Method for drying an irradiated material and infrared irradiation device for carrying out the method

Abstract

Known infrared irradiation devices for drying a material (3) moved through a process chamber (31) comprise a radiator unit (22) with at least one infrared radiator (24) for emitting infrared radiation and a counter-reflector (23) with a reflector wall (30), wherein the reflector wall (30) has a plurality of inlet openings (36) for the inlet of drying gas into the reflector chamber (33). In order to provide an irradiation device for the drying process, which is particularly suitable for drying solvent-based and especially water-based printing inks, characterized by high drying speed and low bubble formation, it is proposed that the reflector wall (30) have at least one outlet opening (37) for the discharge of exhaust air from the reflector chamber (33).

Description

Technical background

[0001] The invention relates to a method for at least partially drying a material to be irradiated which is moved through a process room in a transport direction and a transport plane, wherein the transport plane divides the process room into an irradiation room and a reflector room, comprising the process steps: (a) Emitting infrared radiation towards the irradiated material by means of a radiator unit comprising at least one infrared radiator, and (b) Reflecting infrared radiation back onto the irradiated material using a counter-reflector having a reflector wall facing the transport plane, a cooling gas is introduced into the reflector chamber via inlet openings in the reflector wall.

[0002] Furthermore, the invention relates to an infrared irradiation device for drying a material to be irradiated which is moved through a process chamber in a transport direction and a transport plane, wherein the transport plane divides the process chamber into an irradiation chamber and a reflector chamber, with a emitter unit having at least one infrared emitter for emitting infrared radiation into the irradiation chamber, and with a counter-reflector having a reflector wall facing the transport plane, wherein the reflector wall has a plurality of inlet openings for the inlet of cooling gas into the reflector chamber.

[0003] Such infrared irradiation devices are used, for example, for drying inks, paints, varnishes, adhesives or other solvent-containing layers, in particular for drying sheet-shaped or web-shaped printing materials made of paper, cardboard, carton, film or textiles. State of the art

[0004] The emitter unit comprises at least one, and usually several, infrared emitters. These emitters typically have an emission wavelength in the range of approximately 800 to 2750 nm and generally require active cooling, especially in confined spaces such as those found in printing presses. Particularly when using short-wave infrared radiation, the transmissivity of the substrate can be high, as is the case with paper. Therefore, applications using near-infrared (between 800 and 1500 nm) irradiation devices often incorporate a counter-reflector on the side of the substrate facing away from the emitter unit. One of its main functions is to increase the efficiency of the heating or drying process through multiple reflections.

[0005] Effective and rapid drying of the substrate requires high radiation flux densities. Active cooling is therefore essential to dissipate the heat generated by the radiation unit from the process chamber. Modern IR irradiation devices thus feature an air management system for regulating the supply and exhaust air of process gas for both drying and cooling.

[0006] For example, EP 2 232 181 B1 describes a chamber-type IR irradiation device for drying a coating on a quasi-endless substrate that is guided through a transport channel for the material being irradiated. On one side of the transport channel, several IR-emitting infrared emitters are grouped into a single emitter block. Opposite this, and on the other side of the transport channel, a counter-reflector block is arranged. The IR irradiation device is enclosed in a housing made of metal profiles, which contains fans for cooling the emitters, the material being irradiated, and the counter-reflector.

[0007] One function of the counter-reflector is to reflect the radiation transmitted through the irradiated material, thereby intensifying the infrared irradiation on the material itself through multiple reflections. Another function of the counter-reflector is to act as a water- or air-cooled thermal insulator to protect other components of the system from heat.

[0008] From US patent 4,882,852 A, an infrared dryer with multiple infrared emitters is known, which can be used for drying a moving strip material. The infrared emitters are located on the upper side of the moving strip material; the underside, however, has no emitter but instead a counter-reflector. Cooling air is supplied to both the upper and lower sides of the strip material: on the upper side via air outlet pipes with numerous openings on the surface, and on the lower side via the counter-reflector, which is provided with openings for this purpose. Exhaust air is discharged partly passively into the environment and partly actively via suction boxes located on the upper side of the strip material.

[0009] The patent application US 2014 / 0237844A1 discloses a radiation dryer that enables the targeted cooling of individual parts of a printing medium during the drying process. For this purpose, the radiation dryer has, in addition to a control unit, several independently controllable cooling air nozzles. If the control unit detects an area of ​​the printing medium where the dye is at risk of overheating, this area is supplied with cooling air via the targeted activation of specific cooling air nozzles.

[0010] US patent 2015 / 0202892A1 describes a dryer for a printing system in which a reflective element with variably adjustable reflectivity is arranged between the radiation source and the printing medium. Technical task

[0011] Typical ingredients in varnishes, printing inks, and paints are oils, resins, water, and binders. Solvent-based and especially water-based printing inks and varnishes require drying, which can be based on physical drying processes using temperature and convection.

[0012] A common drying strategy is two-stage. In the first drying stage, rapid pre-drying using infrared radiation is aimed at warming the substrate and bringing the printing ink to the so-called "gel point" as quickly as possible. At the gel point, the binders form a three-dimensional network in which the color pigments are encapsulated. As solvent and other components continue to be removed, further immobilization occurs, and the so-called "critical point" is reached. At this point, the network structure is so rigid that the binders and pigment can no longer move.

[0013] The second drying phase involves final drying, which only removes any remaining moisture, and also utilizes convective drying methods.

[0014] It has been shown that oval bubbles often form in the substrate, protruding on both sides of the substrate and not receding during the further drying process, which is also known as the "blistering effect".

[0015] The invention is therefore based on the objective of providing a drying process that is both effective and fast, and that reproducibly leads to an improved result with regard to the aforementioned blistering.

[0016] Furthermore, the invention is based on the objective of providing an irradiation device for the drying process which is particularly suitable for drying solvent-based and especially water-based printing inks, characterized by high drying speed with low blistering. General description of the invention

[0017] With regard to the method, this problem is solved according to the invention, starting from a method of the aforementioned type, by diverting exhaust air from the reflector chamber via at least one outlet opening in the reflector wall.

[0018] The transport level divides the process space into two half-spaces, one of which extends between the reflector wall and the irradiated material and is referred to here as the "reflector space".

[0019] The counter-reflector has a gas-permeable reflector wall. The cooling gas flowing from the inlet openings into the reflector chamber strikes the irradiated material, specifically the side facing away from the radiation unit. This side is usually uncoated and is referred to as the "back" of the irradiated material. The cooling gas cools the reflector wall and also interacts with the irradiated material, cooling it and potentially contributing to its drying. This can reduce the blistering effect described above.

[0020] It has been shown that blistering is caused by water vapor trapped within the irradiated material. The sudden temperature increase resulting from the infrared radiation leads to a rapid expansion of the water vapor. If the irradiated material is not sufficiently permeable, which is regularly the case with coated paper, for example, the water vapor cannot escape completely before reaching the critical point and can rupture the internal structure of the printed material.

[0021] To achieve complete drying of all printing inks within the specified (short) timeframe, the irradiation power must be adjusted to the least absorbent printing ink. Therefore, particularly when drying coatings with a black or cyan component, which absorb infrared radiation very well, high temperature peaks can occur. Cooling the material being irradiated by the cooling gas flowing towards its back surface counteracts excessively rapid heating of the material during the initial drying phase, specifically between reaching the gel point and the critical point. This contributes to a comparatively gentle drying process during this phase. As a result, the irradiation power, and thus the transport speed, can be increased without damaging the material or its coating.

[0022] The gas-permeable counter-reflector thus not only fulfills the usual functionalities described above, but also, as a result of the introduction of the cooling gas through the inlet openings of the reflector wall, causes an interaction with the irradiated material moving in the transport plane, which enables a controlled temperature development in the irradiated material, which can reduce the occurrence of undesirable phenomena such as bubble formation.

[0023] In a preferred method variant, it is provided that - viewed in the direction of transport - the amount of cooling gas introduced into the reflector chamber varies.

[0024] The amount of cooling gas can be varied continuously or in stages. This is achieved, for example, by controlling the amount of cooling gas introduced through the inlet openings based on location and / or by increasing or decreasing the total cross-sectional area of ​​the inlet openings in uniformly sized sections of the gas-permeable reflector wall in the direction of transport.

[0025] In a preferred method, the temperature of the irradiated material is measured at several positions distributed along the process chamber in the direction of transport.

[0026] By measuring the temperature at several positions, for example at 2 to 8 positions, preferably at 2 to 5 positions, a temperature profile of the material being irradiated is obtained as it moves through the process chamber. This temperature profile can be used to control the amount of cooling gas. According to the invention, exhaust air is discharged from the reflector chamber via at least one outlet opening in the gas-permeable reflector wall. In a preferred method variant, exhaust air is discharged from the reflector chamber via several outlet openings in the gas-permeable reflector wall.

[0027] The moisture contained in varnishes or paints evaporates when heated and can condense on cooler surfaces, such as the actively cooled wall of the counter-reflector, forming deposits that impair the system's functionality, for example, the reflectivity of the counter-reflector. If the reflector wall has inlet openings for the cooling gas and one or more outlet openings through which exhaust air is drawn out of the reflector chamber, moisture from the rear of the irradiated material can also be removed with the exhaust air, thus preventing condensation.

[0028] In another variant of the process, the cooling gas flows from a gas distribution chamber adjacent to the gas-permeable reflector wall into the reflector chamber through the inlet openings.

[0029] The gas-permeable reflector wall seals off the gas distribution chamber on one side. The cooling gas is introduced into the gas distribution chamber at one or more points and flows out of the gas distribution chamber through the inlet openings of the reflector wall into the reflector space. A uniform cooling gas pressure can establish itself within the gas distribution chamber, so that the amount of gas flowing out is determined solely by the distribution and the cross-sectional area of ​​the inlet openings.

[0030] The following describes preferred methods of the process in which the gas-permeable reflector wall is part of a gas distribution chamber.

[0031] In this context, it has also proven advantageous if the gas distribution chamber is divided into several sub-chambers, whereby the amount of cooling gas flowing into the reflector chamber through inlet openings varies from sub-chamber to sub-chamber in the direction of transport.

[0032] Within the fluidically separated subchambers of the gas distribution chamber, independent pressures of the cooling gas can be set. The amount of cooling gas flowing from each subchamber into the reflector chamber then depends on the respective gas pressure and the total cross-sectional area of ​​the inlet openings. An increase in the amount of cooling gas can at least partially compensate for the increasing temperature of the irradiated material in the direction of transport.

[0033] In this context, a method variant is preferred in which at least one first of the sub-chambers is provided with a first cooling gas connection, through which a first cooling gas flow is supplied to first inlet openings, and in which a second of the sub-chambers is provided with a second cooling gas connection, through which a second cooling gas flow is supplied to second inlet openings, wherein the first cooling gas flow is adjustable independently of the second cooling gas flow.

[0034] The gas distribution chamber is advantageously equipped with an exhaust air connection through which at least part of the exhaust air from the reflector chamber is discharged. If the gas distribution chamber is divided into several sub-chambers, it has also proven advantageous if at least one of the sub-chambers is equipped with such an exhaust air connection.

[0035] In this case, the gas-permeable reflector wall has, in addition to the inlet openings, also outlet openings that lead into the subchamber with the exhaust air connection. Through these outlet openings, used exhaust air is removed from the reflector chamber and drawn into the subchamber equipped with the exhaust air connection, from where it is then discharged. Separate control of the exhaust air and the cooling gas supply air ensures the extensive removal of moisture-laden exhaust air from the reflector chamber and prevents condensation.

[0036] The cooling of the counter-reflector and the interaction of the cooling gas with the irradiated material preferably take place independently of a process gas quantity control, by means of which process gas is introduced into the process room via a supply air unit and used exhaust air is removed from the process room via an exhaust air unit.

[0037] The process gas primarily serves to remove moisture from the material being irradiated, whereas the cooling gas primarily serves to regulate the temperature of the counter-reflector and the material being irradiated. Both functions can be performed by one and the same gas; in the simplest case, both the process gas and the cooling gas are air.

[0038] With regard to the irradiation device, the above-mentioned problem is solved according to the invention, starting from a device of the type mentioned at the outset, by the fact that the reflector wall has at least one outlet opening for the discharge of exhaust air from the reflector chamber.

[0039] The transport level divides the process chamber into two half-chambers, one of which extends between the reflector wall and the material being irradiated and is referred to here as the "reflector chamber." The inlet openings are designed to allow cooling gas to flow through them into the reflector chamber and strike the material being irradiated, specifically on the back side of the material facing away from the radiation unit. The cooling gas cools the reflector wall and also interacts with the material being irradiated, cooling it and, if necessary, contributing to its drying. This reduces the blistering effect, as explained in more detail above with reference to the process according to the invention.

[0040] The gas-permeable counter-reflector not only fulfills the usual functionalities described above, but also, as a result of the introduction of the cooling gas through the inlet openings of the reflector wall, it causes an interaction with the irradiated material moving in the transport plane, which enables a controlled temperature development in the irradiated material, which can reduce the occurrence of undesirable phenomena such as bubble formation.

[0041] In a preferred embodiment of the irradiation device, the number and / or the cross-sectional area of ​​the inlet openings varies in the direction of transport.

[0042] This makes it possible to continuously or incrementally change the amount of cooling gas flowing into the reflector chamber through the inlet openings. A variation in the opening cross-section is measured by whether the total opening cross-section of the inlet openings – determined in uniformly sized sections of the reflector wall – increases or decreases in the direction of flow.

[0043] It has proven advantageous if the reflector wall, viewed in the direction of transport, is divided into several sections, and if the number and / or the total opening cross-section of the inlet openings varies from section to section.

[0044] This results in different sections of the reflector wall differing in their permeability to the cooling gas, such that the gas permeability increases or decreases from section to section. The increasing gas permeability in the direction of transport allows a greater quantity of cooling gas to flow into the reflector chamber and at least partially compensate for the rising temperature of the irradiated material in the same direction. Even when the gas-permeable reflector wall is divided into several differently shaped sections, a single-piece design of the reflector wall is preferred.

[0045] In a particularly proven embodiment of the irradiation device, several temperature sensors are distributed along the reflector wall in the direction of transport.

[0046] The temperature of the material being irradiated can be measured at multiple positions, for example at 2 to 8 positions, preferably at 2 to 5 positions, as it moves through the process chamber using temperature sensors. The resulting temperature profile can be used to control the amount of cooling gas. The temperature sensors are preferably designed for non-contact temperature measurement, for example as pyrometers.

[0047] According to the invention, the gas-permeable reflector wall has at least one outlet opening for the discharge of exhaust air from the reflector chamber. In a preferred embodiment of the irradiation device, the gas-permeable reflector wall has several outlet openings for the discharge of exhaust air from the reflector chamber.

[0048] If the reflector wall has, in addition to the inlet openings for the cooling gas, an outlet opening or several outlet openings for the removal of exhaust air from the reflector chamber, moisture is also removed with the exhaust air, thus preventing condensation.

[0049] One embodiment of the irradiation device is characterized by the fact that the reflector wall adjoins a gas distribution chamber.

[0050] The gas-permeable reflector wall seals off the gas distribution chamber on one side. The cooling gas can be introduced into the gas distribution chamber at one or more points, and from there it flows through the inlet openings of the reflector wall into the reflector chamber. A uniform cooling gas pressure can establish itself within the gas distribution chamber, so that the amount of cooling gas flowing out is determined solely by the distribution and cross-sectional area of ​​the outlet openings.

[0051] In this context, it has also proven advantageous if the gas distribution chamber is divided into several sub-chambers.

[0052] Within the gas distribution chamber, the cooling gas pressures can be adjusted in fluidically separated subchambers, differing from one subchamber to the next. The amount of cooling gas flowing out of each subchamber is thus variable and is determined by the cooling gas pressure, the distribution, and the total cross-sectional area of ​​the outlet openings of the respective subchamber. This subdivision allows the amount of cooling gas flowing into the reflector chamber through the inlet openings of the reflector wall to vary, for example, from subchamber to subchamber (viewed in the direction of flow).

[0053] The gas distribution chamber is advantageously equipped with an exhaust air connection through which at least a portion of the exhaust air from the reflector chamber is discharged. If the gas distribution chamber is divided into several sub-chambers, it has also proven beneficial if at least one of the sub-chambers is equipped with such an exhaust air connection.

[0054] In this case, the gas-permeable reflector wall has, in addition to the inlet openings, one or more outlet openings that lead into the subchamber with the exhaust air connection. Through these outlet openings, the exhaust air can be removed from the reflector chamber and introduced into the subchamber equipped with the exhaust air connection, from where it is discharged to the outside. Separate control of the exhaust air and the cooling gas supply air ensures the extensive extraction of moisture-laden exhaust air from the reflector chamber and prevents condensation.

[0055] In a preferred embodiment of an irradiation device, which is equipped with a gas distribution chamber divided into several sub-chambers, at least one first of the sub-chambers is provided with a first cooling gas connection, through which a first cooling gas flow is supplied to first inlet openings, and a second of the sub-chambers is provided with a second cooling gas connection, through which a second cooling gas flow is supplied to second inlet openings, wherein the first cooling gas flow is adjustable independently of the second cooling gas flow.

[0056] Advantageously, the irradiation device has, independently of the gas-permeable counter-reflector, a process gas supply unit for introducing process gas into the process chamber and an exhaust air unit for removing exhaust air from the process chamber.

[0057] The cooling of the counter-reflector and the interaction of the cooling gas with the irradiated material can take place independently of a process gas quantity control, by means of which process gas is introduced into the process room via a supply air unit and exhaust air is extracted from the process room via an exhaust air unit. Definitions Reflector wall

[0058] The reflector wall is provided with inlet openings and, optionally, outlet openings. It consists of a single piece or is composed of several reflector wall sections. The reflector wall sections may differ in the surface area of ​​their inlet openings and, optionally, also in the surface area of ​​their outlet openings. Preferably, the reflector wall forms a wall of a gas distribution chamber. Gas distribution chamber

[0059] The gas distribution chamber consists of a single chamber, or it is multi-part and formed from several sub-chambers. Optionally, the sub-chambers are enclosed by a common reflector wall, or each sub-chamber has its own reflector wall. The sub-chambers are fluidically connected to each other, or they are fluidically separated from each other and may be designed for processing different gas volumes and / or gas pressures. Example of implementation

[0060] The invention is explained in more detail below with reference to an exemplary embodiment and a patent drawing. The drawing schematically illustrates the following: Fig. 1 a printing machine with a printing unit and an infrared drying system and a substrate transported along a transport path and in a transport direction, Fig. 2 a sketch of an irradiation device as part of the drying system of the printing press of Fig. 1 in a longitudinal section, Fig. 3 a three-dimensional representation of an embodiment of the gas distribution chamber with irradiated material moved above it in a top view of the irradiated material, Fig. 4 a gas distribution chamber of the irradiation device with a drawn flow profile of the cooling air, Fig. 5 the gas distribution chamber of the irradiation device with the exhaust air flow profile shown, Fig. 6 a three-dimensional representation of an embodiment of the irradiation device in assembly, and Fig. 7 A diagram showing temperature profiles on the surface of the irradiated material along the process chamber during processing with and without a gas-permeable counter-reflector.

[0061] Fig. Figure 1 schematically shows a printing press in the form of a roll-to-roll inkjet printing press, which is assigned the reference numeral 1. Starting from a unwinder 2, the web of material 3, consisting of a substrate such as paper, reaches a printing unit 40. This unit comprises several inkjet printheads 4 arranged one after the other along the web of material 3, through which solvent-based and, in particular, water-based printing inks are applied to the substrate.

[0062] Viewed in the direction of transport 5, the material web 3 passes from the printing unit 40 via a deflection roller 6 to an infrared drying system 70.

[0063] This is equipped with several dryer modules 7, which are designed for drying the solvent into the material web 3. The dryer modules 7 are each equipped with a counter-reflector unit 23 with a gas-permeable counter-reflector and are described further below with reference to the Fig. Sections 2 to 7 are explained in more detail.

[0064] The further transport path of the material web 3 leads via a traction roller 8, which is equipped with its own traction drive motor and via which the web tension is adjusted, to a winding roller 9.

[0065] The dryer system 70 comprises several dryer modules 7. Each of the dryer modules 7 is equipped with several infrared emitters – in the exemplary embodiment, there are eighteen.

[0066] In infrared heaters, a heating filament made of carbon or tungsten, in the form of a coil or strip, is enclosed in an inert gas-filled heater tube, which is usually made of quartz glass. The heating filaments are connected to electrical terminals that are inserted through one or both ends of the heater tube.

[0067] The dryer modules are arranged in pairs, side by side and one behind the other, in the dryer system when viewed in the direction of transport. Each adjacent pair of dryer modules 7 covers the maximum format width of the printing press 1. Depending on the dimensions and ink coverage of the substrate, the dryer modules 7 and the individual infrared emitters can be controlled electrically independently.

[0068] In an alternative embodiment, the dryer module is equipped with planar infrared emitter panels instead of tubular infrared emitters. The infrared emitter panels comprise a substrate made of an infrared-emitting material and are covered with one or more conductive traces of resistive material for thermal excitation of the infrared emission. In the case of multiple conductive traces, these can be controlled independently to generate a non-homogeneous temperature profile across the infrared emitter surface.

[0069] The transport speed of material web 3 is set to 5 m / s. This is a comparatively high speed, which necessitates a high drying rate. The drying process required to achieve this requirement and the irradiation device used for this purpose are described below using the following example. Fig. 2 to 7 are explained in more detail. Provided that these figures use the same reference numerals as in Fig. 1 are used, so this refers to structurally identical or equivalent components and parts, as explained in more detail above in the description of the printing press.

[0070] The sketch of Fig. Figure 2 shows an irradiation device in the form of a drying module 7 arranged on the material web 3. The drying module 7 consists of an irradiation unit 22 and a counter-reflector unit 23, separated from each other by the material web 3 moving in the transport plane 3a.

[0071] The emitter unit 22 is equipped with several elongated infrared emitters 24, whose longitudinal axes run perpendicular to the transport direction 5 and which are arranged parallel to each other. The emitter unit 22 is equipped with its own air management system, which includes a supply air unit 25 for the supply of drying air and an exhaust air unit 26 for the removal of used air. The supply and exhaust air units (25; 26) are independent of the counter-reflector unit 23 described in more detail below and serve in particular to dissipate excess heat in the rear area of ​​the emitter unit 22 in order to protect the surrounding parts of the printing press 1 from overheating.

[0072] The counter-reflector unit 23 comprises a gas distribution chamber 27, which is equipped with an air inlet 28, an air outlet 29, and a reflector plate 30 provided with a plurality of through-holes. The gas-permeable reflector plate 30 faces the material web 3 and closes off the gas distribution chamber 27 at the top. Several pyrometers 34 are arranged within the gas distribution chamber 27, distributed along the reflector plate 30 in the transport direction 5 and designed to measure the temperature of the underside of the material web.

[0073] The material conveyor 3 is moved in transport direction 5 in transport level 3a through a treatment chamber (=process chamber 31) of the drying module 7. The transport level 3a divides the process chamber 31 into an irradiation chamber 32 facing the radiation unit 22 and a reflector chamber 33 facing the counter-reflector unit 23.

[0074] Fig. Figure 3 shows a three-part counter-reflector unit 23. This unit is modularly constructed from three fluidically interconnected reflector chambers and is encompassed by a common, one-piece frame 35. From the top view of the material web 3 (which simultaneously defines the transport plane 3a) and the counter-reflector unit 23, the reflector plate 30 is visible, which in this embodiment is composed of three reflector plate fields 30a, 30b, 30c, each with a different distribution of inlet and outlet openings (36; 37).

[0075] The reflector plate 30 has numerous through-holes, subdivided into small, closely spaced circular inlet openings 36 and oval outlet openings 37. Viewed from bottom to top (i.e., in the transport direction 5), there are thirteen offset rows of circular inlet openings 36, followed by two rows of oval outlet openings 37. Then come eleven rows of inlet openings 36, another two rows of outlet openings 37, ten more rows of inlet openings 36, two more rows of outlet openings 37, another ten rows of inlet openings 36, and finally three rows of oval outlet openings 37. The circular inlet openings 36 have an inner diameter of 4 mm, and the oval outlet openings 37 have an opening cross-section of 353 mm². 2 .

[0076] The inlet openings 36 are fluidically connected to two gas inlet nozzles 38a; 38b (better seen in Fig. 4) the gas distribution chamber 27 for the supply of dry air to the reflector chamber 33. The outlet openings 37 are fluidically connected to a gas outlet nozzle 39 (better seen in Fig. 5) connected to the gas distribution chamber 27 for the discharge of used air from the reflector chamber 33.

[0077] The opening dimensions and the number and distribution of the through-holes are adapted to the type of product to be irradiated and the radiation source power. A balance must be struck: on the one hand, the temperature of the irradiated material increases in the direction of transport, so that a certain number of inlet openings 36 are required for sufficient and uniform cooling; on the other hand, the humidity also increases steadily, so that a certain number of outlet openings 37 are also necessary. As a rule, the surface area of ​​the outlet openings increases in the direction of transport, and consequently, the surface area of ​​the inlet openings 36 decreases. To achieve optimal drying results, the specific design can be optimized for the application, radiation source type, and radiation source power based on the information above and the exemplary embodiment, for example, empirically through practical tests and / or theoretically using simulations.

[0078] The reflector plate 30 is suitable for reflecting infrared radiation, and the reflector plate material should itself be heat-resistant and preferably also thermally conductive. In the exemplary embodiment, the reflector plate 30 is made of anodized aluminum. Alternatively, the reflector plate 30 consists of aluminum with a metallic surface, stainless steel, in particular polished stainless steel, or other metals, especially precious metals, or of a workpiece coated with one of the aforementioned materials. Viewed in the transport direction 5, the surface area of ​​the outlet openings 37 increases, and that of the inlet openings 36 decreases.

[0079] The three-dimensional views of the counter-reflector unit 23 of Fig. 4 and Fig. Figure 5 shows that the gas distribution chamber 27 is divided into several sub-chambers by means of partitions 41, two of which are each connected to one of the gas inlet nozzles 38a; 38b, and the third sub-chamber is connected to the gas outlet nozzle 39. The flow lines 42 in Fig. Figure 4 indicates the distribution of the dry cooling air from the two gas inlet nozzles 38a; 38b to the inlet openings 36. Fig. The flow lines 43 indicate the distribution of the used exhaust air from the outlet openings 37 to the gas outlet nozzle 39. The supply of dry cooling air via the gas inlet nozzles 38a; 38b and the discharge of the used exhaust air via the gas outlet nozzle 39 are separately controllable.

[0080] Fig. Figure 6 shows a dryer module 7 assembled from two emitter units 22a, 22b and a two-part counter-reflector unit 23.

[0081] The following section explains in more detail a procedure for carrying out the method according to the invention.

[0082] To reduce the blistering effect and improve the efficiency of radiant heat transfer between the infrared emitters 24 of the emitter unit 22 and the printing ink to be dried on the material web 3, the counter-reflector unit 23 with a gas-permeable reflector plate 30 is used. The cooling air flowing from the inlet openings 36 of the reflector plate 30 against the uncoated underside of the material web 3 ensures a uniform temperature distribution in the substrate (paper). This is further enhanced by the use of several reflector plate arrays 30a, 30b, 30c with an adapted distribution of inlet openings 36 and outlet openings 37. The amount of exhaust air extracted is comparatively low at the entry of the material web 3 into the process chamber 31 and increases until it exits the process chamber 31.

[0083] Fig. Figure 7 shows the difference in temperature distribution for a material web after irradiation using a gas-permeable counter-reflector with and without cooling air. The diagram plots the temperature (in °C) measured by pyrometer 34 on the underside of the material web against the pyrometer position number in the transport direction 5, between the entry of the material web 3 into the process chamber and its exit from the process chamber. Curve A shows the temperature profile when using the counter-reflector with cooling air, and curve B shows the temperature profile when using the counter-reflector without cooling air. Both temperature profiles show maximum temperatures shortly after entry T. max1 the material track into the process room and shortly before its exit T max2It is evident that when cooling air is directed against the unprinted side of the paper sheet, a more homogeneous temperature profile with a lower drift in the maximum temperatures T is achieved. max1 and T max2This results in (curve A) as without this measure. Furthermore, the maximum temperature for curve A is significantly lower than the maximum value of curve B. In this example, the difference in the maximum temperatures of curves A and B is approximately 10°C. Curve A remains below 150°C, which in this example can be considered the threshold for blistering. Cooling the substrate from the back prevents not only the highly absorbent ink areas from becoming comparatively hot and potentially overheating. The cooling of the web 3 from the oncoming cooling air counteracts excessively rapid heating of the material between reaching the gel point and the critical point, contributing to a comparatively gentle drying of the material in the initial drying phase. A more homogeneous temperature profile is thus established.This allows the radiation power and thus the transport speed to be increased without damaging the irradiated material or the defendant. Reference symbol list 1 inkjet printing machine 2 liquidators 3 Material track 3a Transport level 40 pressure unit 4 inkjet printheads 5. Transport direction 6 Deflection roller 70 Infrared drying system 7 dryer modules 8 Pulling roller 9 winding roller 22 emitter unit 22a, 22b emitter units 23 Counter-reflector unit 24 infrared heaters 25 Supply air unit 26 Exhaust unit 27 Gas distribution chamber 28 Air intake 29 Air outlet 30 Reflector plate 30a, 30b, 30c reflector plate fields 31 Process room 32 Treatment room 33 Reflector room 34 Pyrometer 35 frames 30 Reflector plate 36 inlet openings 37 outlet openings 38a; 38b Gas inlet nozzle 39 Gas outlet nozzles 41 partition walls

Claims

[1] Infrared irradiation device for drying a material (3) being moved in a transport direction (5) and a transport plane (3a) through a process chamber (31), wherein the transport plane (3a) divides the process chamber (31) into an irradiation chamber (32) and a reflector chamber (33), comprising a radiator unit (22) with at least one infrared radiator (24) for emitting infrared radiation into the irradiation chamber (32), and a counter-reflector (23) with a reflector wall (30) facing the transport plane (3a), wherein the reflector wall (30) has a plurality of inlet openings (36) for the inlet of cooling gas into the reflector chamber (33), characterized by , that for the discharge of exhaust air from the reflector chamber (33) the reflector wall (30) has at least one outlet opening (37). [2] Irradiation device according to claim 1, characterized by, that, viewed in the direction of transport (5), the number and / or the opening cross-section of the inlet openings (36) varies. [3] Irradiation device according to claim 2, characterized by , that the reflector wall (30) is divided into several sections (30a, 30b, 30c) as seen in the transport direction (5), and that the number and / or the total opening cross-section of the inlet openings (36) varies from section to section (30a, 30b, 30c). [4] Irradiation device according to one of the preceding claims, characterized by , that for the discharge of exhaust air from the reflector chamber (33) the reflector wall (30) has several outlet openings (37). [5] Irradiation device according to any one of the preceding claims, characterized by , that several temperature sensors (34) are distributed along the reflector wall (30) when viewed in the direction of transport (5). [6] Irradiation device according to one of the preceding claims, characterized by, that the reflector wall (30) adjoins a gas distribution chamber (27). [7] Irradiation device according to claim 6, characterized by , that the gas distribution chamber (27) is divided into several sub-chambers. [8] Irradiation device according to claim 6 or 7, characterized by , that the gas distribution chamber (27) is provided with an exhaust air connection (39) which is fluidically connected to at least part of the outlet openings (37). [9] Irradiation device according to claim 7 or 8, characterized by , that at least one first of the sub-chambers is provided with a first cooling gas connection (38a) through which a first cooling gas flow (42) is supplied to first inlet openings (36), and that a second of the sub-chambers is provided with a second cooling gas connection (38b) through which a second cooling gas flow (42) is supplied to second inlet openings (36), wherein the first cooling gas flow (42) is adjustable independently of the second cooling gas flow (42). [10] Irradiation device according to any of the preceding claims, characterized by , that a process gas supply unit (25) is provided for introducing process gas into the process room (31) and an exhaust air unit (26) for removing exhaust air from the process room (31). [11] Method for at least partially drying a material to be irradiated (3) moved in a transport direction (5) and a transport plane (3a) through a process room (31), wherein the transport plane (3a) divides the process room (31) into an irradiation room (32) and a reflector room (33), comprising the process steps: (c) Emitting infrared radiation towards the irradiated material (3) by means of a radiator unit (22) comprising at least one infrared radiator (24), (d) Reflecting infrared radiation back onto the irradiated material (3) by means of a counter-reflector (23) which has a reflector wall (30) facing the transport plane (3a), wherein a cooling gas is introduced into the reflector chamber (33) via inlet openings (36) of the reflector wall (30), characterized by , that exhaust air is discharged from the reflector chamber (33) via at least one outlet opening (37) of the reflector wall (30). [12] Method according to claim 11, characterized by , that, viewed in the direction of transport (5), the amount of cooling gas introduced into the reflector chamber (33) varies. [13] Method according to claim 11 or 12, wherein exhaust air is discharged from the reflector chamber (33) via several outlet openings (37) of the reflector wall (30). [14] Method according to any one of claims 11 to 13, characterized by, that the temperature of the irradiated material (3) is measured at several positions distributed in the transport direction (5) along the process chamber (31), for example at 2 to 8 positions, preferably at 2 to 5 positions, and that the measured values ​​are used to control the amount of cooling gas. [15] Method according to any one of claims 11 to 14, characterized by , that the cooling gas flows from a gas distribution chamber (27) adjacent to the reflector wall (30) through the inlet openings (36) into the reflector chamber (33). [16] Method according to claim 15, characterized by , that the gas distribution chamber (27) is divided into several sub-chambers, wherein the amount of cooling gas flowing into the reflector chamber (33) through inlet openings (36) varies from sub-chamber to sub-chamber as seen in the transport direction (5). [17] Method according to claim 15 or 16, characterized by, that the gas distribution chamber (27) is provided with an exhaust air connection (39) through which at least part of the exhaust air from the reflector chamber (33) is discharged. [18] Method according to claim 16 or 17, characterized by , that at least one first of the sub-chambers is provided with a first cooling gas connection (38a) through which a first cooling gas flow is supplied to first inlet openings (36), and that a second of the sub-chambers is provided with a second cooling gas connection (38b) through which a second cooling gas flow is supplied to second inlet openings (36), wherein the first cooling gas flow is adjustable independently of the second cooling gas flow. [19] Method according to any one of claims 11 to 18, characterized by , that process gas is introduced into the process room (31) via an air supply unit (25) by means of a process gas quantity control and exhaust air is extracted from the process room (31) via an exhaust air unit (26).

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