APPLICATION DEVICE AND METHOD FOR COATING A FIBROUS MATERIAL WEB

Abstract

An application device and method for coating a fibrous material web, in particular a paper, packaging or board web. The application device has an application nozzle for applying a coating medium, in particular a starch solution, to a moving surface and the application nozzle has an outlet gap which extends in the width direction of the application nozzle for producing a film of coating medium or a curtain of coating medium. The application nozzle has a gap width across its width direction that may be varied by profiling devices.

Claims

1. An application device for coating a fibrous material web, the application device comprising: an application nozzle for applying a coating medium 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.

2. The application device according to claim 1, wherein the fibrous material web to be coated is a paper web, a web of packaging material, or a web of board material.

3. The application device according to claim 1, wherein the coating medium is a starch solution.

4. The application device according to claim 1, wherein said application nozzle is a curtain nozzle configured to cause the coating medium from said outlet gap to be deposited on the moving surface in a form of a curtain falling freely under an influence of gravity.

5. The application device according to claim 1, wherein said profiling means comprise a baffle, which extends over an entire width of said application nozzle, and said profiling means further comprise a plurality of actuators which are distributed over the width of said application nozzle and which are configured to open said outlet gap locally more or less by moving or deforming said baffle.

6. The application device according to claim 5, wherein said actuators are mechanical actuators configured for actuation selected from the group consisting of manual actuation, actuation by motors, hydraulic actuation, and electromagnetic actuation.

7. The application device according to claim 1, wherein said profiling means comprise a plurality of electromagnetic actuators that are distributed over the width of said application nozzle and that are configured to vary the gap width of said outlet gap locally by varying a magnetic force acting of said electromagnetic actuators.

8. The application device according to claim 7, wherein the electromagnetic force acts by attraction, with the gap width of said outlet gap being varied by more intense or weaker attraction.

9. The application device according to claim 7, wherein the electromagnetic force acts by repulsion, with the gap width of said outlet gap being varied by more intense or weaker repulsion.

10. The application device according to claim 1, which comprises a plurality of actuators configured for varying a gap width of said application nozzle, wherein said actuators are distributed non-uniformly over the width of said application nozzle, and wherein spacing distances between mutually adjacent actuators at marginal edges of said application nozzle are smaller that at a center of said application nozzle.

11. The application device according to claim 1, wherein: said application nozzle is one of two application nozzles, including a first application nozzle for applying the coating medium to a first moving surface formed on a first transfer roll and a second application nozzle for applying the coating medium to a second moving surface formed on a second transfer roll; and said first and second transfer rolls are disposed to form a transfer nip in which the coating medium is transferred from the first moving surface and from the second moving surface onto the fibrous material web.

12. A method of coating a fibrous material web, the method comprising: providing an application device according to claim 1; and coating the fibrous material web with a coating medium by the application device.

13. The method according to claim 12, wherein the fibrous material web is a paper web, a packaging web, or a board web.

14. The method according to claim 12, which comprises coating the fibrous material web indirectly by first applying the coating medium to a moving surface on a transfer roll and transferring the coating medium from the transfer roll to the fibrous material web in a transfer nip.

15. The method according to claim 12, which comprises: a. predefining a predefined profile for a quantity of coating medium to be applied over a width of the application nozzle of the application device; and b. varying the gap width of the outlet gap over the width of the application nozzle to attain the predefined profile.

16. The method according to claim 15, which comprises determining a current profile of a property of the fibrous material web, and determining the predefined profile for the coating medium from the current profile of the property.

17. The method according to claim 16, wherein the property is a strength property of the fibrous material web.

18. The method according to claim 16, which comprises determining the current profile of a property directly, by direct measurement, or indirectly.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0060] FIG. 1 shows an application device according to one aspect of the invention.

[0061] FIG. 2 shows an application device according to a further aspect of the invention.

[0062] 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

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: [0075] 1 Application nozzle [0076] 1a, 1b Application nozzles [0077] 2 Outlet gap [0078] 4 Moving surface [0079] 4a, 4b Moving surface [0080] 5 Blower head [0081] 6 Spray curtain [0082] 7 Supporting surface [0083] 14 Curtain of coating medium [0084] 15 Film of coating medium [0085] 16 Transfer nip [0086] 17 Web, fibrous material [0087] 101 Baffle [0088] 102 Actuators [0089] 103 Mechanical actuators [0090] 105 Electromagnetic actuators [0091] W Gap width