METHOD FOR DRYING A MATERIAL FOR IRRADIATION, AND INFRARED IRRADIATION DEVICE FOR CARRYING OUT SAID METHOD

Abstract

Known infrared irradiation devices for drying a material for irradiation that is moved through a process chamber have a radiator unit with at least one infrared radiator for emitting infrared radiation and have a counter-reflector with a reflector wall, wherein the reflector wall has a plurality of inlet openings for admitting cooling gas into the reflector space. Proceeding from this, in order to provide an irradiation device for the drying method, which irradiation device is, in particular for drying solvent-containing and in particular water-based printing ink, distinguished by high-speed drying with a low level of bubble formation and a low level of condensation in the reflector space at the same time, it is proposed that the reflector wall has at least one outlet opening for conducting waste air out of the reflector space.

Claims

1. Infrared irradiation device for drying a material for irradiation that is moved through a process chamber in a transportation direction and in a transportation plane, wherein the transportation plane divides the process chamber into an irradiation space and into a reflector space, having a radiator unit with at least one infrared radiator for emitting infrared radiation into the irradiation space, and having a counter-reflector with a reflector wall facing the transportation plane, wherein the reflector wall has a plurality of inlet openings for admitting cooling gas into the reflector space, wherein the reflector wall has at least one outlet opening for conducting waste air out of the reflector space.

2. Irradiation device according to claim 1, wherein the number of and/or the opening cross-section of the inlet openings varies as viewed in the transportation direction.

3. Irradiation device according to claim 2, wherein the reflector wall is divided into a plurality of sections as viewed in the transportation direction and that the number of and/or the total opening cross-section of the inlet openings varies from section to section.

4. Irradiation device according to claim 1, wherein the reflector wall has a plurality of outlet openings for conducting waste air out of the reflector space, wherein the number of and/or the total opening cross-section of the outlet openings preferably varies in the transportation direction.

5. Irradiation device according to claim 1, wherein a plurality of temperature sensors is distributed along the reflector wall as viewed in the transportation direction.

6. Irradiation device according to claim 1, wherein the reflector wall adjoins a gas distribution chamber.

7. Irradiation device according to claim 6, wherein the gas distribution chamber is divided into a plurality of sub-chambers.

8. Irradiation device according to claim 6, wherein the gas distribution chamber is provided with a waste air connection that is fluidically connected to at least a part of the outlet openings.

9. Irradiation device according to claim 7, wherein at least one first of the sub-chambers is provided with a first cooling gas connection via which a first cooling gas stream is supplied to first inlet openings, and in that a second of the sub-chambers is provided with a second cooling gas connection via which a second cooling gas stream is supplied to second inlet openings, wherein the first cooling gas stream can be adjusted independently of the second cooling gas stream.

10. Irradiation device according to claim 1, wherein a process gas supply unit for introducing process gas into the process chamber and a waste air unit for discharging waste air from the process chamber are provided.

11. Method for at least partially drying a material for irradiation that is moved through a process chamber in a transportation direction and in a transportation plane, wherein the transportation plane divides the process chamber into an irradiation space and into a reflector space, comprising the method steps: (c) Emitting infrared radiation in the direction of the material for irradiation by means of a radiator unit comprising at least one infrared radiator, (d) Reflecting infrared radiation back onto the material for irradiation by means of a counter-reflector which has a reflector wall facing the transportation plane, wherein a cooling gas is introduced into the reflector space via inlet openings in the reflector wall, wherein waste air is discharged from the reflector space via at least one outlet opening in the reflector wall.

12. Method according to claim 11, wherein the quantity of cooling gas introduced into the reflector space varies as viewed in the transportation direction.

13. Method according to claim 11, wherein waste air is discharged from the reflector space via a plurality of outlet openings in the reflector wall, wherein the number of and/or the total opening cross-section of the outlet openings preferably varies in the transportation direction.

14. Method according to claim 10, wherein the temperature of the material for irradiation is measured at a plurality of positions distributed along the process chamber in the transportation direction (5), for example at 2 to 8 positions, preferably at 2 to 5 positions, and in that the measured values are used to regulate the quantity of cooling gas.

15. Method according to claim 1, wherein the cooling gas flows through the inlet openings into the reflector space from a gas distribution chamber adjoining the reflector wall.

16. Method according to claim 15, wherein the gas distribution chamber is divided into a plurality of sub-chambers, wherein the quantity of cooling gas flowing into the reflector space through inlet openings varies from sub-chamber to sub-chamber as viewed in the transportation direction.

17. Method according to claim 15 or 16, wherein the gas distribution chamber is provided with a waste air connection via which at least a part of the waste air is discharged from the reflector space.

18. Method according to claim 16, wherein at least one first of the sub-chambers is provided with a first cooling gas connection via which a first cooling gas stream is supplied to first inlet openings, and in that a second of the sub-chambers is provided with a second cooling gas connection via which a second cooling gas stream is supplied to second inlet openings, wherein the first cooling gas stream is adjustable independently of the second cooling gas stream.

19. Method according to claim 11, wherein by means of a process gas quantity controller, process gas is introduced into the process chamber via a supply air unit and waste air is discharged from the process chamber via a waste air unit.

Description

EXEMPLARY EMBODIMENT

[0061] The invention is explained in more detail below with reference to an exemplary embodiment and a patent drawing. In detail, the drawing shows in schematic representation:

[0062] FIG. 1 a printing press with a printing unit and an infrared dryer system and a printing substrate being transported along a transportation route and in a transportation direction,

[0063] FIG. 2 a sketch of an irradiation device as part of the dryer system of the printing press of FIG. 1 in a longitudinal section,

[0064] FIG. 3 a three-dimensional representation of an embodiment of the gas distribution chamber with material for irradiation moved over it in a top view of the material for irradiation,

[0065] FIG. 4 a gas distribution chamber of the irradiation device with a drawn-in flow profile of the cooling air,

[0066] FIG. 5 the gas distribution chamber of the irradiation device with a drawn-in flow profile of the waste air,

[0067] FIG. 6 a three-dimensional representation of an embodiment of the irradiation device as assembled, and

[0068] FIG. 7 a diagram with temperature profiles on the surface of the material for irradiation along the process chamber during processing with and without a gas-permeable counter-reflector.

[0069] FIG. 1 is a schematic view of a printing press in the form of an inkjet roll printing press, to which as a whole is assigned the reference number 1. Starting from an unwinder 2, the material web 3, consisting of a printing substrate, such as paper, reaches a printing unit 40. The latter comprises a plurality of inkjet print heads 4 which are arranged one behind the other along the material web 3 and by means of which solvent-containing and in particular water-containing printing inks are applied to the printing substrate.

[0070] As viewed in the transportation direction 5, the material web 3 subsequently passes from the printing unit 40 via a deflection roller 6 to an infrared dryer system 70. The latter is equipped with a plurality of 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 explained in more detail below with reference to FIGS. 2 to 7.

[0071] The further transportation route of the material web 3 proceeds via a draw roller 8 which is equipped with its own traction drive motor and via which the web tension is adjusted, to a take-up roller 9.

[0072] A plurality of dryer modules 7 are combined in the dryer system 70. Each of the dryer modules 7 is equipped with a plurality of infrared radiators, eighteen in the exemplary embodiment.

[0073] In the case of the infrared radiators, a heating filament made of carbon or tungsten in a spiral or strip form is enclosed in a radiator tube filled with inert gas and usually made of quartz glass. The heating filaments are connected to electrical connections that are introduced via one or both ends of the radiator tube.

[0074] In the dryer system, the dryer modules are arranged in pairs next to and behind one another as viewed in the transportation direction. The pair of dryer modules 7 in each case arranged next to one another covers the maximum format width of the printing press 1. In accordance with the dimensions and color assignment of the printing substrate, the dryer modules 7 and the individual infrared radiators are electrically controllable separately from one another.

[0075] In an alternative embodiment, the dryer module is equipped with planar infrared radiator panels instead of tubular infrared radiators. The infrared radiator panels comprise a substrate made of a material emitting infrared radiation and are occupied by one conductor track or a plurality of conductor tracks of resistance material for the thermal excitation of the infrared emission. In the case of an occupation with a plurality of conductor tracks, the conductor tracks can be controllable separately from one another in order to produce a nonhomogeneous temperature profile over the infrared radiator surface.

[0076] The transportation speed of the material web 3 is set to 5 m/s. This is a comparatively high speed which requires high-speed drying. The drying method required to achieve this requirement and the irradiation device used for this purpose are explained in more detail below with reference to FIGS. 2 to 7. Insofar as the same reference signs are used in these figures as in FIG. 1, they denote structurally identical or equivalent components and parts as are explained in more detail above with reference to the description of the printing press.

[0077] The sketch in FIG. 2 shows an irradiation device arranged on the material web 3 in the form of a dryer module 7. The dryer module 7 is composed of a radiator unit 22 and a counter-reflector unit 23, separated from one another by the material web 3 that is moved in the transportation plane 3a.

[0078] The radiator unit 22 is equipped with a plurality of elongated infrared radiators 24, whose longitudinal axes run perpendicularly to the transportation direction 5 and are arranged in parallel to one another. The radiator unit 22 is equipped with its own air management system which comprises a supply air unit 25 for the supply of drying air and a waste air unit 26 for the discharge of spent air. The supply air and waste air units (25; 26) are independent of the counter-reflector unit 23 described in more detail below and serve in particular for dissipating excess heat in the rear space of the radiator unit 22 in order to protect the surrounding parts of the printing press 1 from overheating.

[0079] 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 is a wall of the gas distribution chamber 27 facing the material web 3. It delimits the gas distribution chamber 27 upward and the reflector space 33 downward. A plurality of pyrometers 34 are arranged within the gas distribution chamber 27 and are distributed along the reflector plate 30 in the transportation direction 5 and are designed to measure the temperature of the underside of the material web.

[0080] The material web 3 is moved in the transportation direction 5 in the transportation plane 3a through a treatment space (= process chamber 31) of the dryer module 7. The transportation plane 3a divides the process chamber 31 into an irradiation space 32 facing the radiator unit 22 and a reflector space 33 facing the counter-reflector unit 23.

[0081] FIG. 3 shows a three-part counter-reflector unit 23. The counter-reflector unit is constructed in a modular manner from three reflector chambers fluidically connected to one another and is surrounded by a common, one-piece frame 35. From the plan view of the material web 3 (which simultaneously defines the transportation plane 3a) and of the counter-reflector unit 23, the reflector plate 30 can be seen, which in this embodiment is composed of three reflector plate fields 30a, 30b, 30c with in each case a different distribution of inlet and outlet openings (36; 37).

[0082] The reflector plate 30 has a plurality of the through-holes, which are divided into small, closely distributed circular inlet openings 36 and into oval outlet openings 37. As viewed from bottom to top (i.e., in the transportation direction 5), thirteen rows of circular inlet openings 36 that are offset relative to one another are provided, followed by two rows of oval outlet openings 37. Then come eleven rows of inlet openings 36, again two rows of outlet openings 37, another ten rows of inlet openings 36, another two 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 internal diameter of 4 mm, and the oval outlet openings 37 have an opening cross-section of 353 mm.sup.2.

[0083] The number of outlet openings 37 and/or the total opening cross-section of the outlet openings 37 thus increases in the transportation direction 5 so that in this direction more moisture-laden or spent cooling gas is discharged as waste air from the reflector space 33 into the air outlet 29 of the counter-reflector unit 23.

[0084] The inlet openings 36 are fluidically connected to two gas inlet connectors 38a; 38b (more clearly visible in FIG. 4) of the gas distribution chamber 27 for the supply of dry air into the reflector space 33. The outlet openings 37 are fluidically connected to a gas outlet connector 39 (more clearly visible in FIG. 5) of the gas distribution chamber 27 for the discharge of spent air from the reflector space 33.

[0085] The opening dimensions and the number and distribution of the through-holes 36; 37 are adapted to the type of product to be irradiated and to the radiator power. It is important to find a balance: on the one hand, the temperature of the material for irradiation increases in the transportation direction so that a number of inlet openings 36 is required for adequate and uniform cooling; on the other hand, the air humidity also steadily increases so that a certain number of outlet openings 37 is also required. As a rule, the areal occupancy of the outlet openings 37 increases in the transportation direction and the areal occupancy of the inlet openings 36 is inevitably reduced as a result. In order to obtain an optimal drying result, the specific design can be optimized on the basis of the above information and the exemplary embodiment for the application, the type of radiator and the radiator power, for example empirically by practical experiments and/or theoretically using simulations.

[0086] The reflector plate 30 is suitable for the reflection of infrared radiation and the reflector plate material itself is to be heat-resistant and preferably also heat-conducting. In the exemplary embodiment, the reflector layer 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, in particular of noble metals or of a workpiece which is coated with one of the materials mentioned. As viewed in the transportation direction 5, the areal occupancy of the outlet openings 37 increases and that of the inlet openings 36 decreases.

[0087] The three-dimensional views of the counter-reflector unit 23 in FIG. 4 and FIG. 5 show that the gas distribution chamber 27 is divided by means of partition walls 41 into a plurality of sub-chambers, of which two are in each case connected to one of the gas inlet connectors 38a; 38b, and the third sub-chamber is connected to the gas outlet connector 39. The flow lines 42 in FIG. 4 indicate the distribution of the dry cooling air from the two gas inlet connectors 38a; 38b to the inlet openings 36. In FIG. 5, the flow lines 43 indicate the distribution of the spent waste air from the outlet openings 37 to the gas outlet connector 39. The supply of the dry cooling air via the gas inlet connectors 38a; 38b and the discharge of the spent waste air via the gas outlet connector 39 can be regulated separately from one another.

[0088] FIG. 6 shows a dryer module 7 in the assembly of two radiator units 22a, 22b and a two-part counter-reflector unit 23.

[0089] A procedure for carrying out the method according to the invention is explained in more detail below.

[0090] In order to reduce the blustering effect and to improve the efficiency of radiation heat transfer between the infrared radiators 24 of the radiator unit 22 and the printing ink to be dried on the material web 3, the counter-reflector unit 23 is used with a gas-permeable reflector plate 30. The cooling air flowing from the inlet openings 36 of the reflector plate 30 against the uncoated underside of the material web 3 causes a uniform temperature development in the printing substrate (paper). This is helped by the fact that a plurality of reflector plate fields 30a, 30b, 30c with an adapted distribution of inlet openings 36 and outlet openings 37 is used. When the material web 3 enters the process chamber 31, the quantity of waste air extracted is comparatively small and increases up to the exit from the process chamber 31.

[0091] FIG. 7 shows the difference in the temperature distribution in the case of a material web, during irradiation using a gas-permeable counter-reflector with and without cooling air. In the diagram, the temperature on the underside of the material web measured by means of the pyrometer 34 (in °C) is plotted against the position number of the pyrometer as viewed in the transportation 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 the entry T.sub.max1 of the material web into the process chamber, and shortly before its exit T.sub.max2. It can be seen that using cooling air directed against the unprinted side of the paper sheet results in an overall more homogeneous temperature profile with less drift of the maximum temperatures T.sub.max1 and T.sub.max2 (curve A) than without this measure. In addition, the maximum temperature at curve A is significantly below the maximum value of curve B. In this example, the difference between the maximum temperatures of curves A and B is about 10° C. Curve A remains below 150° C., which in this example can be regarded as a threshold value for bubble formation. Cooling the rear side of the printing substrate prevents not only the highly absorbent ink surfaces from becoming comparatively hot and possibly overheated. The cooling of the rear side of the material web 3 by the inflowing cooling air counteracts a too rapid and excessive heating of the material for irradiation between reaching the gel point and reaching the critical point, which contributes to a comparatively gentle drying of the material for irradiation in the first drying phase. A comparatively more homogeneous temperature profile is established. As a result, the radiation power and thus the transportation speed can be increased without damaging the material for irradiation thereon.

TABLE-US-00001 List of reference signs Inkjet printing press 1 Unwinder 2 Material web 3 Transportation plane 3a Printing unit 40 Inkjet print heads 4 Transportation direction 5 Deflection roller 6 Infrared dryer system 70 Dryer modules 7 Draw roller 8 Take-up roller 9 Radiator unit 22 Radiator units 22a; 22b Counter-reflector unit 23 Infrared radiators 24 Supply air unit 25 Waste air unit 26 Gas distribution chamber 27 Air inlet 28 Air outlet 29 Reflector plate 30 Reflector plate fields 30a, 30b, 30c Process chamber 31 Irradiation space 32 Reflector space 33 Pyrometer 34 Frame 35 Reflector plate 30 Inlet openings 36 Outlet openings 37 Gas inlet connector 38a; 38b Gas outlet connector 39 Partition walls 41