Device and method

Abstract

The invention relates to an application device and method for coating a fibrous material web, in particular a paper, packaging or cardboard web, wherein the application device comprises an application nozzle for applying a coating medium, in particular a starch solution, to a moving surface in an application width (B), and wherein the application nozzle is designed to produce a spray mist of coating medium, characterised in that the application device has limiting means for varying the application width (B).

Description

[0001] Device and method

[0002] The invention relates to an application device for coating a fibrous web according to the preamble of claim 1 and to a method for coating a fibrous web using such an application device.

[0003] During the production or processing of fibrous webs, particularly paper, packaging or cardboard webs, it is common practice to provide these webs with one or more coatings.

[0004] These coatings can, for example, be the application of pigment-containing coatings or barrier media, for example based on polyvinyl alcohol or micro- / nanofibrillated cellulose.

[0005] Another common application is the application of a starch solution to the fibrous web. This can influence the surface of the web, while also improving its strength properties.

[0006] Especially with starch solutions, coating is usually done indirectly. The coating medium is metered onto the moving surface of a transfer roller, from where it is transferred to the fiber web via a transfer nip.

[0007] Various systems are known for dosing onto the transfer roller.

[0008] In a conventional film press, excess coating medium is applied to the transfer roller and then metered to the desired application rate using a suitable doctor blade metering system. The application rate is varied by doctoring off more or less of the excess coating medium. Changing the application rate usually requires changing the doctor rod, which requires the machine to be shut down. Such doctor blade metering systems are described, for example, in document DE102004029565 A1.

[0009] Alternatively, application systems are known, for example from EP3332955 B1, in which the coating medium is sprayed onto the application rollers via a series of spray nozzles. Unlike doctor blade dosing systems, these systems do not require contact dosing systems.

[0010] From the applicant's patent application DE 102022105518.3, an application nozzle is known in which a curtain or film is dispensed from a slot die, which is then atomized by means of a blowing head.

[0011] When changing the grade produced, the difficulty arises that, for example, due to varying shrinkage in the dryer section, the width of the fiber web can vary significantly upon entering the application device. If a more severely shrunk web passes the transfer nip, not all of the coating medium is transferred to the fiber web. Although coating medium is applied to the transfer roller in the edge areas, it cannot be absorbed by the fiber web.

[0012] To keep the transfer rollers clean, narrow edge scrapers are used to remove excess coating medium from the edge area of ​​the roller. To accommodate the changing web width, the edge scrapers are designed to be movable in the width direction of the web, i.e., in the cross-machine direction. The edge scrapers are moved manually. Such edge scrapers are described, for example, in documents DE102004039162 A1 or DE202017101177 U1.

[0013] One disadvantage of the current technology is that these edge scrapers are wear parts that must be replaced regularly. If the edge scrapers are not working properly, additional coating medium from the transfer roller can adhere to the edge of the paper web. Even if these are only small amounts, they accumulate during winding and can lead to a bulge on the edge of the reel. This leads to increased waste.

[0014] The object of the present invention is to overcome the problems of the prior art.

[0015] It is a further object of the invention to propose a possibility for a more cost-effective coating.

[0016] It is also an object of the invention to further automate the coating process.

[0017] The object is achieved according to the invention by an embodiment according to the independent claims. Further advantageous embodiments of the present invention can be found in the subclaims.

[0018] The invention proposes an application device for coating a fibrous web, in particular a paper, packaging, or cardboard web. The application device comprises an application nozzle for applying a coating medium, in particular a starch solution, in a specific application width to a moving surface, and the application nozzle is configured to generate a spray of coating medium. According to the invention, the application device comprises limiting means for varying the application width.

[0019] The inventors realized that it is more practical to adjust the application width directly in the application nozzle. This allows only the exact required application width to be applied to the moving surface. This not only saves unused application medium in the edge area, but also advantageously allows edge scrapers to be dispensed with entirely, further reducing the effort and cost of the coating process. Finally, systems that previously collected and drained the excess, scraped-off coating medium can be dispensed with. This also makes the coating process more cost-effective.

[0020] Thus, it is particularly advantageous if the running surface is provided by the surface of a transfer roller, and the application device also has a transfer nip in which the coating medium is transferred to the fibrous web.

[0021] As with previously known film presses, simultaneous, indirect application on both sides is also possible. For this purpose, a transfer nip can be formed from two transfer rollers, and a coating medium can be applied to each of the two surfaces of the transfer rollers. At least one, preferably both, application nozzles are designed according to aspects of the invention.

[0022] The application width and the width of the running surface can be up to 10m or more on modern systems.

[0023] The inventors have identified those application devices in which the coating medium is sprayed onto the moving surface as particularly suitable for varying the application width.

[0024] Application nozzles for such application devices can be implemented in different ways,

[0025] In one embodiment, the application nozzle may have an outlet gap extending in the width direction of the application nozzle and configured to produce a film of coating medium or a curtain of coating medium. The application nozzle further comprises a blowing head configured to produce a linear jet of gaseous medium. At an impact line, the linear jet of gaseous medium impacts the film or curtain of coating medium. This forms a spray mist. The blowing head is arranged such that the spray mist is directed toward the moving surface.

[0026] Air can be used as a gaseous medium.

[0027] The application nozzle and the outlet gap both extend at least across the application width, usually across the entire width of the moving surface. The same applies to the blow head and the linear jet of gaseous medium.

[0028] In such application nozzles, the limiting means can, for example, comprise an adjustable closure device to close at least one edge zone, in particular both edge zones, of the outlet gap. To vary the application widths, the length of the closed edge zone(s) can be variable.

[0029] For example, a cover element for closing the outlet gap can be provided on at least one, in particular on both edge zones, wherein the at least one cover element is displaceable along the width direction of the application nozzle.

[0030] Alternatively or additionally, the closure device can also be provided with a plug that engages the outlet gap in the edge zones, thus closing them. Here, too, the at least one plug is movable along the width direction of the application nozzle.

[0031] Furthermore, the adjustable closure device can be provided with a servomotor for moving the cover element and / or the plug. This allows the application width to be varied automatically without requiring the machine to be shut down.

[0032] In alternative designs, the coating medium can continue to exit the outlet gap in the edge zone. However, to prevent the coating medium from escaping onto the moving surface, one or more collecting trays can be provided. These collecting trays can be designed so that the spray mist is collected and diverted by the collecting tray before it hits the moving surface. The collecting tray can be designed to be movable along the width direction of the application nozzle. This also allows the application width to be varied very efficiently.

[0033] In an alternative embodiment, it can be provided that the application nozzle has a number of spray nozzles for generating a spray of coating medium, which are distributed across the width of the application nozzle, and that the limiting means are designed to completely or partially close the spray nozzles in at least one edge zone of the application nozzle or to prevent the application of the coating medium to the moving surface...

[0034] This can be achieved, for example, by the limiting means being designed to completely or partially interrupt the supply of coating medium to the spray nozzles.

[0035] Alternatively or additionally, it may be provided that the limiting means are designed to completely or partially block the outlet from the spray nozzles.

[0036] In yet alternative embodiments, it can also be provided that the coating medium continues to emerge from the spray nozzles in the edge zone. However, to prevent the coating medium from emerging onto the moving surface, one or more collecting troughs can be provided. These collecting troughs can be designed so that the coating emerging from the spray nozzles is collected and drained away by the collecting trough before it hits the moving surface. The collecting trough can be designed to be movable along the width direction of the application nozzle. This also allows the application width to be varied very efficiently. Regardless of the design of the application nozzle, it can be advantageous if the application device also comprises sensors for detecting the web edge of the fibrous web, which sensors are arranged at a measuring position in front of the application nozzle as seen in the running direction of the fibrous web.

[0037] These sensors for detecting the web edge can be designed in particular as optical sensors so that the position of the web edge can be determined without contact.

[0038] Furthermore, a control unit can be provided that is configured to vary the application width based on an explicit specification or on suitable measured values. This can advantageously be done based on the determined web edges.

[0039] Furthermore, a method for coating a fibrous web, in particular a paper, packaging or cardboard web, with a coating medium, in particular a starch solution, is proposed, wherein an application device according to one of the aspects of the invention is used for coating.

[0040] In particular, the method may comprise the steps:

[0041] I. Detecting at least one edge of the fibrous web

[0042] II. Adjusting the application width (B) of the coating medium depending on the position of the detected web edge

[0043] Advantageously, the application width is adjusted so that no coating medium is applied outside the web edge. This makes it possible to dispense with the edge scrapers known from the prior art.

[0044] The web edge of the fibrous web can be detected at a measuring position in front of the application nozzle, with no additional drying units located between the measuring position and the application nozzle. This has the advantage that the fibrous web no longer shrinks significantly between the measuring position and the application nozzle. Thus, the detected web edge also corresponds to the web edge at the application device.

[0045] Optical sensors, such as camera systems in conjunction with suitable evaluation software, are very advantageous for detecting the web edge.

[0046] With an application device according to aspects of the invention, further process variants can also be implemented. For example, the grade change can be further automated.

[0047] For this purpose, it is advantageous to store an expected web width or the expected web edge positions for each grade to be produced. These values ​​can either be stored as fixed empirical values ​​or determined or adjusted from measurements from previous production runs.

[0048] The web edge can then be detected by reading the stored values. This even eliminates the need for sensors to detect the web edge.

[0049] If a grade change is pending, a control unit can be used to compare the current position of the web edges with the position of the web edges expected for the new grade.

[0050] If the future web will be narrower than the current one, it is advantageous to first reduce the application width and then start the grade change. Conversely, if the future web is wider than the current one, you can start with the grade change first and then increase the application width once the web has reached its maximum width.

[0051] In this way, it can be avoided that, when changing grades, the coating medium comes into contact with areas that are not covered by the fiber web.

[0052] The invention is explained below with reference to figures. The invention is not limited to the illustrated embodiments. The figures show in detail: Figure 1 shows an application device according to one aspect of the invention.

[0053] Figure 2 shows part of an application device according to a further aspect of the invention

[0054] Figure 3 shows part of an application device according to a further aspect of the invention.

[0055] Figure 1 shows an application device according to a further aspect of the invention. The application nozzle 1 has a nozzle head with an outlet gap 2 extending in the width direction of the application nozzle 1. However, the coating medium is dispensed in the form of a film 15, which is deposited on a support surface 7. This support surface 7 can be designed as a separate component. Alternatively, however, it can also be provided that a portion of the wall of the application nozzle 1 is used as the support surface 7.

[0056] In addition, the application nozzle 1 has a blow head 5 designed to generate a linear jet of gaseous medium, and wherein an impact line is further provided at which the linear jet of gaseous medium impacts the film 15 of coating medium and forms a spray curtain 8. The blow head 5 is arranged such that the spray curtain 8 is directed toward the moving surface 4.

[0057] In the embodiment shown in Figure 1, the running surface 4 is realized by the surface of a transfer roller 40. From this, the coating medium is transferred to the fibrous web in a transfer nip (not shown).

[0058] The application width B of the coating medium is varied across the width of the outlet gap. For this purpose, adjustable closure devices 25 are provided at each of the two edge zones 10 to close the outlet gap 2. In Figure 1, these closure devices 25 are implemented by means of cover elements 30 that close the outlet gap 2 from the outside. These cover elements 30 can be moved manually. Advantageously, suitable servomotors can also be provided for this purpose. In such designs, the adjustment of the application width B can be carried out entirely or largely automatically.

[0059] The application nozzle 1 of Figure 2 differs from the embodiment of Figure 1 in the type of adjustable closure devices 25 on the two edge zones 10. In Figure 2, these are implemented as movable plugs 35. These plugs engage in the outlet gap 2, thereby closing it. Here, too, at least one plug 35, in particular both plugs 35, are designed to be movable along the width direction of the application nozzle 1 to vary the application width B.

[0060] Figure 3 schematically illustrates an application nozzle 1 having a number of spray nozzles 6 for generating a spray mist 8 of coating medium, which are arranged distributed across the width of the application nozzle 1. Furthermore, limiting means are provided here, which, by means of two cover elements 30, completely or at least partially close the spray nozzles 6 in the two edge zones 10 of the application nozzle 1. In alternative embodiments, it is also possible to completely or partially interrupt the supply of coating medium to the spray nozzles 6.

[0061] Here, too, the cover elements 30 are designed to be movable along the width direction of the application nozzle 1. In this way, the application width B can be varied.

[0062] List of reference symbols

[0063] 1 application nozzle

[0064] 2 Outlet gap 4 Running surface

[0065] 6 spray nozzle

[0066] 7 Support surface

[0067] 8 Spray mist from coating medium

[0068] 10 Edge zone 15 Film of coating medium

[0069] 25 adjustable locking device

[0070] 30 cover element

[0071] 35 plugs

[0072] 37 Collecting tray 40 Transfer roller

[0073] B Application width

Claims

Patent claims 1. Application device for coating a fibrous web, in particular a paper, packaging or cardboard web, wherein the application device comprises an application nozzle (1) for applying a coating medium, in particular a starch solution, in an application width (B) onto a moving surface (4), and wherein the application nozzle (1) is designed to produce a spray mist (8) of coating medium, characterized in that the application device has limiting means for varying the application width (B).

2. Application device according to claim 1, characterized in that the running surface (4) is provided by the surface of a transfer roller (40), and that the application device also has a transfer nip in which the coating medium is transferred to the fibrous web.

3. Application device according to one of the preceding claims, characterized in that the application nozzle (1) has an outlet gap (2) which extends in the width direction of the application nozzle (1) and which is designed to produce a film of coating medium (15) or a curtain of coating medium, and the application nozzle (1) further comprises a blow head (5) which is designed to produce a linear jet of gaseous medium, and wherein an impact line is further provided at which the linear jet of gaseous medium impacts the film (15) or curtain (14) of coating medium to form a spray mist (8), and wherein the blow head (5) is arranged such that the spray mist (8) is directed in the direction of the moving surface (4).

4. Application device according to claim 3, characterized in that the outlet gap (2) and / or the linear jet of gaseous medium extend over the width of the moving surface (4).

5. Application device according to one of the preceding claims, characterized in that the limiting means comprise an adjustable Comprise a closure device (25) for closing at least one edge zone (10), in particular both edge zones (10) of the outlet gap (2), wherein the length of the closed edge zone (10) or edge zones (10) is variable.

6. Application device according to claim 5, characterized in that the adjustable closure device (25) has at least one, in particular both edge zones (10) in each case a cover element (30) and / or a plug (35) for closing the outlet gap (2), wherein the at least one cover element (30) is displaceable along the width direction of the application nozzle (1).

7. Application device according to one of claims 5 or 6, characterized in that the adjustable closure device (25) has a servo motor for displacing the cover element (30) and / or the plug (35).

8. Application device according to one of the preceding claims, characterized in that the application nozzle (1) has a number of spray nozzles (6) for generating a spray mist (8) of coating medium, which are arranged distributed over the width of the application nozzle (1), and in that the limiting means are designed to completely or partially close the spray nozzles (6) in at least one edge zone (10) of the application nozzle (1) or to prevent the application of the coating medium to the moving surface.

9. Application device according to one of the preceding claims, characterized in that at least one, in particular both edge zones (10) each has a collecting trough (37) for collecting the application medium before it hits the moving surface (4), wherein the at least one collecting trough (37) is displaceable along the width direction of the application nozzle (1).

10. Application device according to one of the preceding claims, characterized in that the application device also comprises sensors for detecting the web edge of the fibrous web, which sensors are arranged in front of the application nozzle (1) at a measuring position as seen in the running direction of the fibrous web.

11. Application device according to claim 9, characterized in that the sensors for detecting the web edge are designed as optical sensors.

12. A method for coating a fibrous web, in particular a paper, packaging or cardboard web, with a coating medium, in particular a starch solution, characterized in that an application device according to one of the preceding claims is used for coating.

13. The method according to claim 12, characterized in that the method comprises the steps: I. Detecting at least one edge of the fibrous web II. Adjusting the application width (B) of the coating medium depending on the position of the detected web edge 14. Method according to one of claims 12 or 13, characterized in that the application width is adjusted so that no coating medium is applied outside the edge of the web.

15. Method according to one of claims 12 to 14, characterized in that the detection of the web edge of the fibrous web takes place at a measuring position in front of the application nozzle (1), wherein no further drying units are arranged between the measuring position and the application nozzle (1).

16. Method according to one of claims 12 to 15, characterized in that for the types to be produced, an expected web width or the expected positions of the web edge are stored in a control unit and the detection of the web edge is carried out by reading the stored values ​​from the control unit.

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