WO2024193828A1 - Method for cleaning the print head of a cij printer, and cij printer - Google Patents

Abstract

A method for cleaning a print head (40) of a CIJ printer (1), in which at least one fluid required during the cleaning is actively supplied within the print head (40) and is passively removed into a collecting container (51), and a CIJ printer (1) for carrying out this method are provided.

Description

Procedure for cleaning the print head of a CI J printer and CI J printer

The invention relates to a method for cleaning the print head of a CI J printer and a CI J printer for carrying out this method.

Inkjet printers are a widely used class of printers. One family of this class that is particularly suitable for industrial applications and has therefore achieved a high market penetration are the so-called continuous inkjet printers (CIJ printers).

A continuous inkjet printer prints with an ink which is usually mixed with a variable component of solvent in the printer, which in particular enables the viscosity or the jet speed to be regulated.

The ink mixed with the solvent is fed under pressure to a nozzle on the print head, where the drops required for the actual printing process are created from the ink jet according to the basic principle of Rayleigh's disintegration of laminar liquid jets and which is subsequently referred to as the ink outlet nozzle. The formation of drops and in particular the size of the drops is controlled by a modulation which is imposed on the ink jet, for example by suitably excited piezo elements.

The drops thus produced are electrically charged in a suitable manner and guided onto a desired trajectory by deflection electrodes that are also part of the print head, which either leads them to a desired position on a substrate to be printed or, if no printing process is taking place, is intended to lead to a catching device, e.g. a catcher tube, which returns the ink for the purpose of reuse.

As is clear from the above, different fluids are transported and used within the inkjet printer. The components required for this, in particular lines, valves, pumps, compressors and reservoirs including the control electronics of these components, together form the hydraulic system of the CIJ printer. It should be noted that a hydraulic system of a CIJ printer can also have several completely separate hydraulic circuits.

The element to be printed, e.g. a letter or a number, is thus realized by a matrix or bitmap of ink drops, whereby one dimension, i.e. rows or columns of the matrix or bitmap, is usually realized by the deflection of the ink drops and the other dimension is realized by a material feed of the material to be printed.

Long-term operation of a CIJ printer will result in ink deposits in the print head, particularly on the ink exit nozzle, but also on the electrodes, deflection plates and the catcher, which will affect the proper functioning of the CIJ printer. It is therefore common practice to subject these components, and in particular the nozzle, to a cleaning process when necessary.

From the prior art, for example US 8, 628,169 B2, it is known to hang the print head in a cleaning station with a fluid access, into which a Cleaning fluid flows into the inlet contained in the cleaning station until contact is made with the print head or its components to be cleaned, whereby this inflow can also be achieved by a jet directed at a component of the print head to be cleaned. After a defined cleaning time, the cleaning fluid, which can in particular be formed by the solvent for the ink, is then drained off again. In this solution, the cleaning fluid is fed from outside the print head for what is essentially a passive cleaning process; the cleaning process takes place mainly in a bath.

Although this can achieve good cleaning results, the approach has a number of serious disadvantages. In particular, solvent must be present in the cleaning station or must be supplied to it, which requires additional supply lines and possibly additional pumps. In addition, the cleaning process takes a relatively long time.

An alternative approach to this is known in particular from JP 2015 134 435 A. There, an attempt is made to carry out the entire cleaning process when the printer is switched off and completely within the print head by spraying solvent from one or more additional nozzles in the print head onto the components of the print head that are to be cleaned and an attempt is made to actively rather than passively remove the contaminated solvent by sucking it away with the catcher tube. The problem here, however, is that the efficiency of the suction process is not optimal, which means that although the actual cleaning can be done more quickly than in a bath, the time until the cleaned components are removed again is shorter. which are dry, takes longer because the suction through the catcher pipe is not as efficient as one would like.

The object of the invention is therefore to provide a method for cleaning the print head of a CI J printer which, using as few additional components as possible, enables a quick cleaning process and a quick drying process and brings about a good cleaning result, and to provide a CI J printer with which this method can be carried out. These objects are achieved by a method for cleaning a print head of a CI J printer with the features of patent claim 1 and a CI J printer with the features of patent claim 11. Advantageous further developments of the method and of the CI J printer are the subject of the respective dependent claims.

The method according to the invention for cleaning a print head of a CI J printer is characterized in that at least one fluid required for cleaning is actively supplied within the print head - i.e. not through a nozzle arranged outside the print head, for example in a cleaning station -, in particular driven by pressure, and is passively discharged into a collecting container, i.e. without the support of a suction mechanism or the like.

This approach makes it possible to use components already present in the CI J printer, such as pipes and/or pumps, to implement the active supply of the solvent and cleaning by the solvent, particularly under pressure and in a solvent jet, which are crucial for a quick and thorough cleaning of the contaminated parts of the print head. This avoids having to provide such components additionally in the cleaning station or on the collection container.

At the same time, however, such a cleaning station, which is now essentially formed by the collecting container, is still present. After interacting with the parts of the print head to be cleaned, the fluid used for cleaning, in particular solvent, can simply drain passively into the collecting container under the effect of gravity, which promotes a faster drying process without the fluid used for cleaning having to be actively sucked out, which is time-consuming and may not be completely successful. In addition, this makes the construction of the cleaning station very simple and cost-effective.

According to a particularly preferred embodiment of the method, clean solvent required for cleaning is fed - preferably completely - through the collector tube of the print head and sprayed onto the components of the print head to be cleaned. This avoids the need to provide a separate cleaning nozzle inside the print head.

Another feature of the catcher tube is that it is positioned at a point on the print head from which the solvent jet can be directed very directly and with favorable geometric parameters onto the components of the print head to be cleaned, in particular the ink outlet nozzle. This allows deposits to be removed quickly and effectively. In this cleaning operation, the catcher pipe is not configured with negative pressure for suction, but is pressurized and connected to the solvent reservoir.

In order to be able to get the CI J printer ready for use again as quickly as possible, it is advantageous if the process includes a drying step and if air, as an additional fluid required for drying, is fed through the catcher tube of the print head and blown onto the components of the print head that are to be dried. Here, it is particularly advantageous that the air jet for drying is directed directly onto the areas that were previously wetted primarily by the solvent jet, because it comes from the same opening, namely that of the catcher tube. In this configuration, the catcher tube is therefore connected to a compressor and/or a compressed air reservoir.

The efficiency of both the actual cleaning and the drying is further increased if the position at which the fluid required during cleaning - i.e. cleaning liquid, for example in the form of solvent and/or air - is actively supplied within the print head, in particular under excess pressure, is varied during cleaning. This can be achieved in particular by changing the position of the catcher tube within the print head, preferably by moving the catcher tube, which can particularly preferably be carried out essentially parallel to the jet axis of the undeflected ink jet.

While in principle a discontinuous supply of fluid required during cleaning is possible, e.g. in the form of bombarding the individual components with solvent drops, it has been shown that the active supply of fluid during The use of the fluid required for cleaning in a jet leads to better cleaning results , which could be due to the fact that in this case a re - accumulation of previously detached dirt particles is more reliably avoided .

This jet preferably runs essentially parallel to the axis of the direction in which a non-deflected ink jet propagates during printing of the CI J printer. In practice, this choice of direction proves to be particularly efficient for removing deposits on the components to be cleaned.

Preferably, the properties of the jet are varied during the active supply of fluid required during cleaning. For example, by varying the pressure at which solvent sprays out of the catcher tube, the point of impact can be varied and/or the jet profile can be influenced for a given position of the catcher tube. This also makes it possible to adapt the current jet parameters to the component to be cleaned and to efficiently suppress undesirable behavior of the fluid used for cleaning at certain positions, such as droplets spraying when the jet hits the component to be cleaned at a point on the print head that is difficult to dry again.

It can also be advantageous if the variation of the properties of the jet is adapted to the ink used.

The probability of successfully removing even very stubborn deposits or residues during cleaning can be further increased if at least one A pulse-like discharge of at least one fluid occurs, i.e. a pressure surge occurs.

In a preferred embodiment of the method, it is additionally provided that the cleaning success is verified by an electrical check before the end of the method. This can generally be carried out using additional components, but it is also possible to check by appropriately controlling and monitoring the electrodes that are already present in the print head.

The CI J printer according to the invention for carrying out the method according to the invention comprises in particular at least one solvent tank, at least one ink tank and at least one print head, which has a nozzle for ejecting ink, deflection electrodes and a catcher tube for returning ink ejected from the nozzle that is not used for printing. It also has a hydraulic system. The hydraulic system comprises the components required for transporting and using the fluids used in the CI J printer, in particular solvents, concentrated ink, ink and optionally compressed air, in particular lines, valves, pumps, compressors and reservoirs including the control electronics of these components, which can also form different, separate hydraulic circuits. In particular, the ink tank and the solvent tank are also components of the hydraulic system.

An ink tank within the meaning of this disclosure is also to be understood as an ink cartridge or another replaceable reservoir from which the ink is supplied. The term "solvent tank" is to be understood in an analogous manner. It is essential to the invention that the hydraulic system (100) is constructed in such a way that it has means for actively supplying at least one fluid required for cleaning into the print head (40) and that the CI J printer (1) has a collecting container for passively receiving the fluid used for cleaning after it has been used for cleaning.

Particularly preferably, the hydraulic system is constructed in such a way that it sucks a fluid out of the catcher pipe in a first operating mode and feeds a fluid under pressure into the catcher pipe in a second operating mode.

This is the case, for example, when the catcher tube is connected to a supply line, which can be designed as a hose, for example, which is in fluid communication with a suction pump via a two-way valve in the first operating mode, and the ink drops sucked out of the catcher tube are fed to a reservoir, which can be formed, for example, by a mixing tank, while in the second operating mode fluid communication is established between the supply line and a tank for cleaning agents, which can be formed in particular by the solvent tank, wherein a pressure pump is present in order to pressurize the solvent pumped from this tank. Switching between the operating modes can then be carried out in this example simply by switching a two-way valve.

In a preferred embodiment of the CI J printer, the hydraulic system is designed such that in a third operating mode it feeds a different fluid than in the second operating mode under pressure into the catcher tube. Here again, a possible example configuration is given that achieves this and is based on the example configuration described above. To do this, the two-way valve is replaced by a two-way valve, via which, in the third operating mode, fluid communication between the supply line and a connecting line to a compressor and/or a compressed air reservoir can be established, so that compressed air can be blown out of the catcher pipe.

It has also proven advantageous if the hydraulic system is constructed in such a way that the pressure under which the fluid is fed into the catcher pipe is variable. This is particularly the case when the pressure is built up using adjustable pumps or compressors, but can also be achieved using suitable means for influencing the line cross-section or adjustable reducing valves. One advantage of such a construction of the hydraulic system is that the impact point of the jet can be varied and/or the jet profile of the jet can be influenced by the pressure variation. If the hydraulic system is designed to enable a first fluid and a second fluid to be introduced into the catcher pipe for expulsion from the same, in addition to the usual suction function of the catcher pipe, a construction which enables a variable pressure for each of the two fluids can bring particular advantages.

In an advantageous variant of the CI J printer, the hydraulic system is designed in such a way that it has an intermediate storage for a pressurized fluid, the content of which can be introduced into the catcher pipe through other components, in particular lines, of the hydraulic system. Such an intermediate storage, which can also be designed as an additional reservoir, can serve to to enable pulsed discharges of fluid in the form of pressure surges, which brings advantages in the cleaning process.

Another development of the CI J printer provides that the catcher tube can be moved within the print head. It is particularly preferred that the directions in which the catcher tube can be moved also include the direction parallel to the propagation direction. This opens up a further parameter for varying the point of impact of fluid ejected from the catcher tube, which can be very valuable both for a cleaning process with solvent and for a drying process with compressed air.

The invention is explained in more detail below with reference to figures showing exemplary embodiments. They show:

Fig. 1 : A schematic representation of a CI J printer from the outside,

Fig. 2: a schematic representation of essential components of the hydraulic system of the CI J printer from Figure 1 and a schematic representation of the structure of the print head of the CI J printer from Figure 1; and

Fig. 3: a flow diagram of an embodiment of the method.

The CI J printer 1 shown schematically from the outside in Figure 1 has a base unit 10 with HMI display 20, which is connected to the print head 40 via a head line 30 shown in a very shortened form. There is also a cleaning station 50 with a collecting container 51, into which the print head 40 can be used for cleaning completely, or at least with its components to be cleaned (e.g. without its outer housing). In this embodiment, the cleaning station 50 is arranged on the side of a housing wall of the basic device 10, but it can also be implemented as a separate cleaning station.

Figure 2 shows schematically the essential components of the hydraulic system 100 of the CI J printer 1 located within the basic unit 10 as well as the internal structure of the print head 40 of the CI J printer 1.

The hydraulic system 100 has an ink tank 101 and a solvent tank 102. A pump 103 can convey ink from the ink tank 101 into a mixing tank 110 via a line 104 in which a controllable valve 105 is arranged. The pump 103 can also convey solvent from the solvent tank 102 via a line 106 in which a controllable valve 107 is arranged, so that the viscosity or the jet speed can be regulated by adjusting the ratio of ink and solvent in the mixing tank 110.

From the mixing tank 110, the ink mixed with solvent can be led out of the base unit 10 via a line 111 and into an ink supply line running inside the head line 30, where it is conveyed by a pump 112 and flows through a pressure tank 113 inside the base unit. In this example, the pressure tank 113 is pressurized with compressed air from the compressor 150 on one side, which is separated from the ink/hydraulics by a membrane. Accordingly, the wet side deforms the membrane under working pressure and the compressed air forms the counter pressure. Within the print head 40, the ink mixed with solvent passes through the section running in the print head 40

41 of the ink supply line into a tube 42 . At the ink outlet nozzle , which is connected by a nozzle 43 at the outlet of the tube

42 is formed, the drops required for the actual printing process are then created from the ink jet according to the basic principle of Rayleigh decay of laminar liquid jets.

Those drops which are to be printed are charged in a defined manner at the charging electrodes 44 and deflected by the deflection electrodes 45; their trajectory is shown as an example in the representation of the structure of the print head 40 in Figure 2 as a curved dashed line. Those drops which are not to be printed are not charged at the charging electrodes 44 and are therefore not deflected by the deflection electrodes 45; their trajectory is shown as an example in the representation of the structure of the print head in Figure 2 as a straight dashed line and ends in the catching device, here designed as a catcher tube 46, which can be moved within the print head 40 via the drive 47, which is formed by a motor and a spindle on which the catcher tube 46 is mounted, and essentially parallel to the trajectory of the undeflected ink drops.

The catcher pipe 46 is connected to a line 48 shown in dash-dotted lines in Figure 2, the return suction line, which is led back into the base unit 10 through the head line 30.

The return line is connected via the valve block 120 , which has three

Two-way valves 121 , 122 , 123 , to the hydraulic system 100 connected. Depending on the position of the two-way valves

121 , 122 , 123 the catcher pipe 46 and the return suction line connected to it can be used in different ways.

In a first position of the two-way valve 121, the line 48 shown in dash-dotted lines is actually operated as a return suction line. In this position, which is set in particular during regular printing operation, the suction pump 131 sucks fluid - in particular the unprinted ink drops - out of the catcher tube 46. Since the catcher tube 46 in this example is in fluid communication with the mixing tank 110 via the return suction line and the line 132 with suction pump 131, the unused ink drops are returned to the supply in this operating mode and the material used to form them can be used again for printing.

The second position of the two-way valve 121 is selected when fluid is to be transported in the opposite direction through the line 48, which forms the return suction line, so that it exits the catcher pipe 46. The fluid which is then transported through the line 48 and exits the catcher pipe 46 is, depending in particular on the position of the two-way valve 122, either solvent pumped from the solvent tank 102 through the line 142 by a pump 141 or compressed air generated by a compressor 150 and supplied through the line 151 with the two-way valve 123 set accordingly. A pressure tank (not shown) can also be provided, through which compressed air can be provided instead of the compressor or in addition to the compressor 150. How strongly or weakly the solvent exits the catcher pipe can be adjusted, for example, by appropriately controlling the pump 141. During regular printing operation of the CI J printer 1, however, the compressed air generated by the compressor 150 is fed to the pressure tank 113 through the two-way valve 123, which is then in its other switching position, where it is used to form a counterpressure to the working pressure prevailing on the wet side of the membrane of the pressure tank 113.

An exemplary embodiment of the cleaning process, which can be started, for example, with a wizard after the print head 40 has been inserted into the cleaning station 50 in its entirety or at least with its components to be cleaned, can be understood from the flow chart in Figure 3.

In step S 1 , the catcher tube 46 and the return suction line connected to the catcher tube 46 are drained by means of the suction pump in order to remove ink residues still contained in the catcher tube 46 .

In step S2, which can preferably also be carried out completely or partially in parallel to step S1, the catcher tube 46 is moved as far as possible from the ink outlet nozzle and the charging electrodes 44 or deflection electrodes 45, which is referred to below as the "open" position. This is intended to prevent solvent emerging from the catcher tube 46 in the next step, which may still be contaminated with ink residues, from accumulating on components to be cleaned, which would be counterproductive.

In step S3, solvent is introduced into the return suction line and passed through it and the catcher pipe 46. This cleans the return suction line and the catcher pipe 46. Accordingly, at the beginning of step S3, the solvent exiting the catcher tube 46 is initially contaminated with ink residues. This contamination gradually decreases over time. The solvent exiting the catcher tube 46 runs into the collecting container 51 during this step; in particular, the solvent merely swells out of the catcher tube 46, i.e. is not sprayed out of its opening under high pressure as long as the exiting solvent could still be contaminated.

In step S4, the electrode block and nozzle 43 are cleaned. To do this, the catcher tube 46 moves up to the electrode block and the solvent to be fed through the catcher tube 46 is pressurized by the pump 141 so that fresh solvent sprays out of the catcher tube 46 and cleans the nozzle 43 and the charging electrodes 44. Because the opening of the catcher tube is located near the components to be cleaned due to the process and a sharp jet is created by the pressurization with the pump 141, this part of the cleaning process is highly efficient. The efficiency of this process is also contributed to by the fact that the catcher tube 46 and thus also the solvent jet emerging from it are aligned substantially parallel or collinear to the trajectory of the undeflected ink drops, which is particularly advantageous for cleaning the ink outlet nozzle, i.e. the nozzle 43.

In step 5, the deflection electrodes 45 are cleaned. To do this, the catcher tube 46 moves back in the direction of the "open" position. Then the solvent to be fed through the catcher tube 46 is pressurized again by means of the pump 141, so that fresh solvent sprays out of the catcher tube 46 to clean the deflection electrodes 46. clean. A few seconds may be sufficient for this too. It may be useful to use a different pressure; in particular, this can compensate for a different distance between the opening of the catcher tube 46 and the surfaces to be cleaned, and the jet profile can be adjusted using the parameters of the distance of the opening from the surfaces to be cleaned and the pressure of the pump 141.

Also in steps S4 and S5, the dirty solvent produced during the cleaning process (which is produced during cleaning) flows passively under the effect of gravity into the collecting container 51 located below.

It should be noted that the travel paths and the optimal pressures with which the solvent jet is applied can depend on the geometry of the print head 40 to be cleaned and also on the ink used. If stubborn local contamination is to be expected, it can be helpful to cause pulse-like discharges of the fluid used for cleaning, for example by means of brief pressure peaks.

In step S 6, after cleaning with solvent has been completed, the catcher tube 46 is moved a little in the direction of the ink outlet nozzle, i.e. the nozzle 43. There, the line 48, which forms the return suction line during printing, is decoupled from the solvent supply of the CI J printer by switching the valve 122 and connected to its compressed air supply, usually the compressor 150 and/or compressed air tanks, and first the liquid column of solvent still in the return suction line catcher tube is blown out through the catcher tube 46 with the aid of the compressed air. After a few seconds, the catcher tube 46 then moves completely back into the "open" position in step S7 and remains there for a few seconds with the compressor 150 running or the compressed air tank open so that the fluid flowing out through the catcher tube 46 is now air, and dries the deflection electrodes 45 in this position.

In step S 8, the catcher tube 46 in this embodiment moves up to just before the charging electrodes 44 and the nozzle 43 and then completely back to the original "open" position, while compressed air from the compressor or from a compressed air tank flows continuously through the catcher tube 46 in order to further dry the cleaned components. Depending on the structure of the print head 40, however, the drying result can be improved if the pressure of the compressed air fluctuates and, in particular, is pulsed due to pressure surges, which can also occur at specific points along the travel path.

At the end of the cleaning process in step S 9, the catcher tube 46 remains in the "open" position for a few seconds and then moves with the compressed air supply running through the compressor or compressed air tank until it is just before the ink outlet nozzle. There, the compressed air supply is then switched off and by switching the valve 121, the actual function of the line 48 and the catcher tube 46, namely the return of unused ink, is reactivated and the regular printer control for the printing processes is also reactivated.

It is useful to arrange the print head 40 or at least the parts of the print head which have components to be cleaned in the cleaning station 50 during the cleaning procedure, which can be arranged on the CI J printer 1 or designed as a separate device. In particular, it can It may be useful if at least parts of the print head 40 that are to be cleaned are introduced into an interior of the cleaning station 50, because this effectively prevents contaminated solvent from escaping into the environment, for example if spraying the solvent onto the surfaces to be cleaned leads to the formation of droplets that propagate uncontrollably in different spatial directions. It is advantageous if the collecting container 51 is a component of the cleaning station 50 or is detachably connected to it.

List of reference symbols

1 CI J printer

10 Basic device

20 HMI display

30 Head line

40 Printhead

41 Section

42 tube

43 Nozzle

44 charging electrodes

45 deflection electrodes

46 Catch tube

47 Drive

48, 104, 106, 111 Line

50 cleaning stations

51 Collection container

100 Hydraulic system

101 Ink tank

102 Solvent tank

103 Pump

105, 107 valve

110 Mixing tank

113 Pressure tank

120 Valve block

121, 122, 123 Two-way valve

131 Suction pump

132, 142, 151 Line

141 Pump

150 compressor

S1-S9 Step of the procedure

Claims

Patent claims 1. Method for cleaning a print head (40) of a CIJ printer (1), characterized in that at least one fluid required for cleaning is actively supplied within the print head (40) and passively discharged into a collecting container (51). 2. Method according to claim 1, characterized in that clean solvent required for cleaning is fed - preferably completely - through a catcher tube (46) of the print head (40) and sprayed onto components of the print head (40) to be cleaned. 3. Method according to claim 1 or 2, characterized in that the method includes a drying step and that air required for drying is supplied through the catcher tube (46) of the print head (40) and blown onto components of the print head (40) to be dried. 4. Method according to one of claims 1 to 3, characterized in that the position at which fluid required during cleaning is actively supplied within the print head (40) is varied during cleaning. 5. Method according to one of claims 1 to 4, characterized in that the active supply of fluid required during cleaning takes place in a jet. 6. Method according to claim 5, characterized in that the jet runs essentially axially parallel to the direction in which a non-deflected ink jet propagates during printing operation of the CI J printer (1). 7. Method according to one of claims 5 or 6, characterized in that properties of the jet are varied during the active supply of fluid required during cleaning. 8. Method according to claim 7, characterized in that the variation of the properties of the jet is adapted to the ink used in each case. 9. Method according to one of the preceding claims, characterized in that at least one pulse-like discharge of at least one fluid takes place. 10. Method according to one of the preceding claims, characterized in that before completion of the method, the cleaning success is verified by an electrical test. 11. CI J printer (1) for carrying out the method according to one of claims 1 to 10, with - at least one solvent tank (102), - at least one ink tank (101), - a print head (40) having a nozzle (43) for ejecting ink, deflection electrodes (45) and a collecting tube (46) for returning ink not used for printing ejected from the nozzle (43), and - a hydraulic system (100), characterized in that the hydraulic system (100) is constructed such that it has means for actively supplying at least one fluid required for cleaning into the print head (40) and that the CI J printer (1) has a collecting container for passively receiving the fluid used for cleaning after it has been used for cleaning. 12. CI J printer (1) according to claim 11, characterized in that the hydraulic system (100) is constructed such that it sucks a fluid from the catcher tube (46) in a first operating mode and feeds a fluid under pressure into the catcher tube (46) in a second operating mode. 13. CI J printer (1) according to claim 12, characterized in that the hydraulic system (100) is constructed such that in a third operating mode it feeds a different fluid than in the second operating mode under pressure into the catcher tube (46). 14. CI J printer (1) according to claim 12 or 13, characterized in that the hydraulic system (100) is constructed such that the pressure under which the fluid is fed into the catcher tube (46) is variable. 15. CIJ printer (1) according to one of claims 11 to 14, characterized in that the hydraulic system (100) is constructed such that it has an intermediate storage for a pressurized fluid, the content of which can be introduced into the catcher tube (46). 16. CIJ printer (1) according to one of claims 1 to 15, characterized in that the catcher tube (46) can be moved within the print head (40) with a drive (47).