EP3512707B1 - Method and device for ink-jet application on sheet-type substrates - Google Patents

Description

The invention generally relates to the printing processing of substrates, in particular the printing or coating of flat substrates, such as printed matter, paper and cardboard, with color information and/or raised plastic layers.

The printing industry is in a process of change, with conventional processes being increasingly replaced by digital processes. At the same time, the subsequent finishing of printed matter is becoming increasingly important. Post-processing of the printed substrate has largely become established, especially for high-quality printed matter and packaging.

In this context, so-called print finishing processes have become established, in which printed products are provided with raised, haptically detectable coatings. For example, printed sheets for the production of paper or cardboard packaging are provided with such coatings in order to realize specific design ideas. Various coating processes are known from the prior art for producing the raised or relief-like layers mentioned above. A comparatively new process for this is coating using inkjet technology. The production of the coatings with inkjet technology is in the WO 2003/099456 A1 and the WO 2009/012996 A1 described.

Furthermore describes the US2012/314003 relevant state of the art.

In contrast to conventional methods, in which a printing form is produced that contains the entire substrate to be printed, in digital methods each halftone dot is generated individually. The most common method is printing with inkjet printheads (inkjet printheads). The price is determined by the nozzles used.

When printing with inkjet print heads having a plurality of nozzles, the method is known of being able to print on any desired substrate width by moving the print heads in a direction perpendicular to the substrate movement. The substrate is stopped for the head movement and the print head prints the substrate in strips. This operation is described with the English term "scanning mode".

Inkjet printheads have the property that the nozzles of the printhead can exhibit certain deviations in droplet ejection from the direction perpendicular to the nozzle plate over the service life. This trait can play a role from the very beginning of using the head, but usually increases over time. In addition, manufacturing tolerances in the manufacture of the heads can contribute to inaccuracies in drop positioning.

The properties mentioned mean that the print image from inkjet print heads typically has a certain streakiness. To make matters worse, nozzles can fail temporarily or permanently during use. A temporary failure of nozzles is usually counteracted by ejecting liquid from the reservoir through the nozzles (the term “purging” has become common for this) and removing the material that has escaped from the nozzle plate. This reconditioning of the nozzles interrupts the printing process and reduces the productivity of the printing unit. The permanent failure of nozzles in a printhead can generally only be remedied by completely replacing the entire printhead.

In the "scanning mode" technology mentioned above, by moving the heads and printing the substrates in strips, statistical positioning of drops within a raster line from different nozzles encountered streaking. Due to this statistical structure of the print image, missing nozzles can also be tolerated to a certain extent or compensated for.

As inkjet print heads have become more and more reliable and the price per nozzle is becoming cheaper, it has become common practice to build so-called single-pass printing machines to increase productivity. In these machines, the heads are arranged so that the rows of nozzles are arranged transversely, typically essentially perpendicularly, to the substrate movement. Optionally, the heads with the rows of nozzles can also be arranged at an angle deviating from the vertical direction in order to achieve a higher resolution. Basically, this type of use means that a droplet path on the substrate originates from precisely defined nozzles parallel to the substrate movement.

If there is only one nozzle per drop path on the substrate, a deviation in drop direction will result in streaking as described above. The failure of nozzles has an even more striking effect. This problem occurs in particular when applying curable paint or coating components that are suitable for producing raised coatings.

In order to still ensure certain statistics in the nozzle selection, several rows of nozzles can be arranged one behind the other in single-pass operation and these can then be used alternately or at random to generate the individual droplets in a droplet path. In this way, similar to the scanning mode with statistical selection of nozzles for individual droplet positions, the formation of stripes and the failure of nozzles can be concealed to some extent.

However, this solution is technically very complex and also expensive.

A simpler arrangement that avoids streaks in the print or coating pattern would be desirable. This object is solved by the subject matter of the independent claims. Advantageous developments are specified in the dependent claims. Accordingly, the invention provides a method for printing flat substrates according to claim 1.

Due to the to-and-fro movement, directional components in mutually opposite directions, or antiparallel directional components, are generally present in the paths. For example, this results in paths in the form of wavy lines or zigzag lines. The movement of the nozzles can be periodic or even statistical.

The conveying device can be a web feed device in a roll-to-roll printing machine, in which a substrate web is fed to the print heads is moved past. Accordingly, in this device, a substrate in the form of a web-shaped printing pad or substrate web, in particular made of paper or cardboard, is printed, which is provided wound up to form a roll. The printing substrate is unrolled by means of the conveyor device, passed through the device and wound up again after printing.

The fluid application material can be a color or an ink-jet ink, so that a pattern in the form of a colored printed image is generated by the application. The term “colored printed image” is generally to be understood as a pattern that contrasts with the background. Accordingly, black is also to be understood as a printing color in this sense, as is customary in the field of the printing industry.

According to the invention, a polymer coating is applied using the method. For this purpose, a fluid organic polymer material is applied with the ink-jet nozzles and the film is cured to form a solid polymer coating after application. This polymer layer can also be transparent and colorless

The inkjet nozzles can be moved individually or in groups. It is particularly easy to fix the inkjet nozzles in a common holder, which can also be referred to as a pressure bar, and then to pivot this holder transversely to the transport direction.

With the additional reciprocating movement of the nozzles, a streaky appearance of the coating can be counteracted very effectively. A small amplitude of movement is sufficient for this. The amplitude is not greater than 300 times the nozzle spacing, preferably not greater than 100 times the nozzle spacing, particularly preferably not greater than ten times the nozzle spacing, and according to the invention not greater than five times the nozzle spacing, measured from the center of a nozzle to the center of one neighboring nozzle. A streak can occur at failure or Emission reduction of a single nozzle can be suppressed even if the amplitude is smaller or, according to the invention, equal to the simple nozzle spacing.

Furthermore, the invention provides a device for printing flat substrates according to claim 7 .

Fig. 1

eine erste Ausführungsform einer Vorrichtung zur Durchführung des Verfahrens,

Fig. 2

eine weitere Ausführungsform, eingerichtet zur Inline-Beschichtung,

Fig. 3

eine Veranschaulichung einer Tropfenabgabe unter Bestimmung nächstkommender Punkte,

Fig. 4

eine Veranschaulichung der Tropfenabgabe bei Ausfall einer Inkjet-Düse,

Fig. 5

eine Variante des in Fig. 1 dargestellten Ausführungsbeispiels mit mehreren Düsenreihen.

Fig. 6 und Fig. 7

beschichtete Bereiche auf einem Substrat, und

Fig. 8

eine Anordnung einer Halterung mit mehreren Druckköpfen,

Fig. 9

eine Variante der in Fig. 8 gezeigten Anordnung mit in mehreren Reihen gestaffelt angeordneten Druckköpfen,

Fig. 10

ein Testbild zur Kalibrierung der Positionen der Druckköpfe,

Fig. 11

eine modular aufgebaute Druckeinheit.

The invention is explained in more detail below with reference to the enclosed drawings. Show it:

1

a first embodiment of a device for carrying out the method,

2

a further embodiment set up for inline coating,

3

an illustration of a drop delivery with determination of closest points,

4

an illustration of the droplet delivery when an inkjet nozzle fails,

figure 5

a variant of the in 1 illustrated embodiment with several rows of nozzles.

6 and 7

coated areas on a substrate, and

8

an arrangement of a bracket with multiple printheads,

9

a variant of the in 8 shown arrangement with print heads staggered in several rows,

10

a test image to calibrate the positions of the print heads,

11

a modular printing unit.

• eine Auftragsvorrichtung 7,
• eine Steuereinrichtung 13 und
• einer Fördereinrichtung 5, um ein Substrat 3 entlang einer Vorschubrichtung 4 an der Auftragsvorrichtung 7 vorbeizubewegen, wobei die Auftragsvorrichtung 7 mehrere, in einer Reihe quer zur Vorschubrichtung angeordnete Inkjet-Düsen 70 umfasst, und
• die Steuereinrichtung 13 zur Erzeugung rechnergesteuerter Schaltsignale eingerichtet ist, mittels derer die Inkjet-Düsen 70 tropfenweise ein fluides Auftragsmaterial 9 abgeben, wobei
• die Steuereinrichtung 13 weiterhin eingerichtet ist, die Inkjet-Düsen derart anzusteuern, dass auf der Oberfläche 30 eines vorbeibewegten Substrats 3 ein fluider Film 11 des Auftragsmaterials in Form eines Musters 14 mit vorbestimmter Kontur 15, insbesondere unter Aussparung von Bereichen 16 aufgetragen wird. Gemäß einer Ausführungsform sind Tinten als fluides Auftragsmaterial vorgesehen, so dass mit dem Verfahren ein Druckbild auf das Substrat 3 aufgedruckt wird. Das Bedrucken mit Tinten erfolgt erfindungsgemäß

1 shows an example of a device 1 for carrying out the method described above. Without being restricted to the specific example shown, a device 1 according to the invention for coating flat substrates 3 with polymer coatings

• an application device 7,
• a controller 13 and
• a conveyor device 5 to move a substrate 3 along a feed direction 4 past the application device 7, the application device 7 comprising a plurality of inkjet nozzles 70 arranged in a row transverse to the feed direction, and
• the control device 13 is set up to generate computer-controlled switching signals, by means of which the inkjet nozzles 70 emit a fluid coating material 9 drop by drop, wherein
• the control device 13 is also set up to control the inkjet nozzles in such a way that a fluid film 11 of the application material is applied to the surface 30 of a substrate 3 moved past in the form of a pattern 14 with a predetermined contour 15, in particular with areas 16 left out. According to one embodiment, inks are provided as the fluid application material, so that a printed image is printed onto the substrate 3 using the method. The printing with inks is carried out according to the invention

with a polymer coating. According to the invention, the device 1 also has a hardening device 23 in order to harden the fluid film 11 to form a solid polymer coating 12 after it has been applied.

In any case, however, a movement device for moving the inkjet nozzles 70 is provided in order to move the inkjet nozzles 70 in a direction transverse to the feed direction 4, preferably along the longitudinal direction, during the application of the pattern 14 and during the movement of the substrate 3 Row arrangement of the inkjet nozzles 70 to move back and forth periodically, so that the paths that the nozzles 70 cover over the substrate 3 by superimposing the, for example, periodic back and forth movement with the movement along the feed direction 4, have directional components perpendicular to the feed direction . In particular, the paths can have the shape of wavy lines.

In the example shown, the conveyor device 5 comprises a conveyor belt on which the substrates 3 are placed. The substrates 3 in the form of pre-printed printed sheets are taken from a magazine 27 and placed on the conveyor belt.

The nozzles 70 are connected to a reservoir in which the fluid coating material 9 is kept. According to one embodiment, radiation-curable, in particular UV-curable, organic preparations are used as fluid organic coating materials. For example, reactive acrylates mixed with photoinitiators can be used for this purpose. In order to solidify UV-curing lacquers, the curing device 23 has a UV radiation source accordingly.

A drive with an eccentric is shown as a movement device 25 only by way of example, by means of which the holder on which the inkjet nozzles 70 are attached is pivoted transversely, in particular perpendicularly, to the feed direction of the conveyor device 5 .

The substrates 3 are printed with a printed image 18 . The individual elements of the printed image are delimited by a contour 19 . In a preferred embodiment of the invention, such a substrate 3 printed with a printed image 18 is now provided with the polymer coating in such a way that the printed image 18 corresponds to the pattern 14 of the coating 12 . The pattern 14 can in particular correspond to the printed image in such a way that the contours 15, 19 of the printed image 18 and pattern 14 are at least partially parallel, preferably run at least partially congruently as shown. By way of example only, the printed image includes a printed corner and a printed star. The polymer coating 12 then covers, for example, the printed areas as a raised coating and is delimited by contours 15 which are congruent with the contours 19 of the printed image 18 . The coating takes place while leaving out the areas 16 of the surface 30 between the elements of the printing. Of course, these areas can also be printed, but the areas covered with the polymer coating 12 are elements that stand out visually due to their contours 19 (this finishing technique is also referred to as “spot coating”).

2 shows a variant of the in 1 illustrated embodiment. In this variant, a printing device 6 arranged upstream of the application device 7 is provided. Just like the application device 7 , the printing device 6 can be controlled and operated by the control device 13 . In particular, the printing device 6 can be a digital printing device, preferably an inkjet printing device. The printing device 6 first produces the printed image 18 on the substrates 3 in the form of printed sheets, to which the polymer coating 12 is then applied with the application device 7 while leaving out areas 16 corresponding to the printed image 18 .

By recognizing the position of the inkjet nozzles 70 or the print head, when the nozzles are actuated electronically, the next nozzle at the time of firing for a drop position on the substrate 3 can be selected for firing according to a further development of the invention. In this way, even with a very small movement perpendicular to the substrate movement, the formation of stripes and also the visibility of nozzle failures can be drastically minimized, similar to what is described for the scanning mode.

For this purpose, without being restricted to the exemplary embodiments illustrated in the figures, the invention provides that the pattern 14 of the coating is defined by an arrangement of adjacent target areas 140, with a computer 19 determining which of the inkjet nozzles 70 is active during the movement of the substrate 3 on the one hand and the periodic movement of the inkjet nozzles 70, on the other hand, comes closest to a target area 140 or best corresponds to it and sends a control signal to this inkjet nozzle 70, so that the nozzle 70 points to the determined target area 140 as closely as possible, or best matching point 141 a drop 71 of the fluid coating material 9 emits.

In order to realize a position detection, according to one embodiment of the invention, at least one position sensor 21 is provided, which detects the position of the inkjet nozzles in a direction transverse to the feed direction, i.e. in the direction in which the inkjet nozzles 70 are moved backwards and forwards by means of the movement device 25 be moved here. This embodiment is not necessarily connected to the embodiment explained above, in which the distance to a target area is determined.

The procedure with the drop delivery with determination of the closest points is again based on 3 illustrated.

In 3 Illustrated is an array of adjacent target areas 140 which together form one element of a pattern 14 of the polymeric coating. The target areas are preferably stored in the control device 13 in the form of data, which control the nozzles like a print file, or which represent a printed image of the polymer coating to be applied.

The traces 72 of the ink jet nozzles 70 form a pattern of adjacent wavy lines as shown. At one of the target areas 140 here are in the form of boxes, the method of dispensing drops is explained by way of example. The target area 140 is covered by two tracks 72, namely the top two tracks. The upper of these two traces provides the closest match to the target area 140 at a point 141 since that point 141 is closest to the center of the target area. At this point 141, the bead 71 associated with the target area is then dispensed to form part of the polymer film, which is still fluid prior to curing.

Accordingly, the method can also be used if an inkjet nozzle fails. This case is in 4 shown. In the example shown, it was assumed that the second uppermost inkjet nozzle 70 has failed. The pendulum movement of the nozzles means that target areas 140, for which the path of the failed nozzle normally provides the best match, are also either crossed by paths of other nozzles or are at least closely approximated. The method described above is now carried out exactly as described for the present case, but without taking into account the trace of the no longer functional nozzle. One of the target areas 140 is hatched for clarity. It can be seen that the best match would be obtained here with the missing trace. The best approximation is now using the in 4 reaches the track shown below the gap in the tracks, this track even also crossing over the target area 140 in the example shown. The associated inkjet nozzle is controlled by calculating its position and the distance or correspondence of this position to the target area in such a way that a drop is preferably delivered as close as possible to the center of the target area 140 .

Even if a nozzle dropout occurs that has not yet been detected, the method is advantageous because the nozzle dropout appears as a statistical lack of halftone dots and is not readily recognizable as such. Without the movement described, the nozzle failure would be clearly visible as a line.

For the idea of moving the heads or the inkjet nozzles according to the invention, it is advantageous if the position of the nozzles or the print head during droplet ejection is known with an accuracy of <1 μm. This level of accuracy cannot be achieved by positioning using a positioning device (hysteresis).

This accuracy can be ensured by position measurement, for example using linear encoders with appropriate read heads, in that the control device determines and activates the best inkjet nozzle for dispensing drops on a specific target area 140 based on the position measurement. Other options for position detection or precise positioning are also conceivable. Furthermore, an inaccuracy due to temperature expansion, in particular when the fluid and nozzle heads are heated to adjust the viscosity, can be counteracted by positioning a read head at the first and last nozzle of a print head, or more generally by determining their position by means of at least one position sensor 21. In general, the position can be detected by means of a feedback loop.

A further embodiment of the invention, which is suitable for avoiding stripes in the coating pattern as an alternative or in addition to the pendulum movement of the nozzles described above, is described below. This embodiment is based on the use of a plurality of rows of inkjet nozzles which are arranged in a staggered manner along the feed direction.

The use of several rows of inkjet nozzles or also several rows of print heads, which in turn have several nozzles, can pursue other goals in addition to the purpose of generating statistics for nozzle selection along a droplet path on the substrate parallel to the direction of movement of the substrate.

One is to increase the layer thickness or, in the case of ink application, the color depth by overprinting several images. When coating with relief coating applications, the process is suitable for producing high layer thicknesses at higher substrate speeds. The layer thickness can be influenced by several parameters when applied with inkjet nozzles. The droplet size should be mentioned here. The larger the droplets with the same grid width, the greater the layer thickness that can be achieved. In general, without limitation to the specific embodiments, and regardless of whether several rows of nozzles are used, it is therefore provided according to a development of the invention that the inkjet nozzles are controlled by means of a control device in such a way that they emit drops of different sizes, so that the applied amount of fluid is adjusted following a default. In particular, the specification can be stored in a print file, by means of which the control device 13 controls the inkjet nozzles 70 .

With modern print heads, a distinction is made between the native drop and size scaling by multiple drop ejection, in which the individual droplets combine to form a larger drop in flight. The native droplet size can usually only be set within a narrow range for each print head. An extension of the possibilities for controlling commercially available inkjet print heads, which are controlled by piezo actuators, is described, for example, in WO2017/009705 A1 described. According to this method, the native droplet size can be varied within significantly wider limits.

In addition, a print head can only be set within a certain frequency range (droplets per unit of time). The latter property depends on the construction and the type of drop generation. The generation of larger droplets by combining individual droplets according to the method described is therefore at the expense of the possible droplet frequency, since the frequency limitation applies to the individual droplets. through the Possible variations of the individual droplets according to the WO2017/009705 A1 Due to the significantly shorter pulses at the same frequency, it is possible to multiply the droplets in one pulse.

In addition to the droplet size, the grid width can be varied. Usually, the screen ruling in a single-pass machine is defined by the nozzle pitch. No changes can be made here during operation with a fixed geometry.

In the direction of the substrate movement, the droplets can be positioned more closely to achieve greater layer thicknesses (reduction of the screen width in the running direction of the substrate). If only one row of nozzles is used, the application thickness that can be achieved depends on the speed due to the limitation of the droplet ejection frequency.

As a result, higher application thicknesses cause the printing process to slow down. In addition to lower productivity, the achievable minimum line width is also limited because the slowing down of the substrate movement simultaneously results in a longer flow time for the applied layer and the pressure on the edges of the relief structures increases with a higher layer thickness.

Last but not least, in addition to productivity, the quality of the relief coatings that can be achieved is also limited. Even if this can be partially compensated for by the use of pre-curing devices (pinning lamps) located close to the print heads, a higher machine speed is desirable.

As explained above, this disadvantage is compensated for when using several rows of print heads. At the same time, image quality benefits from the use of multiple nozzles per dot, which also helps compensate for banding and nozzle dropouts.

According to one embodiment of the invention, it is accordingly provided that the several rows of inkjet nozzles 70 are staggered along the feed direction 4, or are arranged offset in such a way that target areas the substrate, the extent of which is defined by the area covered by the impinging droplets, are swept over by a plurality of inkjet nozzles 70 . In particular, one inkjet nozzle per row of nozzles can sweep over the respective target area. figure 5 shows an example with two rows of nozzles 73, which are arranged staggered one behind the other in the feed direction 4. The nozzles have the same positions in the direction perpendicular to the feed direction 4 so that they each cover the same target areas on the substrate 3 . As with the in 1 shown embodiment, a movement device 25 can be provided. Provision can be made here for the movement device 25 to move only one of the rows of nozzles or part of the rows of nozzles 73 . In this case, the inkjet nozzles of different rows are shifted relative to each other. However, it is also possible to move all rows of nozzles 73 together, for example by mechanically connecting the rows of nozzles 73 to one another.

If several rows of nozzles 73 are used, the print image can be divided up differently according to statistics or a rule. From simply alternating between rows of nozzles, through a checkerboard pattern, to random or quasi-random patterns. In general, without limitation to the illustrated exemplary embodiments, it is therefore provided in a development of the invention that the target areas are coated along a path swept by a nozzle by several alternating nozzles arranged one behind the other from the different nozzle rows. With this measure, as well as with the pendulum movement of the nozzles described above, streaks in the polymer coating can be suppressed. This embodiment can therefore be provided as an alternative or in addition to the pendulum movement.

• ein Substrat 3 entlang einer Vorschubrichtung 4 mittels einer Fördereinrichtung 5 an einer Auftragsvorrichtung 7 vorbeibewegt wird und
• die Auftragsvorrichtung 7 während der Bewegung des Substrats durch mehrere, in mehreren Düsenreihen quer zur Vorschubrichtung angeordnete Inkjet-Düsen 70 tropfenweise unter Ansprechen auf rechnergesteuerte Schaltsignale ein fluides Auftragsmaterial 9 auf die Oberfläche 30 des Substrats 3 unter Bildung eines fluiden Films 11 in einem Muster 14 mit vorbestimmter Kontur 15, insbesondere unter Aussparung von Bereichen 16 aufträgt, wobei
• hintereinanderfolgend entlang der Vorschubrichtung angeordnete Zielbereiche 140 auf dem Substrat 3 abwechselnd von mehreren in Vorschubrichtung hintereinander angeordneten und damit zu unterschiedlichen Düsenreihen 73 gehörenden Inkjet-Düsen 70 bedruckt werden.

In general, therefore, according to one embodiment of the invention, a method for printing flat substrates is provided in which

• a substrate 3 along a feed direction 4 by means of a Conveyor 5 is moved past an application device 7 and
• During the movement of the substrate, the application device 7 applies a fluid application material 9 drop by drop to the surface 30 of the substrate 3, with the formation of a fluid film 11 in a pattern 14, through a plurality of inkjet nozzles 70 arranged in a plurality of nozzle rows transversely to the feed direction, in response to computer-controlled switching signals applied a predetermined contour 15, in particular with the omission of areas 16, wherein
• target areas 140 arranged one after the other along the feed direction on the substrate 3 are alternately printed by a plurality of inkjet nozzles 70 arranged one behind the other in the feed direction and thus belonging to different rows 73 of nozzles.

In the case of a curable organic fluid coating material for the production of polymeric coatings according to the invention, the film 11 is cured to form a solid polymeric coating 12 after application.

the 6 and 7 12 show two examples of coating patterns 14 for clarification. The coating patterns 14 are divided into an arrangement of target areas 140 corresponding to a pixel representation. These are lined up one behind the other along the transport direction 4. If there is no pendulum movement of the inkjet nozzles 70, then the paths 72 of the nozzles are collinear with the transport direction. The target areas 140 coated by the inkjet nozzles of a specific nozzle row 73 are each shown with the same hatching. At the in 6 example shown alternate progressively in a row along the transport direction 4 from three different hatchings. Thus, three nozzles, each from a different row of nozzles, are operated sequentially.

At the in 7 In the example shown, an alternating, sequential operation of two rows of nozzles follows a checkerboard pattern. In each case two inkjet nozzles 70 of one of the rows of nozzles are operated together, the two adjacent inkjet nozzles of the row of nozzles are suspended. Not for this one operated nozzles, two inkjet nozzles 70 of the next nozzle row 73 step in. This pattern alternates after two successive target areas along the transport direction 4, so that the inkjet nozzles 70 that were previously not activated are now operated.

An arrangement for position determination, as the example of 1 according to a further aspect, can also be used for self-adjustment of the print heads. The general idea is that when at least one position determination per print head is used, a plurality of print heads can be roughly arranged in relation to one another and a calibration is carried out with knowledge of the position data.

8 10 shows an example of an arrangement for carrying out this embodiment for clarification. The inkjet nozzles 70 are integrated in print heads 75 in the usual way. These print heads 75 are fixed next to one another transversely to the feed direction 7 of the device 1 on a holder 32 . Due to tolerances, the actual position can deviate slightly from the intended position. A position shift transverse to the feed direction 4 is particularly critical here, since this in turn can lead to the formation of visible stripes in the polymer coating. The representation is purely schematic. Thus, the print heads 75 can be arranged in two rows one behind the other, in a different way than shown, in order to keep the nozzle spacing between the nozzles of two heads transverse to the feed direction exactly the same as the spacing between adjacent nozzles within a print head. Similarly, an arrangement of the rows of nozzles in a herringbone pattern is also possible.

The print heads 75 are now each assigned position sensors 21 which precisely determine the position of the print head. For example, position markings 77 can be provided for position determination. For clarification, the print head shown on the far right is attached slightly laterally shifted, so that the directional arrow drawn from Position sensor 21 to mark 77 runs slightly obliquely. According to one embodiment of the invention, the interaction of these heads for a print image is now achieved through the combination of knowledge of the position and by measuring a specific print image. For this purpose, it is provided that a print image generated with the print heads 77 is recorded, in particular scanned, deviations from the target image are determined, position changes for the print heads 77 are determined from the deviations and the positions of the print heads are changed by means of an adjusting device 78 until the position sensors 21 measured positions match the determined changes in position.

Furthermore, a very advantageous modular and low-maintenance construction can be achieved with the position sensors.

If the print heads 77 of a printing unit are equipped with a position detector, the arrangement can be made roughly as described above and the mutual alignment can be put into operation very quickly by using the exact position and calculating the interaction for a consistent printed image. For this purpose, according to one embodiment of the invention, the nozzle positions determined from a test print are used as a basis for assigning each nozzle to a specific position for the print. In the case of overlaps, either a redundant nozzle is not used or a pattern is assigned according to which the redundant nozzles are used alternately. With such an arrangement, larger gaps between the nozzles, for example due to a larger distance between two print heads 77 and thus the distance between the adjacent nozzles of the print heads, should be avoided as far as possible, since these gaps are only statistically reduced by the movement of the nozzle rows described above, but possibly cannot be completely hidden.

Today, this can only be achieved using complex mechanical solutions, in which the print heads are either passively aligned with corresponding positioning pins or actively, by installing mechanical or electronic adjustment options for lateral displacement and angle. The positioning usually takes place via a test image and subsequent successive adjustment of the individual head positions.

In order to avoid gaps between the individual print heads and thus larger distances between the outer nozzles of adjacent print heads, it is generally favorable to arrange the print heads 75 in several rows, with the print heads 75 overlapping transversely to the feed direction 4 . As a result, the outer inkjet nozzles 70 of adjacent print heads 75 are spaced apart in the direction along the feed direction 4, but can be positioned arbitrarily with respect to one another, seen in the feed direction 4, in particular with a uniform spacing. 9 shows such an arrangement with two rows of print heads 75 staggered one behind the other in the feed direction 4.

If the mechanical accuracy can be dispensed with by measuring afterwards, the costs and effort are significantly lower. If each print head then has its own electronic control and its own liquid supply (piggyback tank), any complex printing units can be built relatively easily.

For this purpose, according to one embodiment, it is provided that the print heads 77 are equipped with an actuating device along a direction transverse to the transport direction 4 with position detection, a power supply, preferably a fluid supply (e.g. a hose connection with hydrostatic fluid pressure or a separate pump with a connection to a reservoir) and a network connection to the Connection to the control device 13 are provided. As in 8 shown, it is favorable here if the position sensors 21 are part of the print heads 77.

• einer Auftragsvorrichtung 7,
• einer Steuereinrichtung 13 und
• einer Fördereinrichtung 5 vorgesehen, um ein Substrat 3 entlang einer Vorschubrichtung 4 an der Auftragsvorrichtung 7 vorbeizubewegen, wobei
• die Auftragsvorrichtung 7 mehrere, in einer Reihe quer zur Vorschubrichtung angeordnete Druckköpfe 77, jeweils mit mehreren Inkjet-Düsen 70 umfasst, und
• die Steuereinrichtung 13 zur Erzeugung rechnergesteuerter Schaltsignale eingerichtet ist, mittels derer die Inkjet-Düsen 70 tropfenweise ein fluides Auftragsmaterial 9 abgeben, wobei
• die Steuereinrichtung 13 weiterhin eingerichtet ist, die Inkjet-Düsen derart anzusteuern, dass auf der Oberfläche 30 eines vorbeibewegten Substrats 3 ein fluider Film 11 des Auftragsmaterials in Form eines Musters 14 mit vorbestimmter Kontur 15, insbesondere unter Aussparung von Bereichen 16 aufgetragen wird, wobei die Druckköpfe 77 jeweils als Einheit mit einem Positionssensor 21, einer Fluidversorgungseinrichtung zur Versorgung der Inkjet-Düsen 70 mit dem fluiden Auftragsmaterial 9, einer rechnergesteuert, insbesondere mittels der Steuereinrichtung 13 verstellbaren Stelleinrichtung 78 zur Einstellung der Position des Druckkopfs quer zur Vorschubrichtung, sowie einem Anschluss, vorzugsweise einem Netzwerkanschluss zur Verbindung mit der Steuerungseinrichtung 13 ausgebildet sind.

In summary, according to this embodiment of the invention, a device 1 for printing flat substrates with

• an application device 7,
• a control device 13 and
• a conveyor 5 is provided to move a substrate 3 along a feed direction 4 past the application device 7, wherein
• the application device 7 comprises a plurality of print heads 77 arranged in a row transversely to the feed direction, each with a plurality of inkjet nozzles 70, and
• the control device 13 is set up to generate computer-controlled switching signals, by means of which the inkjet nozzles 70 emit a fluid coating material 9 drop by drop, wherein
• the control device 13 is also set up to control the inkjet nozzles in such a way that a fluid film 11 of the application material is applied to the surface 30 of a substrate 3 moving past in the form of a pattern 14 with a predetermined contour 15, in particular with areas 16 left out, wherein the Print heads 77 each as a unit with a position sensor 21, a fluid supply device for supplying the inkjet nozzles 70 with the fluid application material 9, a computer-controlled adjusting device 78, which can be adjusted in particular by means of the control device 13, for setting the position of the print head transversely to the feed direction, and a connection preferably a network connection for connection to the control device 13 are formed.

If the device 2 is designed according to the invention to produce polymer coatings using a fluid organic coating material, the device 1 has a curing device 23 in order to cure the fluid film 11 into a solid polymer coating 12 after application. The adjustment of the print head position does not have to be done by means of a printed image. In general, the embodiment described above can initially be used to set the arrangement of the print heads 77 relative to one another as precisely as possible, even if there are inaccuracies during assembly. The inaccuracies are caused by the adjusting devices compensated based on the measured position data. This adjustment can be made by the control device 13, but optionally also by a computing device in the print head 77. Furthermore, the positional data need not necessarily reflect positions relative to a fixture. According to a development of the invention, it is provided that the position sensors 21 are set up to determine positions relative to other print heads. In this way, an exact alignment of the print heads 77 with one another can be achieved by adjustment.

In a further development of the invention, the inkjet nozzles can also be actuated taking into account the measured position. Print data or control signals for the inkjet nozzles 70 can then be corrected even if the position of the print head does not exactly match the intended position.

10 shows a schematic of a test image 35 on a substrate 3, on the basis of which the control signals of the nozzles are corrected or adjusted in order to obtain a printed image that is as uniform as possible. The test image 35 can be used as in 10 shown are formed from lines 37 printed by individual nozzles. The target positions 38 of the lines 37 are in 10 shown as dashed lines. In order to prevent the lines 37 from being too close to one another or even running into one another, the lines of adjacent nozzles can be applied offset to one another along the feed direction, as shown.

As described above, the print image produced can be recorded, for example, by scanning or photographing the test image 35 . Then deviations from the target image are determined. Changes in position for the print heads can then be determined from the deviations and the positions of the print heads can be changed by means of an adjusting device 78 until the positions measured by position sensors 21 match the determined changes in position. According to an alternative or additional embodiment, given the positions of Printheads can also select nozzles based on proximity to target position. For example, if two nozzles are in the same position, either a nozzle can be selected or a pattern for alternating nozzles can be specified as described in the text. The triggering times of the nozzles can also be adjusted so that the droplets are emitted by the nozzles as close as possible to the respective desired position 38 .

The invention can generally be implemented in a particularly advantageous manner with a modular structure. With such a modular structure, printing modules 81 are connected to form an application device 7 . The application device 7 contains all of the print heads of a printing device 1 according to the invention.

The pressure modules 81 can be fastened next to one another on a traverse or axle 82, in particular by means of suitable axle attachments 83. At the in 11 example shown are the modules 81 according to the example of FIG 9 arranged in two rows. For this purpose, the printing modules 81 are mounted on two axes 82 positioned one behind the other in the feed direction 4 .

The print modules 81 each include at least one print head 75. In order to carry out the method described above with the correction of the print image, each module can be equipped with a position sensor 21. According to a simple embodiment, the position sensor can measure a relative displacement, for example by the sensor measuring the distance to the adjacent printing module 81 . It is also possible to provide one or more position markings. Thus, an encoder ruler can be present as a position marker, which extends along the axis 82 .

Furthermore, a print module 81 can include control electronics 84, which control the print head 75, and possibly others Tasks such as communication with a higher-level control device 13 and/or position correction calculations can be carried out.

A print module 81 has an electronic interface 85 at least for the transmission of the print data. The energy supply can also be provided via the interface.

Furthermore, connections for supplying the tank with the fluid to be applied, possibly also a connection for supplying the tank with a regulated negative pressure, can be provided.

It is preferred if, as in the example shown, the pressure modules 81 are connected to one another with connecting lines. In the example, the connecting lines are each drawn between the interfaces 85 of adjacent modules 81 . It is also possible to connect the print modules to a common bus.

The pressure modules 81 can be roughly aligned with one another on the axis 82 . By printing a nozzle test pattern and digitally capturing the pattern, the positions of the print heads 75 relative to one another can be determined and the structure of the print image can be defined on the basis of the determined positions. The nozzle rows of the print heads should preferably fit together at least without a gap, but ideally a certain overlap is set and the redundant nozzles are operated selectively using a control pattern. The advantage of this type of calibration is that the mechanical alignment of the heads to each other, as explained above, does not have to be in the range of the usual tolerances.

The alignment of the print image can be controlled by the position sensors 21 to match the head movement to avoid streaks. Also can Unfavorable head positions (e.g. with 1.5 times the nozzle spacing) can be corrected in a targeted manner. The latter can also be done electronically.

A clear advantage results from the possibility to calibrate the pressure unit at the operating temperature.

In order to realize the back and forth movement of the print heads 75 to avoid streaks, adjusting devices 78 can be integrated in the print modules 81, which can move the print head 75 relative to the print module and transversely to the feed direction.

The modular design of the application device 7 described above is particularly advantageous in order to be able to easily expand a printing device. For example, in order to achieve a desired print width, a corresponding number of print modules can be mounted on one or more axes and connected to one another. The lateral adjustment of the print heads then takes place, for example, with the aid of a test image and/or also by evaluating the data from the position sensors.

• eine Auftragsvorrichtung 7,
• eine Steuereinrichtung 13 und
• eine Fördereinrichtung 5 aufweist, um ein Substrat 3 entlang einer Vorschubrichtung 4 an der Auftragsvorrichtung 7 vorbeizubewegen, wobei die Auftragsvorrichtung 7 mehrere in Richtung quer zur Vorschubrichtung 4 versetzt auf mindestens einer Achse 82 lösbar befestigte Druckmodule 81 mit jeweils mindestens einem Druckkopf 75 aufweist, wobei die Druckmodule 81 jeweils einen Tank, eine Ansteuerelektronik 84 und eine Schnittstelle 85 aufweisen, wobei die Druckmodule 81 mittels deren Schnittstellen zum Austausch von Daten aneinander koppelbar sind, und

wobei die Druckbreite der Vorrichtung 1 anpassbar ist, indem Druckmodule 81 an der Achse 82 befestigt und über deren Schnittstelle 85 mit der in Fig. 1 nicht dargestellten Steuereinrichtung 13 verbunden werden.Without being restricted to the specific example shown, the invention also provides a device 1 for printing flat substrates, which

• an application device 7,
• a controller 13 and
• has a conveyor device 5 in order to move a substrate 3 past the application device 7 in a feed direction 4, wherein the application device 7 has a plurality of printing modules 81 which are offset in a direction transverse to the feed direction 4 and are detachably attached on at least one axis 82, each with at least one print head 75, the Print modules 81 each have a tank, control electronics 84 and an interface 85, the print modules 81 being able to be coupled to one another by means of their interfaces for exchanging data, and

wherein the print width of the device 1 is adjustable by attaching print modules 81 to the axis 82 and connecting them via their interface 85 to the in 1 not shown control device 13 are connected.

According to the invention, the reciprocating movement of the print heads is also implemented in the modular design of the device described above. It is precisely in this way that mechanical inaccuracies when mounting the modules on the axis can be compensated. In order to realize the movement, an adjusting device 78 can be provided on the axle or axles 82 . However, it is also advantageous if the modules 81 each have such adjusting devices 78 . This simplifies the mechanics of the application device. Above all, however, an adjusting device 78 integrated in the module 81 enables different movements of the print heads 75 of the modules 81 to be carried out.

Reference List

Polymer coating device 1 substrate 3 feed direction 4 conveyor 5 tank 6 application device 7 order material 9 fluid film 11 control device 13 sample 14 Solid polymer coating 12 contour of 14 15 Recessed Area 16 print image 18 contour of 18 19 position sensor 21 curing device 23 moving device 25 magazine 27, 28 surface of 3 30 bracket 32 35 test pattern 37 Printed line 38 target position of 37 inkjet nozzle 70 drops 71 Path from 70 72 row of nozzles 73 printhead 75 position marker 77 adjusting device 78 pressure module 81 axis 82 axle attachment 83 control electronics 84 interface 85 connection line 86 target area 140 best matching point of 72 with 140 141

Claims (12)

1. A method for printing sheet-like substrates, wherein

   - a substrate (3) is moved past an application device (7) along a feed direction (4), by a conveyor device (5); and

   - while the substrate is moved, the application device (7) applies, drop by drop, a fluid application material (9) onto the surface (30) of the substrate (3) in a pattern (14) with a predetermined contour (15), in particular by sparing areas (16), using a plurality of inkjet nozzles (70) that are arranged in a line transverse to the feed direction, in response to computer-controlled switching signals; wherein

   - while the pattern (14) is applied and the substrate (3) is moved, the inkjet nozzles (70) are reciprocated in the direction transverse to the feed direction (4), preferably along the longitudinal extension of the line array of the inkjet nozzles (70), so that the paths (72) the nozzles (70) cover over the substrate have directional components perpendicular to the feed direction (4), due to the superposition of the reciprocating movement with the movement along the feed direction (4);

   wherein a fluid organic coating material is applied as the fluid application material, and wherein, once applied, the film (11) is cured to form a solid polymer coating (12); and wherein an amplitude of the movement of the inkjet nozzles (70) transverse to the feed direction (4) is not greater than five times the nozzle spacing and is at least equal to a single nozzle spacing as measured from the centre of one inkjet nozzle (70) to the centre of an adjacent inkjet nozzle (70); and

   wherein the coating pattern (14) is defined by an array of adjacent target areas (140), wherein a computer (19) determines which one of the inkjet nozzles (70) comes closest to or best matches a target area (140) during the movement of the substrate (3) on the one hand and the periodic movement of the inkjet nozzles (70) on the other hand, and sends a control signal to this inkjet nozzle (70) so that the nozzle (70) dispenses a drop (71) of the fluid organic coating material (9) to said determined point (141) closest to or best matching the target area (140).
2. The method according to the preceding claim, wherein the position of the inkjet nozzles (70) in the direction in which the inkjet nozzles (70) are reciprocated by the movement device (25) is measured by at least one position sensor (21).
3. The method according to claim 1, characterized in that a substrate (3) provided with a printed image (18) is provided with the polymer coating in such a way that the printed image (18) corresponds to the pattern (14) of the coating (12), in particular such that the contours (15, 19) of the printed image (18) and the pattern (14) extend at least partially parallel, preferably congruent.
4. The method according to any one of the preceding claims, characterized in that the inkjet nozzles are controlled by a control device so as to dispense drops (71) of different sizes, so that the layer thickness is adjusted according to a template, wherein the template is in particular stored in a print file which is used by the control device (13) to control the inkjet nozzles (70).
5. The method according to any one of the preceding claims, characterized in that target areas that are successively arranged along the feed direction (4) are alternately printed by a plurality of inkjet nozzles (70) that are successively arranged in the feed direction.
6. The method according to any one of the preceding claims, characterized in that the inkjet nozzles (70) are integrated in a plurality of print heads (77), each of the print heads (77) having associated therewith a position sensor (21); and wherein

   - a print image generated by the print heads (77) is captured, in particular scanned;

   - deviations from the target image are identified;

   - based on the deviations, changes in position are determined for the print heads (77); and

   - the positions of the print heads are changed by an actuator (78) until the positions measured by the position sensors (21) match the determined position changes.
7. An apparatus (1) for printing sheet-like substrates, comprising

   - an application device (7);

   - a control device (13); and

   - a conveyor device (5) for moving a substrate (3) along a feed direction (4) past the application device (7); wherein

   - the application device (7) comprises a plurality of inkjet nozzles (70) arranged in a line transverse to the feed direction; and

   - the control device (13) is configured for generating computer-controlled switching signals based on which the inkjet nozzles (70) dispense a fluid application material (9), drop by drop; wherein

   - the control device (13) is furthermore configured for controlling the inkjet nozzles such that a fluid film (11) of the application material in the form of a pattern (14) with a predetermined contour (15), in particular with spared areas (16), is applied to the surface (30) of a substrate (3) moving past; wherein

   - a movement device (25) is provided for moving the inkjet nozzles (70) so as to reciprocate the inkjet nozzles (70) in the direction transverse to the feed direction (4), preferably along the longitudinal extension of the line array of the inkjet nozzles (70), so that the paths (72) the nozzles (70) cover over the substrate have directional components perpendicular to the feed direction (4) due to the superposition of the periodic reciprocating movement with the movement along the feed direction (4); wherein

   an amplitude of the movement of the inkjet nozzles (70) transverse to the feed direction (4) is not greater than five times the nozzle spacing and is at least equal to a single nozzle spacing as measured from the centre of one inkjet nozzle (70) to the centre of an adjacent inkjet nozzle (70); and

   comprising a curing device (23) for curing the fluid film (11), once applied, to form a solid polymer coating (12); and wherein

   the apparatus is adapted to define the coating pattern (14) by an array of adjacent target areas (140), wherein a computer (19) determines which one of the inkjet nozzles (70) comes closest to or best matches a target area (140) during the movement of the substrate (3) on the one hand and the periodic movement of the inkjet nozzles (70) on the other hand, and sends a control signal to this inkjet nozzle (70) so that the nozzle (70) dispenses a drop (71) of the fluid organic coating material (9) to said determined point (141) closest to or best matching the target area (140).
8. The apparatus according to the preceding claim, characterized by at least one position sensor (21) measuring the position of the inkjet nozzles (70) in the direction in which the inkjet nozzles (70) are reciprocated by the movement device (25).
9. The apparatus according to any one of the preceding claims, characterized by a plurality of lines of inkjet nozzles (70), which are staggered along the feed direction (4).
10. The apparatus according to any one of the preceding claims, characterized in that the control device (13) is adapted to control the inkjet nozzles (70) so as to dispense drops (71) of different sizes, so that the amount of applied fluid is adjusted according to a template, in particular by the control device being adapted to control the inkjet nozzles (70) using a print file in which the template is saved.
11. The apparatus according to any one of the preceding claims, characterized by a plurality of print heads each one having a plurality of inkjet nozzles (70), wherein each of the print heads (77), as a unit, includes a position sensor (21), a fluid supply device for feeding the fluid application material (9) to the inkjet nozzles (70), a computer-controlled actuator (78) that is adjustable in particular by the control device (13) for adjusting the position of the print head transverse to the feed direction, and a connection, preferably a network connection for providing a link to the control device (13).
12. The apparatus (1) according to any one of the preceding claims, wherein the application device (7) comprises a plurality of printing modules (81) that are releasably mounted on at least one shaft (82) so as to be offset in the direction transverse to the feed direction (4), each one having at least one print head (75), the printing modules (81) each having a tank, control electronics (84) and an interface (85), wherein the printing modules (81) can be coupled to one another for data exchange through their interfaces (85), wherein, preferably, the apparatus is adapted for an extension of the printing width by mounting one or more printing modules (81) on the shaft (82) and connecting them to the control device (13) via the interface (85) thereof.

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