.

[0015] In various embodiments, the printer includes electrodes configured to charge only a portion of the carrier fluid flow such that the carrier fluid flow extracts the printing fluid when a portion of the carrier fluid flow passes the extraction port, and such that the carrier fluid flow does not extract the printing fluid when an uncharged portion of the carrier fluid flow passes the extraction port.

[0016] In various embodiments, a portion of the carrier fluid flow passes through the extraction ports without extracting printing fluid and is collected and returned to the carrier fluid source that supplies carrier fluid to the first nozzles.

[0017] In various embodiments, the printer is a drop-on-demand printer and the stream of carrier fluid is a stream of droplets, each droplet of carrier fluid extracting a droplet of printing fluid from an extraction port and carrying the respective droplet of printing fluid to a printing surface.

[0018] In various embodiments, the carrier fluid has a viscosity of less than 10 centipoise and the printing fluid has a viscosity of greater than 30 centipoise.

[0019] In various embodiments, the potential difference is at least 500V and the carrier fluid stream has a velocity high enough to maintain a gap between the carrier fluid stream and the extraction orifice of the second nozzle.

[0020] In various embodiments, the printing fluid can be dissolved in a carrier fluid, and the potential difference attracts a flow of the carrier fluid over the first nozzle during a cleaning mode of the printer.

[0021] It is anticipated that any of the individual features of the embodiments described above, and any of the individual features of any other embodiments detailed in the drawings or specification below, may be combined in any combination to define the invention, except where the features are incompatible. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a cross-sectional view of an electrohydrodynamic printer having a fluid extractor in a continuous flow configuration. [Diagram 2] FIG. 1 is a cross-sectional view of an electrohydrodynamic printer having a fluid extractor in the form of a uniform droplet stream. [Diagram 3] FIG. 2 is a cross-sectional view of an electrohydrodynamic printer having a fluid extractor in the form of a non-uniform droplet stream. [Figure 4] 2 is an enlarged view of a portion of FIG. 1 showing a carrier fluid stream joined with an immiscible printing fluid; [Diagram 5] FIG. 4 is an enlarged view of a portion of FIG. 3 showing the carrier fluid stream joined with the immiscible printing fluid. [Figure 6] FIG. 5 shows an alternative version of FIG. 4 in which the carrier fluid stream can mix with the printing fluid. [Figure 7] FIG. 6 shows an alternative version of FIG. 5 in which the carrier fluid stream can mix with the printing fluid. [Figure 8] FIG. 2 is a diagram of the printer of FIG. 1 in cleaning mode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Description of the embodiment FIG. 1 shows a schematic of a portion of an electrohydrodynamic (or e-jet) printer 10 equipped with a fluid extractor 12. The fluid extractor 12 is itself a jet or stream of carrier fluid 14 at a different potential compared to the printing fluid 16 provided at an extraction port 18 of an ink nozzle 20. When the fluid stream passes the extraction port 18 with a sufficient combination of potential difference (V1-V2) and distance (D), the printing fluid 16 is extracted from the ink nozzle 20 and merges with the extraction stream 12 to be carried towards a printing surface 22, such as the surface of a substrate 24 or a layer of previously deposited printing material. The use of the fluid extractor 12 enjoys the benefits of a solid-state extractor, such as those detailed by Barton et al. in the aforementioned U.S. patent, while additionally addressing certain problems that may occur with solid-state extractors, such as the potential for arcing between the ink nozzle and the extractor, ink piling up on the extractor, and the relatively limited throw distance (H) between the ink extraction point and the printing surface 22. The fluid extractor enables printing of high viscosity fluids with the throw distances normally associated with industrial continuous ink jet (CIJ) printers.

[0024] In the example of FIG. 1, the printer 10 includes a first nozzle 26 containing a carrier fluid 14, and a second nozzle (i.e., an ink nozzle) containing a printing fluid 16. As used herein, ink or printing fluid is any fluid that flows under pressure. Some printing fluids can solidify after deposition. Solidification can occur through a variety of mechanisms, such as solvent evaporation, chemical reaction, cooling, or sintering. In some cases, the printing fluid is a functional ink, which is a printing fluid that provides a function other than coloring once the printing fluid solidifies on the printed surface. Examples of such functions include electrical conductivity, dielectric properties, physical structure (e.g., stiffness, elasticity, or frictional resistance), electromagnetic shielding or filtering properties, optical properties, electroluminescence, bioactivity, and the like. Some other printing fluids, such as lubricants, are not intended to solidify after deposition.

[0025] Although not explicitly shown, the nozzles 20, 26 may be part of a print head of the printer 10, which is configured to move relative to the printing surface 22. The print head may include, for example, a housing or other structure that supports the nozzles 20, 26 and / or includes one or more couplings configured to provide pressure to the fluids 14, 16 within the nozzles and to apply a voltage to the nozzles and / or their contained fluids. The printer 10 may also include other components not shown, such as a base, a drive mechanism for moving the print head and the printing surface 22 relative to one another, a number of ink nozzles 20 or carrier fluid nozzles 26, a directional field generator, an on-board ink supply, a means for pressurizing the fluids 14, 16 in the nozzles, an air or other gas connector, a pressure control device, or one or more power sources, and associated controls for selectively controlling the extraction field generated between the extractor 12 and the extraction port 18, to name a few.

[0026] The carrier fluid nozzles 26 are configured to direct a carrier fluid stream 12 towards the printing surface 22, and the ink nozzles 20 are configured to provide the printing fluid 16 at the extraction orifices 18. The relative orientation of the nozzles 20, 26 is such that the carrier fluid stream 12 passes the extraction orifices 18 as it flows towards the printing surface 22. In the illustrated example, the central longitudinal axes A1, A2 of the respective nozzles 26, 20 intersect in the XZ plane. The first nozzle axis A1 is vertical and perpendicular to the printing surface 22, and the second nozzle axis A2 is horizontal and parallel to the printing surface in FIG. 1. However, the orientation of these nozzles is not essential, as the nozzle axes may intersect each other and / or the printing surface at an oblique angle.

[0027] The carrier fluid 14 may be a relatively volatile liquid solvent (e.g., an organic solvent) having a relatively low viscosity, such as 10 centipoise (cps) or less. In some embodiments, the carrier fluid 14 includes a solvent or liquid that is also included in the printing fluid 16. For example, it may be a liquid in which the solid components of the printing fluid are dissolved, suspended, or emulsified. Due to a sufficiently high pressure P1 applied to the fluid 14 in the nozzle 26, a high velocity stream of carrier fluid 12 is generated at the nozzle outlet 28 and directed towards the printing surface 22. The outlet 28 may range from 1 μm to 100 μm, 20 μm to 100 μm, or 20 μm to 70 μm. The pressure P1 may range from 5 psi to 500 psi (34 kPa to 3.4 MPa). The pressure P1 may be significantly higher than conventional low resolution CIJ ink pressures, which are typically 50 psi or less. The high pressure P1 of the carrier fluid 14 allows for higher resolution printing when the carrier fluid stream is a stream of droplets, as discussed further below.

[0028] A relatively high velocity (v) of the carrier fluid stream may be both necessary and advantageous. Higher velocities may lead to faster printing. However, below a threshold velocity, the carrier fluid stream will flow over the ink nozzle 20 due to the potential difference and resulting electrical attraction. The threshold velocity depends on several factors, including the potential (V1-V2), the distance (D) between the extractor 12 and the extraction port 18, the viscosity of the printing fluid 16, the size of the extraction port, and the conductivity of the fluids 14, 16. In one non-limiting example, where the potential between the fluids 14, 16 is approximately 2000V, the threshold velocity ranges from approximately 6 m / s to approximately 11 m / s. The printer 10 is capable of producing carrier fluid streams having velocities (v) comparable to those of CIJ printers, such as in the range of 20 m / s to 50 m / s.

[0029] Carrier fluid 14 may in some cases be conductive, thereby allowing the carrier fluid to more readily accept charge from an applied voltage (V1). One particular example of a conductive carrier fluid is SIGNASPRAY 100, having an electrical conductivity of greater than 20,000 μS / cm. (R) (Parker Laboratories, Inc., Fairfield, NJ, USA). Another example of a conductive carrier fluid 14 is a solvent having a suspension of metal (e.g., silver) particles, such as nanoparticles. Of course, a solid amount of the carrier fluid 14 will be present in the deposited ink. In other cases, the carrier fluid 14 is non-conductive. One example of a suitable non-conductive carrier fluid is isopropyl alcohol (IPA), which has a conductivity of approximately 0.06 μS / cm. A non-conductive carrier fluid increases the arcing threshold and allows the use of higher voltages, resulting in higher printing fluid extraction rates and faster printing processes. As mentioned above, the carrier fluid may include or be a solvent that is also part of the printing fluid 16. In some cases, the solvent that evaporates from the printing fluid 16 during travel from the extraction port 18 to the printing surface is filled by the carrier fluid so that the deposited fluid maintains the desired solvent amount.

[0030] The printing fluid 16 may have a high viscosity relative to the carrier fluid 14. The viscosity of the printing fluid may range, for example, from 1 cps to 300,000 cps. In various embodiments, the viscosity of the printing fluid may be 300,000 cps or less, while it may be greater than 10 cps, greater than 30 cps, greater than 100 cps, greater than 1000 cps, greater than 10,000 cps, or greater than 100,000 cps. Many functional inks have high viscosity due to high solids content and / or particle size. The back pressure P2 of the printing fluid 16 at the ink nozzle 20 may be low compared to the pressure P1 at the other nozzles 26, such as between 0.5 psi and 200 psi (3.4 kPa to 1.4 MPa). The extraction orifices 18 may range from 1 μm to 200 μm. In one embodiment, the extraction orifices 18 range from 20 μm to 100 μm. Higher resolution printing typically requires smaller extraction ports 18, such as 1 to 2 μm openings.

[0031] The potential difference between the carrier fluid 14 and the printing fluid 16 before they join along the fluid extraction stream 12 may range from 500V to 5000V, or from 1000V to 5000V. Various combinations of applied voltages (V1, V2) are possible, and the voltages may be applied in various ways. For example, one or both of the nozzles 20, 26 may be formed from a conductive material, such as a metallic material (e.g., stainless steel), and a voltage may be applied to the nozzles 20, 26 with the fluids 14, 16 in contact with the interior of the nozzle. In another example, each of the nozzles 20, 26 has a conductive portion, and a voltage is applied to that portion of the nozzle. For example, the nozzles 20, 26 can be formed from a non-conductive material (e.g., plastic) with a metal layer plated or deposited on the interior surface, or the nozzles may include a conductive tip with a corresponding extraction orifice 18 or outlet 28. In other embodiments, each of the voltages is applied to an electrode that is at least partially immersed in the fluid in the nozzle or in a reservoir that supplies the nozzle.

[0032] In one example, the voltage on the printing fluid 16 is greater than the voltage on the carrier fluid 14 (V2>V1). For example, a high voltage (500-5000V) may be applied to the printing fluid 16 when the carrier fluid 14 is grounded or floating with no applied potential. This arrangement is particularly suitable when using a conductive carrier fluid. This is similar to the preferred arrangement with a solid-state extractor, in which the extractor is grounded and a high voltage pulse is applied to the printing fluid to cause the printing fluid to be attracted towards the extractor and thereby extracted from the ink nozzle. In this arrangement, the charge density at the extraction port 18 is very high due to the sharp nozzle tip, which tends to make the arcing threshold higher than the extraction threshold, thereby allowing the extraction of the printing fluid 16 without arcing. This arrangement may be limited by the fact that the printing surface 22 may be at the same potential as the carrier fluid 14 (i.e. zero applied voltage or ground). This means that the high voltage printing fluid 16 can be attracted to both the carrier fluid stream 12 and the printing surface 22, i.e., the proximity of the printing surface 22 to the ink nozzles 20 can affect the trajectory of the extracted printing fluid. This can be problematic, for example, when printing on polymeric substrates in close proximity and / or when using non-conductive carrier fluids. When appropriate, the use of a conductive carrier fluid in this arrangement helps to alleviate such problems by making the carrier fluid a more dominant element in the electric field close to the extraction port 18.

[0033] In another example, the voltage on the printing fluid 16 is lower than the voltage on the carrier fluid 14 (V2 < V1). For example, when the printing fluid 16 is grounded or floating with no potential applied, a high voltage may be applied to the carrier fluid 14. In this arrangement, there is no high charge density at the extraction port 18 of the ink nozzle 20. Thus, depending on this arrangement, some types of printing fluid may not be extractable. However, for fluids that can be e-jet printed with a relatively low charge density, this arrangement will avoid substrate interference because the printing fluid 16 and the substrate 24 are at the same potential. The flow 12 of the carrier fluid is the only attracting feature for the printing fluid in the overall system. Even if the printing surface 22 has some residual static electricity, the magnitude of the charge in the flow of the carrier fluid will easily overcome any attraction of the extracted printing fluid to the substrate. In some cases, there may be an advantage to not grounding the printing fluid (i.e., allowing the printing fluid to have a potential at which it is electrically floating) in order to effectively limit the current flow in an arc discharge event. Since there is no path for the charge to leave the printing fluid, the amount of charge transferred from the carrier fluid to the printing fluid is limited. Limiting the charge passing through the ink nozzle 20 helps reduce the heat generated by the current of the arc discharge and thus reduces the possibility of the nozzle clogging with thermosetting printing fluid.

[0034] In another example, non-zero voltages of opposite polarity are applied to the carrier fluid 14 and the printing fluid 16. For example, a high magnitude negative voltage (e.g., V1=-2000V to -5000V) may be applied to the carrier fluid 14, while a moderate voltage (e.g., V2=500V to 1500V) may be applied to the printing fluid 16 at the ink nozzle 20, so that the extraction stream 12 is at a lower potential than the printing fluid 16 and the printing surface 22. In this arrangement, the potential difference between the ink nozzle and the substrate 24 and other nearby components is insufficient to extract the printing fluid 16 from the nozzle, but the positive voltage applied to the printing fluid is sufficient to provide a significant level of charge density at the ink nozzle 20. The effect is that the negatively charged extraction stream 12 is the only feature that provides a sufficient potential difference to extract the printing fluid as it passes through the extraction port 18. This reduces the probability that the extracted printing fluid will be attracted to anything other than the carrier fluid stream with which it merges and continues toward the printing surface.

[0035] In a particular embodiment, a charge of 1000V is applied to the ink nozzles 20 and a charge of -2000V is applied to the carrier fluid 14. These voltage levels are sufficient for the extracted printing fluid to effectively discriminate between the carrier fluid stream 12 and the substrate, so that the extracted ink is attracted by the extracted stream 12 to join the carrier fluid without significant competition from the substrate or other uncharged components. This is true even when the carrier fluid 14 is substantially non-conductive (e.g., IPA).

[0036] The throw distance (H) of the printing fluid may range from 5 mm to 15 mm and is determined in large part by the characteristics of the carrier fluid stream 12, which may be a continuous stream, a uniform droplet stream, or a non-uniform droplet stream (e.g., drop-on-demand). The rate of extraction of the printing fluid is determined by the electric potential, the back pressure (P2), the distance (D) between the extraction port 18 and the carrier fluid stream, the size of the extraction port, and the characteristics of the printing fluid 16 (e.g., conductivity, viscosity, etc.). The example of FIG. 1 depicts a continuous stream 12 of carrier fluid. In the continuous stream format, the carrier fluid can extract the printing fluid 16 in a continuous stream without breaking into individual droplets, so that the two streams merge and continue toward the printing surface, generally in the direction of the carrier fluid flow.

[0037] FIG. 2 shows a schematic of an example of an electrohydrodynamic printer 10 in which the extractor 12 is a stream of uniform droplets 30 of carrier fluid. "Uniform" as used herein means that the droplets 30 of the stream 12 are evenly spaced in the direction of travel and are the same size as each other. The ejection and formation of the stream of carrier fluid shown in FIG. 2 is similar to the way ink jetting occurs in CIJ printing. However, in this case, the fluid that breaks into droplets is the carrier fluid 14, not the printing fluid 16. The carrier fluid 14 at the nozzle 26 is pressurized with a pressure P1. However, unlike the continuous flow of carrier fluid in FIG. 1, where a constant pressure is applied to the nozzle 26, the pressure P1 applied to the carrier fluid 14 at the nozzle 26 varies with a constant frequency. One way to vary the pressure with a constant frequency is by a piezoelectric element 32. The piezoelectric element 32 mechanically deflects when a voltage is applied to it. The element 32 is configured to increase the pressure at the nozzle 26 when it deflects, i.e., by slightly reducing the amount of carrier fluid 14 at the nozzle. A voltage to the piezoelectric element 32 is applied at a very high frequency, such as ultrasonic vibrations (e.g., greater than 20 kHz), to break up the stream of carrier fluid into a uniform stream of droplets 30 as it exits the nozzle 26.

[0038] As the carrier fluid stream passes by the charging element 34, the charging element 34 imparts an electric charge to a portion of the droplets. In this example, the charging element 34 is a charging ring through which the carrier fluid stream passes. A voltage V1 is applied intermittently to the charging element 34 to selectively charge a portion of the droplets that pass by. In particular, only the droplets 30 that extract the droplets of printing fluid 16 from the ink nozzle 20 and that are intended to reside on the printing surface are charged. The charging element 34 may also be referred to as an electrode.

[0039] When passing through the extraction opening 18 of the ink nozzle 20, each of the droplets 30 of the first portion of the carrier fluid droplets (i.e., the charged droplets) extracts a droplet of printing fluid 16 that merges with the respective droplet of carrier fluid that is carried towards the printing surface 22. The second portion of the droplets 30 (e.g., the uncharged droplets) does not extract a droplet of printing fluid but simply remains in the original direction of carrier fluid flow.

[0040] After passing the ink nozzles 20, the stream of carrier fluid passes through a directing unit 36, which in this case includes a pair of oppositely charged plates. A second portion of the uncharged droplets of carrier fluid are not affected by the directing unit 36 ​​and continue along the original direction of the stream 12 into the interior of a collector 38. In the collector 38, the carrier fluid is returned to a carrier fluid source 40 which supplies clean carrier fluid to the nozzles 26 or stores it for reuse. The first portion of the charged droplets 30', each now merged with a droplet of printing fluid, are directed by the directing unit 36 ​​away from the collector 38 and towards the printing surface 22 to be deposited in the desired location as part of the printing pattern 42.

[0041] In Figure 2, the substrate 24 and printing surface 22 are shown generally in plan view to show the printing pattern 42 in the same view as the print head. The magnitude of the charge applied to each of the charged droplets 30' can be the same, the voltage applied across the opposing faces of the directing unit can be constant, and the print head and / or substrate 24 are moved relative to one another to produce the desired pattern 42. In such an arrangement, each of the charged droplets 30' carrying printing fluid is redirected laterally from the axis A1 of the carrier fluid flow by the same amount, and the movement of the substrate relative to the print head is relied upon to form the desired pattern 42 of the printed material.

[0042] In some embodiments, the charge applied to each of the charged droplets is changed so that the effect of the directing unit is changed. In other words, more highly charged droplets are more affected by the directing unit and are redirected laterally by a larger amount. Alternatively or additionally, the voltage on the directing unit is changed with a similar effect. In this manner, the relative movement between the print head and the substrate 24 can be made simpler. For example, a number of differently charged droplets carrying printing fluid can be deposited successively on the printing surface 22 as a train of droplets in the x direction, the print head does not move relative to the substrate 24 in the x direction, and then the substrate and / or print head is indexed in the y direction to begin deposition of another train of droplets. The length of the train of droplets without movement of the print head or substrate in the train direction is of course limited to the total amount of redirection that the directing unit 36 ​​can perform. In some embodiments, the directing unit 36 ​​is configured to redirect the charged droplets in one or more directions, such as the x direction, the y direction, and any combination of x and y.

[0043] FIG. 3 shows a schematic of an example of an electrohydrodynamic printer 10 in which the extractor 12 is a non-uniform stream of droplets 30 of carrier fluid. In a non-uniform stream of droplets, the spacing between individual droplets varies from droplet to droplet. This configuration can function as drop-on-demand printing, where droplets of carrier fluid 30 are generated only when needed to be extracted to carry corresponding droplets of printing fluid 16 to the printing surface 22. The ejection and formation of the carrier fluid stream shown in FIG. 3 is similar to the way that ink jets are created in non-industrial inkjet printers. The carrier fluid 14 in the nozzle 26 is subjected to pressure pulses when a droplet of carrier fluid is desired. In this case, each pressure pulse is provided by a piezoelectric element 32 that deflects in a direction that causes a small decrease in the work of the carrier fluid 14. A corresponding amount of carrier fluid 14 is released through the outlet 28 with each pressure pulse. The pressure pulses may also be created in other ways, such as by thermal energy (e.g., bubble ejection). In another example consistent with the drop-on-demand embodiment of FIG. 3, the carrier fluid 14 at the nozzle 26 is pressurized in the range of 5 psi to 150 psi, and a solenoid or piezoelectric controlled droplet release valve is used to create a stream of carrier fluid.

[0044] Each droplet 30 in the carrier fluid stream 12 is charged, and each droplet therefore extracts a droplet of the printing fluid 16 as it passes through the extraction port 18 of the ink nozzle 20. Each extracted droplet of printing fluid merges with a corresponding droplet of carrier fluid and is deposited on the printing surface. The printing pattern is controlled by the relative motion of the print head and the printing surface 22 in the x and y directions, as well as the timing of the pressure pulses and the formation of the corresponding droplets. In this example, the carrier fluid is charged by application of a voltage (V1) through an electrode 44 that contacts the carrier fluid 14 in the nozzle 26. In other embodiments, the carrier fluid droplets may pass an electrode external to the charged nozzle 26, as shown in FIG. 2. Because all droplets 30 in the droplet stream are charged to extract printing fluid, a non-directional field is required to direct the charged droplets towards the printing surface and the uncharged droplets away from the printing surface. However, a directional field can optionally be used for additional control over the droplet trajectory, and the amount of charge on each of the droplets can be varied by changing the electrode or charging element voltage (V1).

[0045] Highly viscous printing fluid 16 is successfully printed using a carrier fluid stream as an extractor. In a working example, the printing fluid 16 is a silver nanopaste that is typically only printable by screen printing (DGP-NO, ANP Materials, Milpitas, CA, USA, www.anapro.com). The printing fluid has a viscosity between 50,000-150,000 cps and contains 70-80 wt% silver nanoparticles. The ink nozzle 20 has a 70 μm extraction port 18 spaced from the extraction stream 12 by a distance (D) of 200 μm. The electrical potential between the carrier fluid 14 and the printing fluid 16 is 2000 V. By a stream 12 of carrier fluid 14 at a velocity between 6 m / s and 11 m / s, the printing fluid 16 is extracted from the ink nozzle 20, merged with the carrier fluid stream and carried to the printing surface.

[0046] Figures 4-7 show different ways in which the extracted printing fluid 16 joins the flow of carrier fluid 14. Figure 4 is an enlarged view of a portion of the continuous flow of carrier fluid 14 of Figure 1. In this example, the printing fluid 16 is not miscible with the carrier fluid 14. Therefore, the two fluids 14, 16 do not mix as they move towards the printing surface. This may be a desirable situation to prevent the carrier fluid 14 from diluting the printing fluid 16, which would otherwise change the solvent to solute ratio if the carrier fluid and the printing fluid were miscible. The carrier fluid 14 can be chosen to have a very low boiling point (e.g. acetone) to evaporate at least a part of the carrier fluid on its way towards the printing surface, so that the printing fluid 16 is deposited with a minimum amount of carrier fluid. The same idea applies to the flow of carrier fluid in the form of uniform or non-uniform droplets 30, as shown in Figure 5, which is an enlarged view of a portion of the carrier fluid flow of Figure 3.

[0047] FIG. 6 is an alternative version of FIG. 4 in which the printing fluid 16 can mix with the carrier fluid 14. The two fluids 14, 16 mix when they meet and / or move towards the printing fluid. This may be a desirable situation when the printing fluid 16 is prepared with a low boiling point solvent that is partially evaporated during the movement from the ink nozzle 20 to the printing surface. The carrier fluid 14 can contain the solvent that evaporates from the printing fluid 16 or it can be the same solvent, thereby replenishing the evaporated solvent, so that the printing fluid is deposited with a solvent to solute ratio very close to that of the printing fluid at the nozzle, or with some different ratio. The same idea applies to the flow of the carrier fluid in the form of uniform or non-uniform droplets 30, as shown in FIG. 7, an alternative version of FIG. 5 in which the printing fluid 16 can mix with the carrier fluid 14.

[0048] FIG. 8 shows the cleaning mode of the printer when applied to the configuration of FIG. 1. When the printing fluid 16 is soluble or otherwise compatible with the carrier fluid 14, the carrier fluid is used as a cleaning or anti-clogging agent for the ink nozzles 20. When the printer is not printing, the back pressure is removed from the printing fluid 16, and the pressure P1 of the carrier fluid 14 is reduced so that the velocity of the carrier fluid stream 12 exiting the nozzles 26 is not high enough to cause the carrier fluid stream to pass the ink nozzles 20 when a voltage is applied to the respective fluid. As a result, the carrier fluid stream is attracted to the nozzles 20, helping to maintain a clean nozzle tip and preventing the printing fluid 16 from drying up or otherwise clogging the extraction ports 18.

[0049] The foregoing description is understood to be a description of one or more embodiments of the present invention. The present invention is not limited to the specific embodiments disclosed herein, but rather is defined solely by the following claims. Moreover, any claims contained in the foregoing description relate to the disclosed embodiments and are not to be construed as limiting the scope of the invention or the definition of any term used in the claims, unless the term or phrase is expressly defined above. Various other embodiments, as well as various changes and modifications to the disclosed embodiments, will be apparent to those skilled in the art.

[0050] As used in this specification and the claims, the terms "eg," "for example," "for instance," "such as," and "like," as well as the verbs "comprising," "having," "including," and other verb forms thereof, when used in combination with a list of one or more components or other items, should each be construed as open-ended, meaning that the list is not to be construed as excluding other additional components or items. Furthermore, the term "electrically connected" and variations thereof are intended to encompass both wireless electrical connections and electrical connections made through one or more wires, cables, or conductors (wired connections). Other terms should be construed using their broadest reasonable meaning unless used in a context requiring a different interpretation.

Claims

1. A fluid extractor; The extractor is a liquid stream at a different potential compared to a printing fluid in a printing fluid supply source, and as the liquid stream passes an extraction port in the printing fluid supply source, the printing fluid is extracted from the extraction port.

2. A printer as described in claim 1, wherein the liquid flow merges with the extracted printing fluid and carries the printing fluid towards a printing surface.

3. The printer of claim 1 , wherein the flow of liquid is a continuous flow.

4. The printer of claim 1 , wherein the liquid stream is a uniform stream of droplets.

5. The printer of claim 4 , wherein each of the first portions of the droplets extracts a droplet of the printing fluid and each of the second portions of the droplets does not extract a droplet of the printing fluid.

6. 6. The printer of claim 5, wherein the first portion of the droplet carries the extracted printing fluid and is directed toward a printing surface, and the second portion of the droplet is not directed toward the printing surface.

7. The printer of claim 1 , wherein the liquid stream is a non-uniform stream of droplets.

8. a first nozzle configured to direct a stream of carrier fluid toward the printing surface; a second nozzle configured to provide printing fluid at an extraction port, the extraction port being spaced from the carrier fluid stream in a direction transverse to a flow direction of the carrier fluid, the carrier fluid stream passing the extraction port as it flows towards the printing surface; A printer, wherein a potential difference between the carrier fluid and the printing fluid causes the printing fluid to be extracted from the second nozzle.

9. The printer of claim 8 , wherein the extracted printing fluid merges with the flow of carrier fluid for transport towards the printing surface.

10. The printer of claim 8 , wherein the carrier fluid is uniformly pressurized within the first nozzle to provide a continuous flow of the carrier fluid.

11. 9. The printer of claim 8, wherein the pressure of the carrier fluid at the first nozzle is varied at a constant frequency to shape the carrier fluid stream into a uniform stream of droplets.

12. The printer of claim 11 , further comprising a piezoelectric element configured to deform at the constant frequency to vary the pressure of the carrier fluid at the first nozzle.

13. 9. The printer of claim 8, further comprising an electrode external to said first nozzle, said stream of carrier fluid being charged by said electrode to provide at least a portion of said potential difference.

14. 9. The printer of claim 8, further comprising an electrode configured to charge only a portion of the carrier fluid flow such that the carrier fluid flow extracts the printing fluid when a portion of the carrier fluid flow passes past the extraction port and such that the carrier fluid flow does not extract the printing fluid when an uncharged portion of the carrier fluid flow passes past the extraction port.

15. 9. The printer of claim 8, wherein a portion of the flow of carrier fluid passes through the extraction port without extracting the printing fluid and is collected and returned to a carrier fluid supply source that supplies the carrier fluid to the first nozzle.

16. 9. The printer of claim 8, wherein the printer is a drop-on-demand printer, and the stream of carrier fluid is a stream of droplets, each droplet of the carrier fluid extracting a droplet of the printing fluid from the extraction port and carrying the respective droplet of the printing fluid to the printing surface.

17. 9. The printer of claim 8, wherein the carrier fluid has a viscosity less than 10 centipoise and the printing fluid has a viscosity greater than 30 centipoise.

18. 9. The printer of claim 8, wherein the potential difference is at least 500V and the flow of carrier fluid has a velocity high enough to maintain a gap between the flow of carrier fluid and the extraction orifice of the second nozzle.

19. The printer of claim 8 , wherein the printing fluid is dissolvable in the carrier fluid, and the potential difference attracts a flow of the carrier fluid to the first nozzle during a cleaning mode of the printer.

20. The printer of claim 8, wherein the carrier fluid is a liquid.

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