Applicator, film applicator and method

Abstract

Application device for applying a liquid or pasty coating medium to a moving surface, in particular to a moving surface in a machine for producing or processing a fibrous web, wherein the application device comprises an application nozzle which is configured to spray the coating medium in the form of a spray curtain onto the moving surface, wherein the spray curtain extends over the entire application width of the application device, characterized in that the application device has a first guide element for guiding air flows, which extends over the entire application width of the application device and which is arranged on a first side of the application nozzle in the immediate vicinity of the nozzle outlet of the application nozzle, wherein the first guide element is curved. In addition, a film application unit and application method.

Description

[0001] The invention relates to an application device for applying a coating medium to a moving surface according to the preamble of claim 1 as well as to an associated application method and a film application unit.

[0002] For applying liquid starch solutions or low-viscosity liquids to a substrate, it is known to spray the coating medium in the form of a fine spray directly onto the substrate, or to spray it indirectly onto an application roller and from there to transfer it to the substrate.

[0003] Such application processes are described, for example, in the documents DE102022105518 A1, DE202015009603 U1 or EP3332955 B1.

[0004] There are different types of sprays that differ in the size of the atomized liquid droplets: coarse sprays, medium-fine sprays, fine sprays and mist sprays.

[0005] Various physical principles are used to generate spray.

[0006] Single-component spray-generating principles use only the liquid to be atomized and generate the spray by accelerating thin liquid jets produced by suitable fine nozzles. The acceleration of the liquid is generated by a high pressure difference at the outlet of the spray nozzle channel. Due to the sharp increase in velocity, the fine liquid threads break down into fine droplets. The higher the acceleration, the finer the generated spray.

[0007] Special features in the geometry of the nozzle opening can influence the shape of the spray flow or resulting spray curtain. Typically, a triangular or three-dimensional conical spray geometry is created.

[0008] Other single-component spray-generating processes use centrifugal forces to accelerate the liquid to create spray.

[0009] Multi-component spray-generating principles use at least one other substance (e.g. gases or other liquids) and pressure to accelerate the liquid to be atomized.

[0010] One of the challenges in spray production and application is avoiding or controlling secondary spray. Secondary spray consists of the remaining portion of the spray that is not transferred to the substrate or surface. An optimal spray transfer rate of 100% is generally not achievable. Reasons for this include the geometry of the spray curtain or spray cone used, an unfavorable impact angle relative to the surface, and thus reflection of the spray during spray transfer.

[0011] Other reasons for the formation of secondary spray are deflecting air currents that occur due to negative pressure effects or turbulence effects in the vicinity of the spray flow (Bernoulli or Venturi effects or Coanda effects, external flows, etc.).

[0012] Secondary spray poses a problem because these spray flows are difficult to control and lead to pollution and contamination of the machine's surroundings.

[0013] To capture and neutralize the secondary spray, state-of-the-art extraction systems or devices are used to capture, filter, or separate these fine liquid droplets. Vacuum chambers, cyclones, centrifuges, electrostatic precipitators, etc. are some of the devices used for this purpose. One such system is described, for example, in EP3332955 B1.

[0014] These systems are usually complex to install and operate, expensive and usually consume a lot of energy.

[0015] The object of the invention is to propose an application device that enables a stable spray application, in particular a spray application of starch, in a simple and cost-effective manner. A further object of the invention is to reduce the tendency of the application device to become dirty.

[0016] The object is achieved according to the invention by an embodiment according to the independent claim. Further advantageous embodiments of the present invention can be found in the subclaims.

[0017] Proposed is an application device for applying a coating medium to a moving surface, in particular to a moving surface in a machine for producing or processing a fibrous web. The application device comprises an application nozzle configured to spray the coating medium onto the moving surface in the form of a spray curtain, the spray curtain extending across the entire application width of the application device.

[0018] According to the invention, it is provided that the application device has a first guide element for guiding air flows, which extends over the entire application width of the application device and which is arranged on a first side of the application nozzle in the immediate vicinity of the nozzle outlet of the application nozzle, wherein the first guide element is curved or angled.

[0019] In particularly preferred embodiments, it can be provided that the application device has a second guide element for guiding air flows, which extends over the entire application width of the application device and which is arranged on a second side of the application nozzle in the immediate vicinity of the nozzle outlet of the application nozzle, wherein the second guide element is curved or angled, and wherein the second guide element is arranged on a different side of the application nozzle than the first guide element.

[0020] The coating medium can be a liquid or pasty coating medium, or a dry powder or fiber-containing medium. The coating medium can preferably be a starch solution, but can also be a coating color, a barrier medium, or another suitable medium.

[0021] The moving surface intended for the application of the coating medium can be realized in particular in the form of a moving paper web (direct application) or in the form of a transfer surface, e.g. a transfer roller (indirect application).

[0022] The speed of the running surface essentially corresponds to the production speed and can, for example, be 1000 m / min and more, in particular 1200 m / min, 1400 m / min, 1600 m / min up to 2000 m / min or more in modern paper machines.

[0023] By applying the spray curtain to the running surface, two sides of the application nozzle are created, namely one side in the running direction of the surface in front of the application area of ​​the spray curtain, and another side afterthe application area of ​​the spray curtain. These sides are what we mean below when we refer to a "first side" or a "second side" of the application nozzle. Unless otherwise stated, the first side can be located either before or after the application area. The second side is then the side that is not the first side.

[0024] Through experimental observation and measurement of the environment of known spray-generating devices (spray nozzles), the inventor discovered that multiple, sometimes turbulent, flow processes arise in the immediately surrounding air space as the spray flows out of the spray nozzle. The inventor further recognized that these flow processes have a strong influence on both the spray application result and the process stability, as well as on the formation of secondary spray.

[0025] After leaving the application nozzle, the spray curtain expands into a spray wedge until it reaches the moving surface. The opening angle of this spray wedge is determined primarily by the size of the nozzle gap, the shape, sharpness, and geometry of the nozzle end edges, and the velocity of the escaping gas. (In this application, the spray wedge is sometimes referred to as a spray cone, although this is not a cone in the mathematical sense.)

[0026] At both edges of the spray wedge, the fine spray droplets are slowed down slightly by air friction and thus deflected slightly outward. The high velocity of the spray droplets (which can range from 5 m / s to over 10 m / s to over 18 m / s) generates negative pressure effects that accelerate the surrounding air, causing it to travel with the spray flow. This creates turbulent circulation zones around the spray curtain or spray cone, deflecting more spray droplets outward. This process enhances the formation of secondary spray.

[0027] If additional air currents occur in the vicinity of the spray wedge (e.g. air currents from the moving surface or other moving components), these can also cause additional spreading and scattering of the secondary spray in the surrounding area.

[0028] The effects described are detrimental for two reasons, among others. Firstly, the secondary spray that is not transferred to the moving surface can accumulate uncontrollably on machine parts and the application device itself, causing contamination. Furthermore, the turbulent flows can affect the spray curtain itself, thereby impairing the application result.

[0029] To avoid or at least significantly reduce these disadvantages, a guide element is provided in an application device according to aspects of the invention. This guide element is positioned in the immediate vicinity of the nozzle outlet and is curved or angled. Advantageously, such a guide element can be provided on each side of the nozzle.

[0030] Such a guide element works in two ways. First, its mere existence shields the area around the nozzle outlet from turbulence or air currents, preventing secondary spray from accumulating directly on the application nozzle. This prevents contamination of the application nozzle and thus disruption of the spray curtain.

[0031] The curved or angled shape introduced within the scope of the invention also makes it possible to specifically direct the air currents and, in particular, to keep them away from the spray curtain. This also makes it possible to significantly reduce the formation of secondary spray or to direct the secondary spray in such a way that it does not flow into the area surrounding the machine or accumulate on neighboring components.

[0032] In this case, the effect of avoiding or reducing secondary spray is also based on the fact that the resulting secondary spray can be reoriented back to the primary spray by the guiding elements or is directed in a spatial direction in which it cannot produce any negative effects.

[0033] In principle, both guide elements can be designed with convex or concave curvature. It is also possible for one guide element to be convex and the other concave or angled.

[0034] Experimental studies with various guide element geometries have shown that concave surfaces are very well suited to intercepting these disruptive air currents and harmful secondary spray currents and orienting them toward the primary spray cone, thus reducing or preventing the escape of secondary spray into the vicinity of the spray nozzle. The main goal of this measure is to prevent deposits and contamination on the surfaces of the spray nozzle or machine parts caused by secondary spray. It can also prevent spray mist from escaping into the vicinity of the application device.

[0035] Even when using a convex guide element, for example in the form of a cylindrical guide element, it is possible to achieve, through an appropriate arrangement and the systematic sequence of fluid-mechanical effects (Coanda effect, Venturi effect and Magnus effect), that the secondary spray is transported back towards the primary spray curtain and is accelerated again towards the moving surface.

[0036] It is clear to those skilled in the art that a guide element is to be understood as a curved guide element even if the guide element may also have a certain non-curved area outside the curved zone, which does not serve to guide the flow but, for example, to secure the guide element. The same applies to an angled guide element.

[0037] The first guide element and / or the second guide element can in particular have a distance of less than 40 mm, in particular between 0 mm and 30 mm, from the outlet of the application nozzle. A distance of 0 mm means that the guide element touches the application nozzle and is possibly also connected to it. In the case of a contacting guide element, contamination of the application nozzle can be very effectively avoided. However, in some applications this may not be possible or not desired, so the guide element is arranged at a certain distance from the application nozzle. A distance of more than 30 mm or more than 40 mm is often too great, so that the desired effect of the guide elements can only be achieved to a very reduced extent.With small distances in the range of 1 mm to 5 mm between the application nozzle and the curved guide element, the resulting Venturi effect, which occurs at this gap between the guide element and the air nozzle outlet opening, can be used positively and profitably, so that the tip of the application nozzle is efficiently and safely protected from contamination with secondary spray.

[0038] With regard to the curvature, the skilled person has freedom to adapt it to the current geometry of the device and the prevailing flow conditions. It will usually be advantageous if the first guide element and / or the second guide element have radii of curvature between 2 mm and 40 mm, preferably less than 20 mm. The guide element can be designed in the shape of a circular arc and have a single radius of curvature. Alternatively, the radius of curvature can also vary over the course of the guide element.

[0039] To optimize flow guidance, the arc length of the guide elements can be varied. In the specific case of the convex guide element, it has already been described that a cylindrical element with an arc length of 360° is advantageous. However, especially with concave guide elements, it can be advantageous to provide significantly shorter arc lengths due to the different operating principles. Thus, in advantageous embodiments, the arc length of the first guide element and / or the second guide element can be between 20° and 120°, preferably between 30° and 90°.

[0040] For angled guide elements, the size of the angle can be, for example, between 45° and 135°, in particular between 90° and 135°.

[0041] Furthermore, the inventor has recognized that it is advantageous if the second guide element differs from the first guide element in shape and / or size and / or distance from the application nozzle.

[0042] This is understandable since the flow conditions on the first side and the second side differ significantly, mainly due to the effect of the moving surface.

[0043] On the side in the direction of travel of the surface in front of the application area of ​​the spray curtain, air entrained by the moving surface is transported towards the spray curtain, while on the side after the application area the air is transported away from the application area.

[0044] Furthermore, the formation of the secondary spray also varies. When the coating medium hits the moving surface, it is accelerated tangentially toward the moving surface. The portion of the coating medium that is not transferred to the moving surface moves away from the surface approximately tangentially in the direction of movement. Experimentally, this can be observed as a thin jet of secondary spray.

[0045] Therefore, the flow conditions on the two sides of the application nozzle will differ, making it advantageous to adapt the guide elements to these flow conditions by different shapes and / or sizes and / or spacing.

[0046] Furthermore, it may be advantageous if the application nozzle is arranged such that the spray curtain hits the moving surface at an angle of 55° or less, for example 45° or less, preferably 40° or less, particularly preferably 35° or less.

[0047] The angle of impact can be considered the angle formed by an imaginary line in the center of the spray cone with the tangent of the moving surface. The spray cone should ideally be directed against the direction of the moving surface.

[0048] With such an alignment of the spray cone in combination with one or more curved guide elements, the secondary spray can be avoided, directed and controlled particularly effectively.

[0049] The application nozzle can be implemented in various ways. In an advantageous embodiment, the application nozzle can comprise a fluid head configured to generate a film of coating medium, and the application nozzle can further comprise a blowing head configured to generate a linear jet of gaseous medium, wherein the jet of gaseous medium impinges on the film of coating medium at the nozzle outlet, forming a spray curtain.

[0050] The gaseous medium can be air.

[0051] However, for specific coating media, it may also be advantageous to use a different gas, especially if you need or want to avoid excessive reaction of the coating medium with oxygen.

[0052] Such application nozzles can be designed in such a way that the film of coating medium is guided onto the wall of the application nozzle before the jet of gaseous medium impacts.

[0053] With such nozzles, disruptive deposits of secondary spray on at least part of the application nozzle are avoided by continuously flushing this area with coating medium. Similar to the return of the secondary spray to the spray curtain through a suitable flow line, the coating medium in the secondary spray is directly reused and does not contribute to contamination.

[0054] This also allows for a more flexible design of the guide element, as it can now be positioned relatively easily at a certain distance from the nozzle outlet without risking unwanted contamination of the nozzle by secondary spray.

[0055] Furthermore, a film applicator for applying a liquid or pasty coating medium to a fibrous web is proposed, comprising a first applicator roller and a second applicator roller, which form a transfer nip through which the fibrous web is guided, wherein the film applicator has a first application device for applying a coating medium to the first application roller and / or a second application device for applying a coating medium to the second application roller. At least the first application device or the second application device is designed according to aspects of the present invention. In advantageous embodiments, both application devices can also be designed according to aspects of the present invention.

[0056] One or both application rolls may have a roll hardness of 10 P&J or more, especially 20 P&J or more. Such rolls are more commonly referred to as soft rolls.

[0057] It is also possible for one or both rollers to have a hardness of less than 10 P&J, particularly above 50 ShoreD and above 60 ShoreD or above 70 ShoreD. Such rollers are referred to as hard rollers.

[0058] If a film applicator with two hard rollers (in this sense) is used to apply starch solution, it is referred to as a hard-nip sizer. Application devices according to aspects of the present invention are particularly suitable for such a hard-nip sizer, since the application of the coating medium to the rollers is contactless, i.e., without the use of doctor elements that are in contact with the moving surface.

[0059] Furthermore, a method for applying a coating medium to a moving surface, in particular to a moving surface in a machine for producing or processing a fibrous web, using an application device according to one aspect of the invention or using a film applicator according to another aspect of the invention, is described. The coating medium can, in particular, be a starch solution or another suitable coating medium.

[0060] The invention is further explained below with reference to figures. However, the invention is not limited to the embodiments shown.

[0061] The figures show in detail: Figure 1 shows a state-of-the-art application nozzle

[0062] The Figures 2 to 5 each show an application nozzle according to an aspect of the present invention.

[0063] Figure 1shows an application nozzle 1 with a fluid head 2, which is designed to produce a film of coating medium 15. The application nozzle 1 further has a blow head 3, which is designed to produce a linear jet of gaseous medium 6, which impacts the film 15 of coating medium at the nozzle outlet 1a, thereby forming a spray curtain 5. The blow head 3 is designed as a slot nozzle. In the form of this spray curtain 5, the coating medium is applied to the moving surface 4. The spray curtain 5 extends over the entire application width, for example over the entire width of the fibrous web to be coated. Such application nozzles 1 are known per se from the prior art.

[0064] After leaving the application nozzle 1, the spray curtain 5 expands into a spray wedge 5 until it reaches the moving surface 4. The opening angle of this spray wedge 5 is determined in particular by the size of the nozzle gap, the shape, sharpness, and geometry of the nozzle end edges at the nozzle outlet 1a, and the velocity of the escaping gas 6. At the edges of the spray wedge 5, the fine spray droplets are slightly slowed down by air friction and thus deflected slightly outward. This creates a secondary spray 8. The high velocity of the spray droplets (which can be up to 18 m / s or more) generates negative pressure effects that accelerate the surrounding air, causing it to travel with the spray flow. This creates turbulent circulation zones 7 in the vicinity of the spray curtain 5 or the spray cone 5, so that more spray droplets are deflected outward. This process intensifies the formation of the secondary spray 8.

[0065] If additional air currents occur in the vicinity of the spray wedge 5 (for example, air currents from the moving surface 4 or other moving components), these can also cause additional spreading and scattering of the secondary spray 8 in the surrounding area.

[0066] In contrast, Figure 2 an application nozzle 1 according to one aspect of the invention. It differs from the nozzle in Figure 1in that a first guide element 11 is provided for guiding air flows 7, which extends over the entire application width of the application device, and which is arranged on a first side of the application nozzle in the immediate vicinity of the nozzle outlet 1a of the application nozzle 1. The first guide element 11 is curved here, in particular concave. In addition, a second guide element 12 is provided for guiding air flows 7, which extends over the entire application width of the application device, and which is arranged on a second side of the application nozzle 1 in the immediate vicinity of the nozzle outlet 1a. The second guide element 12 is also Figure 2curved, in particular concave, and is located on the other side of the application nozzle 1 than the first guide element 11. Here, the first guide element 11 is arranged on the side after the impact area of ​​the spray curtain 5 on the running surface 4, and the second guide element 12 on the side in front of the impact area.

[0067] Concave guide elements 11, 12 are very well suited to intercepting the disruptive air currents 7 and the harmful secondary spray currents 7 and orienting them in the direction of the primary spray cone 5, so that the outflow of secondary spray 8 into the vicinity of the application nozzle 1 is reduced or prevented. This prevents deposits and contamination on the surfaces of the application nozzle 1 or machine parts caused by secondary spray 8. Likewise, the outflow of spray mist 8 into the vicinity of the application device can be prevented.

[0068] The first guide element 11 is in Figure 2 arranged at a distance from the nozzle outlet 1a. This distance, which can be, for example, 5mm-10mm, rarely 30mm or more, is necessary here, among other things, because the film 15 of coating medium is guided onto the wall of the application nozzle 1 before the jet of gaseous medium 6 impacts. Therefore, the first guide element 11 cannot be in contact with the application nozzle 1 in this case. On the other hand, it is not disruptive if secondary spray is guided onto the wall of the application nozzle due to the distance. Due to the constant flushing by the film of coating medium 15, contamination cannot occur here. This is different in the case of the second guide element 12, which is arranged on the other side. Here, it is entirely possible for the second guide element 12 to be in direct contact with the application nozzle 1, whereby deposits of secondary spray 7, 8 can be effectively prevented.

[0069] When setting small distances (approx. 1 mm to 5 mm between spray nozzle 1 and curved guide element 11, 12), the resulting Venturi effect, which occurs at this gap between guide element 11, 12 and air nozzle outlet opening 1a, can be used, so that the tip of the spray nozzle is efficiently and safely protected from contamination with secondary spray.

[0070] In addition, an optional housing 20 may be provided, which is preferably designed such that a completely or largely enclosed application space is formed by the running surface 4, the guide elements 11, 12, the application nozzle 1 and the housing 20. This also serves the purpose of preventing contamination by the secondary spray on the system or the application nozzle 1. Depending on the design of the guide elements 11, 12, this housing 20 may be omitted. Figure 2In addition, discharge channels 21 are provided in the housing 20 shown in order to be able to discharge coating medium that should be deposited on this housing 20 for further use.

[0071] Housings 20 of this type can, even if not explicitly mentioned, be provided and advantageous in all application devices according to aspects of the invention.

[0072] In principle, it is possible for the first guide element 11 and / or the second guide element 12 to be attached directly to the housing 20 or to be designed as an integral part of this housing 20. This simplifies the assembly of the guide elements and can also provide advantages in terms of manufacturing technology.

[0073] However, it may also be advantageous if these guide elements 11, 12 are not permanently connected to the housing 20. This is particularly advantageous when a sensitive and precise adjustment of the guide elements 11, 12 is necessary to achieve optimal flow guidance of the flows 7. In this case, it is advantageous if the guide elements 11, 12 are not permanently connected to the housing and, if applicable, also not to the application nozzle 1.

[0074] Figure 3 shows an application nozzle 1 according to a further aspect of the invention. It differs from the device of Figure 2This is due to the fact that the first guide element 11 is not concave, but convex in the shape of a cylinder. Here, the first guide element 11 acts by combining the flow effects of the fluid mechanics of air and spray in conjunction with suitable geometries in the application zone to generate targeted flow effects for the return of secondary spray 8.

[0075] The Coanda effect C occurs wherever a flow flows over a curved surface. The curvature of a surface creates a vertical pressure gradient on a flow tangential to the curved surface, so that the air flow is deflected in the direction of the curvature.

[0076] The pressure gradient is calculated as: dP / dr = ß.(dV 2< / r) (P: pressure, r: radius, ß: density of the medium, V: velocity). The higher the flow velocity and the smaller the radius of curvature, the stronger the pressure gradient, which causes the flow deflection.

[0077] The Venturi effect (V) is based on the conservation of energy. The Bernoulli effect (Venturi effect) is the decrease in static pressure in flowing fluids with increasing flow velocity. If a fluid flows through a channel and a second channel is connected to the side of the channel, a negative pressure is created in the second channel when the flow velocity in the first channel increases. The higher the flow velocity in the first channel, the greater the negative pressure, or suction effect, in the second channel.

[0078] The Magnus effect M is a phenomenon in fluid mechanics and describes the transverse force (force) experienced by a rotating round body (cylinder or sphere) in a flow. In the boundary layer, friction on the curved rotating surface creates a circulating flow, and on the side of this surface facing away from the flow, the air separates from the boundary layer (boundary layer separation). This creates a flow outside the boundary layer that satisfies the Bernoulli principle. If the curved surface around which the flow is flowing is not rotating, boundary layer separation occurs symmetrically. The Magnus effect arises because, with a rotating surface, boundary layer separation occurs later on one side of the rotating body, namely the side where the flow is in the same direction as the direction of rotation of the curved body. This gives the flow an impulse towards the side of the body rotating against the flow.The counterforce to this is the lateral deflection force of the curved body.

[0079] At the Figure 3 In the embodiment shown, the secondary spray 8 is returned to the spray generation zone of the application nozzle 1 so that the secondary spray 8 can mix with the primary spray and be reapplied to the moving surface 4. The portion of very fine secondary spray 8 that can pass through or overcome the gap between the guide element 11 and the moving surface 4 is transported further to the moving surface 4 by the Coanda effect C until the Magnus effect M initiates boundary layer separation.

[0080] If, for example, in an application in a film applicator, the relative position of the application device is selected such that the effect of the boundary layer separation due to the Magnus effect M has not yet grown sufficiently up to the transfer nip, the remaining secondary spray 8 can be guided stably up to this nip on the running surface 4, in this case the roller surface 4.

[0081] In this design, the distance between the first guide element 11 and the outlet 1a of the application nozzle 1 will often be somewhat greater than with concave guide elements. However, a distance of 40 mm, preferably 30 mm, should not be exceeded.

[0082] The Figure 4 The application nozzle 1 shown essentially corresponds to the one shown in Figure 2The difference lies in the arrangement of the application nozzle 1 relative to the running surface, or rather the angle of incidence θ of the spray curtain 5 on the running surface 4. While the spray curtain 5 in Figure 2 perpendicular to the running surface 4, the nozzle 1 is in Figure 4 inclined so that the spray curtain impacts at a smaller angle θ. The impact angle is advantageously less than 45°, preferably less than 40°, in particular 35° and less.

[0083] The angle of impact can be considered to be the angle θ that an imaginary line in the center of the spray cone 5 describes with the tangent of the running surface 5.

[0084] As in Figure 4As shown, the spray cone 5 is advantageously directed against the running direction B of the moving surface 4. When the coating medium 5 impacts the moving surface 4, the coating medium is accelerated tangentially in the direction of the moving surface. The part of the coating medium that is not transferred to the surface is reflected and moves approximately tangentially away from the surface in the direction of movement B of the surface 4. If the spray curtain 5 is directed against the running direction B of the moving surface 4, the reflected part is moved back in the direction of the spray curtain 5 and can, in particular in combination with a flat impact angle θ, be at least partially absorbed again by this spray curtain 5.

[0085] The Figure 5 The version shown is similar to that of Figure 4However, the application device here has only a first guide element 11. This guide element 11 is designed as an angled guide element 11. The angle λ of the angled guide element 11 can in particular be between 45° and 135°.

[0086] For structural reasons, both the angled and curved guide elements 11, 12 often have a relatively thick material. Since the guide elements 11, 12 are located in the immediate vicinity of the nozzle outlet, this thickness can sometimes be disruptive. Therefore, the curved or angled guide elements 11, 12 can be provided with a chamfer 25. This is exemplified in Figure 5 Such a guide element 11 with one or more bevels 25 shall be referred to as angled or curved in the context of this application. List of reference symbols

[0087] 1Application nozzle 1aNozzle outlet 2Fluid head 3Blow head 4Moving surface 5Spray curtain 6Jet of gaseous medium 7Air flow, circulation zone 8Secondary spray 11First curved or angled guide element 12Second curved or angled guide element 15Film of coating medium 20Housing 21Discharge channel 25Bevel BDirection of movement / running direction of the surface CCoanda effect MMagnus effect VVenturi effect θImpact angle λAngle of the angled guide element

Claims

1. Application device for applying a coating medium to a moving surface (4), in particular to a moving surface (4) in a machine for producing or processing a fibrous web, wherein the application device comprises an application nozzle (1) which is designed to spray the coating medium in the form of a spray curtain (5) onto the moving surface (4), wherein the spray curtain (5) extends over the entire application width of the application device, characterized in that the application device has a first guide element (11) for guiding air flows, which extends over the entire application width of the application device and which is arranged on a first side of the application nozzle in the immediate vicinity of the nozzle outlet (1a) of the application nozzle (1), wherein the first guide element (11) is curved or angled.

2. Application device according to claim 1, characterized in thatthe application device has a second guide element (12) for guiding air flows, which extends over the entire application width of the application device and which is arranged on a second side of the application nozzle in the immediate vicinity of the nozzle outlet (1a) of the application nozzle (1), wherein the second guide element wherein the second guide element (12) is curved or angled, and wherein the second guide element (12) is arranged on a different side of the application nozzle (1) than the first guide element (11).

3. Application device according to one of the preceding claims, characterized in that the first guide element (11) and / or the second guide element (12) is / are convex.

4. Application device according to one of the preceding claims, characterized in that the first guide element (11) and / or the second guide element (12) is / are concave.

5. Application device according to one of the preceding claims, characterized in thatthe first guide element (11) and / or the second guide element (12) have a distance of less than 40 mm, in particular between 0 mm and 30 mm, from the outlet (1a) of the application nozzle (1).

6. Application device according to one of the preceding claims, characterized in that the first guide element (11) and / or the second guide element (12) are designed as curved guide elements (11, 12) and have radii of curvature that are between 2 mm and 40 mm, preferably less than 20 mm 7. Application device according to one of the preceding claims, characterized in that the arc length of the first guide element (11) and / or the second guide element (12) is between 20° and 120°, preferably between 30° and 90°.

8. Application device according to one of claims 1 to 5, characterized in that the first guide element (11) is designed as an angled guide element (11) and in particular has an angle (λ) between 45° and 135°, preferably between 90° and 135°.

9. Application device according to one of the preceding claims, characterized in that the application nozzle (1) is arranged such that the spray curtain (5) strikes the moving surface (4) at an angle of 45° or less, preferably 40° or less, particularly preferably 35° or less.

10. Application device according to claim 9, characterized in that the spray curtain (5) is directed against the running direction (B) of the running surface (4).

11. Application device according to one of the preceding claims, characterized in that the application nozzle (1) comprises a fluid head (2) which is designed to produce a film of coating medium (15) and the application nozzle (1) further comprises a blowing head (3) which is designed to produce a linear jet of gaseous medium (6), wherein the jet of gaseous medium (6) impacts the film (15) of coating medium at the nozzle outlet (1a) to form a spray curtain (5).

12. Application device according to claim 11, characterized in that the film (15) of coating medium is guided onto the wall of the application nozzle (1) before the jet of gaseous medium (6) impacts.

13. Film applicator for applying coating medium to a fibrous web (4), comprising a first applicator roller and a second applicator roller which form a transfer nip through which the fibrous web is guided, wherein the film applicator has a first applicator device for applying a coating medium to the first applicator roller and / or a second applicator device for applying a coating medium to the second applicator roller, and wherein the first applicator device and / or the second applicator device is designed according to one of the preceding claims.

14. A method for applying a coating medium to a moving surface (4), in particular to a moving surface (4) in a machine for producing or processing a fibrous web using an application device according to one of claims 1 to 12, wherein the coating medium can in particular be a starch solution.

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