FI100643B - A method of coating paper or paperboard on both sides - Google Patents

Description

100643

METHOD OF COATING PAPER OR BOARD ON BOTH SIDES

The normal field of application of the developed method is to coat paper or board with the same coating unit on both sides without intermediate drying and at the same time to provide surface gluing. If desired, the following coatings can also be applied immediately afterwards.

10 Today, high-speed machines, both paper and board, are generally coated one after the other, one at a time, after which this coating is dried with a dryer behind the coating unit. There are also coating techniques that allow both sides to be coated simultaneously, but their use is often limited, especially by high-speed machines, by measurement and control technology. As control technology develops, simultaneous separate coating is also likely to occur for high-speed discrete coating machines and on-line coating machines.

However, no technique exists yet in which all four coatings could be made in the same unit without intermediate drying. However, good quality rigid specialty papers and cartons would often be advantageous to double-coat on both sides.

25 The developed method can also be used to apply a certain type of surface sizing to paper.

• · · '· ·,! The object of the invention is achieved by a method which is characterized by what is stated in the claims.

·: · 30 • «·

The advantages of the invention are the considerable simplification of the coating machine as well as the decisive shortening of the length. This ‘’ means financial savings. The machine-contaminating effect 35 of possible holes in the base paper is also considerably reduced when the one-sided wet web is not conveyed over the rollers. Another advantage is that a water-repellent surface sizing is obtained on the paper, which prevents the swelling of the thermohelier fibers and the deterioration of the print.

100643 2 As a result, more cheap pulp can be used in fine papers instead of expensive pulp while still keeping the print good.

Figure 1 shows a cross-section of a device according to the method, in which the strip of paper to be coated enters the coating unit from above and falls further down there into a dryer, which may be, for example, Lei jukui only. Figure 2 shows the principle of surface sizing with a coater with cross-sections of the paper structure. Figure 2 A is a section immediately after coating and Figure 2 B is a cross-section of the coating after exit.

Figure 1 explains the coating method to a practical level 15. The double-sided coating takes place on the paper web (3) in a vacuum, for example by the nip press technique shown in the figure, in which the coating paste is applied to the surface of two rolls, from where it is pressed simultaneously on both sides of the paper. The loose humidity control of the coating lo-20 takes place at the temperature of the pressing roll on the surface of which the coating film is before pressing. and by adjusting the prevailing vacuum so that it enters the surface of the paper (3) as dry as possible. As the base-coated paper exits the vacuum chamber, external pressure pushes the coating moisture into the base paper structure, which is at the exit. At the same time, the phenomenon of FIG. 30 surface gluing (10). Surface gluing prevents printing ·. too much water to swell the water-absorbent pulp fibers, whereby the formation of a typical wrinkle surface on the print is prevented even when mechanical pulps are used. If the coating rolls forming the press-35 nip are elastically coated, a separate vacuum lock (4) may not be required. The penetration of too much moisture from the coating into the porous base paper in the vacuum can be enhanced by the hot air blower 100643 3 as soon as the paper has left the vacuum chambers (5). After this rapid blow-drying operation, the coated paper is once again in a coating condition. Next, a new mo-5 mild surface coating can normally be applied on top of the base coat. After this second coating, the coated paper then has to be dried normally, for example with a Lei dryer.

The invention is not limited to the application described above, but can be modified as the coating technique and the material to be coated vary within the scope of the claims.

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Claims (4)

1. A method for coating web material such as paper or cardboard on both sides of the coating butter, characterized in that the coating is carried out when the web is in vacuum and the dry matter content of the coating butter is so high that coating is still possible, whereby drying of this coating layer takes place so that the air pressure forces the moisture to penetrate through the coating layer into the base paper in vacuum as the coated paper (3) exits a vacuum coating machine (5) to the air pressure. Method according to claim 1, characterized in that when the coated paper web (3) exits the coating machine (5) to the air pressure, dry hot air (7) is blown against it. Method according to claims 1 and 2, characterized in that fine adjustment of the water content of the coating smear is carried out in the vacuum coating machine (5) by adjusting the temperature of the coating parts (1) in the coating machine and / or the vacuum. 4. A method according to claims 1 to 3, characterized in that latex-type adhesives are added to the coating composition in such an amount that, when discharged from the coating machine, it partially penetrates the surface of the paper, thereby providing a surface adhesion which prevents water penetration. • I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I