Process and apparatus for drying a liquid layer deposited onto a moving carrier material.

p0001The invention relates to a method and an apparatus for drying a coating applied on a moving through a drying zone carrier liquid layer, which contains vaporizable solvent components and non-vaporizable components.

p0002During the drying of large-scale, web-shaped goods on which liquid layers are applied, different drying methods and drying devices are applied. Typical drying goods are, for example, metal or plastic bands on which liquid layers are applied that are usually made of volatile solvent components that are removed from the liquid film during the drying process, and of non-volatile components, which remain on the substrate after drying.

p0003The surfaces of the support materials obtained by coating the specific characteristics which are present only after the drying process in the form in which they are desired for the later use. As example of this, the coating of metal strips may be called with light-sensitive layers which are assembled to printing plates. The coating of metal strips or plastic films with substances in the form of a solvent-containing wet film, hereinafter called liquid film, and its subsequent drying thus represent an operation that requires special equipment, to ensure the desired quality of the product layers. A key factor here is the step of drying the film as a final process step of coating.

p0004In the drying of liquid films on substrates, it is usual, a heated gas, particularly air, to flow to remove the solvent components of the film layer over the surface of support materials. In this case, the heated gas stream is brought into direct contact with the liquid film, which is applied in a uniform layer distribution on the support material, which passes through a drying apparatus. To ensure that streaks and melierfreie, dried film surface, a uniform distribution of the remaining components, the driers are equipped with devices which are intended to bring a convenient and uniform distribution of the air flow through the liquid film. Thus a uniform drying over the entire width of the coated web is desired. Furthermore, known drying installations on facilities to minimize disruption of the movement of air, which, in part, detrimental because turbulent flow movements on the film surface and cause Meliererscheinungen.

p0005A typical construction of such a drying apparatus is in accordance with US patent 3,012,335 therein, from a supplied with gas dryer gas space, which is arranged over a certain length over the coating path, via means of a plurality of slots, nozzles, holes or porous solids direct gas space the liquid to be dried film as uniformly as possible to supply gas dryer. The continously coated tape or coated boards on a circulating conveyor belt are in this case passed continuously and with the release of solvent vapor to the drying air through the drying apparatus. Here, the supplied air dryer in an open circuit can constantly renewed and enriched solvent air be completely discharged. It can also be a re-circulation process are applied with partially renewed or dissipated drier air.

p0006Difficulties in discharging the drier air from the drying space often are that when arranged transversely to the strip running direction longitudinal nozzles or longitudinal slots, due to the pressure gradient in the lateral outflow, a reduction of the nozzle exit velocity occurs at midspan and therefore also affects the heat and mass transfer transversely to the strip running direction becomes. The consequence of this is an edge overdrying, which causes many coating operations to undesired textures of the dried films.

p0007In the journal "Chemie-Ingenieur-Technik", Volume 42, Issue 14 (1970), pp 927-929, Volume 43, Issue 8 (1971), pp 516-519 and Volume 45, Issue 5 ( 1973), pp 290-294 are therefore given optimization suggestions concerning the design of nozzle arrays in slot nozzle dryers which are designed to provide constant heat and mass transfer over the entire bandwidth of a dryer. To optimize slot nozzle dryers mass transfer measurements are correlated empirically with impingement of slot nozzle arrays with different nozzle areas in a wide range of external influencing factors. The relationship found is used to determine optimum nozzle geometries with respect to the fan power per m² goods area. It turns out that a constant heat and mass transfer is achieved over the web width, characterized in that the nozzle slots continuously from the web edge to the center have increased slot width.

p0008When drying large area webs high uniformity of heat and mass transfer over the web width must often be required in order to avoid local over-drying and associated deterioration. In these cases, preferably slot nozzle arrays are used, in which the slots are arranged transversely to the running direction of the web. The observed edge overdrying in the slot nozzle dryers with outflow in the slot direction is due to the distribution of exit velocity along the slots. To avoid this edge overdrying, follows for jet dryer therefrom, inter alia, that the flow-off should be possible 3.5 times the nozzle outlet area in order to obtain a uniform drying across the width of the web.

p0009It is state of the art, contactless make in flotation dryers for sheet or metal strips by means of a carrier air jet system, a surface treatment (magazine "gas heat internationally", Volume 24 (1975), No. 12, pp. 527-531). It is thereby enriched solvent dryer air sucked directly into the nozzle arrays again to eliminate the unwanted transverse flow. This results in so-called jet dryer or impact jet dryer, in which mainly the stagnation point-like flow of individual nozzles is disadvantageous that tends both laminar and in turbulent flow form to physical flow instabilities that inevitably lead particularly in low-liquid films in irreversible drying structures.

p0010To avoid stagnation point-like flows in the initial region of the dryer apparatus, the drying air is fed from an anteroom via suitable inlet openings and flow deflectors in a calming space to the PCT application WO82 / 03450, from there, a portion of the dryer air over a arranged in close proximity to the liquid film porous filter element to the web to be dried. The operation of such a drying is based on the fact that forms between the porous shield and the liquid to be dried film a calmed, to solvent but highly enriched, low air flow, which is constantly renewed by exchange with the the porous medium transversely flowing residual air and thus, due to the relatively short length, a pre-drying of the liquid film is achieved with a reduced tendency to Meliererscheinungen.

p0011This type drying is characterized by vast diffusion of the solvent vapor / air mixture through the porous shield, which in almost completely absent convective transport within the space between the belt and shield complete desiccation of the liquid film is only possible in very large dryer lengths or switching in subordinate auxiliary dryers.

p0012A particular disadvantage of previously used drying devices is that due to the solvent-laden air flows a compatible with the outside atmosphere sealing means must be provided within the dryer chamber. Depending on the size of the absolute pressure within the drying room directly above the liquid film flows in vacuum conditions, either a part of the required fresh air over the finite sealing gap inwards or at elevated pressure conditions a part of the solvent-laden air to the outside, by the flow in the sealing gap on the undried liquid film irreversible structures can be produced.

p0013Object of the invention is to provide a method and an apparatus with which to support materials applied liquid layers in continuous operation can be dried so that the surface structures that interfere with the uniform distribution of the dried film layer and impair the desired properties could, both high not occur for low-viscosity liquid layers.

p0014This object is achieved by a method of the kind described in the opening such that a gas flows in the longitudinal direction of the carrier material parallel to the liquid layer and is accelerated in the direction of flow within the drying zone.

p0015The gas flows at the same or opposite direction to the running direction of the carrier material along and parallel to the liquid layer and is accelerated in the direction of flow within the drying zone.

p0016In embodiment of the method, the initial rate is v₁ the gas flow increased v₂ to a top speed that is v₁ up to 1000 times value of the initial velocity. There, the velocity distribution of the gas flow in the individual cross sections of the drying zone is adjusted transversely to the running direction of base material constant.

p0017In an embodiment of the method, the gas is heated and the total gas stream is extracted at one end of the drying zone. Suitably the drying zone is designed so that damped at the inlet and in the drying zone occurring disorders such as vortex and turbulence in the gas flow, through the accelerated gas flow and laminar. Thereby, the method is either applied in such a way that the flow through the drying zone takes place at a constant volumetric gas flow, wherein the cross section of the drying zone is continuously reduced in the running direction of the carrier material or in such a way that the gas flow is in the direction of the carrier material is constantly increasing, with a constant cross-section the drying zone or even with decreasing cross-section of the drying zone.

p0018In the method, introduced into the drying zone turbulence of the gas flow are immediately attenuated by the direction of flow locally accelerated gas flow and obtain a substantially laminar flow.

p0019In a further embodiment of the method the carrier material runs vertically through the drying zone through and carries a side of the substrate a liquid layer, which is dried.

p0020It is also possible that the carrier material is provided on both sides with liquid layers and both sides of the substrate are dried by opposite direction to the vertical direction of the substrate flowing drying gas. The carrier material can pass even with the applied on its lower liquid layer horizontally or obliquely through the drying zone, wherein the drying gas flows below the carrier material along the hanging liquid layer.

p0021Thereby, the method is either applied in such a way that the flow through the drying zone takes place at a constant volumetric gas flow, wherein the cross-section of the drying zone against the running direction of the carrier material constantly less or such that the volume of gas flow against the running direction of base material is constantly increasing, with uniform cross-section of the drying zone or even with ever a decreasing cross-section of the drying zone.

p0022In the process, for example, the support material occurs below through the dryer inlet in the drying zone, leaves it up through the dryer outlet and directed from top to bottom total gas stream is sucked close to the dryer inlet.

p0023An apparatus for drying a coating applied to a moving carrier material liquid layer, which contains vaporizable solvent components and non-vaporizable components, having a drying channel, through which the carrier material runs in the longitudinal direction, with a gas-permeable channel-covering surface, flows through which a stream of drying gas into the drying channel, characterized characterized in that the channel-covering surface is formed as a gas-permeable surface, with an adjustable in the longitudinal direction of the drying channel permeability of the surface for the drying gas stream.

p0024In a development of this device, the channel-covering surface is inclined with respect to the horizontally extending channel base surface, wherein the channel inlet height of the drying channel is greater than the Kanalauslaßhöhe.

p0025In another embodiment of the device the channel-covering surface is inclined to the vertically extending channel base surface, wherein the channel inlet width of the drying channel is smaller than the Kanalauslaßbreite. Here, the channel inlet is the region where the coating material enters the channel.

p0026The further development of the invention results from the features of claims 19 till 35, 37 and 43rd

p0027With the invention, the advantages are achieved that with relatively simple construction which cause a certain gas flow management in the drying channel, the desired interference-free drying low- and high-viscosity liquid layers on substrates. The mean velocity of the gas flow from an inlet velocity v₁ v₂ at an exit velocity over the length of the drying channel, which is considerably greater than V₁, increased. The velocity distribution is made constant in the individual drying channel cross-section, and the geometry of the drying channel is designed so that the gas disturbances occurring in the inlet cross-section and in the drying channel to be stripped by the gas accelerating and that the necessary drying total air stream is sucked off at the end of the drying channel.

p0028The gas stream is at the channel inlet, where the liquid layer is most sensitive to Verblasungen, laminar. The high flow rate results in the channel inlet area to a quick dissipation of the solvent. The liquid layer dries quickly and is stable to turbulent flows, which may occur at the expanded channel outlet. In a vertical tape of Tägermaterials from bottom to top, the heavy solvent vapors are exhausted through the opposing gas flow in the direction of gravity, and not the opposite thereof.

p0029It must be set no slow-flow inlet zone, and it does not matter whether occurring turbulence in the low flow velocities at wide channel outlet or not, since the layer is there already dry. The air flow can be greatly accelerated and thus the drying section are shortened ver. The heat transfer in the drying zone is determined inter alia by the gas velocity. In the same direction the gas flow Bandanwärmung and thus the drying takes place closer to the channel outlet, closer to oppositely directed gas flow at the channel inlet of the drying zone.

p0030The invention is explained below with reference to exemplary embodiments schematically shown in more detail. Show it:<ul><li>Fig. 1 is a schematic sectional view of a first embodiment of the drying apparatus according to the invention,</li><li>Fig. 2 is a schematic sectional view of a second embodiment of the drying apparatus according to the invention, with a narrowing drying duct having a rectangular cross-section</li><li>3 shows a section along the line I -.. I of the drying apparatus of Figure 2,</li><li>FIGS. 4A and 4B each is a perspective view of a drying channel with a trumpet-shaped geometry which can be used in place of the drying channel of rectangular cross section in the embodiments of Figures 1 to 3, 9 and 10, </li><li>Fig. 5A is a sectional view of a third embodiment of the drying apparatus with variable permeability of the top surface, partially broken away, according to the invention,</li><li>FIG. 5B is a sectional view of a fourth embodiment of the invention, similar to FIG. 5A, with constant permeability of the top surface,</li><li>Fig. 6 shows a fifth embodiment of the drying apparatus according to the invention in section;</li><li>Fig. 7 is a velocity profile of the gas flow in dependence of the channel length of the drying channel,</li><li>Fig. 8 is a pressure profile, namely the static negative pressure of the gas flow relative to atmospheric pressure, as a function of the channel length of the drying channel,</li><li>Fig. 9 is a sectional view of a sixth embodiment of the drying device for one-sided drying of the carrier material according to the invention,</li><li>Fig. 10 is a schematic sectional view of a seventh embodiment of the drying apparatus for drying both sides of the carrier material according to the invention, with two narrowing drying channels with rectangular cross section,</li><li>Fig. 11A and 11B is a schematic detail section in the area of ​​the channel inlet of a drying apparatus, in the negative pressure, the carrier material is guided, and a schematic sectional view in the region of the channel inlet in a slightly modified embodiment compared to FIG. 11A,</li><li>FIG. 12A is a sectional view of an eighth embodiment of the drying apparatus with variable permeability of the top surface according to the invention,</li><li>FIG. 12B is a sectional view of a ninth embodiment of the invention, similar to FIG. 12A, with constant permeability of the top surface,</li><li>Fig. 13 shows a tenth embodiment of the drying apparatus according to the invention, in section, in which the running direction of base material strip and the direction of flow of the drying gas are in the same direction, and</li><li>Fig. 14 is a schematic sectional view of an eleventh embodiment with a horizontally guided strand of the substrate web on which a liquid layer is applied, which faces downward.</li></ul>

p0031In figure 1 a first embodiment of a drying apparatus 1 is shown according to the invention in a schematic sectional view. A carrier material strip 4, such as a metal tape of aluminum foil or a tape runs past a slot die 34, from which a liquid layer is applied to the carrier material strip 4, which contains vaporizable solvent components and non-evaporable components. The carrier material belt 4 is passed around a guide roller 35 and passes through an inlet channel 27 which has an inlet cross-section A1, in a drying channel 2. The base substrate tape 4 runs in the drying channel 2 and in a subsequent to the drying channel 2 passage channel 20 on support rollers 6 which recessed in the horizontal channel base surface 3 and are embedded in the duct floor. The drying apparatus 1 can be designed as a dryer, in which the carrier tape 4 is guided freely suspended over air jets carrying through the drying channel 2 and the carrier air is discharged laterally.

p0032A channel-covering surface 7 is designed as a gas-permeable surface that is inclined with respect to the horizontally extending channel base surface 3, wherein the channel inlet height h1 of the channel inlet 27 of the drying channel 2 is greater than the Kanalauslaßhöhe h2 of the passage outlet 28, having an outlet section A2. The channel-covering surface 7 is for example equal to 3 ° 9 'inclined to the horizontal channel base surface 3 at an angle, wherein the permeable channel-covering surface, starting extends to the channel inlet 27, over the entire length of the drying channel second

p0033Above the drying channel 2 there is a drying chamber 5, the intermediate wall 10 separates from a gas exchange chamber 15th In the gas exchange chamber 15, a fan 12 and a fan is arranged, the fan output is 16 directed to a heat exchanger 17 in the partition 10th In a bottom surface 18 of the gas exchange chamber 15 there is an opening in which a choke device, for example, is arranged a throttle valve 13 which is adjustable about a horizontal axis. The gas exchange chamber 15 has a gas inlet 19 that connects to the top surface of the gas exchange chamber 15 and the throttle device includes a throttle fourteenth The throttle device may consist, inter alia, of two mutually displaceable perforated plates or of a slat screen device.

p0034The fan 12 is a double-flow circulation fan with return blades, wherein the gas from the inlet 19 to the back vanes added stream of fresh gas is fed into the drying space. 5

p0035The flow-through channel 20, which connects to the drying channel 2, has a uniform cross section corresponding to the Kanalauslaßquerschnitt A2 of the drying channel. The underside of the bottom surface 18 of the gas exchange chamber 15 is at the same time the top surface of the furnace channel. Above the top surface of the flow channel, according to the gas exchange chamber 15 is a fan or a suction fan 9, the suction opening is located in the top surface of the furnace channel. In an outlet 11 of the suction fan 9, a throttle valve 8 is arranged.

p0036The channel-covering surface 7 consists for example of a continuous filter with constant permeability.

p0037Figure 2 shows a schematic sectional view of a second embodiment of the drying apparatus 1 according to the invention, which has compared to the first embodiment on the top side of the channel-covering surface 7 additional metering devices 21 for the gas to be added. In the gas is in general to heated air. The drying channel 2 is similar to the drying duct of the first embodiment formed with a horizontal Kanalgrund- or bottom surface 31 and a thereto inclined channel-covering surface 7 has the gas or air flow in the inlet cross-section A₁ of the channel inlet an inlet velocity v₁ of nearly zero, while the outlet speed v₂ in the outlet area can be up to 75 m / sec A₂ of the passage outlet. In Figure 2, for reasons of clarity, the suction fan, which is covered in Figure 1 by the reference numeral 9, is not shown, though it, as in the first embodiment is available.

p0038The metering devices 21 consist of boxes with two mutually displaceable diaphragms 22, 23, whose opening cross-sections are adjustable. This aperture 22, 23 are either directly above one another or have, as shown, a distance from each other on. Depending on the setting of the opening sections of the pinhole 22, 23 (see FIG. Fig.en 3A and 3B), different permeabilities of the individual boxes of the metering devices 21 so that sections, to pass through according to the lengths of the boxes, different amounts of air, the channel-covering surface 7. Thus, it is possible to the without the dosing adjusting different gas flow distribution over the length of the drying channel 2 to settle in the drying channel 2 inflowing gas or air flow in addition differently.

p0039Above the carrier belt 4 prevails in the gas exchange chamber 15, for example, a negative pressure of 3.35 mbar with respect to atmospheric pressure, while the blower output of the blower 12, an overpressure of 1.4 mbar is present. In the drying chamber 5 above the dosing 21 of overpressure is about 1.1 mbar.

p0040The bottom surface 31 of the drying apparatus has a plurality of openings 32, one of which the gas exchange chamber 15 is opposite to and acted upon by the same suction pressure or under pressure as prevails in the gas exchange chamber. This ensures that the carrier tape material 4 which passes through the drying channel 2 on support rollers 6, is acted upon from both sides with the same negative pressure, so that a lifting of the carrier material strip 4 is prevented, as normally occurs in the direction of gas exchange chamber 15, if only prevails in this vacuum.

p0041The remaining openings 32, which can also be arranged in the side walls, just above the soil surface, allowing a suction which are in close proximity to the side walls of the gas layers.

p0042As can be seen from Figure 3, which shows a section along the line I - I represents the drying apparatus 1 according to Figure 2, the drying channel cross-section is rectangular, with the channel height in the direction of the Kanalauslaßquerschnitt A₂ linearly reduced. The channel-covering surface 7 and the metering devices 21 are embedded for example in the sidewalls 29, 30 of the drying channel second In the bottom surface 31 of one of the openings can be seen 32nd

p0043In the figures 4A and B depending on a drying channel 2 is shown in perspective that has a longitudinally from the channel inlet to the channel outlet tapering trumpet-shaped geometry. Such a drying channel can be used in the embodiments of Figures 1 to 3, 9 and 10 instead of the drying channels shown there. By tapering trumpet-shaped geometry of the drying channels ensures that there is an acceleration of the air or gas flow in the flow direction. The drying duct according to Fig. 4A has a curved top surface and curved side walls, while the drying duct rectangular in Fig. 4B are cross-sectional, that is oriented perpendicularly to the bottom surface of side walls, but has a curved top surface.

p0044The acceleration of the flow in the drying channel can be achieved by two different modes of operation, or by a combination of these two modes of operation. In the first mode of operation the flow through the drying channel 2 is effected with a constant air flow, which is present in all cross-sections of the drying channel, wherein the cross-sections of the drying channel in the strip running direction of the inlet cross section A₁ to the outlet section A₂ are constantly smaller. The length-dependent reduction of the channel cross-section is designed so that stripped in the flow introduced disorders and the flow therethrough is laminar. This is done in such a way that, for example v₁ across the suction fan 9 and the fan with closed throttle devices 13 and 14 of the first embodiment of Figure 1, the required for the drying gas or air flow with the entrance speed sucked in via the duct inlet 27 to the inlet cross-section A1 and over the inclined in the strip running direction channel-covering surface 7 on the exit velocity v₂ the channel outlet 28 to the outlet area A₂ is accelerated. The setting of adequate air volume stream takes place here by speed control of the exhaust fan 9 and the fan and speed-independent operation by adjusting the throttle valve 8 in the outlet 11 of the suction fan. 9

p0045In the second operation, the addition of the necessary for the drying gas or air volume flow via suitable metering devices, which are mounted in or over the channel-covering surface is done. The gas or air flow in the drying channel is in the tape running direction is constantly increasing or adjusted so that interference is stripped and the gas or air flow changes into a laminar flow. For this purpose, in the embodiments of the invention, as illustrated in Figures 1 to 5B, the embodiments according to Figures 5A and 5B will be described in more detail below, the drying required gas or air flow in the drying chamber 5 via the blower 12 or the circulation fan with back vanes at open throttle 13 and 14 promoted. From the drying space 5, the amount of air or gas flows through the metering apparatus and the channel-covering surface 7 in the drying channel 2 and is accelerated in the latter to the exit velocity v₂ in the outlet section A₂. The fan 9 and the fan case is adjusted so that only the on the back vanes of the blower 12 or the circulation fan added gas is exhausted from the drying chamber 5 and the amount of residual gas is constantly conveyed in the circulation. It is thereby achieved that in the inlet cross-section A₁ almost no flow or only a very low flow occurs.

p0046In the embodiments of the invention, as illustrated in Figures 9 to 12B, the embodiments will be described in greater detail in FIGS 12A and 12B, the need for drying gas or. Air flow through the metering apparatus and the channel-covering surface 7 and / or the channel outlet 28 conveyed into the drying channel 2 and in this accelerated to the exit velocity in the channel inlet cross-section.

p0047It is thus achieved that the channel inlet cross-section occurs the maximum velocity over the length of the drying channel.

p0048In the first operation of the embodiments of FIGS. 1 to 5B of the inlet cross-section A₁ is designed as large for optimum operation, and the initial velocity v₁ so small held that occur on the liquid to be dried film no Anfangsstöreffekte in the form of mottling or large Verblasungen ,

p0049In the simplest case of operation, the coated substrate tape 4 is guided in the immediate vicinity of the horizontal channel base surface 3 and the flow acceleration brought about by the flow direction in a straight line sloping channel-covering surface. 7 The shape of the channel cross-section is rectangular, and the channel height decreases linearly from the channel inlet height h1 to h2 Kanalauslaßhöhe. The same effect is achieved, for example those shown in Figures 4A and B trumpet shaped geometries of the drying channel second In addition, other channel geometries are possible, as long as they bring a required direction of flow acceleration.

p0050In the first mode of operation according to the embodiments of FIGS. 9 to 12B, the coated substrate material band 4 is guided in the immediate vicinity of the vertical channel base surface 3 and the flow acceleration brought about by the converging in the flow direction to the channel base surface channel-covering surface 7. The shape of the channel cross-section is rectangular, and the channel width decreases linearly from the Kanalauslaßbreite b2 on the channel inlet width b1. The same effect is achieved, for example those shown in Figures 4A and B trumpet shaped geometries of the drying channel second In addition, other channel geometries are possible, as long as they bring a required direction of flow acceleration.

p0051In the second operation, in particular those stemming good drying results, if, in a rectangular channel cross section horizontally or vertically extending channel-covering surface 7 is designed as a continuous, gas-permeable filter. At constant channel cross-section over the length of the drying channel, in other words, with a horizontally or vertically and extending parallel to the channel base surface channel top surface is at a constant Filterpermeabilität along the Trock voltage channel due to the rising gas stream of from the desired acceleration of the flow, which, in addition can still be controlled by the changing permeability of the continuous filter. The channel-covering surface 7 need not consist of a continuous filter, but rather may also juxtaposed, equally thick filter mats 26 (see. FIGS. 5A and 12A) are made with different permeability. This can also be achieved in that the filter mats have the same consistency or same construction, but have different thicknesses. Another possibility is, however, to design the filter mats having the same thickness, with different structure and different consistency.

p0052In an inclined channel-covering surface 7 of the quantity of gas flow and thus the flow acceleration is determined by the inclination of the channel-covering surface. If the inclined channel-covering surface 7 consists of a continuous filter or filter mats, possess these expediently uniform structure and uniform consistency and thus constant permeability over the length of the drying channel. 2

p0053The combined use of the first and second mode of operation has especially advantageous when, liberated solvent vapors should be exhausted already in the coating, which is performed usually immediately before the drying apparatus 1 through the slot die 34th

p0054The accelerated flow both in the first and in the second mode transmits apparent upon in several ways for quick drying the liquid layer and the free surface structure refinement of the coated carrier material strips. Tests carried out show that macroscopic flow turbulence, which are produced for example by the addition points of the gas or air stream, be attenuated in the drying channel 2 at the correct setting of the first or second mode of operation, that disturbance of the drying process may occur immediately after the addition points more, ie the flow is laminar already very close to the place of origin of the turbulence. Observations show that this is enforced by the induced acceleration of the turbulent sections of the gas or air flow while the longitudinal alignment or longitudinal deformation of this turbulent areas.

p0055The accelerated gas or air flow is parallel to the substrate tape in tape nearby and is the same or opposite directions directed to the running direction thereof, so that the diffusion paths of the evaporating through the relative to the liquid film immmer faster expectant air / gas flow and its boundary layer flow near the liquid film be solvent kept small and therefore at high terminal velocity of the gas / air flow, but less drying channel length, a large heat and mass transfer is made possible by the liquid layer to the drying medium.

p0056In a convergent drying tunnel at air flow from top to bottom and the opposite direction to the strip running direction, layers are produced without Verblasungen, wherein the air flow and the solvent vapors of gravity follow.

p0057The present across the width of the material to be dried, liquid coated substrate web 4 constant rate of flow results in a very uniform drying of the liquid film transversely to the running direction. This means that the velocity distribution of the gas / air flow in the individual cross sections of the drying zone and the drying channel has to be held transversely to the running direction of the substrate web constant.

p0058Figure 5A shows a schematic sectional view of a third embodiment of the drying apparatus 1, wherein the drying channel 2 has a horizontally extending channel-covering surface 7, which runs parallel to the channel base surface 3rd The horizontal channel-covering surface 7 consists of juxtaposed, equally thick filter mats 26 that have different permeability for a gas or air. In Figure 5A, the different permeability is indicated by different degrees hatching of the individual filter mats 26, in such a way that the filter mat near the channel inlet is more shaded, according to their lower permeability, and the hatching of the filter mats 26 remo men toward the passage outlet to indicate that the permeability of the filter mats increases in the running direction of the substrate web 33rd The remaining components of the drying apparatus, which correspond to the components of the first and second embodiment of the drying apparatus are denoted by the same reference numerals as in FIGS. 1 to 3 Before the channel inlet 27 of the drying channel 2 is a Abdichtmatte 36. The channel cross sections are constant over the length of the drying channel. 2 Due to the different permeabilities of the filter mats 26 each have a different gas / air quantity flows through the filter mat 26, as indicated by the size of the ge is indicated bent arrows P₁ to P₅, which are assigned to the individual filter mats 26th By carried out towards the channel exit gain of the supplied gas / air volume results in an acceleration of the flow in the direction of the substrate web 33. This acceleration or the speed increase of the flow on the channel outlet through is given by the increasing speed of arrows v_iWhich are located parallel to the carrier material web 33, as indicated.

p0059The fourth embodiment shown in Fig. 5B, will match with the exception of the top surface, with the third embodiment. The top surface 7 of the fourth embodiment has constant permeability over the channel length. Since the upper surface on the amount of gas supplied current increases in the direction of outlet section even at a constant permeability of the top surface, an acceleration of the flow takes place in running direction of base material strip 33rd

p0060Of course, it is also possible that the built up of filter mats 26 of gas / air-permeable channel-covering surface 7 is not horizontal, ie parallel to the channel base surface 3, extends, but, as with the first and second embodiment of the drying apparatus according to the invention, is inclined to the channel base surface 3 , The channel-covering surface 7 may be made from lined-up filter mats of the same structure and the same consistency, but different thicknesses exist, wherein the thickness of the filter mats decreases in the direction of the substrate web 33, in other words, the permeability of the filter mats increases toward the passage outlet.

p0061In the filter or the filter mats is commercially available so-called Laminardurchflußfilter as they are used for example in Zuluftfilteranlagen of clean-rooms. Filter These filter elements out one hand dirt particles from the gas / air flow and ensure the other hand for a very uniform laminar flow through the individual filter elements and into the drying channel into.

p0062Figure 6 shows a fifth embodiment of the drying apparatus according to the invention in section, wherein the channel-covering surface 7 is inclined relative to the horizontal channel base area 3rd The channel-covering surface 7 is gas / air-permeable and consists of a continuous filter but can also be made of rows of filter mats, as shown in Figure 5A. Above the channel-covering surface 7 are metering devices 24, the fins contain 25, which are mutually adjustable. The single blade is parallel to the channel-covering surface 7 and is adjustable along its longitudinal axis. The arrangement of the blades 25 and their adjustability is approximately comparable to the sun visor, which are composed of blades and is indicated in Fig. 6, in which the fins 25 near the inlet cross-section A₁ are parallel and displayed near the outlet section A₂ perpendicular to the deck surface 7.

p0063The remaining components of the fifth embodiment correspond to the corresponding components of the first to third embodiments of the drying apparatus, and their description will not be repeated.

p0064Figures 7 and 8 show a speed profile of the gas / air flow or a pressure profile, namely the static negative pressure of the flow in relation to the atmospheric pressure, each as a function of the channel length of the drying channel. The course of the velocity profile is very similar to the shape of the pressure profile over the channel length. By the middle of the channel length, which is about 5.4 m in the present case, the velocity of the flow and the negative pressure increases approximately linearly with the channel length, while in the second half of the drying channel a strong exponential increase these variables occurs.

p00659 shows a sixth embodiment of the drying device 1 is shown according to the invention in a schematic sectional view. The carrier material strip 4, such as a metal strip made of aluminum or a foil strip running past the slot die 34, from which a liquid layer is applied to the carrier material strip 4, which contains vaporizable solvent components and non-evaporable components. The carrier material belt 4 is passed around the guide roller 35 and runs vertically upwards through a duct inlet 27, having a channel inlet width b1, in the drying channel 2 a. The carrier material belt 4 runs in the drying channel 2 to carrier rollers 6 which recessed in the vertical channel base surface 3 and are embedded in the duct floor. The drying apparatus 1 can be designed as a dryer, in which the carrier tape 4 is guided freely suspended over air carrying nozzle. The substrate material band can be guided in the channel inlet area by vacuum on the channel bottom fitting and then through supporting rolls through the drying channel. 2

p0066The channel-covering surface 7 is designed as a gas-permeable surface that is inclined relative to the vertically extending channel base surface 3, wherein the channel inlet width b1 of the channel inlet 27 of the drying channel 2 is smaller than the Kanalauslaßbreite b2 of the passage outlet 28 is. The channel-covering surface 7 extends, for example, starting at the channel inlet 27, over the entire length of the drying channel second

p0067The channel-covering surface 7 consists of a continuous filter with constant permeability. The cross-sections of the drying channel 2 are rectangular, with the channel width of the channel inlet 27 increases linearly in the upward direction on the Kanalauslaßbreite b2. Laterally from the drying duct 2, an air space 67 of the drying apparatus is 1. In the vertical side wall of the air chamber 67 inlet ducts 44, 45, 46 are arranged, by the drying gas, in particular heated air flows and in the channel-covering surface 7 in the direction of the arrows P the drying channel 2 occurs. Upwardly the channel outlet 28 of the drying channel 2 is closed by a Einströmkasten 39 with a filter mat 48, by the drying gas in the flow direction B downwards in the opposite direction to the running direction A of the substrate web 4, flows through the channel inlet 27 into a suction box 37, the channel inlet to closes downwards. The suction box 37 is equipped with a filter mat 47 and a diagonally arranged perforated baffle 49 which prevents the formation of eddies in the gas flow. It may also be 39 equipped with a perforated baffle 73 of Einströmkasten. The baffle 49 can also be omitted if the filter mat 47 alone is sufficient to suppress vortex formation. In the event that the incoming via the channel outlet gas flow in the convergent drying duct 2 alone is sufficient for drying, the channel-covering surface 7 can be made of impermeable material, and blowing a drying gas through the side wall falls ent, so that the inflow channels of the vertical side wall can be omitted drying device. 1

p0068The drying channel 2 is completed on channel inlet 27 and the channel outlet 28 by leaf seals 38 and 40, or labyrinth seals as tightly as possible against the moving substrate material band. 4 The lamellae seals 38 and 40 are mounted on the vertical outer walls of the suction box 37 and the Einströmkastens 39 which are facing the carrier material band. 4 At the channel inlet 27 for the carrier material strip 4, the drying gas is drawn through the suction box 37 therethrough, depending on the narrowing of the channel cross-section and the amount of the fed or sucked off the drying gas results in a speed increase of the gas flow from top to bottom in the drying channel 2, suppresses turbulence. The duct outlet 28 emerging from the substrate material band 4 is guided by a guide roller 36 from the vertical direction in a certain direction for further processing.

p0069When the running direction A of the substrate tape 4 opposing flow of the drying gas can be seen that in the convergent downward drying channel 2, the liquid layer structure freely dried on the substrate band 4 without Verblasungen. In this type of drying, the gas flow and the liquid layer resulting from the solvent vapors of gravity follow. The dried in the opposite direction to the laminar, accelerated downward gas flow layer on the Trä germaterialband 4 shows no Verblasungen caused sometimes by force of gravity and peeled falling solvent vapors. This can be demonstrated by stall tests, in which the provided with the liquid substrate material band 4 stopped in the drying channel 2, and is shown with the help of Strömungsprüfröhrchen that vortex of solvent vapors not occur.

p0070Fig. Figure 10 shows a schematic sectional view of a seventh embodiment of the drying apparatus for drying both sides of the carrier material strip 4 which carries a layer of liquid, for example, on both sides and vertically passes from below upward through the drying apparatus. The two drying channels 2 and 2 'are formed symmetrically to the vertical. In Figure 10, the external of the drying channel 2 components that connect to the Einströmkasten 39 and the suction box 37, shown as the same, the right drying channel 2 'connected components have been omitted to simplify the drawing.

p0071The carrier material belt 4 runs obliquely from top to bottom in a container 50 with the liquid to be applied from vaporizable solvent components and non-vaporizable components a and around a deflecting roller 51 vertically upwardly through the nip of nip rolls 52, 53 and between the suction boxes 37, 37 'guided in the drying apparatus.

p0072In the container 50, the carrier material sheet 4 is coated on both sides with liquid, the excess of which is squeezed off in the gap between the nip rollers 52, 53rd Of course, other known application methods can be used for coating both sides of the substrate web. 4 Inside the drying device separates the carrier material strip 4, the two drying channels 2, 2 'from one another, and enters between the two Einströmkästen 39, 39' of the drying apparatus from. The drying gas is about the filter mats or metal mesh or the like of Einströmkästen 39, 39 'in the drying channels 2, 2' in the flow directions B, B vertically downward, the opposite direction to the running direction A of the carrier material strip 4, blown '. The drying channel cross-sections are narrowing down, resulting in an acceleration of the drying gas flows in the direction of the channel inlets. The drying gas is sucked through the filter mats or metal mesh of the suction boxes 37, 37 ', which close the channel inlets downward. The aspirated through the left suction 37 drying gas flows through a recirculation line 54, in which a throttle valve 55 is arranged in a ventilation box 56. The ventilation box 56 has a fresh air supply line, in which a throttle 58 is mounted for controlling the supplied quantity of fresh air. The fresh air flows in the flow direction C in the ventilation box 56. In addition to the vent box 56 an exhaust duct is attached, is dissipated in the power consumed in the flow direction D air. This exhaust duct is a throttle valve 59 for regulating the exhaust air amount.

p0073Of the vent box 56, the air recirculation line leads through a heat exchanger 57 through, in which the air flowing in the circulating-air line air is heated before it enters via a throttle valve 60 in the Einströmkasten 39th

p0074From the drying duct 2 'via the suction box 37' flowing amount of air circulates in the same manner as described above, through the components for conditioning the circulating air and not shown is 'in the drying channel 2' returned via the Einströmkasten 39th

p0075In Fig. 11A, the area of ​​the inlet channel 27 is shown a further embodiment of the invention in detail. This embodiment corresponds essentially to the embodiment according to Fig. 9, with the difference that the carrier material strip 4 is not running over rollers, which are inserted in the channel base surface, but the back of the carrier material strip 4 is applied in the suction region of the channel inlet with negative pressure, thereby ensuring in that the carrier material band is not deflected by the generated heat at the top of gas flow. There is an opposite drying gas flow to the vertically upward direction of the substrate web. 4 In suction there is a vacuum chamber 41 that is open, for example, through a porous plate 42 against the backside of the substrate web 4 through. Inside the vacuum chamber, a perforated plate 68 is arranged, which ensures a uniform discharge of the exhausted gas and the extracted air. The channel inlet 27 is, as in the case of the embodiment of FIG. 9, completed by a suction box 37 downwards. The accelerated in the direction of flow B gas flow passes through a filter mat 47, a metal mesh or the like in the interior of the suction box 37, in which even a diagonally arranged, perforated baffle plate 49 may be present. This baffle is not necessarily required and may be omitted, if it does not come to the formation of vortices within the suction box 37th Purpose of the baffle plate 49, it is namely to prevent vortex formation within the suction box 37, so that an over the entire width of the dryer even extraction is guaranteed. On the vertical outside of the suction box 37, facing the front of the carrier tape 4, a leaf seal 38 or a labyrinth seal is arranged that the inlet channel as close as possible, but without contact, closes against the moving substrate material band. 4 is in the interior of the drying channel, as in the case of the embodiment of FIG. 9, by the inclined channel-covering surface 7 of drying gas or drying air is fed.

p0076In FIG 11B, the suction of an embodiment is shown, which substantially corresponds to the embodiment of FIG. 11A, with the only difference that instead of the leaf seal, a blade seal 43 is mounted on the vertical outer side of the suction box 37 and the channel inlet as close as possible to the carrier material strip 4 concludes. again is a vacuum chamber 41, which prevents a deflection of the carrier material strip 4 by the resultant gas flow at the top at the back of the substrate web. 4

p0077Figure 12A shows a schematic sectional view of an eighth embodiment of the drying apparatus 1, wherein the drying channel 2 has a vertically extending channel-covering surface 7, which extends parallel to the vertical channel base surface 3rd The channel-covering surface 7 consists of juxtaposed, equally thick filter mats 26 that have different permeability for a gas or air. In Figure 12A, the differential permeability is indicated by different degrees hatching of the individual filter mats 26, in such a way that the filter mat is shaded stronger near the channel outlet, according to their lower permeability, and the hatching of the filter mats 26 decrease in the direction of the channel inlet to display that the permeability of the filter mats increases counter to the running direction A of the substrate web 33rd The remaining components of the drying apparatus 9 and 11A coincide with the components of the embodiments of the drying apparatus according to FIGS. Are assigned with the same reference numerals as in Figures 9 and 11A. Before the channel inlet 27 of the drying channel 2 there is a suction box 37 with a filter mat 47. The channel cross sections are constant over the length of the drying channel. 2 Due to the different permeabilities of the filter mats 26 each have a different gas / air quantity flows through the filter mat 26, which is indicated by the size of the curved arrows P₁ to P₄, which are assigned to the individual filter mats 26th About the Einströmkasten 39 to the filter mat 48 flows from above the air or gas in the drying channel 2. By the carried out in the direction of the channel inlet increase of the supplied gas / air flow results in an acceleration of the flow opposite to the running direction of base material strip 33. This acceleration or . this increase in speed of the flow at the inlet channel towards is the increasing speed arrows v_iWhich are located parallel to the carrier material web 33, as indicated. The lateral supply of drying gas or air through the channel-covering surface 7 via inflow passages 61 of the drying apparatus. 1

p0078The ninth embodiment shown in Fig. 12B, will match with the exception of the top surface, with the eighth embodiment. The top surface 7 of the ninth embodiment has constant permeability over the channel length. Since the upper surface on the amount of gas supplied current increases in the direction of the inlet channel even at a constant permeability of the top surface, is carried out an acceleration of the flow opposite to the running direction of base material strip 33rd

p0079The inflow and the suction box are sealed by means of labyrinth seals 40 and 38 against the substrate material band 33, and a vacuum chamber 41 keeps the pressure on the back of the substrate web 33 in the region of the channel inlet to a belt deflection at the front of the tape 33 by the flow to prevent.

p0080The channel-covering surface 7 may be made from lined-up filter mats of the same structure and the same consistency, but different thicknesses exist, wherein the thickness of the filter mats decreases counter to the running direction of base material strip 33, in other words, the permeability of the filter mats increases toward the channel inlet.

p0081Figure 13 shows a tenth embodiment of the drying apparatus according to the invention in section, wherein the channel-covering surface 7 converges against the vertical channel base surface 3 in the direction of channel outlet. The channel-covering surface 7 is gas / air-permeable and consists of a continuous filter, but can also be made of rows of filter mats, as shown in Figure 12A.

p0082The channel inlet of the drying channel 2 is greater than the channel outlet. The cross-sections of the drying channel 2 are rectangular, with the channel width of the passage inlet towards the top linearly decreased to the width of the passage outlet. Side channel is of the drying air space 69 of the drying apparatus. In the vertical side wall of the air chamber 69 inlet ducts 62 are arranged through the drying gas such as heated air, and flows through P4 enters into the drying channel 2 by the channel-covering surface 7 in the direction of arrows P1. The increasing size of the arrows P1 through P4 indicates that the flow of the drying gas within the drying channel 2 increases from below towards the top, that is, in other words, that the flow velocity increases in the direction of channel outlet.

p0083The carrier material strip 4 is guided around a deflection roller 35, 34 is opposite to a slot die in 7 o'clock position with a small gap. Through the slot die 34, a liquid layer of vaporizable solvent components and non-vaporizable components is applied to the front side of the carrier material strip 4, which enters vertically upwards through the inlet duct into the drying channel second The carrier material band 4 runs on bearing rollers 6, which are arranged at a small distance from the channel base surface 3 laterally.

p0084The channel inlet is closed by a Einströmkasten 39 with a filter mat 48, and all or a portion of the drying gas flows through the Einströmkasten 39 and the filter mat 48 in the flow direction B. Upwards in the same direction to the running direction A of the substrate tape 4 through the drying channel 2

p0085The channel outlet includes a suction box 37 with a filter mat 47 from through which the drying gas is exhausted.

p0086The drying channel 2 is as close as possible, but without touching the channel inlet and channel outlet by lamellar seals 40 or 38 or labyrinth seals, sealed against the moving substrate material band. 4 The lamellar seals 38, 40 are located at the vertical outer walls of the suction box 37 and the Einströmkastens 39 facing the substrate tape. 4

p0087The light emerging from the channel outlet carrier tape 4 is guided over a guide roller 36 and directed from the vertical direction in an oblique downward direction for further processing.

p0088When the running direction A of the carrier material strip 4 equidirectional flow of the drying gas is achieved that the channel inlet of the vertical dryer laminar flow must be generated with a minimum speed, which prevents the falling of the exiting of the liquid layer on the carrier material strip 4 solvent vapors. To carry the solvent vapors in the running direction of the substrate web 4, the flow velocity at the channel inlet is set so high that the force of gravity is overcome by the flow rate of the drying gas. This is done in such a way that the channel inlet of the drying gas already laminar flows in through appropriate action on Einströmkasten 39 as the attachment of the filter pad 48 and a perforated plate 70 inside the Einströmkastens, the drying gas. Thus, the solvent vapors can then be discharged at the rate required to the top. This reduces the risk of the occurrence of Verblasungsstrukturen to the coated front side of the carrier material strip 4 is avoided.

p0089In the eleventh embodiment of the invention according to figure 14 of the drying duct 2, an upper run 65 and a lower run 66 of the carrier material strip 4 are horizontal. In this embodiment, the flow direction B of the drying gas which flows through the Einströmkasten 39 in the drying channel 2 and flows through the suction box 37, in the opposite direction is to the running direction A of the lower strand of the substrate web 4 through the drying channel 2, and the flow is accelerated in the direction of flow B ,

p0090This embodiment is used for example to a dried first layer S1 while applying a second layer S2 on the substrate band. 4 For example, the top of the upper strand 65 is already provided with a dried first liquid layer and is guided through a revolving roller 63rd A slot die 64 is positioned in the 11 o'clock position and a small distance from the deflection roller 63rd Through the slit die 64, the second liquid is keitsschicht on the dried first liquid layer on the carrier material strip 4 applied. The second liquid layer passes through suspended from the underside of the horizontally guided strand 66, the drying channel 2. The carrier material belt 4 is below and guided along a horizontal channel wall 72 of the drying channel second A channel bottom 71 of the drying channel 2 converges in the flow direction B of the drying gas. The channel inlet of the drying channel 2 for the carrier material belt 4 has a smaller height than the channel outlet, which the vertically aligned Einströmkasten 39, comprising a filter mat 48 terminates. The channel inlet is closed by the suction box 37 and the filter mat 47th Both the inflow and the suction wear on their horizontal top labyrinth seals, which seal the channel outlet and the inlet channel to the lower run 66 of the substrate web. 4

p0091This embodiment of the drying channel is in their arrangement and mode of operation similar to the right half of the embodiment of Figure 10 when it is contemplated that the drying channel 2 is horizontally and not vertically, as in the embodiment according to Figure 10, and in that it concerns the applying and drying a second layer on a first layer of the carrier material band.

p0092In the following three embodiments and two comparative examples are given of carrier material webs, on which are applied to drying liquid layers.

Embodiment 1

p0093On a pre-treated for offset printing purposes aluminum web 4 of 0.1 mm thickness, the solution of a photosensitive polymer material in an organic solvent at a running speed of 8 m / min the aluminum web 4 uniformly applied by a suitable coating method. The solution has a dynamic viscosity of 1.4 mPas, and the thickness of the liquid film is 27 microns.

p0094Immediately after the slot die 34, the aluminum web travels in a drying apparatus 1 a according to one of the embodiments according to figures 1 to 4 or the sixth The Kanalauslaßhöhe h2 the channel outlet is 2 cm, channel inlet height h1 in the channel inlet is 30 cm. With a total length of the drying channel 2 of 1.2 m, the channel-covering surface 7 is inclined to the plane of the path at an angle of 13.1 °. The circulation fan 12 is not turned on and the throttle valve 13 is closed. The power of the suction fan 9 is adjusted so that at the entrance of the drying channel 2 is an air speed of v₁ equal to 0.3 m / sec prevails. This results in Auslaußquerschnitt A2 of the drying channel 2, an air velocity of v₂ equal to 4.5 m / sec. For the complete removal of solvent residues from the almost dried film of liquid on the aluminum sheet 4, a nozzle dryer is connected downstream according to the prior art in which the air flow is generally highly turbulent.

p0095The photosensitive layer obtained the aluminum sheet 4, which is then processed to give printing plates, is very uniform in thickness and in visual appearance. With a reflection densitometer, a uniform optical density of 1.47 is measured over the entire coated plate surface.

Comparative Example 1 (to the exemplary embodiment 1)

p0096The experimental procedure corresponds broadly to that of the embodiment 1, however, the suction fan is in the drying apparatus 1 9 is not turned on, so that the coated aluminum sheet is 4 slightly dried while passing through the first drying section only by evaporation of a small portion of the solvent. The actual drying of the liquid film takes place in the downstream jet dryer.

p0097There is obtained a layer with a cloudy or mottled structure. Thin and thick places with an area extent of 5 to 20 mm diameter are irregularly distributed over the entire surface. Densitometric measurement gives no uniform optical density, this will vary rather in size, depending on the measurement site from 1.43 to 1.50.

Embodiment 2

p0098On a polyester film of 125 microns thickness by a suitable coating method, a Vesikularfilmlösung dissolved in an organic solvent, is applied. The coating speed is 5 m / min. The solution has a dynamic viscosity of 5.5 mPas, the thickness of the applied liquid film is 40 microns. The liquid film is in the same way as described with reference to the Embodiment 1, dried.

p0099To check the uniformity of the film, the film is irradiated over a large area in a printing frame with UV light and then developed by briefly heating to 100 ° C. The thus caused clouding of the film is uniform over the entire area.

Comparative Example 2 (Practical Example 2)

p0100The coating and drying run similarly to the embodiment 2, notwithstanding, however, the suction fan is in the drying apparatus 1 9 is not turned on. The actual drying of the liquid film takes place as in Comparative Example 1 only in the downstream nozzle dryer.

p0101After the UV exposure and thermal development at 120 ° C appears in transmitted light a cloudy structure of Vesikularfilms on the polyester film. Here small and large sites of 5 to 20 mm diameter are irregularly distributed over the surface.

Embodiment 3

p0102On a pre-treated for offset printing purposes aluminum web as a carrier material strip 4, with a thickness of 0.3 mm, is applied at a belt speed of 15 m / evenly a solution of a photosensitive polymer material min.

p0103The liquid film is 33 microns thick. The solution has a dynamic viscosity of 2.9 mPas.

p0104There is a drying apparatus 1, as shown in Figure 2 is used. The channel inlet height h1 is 0.5 m and the Kanalauslaßhöhe h2 = 0.1 m. The channel-covering surface 7 is constructed as a porous filter and inclined with respect to the aluminum web and the carrier material strip 4 at an angle of 4.3 °.

p0105The circulation fan 12 is open in operation and the throttle valve. 13 The position of throttle 14 is chosen so that an air volume flow of 1000 m³ / h of fresh air is sucked into the drying space. 5 An equal amount of air is sucked through the suction fan 12 from the drying duct 2, so that it can not come to an enrichment of evaporated solvents in the drying air. The precise adjustment of the air flow at the suction fan 12 is achieved in that the inflow v₁ is almost zero. The channel length of the drying channel 2 is approximately 5.7 m.

p0106On the thus-dried aluminum sheet surface not thick and thin places can be seen. The measured in reflectance optical density is constant over the total area.

p0107In practice it is worked with channel lengths of the drying channels 10 to 12 m, the channel length and the volume flow of the drying gas depend partly on the throughput speed of the substrate web through the drying apparatus.