EP3169523A1 - Inkjet printing method, and assembly for carrying out the method - Google Patents

Abstract

The invention relates to an inkjet printing method, wherein a printhead of an inkjet printer is directed in the direction of a substrate to be printed, and wherein ink drops are generated in the printhead of the inkjet printer, which ink drops, after being discharged from the nozzle of the printhead, are directed into a zone with locally increased temperature, such that the volume of the drops is actively reduced during the flight phase to the substrate. The invention also relates to an assembly for carrying out the method.

Description

 Ink jet printing method and arrangement for carrying out the method

The invention relates to an ink jet printing method and to an arrangement for carrying out the method.

State of the art

 During ink-jet printing, ink drops are typically produced in a nozzle of the printhead. Figure 1a shows the related art.

The drops are produced either by a thermal process with an air bubble (thermal ink-jet) or by means of a pressure pulse generated by either a piezo-crystal (piezo ink-jet) or electrostatically (super-fine ink-jet®).

A distinction is made between CIJ printers (Continuous Ink Jet) and DOD printers (Drop on Demand). In CIJ printing, the ink jet exits through a nozzle from the print head. This beam is modulated by a piezoelectric transducer located behind the nozzle, so that a uniform decay into individual drops is achieved. Over a

Charging electrode, the droplets thus formed are now more or less electrostatically charged. The 10 to 40 m / s fast drops then fly through a larger deflection electrode, where they - depending on their specific electrical charge - are deflected laterally. Depending on the device type, the charged or uncharged drops reach the substrate. Unnecessary drops are collected again at the print head and returned to the ink circuit. In the DoD process, unlike Cl J printers, only the ink drop leaves the nozzle that is actually needed. The devices are additionally distinguished by the technique with which the ink droplets are ejected. A) Bubble jet printers produce tiny drops of ink by means of a heating element which heats the water or solvent in the ink. In the process, a tiny vapor bubble explosively forms, which presses an ink drop out of the nozzle due to its pressure. b) Piezo printers use the piezoelectric effect for pressing the printing ink through a fine nozzle, wherein ceramic elements deform under electrical tension. The ink forms drops whose volume can be controlled by the magnitude of the applied electrical pulse. c) In the case of pressure valve printers, individual valves are attached to the nozzles, which open when a drop is to leave the nozzle. In either case, the drop comes out of the nozzle, is jetted, and lands on a substrate. Several jetted drops that land on the substrate form the printed structure.

The resolution of the printed structure is defined by the size of individual drops and the distance between individual drops. In general, the smaller a single drop, the greater the resolution when printing. Therefore, an effort is to produce smaller drops.

In general, the size of the drop in the formation in the nozzle is influenced. If, for example, nozzles with a small diameter are used in the print head, smaller drops are produced than when printing with larger nozzles in the print head. With a piezo print head, the applied voltage shape and the time, or the temperature of the printhead and the ink itself play a major role. By modifying the voltage shape and the temperature, the size of the droplet can be significantly reduced, as described in Meier et al., (Phys., Status Solidi A (2009) Inkjet printed, conductive, 25 μm wide silver tracks on unstructured polyimides. 206, 1626-1630). In addition, the interaction between the drop and the substrate is of great importance. For example, if a hydrophobic ink is printed, the hydrophilic modification of the substrate can result in a significant reduction in drop size on the substrate. This allows a denser placement of the drops, combined with a greater resolution. From the publication by Perelaer et al. (Macromolecular Chemistry and Physics (2009), Droplet tailoring using evaporative inkjet printing, Vol. 210, 387-393), it is known that a greater distance between the printhead (s) and the substrate causes partial evaporation of the ink solvent takes place, whereby the drops are correspondingly smaller. In addition to the distance, the method also takes into account the composition of the ink. A disadvantage of the larger distance is a scattering of individual drops generated, whereby errors in the placement of individual drops occur. This reduces the resolution of the printed structure.

Publication WO 2013/166219 A1 discloses a device which permits in-flight drying of ink droplets. For this purpose, an environment of different tempered zones is generated between the printhead and the substrate to be printed. The

Apparatus comprises a plurality of structures, such as spacers, which form a heat shield of Separate printhead, additional spacers that separate the heat shield from a condensation shield and energy sources on the condensation shield. The temperature at the printhead should be low and high between the heat shield and condensation shield, as well as the condensation shield and substrate so that vapors rising from the substrate do not reach the printhead. During the process, the condensation shield is heated to a temperature above the condensation temperature of the carrier liquid of the ink to prevent condensation of the vapors. This arrangement is disadvantageously complex.

Publication WO 2010/134072 A1 discloses a printhead for an ink jet printer which is provided with a heat shield in the direction of the substrate in order to avoid the transfer of heat between a heated substrate and the printhead. This arrangement also serves to provide corrosion protection of the printhead by keeping ascending vapors and heat away from it.

Unfortunately, it is not possible to achieve a significant reduction in the drop volume with any of the methods or devices referred to. Object of the invention

The object of the invention is to provide or provide a method and an arrangement with which a significant reduction of the drop volume and thus a higher resolution in the case of ink jet printing can be achieved.

The object is achieved by the method and the arrangement according to claim 1 or arrangements according to the independent claims. Advantageous embodiments of this result in each case from the back-related claims.

Description of the invention

In the ink jet printing method of the present invention, a print head of an ink jet printer is oriented toward a substrate to be printed. Ink drops are generated in the printhead of the inkjet printer. The droplets, after exiting the nozzle of the printhead, are directed into a zone of locally elevated temperature so that the volume of the droplets during the flight phase to the substrate is actively reduced. The inventive method and arrangement allow the reduction of individual drops in the inkjet printing process 'in flight'. The reduction is followed by the local rapid heating of the drop and the resulting increased evaporation rate, which causes a significant drop volume reduction in a short time. The heating is realized by the local supply of energy to the drop. The energy supply can be effected for example by the interaction of the drop with light or with at least one heating wire.

The light as well as the or the heating wires produce according to the invention in the beam path of an ink jet printer, a zone with locally elevated temperature. The droplets pass according to the invention after their exit from the nozzle of the printhead first a first cold zone, then the zone with locally elevated temperature and then a second cold zone before they impact the substrate. According to the invention, the printhead and the substrate are not influenced by the locally elevated temperature zone. Therefore, according to the invention, with the method as well as with the arrangement and the zone with locally increased temperature generated there is a locally limited energy supply to the drop. This leads to an active volume reduction of the drop and thus to an improvement of the resolution in the printing process.

An ink drop can z. B. by a small conductive grid with at least one or more heating wires, is passed through the stream and thereby a local temperature increase is generated, are passed. Thus, one or more heating wires can be used, which generate the zone with locally elevated temperature. Of course, the heating wires are not touched by the passing drops.

Alternatively, or in combination with the grid, light of a suitable wavelength may also be irradiated onto the drop after the drop has been jetted out of the nozzle of the printhead. By absorbing the optical or thermal energy through the ink constituents of the droplet, the liquid within the droplet is heated and partially or largely evaporated. The evaporation is thereby actively increased. This leads to the desired reduction of the drop volume compared to the volume of the drop at the exit from the printhead nozzle. Other properties of the droplet, such as its shape, its speed, the viscosity, the surface tension and / or the density, can also be changed in a targeted manner by active evaporation. The goal of the energy supply, as realized eg by optical or thermal methods, is the reduction in volume and, as a result, a smaller drop of ink than printing (pixels) on the substrate. This allows the desired higher resolution of the structures produced by the inkjet printing process of the invention. By the ink jet printing method according to the invention is advantageously a significant

Reduction of the drop volume by at least 10%, 1 1, 12, 13, 14, 15, 16, 17, 18, and 19% causes. A drop of, for example, 1 pL volume then has at most a volume of about 900 fl_ after passing through the zone of locally elevated temperature.

With the ink-jet printing method according to the invention, it is particularly advantageous to reduce the volume of the drop by at least 20%, more preferably by at least 21, 22, 23, 24, 25, 26, 27, 28, 29, 30%, more preferably by at least 31, 32 , 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57 , 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 49, 80, 81, 82 , 83, 84, 85, 86, 87, 88, 89 or even 99% or any intermediate value.

As a result, the ink jet printing method proposed advantageously increases the resolution by at least 1, 2, 3, 4, 5, 6, 7, 8, 9 or even at least 10%, particularly preferably at least 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30%, further preferably at least 31, 32, 33, 34, 35, 36, 37, 38 , 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63 , 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 49, 80, 81, 82, 83, 84, 85, 86, 87, 88 , 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.1, 99.2, 99.3, 99.4, 99.5, 99.6, 99.7 , 99.8, 99.9 or even 99.99%, or any intermediate value thereof.

In one embodiment of the invention, a light source with a specific wavelength, beam properties such as diameter, shape, power, pulsed or continuous, is used. The light source is placed such that the light beam radiates locally between the printhead (thermal, piezo-based printhead, or super-fine inkjet® and Aerosol-Jet® printhead) of an inkjet printer and the substrate. For this purpose, one can advantageously place the light source directly next to the print head or the light with a beam guide, z. B. an optical fiber, or via deflecting mirror to the print head. These printheads can of course also be used with the grid according to the invention with heating wire or heating wires as an attachment. Alternatively, one may set up a printhead in which the light source and / or the light pipe are integrated in the printhead so that the light will radiate locally into the space between the printhead and the substrate. The light source can produce only one or more beams, e.g. B. by splitting the beam of a light source in several with optical see fibers or by using two or more light sources with the same or different optical properties. This has the advantageous effect that drops from several nozzles at the same time or the drops from a nozzle with different colors are to be irradiated.

A light source as a first alternative is to generate a sufficiently large beam so that the droplet emerging from the nozzle has a sufficient contact surface with the light beam and thereby has sufficient contact time with the light beam. The jet has no contact with the print head and the substrate, so that the printing properties of the ink are not affected before the flight phase, or no interaction with the printed structures. It is particularly advantageous to use collimated light from a coherent light source.

 This has the advantageous effect that the diameter of the light beam can be kept constant over longer distances and not diverged. Alternatively, if longer interaction times between the drop and the beam are desired, a diverging light source may be used which illuminates a larger area and thereby increases the time the drop is in the illuminated area. This advantageously causes a further reduction in the volume of the drop.

Blocking of the jet passed through the drop can e.g. B. by attaching a beam trap at the light source outlet existing opposite side of the print head can be realized. The light source may be a laser that is pulsed or continuous. An LED or other light-producing system may also be used. The light source or multiple light sources should be selected so that their wavelength is well absorbed by the solvent or solvents of the printing ink, or the content dissolved in the solvent. The interaction time between the drop and the light or heating wire (s) becomes very short because the velocity of the drop is usually quite high. Normally, the velocity of the drop is in the range between 100 m / s and 0.01 m / s. This means that the flight times of the drop through the light beam or past the heating wires, ie the interaction times, are between 1 ns to 10 ms, and are dependent on the droplet size and the beam width or the temperature. Therefore, the light source and heater wire (s) should have enough power to actively evaporate enough solvent of the ink in the short interaction times of 1 ns to 10 ms, but on the other hand not be too high, and in particular not the temperature of the printhead or the substrate.

The light source and heating wires may or may not interact with the functional material of the ink. The light source as well as the heater wire (s) may effect "in-line sintering" of metal nanoparticles, or "in-flight cross-linking" of a polymer in the ink.

For different inks, different systems can be used to create a locally elevated temperature zone. For water-based inks are z. B. near the infrared emitting light sources particularly suitable because water absorbs particularly well in this wavelength range.

The locally elevated temperature zone is created between the substrate and the printhead. The ink drops pass through this zone after they leave the nozzle of the printhead and before they land on the substrate. The droplet is heated locally by means of a light beam and / or by heating wire or heating wires, and the solvents within the droplet are actively evaporated in this way, at least partially or completely evaporated. As a result, this always leads to a reduction in the drop volume, or else to a change in other drop properties, such as its shape, speed, viscosity, surface tension, density. The resulting, smaller drop is printed on the substrate.

According to the invention, the method advantageously also permits a denser positioning of individual drops relative to one another, and correspondingly a higher resolution and smaller minimum structures.

A light beam as the first alternative to produce a zone with locally elevated temperature should advantageously have an adjustable power, so that the evaporation rate and thus the resulting drop size can be regulated. If one or more heating wires are used as an alternative, they should be supplied with current from an adjustable current or voltage source.

A light source should also have a switch so that light can be turned on and off as needed. The light beam according to the invention should also have a mechanism that can adjust the position of the beam in the X, Y and Z directions. This may be necessary to better hit the jet with the drops.

As an alternative to or in combination with one or more light sources for the local heating of the droplets, it is particularly advantageous to use a conductive grid preferably made of metal or other conductive material. The grid has openings large enough to allow individual drops to pass through the spaces between the heating wires. A grid can only include one heating wire. Then the drop happens in the immediate vicinity of the heating wire and the zone generated by this locally elevated temperature. The conductive grid preferably comprises two electrically conductive plates z. B. of an electrically conductive metal, which are both electrically isolated from each other and are arranged on a substrate. The substrate serves as a heat shield. Between the two plates of at least one heating wire is stretched and connects the two plates together. The electrical resistance in the heating wire or in the heating wires is thus at least an order of magnitude 10 times, preferably 20 times, 30, 40, 50, 60, 70, 80, 90 or 100 times or even up to 1000 times or preferably even up to 10000 times or any intermediate value thereof higher than in the feeding plates.

This has the advantageous effect that with the energy supply only the one or more heating wires, but not the plates themselves are heated. As a result, the zone with locally elevated temperature in the immediate vicinity of the heating wires or not but produced in the plates. The higher the resistance ratio between the heater wire (s) and the plates, the better. The ratio is significantly influenced by the materials and the geometry of the plates and the heating wire (s).

If an adequate current is passed through this grid or its heating wires, then the heating wire (s) are heated and thereby generate a local temperature increase in the immediate vicinity of his or her heating wires. As the drops fly along the heater wire (s) without touching them, they will pass through heated there existing elevated temperature and in this way actively increases the evaporation rate, preferably the solvent of the ink. As a result of this active evaporation, the drop volume becomes smaller.

So much energy is supplied that the temperature of the droplet during the passage of the zones with locally elevated temperature should not exceed the boiling point of the droplet or its constituents. The temperature of the heater wire (s) must be high enough to vaporize enough solvent of the ink in these short interaction times of only 1 ns to 10 ms. On the other hand, however, it must not be too high and must not influence the temperature of the print head and the substrate.

The arrangement may in this sense have an attachment with at least one or more heating wires for a thermal evaporation of preferably the solvent of the ink. The drops from the printhead are heated by the local temperature gradient and evaporated. The local temperature gradient is generated by the heating of a grid or by heating, for example, two parallel heating wires or alternatively or in combination with one or more light sources.

The arrangement may in this sense also have an attachment with at least one or more light sources for a thermal evaporation of preferably the solvent of the ink. The drops from the print head are heated up by the local temperature gradient and evaporated. The local temperature gradient is generated by the heating of the ink in the light beam of a light source or alternatively or in combination with one or more heating wires.

An inventive attachment for an existing printhead system is provided for this purpose. The attachment for the generation of the local temperature gradient can be in two parts. A first part is fixed and attached to or on the printhead or printhead holder. The other part is fixed rigidly or reversibly on the first part, e.g. B. by gluing or by a magnetic mechanism.

An inventive attachment for a printhead of an inkjet printer preferably comprises: a heat shield to be aligned with the substrate with an opening for the ink,

two electrically conductive plates arranged directly on the heat shield, to be aligned with the substrate, and provided with electrical leads, which are individually separated from one another by a gap,

- Wherein the space between the plates is arranged below the opening of the heat shield, and

at least one heating wire connecting the two plates,

- The electrical leads conduct electricity through the plates in the at least one heating wire to produce a zone with locally elevated temperature.

 The electrical resistance in the heating wire or in the heating wires can thereby in operation by at least an order of magnitude 10 times, preferably 20 times, 30 times, 40 times, 50 times, 60 times, 70 times, 80 times Be 90 times or 100 times or even up to 1000 times or preferably even up to 10000 times or any intermediate value thereof higher than in the feeding plates. This has the advantageous effect that the zone with locally elevated temperature is generated only on the heating wire but not on the plates.

The attachment according to the invention for a printhead holder thus comprises in particular a heat shield. The heat shield is made of an electrically and thermally insulating material, such. B. anodized aluminum. The heat shield has a small opening for the ink drops. The heat shield protects the printhead advantageous from elevated temperature.

Immediately on the heat shield, ie without further spacers to the heat shield, two thin electrically conductive plates are arranged on the heat shield. The plates are electrical conductors, z. As thin metallic plates or sheets of steel. The two plates may be glued to the heat shield or otherwise arranged directly on the heat shield. The two plates on the heat shield are individually insulated from each other electrically. That is, the two plates have a space between them so that they have no physical contact with each other. This space is located directly opposite the opening in the heat shield, so that the drops emerging from the nozzle pass through the attachment in the direction of the substrate without contact with the heat shield, the plates or the heating wires spanned therebetween. Of course, other materials for the heat shield and / or the plates can be used. As a material for the heat shield z. But not exclusively glass, quartz and ceramics into consideration. These materials are advantageously well processable and inexpensive. The opening in the heat shield can z. B. be 0.5 mm wide. As a material for the plates in addition to the steel mentioned z. B. but not exclusively carbon and copper and z. As indium titanium oxide (ITO) into consideration.

The person skilled in the art can freely combine these materials in order to produce the attachment for the printhead according to the invention.

For example, glass with an opening of 0.5 mm can be used as a heat shield. Then directly 0.5 mm thick steel plates are glued on. The heating wire is glued as described with conductive silver glue between the steel plates and baked.

For example, glass with an opening of 0.5 mm can be used as a heat shield. This is immediately z. B. 0.1 mm thick carbon plates glued. The heating wire is glued to the carbon plates with conductive carbon paste. For example, a ceramic with an opening of 0.5 mm can be used as a heat shield. This is immediately z. B. 0.1 mm thick copper plates glued. The heating wire is glued to the carbon plates with conductive silver glue.

Glass or quartz can also be processed by optical lithography. The glass or quartz is used as a heat shield and has an opening of 0.5 mm. Two ITO (indium tin oxide) plates are deposited thereon 1 pm thick and patterned with optical lithography. Between the plates, the heating wire or a grid of tungsten 10 pm wide on the glass or quartz and between the ITO plates deposited and patterned with optical lithography, so that the two ITO plates are bridged with the tungsten wires. A person skilled in the art can use further deposition methods from optical lithography in order to produce an article according to the invention.

At least one thin heating wire is arranged as a connection between the two plates. The attachment then includes the heat shield, the plates disposed thereon and the heating wire therebetween, and electrical leads to the two conductive plates so that they can be connected to a power source or source of voltage that heats the heating wire. There is no additional space between the heat shield and the conductive plates. The attachment of heat shield and plates is therefore advantageous very thin and can be readily arranged space between a nozzle of a printhead and the substrate. The arrangement of heat shield and electrically conductive plates with heating wires is total preferably between 0.5 to 5 mm thick. The attachment of the attachment to the print head also consumes no further space in the beam direction of the ink. This also ensures that the assembly can be arranged or affixed without problems between a printhead and the substrate.

The attachment of the attachment according to the invention on the print head z. As by sticking, clamping devices or inserted slots in the printhead, in which the arrangement of heat shield and plates can be pushed. Of course, the type of attachment, which is within the expertise of a person skilled in the art, can also be done in other ways, for. B. by one or more retractable in the material of the printhead magnets, if the article comprises magnetic material such. B. the steel plates mentioned. The attachment can also be screwed or otherwise attached to the printhead. The type of attachment should not affect the thickness of the attachment. After attachment, the heating wires are placed very close to the substrate.

A second attachment according to the invention for a print head of an ink jet printer thus comprises:

a heat shield to be aligned with the substrate with an opening for the ink; at least one light source radiating into the jet path below the opening of the heat shield and creating a zone of locally elevated temperature for the ink droplets.

 This essay is also very thin.

An inventive article should be attached to the print head so that a fine adjustment can be made. The adjustment takes place in the plane so that the drops jet or fly along on the or the heating wires and must pass through the zone with locally elevated temperature.

It can be modified with the articles of the invention any printheads, especially those of industrial printers. Such an inventive article can be arranged in an inventive arrangement of printhead with nozzle, z. B. by small retractable magnets arranged on the printhead, which attract and hold the metallic plates of the article according to the invention through the heat shield. Other types of attachment are possible. It should be noted that the space available in the beam is usually limited. The fasteners have to be adapted thereto, that is, they should not take up any space in the direction of the ink jet.

The type of attachment is such that the attachment according to the invention after its attachment to the print head are advantageously also aligned in the plane, so that the drops are jetted directly along the heating wires or through the substrate without touching them, or through the Light beam fly. Adjustment screws can be used to align the attachment.

The attachment of the attachment is such that the thickness of the attachment is advantageously not increased by the fastening means, because the space between the substrate and a print head is usually very limited. The attachment may also consist of a heat shield and arranged thereon light sources that radiate in the space between the print head and substrate and generate the zone with locally elevated temperature.

A drop from the nozzle of a print head must fly through the attachment in the direction of the substrate. To this end, after leaving the nozzle, he will first pass through the opening in the heat shield and immediately thereafter fly past the heating wire or the heating wires or pass the light beam without having to pass an intermediate space between the heat shield and the two plates.

This article of heat shield and preferably metallic plates with heating wire or heating wires or light source is very thin overall, z. B. only 0.5, 0.6, 0.7, 0.8, 0.9 or 1 mm, or 2, 3, 4, 5, 6, 7, 8, 9 or 10 mm or an intermediate value assuming thin. This advantageously produces a zone of locally increased temperature between the printhead and the substrate so that a cold zone on the printhead, then the locally elevated temperature zone and a second cold zone on the substrate are produced in the blast path of the printer.

The beam path in the print head then consists of the printhead with nozzle, the attachment according to the invention for the printhead and the substrate to be printed. The article has the heat shield in the printing direction or direction to protect the printhead and the nozzle and the ink. Below the heat shield are in an alternative, the two plates, preferably metal plates that carry the heating wires or the and / or alternatively arranged the means for generating the light.

In the heat shield and optionally the plates of the essay openings are arranged congruent to the passage of the flying drops on the substrate.

In the alternative with only one or more heating wires, the beam path of the printer, the printhead with the nozzle, and preferably a heat shield with an opening, as well as arranged in the direction of substrate, the plates with the heated heating wires or the heating zone, which locally increased temperature generate, on.

The two metal plates are therefore together by one or more thin, that is in diameter z. B. 1 μηι, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101 ..., 398, 399 or 400 μηη thickness or any intermediate value assuming wires of metallic conductors such. As gold, tungsten, copper, aluminum, carbon, constants, manganin, chromium, titanium, or other metallic compounds electrically connected. The panels are electrically isolated from each other without the heater wire (s).

The applied current flows through the wire (s). For example, the current may have a current of 1_μΑ, 1 mA to 150 A, or any intermediate value as long as it produces only the temperature gradient. The current produces Joul heating of the heater wire (s). According to the invention, the electrical resistance of the or Wires are large compared to the two (metal) plates, which heats the wires by the current much more strongly than the (metal) plates themselves. In this way, the local generation of the temperature profile is generated and also the printhead and the substrate Advantageously protected from the temperature. Therefore, only at and between the wires or by the light source is a temperature gradient relative to the remaining space around the printhead generated. The temperature gradient between two wires depends on the distance of the wires from each other. The spacing of the wires is preferably established so that the gradient is strongest and that the drops can fly through the wires without touching the wires. The distance is z. B. between 10 .mu.m and 1 mm and best between 50 μιη set up to 100 μιη. The temperature gradient or a high temperature field is used for the passage of generated drops. The jetted out of the nozzle of the printhead drops are thereby accelerated by the wires on the way to the substrate. During the passage, the drops are heated and the solvents of the ink are partially or completely evaporated. By this evaporation the size of the drops after the passage in the

Compared to the size before the flight drastically reduced. This allows the placement of smaller drops on the substrate and thereby achieving higher resolution in the ink jet printing process.

In both presented alternatives, that is to say use of one or more light sources or one or more heating wires, it is particularly advantageous to provide or use a trigger around the print head for the removal of solvent vapors. This deduction can z. B. be realized as an essay for the printhead and used. For this purpose, extraction tubes made of metal or of plastic or another material inert for ink solvent are built up along the printhead from both sides. The selected material can thus achieve a good corrosion protection for the attachment against the solvent. These tubes are connected by means of hoses to a pump, a trigger or other means for generating a negative pressure. The airflow created by the vacuum should be strong enough to remove the vaporized solvent from the pressure area, but not so strong as to affect the flight path of the jetted drop. The trigger thus serves only to remove evaporated solvent from the pressure range and thus the subsequent drops, or their physical properties are not affected. The print can either be integrated into an existing printhead, or it can be considered as to be used on a part of the design for a new printhead. Alternatively, the entire printer may be in a protected or extracted atmosphere.

In the zone of locally elevated temperature, a temperature is produced in the drop, which is below the boiling point of the solvent or the solvent mixture of the ink. On the other hand, the print image on the substrate would be unmanageable, otherwise the drops would burst.

A person skilled in the art will, depending on the constituents and in particular the solvents of the ink used increase the temperature in the zone with locally increased temperature by means of heating wire and / or light source that produces the desired printed image and at the same time the resolution, compared to a standard ink jet printing process without a active reduction of the volume by increasing the temperature of the ink drops, is significantly increased.

For the method according to the invention can advantageously be used an ink whose solvent absorbs light or temperature particularly strong and thus the evaporation and reduction of the drop in flight with low energy proceeds in a shorter time.

Any or all of the solvents of the ink should then have a strong absorption at the wavelength of light used.

The heating mechanism used itself must not heat the print head, nor should it change the physical properties of the ink and affect the jetting behavior of the ink from the nozzles. For this purpose, it can be advantageously provided that a heat shield is arranged between the print head and the zone with locally elevated temperature.

For the ink-jet printing method of the invention, the printhead should be advantageously protected by a heat shield from the locally elevated temperature zone. This has the particularly advantageous effect that the physical properties of the ink are not already changed by increased temperature entry before exiting the nozzle. Furthermore, thereby clogging of the nozzle of the print head is particularly suitably prevented.

The arrangement according to the invention has an inkjet printhead with a nozzle. The arrangement furthermore has at least one heating wire or a metallic grid to be acted upon by an electric current or, alternatively or in combination, one A light source for generating a jet between the nozzle of the ink jet printhead and a substrate to be printed on.

The heating wires or the light source are used to generate a zone with locally elevated temperature or local heating of the ink emerging from the printhead nozzle, whereby actively reduces the volume of the drop that passes through the zone on the way to the substrate.

For this variant, the two ends of a heating wire to two metallic conductors z. B. attached as a metallic grid.

Particularly advantageous are the two electrical conductors z. B. the metallic plates, with which electrical current is conducted into the heating wires, directly to a to

Printhead-aligned heat shield arranged. That is, there are no spacers between the metal plates and the heat shield.

 Regardless of the type of arrangement or attachment according to the invention, that is to say with at least one or more heating wires or with at least one light source, it is particularly advantageous to produce a zone of elevated temperature with a temperature profile between the print head and the substrate.

The attachment according to the invention or the arrangement according to the invention with heating wire or light source generates the zone with locally elevated temperature. In the zone, a temperature profile is generated such that over a path length of about 1 mm a temperature difference of at least 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 ° C, further preferably at least 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 49, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89 or even 90 ° C, also preferably at least 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182 , 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, or 200 ° C, or any intermediate value.

The temperature gradient generated by the arrangement or attachment according to the invention in the zone with locally elevated temperature has regions of different temperature. These are between about 25 ° C in the edge region of the zone and 225 ° C directly on the heating wires or in the spot of the light source.

At a free path along the y-axis of the print jet, ie, in the beam path of the printer, from 0 mm at which the heater wire (s) or the light beam are positioned up to about 0.5 mm, temperature differences of up to 150 ° C are produced , On a path length along the y-axis between 0 mm and 1 mm temperature differences of optionally up to about 200 ° C are generated.

The temperature profile generated during the process of the invention is particularly advantageous due to a heat shield of asymmetric nature, which means that the printhead is in cooling while the droplet is passing through the hot zone before falling onto the cool substrate.

The following ink can be z. But not exclusively during the ink jet printing process of the invention. The ink may preferably consist of at least two solvents having different boiling points and vapor pressures, and optionally also different viscosities and surface tensions. The

Ink may preferably comprise at least one active material, that is, it should then comprise a polymer, metal nanoparticles, carbon nanoparticles, or the like. The ink may or may not contain additional ingredients such as surfactants, adhesives, defoamers. By heating in flight, a first solvent with lower boiling point and vapor pressure is much more evaporated than another. In this way, the pressure on the substrate causes the droplet to consist essentially of the solvent with higher boiling point and lower vapor pressure. If the remaining solvent has a higher viscosity, then the total viscosity of the drop is higher than before. As a result, the tropics on the substrate will flow less and remain smaller than a lower viscosity drop. If the solvent remaining in the drop has a higher surface tension, then the total surface tension of the drop is higher. As a result, the droplet forms a large contact angle with the substrate and, on the whole, wets a smaller spot on the substrate than a droplet with a lower surface tension. However, according to the invention, the surface tension should not be higher than 40-50 mN / m in order to avoid the re-accumulation of the drops on the substrate and lubrication of the printed structures. The concentration of active material such. As polymer, metal nanoparticles, carbon nanoparticles or other materials may, in comparison to an ink jet printing Procedures are kept low in the prior art. Evaporation of solvent in flight will increase the weight fraction of the active material in the drop. This allows for the incorporation of a lower level of active material in ink production. In addition, a smaller concentration of the active material allows for a smaller thickness of the printed structures and layers on the substrate as compared to the higher active material inks. By a greater concentration of the active material in the droplet, the so-called coffee-ring or coffee-stain effect is reduced. If the viscosity of the solvent with the higher boiling temperature is also higher, this will further promote the reduction of the coffee-ring or coffee-stain effect.

embodiments

In addition, the invention will be explained in more detail with reference to some embodiments and the accompanying figures, without this being intended to limit the invention. On the contrary, the skilled person should, with due appreciation of the exemplary embodiments, be allowed to combine these with one another in order to arrive at objects which are undoubtedly also included in the invention.

Unless otherwise indicated, identical reference numerals in the figures denote identical objects.

FIG. 1 shows a schematic representation of a method according to the invention and FIG

 Arrangement (B-E) and the prior art (A).

Figure 2 Schematic representation of a method according to the invention and the

 Arrangement.

Figure 3 zone with locally elevated temperature and temperature profile. The following composition of the ink can be used. The ink has thiol-stabilized gold nanoparticles of 2 to 10 nm in diameter. The gold particles have 2 wt% by weight of the ink; The ink has 90% v / v toluene, that is 90% by volume. 10% v / v is a-terpineol (10% volume fraction). Due to the high density, one can neglect the volume of gold nanoparticles in the drop. A volume of 1 pL of the drop of this ink will therefore consist volumetric almost exclusively of solvent. The weight of the drop is 98% solvent and only 2% gold nanoparticles. VTOIUOI = 0.90 pL; V _a -Terpineoi = 0.10 pL; m-roiuene = V _TO I _UO I * pToiuoi = 0.90 pL ^* 870 g / L = 783 pg

Tla-terpineol = _a . _Te rpineol ^* P a -terpineol = 0.10 pL ^* 930 g / L = 93 pg ^ gold nanoparticles = 18 pg m-drop = 783 + 93 + 18 = 894 pg Such an ink may be generated by heating in flight after exiting from Nozzle and pass the zone with locally elevated temperature to lose up to 90% of the solvent. This means that the drop volume can be reduced from 1 pL to 100 fL. Due to the difference in boiling point between toluene (boiling point = 111 ° C) and a-terpineol (boiling point = 218 ° C) and due to the higher vapor pressure, mainly the toluene is evaporated. This means that the mass of the printed drop will only consist of the mass of the a-terpineol and the gold nanoparticles. m'drop = 93 + 18 = 111 pg

The generated new concentration of the gold nanoparticles in the drop is then

Ceopan nanoparticles = 18/111 ^* 100% = 16.2 wt%. The diameter of the drop drops, if one assumes a spherical teardrop shape, by evaporating from about 90% of the solvent from 6.2 μιτι (1 pL drops) to 2.9 μιτι (100 fL drops).

Thanks to the higher viscosity and surface tension of a-terpineol, the reduced droplet will also flow less and thus print much smaller on the substrate, ultimately achieving the greater resolution in the print. As a result, an increase in the resolution of more than a factor of 2 is achieved in the present case. These or other inks can be readily used during the ink-jet printing process.

The designated in the figures deduction or the steam trap for the extraction of the resulting solvent vapors is z. B. made of aluminum and arranged as a part of the total essay to the printhead. For this simple magnetic pads can be used. Basically, the trigger or vapor trap is fabricated as a slot on two or all four sides along the printhead in the aluminum housing. This slot is connected to a hollow channel in the attachment and discharged to the outside through a hose. At the end of the tube, a fan or a small vacuum pump can be arranged, which generates the negative pressure and thereby causes the flow of solvent vapor, which forms below the print head, to the outside. This river is not too high, so as not to distract the jetted drops from a straight trajectory. But he should be strong enough to suck the solvent vapors to the outside. The trigger is optional at a low pressure frequency, that is, when the volume of solvent vapors is very small overall, it is not absolutely necessary because the droplets pass passively outward through a diffusion and convection in the air and away from the print head. However, it is partly mentioned for the present embodiments.

As printhead for the embodiments printheads of Dimatix ™ (Fujifilm) are used, for. A DMC and a DMCLCP 1 and 10 pL. The printheads are mounted in an ink jet printer OJ300 from UniJet. The material used for the attachment, for the jet trap and for the steam trap is anodized aluminum.

First embodiment:

A first embodiment relates to a pulsed infrared laser with a wavelength of 780-5000 nm, with a pulse duration of 1 s-1 fs and with a power of 1 mW to 10 W. This is mounted on the printhead as described and generates the zone as a light source with locally elevated temperature.

Second embodiment:

A second embodiment relates to another attachment equipped with two heating wires for thermal evaporation of the solvents of the ink. The drops from the print head are heated by a local temperature gradient and evaporated. The local temperature gradient is generated by heating from a grid or by heating two parallel heating wires. The attachment for the generation of the local temperature gradient is in two parts. One part is fixed and attached to the printhead or printhead holder. The other part is attached to the first part, but can also be removed. The second part consists of two large metal plates that are electrically isolated from each other. The two metal plates are interconnected by thin, that is in diameter z. B. 1 μιη, 12.5 μιτι, 25 μηι, 50 μηι to 200 μιτι thick or intermediate value wires from z. As gold, tungsten, copper, aluminum, carbon, constantan, manganin, chromium, titanium, or other metallic compounds electrically connected. The current flows through these two wires. For example, the current may have a current of 1 μΑ, 1 mA to 100 A. The current generates Joul heating of the heating wires. Because the wires have a much higher resistance compared to the two metal plates, they are much more heated than the metal plates themselves. In this way, the local generation of the temperature profile is generated. Therefore, a temperature gradient is created between the wires relative to the remaining space around the printhead. The temperature gradient between two wires depends on the distance between the two wires. The spacing of the wires is set so that the gradient is strongest and that the drops can fly through the wires without touching the wires. The distance is between 10 μπι and 1 mm, preferably between 50 μιτι or 100 μηι set up. The temperature gradient or a high temperature field is used for the passage of generated drops. The jetted out of the nozzle of the printhead drops are thereby accelerated by the wires on the way to the substrate. During the passage, the drops are heated and the solvents of the ink are partially or completely evaporated. This evaporation drastically reduces the size of the drops after the flight compared to the size before the flight. This allows the placement of smaller drops on the substrate and thereby achieving higher resolution in the ink jet printing process.

Third embodiment

According to the third embodiment, the drops of the ink in the printhead are generated by a piezo element and reach the substrate barrier-free after a flight phase. An "in-flight" vaporization device of drops of light energy is mounted on the printhead and comprises the light source that irradiates the generated drops with a thin beam from the light source after exiting the nozzle Heating, the solvent of the drop is partially evaporated. After interacting with the beam, the smaller drop lands on the substrate.

A beam trap is positioned opposite the light source for the light in the attachment. The jet trap blocks the light and suppresses unwanted scattering. The jet trap consists of anodized aluminum.

Furthermore, the article also has a steam trap for the extraction of solvent vapors. The generated drops are irradiated by a thin beam from the light source. Local heating in the jet partially vaporizes the solvent of the droplet. The solvent vapors are extracted in the steam trap by means of a slight negative pressure. After interacting with the beam, the smaller drop lands on the substrate.

Fourth Embodiment

FIG. 1 shows a schematic description of an inkjet printhead on which heating wires according to the invention are arranged to produce a zone with a locally elevated temperature.

The drops 7 are generated from the ink in the print head 5 by a piezoelectric element and, after leaving the nozzle 1, reach the substrate 4 in a barrier-free manner after a flight phase. This process is shown as prior art in FIG. 1A.

Figure 1B shows the side view of the inkjet print head 5 with the attachment 8 for "evaporating" drops 7 by heating the drops by means of heating wires The generated drops 7 emerge from the nozzle 1, fly between the wires between 1) From one metal plate to the other, a current is passed through the two thin wires The current produces the required Joule heating in the wires, but not in the metal plates 3, because their area is much The heating creates a temperature gradient between the environment around the wires and the remaining space around the printhead The metal plates are located on the heat shield (not shown) which is aligned with the printhead. The drops 7 pass through the heating wires and evaporate. The steam 7 'is sucked off via the steam trap (not shown) in the attachment 8.

As a result, this reduces the volume of the drop and prints drops 7 "onto the substrate Figure 1C shows schematically the bottom view of such an ink jet print head 5 with the top 8 for active" on-the-fly "evaporation of drops by heating by local evaporation a heating wire 6. Shown are the two metal plates 3a, 3b. The metal plates are arranged on the heat shield and like these components of the attachment 8 for the print head, which is not shown because of the view from below. The metal plates are of course provided with means for applying a current (not shown). Therefore, a direct current or an alternating current can be applied to the plates. This heats a thin wire 6 which is located below the nozzle 1. Two horizontal slots 9 are provided in the attachment as a vapor trap for the vaporized solvent 7 '. At the steam trap 8 is a slight negative pressure, which sucks the vapor 7 'from the critical zone between the print head and substrate.

Figure 1D is a side view rotated 90 ° in comparison to Figure 1B. At the print head 5, the attachment 8 is arranged. The steam trap 9 is realized as a circumferential groove, which is arranged in the edge region of the attachment 8. The solvent vapors are sucked into the steam trap by a small vacuum. After interaction with the wires, the volume smaller drop 7 "lands on the substrate 4.

Figure 1E schematically shows a bottom view of the second part of the attachment 8 for "evaporating" drops with localized heating by heating alternatively with two wires 6a, 6b. The second part of the attachment comprises the two metal plates 3a and 3b. Each of two silver dots 7a and 7c, and 7b and 7d are respectively provided for the heater wires for attachment to the metal plates, and the metal plates have a space therebetween so as to be free from each other the heating wires are electrically isolated from each other.

Current flows through the two wires 6a and 6b and generates the heating of the wires 6a and 6b and thereby the desired temperature gradient below the printhead aligned with the substrate and the remainder of the printhead environment. The generated drops fly out of the printhead nozzle 1 between the heating wires 6a and 6b and become thereby partially evaporated by the temperature gradient. After interacting with the wires, the smaller drop lands on the substrate 4.

Reference numeral 9 denotes the opening between the metal plates in which the heating wires are clamped. In an extension of Figure 1, Figure 2 shows in its upper part A in cross-section an inventive arrangement or attachment for performing the method. The assembly is cut at the location of the nozzle 21 of the printhead 25 and shows its orientation above the openings in the heat shield 22 and the metal plates 23a, 23b.

The attachment according to the invention comprises the heat shield and the two metallic plates 23a, 23b.

The heat shield 22 is made on the surface of non-conductive anodized aluminum and has the dimensions B x H x T of 100 x 0.5 x 20 mm. Two metal plates arranged thereunder are electrically insulated from one another (see FIG. 2B) and have the reference numerals 23a and 23b. The metal plates 23a and 23b are made of steel. They each have a dimension of 45 x 0.5 x 20 mm (W x H x D). The entire height of heat shield 22 and metal plates 23 is advantageously only about 1 mm. The two plates 23a and 23b are provided with leads for applying an electric current. This is shown in the figure B in the lower part of Figure 2. The two heating wires 26a, 26b have a diameter of in each case 25 to 80 μm and a length of approximately 5 mm, since the opening has corresponding dimensions. The wires are attached to the metallic plates 23a and 23b with two silver glue drops 27a, 27b, respectively. Only the silver glue drops on the left metal plate are provided with reference numerals, otherwise the arrangement corresponds to that in FIG. 1 E.

This article of the invention heat shield 22 and metallic plates 23 together with heating wire or heating wires and electrical leads is baked for rigid attachment of the heating wires at about 150 ° C for about one Λ hour. The two wires 26a, 26b then have a distance between 50 to 200 microns, depending on their positioning to each other.

The attachment is preferably inserted into an existing printhead system having one or more nozzles via magnets buried in the printhead. The metallic steel plates th are aligned to attach the essay on the print head 25 to the substrate and the heat shield according to the printhead. The attachment is arranged in a particularly simple manner by the magnets sunk in the material of the print head (not shown). These attach the attachment to the printhead so that it can still be adjusted. FIG. 3 shows a temperature profile generated according to the invention, which was simulated with the program Comsol (Comsol Inc., USA).

In the 2D simulation (cross section), two copper wires with a diameter of 25 μm are arranged side by side with a spacing of 100 μm. 500 pm away from the wires, an aluminum heat shield 32 is disposed with an opening below the nozzle. The opening has a length of 500 pm. The heat shield also has a thickness of about 500 pm. Through the wires, current of 150 mA is conducted to produce Joul heating of the heating wires. The room temperature is set at 20 ° C and the temperature gradient generated by Joule heating is recorded with different black and white fillings in Figure 3 as a 2D temperature profile. Shown schematically are the heat shield 32 and the nozzle 31. These as well as the substrate 34 are recessed from the local temperature increase, as the simulation shows.

It is clear that by means of the inventive arrangement of printhead and heat shield, as indicated, carried out the inventive method and the zone with locally elevated temperature in different temperature ranges can be generated and broken down.

The temperature gradient shown in FIG. 3 therefore has, for example, regions of different temperature. These are between about 25 ° C at the edge region and about 105 ° C directly to the heating wires and are generated by the two heating wires used for the simulation at a current of 150 mA. The temperature gradient is given on a free path of about 3 mm. On the free path of the y-axis of 0 mm (positioning of the heating wires) up to about 0.5 mm in the present case, temperature differences of about 68 - 105 ° C achieved, resulting in a temperature difference of almost 40 ° C. On the Y-axis path between 0 mm and 1 mm, temperature differences of even about 80 ° C are achieved. The temperature profile is, due to a heat shield 32, asymmetric type, what means that the printhead is in cooling while the drop passes through the hot zone and falls onto the cold substrate.

With such an arrangement according to the invention or the attachment according to the invention, as shown in FIGS. 1B-1E and FIG. 2, it is correspondingly possible to locally heat an ink drop conducted through the openings of the heat shields and plates and to reduce the volume of the ink To reach at least 10% of the original volume.

It is understood that this simulation is exemplary. It is possible within the scope of the invention to produce other temperature gradients. For this purpose, a person skilled in the art will adapt the material of the heating wires, the plates, and the heat shield to the conditions on the print head and achieve the desired volume reduction of the drop.

It is further understood that a person skilled in the art can freely choose the materials and combine them. So it is possible to combine the materials as follows.

Embodiments 5 to 9 For example, glass having an opening of 0.5 mm can be used as a heat shield. Then immediately two 0.5 mm thick steel plates are glued on. The heating wire is glued to the steel plates as described with conductive silver glue and baked.

For example, glass with an opening of 0.5 mm can be used as a heat shield. Immediately two 0.1 mm thick carbon plates are glued to it. The heating wire is glued to the carbon plates with conductive carbon paste.

For example, a ceramic with an opening of 0.5 mm can be used as a heat shield. This is immediately z. B. 0.1 mm thick copper plates glued. The heating wire is glued to the copper plates with conductive silver glue.

One skilled in the art can use lithographic techniques to process the article. Thus, glass or quartz can be processed as a heat shield with the methods of optical lithography. The glass or quartz is used as a heat shield and have an opening of 0.5 mm. Two ITO (indium tin oxide) plates are deposited thereon 1 m thick and patterned with optical lithography. Between the plates are the Filament or grid of tungsten 10 pm wide deposited on the glass or quartz and between the ITO plates and patterned with optical lithography, so that the two ITO plates are bridged with the tungsten wires.

A person skilled in the art can use further deposition methods from optical lithography in order to produce an article according to the invention.

Claims

Patent claims

An ink jet printing method in which a print head (5) of an inkjet printer is oriented toward a substrate (4) to be printed, and wherein ink drops (7) are produced in the print head of the inkjet printer after exiting the nozzle (1) of the print head be directed into a zone of locally elevated temperature, so that the volume of the drops is actively reduced during the flight phase to the substrate.

2. Ink-jet printing method according to the preceding claim,

 characterized in that

 a significant reduction of the drop volume by at least 10%.

3. Ink-jet printing method according to one of the preceding claims,

 characterized in that

 a reduction in the drop volume by at least 20%, more preferably at least 30%, 40%, 50%, 60%, 70%, 80% or up to 99.99%, or any intermediate value thereof.

4. An ink-jet printing method according to one of the preceding claims,

 in which the zone of locally elevated temperature is generated by at least one heating wire or by at least one light source.

5. Ink-jet printing method according to the preceding claim,

 characterized in that

 the zone of locally elevated temperature is generated by an arrangement of at least two heating wires, between which the drops are conducted.

6. An ink-jet printing method according to one of the preceding claims,

 characterized in that

the drops (7) are passed through a zone of locally elevated temperature, which has a temperature difference of at least 10 ° C., preferably at least 200 ° C., over 1 mm path length.

An ink-jet printing method according to any one of the preceding claims,

 characterized in that

 the printhead (5) is protected by a passively or actively cooled heat shield (2) from the zone of locally elevated temperature.

8. Arrangement comprising an inkjet printhead (5, 25) having a nozzle (1, 21) and at least one heating wire (26a, 26b) to be acted upon by electric current or a light source between the nozzle of the inkjet printhead and a substrate (4, 24) to be printed ) for generating a zone of locally elevated temperature and heating the ink emerging from the printhead nozzle (7).

9. Arrangement according to one of the preceding claims,

 marked by

 at least two heating wires, between which the ink is directed towards a substrate.

10. Arrangement according to the preceding claim,

 characterized in that

 the ends (7a, 7c) of the heating wire are fixed to two plates (3a, 3b; 23a, 23b) which are electrically insulated from one another.

11. Arrangement according to one of the preceding claims,

 in the

 the two plates (3a, 3b, 23a, 23b) are arranged directly on a passively or actively cooled heat shield (22) aligned with the print head (25).

12. Arrangement according to one of the preceding claims,

 characterized in that

 the heating wire or the light source between the printhead and the substrate can produce an elevated temperature zone with a temperature profile having a temperature difference of at least 10 ° C over a path length of 1 mm.

13. An attachment for a printhead of an ink jet printer, comprising

a heat shield with an opening, two conducting plates arranged directly on the heat shield, to be aligned with the substrate and provided with electrical leads, which are separated from one another by a gap,

- Wherein the space between the plates is arranged below the opening of the heat shield, and

at least one heating wire connecting the two plates,

- The leads conduct electricity through the plates in the at least one heating wire to produce a zone with locally elevated temperature.

Printhead with means for attaching an attachment according to the preceding claim.