METHOD FOR DRYING A SUBSTRATE, DRYER MODULE FOR CARRYING OUT THE METHOD, AND DRYER SYSTEM

Abstract

Methods for drying a substrate. The methods include the following steps: (a) emitting infrared radiation towards a substrate moving through a process space using an emitter unit comprising at least one inflated emitter, (b) generating at least two process gas streams of a process gas directed towards the substrate, (c) drying the substrate by the action of infrared radiation and process gas on the substrate, and (d) extracting moisture-laden process gas from the process space via an extraction duct, forming an exhaust air stream leading away from the substrate. To specify a drying method which is reproducible and effective and leads to an improved result, in particular in terms of homogeneity and speed of drying of the substrate, the at least two process gas streams are guided to the infrared emitter before they act on the substrate, and an exhaust air stream is spatially assigned to each process gas stream.

Claims

1. A method for at least partially drying a substrate, comprising the steps of: (a) emitting infrared radiation towards a substrate that moves through a process space along a transport path and in a transport direction, by using an emitter unit comprising at least one infrared emitter; (b) generating at least two process gas streams of a process gas directed towards the substrate; (c) at least partially drying the substrate by the action of infrared radiation and process gas on the substrate; and (d) extracting moisture-laden process gas out of the process space via an extraction duct, forming an exhaust air stream leading away from the substrate, wherein the at least two process gas streams are guided to the infrared emitter before they act on the substrate, and an exhaust air stream leading away from the substrate is spatially assigned to each process gas stream directed towards the substrate.

2. The method according to claim 1, wherein the at least one infrared emitter has a longitudinal axis and one of the at least two process gas streams flows over the at least one infrared emitter on each side of its longitudinal axis.

3. The method according to claim 1, wherein the at least two process gas streams act on the substrate to be dried in a strip-shaped manner, and a strip-shaped exhaust air stream is spatially assigned to each of the strip-shaped process gas streams.

4. The method according to claim 1, wherein for the purpose of a planar infrared irradiation of the substrate, the emitter unit comprises a plurality of infrared emitters having longitudinal axes running parallel to each other in each case.

5. The method according to claim 4, wherein one of the process gas streams directed towards the substrate is guided around each of the longitudinal axes of the plurality of infrared emitters, and wherein adjacent process gas streams of adjacent infrared emitters are spatially assigned to a common exhaust air stream.

6. The method according to claim 4, wherein the longitudinal axes of the plurality of infrared emitters form an angle of less than 30 degrees with the substrate transport direction.

7. The method according to claim 4, wherein the process space is formed in an infrared dryer module having a combination of the following components, viewed in the transport direction of the substrate: a front air knife, an irradiation space fitted with the plurality of infrared emitters arranged parallel to each other, an air exchanger unit with an integrated extraction mechanism and a rear air knife.

8. The method according to claim 7, wherein the front air knife is followed in the transport direction by an additional extraction mechanism.

9. The method according to claim 4, wherein each of the plurality of infrared emitters has a length and the method further comprises the step of imposing a volume characteristic on the at least two process gas streams, which increases in the substrate transport direction at least partially over the length of the infrared emitter.

10. The method according to claim 1, wherein the process space is formed in an infrared dryer module and the method further comprising the step of adjusting, by way of a process gas quantity control unit, the gas volume V.sub.in introduced into the dryer module to be smaller than the gas volume V.sub.out extracted out of the dryer module.

11. An infrared dryer module for drying a substrate that moves through a process space in a substrate plane and in a transport direction, the dryer module comprising: (a) an emitter unit comprising at least one infrared emitter having a longitudinal axis and emitting infrared radiation towards the substrate plane; (b) a process gas supply unit with a process gas collection space having at least one inlet opening for the introduction of process gas from the process gas collection space into the process space and with a gas guiding element which extends in the direction of the substrate plane and borders the at least one inlet opening; (c) an exhaust air unit with at least one extraction duct for discharging moisture-laden process gas from the process space, wherein the at least one infrared emitter is arranged in relation to the at least one inlet opening such that, together with the gas guiding element, it forms an inlet channel for the process gas on each side of its longitudinal axis, and wherein at least one process gas extraction duct is adjacent to each process gas inlet channel.

12. The dryer module according to claim 11, wherein the gas guiding element and the extraction duct have a common wall section, which ends at a distance from the substrate plane.

13. The dryer module according to claim 11, wherein the emitter unit comprises a plurality of infrared emitters, which have longitudinal axes running parallel to each other in each case.

14. The dryer module according to claim 13, wherein a common extraction duct is arranged between adjacent infrared emitters.

15. The dryer module according to claim 13, wherein the longitudinal axes of the infrared emitters form an angle of less than 30 degrees with the substrate transport direction.

16. The dryer module according to claim 13, further comprising, located the process space, and viewed in the transport direction, a front air knife, an irradiation space fitted with the plurality of infrared emitters arranged parallel to each other, an air exchanger unit with an integrated extraction mechanism and a rear air knife.

17. The dryer module according to claim 16, wherein the front air knife is followed in the transport direction by an additional extraction mechanism.

18. The dryer module according to claim 13, wherein each of the plurality of infrared emitters has a length and a volume characteristic is imposed on the process gas stream, which increases in the substrate transport direction at least partially over the length of the infrared emitter.

19. A dryer system for drying a substrate moving through a process space in a substrate plane and in a transport direction, containing multiple dryer modules according to claim 13 which are arranged next to one another and/or one behind another in the transport direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0090] The invention will be explained in more detail below with reference to exemplary embodiments and patent drawings. In detail, the drawings show schematic illustrations and include the following figures:

[0091] FIG. 1 shows a printing machine with a printing unit and an infrared dryer system and a print substrate which is transported along a transport path and in a transport direction;

[0092] FIG. 2 shows a dryer module according to the invention as part of the dryer system of the printing machine of FIG. 1 in a longitudinal section in the print substrate transport direction;

[0093] FIG. 3 shows a detail of the irradiation unit of the dryer module according to the invention in a section along the line A-A of FIG. 2; and

[0094] FIG. 4 shows a detail of the irradiation unit in a plan view of emitter units in the direction of the arrow X of FIG. 3.

DETAILED DESCRIPTION

[0095] In infrared emitters, a heating filament composed of carbon or tungsten in coil or strip form is enclosed in an inert-gas-filled emitter tube, which is usually made of quartz glass. The heating filaments are joined to electrical connections, which are introduced via one end or both ends of the emitter tube.

[0096] FIG. 1 shows a diagram of a printing machine in the form of a roll-fed inkjet printing machine, which is assigned the overall reference number 1. Starting from an unwinder 2, the material web 3 composed of a print substrate, such as, e.g., paper, passes to a printing unit 40. This printing unit 40 comprises multiple inkjet printing heads 4 arranged one behind the other along the material web 3, by which solvent-based, and in particular water-based, printing inks are applied on to the print substrate.

[0097] Viewed in the transport direction 5, the material web 3 then passes from the printing unit 40 via a deflecting roller 6 to an infrared dryer system 70. This infrared dryer system 70 is fitted with multiple dryer modules 7, which are designed for drying the solvent or for its absorption into the material web 3.

[0098] The further transport path of the material web 3 passes via a traction 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.

[0099] In the dryer system 70, multiple dryer modules 7four in the exemplary embodimentare grouped together. Each of the dryer modules 7 is equipped with multiple infrared emitterseighteen in the exemplary embodiment.

[0100] The dryer modules 7 are arranged in pairs in the dryer system 70, one beside the other and one behind the other viewed in the transport direction 5. The pairs of dryer modules 7 arranged one beside the other each cover the maximum format width of the printing machine 1. Corresponding to the dimensions and ink coverage of the print substrate, the dryer modules 7 and the individual infrared emitters can be electrically controlled separately from each other.

[0101] The transport speed of the material web 3 is set at 5 m/s. This is a comparatively high speed, which is made possible by an optimization of the individual processing steps and which requires in particular a high drying rate. The drying method needed in order to meet this requirement and the dryer module 7 employed for this purpose will be explained in more detail below with reference to FIGS. 2 to 4. Where the same reference numbers are used in these figures as in FIG. 1, they refer to identically constructed or equivalent components and parts, as explained in more detail above with reference to the description of the printing machine.

[0102] In the embodiment of the dryer module 7 according to the invention shown in FIG. 2, a housing 21 encloses a treatment space (or process space) for the material web 3 having the following components (viewed in the transport direction 5): a front air knife 22 with an air baffle 22a, an extraction mechanism 23 immediately downstream of the front air knife 22, an infrared irradiation chamber 25 fitted with the eighteen infrared emitters 24, of which the longitudinal axes 24a run approximately in the transport direction 5 and which are arranged parallel to each other, an air exchanger unit 26 having alternately arranged gas inlet nozzles 26b and extraction ducts 26a and a rear air knife 27 having a final air baffle 27a.

[0103] The directional arrows 28 indicate an air stream directed on to the surface of the material web 3, and the directional arrows 29 indicate an air stream leading away from the material web 3, as well as a mutual interaction 35 of these air streams, which will be explained with reference to FIG. 3. The increasing length of the directional arrows 28; 29 in the transport direction 5 symbolizes the increase in the respective flow volumes. The surface of the material web 3 corresponds at the same time to the substrate plane 3a.

[0104] The cross-section shown in FIG. 3 comprises a section of the infrared irradiation chamber 25 along four identically constructed infrared emitter units 30. The cross-section shows an extraction space 31, a gas-feeding space 32 and the actual infrared substrate-treatment space 33.

[0105] The gas-feeding space 32 is connected to a gas inlet 36 and is composed of multiple gas-collecting spaces 32a, which are in fluid connection with each other by way of lines 32b. Each emitter unit 30 has a gas-collecting space 32a. Each gas-collecting space 32a is provided with a central, elongated opening 37 to the substrate-treatment space 33. The elongated opening 37 has the shape of a longitudinal slit extending in the substrate transport direction 5 (perpendicular to the paper plane), which is delimited on both longitudinal sides by gas-guiding elements 38a; 38b. In the cross-section shown in FIG. 3, the gas-guiding elements 38a; 38b arch over the infrared emitter 24 in a bell-like manner and are also referred to collectively below as an air-conducting bell 38. The air-conducting bell 38 ends at a distance of around 10 mm in front of the surface of the material web 3 (the substrate plane 3a).

[0106] The extraction space 31 has a gas outlet 34, which is connected to a fan (not shown in the figure). Slot-shaped extraction ducts 39, which run between adjacent IR emitter units 30 and each of which ends in front of the substrate plane 3a with the gas-guiding elements 38a and/or 38b, lead into the extraction space 31.

[0107] The infrared emitters 24 arranged in the substrate-treatment space 33 are in the form of commercial twin tube emitters. They consist of a quartz glass bulb having a cross-section in a figure-of-eight shape, enclosing two sub-areas separated from each other by a central web. Their nominal output is 3,500 W. The total emitter length is 70 cm and the external dimensions of the bulb are 3414 mm.

[0108] FIG. 4 shows a detail of the irradiation unit in a plan view of emitter units 30 in the direction of the arrow X of FIG. 3. From the plan view of the emitter units 30 in FIG. 4, the opening 37 into the substrate-treatment space 33 for the cooling air can be seen and, behind it, the infrared emitters 24. The opening width of the elongated opening 37 broadens continuously in the transport direction 5. The width of the extraction ducts 39, on the other hand, remains constant in the transport direction 5. The transport direction 5 forms an angle of 10 degrees with the longitudinal sides of the extraction ducts 39, and with the longitudinal axes 24a of the infrared emitters 24 (not visible in the figure), respectively.

[0109] The method according to the invention will be explained in more detail below by way of example, with reference to FIGS. 1 to 4:

[0110] The components of the dryer module 7 of FIG. 2 have the following functions and effects.

[0111] The front air knife 22, with the aid of the air baffle 22a, generates an intensive air stream 22b directed toward the substrate plane 3a (and onto the surface of the print substrate of the material web 3) in the transport direction 5, which breaks through the laminar flow boundary layer on the material web 3, generates turbulence and thus promotes evaporation right at the beginning of the drying process. By way of the extraction mechanism arranged downstream of the front air knife 22 in the transport direction 5, part of the air and of the components that have been swirled up by the front air knife 22 are extracted out of the dryer module 7.

[0112] So that, as far as possible, no toxic or otherwise undesirable substances in gaseous and liquid form leave the process space unfiltered and in an uncontrolled manner when the material web 3 issues from the dryer module 7, the rear air knife 27, with the aid of the air baffle 27a, likewise generates an intensive air stream directed onto the surface of the print substrate of the material web 3, which breaks through the laminar flow boundary layer on the material web 3. The process gas 27b thereby accumulating upstream of the rear air knife 27 is removed by the air exchanger unit 26 which is arranged upstream in the transport direction 5. For this purpose, multiple air curtains running transverse to the transport direction 5 are generated by the air exchanger unit 26. Using alternating gas inlet nozzles 26b and extraction ducts 26a, a supply air stream directed onto the surface of the print substrate of the material web 3 is generated at each air curtain, and this is drawn off again by an exhaust air stream immediately after impinging on the surface of the print substrate. The air exchanger unit 26 can entrain the moisture obtained as a result of the action of the infrared radiation using intensive air turbulence and can remove it by way of its integrated extraction mechanism, so that undesirable components cannot leave the dryer module 7 in an uncontrolled manner.

[0113] The treatment of the print substrate of the material web 3 in the infrared irradiation chamber 25 comprises heating using infrared radiation while at the same time exposing to dry air. In order that both treatments act as effectively as possible on the print substrate of the material web 3, the cooling air flowing into the substrate-treatment space 33 from the gas-feeding space 32 through the elongated opening 37 is divided into two process gas streams flowing along the directional arrows 28, which are guided to the infrared emitter 24 and partially around the bulb thereof. The infrared emitter 24 is cooled during this process and, at the same time, the cooling air is heated.

[0114] Between the wall of the infrared emitter 24 and the air-conducting bell 38, a narrow gap is obtained, which accelerates the two air streams flowing along the directional arrows 28 towards the print substrate of the material web 3, so that they act intensively thereon and transfer moisture into the gaseous phase or absorb it. As a result of being heated, the cooling air has an increased absorption capacity for moisture.

[0115] An exhaust air stream flowing along the directional arrows 29 leading away from the print substrate of the material web 3 is spatially assigned to each air stream flowing along the directional arrows 28 directed onto the print substrate of the material web 3, in that the directions of the inflowing air stream flowing along the directional arrows 28 and the aspirated air stream flowing along the directional arrows 29 are directed in practically opposite directions (in the exemplary embodiment they form an angle of less than 30 degrees with each other) and converge in an interaction region 35, the interaction region 35 lying on the surface of the print substrate of the material web 3. Each of the two air streams flowing along the directional arrows 28 therefore merges with an exhaust air stream flowing along the directional arrows 29 on the surface of the print substrate of the material web 3. The resulting forced interaction between the air stream flowing along the directional arrows 28 and the exhaust air stream flowing along the directional arrows 29 leads to gas turbulence in the interaction region 35, i.e., in close proximity to the surface of the print substrate of the material web 3, which can cause a disturbance, reduction or even separation of the fluid dynamic laminar flow boundary layer and an associated improvement in mass transfer and in particular the removal of moisture from the print substrate of the material web 3.

[0116] An exhaust air stream flowing along the directional arrow 29 runs between two air streams flowing along the directional arrows 28 in each case, one of which is to be assigned to one infrared emitter 24 and the other to the adjacent infrared emitter 24. As shown in FIG. 3, the following flow sequence is obtained between adjacent infrared emitters 24: air stream flowing along the directional arrow 28exhaust air stream flowing along the directional arrow 29air stream flowing along the directional arrow 28. These air streams flowing along the directional arrows 28 interact with the common exhaust air stream flowing along the directional arrow 29 and they can preferably also interact with each other, specifically on the common strip-shaped interaction region 35 on the surface of the print substrate of the material web 3. The mutual interactions of the air streams flowing along the directional arrows 28, 29, 28 generate a particularly intensive gas turbulence in the common strip-shaped interaction region 35 of the substrate surface, which disturbs, reduces or separates the laminar flow boundary layer at the print substrate surface particularly effectively so that rapid drying is achieved. The common utilization of an exhaust air stream flowing along the directional arrow 29 by two adjacent air streams flowing along the directional arrows 28 allows a close spatial arrangement of the infrared emitters 24 of the emitter array and thus effective drying at the same time as a compact construction.

[0117] Although illustrated and described above with reference to certain specific embodiments and examples, the present disclosure is nevertheless not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the spirit of the disclosure.