DE102020108317A1 - Inkjet printhead - Google Patents

Abstract

An inkjet printhead for printing on a substrate, comprising:
at least one nozzle adapted to dispense at least one electrically conductive drop of liquid; and
an outlet channel arranged on the nozzle, wherein the electrically conductive liquid drop can be dispensed through the outlet channel in the direction of the substrate to be printed;
wherein an acceleration means is provided on the outlet channel which is adapted to generate a current flow through the electrically conductive liquid drop and a magnetic field in order to accelerate the electrically conductive liquid drop by means of a force in the outlet channel in the direction of the substrate to be printed.
Furthermore, a printing device and a method for printing on a substrate are proposed.

Description

The invention relates to an ink jet print head for printing on a substrate. The invention also relates to a printing device and a method for printing on a substrate.

For printing sheets of paper with ink, digital printing using ink jet print heads is widespread. However, the inkjet printhead has also established itself in the printing of other media, such as, for example, the printing of housing parts made of plastic. The term “digital printing” is usually understood to mean printing processes in which the print image is transferred directly from a file or a data stream from a computer to a printing machine without using a static printing form. With its dynamic print image generation, digital printing opens up the possibility of inexpensive individual printing of substrates.

In digital printing with an inkjet printhead, small drops of liquid, such as drops of ink, are ejected from the inkjet printhead. After leaving the inkjet printhead, the liquid droplets typically cover a distance of a few millimeters and then hit the substrate to be printed. As soon as an uneven surface, for example the uneven surface of a plastic housing, is to be printed, the inkjet printhead cannot be brought as close as desired to the surface of the substrate to be printed due to the geometry of the substrate to be printed. When printing over a larger distance that is necessary as a result, the quality of the print image is reduced, for example due to the resulting blurring. This is due, among other things, to the movement of the liquid droplets through the air, since the liquid droplets are slowed down and deflected when they collide with air molecules.

In order to stabilize the trajectory, the kinetic energy of the dispensed liquid drop can be increased, for example. Since the mass of the liquid drop cannot be increased at will without impairing the quality, an increase in the speed of the drop is advisable. On the other hand, the exit speed of the liquid droplets cannot be increased as desired, for example by means of a piezomechanical actuator. It is therefore advisable to further accelerate the liquid drop after it has been ejected from the ink jet nozzle.

To adjust the printing distance, describes, for example, the EP 3 069 884 A1 a printhead with comb electrodes that are connected to a voltage source and generate an electrical field that can be used to accelerate a drop of liquid.

The devices known from the prior art for increasing the drop speed are, however, space-consuming and complex to implement.

It is an object of the present invention to provide an improved ink jet printhead with a more stable trajectory for the liquid droplets emerging from the ink jet printhead.

This object is achieved by an object with the features of claim 1.

• - zumindest eine Düse, angepasst zumindest einen elektrisch leitfähigen Flüssigkeitstropfen abzugeben; und
• - einen Austrittskanal, angeordnet an der Düse, wobei der elektrisch leitfähige Flüssigkeitstropfen durch den Austrittskanal in Richtung des zu bedruckenden Substrats abgebbar ist;
• - wobei am Austrittskanal ein Beschleunigungsmittel vorgesehen ist, das angepasst ist, einen Stromfluss durch den elektrisch leitfähigen Flüssigkeitstropfen sowie ein Magnetfeld zu erzeugen, um den elektrisch leitfähigen Flüssigkeitstropfen mittels einer Kraft in dem Austrittskanal in Richtung des zu bedruckenden Substrats zu beschleunigen.

Thereafter, there is provided an inkjet printhead for printing on a substrate, comprising:

• - At least one nozzle adapted to dispense at least one electrically conductive drop of liquid; and
• - An outlet channel, arranged on the nozzle, wherein the electrically conductive liquid drop can be dispensed through the outlet channel in the direction of the substrate to be printed;
• - An acceleration means is provided on the outlet channel which is adapted to generate a current flow through the electrically conductive liquid drop and a magnetic field in order to accelerate the electrically conductive liquid drop by means of a force in the outlet channel in the direction of the substrate to be printed.

The nozzle can be connected to a fluid reservoir and drops of the electrically conductive fluid can be released in a targeted manner by pressure surges from a piezomechanical actuator. In a rest position, the nozzle can be tightly closed by a negative pressure applied above the nozzle, so that the electrically conductive liquid is prevented from flowing out. The electrically conductive liquid drop can be a drop of a printable medium, for example an ink drop of an electrically conductive ink.

The outlet channel can be designed as a hollow cylinder or tubular and arranged between the nozzle and the substrate to be printed so that the electrically conductive liquid drop passes through the outlet channel before it is released onto the substrate to be printed. For example, a central axis of the outlet channel can also be a central axis of the nozzle. The central axis can extend, for example, at right angles to the substrate to be printed.

The outlet channel comprises an acceleration means which is adapted to generate a current flow through the electrically conductive liquid droplet. Furthermore, the acceleration means is adapted to generate a magnetic field in order to accelerate the electrically conductive liquid drop by means of a force in the outlet channel in the direction of the substrate to be printed. The term “to accelerate in the outlet channel” can be used to describe an acceleration of the electrically conductive liquid drop along the outlet channel.

In examples, the accelerating means can comprise two electrodes which can be arranged in the outlet channel or can be designed as parts of the outlet channel. The electrodes can be designed as electrical conductors, for example. When the electrically conductive liquid drop runs through the outlet channel, a circuit between the electrodes can be closed by the electrically conductive liquid drop. For this purpose, the distance between the two electrodes can be adapted to a size of the electrically conductive liquid drop so that the electrically conductive liquid drop can touch both electrodes in order to close the circuit. The electrically conductive liquid drop can then be accelerated by the resulting Lorentz force which the electrically conductive liquid drop experiences as a result of the magnetic field acting on it. The Lorentz force acts in the direction of movement of the electrically conductive liquid drop and perpendicular to a current flow direction and to the direction of the magnetic field lines.

In examples, the electrically conductive liquid drop can have a very low resistance in order to prevent increased heat development with the risk of the electrically conductive liquid evaporating. A low resistance of the electrically conductive liquid drop is also advantageous in order to achieve correspondingly high currents at low voltages so that a current flashover or short circuit between the electrodes can be avoided. For example, the electrically conductive liquid drop can have an electrical conductivity of more than 0.1 S / m (Siemens per meter), in particular of more than 1 S / m or more than 10 S / m.

According to the “three-finger rule”, the current flow through the electrically conductive liquid droplet advantageously causes the electrically conductive liquid droplet to accelerate further and further along the outlet channel due to the resulting Lorentz force. As a result, the electrically conductive liquid drop reaches a higher speed at the end of the acceleration path, a higher kinetic energy and thus a more stable trajectory with which larger distances between the print head and the substrate to be printed can be bridged without the quality of the print image being negatively affected.

In one example, the accelerating means comprises at least a first electrical conductor and a second electrical conductor, wherein the first electrical conductor and the second electrical conductor are arranged to be electrically insulating from one another, and wherein the first electrical conductor and the second electrical conductor are matched to the electrically conductive one To be in contact with drops of liquid in the outlet channel. In one example, the first electrical conductor and the second electrical conductor are adapted to be in contact with the electrically conductive liquid drop in the outlet channel in order to generate the magnetic field. In this case, the magnetic field can be generated by the current flow through the electrically conductive liquid drop.

The term “being in contact” can be understood to mean that the electrically conductive liquid drop touches the first and the second electrical conductor at the same time in order to be able to close an electrical circuit.

For example, the first and the second electrical conductor can be formed from an electrically conductive material, such as, for example, from a copper material, and can be arranged in the form of a strip along an inner side of the outlet channel. For example, the first electrical conductor and the second electrical conductor can be arranged essentially opposite one another on the inside of the outlet channel over the entire course direction or only in a partial area of the course direction.

A long acceleration distance can advantageously be achieved by arranging the first and the second electrical conductor over the entire course direction.

In one example, the first electrical conductor and the second electrical conductor run along a longitudinal extension of the outlet channel.

The magnetic component and thus also the acceleration are advantageous when the direction of movement of the electrically conductive liquid drop is perpendicular to the magnetic field lines.

In examples, depending on the area of use, the electrical conductors can also be arranged in a spiral or in some other way in the outlet channel.

In one example, the inkjet print head comprises at least two electrical insulating means, the first electrical conductor and the second electrical conductor being arranged essentially opposite one another and being separated from one another on both sides by means of one of the electrical insulating means for electrically insulating the electrical conductors from one another.

The first electrical conductor and the second electrical conductor can advantageously each be designed as one half of an outlet channel separated along the longitudinal direction. The two halves can each be isolated from one another by means of an electrical insulating means, which can be designed, for example, as a plastic strip or also as an electrically insulating adhesive. The outlet channel can then run on an inside of such an arrangement.

For example, a connection of a power supply, in particular a direct current supply, can be connected to a respective connection on each of the two halves configured as electrical conductors.

A very compact structure is also advantageously achieved by the design described above.

In one example, the inkjet printhead comprises an electrical insulating means, wherein the electrical insulating means is designed as a tubular element, and wherein the outlet channel is formed on an inside of the tubular element.

For example, the electrical insulating means can be designed as a plastic tube and the outlet channel can run on the inside of the outlet channel. In alternative examples, the outlet channel can also be designed differently. For example, the outlet channel can also be configured to be elliptical or rectangular, depending on the configuration of the electrical insulating means.

In one example, the first electrical conductor and the second electrical conductor are arranged as current-conducting paths essentially opposite one another on the inside of the tubular element.

The first electrical conductor and the second electrical conductor can be glued, vapor-deposited or otherwise arranged as conductor tracks on the inside of the tubular element. Furthermore, connection contacts can be arranged on the conductor tracks for connecting the power supply.

Advantageously, a construction that is very favorable in terms of production technology can be achieved through the configuration described above.

In one example, the outlet channel runs in a funnel shape between the nozzle and the substrate to be printed. For example, a diameter of the outlet channel can taper in the direction of the substrate to be printed. For example, the electrical conductors can be arranged at least in some areas on the tapered diameter.

In one example, the nozzle comprises a piezomechanical actuator, in particular a piezomechanical drop-on-demand actuator.

In this example, a piezo element can be deformed by applying an electrical voltage in such a way that the deformation generates a pressure wave in the liquid reservoir, which causes a liquid drop to be ejected through the nozzle.

In particular, the inkjet printhead can be used for a printing technique known as drop-on-demand. Advantageously, only drops of liquid are ejected when they are actually needed.

In one example, the electrically conductive liquid drop comprises an electrically conductive ink, an electrically conductive adhesive, an electrically conductive lubricant, or an electrically conductive coating agent.

In addition to electrically conductive ink, for example for writing on a housing, adhesive, lubricant or coating agent can also advantageously be printed onto the substrate.

In one example, the acceleration means has a means for generating the magnetic field, in particular a permanent magnet or an electric magnet. The means for generating the magnetic field can, for example, be arranged at least in certain areas on the outlet duct in order to generate a magnetic field perpendicular to the direction of the current. The means for generating the magnetic field can be used in addition to the first electrical conductor and the second electrical conductor.

The invention also relates to a printing device for printing on a substrate, comprising an ink jet printhead as described herein.

In one example, the printing device has a power source, in particular one Direct current source to generate a current flow through the electrically conductive liquid drop.

Furthermore, in one example, the printing device can have a control means which, for example, can be comprised by the power source and, in addition to the power source, can be further adapted to control the nozzle and / or the means for generating the magnetic field.

• Abgeben zumindest eines elektrisch leitfähigen Flüssigkeitstropfens durch eine Düse eines Tintenstrahldruckkopfs; und
• Beschleunigen des elektrisch leitfähigen Flüssigkeitstropfens in einem Austrittskanal angeordnet an der Düse in Richtung des zu bedruckenden Substrats, wobei das Beschleunigen aufweist:
  • Erzeugen eines Stromflusses durch den elektrisch leitfähigen Flüssigkeitstropfen sowie ein Magnetfeld, um den elektrisch leitfähigen Flüssigkeitstropfen mittels einer Kraft in dem Austrittskanal in Richtung des zu bedruckenden Substrats zu beschleunigen.

The invention further relates to a method for printing a substrate, comprising:

• Dispensing at least one electrically conductive liquid droplet through a nozzle of an inkjet printhead; and
• Accelerating the electrically conductive liquid drop arranged in an outlet channel on the nozzle in the direction of the substrate to be printed, the accelerating comprising:
  • Generating a current flow through the electrically conductive liquid drop and a magnetic field in order to accelerate the electrically conductive liquid drop by means of a force in the outlet channel in the direction of the substrate to be printed.

• 1 eine Ansicht eines Tintenstrahldruckkopfs gemäß einer ersten Ausführungsform;
• 2A, 2B Schnittansichten von zwei Ausgestaltungsmöglichkeiten des Austrittskanals entlang der in 1 gezeigten Schnittlinie A-A; und 3 eine Ansicht eines Tintenstrahldruckkopfs gemäß einer zweiten Ausführungsform.

The idea on which the invention is based is to be explained in more detail below with reference to the exemplary embodiments shown in the figures. Show it:

• 1 Fig. 3 is a view of an ink jet print head according to a first embodiment;
• 2A , 2 B Sectional views of two design options for the outlet channel along the in 1 section line AA shown; and 3 Fig. 3 is a view of an ink jet print head according to a second embodiment.

1 Figure 13 is a view of an ink jet printhead 1 according to a first embodiment. The inkjet printhead shown 1 has a nozzle 3 on, which is adapted to an electrically conductive liquid drop 7th submit.

The nozzle shown 3 is connected to a fluid reservoir and has a piezomechanical actuator which can be deformed by applying an electrical voltage in such a way that the deformation generates a pressure wave in the fluid reservoir that causes the electrically conductive liquid drop to be ejected 7th through the nozzle 3 causes.

The inkjet printhead shown 1 can be used for a printing technique known as drop-on-demand.

The example in 1 Electrically conductive liquid droplets shown 7th may, as an alternative to an electrically conductive ink, also comprise an adhesive, a lubricant, a coating agent, or some other electrically conductive liquid that adheres to a substrate 17th should be applied. The substrate 17th is in 1 as a substrate 17th with a flat surface such as a sheet of paper is shown. In embodiments that are not shown, the substrate can also comprise a surface with a three-dimensional surface.

Furthermore, in 1 an outlet channel 5 shown on the nozzle 3 is arranged. As shown, the electrically conductive liquid drop becomes 7th through the outlet channel 5 in the direction of the substrate to be printed 17th submitted.

How to continue in 1 shown is the central axis of the outlet duct 5 also a central axis of the nozzle 3 . In the embodiment shown, the central axis extends at right angles to the substrate to be printed 17th .

The accelerator 9 points in the 1 a first electrical conductor 11a and a second electrical conductor 11b on, which act as electrodes in or on the outlet channel 5 are arranged. Also in 1 shown that the first electrical conductor 11a and the second electrical conductor 11b one connection contact each for connecting a power source 19th exhibit. For this purpose, an electrical conductor with a positive pole is the power source 19th connected and the other electrical conductor is connected to a negative pole of the power source 19th .

The first electrical conductor 11a and the second electrical conductor 11b extend in the in 1 embodiment shown over the entire length of the outlet channel 5 . In embodiments that are not shown, the electrical conductors can also be designed in such a way that they only extend over a partial area of the length of the outlet channel.

Furthermore, in 1 shown that the electrically conductive liquid drop 7th through the outlet channel 5 running and creating a circuit between the first electrical conductor 11a and the second electrical conductor 11b closes. This is the distance between the first electrical conductor 11a and the second electrical conductor 11b chosen such that the electrically conductive liquid drop 7th both electrical conductors 11a , 11b can touch to complete the circuit. The flow of current through the electrically conductive Liquid drops the magnetic field B. be generated.

An acceleration of the electrically conductive liquid drop 7th takes place through the resulting Lorentz force F _L that the electrically conductive liquid drop 7th by a magnetic field B. learns.

As in 1 shown, the Lorentz force acts F _L in the direction of movement of the electrically conductive liquid drop 7th .

In 1 also a means 13th to generate a magnetic field B. on or around the outlet duct 5 arranged to the magnetic field B. perpendicular to the direction of the current. The middle 13th to generate the magnetic rock B. can have a height equal to the height of the electrical conductor 11a , 11b is equivalent to.

the 2A and 2 B show sectional views of two design options for the outlet channel 5 along the in 1 shown section line AA.

In 2A becomes a possible structure of the outlet channel 5 and the accelerator 9 shown, the first electrical conductor 11a and the second electrical conductor 11b are arranged essentially opposite one another and from one another by means of an electrical insulating means 15a , 15b are separated to electrically isolate the electrical conductors 11a , 11b against each other. As in 2A shown can be the first electrical conductor 11a and the second electrical conductor 11b thereby part of the outlet channel 5 form.

The middle 13th to generate a magnetic field B. is around the outlet duct 5 arranged to the magnetic field B. as shown, perpendicular to the direction of the current to generate. Depending on the area of application, the agent can 13th to generate a magnetic field B. but also not exactly perpendicular, but at a certain angle to the electrical conductors 11a , 11b be arranged.

In 2 B becomes an alternative structure of the outlet channel 5 and the accelerator 9 shown, the electrical insulating means 15th is designed as a tubular element, and wherein the outlet channel 5 runs on an inside of the tubular element. Like it in 2 B is shown, the first electrical conductor 9a and the second electrical conductor 9b as current-conducting paths are essentially opposite one another on the inside of the electrical insulating means shown as a tubular element 15th arranged. The first electrical conductor 11a and the second electrical conductor 11b can in the in 2 B structure shown on the inside of the outlet duct 5 be glued, vapor-deposited or otherwise arranged.

3 Figure 13 is a view of an ink jet printhead 1' according to a second embodiment. In the in 3 In the embodiment shown, the inkjet printhead shown differs 1' from the one previously in 1 inkjet printhead shown in that the exit channel 5 ' funnel-shaped between the nozzle 3 ' and the substrate to be printed 17 ' runs. As in 3 shown, a diameter of the outlet channel tapers 5 ' in the direction of the substrate to be printed 17 ' .

List of reference symbols

1, 1 '

Inkjet printhead

3, 3 '

jet

5, 5 '

Outlet channel

7, 7 '

Liquid drop

9, 9 '

Accelerators

11a, 11a '

first electrical conductor

11b, 11b '

second electrical conductor

13, 13 '

Means for generating a magnetic field

15, 15a, 15b

electrical insulating material

17, 17 '

Substrate

19, 19 '

Power source

B.

Magnetic field

FL

Lorentz force

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 3069884 A1 [0005]

Claims (13)

Ink jet print head for printing on a substrate (17, 17 '), comprising: - at least one nozzle (3, 3') adapted to dispense at least one electrically conductive liquid drop (7, 7 '); and - an outlet channel (5, 5 '), arranged on the nozzle (3, 3'), wherein the electrically conductive liquid drop (7, 7 ') through the outlet channel (5, 5') in the direction of the substrate (17 , 17 ') can be delivered; - An acceleration means (9, 9 ') being provided on the outlet channel (5, 5') which is adapted to generate a current flow through the electrically conductive liquid droplet (7, 7 ') and a magnetic field (B) to generate the electrically to accelerate conductive liquid droplets (7, 7 ') by means of a force (F _L ) in the outlet channel (5, 5') in the direction of the substrate (17, 17 ') to be printed. Inkjet printhead Claim 1 , characterized in that the acceleration means (9, 9 ') has at least a first electrical conductor (11a, 11a') and a second electrical conductor (11b, 11b '), the first electrical conductor (11a, 11a') and the second electrical conductors (11b, 11b ') are arranged so as to be electrically insulating from one another, and wherein the first electrical conductor (11a, 11a') and the second electrical conductor (11b, 11b ') are adapted to the electrically conductive liquid drop (7, 7 ') to be in contact in the outlet channel (5, 5') to generate the magnetic field (B). Inkjet printhead Claim 2 , characterized in that the first electrical conductor (11a, 11a ') and the second electrical conductor (11b, 11b') run along a longitudinal extension of the outlet channel (5, 5 '). Inkjet printhead according to one of the Claims 2 or 3 , characterized by at least two electrical insulating means (15a, 15b), the first electrical conductor (11a, 11a ') and the second electrical conductor (11b, 11b') being arranged essentially opposite one another and from one another on both sides by means of one of the electrical insulating means (15a, 15b) are separated in order to electrically isolate the electrical conductors (11a, 11a ', 11b, 11b') from one another. Inkjet printhead according to one of the Claims 2 or 3 , characterized by an electrical insulating means (15), wherein the electrical insulating means (15) is designed as a tubular element, and wherein the outlet channel (5, 5 ') is formed on an inside of the tubular element. Inkjet printhead Claim 5 , characterized in that the first electrical conductor (11a, 11a ') and the second electrical conductor (11b, 11b') are arranged as current-conducting paths essentially opposite one another on the inside of the tubular element. Ink jet print head according to one of the preceding claims, characterized in that the outlet channel (5 ') runs in a funnel shape between the nozzle (3') and the substrate (17 ') to be printed. Ink jet print head according to one of the preceding claims, characterized in that the nozzle (3, 3 ') comprises a piezomechanical actuator, in particular a piezomechanical drop-on-demand actuator. Ink jet print head according to one of the preceding claims, characterized in that the electrically conductive liquid drop (7, 7 ') comprises an electrically conductive ink, an electrically conductive adhesive, an electrically conductive lubricant, or an electrically conductive coating agent. Ink jet print head according to one of the preceding claims, characterized in that the acceleration means (9, 9 ') has a means (13, 13') for generating the magnetic field (B), in particular a permanent magnet or an electric magnet. Printing device for printing on a substrate (17, 17 '), having an inkjet print head (1, 1') according to one of the preceding claims. Printing device according to Claim 11 , characterized by a current source (19, 19 '), in particular a direct current source, for generating a current flow through the electrically conductive liquid drop. A method for printing on a substrate (17, 17 '), comprising: dispensing at least one electrically conductive liquid drop (7, 7') through a nozzle (3, 3 ') of an inkjet printhead (1, 1'); and accelerating the electrically conductive liquid drop (7, 7 ') in an outlet channel (5, 5') arranged on the nozzle (3, 3 ') in the direction of the substrate (17, 17') to be printed, the accelerating comprising: generating a current flow through the electrically conductive liquid drop (7, 7 ') and a magnetic field (B) to the electrically conductive liquid drop (7, 7') by means of a force (F _L ) in the To accelerate the outlet channel (5, 5 ') in the direction of the substrate (17, 17') to be printed.

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