FI96893B - Method for coating a paper web - Google Patents

Description

96893

METHOD FOR COATING A PAPER WEB

The present invention relates to a method for coating a paper web, with a basis weight of 30 to 70 g / m 2, in which a coating is applied to the surface of the web to be driven and the coating is smoothed by molding.

In particular, the invention relates to a method for coating a paper web in which the driving speeds are high, i. more than 1000 m / min, preferably more than 1200 10 m / min, even more than 1400 m / min, up to a speed of 2000 m / min or even more.

In this context, paper means printing paper, e.g. LWC and MWC (light weight coated, i.e. MWC = medium 15 weight coated), in particular wood-containing printing paper with a basis weight of the order of 30-70 g / m2.

When coating paper at high speeds, there are problems with the quality of the coating, such as Kiillo, the smoothness and flawlessness of the coating, etc., and the runnability of the paper. In addition, at the said high driving speeds, the control of the moisture gradient and the formation of the blade beard: the blade causes problems. These disadvantages have not been remedied by previously known methods.

Disadvantages are problematic, especially for the relatively. with small amounts of coating, e.g. 6-14 g / m.

It is an object of the present invention to obviate the above drawbacks. In particular, it is an object of the invention to provide a new method for coating a paper web, which method allows the coating to be carried out at a high running speed.

It is a further object of the invention to provide a novel paper coating method with 2 96893 high quality criteria for the paper to be coated, in particular with coating amounts of 6-14 g / m 2.

In particular, it is an object of the invention to provide a novel paper coating method which is particularly suitable for coating wood-containing printing papers, e.g. LWC and MWC and similar grades of paper, preferably in the range of 30-70 g / m 2 of base paper.

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

The invention is largely based on the fact that in the method according to the invention, in its first step, the amount of coating remaining on the web is so thin, i. 12 to 30 g / m 2, even 12 to 20 g / m 2, that steam can be added to the surface of the web, whereby the moisture-15 gradient of the web changes so that the formation of the blade beard is controlled, i. the front blade and / or patterning blade does not form a blade beard that makes it difficult to drive. If steam is applied to the surface of the web in a conventional paper web coating method, the addition of steam 20 generally does not improve the runnability of the web, i.

the added steam is not useful for the runnability of the web. Further, if the method does not use a two-stage coating, i.e. the method does not use a pre-blade, and if the amount of coating applied to the web does not correspond to that set forth in claim 1, the addition of steam does not achieve those advantages and the corresponding product cannot be produced other than by the method of the present invention.

When performing the coating pre-coating 30 (first step) immediately after coating, formulate with the help of a pre-blade so that the web is left with:. the amount of coating is 12 to 30 g / m 2, preferably 12 to 20 g / m 2; g / m2, by applying steam to the web and smoothing the coating smoothed with the pre - blade by means of a patterning blade. 35 (second stage) so that the amount of coating remaining on the web after leveling is 6-14 g / m 2, the coating is filled. desired quality criteria, i.e. the desired gloss, potassium 3 96893 lentering properties and the like are achieved. Furthermore, when using the method according to the invention, no blade beard is formed on the pre-blade and / or the patterning blade, which would form a runnability limiting factor 5 in connection with the coating when using the current methods.

In particular, it should be noted that in the second step, the coating is removed from the surface of the web and the remaining coating is smoothed. Previously, two- to 10-stage pavement leveling has not been implemented at high driving speeds, i. more than 1000 m / min, preferably more than 1200 m / min, not to mention driving speeds of more than 1400 m / min. Furthermore, the use of steam at the driving speeds in question, and in particular at low coatings and in two-to-15-stage coatings, to eliminate runnability problems is new and surprising; in particular, the retention of steam on the surface of the paper web and even its adhesion to the surface of the web and its migration with the web is new and surprising.

FI 2701/65 discloses a method and apparatus for providing a uniform moisture profile to a web by an electrostatic method by conducting the web through a direct voltage field. The publication thus referred to relates to a completely different technology from the present application. Furthermore, the publication does not show the method according to the present application.

··· Publication FI 79578 relates to a scraping method, • · · ·. ·. * In which the coating is scraped by means of a gas jet using, for example, steam, etc. However, the publication does not show a two-stage drawing according to the present application.

FI 83350 relates to two-stage scraping • · * * ··· using a drag scraper blade and a second blade; the publication does not appear to show steaming or in general. 35 method according to the invention.

Publication GB 912 692 relates to a paper coating • <a method in which the paper web is applied e.g. 4 96 893 steam which the steam of the paper web and the blade trailing side of the area defined. The method can also be used at high driving speeds. However, the publication does not disclose a two-stage coating or a coating with its own low coating volumes as in the present application.

Journal article Tappi J. Sept. 1992, pp. 161-169, Ortman and Donigian: Mechanism and prevention of coat weight ..., generally relates to single-stage coating. The publication also describes (Figure 1) a two-stage coating, i. In step 1, the coating is applied by means of a roller and in step 2, the coating is formed by means of a blade. However, the method of the present invention, in which the coating 15 is formed with a pre-blade in step 1 and a patterning blade in step 2, does not appear to have become known from the referenced publication, let alone the use of coating amounts and evaporation according to the invention.

In general, the above publications do not relate to two-stage coating, and the methods and devices disclosed in the referenced publications are not intended to eliminate the disadvantages specifically at high driving speeds, low coating volumes, two-stage coating; maladministration. In view of the detailed attributes of the method according to the invention set out in the claims (in particular the driving speed, the leveling of the coating in two steps by formula, the amounts of steam and the addition of steam at a well-defined point after the leveling 1), the invention clearly differs substantially from with particular reference to the benefits of the invention:.

• · The method of application of the coating to the web can be any method of application known per se. The method of this is suitable for use, for example, in connection with an application roll, a nozzle coating (in which case the web-side edge of the nozzle can form a pre-blade) or, in general, any coating method known per se. Essential to the method is that in the second smoothing step, the coating is removed from the surface of the paper web while coating the remaining coating.

Steaming can be performed near the pre-blade or near the patterning blade or anywhere between them. In connection with steaming, it should be noted that a large amount of steam lowers the dry matter content of the pasta.

Thus, the amount of steam can be advantageously selected so as not to substantially reduce the dry matter content of the coating paste.

The effect of the steam can be enhanced by applying steam to the surface of the web by means of a special housing which forms a housing delimiting the web from one side of it to the edge, which is sealed on the walls of the housing to the edges of the counter roll, a certain distance, e.g.

0.05 to 0.7 m or more in the direction of web travel.

Smoothing the coating with a pre-blade, i.e. the first leveling step, and the leveling of the coating remaining on the surface of the web and the removal of a part of the coating with a patterning blade, the second patterning step, are preferably performed against one and the same counter roll so that the counter roll supports the web on the opposite side to the coating.

The leveling of the coating by means of a patterning blade, the second leveling step, is preferably carried out immediately after leveling with the pre-blade, the first step, e.g. 5 cm to 0.7 m (up to 2 m) up to 30 after the pre-blade.

When using the method according to the invention, the coating forms an even more uniform coating of better quality. The method is suitable for use with any of the known paper coatings.

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The invention will now be described in detail by way of example with reference to the accompanying drawing, in which Figure 1 shows a side view and a diagram of an embodiment of the method according to the invention, and Figure 2 shows another embodiment of the method according to the invention in a side view and a diagram.

In Figures 1-2, in the paper machine, the endless paper web moving in the direction of travel a 10 is led to run against the counter roll 2, partly rotating over it and resting thereon. The coating is applied to the surface of the web by means of a coating device 3 in a manner known per se. After the coating device 3, in the direction of travel 15a of the web 1, a pre-blade 4 is placed, which smoothes the coating applied to the surface of the web so that the amount of coating remaining on the surface of the web is 12-30 g / m 2, preferably 12-20 g / m 2. After smoothing with the pre-blade 4, a first smoothing step, steam is introduced onto the surface 20 of the web, e.g. by means of a steam nozzle 5. The steam travels some distance with the web and acts on the leveled coating in the first leveling step. Next, when moving in the direction of travel a, the web and the applied, smoothed and steamed coating applied to its surface proceed to the second smoothing step, where the coating is formed by the patterning blade 6 so that the amount of coating remaining on the web after coating is 6-14 g. / m2. In the second leveling step, a part of the coating is removed from the surface of the web and at the same time the coating is leveled again. The quality of the coating of the obtained paper is of a high standard and of high quality.

In Fig. 1, the first coating step is carried out by means of a conventional application roller 3. Mene- ·. ' In the system, a coating is applied to the surface of the applicator roll 3, e.g. from a tray 7. The pre-blade 4 removes i «

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7 96893 excess coating which is returned to circulation, i. to the trough 7.

In Figure 1, the steaming is carried out by means of a special housing 8 which surrounds the web on its opposite surface relative to its support roll 2 5. The steaming housing 8 promotes the ingress of steam onto the surface of the web and thus the wetting effect of the coating. Furthermore, the steam, apparently due to the wetting effect, prevents the blade beard from forming in the patterning blade 6, which would otherwise form a general limiting factor for the coating.

In Figure 2, the coating of the first stage is carried out using the so-called suutinpäällystystä. The edge below the nozzle, in the direction of travel a of the web, then forms a pre-blade which smooths the coating.

The speed of the paper web in the method according to Figures 1-2 can vary e.g. more than 1000 m / min, preferably more than 1200 m / min, up to e.g. 2000 m / min, even more than this.

Example 1 To determine the applicability and advantages of the method, in this experiment the paper web was coated using the method according to the invention. In steam test 1, roller application, pre-blade patterning, treatment side was steamed (machine side without steam), 25 and blade patterning were used. In steam experiment 2, the same * was used. roll application, pre-blade patterning, steaming and *; * j blade patterning. The reference was paper coated with a normal blade coating, in which the coating was applied to the surface of the web using a roller applicator 30 and was normally formulated as a 1-step blade pattern. The base paper of the web used was wood-containing paper: 34 g / m 2. The paste used contained 100 parts of kaolin and 10 parts of latex, dry matter content. * * 62.7% by weight, evaporation for the entire width of the web or 1/2 the width, the test run speed was 1200 m / min in the steam tests. The coating volume target for coating steps 1 and 2 was 10; : g / m In the reference test, the test speed was 1200 m / min.

8 96893

The dry matter content of the pasta machine cycle did not change during the application phase during the run, although different test points were run on the same pasta for about 15-20 minutes. Especially during steaming, no changes were observed in the dry matter of the pasta. The dry matter content of the pasta at the start was 62.6 wt% and at the end of the whole run 62.4 wt%. The effect of steam was observed on a pasta sample from the second blade. The dry matter content of the paste to be formulated decreased by about 2.5% by weight (initial value 62.6% by weight, 10 samples about 60% by weight). The moisture was presumably on the surface of the molded paste. The amount of coating measured on the surface of the paper was 10 g / m2.

The moisture gradient required for feeding was obtained by passing steam through the nozzle after the pre-blade 15 to the surface of the paste at a distance of about 0.6 kg H 2 O / min / width meter.

The test results are shown in Table 1, where hp means the treatment side of the web, kp the machine side of the web.

20 TABLE 1

Reference Steam test 1 Steam test 2,! Kiilto, Hunter, see 12.9 12.7 (hp) /12.5 (kp) 12.7 · '; Karheus, Bendtsen 150 150 (kp) / 130 (kp) 150: · ί · 25 4 ·. The working examples are intended only to illustrate the invention, and the embodiments of the invention may vary within the scope of the appended claims.

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Claims (5)

96893 A method for coating a paper web, 30-70 g / m 2, in which method a coating is applied to the surface of the web to be run and the coating 5 is smoothed by molding, characterized in that the web running speed is more than 1000 m / min; that the leveling of the coating is performed in two steps; that the amount of coating remaining on the web in the first step is 12-30 g / m 2, preferably 12-20 g / m 2 after leveling with the pre-blade 10; that steam is applied to the surface of the web immediately after smoothing with the pre-blade; and that the pre-blade coated coating and the steamed coating are smoothed in the second step by means of a patterning blade so that the amount of coating remaining on the web after smoothing in the second step is 6-14 g / m 2. Method according to Claim 1, characterized in that the leveling of the coating by means of the patterning blade is carried out immediately after the leveling by means of the pre-blade 20. A method according to claim 1 or 2, characterized in that the application of the coating on the web is performed using a nozzle coating; or alternatively an applicator roller. According to one of claims 1 to 3 *. *: method, characterized in that the dry matter content of the paste is of the order of 56-66%, preferably: V: 58-64%. Method according to one of Claims 1 to 4, characterized in that the coating is smoothed with a pre-blade so that after the pre-blade. the amount of coating remaining on the web is of the order of • ·: 2 ka 12-18 g / m 2 and that the amount of coating remaining on the surface of the web after smoothing with a patterning blade is 35 6-12 g / m 2. 96893