ES2968355T3 - Method for transporting print media and for cleaning the face plate of a nozzle - Google Patents

Abstract

The invention relates to a method for transporting fragmented printing media (101) into the effective region of a print head (103) and out of said effective region again, and for cleaning at least a portion of at least one front panel. nozzle (105). provided in the printing head (103), wherein the method comprises the steps of: a) providing a printing system (100) comprising the printing head (103) having the nozzle front panel (105), in wherein the print head (103) comprises at least one print module (107) having at least one nozzle panel (109), from which droplets of a printable composition can be discharged; b) transporting the printing media (101) in a transport direction (T) such that the printing media (101) can be transported within the effective region of the front panel of the nozzle (105) and outside said region again; c) cleaning at least a portion of the front panel of the nozzle (105) by means of one or more fluid flow configurations (111) from a fluid flow activating cleaning device (114), wherein the flow configurations of fluid (111) comprise at least one fluid flow directed against at least a portion of the nozzle front panel (105), wherein the nozzle front panel (105) comprises the nozzle panel (109), where at least some of the printing media (101) is transported in the transport direction (T) so that it is separated from at least one of its closest adjacent printing media (101), as a result of which gaps (L) are produced ) between these adjacent spaced printing means (101) in the transport direction (T) and the cleaning device (114) activate the flow of fluid not necessarily always but exclusively in the region of the spaces (L) and so that is synchronized with said spaces. (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Method for transporting print media and for cleaning the face plate of a nozzle

The present invention relates to a method for transporting ceramic printing media piecemeal in and out of the effective area of a printing head and for cleaning at least a part of at least one face plate of a nozzle disposed in the printing head. The invention further relates to a printing system for carrying out the method according to the invention.

Printing systems can print on various printing media, such as ceramic tiles, paper sheets, corrugated cardboard sheets, metal plates, wooden plates or glass plates, with a print head that typically includes multiple print modules with multiple nozzle plates with nozzles from which drops of a printable composition can be dispensed. In any case, the nozzle plates must be cleaned from time to time to enable trouble-free printing operation, both as the production of defect-free printed media is of great importance. According to the invention, ceramic printing media are printed.

Over time, during printing, dirty nozzle plates may result that must be cleaned when, for example, the surface of the nozzle plate becomes undesirably wet with ink, which must therefore be cleaned regularly.

In DE 10256879 A1 such regular cleaning of a nozzle plate of a print head is achieved by interrupting the printing operation before cleaning and then moving the print head far enough away from the conveyor belt described in the document to transport a printing medium so that a cleaning device parked next to the print head can be moved from its parking position to the area between the print head and the conveyor belt and placed there accordingly for cleaning. Cleaning of the nozzle plate is carried out in such a way that a pulse of a gas stream passes through the nozzle plate, whereby paint residues and/or foreign particles adhered to the nozzle plate are transported to an edge of evacuation and there they are detached from the nozzle plate.

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

DE 10256879 A1 describes a method for transporting containers into the effective area of a direct print head and out of this effective area again and for cleaning at least a part of at least one nozzle face plate arranged on the head. direct printing, in which a print head that is not currently needed is transferred to a cleaning device that sits between two containers and is then sprayed with cleaning fluid.

It would be desirable to have a method that can be used to at least reduce the frequency at which conventional methods must make interruptions at defined time intervals in the transport of the printing medium for cleaning the nozzle plate, both in the operation of printing and in the transit operation of the printing system.

Transit operation of a printing system will hereinafter be understood as the use of the same, at least for a given period of time, exclusively as a transit system, in which the printing media pass through the effective area of a print head of this printing system without printing and only printing on another printing system located behind this printing system.

Therefore, the objective of the invention is to provide a method of increasing the yield of waste-free printing media across the effective area of a nozzle faceplate of a printing system by reducing or even avoiding interruptions in transportation for cleaning. the front nozzle plate.

According to the invention, the objective is achieved with a method comprising the characteristics of claim 1. The subordinate claims refer to other advantageous and, where appropriate, additional embodiments of the invention.

The invention is based on the idea of transporting printing media in and out of the effective zone of a nozzle faceplate, with at least a portion of the printing media being transported at a distance of at least one of its closest printing media. , thus creating spaces between them in the transport direction and cleaning of the nozzle face plate is carried out with a liquid jet directed against the nozzle face plate in such a way that a cleaning device does not activate the liquid jet always necessarily, but only in the area of spaces and synchronized with them. A method according to the invention for transporting printing media is carried out with a printing system comprising a printing head, in which printing head at least one nozzle front plate is provided, the printing head comprising at least one module printing with at least one nozzle plate from which drops can be dispensed. Cleaning of at least a portion of the nozzle faceplate is carried out using one or more liquid jet configurations from a cleaning device that activates the liquid jet. The nozzle face plate comprises the nozzle plate.

The invention is further based on the idea that the printing media is provided as ceramic printing media and is transported to the effective region of the nozzle face plate in a state moistened with water and at a temperature of between 30°C and 120°C. C, the nozzle face plate being tempered to a temperature that is lower than the temperature of the printing media during its transportation through the effective area of the nozzle face plate, the nozzle face plate and the printing media being aligned the effective area of the nozzle face plate with each other in such a way that drops form on the nozzle face plate as time progresses due to condensation of water vapor and continue to grow until, by the force of gravity , after a certain time they fall onto the printing media and/or hang from the nozzle face plate in such a way that they are dragged by the printing media.

In the following, printing medium refers to a medium that is to be printed. A print medium must be distinguished from a placeholder dummy that cannot be printed or will not be printed and which may also form a space between subsequent adjacent print media.

Accordingly, Method according to the invention is a method for transporting printing media piece by piece into the effective area of a printing head and again out of this effective area, as well as for cleaning at least a part of at least one front plate of nozzles arranged in the printing head, the method comprising the following steps:

a) providing a printing system comprising the printing head with the nozzle face plate, the printing head comprising at least one printing module with at least one nozzle plate from which drops of a printable composition can be dispensed,

b) transporting the printing media along a transport direction, so that the printing media is transported in and out of the effective area of the nozzle face plate,

c) cleaning at least a portion of the nozzle face plate by means of one or more liquid jet configurations from a cleaning device that activates the liquid jet, the liquid jet configurations comprising at least one directed liquid jet against at least a part of the nozzle face plate,

the nozzle front plate comprising the nozzle plate, at least some of the printing means being transported in the transport direction at a certain distance from at least one of its nearest neighboring printing means, whereby between these printing means neighbors separated from each other, spaces occur in the direction of transport and the cleaning device activates the liquid jet not necessarily always, but exclusively in the area of the spaces and in a synchronized manner with them.

According to the invention, the printing media are provided as ceramic printing media and are transported in a state moistened with water and at a temperature between 30 ° C and 120 ° C to the effective area of the nozzle front plate, the front plate being nozzles tempered at a temperature that is lower than the temperature of the printing media during transport thereof through the effective area of the nozzle face plate, the nozzle face plate and the printing media being in the effective area of the front plate of nozzles aligned with each other in such a way that, as time progresses, drops form due to the condensation of water vapor on the front plate of nozzles and continue to grow until after a certain time they fall due to the force of gravity on the printing medium and/or hang from the nozzle face plate in such a way that they are dragged by the printing medium.

The method according to the invention is particularly suitable if, for example, the nozzle front plate of the printing system is used under working conditions in which large quantities of liquid condense on the nozzle front plate in a very short time.

Such contamination is known in the ceramic industry when ceramic printing media, after having been produced in a pressing device and having passed through several stations, are then transported in and out of the printing system in a state moistened with water and at a temperature of printing media between 30°C and 120°C. The water in the ceramic printing medium passes into the gas phase, in which the gas water can condense again on the nozzle face plate.

Then, when further printing, a part of the composition printed on these printing media passes into the gas phase, where it can condense again on the nozzle front plate. As time passes, the droplets continue to grow until the force of gravity acting on the droplets exceeds the retention forces on the nozzle face plate, causing the droplets of the composition to break off and fall onto the media. impression.

Waste products produced in this way and in the ways described below cannot be used as high-quality products, but can at best be sold on the market as inferior second-class products, although in In any case they can be classified as waste.

It is clear that the printable composition comprises a volatile component, at least in the case described above. Typically it is water and/or a polyglycol. If printing media is printed in a printing system with an enamel suspension as a printable composition, relatively large quantities are often used, in particular maximum quantities greater than 200 g/m2 up to 1500 g/m2 based on an entire application. the surface onto the printing media to produce relief or all-over decorations. The enamel slurry is often tempered to a temperature between 30°C and 50°C before printing on the medium. In this case there is a significant rate of evaporation of the liquid from the enamel suspension applied on the printing medium, of which a part condenses again on the nozzle front plate, so that without adequate repeated cleaning of the plate front of nozzles, this ends up especially dirty.

During an investigation, the inventors observed that if large quantities of printed enamel composition are printed, even if the nozzle face plate is electrically heated to temperatures of, for example, 50 ° C, it may happen that the problem of water condensation is partially resolved but completely insufficient.

Liquid condensation in the air can cause another problem. As is known, printing of the printing media is normally carried out at a very low height of a fraction of a millimeter or a few millimeters between the nozzle face plate and the surface of the printing media. Therefore, the droplets that form over time on the nozzle face plate do not even need to fall onto the printing media by the force of gravity to contaminate them, but can grow to such a size that they hang “at the side”. "eye level" with the transported printing media, that is, at least at the height of the surface of the printing media, whereby they are dragged by the printing media. This often results in longitudinal fouling forming on the surface of the printing media.

Another cause leading to nozzle contamination, particularly when printing on ceramic printing media with the glaze slurry, is due to the rebound of droplets from the surface of the printing media to be printed onto the faceplate. of nozzles. Several variables influence rebound behavior. These include, but are not limited to, the size and speed of the droplets, as well as the distance between the nozzle face plate and the surface of the printing medium to be printed.

In addition, the nozzle face plates can become dirty if, due to improper injection behavior, so-called satellites or satellite drops form in the emitted main droplets, which are released together with the main drop in the form of very small droplets. The droplets form a mist that settles on the nozzle face plate and can contaminate it.

On the other hand, contamination of the nozzle front plate can also be caused by manual cleaning. Manual cleaning removes dried ink residue from clogged nozzles. However, if the nozzle face plate is not dried sufficiently, so much cleaning fluid may remain on the nozzle face plate that over time it may drop onto the print media or be washed away by the print media. printing media as indicated above.

In a particularly preferred embodiment of the method according to the invention, at least the entire surface of the nozzle face plate to which the printing media is exposed during transport through the effective area of the nozzle face plate is cleaned.

This has the advantage that contamination of the printing media over the entire surface of the printing media can be avoided. According to a preferred embodiment of the envisaged print head, it comprises at least two print modules, each with at least one nozzle plate, the print modules being arranged one behind the other in the transport direction of the print media. The nozzle face plate comprises the nozzle plates of the printing modules.

The nozzle face plate may comprise the nozzle plate and at least one frame plate, the side of the nozzle face plate being oriented towards the printing means in the same plane in particular as 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 liquid jet sequentially.

This embodiment is advantageous because the spaces between the printing means arranged in the transport direction can be chosen, for example, to be relatively narrow in relation to the length of the nozzle face plate in the transport direction.

According to another preferred embodiment, during the transport of the printing media through the effective area of the nozzle face plate, the cleaning of at least a part of the nozzle face plate is carried out at the same time at least temporarily according to the step ( c).

According to a particularly preferred embodiment, the method comprises step (d) of printing the printing media, wherein the at least one nozzle plate of the at least one printing module dispenses droplets of the printable composition, preferably an ink or an enamel suspension.

The printable composition used, preferably the ink or enamel suspension, may comprise at least one volatile component, preferably water and/or at least one non-aqueous polar solvent. The non-aqueous polar solvent is usually a polyglycol. According to a preferred embodiment of the enamel or ink suspension, water is present in the enamel or ink suspension in a proportion between 30% by weight and 60% by weight with respect to the weight of the enamel suspension. enamel or ink.

According to a particularly preferred embodiment, the printing head comprises a gas flow module having at least a first and a second slotted nozzle in the nozzle front plate, the method being released in the method at least when printing the printing media according to the step (d) a gas in the gap between the nozzle face plate and the printing media to be printed by the first slotted nozzle and drawn in again through the second slotted nozzle, so that a gas is generated in the gap. laminar gas flow.

Such a method has the advantage that if, for example, there is air containing water in the space between the printing media and the nozzle front plate, this is partially removed and the amount of water that can and does condense on the front plate of nozzles.

According to a preferred embodiment, the nozzle face plate is configured as a closed, liquid-tight nozzle face plate, except for the nozzle openings and preferably except for the slotted nozzle openings of the gas flow module. According to a particularly preferred embodiment, the print head is configured as a closed, liquid-tight print head.

These variants are advantageous because they allow the penetration of ambient humidity and other volatile components of an ink or enamel suspension from the gas phase to the print head to be reduced or prevented. The penetration of ambient moisture into the print head may cause damage to the print head.

According to another particularly preferred embodiment, cleaning is carried out at periodic time intervals, the duration of the respective interval being chosen as short as necessary but as long as possible, so that waste-free production occurs within the duration of the corresponding interval. during transportation or transportation and printing of the printing media by the effective area of the nozzle face plate, a certain longer interval duration compared to the respective interval duration having led to a waste of printing media.

This variant is advantageous because it allows the production of waste-free printing media to be further increased.

According to another particularly preferred embodiment, during transport of the printing media through the effective area of the nozzle face plate, printing according to step (d) and cleaning at least part of the nozzle face plate according to step (c) are carried out simultaneously at least temporarily.

In this way, the liquid jet can preferably be activated with the cleaning device at least during printing according to step (d), so that the liquid jet does not cross the flight paths of the droplets released from the printing plate. nozzle or from the nozzle plates.

The transport of the recording media can be carried out on a transport plane along the transport direction, the front nozzle plate of the recording head being arranged above the transport plane, the transport being carried out according to the pitch ( b) and cleaning according to step (c) at the same height of impression.

In a preferred embodiment of the method, transport according to step (b) and cleaning according to step (c) and printing according to step (d) take place at the same height (X), preferably at the same nominal height.

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

(e) detecting an actual height by a sensor before transporting the printing media to the effective area of the nozzle face plate,

(f) adjust the actual height using a printing system positioning device if the actual recorded height does not correspond to a nominal height.

This variant is advantageous because it allows different printing media with different thicknesses to be transported through the effective area of the nozzle front plate.

The nominal height preferably corresponds to a predetermined value in a range between 0.4 mm and 15.0 mm. The person skilled in the art knows what is the nominal height to which the nozzle front plate must be adjusted to obtain a high quality print and that this depends on several variables, such as drop size, drop speed and straightness of the falling path of the drops.

According to a preferred embodiment of the method, in step (a) a single-pass inkjet printer is provided as the printing system, transportation of the printing media takes place at a constant speed in the transportation direction, and preferably at a speed of at least 3 m/min, with particular preference at a speed of at least 12 m/min.

This embodiment offers, for example, the advantage that printed media can be produced on an industrial scale.

The liquid may be a gaseous and/or liquid liquid, preferably a gas or a mixture of gases, especially preferably air.

According to a preferred embodiment of the method, the liquid jet is supplied from one or more nozzles of the cleaning device, the nozzles preferably being configured as flat jet nozzles.

The cleaning device can operate in such a way that the jet of liquid supplied at each point of at least a part of the nozzle face plate has at least a velocity high enough to be capable of entraining droplets of a liquid hanging on the surface. at least one part of the nozzle face plate, preferably having a speed high enough to completely clean the part of the nozzle face plate or completely remove the liquid adhering to the nozzle face plate.

The cleaning device or the nozzle or multiple nozzles of the cleaning device may operate in such a way that the jet of liquid delivered at each point of at least a part of the nozzle face plate has a velocity of at least 5 meters/second. . preferably at least 7 meters/second, particularly preferably at least 10 meters/second, most preferably 15 meters/second.

According to a preferred embodiment of the invention, the one or more nozzles of the cleaning device are arranged movably in the transport direction, the one or more nozzles moving during cleaning according to step (c) in the direction of transport. transport, preferably synchronously with the spaces.

This preferred variant is advantageous in that it allows a smaller number of nozzles to be provided for cleaning at least a part of the front nozzle plate than with stationary nozzles.

According to another preferred embodiment of the method, cleaning is performed through various liquid jet configurations with at least two liquid jets directed against each other and against at least a portion of the nozzle face plate. These are preferably dispensed from at least two nozzles arranged along the transport direction.

This preferred embodiment is advantageous when, for example, it is necessary to clean front panels of very large nozzles that extend transversely to the direction of transport.

The method according to the invention is preferably used for the production of embossed or full-surface decorative enamels on printing media, the printing being carried out according to step (c) by applying drops of an enamel suspension in relative application amounts of between > 200 g/m2 and 1500 g/m2 based on a full surface application on the printing media (101), preferably between > 300 g/m2 and 1500 g/m2 based on a full surface application on the printing means (101).

According to a particularly preferred embodiment of the method, large quantities of enamel suspension are thus printed with a printing system configured as a single-pass inkjet printer, preferably as a single-pass inkjet printer with driven printing modules. by plunger.

As an example of such enamel suspensions, mention may be made of the enamel suspensions described in the description of the Italian application IT 102019 000001 387 of the applicant of the same name.

As an example of plunger-operated printing modules, it is worth mentioning those mentioned in the description of WO 2013/013983 A1 or WO 2019/042585 A1 and WO 2019/042586 A1 by the applicant of the same name, in which they are called printing heads of inkjet for inkjet printers and may be printing modules of a print head of the printing system according to the invention. Due to the large inner diameter of the nozzles of between 250 pm and 350 pm, inkjet printing inks with larger particles can be printed in such printing modules than in typical state-of-the-art piezoelectrically driven inkjet printing devices. technique, which normally comprise nozzles with an internal diameter of up to 50 pm.

According to a preferred embodiment of the method, the printing media is printed with drops of an enamel or ink suspension tempered at a temperature in the range between 25 ° C and 50 ° C, preferably between 25 ° C and 45 ° C, particularly preferably between 30°C and 40°C.

The printing media may be transported within the effective print head area of the printing system at a temperature of between 30°C and 120°C, preferably between 40°C and 100°C, especially preferably between 50°C. and 90 °C, very particularly preferably between 55 °C and 85 °C.

In another preferred embodiment of the method, the printing media is ceramic printing media, in particular unfired ceramic tiles, and is transported in a water-moistened state and at a temperature of between 30°C and 120°C, preferably between 40°C. C and 100 °C, with particular preference between 50 °C and 90 °C, very particularly preferably between 55 °C and 85 °C to the effective area of the nozzle face plate, the nozzle face plate being tempered at a temperature that is less than the temperature of the printing media during transport thereof through the effective area of the nozzle face plate, the nozzle face plate and the printing media being aligned essentially horizontally with each other in the effective area of the nozzle face plate.

According to a particularly preferred embodiment, the nozzle front plate is tempered at a temperature lower than the temperature of the printing media during transport thereof through the effective area of the print head and which is between 25 ° C and 50 °C, preferably between 25 °C and 45 °C, with particular preference between 30 °C and 40 °C.

The print head is normally provided such that the temperature of the nozzle face plate is largely determined or at least largely co-determined by the temperature of the tempered glaze or ink slurry.

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

According to a particularly preferred embodiment of this first variant of the method, the transport device is designed as an endless conveyor belt preferably having a longitudinal direction and a transverse direction perpendicular to it, the transverse direction of which is at least as wide as the area effective of the nozzle front plate, the endless conveyor belt being particularly preferably provided with a cleaning unit to remove drops accumulated on the endless conveyor belt.

According to a second preferred variant of the method, the printing system is provided with a transport device for transporting the printing media in the transport plane along the transport direction, the front nozzle plate of the printing head being arranged above the transport plane and the one nozzle or several nozzles being arranged inside or outside but below the transport plane in the transport device along the transport direction.

According to a particularly preferred embodiment of this second variant of the method, the transport device is designed as a belt conveyor belt with at least two parallel belts spaced apart and arranged transversely to the direction of transport, the belts being driven synchronously.

According to the method according to the invention, the printing media are preferably ceramic printing media, paper sheets, corrugated cardboard sheets, metal plates, wooden plates or glass plates, the printing media being particularly preferably printing media. ceramics such as unfired tiles.

According to the first and second variants of the preferred embodiments of the method, the method preferably comprises the following steps:

• providing a conveyor and transporting the printing media with the conveyor to the transport device of the printing system, which is arranged after the conveyor;

• transfer printing media from the conveyor to the transport device;

• create a space between the closest adjacent print media before or during the transfer of print media from the conveyor to the transport device.

According to the invention, the objective is also solved by a printing system according to claim 14. This is achieved with a printing system that comprises:

a) a transport device for printing media;

b) at least one print head with at least one nozzle face plate disposed on the print head, the print head comprising at least one print module with at least one nozzle plate for dispensing droplets of a printable composition;

c) a cleaning device that allows activating a jet of liquid directed against at least a part of the nozzle front plate;

wherein the nozzle face plate comprises the nozzle plate, the cleaning device being designed such that one or more liquid jet configurations with at least one liquid jet directed against at least a portion of the nozzle face plate is can activate synchronized with the spaces between adjacent printing media in the transport direction.

According to the invention, the printing system comprises a control device for carrying out at least one method according to the invention.

In a preferred embodiment of the printing system, the cleaning device comprises one or more nozzles through which a jet of liquid can be dispensed, the one or more nozzles particularly preferably being flat jet nozzles.

According to a preferred embodiment of the printing system, the nozzle face plate comprises the nozzle plate and at least one frame plate, the side of the nozzle face plate being oriented towards the printing medium in the same plane that in particular the nozzle plate and frame plate.

According to another preferred embodiment, the printing head comprises at least two printing modules, each with at least one nozzle plate, the printing modules being arranged one behind the other when viewed in the direction of transport of the printing media. The nozzle face plate comprises the nozzle plates of the printing modules.

According to a preferred embodiment, the printing system according to the invention comprises a supply system and the at least one printing module, which can supply the at least one printing module with the printable composition, preferably the enamel suspension or the ink, comprising the ink supply system means for tempering the glaze suspension or ink to a working temperature in the range of 25°C to 50°C, so that drops of the printable composition can be dispensed at said temperature when printing of work.

According to another preferred embodiment, the printing system is configured as a single-pass printing system, preferably as a single-pass printing system with plunger-driven printing modules.

The invention is explained below in more detail by means of a preferred embodiment example with reference to the accompanying drawings.

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

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

Figures 3A to 3F show sketches of the principle of a particularly preferred method according to the invention during transport of printing media through the printing system of Figures 1 and 2.

By way of introduction, it should be noted that in the figures the same parts are provided with the same reference signs or the same names of components, so that the disclosures contained in the complete description can be transferred in an analogous manner to the same parts with the same reference signs or the same component names.

Figure 1 shows a side view of the transport of ceramic printing media 101 from a conveyor 131 to a transport device 121 of a printing system 100, as well as the transport of the printing media 101 along a direction T of transport into the effective region of a print head 103 of the printing system 100 and again out of it. The transportation of the printing media 101 is carried out in the printing system 100 by means of an endless conveyor belt 123 of the transport device 121. The conveyor 131 transports ceramic printing media 101 that were produced in a previous step by means of a pressing device and after one or more pretreatment stations, for example for drying and/or wetting with water and/or for applying slip to the media 101. printing materials (not shown) that have a temperature greater than 50 °C and are moistened with water.

The printing system 100 is designed as a single-pass inkjet printing system with plunger-actuated printing modules 107 for printing glaze suspensions in large quantities onto the ceramic printing media 101 (not shown). The print head 103 of this printing system 100 comprises ten plunger-actuated print modules 107, each with a nozzle plate 109 with nozzles 110 for dispensing drops of the enamel suspension. The ten printing modules 107 are arranged one behind the other seen in the direction T of transport of the printing means 101.

The printing system 100 is designed in such a way that the transport of the printing media 101 can be carried out in a transport plane TE along the transport direction L, the front nozzle plate 105 of the printing head 103 being arranged and, in particular, each nozzle plate 109, on the transport plane TE at a height X.

The transport device 121 of the printing system 100 includes the endless conveyor belt 123 and also a cleaning unit 127 for removing drops of the polish suspension (not shown) that fall on the endless conveyor belt 123 after cleaning. the front nozzle plate 105, the endless conveyor belt 123 being continuously guided on two deflector rollers 125 during the printing operation.

The print head 103 is described in detail in Figure 2. It comprises a nozzle front plate 105, comprising ten printing modules (see "107" in Figure 1), each with a nozzle plate 109 and a plate 113, the side of the front nozzle plate 105 facing the printing means 101 being in the same plane as in particular the nozzle plates 109 and the one frame plate 113 (see Figure 1).

The cleaning device 114 of Figure 2 is arranged laterally on the front nozzle plate 105 and designed in such a way that it can activate various liquid jet configurations 111 (see Figures 3A-3E) with several liquid jets directed against the at least a part of the nozzle front plate 105 synchronously with the space L between the adjacent printing means 101 in the transport direction T.

The method according to the invention to be carried out using the device according to the invention is described in detail below.

In the process, as explained above, the printing media 101 is first transferred from a printing device (not shown) via the conveyor 131 to the transport device 121 of the printing system 100 at a media temperature 101 of printing over 50 ° C and then transported piece by piece along the transport direction T in such a way that the printing media 101 is transported into and out of the effective area of the plate again. 105 nozzle front.

Cleaning of the nozzle front plate 105 can be carried out at periodic time intervals, the duration of the corresponding interval being chosen to be as short as necessary but as long as possible, so that within the respective intervals can ensure waste-free production of printing media 101 during transportation and printing of the printing media 101, at least across at least a portion of the effective area of the nozzle front plate 105, having conducted a certain interval duration longer compared to the duration of the interval corresponding to a waste of printing media 101.

The time intervals to be selected are preferably adapted to different transport speeds and temperatures of the printing media 101 and also to different application quantities and temperatures of the glaze suspension or ink to optimize the time intervals. It is important, however, that the time intervals are chosen to be as long as possible, but short enough to avoid dripping of liquid droplets from the front nozzle plate 105. It is also important to start with short time intervals to avoid corresponding defects or at least keep the nozzle front plate 105 under constant observation, so that a cleaning step is executed in time as the liquid concentration progresses before the comes off.

There are different ways in which the person skilled in the art can achieve optimized time intervals. For example, you can perform a series of tests for a certain printing operation of the printing system 100 with different time intervals and thus check up to which time interval you still obtain an acceptable surface for it, that is, sufficiently clean, of the front nozzle plate 105, with which no liquid or dirt is released from the front nozzle plate 105.

The inventors have observed that, for example, when printing ceramic printing media 101 that is transported at a transport speed of 20 m/min at a printing media temperature of 80 ° C through the effective area of the plate 105 nozzle front of this printing system 100 and with a selected enamel suspension with a water content of 30 wt% based on the total weight of the enamel suspension in application quantities of 1000 g/m2 based on one application of full surface, the printing media 101, the time intervals at which the nozzle front plate 105 must be cleaned to obtain a smear-free printed printing media 101 had to be adjusted to approximately 2 minutes.

Below, the individual steps for cleaning the nozzle front plate 105 will be described again by way of example based on those in Figures 3A to 3F.

After a predetermined time interval has elapsed, a gap L is created between the next adjacent printing media 101 on the conveyor 131 or, at the latest, when the printing media 101 is transferred from the conveyor 131 to the transport device 121.

In the input area of the printing system 100, when a trailing edge of a first printing medium 101 passes a sensor (not shown), a counter of a counting mechanism is started and, when a leading edge of another Printing medium 101 passes the sensor, another counter of the counting mechanism is started. When the distance between the first and the other printing medium 101, 101 with or without starting the other counter of the counting mechanism reaches a counter reading that corresponds to the equivalent distance from the sensor position to the center of the space, then The four nozzles 115 of the first group 114A of nozzles of the cleaning device 114 are activated, in such a way that the cleaning device 114 activates the liquid jet exclusively in the area of space L and synchronized with it. The 115 nozzles are designed as flat jet nozzles.

The four nozzles 115 of the first nozzle group 114A are connected via liquid lines 117 to an externally controlled 2/2-way process valve 119 (see Figure 3A), which in turn is connected to a compressor to apply a certain pressure to the liquid (not shown).

The time interval between two valve actuations of the same nozzle group 114A is 2 minutes, with the duration of the valve actuation to activate the liquid flows from the nozzles 115 of the nozzle group 114A being 1000 milliseconds. In this example, the flat jet nozzles operate with a pressure of 2.5 bar and a liquid flow rate of 20 liters/minute to 25 liters/minute per nozzle 115. Therefore, the nozzle group 114A with 4 nozzles 115 operates with a total liquid flow rate of 80 liters/minute to 100 liters/minute.

The cleaning device 114 includes five groups 114A, 114B, 114C, 114D, 114E of nozzles, each of which is connected through liquid lines 117 to an externally controlled 2/2-way process valve 119 (see Figure 2), which are connected to a compressor to apply a certain pressure to the liquid (not shown).

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

The following Figures 3B to 3F show further sketches of the principle of the especially preferred method according to the invention during the transport of the printing media 101 through the effective zone of the front nozzle plate 105.

Figure 3B describes a time when no liquid jet is activated, since when activated from a nozzle group 114A or 114B, the liquid droplets hanging from the nozzle front plate 105 would be activated by the liquid jet. not only in the area of the L spaces, but also in the area of the printing media 101, which would thus be contaminated.

Figures 3C to 3F describe different times during the progressive transport of the printing media 101 through the effective area of the front nozzle plate 105, in which the cleaning device 114 activates the liquid jets sequentially and synchronously with the space L through the nozzles 115 of the respective groups 114B, 114C, 114D, 114E of nozzles. With this method, at least the entire surface of the nozzle front plate 105 to which the printing media 101 is exposed during transport through the effective area of the nozzle front plate 105 is cleaned.

According to another embodiment of the method not shown in the figures, the printing media, on which an enamel suspension has been applied with the printing system to produce a relief or all-over decorative enamel, can be transported from the system to another printing system to print a color image on the applied decorative glaze. The other printing system can be a normal inkjet printer for printing ceramic printing media with colored ink. The distance between the two printing systems is chosen so that the enamel suspension can at least partially dry, so that the colored ink does not mix with the applied enamel suspension. Alternatively or additionally, the print media printed with the first printing system may be at least partially dried with at least one suitable drying source, such as, for example, an IR source, before being printed with the other printing system. After the application of the colored ink on the embossed or full-surface decorative glaze is complete, the ceramic printing media printed in this way can be transferred to a kiln, fired in it and finally, if necessary, cut to shape. extent.

Claims (15)

1. Method for transporting printing media (101) piecemeal into and out of the effective area of a printing head (103) and cleaning at least a portion of at least one nozzle front plate (105) disposed on the head. (103) printing, the method comprising the following steps: a) the provision of a printing system (100) comprising the printing head (103) with the front nozzle plate (105), the printing head (103) comprising at least one printing module (107) with at minus a nozzle plate (109) from which drops of a printable composition can be dispensed, b) transporting the printing media (101) along a transport direction (T) so that the printing media (101) is transported into and out of the effective area of the front plate (105) again. of nozzles, c) cleaning at least a part of the front nozzle plate (105) by means of one or more liquid jet configurations (111) from a cleaning device (114) that activates the liquid jet, comprising the configurations liquid jet (111) at least one liquid jet directed against at least a part of the nozzle front plate (105), the front nozzle plate (105) comprising the nozzle plate (109), at least some of the printing means (101) being transported in the transport direction (T) at a distance of at least one of its means (101). ) closest adjacent printing means, so that spaces (L) are formed in the transport direction (T) between these adjacent printing means (101) that are separated, and activating the cleaning device (114) the liquid jet not necessarily always, but exclusively in the region of the spaces (L) and synchronized with them, characterized in that the printing media (101) are ceramic printing media and are transported moistened with water at a temperature of between 30 ° C and 120 ° C to the effective area of the front nozzle plate (105), the front nozzle plate (105) being tempered at a temperature that is lower than the temperature of the printing media (101) during transport thereof to through the effective area of the nozzle front plate (105), the nozzle front plate (105) and the printing means (101) being aligned with each other in the effective area of the nozzle front plate (105) in such a way that, as time progresses, drops form on the front nozzle plate (105) due to the condensation of water vapor and continue to grow until, after a certain time, they fall on the printing means (105) due to the force of gravity and/or hang from the nozzle front plate (105) in such a way that they are dragged by the printing means (101). 2. Method according to claim 1, characterized in that at least the entire surface of the front nozzle plate (105) to which the printing means (101) is exposed during transport through the effective area of the plate is cleaned. (105) nozzle front. 3. Method according to claim 1 or 2, characterized in that the ceramic printing media is in particular unfired ceramic tiles and is transported in a state moistened with water and at a temperature of between 40 ° C and 100 ° C, preferably between 50 °C and 90 °C, to the effective area of the front nozzle plate (105). 4. Method according to at least one of the preceding claims, characterized in that the front nozzle plate (105) comprises the nozzle plate (109) and at least one frame plate (113), the side of the plate (105) being ) nozzle front facing the printing means (101) in the same plane as in particular the nozzle plate (109) and the frame plate (113). 5. Method according to at least one of the preceding claims, characterized in that the cleaning device (114) activates the liquid jet sequentially. 6. Method according to at least one of the preceding claims, characterized in that during the transport of the printing means (101) through the effective area of the front nozzle plate (105), the cleaning of at least a part of the nozzle front plate (105) according to step (c) is carried out at least temporarily at the same time. 7. Method according to at least one of the preceding claims, characterized in that the method comprises the step of: d) printing the printing means (101) as long as the at least one nozzle plate (109) of the at least one printing module (107) dispenses drops of the printable composition, preferably an ink or an enamel suspension. 8. Method according to claim 7, characterized in that during the transport of the printing means (101) through the effective area of the front nozzle plate (105), the printing according to step (d) and the cleaning of al At least a portion of the nozzle front plate (105) according to step (c) are carried out at least temporarily at the same time. 9. Method according to at least one of the preceding claims, characterized in that in step (a) a single-pass inkjet printer is provided as a printing system (100), carrying out the transport of the media ( 101) printing at a constant speed in the direction (T) of transport, and preferably at a speed of at least 3 m/min, with particular preference at a speed of at least 12 m/min. 10. Method according to at least one of the preceding claims, characterized in that the liquid is a gaseous and/or liquid, preferably a gas or a mixture of gases, especially preferably air. 11. Method according to at least one of the preceding claims, characterized in that the liquid jet is discharged from one or more nozzles (115) of the cleaning device (114), the nozzles (115) being preferably configured as flat jet nozzles. . 12. Method according to claim 11, characterized in that the one nozzle (105) or the several nozzles (115) of the cleaning device (114) are provided so that they are arranged movably in the direction (T) of transport, moving during cleaning according to step (c) the one nozzle (115) or the several nozzles (115) in the transport direction (T), preferably synchronously with the spaces (L). 13. 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, the duration of the respective interval being selected to be as short as necessary but as long as possible, so that, during transportation or transportation and printing of the printing media (101), a stain-free production of the printing media (101) is guaranteed at least across at least a portion of the area. effective of the nozzle front plate (105) within the duration of the respective interval, a certain longer interval duration compared to the duration of the respective interval having led to a waste of printing media (101). 14. Printing system (100) comprising to. a transport device (121) for printing media (101); b. at least one printing head (103) with at least one nozzle front plate (105) arranged on the printing head (103), the printing head (103) comprising at least one printing module (107) having at least one at least one nozzle plate (109) for dispensing droplets of a printable composition; c. a cleaning device (114) that allows activating a jet of liquid directed against at least a part of the front nozzle plate (105); the front nozzle plate (105) comprising the nozzle plate (109), the cleaning device (114) being configured in such a way that one or more liquid jet configurations (111) can be activated with at least one jet of liquid. liquid directed against at least a part of the front plate (105) of nozzles synchronously with spaces (L) between the adjacent printing means (101) in the direction (T) of transport, characterized in that the printing system comprises a device control to carry out at least one method according to at least one of claims 1 to 13 and why the printing system is suitable to carry out that method. 15. Printing system (100) according to claim 14, characterized in that the cleaning device (114) comprises one or more nozzles (115) through which the liquid jet can be dispensed, the one or more nozzles being (115) flat jet nozzles.