EP2576900B2 - Method for producing a coated multilayer fibrous web - Google Patents

Description

The invention relates to a method for the production of a coated, three-layer fibrous web, in particular packaging paper or cardboard web, in which a material flow is first generated, which is then successively followed by three material flows, at least one wire section to form a three-layer fibrous web, a press section, a dryer section with dryer groups and is then fed to a reel.

The document WO2006 / 024695A1 discloses a process unit with metal belt for smoothing paper webs.

The multi-layer coating of paper or cardboard is the subject of the document EP1249533A1 .

Cardboard and packaging papers are usually dried with drying cylinders of a single-row and / or two-row drying section during their production in the paper machines. There are also optional suction elements, primarily for web stabilization. A disadvantage is the large amount of space required for such drying sections and also the limited drying capacity. Especially with regard to the required machine speeds, which are becoming ever higher, the drying zones must be made longer in relation to the total machine length.

The smoothness of the cardboard to be produced or the packaging paper is usually produced in the production of cardboard with the help of conventional calenders, such as hard-nip calenders with high maximum pressures and short dwell times of the fibrous web in the nip. The disadvantage of this technology is the loss of web thickness. In other conventional smoothing processes with SoftNip calenders, soft roll covers are used to increase the dwell time in the nip. The disadvantage here is the slight increase in smoothness and the loss of volume. Other conventional smoothing processes, such as wide nip calendering or shoe smoothing, use soft covers on the unheated roller. A disadvantage here is also only a slight increase in smoothness with a simultaneous loss of volume.

The fibrous web or packaging paper or cardboard web is usually also coated with a pigment coating. This achieves the whiteness, smoothness, gloss and opacity of the web. This also increases the printability of the web material, so that it can serve as an information and advertising medium.

In addition to digital printing, printing takes place primarily in the form of offset printing and gravure printing.

The fibrous web is coated at least once on the cover side. The reverse side can be left uncoated or is also coated at least once. Coats of up to 80g / m ^{2 are} applied per side. Up to now, application has been carried out with conventional coating units, such as film presses, coaters with roller application (LDTA applicators with a long exposure time for the coating medium), coaters with free-jet nozzles, or with application units with a short dwell time of the medium on the web (so-called short dwell time applicators or SDTA ).

The disadvantage is that with these conventional types of application only a limited application capacity and thus poor coverage and opacity of the fiber web or packaging paper and cardboard web produced can be achieved.

It is therefore the object of the invention to provide a method for producing a coated, three-layer fibrous web, in particular a packaging paper or cardboard web, which does not have the disadvantages of the prior art.

The object of the invention is achieved with a method according to the features of claim 1.

According to the invention, it is provided that the fiber web produced in three layers is pre-smoothed with a belt calender within or after an after-dryer section and then the top layer of the fiber web is coated with a white pigment-containing coating layer using a curtain applicator and then dried and that in the press section (II ) at least one smooth roller is used, which acts at least on the top layer.

The inventors have found that with the specified pre-smoothing process,

i.e. a belt calender is used to produce a smoother paper than before, i.e. what was previously done either without pre-calendering or with other calendering units. The smoothing of the belt according to the invention leads to better coverage of the white coating layer subsequently applied with the curtain applicator. Due to the high smoothness of the web, there is a far lower risk of the curtain tearing off during coating, even with low coat weights or low viscosity of the application medium used for curtain coating and high web speeds. This is regarded as a particular advantage of the invention. In addition, the smoothness of the web only needs to be present on one side before coating, because the product resulting from the fibrous web produced is preferably only printed on one side.

The belt used to pre-smooth the fibrous web consists of more than 70% plastic. The temperature of the belt surface in contact with the fibrous web is more than 80 ° C.

Another advantage is that because of the white pigment-containing curtain coating, which is very even and covers well, only a low weight per unit area of the white and expensive fiber layer (top layer) is required. This saves expensive raw materials without the lower fiber layers showing through and without the print quality worsens.

The method according to the invention offers the possibility of producing the fibrous web in three layers, namely back layer, middle layer, top layer - depending on the desired application. White or bleached and / or deinked and / or wood-free fibers, which are expensive, are provided for the top layer. It is all the more advantageous that these substances can be saved to a large extent because the white coating described is applied to the top layer with the help of a curtain coating. In certain cases (e.g. with white multiple lines) the white top layer can even be completely replaced with the white line layer.

A curtain coater applies the application medium in a ratio of 1: 1, i.e. without excess, onto the running fibrous web during its manufacturing process. So only the amount of coating material or pigment-containing application medium that is to remain there is applied to the web. This saves the doctoring and the corresponding doctor devices. The at least one coating layer can be applied with a single or multi-layer curtain applicator in the form of a slot die or a so-called sliding layer nozzle.

It is useful if a condensation press drying is provided within the pre-dryer section. This could also be carried out after the dewatering in the press section and / or in an after-dryer section. This offers the advantage of an increased evaporation rate of more than 40 kg / m ² h and the smoothing of the fibrous web. This type of drying, with which conventional drying cylinders can be partially saved, should take place in an area in which the web has a dry content of more than 50% to about 90%, preferably more than 55%. At least one such drying should, as said, preferably be carried out within the pre-dryer section, it also being conceivable to also provide this in the after-dryer section. The mentioned high evaporation rate and smoothness come about because the fibrous web is guided with one side over a preferably steam-heated cylinder and with the other side over a sieve and an overlying impermeable covering. In this case, a contact pressure against the cylinder is exerted in this section with a pressure hood covering part of the outer circumference of the cylinder. A particular advantage is an improved heat transfer from the steam interior of the drying cylinder to the fibrous web. In addition, the drying speed can be increased without the need for machine extensions. The paper strength and the surface properties are increased despite the possible saving of raw fibers. The application of starch can also be reduced.

The production method according to the invention can be made even more advantageous in that at the beginning of the production process for the formation of the top layer of the three-layer fibrous web, a fine material is fed into the headbox. This results in a very smooth top layer, which forms a particularly good basis for the subsequent coating layer and which results in a very even covering of the fibrous web.

The headbox can also be designed as a perforated roll headbox or as a hydraulic headbox. At least one headbox is optionally equipped with a dilution water control. The advantage of this is that a weight per unit area profiling is achieved without adjusting the lip and thus the fiber orientation. The middle layer is preferably equipped with a dilution water control with the advantage that the cross-sectional weight profile of the entire cardboard web can be influenced most strongly by the layer with the largest proportion of the total weight per unit area (middle layer).

All known shape combinations can be used in the wire section. It is preferred to use Fourdrinier wire, but also combinations of Fourdrinier wire and hybrid formers, for example the Duo D or Duo DK sold by the applicant's company, also as combinations of at least one gap former and at least one Fourdrinier wire. It is advantageous if the said former is equipped with a sieve shaking device, for example with the Duo Shake sold by the applicant's company. In the case of multi-layer concepts, this should preferably be provided for the layer with the highest layer weight per unit area, such as the middle ply.

All known press combinations can be used in the press section.For example, a tandem NipcoFlex press (TNFP) with an offset press that is fourfold felted and / or a press unit consisting, for example, of a suction press roll in the first nip, a NipcoFlex press in the second nip and an offset press in the third nip. The press concepts can be designed with a closed or open web guide. The framing, i.e. the supporting frames for the presses, can be designed as so-called cantilevers. It is also possible to use sewn or seamless felts in the press section. With the mentioned press concepts, dry contents of up to 57% can be achieved.

In the context of the invention, at least one smooth roller is used in the press section, which acts at least on the top layer. This can be done with the help of a known tandem press with three felts and a smooth roller, which is usually arranged at the bottom, or with a so-called offset press, in which a nip is carried out without any covering. This measure also contributes to a smoother top layer, which in turn can be coated more evenly.

To increase the efficiency of the process, it is expedient to carry out an impingement drying process known per se directly after the press section and before the first heated drying cylinder of the drying section. This increases the dryness of the web and reduces the risk of breakage in the dryer section. A speed of greater than 1000 m / min, in particular greater than 1200 m / min, is thus possible.

With regard to the quality of the packaging paper or cardboard web, it can also be advantageous if, in addition to tape smoothing, the web is subjected to condensation press smoothing after predrying and before a later coating with the at least one white coating layer. This smoothing process leads to even higher smoothing values. The condensation press smoothing works in a similar way to the condensation press drying, whereby the fibrous web is guided over a heated cylinder and brought into direct contact with a metal belt running over the cylinder, over which there is a pressure hood. A sieve or a covering is not available here.

In the case of condensation press drying and also in condensation press smoothing, the cylinder (drying cylinder or smoothing cylinder) is preferably heated with steam in each case, the cylinder surface reaching a temperature between 60 and 250 ° C, preferably 130 to 190 ° C.

The method according to the invention can be further expedient if, following the curtain coating, the same side of the web is coated a second time with a conventional coating unit, such as a direct application blade coating unit, dried and then the other side of the web is also coated with a conventional coating unit and then dried with dryers becomes.

With regard to the quality of the fiber web produced, it is when it is smoothed before it is rolled up, i.e. within a final group of the production machine.

This smoothing unit has a heating roller which is provided with a plastic jacket which has a metallic coating with a thickness of <200 μm. This achieves an enormous increase in smoothness and an even better gloss.

The fibrous web can then be fed to a cooling group and then to the reel.

According to a first variant, it is possible that the cardboard or the paper has three layers consisting of a fiber top layer made of bleached cellulose, a middle layer made of wood-containing raw material and / or waste paper and a back layer made of bleached cellulose or a mixture of bleached cellulose Pulp with proportions of wood-containing raw material, to which proportions of waste paper stock are also added.

Depending on the quality of the cardboard, the ceiling is made of 100% bleached cellulose and is coated at least once. The insert, i.e. the middle days, is light and consists either of 100% wood-containing raw material or parts of recycled paper are added.

The back is light-colored and consists either of 100% bleached cellulose or a mixture of bleached cellulose with proportions of wood-containing raw material. Waste paper stock can also be added to the back. The back can optionally be painted with at least one line. If waste paper is used, it can optionally be deinked in the stock preparation.

Depending on the quality of the raw material used and the amount of coating applied, a distinction is made between qualities with the following abbreviation, whereby the number 1 denotes the type with the highest quality. In the case of the GG types, the coating paste is enriched with plastics. variety Line weight GC1 Painted > 18 g / m ² Better raw material than GC2 and GC3 GC2 Painted > 12 g / m ² GG1 Cast painted Wood-free back GG2 Cast painted Back light

The following can be considered as standard for waste paper stock: MW OCC NP White Shavings American Standard (ISRI) ISRI 1.2 ISRI 11.12 ISRI 6.7 ISRI 28.30.31 European Standard (CEPAC) A2, A4 A5 E12 C15, C16, C17 DIN / ISO / ONORM B12, B19 W52, W41 R12, O14, Q14

Folding boxboard is cardboard with a mass per unit area in the range of 160 - 500 g / m ² with the following characteristics Cardboard properties unit values Measurement method Specific bending stiffness CD Nmm until 100 L&M DIN 53121, 1996-12; DIN 53121, 1996-12) Specific bending stiffness MD Nmm up to 200 Roughness ceiling µm <10 PPS-10S ISO 8791-4, 1992-04 Roughness back µm <15 Splitting strength MD J / m ² up to 800 J / m ² Scott crack strength tester TUM 403, 1991 Cleavage strength CD J / m ² up to 800 J / m ²

The top layer can consist of 100% bleached cellulose or 100% recycled paper, depending on the quality of the cardboard. But it is also possible to produce the top layer from a mixture of bleached cellulose and waste paper. However, the top layer can also contain only a slight amount of wood, and the wood pulp can also be bleached or can also be wood-free. The ceiling should always be painted.

The insert mostly consists of mixed waste paper or optionally with proportions of mechanical wood pulp. Any mixing ratio is possible.

The back is made of recycled paper and may contain bleached and / or unbleached cellulose. The reverse side can be either coated or uncoated. Depending on the raw material used, a distinction is made between qualities with the following abbreviation, with the number 1 indicating the variety with the highest quality. The total proportion of mixed waste paper stock can be found in the following table

The usual proportions of recycled paper, based on the total product, are given as examples. variety Waste paper GT1 80% - 100% GT2 80% - 100% GD1 15% - 65% GD2 70% - 90% GD3 80% - 100%

This three-layer fiber web or packaging paper or cardboard web described above always has a "white" fiber cover layer, which is then provided with the white coating layer.

With the present process according to the invention, packaging paper and cardboard of particularly high quality and printing properties can be produced for the first time.

The advantages of the process also consist in energy and raw material savings. The process itself is characterized by an improvement in runnability (running properties).

The invention will be explained below on the basis of an exemplary embodiment.

• Figur 1: eine Darstellung eines Verfahrensschemas zur Herstellung einer dreilagigen, gestrichenen Faserstoffbahn
• Figur 2: eine schematische Darstellung des Konstantteiles zur Herstellung eines Stoffgemischs für die Herstellung einer Faserstoffbahn gemäß Figur 1.

Show it

• Figure 1 : a representation of a process scheme for the production of a three-layer, coated fibrous web
• Figure 2 : a schematic representation of the constant part for the production of a mixture of substances for the production of a fibrous web according to FIG Figure 1 .

In the Figure 1 shows a process scheme for the production of a three-layer, coated paper or cardboard web.

The material flow S originating from a stock preparation system is fed to a wire section I from a headbox 1 with a dilution water control. The wire section consists of three Fourdrinier wires 2, 5 and 6 to form a three-layer web B. The Fourdrinier wire 2 is used to form a middle layer, the Fourdrinier wire 5 of the top layer and the Fourdrinier wire 6 forms the back. The fourdrinier wire 2 of the middle layer is equipped with a former 3 (traded by the applicant's company under the name DuoFormer D) and with a sieve shaking device 4 (traded by the applicant's company under the name Duo Shake).

• Rückenlage, Mittelage, Decklage.
• Die Bahn B wird danach sukzessive durch Entwässerungselemente in der Siebpartie entwässert bis sie am Ende der Siebpartie I einen Trockengehalt von >16% hat.

The fabric of the individual layers is sprayed from the corresponding headboxes 1, 1 a onto the respective fourdrinier wires 2, 5, 6 and dewatered on them. At the contact points of the fourdrinier wires, the layers are rubbed together. The layer structure is as follows from bottom to top:

• Supine position, middle position, top position.
• The web B is then successively dewatered by dewatering elements in the wire section until it has a dry content of> 16% at the end of wire section I.

From wire section I, web B is transferred into press section II via various removal elements presses 7. Press section II with presses 7 consists of a double-felted suction press roll 7.1 in the first nip and a double-felted Nipco Flex press in the second nip and an offset press in the third nip. After press section II, web B has a dry content of up to 57%. This press concept can be designed with a closed or open web guide. The frame can also be designed as a cantilever. It is possible to add sewn or seamless felts in the press section II

After leaving the press section II or the presses 7, the further drying of the web B takes place by means of conventional drying cylinder groups 8a within a pre-drying section III, which here have two-row drying cylinder arrangements. Subsequent to the drying groups 8a, for example a drying unit 9 with condensation press drying is installed. The paper web is dried much more intensively and the smoothness of the web side in contact with the cylinder is significantly increased. Such a drying arrangement is for example from EP 1586 698 A1 and the EP 0988 417 B1 known. This technology used here is particularly energy-efficient, since, in addition to the high specific evaporation of more than 40 kg / m ² h, there is also a significant increase in the smoothness of the packaging paper or cardboard inside the dryer section hood. The preferred installation position of this condensation press dryer is in a range above 50% to approx. 90% dry content, but primarily above 55% dry content. The integration of one or more such drying units is preferably carried out in the pre-dryer section III, but it is also conceivable to provide such units in a subsequent after-dryer section. Here, too, the condensation press dryer 9 offers the advantage of increased evaporation rates and paper flattening.

These drying units 9 can be installed in a "line", i.e. at the level of the conventional drying section as well as in the machine cellar. The advantage of the installation in the machine basement is that the drying unit (s) 9 can be removed from the line and the drying process can only be carried out with a conventional drying section. It is also possible with existing machines that are drying limited to achieve an increase in production by installing one or more drying units 9 by replacing conventional drying cylinders.

After this drying unit 9 there is a further conventional drying cylinder group 8b in the example shown.

After the end of the pre-dryer section III, starch is applied. This is done with a film press 10. With the help of this film press in the example, the starch is applied simultaneously to both sides of the web in an indirect manner. This means that the starch is applied to the circumference of an application roller and in between the two Rolling existing nip delivered to the surface of the two web sides. The advantage of this application of starch is that an inferior raw material can be used for the middle ply and still achieve a high level of strength for the paper or cardboard. It is also conceivable to use a so-called size press instead of the said film press, which as in FIG EP 1198643 A1 described, is equipped. Here specially designed feed nozzles protrude into the gusset in order to form an application medium sump in the application rollers that form a gusset and a nip. This arrangement is called "SizeWings" by those skilled in the art and offers the advantage that the application medium (sizing agent) takes longer to act on the fibrous web and, at the same time, the formation of turbulence in the sump is avoided. This also avoids the risk of foams forming, which would have a negative effect on the web properties.

This is followed by an after-dryer section IV with a conventional drying cylinder group 11, which in the example is designed in two rows. At the end of the after-dryer section IV there is a cooling group 12, which consists of two cooling cylinders, the upper cylinder being felted. The fibrous web B is lowered to below 70 ° C. with the aid of these cooling cylinders.

This is followed by a pre-smoothing of the raw cardboard or fibrous web B with a smoothing device 13. This can also be arranged within the after-dryer section IV, as has already been described in the explanation of the condensation press drying. In this case, however, no cooling group is provided in front of the unit 13.

In the example, a belt calender is used as the smoothing unit 13. This belt calender has a single or multi-layer belt or belt with a coating on the facing side of the fibrous web. The tape consists mainly, i.e. more than 70%, of plastic. The temperature of the calender is more than 80 ° C on the belt surface when the belt is in contact with the fibrous web. A very volume-saving and excellent smoothness is achieved hereby.

In contrast to conventional calenders (hard-nip calenders or HNC, soft-nip calenders or SNC, wide-nip calenders, shoe calenders), a design using so-called CeraSoft calender technology and / or Valzone technology is also conceivable. In contrast to conventional calenders (HNC, SNC, Breitnip, shoe calender), all of the above-described calender technologies offer the advantage of particularly high increases in smoothness with a particularly low loss of volume. In addition, by using these technologies, inferior, cheaper raw materials can be used with at the same time a particularly low loss of volume and excellent smoothness without loss of strength of the uncoated cardboard web. Especially with regard to calendering errors, e.g. mottling, optimal results can be achieved with this technology without risk. It is also conceivable to use the calender 13 for subsequent smoothing of the coated web B. The preferred installation position of a calender for pre-smoothing is in a range of more than 55% to approx. 90% dry content, but primarily more than 60% dry content of the web.

In a coating section V, which follows the pre-smoothing, a white line is first applied to the white top layer of the fibrous web B. This takes place with a non-contact coating unit 14 in the form of a curtain coater 14.1 (curtain coater), which has a slot nozzle or sliding layer nozzle (slide die). With the curtain coat, a particularly large amount of coating color containing white pigments is applied very evenly, even at increased speeds, and particularly good coverage and thus surface quality is achieved. Another possible execution of a curtain commissioned work is based on EP A1-1 255 615 and is referred to in specialist circles as "slide die", ie sliding layer nozzle.

One application unit can apply coat quantities of up to 60g / m ² , which otherwise could only be achieved with several conventional coating units. Single-layer as well as multi-layer curtain applicators come into consideration, which reduces the space requirement in the machine. In the example shown, the Figure 1 a single-layer application unit is provided.

In the in Figure 1 The example shown, the top layer is coated a second time with a conventional coating unit 15. Then the back of the fibrous web is also coated with a conventional coating unit 16. As conventional coating units 15 and 16, for example, a free jet nozzle unit, which is followed by a doctor element, or an application unit with a short dwell time (SDTA) or otherwise known doctor blade coater. Contactless dryers, not specifically designated here, ie air dryers and infrared dryers, are attached to each of the coating units.

In a subsequent correction group 17, the upper side and the lower side of the web B - that is, the top layer and back - are heated to different degrees, as a result of which the tendency of the web to roll (curl) is reduced. This correction group 17 consists of a conventional one or two-tier dryer group (in the example the drying cylinders are arranged in two rows), which are equipped with or without dryer fabrics at the top and bottom. However, the correction group 17 is preferably equipped with 2 drying wires, one for the upper row and one for the lower row of drying cylinders. The upper and lower drying cylinders within the correction group are heated in such a way that the cylinder surface temperatures differ from one another by at least 10 ° C.

The web is then re-calendered in a calender. In the example, a soft nip calender is used for this, which creates a particularly high gloss effect on the finished paper or cardboard and reduces the micro-roughness.

Instead of this soft nip calender, a so-called Terra X calender sold by the applicant's company could also be used. Such a calender has a heated roller with a plastic jacket which is provided with a metallic layer. The thickness of the plastic jacket is approx. 5 to 50mm and the metallic layer is approx. 5 to 100 µm thick.

A cover layer on an elastic roller is for example in the DE 10 2008 037 999 A1 disclosed.

Before the reel 20 on a roller without a center drive, the web B is cooled to temperatures below 70 ° C. with a cooling group 19.

In the example shown, the cooling group 19 is only felted at the bottom. The advantage of this is that the upper side of the web B smoothed in the soft nip calender 18 no longer comes into contact with the wire and the glossy effect is thereby retained.

The arrangement of the cooling group 19 in front of the reel 20 - as in Figure 1 has shown the advantage that the thermal change in length of the web on the roller is reduced, as a result of which better winding properties are achieved.

With regard to the roll-up 20, it should be added that configurations of rollers with a center drive are also conceivable. Compared to scooters without a center drive, finer adjustments to the winding properties can be achieved.

In the Figure 2 the production of the mixture of substances for the production of the fibrous web is shown schematically.

The example sketch above relates to a constant part of a web manufacturing machine or system in which the top ply, the middle ply and the back ply consist of 100% virgin fiber. Therefore, a cleaner stage is provided in the respective material strand, as this is not provided in the material preparation.

The stream S coming from the stock preparation is premixed in a mixer 30 (ComMix) together with the white water, if necessary with additives, e.g. retention agents. The broke is preferably mixed into the middle ply's machine chest. It is also conceivable that the committee in the ComMix is led by Top Ply or Back Ply. To further dilute the amounts of substance, the suspension is mixed with white water in a further mixer 31, a so-called hydromix. The concentration of the pulp suspension after the hydromix is higher than the concentration of the headbox with the advantage that a smaller number of assemblies can be selected for the subsequent cleaning device 32 (cleaner or EcoMizer). Small impurities, e.g. fine sand, are removed in this cleaning device 32. A further dilution with white water to the desired headbox concentration and optionally a mixture with additives then takes place in the mixer 33. A headbox pump 34 guides the suspension through a cleaning sieve 35 (HB Screen, MSA, MST, MSS) to destroy fiber flocks and for final cleaning. In addition, there is a reduction in stock pulsations, whereby stock fluctuations in the headbox 36 in the machine direction are avoided. The necessary amount of retention agent 37 can be added to the pulp suspension upstream of the headbox 36. The water required for the dilution water control at the headbox 36a of the middle ply (Midde Ply) is taken from a white water channel and, after processing in a device 38 in a sifter, is fed to the headbox.

List of reference symbols

I.

Wire section

II

Press section

III

Pre-dryer section

IV

After-dryer section

V

String section

1

Headbox

2

Fourdrinier

3

Former

4th

Sieve shaking device

5

Fourdrinier

6

Fourdrinier

7th

Press

7.1

Suction press roll

8a

Drying group

8b

Drying group

9

Drying unit with condensation press drying

10

Film press

11

Drying cylinder

12th

Cooling group

13

Smoothing unit with condensation press smoothing

14th

Coating unit

14.1

Curtain commissioned work

15th

Coating unit

16

Coating unit

17th

Correction group

18th

Calender

19th

Cooling group

20th

Winding up

30th

mixer

31

mixer

32

Cleaning facility

33

Headbox pump

34

mixer

35

Cleaning sieve

36, 36a

Headbox

37

Retention aid

38

Processing facility

Claims (13)

1. A method for producing a coated, three-layer fibrous web, in particular a packaging paper web or board web, in which first of all a stock stream is produced, which is then successively fed to three headboxes (1, 1a), at least one wire section (I) for forming a three-layer fibrous web (B), a press section (II), a drying section (III) comprising drying groups (8a, 8b) and then to a reel-up,
   wherein
   the drying groups (8a, 8b) are disposed within a pre-dryer section (III) and starch is applied after the end of the pre-dryer section and an after-dryer section (IV) follows, with the fibrous web (B) produced with three layers being pre-calendered by a belt calender (13) within or following the after-dryer section (IV) and, after that, the top layer of the fibrous web (B) being coated with a white pigment-containing coating layer with the aid of a curtain applicator (14.1) and then being dried and, in the press section (II), at least one smooth roll being used which acts at least on the top layer.
2. A method in accordance with claim 1,
   characterized in that
   the fibrous web (B) is produced in three layers, specifically the back layer, middle layer and top layer, with the top layer containing white or bleached and/or deinked and/or wood-free fibers.
3. A method in accordance with claim 1 or claim 2,
   characterized in that
   a condensation press drying (9) is carried out following the drying in the drying section (III) or between the individual dryers (8a) or following the dewatering in the press section (II).
4. A method in accordance with at least one of the preceding claims,
   characterized in that,
   following the curtain coating (14.1), the same web side is coated a second time with a conventional coating unit (15), such as a direct-application blade coating unit, is dried and, after that, the other web side is likewise coated with a conventional coating unit (16) and is then dried by dryers (17).
5. A method in accordance with at least one of the preceding claims,
   characterized in that
   the coated web is fed to a correction group (17), a following calendering unit (18), a cooling group (19) and then to the reel-up (20).
6. A method in accordance with claim 1 or claim 2,
   characterized in that,
   for the formation of the top layer of the three-layer fibrous web (B), fines are led into the headbox (1).
7. A method in accordance with claim 1,
   characterized in that
   the at least one white coating layer is applied using a curtain applicator (14.1) applying one or multiple layers, in the form of a slot die or a slide die.
8. A method in accordance with claim 5,
   characterized in that
   the calendering unit (18) used in the final group of the production machine has a heated roll with a plastic coating which is provided with a metallic layer.
9. A method in accordance with claim 8,
   characterized in that
   the thickness of the plastic coating is about 5 to 50 mm and the metallic layer has a thickness between 5 and 100 µm.
10. A method in accordance with any one of the preceding claims,
    characterized in that
    an impingement drying known per se is performed directly after the press section (II) and still before the first heated drying cylinder of the drying section (III).
11. A method in accordance with claim 1,
    characterized in that,
    during the pre-calendering of the fibrous web (B), a belt is used of which more than 70% consists of plastic and which has a temperature of more than 80°C at the belt surface which is in contact with the fibrous web.
12. A method in accordance with any one of the preceding claims,
    characterized in that
    a coated board, in particular a chromo or chromo-substitute board or a liquid board, or coated packaging paper, a coated liner with a white top layer (CWTTL coated white top test liner) or a coated kraft liner with a white top layer (CWTKL = coated white top kraft liner) is produced thereby.
13. A method in accordance with claim 12,
    characterized in that
    the board or the paper has three layers, which comprise a fiber top layer made of bleached pulp, a middle layer made of wood-containing raw material and/or wastepaper stock, and a back layer made of bleached pulp or a mixture of bleached pulp with proportions of wood-containing raw material to which proportions of wastepaper stock are also added.

Images