DE102023106575A1 - Application device and process - Google Patents

Abstract

Application device and method 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, in particular a starch solution, to a moving surface, and wherein the application nozzle has an outlet gap which is designed to produce a film of coating medium or a curtain of coating medium, characterized in that the gap width (W) of the outlet gap is designed to be variable in order to vary the application quantity.

Description

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.

During the production or processing of fibrous webs, in particular paper, packaging or cardboard webs, it is common practice to provide these webs with one or more coatings.
These coatings can, for example, be the application of pigment-containing coating colors or barrier media, for example based on polyvinyl alcohol or micro-/nanofibrillated cellulose.

Another common application is the application of a starch solution to the fibrous web. This can influence the surface of the web, while the application of starch can also improve the strength properties of the fibrous web.

Various application devices are known from the state of the art.

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 dosed to the desired application quantity using suitable doctor blade dosing systems. 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.

Such doctor blade dosing systems are described, for example, in the document DE102004029565 A1 described. In order to enable better penetration of the starch into the fibrous web, transfer rollers with very hard surfaces have recently been used more and more frequently. In this case, such dosing systems prove to be disadvantageous, as the hard roller surfaces cause the doctor rods to wear out very quickly.

Alternatively, for example, from the EP3332955 B1 Application systems are known in which the coating medium is sprayed onto the application rollers via a series of spray nozzles. In contrast to doctor blade dosing systems, these systems do not require contact dosing systems. Since the application quantity is dosed by adjusting the application quantity of the spray nozzles, it is not necessarily necessary for the machine to be shut down.

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.

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

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

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

The object is achieved according to the invention by an application device according to claim 1, and a method according to claim 9. Further advantageous embodiments of the present invention can be found in the subclaims.

An application device is proposed 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 which is designed to produce a film of coating medium or a curtain of coating medium. According to the invention, it is provided that the gap width of the outlet gap is designed to be variable in order to vary the application quantity and/or to adapt the internal nozzle pressure of the application nozzle.

Application nozzles with an outlet gap are already known per se. This is how the DE202020107431 U1 a curtain nozzle with a uniform nozzle gap. From the patent application EN 102022105518.3 The applicant is aware of an application nozzle in which a curtain or film is dispensed from a slot nozzle, which is then atomised by means of a blowing head.

These nozzles are advantageous compared to doctor blade dosing systems because the dosing does not require any contacting doctor blade elements and therefore no wearing parts. In addition, excess application is avoided, which eliminates the need for time-consuming return and processing of the excess application medium.

Compared to spray nozzles, such application nozzles with an outlet gap have the advantage that they are not only cheaper than a large number of spray nozzles. They are also much less prone to contamination.

However, these application nozzles still have the disadvantage that the application quantity can only be varied within relatively small limits.

The inventors have now realised that this disadvantage can be overcome by moving away from a previous basic principle of nozzle construction. Until now, the aim when building a curtain nozzle, for example, was to keep the outlet gap as constant as possible. DE202020107431 U1 For example, a considerable amount of effort is made to maintain the consistency of the gap. This is because curtain coating systems have so far been used almost exclusively in the area of coating with pigment-based coating colors. Here, this level of precision is very important for even coverage of the web and the associated uniform surface properties.

In the future, however, such nozzles will increasingly be used for applying starch. In this case, a high degree of accuracy of the gap is less important than the ability to vary the amount of starch applied over a very wide range. The present invention therefore proposes that the gap width of the outlet gap be made variable.
By varying the gap width, a very large range of order quantities can be covered in an elegant way. For example, if the gap width is increased from 0.5 mm to 1 mm, the order quantity can be doubled. If it is increased to 2 mm, it can even be quadrupled. Such large variations are advantageous for the system operator, as they allow a wide range of paper types with very different order quantity requirements to be produced on the same system. And this - if the application device is designed accordingly - without the system having to stop.

Alternatively or additionally, the variation of the gap width can also be used to adjust the internal nozzle pressure of the application nozzle.
The internal nozzle pressure is an important parameter for a curtain nozzle or for the nozzles with a blowing head described. As a rule, the coating medium should not be pressed out of the outlet gap, but should leave the gap freely under the influence of gravity. The internal nozzle pressure should therefore not be too high. However, depending on the rheology of the coating medium, different internal nozzle pressures can arise with the same delivery rate and the same gap width. With an application nozzle according to one aspect of the invention, the gap width can now be adjusted so that the internal nozzle pressure is in the desired range.

It is helpful to have a suitable sensor system for determining the internal pressure of the nozzle. This measurement can be carried out directly inside the application nozzle. However, since such internal sensors can potentially become dirty more easily, it is usually more practical to determine the pressure in an inlet of the coating medium.

The variation of the gap width can be achieved in different ways or with different adjusting devices.
For example, a fixed gap with a large gap width can be provided, which is more or less covered by a movable cover. Alternatively, it can be provided that at least one wall of the outlet gap is formed from a movable wall element. The outlet gap itself can then be made narrower or wider by means of this wall element.

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 1 can be up to 10m or more, it will often be useful to provide several actuators to change the gap width, which are distributed across the width of the application nozzle. The actuators can be moved manually or by motor.
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 only less than 10%.

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

Advantageously, the application device will be designed such that the application quantity can be varied between a minimum quantity and a maximum quantity 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.

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 the gap width can be adjusted motorically and/or hydraulically and/or pneumatically.

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.
In modern systems, the width of the fibrous web, and thus the width of the application nozzle, can be up to 10m or more. It will therefore often be useful 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 set up to automatically change the gap width. This control unit can, for example, be integrated into the central machine and system control. This enables a high degree of automation and, for example, the gap width can be adjusted based on measured or specified values from the machine control.

Designs can 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 in the DE202020107431 U1 described curtain nozzle.

In particularly preferred embodiments, it can be provided that the application nozzle further comprises a blow head which is designed to generate a linear jet of gaseous medium, and wherein an impact line is also provided at which the linear jet of gaseous medium impacts the film or curtain 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 moving surface. The gaseous medium can in particular be air.

This then represents an improvement in EN 102022105518.3 described application device.

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.

The application device according to aspects of the invention can be used for coating fibrous webs on one or both sides.

For a two-sided coating, it can be provided, for example, that the application device has a first application nozzle for application to a first running surface and a second application nozzle for application to a second running surface, wherein the first running surface and the second running 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.

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

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 have a hardness of over 55 ShoreD, in particular over 90 ShoreD.

An application device for applying starch that comprises two hard rollers is called a “hard nip sizer”. This allows particularly good penetration of the starch into the fibrous web.

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.

In preferred embodiments, the coating medium may be a starch solution.
Alternatively, a variety of barrier media can be used as a coating medium. These can in particular be fiber-containing media such as MFC (microfibrillated cellulose) or NFC (nanofibrillated cellulose).

Advantageously, the coating can be carried out 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".

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 determines an optimal gap width from the parameter and the default values. This gap width can then be set automatically using motorized or hydraulic and/or pneumatic actuators. This means that operator intervention can be completely dispensed with.

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

Since many strength measurements today are still destructive measurements that can only be carried out in the laboratory and not in a running machine, the 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.

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

A very advantageous application of the present invention is the improvement of the type change in a paper machine. This means that when changing from a first type of fibrous web to a second type, the application quantity can be automatically changed from a first specified value to a second specified value by changing the gap width. This simplifies the type change for the operator. It also gives him more flexibility in production planning, since it is now possible to change directly from a type with a high demand for starch, for example, to a type with a low starch demand without the need for a machine downtime.

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

• 1a und 1b zeigen eine Auftragsdüse gemäß einem Aspekt der Erfindung- 2 zeigt eine Auftragsvorrichtung gemäß einem weiteren Aspekt der Erfindung Die 1a und 1b zeigen eine Auftragsdüse 1, die als Vorhangdüse 1 ausgeführt ist. Dabei wird das Beschichtungsmedium, zum Beispiel eine Stärkelösung in einem Verteilkanal 10 geführt, und über die Breite der Auftragsdüse 1 verteilt. Die Breite der Auftragsdüse 1 erstreckt sich üblicherweise über die gesamte Breite der laufenden Oberfläche 4 bzw. der zu beschichtenden Faserstoffbahn. Das Beschichtungsmedium tritt durch einen Auslassspalt 2 aus der Auftragsdüse 1 aus, und fällt dann unter Einfluss der Schwerkraft in Form eines Vorhangs nach unten auf eine laufende Oberfläche.

The figures show in detail:

• 1a and 1b show an application nozzle according to one aspect of the invention- 2 shows an application device according to another aspect of the invention. 1a and 1b show an application nozzle 1 which is designed as a curtain nozzle 1. The coating medium, for example a starch solution, is guided in a distribution channel 10 and distributed over the width of the application nozzle 1. The width of the application nozzle 1 usually extends over the entire width of the running 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 onto a running surface in the form of a curtain under the influence of gravity.

To vary the gap width W, the adjusting means 3 of the application nozzle 1 of the 1a and 1b a wall of the outlet gap 2 is formed from a movable wall element 7. The outlet gap 2 can then be made narrower or wider by this wall element 7. 1a shows a position with a large gap width W. To vary the application quantity, this gap width W can be adjusted as shown in 1b shown, can be reduced. 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 10m or more, it will often be expedient to provide several adjusting screws 9 or other actuators to change the gap width W, which are distributed over the width of the application nozzle 1. The adjusting screws 9 can be moved manually or by motor.
To automate the adjustment, a motor or a hydraulic and/or pneumatic drive of the actuators is advantageous. These can be connected to a control unit that can automatically change the gap width W depending on the specified values without the system having to be shut down.

In the application device of the 2 an application nozzle 1 is shown 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.

The application nozzle 1 comprises a nozzle such as that shown in the 1a and 1b In contrast, the coating medium does not fall down 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 blowing 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.

Here too, the change in the application quantity is achieved by varying the gap width W of the outlet gap 2. This is done as described under 1a and 1b described, via suitable adjusting means 3. The blow head 5 or the linear jet of gaseous medium does not contribute to the variation of the application quantity. This makes it possible, among other things, to adjust the atomization of the spray mist 6 or the angle of impact of the spray mist 6.

List of reference symbols

1

Application nozzle

2

Outlet gap

3

Settling agent

4

Running surface

5

Blow head

6

Spray curtain

7

Wall element

8

Support surface

9

Actuator, adjusting screw

10

Distribution channel

W

Gap width

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• DE 102004029565 A1 [0006]
• EP 3332955 B1 [0007]
• DE 202020107431 U1 [0014, 0018, 0029]
• EN 1020221055183 [0014, 0031]

Claims (14)

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, characterized in that the gap width (W) of the outlet gap (2) is designed to be variable in order to vary the application quantity and/or to adapt the internal nozzle pressure of the application nozzle. Application device according to Claim 2 , characterized in that adjusting means (3) are provided for changing the gap width, which comprise a panel and/or a movable wall element (7). Application device according to one of the preceding claims, characterized in that adjusting means (3) are provided for changing the gap width, which have one or more actuators (9) which are arranged in particular evenly distributed over the width of the application nozzle (1). Application device according to Claim 3 , characterized in that the change in the gap width can be carried out motorically and/or hydraulically and/or pneumatically. Application device according to one of the preceding claims, characterized in that the application device has a control unit which is designed to automatically change the gap width. Application device according to one of the preceding claims, characterized in that by changing the gap width, 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. 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 running surface and a second application nozzle for application to a second running surface, wherein the first running surface and the second running 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. Application device according to Claim 7 , 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. 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. Procedure according to Claim 9 , characterized in that the coating medium is a starch solution or a barrier medium. Procedure according to one of the Claims 9 or 10 , characterized in that the coating is carried out indirectly, wherein the coating medium is first applied to a running surface in the form of a transfer roller and from there transferred to the fibrous web in a transfer nip. Procedure according to one of the Claims 9 until 11 , characterized in that a parameter for the strength of the fibrous web is determined, and the variation of the application quantity takes place depending on this parameter. Procedure according to Claim 12 , characterized in that the determination of the characteristic value takes place directly by direct measurement or indirectly. Procedure according to one of the Claims 9 until 13 , characterized in that when changing from a first type of fibrous web to a second type by changing the gap width, the application quantity is automatically changed from a first specified value to a second specified value.

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