EP1361958A1

EP1361958A1 - Method and device for filling print heads

Info

Publication number: EP1361958A1
Application number: EP02740079A
Authority: EP
Inventors: Reto Eicher; Hansjörg UNTERSANDER; Peter Zünd; Stefan Wagler
Original assignee: Zuend Systemtechnik AG
Current assignee: Zuend Systemtechnik AG
Priority date: 2001-02-14
Filing date: 2002-01-11
Publication date: 2003-11-19
Also published as: WO2002064375A1; WO2002064375A8

Abstract

In order to fill and clean print heads (1), a cleaning fluid (31) is fed to the print chambers (3) on the jet side and air is forced out of the print chambers (3) and the distributor (7) by means of the cleaning fluid. The cleaning fluid (31) is displaced from the print head by the ink (25) after subsequent suctioning of the cleaning fluid (31) by the cleaning head (17). No air can enter the print chambers (3) when the ink (25) is suctioned. The cleaning fluid (31) can also be used to clean the print chambers (3) and the jets (5). Print chambers (3) that are devoid of air pockets enable immaculate homogeneous printing without the need for any positioning time. Wastage of expensive printing ink is also avoided.

Description

Method and device for filling printheads

The invention relates to a method and a device for filling print heads in single- and multi-color printing devices according to the preamble of claims 1 and 7.

Printheads for printing electronically generated or electronically captured images and fonts are used today in all areas of printing technology. Printheads are not only used in small printing devices for private use, but also in devices that can be used to print large-area rigid plates, flexible sheets or endless tapes made of any material. Such prints can be, for example, posters or plates for exhibition stands; tarpaulins for trucks or tarpaulins for perimeter advertising in sports stadiums or on other occasions can also be printed in this way. Print heads in such systems are usually arranged so that they can be moved over the print template and must be able to work properly for a long time without interruption. Their maintenance may - if necessary - only take a short time, as the printing machine is shut down during this time.

With print heads that work according to the piezo inkjet process, a static negative pressure must be present inside, ie in the print rooms of the print head, in order to avoid that the ink flows out through the fine nozzles, which are below when horizontal printing occurs. A vacuum of 1 - 2 mbar is usually sufficient. The vacuum can be easily created by placing the ink tank slightly below the printhead. Air bubbles form in the pressure chambers during conventional filling with ink. In the case of a plurality of print heads lying next to one another, for example four in the case of multicolor printing, air bubbles of different sizes can consequently be present not only in the four print heads lying next to one another but also within the individual pressure chambers of each print head. The air pockets mean that there are different ink levels within the individual printheads and consequently the static ink pressure is not the same across all nozzles. As a result, the function of the print heads is unstable. Even the most complex filling, maintenance and cleaning instructions recommended by the manufacturers of the printheads have so far only produced unsatisfactory results. Printheads can also be used for long-term commercial use clog with the finest colored grains present in the ink, so that regular, constant printing is impossible. The manufacturers of the printheads have so far not been able to solve this problem satisfactorily.

The irregular filling of the pressure rooms due to the formation of bubbles and the sheer impossibility of periodically cleaning the filters in the pressure rooms leads to interruptions in operation and in particular to a huge loss of expensive ink before the printing process is resumed.

The object of the invention is to provide a method and a device for filling and cleaning print heads in which the formation of bubbles within the print heads and the associated lines can be avoided. Another object of the invention is to provide a method and a device with which cleaning and the subsequent refilling of print heads with ink is possible in a short time.

These tasks are solved by a method with the features of claim 1 and by a device with the features of claim 7.

By introducing liquid through the spray nozzles Any air present in the interior of the pressure chambers can be displaced into the pressure chamber of the print heads and discharged there. The pressure spaces made bubble-free in this way can then be filled with ink in a known manner by applying a vacuum to the nozzles from the ink container. When filling, the liquid used to evacuate the air in the printhead is again sucked through the nozzles and sent to a waste ink container. In a preferred embodiment of the invention, the liquid for expelling the bubbles from the pressure chambers of the printhead is a cleaning liquid, for example a solvent, which, when penetrating through the nozzles into the pressure chamber, both cleans and exposes the nozzle cross-sections of any deposits and also deposits that are deposited in the pressure rooms Residues on the filters dissolves. Larger particles that cannot be dissolved can be sucked out to the rear. The residues dissolved in the cleaning liquid can be sucked off through the nozzles during the subsequent filling.

The use of cleaning fluid can also be dispensed with if there is no contamination in the print heads, but only trapped air has to be expelled from them. Air bubbles can not only with the conventional filling type form, but by oxygen contained in the ink. Instead of cleaning fluid, new ink is sucked through the nozzles into the print heads and the air is expelled.

It has proven to be particularly advantageous if a riser pipe is provided above the distribution space, which connects the adjacent pressure spaces, through which the air pressed out of the pressure spaces can be led out.

In a further very advantageous embodiment of the invention, in which the printheads are also filled from below through the nozzles, the vacuum in the at least one printhead is applied to the riser pipe and the ink is sucked out of a container into which the printhead is immersed on the nozzle side , The air in the printhead is completely removed by the vacuum on the riser tube and it can be filled with ink without bubbles by returning a portion of the ink that has risen into the riser tube through the printhead into the ink feed line, and the ink level, which is preferably visible through a sight glass, can be adjusted. This type of filling enables the printheads to be filled without loss of ink.

Using two illustrated exemplary embodiments, the

Invention explained in more detail. Show it

Figure 1 is a schematic representation of a Printing device with a print head and

Ink tank as well as one at the nozzles of the

Print head with a cleaning head

Waste ink container and a vacuum pump before filling an empty printhead, Figure 2 shows the representation of the device according to Figure 1

Start of the filling process, Figures 3 - 5 further process steps during the

Filling process, Figure 6 shows the device at the end of the filling process, the cleaning head has moved away, Figure 7 shows a printing device according to the invention with a

Container with cleaning liquid and a suction device opening into the ink line, the

Printhead is empty, FIG. 8 printhead at the beginning of the filling process,

Pressure rooms filled with cleaning fluid, Figures 9 and 10 printhead partially and entirely

11 filled the cleaning liquid at the beginning of the filling process

Ink; Ink displaces cleaning fluid in front of the distributor head, Figure 12 shows the distributor and parts of the pressure chambers

Ink filled, Figure 13 the printhead is completely filled with ink, FIG. 14 the filled print head with the one moved away

Cleaning head, Figure 15 an empty print head in another

Design at the beginning of the filling process through the nozzles from below, FIG. 16 shows an illustration when the filling is approximately full

Printhead, FIG. 17 shows a representation with a completely filled but not yet vented distributor, FIG. 18 shows a representation with a completely filled, vented distributor,

Sucking the ink out of the ink tank, Figure 20 is an illustration with already filled

Ink line, FIG. 21 emptying the cleaning head, FIG. 22 cleaning head moved away, FIG. 23 one removed from the printing device

Printhead on a filler

24 the print head in FIG. 23 after the first

Method step, FIG. 25 printhead with lowered ink level (ink fed into the supply line), FIG. 26 drawing additional ink through the nozzle into the

Riser, Figure 27 Printhead out of the ink tank and Figure 28 is a perspective view of the printhead fill and clean device.

A conventional print head 1, as shown in FIGS. 1 to 6, comprises one or more pressure chambers 3, a multiplicity of very fine ink outlet nozzles, in short nozzles 5, which are located at one end of the pressure chambers 3 on the nozzle side, and a distributor 7, which is connected to the pressure chambers 3 by means of distributor lines 9. Distribution valves 11 are used in the distribution lines 9. A feed line 13 leads from distributor 7 to an ink tank 15. The remaining parts of the print head 1, as it is, for example, from XaarJet Ltd. , Science Park, Cambridge, England, manufactured and sold under the name XaarJet (registered trademark of XaarJet Ltd.) are not described in detail since their function and training are not required for an understanding of the present invention. For the same reason, the electronic control and drive elements for the operation of the print heads 1 are neither shown nor described.

Below the print head 1, an example trough-shaped cleaning head 17 is shown in Figure 1, which is airtight from below to the other by sealing elements, not shown Underside of the print head 1 nozzles 5 has moved up. The cleaning head 17 is connected to a waste tank 21 via a waste line 19. A suction line 23 leads from the waste tank 21 to a vacuum pump P.

In the starting position according to FIG. 1, the ink 25 required for operation is located in the ink tank 15 and there may be some ink in the waste tank 21, here referred to as waste ink 25 ', which was sucked out of the print head 1 during an earlier filling. The print head 1 is still empty, and the conventional filling of the print head 1 with ink 25 will now be explained in more detail with reference to FIGS. 2 to 6. A vacuum is applied to the cleaning head 17 by the pump P, which vacuum propagates through the nozzles 5, the first pressure chamber 3, the opened distributor valve 11 above the pressure chamber 3, the distributor line 9, the distributor 7 and the feed line 13 and ink 25 sucks from the ink tank 15. The first pressure chamber 3 is filled to about a quarter with ink 25 in FIG. The remaining pressure chambers 3 are still empty, since their distributor valves 11 are closed. One after the other, the remaining pressure chambers 3 are connected to the distributor 7 by opening the associated distributor valves 11 and ink 25 is sucked in. The distribution valves 11 are opened and closed sequentially (compare FIGS. 3 to 5). While the pressure spaces 3 are being filled, ink 25 already passes through the nozzles 5 through into the cleaning head 17 and from there through the waste line 19 into the waste tank 21. The inside of the pressure chambers 3, in which filters (not shown for the sake of clarity) are also used, is also air that only slowly passes through the pressure chambers 3 sucked-in ink 25 flowing in along the walls is displaced. A complete displacement of the air in the head spaces 27 via the ink 25 sucked into the pressure spaces 3 is not possible. It is known from practice that the individual pressure spaces 3 of a print head 1 always have unequal fill levels, for example ^ and h ₂ (compare FIG. 6). This has the result that uneven pressures prevail due to the uneven static pressure of the ink columns present in the individual pressure chambers 3, and thus the print head 1 does not work. It can also be seen from FIG. 6 that at the end of the filling process prescribed by the supplier of the print heads 1, the cleaning head 17 is moved downward. It should also be noted that the larger amount of ink that has accumulated in the waste tank 21 must already be disposed of. Filling according to the conventional procedure is therefore unsatisfactory both from a printing point of view and from an economic and ecological point of view (necessarily large waste of expensive ink).

The first embodiment is shown in FIGS the filling, which at the same time includes cleaning the print head 1, is described. In the figures, only those parts that are referred to in the description are provided with reference numerals.

FIG. 7 shows the print head 1 of a printing device at the beginning of the filling process, as can also be seen in FIG. 1. The print head 1 or its print rooms 3 are empty, i.e. they are filled with air; there is ambient pressure. The cleaning head 17 is in an airtight connection with the part of the print head 1 on the nozzle side. A liquid line 29 for cleaning liquid 31 opens into the waste line 19, which leads from the cleaning head 17 to the waste tank 21

Cleaning liquid valve, short liquid valve 33, the passage of cleaning liquid 31 in the liquid line 29 can be opened or closed. A waste valve 35 is inserted between the mouth of the liquid line 29 into the waste line 19 and the waste tank 21, with which the inlet to the waste tank 21 can be closed. A vacuum line 37, in which a vacuum valve 39 is inserted, also opens into the feed line 13. The vacuum line 37 is connected to a vacuum source Q. The remaining elements of the printing device correspond to those in FIG. 1. In the first method step of filling the printhead 1 with ink 25, the cleaning liquid 31 becomes one receiving cleaning tank 41 cleaning liquid 31 through the opened liquid valve 33 into the cleaning head 17 and from there simultaneously through the nozzles 5 at the end of the pressure chambers 3 evenly through all pressure chambers 3. Of course, during this suction process, triggered by the vacuum pump Q, the waste valve 35 and an ink valve 43 inserted in the ink line 13 are closed (FIG. 8). In FIG. 9, the distributor 7 is already filled with cleaning liquid 31 to the level h ₃ , which lies on the upper edge of the feed line 3. It should be noted that the simultaneous suction of cleaning fluid 31 through the nozzles 5 into the pressure chambers 3 from below means that all pressure chambers 3 are completely filled with cleaning fluid 31 and that little air is only present in the head space region 45. In a preferred embodiment of the invention, a riser pipe 47 with a riser valve 49 is placed on the distributor 7. The latter is of course closed during the suction of cleaning fluid 31. In the following step, the remaining air can be sucked out of the head space area 45 of the distributor 7 through the opened riser valve 49 by means of a vacuum R attached to the riser 47 (FIG. 10).

In the next step, the vacuum valve 39 and the liquid valve 33 are closed and the ink valve 43 and the waste valve 35 opened and then the pump P started. Ink 25 can now be sucked out of the ink tank 15 by the negative pressure generated by the pump P in the waste tank. This gradually displaces the cleaning liquid 31 from the feed line (FIG. 11), the distributor 7 (FIG. 12), the pressure chambers 3 and the cleaning head 17. As soon as undiluted ink 25 drips into the waste tank 21 (FIG. 13), the cleaning head 17 can move from the shower side End of the print head 1 moved away (Figure 14) and the printing operation can be started. The pressure chambers 3 and the distributor 7 are now uniform and also completely filled with ink 25 without air. Uniform print quality is therefore guaranteed immediately. The loss of ink through the filling process is minimal; it only includes the amount that was diluted by the latter when the cleaning liquid 31 was displaced. By drawing cleaning liquid 31 into the print head 1, ink residues located therein can be simultaneously dissolved and completely removed from it. Consequently, all the lines within the print head 1 and also the filters (not shown) arranged there are cleaned in the pressure spaces 3. This is a perfect prerequisite for high print quality over a long, trouble-free period of operation. Interruptions due to constipation, which lead to poor print quality, can result in a absolute minimum can be reduced. In addition, the high loss of expensive printing ink is eliminated due to the frequent refilling due to constipation. Furthermore, there is no need for valves between the distributor 7 and the individual pressure chambers 3, since these are not required. The costs for the additional liquid tank 41 holding the cleaning liquid 31 and the liquid valve 33 arranged therein and the vacuum valve 39 are negligibly small compared to the loss of expensive ink 25 and in particular the time-consuming interruptions during the printing process.

Ink can be supplied through the riser valve 49 before the start of or during the suction of the cleaning liquid 31.

FIGS. 15 to 22 show a further particularly advantageous embodiment of the invention, in which the printhead 1 is filled analogously to the method described in FIGS. 7 to 14, but without the use of cleaning fluid 31. This configuration is useful when cleaning the print head 1 is not necessary or when a new print head 1 is started up for the first time.

All parts are identified with the same reference numerals as in the previous examples and only those necessary for the explanations are given Reference numerals used in the figures. After the cleaning head 17 has been brought up to the end of the print head 1 on the nozzle side, the air is sucked out of the distributor 7, the pressure chambers 3 and the cleaning head 17 by the vacuum source Q. A three-way valve 51, which connects an additional ink tank 53 to the liquid line 29 via a dip tube 55, draws new ink 25 into the cleaning head instead of cleaning fluid 31 (FIG. 15). From there, this ink 25 simultaneously arrives from below through all pressure spaces 3 in the distributor 7 and displaces the air completely from the pressure spaces 3 into the head space of the distributor 7 (FIG. 16). As soon as the ink 25 has also completely filled the feed line 13 (ink reaches the vacuum valve 39), the vacuum valve 39 is closed and residual air is sucked out of the head space region 45 of the distributor 7 from the riser pipe 47 through the open riser valve 49 (FIG. 18). Now the riser valve 49 and the three-way valve 51 are closed. The vacuum valve 39 is opened again, and the ink valve 43 is also opened. The vacuum source Q now draws ink 25 from the ink tank 15 into the ink line 13 (FIG. 19). As soon as the ink line 13 is also completely filled with ink 25 (FIG. 20), the vacuum valve 39 is closed and a vacuum is applied to the waste tank 21 with the pump P, so that the cleaning head 7 is emptied through the now opened waste valve 35 (FIG. 21) and then the cleaning tank 7 can be moved away from the cleaning head 1 (FIG. 22). Residual ink located in the cleaning head 7 drips into the waste tank 21. The loss of expensive printing ink 25 is negligible, since immediately after reaching the vacuum valve 39 the ink flow into the printing head 1 can be interrupted and only the minimal amount of residual ink is sucked off in the cleaning head 21 and the Disposal must be supplied.

If cleaning of the printhead 1 becomes necessary as a result of blockage, the printhead 1 can be cleaned by moving the three-way valve 51, as described for FIGS. 7 to 14. The additional ink tank 53 remains closed by the three-way valve 51 during the cleaning process.

In FIG. 23 the print head 1 is inserted into a print head filling device 61 (see also FIG. 28). The print head 1 comprises a plurality of pressure chambers 3, a distributor 7 and a riser pipe 47. A connecting line 63, which leads to a pump R, is connected to the latter. In this exemplary embodiment, it is configured schematically as a piston pump. The lower end of the print head 1 on the nozzle side with the nozzles (not visible in FIG. 23) is immersed in a bowl-shaped container 67 which contains ink 25. The feed line 13, which is connected to the distributor 7 via the pressure chambers 3, leads to the lower end of a sight glass 69, the upper end of which is connected to an ink tank 71. A shut-off valve 73 is inserted between the sight glass 69 and the ink tank 71. The printhead 1 is fastened in the printhead filling device 61 to the vertical support 75 and, together with the support shell 77 for the ink tank 71, can be moved vertically and fixed in the desired height position by a locking screw 79.

At the beginning of the filling process, the print head 1 is fixed with the locking screw 79 at a level at which the lower end on the nozzle side is immersed in the ink 25 on the container 67 to such an extent that no air can reach the nozzles 5. By pulling in the direction of the arrow p on the piston 81 of the pump R, air is drawn out of the print head 1 and ink 25 is sucked through the nozzles 5 into the pressure chambers 3 from below. The pressure chambers 3 are consequently filled from below and the air drawn off at the top. In Figure 24, the ink level has risen to the height h ₄ in the riser 47. The ink in the pressure chambers 3 is not visible in FIGS. 23-27. In any case, the pressure chambers 3 no longer contain air, since this has been completely led out of the print head 1 by the ink 25 flowing in from below. The valve 73 is closed during the drawing of ink into the print head 1 and at the same time evacuating the air therein. It cannot False air can get into the printhead. Now the valve 73 is opened and the pump R partially displaces the ink 25 located in the riser pipe 47 back into the print head 3 and out of it through the feed line 13 into the sight glass 69 (see FIG. 25). The sight glass 69 is filled up to a predetermined height h ₅ . Afterwards (FIG. 26), a little ink 25 is preferably sucked back into the riser pipe 47 by the pump R, so that the latter is filled up to the level h ₄ .

Now the print head 1 can be lifted out of the container 67 with the ink 25, the connecting line 63 can be detached from the pump R. The print head 1 is then returned together with the ink container 71 and the sight glass 69 into the printing device and fastened there.

Alternatively, of course, a filling according to the method according to the invention would also be possible within the printing device. The cramped spatial conditions make it useful, however, to insert the printhead 1 into a filling device 61 especially suitable for the filling process. In this (FIG. 28) the vacuum can be generated instead of with a piston pump with the vacuum network of the company and monitored with a suitable pressure gauge that is suitable for this.

Claims

claims

1. A method for filling printheads (1) in single and multicolor printing devices with a separate ink tank (15), characterized in that the filling of the at least one printhead (1) with the help of one on the outside of the nozzles (5) Printhead (l) brought up, liquid-containing container (17, 67) takes place, from which liquid flows through the nozzles (5) into the printhead (1) and with the inflowing liquid the air contained in the pressure chambers (3) is led out.

2. The method according to claim 1, characterized in that the container (67) contains ink (25) as a liquid and the liquid through a riser pipe (47) arranged above the pressure chambers (3) of the print head (1) by applying a vacuum the nozzles (5) are sucked into the pressure chambers (3) from below until the print head (1) is filled with ink (25).

3. The method according to claim 2, characterized in that after the filling of the print head (1) by returning ink (25) from the riser (47), the feed line (13) leading to the ink tank (71) at least partially with ink (25) is filled.

4. The method according to claim 1, 'characterized in

that the liquid-containing container (17) comprises a cleaning head that can be placed under vacuum, over which the print head (1) is guided and brought into airtight contact,

- That by applying a vacuum to the distributor (7) above the pressure chambers (3) through the nozzles (5) through a cleaning fluid (31) from the container (17), the pressure chambers (3) of the distributor (7) and one for a separate ink tank (15) leading feed line (13) is sucked in and the printhead (1) is made air-free and

- That by applying a vacuum to the container (17) and opening a previously closed ink valve (43) in the feed line (13) ink (25) above the distributor (7) is sucked into the printhead (1) until die.darin located cleaning liquid (31) has flowed out through the nozzles (5) and pure ink (25) flows.

5. The method according to claim 1, characterized in

- That by applying a vacuum to the distributor (7) Ink (25) is sucked in from the pressure tank (3) through the nozzles (5) from an additional tank (53) connected to the container (17) into the print head (1) as far as the feed line (13) and the ink is drawn into the print head (1 ) air is expelled and

- That by applying a vacuum to the container (17) and opening a previously closed ink valve (43) in the feed line (13) ink (25) from the ink container (15) via the distributor (7) sucked into the print head (1) becomes.

6. The method according to claim 4, characterized in that the suctioned cleaning liquid (31), which is partially permeated with ink (25), is guided into a waste tank (21).

7. Apparatus for carrying out the method according to claim 1, comprising at least one print head (1) with pressure chambers (3) and a distributor (7) connecting the pressure chambers (3), an ink feed line (13) and an ink tank (15, 71), a container (17, 67) for liquid (25, 31) into which the nozzle-side end of the print head (1) can be immersed or connected in an airtight manner, characterized in that on one of the two sides of the nozzles (5) outside the print head (1) a pump (P, Q, R) is operatively connected to the nozzles (5) via a line (13, 63) and is designed to introduce or suction liquid (25, 31) through the nozzles (5) into the pressure chamber (3) ,

8. The device according to claim 7, characterized in that a riser pipe (47) is connected to the distributor (7) and the end of which is connected to a suction pump (R).