COATING OF FIBRE WEBS

Description

[0001] The invention relates to a plant for producing a multi-coated fibrous web, in particular a cardboard or packaging web, according to the preamble of claim 1, and to a corresponding method for producing the same according to the preamble of claim 8.

[0002] The growing demand for recyclable packaging, especially flexible packaging and cardboard packaging in the food sector, is leading to major challenges in the manufacturing and, in particular, coating processes as well as the corresponding coating units.

[0003] Of particular importance is the creation of various barrier effects against substances such as gas, moisture, water vapor, etc. in the fibrous web.

[0004] By applying specific media, a barrier effect against specific migrants can be achieved. However, there is no universal barrier, meaning that different media must be applied to the fiber web to adapt it to the needs of the packaged product and its life cycle.

[0005] The requirements of subsequent processing steps must also be met. In cardboard applications, for example, the barrier against mineral oil plays a role. These products tend to become sticky during further processing. To prevent resulting production disruptions, a second pigment-based film can be applied.

[0006] In cardboard applications, as well as flexible packaging, strength properties are also important. These are often contradictory in nature. High internal strength is required, which is achieved through deep penetration of starch, i.e., low viscosity and / or low solids content. However, surface strength and stiffness are also important. For this, the starch must remain on the surface, i.e., high solids content and / or higher viscosity. To meet these requirements, the starch is applied using a starch solution whose solids content and / or viscosity represent a compromise.

[0007] The examples show that in the future, more and more different types of coatings will have to be applied in the production of fibrous webs such as cardboard or packaging webs than is usual today.

[0008] This presents the operator of such a plant with the problem of having to equip their existing system with additional coating devices. However, current machine configurations often allow little flexibility when it comes to expanding with additional coating units. This typically requires extensive interventions in the mechanical engineering and production process, which is associated with considerable effort and expense. Furthermore, the addition of additional coating units usually results in an extension of the system, meaning that there is usually no longer sufficient space for it in the existing factory hall.

[0009] The documents WO 2005 / 052252 A1 and DE 10 2004 036276 A1 show paper machines with coating devices.

[0010] It is also known from prior art, such as DE 10 2006 057 870, to apply several different media to a paper web in a single coating unit. Such a multi-layer application could, in principle, allow an existing system to be expanded with additional coating options at little expense. However, it has been shown that the high demands placed on barrier coatings cannot be easily met using such multi-layer applications.

[0011] 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 coating systems so that they can be used for the production of fibrous webs with barrier properties.

[0012] It is a further object of the invention to expand the coating possibilities in existing systems with little effort.

[0013] 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 8.

[0014] Further advantageous embodiments are described in the subclaims.

[0015] 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, wherein the system comprises an application device for the multi-layer application of at least a first application medium and a second application medium in a common treatment nip to a first side of the fibrous web. According to the invention, 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.

[0016] Wet calendering devices per se are already known. They can take various forms, for example, as Yankee or Yankee cylinders, offset presses, or similar. At higher machine speeds, the wet calendering device can also be equipped with a single felt (single-felted calendering press). In such wet calendering 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 calendered and / or compacted.

[0017] One advantage of this wet smoothing process is the very favorable ratio of smoothness gain to thickness or strength loss of the fibrous web. A significant increase in smoothness is achieved while preserving volume, thus largely preserving the flexural rigidity of the web.

[0018] The inventors have recognized that the high smoothness in combination with the compaction of the fibrous web or its surface is very advantageous for the application of multi-layer coatings, in particular barrier coatings.

[0019] For example, if desired, improved holdout of the coating medium can be achieved by compacting the web. In this case, the moist coating medium does not penetrate as deeply into the fibrous web.

[0020] Furthermore, the improved smoothness of the web allows for complete surface coverage with smaller amounts of coating medium. Complete surface coverage is a crucial criterion, especially for barrier applications. Since only a smaller amount of coating medium needs to be applied, the amount of moisture applied to the web is also reduced. This is a significant advantage, especially for highly diluted barrier media.

[0021] Due to these advantageous properties of the fibrous web, it is now surprisingly possible to apply even very diluted application media to the fibrous web without the need for intermediate drying of the web.

[0022] This means that a multi-layer application of barrier medium can now be carried out using an application device.

[0023] This is also advantageous for retrofits. For example, if a system already includes a wet smoothing system, it can be expanded to include the ability to apply multiple coatings, saving space and money.

[0024] On the other hand, a wet decurling system—for example, an offset press—can often be relatively easily integrated into an existing system that already has a conventional film press, for example. This film press can then also be converted quite easily to a multi-layer decurling system. The existing drying equipment can then continue to be used.

[0025] The application device can also be configured to transfer additional application media in the common treatment nip in addition to the first application medium and the second application medium. In addition to two-layer application, a three-layer application can also be advantageous.

[0026] All known application media can be used as application media within the scope of the present application. In particular, starch solutions, pigment inks, and barrier media such as PVA, EVAC, etc. can be used. As described, the high dilution typically required for this purpose is no obstacle to use in an embodiment according to one aspect of the present concept.

[0027] It is advantageous if the application media can be applied in a suitable viscosity. Examples are:

[0028] 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 inks.

[0029] However, the present invention is not limited to these viscosity ranges. It is provided that the application device is designed as a film press, wherein the treatment nip is formed by an application roller and a counter element, in particular a counter roller, and wherein application units are provided in order to deposit the first application medium and the second application medium one above the other on the application roller, which can be transferred together in the treatment nip onto the fibrous web.

[0030] Furthermore, it may 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.

[0031] The application to the second side can be a single-layer application or a multi-layer application.

[0032] In an advantageous embodiment, at least one, and 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 rollers of such a film press have a roller hardness in the range between 0 P&J and 5 P&J (or even between 0 P&J and 1 P&J), this is often referred to as "hard nip application." In advantageous embodiments, a non-contact deflection element is provided directly downstream of the application device, particularly directly downstream of the film press. Because the multi-layered application medium usually dries rather slowly, the web is often not yet sufficiently dry when a deflection of this web is necessary for structural or technological reasons. However, using a non-contact deflection device—for example, a so-called "air turn"—such deflection is also possible for still-moist webs.

[0033] The wet smoothing device can, in particular, have a smoothing section—that is, the section where the fibrous web is in contact with the wet smoothing device—that 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 section can be significantly longer, for example, 6 m or more.

[0034] In an advantageous embodiment, the wet smoothing device can comprise or consist of a Yankee cylinder. These can be used particularly in plants for the production of one-side smooth paper (MG paper).

[0035] 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. It is, in particular, unfelted. An offset press is often designed as an unfelted roller nip. An offset press is usually located before the fiber web enters the dryer section.

[0036] In particular - but not exclusively - in such an embodiment, it may be advantageous if means for further drying the fibrous web, in particular drying cylinders for thermal drying of the fibrous web, are arranged between the wet smoothing device and the application unit.

[0037] Thus, wet smoothing can be carried out at the most suitable dry content of the fibrous web, regardless of the dry content of the web required for coating.

[0038] Furthermore, it may be advantageous if the system includes a calender located downstream of the wet smoothing device and upstream or downstream of the application device. Such a calender can be used to calibrate the thickness of the fibrous web. Alternatively or additionally, a calender can also be used to further optimize surface roughness and / or surface porosity.

[0039] Several calenders can also be provided, for example a hardnip calender for thickness calibration, as well as a softnip calender or a belt calender to improve the surface quality.

[0040] The combination of wet smoothing with a calender - which in contrast can be described as dry smoothing -, in particular with a soft nip calender, and their positioning in front of the multi-layer application device further improves the positive properties of the fibrous web for the use of multi-layer application, so that this represents a very advantageous embodiment of the invention.

[0041] Furthermore, it may 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 be designed in particular as a pump-like degasser.

[0042] Pump-type deaerators are known from the prior art, e.g. US 7,597,732. They usually work via a stator / rotor system and are used, for example, in the food industry for deaerating pasty media such as ketchup. The gas-liquid separation process here is based on the strong centrifugal force generated by a separation impeller. Vacuum is used here only to extract the separated air, but not for the actual gas-liquid separation. Compared to the vacuum deaerators commonly used in the paper industry, pump deaerators have a larger capacity and can also be used to deaerate large quantities of application medium. This is particularly advantageous if, for example, the first application medium is applied in excess and then doctored off. In this case, usually over 90% of the application medium - e.g. the starch - is recycled.In this case, ten times more application medium must be degassed than is applied to the web. The use of pump-type deaerators is particularly advantageous here.

[0043] With regard to the method, the object is achieved by a method for producing a multiply coated fibrous web, in particular a cardboard or packaging web, wherein at least a first application medium and a second application medium are 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.

[0044] The advantages of this procedure were already explained in the discussion of the system.

[0045] The dependent claims describe advantageous embodiments of the method.

[0046] Preferably, the dry content of the fibrous web when entering the wet smoothing device can be between 35% and 65%, in particular between 40% and 60%.

[0047] 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.

[0048] Within this framework, the various wet smoothing devices can differ greatly.

[0049] If wet calendering takes place in the press section, e.g., in an offset press and / or other smooth nips, both the dry content and the temperature of the fiber web will tend to be in the lower range. Temperatures between 40°C and 60°C are often used, combined with a dry content between 35% and 50%.

[0050] If wet calendering is performed using a Yankee cylinder, for example, the web temperature will tend to be higher simply due to the heating of this cylinder. Furthermore, Yankee cylinders are advantageously only used when the web has a higher dry content. Thus, combinations are 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 upon entering the wet calendering device is greater than 45%, often between 50% and 60%.

[0051] The preferred choice of wet smoothing device, as well as the web temperature and dry content, may vary depending on the type of fibrous web produced on the plant.

[0052] 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 entering the treatment nip.

[0053] Furthermore, it can advantageously be provided that the fibrous web is additionally calendered by at least one calender nip, wherein the web is dried to a dry content of more than 65% before calendering.

[0054] In particular, it may be advantageous if the fibrous web is moistened after reaching at least 65% dry content but before passing through a calender nip, wherein in particular less than 15 g / m 2< of water, preferably between 5 g / m 2< and 10 g / m 2< of water is applied to the fibrous web.

[0055] To increase the efficiency of the calender or to properly condition the fibrous web, it may be necessary to temper the web before entering the calender nip. Heating the web may be advantageous for some applications. Cooling the web may be advantageous for others.

[0056] The tempering of the fibrous web, and in particular the tempering of the first side of the fibrous web, can be achieved 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.

[0057] The invention is further explained below using schematic representations. The features mentioned can be advantageously implemented not only in the illustrated combination, but also individually combined with one another. The figures show in detail: Figure 1 shows a section of a plant for producing a fibrous web according to one aspect of the invention Figures 2a and 2b each show an application device suitable for use in a system according to one aspect of the invention. Figure 3shows another application device suitable for use in a system according to one aspect of the invention.

[0058] The figures are described in more detail below.

[0059] Figure 1 shows a section of a plant for producing a fibrous web 1 according to one aspect of the invention. The fibrous web 1 was formed on a sheet forming section of the plant (not shown in the figure). It is then transferred to a press section in a relatively moist state—usually with a dry matter content between 10% and 20%. The press section in Figure 1 includes, for example, a shoe press 10. The fibrous web 1 usually runs between two coverings, which are not explicitly mentioned in the Figure 1 shown, through the press nip.

[0060] In this example, the system features a wet smoothing device 4 in the form of a Yankee cylinder 4. Advantageously, the first side 1a of the fibrous web 1 is in contact with the surface of the Yankee cylinder 44. This achieves the wet smoothing effect directly on the side 1a that is to be coated subsequently. Upon entering the wet smoothing device 4, in this case upon transfer to the Yankee cylinder 44, the fibrous web typically has a dry content of less than 60%, usually less than 50%. The smoothing section, i.e., the section over which the first side 1a of the fibrous web 1 is in contact with the Yankee cylinder 44, is typically very long. Modern Yankee cylinders can have diameters of over 6m, even over 7m. However, even with a diameter of 4m and a wrap angle of only 180°, the smoothing section is over 6m.

[0061] This Yankee cylinder 44 is heated from the inside, for example, with steam. A hood 41 is also provided, which is designed to apply hot gas to the second side 1b of the fibrous web 1, thereby increasing the drying effect. Due to the hot surface of the Yankee cylinder 44 and the exposure of the web to hot gas from the hood, the fibrous web 1 heats up as it passes through this wet smoothing device. The web 1 can heat up considerably and, at least temporarily, reach temperatures between 80°C and 120°C.

[0062] After the fibrous web has left the Yankee cylinder 44, the Figure 1 a calender 9 is provided. This calender 9 can advantageously be a soft nip calender 9, which in particular further smooths or compacts the first side 1a of the fibrous web 1. Before entering the calender nip, Figure 1A conditioning device 11 is also arranged. This is not absolutely necessary, but conditioning the web 1—and here especially the first side—by moistening and / or tempering can be advantageous.

[0063] Downstream of the calender 9, at least one application device 2 for multi-layer application is provided. 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.

[0064] Each of the two rollers 5, 6 can have a roller hardness between 0 P&J and 80 P&J. The hardness of the two rollers 5, 6 can be the same or different.

[0065] 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 already applied first application medium. The two films of the first and second application medium are then transferred together to the first side 1 of the fibrous web in the common treatment nip 3.

[0066] In the Figures 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.

[0067] In both cases, the common treatment nip 3 is formed by two rollers 5, 6, through which the fibrous web 1 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.

[0068] In the example in Figure 2a a multi-layer application is even carried out on both sides 1a, 1b - namely two layers each, while in the execution in Figure 2b the second side 1b only receives a single layer application.

[0069] In Figure 2aTwo applicators 7, 8 are arranged on the applicator roller 5. Two applicators 7a, 8a are also arranged on the counter roller 6. For example, applicators 7 and 7a, as well as 8 and 8a, are designed as identical applicators. Applicators 7 and 7a are film applicators, and applicators 8 and 8a are curtain applicators. However, other known applicators could also be used.

[0070] In Figure 2b A film application unit 7, 7a is arranged on the application roller 5 and on the counter roller 6. This is the only application unit on the counter roller 6. If application is carried out via the counter roller 6, a single-layer application as shown here as an example will often be advantageous. However, multi-layer application via the counter roller 6 is not excluded. On the application roller in Figure 2bAnother application unit 8 is arranged. This is designed as a so-called 'multilayer curtain'. Here, a two-layer film of application medium is deposited onto the application roller 5 in a single application unit 8. Together with the layer from the film application unit 7, this example results in a three-layer application.

[0071] In an alternative embodiment of an application device, when executed according to Figure 2b the film application unit 7 of the application roller 5 can be omitted, so that a two-layer application takes place via the application roller 5.

[0072] Figure 3 shows another suitable application device 2. While the application roller 5 and its application units 7, 8 as in Figure 2a are executed, consists in Figure 3The counter element 6a does not consist of a counter roller 6, but of a rotating belt 60. The common treatment nip 3 is created by pressing the belt 60 against the application roller 5. The resulting common treatment nip 3 is significantly longer than the roller nips shown above. The belt 60 can be designed as a plastic belt or a metal belt.

[0073] As in Figure 3 As shown, an applicator 8a can also be arranged on the circulating belt 60 to coat the second side 1b of the fibrous web. In alternative embodiments, however, this applicator 8a can also be omitted.

[0074] The examples shown are intended to illustrate the diverse possibilities of the present invention. However, this invention is not limited to the examples shown. List of reference symbols

[0075] 1Fibrous web 1aFirst side 1bSecond side 2Applicator 3Common treatment nip 4Wet smoothing device 5Applicator roll 6Counter roll 6aBelt element 7Applicator unit 7aApplicator unit 8Applicator unit 8aApplicator unit 9Calender 10Shoe press 11Conditioning device 40Yankee cylinder 41Hood 60Belt

Claims

1. installation for the production of a multi-coated fibrous web (1), in particular a cardboard or packaging web, wherein the installation comprises an application device (2) for the multilayer application of at least a first application medium and a second application medium in a common treatment nip (3) to a first side (1a) of the fibrous web (1), characterized in that, in the running direction of the fibrous web (1), before the application device (2), a wet smoothing device (4, 40) for pre-smoothing the fibrous web (1) is arranged in the running direction of the fibrous web (1), and in that the application device (2) is designed as a film press, wherein the common treatment nip (3) is formed by an applicator roller (5) and a counter element (6, 6a), in particular a counter roller (6), , and wherein applicators (7, 7a, 8, 8a) are provided for depositing the first application medium and the second application medium one above the other on the application roller (5), which can be transferred together to the fibrous web (1) in the treatment nip (3).

2. installation according to one of the preceding claims, characterized in that a contactless deflection element is provided directly after the application device, in particular directly after the film press.

3. installation 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.

4. Installation according to one of the preceding claims, characterized in that the wet smoothing device (4, 40) comprises or consists of a Yankee cylinder (40).

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

6. Installation according to one of the preceding claims, characterized in that the installation comprises a calender (9) which is arranged after the wet smoothing device (4, 40) and before or after the application device (2).

7. System according to one of the preceding claims, characterized in that the system comprises at least one degassing device for degassing the first application medium and / or the second application medium, wherein the degassing device in particular as pump-type degasser.

8. 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 in a common treatment nip (3) are applied 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) and in that the application device (2) is designed as a film press. (2) is designed as a film press, wherein the common treatment nip (3) is formed by an applicator roller (5) and a counter element (6, 6a), in particular a counter roller (6), and wherein applicators (7, 7a, 8, 8a) are provided for depositing the first application medium and the second application medium one above the other on the applicator roller (5), which together are placed in the treatment nip (3), characterized in that the applicator device (2) is designed as a film press. can be transferred to the fibrous web (1).

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

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

11. Method according to 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%.

12. Method according to 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 calendered before the calendering to a dry content of more than 65%.

13. Process according to claim 12, characterized in that the fibrous web (1) after reaching of at least 65% dry content but before passing through a calender nip, in particular less than 15 g / m2 of water, preferably between 5 g / m2 and 10 g / m2 of water being applied to the fibrous web (1).