Cleaning procedure for cleaning nozzle surfaces of an array of inkjet heads

Description

[0001] The invention relates to a method for cleaning nozzle surfaces of an arrangement of inkjet print heads having the features of the preamble of claim 1. field of technology

[0002] The invention lies in the technical field of the graphic arts industry, and therein in particular in the field of industrial, i.e., highly productive and high-quality inkjet printing on flat substrates, i.e., the image-wise application of extremely fine drops of liquid ink onto sheet-, web-, foil-, or label-shaped printing materials, preferably made of paper, cardboard, paperboard, plastic, metal, or composite material. In particular, the invention lies in the sub-field of cleaning the print heads or the sensitive nozzle surfaces. State of the art

[0003] DE 10 2020 105 736 A1 discloses an inkjet printhead cleaning process using ultrasound. A cleaning fluid subjected to ultrasonic vibrations is applied from a cleaning tray to the nozzle surface of a printhead of a print bar, flows through a gap between the cleaning tray and the printhead, and is collected in a collecting tray. Relative movement can be generated by moving the printheads along the cleaning tray. Furthermore, "purging"—i.e., ejecting and injecting cleaning fluid—is possible during cleaning.

[0004] The problem that can arise is that cleaning fluid and contaminants get into the print heads.

[0005] US 5,574,485 discloses a cleaning method for cleaning nozzle surfaces of an array of inkjet print heads, wherein a cleaning carriage moves along the array and cleans the nozzle surfaces with a cleaning fluid subjected to ultrasonic vibrations. The document does not disclose that different processes occur on an outward and a return path of the movement, or that any components could be deactivated. An ultrasonic cleaning device and two suction devices are activated on both paths, with the suction devices being arranged upstream and downstream of the ultrasonic cleaning device in the direction of movement. A rinsing device, as a third device besides the ultrasonic cleaning device and suction device, is not disclosed.

[0006] US 2022 / 008893 A1 discloses a similar method with two similar devices and does not come any closer to the invention than US 5,574,485. This document also does not disclose that different processes take place on the outward and return paths of the movement, or that any components could be deactivated. Technical task

[0007] It is therefore an object of the present invention to provide an improvement over the prior art which makes it possible, in particular, to prevent the penetration of cleaning fluid together with contaminants into the interior of print heads or into their ink supply system.

[0008] In particular, it is important to prevent cleaning fluid from getting into the nozzles and contaminating the ink there, as this can lead to the problem that the contaminated ink does not cure or does not cure correctly and the ink has to be replaced. Inventive solution to the problem

[0009] This object is achieved according to the invention by a method according to claim 1.

[0010] Advantageous and therefore preferred developments of the invention emerge from the subclaims as well as from the description and the drawings.

[0011] A cleaning method according to the invention for cleaning nozzle surfaces of a lateral arrangement of inkjet print heads, i.e. an arrangement extending over the width of a printing material to be printed, wherein a cleaning carriage also carries out a lateral movement along the arrangement and cleans the nozzle surfaces with a cleaning fluid subjected to ultrasonic vibrations, is characterized in that the cleaning carriage comprises an ultrasonic cleaning device, a suction device and a rinsing device and the movement of the cleaning carriage takes place on an outward path and a return path, and that on the outward path the ultrasonic cleaning device and the suction device following it are activated and the rinsing device following the two is deactivated and that on the return path the

[0012] The rinsing device and the suction device following it are activated and the ultrasonic cleaning device following the two is deactivated. Advantageous embodiments and effects of the invention

[0013] The respective method according to the invention advantageously makes it possible to prevent the penetration of cleaning fluid including contaminants into the interior of print heads or into their ink supply system.

[0014] The inventive suctioning of the cleaning fluid of the ultrasonic cleaning device prevents this fluid and any possible contaminants carried along with it from passing through the nozzle openings into the print heads and from there into the ink supply system and becoming distributed there. The suctioning therefore preferably takes place directly after cleaning with ultrasound, i.e. at a very short spatial and therefore also temporal interval. The spatial distance (between the adjacent walls of the ultrasonic cleaning device and the suction device or between the respective centers of the two devices) is preferably a few millimeters to a few centimeters, e.g. less than 5 cm or less than 3 cm or less than 1 cm. The same applies to the interaction of the suction device and the rinsing device, if provided, and the distances between them.

[0015] The "arrangement of inkjet print heads" can also be referred to as a so-called print bar. A print bar extends laterally across the entire width of the substrate to be printed. In multi-color printing, several print bars can be arranged one after the other in the direction of transport of the substrate. The print bars with the print heads are preferably arranged laterally immobile in an inkjet printing press. The relative movement for cleaning is generated by the lateral movement of the cleaning carriage. Further developments of the invention

[0016] In the following, preferred developments of the invention are described as methods (short: developments).

[0017] A further development can be characterized in that the activated ultrasonic cleaning device releases the cleaning fluid, in particular upwards.

[0018] A further development can be characterized in that the cleaning fluid is dispensed from a chamber that is open to the inkjet print heads.

[0019] A further development can be characterized by the fact that the cleaning fluid is released from the chamber as a splash bath.

[0020] A further development can be characterized by the discharge as a surge bath, overflowing over a wall leading in the outward direction and another wall trailing in the outward direction. Overflow over side walls can also be provided.

[0021] A further development can be characterized by collecting overflowing cleaning fluid in the surge bath and either draining / disposing of it or returning it to the chamber. A pump can be used for this purpose.

[0022] A further development can be characterized in that the collection takes place in a collection channel that runs adjacent to the wall and the other wall and is preferably open at the top.

[0023] A further development can be characterized in that an activatable and deactivatable ultrasonic source arranged on or in the chamber causes the cleaning fluid to vibrate ultrasonically. The ultrasonic source is preferably located at the bottom of the chamber.

[0024] A further development can be characterized in that the activated flushing device releases a flushing liquid, preferably upwards.

[0025] A further development can be characterized in that the rinsing fluid is dispensed from a further chamber that is open to the inkjet print heads and is different from the chamber. The further chamber can be provided as an open channel. The further chamber is preferably smaller than the chamber (in terms of the fluid volume contained). The chamber and the further chamber preferably extend transversely / laterally across the array of print heads or at least transversely across the section of the nozzle surfaces that needs to be cleaned.

[0026] A further development can be characterized by the fact that the cleaning fluid and the rinsing fluid are identical. Both can preferably be supplied from a common reservoir, meaning only one fluid can be used. One or two pumps can be provided for this purpose.

[0027] A further development can be characterized by the fact that on the outward path the suction device sucks in air and thereby sucks in cleaning fluid and contamination from the nozzle surfaces.

[0028] A further development can be characterized in that on the return path the suction device sucks in air and / or the rinsing liquid of the rinsing device and thereby sucks in cleaning liquid and contamination from the nozzle surfaces.

[0029] A further development can be characterized in that the suction is carried out through a suction channel of the suction device formed in the cleaning carriage, with a suction opening open toward the inkjet print heads. This channel is preferably at least as long as the chamber and the additional chamber in the transverse direction to the arrangement of the print heads.

[0030] A further development can be characterized in that the extracted cleaning liquid and / or rinsing liquid is led to a liquid separator.

[0031] A further development can be characterized in that the extracted cleaning liquid and / or rinsing liquid is fed back to the ultrasonic cleaning device or the rinsing device via a return channel.

[0032] A further development can be characterized by the fact that the extracted cleaning liquid or rinsing liquid is led to a waste container.

[0033] A further development can be characterized in that an adapter for the ultrasonic cleaning device is provided in front of the first inkjet print head of the arrangement and that the ultrasonic cleaning device is moved towards the adapter and filled there with cleaning fluid, preferably completely filled.

[0034] A further development can be characterized in that after the last ink print head of the arrangement, a further adapter for the ultrasonic cleaning device is provided and that the ultrasonic cleaning device is moved towards the further adapter and emptied of cleaning fluid there, preferably completely emptied.

[0035] The adapters can preferably be provided as suitable covers for the ultrasonic cleaning device or its chamber.

[0036] A further development can be characterized by the fact that the cleaning carriage is provided on a horizontally movable cleaning drawer.

[0037] A further development can be characterized by the fact that the cleaning carriage is moved with the cleaning drawer, preferably from a parked position of the drawer. A further development can be characterized by the fact that the cleaning drawer is moved horizontally beneath the array of inkjet print heads.

[0038] A further development can be characterized by the fact that a roller table intended for transporting the printing material is lowered.

[0039] A further development can be characterized by the fact that the cleaning drawer is moved into the space created by the lowering.

[0040] A further development can be characterized in that the cleaning carriage is provided as part of a cleaning box with a tub, wherein the cleaning box is provided on the cleaning drawer.

[0041] A further development can be characterized by the fact that when the cleaning carriage stops between its outward and return travel, the inkjet print heads eject ink into a tray in the cleaning box ("purging").

[0042] A further development can be characterized by providing several cleaning boxes on the cleaning drawer, each with a tub and a cleaning carriage that can be moved relative to and along the box. Preferably, all cleaning carriages are moved together.

[0043] A further development can be characterized by providing a corresponding number of cleaning boxes for the simultaneous cleaning of multiple inkjet print head arrangements. For example, four (for CMYK), seven (for CMYK+OGV), or eight (for CMYK+OGV+white) cleaning boxes can be provided for the corresponding number of inks in multi-color printing.

[0044] A further development can be characterized by the cleaning carriage being spring-loaded against the cleaning box. This allows the cleaning carriage to be spring-loaded against the print heads and guided along them (while avoiding contact with the nozzle surfaces). A clearance accuracy of + / - 0.02 mm can be maintained. During cleaning and rinsing, the carriage preferably moves at a speed of 20 to 80 mm / s on the outward and reciprocating travels.

[0045] A further development can be characterized by maintaining a predetermined distance between the ultrasonic cleaning device, the suction device, and the rinsing device on the one hand, and the nozzle surfaces on the other. This can prevent damage to the sensitive nozzle surfaces.

[0046] A further development can be characterized by the fact that the cleaning drawer is motor-driven.

[0047] A further development can be characterized by the fact that a motor is provided for the motor drive.

[0048] A further development can be characterized by the fact that the cleaning process is carried out in an inkjet printing machine.

[0049] A further development can be characterized in that an arrangement of inkjet print heads is cleaned by means of one cleaning box.

[0050] A further development can be characterized in that several parallel arrangements of inkjet print heads are cleaned by means of several parallel moving cleaning carriages.

[0051] A further development can be characterized by the fact that several cleaning carriages are moved together.

[0052] A further development can be characterized in that a cleaning drawer with several cleaning boxes is moved motor-driven and horizontally from a lateral parking position - to the transport direction of a printing material - into a cleaning position, that in the cleaning position several cleaning carriages are moved together along a corresponding number of printing bars horizontally for cleaning and horizontally back for rinsing, whereby an ultrasound source is activated during cleaning and that the cleaning drawer is finally moved back into the parking position.

[0053] The features and combinations of features disclosed in the above sections Technical Field, Invention and Further Developments as well as in the following section Exemplary Embodiments represent - in any desired combination with one another - further advantageous developments of the invention. Embodiments of the invention and figures

[0054] The Figures 1 to 3show a preferred embodiment of the invention and the further developments. Corresponding features are provided with the same reference numerals in the figures. Figures 1 to 3 show a device carrying out a preferred embodiment of a cleaning method according to the invention.

[0055] An inkjet printing machine 10 for industrial, i.e., highly productive and high-quality inkjet printing, preferably for printing on web-like substrates, e.g., paper or label material, comprises at least one arrangement 11 (or a so-called print bar) oriented transversely to the substrate or its transport direction, of several inkjet print heads 12, preferably arranged in a row, directed downwards, and stationary during printing. Each print head 12 has a nozzle surface 13 with a plurality of nozzles 14 for the controlled ejection of ink 15 in the form of individual, extremely fine droplets, in accordance with the image information to be printed. These nozzle surfaces are very sensitive and must therefore be carefully cleaned of possible contaminants 16, such as hardened ink 15 and / or (e.g., paper) dust.

[0056] The device preferably comprises a plurality of elongated cleaning boxes 21 arranged parallel to one another and preferably jointly movable horizontally, parallel to the print bars (to their longitudinal extent). All boxes 21 can preferably be arranged on a horizontally movable cleaning drawer 20 and can be moved together with it in the forward direction 71 and the forward direction 72. By way of example, in the Figures 1 and 2 only one box 21 shown in section from the side; in the Figure 3 two.

[0057] The drawer 20 is preferably motor-driven and can be moved back and forth in the above-mentioned transverse direction between a cleaning position and a parking position. During printing, the drawer is retracted into the parking position, and the nozzle surfaces are exposed above the substrate transported underneath. The cleaning boxes 21 each comprise an upwardly open tray 22 for the so-called purging of the print heads 12 and a cleaning carriage 23 that can be moved back and forth upwards for cleaning and rinsing the nozzle surfaces 13 and / or the nozzles 14. Figure 1the carriage 23 is shown in a cleaning position 24, i.e. it is located a short distance below the nozzle surfaces 13. The cleaning carriage can be moved back and forth along the nozzle surfaces (when the drawer 20 is in its cleaning position). This movement can be motor-driven, e.g. by means of a motor with a belt drive (not shown). The forward movement (preferably in the direction of the operating side BS of the machine) is used for cleaning, while the backward or forward movement (preferably in the direction of the drive side AS of the machine) is used for rinsing after cleaning. The cleaning carriage is preferably positioned and movable at a short distance 25 from the nozzle surface. The gap created by the distance between the carriage and the nozzle surfaces prevents direct contact between the two and thus possible damage to the nozzle surfaces. In addition, the gap serves to absorb liquid for cleaning and / or rinsing.

[0058] The cleaning carriage 23 comprises three devices: an ultrasonic cleaning device 30, a suction device 40, and a rinsing device 50. These devices can be provided in a common block of the carriage. Device 30 operates with a cleaning fluid 60; device 50 with a rinsing fluid 61.

[0059] Figure 2 shows the same device as Figure 1, albeit less detailed. It can be seen, however, that the print bar 11 shown has an adapter 17 and a further adapter 18 at the beginning and end of the row of print heads 12. The two adapters have respective adapter surfaces that lie in the same plane as the nozzle surfaces 13. The adapters can be designed as blocks made of aluminum. In this way, the adapters can be used for processes that could load, contaminate, or damage the print heads. The adapter 17 or its adapter surface serves, for example, to close the device 30 when it is being filled with cleaning fluid, although a gap remains between the adapter 17 and the device 30 (similar to the gap between the print heads 12 and the device 30); in contrast, the further adapter 18 or its adapter surface serves, for example, to regulate the device 40 or the negative pressure required for suction in the device 40.Filling and emptying therefore preferably does not take place adjacent to a print head 12, but rather at the adapters. After filling, an ultrasound source and the suction system are activated (see below), and the cleaning carriage 23 preferably moves once beneath the nozzle surfaces (cleaning pass; outward pass). This is followed by optional purging, i.e. the print heads eject ink into the tray 22 to force any cleaner residue out of the print heads. To rid the print heads and their nozzle surfaces of any ink residue, a final rinsing pass (return pass) with the addition of rinsing fluid is carried out (see also below). It is of course also possible to perform the cleaning pass and the rinsing pass in the other direction, provided that only cleaning and rinsing are carried out first.

[0060] In the Figures 2 and 3A side wall 19 of the printing press 10 can also be seen (on the drive side AS of the press); the drawer 20 is preferably moved back and forth through an opening 19a in the side wall (or parts, e.g., laterally extending supports of the drawer, are moved through corresponding openings 19a). The parking position is preferably located behind the side wall (and the print heads and the transport path for the printing substrate are in front of the side wall). The movement is preferably carried out by means of a motor 26, which drives the drawer.

[0061] In Figure 1an activatable ultrasound source 31 is shown at the bottom of a chamber 32 for dispensing cleaning fluid 60. The device 30 forms a surge bath 33 with a respective overflow 34 over a leading wall 35 (on the outward path) and a further trailing wall 36 (on the outward path). The cleaning fluid is subjected to ultrasonic vibrations during cleaning or on the outward path and comes into contact with the nozzle surfaces 13, thereby cleaning. Excess fluid 60 is returned via one or more collecting channels 37 to a fluid separator 43 and then disposed of in a waste container 45. This can be done without a pump, solely via the gravity of the fluid. The cleaning fluid can be supplied from a reservoir 46 via a line. A pump can be used for this purpose.

[0062] On the (in the Figure 1Along the entire cleaning movement (leading, for example, to the right), in addition to the cleaning device 30, the suction device 40 following it is also activated. The device 40 comprises a suction channel 41 with a suction opening 42 open upwards towards the nozzle surfaces 13. Liquid 60 discharged by the device 30 which is not returned via the collecting channels 37, e.g. because it adheres to the nozzle surface, is suctioned off by the device 40, preferably together with air 62. Such suctioned-off liquid is conveyed via a return channel 44 and / or a return line 44 to a liquid separator 43 and from there to a waste container 45 and disposed of.

[0063] The Figure 1 The device shown further comprises the rinsing device 50. This is mounted on the (in the Figure 1The device 50 releases a rinsing liquid 61 from a further chamber 51, preferably with a rinsing slope 52 in the direction of the suction device 40, which is sucked away by the suction device 40, preferably together with air 62. The sucked-away liquid 61, which carries contaminants, passes through the return channel 44 to the liquid separator 43 and is from there guided to the waste container 45 and disposed of. The supply of rinsing liquid can be from a storage container 46 via a line. A pump can be used for this purpose. The rinsing liquid and the cleaning liquid can preferably be the same liquid. As an alternative to the illustrated embodiment of the rinsing device 50 with a further chamber 51 with a rinsing slope 52, the rinsing device can also have a device for spraying the rinsing liquid 61, e.g.a spray bar with spray nozzles.

[0064] In Figure 3 A perspective view of a printing press 10 is shown. Parts of the press not relevant to the invention have been omitted for clarity. Visible are the side wall 19 with several openings 19a, the cleaning drawer 20 in the cleaning position 24, two exemplary cleaning boxes 21, each with a cleaning carriage 23, and an exemplary print bar 11 with print heads 12. List of reference symbols

[0065] 10Inkjet printing machine 11Arrangement(s) / Printbar / Printbar 12Inkjet print heads 13Nozzle surfaces 14Nozzles 15Ink 16Contamination 17Adapter 18Additional adapter 19Side wall 19aOpenings 20Cleaning drawer 21Cleaning box(es) 22Tub(s) 23Cleaning carriage 24Cleaning position(s) 25Gap 26Motor 27Belt 30Ultrasonic cleaning device 31Ultrasonic source 32Chamber for dispensed cleaning fluid 33Splash bath 34Overflow 35Leading wall 36Trailing further wall 37Collecting channel / collecting line 40Suction device 41Suction channel 42Suction opening 43Liquid separator 44Return channel / return line 45Waste container 46Storage container 50Flushing device 51Additional chamber for dispensed rinsing liquid 52Rinsing slope 60Cleaning fluid 61Rinsing fluid 62Air 70Movement of the cleaning carriage 71Outward path 72Return path

Claims

1. Cleaning method for cleaning nozzle surfaces of a lateral arrangement of ink print heads, i.e. an arrangement of ink print heads extending over the width of a substrate to be printed, wherein a cleaning carriage (23) executes a likewise lateral movement (70) along the arrangement (11) and cleans the nozzle surfaces (13) with a cleaning liquid (60) set to ultrasonic vibrations, wherein the cleaning carriage (23) comprises an ultrasonic cleaning device (30), a suction device (40) and a rinsing device (50), and the movement (70) of the cleaning carriage takes place on an outward path (71) and a return path (72), characterized in that on the outward path the ultrasonic cleaning device and the suction device following it are activated and the rinsing device following the two is deactivated, and in that on the return path the rinsing device and the suction device following it are activated and the ultrasonic cleaning device following the two is deactivated.

2. Method according to claim 1, characterized in that the activated ultrasonic cleaning device (30) dispenses the cleaning liquid (60).

3. Method according to claim 2, characterized in that the cleaning liquid (60) is dispensed from a chamber (32) which is open towards the ink print heads (12).

4. Method according to claim 3, characterized in that the cleaning liquid (60) is dispensed from the chamber (32) as a surge bath (33).

5. Method according to one of the preceding claims, characterized in that the activated rinsing device (50) dispenses a rinsing liquid (61).

6. Method according to claim 5, characterized in that the rinsing liquid (61) is dispensed from a further chamber (51) which is open towards the ink print heads (12) and is different from the chamber (32).

7. Method according to one of the preceding claims, characterized in that the suction device (40) sucks in air (62) on the outward path (71) and thereby sucks in cleaning fluid (60) and contamination (16) from the nozzle surfaces (13).

8. Method according to one of the preceding claims, characterized in that the suction device (40) sucks in the rinsing liquid (61) of the rinsing device (50) on the return path (72) and thereby sucks in cleaning liquid (60) and contamination (16) from the nozzle surfaces (13).

9. Method according to one of the preceding claims, characterized in that the suction takes place through a suction channel (41) of the suction device (40) formed in the cleaning carriage (23) with a suction opening (42) open towards the ink print heads (12).

10. Method according to one of the preceding claims, characterized in that an adapter (17) for the ultrasonic cleaning device (30) is provided upstream of the first ink print head (12) of the arrangement (11), and in that the ultrasonic cleaning device is moved towards the adapter and filled there with cleaning liquid (60).

11. Method according to claim 10, characterized in that a further adapter (18) for the ultrasonic cleaning device (30) is provided after the last ink print head (12) of the arrangement (11), and in that the ultrasonic cleaning device is moved to the further adapter and emptied of cleaning liquid (60) there.

12. Method according to one of the preceding claims, characterized in that the cleaning carriage (23) is provided on a horizontally movable cleaning drawer (20).

13. Method according to claim 12, characterized in that the cleaning carriage (23) is provided as part of a cleaning box (21), wherein the cleaning box is provided on the cleaning drawer (20).