EP2153998B1 - Ink supply system and method for cleaning such an ink supply system - Google Patents

Description

The invention relates to an ink supply system as described in the preamble of claim 1, and a method for cleaning such an ink supply system, as indicated in the preamble of claim 13.

Ink jet printer ink supply systems are known which include a printhead assembly having at least one printhead. According to EP 1 831 025 B1 ( WO 2006/064036 A , Such system includes a feed tank containing an ink supply for an ink jet print head and a return tank containing an excess of ink not used by the ink jet head. An intermediate container containing a larger supply of ink is connected via a line with the interposition of a filter arrangement, with the feed tank. Depending on the fill level of the ink in the feed tank, ink is conveyed from the intermediate tank into the feed tank via a conveying medium. From the inlet tank, the ink is supplied via a supply line of a first connecting line of a flow channel in a print head, the second connecting line of this flow channel is connected via a further connecting line to the return tank, which is connected via a further connecting line with the interposition of a filter assembly and a conveying means with the intermediate container is. During the printing operation, a pressure difference is established in the interior between the interior of the feed tank and the interior of the return tank via a means, such as a vacuum generator, so that the ink is transported from the feed tank through the print head to the return slab by this pressure difference. In addition to supplying the ink to the printhead (s), it is also known to flush the printhead in such an ink jet printing system to remove contaminants. For this purpose, a positive pressure is applied to both the feed tank and the return tank, which ensures that the ink contained in the two tanks is flushed out through the print head. A disadvantage of this system is that by flushing the ink through the ink jet print head through the fine holes of the individual ink jet nozzles pressed by system deposited impurities by the pressure in the fine nozzle openings of the individual nozzles of the print head and thus they can be blocked.

The invention has for its object to provide an ink supply system in which the ink can be continuously recycled and which allows the discharge of circulating contaminants with minimal effort.

This object of the invention is solved by the features in claim 1. An advantage of this ink supply system that in the printing operation, the sensitive control and keeping constant the pressure in the print head can be achieved. The arrangement of the individual components can be achieved only by low overhead, the cleaning of the return and inlet tanks, as well as the lines and the flow channels in the printhead or in the printheads without ink loss and by suction from the interior of the printhead or the printheads. As a result, laying the fine nozzle holes of the print heads is additionally avoided. A further, additional advantage is achieved by the flow through the lines, the tanks and the flow channels in the print head or in the print heads, as in the main flow direction deposited or adhering residues can be better removed with the counterflow and detached from the walls.

Through the development according to claim 2, the resulting in the course of the return of the ink from the return tank on the print head in the feed tank ink can be pumped back directly into the intermediate tank, so that they are there with the circulating, or fresh ink mixed and the appropriately trained filter can be fed again into the ink supply circuit.

A further embodiment variant according to claim 3 is advantageous since in this way the excess ink can be removed more precisely from the return tank.

With other embodiments according to claim 4 it is achieved that the pressure balance in the ink between the levels in the feed and return tank in relation to the nozzle holes of the print head can be accurately controlled and unwanted dripping of ink even with changing liquid levels in the supply and Return tanks, for example, when refilling or pumping ink, prevents and also when stopping the printing device or in printing pauses, a sufficient retention pressure of the ink in the region of the nozzle holes of the print heads can be achieved. In order to in conjunction, for example, the arrangement of pressure control means according to claim 5 is advantageous.

By a variant according to claim 6 constant pressure conditions in the ink in the region of the print head can be easily achieved. Whereby the means for maintaining a pressure difference according to claim 7 may be advantageously formed.

With another embodiment according to claim 8, it is possible to completely empty the return tank and thus also make sure that the impurities located in the bottom area can be sucked.

Furthermore, the further embodiment according to claim 9 is advantageous, since thus a complete emptying of the intermediate tank can be ensured.

Advantageous is a variant according to claim 10, since thus in the course of the cleaning process and the feed tank can be completely emptied.

A simplified admission of the inlet and return tanks with pressure medium is achieved by the development according to claim 11.

However, the present object of the invention is also solved independently by a method for cleaning an ink supply system, as described in claim 13. The advantage here is that a removal of impurities such as those caused by sedimentation in the sense of self-cleaning by means of the ink used is possible and thus the interruptions can be shortened and at the same time the cleaning runs can be carried out in an advantageous manner at shorter intervals. In addition, no additional cleaning liquid is required for this cleaning and is therefore significantly reduced by the interruption period for the cleaning cycle. In addition, the elimination of an additional cleaning liquid, the subsequent printing process can not be adversely affected. At the same time this process due to the reversal of the flow direction, a better removal of residues and impurities on the pipe walls or in the individual tanks, and possibly obtained from adhering to the walls of sedimentation or air bubbles. By reversing the flow direction of the ink against the flow direction during the printing process, the entire print head and the feed tank is rinsed and emptied during cleaning, so that all residues and sedimentation are derived safely.

Advantageously, the further procedure according to claim 14, since the ink flows in recirculation from the return tank via the feed tank in the intermediate tank fresh over the bottom of the feed tank and can better mitschwemmen there located impurities.

By the process variant according to claim 15, a suction of the impurities, in particular from the edge region of the nozzle bores in the print head is achieved, thus further reducing the formation of deposits or the risk of laying these fine nozzles.

By the alternative procedure according to claim 16, the flow rate of the ink through the feed tank can be additionally increased, so that there located impurities are better removed.

By the method variant according to claim 17 ensures that over the entire printing operation as constant as possible ink quality is achieved.

An improved cleaning effect is achieved by the example procedure according to claim 18, since during the cleaning of the feed tank, the inflow of fresh ink from the intermediate tank is prevented via the filter.

For a better understanding of the invention, this will be explained in more detail with reference to the following figures.

Fig. 1

eine Tintenstrahldruckvorrichtung mit einem Tintenversorgungssystem in stark vereinfachter, schematischer Darstellung, in der Betriebsart "Druckbetrieb";

Fig. 2

das Tintenversorgungssystem nach Fig. 1 in der Betriebsart "Reinigung" in stark vereinfachter, schematischer Darstellung;

Fig. 3

einen Teil eines Strömungskanals mit der schematischen Darstellung einer an der Kanalwand anhaftende Verunreinigung in stark vereinfachter, schematischer Dar- stellung in Seitenansicht geschnitten.

Each shows in a highly schematically simplified representation:

Fig. 1

an ink jet printing device with an ink supply system in a highly simplified, schematic representation, in the operating mode "printing operation";

Fig. 2

the ink supply system after Fig. 1 in the "Cleaning" mode in a highly simplified, schematic representation;

Fig. 3

a section of a flow channel with the schematic representation of an adhering to the channel wall impurity cut in a highly simplified, schematic representation in side view.

It should be noted that in the differently described embodiments, identical parts are provided with the same reference numerals or the same component designations, wherein the disclosures contained in the entire description can be mutatis mutandis to the same parts with the same reference numerals or identical component names. Also, the location information chosen in the description, such as top, bottom, side, etc. related to the immediately described and illustrated figure and are to be transferred to the new situation mutatis mutandis when a change in position. Furthermore, individual features or combinations of features from the different exemplary embodiments shown and described can also represent independent, inventive or inventive solutions.

All statements on ranges of values in the description of the present invention should be understood to include any and all sub-ranges thereof, e.g. the indication 1 to 10 should be understood to include all sub-ranges, starting from the lower limit 1 and the upper limit 10, i. all subregions begin with a lower limit of 1 or greater and end at an upper limit of 10 or less, e.g. 1 to 1.7, or 3.2 to 8.1 or 5.5 to 10.

The Fig. 1 shows a part of an ink jet printer 1 with an ink supply system 2 in a highly simplified, schematic representation For the sake of clarity, the ink supply system 2 is shown only for a color or an ink. Thus, for an ink jet printer 1 for printing multicolor images, there are several Provide ink supply systems 2 at least for the number of colors to be printed.

The inkjet printer 1 has a horizontally arranged transport device 3 for advancing an example. on it, held against displacement, to be printed object 4 in a feed direction 5 (as shown perpendicular to the plane out) on. Above the transport device 3 is a printhead assembly 6 with printheads 7, through which the underlying moved object 4 is printed with ink.

It should be noted that the illustrated ink supply system 2 may be used for both single pass printing installations where the printheads are themselves. Thus, further, a transport device 3 can be printed on an object to be printed 4 in the entire, maximum printing width continuously with the desired colors and, if desired, additionally with the color WHITE, a transparent ink layer and / or a protective layer. Of course, the ink supply system 2 but also for scan - print heads used with which different printheads with different printheads, and optionally the color WHITE and / or transparent and / or protective layers can be applied, but the one or more printheads only one Part of the width of the object to be printed 4 extend and in each case the color, during a movement transverse to the longitudinal direction of the object to be printed 4, is applied and the object to be printed 4 after each cross feed of the print head over the width and the transport device 3 by a voreinstellbares Extent in the conveying direction is moved intermittently forward. Furthermore, it is also possible to use the ink supply system 2 for printing devices in which the ink droplets are deflected after exiting the printhead by an electromagnetic field so that they impinge on the correct location of the object to be printed.

The object 4 to be printed may be different materials, for example film-like materials made of paper, plastic, metal, textile and the like, or nonwovens, nets and the like, but it is also possible to print plate-shaped material and band-shaped material from the abovementioned materials , In particular, it is possible plate-like material or components or films made of wood, for example, with different wood structure to this wood, ceramic as ceramic components as burned goods or as green compacts, natural stones or other natural materials such as mats, nets, nonwovens or leather and other building materials such as plasterboard, plaster components or the like to print.

The transport device 3 is formed for example by a circulating conveyor belt, which is guided or driven via at least two deflection rollers. The moving in the direction of feed 5 upper portion of the conveyor belt is supported by one or more guide plates on its underside, so that a correspondingly uniform horizontal movement of the object 4 in the feed direction 5 is achieved. Of course, it is also possible instead of a conveyor belt, a movable carriage on which the objects to be printed 4 are held by vacuum or chuck, or to move the objects to be printed 4 on a roller conveyor or guided between guide rollers below the printhead assembly 6. The printhead assembly 6 has in the present embodiment for each color a plurality of printheads 7, so that the entire width of the print medium or the object 4 can be printed at once, without the printhead assembly 6 must move relative to the feed direction in the lateral direction. That the printhead assembly 6 is stationary during printing in the lateral direction and thus arranged stationary with respect to the transport device 3.

Each of the print heads 7 has a nozzle row formed by a plurality of juxtaposed and usually linearly aligned nozzles 8. For printheads 7, as commonly used in so-called large-format printing, for example, based on piezoelectric ink ejection, the nozzle row contains, for example, 128 juxtaposed nozzles 8 (shown in FIG Fig. 1 only schematically) are indicated by dashed lines. A single print head 7 or a nozzle row accordingly has a printing width 9 measured perpendicularly with respect to the feed direction 5. The print heads 7 and their nozzle rows are lined up close to each other, so that a total print area width 10 of the print head assembly 6 results. So that the printing width 9 of the nozzle rows 8 can be lined up without gaps, the print heads 7 must be arranged alternately offset with respect to the feed direction 5, which in the illustration in accordance with Fig. 1 additionally indicated by a slight vertical displacement. The printheads 7 could instead of perpendicular also arranged obliquely with respect to the feed direction 5 In this case, a smaller printing width 9 can be achieved, but vice versa, but a higher resolution or pixel density can be achieved.

The ink supply system 2 first comprises a main tank 11 from which an intermediate tank 12 is supplied with ink. These are connected via a feed tank 13, in which a conveyor 14 is arranged. To supply the print heads 7 from the intermediate tank 12 with ink, it is connected to the print head arrangement 6 or the print heads 7 via a filling line 15. Thus, a plurality of printheads 7 are each connected by a conduit to the common sub-tank 12. It may be more advantageous that all of the intermediate tank 12 with the printheads 7 connecting filling lines 15 have a directed from the intermediate tank 12 to the printheads 7 slope. This has the advantage that air bubbles, which can arise from different causes in the pumped ink, can always escape upward and so a number of possible malfunctions of a print head 7 can be reduced.

In the filling line 15, a conveying means 16 is arranged, with which the ink is conveyed from the intermediate tank 12 through the filling line 15 to a feed tank 17 arranged between the latter and the printing heads 7. For the separation of impurities, such as, for example, sedimentation or agglomeration in the ink, a filter arrangement 18 is arranged in the filling line 5 between the intermediate tank 12 and the feed tank 17. The feed tank 17 is connected via a first connecting line 19 to an inlet of a flow channel 20 in the print head 7. In a region of the flow passage 20 opposite the first connecting line, a second connecting line 21 is connected, which connects the flow passage 20 with a return tank 22.
In this return tank 22, a suction pipe 23 is arranged, which is connected to a Rücktörderleitung 24, which opens into the intermediate tank 12. For conveying excess ink from the return tank 22 into the intermediate tank 12, a conveying means 25, for example a piston pump or vane pump, is arranged. In addition, a drain line 26 is arranged between the feed tank 17 and the intermediate tank 12, which is preferably connected in the bottom region of the feed tank 17.

It is likewise advantageous if the first connecting line is connected between the feed tank 17 and the print head 7 in the bottom area of the feed tank 17.

In the discharge line 26, a conveying means 27, for example a pump, can preferably be arranged. However, the drain line 26 can also be activated via a valve arrangement 28, if necessary, in which the line connection between the feed tank 17 and the intermediate tank 12 is opened, whereas it is preferably closed in normal printing operation.

Accordingly, it is also possible to arrange valve assemblies 29 and 30 in the filling line 15 and in the return line 24. Thus, these lines can be opened or closed as needed.

Preferably, all valve arrangements are fluid valves, which can preferably be adjusted via electromechanical drives as a function of the control commands of a central control device 31, adapted to the respective operating states. Of course, a manual adjustment of these valve arrangements, for example by emergency button or push button, possible.

At least the return tank 22, but preferably also the Zulauftänk 17 is at least alternately connected to a means 32, in particular a vacuum module, for controlling the back pressure at the print head 7. About this means 32, in particular a vacuum module, which may be formed for example by a vacuum generating plant such as a vacuum pump or a Venturi - nozzle assembly, in the inlet and / or return tank 17, 22, a corresponding back pressure to the hydrostatic pressure of the ink in the Nozzle 8 of the print head 7 are constructed.

For this purpose, at least the return tank 22, but preferably also the feed tank 17, via pressure ports 33, 34 connected to the means 32 and the vacuum generation system. Preferably, it is possible that a central vacuum generating system or vacuum pump is present and this is alternately connected via the pressure connection only with the return tank 22 or only with the feed tank 17, including a valve assembly 35, which as well as the aforementioned valve assembly 28, 29 is formed can be provided. The means 32 for controlling the back pressure further comprises active pressure control means 36. These are directly or via the control device 31 with sensor devices 37 and / or 38 and / or 39 in the return and / or inlet and / or intermediate tank 22, 17, 12 connected. They serve predominantly for determining the liquid levels in the individual tanks and can thus also be used to control the conveying means 16 and 25 via the control device 31.

The means 32 for maintaining a pressure difference, for example the vacuum system, is designed such that both the pressure difference necessary for the ink flow is generated and the pressure drop caused by the hydrostatic pressure of the liquid columns is compensated, so that the absolute pressure of the liquid column in the region of the nozzle openings (8) the print heads are less than the ambient air pressure. For this purpose, the inlet and / or return tank 17, 22 is connected to the vacuum system in such a way that the air located above a liquid level of the liquid levels 40, 41 of the ink can be placed under negative pressure relative to ambient air pressure. This is necessary to prevent bleeding of the filled inks through the nozzle opening of the print heads 7 due to the dead weight of the ink. In the inlet and / or return tank 17, 22 sensor devices 37, 38 are further arranged for level monitoring, with which the liquid levels 40, 41 of the ink can be measured. With the aid of the sensor device or devices 37, 38, the liquid level 40, 41 in the tanks can be monitored in the control device 31 and can be topped up by corresponding activation of the conveying means 16 from / to the intermediate tank 12, so that the liquid level 40, 41 is preferably kept constant can be.

Keeping the level of the liquid level at least approximately constant is important in that the height difference between the liquid level 40, 41 and the nozzle openings of the nozzles 8 in the print heads 7 corresponding hydrostatic pressure of the ink for the pressure ratios of the ink in the print heads 7 and thus is responsible for a trouble-free operation. Thus, in the stationary case, when no ink is ejected through the nozzles 8 of the print heads 7 and the ink circulates only in the circuit between the sub-tank 12, the feed tank 17, the return tank 22 and the sub-tank 12, the sum of the above liquid level in the air pressure prevailing in the tanks 17, 22 and the hydrostatic pressure of the ink liquid are equal or slightly smaller than the ambient air pressure. In the operating state in which 7 ink is ejected through the nozzles 8 of the printheads, it comes through with the flow of the ink in the lines connected flow resistance to a fluid pressure of the ink in the printheads 7 reducing pressure loss. The air pressure generated by the means 32 above the liquid level 40, 41 in the tank or in the tanks 17, 22 should therefore be adjusted so that the fluid pressure of the ink in the print heads 7 in each operating state between standstill and maximum ink ejection in a for the trouble-free operation of the printheads 7 required pressure - tolerance field is.

Quite generally speaking, the negative pressure or the air pressure prevailing over the liquid level 40, 41 must be set in such a way that on the one hand the pressure difference necessary for the ink flow and the correct meniscus negative pressure prevail at the nozzle opening.

The representation in Fig. 2 corresponds to the illustration in Fig. 1 , which is why the same reference numerals have been used for the same parts.

The process flow in the operation of the ink jet printer 1 is as follows.

The ink is sucked from the intermediate tank 12 via a suction nozzle of a filling line 15 by a conveyor 16, for example, a feed pump from the intermediate tank 12 and cleaned by a, for example, between the intermediate tank 12 and the conveyor 16 arranged filter assembly 18 and optionally additionally degassed via a degassing 42 before it is supplied to the feed tank 17 after passing through a valve arrangement 29 opened in this case for the passage. The fill level 40 of the ink is monitored in the feed tank 17 by a sensor or a sensor arrangement 38. About the means 32 for controlling the pressure conditions in the feed tank 17 and in the return tank 22 is, for example, by applying a negative pressure in the interior of the return tank 22 at a corresponding in Fig. 1 shown position of the valve assembly 35, the ink forcibly fed via the first connecting lines 19, each independently, the flow channels 20 in each parallel connected printheads 7, from where the ink by applying for example piezo elements or by any other from the prior Technique known pressure generator for ejecting an ink drop from a nozzle 8 of the print head 7, the ink is discharged onto the object 4 pointwise.

Regardless of how many drops of ink are dispensed by a print head 7 in the unit time, regardless of this, the flow of ink through negative pressure prevailing in the return tank 22 is forced through the second connecting line 21 into the return tank 22. If a predeterminable fill level 41 is exceeded there, the excess ink is returned via the suction line 23 to the return line 24 and from this, optionally with the interposition of a degassing unit 43, to the intermediate tank 12.

For this forced recycling of the excess ink from the return tank 22, a conveying means 25, for example a pump, may also be controlled by the central control means 31 in dependence on the level 41, which may be monitored with one or more sensor devices 37.

During the printing process, the flow of ink through the drain line 26 is inhibited. This can be done by stopping the conveyor 27 and / or by shutting off the line through the valve assembly 28, such as in Fig. 1 also shown, done. In order to prevent and / or remove deposits by particle agglomeration, sedimentation, gelation or the like, it is now possible with the ink supply system 2 described, intermittently, ie in a previously determinable or controlled dependence on the flow rate of the ink and the amount of ink consumed To reverse ink flow in the connecting lines 19 and 21. Thus, such deposits and contamination can be kept in limbo, or a solid adhesion and deposition, especially a resistant deposit, only by the reversal of the flow direction of the ink, advantageously also during a continuous printing process can be reduced. This reversal of the direction of flow of the ink through the connection lines 19 and 21 can be achieved, for example, by adjusting the valve assembly 35 in the feed tank 17, a higher negative pressure is built up as in the return tank 22 and thus the ink is forced from the return tank 22 into the feed tank 17th flow back.

For example, a mode may be provided in which the period during the reversing passage of the ink, in the direction opposite to the normal direction to keep relatively short, so that any overheating in the printheads 7 by supply the optionally slightly warmer ink in the return tank 22 relative to the feed tank 17 can be avoided.

An improvement is to be achieved if the conveying means 16 and 25 are designed either for reversible conveying of the ink or parallel connected conveying means are arranged in order to reverse the ink passage in the return line 24 and the filling line 15 at any time.

It is also advantageous if the circulation of the ink takes place directly between the feed tank 17 and the return tank 22. This arrangement for printing operation even in normal operation has the advantage that when scanning printheads, that is those that are moved back and forth intermittently transversely to the feed direction of the object to be printed 4, the moving masses could be reduced by eliminating the mitzubewegenden Entleenmgsleitung 26. In this case, it can also be advantageous to arrange a filter arrangement 18 or a degassing unit 43 in the line between the return duct 22 and the inflow tank 17.

In this circulation line 44 and a corresponding conveyor 46 may be arranged.

The control of the negative pressure conditions in the inlet and return tanks 17, 22 and the various conveying means 16, 25 can be done by the central control device 31, according to the known specifications. Via the control device 31, the means 32 with the active pressure control means 36 can be controlled accordingly to ensure the previously described pressure conditions in the inlet and return tanks 17, 22 and in the printheads 7, in particular in the outlet region 8. For this purpose, for example, instead of or in addition to the regulation of the pressure in the vacuum module, means 32, also in the inlet and / or return tank and / or in the flow channel pressure sensors 45 may be arranged.

In Fig. 2 It is shown that between the previously described, short-term reversals of the ink flow between inlet tank 17 and return tank 22 or alternatively only a cleaning of the inlet and outlet tanks 17 and 22 by reversing the by negative pressure forced delivery of the ink from the return tank 22 into the feed tank 17, can be achieved.

This can be done, for example, that the negative pressure in the feed tank 17 by switching the valve assembly 35 in the in Fig. 2 shown position is increased and thus the ink from the flow channels 20 of the individual print heads 7 the connecting lines 19, 21 and the return tank 22 is withdrawn. The resulting ink in the feed tank 17 excess ink can be sucked by opening the valve assembly 28 and / or actuation of the loading of the conveyor 27 into the intermediate tank 12. Thus, during the printing process due to physical / chemical processes in the ink resulting particle agglomerations, sedimentation, gelation and the like, on the connecting lines or in the tanks, such as in Fig. 3 indicated schematically adhere, are easily replaced by the normal pressure to the opposite flow direction and reclaimed into the feed tank 17 and into the intermediate tank 12.

As a result, the deposits 47 which may be present in the flow channels 20 of the print heads 7 or impurities which otherwise lead to irretrievable nozzle fissures are flushed out.

The parallel connection of printheads 7, especially the parallel connection of each printhead 7, between the inlet and outlet tanks 17, 22, has the advantage that the degree of contamination and disturbances due to contamination can be significantly reduced, since the ink only by a single Flow channel 20 of a single printhead 7 flows through.

In this operating state is like in Fig. 2 shown position of the valve assemblies 29 and 30, the supply of fresh ink through the filling line 15 and the discharge of ink from the return tank 22 via the return line 24 prevented.

The advantage here is that the impurities are sucked out of the flow channels 20 and thus clogging of the fine nozzle channels by the negative pressure in the feed tank 17 can be removed more easily and gently, in contrast to pressurization with overpressure.

This cleaning process or cleaning cycle can be further enhanced by the fact that after the interruption of the ink supply from the filling line 15 and the ink discharge through the return line 24 by a correspondingly applied negative pressure in the return tank 22, the entire ink supply from the feed tank 17 via the bottom area and sucked through the Printheads 7, possibly even with a higher flow rate, can be washed through. When the feed tank 17 is then emptied, the negative pressure can be applied via the means 32, for example by switching the valve arrangement 35, exclusively to the feed tank 17 or a higher pressure in the return tank 22 than in the feed slab 17.

This is sucked out of the bottom region of the return tank 22 and fed through the connecting lines 19, 21 and the flow channels 20 of the print heads 7 into the feed tank 17 and from there via the discharge line 25 to the intermediate tank 12.

The aforementioned impurities resulting from these cleaning operations do not interfere with the further use of the ink since they mix with the ink supply in the intermediate tank 12 and with the fresh ink optionally supplied from the main tank 11 and the conveyance of the ink from the intermediate tank 12 via the filter assembly 18, in which these impurities are then finally eliminated and removed from the ink circulation.

In Fig. 3 is purely schematic part of a channel such as the inlet channel 13, the flow channel 20 or a line such as the filling line 15 and the connecting line 19 and 21 cut in side view shown. In this channel or in this line adheres to a formed, for example, by particle agglomeration, sedimentation, gelation and the like deposit 47 at. It is now shown schematically that this deposit 47 in the flow direction 48, which is present for example in the normal pressure operation, abuts an inner wall 49 of the line 19. If now the flow direction 48 is reversed to a flow direction 50, as with a dashed arrow, the deposit 47 provides greater resistance to the flowing medium and can therefore, as with dashed lines Lines indicated, more easily lifted from the inner wall 49 and by the thus additionally opposite to the flow resistance, are more easily detached from the inner wall 49 and flushed out.

As a result, the cleaning effect can be additionally reinforced when using an opposite flow direction 50.

The ink supply system described above also requires heating and temperature control of the ink. For this purpose, it is possible, for example, that the ink is already preheated or heated in the main tank 11. For this purpose, electrical heating elements 51 may be arranged in the main tank as well as temperature sensor 52. The control of the heating elements 51 under monitoring with the temperature sensors 52 may be effected via the control device 31.

However, it is essential that the ink in the intermediate tank 12 is precisely controlled and controlled by means of heating elements 51 on the basis of the temperatures measured by the temperature sensors 52 and the ink is kept at the temperature required in the print heads 7. Optionally, it is also possible to slightly exceed this temperature, so that despite possible cooling in the transport lines from the intermediate tank 12 to the printheads 7, the ink with the desired temperature to the feed tank 17 and the printheads 7 can be supplied.

In a particularly advantageous further development, two heating stages are provided in the ink supply system according to the invention, and in addition to the first heating stage, namely the heating elements 51 in the intermediate tank 12, a heating element 51 is also arranged in the feed tank 17 and the temperature in this feed tank 17 with temperature sensor 52 is precisely monitored. The heating elements 53 can be performed with lower power than the heating elements 51 in the intermediate tank 12 and therefore, even with the appropriate use of temperature sensors with very high accuracy, an exact control of the temperature in a range of +/- 0.2 ° C possible.

As in the intermediate tank 12, the control can take place by means of the control device 31.

These two heat levels can ensure that the temperature of the ink in the printheads 7 can be maintained extremely accurately. This is particularly advantageous for achieving a high-quality printing result, since the temperature has a very high influence on the viscosity and thus on the drop formation on ejection of the inks onto the print heads 7.

For example, it is also possible to arrange heating elements 51 or 53 in the return tank 22. These heating elements in the return tank 22 can be used to heat the ink to a higher temperature during the cleaning process, so that a higher viscosity is achieved. This favors the flow properties of the ink during the cleaning process and the flushing out of impurities or the dissolution of sedimentations or agglomerations. In this context, it may also be possible to increase the temperature of the ink with the heating elements 53 in the short term before the start of the cleaning process, especially when the ink is first pumped from the feed tank 17 into the return tank 22, in order to already flush the print heads 7 in the direction of the return tank 22 to take advantage of these advantages of the higher viscosity of the ink can.

The embodiments show possible embodiments of the ink supply system 2, it being noted at this point that the invention is not limited to the specifically illustrated embodiments thereof, but rather various combinations of the individual embodiments are possible with each other and this possibility of variation due to the teaching of technical action representational invention in the skill of those skilled in this technical field. So are all conceivable embodiments, which are possible by combinations of individual details of the illustrated and described embodiment variant, includes the scope of protection.

For the sake of order, it should finally be pointed out that in order to better understand the structure of the ink supply system, these or their components have been shown partially unevenly and / or enlarged and / or reduced in size.

The task underlying the independent inventive solutions can be taken from the description.

REFERENCE NUMBERS

1

inkjet

2

Ink supply system

3

transport means

4

object

5

feed direction

6

Printhead assembly

7

printhead

8th

jet

9

print width

10

Print Area Width

11

main tank

12

intermediate tank

13

inlet channel

14

funding

15

filling line

16

funding

17

supply tank

18

A filter assembly

19

First connection line

20

flow channel

21

Second connecting cable

22

Return tank

23

suction

24

Rückforderleitung

25

funding

26

drain line

27

funding

28

valve assembly

29

valve assembly

30

valve assembly

31

control device

32

medium

33

pressure connection

34

pressure connection

35

valve assembly

36

Active pressure control means

37

sensor device

38

sensor device

39

sensor device

40

liquid Level

41

liquid Level

42

degassing

43

degassing

44

circulation line

45

pressure sensor

46

funding

47

deposit

48

flow direction

49

inner wall

50

flow direction

51

heating elements

52

temperature sensor

53

heating element

54

55

Claims (24)

1. Ink supply system (2) for an inkjet printer (1) with a print head assembly (6) comprising at least one print head (7) with one or more nozzles (8) for at least one colour, in which the print head (7) is connected via a first connecting line (19) to a supply tank (17), which is connected to an intermediate tank (12) via a filler line (15) with an interconnected conveyance means (16) and filter assembly (18), and via a second connecting line (21) to a return tank (22) and to a means (32) by means of which a differential pressure can be maintained between a pressure in the supply tank (17) and a pressure in the return tank (22) when necessary, and the means (32) controls a flow of ink from the supply tank (17) via at least one flow channel (20) in the print head (7) to the return tank (22), and the return tank (22) is connected to the intermediate tank (12) via a return line (24), optionally with an interconnected conveyance means (25), characterised in that the ink supply system (2) has a controller (31) which can be set so that the means (32) can be activated by it in such a way that the pressure differential between the pressure in the return tank (22) and the pressure in the supply tank (17) is intermittently varied so that the differential pressure causes a flow of ink from the return tank (22) to the supply tank (17) through the print head (7).
2. Ink supply system (2) as claimed in claim 1, characterised in that the supply tank (17) is connected to the intermediate tank (12) by a drainage line (26) which can be activated as necessary.
3. Ink supply system (2) as claimed in claim 2, characterised in that a conveyance means (27) is disposed in the drainage line (26).
4. Ink supply system (2) as claimed in claims 1 to 3, characterised in that the means (32) for controlling the counter-pressure at the print head (7) comprises a pressure connection on the supply and return tank (17, 22).
5. Ink supply system (2) as claimed in claims 1 to 4, characterised in that the controller (31) for controlling a counter-pressure at the print head (7) comprises an active pressure controller.
6. Ink supply system (2) as claimed in claims 1 to 5, characterised in that the pressure controller (36) has sensor devices (37, 38) for ascertaining the fluid levels (40, 41) in the supply and/or return tank (17, 22).
7. Ink supply system (2) as claimed in claims 1 to 6, characterised in that the means (32) for maintaining a differential pressure comprises means for maintaining a difference in level between the fluid levels (40, 41) in the supply and/or return tank (17, 22).
8. Ink supply system (2) as claimed in claims 1 to 7, characterised in that the means (32) for maintaining the differential pressure between the supply and return tank (17, 22) necessary for causing the ink flow is designed such that this differential pressure, as a sum of the hydrostatic pressures of the fluid levels (40, 41) in the supply and return tank, causes the absolute pressure in the fluid columns in the vicinity of the nozzle openings (8) of the print heads to assume a level below the ambient air pressure.
9. Ink supply system (2) as claimed in claims 1 to 8, characterised in that the second connecting line (21) is connected in the vicinity of the bottom of the return tank (22).
10. Ink supply system (2) as claimed in claims 1 to 9, characterised in that the drainage line (26) between the supply tank and intermediate tank (17, 12) is connected in the vicinity of the bottom of the supply tank (17).
11. Ink supply system (2) as claimed in claims 1 to 10, characterised in that the first connecting line (19) between the supply tank and print head (7) is connected in the vicinity of the bottom of the supply tank (17).
12. Ink supply system (2) as claimed in claims 1 to 11, characterised in that a valve assembly (35) is disposed between the means (32) for generating or maintaining the differential pressure in the supply and return tank (17, 22), for selectively connecting the means (32) to the supply tank or to the return tank (17, 22).
13. Method of cleaning an ink supply system (2) in which the ink circulates from a supply tank (17) via the print head (7) to a return tank (22) and back to the supply tank (17) during printing, in particular as claimed in one of claims 1 to 12, characterised in that the flow direction of the ink in the vicinity of the print head (7) is at least intermittently reversed at least once for a predetermined period of time during the cleaning process.
14. Method of cleaning an ink supply system (2) as claimed in claim 13, characterised in that all of the ink is drained out of the supply and return tank (17, 22) into the intermediate tank (12) during or after the cleaning process.
15. Method of cleaning a print head as claimed in claim 13 or 14, characterised in that the ink is fed from the return tank (22) through the print head (7) into the supply tank (17) and from there into the intermediate tank (12) whilst the print head (7) is being cleaned.
16. Method of cleaning a print head as claimed in one of claims 13 to 15, characterised in that all of the ink is fed from the supply tank (17) through the print head (7) into the return tank (22) during the cleaning process, after which the direction of ink conveyance is reversed and all of the ink in the return tank (22), connecting lines (19, 21), print head (7) and supply tank (17) is drained into the intermediate tank (12).
17. Method of cleaning a print head as claimed in one of claims 13 to 16, characterised in that a negative pressure is generated in the supply tank (17) in order to suck the ink out of the return tank (22) via the print head (7) into the supply tank (17).
18. Method of cleaning a print head as claimed in one of claims 13 to 17, characterised in that the ink is pumped from the supply or return tank (17, 22) into the intermediate tank (12) by means of a conveyance means (27, 25).
19. Method of cleaning a print head as claimed in one of claims 13 to 18, characterised in that a vacuum is generated alternately in the return or supply tank (22, 17) or inside the return or supply tank (22,17) during the cleaning process in order to convey the ink from the supply tank into the return tank (17, 22) and from the return tank into the supply tank (22, 17) via the print head (7).
20. Method of cleaning a print head as claimed in one of claims 13 to 19, characterised in that the ink fed from the intermediate tank (12) to the supply tank (17) is filtered and fresh ink is added from a main tank (11) during printing or whilst cleaning the ink returned to the intermediate tank (12).
21. Method of cleaning a print head as claimed in one of claims 13 to 20, characterised in that the supply of fresh ink to the supply tank (17) is interrupted during the alternate filling and draining of the supply and return tank (17, 22).
22. Method of cleaning a print head as claimed in one of claims 13 to 21, characterised in that the ink in the intermediate tank (12) is preheated to close to the required process temperature during a first heating stage and is then heated to the precise printing temperature in the supply tank (17).
23. Method of cleaning a print head as claimed in one of claims 13 to 22, characterised in that the ink is held at the desired printing temperature within a tolerance range of +/- 0.5°C and preferably +/- 0.2°C.
24. Method of cleaning a print head as claimed in one of claims 13 to 23, characterised in that the ink is heated to above the temperature required for printing during the cleaning process.

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