Application 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, and wherein the application nozzle has an outlet gap designed to produce a film of coating medium or a curtain of coating medium, wherein means are provided to vary the application amount and the variation is based on a strength variable.

Description

[0001] Application device and method

[0002] The invention relates to an application device for coating a fibrous web, in particular a paper, packaging or cardboard web according to the preamble of claim 1, and to a method for coating 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-Znanofibrillated 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] Various application devices are known from the state of the art.

[0007] For example, the starch solution can be applied using a film press. The coating medium is applied in excess to the transfer roller and then metered to the desired application quantity using a suitable doctor blade metering system. The application quantity can be varied by doctoring off more or less of the excess coating medium. Changing the application quantity usually requires changing the doctor blade, which requires the machine to be shut down.

[0008] Such doctor blade metering systems are described, for example, in document DE102004029565 A1. To enable better penetration of the starch into the fiber web, transfer rollers with very hard surfaces have recently been increasingly used. In this case, such metering systems prove to be disadvantageous, as the hard roller surfaces cause the doctor blades to wear very quickly.

[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. Since the application quantity is metered by adjusting the application quantity of the spray nozzles, this does not necessarily require the machine to be shut down.

[0010] However, both the doctor blade dosing systems and the spray nozzles have the disadvantage that the application quantity can only be varied within relatively small limits.

[0011] The object of the invention is to overcome the weaknesses of the prior art.

[0012] In particular, the object of the invention is to propose an application device in which the application quantity can be varied within a wide range without the machine having to be stopped.

[0013] Furthermore, it is an object of the invention to propose an application device which is both low-wear and low-maintenance.

[0014] The object is achieved according to the invention by an application device according to claim 1 and a method according to claim 11. Further advantageous embodiments of the present invention can be found in the subclaims.

[0015] Proposed is an application device for coating a fibrous web, in particular a paper, packaging, or cardboard web, wherein the application device comprises an application nozzle for applying a coating medium to a moving surface, and wherein the application nozzle has an outlet gap which extends in the width direction of the application nozzle and is designed to produce a film of coating medium or a curtain of coating medium. Furthermore, the application device comprises means for varying the application quantity. Finally, it is provided that the application device has a control unit which is configured to determine a variation in the application quantity from at least one provided parameter for the strength of the fibrous web.

[0016] Such a device is particularly suitable for applying starch. Starch application is one way to influence the strength of a fibrous web. For a web with insufficient strength values, greater strength can be achieved by applying starch—or similar suitable coating media. However, to keep the costs for the coating medium low, it is advantageous not to apply more coating medium than necessary. The present application device, which includes both means for varying the application quantity and a control unit that determines an optimized application quantity based on one or more strength parameters, is therefore very advantageous for enabling cost-effective operation of the system.

[0017] In combination with appropriate actuators, the application device can also be easily integrated into a closed control loop.

[0018] The strength of a fibrous web can be described in various ways. For example, there is the tensile strength and tear propagation resistance in the machine and cross directions, the bursting strength, and the splitting strength, to name just a few. Typically, not all of these strength values ​​are relevant for a specific product, but rather only a single one or a small number of strength values. Parameters can be provided in the control unit for these strength value(s) relevant to the produced fibrous web.

[0019] The parameter(s) can be determined directly through direct measurement or indirectly. Since many strength measurements today are still destructive and can only be performed in the laboratory, not in a running machine, the strength parameters are often determined indirectly.

[0020] This can be done, for example, by measuring a quantity which is known - e.g. from tests - to correlate with the desired strength parameter.

[0021] Alternatively, more complex dependencies can also be used. For example, the strength parameter can be modeled from a variety of measured variables. This can be, for example, a physical or purely statistical model. Such model-based determinations of parameters are sometimes referred to as "virtual sensors."

[0022] Application nozzles with an outlet gap are already known per se. For example, DE202020107431 U1 describes a curtain nozzle with a uniform nozzle gap. The applicant's patent application DE 102022105518.3 describes an application nozzle in which a curtain or film is dispensed from a wide-slot nozzle, which is then atomized by a blowing head.

[0023] These nozzles offer advantages over doctor blade dispensing systems because they do not require contacting doctor blade elements and therefore no wearing parts. Furthermore, they prevent excess application, eliminating the need for time-consuming recycling and processing of excess application medium.

[0024] Compared to spray nozzles, these application nozzles with an outlet gap have the advantage of not only being more cost-effective than using a large number of spray nozzles, but also being significantly less prone to contamination.

[0025] The means for varying the application rate can, for example, comprise a conveying device (e.g., a pump) with a variable delivery rate. This can be implemented, for example, in the form of a speed-controlled pump. This design is advantageous because it can usually be retrofitted very quickly and easily, even to existing application nozzles.

[0026] However, these application nozzles still have the disadvantage that the application quantity can usually only be varied within relatively small limits, which is completely sufficient in some applications with a relatively small variation in the strength values, while in other applications a larger variation in the application quantity may be necessary.

[0027] The inventors have now recognized that this disadvantage can be overcome in a further embodiment of the invention by deviating from a previous basic principle of nozzle design. Previously, the goal, for example, when constructing a curtain nozzle, was to keep the outlet gap as constant as possible. DE202020107431 U1, for example, expends considerable effort to maintain the consistency of the gap. This is due to the fact that curtain applicators have so far been used almost exclusively for coating with pigment-containing coating colors. Here, this precision is very important for uniform coverage of the web and the associated uniform surface properties.

[0028] In the future, however, such nozzles will increasingly be used for starch application. In this case, the high precision of the gap is less important than the ability to vary the amount of applied starch over a very wide range. Therefore, the present invention proposes a variable gap width for the outlet gap.

[0029] By varying the gap width, a very wide range of application quantities can be covered in an elegant way. For example, increasing the gap width from 0.5 mm to 1 mm can double the application quantity. Increasing it to 2 mm can even quadruple it. Such large variations are advantageous for the system operator, as they allow, for example, a wide range of paper grades with very different requirements and application quantities to be produced on the same system. And this—with the appropriate design of the application device—can be achieved without system downtime.

[0030] Alternatively or additionally, the variation of the gap width can also be used to adjust the internal nozzle pressure of the application nozzle.

[0031] The internal nozzle pressure is an important parameter for a curtain nozzle or the described nozzles with a blowing head. Generally, the coating medium should not be forced out of the outlet gap, but rather leave the gap freely under the influence of gravity. Thus, the internal nozzle pressure should not be too high. However, depending on the rheology of the coating medium, different internal nozzle pressures can arise with the same flow rate and the same gap width. With an application nozzle according to one aspect of the invention, the gap width can be adjusted so that the internal nozzle pressure is within the desired range.

[0032] It is helpful to have a suitable sensor for determining this internal nozzle pressure. This measurement can be performed either directly inside the application nozzle. However, since such internal sensors are potentially more susceptible to contamination, it is usually more practical to perform the pressure measurement in an inlet of the coating medium.

[0033] The gap width can be varied in different ways or with different adjusting devices.

[0034] For example, a fixed gap with a large gap width can be provided, which is more or less covered by a movable cover.

[0035] Alternatively, at least one wall of the outlet gap can be formed from a movable wall element. This wall element can then be used to make the outlet gap itself narrower or wider.

[0036] The panel or wall element can be moved using one or more adjusting screws, threaded spindles, or similar actuators. Since the width of the application nozzle can be up to 10 meters or more, it is often advisable to provide several actuators distributed across the width of the application nozzle to change the gap width. The actuators can be moved manually or by motor.

[0037] In order to achieve a uniform gap width across the width of the application nozzle, it is often advantageous if the actuators are evenly distributed across the width of the application nozzle, so that the distances between adjacent actuators across the width of the application nozzle are the same or differ by less than 10%.

[0038] Other adjustment devices for varying the gap width are also conceivable.

[0039] Advantageously, the application device will be designed such that the application quantity can be varied between a minimum quantity and a maximum quantity by means of the means for varying the application quantity, such as by changing the gap width, wherein the maximum quantity is at least 30%, in particular at least 50%, preferably at least 100% above the minimum quantity.

[0040] In order to be able to vary the gap width of the outlet gap without having to stop the system, it is particularly advantageous if the variation of the gap width can be carried out by motor and / or hydraulic and / or pneumatic means.

[0041] The application nozzle usually extends over the entire width of the fiber web to be coated or over the entire width of the running surface.

[0042] In modern systems, the width of the fiber web, and thus the width of the application nozzle, can be up to 10m or more. It is therefore often expedient to provide several actuators distributed across the width of the application nozzle to change the gap width. Furthermore, the application device can have a control unit that is designed to automatically change the gap width. This control unit can, for example, be integrated into the central machine and system control system and, in particular, also be the same control unit that is used to determine the variation in the application quantity. This allows a high degree of automation and, for example, the gap width can be adjusted based on measured or specified values ​​from the machine control system.

[0043] Designs may be provided in which the application nozzle is designed as a curtain nozzle, in which the coating medium is deposited from the outlet gap in the form of a freely falling curtain onto the moving surface under the influence of gravity. This then represents an improvement on the curtain nozzle described in DE202020107431 U1.

[0044] In particularly preferred embodiments, the application nozzle may further comprise a blowing head configured 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 or curtain of coating medium, forming a spray curtain. The blowing head is arranged such that the spray curtain is directed toward the moving surface. The gaseous medium may, in particular, be air.

[0045] This then represents an improvement of the application device described in DE 102022105518.3.

[0046] Both the outlet gap and the linear jet of gaseous medium usually extend over the entire width of the running surface or the fibrous web.

[0047] The application device according to aspects of the invention can be used for single-sided or double-sided coating of fibrous webs. For double-sided coating, for example, the application device can be provided with a first application nozzle for application to a first moving surface and a second application nozzle for application to a second moving surface, wherein the first moving surface and the second moving surface are each designed as the surface of a transfer roller, and the two transfer rollers form a transfer nip in which the coating medium can be transferred to the fibrous web.

[0048] The same or different coating media can be applied to both sides.

[0049] One or both transfer rollers can be designed as hard rollers. This means that the surface of the first transfer roller and / or the surface of the second transfer roller has a hardness of over 55 ShoreD, in particular over 90 ShoreD.

[0050] A starch application device comprising two hard rollers is called a "hard-nip sizer." This allows for particularly good penetration of the starch into the fiber web.

[0051] The invention further comprises a method for coating a fibrous web, in particular a paper, packaging or cardboard web, in which a coating medium is applied to a moving surface by means of an application device, wherein the application device is designed according to one aspect of the invention.

[0052] In preferred embodiments, the coating medium may be a starch solution.

[0053] Alternatively, a variety of barrier media can be used as the coating medium. These can, in particular, be fiber-containing media such as MFC (microfibrillated cellulose) or NFC (nanofibrillated cellulose). Advantageously, the coating can be applied indirectly, with the coating medium first being applied to a moving surface in the form of a transfer roller and then transferred to the fibrous web in a transfer nip. Such an indirect application can be carried out, for example, using a "hard nip sizer."

[0054] In preferred embodiments, it can be provided that a parameter for the strength of the fibrous web is determined, and the application quantity is varied depending on this parameter. The application quantity can be varied either by an operator after assessing the parameter. However, it is particularly advantageous if this change is made automatically by the control unit. For this purpose, default values ​​or default curves can be stored in the control unit, and the control unit can determine an optimal conveying capacity or an optimal gap width from the parameter and the default values. This gap width can then be adjusted automatically using motor-driven or hydraulic and / or pneumatic actuators. This means that operator intervention can be completely dispensed with.

[0055] The variation of the delivery rate, e.g. via a pump speed, can also be automated and without operator intervention.

[0056] The parameter can be determined directly by direct measurement or indirectly.

[0057] Since many strength measurements today are still destructive and can only be performed in the laboratory, not on a running machine, strength parameters are often determined indirectly. This can be done, for example, by measuring a value that is known—e.g., from tests—to correlate with the desired strength parameter.

[0058] Alternatively, more complex dependencies can also be used. For example, the strength parameter can be modeled from a variety of measured variables. This can be, for example, a physical or purely statistical model. Such model-based determinations of parameters are sometimes referred to as "virtual sensors."

[0059] A very advantageous application of the present invention is the improvement of grade changes in a paper machine. For example, it can be provided that when changing from a first grade of fibrous web to a second grade, the application quantity is automatically changed from a first specified value to a second specified value by changing the gap width. This simplifies grade changes for the operator. It also gives them more flexibility in production planning, since they can now change directly from a grade with a high starch requirement, for example, to a grade with a low starch requirement without requiring a machine downtime. This is particularly advantageous because during a grade change it is often not possible to provide a strength parameter at all or only very imprecisely.

[0060] The invention is explained below with reference to figures. The invention is not limited to these embodiments.

[0061] The figures show in detail:

[0062] Figures 1 a and 1 b show an application nozzle according to one aspect of the invention. Figure 2 shows an application device according to a further aspect of the invention.

[0063] Figures 1a and 1b show an application nozzle 1 designed as a curtain nozzle. The coating medium, for example a starch solution, is guided in a distribution channel 10 and distributed across the width of the application nozzle 1. The width of the application nozzle 1 usually extends across the entire width of the moving surface 4 or the fibrous web to be coated. The coating medium exits the application nozzle 1 through an outlet gap 2 and then falls downwards under the influence of gravity in the form of a curtain onto a moving surface. To vary the gap width W, the adjusting means 3 of the application nozzle 1 of Figures 1a and 1b comprise a wall of the outlet gap 2 formed from a movable wall element 7. The outlet gap 2 can then be made narrower or wider by this wall element 7. Figure 1a shows a position with a large gap width W.To vary the application quantity, this gap width W can be reduced, as shown in Figure 1 b. For this purpose, the adjusting means 3 of the application nozzle 1 have suitable actuators 9. An adjusting screw 9 is shown as an example. Since the width of the application nozzle 1 can be up to 10 m or more, it will often be expedient to provide several adjusting screws 9 or other actuators distributed across the width of the application nozzle 1 to change the gap width W. The adjusting screws 9 can be moved manually or by motor.

[0064] For automated adjustment, a motorized or hydraulic and / or pneumatic drive for the actuators is advantageous. These can be connected to a control unit that can automatically change the gap width W depending on specified values ​​without requiring a system shutdown.

[0065] The application device of Figure 2 shows an application nozzle 1, which applies the coating medium to a moving surface 4 in the form of a transfer roller 4. The coating medium can then be transferred from the transfer roller 4 to the fibrous web in a transfer nip.

[0066] The application nozzle 1 comprises a nozzle like the one shown in Figures 1a and 1b. In contrast, the coating medium here does not fall downwards in the form of a curtain, but is deposited as a film on a support surface 8 and guided by this support surface 8. Furthermore, the application nozzle 1 further comprises a blow head 5 which is designed to generate a linear jet of gaseous medium. The gaseous medium can be air. The linear jet of gaseous medium impacts the film of coating medium at an impact line, forming a spray curtain 6. The blow head 5 is arranged such that the spray curtain 6 is directed in the direction of the moving surface 4.

[0067] Here, too, the application rate is varied by varying the gap width W of the outlet gap 2. This is done, as described in Figures 1a and 1b, using suitable adjusting means 3. The blow head 5, or the linear jet of gaseous medium, does not contribute to the variation in the application rate. This allows, among other things, the atomization of the spray mist 6 or the angle of impact of the spray mist 6 to be adjusted.

[0068] List of reference symbols

[0069] 1 application nozzle

[0070] 2 Outlet gap 3 Adjusting agent

[0071] 4 Running surface

[0072] 5 Blow head

[0073] 6 spray curtain

[0074] 7 Wall element 8 Support surface

[0075] 9 Actuator, adjusting screw

[0076] 10 distribution channel

[0077] W gap 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, to a moving surface (4), and wherein the application nozzle (1) has an outlet gap (2) which extends in the width direction of the application nozzle and which is designed to produce a film of coating medium or a curtain of coating medium, and wherein the application device comprises means for varying the application quantity, characterized in that the application device has a control unit which is designed to determine a variation in the application quantity from at least one provided characteristic variable for the strength of the fibrous web. 2) Application device according to claim 1, characterized in that the means for varying the application quantity comprise a conveying device whose conveying quantity is variable. 3) Application device according to one of the preceding claims, characterized in that the gap width (W) of the outlet gap (2) is designed to be variable in order to vary the application quantity. 4) Application device according to claim 3, characterized in that adjusting means (3) are provided for changing the gap width, which comprise a diaphragm and / or a movable wall element (7). 5) Application device according to one of claims 3 or 4, characterized in that adjusting means (3) are provided for changing the gap width, which have one or more actuators (9), which are in particular evenly distributed over the width of the application nozzle (1). 6) Application device according to claim 5, characterized in that the change in the gap width can be effected by motor and / or hydraulic and / or pneumatic means. 7) Application device according to one of the preceding claims, characterized in that the control unit is designed to automatically change the application quantity. 8) Application device according to one of the preceding claims; characterized in that the application quantity can be varied between a minimum quantity and a maximum quantity, wherein the maximum quantity is at least 30%, in particular at least 50%, preferably at least 100% above the minimum quantity. 9) Application device according to one of the preceding claims, characterized in that the application device has a first application nozzle for application to a first moving surface and a second application nozzle for application to a second moving surface, wherein the first moving surface and the second moving surface are each designed as a surface of a transfer roller, and the two transfer rollers form a transfer nip in which the coating medium can be transferred to the fibrous web. 10) Application device according to claim 9, characterized in that the surface of the first transfer roller and / or the surface of the second transfer roller have a hardness of over 55 ShoreD, in particular over 90 ShoreD. 11 ) Method for coating a fibrous web, in particular a paper, packaging or cardboard web, in which a Coating medium is applied to a moving surface (4) by means of an application device, characterized in that the application device is designed according to one of the preceding claims, wherein a parameter for the strength of the fibrous web is determined, and the variation of the application quantity takes place as a function of this parameter. 12) Method according to claim 9, characterized in that the coating medium is a starch solution or a barrier medium. 13) Method according to one of claims 9 or 10, characterized in that the coating is carried out indirectly, wherein the coating medium is first applied to a moving surface in the form of a transfer roller and from there transferred to the fibrous web in a transfer nip. 14) Method according to one of claims 11 to 13, characterized in that the determination of the characteristic value takes place directly by direct measurement or indirectly. 15) Method according to one of claims 11 to 14, characterized in that when changing from a first type of fibrous web to a second type, the application quantity is automatically changed from a first specified value to a second specified value by adjusting the means for varying the application quantity.

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