EP3752365B1 - Print head and printing method - Google Patents

Description

The invention relates to a print head according to the first claim and a printing method according to the ninth claim.

Jet printheads are a central component in printing technology. With them, liquids (inks) are removed from a reservoir, for example a cartridge, and accelerated in the direction of a surface to be printed for the printing process. The printing is dosed, i.e. the liquids are only transported in individual drops onto the surface to be printed. Various actuator and dosing concepts are used for this, such as piezoelectric, electrostatic or thermally based. The so-called drop-on-demand technique is preferably used, in which one or more drops are released only when a control signal is present. A quasi-continuous printing process, the so-called continuous drop method, takes place by repetitions of the control signal, preferably with repetition frequencies of more than 1 kHz. Accordingly, various printing technologies are known, which differ in particular by the function of the print head used, in particular the non-contact piezo inkjet technology, the electrohydrodynamic inkjet technology, the aerosol jet technology, but also the ultrasonic dosing method, in which the printing liquid comes into direct contact with the substrate to be printed via a meniscus.

The print head mentioned at the outset is used in particular and preferably in the field of non-contact digital jet printing methods for functional printing, ie printing of functional structures (eg conductor tracks, resistors, capacitors, biological substances, etc.).

The piezo inkjet technique is the most widespread method. A piezo element acts on a volume of ink in the printing nozzle, with a pressure or pressure pulse being exerted on the printing ink, which causes at least one drop of ink to be ejected from the printing nozzle and sprayed onto the object to be printed. Inks in a preferred viscosity range of between 5 and 40 mPa·s are used for printing. A further viscosity range is covered in particular by aerosol jet technology and electrohydrodynamic inkjet technology, with aerosol jet technology having the additional advantage of producing structures in the single-digit mm range, despite major topology jumps on the surface to be printed, without vertical Tracking the print nozzle to be able to print.

An aerosol jet printing system and printing method for functional printing is available from Optomec Inc. (Albuquerque, New Mexico, USA) in US Pat U.S. 7,270,844 B2 been revealed. Exemplary deposition head arrangements are given in JP S57 34971 A , EP 1 830 927 B1 and U.S. 9,114,409 B2 described. In this, an aerosol is guided in an enveloping gas flow via a channel into a separate chamber and from there via a pressure nozzle arrangement in the direction of an object to be printed.

The aerosol jet printing method disclosed includes in particular generation of an aerosol from ink, concentration of the aerosol, transport of the aerosol with gas to the print nozzle arrangement, concentration of the aerosol, for example in the aforementioned chamber, and hydrodynamic focusing of the aerosol jet in the print nozzle. The aerosol is generated either pneumatically or by ultrasound in the separate chamber of the printhead. The generated aerosol is conveyed with the help of a transport gas via line systems to the pressure nozzle and bundled there by means of a focusing gas (also an enveloping flow). The operating mode of the system is immutable. Before the actual printing process, the aerosol jet is adapted to the respective conditions by setting various parameters (in particular volume flow of the transport gas, volume flow of the focusing gas, choice of nozzle and atomizer, etc.). As soon as the aerosol jet is stable, printing can begin. The aerosol volume flow remains constant throughout the printing process, the jet intensity is not regulated and not varied. The dosing quantity per time is therefore constant. In order to be able to create interruptions in the printed image, the aerosol jet must be interrupted after the nozzle. This is done using a mechanical ink catcher that is positioned between the nozzle and the substrate.

The disadvantage of the aforementioned method is that the print head must always be aligned with the earth’s gravitational field and therefore cannot be aligned with the surface to be printed at will without additional measures such as mechanical decoupling of the chamber for aerosol generation and the nozzle. This local separation into several subsystems requires a line system to convey the aerosol flow to the pressure nozzle. This increases the dead volume. In addition, long lines can influence the aerosol (e.g. change in droplet size due to agglomeration and merging of small droplets, deposits of droplets on the walls). The line systems are then contaminated with a substance and must be cleaned or replaced if another fluid is to be printed without contamination.

A further limitation results from the design of the print head due to the system. A complete cleaning or intermediate cleaning (e.g. when changing the liquids to be printed) is achieved in particular by separating the equipment of aerosol generation and printing nozzle is more difficult and is therefore more complex than, for example, a comparable inkjet printing system.

Representing an ultrasonic dosing process, in U.S. 7,467,751 B2 and U.S. 7,095,018 B2 discloses an ultrasonic plotting system and printing method by Sonoplot Inc. (Middleton, Wisconsin, USA).

As for the aforementioned aerosol jet printing system, the need for separate subsystems for conveying the fluid to be printed is also limiting for the aforementioned ultrasonic dosing method.

Printing three-dimensional structures on the surface of a substrate poses a particular challenge when using the aforementioned technologies. For such printing, one- or multi-axis relative movements between the print head and substrate must be enabled, for example by means of an electromechanical positioning system. With each change of direction, axis acceleration and deceleration occur, which are recorded by the print head. If the printing process occurs simultaneously with one of the aforementioned axis accelerations and decelerations, e.g. with a constant volumetric aerosol flow rate, the amount of ink deposited on the substrate will inevitably vary with each applied change. The properties of the printed structure (e.g. resistance of a printed electrode) depend on its geometry (e.g. changes in direction, radii, lengths, topography, etc.) in the cited aerosol jet printing system, for example.

The previously cited aerosol jet printing system and printing method for functional printing does not disclose a solution to the aforementioned problem, since the process of aerosol generation is designed for a constant aerosol mass flow and neither repeated interruptions during the printing process nor regulation of the aerosol mass flow are provided. A simple change between different fluids in a print head is also not provided.

The state of the art cited with regard to the ultrasonic dosing method does not show any possibility of contactless printing of the aforementioned structures. The process described there requires precise distance control between the nozzle and the substrate and is only suitable for flat substrates such as silicon wafers.

Proceeding from this, one object of the invention is to improve the aforementioned jet print head in such a way that the aforementioned limitations and disadvantages and their effects are avoided or reduced.

In particular, one object is to propose a jet print head which is also suitable for printing on three-dimensional structures of the type mentioned at the outset.

Another object is to propose a jet print head that is suitable for a faster changeover compared to conventional systems while avoiding cross-contamination and/or liquid carryover of the liquids to be printed in the printing system.

A further object is to propose a corresponding printing method, in particular for printing structures, preferably functional structures, on a surface using the jet print head.

It goes without saying that the tasks mentioned also apply in principle to the corresponding uses of the jet print head as well as the printing process for solving the tasks mentioned.

The object is achieved with a jet print head and a printing method having the features of claims 1 and 14, respectively. Subclaims related to this state advantageous configurations.

The advantageous configurations and versions each have features which, within the scope of the invention, can also be combined with any version individually or in any combination.

The invention is based on a print head comprising a capillary for a liquid as the printing fluid with a nozzle opening which opens into an antechamber. The capillary adjoins an actuator directly or indirectly via other components such as an elastic element and/or fastening means for the capillary (e.g. clamping means), i.e. it is in solid contact with it. The piezoelectric actuator is preferably firmly connected to the capillary. Furthermore, said antechamber has an outlet opening aligned with the nozzle opening of the capillary, i.e. the axes of symmetry of the capillary and outlet opening preferably coincide. Furthermore, inlet openings opening into the antechamber are provided for a guide gas which, together with the pressure fluid, leaves the antechamber via the outlet opening in the direction of a surface to be printed.

The actuator is preferably a piezo actuator. Alternatively, especially in the case of larger print head designs, electromechanical actuators are also suitable, or in particular in the case of very small designs, electrostatic actuators are also suitable as actuators.

In further configurations, the actuator consists of a plurality of components, including also actuator-passive components.

Actuator-passive components include, for example, at least one elastic element, at least one elastic cup spring element and/or at least one elastic bending element or bending strip as a connecting component between the capillary and the print head housing. They serve, in particular, to guide the capillary and preferably allow only unidirectional axial mobility of the capillary in the print head housing, which is flexible about a basic position. Actuator-passive components preferably also include a lever mechanism between an actuator-active component of the actuator, for example a piezoelectric transducer (piezoelectric actuator), which is preferably in contact with the actuator-passive components, more preferably can be mechanically excited by them.

As a solution to the problem, it is proposed that the liquid from the capillary is first atomized directly at the nozzle opening with an axial oscillating movement of a capillary and forms an aerosol with the guide gas. The aerosol is thus not conducted into the antechamber in a preconditioned manner, but rather forms in an advantageous manner at as late a point in time as possible just shortly before the printing process in the antechamber.

The capillary, preferably a glass capillary, is connected to at least one reservoir, preferably at least one cartridge for the liquid (pressure fluid). The capillary thus has non-continuous or preferably continuously conveying feeding means for the pressure fluid into the capillary, preferably at the end of the capillary (proximal end of the capillary) opposite the nozzle opening (distal end of the capillary). This is preferably done without contact by means of a supply line either to the capillary, for example through a line into the named proximal end of the capillaries protruding outlet opening of the supply line, or by means of an elastic hose connection preferably between the proximal end of the capillary and said outlet opening of the supply line. The supply line represents a connection between at least one reservoir of the fluid to be printed and the capillary. The fluid is preferably conveyed capillary, ie fluid losses in the capillary via the nozzle opening during the printing process are compensated by capillary suction of fluid components. However, one embodiment provides for the feed line to be provided with its own active fluid feed means (feed pump). A further optional configuration comprises at least one mixing chamber for mixing or homogenizing fluid components, for example from different reservoirs and brought together in the mixing chamber. It is within the scope of the invention to locate said mixing chamber functionally in the capillary and to provide a separate supply line directly into the capillary for each reservoir involved.

The capillary is preferably connected to the supply line via a preferably flexible hose to improve the mobility of the print head and to reduce the movable masses required for a positioning movement of the print head. The liquid is transported via the hose through the capillary and the nozzle opening into the antechamber. The transport (conveyance) preferably takes place, i.e. not necessarily without a feed pump.

The at least one inlet opening for the guide gas is preferably arranged at the side of the capillary. The alignment of the at least one inlet opening and thus the inlet opening is also preferably aligned at an acute angle to the axis of symmetry of the capillary towards the outlet opening, ie the alignment consists vectorially of a orthogonal and a vector aligned parallel to the axis of symmetry, the parallel partial vector pointing in the direction of the outlet opening as viewed from the nozzle opening.

In a preferred embodiment, said alignment crosses the axis of symmetry of the capillary within the antechamber. If the fluid to be printed from the capillary is a liquid or a suspension and emerges from the nozzle opening as a sprayed jet, this jet crosses the flow of the guide gas. When they meet, an aerosol is formed.

A key feature relates to the arrangement of the actuator in the print head, its arrangement in relation to the capillary and the design of the actuator movement. The actuator is preferably fixed in the antechamber of the print head, more preferably opposite to the outlet opening. The actuator movement serves to move the capillary relative to the antechamber and includes forward and backward movements, preferably only axially to the axis of symmetry of the capillary and outlet opening. In addition to the design and direction of action of the actuator, it is also determined by the fixed points, i.e. the attachment points of the actuator in the print head on the one hand and by the arrangement of the receptacle for the capillary on, in or above the actuator away from the fixed points on the other. Preferably, the attachment for fixing the piezoelectric actuator in the antechamber takes place by means of gluing, clamping or screwing.

If the actuator, preferably a piezo actuator, is designed as an oscillating actuator, preferably an oscillating actuator that can be operated in resonance, it preferably comprises a plate, disc, ring, cross or bar-shaped flexural oscillating actuator, at least one preferably ring-shaped translational actuator or one or more shearing oscillating actuators with a preferably centered on the actuator for the capillary. The oscillating bending actuator and the aforementioned attachment points (fixed points) to the antechamber extend symmetrically, preferably rotationally symmetrically, around the receptacle and thus around the axis of symmetry of the capillary and the outlet opening. A preferred embodiment provides for the attachment points to be designed as fixed supports for the oscillating actuators in order to achieve the highest possible oscillating amplitudes. A piezo bending vibration actuator, which is preferably fixed elastically at both ends, preferably reaches the maximum amplitude in its middle. They are preferably formed by at least two individual points or, in particular in the case of a plate-shaped or disc-shaped oscillating bending actuator, by support lines. If an actuator is preferably firmly clamped on one side only, the maximum amplitude occurs at the other end.

An alternative configuration of the piezo actuator includes a stack of layers of disk-shaped individual piezo actuators, the deflections of which add up to form an overall deflection. Alternatively, so-called D31 converters or shear actuators can also be used, the actuator movement of which can be tapped transversely to the applied electrical field and is used for the axial movement of the capillary. Compared to a oscillating bending actuator, these configurations are significantly stiffer and are particularly suitable for non-resonant guided actuator movements, for example for square-wave or sawtooth-shaped oscillations or individual impact movements.

The capillary is moved back and forth axially by the piezoelectric actuator, preferably in an oscillating manner, either in resonance or following a predeterminable, preferably cyclic curve (oscillation, eg sawtooth, rectangular, etc.). The capillary and thus also its nozzle opening is moved back and forth with each movement cycle, with each change of direction, deceleration or jerk, an acceleration acts on the capillary and nozzle opening and thus also on the pressure fluid located in the nozzle opening. If the nozzle opening is accelerated during retraction, i.e. by a distal change of direction, i.e. towards the outlet opening, the mass inertia of the pressure fluid alone causes fluid components to be pressed out of the nozzle opening and drops or other fluid components to be detached, particularly on the nozzle outlet surface of the capillary wall. With each oscillation cycle, drops of the pressure fluid are thus detached from the nozzle opening and are absorbed by the guide gas. The components of the guide gas and the detached components of the printing fluid form an aerosol that is conducted from the antechamber via the outlet opening to the surface to be printed. Printing takes place immediately after aerosol formation, which advantageously reduces the risk of segregation.

The aligned arrangement of nozzle opening and outlet opening is particularly advantageous for the aforementioned process, since the detaching droplets not only form an aerosol due to their speed and mass inertia during detachment, but also an impulse on the aerosol flow in the direction of the outlet opening and thus the exercise surface to be printed. The aerosol flow speed is already high at the nozzle exit. With the guide gas flow, which is initially formed around the aerosol flow preferably as a sheath flow and is also at least partially mixed in the antechamber towards the outlet opening, the aerosol flow is focused in the direction of the center of the jet. It is advantageous here that the droplets contribute significantly to the total momentum of the aerosol due to a density that is significantly higher than that of the guide gas.

In the aforementioned aerosol formation, preferably only part of the guide gas flow is transferred into the aerosol, i.e. it absorbs the droplets that are released. However, the remaining portion of the guiding gas flow leaves the antechamber together with the aerosol flow formed via the outlet opening. Since the aerosol flow is concentrated around the axis of symmetry of the capillary and thus around the outlet opening due to the aforementioned momentum consideration, the remaining portion of the sheath gas flow is displaced into the edge areas of the outlet opening and thus forms a sheath flow around the aerosol flow. This bypass flow reduces contact of the aerosol with the inner wall of the outlet opening, thereby reducing accumulation of aerosol components and advantageously also clogging of the outlet opening with the pressurized fluid.

The mass flow of the aerosol can be regulated, preferably by changing the process parameters of fluid pressure in the capillary, by changing the voltage amplitude and frequency when driving the actuator and by changing the control signal, e.g. from a sine function to another periodic function (e.g. sawtooth shape, rectangular shape) or by a Superposition with a phase-shifted periodic signal.

Due to the amplitude of the axial reciprocating movement, the volume flow of detached drops and thus also the speed of the ongoing separation and atomization of the liquid, i.e. the pressure fluid at the nozzle opening, can be adjusted and regulated. With the frequency remaining the same, the amount of flow in particular, but also the droplet size of detached droplets and thus also the aerosol properties, can be adjusted with the amplitude height.

In particular, the size of the detached droplets, an essential feature of a developing aerosol, can be adjusted by the frequency of the axial reciprocating movement. The frequency is preferably between 50 kHz to 2 MHz. through on In addition, the scattering area of the detached droplets, which extends conically around the axis of symmetry, can be increased by the lateral harmonic frequencies impressed on the fundamental oscillation.

The aforesaid scattering area of the detached droplets, which extends conically around the axis of symmetry, can also be preset by designing the nozzle opening, in particular its diameter, a sharp-edged capillary edge produced by a breaking edge of the capillary. Likewise, a capillary edge that does not extend orthogonally to the capillary axis enables a preferred direction of deflection of the detached drops.

The behavior of the aerosol generation can be controlled by the process parameters mentioned. In the final installation state, these parameters are reduced to the following main influencing factors: frequency, mode of vibration, amplitude, fluid pressure. If the excitation of the piezo element is switched off, the generation of aerosol is interrupted. No more liquid is ejected from the nozzle (neither in aerosol form nor in any other form). This binary behavior is used to switch off the aerosol jet if there is an interruption in the printed image, without the need for a mechanical ink catcher.

A change in the individual parameters frequency, mode of oscillation, amplitude and fluid pressure or a combination of these parameters leads to a change in the mass flow of the aerosol (liquid) leaving the nozzle opening and thus the outlet opening, which means that acceleration of the axes of the pressure system has an influence on the homogeneity of the Print image (homogeneity of the printed structures) can be compensated.

The capillary preferably borders on a piezo actuator, i.e. it is in solid contact with it. In such a configuration, the piezoelectric actuator has a receptacle for the capillary. The receptacle connects to the capillary and also performs the same axially oscillating or oscillating movements that are preferably imposed by the piezoelectric actuator. They form a common vibration system. In the case of a capillary oscillating in resonance, the receptacle serves as part of the oscillating mass on the oscillating actuator.

For this purpose, one embodiment of the receptacle provides for the piezo actuator of the print head to be configured preferably with clamping means in which the capillary is clamped in a non-positive manner. These means preferably consist of a bore in the actuator or a preferably elastic component that is mounted or inserted on the actuator and that preferably has a transition fit with the piezo actuator, preferably with a sliding fit (according to: Dubbel: Taschenbuch für den Maschinenbau, Springer Verlag, 14th edition (1981 ) p. 339) . Compared to tighter transition fits or press fits, the capillary can still be replaced manually from the print head without additional pressing or striking tools and without the risk of damaging the glass capillary. An alternative embodiment provides a clamping means designed with an elastic clamping element such as a spring element, which presses the capillary on the piezoelectric actuator onto a counter surface that determines the capillary alignment, preferably with a guide groove or a stop for the capillary, and fixes it axially in a non-positive and/or frictional manner. On the part of the capillary, in particular a glass capillary, an optional tube jacket encasing the capillary and firmly attached (e.g. glued on or pressed) over it is advantageous in the aforementioned configurations, which in its length is further preferably limited to the clamping area of the acting clamping means, which is significantly shorter than the length of the capillary.

A distinction is made, particularly within the scope of the application, in principle between three basic types of mechanical connection, a non-positive connection, a material connection and a form-fit connection, with mixed forms often also being used. A non-positive connection between two surfaces is characterized by the fact that the surfaces are pressed against one another with a force, e.g. by clamping means, and static friction is generated solely by the surface pressure, which fixes the two surfaces to one another. An adhesive material transition, as occurs in the case of material connections, for example when two surfaces are welded, glued or soldered, does not exist in the case of a non-positive connection. This differs from form-fitting connections, in which topographies or additional elements interlock between the two surfaces and thus hold the surfaces together. Examples of this are riveted connections between two sheets of metal, a tongue and groove connection or elements that act against a mating fit, such as steps, grooves, collars or webs.

The aforementioned clamping means simplify interchangeability in the print head. In particular, a change in the liquid to be printed, but also in the scattering range of the detached drops, which is decisively determined by the design of the nozzle opening, can be implemented by exchanging the capillary. A further advantage of such a change of the pressure medium and/or the scattering area is ensured by the fact that the aerosol is only generated when required (aerosol-on-demand) and only when the paste or the liquid leaves the nozzle opening in the antechamber. The in the antechamber via the inlet openings introduced jacket gas not only as an optional component of the forming aerosol, but in particular as a jacket flow around the aerosol, namely in the antechamber as well as in the subsequent outlet opening. This reduces the contact of the pressure medium (paste or liquid) and the aerosol containing it with the inner walls of the antechamber and the outlet opening and significantly prevents their contamination. This in turn makes it easier to change the liquid to be printed during a printing process, since no further cleaning processes are required apart from replacing the capillary and the feed means provided for the liquid to be printed.

A further configuration of the receptacle of the capillary provides for an additional design acting in an axially positive manner with respect to the axis of symmetry to be provided between the capillary of the receptacle and the piezoelectric actuator and/or an elastic element. This includes, for example, steps or webs firmly connected to the capillary or formed onto it, which positively engages in a design of the capillary receptacle or the clamping means provided with this in mating fit as a stop oriented on one side or both sides. It is advisable to provide the aforementioned enveloping pipe jacket with circumferential grooves or collars or to use the end areas of the pipe jacket for a form-fitting axial fixation. The particular advantage of this preferably additional configuration is that, on the one hand, possible slipping processes between the receptacle and the capillary that have a dampening effect on an axial movement are prevented or reduced, and on the other hand, positioning of the capillary in the antechamber when replacing or installing a capillary is simplified due to the form-fitting stop becomes reproducible.

The paste or liquid passed through the capillary is the material to be printed. It is present in one phase or, for example as a suspension, in multiple phases. It is within the scope of the invention to also provide multiphase components that react with one another, which are preferably taken from two or more separate reservoirs and brought together between the reservoir and the nozzle opening and are preferably also mixed or suspended there. As an example, multi-component epoxy resins are mentioned here, the components of which, like in other multi-component systems, are preferably mixed in the capillary, fed as a mixture through the nozzle opening into the antechamber, from there through the outlet opening onto the surface to be printed and only harden on the surface.

A further embodiment of the print head provides means for generating an electrostatic field orthogonal to the axis of symmetry at the outlet opening. This gives the opportunity to further manipulate the aerosol stream after an optional ionization, in particular to deflect it, to focus it or to further atomize it. The means for this purpose preferably comprise electrodes in or around the outlet opening.

A further configuration of the print head provides for providing means for generating an electrostatic field parallel or concentric to the axis of symmetry at the outlet opening. While one electrode is arranged orthogonally to the axis of symmetry around the outlet opening, the second electrode is covered by an electrically conductive substrate to be printed as a whole or part of it or, in the case of an electrically non-conductive substrate (e.g. polymer films), by electrically conductive additional elements such as an intermediate plate or layer in or under the substrate educated. Such an electrode arrangement is preferably used for focusing on the substrate.

The solution to the stated object also includes a printing method for printing a structure, preferably a raised structure, on a surface when using an aforementioned print head. A liquid or a paste is conducted via the capillary via the nozzle opening into the antechamber, the nozzle opening being moved back and forth via a piezoelectric actuator, the liquid or the paste being continuously separated as fluid droplets and atomized at the nozzle opening. A guide gas is introduced into the antechamber around the capillary via the at least one inlet opening, with the guide gas being composed of a first portion in the antechamber with the fluid droplets to form an aerosol flow and a second portion between the nozzle opening and the outlet opening forming a sheath flow around the aerosol flow . The second proportion preferably predominates over the first proportion, with the first proportion not being present or being almost zero (second proportion over 95%) in a particularly preferred embodiment. The aerosol stream, which is surrounded and focused by the sheath stream, is then directed via the exit opening from the antechamber onto a surface of a substrate, where the fluid droplets are applied to the surface.

An oscillating system is preferably formed from the oscillating actuator, capillary with the liquid or paste contained therein and the receptacle for the capillary and possibly other oscillating components (e.g. fluid connection), which is more preferably excited in a resonance oscillation.

1. 1. Das bauartbedingte geringe Volumen und damit auch das geringe ungenutzte Totvolumen (Volumina, in denen sich aber insbesondere Flüssigkeitsbestandteile anreichern und im ungünstigen Fall auch für längere Zeit festsetzen können) der fluidführenden Bauteile ermöglicht geringe Flüssigkeitsverluste beim Drucken wie auch eine bessere Dosierbarkeit und Mischeinstellungen auch geringerer Flüssigkeitsmengen.
2. 2. Durch die kurzen Wege und Zeiten zwischen der Aerosolbildung und dem Aufdrucken ist eine Eliminierung von größeren Tropfen oder Agglomeraten der Flüssigkeit oder Homogenisierung des Aerosols nicht erforderlich.
3. 3. Damit sind auch komplexe Führungen des Druckkopfes während des Druckvorgangs ohne mechanische Entkopplung der Aerosolerzeugung möglich, insbesondere auch ein Überkopf-Druck.
4. 4. Eine Reduzierung der Aerosol führenden Komponenten und die Aerosolführung im Druckkopf ermöglichen eine reduzierte Kontaminierung dieser mit Aerosol, was wiederum einen Wechsel des zu druckenden Druckmediums während des Druckvorgangs signifikant vereinfacht und beschleunigt.
5. 5. Es wird kein zusätzlicher Tintenfänger oder Shutter an der Austrittsöffnung benötigt, um Unterbrechungen im Druckbild erzielen zu können. Dies beruht auf dem binären Verhalten der neuen Einrichtung zur Aerosolerzeugung (Aerosol-on-Demand).
6. 6. Es wird kein Aerosol-Konzentrator mehr benötigt.
7. 7. Die Reinigung des Druckkopfes bzw. der Wechsel desselben nach Wechsel der zu druckenden Flüssigkeit ist nicht mehr notwendig. Es genügt, die Kapillare aus dem Druckkopf auszutauschen (sowie den Fluidanschluss mit Tintenkartusche außerhalb des Druckkopfes). Dabei handelt es sich um kostengünstige Standard-Einwegkomponenten. Dies beruht auf der Klemmvorrichtung für Glaskapillaren der neuen Einrichtung zur Aerosolerzeugung.
8. 8. Die vorgenannten Ausgestaltungen mit kurzen Wegen zwischen Düsenöffnung und Austrittsöffnung sowie der Mantelstrom reduzieren die Einflüsse der Gravitationskräfte während des Druckvorgangs. Durch Anpassung der Prozessparameter kann somit auch über Kopf gedruckt werden, ohne dass eine mechanische Trennung von Aerosol-Erzeugung und Druckdüse notwendig ist. Dies begünstigt wiederum ein kompakteres Design des Druckkopfes.

The printhead and the printing process described have the following additional advantages:

1. 1. The design-related low volume and thus also the low unused dead volume (volumes in which liquid components in particular accumulate and, in the worst case, can also settle for a longer period of time) of the fluid-carrying components enables low liquid losses during printing as well as better dosing and mixing settings lower amounts of liquid.
2. 2. Due to the short distances and times between aerosol formation and printing, it is not necessary to eliminate larger droplets or agglomerates of the liquid or to homogenize the aerosol.
3. 3. Complex guidance of the print head during the printing process is thus also possible without mechanical decoupling of the aerosol generation, in particular overhead printing.
4. 4. A reduction in the aerosol-carrying components and the aerosol routing in the print head enable reduced contamination of these with aerosol, which in turn significantly simplifies and accelerates changing the print medium to be printed during the printing process.
5. 5. No additional ink catcher or shutter is required at the exit opening in order to be able to achieve interruptions in the printed image. This is based on the binary behavior of the new device for aerosol generation (aerosol-on-demand).
6. 6. No more aerosol concentrator needed.
7. 7. It is no longer necessary to clean the print head or change it after changing the liquid to be printed. It is sufficient to replace the capillary from the printhead (and the fluid connection with the ink cartridge outside the printhead). These are inexpensive, standard, single-use components. This is due to the glass capillary clamping device of the new aerosol generation facility.
8. 8. The aforementioned configurations with short distances between the nozzle opening and the outlet opening as well as the bypass flow reduce the influence of the gravitational forces during the printing process. By adjusting the process parameters, it is also possible to print overhead without the need for a mechanical separation of the aerosol generation and the print nozzle. This in turn favors a more compact design of the print head.

Thanks to a preferred clamping connection between the capillary and the piezo element, replacing all the fluid-carrying components, preferably as disposable components, is simpler and therefore quicker and/or more economical than the prior art mentioned above. The otherwise often tedious cleaning is reduced due to the late aerosol formation, the small, fundamentally short paths and thus correspondingly small surface and volume areas that can be contaminated with aerosol (including the aforementioned dead volumes) between the nozzle outlet and the outlet opening, as well as the aforementioned through the guiding fluid, in particular as a sheath flow around the aerosol effecting reduction of a risk of contamination in these surface areas to a minimum. This is just as advantageous for a quick and economical change of the pressure medium (liquid or paste from the capillary) by replacing the capillary during a printing process, as well as for a significant reduction in the probability of failure due to ongoing deposits of pressure medium in the outlet opening and the antechamber, up to a complete one Constipation. Since the aerosol is preferably focused directly after exiting the capillary by the guide gas flow and/or by electric fields, no contamination of other parts of the print head, in particular the focusing nozzle, takes place. This makes it possible to use one and the same print head for different print media (pastes, liquids, eg fluids, inks) without having to risk cross-contamination between these print media. This is of particular interest for a preferred use of the print head and/or the printing process for the production of printed electronics (conductor tracks, components, etc.) or for biologically or chemically active coatings.

• Stabiler sehr starker und sehr dünner Aerosolstrahl aus der Glaskapillare. Die Strahlrichtung scheint durch Unebenheiten von Funktionsmustern der Glaskapillaren vorgegeben zu sein. Die Tropfengröße ist kleiner 1 um.
• Breiter glockenartiger Aerosolnebel am Austritt der Glaskapillare. Die Tropfengröße ist größer als beim vorhergehend beschrieben Aerosolstrahl.
• Stabile sehr starke und sehr dünne Aerosolstrahlen die unter 90° zur Kapillar-Achse aus deren Spitze austreten. Die Strahlrichtung scheint durch Unebenheiten von Funktionsmustern der Glaskapillaren vorgegeben zu sein. Die Tropfengröße ist kleiner 1 um.

The invention was tested in various configurations. Both clamp and adhesive connections between a piezo element and a glass capillary have already been successfully tested. The following three modes of aerosol generation were used:

• Stable, very strong and very thin aerosol jet from the glass capillary. The direction of the beam seems to be determined by the unevenness of the functional patterns of the glass capillaries. The droplet size is less than 1 µm.
• Broad, bell-like aerosol mist at the exit of the glass capillary. The droplet size is larger than in the aerosol jet described above.
• Stable, very strong and very thin aerosol jets that emerge from the tip at 90° to the capillary axis. The direction of the beam seems to be determined by the unevenness of the functional patterns of the glass capillaries. The droplet size is less than 1 µm.

• Fig.1a und b je eine schematische Schnittdarstellung eines Druckkopfes,
• Fig.2a bis e in schematischer Detaildarstellung verschiedene Ausgestaltungen der Aufhängung der Kapillare im Druckkopfgehäuse mit Translationsaktoren (a) bis (c), Biegeaktoren (d) sowie Scheraktoren (e), die die Funktion des Aktors sowie des elastischen Elements vereinen,
• Fig.3a bis e schematische Darstellungen verschiedener Ausgestaltungen der Aufhängung der Kapillare im Druckkopfgehäuse mit separaten elastischen Elementen und separaten Aktoren,
• Fig.4 eine schematische Anordnung einer Kapillare mit Bund in einer Aufnahme sowie
• Fig.5a bis d in prinzipieller Schnittdarstellung mögliche Anordnung einer Kapillare in einer mit Klemmmitteln ausgestalteter Aufnahme.

The invention is explained in more detail using exemplary embodiments, the following figures and descriptions. The features shown and their combinations are not only limited to these exemplary embodiments and their configurations. Rather, these can be combined to represent other possible configurations that are not explicitly shown as exemplary embodiments. Show it

• Fig.1a and b each a schematic sectional view of a print head,
• Fig.2a to e in a schematic detailed representation of various configurations of the suspension of the capillary in the print head housing with translation actuators (a) to (c), bending actuators (d) and shear actuators (e), which combine the function of the actuator and the elastic element,
• Figure 3a to e schematic representations of different configurations of the suspension of the capillary in the print head housing with separate elastic elements and separate actuators,
• Fig.4 a schematic arrangement of a capillary with collar in a recording and
• Fig.5a to d in a basic sectional representation of a possible arrangement of a capillary in a receptacle equipped with clamping means.

Fig.1a and b schematically represent a print head in two configurations of the print head. The central components of the print head are the print head housing 1 with an outlet opening 2 and the capillary 4 with a nozzle opening 5 , which is suspended concentrically about an axis of symmetry 3 or, in the case of a flat nozzle , a plane of symmetry 6 so that it can move axially Antechamber 8 arranged. The capillary 4 is suspended in the housing via at least one elastic element 7 and guided axially along the axis of symmetry or plane of symmetry. In the embodiment shown, the capillary 4 is fixed in a separate receptacle 9, preferably provided with clamping means. Rotating and tilting movements of the capillary are not possible or only possible with high forces. The elastic compliance of the suspension formed in this way The capillary is significantly higher in the axial direction than orthogonally to the aforementioned axis of symmetry or plane of symmetry. At least one of the elastic elements is also equipped with an actuator 10 ( Fig.1a ) connected or forms a constructive unit with it. For example, the elastic element is formed by the actuator ( Fig.1b ).

Furthermore, the print head housing 1 has at least one inlet opening 11 for a guide gas and a feed means 12 for the liquid to be printed. The flow paths for the guide gas 13 and for the liquid 14 to be printed are shown in Fig.1a and b indicated. As shown by way of example, the inlet openings are preferably arranged laterally around the capillary 4 and proximal to the nozzle opening 5 in order to form a sheath flow in the antechamber. The suspension of the capillary in the print head, comprising the aforementioned elastic elements and the actuator, must, if they are arranged distally to the inlet openings 11 , allow flow to flow axially around or through them, ie possibly be provided with cutouts through which flow can flow axially.

In the Fig.1a inlet openings 11 shown lead laterally into the print head housing. The connections of the inlet openings are thus arranged laterally, with the result that a larger proximal cover area 15 located above the inlet openings is available for configurations in favor of better interchangeability of the capillary including the feed means 12 . Any dead volumes 16 through which the guide gas does not flow can be minimized in general and in particular in the mentioned cover area by a corresponding design of the print head housing 1 or by components that are not shown (eg a cover closure system). The print head housing 1 is basically a non-illustrated embodiment, for example, for a Replacing the capillary can be dismantled or opened. The cover area 15 can preferably be removed from the rest of the print head housing, while the print head housing is held, for example, via its lateral surfaces.

Fig.1b FIG. 12, on the other hand, shows an embodiment in which the inlet openings 11 are arranged in the proximal cover area 15 in the immediate vicinity of the feed means 12. FIG . This means that the intake openings are no longer as in Fig.1a shown arranged on the lateral surface of the print head housing, whereby the lateral surface is advantageously available for handling the print head housing in a printing device, ie it can also be universally clamped and exchanged. Furthermore, this arrangement supports a slimmer design of the print head housing, which, for example, accommodates a closer arrangement of a plurality of print head housings and also storage of the same. The print head housing as such can also be moved and aligned better in a printing device or by means of a manipulator if the connections are bundled, i.e. combined in a connection line, the realization of which is achieved by the aforementioned close arrangement of the inlet openings 11 in the proximal cover area 15 in the immediate vicinity of the feed means is favored. This arrangement is also advantageous if the connections of the inlet openings and the feed means have to be changed together, for example when changing capillaries, for example if the guide gas and the liquid to be printed have to be matched to one another, for example chemically. In addition, the connections can be made more compact, so that the print head housing 1 is easier to grasp, which in turn is very beneficial for the integration of the print head as a whole in a manipulator or robot system.

Said suspension for the capillary in the print head housing comprises at least one elastic element, at least one actuator, preferably also a separate receptacle for the capillary. The receptacle further preferably comprises clamping means for a non-positive fixation of the capillary. Optionally, the capillary has at least one three-dimensional surface structure on the outer surface of the jacket, which can be held in a form-fitting manner by the receptacle by means of a negative structure that at least partially corresponds to this surface structure.

Fig.2a to e show examples in detail of various configurations of the suspension of the capillary in the print head housing with translation actuators (a) to (c), bending actuators (d) and shear actuators (e), in which the function of the actuator and the elastic element are combined.

Fig.2a shows an embodiment with a one-sided translation actuator, for example a piezoelectric actuator of type d31 (transversal actuator) or type d33 (longitudinal actuator, in single-layer or multi-layer construction), which is attached to a projection 17 on the inner wall of the print head housing and acts against a capillary receiving element 18 . The one-sided arrangement of the actuator shown is only suitable for guided actuator movements in the non-resonant frequency range. However, one embodiment provides for two or more of the aforementioned translation actuators to be arranged on both sides of a capillary or at a regular distance from one another circumferentially around a capillary that is rotationally symmetrical in this case and to be operated synchronously, which creates axial symmetry around the capillary and thus also makes resonance operation possible is.

Fig.2b and c show configurations with an annular translation actuator 19 running around the capillary, designed, for example, as a piezoelectric d31 actuator 21 (see FIG Fig.2b ) or d33 actuator 22 (see Fig.2c ), which is well suited for resonant oscillating movements due to its symmetry around the capillary. The basic structure is similar to that in Fig.2a For this purpose, the capillary receiving element has an additional ring-shaped oscillating mass 20 which influences the resonance frequency and is arranged around the capillary. As in Fig.2c indicated, the oscillating mass can be designed in two parts, with the capillary being clamped between the two parts in principle in a non-positive or positive manner.

Fig.2d shows a suspension with oscillating bending actuators, preferably multi-layer piezoelectric d31 actuators with opposite polarity or a d31 actuator applied to a bending element, which are preferably clamped to the inner wall of the print head housing and act on the surface of the capillary at the other end. Fig.2d shows an example of an embodiment with two strip-shaped oscillating bending actuators arranged in mirror image on a plane to the capillaries. For a more stable arrangement, which only allows axial movements of the capillary, it is advantageous to provide this arrangement on the capillary a second time in parallel on another.

Fig.2e shows an example of an embodiment in which the actuator is configured as a shear-vibration actuator 23, for example a piezoelectric d15 converter. It is fixed (eg glued) to the side of the capillary 4 or, as shown, to the separate receptacle 9 for the capillary 4 . On the other side, it is fixed on a projection 17 on the print head housing side. Shown is an embodiment with a single Scherschwingaktor, with further configurations with two or more such actuators are conceivable more preferably uniformly, ie arranged at a uniform angle to one another around the capillary.

The capillary is suspended in the print head housing, for example, with coupling gear arrangements with solid-state or conventional joints in such a way that a translation is primarily generated in the capillary direction and the parasitic translation perpendicular to the capillary direction is suppressed or compensated for as far as possible and the capillary also oscillates moments free as possible . Figure 3a to e disclose exemplary configurations of the suspension of the capillary in the print head housing with separate elastic elements 28 and separate actuators 10. The suspensions are always designed in such a way that the capillaries 4 used in the elastic elements 28 can always be moved axially, i.e. in the direction of the axis of symmetry 3 and the movement can be caused by the actuators 10 . The actuators 10 act—as shown in the illustrated embodiments—preferably directly on the elastic elements 28 , deforming them and thus causing the aforementioned axial displacement of the capillary 4 . The elastic elements preferably extend around the capillary in a rotationally symmetrical manner or in the same way and at equal angular distances from one another. The elastic elements 28 in turn have elastic solid-state joints 29 or elastic bending strips 31 .

A refinement group is Figure 3a to c represented. It provides at least two elastic elements 28 of the same design and oriented towards the capillary 4 , which are preferably designed as a truss, the truss elements being connected to one another and preferably pivotable about an axis in relation to one another with joints, preferably the aforementioned elastic solid-state joints 29 . The actuators 10 are preferably piezoelectric ring actuators (eg ring-shaped translation actuator 19) or individual actuators, which are each arranged with the elastic elements around the capillary.

Figure 3a 12 shows an embodiment with an actuator which acts axially to the capillary and is arranged on a projection 17 around the capillary, preferably an annular d31 actuator. This preferably acts axially on a first flexure joint of the elastic elements designed as a parallelogram guide with four truss elements each, which are firmly inserted into the print head housing 1 via a truss element with two elastic flexure joints 29 on one side and via another truss element arranged opposite the first with two other elastic solid joints 29 are connected to the axially movable capillary in the print head housing.

Fig.3b shows a further embodiment of a suspension of the capillary with elastic elements, each of which comprises a series connection of a parallelogram guide and a further quadrangular truss with four truss elements. Fig.3c shows an embodiment of an elastic element with five elastic flexure joints, with two of these flexure joints being arranged in an axial sequence on the capillary or in a radial sequence on a projection on the inner wall of the print head housing, and the fifth flexure joint in turn being controllable radially to the capillary via the actuator and is movable. In both of the aforementioned configurations, the ring-shaped translation actuator 19 is firmly inserted into the print head housing 1 and is oriented radially to the capillary in its stroke alignment. Fig.3b and c thus represent exemplary configurations in which radial adjustment movements are deflected by an actuator into axial capillary movements.

Fig.3d represents an exemplary embodiment in which the capillary 4 in the print head housing is inserted and guided in an axially movable manner by two preferably rotationally symmetrical and/or prestressed plate spring elements 30, which form the elastic elements. One of these plate spring elements is preloaded and deflected axially to the capillary by a ring actuator, preferably a ring-shaped d31 actuator, with the arrangement of the ring actuator on a projection 17 around the capillary as in FIG Figure 3a described.

Figure 3e shows a further exemplary embodiment in which the capillary 4 in the print head housing is inserted and guided axially by three elastic flexible strips 31 (alternatively flexible sheet metal elements), which form the elastic elements, and are axially movable. In the example, two of the bending strips are preferably used only for guiding the capillary in parallel, while at least a third bending strip is preferably designed as an actuator or can be controlled by an actuator to stimulate a capillary movement. At least one of these bending strips is preferably coated with a piezoelectric material and forms a bimorph bending actuator with it, via which the capillary can be moved axially.

The aforementioned configurations, in particular those in Fig.1a and b as well Fig.2a The receptacles 9 illustrated to e preferably comprise clamping means for the capillary 4, which enable the capillary to be pulled out axially in the proximal direction, ie away from the outlet opening. The clamping means are preferably designed as a slotted tubular element prestressed around the capillary, alternatively by resilient inserts in the tube, two clamping elements for the capillary that act against one another, or by an elastic element with a bore dimensioned as a press fit for the capillary.

Fig.4 shows an exemplary arrangement of a capillary 4 in a receptacle 9, the capillary shown having a collar 24 (preferably an elevation on the capillary or a ring fixed on the capillary) as a stop for precise adjustability. This enables the capillary to be inserted into a reproducible position in the receptacle. One embodiment provides for a tube casing that is additionally fixed to the capillary and protects it mechanically, with or without the aforementioned collar, on which the receptacle acts.

Fig.5a to d show a basic sectional view of a possible arrangement of a capillary 4 in a receptacle 9 equipped with clamping means, Fig.5a and b each show an embodiment with four or three contact lines 25, Fig.5c an embodiment with a contact line 25 and a contact surface 26 and Figure 5d an embodiment with only one contact surface 26. The prestressing takes place, as shown, via elastic tie rods 27, such as adjustable via elastic expansion screws. Further combinations, such as configurations with two opposing contact surfaces or with elastic intermediate elements (eg made of elastomers) are also expressly mentioned. Clamping via contact surfaces is gentler than clamping via contact lines, especially for capillaries made of brittle materials such as glass, but requires a more precise and therefore more complex adjustment of the contact surfaces to avoid stress singularities in the capillary.

Reference list:

1

printhead housing

2

exit port

3

axis of symmetry

4

capillary

5

nozzle opening

6

plane of symmetry

7

elastic element

8th

antechamber

9

separate recording

10

actuator

11

intake port

12

feed means

13

guide gas

14

liquid to be printed

15

proximal flap area

16

dead volume

17

head Start

18

capillary receiving element

19

annular translational actuator

20

vibration mass

21

d31 actuator

22

d33 actuator

23

heavy-duty actuator

24

Federation

25

contact line

26

contact surface

27

Elastic tie rod

28

elastic element

29

Elastic solid joint

30

disc spring element

31

Elastic bending strips

Claims (18)

1. Print head, comprising a capillary (4) that adjoins at least one elastic element (7, 28) around an axis of symmetry (3) for a fluid to be printed onto a substrate with a nozzle opening (5), which opens into a pre-chamber (8), wherein

   a) the pre-chamber has an outlet opening (2), which is flush with the nozzle opening of the capillary in its axial alignment to the axis of symmetry (3), and at least one inlet opening (11) for a guiding gas (13),

   b) the at least one elastic element forms a guide for the capillary only in its axial orientation,
   and

   c) feeding means (12) provided for the fluid that is to be printed into the capillary,
   characterised in that

   d) a mechanical vibration system comprising the at least one elastic element (7, 28) and the capillary (4) with the fluid contained in it, and

   e) a piezo actuator (10, 19) with a mechanical interaction of force with the vibration system.
2. Print head according to claim 1, characterised in that the at least one elastic element (7, 28) is formed by at least one linkage arrangement with solid body or conventional links.
3. Print head according to claim 1 or 2, characterised in that a plurality of elastic elements, which are configured as the same type and are oriented about and towards the capillary (4), are provided.
4. Print head according to any one of the preceding claims, characterised in that the at least one elastic element (7, 28) is configured as a bracing piece with several bracing elements, wherein the bracing elements are connected to one another, and are preferably configured such that they can pivot in relation to one another about an axis with links, preferably the aforementioned elastic solid body links (29).
5. Print head according to any one of the preceding claims, characterised in that at least one of the at least one elastic elements (7, 28) is formed by a dish-shaped or bar-shaped elastic element.
6. Print head according to any one of the preceding claims, characterised in that at least one of the at least one elastic elements (7, 28) is formed by the actuator (10, 19).
7. Print head according to claim 6, characterised in that the actuator (7, 28) is formed by a dish-shaped or bar-shaped bending actuator, and a receiver for the capillary is arranged in the middle in the bending actuator.
8. Print head according to claim 7, characterised in that the receiver comprises at least one clamping means for receiving the capillary (4).
9. Print head according to claim 8, characterised in that the at least one clamping means is a part of a vibrateable mass on the at least one elastic element.
10. Print head according to any one of the preceding claims, characterised in that outlet opening (2), the pre-chamber (8), or the at least one elastic element (7) comprises a rotationally-symmetrical extension about the axis of symmetry of the capillary (4).
11. Print head according to any one of the preceding claims, characterised in that outlet opening (2) comprises means for producing an electrostatic field orthogonally to the axis of symmetry (3).
12. Print head according to claim 11, characterised in that the means comprise electrodes in or around the outlet opening (2) and/or are configured as electrically conductive areas in or beneath the substrate.
13. Print head according to any one of the preceding claims, characterised in that at least one ring electrode or at least one pneumatic lens is arranged about the outlet opening, or the outlet opening is configured as a ring electrode.
14. Printing method for printing a structure onto a surface with the use of a print head according to any one of the preceding claims, wherein

    a) by means of the capillary (4), a fluid is guided via the nozzle opening (5) into the pre-chamber (8), wherein the nozzle opening is moved by the mechanical vibrating system backwards and forwards in the axial direction of the capillary, wherein the fluid is constantly separated and nebulised as fluid droplets at the nozzle opening,

    b) by means of the at least one inlet opening (11), a guiding gas (13) is introduced into the pre-chamber (8) about the capillary, wherein the guiding gas is merged in a first portion in the pre-chamber with the fluid droplets forming an aerosol flow, and, in a second portion forms a surrounding casing flow around the aerosol flow between the nozzle opening and the outlet opening,

    c) the aerosol flow surrounded by the casing flow is guided via the outlet opening out of the pre-chamber onto a surface of a substrate, and

    d) the fluid droplets are applied onto the surface.
15. Printing method according to claim 14, characterised in that the aerosol flow is focussed in the pre-chamber (8) or out of the pre-chamber.
16. Printing method according to claim 14 or 15, characterised in that the vibrating system is excited by the actuator (10, 19) in a resonance vibration.
17. Printing method according to any one of claims 14 to 16, characterised in that the aerosol flow, when passing through the outlet opening, is electrostatically directed, focussed, or further nebulised.
18. Printing method according to any one of claims 14 to 17, characterised in that the speed of the running separation and nebulisation of the fluid at the nozzle opening can be regulated by way of the amplitude, frequency, or the signal form of the vibration.

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