Printing unit for an ink jet printing device

Abstract

A printing unit (140) for an inkjet printing device (100) is described, comprising at least one printing bar (102) with a cover unit (200) for the printing bar (102). The cover unit (200) is configured to protect the printing bar (102) from an ambient climate created by an air conditioning fluid (203) when the printing bar (102) is in its parked position. The printing unit (140) further comprises a ventilation unit (310) connected to the cover unit (200) via a ventilation line (304). The ventilation unit (310) is positioned high above the air conditioning fluid (203) such that no air conditioning fluid (203) can reach the ventilation unit (310) when the printing bar (102) is moved into the parked position via the ventilation line (304).

Description

[0001] The invention relates to a printing unit for an inkjet printing device, which has a cover unit for each of the one or more printing bars of the printing unit for covering the nozzle plates of the one or more printheads of the individual printing bars.

[0002] An inkjet printing device for printing on a recording medium comprises a printing unit with at least one print bar, wherein the print bar has one or more print heads, each with one or more nozzles. The individual nozzles are each configured to eject ink droplets to print pixels of a printed image onto the recording medium.

[0003] When the printing process of the inkjet printer is interrupted, the print bar can be moved to a park position in which the nozzle plates of the one or more printheads of the inkjet printer are covered to prevent the nozzles of the one or more printheads from drying out during the printing break.

[0004] This document addresses the technical problem of providing a particularly efficient and durable cover for the nozzle plates of one or more printheads of the print bar of a print unit of an inkjet printing device. This problem is solved by the features of independent device claim 1 and independent device claim 10.

[0005] According to one aspect, a printing unit for an inkjet printing device is described. The printing unit comprises at least one print bar with at least one printhead, as well as a cover unit for the print bar. The cover unit is configured to cover the nozzle plate of the printhead of the print bar with a container when the print bar is in its parked position, and to hold climate control fluid in the container, the climate control fluid typically creating a specific ambient climate within the container.

[0006] The pressure mechanism further includes a ventilation unit, which is connected via a ventilation line to the filling opening of the cover unit's reservoir. The ventilation unit is positioned at a height difference above the filling opening, such that air conditioning fluid, which is forced into the ventilation line through the filling opening when the pressure bar is moved to the park position, cannot reach the ventilation unit.

[0007] According to another aspect, a printing unit for an inkjet printing device is described, wherein the printing unit comprises a plurality of print bars, and wherein each print bar of the plurality of print bars comprises at least one printhead. The printing unit further comprises a plurality of cover units for the corresponding plurality of print bars, wherein each cover unit of the plurality of cover units is configured to cover a nozzle plate of the printhead of the respective print bar with a container in the parked position of the respective print bar of the plurality of print bars, and to hold cooling fluid in the container of the respective cover unit.

[0008] The printing unit further comprises a common ventilation unit and a plurality of ventilation lines for the corresponding plurality of cover units, wherein the individual ventilation lines of the plurality of ventilation lines each connect the common ventilation unit to the filling opening of the container of the respective cover unit of the plurality of cover units by means of an air-conducting connection.

[0009] Exemplary embodiments of the invention will now be described in more detail with reference to the schematic drawing. These show: Fig. 1 a block diagram of an exemplary inkjet printing device; Figures 2a to 2 an exemplary cover unit for a print bar in different states; Figure 3 the lowering of a print bar into a cover unit; and Figure 3 a printing unit with multiple print bars and cover units.

[0010] The in Fig. 1 The illustrated inkjet printing device 100 is designed for printing on a sheet-shaped, flat, disc-shaped, or tape-shaped recording medium 120. The recording medium 120 can be made of paper, cardboard, carton, metal, plastic, textiles, a combination thereof, and / or other suitable and printable materials. The recording medium 120 is guided through the printing unit 140 of the printing device 100 along the transport direction 1, which is indicated by an arrow.

[0011] In the illustrated example, the printing unit 140 of the printing device 100 comprises two printing bars 102, each printing bar 102 being usable for printing with ink of a specific color, e.g., black, cyan, magenta, and / or yellow, and optionally MICR ink. Different printing bars 102 can be used for printing with different inks. Furthermore, the printing device 100 typically includes at least one fixing or drying unit (not shown) configured to fix a printed image printed onto the recording medium 120.

[0012] A print bar 102 can comprise one or more print heads 103, which may be arranged side by side in several rows to print the pixels of different columns 31, 32 of a print image onto the recording medium 120. In the Fig. 1 In the example shown, a print bar 102 comprises five print heads 103, each print head 103 printing the pixels of a group of columns 31, 32 of a print image onto the recording medium 120.

[0013] Each printhead 103 of the printing unit 140 comprises in the Fig. 1 In the illustrated embodiment, several nozzles 21, 22 are provided, each nozzle 21, 22 being configured to fire or propel ink droplets onto the recording medium 120. For example, a printhead 103 of the printing unit 140 can comprise several thousand effectively used nozzles 21, 22 arranged along several rows transverse to the transport direction 1 of the recording medium 120. By means of the nozzles 21, 22 of a printhead 103 of the printing unit 140, pixels of a line of a printed image can be printed onto the recording medium 120 transverse to the transport direction 1, i.e., along the width of the recording medium 120.

[0014] The printing device 100 further comprises a control unit 101, e.g. a control hardware and / or a controller, which is set up to control the actuators of the individual nozzles 21, 22 of the individual printheads 103 of the printing unit 140 in order to apply a printed image to the recording medium 120 depending on print data.

[0015] The printing unit 140 of the printing device 100 thus comprises at least one printing bar 102 with K nozzles 21, 22, which can be controlled with a specific line rate to print a line, running perpendicular to the transport direction 1 of the recording medium 120, with K pixels or K columns 31, 32 of a printed image onto the recording medium 120, e.g. with K>1000. In the illustrated example, the nozzles 21, 22 are fixed in the printing device 100, and the recording medium 120 is moved past the stationary nozzles 21, 22 at a specific transport speed.

[0016] The printing device 100 can have a cover unit 200 for each individual printhead 103 or for the printheads 103 of a print bar 102, with which the nozzle plate 160 of at least one printhead 103 can be covered when the printing device 100 is in a standby mode (see Figuren 2a bis 2d The cover unit 200 of a pressure bar 102 can be designed as a flap that can be folded onto or away from the nozzle plate 160 of the at least one print head 103 of the pressure bar 102 (as shown in the Figuren 2a bis 2d shown).

[0017] The cover unit 200 can therefore also be referred to as a parking flap or a protective flap.

[0018] The cover unit 200 can comprise a container 202 with a pressure-lock opening 204, wherein the nozzle plate 160 of a printhead 103 of the pressure lock 102 can be guided through the pressure-lock opening 204 into or onto the container 202. In particular, the pressure-lock opening 204 of the container 202 can be configured such that the container 202 can be closed by the nozzle plate 160 of a printhead 103 and / or by the pressure lock 102 to form a closed, in particular fluid-tight, container 202 when the nozzle plate 160 and / or the pressure lock 102 has been guided into or onto the container 202. In this case, the nozzle plate 160 of a printhead 103 and / or the pressure bar 102 form part of the wall of the container 202 and face the interior of the container 202.

[0019] The cover unit 200 can be configured to provide specific climatic conditions for the nozzle plate 160 of a printhead 103, thereby at least slowing down or reducing the drying of ink in the nozzles 21, 22 of the printhead 103. In particular, the interior of the container 202 of the cover unit 200 can contain a climate control fluid 203, especially a climate control liquid, by which specific climatic conditions can be created inside the container 202 of the cover unit 200. For example, the climate control fluid 203 can create a relatively high humidity level compared to the humidity outside the container 202 of the cover unit 200. The climate control fluid 203 can, for example, contain demineralized water.By using an air conditioning fluid 203, the functionality of a printhead 103 can be reliably and efficiently maintained over relatively long periods of inactivity.

[0020] Fig. 2a Figure 1 shows a pressure bar 102, in a view perpendicular to the transport direction 1. The pressure bar 102 has several printheads 103, each with a nozzle plate 160, which are covered by the cover unit 200. The pressure bar 102 is in a rest or park position, in which the cover unit 200 is intended to prevent the ink within the printheads 103 of the pressure bar 102 from drying out, or to slow down the drying process.

[0021] To move the pressure bar 102 into a pressure position, the pressure bar 102 can be raised in an upward direction 211, so that the container 202 of the cover unit 200 can be positioned along the direction of rotation 212 about the axis of rotation 201 of the container 202 (see Fig. 2b The container 202 of the cover unit 200 can then be positioned so that the positioned container 202 is arranged in the transport direction 1 of the recording carrier 120 in front of or behind the pressure bar 102, as shown in Fig. 2c The pressure bar 102 can then be lowered along the lowering direction 213 on the erected container 202 in order to position the nozzle plates 160 of the one or more printheads 103 of the pressure bar 102 directly above a recording medium 120, as shown in Fig. 2d As shown. Between the nozzle plates 160 of the one or more printheads 103 and the recording medium 120, there is then only a relatively small pressure gap, which is, for example, 2 mm, 1 mm or less in size. The pressure bar 102 is then in the printing position. As can be seen from the Figuren 2a bis 2d As can be seen, the pressure bar 102 can be moved back and forth between the rest or park position and the pressure position by an efficient translational movement, in particular an up-down movement.

[0022] The container 202 of the cover unit 200 typically has a wall segment 205 on the side of the pressure latch opening 204 for the pressure latch 102 and at the end where the pivot axis 201 is located. This wall segment is designed such that the erected container 202 forms a basin for receiving the air conditioning fluid 203, in particular the air conditioning liquid. This ensures that the air conditioning fluid 203 remains in the container 202 even when the container 202 is in the extended position.

[0023] Fig. 3a Figure 1 shows an exemplary cover unit 200 for a pressure bar 102 in a situation where the pressure bar 102 is lowered along the lowering direction 213 to position the nozzle plates 160 of the one or more printheads 103 of the pressure bar 102 in the pressure bar opening 204 of the cover unit 200. The lowering of the pressure bar 102 takes place at a specific lowering speed.

[0024] Fig. 3a Figure 2 shows a filling opening 302 of the cover unit 200, through which air conditioning fluid 203 can be filled into the container 202 of the cover unit 200. The filling opening 302 can be arranged at a specific height 321 above the bottom of the container 202 (see Figure 2). Fig. 3b The height 321 of the filling opening 302 determines the fill level and thus the quantity of air conditioning fluid 203 in the container 202. The container 202 can be filled with air conditioning fluid 203 up to the height 321 of the filling opening 302 in a single filling operation. Further details regarding the filling process will be provided in connection with Fig. 3b explained.

[0025] The lowering of the pressure bar 102 at the lowering speed leads to an overpressure in the container 202 of the cover unit 200 at the moment when the lower part of the pressure bar 102, on which the nozzle plates 160 of the one or more printheads 103 are arranged, is inserted into the pressure bar opening 204 of the cover unit 200. This overpressure can cause air conditioning fluid 203 to be forced out of the container 202 through the filling opening 302.

[0026] Fig. 3b Figure 1 illustrates a printing unit 140 with a plurality of pressure bars 103 and a corresponding plurality of cover units 200. Each cover unit 200 has a filling opening 302 for filling the reservoir 202 of the respective cover unit 200 with air conditioning fluid 203. Air conditioning fluid 203 can be fed into the filling opening 302 of the first cover unit 200 of a first pressure bar 102 via a filling line 302. When the container 202 of the first cover unit 200 is filled with air conditioning fluid 203 up to the filling opening 302, the air conditioning fluid 203 flows via a connecting line 303 from the filling opening 302 of the first cover unit 200 to the filling opening 302 of the second cover unit 200 for the second pressure lock 102. As a result, the container 202 of the second cover unit 200 is filled with air conditioning fluid 203 up to the level of the filling opening 302.Once the filling of the container 202 of the second cover unit 200 is complete, air conditioning fluid 203 flows via a further connecting line 303 from the filling opening 302 of the second cover unit 200 to the filling opening 302 of the third cover unit 200 for the third pressure latch 102.

[0027] Similarly, a cascade can be provided for filling the containers 202 of the plurality of cover units 200 for the plurality of pressure bars 102. The filling process is completed when the container 202 of the cover unit 200 of the last pressure bar 102 is filled with air conditioning fluid 203 up to the height 321 of the filling opening 302.

[0028] The filling of the containers 202 of the individual cover units 200 can be effected while the individual pressure latches 102 are arranged in the pressure latch openings 204 of the corresponding cover units 200. To ensure reliable venting of the containers 202 during filling, each container 202 of the individual cover units 200 can have a vent line 304 through which air 311 can be discharged from the respective container 202. The vent lines 304 can each be arranged at the filling opening 302 of the respective container 200. Furthermore, the vent lines 304 can each be coupled to a vent unit 310. The individual vent lines 304 can thus each run between the filling opening 302 of the container 202 of a cover unit 200 and the vent unit 310. For the large number of cover units 200, a common ventilation unit 310 can advantageously be used.

[0029] The ventilation unit 310 can be configured to control the volume flow of air 311 into and / or out of the containers 202 of the individual cover units 200. The volume flow of air 311 into the individual containers 202 can be limited, while the volume flow of air 311 out of the individual containers 202 is essentially not limited or only to a reduced extent. This ensures reliable filling on the one hand and reliably prevents evaporation of the air conditioning fluid 203 on the other.

[0030] The ventilation unit 310 can be designed as an air filter to filter air 311 that is introduced into the individual containers 202. This reliably prevents contamination of the cover units 200.

[0031] Alternatively or additionally, the ventilation unit 310 can be designed as a silencer to dampen flow noise of the incoming and / or outgoing air 311.

[0032] The overpressure created when the pressure bars 102 are lowered into the containers 202 of the individual cover units 200 can cause air conditioning fluid 203 to be forced from the individual containers 202 through the respective filling openings 302 into the ventilation lines 304. This could cause air conditioning fluid 203 to reach the ventilation unit 310, potentially impairing its function. To reliably prevent such impairment, the ventilation unit 310 is preferably arranged at a height 322 that is a certain differential height 323 above the height 321 of the filling openings 302 of the individual cover units 200. This differential height 323 is typically dependent on the maximum overpressure that can be generated in the individual cover units 200.The maximum possible overpressure typically depends on the lowering speed of the individual pressure bars 102.

[0033] As explained above, when the pressure bars 102 are parked in their respective parking positions, overpressure is created in the respective parking flap, i.e., cover unit 200. This overpressure can cause air conditioning fluid 203, e.g., demineralized water, located in the respective parking flap 200, to be forced upwards through the cascade towards the ventilation unit 310. This can cause the ventilation unit 310 to become wet and dirty, and eventually clogged. The individual parking flaps 200 often contain a mixture of air conditioning fluid 203 and ink, as ink can drip from the one or more printheads 103 of the respective pressure bar 102 when parked. This further accelerates the contamination and clogging of the ventilation unit 310.As a consequence of an impaired ventilation unit 310, the air conditioning of one or more printheads 103 in the parked state may be impaired, which can lead to the drying out of nozzles 21, 22 if the printing device 100 remains idle for a relatively long time.

[0034] Through the in Fig. 3b The illustrated ventilation of the cover units 200, and the use of a relatively high-mounted ventilation unit 310, which preferably supplies several cover units 200, reliably prevent contamination and clogging of the ventilation unit 310. The air conditioning fluid 203, which is flung upwards when the pressure latches 102 are parked, cannot reach the relatively high-mounted ventilation unit 310. This increases the service life of the ventilation unit 310.

[0035] A printing unit 140 for an inkjet printing device 100 is thus described. The printing unit 140 comprises at least one print bar 102 with at least one print head 103. Typically, the print bar 102 includes several print heads 103, which are arranged side by side, for example, with respect to the transport direction 1, in order to increase the printing width of the printing device 100.

[0036] The printing unit 140 further comprises a cover unit 200 for the printing bar 102. The cover unit 200 is configured to cover the nozzle plate 160 of the printhead 103 of the printing bar 102 with a container 202 when the printing bar 102 is in its parked position. For this purpose, the container 202 has a printing bar opening 204 in which the printing bar 102 can be placed. The cover unit 200 is further configured to hold air conditioning fluid 203 in the container 202. The air conditioning fluid 203 may comprise demineralized water, in particular...

[0037] The container 202 of the cover unit 200 can be configured to rotate about a pivot axis 201, so that the container 202 can be positioned in an upright position or in a covered position by rotating it about the pivot axis 201. In the covered position, the nozzle plate 160 of the printhead 103 of the print bar 102 can be received in the print bar opening 204 of the container 202 and thereby covered. Alternatively, in the upright position, the container 202 can be positioned along the transport direction 1 behind or in front of the print bar 102 such that the print bar 102 can be lowered past the container 202 towards the recording medium 120 in order to move the print bar 102 from the park position to the printing position, as exemplified in the Figuren 2a bis 2d described.

[0038] The printing mechanism 140 further comprises a ventilation unit 310, preferably exactly one ventilation unit 310, which is connected via a ventilation line 302 to the filling opening 302 of the container 202 of the cover unit 200. The ventilation unit 310 is preferably arranged at a specific height difference 323 above the filling opening 302, so that air conditioning fluid 203, which is forced through the filling opening 302 into the ventilation line 302 when the pressure bar 102 is moved into the park position due to the overpressure generated in the container 202, does not reach or cannot reach the ventilation unit 310.

[0039] The ventilation unit 310 can be configured to filter air 311, which is drawn from the outside via the ventilation unit 310 and via the ventilation line 304 into the container 202 of the cover unit 200. This allows for particularly gentle parking of the pressure bolt 102.

[0040] Alternatively or additionally, the ventilation unit 310 can be designed as a silencer. In particular, the ventilation unit 310 can be designed to dampen airflow noise 311 in the ventilation line 304. This can increase the comfort of the pressure system 140.

[0041] Alternatively or additionally, the ventilation unit 310 can be configured to restrict the volume flow of air 311 from the outside via the ventilation unit 310 into the ventilation line 304 more significantly, in particular by a factor of 2 or more, than the volume flow 311 of air 311 from the ventilation line 304 via the ventilation unit 310 to the outside. This allows for particularly gentle parking of the pressure bar 102 (even for relatively long parking periods).

[0042] The pressure bar 102 can be positioned in the pressure bar opening 204 of the container 202 of the cover unit 200 at a specific lowering speed when the pressure bar 102 is moved into the park position, the lowering speed typically being determined by the design of the pressure mechanism 140. The differential height 323 can depend on the lowering speed and can, in particular, increase with increasing lowering speed. In other words, the differential height 323 can be determined as a function of the lowering speed.

[0043] A printing unit 140 for an inkjet printing device 100 is described, comprising at least one printing bar 102 with a cover unit 200 for the printing bar 102. The cover unit 200 is designed to protect the printing bar 102 from the ambient climate created by an air conditioning fluid 203 when the printing bar 102 is in the parked position. The printing unit 140 further comprises a ventilation unit 310, which is connected to the cover unit 200 via a ventilation line 304. The ventilation unit 310 is preferably positioned high above the air conditioning fluid 203 such that no air conditioning fluid 203 can reach the ventilation unit 310 when the printing bar 102 is moved into the parked position via the ventilation line 304. This reliably prevents any impairment of the ventilation unit 310.

[0044] The pressure device 140 can include a fluid line 301, 303, e.g., a filling line 301 or a connecting line 303, which is connected to the filling opening 302 and which is configured to convey air conditioning fluid 203 from outside the container 202 of the cover unit 200 through the filling opening 302 into the container 202. The control unit 101 of the pressure device 140 or the pressure device 100 can be configured to cause, in particular by means of a pump, the container 302 to be filled with air conditioning fluid 203 via the fluid line 301, 303, in particular precisely, up to the height 321 of the filling opening 302. In this way, the ambient climate in the container 202 of the cover unit 200 can be precisely controlled.

[0045] The printing mechanism 140 preferably comprises a plurality of pressure bars 102 and a plurality of cover units 200 for the corresponding plurality of pressure bars 102. Furthermore, the printing mechanism 140 can comprise a plurality of vent lines 302 for the corresponding plurality of cover units 200. The individual vent lines 302 of the plurality of vent lines 302 can each connect the vent unit 310 to the filling opening 302 of the container 202 of the respective cover unit 200 of the plurality of cover units 200 in an air-conducting manner. The printing mechanism 140 preferably has only a single vent unit 310 for the plurality of cover units 200.

[0046] A single ventilation unit 310 can therefore be used for the multiple cover units 200. This allows for the provision of a particularly efficient printing unit 140.

[0047] The plurality of pressure bars 102 and the corresponding plurality of cover units 200 can be arranged one behind the other along the transport direction 1. The pressure mechanism 140 can have a connecting line 303 between each pair of cover units 200 arranged directly one behind the other, which fluid-conductingly connects the filling openings 302 of the containers 200 of the two cover units 200. This can be done in particular by forming a cascade of cover units 200 with the plurality of cover units 200, which can be successively filled with air conditioning fluid 203 starting from a first cover unit 200 of the cascade. In this way, the filling of the containers 202 of the plurality of cover units 200 can be effected in a particularly efficient manner.

[0048] According to another aspect, a further printing unit 140 for an inkjet printing device 100 is described. The measures described in this document are also applicable to this printing unit 140, individually or in combination.

[0049] The printing unit 140 comprises a plurality of printing bars 102, each printing bar 102 of the plurality of printing bars 102 comprising at least one printhead 103. Furthermore, the printing unit 140 comprises a plurality of cover units 200 for the corresponding plurality of printing bars 102. Each of the individual cover units 200 of the plurality of cover units 200 is configured, in the parked position of the respective printing bar 102 of the plurality of printing bars 102, to cover the nozzle plate 160 of the printhead 103 of the respective printing bar 102 with a container 202, and to receive air conditioning fluid 203 in the container 202 of the respective cover unit 200.

[0050] The printing unit 140 further comprises a ventilation unit 310 and a plurality of ventilation lines 302 for the corresponding plurality of cover units 200. The individual ventilation lines 302 of the plurality of ventilation lines 302 each connect the common ventilation unit 310 to the filling opening 302 of the container 202 of the respective cover unit 200 of the plurality of cover units 200 in an air-conducting manner.

[0051] Furthermore, this document describes an inkjet printing device 100 which includes at least one of the printing units 140 described in this document. Bezugszeichenliste

[0052] 1 Transport direction (of the recording medium) 21, 22 Nozzle 31, 32 Column (of the printed image) 100 Printing device 101 Control unit 102 Print latch 103 Print head 120 Recording medium 140 Printing unit 160 Nozzle plate 200 Cover unit (parking flap) 201 Pivot axis 202 Container 203 Air conditioning fluid, in particular air conditioning fluid 204 Print latch opening 205 Wall segment 211 Upward direction 212 Direction of rotation 213 Downward direction 301 Fluid line (filling line) 302 Filling opening 303 Fluid line (connecting line) 304 Venting line 310 Venting unit 311 Air 321 Height of the filling opening / Fill level (Air conditioning fluid) 322 Height of the ventilation unit 323 Difference in height of the ventilation unit above the filling opening

Claims

1. A printing unit (140) for an inkjet printing device (100); wherein the printing unit (140) comprises - at least one printing bar (102) with at least one print head (103); - a covering unit (200) for the printing bar (102), wherein - the covering unit (200) is designed to cover a nozzle plate (160) of the print head (103) of the printing bar (102) with a container (202) in a parking position of the printing bar (102); - the covering unit (200) is designed to hold air conditioning fluid (203) in the container (202); and - a ventilation unit (310) which is connected in an air-conducting manner to a filling opening (302) of the container (202) of the covering unit (200) via a ventilation line (302);wherein the ventilation unit (310) is arranged with a differential height (323) above the filling opening (302) so that air conditioning fluid (203) which is pressed through the filling opening (302) into the ventilation line (302) when the pressure bar (102) is transferred into the parking position does not reach the ventilation unit (310); 2. Printing unit (140) according to claim 1, wherein - the container (202) of the cover unit (200) has a pressure bar opening (204); - the pressure bar (102) is placed in the pressure bar opening (204) of the container (202) of the cover unit (200) at a specific lowering speed when the pressure bar (102) is transferred into the parking position; and - the differential height (323) depends on the lowering speed, and in particular increases with increasing lowering speed.

3. Printing unit (140) according to one of the preceding claims, wherein the printing unit (140) comprises - a liquid line (301, 303) which is connected to the filling opening (302) and which is designed to conduct air-conditioning liquid (203) from outside the container (202) of the cover unit (200) through the filling opening (302) into the container (202); and - a control unit (101) which is designed to cause, in particular by means of a pump, the container (302) to be filled with air-conditioning liquid (203) via the liquid line (301, 303) up to a height (321) of the filling opening (302).

4. Printing unit (140) according to one of the preceding claims, wherein - the ventilation unit (310) is designed to filter air (311) that is guided from the outside via the ventilation unit (310) and via the ventilation line (304) into the container (202) of the cover unit (200); - the ventilation unit (310) is designed as a silencer; - the ventilation unit (310) is designed to dampen flow noises of air (311) in the ventilation line (304); and / or - the ventilation unit (310) is designed to restrict a volume flow of air (311) from the outside via the ventilation unit (310) into the ventilation line (304) more strongly, in particular by a factor of 2 or more, than a volume flow (311) of air (311) from the ventilation line (304) via the ventilation unit (310) to the outside.

5. Printing unit (140) according to one of the preceding claims, wherein the printing unit (140) comprises - a plurality of printing bars (102); - a plurality of cover units (200) for the corresponding plurality of printing bars (102); and - a plurality of ventilation lines (302) for the corresponding plurality of cover units (200); wherein the individual ventilation lines (302) of the plurality of ventilation lines (302) each connect the ventilation unit (310) to the filling opening (302) of the container (202) of the respective cover unit (200) of the plurality of cover units (200) in an air-conducting manner.

6. Printing unit (140) according to claim 5, wherein the printing unit (140) has only a single ventilation unit (310) for the plurality of cover units (200).

7. Printing unit (140) according to one of claims 5 to 6, wherein - the plurality of printing bars (102) and the corresponding plurality of covering units (200) are arranged one behind the other along a transport direction (1) of a recording medium (120) to be printed by the printing unit (140); - the printing unit (140) has a connecting line (303) between each two covering units (200) arranged directly one behind the other, which connecting line connects the filling openings (302) of the containers (200) of the two covering units (200) to one another in a liquid-conducting manner, in particular in such a way that a cascade of covering units (200) is formed, which can be gradually filled with air-conditioning liquid (203) starting from a first covering unit (200) of the cascade of covering units (200).

8. Printing unit (140) according to one of the preceding claims, wherein the container (202) of the covering unit (200) is designed - to be rotated about a rotation axis (201), so that the container (202) can be arranged in an erected state or in a covering state by rotation about the rotation axis (201); - in the covering state, to receive the nozzle plate (160) of the print head (103) of the printing bar (102) in a printing bar opening (204) of the container (202) and thereby cover it; and - in the erected state, to be placed behind or in front of the printing bar (102) along a transport direction (1) of a recording medium (120) to be printed by the printing unit (140) in such a way that the printing bar (102) can be lowered past the container (202) towards the recording medium (120) in order to transfer the printing bar (102) from the parking position into a printing position.

9. Printing unit (140) according to one of the preceding claims, wherein the air conditioning liquid (203) comprises, in particular is, demineralized water.

10. A printing unit (140) for an inkjet printing device (100); wherein the printing unit (140) comprises - a plurality of printing bars (102); wherein the individual printing bars (102) of the plurality of printing bars (102) each comprise at least one print head (103); - a plurality of cover units (200) for the corresponding plurality of printing bars (102), wherein - the individual cover units (200) of the plurality of cover units (200) are each designed to cover a nozzle plate (160) of the print head (103) of the respective printing bar (102) with a container (202) in a parked position of the respective printing bar (102) of the plurality of printing bars (102); and - the individual cover units (200) are each designed to receive air conditioning fluid (203) in the container (202) of the respective cover unit (200); - a ventilation unit (310); and - a plurality of ventilation lines (302) for the corresponding plurality of cover units (200);wherein the individual ventilation lines (302) of the plurality of ventilation lines (302) each connect the ventilation unit (310) to a filling opening (302) of the container (202) of the respective cover unit (200) of the plurality of cover units (200) in an air-conducting manner;

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