FI96340C - Method and apparatus for coating a paper web - Google Patents

Description

96340

METHOD AND APPARATUS FOR COATING A PAPER WEB

The invention relates to a method for coating a paper web, in which a layer of paste is applied to the surface of the applicator roll, the paper web is guided through a nip formed by the app-5 licking roll and the counter roll so that the paste moves from the applicator roll to the web surface.

The invention further relates to a coating apparatus for coating a paper web, the apparatus 10 comprising an applicator roll provided with a paste applicator for applying paste to the surface of the applicator roll and a counter roll forming a nip with the applicator roll, the web being passed through the nip to the applicator roll surface to transfer to the surface of the web.

In paper coating, film transfer technique is commonly used, especially to apply thin coating layers to the surface of the web. However, the coating formed by the film transfer technique is not completely satisfactory in some respects, i.e. the coating result may be uneven.

It is an object of the present invention to further develop a coating method based on film transfer technology so that the coating result obtained is better than before.

It is a further object of the invention to provide a coating device for carrying out the method.

For aspects of the invention, reference is made to the claims.

The method according to the invention is based on the fact that the paste or the coating in general transferred to the surface of the web by the film transfer technique is formulated, using a counter roll as a support roll. Formulation can be performed with an air or blade stencil.

Thus, in the method according to the invention, 10-45 g / m 2, preferably 2 96340 12-20 g / m 2, of paste are transferred to the surface of the web. The paste is applied to the surface of the applicator roll and the web is passed through a nip formed by the applicator roll and the counter roll, whereby the coating is transferred to the surface of the web from the surface of the applicator roll. In the formulation step 5, the excess coating paste is formulated off and the amount of coating is adjusted.

Thanks to the invention, the coating of the paper web can be carried out at high driving speeds, because the pressure under the blade remains relatively low, i. Only a relatively small amount of coating needs to be scraped off the surface of the paper.

Furthermore, when using the method according to the invention, a smaller water / paper contact is formed in the coating, since the amount of coating is preferably in the maximum order of magnitude of 20-30 g / m 2. Due to the significantly lower paste circulation, considerable savings are achieved in the dimensions of the paste circulation pipes and pumps as well as the tanks. Furthermore, due to the small amounts of coatings, 20 small angle formulations can be used in the formulation, e.g. of the order of less than 45 °, suitably less than 30 °, even less than 15 ° blade angle.

Thanks to the invention, a significant qualitative improvement is achieved in the coating compared to e.g. the principle of contour-couting, which according to the invention can be combined with a blade coating.

Methods for coating a paper web are already known from patent application FI 893468 and patent publication FI 88423, in which the coating takes place in two steps, the second step being performed against a roll. In addition, in said publications, scraping is carried out at both stages immediately after the application of the coating. - In contrast to the publications cited in the present application, the coating takes place in one step. Scraping is performed immediately, i.e. without a new coating step, after a nip where the paste moves from the applicator roll to the surface of the web.

3,96340

Furthermore, the patent publication FI 80314 discloses a method for wiping and smoothing a coating paste, in which case the paste is first smoothed by the so-called by means of an additional sweeping blade and then by means of a special 5 scraper blade. Further, U.S. Pat. No. 4,250,211 discloses a method in which the paste is applied first to the surface of the roll and then to the surface of the web. A special final coating is then applied to the surface of the web using a special applicator. - The method and apparatus according to the present application have not become known from these publications either.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which Figure 1 schematically shows a side view of a coating device according to the invention for carrying out the method according to the invention, and Figure 2 schematically shows paper webs coated by certain methods.

Figure 1 shows a device according to the invention for coating a paper web 1, which device comprises an applicator roll 2 provided with a paste applicator 3, in the embodiment shown a conventional applicator bar, instead of which any other coating method can be used, e.g. blade coating, rod coating to apply the paste to the surface of the applicator roll. The device further comprises a counter roll 4 which forms a nip 5 with the applicator roll. The web 1 to be coated is guided 30 passing through a nip to the surface of the applicator roll to transfer the paste applied to the surface of the web. In this respect, the device corresponds to a conventional coating device based on film transfer technology.

In addition, the device according to the invention includes a blade unit 6, e.g. an air blade or suitably a blade stencil. The blade unit is placed against the counter roll 4 so that when the web 1 is arranged to pass through the nip 5 96340 and further fold partially around the counter roll 4, the blade unit is arranged at the web supported by the counter roll to form a coating applied to the web against the counter roll.

5 Figure 2 shows the paper web 1 coated with three different coating methods. Figure a corresponds to a contour-couting coating according to the prior art, in which case the coating follows the shape of the paper. Figure b corresponds to a blade coating in which the scraper blade cuts the surface formed by the pas-10 tan substantially flat, however, relatively strong corrugated thicker and thinner points are formed in the web. Figure c corresponds to paper coated by the method of the present invention, with the coating initially drawn as in Figure a (shown by dotted lines) and then the highest peaks aligned with a scraper.

The exemplary embodiment is intended to illustrate the invention without limiting it in any way.

li

Claims (3)

A method for coating a paper web, wherein a layer of paste is applied to the surface of an application roller, the paper web is guided through the nip formed by the application roller and a nip, such that paste is transferred from the application roller to the surface of the web, characterized in that: to the surface of the web using film transfer technology, 10 - 45 g / m2, preferably 12 - 20 g / m2 of paste is transferred, and the paste is formed by using the counter roll as a support roll and by using an air or ground template. 2. A method according to claim 1, characterized in that the molding is used with small angle molding with a cutting angle of the order of magnitude below 45 °, preferably below 30 °, advantageously below 15 °. 3. Coating device for coating a paper web (1), to which the device belongs an application roller (2), which is provided with a spreading device (3) for spreading the paste on the surface of the application roller, and a counter roll (4), which together with the application roller forms a nip (5), the web being guided through the nip for transferring the paste applied to the application roller to the surface of the web, characterized in that the counter roll (4) is provided with an air gap. or frame template (6) which is arranged to form on the surface of the web the spreading paste by using the counter-roll as the support roll and the cutting angle of the template stand (6) is of the order of below 45 °, preferably below 30 °, advantageously below 15 °. 1