EP0670004B1 - Process and device for coating a travelling material web - Google Patents

Abstract

The invention is directed to a process and system for coating a traveling material web, especially paper or cardboard, with at least one liquid medium, in which the coating medium is conveyed to an applicator device with a spray nozzle fitted in a vacuum chamber to generate a spray mist. The spray mist is applied to the material web according to the invention in that it is applied to the outside of at least one roll and transferred to the material web from the roll.

Description

The invention relates to a method for coating a running web of material in accordance with the preamble of patent claim 1 and a coating device in accordance with the preamble of patent claim 2.

Coating devices for paper and cardboard are widely known, z. B. according to GB 21 03 115 A, the transfer of coating material from the roll shells of two mutually associated, forming a press nip rolls between them on the web in the press nip. Nozzle applicators or dipping rollers are used as applicators. The application unit uses a doctor blade to smooth and dose the application layer.

For the coating of running webs, application devices are also known which work in the manner of a pouring application device, and the uniformity and adhesiveness of the casting layer is improved by the fact that it is preceded by a chamber under vacuum, which is arranged on the counter roller guiding the material web . A casting process which works with the vacuum chamber is described in US Pat. No. 3,735,729, which is, however, not used for paper webs. It is mainly used for coating photo paper because the coating materials have a higher consistency there. There are considerable problems for coating paper webs with glue that has a very low consistency and viscosity.

All of these inventions are suitable for the application of relatively large amounts of coating compound per m ^{2 of} web area. However, they fail if an extremely small application weight per m ^{2 is} desired.

EP 04 35 904 B1 discloses a method and a device for coating paper, cardboard or a similar substrate, which moves continuously along a path.

The coating medium is broken down into mist and fed to an application nozzle with an application surface. A vacuum chamber is arranged adjacent to the application area for receiving excess mist.
The spray mist generated is applied directly to the substrate (paper web) by a "positive force" (overpressure) using the application nozzle. With this method too, it is doubtful whether an extremely low application weight per m ² can be applied to the paper web with the uniformity required for many types of paper.

Finally, it is also known to arrange the air knife arrangement in a large vacuum container in so-called air knife devices. In this case, however, the air knife does not apply any coating, but coating compound is scraped off and metered on the web.

The object of the invention is to provide a method and an application device or coating device for running webs of goods with very small, extremely thin application layers and nevertheless uniform application quantities, in particular for glue application.

This object is achieved by the features of the characterizing part of patent claims 1 and 2.

The spraying of coating material is common in many areas of technology, but is hardly used for coating running webs of paper or cardboard.

According to the indirect order, ie. H. that spray is applied to a bare roller and removed from the web, an order is achieved that is both extremely thin and very even, especially across the web direction. The equalization takes place according to the invention at the contact point between the web and the roll, where the web takes over the thin liquid film from the roll. The web can rest against the roller under a certain tension, the web being deflected. However, the web is preferably allowed to run through the press nip formed by two rollers. This enables double-sided orders.

The invention makes use of the vacuum (vacuum) chamber known from EP 04 35 904 B1, which is arranged around the spray nozzle.

In the case of the present invention, too, this serves to suck off excess mist from the coating medium. However, part of the mist can deposit on the inner wall surface.

According to an important idea of the invention, the arrangement of a side wall on the draining side of the associated roller surface next to the spray nozzle, within the vacuum chamber, creates an impact surface for part of the excess spray. The baffle surface (side wall) is preferably designed or enlarged such that it forms an inner chamber around the spray nozzle. In this chamber there is a certain overpressure due to the spray mist ejected from the spray nozzle.

The baffle surface (side wall or inner chamber) on the one hand causes the spray to reach the roller better, and on the other hand a relief of the vacuum chamber is provided, which enables coating medium (spray) emerging from the spray nozzle not to leave the chamber, ie the gap between the chamber and the counter roll can escape into the environment. The air flowing in from the environment retains the spray in the chamber, so that this can be reflected in the invention partly on the baffle and partly on the inner wall of the outer chamber. The deposited coating medium can run off via an outflow. Precipitated mist remaining in the outer or inner chamber is fed to a separator, for example via a suction fan, whereby the separated medium and the medium flowing directly out of the chamber can be fed to a common collecting container for reuse.

The invention is explained below on the basis of the exemplary embodiment illustrated in the figures of the drawing.

Fig. 1:

Eine prinzipmäßige Gesamtdarstellung

Fig. 2:

Eine Einzelheit hinsichtlich der erfindungsgemäßen Beschichtungseinrichtung

Fig. 3:

Beschichtungseinrichtung mit einer anderen Schaberanordnung

Fig. 4:

Die Beschichtungseinrichtung mit einer anderen Variante zur inneren Kammer.

Show it:

Fig. 1:

A general presentation in principle

Fig. 2:

A detail regarding the coating device according to the invention

Fig. 3:

Coating device with a different scraper arrangement

Fig. 4:

The coating device with another variant to the inner chamber.

In Fig. 1, the web C is guided in a press nip 11 formed between two press rolls 1 and 2 and coated there. Guide rollers 22 and 23 are provided for the correct guidance of the web. The application units for the coating medium are designated 10 and 10 'here and are arranged essentially below the respectively assigned press roll; they extend essentially over the entire length of the press rolls.

Instead of the two press rolls 1 and 2, each with an applicator unit 10 and 10 'for simultaneous coating of both web sides, it is also possible to use only one applicator roller with one applicator unit 10 or 10' for coating only one web side and an associated counter roller.

The application works can be seen in FIGS. 2, 3 and 4, where one (10) is shown. It essentially has a spray nozzle 4. As already described, this application unit sprays fine, mist-like spray jets of the coating medium onto the outer surface of the press roll (here 1). As can be seen in FIG. 4, the spray nozzle 4 is arranged in a chamber 3 which is under negative pressure. In its running and running side against the surface of the associated press roll 1 or 2 (only application or press roll 1 shown in Fig. 4), it is sealed with a gap 16 or 16 ', i.e. the coating medium emerging from the spray nozzle 4 is retained at this point and can therefore not get into the environment.

4 shows an embodiment of the invention. In the chamber 3, a side wall 7 is arranged at a short distance from the spray nozzle 4 on the draining side. This side wall 7 acts as an impact surface for part of the excess spray which is sucked into the vacuum chamber 3 via the gap 18 'and from there can be fed to a separator (not shown in the drawing) via a trigger 30 (e.g. suction fan) . On the inner walls of the chamber 3, the back flowing coating medium runs off through a drain 28 and can be combined with the medium separated in the separator and thus be reused.

In another embodiment, the spray nozzle 4, as shown in FIGS. 2 and 3, is arranged within an inner chamber 5, the chamber 5 being delimited from its interior by means of gaps 18 and 19, as seen in the direction of travel of the roll surface. This inner chamber 5 is arranged inside the outer chamber 3, which is under vacuum from the atmosphere, which can be, for example, between 50 and 300 MPa.

As can be seen in the embodiment variants according to FIGS. 1 to 3, a scraper 6 can be located on the upstream side of the chamber 3 as a seal for the chamber 3. The scraper is held in a holder 12 by means of pressure hose 14, which presses it against the rear wall of the vacuum chamber 3.

Another pressure hose 15 is arranged in a holder 13 and presses the scraper against the outer surface of the roller 1 with a variable, adjustable contact pressure. This contact pressure can also be kept constant by means of the pressure hose 15.

In FIG. 2, the scraper 6 is designed as a so-called piercing scraper, which is used for rollers with a hard surface. This scraper 6 is called a plunger because it is inclined in the opposite direction to the direction of the press roll 1 or 2.

In Fig. 3, the scraper is designed as a so-called drag scraper and is so named because it is dragged or carried along by the running roller. The drag scraper is used for rollers with a soft surface.

By pressing the glue mass that passes from the roller surface onto the web, this is further and very evenly leveled, provided there are still irregularities in the layer. Extremely low application weights of between 0.3 and 0.8 g / m ² , based on dry matter, are achieved. This is a very small order quantity, which cannot be applied with the necessary uniformity using the means according to the prior art, in particular EP 04 35 904 B1, especially since according to this solution the order quantity is applied directly to the web.

Due to the design of the application unit as a spray device, it is not absolutely necessary that it be arranged below the press rolls, but it can also spray the upper parts of the outer surface thereof. Then the path and the direction of rotation of the rollers are preferably reversed as shown in Fig. 1.

Claims (12)

1. A method for the coating of a continuous web of material, in particular paper or cardboard, with at least one fluid medium, in which the coating medium is supplied to an application device with a spray nozzle for the production of a spray mist, in which
   the spray mist is applied in an indirect manner onto the web of material (9) in such a way as to be applied onto the covering surface at least of one roller (1,2) and transferred from the roller onto the web of material (C),
   characterised in that the spray nozzle is arranged in a low-pressure chamber (3) and that
   a portion of the spray mist is collected in the low-pressure chamber (3) and is deposited partially against a wall (5, 7) situated within the low-pressure chamber (3) and constructed as an impact surface, and is drawn off therefrom.
2. A device for coating a continuous web of material, in particular paper or cardboard, with at least one fluid medium, in which an application device (10, 10') for the coating medium is provided with a spray nozzle (4) for the production of a spray mist, in which the spray nozzle (4) is directed towards the covering surface of a roller (1, 2) which transfers the coating medium onto the web of material (C), characterised in that the spray nozzle is arranged in a low-pressure chamber (3) and that within the low-pressure chamber (3) on the run-off side of the associated roller surface a side wall (5, 7), acting as an impact surface, is arranged.
3. A device according to Claim 2, characterised in that the side wall (7) is constructed such that it forms an inner chamber (5).
4. A device according to Claim 2 and 3, characterised in that the inner chamber (5) on the run-out and run-up side is sealed with respect to the surface of the associated roller (1, 2) with a gap (18, 19) in each case, and the side wall (7) acting as an impact surface is sealed with respect to the surface of the associated roller (1, 2) with a gap (18').
5. A device according to Claim 2, characterised in that the chamber (3), under vacuum, is sealed at least on its run-out side with respect to the surface of the associated roller (1, 2) with a gap (16).
6. A device according to Claim 2, characterised in that the chamber (3), under vacuum, on the run-up side is sealed with respect to the surface of the associated roller (1, 2) with a gap (16').
7. A device according to Claim 2, characterised by a scraper (6) as seal of the outer camber (3) on its run-up side on the associated roller surface.
8. A device according to Claim 7, characterised in that the scraper (6) is constructed as a piercing scraper such that it is inclined in a direction which is opposed to the running direction of the roller (1, 2).
9. A device according to Claim 7, characterised in that the scraper (6) is constructed as a drag scraper such that it is inclined in the running dirction of the roller (1, 2).
10. A device according to one of Claims 2, 5, 6 or 7, characterised by an outlet (28) which branches off from the outer chamber (3), in order to remove the collected coating substance.
11. A device according to Claim 3 or 4, charcterised in that the outlet (28) branches off from the inner chamber (5) and passes through the outer chamber (3).
12. A method according to Claim 1, characterised in that the coating weight per side of the web of material in the case of glue amounts to between 0.3 and 0.8 g/m² in relation to dry matter.

Images