Application unit

Abstract

The invention relates to an application unit for applying a liquid or pasty coating medium to a moving surface, in particular to a rotating transfer roller, of a machine for producing or processing a fibrous web, wherein the application unit comprises an application nozzle for generating a primary spray of coating medium, wherein the application unit has an application chamber which is delimited on one side by the moving surface, and has at least one opening to the surroundings, and wherein the application nozzle is directed onto the moving surface such that, during operation of the application unit, a secondary spray of coating medium is generated in the interior of the application chamber, characterised in that the application unit has a deflection element which is arranged in such a way that the secondary spray exiting from the opening strikes the deflection element directly.

Description

[0001] Commissioned work

[0002] The invention relates to an application device for applying a liquid or pasty coating medium to a moving surface according to the preamble of claim 1.

[0003] A variety of coating processes are known for applying coating media to paper or board webs. Film presses are often used, particularly for starch application. A film of the coating medium is applied to a transfer roller and then transferred to the fiber web in a transfer nip.

[0004] Often, the coating medium is applied in excess to the transfer roller and then metered to the desired application quantity using suitable doctor blade metering systems. Such doctor blade metering systems are described, for example, in document DE102004029565 A1.

[0005] As part of the further development of the film press, the use of application rolls with very hard roll covers (0 to 5 P&J, or over 60 ShD) was introduced when operating the film press with higher nip loads (80 to 180 kN / m).

[0006] The high pressure and the short residence time of the substrate in the nip due to the very small contact zone between the rollers in the roller nip leads to a better penetration and distribution of the starch into the structure of the fibrous web, so that a higher efficiency of the starch (higher strengths with the same application quantity) can be achieved.

[0007] The use of very hard roller covers in doctor blade metering systems leads to increased wear on the metering elements used, as these metering elements are in direct contact with the rotating roller surface. The hard roller covers also experience wear or can develop marks, for example, on the profile of the doctor rods. The option of slightly varying the application rate of the volumetric metering element by changing the contact pressure on the metering element is also no longer possible, as the surface of the application roller cannot be deformed due to its increased hardness. Thus, a slight adjustment of the application rate of the volumetric metering element is no longer possible.

[0008] In the past, contactless dosing systems were therefore developed, particularly for use with hard rollers, in which the coating medium is no longer added in excess, but is dosed before it is applied.

[0009] For example, EP3332955 B1 discloses coating units in which the coating medium is sprayed onto the application rollers via a series of spray nozzles. The coating medium is applied in a pre-dosed manner; contacting dosing elements are eliminated. Thus, such spray coating units are particularly suitable for application to hard rollers.

[0010] However, during spray application, not the entire amount of sprayed coating medium is transferred to the surface of the application roller. Typically, a transfer rate of 80%-95% can be achieved. The remaining coating medium that is not transferred to the application roller—5%-20%, as much as a secondary spray of coating material—forms a secondary spray that remains in the spray chamber. This secondary spray would quickly contaminate the entire spray chamber and its internal components. To prevent this, EP3332955 B1 provides the spray chamber with an exhaust system. This exhaust system extracts the secondary spray and recirculates it for reuse.

[0011] However, such extraction is structurally complex and generates considerable operating costs due to the continuous provision of negative pressure. To avoid these costs, special spray application units have been developed, which are described in the documents DE 10 2022 105 510 A1 and DE 10 2022 105 518 A1. These units use a special application chamber that is largely enclosed and is flushed by the coating medium itself. If the resulting secondary spray deposits on the boundaries of the application chamber, it is directly absorbed by the supplied coating medium and directly fed back into the coating process. The problem of contamination can thus be largely avoided. However, this application chamber also has a small opening through which a small portion of the secondary spray can escape into the environment, which can lead to contamination of the surrounding machine parts with coating medium.To avoid this, an extraction system is often required here as well. Even though this extraction system can be relatively small and simple, it would still be desirable to be able to do without it.

[0012] It is therefore the object of the invention to overcome the disadvantages of the prior art.

[0013] In particular, the invention aims to propose an application unit that does not require extraction for the secondary spray. It is also an object of the invention to enable reliable recirculation and recycling of the coating medium contained in the secondary spray. Furthermore, it is an object of the invention to prevent contamination of the machine parts by the coating medium. Finally, it is an object of the invention to reduce the operating costs, in particular the energy consumption, of such an application unit.

[0014] 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.

[0015] An application unit is proposed for applying a liquid or pasty coating medium to a moving surface of a machine for producing or processing a fibrous web, wherein the application unit comprises an application nozzle for generating a primary spray of coating medium, wherein the application unit has an application space which is delimited on one side by the moving surface and has at least one opening to the environment, and wherein the application nozzle is directed towards the moving surface in such a way that, during operation of the application unit, a secondary spray of coating medium is generated inside the application space.

[0016] According to the invention, it is provided that the application unit has an impact element which is arranged in such a way that the secondary spray emerging from the opening directly hits the impact element.

[0017] The moving surface can, for example, be the surface of a rotating transfer roller, from which the coating medium is then transferred to a moving fiber web in a transfer nip.

[0018] It is also conceivable for the fibrous web itself to provide the running surface, so that the coating medium is applied directly to the fibrous web. The fibrous web can run freely, but is preferably supported by a roller or a covering.

[0019] The coating medium can, in particular, be a starch solution. Alternatively, the coating medium can consist solely of water or of coating colors with finely dispersed, solid microparticles, such as mineral coating pigments such as CaCO3, kaolin, talc, or other mineral pigments, or with polymer pigments. Aqueous dispersions of fiber-based substances such as nanofibrillated cellulose, microfibrillated cellulose, nanocellulose, and pulp fibers are also possible. Other coating media are also possible.

[0020] The application space and its opening to the environment can be realized in very different ways, as the examples shown in the figures illustrate.

[0021] Unless otherwise stated, percentages in this application are always to be understood as percentages by weight (wt%). Spray application units generally apply liquid quantities in the range of 3 ml / m 2up to 50 ml / m 2 on surfaces or substrates moving at speeds in the range of 400 to 2000 m / min. Depending on the atomization principle used to generate the spray, air volumes in the range of 200 to 2000 m 3 / h / m may be contained in the spray.

[0022] As already explained, when applying the primary spray to a moving surface, a transfer rate of between 80 and 95% can be achieved, so that between 5% and 20% of the original amount of coating medium remains in the air volume of the reflected secondary spray. For example, if a primary spray with an air volume of 1000 m 3 / h / m with a liquid flow of 20 L / min / m is applied to a substrate, approximately 16 to 19 L / min / m are transferred to the substrate. The remaining liquid flow (1 to 4 L / min / m) remains in the air flow at 1000 m 3 / h / m, and in the worst case scenario, are transported by this airflow into the machine shop, where they would condense on machinery and furniture. In addition to soiling the machine, this also results in large quantities of coating medium being lost. For this reason, the air is often extracted with the secondary spray, which, however, entails significant costs, particularly energy costs for operating the extraction system.

[0023] All of this can be avoided by commissioned works according to aspects of the present invention.

[0024] The inventor has recognized that the application of the primary spray to the running surface can be understood as a dehumidification of this spray, with 80-95% of the moisture contained remaining on the surface.

[0025] If the flow of the secondary spray can be guided in such a way that it can also impact a suitably shaped surface (= impact element), the process of "dehumidification" or liquid removal repeats with a transfer rate in the range of 80% to 95%. Thus, in the above example, with a residual liquid flow of 1 to 4 L / min / m, only 0.2 to 0.8 L / min / m remain from the secondary spray flow after impact with a suitable surface. By repeating or cascading the process further, further "dehumidification" or liquid removal from the air flow of the secondary spray can be achieved, so that only a minimal amount of liquid is transported further with the air.

[0026] The principle of the baffle plate effect for dehumidification or the removal of liquid droplets from the secondary spray has been experimentally tested and confirmed. The orientation or shape of the baffle element can be selected or adjusted to achieve optimal separation of air and liquid from the secondary spray.

[0027] No additional energy is required to dehumidify the secondary spray using impact elements. Instead, the energy used to generate the primary spray, which feeds the flow of the secondary spray, can be used for dehumidification; this energy was previously released unused into the environment.

[0028] For application units according to aspects of the present invention, various application nozzles can be used.

[0029] In particular, conventional spray nozzles, such as those described in EP3332955, can be used. In this case, the application chamber is formed by the interior of the enclosure. For this purpose, an opening to the environment can be provided in the application chamber, with a suitable baffle element installed. The extraction system described in EP3332955 can then be dispensed with.

[0030] Application units according to aspects of the invention are also very advantageous in combination with the application nozzles described in DE10 2022 105 518 or DE 10 2022 105 510. For example, it can be provided that the application unit comprises an application nozzle for generating a primary spray in the form of a spray curtain of coating medium, and the application space is formed and delimited by

[0031] • the running surface

[0032] • at least part of the wall of the application nozzle

[0033] • the spray curtain

[0034] • the opening in the form of the narrowest gap between the running surface and the application nozzle.

[0035] It is possible, but not absolutely necessary, that a film of flowing coating medium is applied to the boundary provided by at least part of the wall of the application nozzle.

[0036] In particular, it can be provided that this application nozzle comprises a fluid head which is designed to produce a film of coating medium and the application nozzle further comprises a blow head which is designed to produce a linear jet of gaseous medium - preferably of air -, wherein an impact line is further provided at which the linear jet of gaseous medium impacts the film of coating medium to form a spray curtain, and wherein the blow head is arranged such that the spray curtain is directed in the direction of the running surface.

[0037] The order space can be formed and limited by

[0038] • the running surface

[0039] • the wall of the blow head

[0040] • the spray curtain

[0041] • the opening in the form of the narrowest gap between the moving surface and the die head, whereby the coating medium from the fluid head is applied to the die wall in such a way that the entire die wall inside the application chamber is covered with flowing coating medium. In the latter application nozzles, the opening of the application chamber to the environment is already created by the design of the gap between the moving surface and the wall of the application nozzle. Existing application units of this type can be easily retrofitted by attaching an impact element at a suitable location near this opening.

[0042] When building or renovating such systems, the application nozzle can already be installed in a suitable position on the machine so that there is sufficient space for an impact element.

[0043] The impact element can be implemented in various ways. In preferred embodiments, the impact element can comprise or consist of a baffle plate. Such a baffle plate can be designed as a straight plate in the impact area of ​​the primary spray, or as a convex or concave curved baffle plate. The radius of curvature of the convex or concave baffle plate can be, for example, between 1 cm and 60 cm.

[0044] The use of curved baffles is advantageous, among other things, because they allow the flow of the secondary spray to be directed and channeled. This allows for simple and compact cascaded baffle elements with multiple baffles.

[0045] A metal is suitable as a material for these impact plates - especially a corrosion-resistant steel or a polymer material.

[0046] During operation of an applicator according to aspects of the invention, the deposited coating medium settles on the impact element and then flows further under the influence of gravity or the momentum it contains. To enable reuse of this coating medium, preferred embodiments also provide a collecting device for returning the coating medium deposited from the secondary spray by the impact element for reuse. Such a collecting device can, for example, be integrated directly into the impact element in the form of a collecting channel. The opening for the discharge of the secondary spray can be designed in the form of a gap. This gap can, in particular, extend across the entire width of the applicator.

[0047] The opening can also be equipped with additional guide elements to ensure a defined point of impact of the main direction of the secondary spray on the impact element.

[0048] Furthermore, it can be provided that the impact element, in particular the impact plate, is arranged in such a way that at the point of impact of the main direction of the secondary spray emerging from the opening, the tangent of the impact element forms an angle of between 30° and 60°

[0049] During the tests, it was found that the separation of liquid and air is particularly efficient at impact angles in this range.

[0050] In addition, with this inclination, the deposited coating medium can flow downwards and the dehumidified air can be discharged upwards.

[0051] It may be advantageous if the point of impact and / or angle of impact of the main direction of the secondary spray on the impact element can be changed. This can be advantageous, for example, if the flow conditions of the emerging secondary spray change when the application rate or operating speed changes.

[0052] To adjust the impact point or angle, the impact element can be designed to be movable. In particular, the distance to the opening and / or the angle of inclination can be changed.

[0053] Alternatively or additionally, it is also possible for the opening itself to be adjustable. For example, if additional guide elements are provided at the opening, these can be adjustable to change the size of the opening and / or the main direction of the secondary spray. In advantageous embodiments, the impact element can be integrated into a larger structure, in particular into a housing. This allows for an efficient and compact implementation of this impact element.

[0054] The invention is explained below with reference to the figures. The figures show in detail:

[0055] Figure 1 : Commissioned work according to the state of the art

[0056] Figure 2: Application work according to one aspect of the invention

[0057] Figure 3: Application work according to a further aspect of the invention

[0058] Figure 4: A baffle element for an applicator according to a further aspect of the invention.

[0059] Figure 5 Application unit according to a further aspect of the invention

[0060] Figure 1 shows an applicator 10 for applying a liquid or pasty coating medium 15 to a moving surface 4, as is known, for example, from the documents DE 10 2022 105 510 A1 and DE 10 2022 105 518 A1. The applicator 10 comprises an application nozzle 1 for generating a primary spray 5 in the form of a spray curtain 5a, which extends essentially across the entire width of the application nozzle 1. The moving surface 4 can be, for example, the surface 4 of a rotating transfer roller. A starch solution 15 can be selected as the coating medium 15.

[0061] The application unit 10 has an application space 20 which is formed and limited by

[0062] • the running surface 4

[0063] • at least part of the wall of the application nozzle 1

[0064] • the spray curtain 5a

[0065] • an opening 7 in the form of the narrowest gap 7 between the moving surface 4 and the application nozzle 1. A film of flowing coating medium 15 is applied from a fluid head 2 to the part of the wall of the application nozzle 1 that delimits the application space 20. The application nozzle 1 further comprises a blow head 3, which is designed to generate a linear jet of gaseous medium—usually air—which impacts the film of coating medium 15 at an impact line, thereby forming the spray curtain 5a. The blow head 3 is arranged such that the spray curtain 5a is directed in the direction of the moving surface 4.

[0066] A large portion of the coating medium 15 contained in the spray curtain 5a is transferred to the moving surface 4, but not all of it. As a result, during operation of the application unit 10, a secondary spray 6 is created from the portion of the coating medium 15 that was not transferred to the moving surface 4. This secondary spray 6 is created, at least for the most part, inside the application chamber 20.

[0067] In this embodiment, the coating medium 15 of the secondary spray 6 will largely accumulate on the moving surface 4, the wall of the application nozzle 1, or the spray curtain 5a, where it is transported further with the coating medium 15 already present there. However, a certain portion of the secondary spray 6 will leave the application chamber 20 through the opening 7 in the direction H of the surroundings.

[0068] The coating medium 15 contained in this part of the secondary spray 6 can precipitate on machine parts and contaminate them. Furthermore, the medium 15 cannot be recycled and reused.

[0069] The applicator 10 shown in Figure 2 is designed according to one aspect of the invention. The applicator 10 shown in Figure 1 is extended by a baffle element 8 in the form of a baffle plate 8. The baffle plate 8 is designed as a straight plate 8, which is arranged such that the secondary spray 6 emerging from the opening 7 directly strikes the baffle element 8. The baffle element 8 is advantageously arranged such that it forms an angle of between 30° and 60° with the main direction H of the secondary spray 6 emerging from the opening 7.

[0070] The baffle plate effect creates a separation between the liquid coating medium 15 and the gas - usually the air of the secondary spray 6. The coating medium precipitates on the baffle plate 8 and runs along it under the influence of gravity and the momentum it contains.

[0071] In addition, the impact element 8 in Figure 2 has a collecting device 9 for returning the coating medium 15 separated from the secondary spray 6 by the impact element 8 for reuse. The collecting device 9 can, for example, be integrated into the impact element 8 as a collecting channel 9.

[0072] Figure 3 shows an applicator 10 according to a further aspect of the invention. Similar to the document EP3332955, the coating medium 15 is sprayed onto the applicator roller 4 via a series of spray nozzles in the form of a primary spray 5. Here, too, only a portion of the coating medium 15 is transferred to the roller 4, while the remaining portion forms a secondary spray 6. In order to prevent uncontrolled escape of the secondary spray 6 into the environment, the applicator 10 in Figure 3 has a housing 25. The interior of this housing 25 forms the application space 20. In contrast to the applicators 10 of the prior art, the applicator 10 in Figure 3 does not have an extraction system. Instead, an opening 7 to the environment is provided in the housing 25, from which opening the secondary spray 6 can escape. Here, too, a baffle element 8 is provided, which is arranged so that the secondary spray 6 emerging from the opening 7 hits the baffle element 8 directly.The impact element 8 in Figure 3 is designed as a convex impact plate 8. This convex impact plate 8 can be designed such that it has a radius of between 1 cm and 60 cm at the point of impact of the main direction H of the secondary spray.

[0073] Figure 4 shows another possible embodiment of an impact element 8. The impact element 8 has two impact plates arranged in a cascade. The secondary spray 6 emerging from the opening 7 strikes the first impact plate. As a result, the majority of the coating medium 15 contained therein is separated and collected in a collecting device 9. The air flow of the secondary spray 6 and the remaining coating medium 15 contained therein is directed by a suitable shape of the impact plate so that it strikes a second impact plate. There, the liquid and air are again separated by means of the impact plate effect. After such a second dehumidification, the air flow of the secondary spray 6 usually only contains minimal amounts of coating medium 15. If required, a third or further cascading stages can also be added.

[0074] Figure 5 shows an embodiment of an applicator 10 according to a further aspect of the invention. A primary spray 5 is again generated by means of an applicator nozzle 1. This primary spray 5 can be generated via a number of spray nozzles, similar to that shown in Figure 3. Alternatively, the primary spray 5 can be provided in the form of a spray curtain 5. In the latter case, the applicator nozzle can then have a blower head 3 and a fluid head 2—similar to the applicator nozzles 1 in Figures 1 or 2. The primary spray 5 is directed onto the moving surface 4, which is formed by the surface 4 of a rotating transfer roller.

[0075] When executing Figure 5, the application space 20 is again formed and limited by

[0076] • the running surface 4

[0077] • the primary spray 5, in particular the spray curtain 5a

[0078] • and part of the wall of the application nozzle 1

[0079] The application chamber 20 is kept very small in this embodiment. The opening 7 in the form of the narrowest gap 7 between the moving surface 4 and the application nozzle 1 can be designed by the construction of the application nozzle 1 itself, for example by suitable attachments to this application nozzle 1. In the case of Figure 5, for example, a collecting device 9 for the deposited coating medium 15 is provided for this purpose, but other designs are possible. Such integral attachments such as this collecting device 9 can be regarded as parts of the application nozzle 1. The secondary spray 6 emerges from the opening 7 essentially along the main direction H and strikes the impact element 8 again. This impact element 8 is designed here in the form of a baffle plate 8. The baffle plate 8 is expanded in such a way that it forms a further housing 25 or is integrated into it. The deposited coating medium can then be distributed along the baffle plate 8 orParts of the housing and, if applicable, parts of the application nozzle are removed. The coating medium is collected in the collecting device 9 and returned for reuse.

[0080] Even in this embodiment of the impact element 8 as part of a housing 25, the impact element 8 can be shaped and / or arranged differently as required. Straight, concave, or convex impact elements 8 are possible. Likewise, the angle at which the main direction H strikes the impact element 8 can be adjusted as required, for example, between 30° and 60°.

[0081] Furthermore, the housing 25 of Figure 5 has an articulated connection 30. This is optional, but generally proves to be very advantageous. As a result, part of the housing 25 functions as a folding element 25a. The folding element 25a can be folded away via the articulated connection 30, making the interior of the enclosed space accessible for maintenance work. Instead of an articulated connection 30, alternative movable connections 30 can also be provided to ensure accessibility to the enclosed space. In contrast to conventional housings 25, such housings 25, which partially provide the function of an impact element 8, have potentially greater wear at the impact point. Furthermore, depending on the operating conditions, deposits of coating material can also occur in the area of ​​the impact point.Therefore, the possibility of simple and quick inspection and maintenance, which is made possible by such a movable connection, is very advantageous.

[0082] Between the housing 25, in particular the flap element 25, and the moving surface 4, an outlet 70 is usually located due to the design. Due to the efficient dehumidification of the secondary spray 6 by means of the impact element 8, the air thus entering is barely loaded with coating medium. Furthermore, this outlet can be kept small, in particular smaller than the opening 7. List of reference symbols

[0083] 1 application nozzle

[0084] 2 fluid head

[0085] 3 Blow head

[0086] 4 Running surface

[0087] 5 Primary spray

[0088] 5a Spray curtain

[0089] 6 Secondary spray

[0090] 7 Opening

[0091] 8 Impact element, impact plate

[0092] 8a Additional impact element

[0093] 9 Collection facility

[0094] 10 commissioned works

[0095] 11 Wall of the blow head

[0096] 15 Coating medium

[0097] 20 order room

[0098] 25 Enclosure

[0099] 25a Folding element

[0100] 30 Movable connection; articulated connection.

[0101] 70 Outlet enclosure

[0102] H Main direction

Claims

Patent claims 1 applicator (10) for applying a liquid or pasty coating medium to a moving surface (4) - in particular to a rotating transfer roller (4) - of a machine for producing or processing a fibrous web, wherein the applicator (10) comprises an application nozzle (1) for generating a primary spray (5) of coating medium, wherein the applicator (10) has an application chamber (20) which is delimited on one side by the moving surface (4) and has at least one opening (7) to the environment, and wherein the application nozzle (1) is directed towards the moving surface (4) in such a way that, during operation of the applicator (10), a secondary spray (6) of coating medium (15) is created inside the application chamber (20), characterized in that the applicator (10) has an impact element (8) which is arranged in such a way that the secondary spray (6) emerging from the opening (7) strikes the impact element (8) directly. 2 Application unit (10) according to claim 1, characterized in that the application unit (10) comprises an application nozzle (1) for generating a primary spray (5) in the form of a spray curtain (5a) of coating medium, and the application space (20) is formed and limited by • the running surface (4) • at least part of the wall of the application nozzle (1) • the spray curtain (5a) • the opening (7) in the form of the narrowest gap (7) between the running surface (4) and the application nozzle (1) Applicator (10) according to claim 2, characterized in that a film of flowing coating medium (15) is applied to the boundary provided by at least part of the wall of the applicator nozzle (1). Applicator (10) according to claim 2 or 3, characterized in that the applicator nozzle (1) comprises a fluid head (2) designed to produce a film of coating medium (15), and the applicator nozzle (1) further comprises a blow head (3) designed to produce a linear jet of gaseous medium, wherein an impact line is further provided at which the linear jet of gaseous medium impacts the film of coating medium (15) to form a spray curtain (5a), and wherein the blow head (3) is arranged such that the spray curtain (5a) is directed in the direction of the moving surface (4).Application unit (10) according to claim 3, characterized in that the application space (20) is formed and limited by. • the running surface (4) • the wall of the blow head (11) • the spray curtain (5a) • the opening (7) in the form of the narrowest gap (7) between the moving surface (4) and the blow head (3), and wherein the coating medium from the fluid head (2) is applied to the wall (11) of the blow head (3) in such a way that the entire wall (11) of the blow head (3) inside the application space (20) is covered with flowing coating medium (15). Application unit (10) according to one of the preceding claims, characterized in that the impact element (8) comprises or consists of an impact plate (8). Applicator (10) according to claim 6, characterized in that the impact plate (8) is designed as a straight, convex, or concave impact plate (8). Applicator according to one of the preceding claims, characterized in that the impact element (8) has a plurality of impact plates (8) arranged in a cascading manner. Applicator (10) according to one of the preceding claims, characterized in that a collecting device (9) is additionally provided for returning the coating medium (15) separated from the secondary spray (6) by the impact element (8) for reuse. Applicator (10) according to one of the preceding claims, characterized in that the opening (7) is designed in the form of a gap which extends in particular over the entire width of the applicator (7).Applicator (10) according to one of the preceding claims, characterized in that the impact element (8), in particular the impact plate (8), is arranged such that it encloses an angle of between 30° and 60° with the main direction (H) of the secondary spray (6) emerging from the opening (7). Applicator (10) according to one of the preceding claims, characterized in that the impact element (8) comprises a convex or concave impact plate (8) which has a radius of between 1 cm and 60 cm at the point of impact of the secondary spray (6). Applicator (10) according to one of the preceding claims, characterized in that the impact element (8) and / or the opening (7) is adjustable such that the point of impact and / or the. The angle of impact of the main direction of the secondary spray (6) on the impact element (8) can be varied. The applicator (10) according to one of the preceding claims, characterized in that the impact element (8) is integrated into a larger structure, in particular into a housing (25).

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