WO2021104742A1

WO2021104742A1 - Coating pulp webs

Info

Publication number: WO2021104742A1
Application number: PCT/EP2020/078991
Authority: WO
Inventors: Franziska FERRER; Sebastian Bläsing; Benjamin Méndez-Gallon; Christoph Henninger
Original assignee: Voith Patent Gmbh
Priority date: 2019-11-29
Filing date: 2020-10-15
Publication date: 2021-06-03
Also published as: DE102019132446A1; EP4065769A1; CN114667377B; CN114667377A

Abstract

The invention relates to a system and to a method for producing a multiply coated pulp web, in particular a paperboard web or packaging web, the system comprising an application device for applying at least a first application medium and a second application medium to a first side of the pulp web in multiple layers in a joint treatment nip, a wet-smoothing apparatus for pre-smoothing the pulp web being arranged upstream of the application device in the running direction of the pulp web.

Description

Coating of fibrous webs

The invention relates to a system for producing a multi-coated fibrous web, in particular a cardboard or packaging web, according to the preamble of claim 1, and a corresponding method for production according to the preamble of claim 9.

The growing demand for recyclable packaging, in particular flexible packaging and cardboard packaging in the food sector, leads to major challenges in the manufacturing and, in particular, coating processes and the corresponding coating units.

The creation of various barrier effects against substances such as gas, moisture, water vapor or the like in the fibrous web is of particular importance. By applying certain media, a barrier effect against specific migrants can be achieved. However, there is no universal barrier, i.e. different media have to be applied to the fibrous web in order to adapt it to the needs of the packaged goods and their life cycle. Requirements for further processing steps must also be met. In cardboard applications, for example, the barrier against mineral oil plays a role. These products tend to be sticky in further processing. A second pigment-based film can be applied to prevent production disruptions resulting from this.

In the case of cardboard applications but also flexible packaging, strength properties are also in the foreground. These are often of a contradicting nature. High internal strengths are required, which are achieved through deep penetration of starch, i.e. low viscosity and / or low solids contents. However, emphasis is also placed on surface strength and rigidity. For this, the starch must rather remain on the surface, ie high solids content and / or higher viscosity. In order to meet these requirements, the Starch application with a starch solution whose solids content and / or viscosity represents a compromise.

The examples show that in the future, when producing fibrous webs such as cardboard or packaging web, more and more different types of coatings will have to be applied than is customary today.

This presents the operator of such a system with the problem of having to equip his existing system with additional coating devices. However, current machine configurations often only allow little flexibility in terms of expansion with additional commissioned units. Usually, deep interventions in the machine construction and production process have to be undertaken, which is associated with high effort and costs. In addition, the provision of further commissioned works usually leads to an extension of the system, so that there is usually no longer enough space in the existing workshop.

From the prior art, such as DE 102006 057 870, it is known to apply several different media to a paper web in a coating unit. With such a multi-layer application, an existing system could in principle be expanded with additional coating options with little effort. However, it has been shown that the high requirements placed on barrier coatings cannot be easily produced by means of such multi-layer applications. It is therefore an object of the present invention to overcome the problems of the prior art. In particular, it is an object of the invention to further develop the known multi-layer applicator units in such a way that they can be used for the production of fibrous webs with barrier properties.

It is a further object of the invention to expand the possibilities of coating in existing systems with little effort. The object is completely achieved by a system according to the characterizing part of claim 1 and a method according to the characterizing part of claim 9.

Further advantageous designs are described in the subclaims. With regard to the system, the object is achieved by a system for producing a multi-coated fibrous web, in particular a cardboard or packaging web, the system having an application device for multi-layer application of at least a first application medium and a second application medium in a common treatment nip on a first side of the Includes fibrous web. According to the invention it is provided that a wet smoothing device for pre-smoothing the fibrous web is arranged upstream of the application device in the running direction of the fibrous web.

Wet smoothing devices per se are already known. They can be designed in various forms, for example as a Yankee or smoothing cylinder, as an offset press or the like. At higher machine speeds, the wet smoothing device can also be provided with a single felt (single felted smoothing press). In such wet smoothing devices, a relatively moist fibrous web - advantageously with a dry content of up to 65%, preferably between 35% or 40% and 60% dry content - can be smoothed and / or compacted.

One advantage of this wet smoothing is the very favorable ratio of the increase in smoothness to the loss of thickness or strength of the fibrous web. A high increase in smoothness is generated in a volume-saving manner, and the flexural rigidity of the web is largely retained.

The inventors have recognized that the high smoothness in connection with the compaction of the fibrous web or its surface is very advantageous for the application of multi-layer coatings, in particular of barrier coatings.

On the other hand, if desired, an improved holdout of the coating medium can be achieved by compressing the web. In this case, the moist coating medium does not penetrate so deeply into the fibrous web. Furthermore, the improved smoothness of the web enables the surface to be completely covered with smaller amounts of coating medium. The Complete coverage of the surface is an essential criterion, especially for barrier applications. Since only a smaller amount of coating medium needs to be applied, the amount of moisture that is applied over it to the web is also reduced. This is an important advantage, especially with the very highly diluted barrier media.

By virtue of these advantageous properties of the fibrous web, it is now surprisingly possible to apply even very highly diluted application media to the fibrous web without an interposed drying of the web being absolutely necessary for this purpose. Thus, a multi-layer application of barrier medium can now also take place via an application device.

This is also advantageous for conversions, among other things. For example, if a system already includes a wet smoothing device, this system can be expanded to include the option of applying multiple coatings, saving space and money.

On the other hand, a wet smoothing device - for example an offset press - can often be installed relatively easily in an existing system that already has a classic film press, for example. This film press can then also be converted into a multi-layer application mechanism quite easily. The existing drying facilities can then continue to be used.

The application device can also be set up to transfer not only the first application medium and the second application medium but also further application media in the common treatment nip. In addition to the two-layer application, a three-layer application can in particular also be advantageous. All known application media can be used as application media in the context of the present application. In particular, starch solutions, pigment colors and barrier media such as PVA, EVAC etc. can be used. As described, the high dilution usually required for this is not Obstacle to use in an embodiment according to an aspect of the present idea.

It is advantageous if the application media can be applied in a suitable viscosity.

Examples are:

5 mPas - 100 mPas (T: 60 °, 100 rpm Brookfield) for starch solutions 10 mPas - 1500 mPas (T: 40 ° C, 100 rpm Brookfield) for barrier media 100 mPas - 1500 mPas (T: 30 °, 100 rpm -Brookfield) for pigment colors.

However, the present invention is not limited to these viscosity ranges. An advantageous embodiment can therefore be if the application device is designed as a film press, the treatment nip being formed by an application roller and a counter-element, in particular a counter-roller, and with application units being provided around the deposit the first application medium and the second application medium on top of one another on the application roller, which can be transferred together in the treatment nip onto the fibrous web. Furthermore, it can be advantageous if, in addition to the multi-layer application to the first side of the fibrous web, an application medium is also applied to the second side of the fibrous web in the same application unit.

The application on the second side can be a single-layer application or a multi-layer application. In an advantageous embodiment, at least one, in particular all of the rollers of such a film press can have a roller hardness between 0 Pusey &

Jones (P&J) and 80 P&J, specifically between 5 P&J and 50 P&J.

If both rolls of such a film press have a roll hardness in the range between 0 P&J and 5 P&J (or even between 0 P&J and 1 P&J) one often speaks of a "hard-nip application"

In advantageous embodiments, a contactless deflecting element can be provided directly after the application device, in particular directly after the film press. Because the application medium applied in multiple layers usually dries slowly, the web is often not yet sufficiently dry when this web has to be deflected for structural or technological reasons. By means of a non-contact deflection device - for example a so-called "air turn" - such a deflection is possible even when the webs are still damp.

The wet smoothing device can in particular have a smoothing section - that is, the section in which the fibrous web is in contact with the wet smoothing device - which has a length of at least 10 mm, in particular more than 20 mm, preferably more than 500 mm. Depending on the design of the wet smoothing device, this distance can be significantly larger, for example 6 m or more.

In an advantageous embodiment, the wet smoothing device can comprise or consist of a Yankee cylinder. These can be used in particular in systems for the production of paper that is smooth on one side (MG paper).

In a further advantageous embodiment, the wet smoothing device can comprise or consist of an offset press. An offset press has a smooth press nip. In particular, it is unfelted. An offset press is often designed as a non-felted roll nip. An offset press is usually arranged in front of the entry of the fibrous web into the dryer section.

In particular - but not exclusively - in such an embodiment it can be advantageous if means for further drying of the fibrous web, in particular drying cylinders for thermal drying of the fibrous web, are arranged between the wet smoothing device and the applicator.

Thus, the wet smoothing can be carried out at the most suitable dry content of the fibrous web, regardless of which dry content of the web is required for the coating.

Furthermore, it can be advantageous if the system has a calender which is arranged after the wet smoothing device and before or after the application device is. Such a calender can be used for calibrating the thickness of the fibrous web. Alternatively or additionally, a calender can also be used to further optimize the surface roughness and / or the surface porosity.

Several calenders can also be provided, for example a hard-nip calender for calibrating the thickness, and a soft-nip calender or a belt calender to improve the surface quality.

The combination of wet smoothing with a calender - which, in contrast, can be called dry smoothing -, in particular with a soft nip calender, and its positioning in front of the multi-layer application device improves the positive properties of the fibrous web for the use of multi-layer application even further, so that this represents a very advantageous embodiment of the invention.

Furthermore, it can be advantageous if the system comprises at least one degassing device for degassing the first application medium and / or the second application medium, wherein the degassing device can in particular be designed as a pump-like degasser.

Pump-like ventilators are known per se from the prior art, for example US Pat. No. 7,597,732. They usually work via a stator / rotor system and are used, for example, in the food industry for venting pasty media such as ketchup. The process of gas-liquid separation is based on the strong centrifugal force generated by a separation impeller. A vacuum is used here only for sucking off the separated air, but not for the actual gas-liquid separation. In comparison with the vacuum deaerators commonly used in the paper industry, pump deaerators have a larger capacity and can also be used to deaerate large amounts of application medium. This is particularly advantageous if, for example, the first application medium is applied in excess and then wiped off. In this case, more than 90% of the application medium, eg the starch, is usually returned. In this case, ten times more application medium has to be degassed than is applied to the web. The use of the pump-type ventilator is very advantageous here. With regard to the method, the object is achieved by a method for producing a multi-coated fibrous web, in particular a cardboard or packaging web, with at least a first application medium and a second application medium being applied to a first side of the fibrous web in a common treatment nip. It is provided that the fibrous web passes through a wet smoothing device before the common treatment nip.

The advantages of this process have already been explained in the discussion of the system. The dependent claims describe advantageous embodiments of the method.

The dry content of the fibrous web upon entry into the wet smoothing device can preferably be between 35% and 65%, in particular between 40% and 60%.

Furthermore, the temperature of the fibrous web in the wet smoothing device can be at least temporarily between 40 ° C and 120 ° C, in particular between 40 ° C and 60 ° C or between 80 ° C and 120 ° C. The various wet smoothing devices can differ greatly within this framework.

If the wet smoothing takes place in the area of the press section, e.g. in the form of an offset press and / or another smooth nip, both the dry content and the temperature of the fibrous web will tend to be in the lower range. Often temperatures between 40 ° C and 60 ° C combined with a dry content between 35% and 50% are used.

If wet smoothing takes place, for example, by means of a Yankee cylinder, the web temperature will tend to be higher due to the heating of this cylinder alone. In addition, Yankee cylinders are advantageously only used when the web has a higher dry content. Combinations are therefore common in which the web temperature is between 80 ° C and 120 ° C at least in places, and the dry content of the fibrous web when entering the wet smoothing device is greater than 45%, often between 50% and 60%.

The preferred choice of wet smoothing device, as well as the web temperature and dry content, can differ depending on the type of fibrous web produced on the system.

In a further advantageous embodiment of the method it can be provided that the fibrous web has a dry content of more than 85%, in particular between 88% and 98%, before it enters the treatment nip.

Furthermore, it can advantageously be provided that the fibrous web is additionally calendered by at least one calender nip, the web being dried to a dry content of more than 65% prior to calendering.

In particular, it can be advantageous here if the fibrous web is moistened after reaching at least 65% dryness but before passing through a calender nip, in particular less than 15 g / m ^{2 of} water, preferably between 5 g / m ² and 10 g / m ² are applied to the fibrous web in water.

In order to increase the efficiency of the calender or to suitably condition the fibrous web, provision can be made for the web to be tempered before it enters the calender nip. For some, it can be advantageous to heat the web after use. In other applications it can be advantageous to cool the web.

The tempering of the fibrous web, and in particular the tempering of the first side of the fibrous web, can be implemented by applying a suitable fluid, for example water, steam or air, to the web, and in particular to the first side of the fibrous web.

In the following, the invention is further explained with the aid of schematic representations. The features mentioned cannot only be used in the combination shown can be implemented advantageously, but can also be combined individually with one another. The figures show in detail:

FIG. 1 shows a section of a system for setting a fibrous web according to one aspect of the invention

FIGS. 2a and 2b each show an application device which is suitable for use in a system according to one aspect of the invention.

FIG. 3 shows a further application device which is suitable for use in a system according to one aspect of the invention.

The figures are described in more detail below.

FIG. 1 shows a section of a system for setting a fibrous web 1 according to one aspect of the invention. The fibrous web 1 was formed on a sheet-forming section of the system, not shown in the figure. It is then transferred to a press section while it is still relatively moist - usually with a dry content between 10% and 20%. The press section in FIG. 1 comprises, for example, a shoe press 10. The fibrous web 1 generally runs through the press nip between two coverings that are not explicitly shown in FIG.

In this example, a wet smoothing device 4 in the form of a Yankee cylinder 4 is provided in the system. The first side 1 a of the fibrous web 1 is advantageously in contact with the surface of the Yankee cylinder 44. In this way, the wet smoothing effect is achieved directly on side 1a, which is to be coated in the following. When entering the wet smoothing device 4, in this case when it is transferred to the Yankee cylinder 44, the fibrous web generally has a dry content of less than 60%, usually less than 50%. The smoothing section, that is to say the section on which the first side 1a of the fibrous web 1 is in contact with the Yankee cylinder 44, is usually very long. Modern Yankee cylinders can have a diameter of over 6m, even over 7m. But even with a diameter of 4m and a wrap of only 180 °, a smoothing distance of over 6m results. This Yankee cylinder 44 is heated from the inside, for example with steam. In addition, a hood 41 is also provided, which is set up to apply hot gas to the second side 1b of the fibrous web 1 and thereby increase the drying effect. As a result of the hot surface of the Yankee cylinder 44 and as a result of the application of hot gas from the hood to the web, the fibrous web 1 is heated as it passes through this wet smoothing device. The web 1 can heat up considerably and at least temporarily reach temperatures between 80.degree. C. and 120.degree. After the fibrous web has left the Yankee cylinder 44, a calender 9 is provided in the system in FIG. This calender 9 can advantageously be a soft nip calender 9, which in particular further smoothes or compresses the first side 1 a of the fibrous web 1. A conditioning device 11 is also arranged in FIG. 1 in front of the entry into the calender nip. This is not absolutely necessary, but conditioning of the web 1 - and here especially the first side - by moistening and / or tempering can be advantageous.

After the calender 9, at least one application device 2 is then provided for multi-layer application. The application device shown here comprises an application roller 5 and a counter roller 6 which together form a common treatment nip 3 through which the fibrous web 1 passes.

Each of the two rollers 5, 6 can have a roller hardness between OP&J and 80 P&J. The hardness of the two rollers 5.6 can be the same or different.

Two application units 7, 8 are provided for the application roller. The first application unit 7 - for example a film application unit 7, applies a first application medium to the application roller. A second application unit 8 - for example a spray or curtain application unit 8 - then deposits a second application medium onto the first application medium that has already been applied. The two films from the first and second application medium are then transferred together in the common treatment nip 3 to the first side 1 of the fibrous web. In FIGS. 2a and 2b, application devices 2 for multi-layer application are shown, which are suitable for a system according to one aspect of the invention.

In both cases, the common treatment nip 3 is formed by two rollers 5, 6 through which the fibrous web is guided. It can be seen here that, in addition to the actual application roller 5, the counter roller 6 can also be used to apply application medium to the fibrous web 1. In both application devices 2 shown, both the first side 1a and the second side 1b of the fibrous web 1 are coated in the common treatment nip 3.

In the example in FIG. 2a, a multilayer application is even carried out on both sides 1a, 1b, namely in two layers, while in the embodiment in FIG. 2b, the second side 1b is only applied in one layer.

In FIG. 2a, two application mechanisms 7, 8 are arranged on application roller 5. Likewise, two application units 7a, 8a are arranged on the counter roll 6. As an example, the commissioned works 7 and 7a as well as 8 and 8a are executed as identical commissioned works. The commissioned units 7 and 7a are film commissioned units and the commissioned units 8 and 8a are curtain commissioned units. However, other known commissioned works could also be used. In FIG. 2b, a film applicator unit 7, 7a is arranged on the applicator roller 5 and on the counter roller 6. On the counter roll 6, this is the only application unit. If an application is carried out via the counter roller 6, a single-layer application, as shown here by way of example, will often be advantageous. Nevertheless, a multi-layer application via the counter roller 6 is not excluded. Another application mechanism 8 is arranged on the application roller in FIG. 2b. This is exemplified as a so-called .multilayer curtain '. Here, in a single application unit 8, a two-layer film of application medium is deposited on application roller 5. Together with the layer of the film applicator unit 7, a three-layer application results in this example. In an alternative embodiment of an application device, in the embodiment according to FIG. 2b, the film applicator unit 7 of the applicator roller 5 could be omitted, so that a two-layer application takes place via the applicator roller 5. FIG. 3 shows a further suitable application device 2. While the application roller 5 and its application units 7, 8 are designed as in FIG. 2a, the counter-element 6a in FIG realized in that the band 60 is pressed against the application roller 5. The resulting common treatment nip 3 is significantly longer than the roller nips shown above. The band 60 can be designed as a plastic band or as a metal band.

As shown in FIG. 3, an applicator 8a can also be arranged on the revolving belt 60 in order to also coat the second side 1b of the fibrous web. In alternative embodiments, this commissioned work 8a can also be dispensed with.

The examples shown are intended to illustrate the many possibilities of the present invention. However, this is not limited to the examples shown.

List of reference symbols

1 fibrous web

1 a first page 1 b second page

2 application device

3 common treatment nipples

4 wet smoothing device

5 applicator roller 6 counter roller

6a band element

7 commissioned work

7a commissioned work

8 commissioned work 8a commissioned work

9 calenders

10 shoe press

11 Conditioning device

40 yankee cylinder 41 hood

60 volume.

Claims

1. Plant for the production of a multi-coated fibrous web (1), in particular a cardboard or packaging web, wherein the plant includes an application device (2) for multi-layer application of at least a first application medium and a second application medium in a common treatment nip (3) on a first Side (1a) of the fibrous web (1), characterized in that a wet smoothing device (4, 40) for pre-smoothing the fibrous web (1) is arranged in front of the application device (2) in the running direction of the fibrous web (1).

2. Plant according to claim 1, characterized in that the application device (2) is designed as a film press, wherein the common treatment nip (3) by an application roller (5) and a counter element (6, 6a), in particular a counter roller (6), is formed, and application units (7, 7a, 8, 8a) are provided to deposit the first application medium and the second application medium on top of each other on the application roller (5), which can be transferred together in the treatment nip (3) to the fibrous web (1) .

3. System according to one of the preceding claims, characterized in that a non-contact deflection element is provided directly after the application device, in particular directly after the film press.

4. Plant according to one of the preceding claims, characterized in that the wet smoothing device (4, 40) has a smoothing section which has a length of at least 10 mm, in particular more than 20 mm, preferably more than 500 mm.

5. Plant according to one of the preceding claims, characterized in that the wet smoothing device (4, 40) a

Yankee cylinder (40) comprises, or consists of.

6. Installation according to one of the preceding claims, characterized in that the wet smoothing device (4) comprises or consists of an offset press.

7. Plant according to one of the preceding claims, characterized in that the plant has a calender (9) which is arranged after the wet smoothing device (4, 40) and before or after the application device (2).

8. Plant according to one of the preceding claims, characterized in that the plant comprises at least one degassing device for degassing the first application medium and / or the second application medium, the degassing device being designed in particular as a pump-like degasser.

9. A method for producing a multi-coated fibrous web

(1), in particular a cardboard or packaging web (1), wherein at least a first application medium and a second application medium are applied in a common treatment nip (3) to a first side (1a) of the fibrous web (1), characterized in that the fibrous web (1) passes through a wet smoothing device (4, 40) before the common treatment nip (3).

10. The method according to claim 8, characterized in that the dry content of the fibrous web (1) when entering the wet smoothing device (4, 40) is between 35% and 65%, in particular between 40% and 60%.

11. The method according to any one of claims 8 or 9, characterized in that the temperature of the fibrous web (1) in the wet smoothing device (4, 40) at least temporarily between 40 ° C and 120 ° C, in particular between 40 ° C and 60 ° C or between 80 ° C and 120 ° C.

12. The method according to any one of claims 8 to 10, characterized in that the fibrous web (1) has a dry content of more than 85%, in particular between 88% and 98%, before entering the common treatment nip (3).

13. The method according to any one of claims 8 to 11, characterized in that the fibrous web (1) is additionally calendered by at least one calender nip, the web (1) being dried to a dry content of more than 65% prior to calendering.

14. The method according to claim 12, characterized in that the fibrous web (1) is moistened after reaching at least 65% dry matter but before passing through a calender nip, in particular less than 15 g / m ^{2 of} water, preferably between 5 g / m ² and 10 g / m ² of water are applied to the fibrous web (1).