CN114126879A

CN114126879A - Method for conveying printing media and for cleaning a nozzle front plate

Info

Publication number: CN114126879A
Application number: CN202080038990.1A
Authority: CN
Inventors: M·科弗勒; S·瓦尔德纳
Original assignee: Duest Group Co ltd
Current assignee: Duest Group Co ltd
Priority date: 2019-08-07
Filing date: 2020-08-05
Publication date: 2022-03-01
Anticipated expiration: 2040-08-05
Also published as: EP3953186B1; BR112021023676A2; EP3953186C0; EP3953186A1; PL3953186T3; WO2021023400A1; ES2968355T3; CN114126879B

Abstract

The invention relates to a method for transporting individual printing media (101) into and out of the operating range of a printing head (103) and for cleaning at least one part of at least one nozzle front plate (105) arranged at the printing head (103), wherein the method comprises the following steps: a) providing a printing system (100) comprising a print head (103) with a nozzle front plate (105), wherein the print head (103) comprises at least one printing module (107) with at least one nozzle plate (109) from which drops of a printable composition can be output; b) conveying the printing medium (101) in a conveying direction (T) in such a way that the printing medium (101) is conveyed into the operating range of the nozzle front plate (105) and conveyed out of the operating range again; c) cleaning at least a portion of the nozzle front plate (105) by means of one or more fluid flow arrangements (111) from a cleaning device (114) activating the fluid flow, wherein the fluid flow arrangement (111) comprises at least one fluid flow directed towards at least a part of the nozzle front plate (105), wherein the nozzle front plate (105) comprises a nozzle plate (109), wherein at least some of the print media (101) are transported in a transport direction (T) spaced apart from at least one of its nearest neighboring print media (101), thereby creating a gap (L) between the spaced-apart adjacent print media (101) in the transport direction (T), and the cleaning device (114) does not need to activate the fluid flow all the time, but only in the region of the gap (L) and in synchronism with the gap.

Description

Method for conveying printing media and for cleaning a nozzle front plate

Technical Field

The invention relates to a method for transporting piece-by-piece printing media into and out of the operating range of a printing head and for cleaning at least one part of at least one nozzle front plate arranged on the printing head. The invention further relates to a printing system for carrying out the method according to the invention.

Background

Printing systems are able to print different print media, such as, for example, ceramic tiles, paper, corrugated cardboard, metal sheets, wood or glass sheets, using a print head, which typically comprises a plurality of printing modules with a plurality of nozzle plates with nozzles from which droplets of a printable composition can be output. In any case, the nozzle plate must be cleaned from time to time in order to be able to carry out fault-free printing operations, wherein the production of defect-free printed printing media is of great importance.

If, for example, a nozzle plate surface which has to be cleaned accordingly regularly is undesirably wetted with ink, a contaminated nozzle plate to be cleaned can form over time during a printing operation.

Such regular cleaning of the nozzle plate of the print head is achieved in DE 10256879 a1 by: before cleaning, the printing operation is interrupted and the printing head is then removed from the transport belt for transporting the print, which is disclosed in this document, so far that the cleaning device parked next to the printing head can be guided from its parking position into the region between the printing head and the transport belt and correspondingly guided therein for cleaning. The nozzle plate is cleaned in such a way that pulses of an air flow are directed onto the nozzle plate, with which pulses ink residues and/or foreign particles adhering to the nozzle plate are transported to a separation edge and separated there from the nozzle plate.

The printing operation of the above-described printing system from the prior art has the disadvantage that it must be interrupted repeatedly at relatively short time intervals in order to clean the nozzle plate, in order not to generate waste.

It would be desirable to provide a method which can be used to at least reduce the frequency of interruptions of the transport of the printing medium, which are necessary in conventional methods and which are to be carried out in specific time intervals, for cleaning the nozzle plate not only in the printing operation but also in the transfer operation of the printing system.

In the following, the transfer operation as a printing system shall mean the use of the printing system as a transfer system, at least for a specific time duration, only in terms of its characteristics, wherein the printing medium passes through the range of action of the printing head of the printing system without being printed and is only printed in a further printing system arranged downstream with respect to the printing system.

Disclosure of Invention

The object of the present invention is therefore to provide a method for increasing the throughput of a printing medium without waste sheets through the operating range of a nozzle front plate of a printing system while reducing or even avoiding interruptions in the transport for cleaning the nozzle front plate.

According to the invention, this object is achieved by a method comprising the features of claim 1. The dependent claims relate to further advantageous and, if appropriate, additionally inventive embodiments.

The invention is based on the following concept, namely: the method comprises the steps of feeding printing media into the active region of the nozzle front plate and feeding printing media out of the active region again, wherein at least some of the printing media are fed at a distance from at least one of the nearest adjacent printing media, thereby creating a gap between these printing media in the feed direction, and cleaning the nozzle front plate is carried out by means of a fluid flow directed towards the nozzle front plate in such a way that the cleaning device does not need to activate the fluid flow all the time, but only in the region of the gap and in synchronism with the gap. The method according to the invention for transporting a printing medium is carried out by means of a printing system comprising a printing head at which at least one nozzle front plate is arranged, wherein the printing head comprises at least one printing module with at least one nozzle plate from which drops can be output. Here, at least a part of the nozzle front plate is cleaned by means of one or more fluid flow arrangements from a cleaning device activating the fluid flow. Here, the nozzle front plate includes a nozzle plate.

The medium that should be printed is referred to as print medium in the following. What should be distinguished from the print media is a "frame sample" (Dummy) or "placeholder" that is not printable or should not be printable, which is also capable of forming a void between nearest adjacent print media.

In contrast, the method according to the invention is a method for transporting a piece-by-piece printing medium into and out of the operating range of a printing head and for cleaning at least one part of at least one nozzle front plate arranged at the printing head, wherein the method comprises the following steps:

a) providing a printing system comprising the print head with the nozzle front plate, wherein the print head comprises at least one printing module with at least one nozzle plate from which droplets of a printable composition can be output;

b) conveying the printing medium in a conveying direction in such a way that the printing medium is conveyed into and out of the operating range of the nozzle front plate;

c) cleaning at least a portion of the nozzle front plate by means of one or more fluid flow arrangements from a cleaning device activating a fluid flow, wherein the fluid flow arrangement comprises at least one fluid flow directed towards at least a portion of the nozzle front plate.

According to the invention, the nozzle front plate comprises a nozzle plate, wherein at least some of the printing media are transported in the transport direction spaced apart from at least one of their nearest neighboring printing media, whereby gaps are created between these spaced apart neighboring printing media in the transport direction, and the cleaning device does not need to activate the fluid flow all the time, but only in the region of and in synchronism with these gaps.

The method according to the invention is particularly suitable if, for example, the nozzle front plate of the printing system is used under operating conditions in which a large amount of liquid condenses at the nozzle front plate in the shortest time.

Such a contamination burden is known, for example, from the ceramic industry when a ceramic printing medium is conveyed into and out of the printing system after it has been produced in a press and has passed through several stations and subsequently in a state wetted with water and when the temperature of the printing medium lies between 30 ℃ and 120 ℃. In this case, the water from the ceramic printing medium is converted into a gas phase, from which the gaseous water can again condense at the nozzle front plate.

If additional printing is then carried out, the components printed on these print media are converted into a gas phase, from which they can condense again at the nozzle front plate. Over time, the drops grow increasingly larger until the gravitational force acting on the drops exceeds the holding force at the nozzle front plate, whereby the drops of the composition break off and fall onto the print medium.

The waste-leafed products produced in this way and by the way described below cannot be used as high-quality products, but can be sold on the market at best as a class two low-quality product, in which they can be classified as waste anyway.

It is clear that the printable composition contains a volatile proportion at least in the above-mentioned case. This is typically water and/or polyethylene glycol. If the printing medium is printed in the printing system using a glaze suspension as a printable component, then a relatively large amount, in particular greater than 200g/m, will often be used in relation to the overall application²To 1500g/m²To the print medium in order to produce a relief-like or full-face decoration. The enamel suspension is often tempered to a temperature of between 30 ℃ and 50 ℃ before the medium is printed. In this case, a significant evaporation rate of the liquid from the glaze suspension applied to the printing medium occurs, which in turn partially condenses at the nozzle front plate, so that it becomes particularly heavily contaminated without a corresponding repeated cleaning of the nozzle front plate.

The inventors have observed in their research that if a large amount of the printed glaze composition is printed, even if, for example, the nozzle front plate is electrically heated to a temperature of 50 ℃, it may still be possible, although in part, to provide a remedy to the problem of water condensation to a completely insufficient extent.

Condensation of liquid from the air can cause another problem. Printing of print media is generally known to be carried out at a very low height of a fraction of a millimeter or a few millimeters between the nozzle front plate and the surface of the print medium. The drops formed over time on the nozzle front plate therefore do not even have to fall down by gravity onto the print medium, thereby contaminating it, but can grow to a size in which they hang down with the transported print medium at the "line of sight", i.e. at least at the level of the surface of the print medium, as a result of which they are carried along by the print medium. This often results in longitudinally stretched soil being created on the surface of the print medium.

Another cause of nozzle contamination, particularly when printing ceramic print media with enamel suspensions, is due to the rebound of the droplets from the surface of the print medium to be printed back onto the nozzle front plate. A number of variables contribute to the rebound characteristics. The variables include the size and velocity of the drops and also the spacing between the nozzle front plate and the surface of the print medium to be printed.

Furthermore, if a so-called satellite (Satelliten) or satellite drop (satellitener pfchen) is formed in the output main drop due to defective ejection characteristics, which is output together with the main drop in the form of a very small droplet, the nozzle front plate may be contaminated. In this case, the small droplets form a droplet mist which is deposited on the nozzle front plate and can contaminate the latter.

On the other hand, contamination of the nozzle front plate may even be the result of manual cleaning. By manual cleaning, it is possible to remove dried ink residue from clogged nozzles. However, if the nozzle front plate is not sufficiently dry, so much cleaning liquid may remain on the nozzle front plate that this liquid may fall in the form of droplets onto the print medium over time or may be carried along by the print medium as explained in the manner described above.

In a particularly preferred embodiment of the method according to the invention, at least the entire surface of the nozzle front plate to which the printing medium is exposed during the transport through the region of action of the nozzle front plate is cleaned.

This has the advantage that contamination of the print medium over the entire surface of the print medium can be prevented. According to a preferred embodiment of the printing head provided, the printing head comprises at least two printing modules each having at least one nozzle plate, wherein the printing modules are arranged one behind the other, as seen in the transport direction of the printing medium. The nozzle front plate here comprises the nozzle plate of the printing module.

The nozzle front plate can comprise a nozzle plate and at least one frame plate, wherein the side of the nozzle front plate facing the print medium lies in a plane, in particular, with the nozzle plate and the frame plate.

According to a particularly preferred embodiment of the method according to the invention, the cleaning device activates the fluid flow sequentially.

This embodiment is advantageous because the spacing between the print media arranged in the transport direction can be selected to be relatively narrow, for example, with respect to the length of the nozzle front plate in the transport direction.

According to a further preferred embodiment, at least a part of the nozzle front plate is cleaned at least temporarily simultaneously during the transport of the printing medium through the region of action of the nozzle front plate according to step (c).

According to a particularly preferred embodiment, the method comprises a step (d) of printing the print medium in such a way that: at least one nozzle plate of the at least one printing module outputs drops of a printable composition, preferably an ink or glaze suspension.

The printable composition used, preferably the ink or enamel suspension, can comprise at least one volatile component, preferably water and/or at least one non-aqueous polar solvent. The non-aqueous polar solvent is typically polyethylene glycol. According to a preferred embodiment of the glaze suspension or ink, the water is present in the glaze suspension or ink in a proportion of between 30 and 60 percent by weight, relative to the weight of the glaze suspension or ink, respectively.

According to a particularly preferred embodiment, the printing head comprises a gas flow module having at least one first and one second slot nozzle in a nozzle front plate, wherein in the method, at least during the printing of the printing medium according to step (d), in a gap between the nozzle front plate and the printing medium to be printed, gas is discharged from the first slot nozzle and is sucked in again through the second slot nozzle, so that a laminar gas flow is generated in the gap.

Such a method has the advantage that if water-containing air is present, for example in the gap between the printing medium and the nozzle front plate, it is partially removed and thus reduces the amount of water that can condense at the nozzle front plate.

According to a preferred embodiment, the nozzle front plate is designed as a closed, liquid-tight nozzle front plate, except for the opening of the nozzle and preferably except for the opening of the slot nozzle of the gas flow module. According to a particularly preferred embodiment, the print head is designed as a closed, liquid-tight print head.

These improvements are advantageous because the entry of atmospheric moisture and other volatile constituents of the ink or glaze suspension from the gas phase into the print head can thereby be reduced or avoided. The ingress of atmospheric moisture into the print head can lead to damage to the print head.

According to a further particularly preferred embodiment, the cleaning is carried out at periodic intervals, wherein the respective interval duration is selected to be as short as necessary, but as long as possible, in order to ensure that the printing medium passes through the region of action of the nozzle front plate without waste sheets during the transport or transport and printing of the printing medium within the respective interval duration, wherein a certain further higher interval duration already leads to waste-sheet-bearing printing medium compared to the respective interval duration.

This development is advantageous because the throughput of the printing medium without waste sheets can thereby be further increased.

According to a further particularly preferred embodiment, the printing according to step (d) and the cleaning of at least one part of the nozzle front plate according to step (c) are at least temporarily accompanied simultaneously during the transport of the printing medium through the region of action of the nozzle front plate.

In this way, it is preferably possible to activate the fluid flow with the cleaning device at least during printing according to step (d) in such a way that the fluid flow does not intersect the flight course of the drops emerging from the nozzle plate or from the nozzle plates.

The printing medium can be transported in a transport plane in a transport direction, wherein a nozzle front plate of the printing head is arranged above the transport plane, wherein the transport according to step (b) and the cleaning according to step (c) are carried out at the same height X, preferably at the same target height, between the nozzle front plate and the surface of the printing medium in a direction perpendicular to the transport plane of the printing medium.

In a preferred embodiment of the method, the transport according to step (b) and the cleaning according to step (c) and the printing according to step (d) are carried out at the same height (X), preferably at the same target height.

According to another preferred embodiment of the method, the method comprises the following steps:

(e) the actual height is detected by means of a sensor before the printing medium is fed into the area of action of the nozzle front plate,

(f) if the detected actual height does not correspond to the target height, the actual height is adjusted by means of a positioning device of the printing system.

This development is advantageous because different printing media with different thicknesses can be transported through the area of action of the nozzle front plate.

The target height preferably corresponds to a predetermined value in the range between 0.4 mm and 15.0 mm. The person skilled in the art knows at which target height he should adjust the nozzle front plate in order to obtain a high-quality printing in terms of quality, and the high-quality printing depends on a number of variables, such as, for example, the drop size, the drop velocity and the straightness of the flight trajectory of the drops.

According to a preferred embodiment of the method, a single-pass inkjet printer is provided as printing system in step (a), wherein the transport of the printing medium takes place at a constant speed in the transport direction, preferably at a speed of at least 3m/min, particularly preferably at a speed of at least 12 m/min.

Such an embodiment offers, for example, the following advantages, namely: the printed print medium can be manufactured on an industrial scale.

The fluid can be a gaseous and/or liquid fluid, preferably a gas or a gas mixture, particularly preferably air.

According to a preferred embodiment of the method, the fluid stream is output by one or more nozzles of the cleaning device, wherein the nozzles are preferably configured as flat nozzles.

The cleaning device can be operated such that the output fluid stream has at least such a high speed at each position of at least one part of the nozzle front plate that it is suitable for carrying away together droplets of the liquid that are suspended at least in one part of the nozzle front plate, preferably such a high speed that it completely cleans the nozzle front plate or completely removes liquid adhering to it.

The cleaning device or the nozzle or nozzles of the cleaning device can be operated such that the output fluid flow has a velocity of at least 5 m/s, preferably at least 7 m/s, particularly preferably at least 10 m/s, very particularly preferably 15 m/s at each position of at least one part of the nozzle front plate.

According to a preferred embodiment of the invention, the nozzle or nozzles of the cleaning device are provided in a movable arrangement in the conveying direction, wherein during the cleaning according to step (c) the nozzle or nozzles are moved in the conveying direction, preferably synchronously with the gap.

This preferred development is advantageous because a smaller number of nozzles can be provided in this way, so that at least a part of the nozzle front plate can be cleaned as in the case of a fixedly arranged nozzle.

According to a further preferred embodiment of the method, the cleaning is performed by a plurality of fluid flow arrangements having at least two fluid flows opposite to each other and directed towards at least a part of the nozzle front plate. Preferably, these fluid flows are formed by at least two nozzles arranged in the conveying direction.

This preferred embodiment is advantageous if, for example, a large nozzle front plate extending transversely to the conveying direction has to be cleaned.

Preferably, the method according to the invention is used for producing a relief-like or full-surface decoration enamel on a printing medium, wherein the printing according to step (c) is carried out in such a way that: drops of glaze suspension are applied in a quantity of 200g/m or more for full-surface application²To 1500g/m²Is output onto the printing medium (101), preferably in a quantity of > 300g/m for the overall application²To 1500g/m²The relative coating amounts in between are output onto the print medium (101).

According to a particularly preferred embodiment of the method, such a large quantity of glaze suspension is printed using a printing system which is configured as a single-pass inkjet printer, preferably as a single-pass inkjet printer of a printing module designed to be operated with a ram.

As an example for such a glaze suspension, mention is made here of the glaze suspension described in the description of italian application IT 102019000001387 of the same applicant.

As an example for a printing module operating with a ram, the specifications of WO 2013/013983 a1 or WO 2019/042585 a1 and WO 2019/042586 a1 of the same applicant are mentioned, which printing modules are referred to herein as printing modules for inkjet printing heads of inkjet printers and can be printing heads of a printing system according to the invention. Due to the internal diameter of the nozzles between 250 μm and 350 μm, it is possible for such a printing module to print inkjet printing inks with larger particles than is the case with inkjet printing devices from the prior art which are usually typically operated piezoelectrically, which typically comprise nozzles with an internal diameter of up to 50 μm.

According to a preferred embodiment of the method, the printing of the printing medium is carried out with droplets of a glaze suspension or ink having a temperature which is tempered to a temperature in the range between 25 ℃ and 50 ℃, preferably between 25 ℃ and 45 ℃, particularly preferably between 30 ℃ and 40 ℃.

The printing medium can be conveyed into the range of action of the printing head of the printing system at a temperature of between 30 ℃ and 120 ℃, preferably between 40 ℃ and 100 ℃, particularly preferably between 50 ℃ and 90 ℃, and very particularly preferably between 55 ℃ and 85 ℃.

In contrast, in a preferred embodiment of the method, the printing medium is provided as a ceramic printing medium, in particular as unfired ceramic tiles, and is fed in the wetted state with water and at a temperature of between 30 ℃ and 120 ℃, preferably between 40 ℃ and 100 ℃, particularly preferably between 50 ℃ and 90 ℃, completely particularly preferably between 55 ℃ and 85 ℃ into the region of action of the nozzle front plate, wherein the nozzle front plate is tempered to a lower temperature than the printing medium during its feeding through the region of action of the nozzle front plate, wherein the nozzle front plate and the printing medium are oriented relative to one another in the region of action of the nozzle front plate in such a way that droplets are formed over time by condensation of water vapor at the front nozzle front plate and grow increasingly larger until they either fall down to the printing medium after a specific time due to gravity or fall down to the printing medium after a specific time And/or will hang from the nozzle front plate so that these droplets will be carried along by the print medium.

In a further preferred embodiment of the method, the printing medium is provided as a ceramic printing medium, in particular as unfired ceramic tiles, and is conveyed in the wetted state with water and at a temperature of between 30 ℃ and 120 ℃, preferably between 40 ℃ and 100 ℃, particularly preferably between 50 ℃ and 90 ℃, completely particularly preferably between 55 ℃ and 85 ℃ into the operating range of a nozzle front plate, wherein the nozzle front plate is tempered to a lower temperature than the temperature of the printing medium during its conveyance through the operating range of the nozzle front plate, wherein the nozzle front plate and the printing medium are oriented substantially horizontally relative to one another in the operating range of the nozzle front plate.

According to a particularly preferred embodiment, the nozzle front plate is tempered to a temperature which is lower than the temperature of the printing medium during its transport through the operating range of the printing head and which lies between 25 ℃ and 50 ℃, preferably between 25 ℃ and 45 ℃, particularly preferably between 30 ℃ and 40 ℃.

The print head is typically provided in such a way that the temperature of the nozzle front plate is decisively determined by the temperature of the tempered glaze suspension or ink or at least decisively determined together.

According to a first preferred variant of the method, a printing system is provided with a transport device for transporting a printing medium in a transport plane in a transport direction, wherein a nozzle front plate of the printing head is arranged above the transport plane, and the one or more nozzles are arranged outside at least a part of the nozzle front plate in the transport direction and above the transport plane and are preferably mounted at the printing head.

According to a particularly preferred embodiment of this first variant of the method, the conveying device is provided as a continuous belt conveyor, which preferably has a longitudinal direction and a transverse direction running perpendicular to the longitudinal direction, which is at least as wide as the range of action of the nozzle front plate, wherein particularly preferably the continuous belt conveyor is assigned a cleaning unit for removing droplets collected on the continuous belt conveyor.

According to a second preferred variant of the method, a printing system is provided with a transport device for transporting a printing medium in a transport plane in a transport direction, wherein a nozzle front plate of the print head is arranged above the transport plane and the nozzle or nozzles are arranged at the transport device in the transport direction inside or outside but below the transport plane.

According to a particularly preferred embodiment of this second variant of the method, the conveyor device is provided as a belt conveyor having at least two belts arranged at a distance from and parallel to each other transversely to the conveying direction, wherein the belts are driven synchronously.

According to the method according to the invention, the printing medium is preferably a ceramic printing medium, paper, corrugated cardboard, metal sheet, wood sheet or glass sheet, wherein the printing medium is particularly preferably a ceramic printing medium, such as, for example, unfired bricks.

According to a first and second variant of the preferred embodiment of the method, the method preferably comprises the following steps:

-providing a conveyor and conveying the printing medium with the conveyor to the conveying device arranged after the conveyor;

-transferring the print medium from a conveyor to the transport device;

-creating a gap between nearest adjacent print media before or during transfer of the print media from the conveyor to the transport device.

According to the invention, this object is also achieved by a printing system according to claim 23. This is achieved by a printing system comprising:

a) a transport device for the print medium;

b) at least one print head having at least one nozzle front plate arranged at the print head, the print head comprising at least one printing module having at least one nozzle plate for outputting droplets of a printable composition;

c) a cleaning device capable of enabling activation of a fluid flow directed towards at least a portion of the nozzle front plate.

According to the invention, the nozzle front plate comprises the nozzle plate, wherein the cleaning device is designed such that one or more fluid flow arrangements with at least one fluid flow directed towards at least a part of the nozzle front plate can be activated synchronously with the interspaces between the print media adjacent in the transport direction.

In a preferred embodiment of the printing system, the cleaning device comprises one or more nozzles through which a fluid stream can be output, wherein the one or more nozzles are particularly preferably flat nozzles.

In a further preferred embodiment of the printing system, the printing system comprises a control device for carrying out at least one method according to the invention.

In accordance with a preferred embodiment of the printing system, the nozzle front plate comprises the nozzle plate and at least one frame plate, wherein the side of the nozzle front plate opposite the print medium lies in a plane, in particular with the nozzle plate and the frame plate.

According to a further preferred embodiment, the printing head comprises at least two printing modules each having at least one nozzle plate, wherein the printing modules are arranged one behind the other, as seen in the transport direction of the printing medium. The nozzle front plate here comprises the nozzle plate of the printing module.

According to a preferred embodiment, the printing system according to the invention comprises a supply system and at least one printing module, the supply system being able to supply the at least one printing module with a printable component, preferably a glaze suspension or ink, wherein the ink supply system has means for tempering the glaze suspension or ink to an operating temperature in the range between 25 ℃ and 50 ℃, so that drops of the printable component can be output at this operating temperature during printing.

According to a further preferred embodiment, the printing system is designed as a single-pass printing system, preferably as a single-pass printing system of a printing module which is operated with a ram.

Drawings

The invention is explained in detail below with reference to the drawings by means of a preferred embodiment. Wherein:

fig. 1 shows a schematic side view in cross section of a very particularly preferred variant of a printing system according to the invention;

FIG. 2 shows a schematic bottom view of a print head of the printing system of FIG. 1;

fig. 3A to 3F show schematic illustrations of a very particularly preferred method according to the invention during the transport of the printing medium by the printing system from fig. 1 and 2.

Detailed Description

It is provided firstly that identical components are provided with the same reference numerals or the same component names in the figures, wherein the disclosure contained in the entire description can be transferred to the same components with the same reference numerals or the same component names in a meaningful manner.

Fig. 1 shows a side view of a ceramic printing medium 101 being transported from a conveyor 131 to a transport device 121 of a printing system 100 and transporting the printing medium 101 in a transport direction T into and out of the operating range of a printing head 103 of the printing system 100. The transport of the printing medium 101 takes place in the printing system 100 by means of a continuous transport belt 123 of a transport device 121. The conveyor 131 conveys a ceramic printing medium 101, which is produced in a preceding step by a pressing device and has a temperature of more than 50 ℃ after one or more preceding treatment stations that have been passed and are wetted with water, for example for drying and/or for wetting with water and/or for applying an enamel primer to the printing medium 101 (not shown).

The printing system 100 is configured as a single pass inkjet printing system with a ram operated printing module 107 for mass printing of glaze suspension onto a ceramic printing medium 101 (not shown). The printing head 103 of this printing system 100 comprises ten printing modules 107 operated with rams, each having a nozzle plate 109 with nozzles 110 for discharging drops of the glaze suspension. The ten printing modules 107 are arranged one behind the other, as seen in the transport direction T of the printing medium 101.

The printing system 100 is configured such that the printing medium 101 can be transported in a transport direction L in a transport plane TE, wherein the nozzle front plates 105 and in particular each nozzle plate 109 of the printing head 103 are arranged at a height X above the transport plane TE.

The conveyor 121 of the printing system 100 comprises a continuous conveyor belt 123 and furthermore a cleaning unit 127 for removing droplets (not shown) of the glaze suspension falling onto the continuous conveyor belt 123 after cleaning of the nozzle front plate 105, wherein the continuous conveyor belt 123 is continuously guided in the printing run by two deflection rollers 125.

The print head 103 is depicted in detail in fig. 2. The print head comprises a nozzle front plate 105 which comprises ten printing modules ("107" in fig. 1) each having a nozzle plate 109 and a frame plate 113, wherein the side of the nozzle front plate 105 opposite the print medium 101 lies in a plane, in particular the nozzle plate 109 and this frame plate 113 (see fig. 1).

The cleaning device 114 in fig. 2 is arranged laterally at the nozzle front plate 105 and is configured such that it can activate a multiplicity of fluid flow arrangements 111 (see fig. 3A to 3E) each having a multiplicity of fluid flows directed toward at least a part of the nozzle front plate 105 in synchronism with the interspaces L between the print media 101 adjacent in the transport direction T.

Now, the method according to the invention to be carried out by means of the device according to the invention shall be described in detail below.

In the method, as explained above, the printing medium 101 is first conveyed from a press (not shown) by a conveyor 131 to the conveying device 121 of the printing system 100 at a temperature of the printing medium 101 of more than 50 ℃, and is then conveyed in this way piece by piece in the conveying direction T, so that the printing medium 101 is conveyed into and out of the operating range of the nozzle front plate 105.

The cleaning of the nozzle front plate 105 can take place at periodic time intervals, wherein the respective interval duration is selected to be as short as necessary, but as long as possible, in order to ensure within the respective interval that the printing medium 101 passes through at least a part of the range of action of the nozzle front plate 105 without waste pages during the transport and printing of the printing medium 101, wherein a certain further higher interval duration compared to the respective interval duration already leads to a printing medium 101 with waste pages.

The time intervals to be selected are preferably adapted to different transport speeds and temperatures of the printing medium 101 and also to different application amounts and temperatures of the glaze suspension or ink in order to optimize the time intervals. It is important, however, that the time interval is chosen to be as long as possible, but short enough to prevent drops of liquid from dripping off the nozzle front plate 105. It is also important here to start at short time intervals in order to avoid corresponding defects or at least to keep the nozzle front plate 105 under constant observation, so that a cleaning step is carried out in good time before it comes off while the liquid formation continues.

There are different possibilities for how a person skilled in the art can obtain an optimized time interval. For example, a person skilled in the art can carry out and thus check in a test sequence at differently high time intervals in a specific printing run of the printing system 100: up to which time interval it is maintained that an acceptable, i.e. sufficiently pure, surface of the nozzle front plate 105 is obtained for which no liquid or dirt falls off the nozzle front plate 105.

For example, the inventors have observed that if a ceramic printing medium 101 is conveyed through the reach of the nozzle front plate 105 of this printing system 100 at a conveying speed of 20m/min and at a printing medium temperature of 80 ℃ and with a selected glaze suspension having a water content of 30 weight percentage points with respect to the total weight of the glaze suspension, at 1000g/m for a full-scale coating²The time interval in which the nozzle front plate 105 has to be cleaned in order to obtain a printed printing medium 101 without waste pages must be chosen to be about 2 minutes for printing onto the printing medium 101.

Now, the individual steps of cleaning the nozzle front plate 105 are described below, again by way of example according to fig. 3A to 3F.

After the end of the predefined time interval or at the latest when the printing medium 101 is transferred from the conveyor 131 to the transport device 121, a gap L is produced between the nearest adjacent printing media 101 on the conveyor 131.

In the entrance area of the printing system 100, one counter of the counting mechanism is activated when the trailing edge of a first print medium 101 passes by a sensor (not shown) and another counter of the counting mechanism is activated when the leading edge of another print medium 101 passes by the sensor. If the distance between the first and the

further printing medium

101, 101 reaches a counter state corresponding to a distance equivalent from the position of the sensor up to the distance center of the gap with or without the further counter of the counting mechanism being activated, the four nozzles 115 of the first nozzle group 114A of the cleaning device 114 are activated, and more precisely activated in such a way that the cleaning device 114 activates the fluid flow only in the region of the gap L and synchronously with this gap. The nozzle 115 is configured as a flat nozzle.

The four nozzles 115 of the first nozzle group 114A are connected via fluid lines 117 to an external, pre-controlled 2/2 path process valve 119 (see fig. 3A), which is itself connected to a compressor (not shown) for applying a specific pressure to the fluid.

The time interval between two valve actuations for the same nozzle group 114A is 2 minutes, wherein the duration of the valve actuation for activating the fluid flow from the nozzles 115 of the nozzle group 114A is 1000 milliseconds. In this example, the flat nozzle was operated at a pressure of 2.5 bar and a fluid flow rate of 11520 to 25 liters/min per nozzle. The nozzle group 114A with 4 nozzles 115 is accordingly operated with a total fluid throughput of 80 to 100 l/min.

The cleaning device 114 comprises five

nozzle groups

114A, 114B, 114C, 114D, 114E, which are each connected via a fluid line 117 to an external, pre-controlled 2/2-path process valve 119 (see fig. 2), and a 2/2-path process valve to a compressor (not shown) for applying a specific pressure to the fluid.

According to a preferred embodiment of the method, the time interval between two cleanings of the same component of the nozzle front plate 105 is in the range between 30 seconds and 5 minutes, in particular between 1 minute and 3 minutes, wherein the duration of the cleanings is in the range between 100 milliseconds and 5 seconds, in particular in the range between 300 milliseconds and 1.4 seconds.

Fig. 3B to 3F below show a principle drawing of a particularly preferred method according to the invention during the transport of the printing medium 101 through the region of action of the nozzle front plate 105.

Fig. 3B discloses a point in time when the fluid flow is not activated, since drops of liquid hanging from the nozzle front plate 105 when activating the fluid flow from the

nozzle group

114A or 114B will not only be activated in the area of the gap L, but also in the area of the print medium 101, which will then be contaminated.

Fig. 3C to 3F disclose different points in time during the further transport of the printing medium 101 through the range of action of the nozzle front plate 105, in which the cleaning device 114 activates the fluid flow through the nozzles 115 of the

respective nozzle groups

114B, 114C, 114D, 114E sequentially and synchronously with the gap L. With this treatment, at least the entire surface of the nozzle front plate 105, to which the printing medium 101 is exposed during transport through the region of action of the nozzle front plate 105, is cleaned.

According to a further embodiment of the method, which is not shown in the drawings, the printing medium, on which the printing system for producing the embossed or full-surface decorative glaze has been applied with the glaze suspension, can be transported from the printing system to a further printing system in order to print a color image on the applied decorative glaze. The further printing system can be a very common inkjet printer for printing ceramic printing media with color inks. The distance between the two printing systems is selected such that the glaze suspension is at least partially dried, so that the color ink does not mix with the applied glaze suspension. Alternatively or additionally, the print medium printed with the first printing system can be dried at least partially with at least one suitable drying source, such as for example an IR source, before it is printed with another printing system. After finishing the application of the color ink to the embossed or full-face decorative glaze, the ceramic printing medium thus printed can be transferred to a firing oven, fired therein and then trimmed if necessary.

Claims

1. Method for conveying piece-by-piece printing media (101) into and out of the operating range of a printing head (103) and for cleaning at least one part of at least one nozzle front plate (105) arranged at the printing head (103), wherein the method comprises the following steps:

a) providing a printing system (100) comprising the print head (103) with the nozzle front plate (105), wherein the print head (103) comprises at least one printing module (107) with at least one nozzle plate (109) from which droplets of a printable composition can be output;

b) conveying the printing medium (101) in a conveying direction (T) in such a way that the printing medium (101) is conveyed into and out of the range of action of the nozzle front plate (105);

c) cleaning at least a part of the nozzle front plate (105) by means of one or more fluid flow arrangements (111) from a cleaning device (114) activating the fluid flow, wherein the fluid flow arrangement (111) comprises at least one fluid flow directed towards at least a part of the nozzle front plate (105),

characterized in that the nozzle front plate (105) comprises the nozzle plate (109), wherein at least some of the print media (101) are transported in the transport direction (T) spaced apart from at least one of its nearest neighboring print media (101), whereby a gap (L) is created between these spaced apart neighboring print media (101) in the transport direction (T), and the cleaning device (114) does not need to activate the fluid flow all the time, but only in the region of and in synchronism with the gap (L).

2. Method according to claim 1, characterized in that at least such entire surface of the nozzle front plate (105) is cleaned: the printing medium (101) is exposed to the entire surface during transport through the range of action of the nozzle front plate (105).

3. Method according to claim 1 or 2, characterized in that the printing medium (101) is provided as a ceramic printing medium, in particular as unfired ceramic tiles, and is conveyed in a moistened state with water and at a temperature of between 30 ℃ and 120 ℃, preferably between 40 ℃ and 100 ℃, particularly preferably between 50 ℃ and 90 ℃, into the range of action of the nozzle front plate (105), wherein the nozzle front plate (105) is tempered to a temperature which is lower than the temperature of the printing medium (101) during the conveyance of the printing medium through the range of action of the nozzle front plate (105), wherein the nozzle front plate (105) and the printing medium (101) are oriented relative to one another in the range of action of the nozzle front plate (105) such that droplets are formed by condensation of water vapor at the nozzle front plate (105) over time and grow increasingly larger, until they either fall onto the printing medium (105) after a certain time due to gravity and/or hang from the nozzle front plate (105) in such a way that they are carried along by the printing medium (101).

4. Method according to at least one of the preceding claims, characterized in that the nozzle front plate (105) comprises the nozzle plate (109) and at least one frame plate (113), wherein the side of the nozzle front plate (105) opposite the print medium (101) lies in particular in a plane with the nozzle plate (109) and the frame plate (113).

5. The method according to at least one of the preceding claims, characterized in that the cleaning device (114) activates the fluid flow sequentially.

6. Method according to at least one of the preceding claims, characterized in that the cleaning of at least one part of the nozzle front plate (105) according to step (c) is accompanied at least temporarily simultaneously during the transport of the printing medium (101) through the region of action of the nozzle front plate (105).

7. Method according to at least one of the preceding claims, characterized in that it comprises the steps of:

d) -printing the print medium (101) in a manner that: at least one nozzle plate (109) of the at least one printing module (107) outputs drops of a printable composition, preferably an ink or glaze suspension.

8. Method according to claim 7, characterized in that the printing according to step (d) and the cleaning of at least one part of the nozzle front plate (105) according to step (c) are at least temporarily accompanied simultaneously during the transport of the printing medium (101) through the area of action of the nozzle front plate (105).

9. Method according to at least one of the preceding claims, characterized in that the transport of the printing medium (101) takes place in a transport plane (TE) along the transport direction (T), wherein a nozzle front plate (105) of the print head (103) is arranged above the transport plane (TE), wherein the transport according to step (b) and the cleaning according to step (c) take place at the same height (X), preferably at the same target height, between the nozzle front plate (105) and the surface of the printing medium (101) in a direction perpendicular with respect to the transport plane (TE) of the printing medium (101).

10. Method according to at least one of the preceding claims in connection with claim 9, characterized in that the transport according to step (b) and the cleaning according to step (c) and the printing according to step (d) are carried out on the same height (X), preferably on the same target height.

11. Method according to claim 9 or 10, characterized in that it comprises the following steps:

(g) detecting the actual height by means of a sensor before the printing medium (101) is conveyed into the range of action of the nozzle front plate (105),

(h) -adjusting the actual height by means of a positioning device of the printing system (100) if the detected actual height does not correspond to a target height.

12. Method according to at least one of the preceding claims, characterized in that a single-pass inkjet printer is provided as printing system (100) in step (a), wherein the transport of the printing medium (101) is carried out at a constant speed in the transport direction (T) and preferably at a speed of at least 3m/min, particularly preferably at a speed of at least 12 m/min.

13. Method according to at least one of the preceding claims, characterized in that the fluid is a gaseous and/or liquid fluid, preferably a gas or a gas mixture, particularly preferably air.

14. The method according to at least one of the preceding claims, characterized in that a fluid stream is output by one or more nozzles (115) of the cleaning device (114), wherein the nozzles (115) are preferably configured as flat nozzles.

15. Method according to at least one of the claims related to claim 14, characterized in that the nozzle (105) or nozzles (115) of the cleaning device (114) are provided in a movably arranged manner in the conveying direction (T), wherein the nozzle (115) or nozzles (115) are moved in the conveying direction (T), preferably synchronously with the interspace (L), during the cleaning according to step (c).

16. Method according to at least one of the preceding claims, characterized in that the cleaning is performed by a plurality of fluid flow arrangements (111) with at least two fluid flows directed opposite to each other and towards at least a part of the nozzle front plate (105).

17. Method for producing a relief-like or full-face decor glaze on a printing medium (101) according to at least one of the preceding claims in relation to claim 7, characterized in that the printing according to step (d) is carried out in such a way that: drops of glaze suspension are applied in a quantity of 200g/m or more for full-surface application²To 1500g/m²Is output onto the printing medium (101), preferably in a quantity of > 300g/m for the overall application²To 1500g/m²Is output onto the print medium (101).

18. Method according to at least one of the preceding claims in connection with claim 7, characterized in that the printing of the printing medium (101) is performed with droplets of glaze suspension or ink tempered to a temperature in the range between 25 ℃ and 50 ℃, preferably between 25 ℃ and 45 ℃, particularly preferably between 30 ℃ and 40 ℃.

19. Method according to at least one of claims 14 to 18 in connection with claim 9, characterized in that in the method the printing system (100) is provided with a transport device (121) for transporting the printing medium (101) in the transport plane (TE) along the transport direction (T), wherein a nozzle front plate (105) of the printing head (103) is arranged above the transport plane (TE) and the one or more nozzles (115) are arranged outside at least a part of the nozzle front plate (105) along the transport direction (T) and above the transport plane (TE) and preferably mounted at the printing head (103).

20. Method according to claim 19, characterized in that the conveying device (121) is a continuous belt conveyor, preferably having a longitudinal direction and a transverse direction extending perpendicularly thereto, the transverse direction being at least as wide as the range of action of the nozzle front plate (105), wherein a cleaning unit (127) for removing droplets collected on the continuous belt conveyor is particularly preferably assigned to the continuous belt conveyor.

21. Method according to at least one of claims 14 to 18 in connection with claim 9, characterized in that in the method the printing system (100) is provided with a transport device (121) for transporting the printing medium (101) in the transport plane (TE) along the transport direction (T), wherein a nozzle front plate (105) of the printing head (103) is arranged above the transport plane (TE) and the nozzle (115) or nozzles (115) are arranged at the transport device (121) along the transport direction (T) inside or outside but below the transport plane (TE).

22. Method according to claim 21, characterized in that the conveying device (121) comprises a belt conveyor with at least two belts arranged spaced apart and parallel with respect to each other transversely to the conveying direction (T), wherein the belts are driven synchronously.

23. Method according to at least one of the claims 19 to 22, characterized in that the cleaning according to step (c) comprises the steps of:

-providing a conveyor (131) and conveying the print medium (101) with the conveyor (131) to the conveying device (121) arranged behind the conveyor (131);

-transferring the printing medium (101) from a conveyor (131) to a transport device (121);

-creating a gap (L) between nearest adjacent print media (101) before or during transferring of the print media (101) from the conveyor (131) to the transport device (121).

24. The method according to at least one of the preceding claims, characterized in that the cleaning according to step (c) is carried out at periodic time intervals, wherein the respective interval duration is selected to be as short as necessary but as long as possible, so that it is ensured within the respective interval duration that the printing medium (101) passes at least over at least a part of the range of action of the nozzle front plate (105) without waste pages during the transport or transport and printing of the printing medium (101), wherein a certain further higher interval duration compared to the respective interval duration already results in a printing medium (101) with waste pages.

25. Printing system (100), comprising:

a. a transport device (121) for a printing medium (101);

b. at least one print head (103) having at least one nozzle front plate (105) arranged at the print head (103), the print head (103) comprising at least one printing module (107) having at least one nozzle plate (109) for outputting droplets of a printable composition;

c. a cleaning device (114) capable of enabling activation of a fluid flow directed towards at least a portion of the nozzle front plate (105);

characterized in that the nozzle front plate (105) comprises the nozzle plate (109), wherein the cleaning device (114) is configured such that one or more fluid flow arrangements (111) with at least one fluid flow directed towards at least a part of the nozzle front plate (105) can be activated synchronously with a gap (L) between print media (101) adjacent in the transport direction (T).

26. The printing system (100) according to claim 25, wherein the cleaning device (114) comprises one or more nozzles (115) through which a fluid stream can be output, wherein the one or more nozzles (115) are flat nozzles.

27. The printing system (100) according to at least one of claims 24 or 26, characterized in that it comprises a control device for implementing at least one method according to at least one of claims 1 to 25.