SYSTEM AND METHOD FOR INTERMEDIATE DRYING OF A PRINTING MEDIUM

Description

Field of the invention

[0001] The invention relates to a system and a method for intermediate drying of a printing medium, in particular for printing water-soluble inks on plastic films. Background of the invention

[0002] For printing on plastic films, in addition to printing methods based on printing plates (especially flexographic printing, gravure printing, and offset printing), digital printing processes have also become increasingly established. These processes involve applying the printing ink to the film without a printing plate, for example, using an inkjet process. Water-soluble printing inks can also be used in all printing processes, which is particularly advantageous for printing food packaging.

[0003] Plastic films, such as those made of polypropylene (PP) or polyethylene (PE), are generally non-polar, which makes printing with water-soluble and therefore polar inks difficult. If necessary, the adhesion and drying of water-soluble inks can be improved by applying a primer to the film surface prior to printing. However, even with a primer, a rather complex subsequent final drying of the water-based ink is often necessary, which removes the volatile components from the ink and / or primer by evaporation or convection. In some applications, the drying process is supported by intermediate drying (so-called "pinning") during the printing process, which typically uses convection drying or UV drying methods.However, with the known processes, the drying of water-based inks on plastic films is operational and time-consuming and often only partially successful.

[0004] The publication EP 2 644 391 A1 discloses a printing system with a plurality of inkjet printing units, each of which is followed by infrared drying units.

[0005] A printing system in which a plurality of inkjet printing units are used, followed by microwave heating devices, is known from the publication EP 1 738 916 A1.

[0006] The publication JP 2004-249473 discloses a printing system with several printing units, each of which is followed by UV radiation units.

[0007] Printing systems with two printing units for printing both sides of a plastic film one after the other are known from the publications WO 2015 / 016902 A1 and CN 108407436 A.

[0008] Drying units for printing systems, which can have several infrared drying units in different geometries and spatial arrangements, are known from the publication US 2017 / 0217211 A1.

[0009] Techniques for controlling drying units for inkjet printing systems are described in publications US 2004 / 0189771 A1 and US 2011 / 0290777 A1, as well as in patent US 9,193,182 B1. Therefore, there is a need for a system and method that enables more efficient and faster drying of a printing medium. Overview of the invention

[0010] This object is achieved by a system for intermediate drying of a printing medium according to claim 1 or by a method for intermediate drying of a printing medium according to claim 9. The dependent claims relate to advantageous developments.

[0011] A system according to the invention for intermediately drying a printing medium comprises a first intermediate drying unit, which is arranged downstream of a first printing unit and is configured to at least partially dry a first printing fluid discharged by the first printing unit on a surface of a printing medium. The system further comprises a second intermediate drying unit, which is arranged downstream of a second printing unit, which is different from the first printing unit, and is configured to at least partially dry a second printing fluid discharged by the second printing unit on the surface of the printing medium.

[0012] The invention is based, among other things, on the finding that, in many practical applications, more efficient and complete intermediate drying of water-based inks on non-absorbent surfaces, such as non-polar plastic films, can be achieved with multiple intermediate drying units, each of which can be operatively assigned to the corresponding printing units and arranged spatially downstream. Furthermore, intermediate drying with a plurality of intermediate drying units, each arranged downstream of the corresponding printing units, can effectively prevent successively applied printing inks from running into each other, thus improving the quality of the printing result.

[0013] Intermediate drying or partial drying within the meaning of the present disclosure can be understood as only partially drying the applied printing fluid. In particular, such intermediate drying or partial drying can lead, for example, to increased viscosity (gel formation) of the printing fluid or to the formation of a skin around the droplets of the printing fluid, which can improve the fixation of the droplets of the printing fluid on the printing medium. This can also improve the subsequent application of additional drops, for example, a printing fluid of a different color, and, in particular, reduce the smearing of the droplets into one another (so-called "color bleeding").

[0014] In one embodiment, each printing unit, in particular each printing unit of each printing ink, is operatively assigned a corresponding intermediate drying unit and is spatially arranged downstream.

[0015] In one embodiment, the first intermediate drying unit is arranged downstream of the first printing unit along a relative movement direction of the first intermediate drying unit and the printing medium. Accordingly, the second intermediate drying unit can be arranged downstream of the second printing unit along a relative movement direction of the second intermediate drying unit and the printing medium.

[0016] The relative direction of movement can refer to a transport direction of the printing medium with respect to the (stationary) first or second intermediate drying unit.

[0017] In other embodiments, the first or second intermediate drying unit is movable relative to the printing medium, and the relative direction of movement can relate to a direction of movement of the first or second intermediate drying unit relative to the printing medium, wherein the printing medium can in particular be spatially fixed or stationary.

[0018] In one embodiment, the first intermediate drying unit and the second intermediate drying unit are arranged in series along a relative movement direction of the first intermediate drying unit and the printing medium.

[0019] In particular, the first printing unit, the first intermediate drying unit, the second printing unit and the second intermediate drying unit may be arranged in this order in series along a relative movement direction of the first intermediate drying unit and the printing medium.

[0020] An arrangement "in series" encompasses, for example, both a linear arrangement of the corresponding units along a rectilinear movement path of the printing medium and a sequential arrangement of the respective units along a curved, for example, circular, movement path. This formulation particularly includes the alternating, sequential arrangement of printing units and intermediate drying units over a portion of the circumference of a drum or roller over which the printing medium is transported.

[0021] In one embodiment, the first intermediate drying unit is arranged between the first printing unit and the second printing unit, in particular directly between the first printing unit and the second printing unit.

[0022] The first intermediate drying unit may be arranged between the first printing unit and the second printing unit along a relative movement direction of the first intermediate drying unit and the printing medium.

[0023] According to one embodiment, the second intermediate drying unit is arranged upstream of a third printing unit along a relative movement direction of the second intermediate drying unit and the printing medium.

[0024] An intermediate drying system according to the invention may comprise any number of intermediate drying units, each of which is arranged downstream of corresponding printing units.

[0025] Within the scope of the disclosure, a variety of different printing fluids can be used, provided they are suitable for printing on a given substance. In particular, the printing fluid can comprise or be a water-soluble ink.

[0026] The first printing fluid may comprise or be a printing fluid of a first color. The second printing fluid may comprise or be a printing fluid of a second color that differs from the first color. A third printing fluid dispensed by the third printing unit may comprise or be a printing fluid of a third color that differs from the first color and the second color.

[0027] In the context of the disclosure, a printing unit can refer to any apparatus device which is designed to dispense or apply a printing fluid to a printing medium.

[0028] In one embodiment, the first printing unit and / or the second printing unit and / or the third printing unit comprise an inkjet printing unit configured to dispense a printing fluid using the inkjet process. In other embodiments, the first printing unit and / or the second printing unit and / or the third printing unit comprise a printing form-based printing unit, in particular a flexographic printing unit and / or a gravure printing unit and / or an offset printing unit.

[0029] In some embodiments, the system may in particular comprise the first printing unit and / or the second printing unit and / or the third printing unit.

[0030] Within the scope of the disclosure, a printing medium may include any printable carrier or substrate.

[0031] For example, the printing medium may comprise a plastic. Alternatively or additionally, the printing medium may also comprise paper and / or cardboard and / or metal.

[0032] In one embodiment, the printing medium comprises a film, in particular a plastic film, for example, a plastic film extruded using a blow molding process. The film can comprise, for example, polyethylene terephthalate (PET) and / or polyethylene (PE) and / or low-density polyethylene (LDP) and / or biaxially oriented polypropylene (BOPP).

[0033] The intermediate drying may comprise any process which is suitable for at least partially drying the printing fluid delivered by the corresponding printing unit and applied to the surface of the printing medium.

[0034] The first intermediate drying unit and / or the second intermediate drying unit comprises an infrared intermediate drying unit that can selectively emit infrared radiation onto the surface of the printing medium and / or a near-infrared intermediate drying unit that can selectively emit near-infrared radiation onto the surface of the printing medium. Infrared radiation can be understood as electromagnetic waves in the spectral range between visible light and the longer-wave terahertz radiation.

[0035] Infrared radiation can, for example, have a wavelength of at least 700 nm, preferably at least 800 nm. In one embodiment, infrared radiation has a wavelength of at most 1 mm, in particular of at most 0.5 mm.

[0036] Near-infrared radiation, as defined by the disclosure, can be understood as the sub-range of infrared radiation close to visible light. In one embodiment, near-infrared radiation comprises a wavelength of at least 700 nm, preferably at least 800 nm. Near-infrared radiation, as used herein, can comprise a wavelength of at most 3000 nm, in particular of at most 2500 nm, or at most 1500 nm, or at most 1300 nm.

[0037] The first intermediate drying unit and / or the second intermediate drying unit can in particular comprise at least one elongated infrared emitter element and / or one elongated near-infrared emitter element, which are configured to emit corresponding infrared radiation or near-infrared radiation onto the printing medium.

[0038] The corresponding emitter elements can, for example, comprise quartz emitter elements or rod-shaped halogen emitters.

[0039] The elongated infrared emitter element or near-infrared emitter element can, for example, be arranged transversely to a relative direction of movement of the first or second intermediate drying unit and the printing medium.

[0040] In other embodiments, the elongated infrared emitter element or near-infrared emitter element may be arranged along a relative movement direction of the first or second intermediate drying unit and the printing medium.

[0041] In some embodiments, the first intermediate drying unit and / or the second intermediate drying unit additionally comprises a high-frequency intermediate drying unit or a microwave intermediate drying unit.

[0042] A high-frequency intermediate drying unit may be configured to emit high-frequency electromagnetic waves toward the printing medium.

[0043] In one embodiment, the radio frequency radiation comprises frequencies of at least 9 kHz.

[0044] The radio-frequency radiation may comprise frequencies of no more than 10 THz, in particular of no more than 1 THz.

[0045] The high-frequency radiation, in particular microwave radiation, may comprise electromagnetic radiation with frequencies of at least 1 GHz, in particular of at least 10 GHz.

[0046] In one embodiment, the high-frequency radiation, in particular microwave radiation, comprises frequencies of at most 300 GHz, in particular of at most 100 GHz.

[0047] In one embodiment, the system additionally comprises a first heating unit configured to selectively heat the printing medium in the region of the first intermediate drying unit and / or a second heating unit configured to selectively heat the printing medium in the region of the second intermediate drying unit.

[0048] A heating unit can also be provided that extends over several of the printing units and their respective downstream intermediate drying units, thus heating the printing medium over a longer section of its transport path. This can, for example, also be a heated drum or roller over which the printing medium is transported and around whose circumference at least one first printing unit and first intermediate drying unit, preferably several printing units and intermediate drying units, are arranged.

[0049] The combined use of intermediate drying and temperature-controlled web transport can improve the overall efficiency of the drying process. In particular, this approach can reduce the energy input associated with the intermediate drying units, thus achieving a more gentle drying process overall, especially for thin and delicate plastic films.

[0050] In one embodiment, the system additionally comprises a first cooling unit configured to cool the first printing unit and / or a second cooling unit configured to cool the second printing unit.

[0051] Intermediate drying with simultaneous selective cooling of the printing unit can further improve print stability and print quality, in particular reducing unwanted wetting on a nozzle plate of an inkjet printing unit.

[0052] In one embodiment, the system additionally comprises a final drying unit which is arranged downstream of the second intermediate drying unit along a relative movement direction of the second intermediate drying unit and the printing medium.

[0053] The final drying unit can be configured, in particular, to dry or completely dry the first printing fluid and the second printing fluid following printing on the surface of the printing medium. The final drying unit can be configured to dry or completely dry the printing fluid by means of convection and / or infrared radiation and / or near-infrared radiation.

[0054] The system includes a control unit which is configured to selectively control the first intermediate drying unit and / or the second intermediate drying unit depending on print data of the first printing unit and / or the second printing unit.

[0055] The print data may, for example, include digital print data, in particular TIFF data ("Tagged Image File Format") or PPF data ("Print Production Format") or PDF data ("Portable Document Format").

[0056] The control unit is configured to automatically adjust a drying performance of the first intermediate drying unit and / or the second intermediate drying unit depending on the print data of the first printing unit and / or the second printing unit.

[0057] In this way, the energy input to the print medium can be selectively adapted to the print data in order to prevent excessive thermal stress on sensitive print media, such as thin plastic films.

[0058] The adjustment can be made both within a group consisting of a printing unit and an associated intermediate drying unit and across several groups, so that, for example, the drying performance of the second intermediate drying unit is adjusted to the print data of the first printing unit and the second printing unit.

[0059] The control unit is configured to automatically adapt a drying performance of the second intermediate drying unit to a drying performance of the first intermediate drying unit and / or to automatically adapt a drying performance of the first intermediate drying unit to a drying performance of the second intermediate drying unit.

[0060] By adjusting the drying performance of several

[0061] By combining intermediate drying units, a more complete and efficient intermediate drying of the printing fluid can be achieved. At the same time, print throughput can be increased because the intermediate drying can be delegated, at least in part, to subsequent intermediate drying units.

[0062] In particular, the automatic adjustment of the drying performance of the first and / or the second intermediate drying unit can be combined with the respective adjustment of the drying performance depending on the print data.

[0063] The drying performance of the first intermediate drying unit and / or the second intermediate drying unit can be varied spatially and / or adjusted temporally.

[0064] Spatially varied adaptation may include a variation in the drying performance depending on different positions on the print medium. In particular, the drying performance at a second position on the print medium may differ from the drying performance at a first position on the print medium, which differs from the second position.

[0065] A spatially varied adaptation can be carried out, for example, in the transverse direction of the printing medium, ie in particular perpendicular to the transport direction of the printing medium, in that one or more emitters of the first and / or second intermediate drying unit arranged in a row in the transverse direction of the printing medium are switched on or off separately or their radiation output is adjusted differently.

[0066] In a time-varying adaptation, the drying performance at a second time point may differ from the drying performance at a first time point, which is different from the second time point.

[0067] A time-varying adjustment can be achieved, for example, by operating the respective radiation emitters of one or more intermediate drying units with a time-varying current intensity depending on an input signal that is dependent on print data.

[0068] The invention also relates to a method for intermediate drying of a printing medium, comprising a first intermediate drying of a first printing fluid dispensed by a first printing unit on a surface of a printing medium and a second intermediate drying of a second printing fluid dispensed by a second printing unit after the first intermediate drying on the surface of the printing medium.

[0069] In one embodiment, the method additionally comprises dispensing the first printing fluid onto the surface of the printing medium before the first intermediate drying step and / or dispensing the second printing fluid onto the surface of the printing medium after the first intermediate drying step. For example, the first printing fluid and / or the second printing fluid can be dispensed using an inkjet printing process.

[0070] The first intermediate drying and / or the second intermediate drying comprises selectively irradiating the surface of the printing medium with infrared radiation or with near-infrared radiation.

[0071] According to one embodiment, the method additionally comprises selectively heating the printing medium before and / or during the first intermediate drying and / or before and / or during the second intermediate drying.

[0072] Such selective heating can be realized, for example, in near-infrared intermediate drying units by adjusting the operating voltage of their emitters and thus the near-infrared spectrum emitted by them, in particular depending on printing parameters such as a color of the printing fluid used or several colors of several printing fluids.

[0073] When configuring the first and / or second and possibly further intermediate drying units with several emitters arranged in a row, a spatially selective adaptation of the near-infrared spectrum to the color or other parameters of printing fluids for individual areas of the print image can also be realized.

[0074] By rapidly varying the operating voltage of the aforementioned near-infrared emitters over time, temporally selective irradiation is possible. With a suitable design of the near-infrared intermediate drying unit(s), a combination of spatially and temporally selective irradiation in the aforementioned sense is also possible.

[0075] With such configurations, the drying effect of the corresponding intermediate drying units can be increased not only by varying the radiation power of the corresponding emitters, but also by adjusting the selectivity of the radiation to the absorption properties of the respective printing fluid.

[0076] The method may additionally comprise selective cooling of the first printing unit and / or the second printing unit.

[0077] In one embodiment, the method additionally comprises a final drying of the first printing fluid and the second printing fluid after the second intermediate drying.

[0078] The first intermediate drying and / or the second intermediate drying takes place selectively depending on print data of the first printing unit and / or the second printing unit, wherein the first intermediate drying and / or the second intermediate drying comprises an automatic adjustment of a drying performance depending on print data of the first printing unit and / or the second printing unit.

[0079] In one embodiment, the method comprises automatically adjusting a drying performance of the second intermediate drying to a drying performance of the first intermediate drying and / or automatically adjusting a drying performance of the first intermediate drying to a drying performance of the second intermediate drying.

[0080] Automatic adaptation includes spatial and / or temporal adaptation.

[0081] The invention also relates to a computer-readable program comprising computer-readable instructions, wherein the computer-readable instructions are adapted to carry out a method having one or all of the aforementioned features. Short description of the drawings

[0082] The characteristics and numerous advantages of the solution according to the invention can best be understood from a description of exemplary embodiments with reference to the drawings in which: Fig. 1 shows a schematic representation of a system for intermediate drying of a printing medium according to an embodiment; Fig. 2 shows a schematic representation of a system for intermediate drying of a printing medium according to another embodiment; Fig. 3 shows a flowchart of a method for intermediate drying of a printing medium according to an embodiment; Fig. 4shows a schematic representation of an embodiment of the system according to the invention; Fig. 5 shows a schematic cross-sectional view of a near-infrared dryer of an embodiment of the system according to the invention; and Fig. 6 a schematic bottom view of the main part of the near-infrared dryer according to Fig. 5 shows. Description of embodiments

[0083] Embodiments are described below for the example of intermediate drying for printing a plastic film using a digital inkjet printing process, in particular a plastic film for food packaging. However, the system and method according to the invention can be used for a variety of different printing media and different printing processes.

[0084] Figure 1shows a system 10 for intermediate drying of a printing medium 12, for example a plastic film, in a schematic side view. The system 10 comprises several printing units 14a to 14d, which are arranged along a transport direction T of the plastic film 12 (in Fig. 1 from left to right) are arranged in series, as well as a plurality of intermediate drying units 16a to 16d, which are functionally assigned to the printing units 14a to 14d and are each arranged downstream along the transport direction T. In the embodiment shown, the plastic film 12 is thus moved along the transport direction T one after the other along the first printing unit 14a, the first intermediate drying unit 16a, the second printing unit 14b, the second intermediate drying unit 16b, the third printing unit 14c, the third intermediate drying unit 16c, the fourth printing unit 14d and the fourth intermediate drying unit 16d.

[0085] The plastic film 12 can, for example, have been produced in a blow-mold extrusion device (not shown) that is located upstream of the system 10 or the first printing unit 14a. Additionally, a primer unit (not shown) for applying a primer layer to the plastic film 12 can optionally be located upstream of the system 10 or the first printing unit 14a.

[0086] In the embodiment shown, the Figure 1The printing units 14a to 14d are inkjet printing units, each comprising a plurality of print heads 18a to 18d, each configured to emit a printing fluid as droplets onto the surface of the plastic film 12. In particular, each of the printing units 14a to 14d can emit a printing fluid of a different color, for example, one of the four primary colors cyan, magenta, yellow, and black, in order to thereby compose text and / or graphics of any desired color by superimposing them on the plastic film 12. The print heads 18a to 18d of the printing units 14a to 14d can each be arranged in rows orthogonal to the transport direction T.

[0087] In one embodiment, the printing fluids emitted by printing units 14a to 14d are water-soluble inks, such as those used for food packaging. Such water-soluble inks adhere and dry poorly or only moderately on non-absorbent, non-polar plastic surfaces without additional measures, potentially resulting in smearing and uneven color gradients.

[0088] The system 10 according to the invention is therefore equipped with intermediate drying units 16a to 16d, which intermediately dry the printing fluids dispensed by the respective associated printing unit 14a to 14d, which they are arranged downstream of along the transport direction T, and applied to the surface of the plastic film 12, so that the viscosity of the droplets of the printing fluid increases through gel formation and the adhesion of the droplets to the surface of the plastic film 12 improves. In particular, this effectively prevents liquid droplets of different colors from running into each other due to inadequate adhesion and / or drying (so-called "color bleeding"). In this case, the intermediate drying units 16a to 16d generally do not completely dry the printing fluids on the plastic film 12, but merely fix them sufficiently for the liquid droplets to gel or form a skin.

[0089] In the presentation of the Figure 1 The intermediate drying units 16a to 16d each comprise a plurality of infrared emitter units 20a to 20d, which are configured to selectively irradiate the surface of the plastic film 12 with infrared radiation in the wavelength range from 800 nm to 2,500 nm in order to selectively heat the printing fluid applied to the surface of the plastic film 12 and fix it on the plastic film 12. This wavelength range is occasionally referred to as the near-infrared range because it is adjacent to the visible light spectrum.

[0090] For example, each of the infrared emitter units 20a to 20d may comprise one or more quartz tubes arranged along a direction orthogonal to the transport direction T ("cross track").

[0091] The configuration of the Figure 1, in which at least one intermediate drying unit 16a to 16d is arranged downstream of each of the printing units 14a to 14d, allows the printing fluids discharged from the printing units 14a to 14d to be selectively intermediately dried or partially dried by means of targeted infrared radiation. The printing result can be effectively improved in this way. Furthermore, distributing the intermediate drying across several intermediate drying units 14a to 14d results in a more even distribution of the applied thermal energy and a locally reduced thermal energy input to the plastic film 12. The plastic film 12 is thus dried more gently – an advantage particularly for sensitive, thin plastic films 12.

[0092] In other embodiments, the intermediate drying may be based on other drying effects, for example using high-frequency radiation or microwave radiation.

[0093] In the presentation of the Figure 1 The system 10 comprises four printing units 14a to 14d corresponding to the four primary colors in the CMYK color system and four associated and respectively downstream intermediate drying units 16a to 16d. However, this is merely an example. In other embodiments, the system 10 may have a larger or smaller number of printing units and / or intermediate drying units. Furthermore, the number of intermediate drying units does not necessarily have to correspond to the number of printing units. For example, in some embodiments, individual printing units 14a to 14d or all printing units 14a to 14d may each have multiple intermediate drying units downstream.

[0094] Furthermore, the intermediate drying units 16a to 16d do not necessarily have to be arranged directly or immediately downstream of the corresponding printing units 14a to 14d. For example, additional components or units of the printing environment can be arranged between a printing unit 14a to 14d and its respective downstream intermediate drying unit 16a to 16d.

[0095] Figure 1 shows a configuration in which the printing units 14a to 14d and the intermediate drying units 16a to 16d are spatially stationary and the plastic film 12 moves along the printing units 14a to 14d and the respective spatially downstream intermediate drying units 16a to 16d along the transport direction T. In other embodiments, however, the printing medium can also be stationary, and the printing units 14a to 14d and the intermediate drying units 16a to 16d move along the printing medium in a direction opposite to that in Figure 1shown transport direction T.

[0096] Figure 2 shows a system 10 for intermediate drying of a printing medium, which is similar to the system described above with reference to Figure 1 described system 10 is fundamentally similar, and corresponding elements bear the same reference numerals.

[0097] However, the system 10' additionally comprises a plurality of heating units 22a to 22d, which are configured to selectively heat the plastic film 12 in the region of the intermediate drying units 16a to 16d. For example, each of the heating units 22a to 22d can be located diametrically opposite a corresponding intermediate drying unit 16a to 16d with respect to the plastic film 12 and pre-heat the plastic film 12 to thereby support the drying effect. The heating units 22a to 22d can, for example, be convection heating units.

[0098] Such a combination of intermediate drying units 16a to 16d with a web transport pre-tempered by means of the heating units 22a to 22d can result in a significant increase in drying efficiency with a noticeably reduced energy input of the intermediate drying units 16a to 16d and thus an overall more gentle drying, which in turn enables longer drying lengths.

[0099] As in Figure 2As shown, each of the printing units 14a to 14d can also comprise a corresponding integrated cooling unit 24a to 24d, which is configured to cool the print heads 18a to 18d of the printing units 14a to 14d. This increases print stability, in particular reduces wetting of the print nozzles, and, in conjunction with the local heating by the heating units 22a to 22d below the intermediate drying units 16a to 16d, improves print stability and the quality of the print result. The usually undesirable influence of heating of the print heads 18a to 18d on the opening time of the print nozzles is thus also reduced.

[0100] The Figure 2The system 10' shown also comprises a final drying unit 26, which is arranged downstream of all intermediate drying units 16a to 16d along the transport direction T and which is designed to completely dry out or thoroughly dry the printing fluids discharged by the printing units 14a to 14d on the surface of the plastic film 12, for example by means of convection, which removes the remaining volatile components from the printing fluids or the primer, if present, by evaporation.

[0101] The system 10' of the Figure 2 further comprises a control unit 28, which is communicatively coupled to the intermediate drying units 16a to 16d, for example, exchanging data with the intermediate drying units 16a to 16d via a wired or wireless connection. The control unit 28 can also be communicatively coupled to the printing units 14a to 14d.

[0102] The control unit 28 can be configured to selectively and automatically spatially and / or temporally control the drying performance of the intermediate drying units 16a to 16d depending on the printing parameters and / or the printing data. For example, the control can be based on information relating to the type of printing fluid and / or printing medium as well as the printing speed. Furthermore, the drying performance can be automatically adapted to the current print image, and in particular, the energy input to the plastic film 12 can be limited to the areas relevant to the respective printing fluid and the current print image or to those spatially proximate thereto.

[0103] The control unit 28 can also adjust the drying performance of the intermediate drying units 16a to 16d across the board and coordinate them spatially and / or temporally. For example, the control unit 28 can adjust the drying performance of the last intermediate drying unit 16d spatially and / or temporally to the drying performance of the upstream intermediate drying units 16a to 16c. This adjustment of the drying performance of the intermediate drying units 16a to 16d to one another can be performed alternatively or in addition to adjusting the respective drying performance to the printing parameters and / or printing data.

[0104] This effectively reduces the thermal stress on the plastic film 12. This is particularly advantageous for thin or sensitive plastic films 12.

[0105] Depending on the print data, for example, TIFF ("Tagged Image File Format"), CIP3 or CIP4 ("International Cooperation for the Integration of Processes in Prepress, Press and Postpress Organization"), or PDF ("Portable Document Format") data, the quartz emitter elements of the intermediate drying units 16a to 16d can be controlled individually or in blocks, thus adjusting the drying performance locally and from print job to print job or impression to impression. In conjunction with quartz emitter elements arranged transversely to the transport direction T ("cross track"), a particular advantage of high spatial and temporal resolution of the drying performance results.

[0106] In particular, the drying performance can also be adjusted cyclically within an impression spatially and / or temporally.

[0107] Compared to TIFF data, the cip3 data or cip4 data have the advantage of a smaller data volume and information that is already divided into zones and color separations, so that the control of the intermediate drying units 16a to 16d can be carried out directly from the renderer and with a particularly short response time or high switching power.

[0108] Figure 3 shows a flowchart of a method for intermediate drying of a printing medium according to one embodiment.

[0109] In a first step S10, a first printing fluid dispensed by a first printing unit is intermediately dried on a surface of a printing medium.

[0110] In a second step S12 following the first step S10, a second printing fluid dispensed by a second printing unit after the first intermediate drying, for example a printing fluid of a different composition and / or color, is intermediately dried on the surface of the printing medium.

[0111] Figure 4 shows a schematic representation of a system 110 according to the invention for drying a printing medium 112 in a further embodiment. In Figure 4 are components that are functionally identical or similar to Figure 1 are, with Figure 1 The invention is referred to by the reference numerals and can be largely based on the above description Figure 1 be referred to.

[0112] When configuring the drying system 110 according to Fig. 4The printing medium (plastic film) 112 runs over a temperature-controlled drum 113, on whose outer circumference inkjet printing units 114a-114e are arranged at a distance from one another. Each of the printing units 114a-114e is followed, in the transport direction T of the printing medium 112, by a near-infrared intermediate drying unit 116a-116e, which serves as an intermediate dryer for the printing fluid applied by the preceding printing unit.

[0113] The last near-infrared intermediate drying unit 116e is followed by an additional near-infrared drying unit 117, and downstream in the transport direction T of the printing medium 112, a warm air final drying unit 119 is followed by the near-infrared drying unit 117.

[0114] The temperature-controlled drum 113 can be maintained at a temperature suitable as the base temperature of the plastic film 112 during the printing and drying process, taking into account the operating parameters of the printing and intermediate drying units.

[0115] In addition to the provisions referred to in Figure 1 In the above-mentioned details of the printing and intermediate drying units, it is pointed out that the near-infrared intermediate dryers 116a-116e, as well as the downstream last near-infrared dryer 117, can be designed in the manner of a so-called "air knife", i.e., in addition to the near-infrared (NIR) radiation, they can direct an air stream onto the surface of the printing medium 112 and, at the same time, can suck in the air bouncing off the surface of the printing medium internally as exhaust air.

[0116] The warm air final drying unit 119 is fed with the exhaust air of the last near-infrared intermediate drying unit 116e and the near-infrared dryer 117 following it, so that the waste heat of the latter units is used in an energy-saving manner for the final drying of the print image on the print medium 112.

[0117] The Figures 5 and 6 show a schematic cross-sectional view and a schematic bottom view of a near-infrared intermediate dryer 116, as used in the system configuration according to Fig. 4 is used.

[0118] The near-infrared intermediate drying unit 116 comprises two infrared emitters 121 and 122 (more precisely: two rows of infrared emitters; see below), which are arranged side by side in a central air duct 116.1. The infrared emitters 121, 122 are surrounded by an inlet air stream A1 and heat the inlet air stream before it impinges on the surface of the printing medium (not shown here) transported below the intermediate drying unit 116. The exhaust air A2, which is "reflected" by the printing medium and contains moisture from the previously applied printing fluid, is discharged into two lateral air ducts 116.2, 116.3 of the intermediate drying unit 116 and cleaned or, if necessary, used for another drying task (see above).

[0119] Although in Fig. 5Not shown, suitable flow control means can be assigned to the central air duct 116.1 for supplying supply air A1, allowing throttling of the supply air flow. This is one possibility for the temporal variation of the drying performance of the intermediate drying units mentioned above, for example, depending on the printing parameters of the upstream printing unit or a print image generated by these printing parameters.

[0120] Figure 6 shows a schematic representation of a variant of the embodiment according to Fig. 5 A somewhat simplified version of an intermediate drying unit 116'. This has basically the same structure as the intermediate drying unit 116 according to Fig. 5, however, only one emitter row 121 consisting of several NIR emitters 121.1 to 121.6. It should be noted that in practical implementations of the invention, several rows of NIR emitters are usually present and that the number of emitters forming row 121 is chosen here merely as an example.

[0121] The Fig. 6The arrangement of several NIR emitters shown in the longitudinal direction of the intermediate drying unit 116' (and thus, in the operating position, transverse to the transport direction T of the passing print medium) has several advantages. Firstly, the operation of the intermediate drying unit can be easily adapted to different web widths of the print medium without having to mount intermediate drying units of different lengths in the arrangement and without wasting energy and potentially overheating the print medium. For this purpose, one or more of the edge-near NIR emitters are then switched off according to the width of the print medium web to be processed.

[0122] On the other hand, with sufficiently fast control, the spatial variation of the dryer output mentioned above can also be achieved in adaptation to the printing parameters and / or the print image of the previous printing process. For this purpose, for example, the individual NIR emitters 121.1 to 121.6 are individually activated or deactivated depending on a specific print image. It is also possible to vary their radiation output and / or, if necessary, the wavelength of the maximum radiation output. This represents a combined spatial / temporal variation of the intermediate dryer operation.

[0123] The description of the exemplary embodiments and the drawings serve only to explain the invention and the advantages achieved thereby and are not intended to limit the invention; the scope of protection is determined by the appended claims.

Claims

1. System (10, 10'; 110) for intermediate drying of a printed material (12; 112) with: a first intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) which is arranged downstream of a first printing unit (14a, 14b, 14c, 14d; 114a-114e) and is configured to at least partially surface-dry a first printing liquid outputted from the first printing unit (14a, 14b, 14c, 14d; 114a-114e) on a surface of a printed material (12; 112); and a second intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) which is arranged downstream of a second printing unit (14a, 14b, 14c, 14d; 114a-114e) which is different from the first printing unit (14a, 14b, 14c, 14d; 114a-114e), and is configured to at least partially surface-dry a second printing liquid outputted from the second printing unit (14a, 14b, 14c, 14d; 114a-114e) on the surface of the printed material (12; 112); wherein the first intermediate drying unit and / or the second intermediate drying unit comprises an infrared intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) and / or a near-infrared intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117); characterised in that the system (10, 10'; 110) further comprises a controlling unit (28) which is configured to selectively control the first intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) and / or the second intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) as a function of printing data of the first printing unit (14a, 14b, 14c, 14d; 114a-114e) and / or the second printing unit (14a, 14b, 14c, 14d; 114a-114e); and that the controlling unit (28) is configured to automatically adapt a drying performance of the first intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) and / or the second intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) as a function of printing data of the first printing unit (14a, 14b, 14c, 14d; 114a-114e) and / or the second printing unit (14a, 14b, 14c, 14d; 114a-114e), wherein the controlling unit is configured to adapt in a spatially varied and / or temporally varied manner a drying performance of the first intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) and / or the second intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117).

2. System (10, 10'; 110) according to claim 1, in which the first intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) is arranged between the first printing unit (14a, 14b, 14c, 14d; 114a-114e) and the second printing unit (14a, 14b, 14c, 14d; 114a-114e).

3. System (10, 10'; 110) according to any of the preceding claims, in which the first intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) and / or the second intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) comprise at least one longitudinal infrared emitter element (20a, 20b, 20c, 20d; 121; 121.1-121.6) and / or a longitudinal near-infrared emitter element (20a, 20b, 20c, 20d; 121; 121.1-121.6), in particular at least one quartz emitter element or a high-power halogen spotlight.

4. System (10, 10'; 110) according to claim 3, in which the first intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) and / or the second intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) has a multiplicity of longitudinal infrared emitter elements or near-infrared emitter elements (121.1 - 121.6), wherein in at least one emitter series, several infrared emitter elements or near-infrared emitter elements (121.1 - 121.6) are lined up in longitudinal direction of the intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117), in particular are lined up transverse to a transport direction of the printed material (12; 112).

5. System (10, 10'; 110) according to any of the preceding claims, wherein the first intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) and / or the second intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) has means for orienting a drying fluid, in particular air, onto the surface of the printed material (12; 112) and optionally in addition also means for suctioning the drying fluid rejected by the surface of the printed material (12; 112).

6. System (10, 10'; 110) according to any of the preceding claims, in which the controlling unit (28) is configured to automatically adapt a drying performance of the second intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) to a drying performance of the first intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) and / or to automatically adapt a drying performance of the first intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) to a drying performance of the second intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117).

7. System (10, 10'; 110) according to any of the preceding claims, wherein the controlling unit (28) has controlling means for the separate switching-on / switching-off and / or performance control of individual ones of several infrared emitter elements or near-infrared emitter elements (121.1-121.6) of the first intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) and / or the second intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117).

8. System (10, 10'; 110) according to any of the preceding claims, wherein the controlling unit (28) has controlling means for controlling a drying fluid supplied to the printing material (12; 112) in the first intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117) and / or second intermediate drying unit (16a, 16b, 16c, 16d; 116, 116a-116e; 116', 117).

9. Method for the intermediate drying of a printing material (12; 112) using a system according to any of the preceding claims, with the following steps: first intermediate drying of a first printing liquid outputted from a first printing unit (14a, 14b, 14c, 14d; 114a-114e) on a surface of a printing material (12; 112); and second intermediate drying of a second printing liquid outputted from a second printing unit (14a, 14b, 14c, 14d; 114a-114e) after the first intermediate drying on the surface of the printed material (12; 112); wherein the first intermediate drying and / or the second intermediate drying comprises a selective irradiation of the surface of the printing material (12; 112) with infrared radiation or near-infrared radiation; characterised in that the first intermediate drying and / or second intermediate drying takes place selectively as a function of printing data of the first printing unit (14a, 14b, 14c, 14d; 114a-114e) and / or the second printing unit (14a, 14b, 14c, 14d; 114a-114e); wherein the first intermediate drying and / or the second intermediate drying comprises an automatic adaptation of a drying performance as a function of printing data of the first printing unit (14a, 14b, 14c, 14d; 114a-114e) and / or the second printing unit (14a, 14b, 14c, 14d; 114a-114e); and wherein the automatic adaptation comprises a spatial and a temporal adaptation.

10. Method according to claim 9, further comprising an automatic adaptation of a drying performance of the second intermediate drying to a first drying performance of the first intermediate drying and / or an automatic adaptation of a drying performance of the first intermediate drying to a drying performance of the second intermediate drying.

11. Method according to claim 9 or 10, in which the first intermediate drying and / or the second intermediate drying, in particular the selective irradiation with infrared radiation or near-infrared radiation or the automatic adaptation of the drying performance, comprises a separate switching-on / switching-off and / or a separate control of an irradiation performance of individual ones of several infrared emitter elements or near-infrared emitter elements (121.1-121.6) and / or a control of a fluid jet, in particular air jet, oriented onto the printing material (12; 112).

12. Computer-readable programme which comprises computer-readable instructions, wherein the computer-readable instructions are configured to carry out a method according to any one of claims 9 to 11.