APPLICATION DEVICE AND METHOD FOR COATING A FIBROUS MATERIAL WEB

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation, under 35 U.S.C. § 120, of copending International Patent Application PCT/EP2024/053581, filed Feb. 13, 2024, which designated the United States; this application also claims the priority, under 35 U.S.C. § 119, of German Patent Application DE 10 2023 106 579.3, filed Mar. 16, 2023; the prior applications are herewith incorporated by reference in their entirety.

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to an application device for coating a fibrous material web, or fiber web for short, in particular a web of paper, packaging or board material. The device has an application nozzle for applying a coating medium, in particular a starch solution, to a moving surface of the web. The invention also relates to a method in which the device is used for coating a fiber web.

During the production or processing of fibrous material webs, in particular of paper, packaging or board webs, it is usual to provide these webs with one or more coatings.

These coatings can be, for example, the application of pigment-containing coating colors or barrier media, for example based on polyvinyl alcohol or micro/nano-fibrillated cellulose.

A further frequent use is the application of a starch solution to the fiber web. As a result, firstly the surface of the web can be influenced, secondly the strength properties of the fiber web can also be improved by the starch application.

Various application devices are known from the prior art.

The starch solution may be applied, for example, by means of a film press. The coating medium is applied to a transfer roll in excess and then metered to the desired application quantity by a suitable doctor metering system. A variation in the application quantity is achieved in that more or less of the excess of coating medium is doctored off. To change the application quantity, changing the doctor bar is usually necessary, for which a stoppage of the machine is necessary. Such doctor metering systems are described, for example, in German published patent application DE 10 2004 029 565 A1 and in the counterpart U.S. Pat. No. 8,418,645 B2.

Alternatively, application units are known, for example from European Patent No. EP 3 332 955 B1, in which the coating medium is sprayed onto the application rolls via a row of spray nozzles. As opposed to doctor metering systems, these systems manage without contacting metering systems.

Once more alternatively, application nozzles having an outlet gap are known. Thus, German utility model DE 20 2020 107 431 U1 describes a curtain nozzle having a uniform nozzle gap. An application nozzle in which a curtain or film is discharged from a wide slot nozzle, which is then atomized by means of a blower head, is known from our commonly assigned German patent application DE 10 2022 105 518.3.

Common to all these application units is the fact that they are designed to discharge a quantity of coating medium that is as equal and as uniform as possible over the width of the moving surface.

The properties of a paper web, however, can fluctuate significantly over the web width. Thus, for example, the properties in the edge regions of the web can deviate highly from those in the web center as a result of the web shrinkage during the drying.

The result of this is that the demand, for example for starch, to achieve a certain strength is also unequal over the entire web width.

If the starch is metered so highly to achieve a sufficient strength in the region with the highest demand, it is over-metered in other regions, which is neither economically nor ecologically expedient. If, on the other hand, too little is metered, as a rule the edge region of the web is of lower quality because of a lack of strength.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide an application device which overcomes a variety of the disadvantages of the heretofore-known devices and methods of this general type and which provides for a machine that overcomes the weaknesses of the prior art. It is a further object of the invention to propose an application device which can be matched specifically to the web to be coated. Yet another object of the invention is to provide a device and a method for producing a fibrous material web of sufficient quality and avoiding wastage.

With the above and other objects in view there is provided, in accordance with the invention, an application device for coating a fiber web, such as a paper web, a web of packaging material, or a web of board material. The novel application device comprises:

• • an application nozzle for applying a coating medium, in particular a starch solution, to a moving surface, said application nozzle being formed with an outlet gap which extends in a width direction of said application nozzle and which is configured to produce a film of coating medium or a curtain of coating medium;
  • said application nozzle having profiling devices for varying a gap width of said outlet gap over the width of said application nozzle;
  • said application nozzle further having a blower head configured to generate a linear jet of gaseous medium, and wherein an impingement line is defined along which the linear jet of gaseous medium impinges on the film or the curtain of coating medium for forming a spray curtain, and wherein said blower head is arranged to direct the spray curtain in a direction of the moving surface.

In other words, all of the above objects are achieved by an application device for coating a fibrous material web, or fiber web for short, in particular a paper, packaging or board web, wherein the application device has 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. According to the invention, provision is made for the application nozzle to have profiling means in order to vary the gap width of the outlet gap over the width of the application nozzle.

The application nozzle and the outlet gap usually extend over the entire width of the fiber web to be coated or over the entire width of the moving surface. Since this fiber web is normally somewhat narrower than the transfer roll, provision can be made for no coating medium to be discharged for a few centimeters at the edge of the transfer roll.

The width of the application nozzle can therefore be up to 10 meters or more in modern installations.

By using an application unit according to one aspect of the invention, it is then possible to match the quantity of coating medium over the width of the fiber web specifically to the necessary quantity. This can be done via specific adaptation of the gap width of the outlet gap.

By means of the variation of the gap width, a very great range of application quantities can be covered in an elegant way. If, for example, the gap width is enlarged from 0.5 mm to 1 mm, a doubling of the application quantity can therefore be achieved. Even a fourfold increase with a widening to 2 mm. Such large variations are advantageous for the operator of the installation since, in particular in the edge region of the webs, the properties of the web differ very highly from those in the web center because of the shrinkage, so that in these regions it is possibly necessary for considerably different quantities of starch to be applied. In the case of application nozzles with an outlet gap, this high level of profiling can be very efficiently implemented via a local adaptation of the gap width.

In an advantageous embodiment, provision can be made for the application nozzle to be designed as a curtain nozzle, in which the coating medium from the outlet gap is deposited on the moving surface in the form of a curtain falling freely under the influence of gravity.

Alternatively, provision can be made for the application nozzle to further comprise a blower head, which is designed to generate a linear jet of gaseous medium, and wherein an impingement line is also provided, on which the linear jet of gaseous medium impinges on the film or curtain of coating medium, forming a spray curtain, and wherein the blower head is arranged such that the spray curtain is directed in the direction of the moving surface. In particular, air can be used as the gaseous medium.

In an advantageous embodiment, provision can additionally be made for the application nozzle to have a baffle, which extends in particular over the entire width of the application nozzle, and for the profiling means to comprise a number of actuators which are distributed over the width of the application nozzle and which are configured to open the outlet gap locally more or less by moving or deforming the baffle.

The actuators can be designed, for example, as mechanical actuators and/or electromagnetic actuators.

The mechanical actuators can be actuated manually and/or by motors and/or hydraulically, for example. In particular, an embodiment with actuating screws or threaded spindles is possible.

The baffle can consist of a metal, a plastic, a combination, or other suitable materials.

When electromagnetic actuators are used, the entire baffle can be formed from a magnetic material. Alternatively, however, the baffle can also be formed from a non-magnetic material, for example a plastic to which elements made of a magnetic material and/or suitable permanent magnets are attached for the purpose of cooperation with the electromagnets.

Alternatively or additionally, provision can be made for the profiling means to comprise electromagnetic actuators, which are distributed over the width of the application nozzle and which are configured to vary the width of the outlet gap locally by varying the magnetic force.

It is possible for both attraction forces (narrowing of the outlet gap) and also repulsion forces (widening of the gap) to be generated in order to effect profiling. The advantage with this embodiment is that no mechanical components are needed. The susceptibility to wear can thereby be reduced.

Since the width of the application nozzle can be 1 mm up to 10 mm or more, it will frequently be expedient to provide a plurality of actuators, which are distributed over the width of the application nozzle, for changing the gap width.

In particularly preferred embodiments, provision can be made for the mechanical actuators and/or the electromagnetic actuators to be distributed non-uniformly over the width of the application nozzle, wherein the distances between adjacent actuators are lower at the edges of the application nozzle than in the center of the application nozzle.

This is in particular advantageous to compensate for the shrinkage profile. Since the paper web shrinks very highly at the edge but remains virtually unchanged in the web center, such profiles exhibit sharp gradients in the edge zones but remain largely constant in the center. It is therefore advantageous to provide more actuators in the edge regions. For this purpose, fewer actuators can be provided in the region of the web center, for economic reasons.

It is very advantageous if the application device has a control unit which is configured to vary the gap width automatically. This control unit can, for example, be integrated into the central machine and installation control system. Thus, a high level of automation is possible and, for example, an adjustment of the gap width can be made on the basis of measured or predefined values from the machine control system.

The application device can be designed as a direct application device, in which the coating medium is applied directly to the fiber web as a moving surface.

Alternatively, the application device can also be designed as an indirect application device, in which the coating medium is transferred from the moving surface to the fiber web. The moving surface can be the surface of a transfer roll.

In particular, provision can be made for the application device to have a first application nozzle for the application to a first moving surface and a second application nozzle for the 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 roll, and the two transfer rolls are disposed to form a transfer nip in which the coating medium is transferred to the fiber web.

Such application devices can be used for the simultaneous application, in particular of starch, to both sides of the fiber web.

Furthermore, it may be advantageous if the surface of the first transfer roll and/or the surface of the second transfer roll have a hardness of more than 55 ShoreD, in particular more than 90 ShoreD.

An application device for the application of starch which comprises two hard rolls is designated a “hard-nip sizer.” Particularly good penetration of the starch into the fiber web can be achieved thereby.

With the above and other objects in view there is also provided, in accordance with the invention, a method for coating a fiber web, in particular a paper, packaging or board web, wherein the coating is carried out by means of an application device as described herein.

It is particularly advantageous if the coating medium is a starch solution.

It is preferred for the coating of the fiber web to be carried out indirectly, wherein the coating medium is first applied to a moving surface in the form of a transfer roll and, from there, is transferred to the fiber web in a transfer nip.

In a variant of the method, provision can be made for the method to comprise the steps:

• • predefining a predefined profile for the quantity of coating medium to be applied over the width of the application nozzle, and
  • varying the gap width of the outlet gap over the width of the application nozzle, so that the predefined profile is achieved.

Such a method can be used within an open-loop or a closed-loop control schema.

The predefined profile can be predefined, for example, depending on the grade produced. This predefined profile can be developed from experience or previous trials for the respective grade. If there is a suitable control unit, the profile can be adapted automatically at a grade change without a machine stoppage being needed.

Provision can also additionally be made for a current profile of a property, in particular a strength property of the fiber web, to be determined and the predefined profile for the coating medium to be determined therefrom.

This is a very advantageous embodiment in conjunction with the application of starch, since various strength properties of the fiber web can be influenced via the starch application.

The determination of the characteristic variable can be carried out directly by direct measurement or also indirectly.

Since many strength measurements are today still destructive measurements which can be carried out only in the laboratory but not on the running machine, the characteristic variables for the strength will frequently be determined indirectly.

This can be done, for example, by a variable being measured of which it is known—for example empirically from trials—that this variable is correlated with the desired strength characteristic variable.

Alternatively, more complex dependencies can also be used. For example, the characteristic variable of the strength can be modeled from a large number of measured variables. This can be, for example, a physical or else purely statistical model. Such model-based determinations of characteristic variables are occasionally also called “virtual sensors.”

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in an application device and method, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an application device according to one aspect of the invention.

FIG. 2 shows an application device according to a further aspect of the invention.

FIG. 3 is a highly diagrammatic illustration of a device for the simultaneous application of coating medium on both sides of the fiber web.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawing in detail and first, in particular, to FIG. 1 thereof, there is shown an application device having an application nozzle 1, which is designed as a curtain nozzle 1. The coating medium is deposited onto a moving surface 4 in the form of a free-falling curtain (14). In FIG. 1, the moving surface 4 is the surface of a transfer roll. From this transfer roll, the coating medium can be transferred to the web in a transfer nip. Alternatively, however, the curtain of coating medium 14 can also be applied directly to a fiber web.

The application nozzle 1 normally extends over the entire width of the moving surface 4, at least over the entire width of the fiber web to be coated. Since this fiber web is normally somewhat narrower than the transfer roll, provision can be made for no coating medium to be applied to a few centimeters at the edge of the transfer roll.

The coating medium leaves the curtain nozzle through an outlet gap 2 having a width W. The gap width W is correlated with the discharged quantity of coating medium.

The profiling means for varying the gap width W in the embodiment shown in FIG. 1 comprise a baffle 101, which extends over the width of the application nozzle 1. This baffle 101 can be made of a metal or of plastic. This baffle 101 is arranged at the outlet gap 2 such that the outlet gap 2 can be closed and opened more or less by means of local movement or deformation of the baffle 101, and therefore the local gap width W can be varied.

To move or deform the baffle 101, the profiling means also comprise suitable actuators 102. These actuators 102 can be designed as mechanical actuators 103, for example in the form of threaded spindles 103. These can be actuated manually or by motors or else hydraulically.

In the application nozzle 1 of FIG. 1, the actuators 102, 103 are distributed non-uniformly over the width of the application nozzle 1, wherein the distances between adjacent actuators 102 are lower at the edges of the application nozzle 1 than in the center of the application nozzle 1. This is advantageous in particular to compensate for the shrinkage profile. Since the paper web shrinks very highly at the edge but remains virtually unchanged in the center of the web, such profiles have sharp gradients in the edge zones but remain largely constant in the center. Therefore, fewer actuators can be provided in the region of the center of the web, for economic reasons.

FIG. 2 shows an application device according to a further aspect of the invention. The application nozzle 1 once more has a nozzle head, which has an outlet gap 2 which extends in the width direction of the application nozzle 1. The coating medium is discharged in the form of a film 15, however, which is deposited on a supporting surface 7. This supporting surface 7 can be designed as a separate component. Alternatively, however, provision can also be made for part of the wall of the application nozzle 1 to be used as a supporting surface 7.

In addition, the application nozzle 1 has a blower head 5, which is designed to produce a linear jet of gaseous medium, and wherein an impingement line is also provided, on which the linear jet of gaseous medium impinges on the film 15 of coating medium and forms a spray curtain 6. The blower head 5 is arranged such that the spray curtain 6 is directed in the direction of the moving surface 4.

Here, too, the profiling is not carried out via a variation in the blower head 5 or of the jet of gaseous medium but by means of a variation in the width W of the outlet gap 2. To this end, suitable profiling means are provided on the application nozzle. Instead of the likewise possible baffle 101, actuating means 102 in the form of electromagnetic actuators 105 are provided here. These are distributed over the width of the application nozzle 1 and are configured to vary the width of the outlet gap locally by varying the magnetic force.

Both attraction forces (narrowing of the outlet gap 2) and also repulsion forces (widening of the outlet gap) can be produced in order to effect profiling. In this embodiment, it is advantageous that no mechanical components are needed, whereby the susceptibility to wear can be reduced. These actuators 102, 105 can be arranged uniformly or else once more non-uniformly over the width of the application nozzle.

FIG. 3 shows a so-called “hard-nip-sizer” with two rolls 4 with a moving surface 4a and a moving surface 4b, respectively. The two rolls 4 are disposed to form a nip 16 through which the web 17 travels. In this case, the coating solution is applied indirectly, in that it is first deposited on the moving surface 4a, 4b by way of a curtain 14, before it is transferred onto the web 17 in the nip 16. Both of the application devices 1a and 1b have application nozzles with variable profiles of the gap widths.

The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention:

• • 1 Application nozzle
  • 1a, 1b Application nozzles
  • 2 Outlet gap
  • 4 Moving surface
  • 4a, 4b Moving surface
  • 5 Blower head
  • 6 Spray curtain
  • 7 Supporting surface
  • 14 Curtain of coating medium
  • 15 Film of coating medium
  • 16 Transfer nip
  • 17 Web, fibrous material
  • 101 Baffle
  • 102 Actuators
  • 103 Mechanical actuators
  • 105 Electromagnetic actuators
  • W Gap width