METHOD OF CLEANING NOZZLE SURFACES OF AN INKJET PRINT HEAD ASSEMBLY

Abstract

A method for cleaning nozzle surfaces of an inkjet print head assembly includes using a cleaning slide to carry out a movement along the assembly and clean the nozzle surfaces with a cleaning liquid in ultrasonic vibration. The cleaning slide includes an ultrasonic cleaning device, a suction device, and a rinsing device and the movement of the cleaning slide includes a forward movement and a backward movement. During the forward movement, the ultrasonic cleaning device and the suction device following the ultrasonic cleaning device are activated while the rinsing device following the two is deactivated. During the backward movement, the rinsing device and the suction device following the rinsing device are activated while the ultrasonic cleaning device following the two is deactivated. Cleaning liquid and contamination are advantageously prevented from reaching the interior of print heads or into an ink supply system thereof, preferably in industrial inkjet printing.

Claims

1. A method for cleaning nozzle surfaces of an inkjet print head assembly, the method comprising: providing a cleaning slide including an ultrasonic cleaning device, a suction device, and a rinsing device; using the cleaning slide to carry out a movement along the assembly and clean the nozzle surfaces with a cleaning liquid in ultrasonic vibration; carrying out the movement of the cleaning slide with a forward movement and a backward movement; during the forward movement, activating the ultrasonic cleaning device and activating the suction device following the ultrasonic cleaning device, while deactivating the rinsing device following the two; and during the backward movement, activating the rinsing device and activating the suction device following the rinsing device, while deactivating the ultrasonic cleaning device following the two.

2. The method according to claim 1, which further comprises emitting the cleaning liquid from the activated ultrasonic cleaning device.

3. The method according to claim 2, which further comprises emitting the cleaning liquid from a chamber being open towards inkjet print heads of the inkjet print head assembly.

4. The method according to claim 3, which further comprises emitting the cleaning liquid from the chamber as a surge bath.

5. The method according to claim 1, which further comprises emitting a rinsing liquid from the activated rinsing device.

6. The method according to claim 5, which further comprises emitting cleaning liquid from a chamber, and emitting the rinsing liquid from a different further chamber being open towards inkjet print heads of the inkjet print head assembly.

7. The method according to claim 2, which further comprises during the forward movement, using the suction device to aspirate air and also aspirate the cleaning liquid and contamination off of the nozzle surfaces.

8. The method according to claim 5, which further comprises during the backward movement, using the suction device to aspirate the rinsing liquid of the rinsing device and also aspirate the cleaning liquid and contamination off of the nozzle surfaces.

9. The method according to claim 1, which further comprises: emitting the cleaning liquid from the activated ultrasonic cleaning device; emitting a rinsing liquid from the activated rinsing device; during the forward movement, using the suction device to aspirate air and also aspirate the cleaning liquid and contamination off of the nozzle surfaces; and during the backward movement, using the suction device to aspirate the rinsing liquid of the rinsing device and also aspirate the cleaning liquid and contamination off of the nozzle surfaces.

10. The method according to claim 9, which further comprises carrying out the aspiration through a suction channel of the suction device, the suction channel being formed in the cleaning slide and having a suction opening being open towards inkjet print heads of the inkjet print head assembly.

11. The method according to claim 1, which further comprises providing an adapter for the ultrasonic cleaning device in front of a first inkjet print head of the inkjet print head assembly, and moving the ultrasonic cleaning device towards the adapter to be filled with the cleaning liquid.

12. The method according to claim 11, which further comprises providing a further adapter for the ultrasonic cleaning device after a last inkjet print head of the inkjet print head assembly, and moving the ultrasonic cleaning device towards the further adapter to be emptied of the cleaning liquid.

13. The method according to claim 1, which further comprises placing the cleaning slide on a cleaning drawer being movable in a horizontal direction.

14. The method according to claim 13, which further comprises providing the cleaning slide as a part of a cleaning box, and placing the cleaning box on the cleaning drawer.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0055] FIG. 1 is a diagrammatic, longitudinal-sectional view of a preferred exemplary embodiment of a device for implementing a preferred exemplary embodiment of a cleaning method of the invention;

[0056] FIG. 2 is a cross-sectional view of the device; and

[0057] FIG. 3 is a perspective view of a printing machine.

DETAILED DESCRIPTION OF THE INVENTION

[0058] Referring now in detail to the figures of the drawings, in which corresponding features have the same reference symbols, there is seen an inkjet printing machine 10 for industrial high-quality and high-performance inkjet printing, preferably to print on web-shaped printing substrates such as paper or label material, including at least one assembly 11 (i.e. as a so-called print bar) of multiple inkjet print heads 12 preferably disposed in a row and directed downward and stationary during printing, the assembly 11 being oriented in a transverse direction relative to the printing substrate or rather to the direction of transport thereof). Every print head 12 has a nozzle surface 13 with a plurality of nozzles 14 for emitting ink 15 in the form of tiny individual droplets in a controlled way and in accordance with the information of the image to be printed. These nozzle surfaces are very sensitive and therefore need to be carefully cleaned to remove potential contaminants 16 such as solidified ink 15 and/or dust (e.g. paper dust).

[0059] The device preferably includes multiple elongated cleaning boxes 21 disposed to be parallel to one another and preferably to be jointly movable in a horizontal direction parallel to the print bars (i.e. the direction of the longitudinal extension thereof). All boxes 21 may preferably be disposed on a cleaning drawer 20 movable in a horizontal direction and may be moved together with the drawer 20 in a forward direction 71 and a return direction 72. FIGS. 1 and 2 are sectional views from the side, each figure illustrating an example of a single such box 21; FIG. 3 illustrates two.

[0060] In the aforementioned transverse direction, the drawer 20 is preferably motor-driven to move back and forth between a cleaning position and a park position. During printing, the drawer is retracted and in the park position and the nozzle surfaces are exposed above the printing substrate transported beneath them. Each one of the cleaning boxes 21 includes a trough 22 that is open towards the top to implement a process known as purging the print heads 12, and a cleaning slide 23 movable back and forth in a direction 70 to clean and rinse the nozzle surfaces 13 and/or the nozzles 14 in an upward direction. FIG. 1 illustrates the slide 23 in a cleaning position 24, i.e. it is at a short distance below the nozzle surfaces 13. (When the drawer 20 is in its cleaning position), the cleaning slide is movable back and forth along the nozzle surfaces. This movement may be motor-driven, for instance by a non-illustrated motor with a belt drive. The forward movement (preferably in the direction of the operating side OS of the machine) is for cleaning purposes, whereas the return (or backward) movement (preferably in the direction of the drive side DS of the machine) is for rinsing purposes after the cleaning. The cleaning slide is preferably positioned and movable at a short distance 25 from the nozzle surface. The gap formed by the distance between the slide and the nozzle surfaces prevents direct contact between them, thus avoiding damage to the nozzle surfaces. In addition, the gap is used to receive liquids for cleaning and/or rinsing.

[0061] The cleaning slide 23 includes three devices: an ultrasonic cleaning device 30, a suction device 40, and a rinsing device 50. These devices may be provided in a common block of the slide. The device 30 uses a cleaning liquid 60; the device 50 uses a rinsing liquid 61.

[0062] FIG. 2 illustrates the same device as in FIG. 1 but with less detail. However, it can be seen that the illustrated print bar 11 has an adapter 17 and a further adapter 18 at the start and at the end of the row of print heads 12. Each one of the two adapters has adapter surfaces disposed in the same plane as the nozzle surfaces 13. The adapters may be constructed as aluminum blocks. In this way, the adapters may be used for operations which might put stress on the print heads or contaminate or damage them. The adapters 17, namely the adapter surface thereof, are used, for instance, to close the device 30 when it is being filled with the cleaning liquid, although a gap between the adapter 17 and the device 30 remains (in a way similar to the gap between print heads 12 and device 30), whereas the further adapter 18, namely the adapter surface thereof, is used to control the device 40 or rather the vacuum required in the device 40 for suction purposes. Thus filling and emptying operations are preferably not done near the print head 12 but at the adapters. Once the filling has been completed, an ultrasound source and the suction action are activated (see below) and the cleaning slide 23 passes (preferably once) underneath the nozzle surfaces (cleaning motion; forward movement). Then, an optional purging operation may take place, i.e. the print heads eject ink into the trough 22 to push out cleaning liquid residue that may have entered the print heads. In order to remove ink residue from the print heads, i.e. from the nozzle surfaces thereof, a rinsing movement (return movement) including the introduction of rinsing liquid is carried out (see also below). It is clearly likewise possible to carry out the cleaning movement and the rinsing movement in the respective opposite direction as long as the cleaning operation is done first and the rinsing operation afterwards.

[0063] FIGS. 2 and 3, also illustrate a side wall 19 of the printing machine 10 (on the drive side DS of the machine); the drawer 20 is preferably moved back and forth through an opening 19a in the side wall (or parts, e.g. drawer carriers extending in a lateral direction are moved through corresponding openings 19a). The park position is preferably behind the side wall (with the print heads and the transport path for the printing substrate in front of the side wall). The movement is preferably motor-driven by a motor 26 which drives the drawer.

[0064] FIG. 1 illustrates an activatable ultrasound source 31 disposed on the bottom of a chamber 32 for cleaning liquid 60 to be discharged. The device 30 forms a surge bath 33 with a respective overflow 34 over a leading wall 35 (on the forward movement) and a trailing further wall 36 (on the forward movement). In the cleaning operation, i.e. on the forward movement, the cleaning liquid is caused to vibrate in ultrasonic vibration and contacts the nozzle surfaces 13, causing them to be cleaned. Excess liquid 60 is fed back to a liquid separator 43 through one or more collection channels 37 and subsequently disposed of in a waste container 45. This may be achieved solely through gravity of the ink without any pump. The cleaning liquid may be supplied from a reservoir 46 through a supply line. A pump may be used for this purpose.

[0065] On the forward movement of the cleaning movement (to the right-hand side in the example of FIG. 1), it is not only the device 30 for cleaning that is activated but also the trailing device 40 for suction. The device 40 includes a suction channel 41 with a suction opening 42 open towards the top towards the nozzle surfaces 13. Liquid 60 that was emitted by the device 30 but is not fed back through the collection channels 37, for instance because it adheres to the nozzle surface, is aspirated, preferably together with air 62, by the device 40. Such aspirated liquid is fed back to the liquid separator 43 through a feedback channel 44 and/or a feedback line 44 and then to the waste container 45 to be disposed of.

[0066] The device shown in FIG. 1 further includes the rinsing device 50, which is activated on the backward movement of the cleaning movement (to the left-hand side in the illustrated example of FIG. 1) together with the trailing suction device 40. The device 50 emits a rinsing liquid 61 coming from a further chamber 51, preferably equipped with a rinsing slant 52 in the direction of the suction device 40. The rinsing liquid 61 is aspirated, preferably together with air 62, by the aspiration device 40. In this process, the aspirated liquid 61, which contains contaminants, is fed to the liquid separator 43 through the feedback channel 44 to be fed to the waste container 45 and disposed of. The rinsing liquid may be supplied from the reservoir 46 through a supply line. A pump may be used for this purpose. Rinsing liquid and cleaning liquid may preferably be the same liquid. As an alternative to the illustrated embodiment of the rinsing device 50, which includes the further chamber 51 with the rinsing slant 52, the rinsing device may include a device for spraying on rinsing liquid 61, for instance a spray bar with spray nozzles.

[0067] FIG. 3 is a perspective view of a printing machine 10. Machine parts that are not relevant in the context of the invention have been left out for reasons of visibility. The figure shows the side wall 19 with multiple openings 19a, the cleaning drawer 20 in the cleaning position 24, two examples of cleaning boxes 21, each including a cleaning slide 23, and an example of a print bar 11 with print heads 12.

[0068] The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention.

LIST OF REFERENCE SYMBOLS

[0069] 10 inkjet printing machine [0070] 11 assembly/assemblies/print bar [0071] 12 inkjet print heads [0072] 13 nozzle surfaces [0073] 14 nozzles [0074] 15 ink [0075] 16 contamination [0076] 17 adapter [0077] 18 further adapter [0078] 19 side wall [0079] 19a openings [0080] 20 cleaning drawer [0081] 21 cleaning box(es) [0082] 22 trough(s) [0083] 23 cleaning slide [0084] 24 cleaning position(s) [0085] 25 distance [0086] 26 motor [0087] 27 belt [0088] 30 ultrasonic cleaning device [0089] 31 ultrasound source [0090] 32 chamber for cleaning liquid to be emitted [0091] 33 surge bath [0092] 34 overflow [0093] 35 leading wall [0094] 36 trailing further wall [0095] 37 collection channel/collection line [0096] 40 suction device [0097] 41 suction channel [0098] 42 suction opening [0099] 43 liquid separator [0100] 44 feedback channel/feedback line [0101] 45 waste container [0102] 46 reservoir [0103] 50 rinsing device [0104] 51 further chamber for rinsing liquid to be emitted [0105] 52 rinsing slant [0106] 60 cleaning liquid [0107] 61 rinsing liquid [0108] 62 air [0109] 70 movement of the cleaning slide [0110] 71 forward movement [0111] 72 backward movement