EP0341646B1 - Process and apparatus for drying a liquid layer deposited onto a moving carrier material - Google Patents

Description

The invention relates to a method for drying a liquid layer which is applied to a carrier material moving through a drying zone and which contains vaporizable solvent components and non-vaporizable components, a gas flowing in the longitudinal direction of the carrier material parallel to the liquid layer and being accelerated in the direction of flow within the drying zone, and a device for drying a layer of liquid applied to a moving carrier material.

US-A-3,183,605 describes such a method for drying a layer applied to a carrier material moved through a drying zone, the carrier material being a wire to which, for example, a plastic or enamel layer is applied, the vaporizable solvent components and non-vaporizable ones Contains components. The drying gas for the applied layer flows in the longitudinal direction of the wire transported through a drying channel parallel to the latter and is accelerated immediately after entering the drying channel in the flow direction in that the channel cover surface over a certain section which is significantly smaller than the total length of the Drying channel is inclined to the channel base.

Different drying processes and drying devices are used for drying large, web-shaped goods on which layers of liquid are applied. Typical drying goods are, for example, metal or plastic belts, on which liquid layers are applied, which usually consist of evaporable solvent components that are removed from the liquid film during the drying process, and non-evaporable components that remain on the carrier material after drying.

The coating gives the surfaces of the carrier materials special properties which are only present in the form after the drying process, as are desired for later use. An example of this is the coating of metal strips with light-sensitive layers, which are assembled into printing plates. The coating of metal strips or plastic films with substances in the form of a solvent-containing wet film, in the following liquid film referred to, and its subsequent drying thus represent a process that requires special systems to ensure the desired product quality of the layers. The process step of film drying is essential as the final process measure of the coating.

When drying liquid films on carrier materials, it is customary to allow a heated gas, in particular air, to flow over the surface of the carrier materials to remove the solvent components from the film layer. The heated gas stream is brought into direct contact with the liquid film, which is applied in a uniform layer distribution on the carrier material, which passes through a drying device. For a streak-free and mottled, dried film surface, i.e. To ensure an even distribution of the remaining components, the drying systems are equipped with devices which are intended to achieve a favorable or even distribution of the air flow over the liquid film. The aim is to achieve uniform drying across the entire width of the coated web. Furthermore, known drying systems have devices for minimizing disturbances in the air movements, which, in part due to turbulent flow movements, have a disadvantageous effect on the film surface and lead to mottling there.

A common design of such a drying device According to US Pat. No. 3,012,335, the immediate gas space above the liquid film to be dried is as uniform as possible from a gas space supplied with drying gas, which is arranged over a certain length above the coating web, by means of a plurality of slits, nozzles, holes or even porous solids to be supplied with dryer gas. The continuously coated belt or coated plates on a rotating conveyor belt are continuously passed through the drying device with the release of solvent vapor to the dryer air. The dryer air supplied can be constantly renewed in the open circuit or the air enriched with solvent can be completely removed. A circulating air process with partially renewed or discharged dryer air can also be used.

Difficulties in removing the dryer air from the drying room often consist in the fact that in the case of longitudinal nozzles or longitudinal slots arranged transversely to the direction of belt travel, a decrease in the nozzle outlet velocity occurs in the middle of the field due to the pressure drop in the lateral outflow and thus also affects the heat and mass transfer transversely to the direction of belt travel becomes. The consequence of this is an overdrying of the edges, which leads to undesired structuring of the dried films in many coating processes.

In the trade journal "Chemie-Ingenieur-Technik", 42nd year, issue 14 (1970), pp. 927 to 929, 43rd year, Issue 8 (1971), pp. 516 to 519 and 45th volume, Issue 5 (1973), pp. 290 to 294 therefore give suggestions for optimizing the design of the nozzle fields in slot nozzle dryers, which provide constant heat over the entire range of a dryer. and ensure mass transfer. To optimize slot nozzle dryers, mass transfer measurements in impingement flow from slot nozzle fields with different nozzle areas are empirically correlated in a wide range of external factors. The relationship found is used to determine optimal nozzle geometries with regard to the fan output per m² of goods area. It is shown that a constant heat and mass transfer over the web width is achieved in that the nozzle slots have a continuously increasing slot width from the web edge to the center.

When drying large-area webs, high uniformity of heat and mass transfer across the web width must often be required in order to avoid local over-drying and the associated reduction in quality. In these cases, slot nozzle fields are preferably used, in which the slots are arranged transversely to the running direction of the web. The observed overdrying of the edges in the slot nozzle dryers with outflow in the slot direction can be attributed to the distribution of the exit velocity along the slots. In order to avoid this overdrying of the edges, it follows, among other things, for nozzle dryers that the outflow area should be as much as 3.5 times the nozzle exit area in order to obtain uniform drying over the width of the web.

It is state of the art today to carry out a surface treatment in suspension dryers for foil or metal strips with the aid of an air jet system without contact (magazine "gas warm international", Volume 24 (1975), No. 12, pp. 527 to 531). The dryer air, which is enriched with solvent, is sucked off directly in the nozzle fields in order to eliminate the undesired transverse flow. This results in so-called nozzle dryers or impingement jet dryers, in which the stagnation point-like flow of individual nozzles is disadvantageous, which tends to flow-physical instabilities in both laminar and turbulent flow forms, which inevitably lead to irreversible drying structures, particularly in the case of low-viscosity liquid films.

According to PCT application WO82 / 03450, the dryer air is led from a vestibule via suitable inlet openings and flow deflectors into a calm space, from where part of the dryer air passes through a device arranged in close proximity to the liquid film to avoid stagnation point-like flows in the initial area of the dryer apparatus porous filter element on the web to be dried. The mode of operation of such drying is based on the fact that there is between the porous protective shield and the drying liquid film forms a calmed, but highly enriched, weak air flow, which is constantly renewed by exchange with the residual air flowing transversely over the porous medium and thus, due to the relatively short overall length, a predrying of the liquid film with reduced tendency to mottling is achieved .

This type of drying is characterized by predominant diffusion of the solvent vapor / air mixture through the porous protective shield, which means that if there is almost no convective removal within the space between the belt and the protective shield, complete drying of the liquid film is only possible with very large dryer lengths or with the addition of subordinate auxiliary dryers.

A particular disadvantage of drying devices used hitherto is that a sealing device which is compatible with the outside atmosphere must be created due to the solvent-laden air currents inside the drying room. Depending on the size of the absolute pressure inside the dryer room directly above the liquid film, either a part of the required fresh air flows inwards through the finite sealing gap in the case of negative pressure conditions or a part of the solvent-laden air flows outwards in the case of overpressure conditions, whereby the flow in the sealing gap on the undried liquid film irreversible structures can be created.

The object of the invention is to provide a method and an apparatus with which liquid layers applied to carrier materials can be dried in continuous operation in such a way that surface structures which interfere with the uniform distribution of the dried film layer and impair its desired properties, both for high and high also do not occur for low-viscosity layers of liquid.

This object is achieved by a method of the type described above in such a way that the gas flows in the same direction or in the opposite direction to the direction of travel of the sheet-like support material along and parallel to the liquid layer and is accelerated in the direction of flow within the entire drying zone that the entry velocity v 1 of the gas flow is increased to a final speed v₂, which is up to 1000 times the value of the entry speed v₁ and that the speed distribution of the gas flow in the individual cross sections of the drying zone is set to be constant across the direction of travel of the carrier material.

In one embodiment of the method, the gas is heated and the total gas stream is drawn off at one end of the drying zone. The drying zone is expediently designed in such a way that disturbances occurring in the inlet cross section and in the drying zone, such as eddies and turbulence in the gas flow, are damped and laminar by the accelerated gas flow. The method is used either in such a way that the drying zone is flowed through with a constant gas volume flow, the cross-section of the drying zone in the running direction of the carrier material being continuously reduced, or in such a way that the gas volume flow is continuously increased in the running direction of the carrier material, with a constant cross section the drying zone or even if the cross section of the drying zone decreases.

In the process, the turbulence of the gas flow introduced into the drying zone is immediately dampened by the gas flow locally accelerated in the flow direction and a largely laminar flow is obtained.

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

It is also possible that the carrier material is provided on both sides with liquid layers and both sides of the carrier material are dried by drying gas flowing in the opposite direction to the vertical running direction of the carrier material. The carrier material can also run horizontally or obliquely through the drying zone with the liquid layer applied to its underside, the drying gas flowing below the carrier material along the hanging liquid layer.

The method is used either in such a way that the drying zone is flowed through with a constant gas volume flow, the cross section of the drying zone becoming smaller and smaller in the direction of travel of the carrier material, or in such a way that the gas volume flow is continuously increased against the direction of travel of the carrier material constant cross section of the drying zone or even with a continuously decreasing cross section of the drying zone.

In the method, for example, the carrier material enters the drying zone at the bottom through the dryer inlet, leaves the drying zone at the top through the dryer outlet and the total gas stream directed downwards is sucked off near the dryer inlet.

A device for drying a liquid layer applied to a moving carrier material, which contains vaporizable solvent components and non-vaporizable components, with a drying channel, made of channel top and bottom surface, through which the carrier material runs in the longitudinal direction, is characterized by the fact that the duct cover surface extends parallel or inclined relative to the duct base surface over the entire length of the drying duct, that the duct cover surface is a gas-permeable surface through which a drying gas flow is directed onto the continuous sheet-like carrier material and that the strength of the drying gas flow in The longitudinal direction of the drying channel can be changed by the variably adjustable gas permeability of the channel cover surface and / or by metering devices arranged on the top of the channel cover surface for the gas to be added.

In a further development of this device, the drying duct runs horizontally and the duct inlet height of the drying duct is greater than the duct outlet height.

The further embodiment of the invention results from the features of claims 16 to 30.

In another embodiment of the device, the channel inlet width of the vertical drying channel is smaller than the channel outlet width. The channel inlet is the area in which the coating material runs into the channel, the channel inlet being able to be at the top or bottom in the case of a vertical drying channel.

The further embodiment of the invention results from the features of claims 32 to 38.

With the invention, the advantages are achieved that with relatively simple construction measures that a certain gas flow in the drying channel cause the desired trouble-free drying of low and high viscosity liquid layers on carrier materials is achieved. The mean speed the gas flow from an inlet velocity v₁ over the length of the drying channel to an outlet velocity v₂, which is substantially greater than v₁, increased. The speed distribution is set 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 are dampened by the gas acceleration and that the total air flow required for drying is extracted at the end of the drying channel.

The gas flow is laminar at the channel inlet where the liquid layer is most sensitive to blowing. The high flow velocity in the channel inlet area leads to a rapid removal of the solvents. The liquid layer dries particularly quickly and is then stable against turbulent currents that can occur at the widened channel outlet. When the carrier material runs vertically from bottom to top, the heavy solvent vapors are removed by the opposite gas flow in the direction of gravity and not in the opposite direction.

It is not necessary to set a flow-reduced entrance zone, and it does not matter whether or not turbulence occurs at the wide duct outlet in the region of low flow speeds, since the layer has already dried there. The air flow can be greatly accelerated, thereby shortening the dryer route will. The heat transfer in the drying zone is determined, among other things, by the gas velocity. If the gas flow is in the same direction, the belt is heated and thus it dries closer to the duct outlet, and in the opposite direction the gas is closer to the duct inlet of the drying zone.

• Fig. 1 eine schematische Schnittansicht einer ersten Ausführungsform der Trocknungsvorrichtung nach der Erfindung,
• Fig. 2 eine schematische Schnittansicht einer zweiten Ausführungsform der Trocknungsvorrichtung nach der Erfindung, mit einem sich verengenden Trocknungskanal mit rechteckförmigem Querschnitt,
• Fig. 3 einen Schnitt entlang der Linie I - I der Trocknungsvorrichtung nach Fig. 2,
• Fig. 4A und 4B je eine perspektivische Ansicht eines Trocknungskanals mit trompetenförmiger Geometrie, der anstelle des Trocknungskanals mit rechteckförmigem Querschnitt in den Ausführungsformen nach den Figuren 1 bis 3, 9 und 10 verwendet werden kann,
• Fig. 5A eine Schnittansicht einer dritten Ausführungsform der Trocknungsvorrichtung mit veränderlicher Durchlässigkeit der Deckfläche, teilweise aufgebrochen, nach der Erfindung,
• Fig. 5B eine Schnittansicht einer vierten Ausführungsform der Erfindung, ähnlich Fig. 5A, mit konstanter Durchlässigkeit der Deckfläche,
• Fig. 6 eine fünfte Ausführungsform der Trocknungsvorrichtung nach der Erfindung im Schnitt,
• Fig. 7 ein Geschwindigkeitsprofil der Gasströmung in Abhängigkeit von der Kanallänge des Trocknungskanals,
• Fig. 8 ein Druckprofil, nämlich den statischen Unterdruck der Gasströmung gegenüber Atmosphärendruck, in Abhängigkeit von der Kanallänge des Trocknungskanals,
• Fig. 9 eine Schnittansicht einer sechsten Ausführungsform der Trocknungsvorrichtung für einseitige Trocknung des Trägermaterials, nach der Erfindung,
• Fig. 10 eine schematische Schnittansicht einer siebenten Ausführungsform der Trocknungsvorrichtung für beidseitige Trocknung des Trägermaterials nach der Erfindung, mit zwei sich verengenden Trocknungskanälen mit rechteckförmigem Querschnitt,
• Fig. 11A und 11B einen schematischen Detailausschnitt im Bereich des Kanaleinlasses einer Trocknungsvorrichtung, in der mit Unterdruck das Trägermaterial geführt wird, und eine schematische Schnittansicht im Bereich des Kanaleinlasses in leicht abgewandelter Ausführungsform gegenüber Fig. 11A,
• Fig. 12A eine Schnittansicht einer achten Ausführungsform der Trocknungsvorrichtung mit veränderlicher Durchlässigkeit der Deckfläche nach der Erfindung,
• Fig. 12B eine Schnittansicht einer neunten Ausführungsform der Erfindung, ähnlich Fig. 12A, mit konstanter Durchlässigkeit der Deckfläche,
• Fig. 13 eine zehnte Ausführungsform der Trocknungsvorrichtung nach der Erfindung, im Schnitt, bei der die Laufrichtung des Trägermaterialbandes und die Strömungsrichtung des Trocknungsgases gleichsinnig sind, und
• Fig. 14 eine schematische Schnittansicht einer elften Ausführungform mit horizontal geführtem Untertrum des Trägermaterialbandes, auf dem eine Flüssigkeitsschicht aufgebracht ist, die nach unten weist.

The invention is explained in more detail below with the aid of schematically illustrated exemplary embodiments. Show it:

• 1 is a schematic sectional view of a first embodiment of the drying device according to the invention,
• 2 shows a schematic sectional view of a second embodiment of the drying device according to the invention, with a narrowing drying channel with a rectangular cross section,
• 3 shows a section along the line I - I of the drying device according to FIG. 2,
• 4A and 4B each show a perspective view of a drying duct with a trumpet-shaped geometry, which can be used instead of the drying duct with a rectangular cross section in the embodiments according to FIGS. 1 to 3, 9 and 10,
• 5A is a sectional view of a third embodiment of the drying device with variable permeability of the top surface, partially broken away, according to the invention,
• 5B is a sectional view of a fourth embodiment of the invention, similar to FIG. 5A, with constant permeability of the top surface,
• 6 shows a fifth embodiment of the drying device according to the invention in section,
• 7 shows a velocity profile of the gas flow as a function of the channel length of the drying channel,
• 8 shows a pressure profile, namely the static negative pressure of the gas flow against atmospheric pressure, as a function of the channel length of the drying channel,
• 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,
• Fig. 10 is a schematic sectional view of a seventh embodiment of the drying device for double-sided drying of the carrier material according to the invention, with two narrowing Drying channels with a rectangular cross-section,
• 11A and 11B show a schematic detail in the area of the channel inlet of a drying device, in which the carrier material is guided with negative pressure, and a schematic sectional view in the area of the channel inlet in a slightly modified embodiment compared to FIG. 11A,
• 12A is a sectional view of an eighth embodiment of the drying device with variable permeability of the top surface according to the invention,
• 12B is a sectional view of a ninth embodiment of the invention, similar to FIG. 12A, with constant permeability of the top surface,
• Fig. 13 shows a tenth embodiment of the drying device according to the invention, in section, in which the running direction of the carrier material band and the flow direction of the drying gas are in the same direction, and
• 14 shows a schematic sectional view of an eleventh embodiment with a horizontally guided lower run of the carrier material strip, on which a liquid layer is applied, which points downward.

In Figure 1, a first embodiment of a drying device 1 according to the invention is shown in a schematic sectional view. A carrier material strip 4, for example a metal strip made of aluminum or a foil strip, runs past a slot die 34, from which a liquid layer is applied to the carrier material strip 4, which contains evaporable solvent components and non-evaporable components. The carrier material strip 4 is guided around a deflection roller 35 and runs through a duct inlet 27, which has an inlet cross section A1, into a drying duct 2. The carrier material strip 4 runs in the drying duct 2 and in a through duct 20 adjoining the drying duct 2 on support rollers 6 which are recessed in the horizontal duct base surface 3 or in the duct bottom. The drying device 1 can also be designed as a dryer, in which the carrier material strip 4 is guided freely through the drying channel 2 via air-carrying nozzles and the carrier air is discharged laterally.

A channel cover surface 7 is designed as a gas-permeable surface which is inclined with respect to the horizontally running channel base surface 3, the channel inlet height h1 of the channel inlet 27 of the drying channel 2 being greater than the channel outlet height h2 of the channel outlet 28, which has an outlet cross section A2. The channel cover surface 7 is inclined to the horizontal channel base surface 3, for example at an angle equal to 3 ° 9 ', the permeable channel cover surface, starting at the Channel inlet 27 extends over the entire length of the drying channel 2.

Above the drying channel 2 there is a drying chamber 5, which is separated by an intermediate wall 10 from a gas exchange chamber 15. A fan 12 or a fan is arranged in the gas exchange chamber 15, the fan outlet 16 of which is directed against a heat exchanger 17 in the intermediate wall 10. In a bottom surface 18 of the gas exchange chamber 15 there is an opening in which a throttle device, e.g. a throttle valve 13 is arranged, which is adjustable about a horizontal axis. The gas exchange chamber 15 has a gas inlet 19 which adjoins the top surface of the gas exchange chamber 15 and contains a throttle valve 14 as a throttle device. The throttle device can also consist of two perforated plates which can be displaced relative to one another or a lamella diaphragm device.

The blower 12 is a double-flow circulating blower with back blades, the fresh gas stream added to the back blades from the gas inlet 19 being conveyed into the drying chamber 5.

The flow channel 20, which connects to the drying channel 2, has a constant cross section corresponding to the channel outlet cross section A2 of the drying channel. The underside of the bottom surface 18 of the gas exchange chamber 15 is also the top surface of the Flow channel. Above the top surface of the flow channel, after the gas exchange chamber 15, there is a fan or suction fan 9, the suction opening of which lies in the top surface of the flow channel. A throttle valve 8 is arranged in an outlet 11 of the suction fan 9.

The channel cover surface 7 consists for example of a continuous filter with constant permeability.

FIG. 2 shows a schematic sectional view of a second embodiment of the drying device 1 according to the invention, which, compared to the first embodiment, has additional metering devices 21 for the gas to be added on the upper side of the channel cover surface 7. The gas is generally heated air. The drying channel 2 is similar to the drying channel of the first embodiment, with a horizontal channel base or bottom surface 31 and an inclined channel top surface 7. The gas or air flow in the inlet cross section A 1 of the channel inlet has an entry speed v 1 of almost zero, while the exit speed v₂ can be up to 75 m / sec in the outlet cross-section A₂ of the duct outlet. In FIG. 2, for reasons of better clarity, the suction fan, which is identified by the reference number 9 in FIG. 1, is not shown, although it is present, as in the first exemplary embodiment.

The metering devices 21 consist of boxes with two perforated diaphragms 22, 23, the opening cross sections of which are adjustable. These perforated diaphragms 22, 23 either lie directly one above the other or, as shown, are at a distance from one another. Depending on the setting of the opening cross sections of the perforated diaphragms 22, 23 (see FIGS. 3A and 3B), there are different permeabilities of the individual boxes of the metering devices 21, so that, depending on the lengths of the boxes, different amounts of air flow through the duct cover surface 7. It is thus possible to regulate the gas or air quantity flowing into the drying duct 2 differently over the length of the drying duct 2, in addition to the different gas quantity distribution that occurs without the metering devices.

Above the carrier material band 4 in the gas exchange chamber 15, for example, there is a negative pressure of 3.35 mbar compared to the atmospheric pressure, while there is an excess pressure of 1.4 mbar at the fan outlet of the fan 12. In the drying room 5 above the metering devices 21, the excess pressure is approximately 1.1 mbar.

The bottom surface 31 of the drying device has a plurality of openings 32, one of which is opposite the gas exchange chamber 15 and is subjected to the same suction pressure or negative pressure as that prevailing in the gas exchange chamber. This ensures that the carrier tape material 4, which runs through the drying channel 2 on support rollers 6, is subjected to the same negative pressure from both sides, so that a lifting of the carrier material tape 4 is prevented, as normally occurs in the direction of the gas exchange chamber 15, if only there is negative pressure .

The remaining openings 32, which can also be arranged in the side walls, just above the bottom surface, allow the gas layers located in the immediate vicinity of the side walls to be extracted.

As can be seen from Figure 3, which represents a section along the line I - I of the drying device 1 according to Figure 2, the drying channel cross section is rectangular, the channel height decreasing linearly in the direction of the channel outlet cross section A₂. The channel cover surface 7 and the metering devices 21 are embedded, for example, in the side walls 29, 30 of the drying channel 2. One of the openings 32 can be seen in the bottom surface 31.

FIGS. 4A and B each show a perspective view of a drying duct 2 which has a trumpet-shaped geometry that tapers in the longitudinal direction from the duct inlet to the duct outlet. Such a drying channel can be used in the exemplary embodiments according to FIGS. 1 to 3, 9 and 10 instead of the drying channels shown there. Due to the tapering trumpet-shaped geometry of the drying channels it is ensured that the air or gas flow is accelerated in the direction of flow. The drying channel according to FIG. 4A has a curved top surface and curved side walls, while the drying channel according to FIG. 4B has a rectangular cross section, ie side walls oriented perpendicular to the bottom surface, but has a curved top surface.

The 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 takes place with a constant air volume flow which is present in all cross-sections of the drying channel, the cross-sections of the drying channel in the direction of the belt running from the inlet cross-section A 1 to the outlet cross-section A 2 continuously becoming smaller. The length-dependent reduction of the channel cross-section is carried out in such a way that disturbances introduced into the flow are attenuated and the flow thereby becomes laminar. This is done in such a way that, for example, the gas or air volume flow required for drying is sucked in with the inlet velocity v 1 via the channel inlet 27 with the inlet cross section A1 via the suction fan 9 or the fan when the throttle devices 13 and 14 of the first embodiment according to FIG. 1 are closed and is accelerated via the channel cover surface 7 inclined in the direction of tape travel to the exit velocity v₂ at the channel outlet 28 with the outlet cross section A₂. The setting of the sufficient air volume flow takes place here by speed control of the suction fan 9 or the fan and, in the case of speed-independent operating mode, by adjusting the throttle valve 8 in the outlet 11 of the suction fan 9.

In the second mode of operation, the gas or air volume flow required for drying is added via suitable metering devices which are attached in or above the duct cover surface. The gas or air volume flow in the drying channel is continuously increased in the belt running direction or adjusted so that disturbances are damped out and the gas or air flow changes into a laminar flow. For this purpose, in the embodiments of the invention as shown in FIGS. 1 to 5B, the embodiments according to FIGS. 5A and 5B being described in more detail, the gas or air volume flow required for drying into the drying chamber 5 via the blower 12 or the circulation fan with back blades with open throttle valves 13 and 14 promoted. From the drying chamber 5, the air or gas quantity flows via the metering devices and the channel cover surface 7 into the drying channel 2 and is accelerated therein to the exit velocity v₂ in the outlet cross section A₂. The blower 9 or the fan is set here so that only the gas added via the blades of the blower 12 or the circulation fan is sucked out of the drying chamber 5 and the residual gas quantity is continuously conveyed in the circuit. This ensures that almost no flow or only a very small flow occurs in the inlet cross-section A 1.

In the embodiments of the invention, as shown in FIGS. 9 to 12B, the embodiments according to FIGS. 12A and 12B being described in more detail, the gas or. Air volume flow via the metering devices and the channel cover surface 7 and / or the channel outlet 28 is conveyed into the drying channel 2 and accelerated therein to the exit velocity in the channel inlet cross section.

This ensures that the maximum speed occurs over the length of the drying channel in the channel inlet cross section.

In the first mode of operation of the embodiments according to FIGS. 1 to 5B, the inlet cross-section A 1 is designed so large for optimum operation, or the initial speed v 1 is kept so small that no initial interfering effects in the form of mottling or large-area blows occur on the liquid film to be dried .

In the simplest case of operation, the coated carrier material strip 4 is guided in the immediate vicinity of the horizontal channel base surface 3 and the flow acceleration is brought about by the channel cover surface 7 which is inclined in a straight line in the direction of flow. The shape of the channel cross section is rectangular and the channel height decreases linearly from the channel inlet height h1 to the channel outlet height h2. The same effect will achieved for example with the trumpet-shaped geometries of the drying duct 2 shown in FIGS. 4A and B. In addition, other channel geometries are possible as long as they bring about the acceleration required in the direction of flow.

In the first mode of operation according to the embodiments of FIGS. 9 to 12B, the coated carrier material strip 4 is guided in the immediate vicinity of the vertical channel base surface 3 and the flow acceleration is brought about by the channel cover surface 7 converging in the direction of flow toward the channel base surface. The shape of the channel cross-section is rectangular, and the channel width decreases linearly from the channel outlet width b2 to the channel inlet width b1. The same effect is achieved, for example, with the trumpet-shaped geometries of the drying duct 2 shown in FIGS. 4A and B. In addition, other channel geometries are possible as long as they bring about the acceleration required in the direction of flow.

In the second mode of operation, good drying results are obtained in particular if the horizontal or vertical channel cover surface 7 is designed as a continuous, gas-permeable filter with a rectangular channel cross section. With a constant channel cross-section over the length of the drying channel, ie in other words, with a channel cover surface running horizontally or vertically and parallel to the channel base surface, there is a constant filter permeability along the drying channel due to the increasing gas flow, the desired acceleration of the flow, which can also be controlled by the changing permeability of the continuous filter. The channel cover surface 7 does not have to consist of a continuous filter, but rather can also consist of lined-up, equally thick filter mats 26 (see FIGS. 5A and 12A) with different permeability. This can also be achieved in that the filter mats have the same consistency or structure, but have different thicknesses. Another possibility is to design the filter mats with the same thickness, but with a different structure or different consistency.

If the duct cover surface 7 is inclined, the gas flow rate and thus the flow acceleration is determined by the inclination of the duct cover surface. If the inclined duct cover surface 7 consists of a continuous filter or of filter mats, these expediently have a uniform structure or uniform consistency and thus constant permeability over the length of the drying duct 2.

The combined use of the first and second modes of operation has advantages particularly when solvent vapors which have already been released have to be suctioned off during the coating, which is generally carried out immediately before the drying device 1 through the slot die 34.

The accelerated flow in both the first and the second mode of operation apparently contributes in several ways to the rapid drying of the liquid layer and to the structure-free surface design of the coated carrier material strips. Investigations carried out show that macroscopic flow turbulences, which are generated, for example, by the addition points of the gas or air flow, are damped in drying channel 2 with the correct setting of the first or second mode of operation so that no disturbances in the drying process occur immediately after the addition points, i.e. the flow becomes laminar already in the immediate vicinity of the point of origin of the turbulence. Observations show that this is enforced by the acceleration of the turbulent partial areas of the gas or air flow with simultaneous longitudinal alignment or longitudinal deformation of these turbulent areas.

The accelerated gas or air flow runs near the belt parallel to the carrier material belt and is directed in the same direction or in the opposite direction to its direction of travel, so that the gas / air flow, which is getting faster and faster relative to the liquid film and its boundary layer flow in the vicinity of the liquid film, the diffusion paths of the evaporating Solvent are kept small and thus a large heat and mass transfer from the liquid layer to the drying medium is made possible at a high final velocity of the gas / air flow, but with a small drying channel length.

In a convergent drying channel, with air flow from top to bottom and in the opposite direction to the belt running direction, layers without blowing are created, whereby the air flow and the solvent vapors follow the force of gravity.

The constant velocity of the flow across the width of the liquid-coated carrier material strip 4 to be dried results in very uniform drying of the liquid film transverse to the direction of web travel. This means that the velocity distribution of the gas / air flow in the individual cross sections of the drying zone or the drying channel must be kept constant across the running direction of the carrier material strip.

FIG. 5A shows a schematic sectional view of a third embodiment of the drying device 1, in which the drying duct 2 has a horizontally running duct cover surface 7 which runs parallel to the duct base surface 3. The horizontal channel cover surface 7 consists of lined up, equally thick filter mats 26, which have different permeability to a gas or air. 5A, the different permeability is indicated by hatchings of different strengths of the individual filter mats 26, in such a way that the filter mat near the channel inlet is hatched more, corresponding to its lower permeability, and the hatchings of the filter mats 26 decrease in the direction of the channel outlet. to indicate that the permeability of the filter mats increases in the running direction of the carrier material band 33. The remaining components of the drying device, which correspond to the components of the first and second embodiments of the drying device, are given the same reference numbers as in FIGS. 1 to 3. A sealing mat 36 is located in front of the channel inlet 27 of the drying channel 2. The channel cross sections are constant over the length of the drying channel 2. Because of the different permeability of the filter mats 26, a different amount of gas / air flows through the individual filter mat 26, which is indicated by the size of the curved arrows P₁ to P₅, which are assigned to the individual filter mats 26. The increase in the amount of gas / air supplied in the direction of the channel outlet results in an acceleration of the flow in the running direction of the carrier material band 33. This acceleration or this increase in speed of the flow towards the channel outlet is due to the increasing speed arrows v _i , which are parallel to the carrier material band 33 are indicated.

The fourth embodiment shown in FIG. 5B is the same as the third embodiment except for the top surface. The top surface 7 of the fourth embodiment has constant permeability over the channel length. Since the gas volume flow supplied via the top surface increases in the direction of the outlet cross section even with constant permeability of the top surface, this takes place an acceleration of the flow in the running direction of the carrier material strip 33.

Of course, it is also possible that the gas / air-permeable channel cover surface 7 constructed from filter mats 26 is not horizontal, i.e. runs parallel to the channel base 3, but, like in the first and second embodiment of the drying device according to the invention, is inclined to the channel base 3. The channel cover surface 7 may also consist of filter mats of the same structure and consistency, but of different thicknesses, which are lined up, the thickness of the filter mats decreasing in the running direction of the carrier material band 33, i.e. in other words, the permeability of the filter mats increases in the direction of the channel outlet.

The filter or filter mats are commercially available so-called laminar flow filters, such as those used in supply air filter systems in clean rooms. Such filter elements on the one hand filter dirt particles out of the gas / air flow and on the other hand ensure a very uniform laminar flow through the individual filter elements into the drying channel.

FIG. 6 shows a fifth embodiment of the drying device according to the invention in section, in which the channel cover surface 7 is inclined with respect to the horizontal channel base surface 3. The channel cover surface 7 is gas / air permeable and consists of a continuous filter but can also be made of strung filter mats, as shown in Figure 5A. Dispensing devices 24 containing lamellae 25, which are mutually adjustable, are located above the channel cover surface 7. The individual lamella lies parallel to the channel cover surface 7 and is adjustable along its longitudinal axis. The arrangement of the slats 25 and their adjustability is roughly comparable to sun visors which are made up of slats and is indicated in Fig. 6, in which the slats 25 near the inlet cross section A 1 are shown in parallel and near the outlet cross section A 2 perpendicular to the top surface 7.

The remaining components of the fifth embodiment are the same as the corresponding components of the first to third embodiments of the drying device, and their description will therefore not be repeated.

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

FIG. 9 shows a sixth embodiment of the drying device 1 according to the invention in a schematic sectional view. The carrier material strip 4, for example a metal strip made of aluminum or a foil strip, runs past the slot die 34, from which a liquid layer is applied to the carrier material strip 4, which contains evaporable solvent components and non-evaporable components. The carrier material strip 4 is guided around the deflection roller 35 and runs vertically upwards through a duct inlet 27, which has a duct inlet width b1, into the drying duct 2. The carrier material strip 4 runs in the drying duct 2 on support rollers 6, which are recessed in the vertical duct base 3 or in the duct bottom. The drying device 1 can also be designed as a dryer in which the carrier material strip 4 is guided so as to float over air-carrying nozzles. The carrier material band can also be in contact with the channel bottom by negative pressure in the channel inlet area and then be guided through the drying channel 2 via support rollers.

The channel cover surface 7 is designed as a gas-permeable surface which is inclined with respect to the vertically running channel base surface 3, the channel inlet width b1 of the channel inlet 27 of the drying channel 2 being smaller than the channel outlet width b2 of the channel outlet 28. The channel cover surface 7 extends, for example, starting at the channel inlet 27, over the entire length of the drying channel 2.

The channel cover surface 7 consists of a continuous filter with constant permeability. The cross sections of the drying duct 2 are rectangular, the duct width increasing linearly upwards from the duct inlet 27 to the duct outlet width b2. An air space 67 of the drying device 1 is located to the side of the drying channel 2. Inflow channels 44, 45, 46 are arranged in the vertical side wall of the air space 67, through which drying gas, in particular heated air, flows and through the channel cover surface 7 in the direction of the arrows P in the drying channel 2 enters. At the top, the channel outlet 28 of the drying channel 2 is closed off by an inflow box 39 with a filter mat 48, through the drying gas in the flow direction B downwards, in the opposite direction to the running direction A of the carrier material strip 4, through the channel inlet 27 into a suction box 37 which flows the channel inlet closes at the bottom. The suction box 37 is equipped with a filter mat 47 and a diagonally arranged perforated baffle plate 49 which prevents eddy formation in the gas flow. The inflow box 39 can also be equipped with a perforated baffle plate 73. The baffle plate 49 can also be omitted if the filter mat 47 alone is sufficient to suppress vortex formation. In the event that the gas flow entering the convergent drying channel 2 through the channel outlet is sufficient for drying alone, the channel cover surface 7 can be made of impermeable material and there is no need to blow in a drying gas through the side wall, so that the inflow channels in the vertical side wall of the drying device 1 can be omitted.

The drying duct 2 is closed at the duct inlet 27 and at the duct outlet 28 by lamellar seals 38 or 40 or labyrinth seals as tightly as possible against the moving carrier material strip 4. The lamella seals 38 and 40 are attached to the vertical outer walls of the suction box 37 and the inflow box 39, which face the carrier material band 4. At the channel inlet 27 for the carrier material strip 4, the drying gas is drawn off through the suction box 37, whereby depending on the narrowing of the channel cross section and the amount of the fed or extracted drying gas, a speed increase in the gas flow from top to bottom in the drying channel 2 arises, which suppresses turbulence. The carrier material strip 4 emerging from the channel outlet 28 is guided through a deflection roller 36 from the vertical direction in a certain direction for further processing.

With the flow of the drying gas in the direction opposite to the running direction A of the carrier material strip 4, it can be seen that in the drying channel 2, which converges downward, the liquid layer on the carrier material strip 4 dries without structure, without blowing. With this type of drying, the gas flow and the solvent vapors from the liquid layer follow gravity. The layer on the carrier material belt which is dried in the opposite direction to the laminar, accelerated downward gas flow 4 does not show any blows which may be caused by solvent vapors being released and falling due to gravity. This can be shown by standstill experiments in which the carrier material strip 4 provided with the liquid layer is stopped in the drying channel 2, and it is shown by means of flow test tubes that swirls of solvent vapors do not occur.

10 shows a schematic sectional view of a seventh embodiment of the drying device for drying the carrier material tape 4 on both sides, which, for example, carries a liquid layer on both sides and runs vertically from bottom to top through the drying device. The two drying channels 2 and 2 'are symmetrical to the vertical. In Figure 10, the components located outside the drying duct 2, which connect to the inflow box 39 and the suction box 37, are shown, while the same components connected to the right drying duct 2 'have been omitted to simplify the drawing.

The carrier material strip 4 runs obliquely from top to bottom into a container 50 with the liquid to be applied, consisting of evaporable solvent components and non-evaporable components, and is turned around a deflection roller 51 vertically upward through the gap of squeeze rollers 52, 53 and between the suction boxes 37, 37 'Passed into the drying device.

In the container 50, the carrier material strip 4 is coated on both sides with liquid, the excess of which is squeezed off in the gap between the squeezing rollers 52, 53. Of course, other known application methods for coating the carrier material strip 4 on both sides can also be used. Within the drying device, the carrier material strip 4 separates the two drying channels 2, 2 'from one another and emerges from the drying device between the two inflow boxes 39, 39'. The drying gas is blown over the filter mats or metal mesh or the like of the inflow boxes 39, 39 'into the drying channels 2, 2' in the flow directions B, B 'vertically downward, in the opposite direction to the running direction A of the carrier material strip 4. The drying channel cross sections narrow downwards, which leads to 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 off the channel inlets. The drying gas extracted by the left suction box 37 flows through a recirculation line 54, in which a throttle valve 55 is arranged, into a ventilation box 56. The ventilation box 56 has a fresh air supply line, in which a throttle valve 58 is mounted to regulate the quantity of fresh air supplied. The fresh air flows in the flow direction C into the ventilation box 56. Furthermore, an exhaust air line is attached to the ventilation box 56, in which air used in the flow direction D is discharged. In this Exhaust air line is a throttle valve 59 for controlling the amount of air discharged.

From the ventilation box 56, the circulating air line leads through a heat exchanger 57, in which the air flowing in the circulating air line is heated before it enters the inflow box 39 via a throttle valve 60.

The amount of air flowing out of the drying duct 2 'via the suction box 37' circulates in the same manner as described above, through the components for the treatment of the circulating air, not shown, and is returned via the inflow box 39 'into the drying duct 2'.

11A shows the area of the channel inlet 27 of 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 band 4 does not run over rollers which are embedded in the channel base surface, but rather the back of the carrier material band 4 is subjected to a vacuum in the suction region of the duct inlet, thereby ensuring that the carrier material band is not deflected by the gas flow arising at the top. There is a flow of drying gas in the opposite direction to the direction of upward travel of the carrier material strip 4. In the suction area there is a vacuum chamber 41, which is opposed, for example, by a porous plate 42 Back of the carrier tape 4 is open. A perforated plate 68 is arranged in the interior of the vacuum chamber and ensures a uniform outflow of the extracted gas or the extracted air. As in the case of the embodiment according to FIG. 9, the channel inlet 27 is closed at the bottom by a suction box 37. The gas flow accelerated in the direction of flow B enters the interior of the suction box 37 through a filter mat 47, a metal mesh or the like, in which a diagonally arranged, perforated baffle plate 49 may also be present. This baffle plate is not absolutely necessary and can also be omitted if there is no formation of vortices within the suction box 37. The purpose of the baffle plate 49 is namely to prevent vortex formation within the suction box 37, so that a uniform suction is ensured over the entire dryer width. On the vertical outside of the suction box 37, facing the front of the carrier material band 4, a lamellar seal 38 or a labyrinth seal is arranged, which closes the channel inlet as tightly as possible, but without contact, against the moving carrier material band 4. As in the case of the embodiment according to FIG. 9, drying gas or drying air is fed into the interior of the drying channel through the inclined channel top surface 7.

FIG. 11B shows the suction area of an embodiment which largely corresponds to the embodiment according to FIG. 11A, with the only difference that instead of the lamella seal, a doctor seal 43 is attached to the vertical outside of the suction box 37 and closes the channel inlet as tightly as possible against the carrier material strip 4. On the back of the carrier material band 4 there is again a vacuum chamber 41, which prevents the carrier material band 4 from being deflected by the gas flow which arises at the top.

FIG. 12A shows a schematic sectional view of an eighth embodiment of the drying device 1, in which the drying duct 2 has a vertically running duct cover surface 7 which runs parallel to the vertical duct base surface 3. The channel cover surface 7 consists of lined up, equally thick filter mats 26, which have different permeability to a gas or air. In FIG. 12A, the different permeability is indicated by different hatching of the individual filter mats 26, in such a way that the filter mat near the sewer outlet is more hatched, corresponding to its lower permeability, and the hatching of the filter mats 26 decrease in the direction of the sewer inlet to indicate that the permeability of the filter mats increases counter to the running direction A of the carrier material band 33. The remaining components of the drying device, which correspond to the components of the embodiments of the drying device according to FIGS. 9 and 11A, are given the same reference numbers as in FIGS. 9 and 11A. In front of 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. Because of the different permeability of the filter mats 26, a different amount of gas / air flows through the individual filter mat 26, which is indicated by the size of the curved arrows P₁ to P₄, which are assigned to the individual filter mats 26. Air or gas flows from above into the drying duct 2 via the inflow box 39 with the filter mat 48. The increase in the amount of gas / air supplied in the direction of the duct inlet results in an acceleration of the flow against the direction of travel of the carrier material band 33. This acceleration or This increase in speed of the flow towards the channel inlet is indicated by the increasing speed arrows v _i , which are drawn in parallel to the carrier material band 33. The lateral supply of drying gas or air through the channel cover surface 7 takes place via inflow channels 61 of the drying device 1.

The ninth embodiment shown in FIG. 12B is the same as the eighth embodiment except for the top surface. The top surface 7 of the ninth embodiment has constant permeability over the channel length. Since the gas volume flow supplied via the cover surface increases in the direction of the channel inlet even with a constant permeability of the cover surface, the flow is accelerated counter to the running direction of the carrier material strip 33.

The inflow and suction boxes are sealed against the carrier tape 33 by means of labyrinth seals 40 and 38, respectively, and a vacuum chamber 41 provides negative pressure on the back of the carrier tape 33 in the region of the channel inlet in order to deflect the tape at the front of the tape 33 due to the flow prevent.

The channel cover surface 7 can also consist of filter mats of the same structure and consistency, but of different thicknesses, which are lined up, the thickness of the filter mats decreasing counter to the running direction of the carrier material band 33, i.e. in other words, the permeability of the filter mats increases in the direction of the channel inlet.

FIG. 13 shows a tenth embodiment of the drying device according to the invention in section, in which the channel cover surface 7 converges towards the vertical channel base surface 3 in the direction of the channel outlet. The channel cover surface 7 is permeable to gas / air and consists of a continuous filter, but can also be made of filter mats strung together, as shown in FIG. 12A.

The channel inlet of the drying channel 2 is larger than the channel outlet. The cross sections of the drying channel 2 are rectangular, the channel width decreasing linearly upwards from the channel inlet to the width of the channel outlet. Laterally from the drying channel there is an air space 69 of the drying device. In the vertical side wall of the air space 69, inflow channels 62 are arranged through which drying gas, for example heated air, flows in and enters the drying channel 2 through the channel cover surface 7 in the direction of the arrows P1 to P4. The increasing size of the arrows P1 to P4 indicates that the flow of the drying gas within the drying channel 2 increases from bottom to top, in other words that the flow speed increases in the direction of the channel outlet.

The carrier material strip 4 is guided around a deflection roller 35 which is opposite a slot die 34 in the 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 of the carrier material strip 4, which runs vertically upwards through the duct inlet into the drying duct 2. The carrier material strip 4 runs over support rollers 6, which are arranged laterally at a short distance from the channel base 3.

The channel inlet is closed by an inlet box 39 with a filter mat 48, and all or part of the drying gas flows through the inlet box 39 and the filter mat 48 in the direction of flow B upwards, in the same direction as the direction of travel A of the carrier material band 4, through the drying channel 2.

The duct outlet is closed by a suction box 37 with a filter mat 47 through which the drying gas is sucked off.

The drying duct 2 is sealed at the duct inlet and at the duct outlet by means of lamella seals 40 and 38 or labyrinth seals as tightly as possible, but without streaking, against the moving carrier material strip 4. The lamella seals 38, 40 are located on the vertical outer walls of the suction box 37 and the inflow box 39, which face the carrier material band 4.

The carrier material strip 4 emerging from the channel outlet is guided over a deflection roller 36 and directed from the vertical direction in an obliquely downward direction for further processing.

With the flow of the drying gas in the same direction as the running direction A of the carrier material strip 4, it is achieved that a laminar flow must be generated at the channel inlet of the vertical dryer at a minimum speed which prevents the solvent vapors emerging from the liquid layer on the carrier material strip 4 from falling down. In order to carry the solvent vapors in the direction of travel of the carrier material strip 4, the flow rate at the channel inlet is set so high that the influence of gravity is overcome by the flow rate of the drying gas. This happens in such a way that on Channel inlet of the drying gas by appropriate measures on the inflow box 39, such as attaching the filter mat 48 and a perforated plate 70 inside the inflow box, the drying gas flows in already laminar. This allows the solvent vapors to be discharged upwards at the required speed. This avoids the risk of blown structures occurring on the coated front side of the carrier material strip 4.

In the eleventh embodiment of the invention according to FIG. 14, the drying channel 2, an upper run 65 and a lower run 66 of the carrier material strip 4 run horizontally. In this embodiment, the flow direction B of the drying gas, which flows through the inflow box 39 into the drying channel 2 and flows out through the suction box 37, is opposite to the running direction A of the lower run of the carrier material band 4 through the drying channel 2, and the flow is accelerated in the flow direction B. .

This embodiment is used, for example, when applying a second layer S2 to a dried first layer S1 on the carrier material strip 4. For example, the top of the upper run 65 is already provided with a dried first layer of liquid and is guided around by a revolving roller 63. A slot die 64 is arranged in the 11 o'clock position and at a short distance from the deflection roller 63. The second liquid layer becomes through the slot nozzle 64 applied to the dried first liquid layer on the carrier material tape 4. The second liquid layer runs through the drying channel 2, hanging on the underside of the horizontally guided lower run 66. The carrier material strip 4 is guided below and along a horizontal channel ceiling 72 of the drying channel 2. 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 band 4 has a lower height than the channel outlet which the vertically oriented inflow box 39, which has a filter mat 48, closes. The channel inlet is closed by the suction box 37 and its filter mat 47. Both the inflow and the suction box carry labyrinth seals on their horizontal upper sides, which seal the channel outlet and the channel inlet against the lower run 66 of the carrier material strip 4.

This embodiment of the drying duct is comparable in its arrangement and mode of operation to the right half of the embodiment according to FIG. 10, if it is taken into account that the drying duct 2 is arranged horizontally and not vertically, as in the embodiment according to FIG. 10, and that it is the application and drying of a second layer on a first layer of the carrier material band.

Three exemplary embodiments and two comparative examples of carrier material webs are given below, on which layers of liquid to be dried are applied.

Embodiment 1

The solution of a light-sensitive polymer material in an organic solvent is uniformly applied to an aluminum web 4 of 0.1 mm thickness pretreated for offset printing purposes at a running speed of 8 m / min by an appropriate coating method. The solution has a dynamic viscosity of 1.4 mPas and the thickness of the liquid film is 27 µm.

Immediately after the slot die 34, the aluminum web runs into a drying device 1 according to one of the embodiments according to FIGS. 1 to 4 or 6. The duct outlet height h2 in the duct outlet is 2 cm, the duct inlet height h1 in the duct inlet is 30 cm. With a total length of the drying duct 2 of 1.2 m, the duct cover surface 7 is inclined at an angle of 13.1 ° to the web plane. The circulating air blower 12 is not switched on and the throttle valve 13 is closed. The performance of the suction fan 9 is adjusted so that at the entrance of the drying duct 2 there is an air speed of v 1 equal to 0.3 m / sec. This results in the outlet cross section A2 of the drying channel 2 an air speed of v₂ equal to 4.5 m / sec. For the complete removal of solvent residues from the almost dried liquid film on the aluminum web 4 is followed by a nozzle dryer according to the prior art, in which the air flow is generally very turbulent.

The photosensitive layer of the aluminum web 4 obtained, which is subsequently made into printing plates, is very uniform in its thickness and in its optical appearance. With a reflected light densitometer, a uniform optical density of 1.47 is measured on the entire coated plate surface.

Comparative Example 1 (to Example 1)

The experiment is largely the same as that of embodiment 1, but in the drying device 1 the suction fan 9 is not switched on, so that the coated aluminum web 4 is only slightly dried by evaporation of a small part of the solvent as it passes through the first drying area. The actual drying of the liquid film takes place in the downstream nozzle dryer.

A layer with a cloudy or mottled structure is obtained. Thin and thick spots with a surface area of 5 to 20 mm in diameter are distributed irregularly over the entire surface. The densitometric measurement does not result in a uniform optical density, but its size fluctuates between 1.43 and 1.50 depending on the measurement location.

Embodiment 2

A vesicular film solution, dissolved in an organic solvent, is applied to a polyester film 125 μm thick by a suitable coating process. 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 µm. The liquid film is dried in the same way as described with reference to embodiment 1.

To check the uniformity of the layer, the film is irradiated with UV light over a large area in a copier frame and then developed by briefly heating to 100 ° C. The resulting clouding of the film layer is uniform over the entire surface.

Comparative Example 2 (to Example 2)

The coating and the drying process are similar to those in the exemplary embodiment 2, but in a different way, the suction fan 9 is not switched on in the drying device 1. The actual drying of the liquid film takes place, as in comparative example 1, only in the downstream nozzle dryer.

After UV exposure and thermal development at 120 ° C, a cloudy structure of the vesicular film on the polyester film appears in transmitted light. Are Thin and thick spots from 5 to 20 mm in diameter distributed irregularly over the surface.

Embodiment 3

A solution of a light-sensitive polymer material is uniformly applied to an aluminum web pretreated for offset printing purposes as a carrier material strip 4, with a thickness of 0.3 mm, at a belt speed of 15 m / min.

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

A drying device 1 as shown in FIG. 2 is used. The duct inlet height h1 is 0.5 m and the duct outlet height h2 = 0.1 m. The channel cover surface 7 is designed as a porous filter and inclined at an angle of 4.3 ° against the aluminum web or the carrier material strip 4.

The circulating air blower 12 is in operation and the throttle valve 13 is open. The position of the throttle valve 14 is selected so that an air volume flow of 1000 m³ / h fresh air is sucked into the drying chamber 5. An equal amount of air is sucked out of the drying duct 2 by the suction fan 12, so that there is no accumulation of evaporated solvent in the drying air. Due to the exact setting of the air volume flow on the suction fan 12 achieved that the inflow velocity v₁ is almost zero. The channel length of drying channel 2 is approx. 5.7 m.

No thick and thin spots can be seen on the dried aluminum web surface. The optical density measured in remission is constant over the entire area.

In practice, channel lengths of the drying channels of 10 to 12 m are used, whereby the channel length and the volume flow of the drying gas include depend on the throughput speed of the carrier material strip through the drying device.

Claims (38)

1. A process for drying a liquid layer which has been applied to a carrier material moving through a drying zone and contains vaporizable solvent components and non-vaporizable components, with a gas flowing in the longitudinal direction of the carrier material parallel to the liquid layer and being accelerated within the drying zone in the direction of flow, wherein the gas flows in the same direction as or in the opposite direction to the running direction of the flat-shaped carrier material along and parallel to the liquid layer and is accelerated within the entire drying zone in the direction of flow, wherein the inlet velocity v₁ of the gas flow is increased to a final velocity v₂ which amounts to up to 1000 times the inlet velocity v₁, and wherein the velocity distribution of the gas flow in the individual cross-sections of the drying zone transversely to the direction of running of the carrier material is adjusted to be constant.

2. The process as claimed in claim 1, wherein the gas has been heated and the total gas stream is extracted at one end of the drying zone.

3. The process as claimed in claim 1, wherein the drying zone is designed in such a way that disturbances arising in the inlet cross-section and in the drying zone, such as eddies and turbulences in the gas flow, are damped out, so that the gas flow becomes laminar.

4. The process as claimed in claim 3, wherein the flow through the drying zone takes place at a constant volumetric gas flow rate, the cross-section of the drying zone steadily decreasing in the direction of running of the carrier material.

5. The process as claimed in claim 3, wherein the volumetric gas flow rate is steadily increased in the direction of running of the carrier material, at constant cross-section of the drying zone.

6. The process as claimed in claim 3, wherein the volumetric gas flow rate is steadily increased in the direction of running of the carrier material, at decreasing cross-section of the drying zone.

7. The process as claimed in claim 1, wherein the carrier material runs vertically through the drying zone and one side of the carier material carries a liquid layer which is dried.

8. The process as claimed in claim 7, wherein the carrier material is provided on both sides with liquid layers and both sides of the carrier material are dried by means of drying gas flowing in the direction opposite to the vertical direction of running of the carrier material.

9. The process as claimed in claim 1, wherein the carrier material with a liquid layer applied to its underside runs horizontally or obliquely through the drying zone and the drying gas flows underneath the carrier material along the suspended liquid layer.

10. The process as claimed in claim 1, wherein the flow through the drying zone takes place at a constant volumetric gas flow rate, the cross-section of the drying zone steadily decreasing opposite to the direction of running of the carrier material.

11. The process as claimed in claim 1, wherein the volumetric gas flow rate is steadily increased opposite to the direction of running of the carrier material, at constant cross-section of the drying zone.

12. The process as claimed in claim 1, wherein the volumetric gas flow rate is steadily increased opposite to the direction of running of the carrier material, at decreasing cross-section of the drying zone.

13. The process as claimed in claim 11, wherein the carrier material enters the drying zone at the bottom through the drier inlet and leaves the drying zone at the top through the drier outlet, and the downward-directed total gas stream is extracted near the drier inlet.

14. A device for drying a liquid layer which has been applied to a moving carrier material and contains vaporizable solvent components and non-vaporizable components, having a drying channel comprising a channel-covering surface and a channel base surface, through which the carrier material runs in the longitudinal direction, wherein the channel-covering surface (7) extends parallel or inclined relative to the channel base surface (3; 31), over the entire length of the drying channel (2), wherein the channel-covering surface (7) is a gas-permeable surface through which a drying gas stream is directed onto the running through flat-shaped carrier material (4) and wherein the intensity of the drying gas stream in the longitudinal direction of the drying channel (2) can be varied by the variably adjustable gas permeability of the channel-covering surface (7) and/or by feeding devices (21; 24) for the gas to be supplied which are disposed on the top side of the channel-covering surface (7).

15. The device as claimed in claim 14, wherein the drying channel (2) extends horizontally and the channel inlet height (h₁) of the drying channel (2) is greater than the channel outlet height (h₂).

16. The device as claimed in claim 14, wherein the drying channel (2) is adjoined by a gas exchange chamber (15) which contains a fan (12), the fan outlet (16) of which is directed towards a heat exchanger (17) which is arranged in a partition (10) between the gas exchange chamber (15) and a drying chamber (5) located above the drying channel (2).

17. The device as claimed in claim 16, wherein the gas exchange chamber (15) has a restrictor device (13; 14) both in its bottom surface (18) and in its upper gas inlet (19).

18. The device as claimed in claim 16, wherein the fan (12) is a double flow circulation fan with return blades, and the fresh air added via the return blades is delivered into the drying chamber (5).

19. The device as claimed in claim 15, wherein the drying channel cross-sections are rectangular and the channel height decreases from the channel inlet height (h₁) linearly to the channel outlet height (h₂).

20. The device as claimed in claim 15, wherein the drying channel (2) has a trumpet-shaped geometry which tapers in the longitudinal direction and causes an acceleration of the gas stream in the direction of flow.

21. The device as claimed in claims 14 and 17, wherein the drying channel (2) merges into a passage channel (20), wherein the underside of the bottom surface (18) of the gas exchange chamber (15) is at the same time the covering surface of the passage channel, and wherein a suction fan (9), the suction opening of which is located in the covering surface and in the outlet (11) of which a restrictor device (8) is arranged, is provided downstream of the gas exchange chamber (15) above the covering surface of the passage channel.

22. The device as claimed in claim 14, wherein the feeding devices (21) comprise boxes with two mutually displaceable orifice plates (22, 23), the opening cross-sections of which are adjustable.

23. The device as claimed in claim 14, wherein the feeding devices (24) contain mutually adjustable blades (25).

24. The device as claimed in claim 14, wherein the channel-covering surface (7) comprises a continuous gas-permeable filter.

25. The devices as claimed in claim 14, wherein the channel-covering surface (7) comprises strung-up filter mats (26) having the same thickness and constant or different permeability.

26. The device as claimed in claim 14, wherein the channel-covering surface (7) comprises strung-up filter mats of the same consistency and different thicknesses.

27. The device as claimed in claim 14, wherein the drying channel (2) has a constant cross-section, the permeability of the channel-covering surface (7) increasing in the longitudinal direction from a minimum value in the region of the channel inlet (27) to a maximum value in the region of the channel outlet (28).

28. The device as claimed in claim 14, wherein, in a bottom surface (31) or in side walls of the drying device just above the bottom surface, openings (32) for extracting the gas layers present in the immediate vicinity of the side walls are provided.

29. The device as claimed in claim 16, wherein the bottom surface (31) of the drying device has, opposite the gas exchange chamber (15), an opening (32) which is subjected to the same suction pressure as that prevailing in the gas exchange chamber.

30. The device as claimed in claim 14, wherein a sealing mat (36) is located in front of the channel inlet (27) of the drying channel (2).

31. The device as claimed in claim 14, wherein the channel inlet width (b1) of the vertical drying channel (2) is smaller than the channel outlet width (b2).

32. The device as claimed in claim 31, wherein the drying channel cross-sections are rectangular and the channel width increases from the channel inlet width (b1) upwards limearly to the channel outlet width (b2).

33. The device as claimed in claim 31, wherein the drying channel (2) has a geometry which narrows downwards in the shape of a trumpet and leads to a vertically downward-increasing acceleration of the gas stream flowing in at the top.

34. The device as claimed in claim 14, wherein the drying channel (2) has a constant cross-section, the permeability of the channel-covering surface (7) increasing in the vertical direction from a minimum value near the channel outlet (28) to a maximum value near the channel inlet (27).

35. The device as claimed in claim 14, wherein the inlet gap into the channel inlet (27) is bounded on one side by a lamellar seal (38) from a moving strip (4) of carrier material, and the lamellar seal (38) is located on the vertical outside, facing the strip (4) of carrier material, of an extraction box (37) which closes the drying channel (2) downwards in the region of the channel inlet (27).

36. The device as claimed in claim 35, wherein a vacuum chamber (41), which has a porous plate (42) facing the strip (4) of carrier material, is arranged opposite the extraction box (37) on the other side of the strip of carrier material.

37. The device as claimed in claim 14, wherein the inlet gap into the channel inlet (27) is bounded on one side by a blade seal (43) from a moving strip (4) of carrier material, and the blade seal (43) is located on the vertical outside, facing the strip (4) of carrier material, of an extraction box (37).

38. The device as claimed in claim 35, wherein the channel outlet (28) is bounded by a lamellar seal (40) from the moving strip (4) of carrier material, but for a narrow gap, and the lamellar seal is located on the vertical outside, facing the strip (4) of carrier material, of an inflow box (39) which closes the drying channel (2) upwards in the region of the channel outlet (28) and through which the drying gas stream flows under pressure into the drying channel (2).

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