AT16598U1 - Inkjet printer with head cleaning device - Google Patents

Abstract

An inkjet printer (10) for printing ink on a substrate comprising at least one inkjet printhead (20) for injecting ink onto the substrate while the substrate is being conveyed and a printhead cleaning device (50) for cleaning the at least one printhead which are relatively movable. The printhead has a lower nozzle plate (22) that includes inkjet nozzles (34). The print head cleaning device (50) comprises a cleaning surface (54) which is provided with at least one cleaning fluid supply element (56) for guiding cleaning fluid onto the lower nozzle plate of the print head. 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 pressure, a positive rinsing pressure with respect to the ambient atmosphere and a rinsing pressure. The rinse pressure is higher than the rinse pressure, which is higher than the working pressure of printing.

Description

INK-JET PRINTER WITH PRINT HEAD CLEANING DEVICE The present invention relates to an ink jet printer with a print 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 comprises a nozzle plate, with a plurality of nozzles being 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 blocked by (semi) cured / dried ink and particles / dust from the environment and / or the substrate. Dust can 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. Flushing 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 against 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 is retracted in the nozzle 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

1/12

AT 16 598 U1 2020-02-15 Austrian patent office for various inks.

It is known that the color pressure temporarily increases during maintenance 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 with the ink circulating continuously. This known device comprises 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 forming the nozzle of a print head; 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 by circulating at a higher speed, the back pressure of the nozzles becomes an overpressure during the head cleaning, and thus foreign matters that remain on the nozzle formation surface are prevented from entering the nozzles. The ink is delivered 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 circulation 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 pressed by the scraper out of the corner area along the nozzle shape surface to remove dust and the like. The wiping process is then carried out in the opposite direction with or without the addition of additional cleaning liquid. This cleaning process can be repeated depending on the pressure load. Optionally, the nozzles can be flushed 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 color flow when applying the cleaning liquid and when wiping paint residues, dust and other particles from the nozzle formation area into the ink nozzles and further into the ink 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.

An improved printhead cleaning device and method is therefore required, thereby reducing the risk of (cross) contamination.

In view of the foregoing, 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 containing a plurality of inks

AT 16 598 U1 2020-02-15 Austrian patent office

Jet nozzles includes, a conveyor 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 ink jet printer, and wherein the printhead and the printhead cleaning device are configured to perform a relative movement in a maintenance position, wherein the printhead cleaning device includes an upward cleaning surface that is 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, with an image on the substrate Ejection of ink from the ink jet nozzles onto the substrate is recorded, and to apply a positive rinse pressure with respect to the ambient atmosphere to 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 a pressure during a rinse phase of the cleaning process to be applied to the ink jet nozzles during which the nozzle plate is rinsed with cleaning liquid supplied from the cleaning fluid supply member, the rinsing pressure being higher than the rinsing pressure being higher than the working pressure of the D cogging. The inkjet printer for printing ink on a substrate comprises at least one printhead for applying ink to 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, for each individual ink, e.g. Cyan, magenta, yellow and black, at least one inkjet print head and optionally white, transparent and / or additional carrier colors are provided. In one embodiment, the ink jet printer is of the scan type, with the at least one printhead movable in the width direction of the substrate, e.g. mounted on slides that can be moved back and forth along a mounting rail. In a further embodiment of a single printer, the print heads are arranged fixed 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 printheads 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 printheads. 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 printheads in the print section. Depending on the type of ink curing device, e.g. thermal dryers and / or UV lamps, each print head station for (partial) curing of the ink and a final curing device downstream of the last print head. 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 cleaning surface, which cleans the nozzle plate of the printhead 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

3/12

AT 16 598 U1 2020-02-15 Austrian patent office

Cleaning liquid is expelled, sprayed or flows. The cleaning forms a source of cleaning fluid on the cleaning surface that 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 at the ink jet nozzles, which are configured to apply a negative working pressure of the printing during a printing process. The controller is also configured to apply a positive rinse pressure, advantageously in the range of 80-500 mbar and 100 mbar, with respect to the ambient atmosphere, during an optional rinsing phase of the cleaning process in which the nozzles are rinsed with ink. The open-loop / closed-loop control is also configured to achieve a clear-rinse pressure, advantageously in the range from -10 mbar to +10 mbar, preferably -5 mbar to +5 mbar, during a rinse-off phase of the cleaning process in which the nozzle plate is rinsed with cleaning liquid, better - 3 mbar to +3 mbar, to be used. The rinse pressure is higher than the rinse pressure, the rinse pressure is higher than the working pressure of printing.

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

In this way, contamination of the paint in the nozzles with dirt, cleaning fluid 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.

[0014] 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 rinse pressure or rinse pressure;

optionally interrupting the flow of ink through the printhead;

Flushing the print head nozzles with ink; or

Supply of cleaning liquid to the supply elements of the cleaning liquid of the print head cleaning device.

[0015] During the rinsing process, the ink flows into an outlet bowl. To remove the used cleaning fluid, preferably the printhead cleaning device, also includes at least one baby port connected to pump means configured to apply a reduced pressure to the at least one baby port to remove liquid waste. After contact of the nozzle plate with the cleaning liquid, suction, e.g. With a vacuum pump, a reduced pressure is generated, which further removes the liquid waste adhering to the nozzle plate. Then the instructions include actuating the pump 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 sucking 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.

4.12

AT 16 598 U1 2020-02-15 Austrian patent office

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

Figure 1 shows an embodiment of an inkjet printer with a print head cleaning device according to the invention; Figure 2 shows a schematic view of an embodiment of the print head cleaning device with respect to the print head during cleaning; and Figure 3 Figure 3 shows an example of a scheme defining computer readable control instructions; and Fig. 4 shows an example of a graph of back pressure in the nozzles during printing and maintenance.

In Fig. 1, an ink jet printer is identified by the reference number 10 in its entirety. The printer 10 includes a feed section 12, which in the illustrated embodiment comprises an unwinding roll, from which the substrate 14 to be printed is supplied. The printer also includes a printing section 16 that includes a plurality of printing stations 18, each printing station 18 including at least one ink jet printhead 20 that is movable in the width direction of the printer. Hardening devices (not shown) and a final hardening device 22, e.g. a UV lamp or thermal dryer, which is arranged downstream of the printing section 16, may be present. At the outlet section 24, the now printed substrate 14 is collected and e.g. as shown wound on a roll 26. The substrate 14 is conveyed by the printer via rollers 28, some of which are connected to suitable (electrical) drives (not shown) under the control of a control 30. The printhead maintenance positions are adjacent to one of the long edges of the conveyor.

Fig. 2 shows a schematic representation of an embodiment of the printhead cleaning device 50 in relation to an arrangement of printheads 20 (schematically separated by dashed lines) during cleaning. Each printhead 20 includes a lower nozzle plate 32, with a plurality of nozzles 34 being provided. The nozzles 34 of each printhead 20 are in fluid communication with a common ink reservoir 36 via an internal ink flow channel 38 and a supply and return line 40. The ink flow is generated by the pump 44 in the supply line 40 and the flow and pressure regulator 46. The back pressure is controlled by the flow and pressure regulator 46, which includes a processor 48 and a memory 49.

The cleaning device 50 comprises a cleaning body 52 with an upper cleaning surface 54. In this execution opening in the surface 54 a number of cleaning liquid supply elements 56 are provided, which are connected by means of an internal distributor 58 to a pump 59 and a cleaning liquid container 60. The cleaning device 50 can move in the width direction of the printer with respect to the print head 22, as indicated by arrow A. Along the edges of the cleaning surface 54, one or more discharge channels 62 are provided for discharging liquid waste that extends 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 is provided with a suction opening 66, which is connected to a suitable suction device 68, such as, for example, a vacuum pump. During cleaning, the cleaning liquid supplied through the cleaning openings 56 forms a source 70 on the upper side of the cleaning surface, which 70 makes good contact with the nozzle surface 32 of the print head 22 and flows to the side edges, where it is discharged through the drain channels 62. Drops adhering to the nozzle plate 32 are removed by the scraper 72 and sucked off through the sucking opening 66 by actuating the suction device 68.

Fig. 3 shows a schematic 80 of the instructions given as steps S1 to S9 regarding the performance of a cleaning process after the printing process has ended.

5/12

AT 16 598 U1 2020-02-15 Austrian Patent Office [0026] In S1, the printhead and cleaning device are positioned in a cleaning position relative to one another. Optionally, the back pressure is set in S2 from a negative pressure (negative working pressure of the printing) to a positive rinsing pressure. The nozzles are then rinsed with ink in 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 is interrupted. In the next step, S5 vacuum is applied to the infant opening. Then the nozzle plate is rinsed clear with cleaning liquid in S6. After rinsing, the suction in S7 is stopped. In S8, the back 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 an inactive rest position. Then the printer is ready for a subsequent print job. Figure 4 illustrates the back pressure as a function of the sequential processes performed in the printer according to the scheme of Figure 3 with respect to the ambient pressure. As can be seen, the rinse pressure is positive, while the rinse pressure is in a working area around the ambient pressure, for example ± 3 mbar, which is limited by P RINSE max and P RINSE min.

Claims (11)

An ink jet printer (10) for printing ink on a substrate, comprising at least one ink jet print head (20) for spraying ink onto the substrate, the at least one print head having a lower nozzle plate (22) which has a plurality of ink jet nozzles (34) a conveyor 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, the printhead (20) and the printhead cleaning device (50) being configured, to perform relative movement to each other in a maintenance position, the printhead cleaning device (50) including 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 exert a negative working pressure of the printing with respect to the ambient atmosphere on 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 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 (34) with ink and to apply a rinse pressure to the ink jet nozzles during a rinse phase of the cleaning process, during which the nozzle plate (22) is rinsed with cleaning liquid supplied by the cleaning liquid supply element, the rinsing pressure being higher than the rinsing pressure which is higher than the working pressure of printing. 2. Inkjet printer according to claim 1, wherein the flushing pressure is in the range of 80-500 mbar based on the ambient pressure. 3. Inkjet printer according to claim 1 or claim 2, wherein the rinse aid 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 claims 1 to 3, wherein the controller (47) is configured to interrupt the flow of ink through the ink jet printhead (20) during a cleaning operation. The ink jet printer of any one of claims 1 to 4, wherein the controller (47) includes a processor (48) and memory (49) that stores computer readable instructions (S1-S9) that, when executed by the processor will carry out 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 rinse pressure or rinse pressure; optionally interrupting the flow of ink through the printhead (20); Flushing the printhead nozzles (34) with ink; or Supplying cleaning fluid to the cleaning fluid openings (56) of the print head cleaning device (50). The ink jet printer of any one of claims 1 to 5, wherein the printhead cleaning device (50) also includes at least one orifice (66) connected to a pump device (68) configured to apply a reduced pressure to the at least one orifice Apply liquid waste removal. 7/12 AT 16 598 U1 2020-02-15 Austrian patent office The ink jet printer of claim 5, wherein the instructions further include actuating the pump means (68) so that a reduced pressure is created at the at least one orifice (66) and liquid waste is removed from the nozzle plate (22). The ink jet printer according to any one of claims 1 to 7, wherein the print head (20) is fixedly fixed in the width direction of the printer (10), and the cleaning device (50) is configured to move in the width direction of the printer () during the cleaning process. 10) to perform. The ink jet printer according to any one of the preceding claims 1-7, wherein the print head (20) is configured to move in the width direction of the printer (10), and the maintenance position is arranged along a long side of the printer (10), the Cleaning device (50) is configured to perform a relative movement with respect to the printhead (20) during the cleaning process. The ink jet printer according to any one of claims 1 to 9, wherein the cleaning device (50) is configured to perform a cleaning operation while moving in a single direction. 11. Inkjet printer according to one of claims 1 to 10, wherein the inkjet print head (20) comprises a nozzle plate (22) with inkjet nozzles (34), wherein two or more independent ink paths for different inks from different ink containers to different nozzles (34) in the print head ( 20) are provided.