METHOD FOR DRYING A SUBSTRATE AND AIR-DRYING MODULE AND DRYING SYSTEM

Abstract

A method for at least partially drying a substrate. The method includes: (a) directing a supply air flow onto the substrate with a direction component in either the transport direction, or the opposite direction and (b) directing an exhaust air flow away from the substrate. The method is reproducible and effective and achieves an improved result with respect to the homogeneity and speed of drying because the exhaust air flow is split into a plurality of sub-flows by supplying each of the sub-flows to an individual intake channel, and because, in the event of a supply air flow in the transport direction of movement of the substrate, the supply air flow is arranged spatially upstream of the exhaust air flow and, in the event of a supply air flow in the opposite direction, the supply air flow is arranged spatially downstream of the exhaust air flow.

Claims

1. A method for at least partially drying a substrate moving in a transport direction, comprising the following method steps: (a) generating a supply air flow directed on to the substrate, the supply air flow having a supply air flow direction with a direction component in the transport direction or the direction opposite thereto; (b) generating an exhaust air flow leading away from the substrate; (c) splitting the exhaust air flow into a plurality of sub-flows by supplying each of the sub-flows to an individual intake channel; (d) in the case of a supply air flow having a direction component in the substrate transport direction, arranging the supply air flow spatially upstream of the exhaust air flow; and (e) in the case of a supply air flow having a direction component in the direction opposite to the transport direction, arranging the supply air flow spatially downstream of the exhaust air flow.

2. The method according to claim 1, wherein the exhaust air flow is split into at least three sub-flows.

3. The method according to claim 1, wherein the intake channels each have an intake channel suction opening facing a drying space, and wherein adjacent suction openings differ in their position and orientation in the drying space.

4. The method according to claim 3, wherein the suction openings are delimited by air baffles projecting into the drying space, and each suction opening defines an individual inflow direction for the inflowing sub-flow in each case, wherein the inflow directions of adjacent sub-flows differ from one another.

5. The method according to claim 3, wherein a plurality of suction openings are oriented such that their individual inflow directions run approximately opposite to a main propagation direction of the supply air flow.

6. The method according to claim 1, wherein the supply air flow flows out of a longitudinal slit-shaped nozzle opening and acts on the substrate to be dried in a strip-shaped manner, and the exhaust air flow is removed via a plurality of slit-shaped intake channels.

7. The method according to claim 1, wherein the supply air flow directed on to the substrate has a main propagation direction that forms an angle of between 10 and 85 degrees with the surface of the substrate.

8. The method according to claim 3, further comprising adjusting the gas volume V.sub.in introduced into the drying space so as to be smaller than the gas volume V.sub.out extracted from the drying space.

9. An air dryer module for drying a substrate having a surface and moving in a transport direction through a drying space, the module comprising: (a) a supply air unit including a supply air nozzle for generating a supply air flow directed on to the substrate, the supply air flow having a main propagation direction that forms an angle of between 10 and 85 degrees with the surface of the substrate; and (b) an exhaust air unit for generating an exhaust air flow leading away from the substrate out of the drying space (26), the exhaust air unit including a plurality of intake channels so that split the exhaust air flow into a plurality of sub-flows, wherein the supply air nozzle has a nozzle opening that faces the exhaust air unit.

10. The air dryer module according to claim 9, wherein the exhaust air unit includes at least three intake channels.

11. The air dryer module according to claim 9, wherein the intake channels include suction openings and the module further comprises air baffles that divide the intake channels, projecting into the drying space, and delimit and define at least part of the suction openings of the intake channels.

12. The air dryer module according to claim 11, wherein the supply air flow has a main propagation direction and the suction openings have individual inflow directions that are oriented such that the individual inflow directions run approximately opposite to the main propagation direction of the supply air flow.

13. The air dryer module according to claim 9, further comprising an air supply box in which the supply air unit and the exhaust air unit are integrated.

14. The air dryer module according to claim 9, wherein the distance between the supply air nozzle and the surface of the substrate is less than 10 mm.

15. The air dryer module according to claim 9, further comprising a first surface in which the supply air nozzle is formed and a second surface in which the intake channels are formed, wherein the drying space is delimited by the first surface, by the second surface, and by the substrate.

16. A dryer system for drying a substrate moving through a process space in a substrate transport direction, comprising an infrared dryer module, having a sequence of the following components, viewed in the substrate transport direction: a front air exchanger unit; an irradiation space fitted with a plurality of infrared lamps arranged parallel to one another; and a rear air exchanger unit, wherein the front and/or rear air exchanger unit contains at least one air dryer module according to claim 9.

17. The dryer system according to claim 16, wherein the rear and/or the front air exchanger unit comprises a plurality of air dryer modules arranged one beside the other and/or one behind the other.

18. The dryer system according to claim 16, wherein at least one air dryer module is arranged upstream of the irradiation space and at least one air dryer module is arranged downstream of the irradiation space.

19. The method according to claim 8, wherein Vin and Vout satisfy the equation 1.2Vin<Vout<1.5Vin.

20. The dryer system according to claim 17, wherein at least one air dryer module is arranged upstream of the irradiation space and at least one air dryer module is arranged downstream of the irradiation space.

Description

EXEMPLARY EMBODIMENTS

[0070] The invention will be explained in more detail below with reference to exemplary embodiments and a patent drawing. The individual drawings show the following schematic illustrations:

[0071] FIG. 1 an embodiment of the air dryer module according to the invention in a cross-section along the transport direction of a substrate to be treated,

[0072] FIG. 2 a cutout of the air dryer module with details of the flow behaviour inside the drying space,

[0073] FIG. 3 a further embodiment of the air dryer module according to the invention in a cross-section along the transport direction of a substrate to be treated, and

[0074] FIG. 4 an infrared dryer system equipped with air dryer modules according to the invention in a longitudinal section in the print substrate transport direction.

[0075] In the embodiment of an infrared dryer module 1 shown schematically in FIG. 4, a casing 2 surrounds a treatment space (=process space) for a print substrate 3 (=substrate), having the following components (viewed in the transport direction 5): a front air exchanger unit 6 with its own casing 10 and an additional air baffle 6a, an infrared irradiation chamber 9 fitted with eighteen infrared lamps 8, whose longitudinal axes 8a run approximately in the transport direction 5 and which are arranged parallel to one another, and a rear air exchanger unit 7 with its own casing 10. The directional arrows 20 that are marked in the irradiation chamber 9 indicate an air flow directed on to the surface of the print substrate 3 and the directional arrows 21 indicate an air flow leading away from the print substrate 3, as well as a mutual interaction 22 between these air flows.

[0076] In a dryer system, for example a plurality of the dryer modules 1 are arranged in pairs one beside the other and one behind the other, viewed in the transport direction 5. Each pair of dryer modules 1 arranged one beside the other covers the maximum format width of a printing machine. According to the dimensions and colour assignment of the print substrate, the dryer modules 1 and the individual infrared lamps can be separately electrically controlled.

[0077] The air exchanger units 6; 7 are each equipped with their own casing 10 and are inserted releasably in the casing of the dryer module 1. The air exchanger units 6; 7 are of identical construction; however, in the air exchanger unit 6 the supply air side is upstream of the exhaust air side and in the air exchanger unit 7 it is the other way round. At the exit of the dryer module 1, three air exchanger units 7 are assembled in a group, and the last air exchanger unit 7 is provided with a closing air baffle 7a. The air exchanger units 6; 7 at the same time form air dryer modules within the meaning of the invention. They will be explained in more detail below with reference to FIGS. 1 to 3. Where the same reference numerals are used in these figures as in FIG. 4, they denote components and parts identical or equivalent to those explained above with reference to the description of the infrared dryer module 1.

[0078] The cross-section of an individual air dryer module 6 shown in FIG. 1 comprises a box-like casing 1010 divided into two, which encompasses an upper supply air chamber 13, a middle supply air chamber 14 and a lower supply air chamber 15 on a supply air line (supply air channel), and encompasses a lower exhaust air chamber 16, a middle exhaust air chamber 17 and an upper exhaust air chamber 18 on an exhaust air line (intake channel).

[0079] The upper supply air chamber 13 is connected to a fan 19, by means of which dry supply air is introduced into the supply air line in a controlled manner with the volume V.sub.in. Likewise, the upper exhaust air chamber 18 is connected to a fan (not illustrated in the figure), by means of which the moist exhaust air is removed from the exhaust air line in a controlled manner with the volume V.sub.out. The process gas quantity control for the dryer module 6; 7 here is designed such that 1.2V.sub.in<V.sub.out<1.5V.sub.in. This means that the dryer module 6; 7 is pneumatically neutral in the sense that, nominally, it does not give off any other volume of gas to the environment apart from via the extraction system. On the contrary, a certain volume of extraneous air (about 20 to 50%, based on the supply air volume) is sucked into the drying module. The effect of the inflowing extraneous air is indicated in FIG. 2 with the aid of the flow arrows 37.

[0080] Between upper and middle supply air chambers (13; 14) a front perforated plate 23 is located, and between middle and lower supply air chambers (23; 24) a rear perforated plate 24 is located, wherein the front perforated plate 23 has a first number N1 of supply air through-openings, having a first mean opening cross-section A1, and wherein the rear perforated plate 24 is provided with a second number N2 of supply air through-openings, which are uniformly distributed over the perforated plate 24 and which have a second mean opening cross-section A2, wherein N2>N1 and A1>A2. The front perforated plate 23 creates a uniform distribution of the supply air volume along the rear perforated plate 24, which in turn serves to distribute the supply air uniformly along the slit-shaped air outlet nozzle 25.

[0081] The lower supply air chamber 15 is connected to a slit-shaped air outlet nozzle 25, whose longitudinal axis 25a forms an angle of 30 degrees with the surface of the substrate to be dried (print substrate 3). By way of the slit-shaped air outlet nozzle 25, a supply air stream with a main propagation direction in the direction of the longitudinal axis 25 passes on to the substrate surface and acts on the substrate (3) in a drying manner in the drying space 26.

[0082] From the drying space 26, the moisture-laden process air passes into the lower exhaust air chamber 16. Between lower exhaust air chamber 16 and middle exhaust air chamber 17 a second front perforated plate 28 is located, and between middle and upper exhaust air chambers (17; 18) a second rear perforated plate 29, wherein the second front perforated plate 28 has a first number N3 of exhaust air through-openings having a first mean opening cross-section A3, and wherein the second rear perforated plate 29 is provided with a second number N4 of exhaust air through-openings, which are uniformly distributed over the perforated plate 29 and which have a second mean opening cross-section A4, wherein N4>N3 and A3>A4. The perforation in the second front perforated plate 28 is designed such that an internal pressure that is as uniform as possible is obtained over the length of the lower exhaust air chamber 16.

[0083] The flow boundary layers that are entrained and caught on the moving substrate (3) are broken through by the supply air flow directed on to the substrate surface. The fact that the supply air flow direction has a direction component in the direction 5 of movement of the substrate (3) or in the opposite direction thereto causes a disturbance, reduction or even separation of the fluid-dynamic laminar flow boundary layer and an associated improvement in the mass transfer and in particular in the removal of moisture from the substrate (3) and the drying space 26.

[0084] The flow direction of the supply air running obliquely to the substrate 3 (main propagation direction in the direction of the longitudinal axis 25a) is important for this, as is a splitting of the exhaust air flow by an extraction system which, depending on the transport direction of the substrate, is located either spatially upstream or spatially downstream of the position of the supply air flow. In each case the supply air flow running obliquely to the substrate surface points towards the exhaust air side. The drying space 26 has a substantially triangular shape in the cross-section illustrated.

[0085] FIG. 1 shows the case of a supply air flow having a flow direction component against the transport direction of the substrate 3. The supply air flow here is arranged spatially downstream of the exhaust air flow in the transport direction. As a consequence of the inflow angle and the opposite extraction system, a vortex formation of the inflowing and outflowing drying air starts, as indicated by the directional arrow 27. The direction of rotation of the forming air vortex 27 runs clockwise. To prevent a distinct vortex formation, the exhaust air flow is split into a plurality of sub-flows with the aid of air baffles 30; 31. The air baffles 30; 31 are angled in the opposite direction to the direction of rotation of the forming air vortex and form individual intake channels 41; 42; 43 for a total of three sub-flows, as can be seen from FIG. 2.

[0086] Vortex formation is reduced by splitting the exhaust air flow into a plurality of sub-flows and an initially forming air vortex is channeled in the intake channels 41, 42, 43. The flow behaviour inside the drying chamber 26 is indicated schematically by the flow arrows 37, 38 and 39, with the supply air flowing into the drying space 26 being denoted by the reference numeral 38 and the exhaust air after reversing direction being denoted by the reference numeral 39. The extraneous air flowing in independently thereof is denoted by the reference numeral 37.

[0087] The channeling of the exhaust air flow in the intake channels 41, 42, 43 is effected by the angled air baffles 30; 31, which project into the initially and partially forming air vortex 27 at different positions. They define suction openings 41a, 42a, 43a of the intake channels 41, 42, 43 (marked by broken lines in the drawing). Adjacent suction openings 41a, 42a, 43a differ in their position and orientation in the drying space 26. As a result, sub-flows are picked up from the exhaust air flow vortex 27 at different positions and in different directions. Each of the suction openings 41a, 42a, 43a is defined by an individual surface normal. In each case the surface normal approximately reproduces the inflow direction of the relevant sub-flow into the intake channel 41; 42, 43. The directions of the surface normals and thus the inflow direction differ from each other and form an angle of around 180 degrees+/30 degrees with the supply air flow direction (longitudinal axis 25a).

[0088] The local positions in the drying space 26 at which the splitting of the exhaust air flow takes place are located where said exhaust air flow vortex 27 would otherwise form in a distinct manner. This vortex is at least partially dissipated thereby so that, by splitting the exhaust air flow, the formation of a distinct exhaust air flow vortex is counteracted, and effective, energy-saving extraction becomes possible. In the method according to the invention, thanks to these measures, rapid and effective drying of the substrate 3 is achieved together with low energy consumption.

[0089] FIG. 3 is a diagram of a consecutive arrangement of three air dryer modules 7 according to the invention as in FIG. 1. This arrangement is employed e.g. at the exit of an infrared dryer module 1 according to FIG. 4. As a result, when the print substrate 3 issues from the infrared dryer module 1, as far as possible no toxic or otherwise undesirable substances leave the process space in gaseous and liquid form in an unfiltered and uncontrolled manner.