Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/135—Nozzles
  • B41J2/14—Structure thereof only for on-demand ink jet heads
  • B41J2/1433—Structure of nozzle plates
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/015—Ink jet characterised by the jet generation process
  • B41J2/04—Ink jet characterised by the jet generation process generating single droplets or particles on demand
  • B41J2/06—Ink jet characterised by the jet generation process generating single droplets or particles on demand by electric or magnetic field
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2202/00—Embodiments of or processes related to ink-jet or thermal heads
  • B41J2202/01—Embodiments of or processes related to ink-jet heads
  • B41J2202/02—Air-assisted ejection

Definitions

• the invention relates to a print head for depositing ink on a substrate.
• the invention also relates to a printing system with such a print head and to a method for operating such a print head.
• US 2018/0009223 describes an electrohydrodynamic print head having a nozzle layer comprising a plurality of nozzles. It is based on a structure where the nozzles are arranged on one side and feed ducts extend through a feed layer on the other side.
• Nozzle electrodes are used to accelerate ink away from the nozzles and onto a target.
• the problem to be solved by the present invention is to provide a print head of the type mentioned above that has improved printing quality.
• the print head comprises a nozzle layer.
• This nozzle layer in its turn comprises at least the following parts:
• the ink may be any liquid that can be printed.
• the ventilation openings allow to feed a gas to the region between the printing head and the target and/or to convey gas away from said region. Hence, it becomes possible to control or at least modify the composition of the gas in the space where printing takes place, which provides a wealth of options for controlling the printing process. Some of these options are described below.
• the ventilation openings advantageously comprise at least two types of openings: A first type is designed as suction openings for feeding gas away from the region adjacent to the nozzles. The second type is designed as blow open ings for feeding gas towards said region.
• the invention provides improved printing quality while suffering from less clogging problems.
• the use of many nozzles on a flat multinozzle print head can result in the accumulation of evaporated liquid in the region between the print head and a target that is printed on.
• This problem is particularly pronounced for electrohydrodynamic multi-nozzle print heads like that disclosed in US 2018/009223 where printing resolutions can be in the sub-lOum, potentially even in the sub-lum resolution regime.
• print heads potentially allow the use of millions of nozzles arranged in large nozzle arrays, for example as disclosed in WO 2016/169956.
• nozzles may be arranged in much larger numbers and in rectangular arrays that are largely of similar size along both main array axes.
• ink-jet print heads are normally built such that nozzles are arranged within narrow rectangular or skewed rectangular areas, wherein a fast movement is exercised essentially in direction of the narrow dimension of said rectangular area.
• a pixel position generally obtains a single or a very small number of droplets. Since the movement generally scans the whole width or length of the target, the residence time of the print head on top of a single droplet is very short and hence the printed droplets can dry while there is no print head on top of the target.
• the print head may only return for a second printing cycle once the previously printed droplets have fully dried.
• the present invention provides a solution to allow a print head to operate even at long residence times.
• the invention is particularly useful for large print heads, i.e. for print heads having an array of nozzles with a diameter that exceeds, in all directions, 1 mm, in particular 10 mm.
• the print head comprises an array of nozzles.
• the array can be divided into a plurality of identical unit cells, with each unit cell comprising at least one nozzle and the same arrangement of ventilation openings.
• each unit cell comprising at least one nozzle and the same arrangement of ventilation openings.
• the relative arrangement of the nozzle and the ventilation opening(s) is the same in each unit cell.
• the print head is advantageously an electrohydrodymamic print head and comprises at least one nozzle electrode at each nozzle.
• the nozzle electrode can be positioned to electrohydrodynamically eject ink from the nozzle.
• the print head may further comprise ventilation ducts connected to the ventilation openings in order to convey gas between the ventilation openings and as least one gas source and at least one gas sink.
• the print head may further comprise electrically conductive vias extending through at least part of the ventilation ducts, which allows using the ventilation ducts not only for transporting gas but for transporting electricity, too.
• the invention also relates to a method for operating the print head that comprises at least the following:
• the printing and conveying advantageously takes place concurrently for increased printing speed.
• the method may advantageously comprise:
• a temperature difference between print head and the target Because of this temperature difference, there will be a difference in vapor pressure between liquid deposited on the target and liquid contained within the nozzle in the print head. This pressure difference causes a diffusive motion of evaporated liquid from the higher towards the lower pressure region.
• the higher pressure (i.e. higher temperature) region is on the target and the lower pressure (i.e. lower temperature) region is on the print head.
• the print head is advantageously at a lower temperature than the substrate.
• introduced gas therefore contains less than 50% saturation, more advantageously less than 20% saturation, of the at least one liquid used for printing.
• condensation of liquid on the print head can be prevented, although through proper choice of temperature difference and gas flow minimal condensation conditions may be upheld.
• This is viable because condensation does not immediately occur on the print head even at over-saturated conditions, due to thermodynamic energy barriers associated with the formation of a liquid nucleus, i.e. a growth center, on a dry surface.
• condensation into the liquid formed within the nozzle is readily possible. Therefore, the nozzle can compensate for an over-saturated environment by absorbing small amounts of liquid through condensation.
• Condensation onset on dry parts is advantageously further reduced by coating the print head surface with Teflon or another liquid repellant material.
• the word socialink“ advantageously describes a combination of liquid carrier and a contained material to be deposited.
• the material can be dispersed, dissolved or otherwise stabilized in the liquid. Upon printing of the ink and evaporation of the liquid carrier only the deposited material will remain.
• the contained material is dedicated to be formed into structures of given size, for example into a line of a certain width and height. If ink is deposited into such a line at a high volumetric flow rate, this can result in widening of the line due to liquid accumulation. As a result, a lower volumetric flow rate must be chosen.
• it may be advantageous to increase evaporation rate by introducing a gas circulation between the ventilation openings and, advantageously, by additionally introducing a lower temperature at the print head than at the target. The latter additionally allows to specifically control evaporation rates at the nozzle and the target.
• evaporation at the print head is close to zero or even slightly negative (i.e. slight condensation occurs), which implies that the concentration of contained material within the ink at the nozzle position remains almost constant, thereby reducing the problems associated with clogging or first droplet effects.
• each nozzle has associated at least one ventilation opening all nozzles will have very similar environments in terms of the concentration of gas-dissolved liquid. If, for example, gas would be blown underneath the print head, from one side of the print head towards the other, of between ventilation openings that are separated by several nozzles, such gas would have a higher concentration of liquid where it exits as compared to where it entered (because it continuously takes up liquid along its way underneath the print head). Accordingly, the situation for nozzles at the entry and exit point will not be the same and this can result in a different drying speed and different clogging vulnerability and to non-uniform printing results.
• the invention also relates to a printing system including a print head of this type as well as a target holder and at least one temperature control device for heating or cooling the print head and/or the target holder.
• the system comprises a print head temperature control device for cooling the print head and/or a target temperature control device for heating the target holder.
• the method of the present invention may advantageously comprise the step of controlling the temperature of at least one of the print head and the target holder.
• the target is maintained at a higher temperature than the print head, in particular with a temperature difference between the target and the print head of at least 10°C, in particular of at least 30°C.
• the temperature of the target is advantageously heated, such as to at least 80°C, for supporting in-situ tempering of the deposited material.
• the print head is advantageously operated as an electrohydrodynamic print head, i.e. electrical fields from the nozzle electrodes of the print head are used to eject ink from the nozzles during printing.
• Fig. 1 is a schematic side view of a printer with the print head and the target
• Fig. 2 shows a first arrangement of nozzles and ventilation openings as seen from the bottom of the print head
• Fig. 3 shows a second arrangement of nozzles and ventilation openings as seen from the bottom of the print head
• Fig. 4 shows a third arrangement of nozzles and ventilation open ings as seen from the bottom of the print head
• Fig. 5 is a sectional view of a print head
• Fig. 6 is a sectional view along line VI- VI of Fig. 5,
• Fig. 7 is a sectional view along line VII- VII of Fig. 5,
• Fig. 8 is a sectional view along line VIII- VIII of Fig. 5,
• Fig. 9 shows a fourth arrangement of the nozzles and ventilation openings as seen from the bottom of the print head.
• Fig. 10 shows a fifth arrangement of the nozzles and ventilation openings as seen from the bottom of the print head.
• A“unit cell” of an array of nozzles and ventilation openings is the smallest group of nozzles and ventilation openings having the overall symmetry of the array, and from which the entire array can be built up by repetition in two dimensions.
• Horizontal designates the directions parallel to the planes of the nozzle layer.
• Vertical designates the direction perpendicular to the plane of the nozzle and layer.
• Fig. 1 illustrates a general setup of an embodiment of the invention. It shows a print head 2, which is used to print ink onto a target 4.
• Print head 2 has e.g. the basic design as described in US
• nozzle electrodes located at the nozzles 6 are used to electrohydrodynamically eject ink droplets from the nozzles 6 and an acceleration electrode accelerates ink from the nozzles onto target 4.
• a target holder 8 is arranged below print head 2 and adapted to hold target 4 at a distance of e.g. 0.1 to 2 mm below print head 2.
• the acceleration electrode is associated with the target 4 such that between the two flat surfaces of target 4 and print head 2 a uniform electric can form which accelerates the droplets ejected from any nozzle 6 in perpendicular direction to the print head 2 surface towards target 4 where they are being deposited.
• Print head 2 may comprise, and/or be thermally connected to, a print head temperature control device 10
• target holder 8 may comprise, and/or be thermally connected to, a target temperature control device 12 to expedite the drying of the ink on substrate 8, by introducing a temperature gradient between print head 2 and target 4.
• Temperature control devices 10, 12 may include a resistive heater or a Peltier element or remote heating or cooling of a liquid which passes through the temperature control device 10, 12.
• passive heating or cooling may be employed, e.g. to bring either print head or target, or both, to room temperature.
• print head temperature control device 10 is adapted to cool or heat the ink itself.
• the ink may be cooled or heated outside print head 2 and then fed into print head 2.
• the ink may be recirculated before being printed.
• the printing system may comprise a circulation pump 13 connected to print head 2 for circulating ink through print head 2, advantageously with the ink being temperature-controlled by print head temperature control device 10. Part of the circulated ink is branched off to the nozzles 6 for printing.
• thermoelectric element for heating or cooling a block of metal or other material with good thermal conductivity, such as Aluminum Nitride, with this block being in contact to the feed layer 26. At the same time, this block may be passed by the ink in which case the ink takes up the temperature of the block before entering the feed layer 26.
• the print head temperature control device 10 sets the print head 2 temperature such that it is lower than the temperature set at the target 4 by the target temperature control device 12. In this way, higher liquid evaporation rates are created at the target 4 than at the print head 2. It is understood that both the absolute temperature at print head 2 and target 4 may be above or below room tem perature, while still the print head 2 is at a lower temperature than the target 4 in comparison. For example, the temperature at print head 2 may be chosen 50°C while the temperature at the target 4 may be chosen to be 100°C.
• Such high temperatures at target 4 may be chosen in order to not only enhance evaporation of solvent upon droplet impact but in addition the temperature at the target may also introduce some sort of in-situ temperature sintering of the deposited material contained within the ink. Furthermore, it is possible to adjust for solvents of different vapor pressure. For example, a lower boiling point liquid may be operated with a lower median temperature than a higher boiling point liquid, wherein median temperature described the intermediate temperature between target 4 and print head 2.
• print head 2 comprises a plurality of ventilation openings, which include blow openings 14 and suction open- ings 16.
• the blow openings 14 are used to feed gas to a region 18 below the nozzles 6.
• the suction openings 16 are used to feed gas away from region 18.
• a gas source 20 may comprise a pump or pressure reservoir, and optionally a mass flow controller 20a connected in series to an inlet 21 of the print head.
• the gas sink 22 may comprise a vacuum pump or low pressure reservoir, and optionally a mass flow controller 22a connected in series to an outlet 23 of the print head.
• the mass flow controller comprises a mass flow sensor, a pressure regulator, and a fast switching piezo valve 20b, 22b connected in series. The piezo valve is used for fast on/off switching of the gas source to the inlet or gas sink to the outlet.
• the steady state gas flow is controlled by the pressure regulator, using the mass flow sensor as feedback device.
• the pressure at the pressure regulator may also be set above the requirements for the steady state flow, to improve transient behavior.
• the piezo valve is operated in a linear proportional mode or a pulse width modulated mode to limit and control the steady state flow.
• the pressure regulator can be entirely omitted by using two fast switching piezo valves in a half-bridge configuration and a pressure sensor, applying the aforementioned in a linear proportional or pulse width modulated driving mode.
• Fast switching of the gas flow between on-state and idle state of the print head is beneficial because the gas flow is advantageously adjusted to the printing flow rate and drying speed of ink on the target 4.
• printing flow rate may rapidly go to zero, in which case the gas flow is advantageously reduced to zero as well, in order to not accelerate evaporation of liquid from the nozzle.
• Commercial mass flow controllers enable precise gas flow control and settling times in the order of 100 milliseconds. Faster switching and settling times in the order of 1 to 10 milliseconds or even below 1 millisecond are achieved with piezo valves.
• the printing system of the present invention may include at least one mass flow controller for regulating (i.e. measuring and maintaining at a desired level) the mass flow of the gas passing through the ventilation openings 14, 16 and/or a valve 20b, 22b for controlling the flow of the gas.
• Print head 2 comprises a nozzle layer 24, which includes the noz zles 6 as well as the nozzle electrodes, and feed layer 26.
• Feed layer 26 forms feed ducts for feeding ink to the nozzles as well as ventilation ducts connecting the ventilation openings 14, 16 to their respective gas source 20 and gas sink 22.
• Fig. 2 illustrates a first embodiment, which corresponds to the design illustrated in Fig. 1.
• each nozzle 6 is arranged between one blow opening 14 and one suction opening 16 (i.e. on the connecting line between the blow opening 14 and the suction opening 16).
• the nozzle 6 is arranged at the center between these two ventilation openings 14, 16.
• Fig. 2 shows two rows of nozzles 6 and ventilation openings 14, 16 extending parallel to each other. It depicts only a small part of the array of nozzles 6 and ventilation openings 14, 16 of the array.
• the array can be divided into a plurality of unit cells 28.
• Fig. 2 illustrates two such unit cells 28, each surrounded by a dotted square.
• Each unit cell 28 advantageously comprises at least one nozzle 6, at least part of a blow opening 14, and at least part of a suction opening 16 in order to generate a controlled, local gas flow around the nozzle 6.
• each unit cell 28 contains exactly one nozzle 6, its neighboring blow opening 14 and its neighboring suction opening 16.
• the gas flow generated by the ventilation openings 14, 16 is illustrated by dashed arrows 30.
• Fig. 3 shows another embodiment of the arrangement of nozzles 6 and ventilation openings 14, 16.
• each unit cell 28 consists of two halves a blow opening 14 and two halves a suction opening 16 altematingly arranged at the centers of the edges of a square 32 (which coincides with the border of unit cell 28) and one nozzle 6 in the center of square 32.
• Fig. 4 shows a third embodiment of the arrangement of nozzles 6 and ventilation openings 14, 16.
• each unit cell 28 consists of four quarters of suction openings 16 at the comer of a first square 34, four halves of blow openings at the middle of the edges of the first square 34, and one suction opening 16 in the center of the first square 34.
• the unit cell includes four nozzles 6 at the comers of a second square 36.
• the first and second squares 34, 36 have parallel edges and are concentric, and the first square 34 has twice the diameter of the second square 36.
• each unit cell 28 in the embodiment of Fig. 4 may also be offset by one nozzle distance (e.g. to the right in the figure).
• each unit cell 28 consists of four quarters of blow openings 14 at the comer of first square 34, four halves of suction openings 16 at the middle of the edges of first square 34, and one blow opening 14 in the center of the first square 34.
• the unit cell can be described in more than one way, with the descriptions being interchangeable in that they describe the same physical arrangement of the nozzles 8 and the ventilation openings 14, 16.
• Figs. 5 - 8 illustrate a possible design of the nozzle layer 24 and the feed layer 26 of a print head 2.
• the design of the nozzles 6 in nozzle layer 24 substantially corresponds to the design of the device described in US 2018/0009223.
• each nozzle 6 comprises a spout 40 arranged in a recess 42.
• at least one nozzle electrode 44 surrounds recess 42 and is used to extract ink away from a liquid meniscus formed at spout 40.
• the nozzle electrodes 44 are annular (cf. Fig. 8).
• an optional shield electrode 46 is arranged at a level below the nozzle electrodes 44. It covers substantially all the array of nozzles 6 with the exception of openings at the location of each nozzle 6 and helps to shield the influence of nozzle electrodes 44 of neighboring nozzle 6 and to main tain a uniform electrical field in region 18.
• Nozzle layer 24 may comprise a first dielectric sublayer 48 between the electrodes 44, 46 and a second dielectric sublayer 50 right above the nozzle electrodes 44.
• a third dielectric sublayer 52 forms the spouts 40.
• a fourth dielectric sublayer 54 forms a carrier membrane of the spouts 40 for positioning and holding each spout 40 at the center of its recess 42.
• Feed layer 26 forms feed ducts 56a, 56b for feeding ink to the nozzles 6.
• they include via sections 56a extending vertically upwards from the nozzles 6 and horizontal interconnect sections 56b. The latter run e.g. perpendicular to the sectional plane of Fig. 5, and each of them interconnects a plurality of the via sections 56a.
• the interconnect sections 56b may be connected to larger ink terminals of print head 2, where an ink reservoir may be connected to them.
• the ventilation openings 14, 16 are connected to ventilation ducts 58a, 58b, 58c, which extend through print head 2 to ventilation terminals 60, which can be connected to the gas source 20 and to the gas sink 22.
• the ventilation ducts 58a, 58b, 58c include chimney sections 58a, which extend from the ventilation openings 14, 16 vertically through at least part of print head 2, in particular through nozzle layer 24 and at least part of feed layer 26.
• Ventilation ducts 58a, 58b, 58c include two sets of interconnect ducts 58b, 58c, each of which interconnects a plurality or all of the ventilation openings 14, 16.
• the interconnect ducts 58b, 58c advantageously extend horizontally through print head 2.
• the first set 58b of interconnect ducts interconnects the blow openings 14, and the second set 58c of interconnect ducts interconnects the suction openings 16 (or vice versa).
• the two sets form distinct duct systems for feeding gas to the blow openings 14 and for feeding gas away from the suction openings 16.
• an arrangement of ventilation openings is shown that is essentially equal to that shown in Fig. 3.
• the first and second set of interconnect ducts 58b, 58c are located at different vertical levels in the print head, which makes it easier to keep them separate.
• a single vertical ventilation duct may be formed to continue gas flow to the next higher level of the feed layer 26.
• space is created for the formation of intercon nect ducts of different gas pressure (i.e. dedicated to suction of blowing) or of horizontal interconnect sections carrying ink. This can be important for other embodiments than that shown in Fig. 3.
• This may e.g. be achieved by adjusting the average cross-section and length of uniform ventilation ducts, e.g. chimney section 58a, as compared to their non-uniform counterparts, e.g. of the interconnect ducts 58b, 58c.
• a smaller cross-section and longer length of a given ventilation duct thereby implies a higher pressure drop.
• one way of achieving appreciable results is by reducing the diameter of the blow openings 14 and the suction openings 16 until the pressure drop over uniform parts of the ventilation ducts on averages varies less than a certain percentage. Preferably, such percentage is less than 25% across all blow openings 14 and suction openings 16, more preferably less than 5%.
• operating the print head advantageously comprises at least one of the following steps:
• feed layer 26 comprises several sublayers, which are advantageously of a dielectric material in order to insulate the various electrically conductive tracks within feed layer 26 (to be described below).
• a first sublayer 62a forms the via sections 56a as well as part of the chimney sections 58a.
• a second sublayer 62b forms the interconnect sections 56b of the ink feed ducts for the ink.
• the chimney sections 58a extend through this second sublayer 62b.
• a third sublayer 62c covers second sublayer 62b and closes the interconnect sections 56b from above.
• the chimney sections 58a extend through this third sublayer 62b.
• the third sublayer 62b may also form at least one via section from each interconnect section 56b.
• the same via section may also extend upwards into each of the higher sublayers until there is formed an opening in the topmost layer which allows contacting to an ink source via an ink terminal.
• one such via section 56c and the respective ink port 56d are illustrated, in dotted lines. This exemplifies that after interconnecting feed ducts only few via sections need to be effectively formed all the way to the topmost layer.
• a fourth sublayer 62d forms the first set 58b of interconnect ducts for the gas to the blow openings 14.
• the chimney sections 58a associated with suction openings 16 extend through this fourth sublayer 62d
• a fifth sublayer 62e covers fourth sublayer 62d and closes the interconnect ducts 58b from above.
• the chimney sections 58a associated with suction openings 16 extend through this fourth sublayer 62e.
• a sixth sublayer 62f forms the second set 58c of interconnect ducts for the gas from the suction openings 16.
• the sixth sublayer 62f may also form at least one chimney section from each interconnect duct of the first set of interconnect ducts 58b.
• the same chimney section may also extend into each of the following upper sublayers, until there is formed an opening in the topmost layer in the form of a gas terminal 60 (not shown).
• a seventh sublayer 62g covers sixth sublayer 62f and closes the second set of 58c interconnect ducts from above. It may also form one or more of the gas terminals 60. As mentioned, there are several electrically conductive tracks in print head 2 and in particular in feed layer 26 in order to connect the various elec trodes to one or more voltage sources of the printer.
• They may include suitable electrical vias extending through some or all of the sublayers of the print head.
• print head 2 may contain electrically conductive vias 64 extending at least through part of the ventilation ducts 58a, 58b, 58c.
• electrically conductive vias 64 may extend along at least some of the chimney sections 58a. They may e.g. be formed by an electrically conductive coating extending along at least part of the wall of the respective chimney section 58 a.
• the conductive vias 64 may be connected to the nozzle electrodes 44 as shown in Fig. 8. In order to have different nozzle electrodes 44 connected to at least two different voltage sources, one half of the vias 64 may be connected to a first set of electrically conductive interconnect lines 66a, e.g. at top surface of sublayer 62c (see Fig. 7), while the other half of the vias 64 may be connected to a second set of electrically conductive interconnect lines 66b, e.g. at the top surface of sublayer 62e.
• electrically conducting vias 64 in chimney sec tions 58a may also be used, in addition or alternatively to the above application, to feed voltage to any other electrode(s) in print head 2, such as to shield electrode 46.
• the print head is to be brought to a specific temperature, it is advantageous to at least form some of the electrical vias 64 as separate vias which are completely filled with metal, e.g. by electroplating or by printing a metal ink into the voids.
• a metal with good thermal conductivity like copper can be used to fill such vias.
• the temperature implied onto the print head by a cooling or a heating device is efficiently forwarded to the nozzle layer, across the dielectric layers of the feed layer which by definition do not have very good thermal conductivity properties.
• nozzle layer 24 of print head 2 as well as feed layer 26, form a single, integral body. They may e.g. be manufactured using masking and etching steps as they are known from semiconductor technology.
• feed layer 26 may be made by stacking and patterning of permanent dry film resist, e.g. epoxy-based dry film resist, or from individual patterned glass sheet, particularly laser-patterned glass sheets, which are bonded together, e.g. by adhesive bonding.
• permanent dry film resist e.g. epoxy-based dry film resist
• individual patterned glass sheet particularly laser-patterned glass sheets, which are bonded together, e.g. by adhesive bonding.
• the print head is operated by applying suitable voltage pulses to the nozzle electrodes 44 in order to eject ink from the nozzles 6 onto target 4.
• gas is conveyed through the ventilation openings 14, 16.
• the steps of printing the ink and conveying the gas are concurrent even though they may also take place intermittently as described for an example below.
• the flow rate of gas conveyed through the blow openings 14 to region 18 e.g. the gas volume conveyed each second into region 18
• the flow rate of gas conveyed through the suction openings 16 from region 18 e.g. the gas volume conveyed each second from region 18
• region 18 may be flooded with fresh gas from the blow openings 14, or it may be flooded with fresh gas drawn in horizontally from the edges of region 18 while the old gas is removed by means of the suction openings 16.
• printing may advantageously be interrupted while operating the gas flow in order to avoid asymmetric deflection caused by the gas flow in region 18.
• the gas flow is advantageously deactivated while the temperature difference between print head 2 and target 4 is upheld.
• the lack of liquid on the target implies that the gas flow will end up supporting removal of liquid from the nozzle, due to the absence of a diffusive gas flow from the target towards to print head.
• a gas may be switched from a partially saturated to a fully saturated species.
• the gas conveyed to region 18 through the blow openings 14 may fulfill one or more of the following functions:
• the gas may be used for drying, i.e. for conveying evaporated ink solvent or ink carrier away from region 18.
• the ink comprises a component that is evaporated on target 4, and the concentration of said component is lower in the gas fed through the blow openings 14 to region 18 than in the gas evacuated through the suction openings 16.
• the gas may be an inert gas preventing undesired chemical reactions of the ink with air.
• the gas may include nitrogen or a Nobel gas.
• gas can also be used for both, to support drying and introduce a chemically inert environment
• print head 2 may comprise further nozzles outside said array, e.g. nozzles dedicated to special printing tasks. These further nozzles are advantageously fewer in number (e.g. no more than 10% of all nozzles) and they may or may not be provided with their own ventilation openings.
• the unit cells 28 are squares. It must be noted, though, that they may also be mere rectangles. There is no strict need to have equal nozzle spacing in two perpendicular horizontal directions even though, depending on unit cell design, the higher geometry of a square over a rectangle may be advantageous for maintaining identical gas flows around the nozzles.
• nozzles must not be placed in square-like fashion but may also be placed in a hexagonal fashion. For example, this would be achieved by adding a nozzle 8 to the print head 2 in Fig. 3 at all those positions that form the center of a square which has its edges situated at the position of four neighboring nozzles 8. In this way, the number of nozzles 8 on the print head would be doubled while the number of ventilation openings 14, 16 remains constant, i.e. there will be only one ventilation opening 14, 16 per nozzle 8, and hence there is no more symmetry at the level of a single nozzle, similar to the situation in Fig. 4. This is illustrated in Fig. 9.
• Fig. 10 finally illustrates a design with the nozzles arranged with 3- fold symmetry.

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