APPLICATION DEVICE AND METHOD FOR COATING A FIBROUS MATERIAL WEB

Abstract

An application device and method for coating a fibrous material web, such as a paper web, a web of packaging material, or a web of cardboard. 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 that produces a film of coating medium or a curtain of coating medium. A device is provided for varying the application amount and the variation is based on a strength variable.

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; a device for varying an application amount of coating medium by varying said application nozzle; and a control unit configured to determine a variation in the application amount from at least one characteristic value provided for a strength of the fibrous material web.

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 the device for varying the application amount comprise a conveying system having a variable delivery rate.

5. The application device according to claim 1, wherein said application nozzle is formed with an outlet gap having a gap width, and wherein the application amount is changed by varying the gap width of said outlet gap.

6. The application device according to claim 5, which comprises an actuator for changing the gap width, said actuator including at least one of a cover or a movable wall element.

7. The application device according to claim 5, which comprises an actuator for changing the gap width, said actuator having one or more individual actuators that are distributed along a width of said application nozzle.

8. The application device according to claim 7, wherein said individual actuators are uniformly distributed over the width of said application nozzle.

9. The application device according to claim 6, wherein the gap width is variable by one or more of motor actuation, hydraulic actuation, or pneumatic actuation.

10. The application device according to claim 1, wherein said control unit is configured to automatically change the application amount.

11. The application device according to claim 1, wherein said application nozzle is configured to allow the application amount to be varied between a minimum amount and a maximum amount, the maximum amount being at least 30% greater than the minimum amount.

12. The application device according to claim 11, wherein the maximum amount is at least 50% greater than the minimum amount.

13. The application device according to claim 11, wherein the maximum amount is at least 100% greater than the minimum amount.

14. 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.

15. The application device according to claim 14, wherein at least one of said first surface of said first transfer roll or said second surface of said second transfer roll has a hardness of more than 55 ShoreD or a hardness of more 90 ShoreD.

16. A method of coating a fibrous material web, the method comprising: providing an application device according to claim 1; determining a value for a strength of the fibrous material web; and coating the fibrous material web with a coating medium by the application device, and thereby varying the application amount depending on the characteristic value.

17. The method according to claim 16, wherein the coating medium is a starch solution or a barrier medium.

18. The method according to claim 16, which comprises coating the fibrous material web indirectly by first applying the coating medium to a moving surface on a transfer roll and then transferring the coating medium from the transfer roll to the fibrous material web in a transfer nip.

19. The method according to claim 16, which comprises determining the characteristic value directly, by direct measurement, or indirectly.

20. The method according to claim 16, which comprises, when the fibrous material web is changed from a first type of fibrous web to a second type of fibrous web, automatically changing the application amount from a first default value to a second default value by adapting the device for varying an application amount.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0070] FIGS. 1A and 1B show an application nozzle according to one aspect of the invention;

[0071] FIG. 2 shows an application device according to a further aspect of the invention; and

[0072] FIG. 3 is a highly diagrammatic view of a device for the simultaneous coating of a fiber web on both sides.

DETAILED DESCRIPTION OF THE INVENTION

[0073] FIGS. 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 conventionally extends over the entire width of the moving surface 4 or of the fibrous web to be coated. The coating medium exits from the application nozzle 1 through an outlet gap 2 and then falls downward in the form of a curtain 14 under the influence of gravity onto a moving surface.

[0074] In order to vary the gap width W, an actuating means 3, of the application nozzle 1 of FIGS. 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 the wall element 7. FIG. 1A shows a position with a large gap width W. In order to vary the application amount, this gap width W, as shown in FIG. 1B, can be reduced. For this purpose, the actuating means 3 of the application nozzle 1 have suitable actuators 9. An actuating screw 9 is shown by way of example. Since the width of the application nozzle 1 can be up to 10 m or more, it is frequently expedient, in order to change the gap width W, to provide a plurality of actuating screws 9 or other actuators which are distributed over the width of the application nozzle 1. The actuating screws 9 can be moved manually or else by motor.

[0075] For automation of the adjustment, a motorized or else a hydraulic and/or pneumatic drive of the actuators is advantageous. The latter can be connected to a control unit which can automatically change the gap width W depending on default values without the plant having to be shut down for this purpose.

[0076] The application device in FIG. 2 shows an application nozzle 1 which applies the coating medium to a moving surface 4 in the form of a transfer roll 4. The coating medium can then be transferred in a transfer nip from the transfer roll 4 to the fibrous web.

[0077] The application nozzle 1 comprises a nozzle as illustrated in FIGS. 1A and 1B. In contrast thereto, the coating medium in FIG. 2 does not fall downward in the form of a curtain 14, but rather is deposited as a film onto a support surface 8 and guided by said support surface 8. Furthermore, the application nozzle 1 further comprises a blower head 5 which is designed to produce a linear jet of gaseous medium. The gaseous medium can be air. The linear jet of gaseous medium impacts at an impact line onto the film of coating medium so as to form a spray curtain 6. The blower head 5 is arranged in such a way that the spray curtain 6 is directed toward the moving surface 4.

[0078] The application amount is also changed here by varying the gap width W of the outlet gap 2. This takes place, as described in FIGS. 1A and 1B, via suitable actuating means 3. The blower head 5 or the linear jet of gaseous medium does not contribute to varying the application amount. By this means, inter alia, the atomization of the spray mist 6 or the impact angle of the spray mist 6 can be adapted.

[0079] FIG. 3 illustrates 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 hard 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 (free-falling) curtain 14 of by way of a spray curtain 6as illustrated in FIG. 2, 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. That is, the application of the coating medium onto the moving surfaces 4a, 4b, may be effected by the first embodiment illustrated in FIGS. 1A and 1B, or by the second embodiment illustrated in FIG. 2.

[0080] The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: [0081] 1 application nozzle [0082] 2 outlet gap [0083] 3 actuating means [0084] 4 moving surface [0085] 5 blower head [0086] 6 spray curtain [0087] 7 wall element [0088] 8 support surface [0089] 9 actuator, actuating screw [0090] 10 distribution channel [0091] 14 (free-falling) curtain of coating medium [0092] 16 (hard) nip [0093] 17 fibrous web [0094] W gap width