METHOD FOR COATING A MATERIAL WEB

Abstract

A method for coating a material web (2), in particular a fibrous web, by way of a coating device. The coating device (1) has an application unit (3) for applying a coating medium to the material web. The application unit is arranged in the interior of an enclosure (4), which has first opening for the entry of the material web and a second opening for the exiting of the material web. In the interior of the enclosure there is produced a positive pressure greater than the ambient pressure outside the enclosure during the coating so that air flows from the interior of the enclosure to the outside (5b) of the enclosure through the first opening and/or the second opening.

Claims

1-10. (canceled)

11. A method of coating a material web (2), the method comprising: providing a coating device (1) with an application unit (3) for applying a coating medium to the material web (2) and an enclosure (4), wherein the application unit (3) is disposed in an interior (5a) of the enclosure (4), and the enclosure (4) is formed with a first opening (6) enabling the material web (2) to enter and a second opening (7) enabling the material web (2) to exit from the interior (5a); during a coating process, producing a positive pressure inside the enclosure (4) that is greater than an ambient pressure outside (5b) the enclosure (4), to cause air to flow from the interior (5a) of the enclosure (4) through the first opening (6) and/or the second opening (7) to the outside (5b) of the enclosure.

12. The method according to claim 11, wherein the application unit (3) is a curtain application unit (3).

13. The method according to claim 11, wherein the step of producing the positive pressure comprises blowing an airflow (10) into the enclosure or aspirating an airflow (10) out of the enclosure (4).

14. The method according to claim 13, which comprises adjusting the air flow (10) to more than 1000 m.sup.3/h.

15. The method according to claim 13, which comprises adjusting the air flow (10) to more than 4000 m.sup.3/h.

16. The method according to claim 13, which comprises adjusting the air flow (10) to between 8000 m.sup.3/h and 13000 m.sup.3/h.

17. The method according to claim 11, which comprises blowing the airflow (10) into the enclosure (4) at a temperature of less than 23 C.

18. The method according to claim 17, which comprises blowing the airflow (10) into the enclosure (4) at a temperature of less than 20 C.

19. The method according to claim 18, which comprises blowing the airflow (10) into the enclosure (4) at a temperature of less than 15 C.

20. The method according to claim 11, which comprises measuring at least one parameter selected from the group consisting of a volumetric flow of the air being blown into the enclosure, a temperature of the air being blown into the enclosure, and a moisture content of the air being blown into the enclosure.

21. The method according to claim 11, which comprises measuring an air pressure inside the enclosure (4) at at least one point in the interior (5a) of the enclosure (4).

22. The method according to claim 11, which comprises adjusting the positive pressure in the interior (5a) of the enclosure (4), relative to the ambient pressure outside (5b) the enclosure (4), to at least 8 Pa.

23. The method according to claim 22, which comprises adjusting the positive pressure in the interior (5a) of the enclosure (4), relative to the ambient pressure outside (5b) the enclosure (4), to at least 12 Pa.

24. The method according to claim 11, which comprises causing the air that is supplied via the air flow (10) to escape from the enclosure through one or more of the openings (6, 7) by more than 50%.

25. The method according to claim 11, which comprises causing the air that is supplied via the air flow (10) to escape from the enclosure through one or more of the openings (6, 7) by more than 80%.

26. The method according to claim 11, which comprises enabling the air that is supplied via the air flow (10) to escape completely passively from the enclosure through one or more of the openings (6, 7).

Description

[0034] The invention is explained in more detail below on the basis of a figure.

[0035] FIG. 1 depicts a coating device for the implementation of one aspect of the inventive method.

[0036] Depicted in FIG. 1 is a coating device 1, in which an application unit 3 configured as a curtain application unit 3 is arranged in the interior 5a of an enclosure 4. The material web 2 in question, which may be a paper web or a board web 2, for example, is led through a first opening 6, usually a slot, into the interior 5a of the enclosure 4, and is coated there with a coating medium by means of the coating unit 3. Commonly-used coating media are pigment-containing coating colors, which may contain CaCO.sub.3 or TiO.sub.2, for example. Materials such as polyvinyl alcohol (PVA) have also found an application more recently as a result of their use as a barrier coating. However, other coating materials may also find an application. After coating, the material web 2 exits from the enclosure 4 through a second opening 7. Although only coating with a curtain application unit 3 is illustrated here by way of example, the invention also includes embodiments in which other application units 3 find an application. Similarly, a number of application units 3 may also be provided in the enclosure 4.

[0037] In the embodiment depicted in FIG. 1, an airflow 10 is led into the interior 5a of the enclosure 4 via a fan 8 or some other suitable inlet 8 for the purpose of air-conditioning the enclosure 4. This results in a pressure in the interior 5a of the enclosure 4 which is greater than the pressure outside 5b the enclosure 4. This airflow 10 may exhibit a temperature of less than 23 C., for example. This serves to cool the interior 5a, since heat is introduced continuously into the interior 5a of the enclosure by the material web 2, whereby the latter would heat up without air conditioning. In addition, it could result in the condensation of the moisture present in this air, for example on cool component parts of the application unit 3. If this condensed moisture drips onto the material web 2, for example, the coating or even the material web 2 may be damaged.

[0038] Since the pressure in the interior 5a is greater than the pressure outside 5b, the air will escape from the enclosure 4 via existing openings 6, 7. In particular, exit flows 11 will escape from the first opening 6 and the second opening 7. The exit flow 11 from the first opening 6 in particular is advantageous. In fact, this counteracts the entrainment air entrained by the material web 2. This entrained air is particularly warm and moist. If this entrained air is retained fully or partially outside the enclosure 4, the cost of air conditioning the enclosure falls as well as the energy required for that purpose.

[0039] In the embodiment illustrated in FIG. 1, the whole of the air supplied via the airflow 10 escapes passively from the enclosure 4 through openings 6, 7. In other embodiments, however, provision can be made for a proportion of this air, for example less than 50% and in particular less than 20%, to be removed actively from the enclosure 4 by suction.