DE202019102598U1 - Ink jet printer with head cleaning device - Google Patents

Abstract

An ink jet printer (10) for printing ink on a substrate comprising at least one ink jet printhead (20) for injecting ink onto the substrate, the at least one printhead having a lower nozzle plate (22) comprising a plurality of ink jet nozzles (34) Conveyor (28) for conveying the substrate through the printer and below the at least one printhead, a printhead cleaner (50) for cleaning the at least one printhead of the ink jet printer, the printhead (20) and printhead cleaner (50) configured to be in one Maintenance position to perform a relative movement to one another, the print head cleaning device (50) comprising an upward cleaning surface (54) which is provided with at least one cleaning fluid supply element (56) for guiding cleaning fluid upwards in the direction of the lower nozzle plate of the print head; wherein the printer ( 10) with a control g (47) is provided for adjusting the back pressure of the ink on the ink jet nozzles, which is configured to exert a negative working pressure of printing in relation to the ambient atmosphere on the ink jet nozzles during a printing process, with an image on the substrate being ejected by ink the ink jet nozzles (34) is recorded on the substrate, and to exert a positive ambient atmospheric rinse pressure on the ink jet nozzles during which the ink jet nozzles (34) are flushed with ink during a rinsing phase of the cleaning process, and during a rinsing phase of the cleaning process exert a flushing pressure on the ink jet nozzles during which the nozzle plate (22) is flushed with cleaning fluid supplied by the cleaning fluid supply element, the flushing pressure being higher than the flushing pressure being higher than the working pressure of the printer ckens.

Description

The present invention relates to an ink jet printer having a head cleaning device.

Ink jet printing is a known technique for recording an image on a substrate by controlled spraying of suitable ink jet inks. Typically, the ink jet printing device includes a number of printheads, such as at least one for each color, such as one for each color of cyan, magenta, yellow and black, and optionally supplemented with additional printheads for white and / or transparent inks or supporting colored inks. Each print head includes a nozzle plate, and a plurality of nozzles are provided. The plurality of nozzles are supplied with ink from an ink tank. The printheads can be configured to scan the width of the substrate to be printed back and forth. Alternatively, the displays are arranged stationary in rows, which cover at least the width of the substrate to be printed. The substrate can be paper or paper-based materials, plastic and textile. Typically, the substrate is conveyed from a feed end of the printer through the print path in which the substrate is printed, and optionally further processed, e.g. hardened or dried, conveyed to an exit end. The substrate can be fed as a single sheet or as a web. The entry and exit areas and the conveyor are generally adapted to the configuration of the substrate. For example, if the substrate to be printed is a web wound on a roll, the feed section may include an unwind station, the printing section may include support rolls and / or a drum to which the substrate is temporarily attached, or in the case of textile materials endless conveyor belt provided with an adhesive coating to which the substrate temporarily adheres, and the exit section may comprise a winding roll on which the printed substrate is wound. Sheet feeders are used for a sheet-like substrate.

During printing, the print head nozzles can be partially clogged by (semi) cured / dried ink and particles / dust from the environment and / or the substrate. Dust may also stick to the nozzle plate. This inevitable contamination of the printheads can affect the printing process, which can lead to reduced image quality. Therefore, printhead maintenance is required during operation. As part of the maintenance process, the printheads are often rinsed, wiped, and / or rinsed to restore print performance and image quality. Flushing the printheads involves creating a forced flow of ink (albeit at a much slower rate than the flushing speed when printing) through the nozzles and removing the ink without being jetted onto the substrate. Rinsing involves contacting the nozzle plate with a special cleaning fluid. After rinsing and rinsing, the printhead is often wiped by contact with the nozzle plate, e.g. with a rubber scraper or a color absorbing cloth.

When printing, a back pressure (negative pressure compared to the ambient pressure) is applied to the ink in the nozzle, whereby an ink meniscus is generated in the nozzle itself, so that the ink meniscus in the nozzle is withdrawn and does not protrude from it. If the back pressure was maintained during maintenance, the deposits, cleaning fluid and / or excess paint would be drawn into the nozzles and incorporated into the paint contained in the nozzles. This in turn can lead to discoloration of the respective ink, impair the color strength and physical properties such as surface tension and viscosity and lead to a deterioration in the image quality. Also the cross-contamination of paint from different nozzles, especially if nozzles in the same nozzle plate are supplied with differently colored colors, as are currently being developed. These printheads have two or more independent ink paths for different inks.

It is known that during maintenance, color printing temporarily increases from the usual back pressure to a pressure above ambient pressure. For example, US2016 / 0263898A1 has disclosed a liquid ejection device such as an ink jet printer with a flow-through printhead, wherein the ink circulates continuously. This known device includes a wiping member which wipes on a surface forming the nozzle by making a movement relative to the surface forming the nozzle while contacting the surface of the print head forming the nozzle; a cleaning liquid supply section that supplies cleaning liquid to at least one of a print head and the wiping member; and a circulation speed setting section capable of setting a circulation speed of the ink circulating between an ink storage section and the printhead to a second wiping speed faster than the first speed. It is disclosed that the circulation at higher speed causes the back pressure of the nozzles to become overpressure during the head cleaning and thus prevents Foreign substances that remain on the nozzle formation surface enter the nozzles. The ink is fed to the nozzles from a container via cavities in the printhead. The container in turn is connected to a tank via a collecting duct and a supply duct provided with a circulating pump for generating a circulation flow. The speed and pressure of the ink circulating between the tank and the reservoir is adjusted by an ink circulation mechanism which, in addition to the circulation pump, also includes a pressure adjustment mechanism which includes another pump connected to the tank. In the illustrated embodiments, the cleaning liquid is supplied to a so-called ink-supplied surface, flows down into the corner region between the ink-supplied surface and the nozzle-forming surface. Then the wiper is moved in a first direction and contacts this corner portion on the coloring surface, is bent and moved further in contact with the nozzle-forming surface. In this way, it is assumed that the cleaning liquid is pushed out of the corner area along the nozzle shape surface by the scraper to remove dust and the like. The wiping process is then carried out with or without the supply of additional cleaning liquid in the reverse direction. This cleaning process can be repeated depending on the pressure load. Optionally, the nozzles can be flushed out during forward or backward movement by increasing the speed of the circulating paint to a third speed that is higher than the second speed.

A disadvantage of this known device is the complexity of the operation. In addition, the forced flow of paint when applying the cleaning liquid and when wiping paint residues, dust and other particles from the nozzle formation surface into the ink nozzles and further into the paint circulation mechanism including the container to the tank is still possible. This can still contaminate the paint. If different colored dyes are fed to the nozzles on the same printhead, cross-contamination is still a risk. Forced contact of the wiper with the nozzle-forming surface could also easily damage the nozzles, especially if the inks used are dispersion inks with dispersed dye particles in a solvent. These particles could become trapped between the wiper and the nozzle-forming surface and cause abrasion of the nozzle plate, which affects printing and image quality. The wear on the wiper caused by the particles would also impair the cleaning process.

Therefore, an improved printhead cleaning device and method is required, which reduces the risk of (cross) contamination.

In view of this, the present invention provides an ink jet printer for printing ink on a substrate comprising
at least one ink jet printhead for ejecting ink onto the substrate, the at least one printhead having a lower nozzle plate comprising a plurality of ink jet nozzles,
a conveying device for conveying the substrate through the printer and below the at least one printhead,
a printhead cleaning device for cleaning the at least one printhead of the inkjet printer, and
wherein the printhead and printhead cleaner are configured to move relative to each other in a maintenance position,
wherein the printhead cleaning device includes an upward cleaning surface provided with at least one cleaning fluid supply member for directing cleaning fluid upward toward the lower nozzle plate of the printhead;
wherein the printer is provided with a controller for adjusting the back pressure of the ink on the ink jet nozzles, which is configured to exert a negative working pressure of printing with respect to the ambient atmosphere on the ink jet nozzles during a printing process, an image on the substrate by ejecting Ink is recorded onto the substrate from the ink jet nozzles, and to exert a positive rinse pressure relative to the ambient atmosphere on the ink jet nozzles during a rinsing phase of the cleaning process, during which the ink jet nozzles are rinsed with ink, and to rinse pressure on the during a rinsing phase of the cleaning process To perform ink jet nozzles during which the nozzle plate is rinsed with cleaning fluid supplied from the cleaning fluid supply member, the rinsing pressure being higher than the rinsing pressure being higher than the working pressure of the Printing.

The ink jet printer for printing ink on a substrate comprises at least one printhead for applying ink on a substrate. The ink jet print head has a lower nozzle plate which is provided with a plurality of ink jet nozzles. In one embodiment, at least one inkjet print head and optionally white, transparent and / or additional carrier colors are provided for each individual ink, for example cyan, magenta, yellow and black. In a The embodiment is the scanning-type inkjet printer, the at least one print head being movable in the width direction of the substrate, for example mounted on slides which can be moved back and forth along a mounting rail. In a further embodiment of a single printer, the print heads are fixedly arranged in the width direction of the printer, the number of print heads for one type of ink covering at least the entire width of the substrate to be printed. In this embodiment, the fixed arrangement of the print heads prevents movement in the width direction, although a displacement in the height direction is possible so that the cleaning device (s) can pass under the print heads. In yet another embodiment, the inkjet printheads include nozzle plates with two or more independent ink paths for different inks to different ink containers. The ink jet printer also includes a conveyor for conveying the substrate through the printer from a feed end to an exit end, wherein the substrate is passed under the print heads in the printing section. Depending on the type of ink curing device, for example thermal dryers and / or UV lamps, each printhead station for (partially) curing the ink and a final curing device can be connected downstream of the last printhead. The substrate can be any of the common substrates as discussed above.

The inkjet printer also includes a printhead cleaning device for cleaning the at least one printhead of the inkjet printer. The print heads and the associated cleaning devices can be moved relative to one another. Cleaning is done while the printhead and printhead cleaner are in a maintenance position, e.g. immediately behind the long edge of the conveyor, in the case of a scanning inkjet printer. When the printheads are firmly attached, as described for the single-pass printer, the cleaning device is guided along the printheads. The cleaning device is configured to pass under the printhead.

The cleaning device comprises an upward-facing cleaning surface, which cleans the nozzle plate of the print head above it at a short distance during cleaning. The cleaning surface is provided with one or more supply elements for cleaning liquid, such as nozzles, spray nozzles or bare openings, from which the cleaning liquid is expelled, sprayed or flows. The cleaning forms a source of cleaning fluid on the cleaning surface which touches the nozzle plate well. The cleaning liquid soaks the nozzle plate and loosens dirt, particles and adhering paint residues. The liquid waste is discharged.

The printer is equipped with a controller for adjusting the back pressure of the ink on the ink jet nozzles, which are configured to apply a negative working pressure of the printing during a printing operation. The controller is also configured to apply a positive flushing pressure, advantageously in the range of 80-500 mbar as 100 mbar, with respect to the ambient atmosphere during an optional flushing phase of the cleaning process in which the nozzles are flushed with ink. The controller is also configured to a rinsing pressure during a rinsing phase of the cleaning process in which the nozzle plate is rinsed with cleaning fluid, advantageously in the range from -10 mbar to +10 mbar, preferably -5 mbar to +5 mbar, better -3 mbar up to +3 mbar. The flushing pressure is higher than the flushing pressure, the flushing pressure is higher than the working pressure of the printing.

During the cleaning phase, the back pressure of the paint in the nozzles is set by the control to the pressure required for flushing or rinsing. The ink flow through the printhead is advantageously stopped during the rinsing process.

In this way, contamination of the paint in the nozzles with dirt, cleaning liquid and / or other paint is effectively avoided, while the nozzle plate is thoroughly cleaned by soaking, with or without the use of a wiper mechanism.

• Positionieren des Druckkopfes und der Druckkopfreinigungsvorrichtung in einer Wartungsposition;
• Einstellen des Gegendrucks an den Druckkopfdüsen auf den erforderlichen Durchspüldruck oder Abspüldruck;
• optional das Unterbrechen des Tintenflusses durch den Druckkopf;
• Durchspülen der Druckkopfdüsen mit Tinte; oder
• Zuführen von Reinigungsflüssigkeit zu den Versorgungselementen der Reinigungsflüssigkeit der Druckkopfreinigungsvorrichtung.

In one embodiment, the controller includes a processor and memory that stores computer-readable instructions that, when executed by the processor, execute processes including:

• Positioning the printhead and printhead cleaner in a maintenance position;
• Adjusting the back pressure on the printhead nozzles to the required flushing or flushing pressure;
• optionally interrupting the ink flow through the printhead;
• Flushing the printhead nozzles with ink; or
• Supplying cleaning liquid to the supply elements of the cleaning liquid of the print head cleaning device.

During the flushing process, the ink flows into an outlet bowl. To remove the used cleaning liquid, preferably the Printhead cleaning device also includes at least one suction port connected to pump means configured to apply reduced pressure to the at least one suction port to remove liquid waste. After contact of the nozzle plate with the cleaning liquid, a reduced pressure is generated by suction, for example with a suction pump, which further removes the liquid waste adhering to the nozzle plate. The instructions then include actuating the pumping means so that a reduced pressure is generated at the at least one suction opening and liquid waste is removed from the nozzle plate. Since the cleaning device and the print head typically experience a relative movement in the longitudinal direction of the print head, the suction opening, preferably a slot covering the width of the print head, is advantageously positioned downstream of the cleaning liquid openings in the relative movement direction. Then the cleaning cycle is advantageously carried out only in the case of a relative movement in one direction and not in the case of a backward movement into the starting position, although the suction can be continued during the backward movement.

The printhead cleaning device may comprise a wiping element, which is preferably arranged downstream of the cleaning fluid supply element (s) and upstream of the suction opening, if present.

• 1 zeigt eine Ausführungsform eines Tintenstrahldruckers mit einer Druckkopfreinigungsvorrichtung gemäß der Erfindung;
• 2 zeigt eine schematische Ansicht einer Ausführungsform der Druckkopfreinigungsvorrichtung in Bezug auf den Druckkopf während der Reinigung; und
• 3 zeigt ein Beispiel für ein Schema, das computerlesbare Anweisungen für die Steuerung definiert; und
• zeigt ein Beispiel für ein Diagramm des Gegendrucks in den Düsen beim Drucken und bei der Wartung.

The invention is further illustrated by the accompanying drawing, in which

• 1 shows an embodiment of an inkjet printer with a print head cleaning device according to the invention;
• 2 shows a schematic view of an embodiment of the print head cleaning device with respect to the print head during cleaning; and
• 3 shows an example of a scheme defining computer readable instructions for the controller; and
• shows an example of a graph of back pressure in the nozzles during printing and maintenance.

In is an inkjet printer by the reference number 10 characterized in its entirety. The printer 10 includes a feed section 12 , which in the illustrated embodiment comprises an unwinding roll, of which the substrate to be printed 14 is supplied. The printer also includes a printing section 16 that has multiple printing stations 18 comprises, each printing station 18 at least one inkjet printhead 20 includes, which is movable in the width direction of the printer. Hardening devices (not shown) and a final hardening device can be arranged between adjacent printing stations 22 , for example a UV lamp or thermal dryer, located downstream of the printing section 16 is arranged to be present. At the exit section 24 becomes the now printed substrate 14 collected and, for example, as shown on a roll 26 wound. The promotion of the substrate 14 through the printer is done via rollers 28 , some with suitable (electrical) drives (not shown) under the control of a controller 30 are connected. The printhead maintenance positions are adjacent to one of the long edges of the conveyor.

2 shows a schematic representation of an embodiment of the print head cleaning device 50 with respect to an array of printheads 20 (schematically separated by dashed lines) during cleaning. Any printhead 20 includes a lower nozzle plate 32 , taking a variety of nozzles 34 is provided. The nozzles 34 each printhead 20 are in fluid communication with a common ink tank 36 through an internal ink flow channel 38 and a supply and return line 40 , The ink flow is from the pump 44 in the supply line 40 and the flow and pressure regulator 46 generated. The back pressure is controlled by the flow and pressure regulator 46 controlled / regulated by a processor 48 and a memory 49 includes.

The cleaning device 50 includes a cleaning body 52 with an upper cleaning surface 54 , In this execution opening are in the area 54 a range of cleaning liquid supply elements 56 provided by means of an internal distributor 58 with a pump 59 and a cleaning fluid container 60 are connected. The cleaning device 50 can differ in terms of printhead 22 move in the width direction of the printer as indicated by arrow A. Along the edges of the cleaning surface 54 are one or more drainage channels 62 for discharging liquid waste that goes beyond the cleaning surface into a waste container (not shown). As seen in the indicated width direction, the rear end (downstream end) 64 of the cleaning body 52 with a suction opening 66 provided with a suitable suction device 68 , such as a suction pump, is connected. During cleaning, it forms through the cleaning openings 56 supplied cleaning liquid a source 70 on the top of the cleaning surface that 70 the nozzle area 32 of the printhead 22 well contacted and flows to the side edges where it passes through the drainage channels 62 is carried out. On the nozzle plate 32 sticky drops are removed by the scraper 72 removed and by the suction opening 66 by actuating the suction device 68 aspirated.

shows a scheme 80 of instructions as steps S1 to S9 regarding the execution of a cleaning process after the printing process has been completed.

In S1 printhead and cleaning device are positioned in a cleaning position to each other. Optional is in S2 the back pressure is set from a negative pressure (negative working pressure of printing) to a positive flushing pressure. The nozzles are then flushed out with ink S3 , After the optional rinse, the back pressure is set to a rinse pressure that is lower than the rinse pressure but higher than the working pressure of printing, and optionally the ink flow in S4 interrupted. In the next step S5 vacuum is applied to the suction opening. Then the nozzle plate with cleaning liquid in S6 rinsed. After rinsing, the suction is in S7 stopped. In S8 the counter pressure in the nozzles is set to the negative working pressure of the printing and the ink flow is restarted if necessary. In S9 the print head is brought into its printing position and the cleaning device into a non-active rest position. Then the printer is ready for a subsequent print job.

4 illustrates back pressure as a function of successive processes in the printer according to the scheme of 3 in relation to the ambient pressure. As can be seen, the flushing pressure is positive, while the flushing pressure is in one P _{rinse max} and P _{rinse min} limited working area around the ambient pressure, such as ± 3 mbar.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 2016/0263898 A1 [0005]

Claims (11)

An ink jet printer (10) for printing ink on a substrate comprising at least one inkjet printhead (20) for spraying ink onto the substrate, the at least one printhead having a lower nozzle plate (22) comprising a plurality of inkjet nozzles (34), a conveying device (28) for conveying the substrate through the printer and below the at least one printhead, a printhead cleaning device (50) for cleaning the at least one printhead of the inkjet printer, wherein the print head (20) and the print head cleaning device (50) are configured to perform a relative movement to one another in a maintenance position, wherein the printhead cleaning device (50) includes an upward cleaning surface (54) provided with at least one cleaning fluid supply member (56) for directing cleaning fluid upward toward the lower nozzle plate of the printhead; wherein the printer (10) is provided with a controller (47) for adjusting the back pressure of the ink on the ink jet nozzles, which is configured to apply a negative working pressure of the printing with respect to the ambient atmosphere to the ink jet nozzles during a printing process, wherein an image is recorded on the substrate by ejecting ink from the ink-jet nozzles (34) onto the substrate, and to exert a positive flushing pressure with respect to the ambient atmosphere on the ink-jet nozzles during a flushing phase of the cleaning process, during which the ink-jet nozzles (34) are flushed with ink , and to exert a flushing pressure on the ink jet nozzles during a rinsing phase of the cleaning process, during which the nozzle plate (22) is rinsed with cleaning liquid which is supplied by the supply element of the cleaning liquid, the rinsing pressure being higher than the rinsing pressure, de r is higher than the working pressure of printing. Inkjet printer after Claim 1 , wherein the flushing pressure is in the range of 80-500 mbar based on the ambient pressure. Inkjet printer after Claim 1 or Claim 2 , wherein the flushing pressure is in the range from -10 mbar to +10 mbar, preferably -5 mbar to +5 mbar, in particular -3 mbar to +3 mbar, based on the ambient pressure. The ink jet printer according to any one of the preceding claims, wherein the controller (47) is configured to interrupt the flow of ink through the ink jet print head (20) during a cleaning operation. The ink jet printer of any preceding claim, wherein the controller (47) includes a processor (48) and memory (49) that stores computer readable instructions (S1-S9) that, when executed by the processor, perform processes including : Positioning the printhead (20) and printhead cleaner (50) in a maintenance position; Adjusting the back pressure on the ink jet nozzles (34) to the required flushing pressure or flushing pressure; optionally interrupting the flow of ink through the printhead (20); Flushing the printhead nozzles (34) with ink; or Supplying cleaning liquid to the cleaning fluid openings (56) of the print head cleaning device (50). The ink jet printer of any preceding claim, wherein the print head cleaning device (50) also includes at least one suction port (66) connected to pump means (68) configured to apply reduced pressure at the at least one suction port to remove liquid waste apply. Inkjet printer after Claim 5 , wherein the instructions further include actuating the pump device (68) so that a reduced pressure is generated at the at least one suction opening (66) and liquid waste is removed from the nozzle plate (22). The ink jet printer of any preceding claim, wherein the printhead (20) is fixedly mounted in the width direction of the printer (10) and the cleaning device (50) is configured to move in the width direction of the printer (10) during the cleaning process. Inkjet printer according to one of the preceding Claims 1 - 7 wherein the printhead (20) is configured to move in the width direction of the printer (10) and the maintenance position is located along a long side of the printer (10), the cleaning device (50) is configured to during the cleaning process perform a relative movement with respect to the printhead (20). The ink jet printer according to any one of the preceding claims, wherein the cleaning device (50) is configured to perform a cleaning operation while moving in a single direction. The ink jet printer of any preceding claim, wherein the ink jet print head (20) comprises a nozzle plate (22) with ink jet nozzles (34), two or more independent ink paths for different inks from different ink containers to different nozzles (34) in the print head (20) ,

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