System for multi-layer coating of a moving substrate

Abstract

System (100) for multilayer coating of a running substrate (200), in particular a fibrous web such as a paper web (210), in particular for producing one or more barrier layers, comprising a first application device (800) for applying a first coating material (450) as a pre-coating (400) to the substrate (200); a second application device (850) with a doctor blade element (500) and a curtain application head (870), wherein the application device (400) is configured such that the doctor blade element (500) smooths the pre-coating (400) and the curtain application head (870) applies at least one layer of a second coating material (750) wet-on-wet to the pre-coating (400) of the substrate (200) to produce a coating film (700);a transport system (230) with at least one roller (250) for supporting and guiding the substrate (200) past the first application device (800) and the second application device (850).

Description

[0001] The invention relates to a system and an application device for multi-layer coating of a moving substrate, in particular a fibrous web such as a paper web, for the production of one or more barrier layers.

[0002] Specialty papers are a distinct category of papers that acquire specific properties through coatings or treatments, making them suitable for specialized applications. Unlike conventional papers, which primarily serve as writing or printing surfaces, specialty papers meet particular technical requirements, often achieved through complex functional layers. These layers are applied to the paper using specialized coating processes, imparting unique physical and chemical properties.

[0003] Barrier papers with water vapor barriers prevent moisture from penetrating. They are frequently used in packaging to protect the contents from water or water vapor.

[0004] Barrier papers with oil and grease barriers are coated to prevent the penetration of oils and fats. They are frequently used in food packaging to protect the packaging material and the environment from fatty substances.

[0005] Barrier papers with oxygen barriers prevent the penetration of oxygen, which is particularly important to protect products such as food from oxidation and spoilage.

[0006] Inkjet papers are specially optimized for printing with inkjet printers. The coating ensures that the ink dries quickly and does not run, resulting in sharp and clear print results.

[0007] Carbonless copy paper (CB, Coated Back / CF, Coated Front / CFB, Coated Front and Back) is used for carbonless copy sets where multiple copies of a document are made simultaneously. It consists of several layers that react to pressure and create a copy on the sheet underneath.

[0008] Silicone-coated papers are covered with a layer of silicone, giving them a non-stick surface. They are frequently used as release papers or as a backing for self-adhesive materials.

[0009] Thermal papers react to heat and change color when heated. They are used, for example, in point-of-sale systems and for labels, where they offer a quick and easy way to print information without ink.

[0010] Light- and heat-sensitive photographic papers are specially designed for photography and react to light or heat to create an image. They are suitable for both traditional photographic exposure methods and modern printing processes.

[0011] Technical papers are used in special technical applications, e.g. as a substrate in electronics, for seals, filters or for applications in the automotive industry.

[0012] Papers for medical applications are used, for example, as carrier material for diagnostic tests or as packaging for medical products where special hygienic or sterilizable properties are required.

[0013] Specialty papers are characterized by a multi-layered structure, in which each functional layer is specifically applied to the paper to create particular technical properties. These layers often fulfill different tasks: for example, they can repel moisture, be writable, or react to heat. They also enable high-quality printing using modern printing processes such as offset, inkjet, or digital printing.

[0014] The production of these specialty papers is extremely complex due to the precision required to apply the individual layers. This high precision requirement necessitates the use of specialized machinery and technologies, as multiple layers must be applied precisely and uniformly to achieve the desired properties.

[0015] The application of multilayer barrier films to a fiber web is typically carried out using a multi-layer curtain coater. This technology allows for the simultaneous application of multiple layers of a coating material to a fiber web, particularly paper. In the curtain coater process, the coating material is applied to the paper web as a uniform liquid or paste-like curtain. The process operates wet-on-wet, meaning the individual layers are not allowed to dry in between but are applied directly to one another. This method ensures excellent coverage, meaning the paper is coated evenly and completely without gaps or thin spots.

[0016] The curtain coating process offers good coverage, but the original rough surface of the paper remains intact because the coating follows the paper's contours and does not smooth them. Paper naturally has a rough surface that appears irregular under a microscope. Therefore, curtain coating applies a uniform film to the paper, but the original rough surface of the paper is preserved.

[0017] This type of coating is therefore also called a "contour coating" because it does not smooth out the contours and irregularities of the paper. Rather, the applied coating film conforms to the existing structure. This means that while a continuous coating is achieved, the microscopic irregularities of the paper remain visible even after coating.

[0018] The leveling coat is another method of paper coating which, unlike the contour coat where the natural structure of the paper is preserved, aims to smooth the paper surface and make it more uniform.

[0019] In the leveling coat, the coating material, e.g., a barrier layer or a color layer, is first applied in excess to the paper web and then scraped off with a doctor blade or a coating knife. This means that more material is applied than is actually needed to ensure complete coverage of the entire paper surface.

[0020] In the blade coater process, the coating material is applied to the paper web with a coating blade and spread evenly. The coating blade removes the excess material, leaving a uniform layer. The roll coater process uses a similar principle to the blade coater process, but here the coating material is applied and spread with a rolling doctor blade.

[0021] The goal of smoothing is to fill depressions in the paper surface to achieve a smooth finish. However, this process results in uneven coating thickness. More material is deposited in the paper's depressions, while less coating material is present on the raised areas. The result is a smooth paper surface, but one with highly variable coating thicknesses in certain areas. These techniques are particularly useful when a smooth surface is desired, even if this comes at the expense of a uniform coating thickness.

[0022] Another way to produce multilayer barrier films on paper is the sequential combination of different coating processes. Processes such as blade coating and curtain coating or roll coating and curtain coating are used to achieve the desired properties of the final product.

[0023] In this method, the different application techniques are used sequentially. For example, a layer can first be applied with the blade coater, followed by drying of the paper web, before another layer is applied with the curtain coater.

[0024] The application process is usually "wet-on-dry." This means that after the first layer is applied, the paper is dried before the next layer is applied. This differs from the "wet-on-wet" method, in which several layers are applied without intermediate drying.

[0025] The major advantage of these combination processes lies in the ability to combine different coating materials with varying functions into a multilayer barrier film. Each layer can be optimized for a specific function, such as moisture barrier, oil and grease barrier, or other specialized protective functions. The sequential arrangement enables the production of a multilayer barrier film that combines several different protective functions in a single layer system.

[0026] However, the disadvantages of these methods are not insignificant. The drying process for multilayer barrier films requires careful control of the dryer and web temperatures, as particularly gentle drying is necessary. To maintain the barrier properties, the formation of microbubbles (blistering), which can occur due to water vapor in the individual film layers, must be strictly avoided. Since the barrier materials used are mostly thermoplastic, precise web guidance and drying control in the coating machine are crucial. Only in this way can adhesion or mixing of the barrier films to the guide rollers be prevented.

[0027] The technologically necessary gentle drying of the multilayer barrier film results in long drying distances with larger unsupported sections of the coated substrate. Furthermore, the use of a large number of conventional single-layer coating units leads to a significant increase in the overall length of the paper or coating machine.

[0028] Combining different coating processes therefore requires complex and expensive equipment. This equipment also requires a lot of space, which significantly increases investment costs and the space required in production. This can be a particular challenge for companies that do not have large production areas or high investment budgets.

[0029] Due to the elaborate and complex manufacturing processes, various efforts have been made to simplify the machinery and procedures, but these have not yet yielded the desired results. Simplification would not only increase production speed and reduce costs, but also improve the quality of the specialty papers. The challenge, therefore, lies in producing these highly specialized papers more efficiently and cost-effectively while simultaneously further enhancing their specific properties.

[0030] WO 03 / 049871 A1 discloses a method and a device for curtain coating a continuous paper web, wherein the paper web is moved below a funnel device that provides one or more liquid coating materials in the form of a free-falling curtain which impinges on the paper web at a dynamic wetting line. Edge guide elements serve to stabilize the width and to equalize the flow velocity of the coating curtain and enable the uninterrupted supply of an auxiliary liquid.

[0031] DE 10 2008 040 584 A1 discloses a machine for applying a liquid or pasty coating medium to the surface of a moving web of material, in particular paper or cardboard, by means of a curtain coating unit. The curtain coating unit has a coating head with a sliding or flow surface for the coating medium.

[0032] DE 10 2011 007 026 A1 discloses an application head for applying one or more layers of an application medium in the form of a single- or multi-layer curtain to a substrate.

[0033] EP 1 964 971 A2 discloses a method for producing a coated fibrous web. In this process, one side of the fibrous web is provided with at least three coating layers, the last two coating layers being applied directly and without intermediate drying, i.e., "wet-on-wet", using a coating unit.

[0034] The object of the invention is to develop a system and a method for producing multilayer coatings on a substrate, in particular multiple barrier layers on paper, in which several functional layers are applied directly one on top of the other without the need for a drying step between the application of the individual layers. The invention is also intended to address the requirements for a uniform layer thickness and the prevention of layer mixing. The aim is to increase production speed, reduce energy consumption, and simultaneously ensure the quality and functionality of the multilayer coatings.

[0035] This problem is solved according to the invention with regard to a system for multilayer coating of a moving substrate by the features of claim 1 and with regard to an application device by the features of claim 11. The remaining claims relate to preferred embodiments of the invention.

[0036] The system and method according to the invention are based on simultaneous wet-on-wet multi-layer coating and offer new possibilities for the production of substrates with multi-layer barriers. It is therefore particularly suitable for the production of specialty papers. By combining a blade coater with a curtain coater or a roll coater with a curtain coater, a higher degree of smoothness can be achieved in the multi-layer coating process. Furthermore, the required installation space for a barrier coating application system is reduced, since the multi-layer coating technology reduces the number of coating and drying stations, thereby correspondingly lowering the required building length and thus the investment costs.

[0037] According to a first aspect, the invention provides a system for the multi-layer coating of a moving substrate, in particular a fibrous web such as a paper web, especially for the production of one or more barrier layers. The system comprises a first application device for applying a first coating material as a pre-coating to the substrate; a second application device with a doctor blade element and a curtain application head, wherein the application device is configured such that the doctor blade element smooths the pre-coating and the curtain application head applies at least one layer of a second coating material wet-on-wet to the pre-coating of the substrate to produce a coating film; and a transport system with at least one roller for supporting and guiding the substrate past the first application device and the second application device.

[0038] In advantageous embodiments, a control unit for controlling and synchronizing the coating processes at the first application device and at the second application device may also be provided.

[0039] In a further training course, it is stipulated that the squeegee element is designed as a spreading knife or as a squeegee roller.

[0040] It is particularly advantageous if the application of the second coating material takes place immediately after the squeegee element.

[0041] The optimal distance between the doctor blade and the application of the second coating material can depend on the materials used and the operating speed. A distance of less than 10 cm, particularly less than 5 cm, and preferably less than 1 cm, is usually advantageous.

[0042] In particular, it can also be provided that the second coating material is brought into contact with or guided over the doctor blade before being applied to the primer. In this way, it is possible for the second coating medium to be applied to the primer without any gap after the doctor blade.

[0043] In an advantageous embodiment, an integrated application device is provided which combines the functions of the first application device and the second application device.

[0044] In a further embodiment, the curtain application head comprises several reservoirs for the second coating material and a third coating material and / or a fourth coating material, arranged in such a way that the different coating materials can be applied simultaneously wet-on-wet in a multi-layer curtain application to the substrate in order to enable a multi-layer coating in a single operation.

[0045] In particular, it is provided that the second application device or the integrated application device is designed for applying barrier layers, especially against the permeation of gases such as water vapor and oxygen and / or liquids and / or against UV radiation for the production of specialty papers with specific barrier properties.

[0046] In another embodiment, the control unit is configured to monitor and adjust coating parameters such as the viscosity and temperature of the coating materials in real time, with the control unit using measurement data from sensors and, in particular, artificial intelligence algorithms to monitor and adjust the coating parameters.

[0047] In particular, the substrate is a paper web or a cardboard web with a basis weight of 30 to 250 g / m². 2

[0048] Advantageously, the transport system allows a speed of 300 to 2000 m / min for the moving substrate.

[0049] Advantageously, the coating materials have a solids concentration between 5 and 60%, particularly between 15 and 40%.

[0050] In particular, the temperature of the coating materials is in a range of 20 to 30°C or, if applicable, in a range of 50 to 60°C.

[0051] According to a second, unclaimed aspect, the invention provides a method for multilayer coating of a moving substrate, in particular a fibrous web such as a paper web, especially for producing one or more barrier layers. The method comprises the following process steps: - Supporting the substrate against a roller of a transport system and guiding the substrate past a first application device and a second application device; - Applying a first coating material as a pre-coating to the substrate; - Smoothing of the pre-coating by a doctor blade element of the second application device, wherein the doctor blade element is designed in particular as a coating knife or as a doctor roller; - Applying a second coating material wet-on-wet to the substrate's pre-coating to create a coating film; - Controlling and synchronizing the coating processes to ensure optimal adhesion of the coating film to the substrate.

[0052] In a further training course, it is planned that several layers of coating materials are applied wet-on-wet to the pre-coating of the substrate simultaneously using a curtain application head of the second application device or the integrated application device in a multilayer curtain coating.

[0053] In an advantageous embodiment, it is provided that the second and / or third and / or fourth coating material is / are guided past the doctor blade element in such a way that the second and / or third and / or fourth coating material is / are applied simultaneously to the pre-coating in a guided multi-layer curtain application.

[0054] Advantageously, it is provided that the position and contact pressure of the doctor blade element and coating parameters such as the viscosity and temperature of the coating materials are monitored in real time by sensors and adjusted by the control unit, whereby the control unit uses, in particular, artificial intelligence algorithms to adjust the coating parameters.

[0055] Advantageously, the coating materials have a solids concentration between 5 and 60%, in particular between 15 and 40%, and the temperature of the coating materials is in a range of 20 to 30°C or, if applicable, in a range of 50 to 60°C.

[0056] According to a third aspect, the invention provides an application device for a system and / or a method for multilayer coating of a moving substrate, in particular a fibrous web or a paper web, especially for producing one or more barrier layers. The application device comprises a doctor blade element and one or more reservoirs for a second coating material and / or a third coating material and / or a fourth coating material, wherein the reservoirs are arranged such that the different coating materials can be applied simultaneously wet-on-wet in a guided multilayer curtain application past the doctor blade element onto the substrate, in order to enable multilayer coating in a single operation.

[0057] According to a fourth unclaimed aspect, the invention provides a computer program product comprising an executable program code that performs the method according to the second aspect.

[0058] The invention will now be explained in more detail with reference to exemplary embodiments shown in the drawing.

[0059] This shows: Fig. 1 a block diagram to illustrate a system according to the invention; Fig. 2 a schematic representation of a first embodiment of the system according to the invention; Fig. 3 a schematic representation of a second embodiment of the system according to the invention; Fig. 4 a schematic representation of a third embodiment of the system according to the invention; Fig. 5 a schematic representation of a fourth embodiment of the system according to the invention; Fig. 6 a schematic representation of a fifth embodiment of the system according to the invention; Fig. 7 a schematic representation of a sixth embodiment of the system according to the invention; Fig. 8 a flowchart to explain the individual process steps of a process according to the invention; Fig. 9 a schematic representation of a computer program product.

[0060] Additional features, aspects and advantages of the invention or its embodiments become apparent from the detailed description in conjunction with the claims.

[0061] Fig. Figure 1 shows a system 100 according to the invention for coating a web-shaped substrate 200, in particular a fibrous web or a paper web 210, for the production of one or more barrier layers. The system 100 comprises a transport system 230 that guides a substrate 200 over a roller 250 during the coating process. This roller 250 ensures stable and uniform support and guidance of the web-shaped substrate 200, thereby enabling a uniform application of the coating materials.

[0062] A fibrous web is a flexible, continuous material made up of interconnected fibers. These fibers can originate from various sources, such as wood, plants, synthetic materials, or recycled fibers. The manufacturing process involves forming a uniform, continuous web from these fibers, which are bonded together by mechanical or chemical means.

[0063] Fiber webs are used in various industries and are available in different forms and qualities depending on the type of fibers used and the specific requirements of the end product. They can be, for example, in the form of textiles, nonwovens, felts, or paper.

[0064] A paper web 210 is a special type of fibrous web made from wood fibers or other plant pulps. These fibers are suspended in an aqueous medium, poured onto a screen, and then dewatered, pressed, and dried to create a uniform, thin, and flexible web. Paper web 210 consists primarily of cellulose fibers derived from wood, recycled paper, or other plant sources. These fibers give the paper its characteristic properties, such as strength, flexibility, and the ability to be printed or coated.

[0065] Paper webs are typically produced in large rolls, which are later cut into smaller formats or further processed. Their production requires precise control of humidity, temperature, and pressure to achieve the desired quality. Paper webs are used in a wide variety of applications, from basic writing and printing papers and packaging materials to specialized technical papers with special properties, such as barrier or thermal paper.

[0066] A web-shaped substrate 200, such as a fiber web or a paper web 210, can be subjected to various surface treatments to improve its properties. This includes the inventive method for applying coatings for barrier functions.

[0067] In the process according to the invention, a pre-coating 400, i.e., a first layer of a first coating material 450, is first applied to the substrate 200. This pre-coating 400 serves as a base for the subsequent layers and can have specific properties that are crucial for the adhesion and functionality of the following layers. The pre-coating 400 serves to smooth the surface and improve the adhesion of the subsequent layers.

[0068] After applying the primer 400, it is smoothed with a doctor blade 500, which can be either a coating knife 530 or a doctor blade roller 570. This leveling step ensures an even distribution of the primer 400, resulting in a smooth and homogeneous surface. This evens out any unevenness or local variations in layer thickness, thereby improving the quality of subsequent layers.

[0069] Immediately after leveling, one or more layers of a coating film 700 made of a second coating material 750 are applied to the leveled pre-coating 400. This coating film 700 forms the actual barrier layer or functional surface that gives the substrate 200, such as a fiber web or paper web 210, the desired protective or barrier properties.

[0070] According to the invention, the coating film 700 is applied immediately after the pre-coating 400 has been leveled by the doctor blade element 500. This enables a continuous coating process without intermediate drying and ensures a seamless transition between the pre-coating and the coating film 700. This direct sequence of operations leads to efficient production and improved coating quality.

[0071] Preferably, the coating film is applied such that the coating film 700 is not applied to the substrate 200 as a free-falling curtain, but is guided over the doctor blade 500. This is therefore a guided curtain application, in which the second coating material 750 is applied to the leveled pre-coating 400 by means of the doctor blade 500. This method has the advantage that the coating film 700 is applied to the substrate 200 in a controlled and precise manner, thereby achieving high accuracy and uniformity of the coating. Uncontrolled impact of the second coating material 750 on the substrate 200 is avoided, which is particularly advantageous for thin or sensitive substrates.

[0072] The system 100 according to the invention comprises a first application device 800 for applying the first coating material 450 for the pre-coating 400 and a second application device 850 arranged at a radial distance from the first application device 800. This second application device 850 comprises a doctor blade element 500, which is configured in particular as a coating blade 530 or as a doctor blade roller 570. The doctor blade element 500 distributes the first coating material 450 uniformly on the substrate 200 to produce a uniform and smooth pre-coating 400.

[0073] Furthermore, the second application device 850 comprises a curtain application head 870, which is provided for applying the coating film 700. The second application device 850 is configured such that the second coating material 750 is applied wet-on-wet, in particular in a guided curtain coating process, to the pre-coating 400. The second application device 850 can also have several reservoirs, each containing a further coating material. In particular, the second application device 850 comprises three reservoirs for the second coating material 750 for a first layer of the coating film 700, a third coating material 770 for a second layer of the coating film 700, and a fourth coating material 790 for the top layer of the coating film. Further reservoirs for additional coating materials can also be provided within the scope of the invention.

[0074] A control unit 300 is provided for setting, monitoring, and adjusting the coating parameters, such as the surface tension, viscosity, and temperature of the coating materials 450, 750, 770, and 790, as well as the parameters of the first application device 800 and the second application device 850, such as the position and contact pressure of the doctor blade 500. The control unit 300 is connected to sensors that acquire measurement data in real time during the coating process. This measurement data is evaluated by the control unit 300 in real time. The control unit 300 is therefore an essential component of the system 100, as it monitors and controls the coating process in real time.

[0075] The first order processing device 800, the second order processing device 850, the transport system 230 and the control unit 300 can each be equipped with a storage unit and / or a processor as well as communication interfaces.

[0076] In connection with the invention, a "processor" can be, for example, a machine or an electronic circuit. In particular, a processor can be a central processing unit (CPU), a microprocessor, or a microcontroller, e.g., an application-specific integrated circuit or a digital signal processor, optionally in combination with a memory unit for storing program instructions.

[0077] In the context of the invention, a "storage unit" can refer, for example, to volatile memory in the form of random access memory (RAM), permanent storage such as a hard drive or data carrier, or, for example, a replaceable storage module. The storage module can also be a cloud storage solution.

[0078] In particular, the control unit contains 300 artificial intelligence algorithms, such as a neural network specifically designed to optimize coating parameters, and reinforcement learning methods to continuously learn and adapt to changing conditions.

[0079] The neural network in control unit 300 was trained using extensive training data from previous coating processes. This data includes information on coating parameters such as surface tension, viscosity, temperature, and the resulting layer quality. Through training, the neural network learned to recognize patterns in the measurement data and, based on this, to make predictions about how changes in the parameters will affect the coating quality.

[0080] Additionally, the 300 control unit utilizes reinforcement learning to make real-time decisions and dynamically adapt to new or unexpected conditions during the coating process. With reinforcement learning, the 300 control unit continuously interacts with the coating process, evaluates the results of its adjustments, and adapts its strategies based on reward signals derived from the quality of the coated layers.

[0081] The neural network can calculate and adjust the ideal surface tension in real time by analyzing sensor data to ensure optimal wetting and adhesion of the layers. Furthermore, the AI ​​algorithms can automatically regulate the viscosity of the coating materials 450, 750, 770, and 790 by adjusting parameters such as the mixing ratio and temperature to ensure uniform distribution. The control unit 300 therefore monitors the temperature of the coating materials 450, 750, 770, and 790 and adjusts it accordingly to optimize their respective flow behavior and promote uniform layer formation.

[0082] With each completed coating process, the control unit 300 stores and analyzes the results, leading to continuous improvement of the control algorithms. In this way, the system 100 becomes increasingly accurate and efficient over time.

[0083] Fig. Figure 2 shows a first embodiment of the system 100 according to the invention for coating a paper web 210 to produce one or more barrier layers.

[0084] System 100 comprises a roller 250 over which a paper web 210 is guided. This roller 250 plays a central role in the coating process by continuously transporting the paper web 210 and providing a stable base for the uniform application of the coating materials 450 and 750. The roller 250 is designed to enable precise control of the paper web 210 and uniform application of the coating materials 450 and 750.

[0085] In the area where the paper web 210 contacts the circumferential surface of the roller 250, a first application device 800 is arranged for applying the first coating material 450 for the pre-coating 400. This pre-coating 400 serves as a basis for the subsequent coating by pretreating the surface of the paper web 210 and ensuring optimal adhesion of the subsequent layers.

[0086] A second application device 850 is arranged at a radial distance from the first application device 800, this distance preferably being in a range of one-quarter to one-half of the circumference of the roller 250. This distance enables precise coordination of the two application devices 800 and 850. The second application device 850 is equipped with a doctor blade element 500, which is designed as a coating blade 530. The coating blade 530 distributes the first coating material 450 evenly on the paper web 210 to produce a uniform and smooth pre-coating 400.

[0087] The second application device 850 is additionally equipped with a curtain application head 870, which is responsible for applying the coating film 700. The second coating material 750 is applied wet-on-wet to the pre-coating 400 using a guided curtain coating process. The coating material 750 is guided above the coating knife 530 and comes into contact with the pre-coating 400 at the tip of the coating knife 530. The guided curtain coating process ensures a uniform and complete coating, as the second coating material 750 is applied to the pre-coating 400 of the paper web 210 in the form of a continuous curtain.

[0088] The roller 250 and the two application units 800 and 850 form an integrated solution for producing a multi-layer barrier film. The roller 250 continuously transports the paper web 210, while the first application unit 800 applies the pre-coating 400. The second application unit 850 smooths the pre-coating 400 with the coating knife 530 and applies the second coating material 750 as the final top layer.

[0089] Fig. Figure 3 shows a second embodiment of the system 100 according to the invention for coating a paper web 210 to produce one or more barrier layers.

[0090] The paper web 210 is guided over a continuously rotating roller 250, which ensures a uniform transport speed of the paper web 210. In the area where the paper web 210 contacts the circumferential surface of the roller 250, a first application device 800 is arranged, which applies the first coating material 450 for the pre-coating 400 to the paper web 210.

[0091] A second application device 850 is arranged at a radial distance from the first application device 800. This distance is preferably in a range of one-quarter to one-half of the circumference of the roller 250. The second application device 850 comprises a doctor blade roll 570, which serves to smooth the pre-coating 400. The doctor blade roll 570 rotates in the opposite direction to the rotation of the roller 250 in order to efficiently distribute the pre-coating 400. The rotational movement of the doctor blade roll 570 applies the first coating material 450 evenly to the paper web 210, resulting in a smooth and uniform pre-coating 400. Additionally, the second application device 850 is equipped with a curtain application head 870, which is responsible for applying the coating film 700.

[0092] The doctor blade 570 and the curtain applicator 870 work together as follows: The doctor blade 570 rotates in the opposite direction to the rotation of the roller 250 and comes into contact with the pre-coating 400 at a first engagement edge to distribute the first coating material 450. At the second engagement edge of the doctor blade 570, the second coating material 750 is applied to the pre-coating 400 by the curtain applicator 870.

[0093] The coating material 750 is applied wet-on-wet in a guided curtain coating process as a continuous film onto the pre-coating 400.

[0094] This guided curtain coating process ensures a uniform and seamless coating of the pre-coating 400, as the second coating material 750 is applied to the pre-coating 400 of the paper web 210 in the form of a continuous curtain at the second engagement edge of the doctor blade roll 570.

[0095] Overall, the roller 250 and the two application units 800 and 850 enable an integrated solution for the production of barrier layers. The roller 250 continuously transports the paper web 210, while the first application unit 800 applies the pre-coating 400, and the second application unit 850, with the doctor blade 570, smooths the pre-coating 400 and, with the curtain application head 870, applies the second coating material 750 as the final top layer.

[0096] Fig. Figure 4 shows a third embodiment of the system 100 according to the invention for coating a paper web 210 to produce one or more barrier layers.

[0097] In this embodiment, the paper web 210 is again guided over a continuously rotating roller 250, which ensures a uniform transport speed of the paper web 210. Instead of two separate application devices, this system 100 provides a single, integrated application device 890, which combines the functions of the previously described application devices 800 and 850.

[0098] The integrated application device 890 is designed to apply both the pre-coating 400 and the subsequent coating film 700 to the paper web 210 in a single, continuous process. For this purpose, the integrated application device 890 includes a coating knife 530, which primarily serves to smooth the applied pre-coating 400. The coating knife 530 comprises a first application side 532 and a second application side 534.

[0099] In a first step, the initial coating material 450, which forms the pre-coating 400, is applied to the paper web 210. For this purpose, the coating material 450 is guided along the first application side 532 of the coating knife 530. The coating knife 530 performs the function of both an application element and a doctor blade 500, applying and distributing the coating material 450 evenly onto the paper web 210 to create a smooth pre-coating 400. This smoothing ensures an optimal base for the subsequent coating.

[0100] Immediately after the pre-coating 400 is smoothed, the coating film 700 is applied, also by the integrated application device 890. The coating material 750 for the coating film 700 is guided along the second application side of the coating knife 530 and applied directly at the tip of the coating knife 530 to the smoothed pre-coating 400. The tip of the coating knife 530 serves as a tear-off edge where the continuous film of coating material 750 impacts the pre-coating 400 and "tears off." This tear-off edge ensures that the coating material 750 is applied in a controlled and uniform manner to the surface of the paper web 210, forming the coating film 700.The second coating material 750 is thus applied wet-on-wet in a guided curtain coating process as a continuous coating film 700 onto the pre-coating 400 and forms the final top layer.

[0101] Integrating both functions into a single application unit 890 significantly simplifies the coating process. No additional separate application unit is required, as the coating knife 530 serves both to apply and smooth the pre-coat 400 and to support the curtain coating process. This results in a more efficient and compact machine design, while simultaneously ensuring uniform and high-quality coating of the paper web 210.

[0102] In an advantageous embodiment, the pre-coating can be metered using a special actuation system based on magnetism. In this system, the support and spreading blade, such as a coating knife, is deformed and controlled by magnets (attracting or repelling) so that the desired film thickness of the pre-coating can be precisely set.

[0103] The thickness of the top coat can be achieved by regulating the pump quantity through the wide-slot nozzle used.

[0104] Such magnetic dispensing devices are known per se and are described, for example, in WO 23222299 A1 of the applicant. Their use within the scope of the present invention has surprisingly proven advantageous. In many embodiments, the dispensing element – ​​for example, the spreading blade – is in direct contact with the coating material of the second layer. In the embodiment according to Fig. In step 4, the coating blade is even in contact with the coating material on both sides. This is a hindrance for profiling the pre-coating using the coating blade, as suitable mechanical points of application for the necessary deformation of the coating blade are difficult to find that do not disrupt the flow of the coating medium or that are themselves not disrupted by the coating medium. Magnetic profiling, on the other hand, uses a contactless deformation of the coating blade. The applied magnetic field penetrates the coating medium without interference in all common coating media and is not noticeably affected by the medium.

[0105] Fig. Figure 5 shows a fourth embodiment of the system 100 according to the invention for coating a paper web 210 to produce one or more barrier layers. As in the preceding embodiments, the paper web 210 is continuously guided over a rotating roller 250, which ensures a uniform transport speed and stability of the paper web 210.

[0106] The system comprises two application devices 800 and 850, the first application device 800 serving to apply the first coating material 450 as a pre-coating 400 to the paper web 210. This first application device 800 is arranged in the area where the paper web 210 contacts the circumferential surface of the roller 250.

[0107] The second application device 850 is arranged at a radial distance from the first application device 800, this distance preferably being in a range of one quarter to one half of the circumference of the roller 250. Its function is to apply several coating materials in a multi-layer coating process. This application device 850 is equipped with a coating blade 530, which has a first application side 532 and a second application side 534. Additionally, the second application device 850 comprises three separate storage containers, each containing a second coating material 750, a third coating material 770, and a fourth coating material 790.

[0108] The second coating material 750 is guided along the first application side 532 of the coating knife 530. The coating knife 530 smooths the first coating material 450, which has already been applied, and the second coating material 750 in one step, creating a homogeneous layer on the paper web 210. This smoothing ensures that the pre-coating 400 and the second coating material 750 form a uniform, smooth surface that serves as a base for subsequent coatings.

[0109] The third coating material 770 and the fourth coating material 790 are applied one above the other and simultaneously along the second application side 534 of the coating blade 530. The tip of the coating blade 530 again serves as a release edge for these two coating materials 770 and 790. At this release edge, the controlled and precise wet-on-wet application of the third coating material 770 and the fourth coating material 790 takes place in a guided curtain process onto the already applied and smoothed coating materials 450 and 750, thereby applying a multilayer coating film 700 onto the already smoothed primer 400.

[0110] The result is a precisely controlled, multilayer coating film 700, consisting of several layers of different coating materials 450, 750, 770, 790. This multilayer structure can exhibit specific barrier layers or other functional properties, which are determined by the selection and combination of the coating materials 450, 750, 770, 790.

[0111] The second application device 850 is controlled by the control unit 300, which precisely regulates both the contact pressure and the position of the coating blade 530. This ensures that the thickness and uniformity of the individual layers of the multilayer coating film 700 meet the desired coating specifications.

[0112] The second application device 850 is in turn very precisely controlled by the control unit 300 with regard to the position and contact pressure of the coating knife 530. This control enables precise adjustment of the thickness and uniformity of both the pre-coating 400 and the coating film 700 to meet the requirements of the specific application.

[0113] Fig. Figure 6 shows a fifth embodiment of the system 100 according to the invention for coating a paper web 210 to produce one or more barrier layers. As in the previous embodiments, the paper web 210 is continuously guided over a rotating roller 250, which ensures a uniform and stable transport speed of the paper web 210.

[0114] In this embodiment, system 100 comprises two application devices, 800 and 850. The first application device, 800, is responsible for applying the first coating material, 450, as a pre-coating, 400, to the paper web 210. It is located in the immediate vicinity of the point where the paper web 210 contacts the circumferential surface of the roller 250 and provides a preparatory layer that smooths the surface of the paper web 210 and offers an optimal base for the subsequent coating.

[0115] The second application device 850 is arranged at a radial distance from the first application device 800, this distance being approximately one quarter to one half of the circumference of the roller 250. The second application device 850 comprises a coating knife 530 and two storage containers, each containing the second coating material 750 and the third coating material 770, respectively.

[0116] The second coating material 750 is guided along the first application side 532 of the coating knife 530 and applied to the already applied first coating material 450. The coating knife 530 smooths the first coating material 450 and the second coating material 750 in one step, creating a uniform and homogeneous pre-coating 400 on the paper web 210. This smoothing provides an ideal base on which the third coating material 770 can be applied.

[0117] The third coating material 770 is guided along the second application side 534 of the coating knife 530 and then applied to the smoothed primer 400. At the tip of the coating knife 530, which serves as a tear-off edge, the third coating material 770 is applied wet-on-wet in a guided curtain process precisely onto the smoothed primer 400 to form the second layer of the coating film 700.

[0118] In contrast to the fourth embodiment, this fifth embodiment does not apply a fourth coating material 790, meaning that the coating film 700 consists of one less layer. This simplifies the structure of the coating film 700, reduces the material required, and may still be sufficient to achieve the desired barrier properties or other functional properties.

[0119] The second application device 850 is in turn very precisely controlled by the control unit 300 with regard to the position and contact pressure of the coating knife 530. This control enables precise adjustment of the thickness and uniformity of both the pre-coating 400 and the coating film 700 to meet the requirements of the specific application.

[0120] This fifth embodiment provides a simplified yet effective method for producing a multilayer coating film 700 from two coating materials 750, 770, which meets the technical requirements for a uniform and high-quality coating.

[0121] Fig. Figure 7 shows a sixth embodiment of the system 100 according to the invention for coating a paper web 210 to produce one or more barrier layers. As in the previous embodiments, the paper web 210 is continuously guided over a rotating roller 250, which ensures a uniform transport speed and provides a stable basis for the coating processes.

[0122] System 100 comprises a first application device 800 and a second application device 850, which are arranged on the roller 250 at a radial distance of approximately one quarter to one half of the circumference of the roller 250. The first application device 800 is designed to apply the first coating material 450 to the paper web 210 and produces the pre-coating 400.

[0123] In contrast to the previous embodiment, in this sixth embodiment both the second coating material 750 and the third coating material 770 are guided along the second application side 534 of the coating blade 530. This means that the two coating materials 750, 770 are applied simultaneously and one on top of the other onto the smoothed pre-coating 400.

[0124] First, the initial coating material 450 is applied to the paper web 210 and smoothed by the coating knife 530 to create the pre-coating 400. The coating knife 530 smooths only the pre-coating 400, so that the subsequent coating materials 750 and 770 are applied directly to the smoothed pre-coating 400 without additional smoothing.

[0125] The second coating material 750 and the third coating material 770 are fed from the storage containers via separate feeders along the second application side 534 of the coating blade 530. These coating materials 770 and 790 are applied simultaneously, one on top of the other, onto the already smoothed primer 400. The tip of the coating blade 530 acts as a rip edge, enabling precise and controlled application of both coating materials 750 and 770. The result is a multi-layered coating film 700 that lies on the smoothed primer 400.

[0126] The control of the second application device 850 enables the exact positioning and adjustment of the contact pressure of the coating knife 530 in order to adjust the thickness and uniformity of the pre-coating 400 and the coating film 700.

[0127] This sixth embodiment provides an efficient method for producing a multilayer coating film 700 in which the smoothing is limited to the pre-coating 400. This can be advantageous if the overlying layers are to retain a different structure or texture, or if avoiding further smoothing offers technological or material-related advantages.

[0128] The following sections discuss the rheology of the coating materials 450, 750, 770 and 790, which can be used for the method according to the invention.

[0129] Rheology, i.e., the flow and deformation behavior of coating materials, plays a crucial role in the production of multilayer barrier films. In principle, the same coating material can be used for the various layers (primer, intermediate layer(s), topcoat). However, the greatest advantage of the invention arises when different coating materials are used for the various layers, materials that are specifically tailored to the respective functional requirements and the interactions between the layers. a) Viscosity and flow behavior

[0130] A key parameter is the viscosity of the coating materials 450, 750, 770, and 790. A relatively high viscosity is desirable for the pre-coating 400 to ensure it forms a stable layer that guarantees good adhesion to the paper web 210 and supports the subsequent layers. Higher viscosity can also help control the penetration of the pre-coating 400 into the substrate 200 and stabilize the substrate 200's structure. The layers of the coating film 700 can have lower viscosities to achieve a smoother surface and ensure that these layers are evenly distributed on the pre-coating 400. Lower viscosity allows for better distribution and can reduce the risk of unevenness or defects in the coating film 700. However, depending on the desired properties of the coating film 700, the viscosities can also be adjusted.

[0131] The viscosity setting also influences the mixing of the individual layers. Low-viscosity materials tend to diffuse into the underlying layers, which can impair the barrier properties. Therefore, careful matching of the viscosities of the various coating materials 450, 750, 770, and 790 is important to ensure clear phase separation and achieve the desired functional properties. To avoid color mixing, it is advantageous to ensure a density difference between the various liquid layers. The density of the 400 primer should be at least 30% higher than the density of the subsequent topcoat. The Brookfield viscosity at 25 °C and a rotational speed of 100 rpm should be between 50 and 1400 mPa·s. The viscosity of the first, lower layer should be ≤ 1400 mPa·s, preferably ≤ 1000 mPa·s, and particularly preferably ≤ 700 mPa·s. During the application of the coating film 700, the individual layers at the phase boundaries are subjected to shear stress due to the almost unavoidable differences in strain behavior. A small viscosity difference between adjacent layers helps to mitigate these stress differences during layer strain. - The viscosity of the primer 400 should be higher than that of the topcoat to avoid damage to the applied primer due to tensile stresses at the application point of the topcoat. b) Surface tension and wetting behavior

[0132] Adjusting the surface tension is also important to reduce or prevent the mixing of the individual liquid phases and to avoid coating defects. A properly adjusted surface tension between the layers can improve wettability and adhesion, thereby preventing droplet formation and other defects. The permeability of the phase interfaces also plays a role, as it ensures stable phase separation.

[0133] The surface tension of substrates 200, such as paper and cardboard, is in the range of 40 to 50 mN / m. To ensure good wetting of the substrate 200 by the various layers, the surface tension (or surface energy) of the substrate 200 must be higher than that of the first layer in direct contact with the substrate 200. Ideally, the surface tension of the individual liquid layers decreases gradually from the bottom to the top layer of the multilayer coating. The relationship of the surface tensions should be maintained as follows. σSUBSTRATE>>σ1>σ2>σ3>σ4>σ5

[0134] To ensure stable wetting and reliable spreading of a liquid layer onto a layer below, it is important that the surface tensions of the liquids in the multi-layer application are adjusted accordingly, so that this descending hierarchy of surface tensions is maintained. c) Thixotropy and shear thinning

[0135] Thixotropy and shear thinning are further important rheological properties that must be considered when using coating materials 450, 750, 770, and 790. Thixotropic materials become less viscous under shear stress and become more viscous again after the shear stress is removed. They are therefore particularly suitable for ensuring a stable layer during the coating process without unwanted runoff of the coating material.

[0136] To avoid excessive shear and tensile stresses between the interfaces of the multilayer coating during the coating process, comparable layer strains should be provided in the individual layers. The tensile force, i.e., the force required to stretch each individual liquid element of the multilayer coating, can be used as a parameter. To ensure a stable coating, the absolute difference in the required tensile force between adjacent layers should not exceed 30%. Preferably, this difference should be less than 20%, and particularly preferably less than 5%. This allows the shear and tensile stresses at the phase boundaries to dissipate through viscoelastic strain. d) Additives for modifying rheology

[0137] The flow properties of coating materials 450, 750, 770, and 790 can be further modified through the targeted use of rheology additives. These additives can, for example, specifically influence viscosity, shear thinning, or thixotropy to optimize process stability and coating quality. Furthermore, the flow and wetting properties can be precisely adjusted through the use of dispersions, emulsions, or suspensions.

[0138] The elasticity of coating materials can be optimized by adding thickening agents. Examples of such thickening agents are compounds based on acrylic esters, acrylic acid, methacrylic acid, acrylamide, or acrylomitrile. The amount of these thickening agents should be in the range of 0.01 to 3.0% (T), preferably 0.01 to 0.5% (T), and particularly preferably 0.01 to 0.2% (T). Here, "(T)" represents the percentage of the thickening agent per 100 parts of dry pigment in the coating material.

[0139] In addition to thickeners, other additives can also be used to optimize the properties of coating materials. These include, in particular, emulsifiers or surfactants, as well as surface-active agents.

[0140] Emulsifiers or surfactants are added to improve film stability. Emulsifiers and surfactants can help stabilize the distribution of the coating materials and prevent the formation of bubbles or other defects during application. The amount of these additives is typically in the range of 0.01 to 3.0% (T), with values ​​between 0.01 and 0.5% (T) being preferred and values ​​between 0.01 and 0.2% (T) being particularly preferred, based on the percentage of the additive per 100 parts of dry pigment in the coating material.

[0141] Surfactants improve separation and adhesion between the various interfaces of the multilayer coating. They help optimize the compatibility and interaction between adjacent layers, thereby minimizing potential problems at the phase boundaries. The recommended amount is between 0.01 and 1.0% (T) to achieve the desired effect without compromising the overall properties of the coating material.

[0142] These additives play an essential role in the production of multilayer coatings, as they ensure the consistency and quality of the different layers and improve the overall performance of the final product.

[0143] For the effective application and processing of the coating materials 450, 750, 770, 790, further parameters and boundary conditions must also be taken into account: - Rapid immobilization of the primer: To prevent mixing between the individual layers of the coating film 700, it is advantageous to quickly immobilize the primer 400. This is achieved through dewatering due to the capillary action of the substrate 200. The water retention capacity of the primer 400 should therefore be lower than that of the topcoat applied to it. Rapid drying of the primer 400 helps to ensure clear separation of the layers and to prevent unwanted mixing. - Solids content of the coating materials: The solids content of the coating materials used (450, 750, 770, 790) varies depending on the application and is generally between 5 and 60%. For special barrier materials, a solids content of 15 to 40% is common. The solids content affects the viscosity, drying time, and coating properties of the coating materials. - Specific volume: The specific volume of the coating materials 450, 750, 770, 790 is typically between 0.6 and 1.2 g / cm³. 3 This value is crucial for the density and weight of the coating film 700, which in turn influences the coating process and the final result. - pH value: The pH value of the coating materials 450, 750, 770, 790 should be in the range of 5 to 9. A suitable pH value is important for the chemical stability of the coating materials and their adhesion to the substrate 200. - Surface tension: For good adhesion and optimal mutual wetting of the liquid phases, careful adjustment of the surface tension of the immediately adjacent coating materials 450, 750, 770, 790 is required. Correct surface tension ensures good adhesion between the materials and a uniform coating. - Temperature of coating materials: The temperature of coating materials 450, 750, 770, and 790 is typically in the range of 20 to 30 °C. However, in some special applications, this temperature can be increased to 50 to 60 °C. The temperature affects the viscosity of the coating materials and therefore the quality of the coating.

[0144] The targeted adjustment of the rheological properties of the coating materials 450, 750, 770, and 790 is therefore essential to ensure high quality and functionality of the individual barrier layers of the coating film 700. In particular, optimal matching of viscosities, thixotropy, and surface tensions minimizes the risk of layer contamination and ensures high stability and effectiveness of the barrier properties.

[0145] These barrier coatings play a vital role in the packaging industry and other application areas by performing various protective functions. There are different types of barriers that meet specific requirements: - Gas permeation barriers: These barriers prevent the penetration of gases such as oxygen, water vapor, carbon dioxide, nitrogen, as well as odors and flavorings. For example, an effective water vapor barrier must have a water vapor permeability (WVTR) in the range of 0.1 to 10 g / m². 2 ·d (at 85% relative humidity). Oxygen barriers, on the other hand, must have an oxygen permeability of 0.1 to 100 cm² at a layer thickness of 100 µm. 3 (STP) / m 2 exhibit / d / bar (at 23°C and 50% relative humidity). - Radiation barrier: These barriers protect against UV radiation or visible light to protect sensitive products such as food or electronic components from harmful radiation. - Barrier against biological contamination: These are antibacterial barriers that prevent microbes and bacteria from contaminating the packaged products. - Grease barrier: These barriers protect against the penetration of grease, which is particularly important for food packaging to ensure the product remains fresh and intact. - Barrier against the permeation of contaminants: These barriers prevent the penetration of contaminants such as mineral oils (MOSH & MOAH), printing ink components, or plasticizers, which could compromise the quality and safety of the packaged contents. MOSH (Mineral Oil Saturated Hydrocarbons) and MOAH (Mineral Oil Aromatic Hydrocarbons) are different types of hydrocarbons found in mineral oils. Depending on their structure and chemical properties, they can have varying effects on the environment and health.

[0146] Food packaging often needs to meet multiple barrier requirements simultaneously. Since a single barrier material cannot cover all requirements, multilayer barrier films are frequently applied to substrates as a composite of several barrier layers. These multilayer barriers are the most widely used technology for achieving the required protective functions.

[0147] The production of paper or cardboard webs with specific barrier properties often requires the use of different coating materials. The specific barrier requirements frequently necessitate special polymer-based coating materials, which are achieved through precise formulations and technical adjustments.

[0148] Food packaging often needs to meet multiple barrier requirements simultaneously. Since a single barrier material cannot cover all requirements, multilayer barrier films are frequently applied to substrates as a composite of several barrier layers. These multilayer barriers are the most widely used technology for achieving the required protective functions.

[0149] The production of paper or cardboard webs with specific barrier properties often requires the use of different coating materials. The specific barrier requirements frequently necessitate special polymer-based coating materials, which are achieved through precise formulations and technical adjustments.

[0150] Various polymers are used in the production of barriers for packaging and coating applications. Due to their specific properties, these polymers contribute to improving barrier properties against gases, moisture, light, and other environmental influences. The most commonly used polymers are: - Thermoplastic polymers: These polymers are particularly versatile and are characterized by their ability to be shaped into various forms and repeatedly processed during manufacturing. Depending on their chemical structure and processing conditions, they exhibit different barrier properties. - Liquid crystal polymers (LCPs): LCPs are high-quality polymers characterized by very good chemical resistance and temperature stability. They are frequently used in applications requiring a high barrier effect. - PVDC (polyvinyl chloride) and EVOH (ethylene-vinyl alcohol copolymer): PVDC exhibits optimal barrier properties against gases and moisture and is therefore widely used in the packaging industry. EVOH has an excellent oxygen barrier and is frequently used in multilayer packaging to extend the shelf life of food. - PEN (polyethylene aphthalate) and PAN (polyacrylonitrile): PEN offers excellent barrier properties against oxygen and is valued in the packaging industry for its high transparency and strength. PAN is used for its high strength and chemical resistance and is employed in specialized barrier applications. - BOPP (biaxially oriented polypropylene), PVC (polyvinyl chloride), and PET (polyethylene terephthalate): BOPP is particularly valued for its high strength and flexibility due to its biaxial orientation. PVC is frequently used because of its good barrier properties and availability. PET offers excellent barrier properties against gases and moisture and is often used for food and beverage packaging. - PS (Polystyrene): Polystyrene is another commonly used polymer for packaging and coatings. It offers good mechanical and barrier properties, although its barrier properties against moisture and gases are more limited than those of other polymers. - PE-HD (high-density polyethylene) and PE-LD (low-density polyethylene) as well as PP (polypropylene): PE-HD and PE-LD offer different barrier properties depending on their density, with PE-HD exhibiting higher strength and barrier performance. PP is used in many applications due to its strength, chemical resistance, and processing flexibility.

[0151] These polymers are used either individually or in combination to meet specific barrier requirements. The selection of the appropriate polymer depends on the specific application requirements, such as the desired barrier effect, flexibility, chemical resistance, and processing technique.

[0152] In addition to the common polymers, alternative materials can also be used to manufacture barriers, especially for special applications where exceptional barrier properties are required. - Water-based barrier materials: An important group of barrier materials is based on water-based emulsions and dispersions. These include, for example, fluoride dispersions and wax emulsions. These materials offer a flexible and environmentally friendly alternative to solvent-based barrier materials and can be applied to various substrates to achieve specific barrier properties. - Cellulose-based barrier materials: Newly developed barrier materials include microcrystalline cellulose (MCC), nanofibrillated cellulose (NFC), and oxidized cellulose nanofibers (TOCN). These materials offer new possibilities for creating barriers against oxygen, water vapor, and even hydrogen permeation. MCC, NFC, and TOCN are promising due to their unique structural properties and high surface activity. However, they are still largely in the development stage and are currently used primarily in research and development laboratories. - High aspect ratio nanopigments: Another interesting development for barrier fabrication is the use of nanopigments with a very high aspect ratio. These pigments enable the production of particularly dense barriers with very small application quantities. The nanopigments result in highly viscous colloidal dispersions, although the solids content of these dispersions is usually very low, below 5%.

[0153] The aspect ratio (or side ratio) of nanopigments refers to the ratio of a particle's length to its width or thickness. In nanostructured materials, especially nanopigments, this ratio is crucial for the particles' physical properties and thus for their function in applications such as barriers. A particle with a high aspect ratio is long and thin (e.g., a thread-like or platelet-like structure). This shape allows the particles to overlap within a layer, forming very dense barriers that severely restrict the passage of gases or liquids because it lengthens the path the molecules must diffuse through the coating. This results in improved sealing and greater resistance to the penetration of gases, liquids, or other substances.

[0154] Traditional pigment coating, or "coating," involves applying specially formulated coating inks to paper or cardboard, typically containing pigments and binders. These coatings enhance the surface, improve printability, and can impart specific barrier properties.

[0155] Paints for multi-layer coatings consist of various pigments or pigment mixtures that are adapted to the desired properties of the final product: - Calcium carbonate-based (CaCO3) pigments: These pigments are often used to create a smooth surface and improve the whiteness and opacity of the paper. - Kaolin-based pigments: Kaolin is a natural mineral and is used because of its good opacity and its ability to form an even, smooth layer. - Mixtures of CaCO3 and Kaolin: Combinations of these two pigments offer a balanced ratio between smoothness, opacity and printing properties and are often used for specific requirements. - CaCO3 and kaolin with additions of other pigments: To achieve additional properties such as increased brightness or special optical effects, other pigments such as titanium dioxide (TiO2), barium or calcium sulfate are often added.

[0156] In addition to pigments, paints contain binders that fix the pigments to the substrate surface and ensure the mechanical stability of the coating. The amount of binder, based on the dry weight of the pigments, typically ranges from 4 to 20%. Binders can be of natural or synthetic origin. - Natural binders: These include starch derived from various sources such as corn, potatoes, tapioca, wheat, or barley, as well as casein, a protein obtained from milk. These natural binders are often used to create environmentally friendly coatings. - Synthetic binders: These include latex products based on styrene-butadiene or acrylate. They offer excellent adhesion and flexibility and are particularly resistant to mechanical stress and moisture.

[0157] The choice of pigments and binders is adapted according to the desired end product properties and the specific requirements of the application.

[0158] The proposed coating process is particularly suitable for the production of specialty products such as CB paper (coated back). In this application, a starch film is applied as a pre-coating 400, forming the basis for the subsequent top layer, the so-called CB layer.

[0159] The applied starch solution has a solids content of 2 to 30% and a Brookfield viscosity of 10 to 150 mPa·s. Its density ranges from 0.8 to 1.1 g / cm³. 3 The amount of starch film applied can range between 2 and 20 ml / m². 2 They vary depending on the specific requirements of the product.

[0160] The CB layer consists of a dispersion of CB capsules with a particle size of 5 to 12 µm (e.g., Baymicron) and various synthetic and natural solvents and binders such as polyvinyl alcohol and starch. This CB dispersion has a solids content of 20 to 50% and Brookfield viscosities of 100 to 400 mPa·s. The CB layer thickness typically applied is in the range of 5 to 30 µm, which necessitates precise control of the application process.

[0161] The substrates onto which these layers are applied can be films or paper and cardboard webs with a basis weight of 30 to 250 g / m². 2 Production speeds range from 300 to 2000 m / min, enabling efficient and rapid manufacturing.

[0162] In Fig. Figure 8 describes the process steps for the multilayer coating of a moving substrate 200, in particular a fibrous web such as a paper web 210, especially for the production of one or more barrier layers.

[0163] In step S10, the substrate 200 is supported on a roller 250 of a transport system 230 and guided past a first application device 800 and a second application device 850.

[0164] In step S20, a first coating material 450 is applied as a pre-coating 400 to the substrate 200.

[0165] In step S30, the pre-coating 400 is smoothed by a doctor blade element 500 of the second application device 850, wherein the doctor blade element 500 is designed in particular as a coating knife 530 or as a doctor blade roller 570.

[0166] In step S40, a second coating material 750 is applied wet-on-wet to the pre-coating 400 of the substrate 200 to create a coating film 700.

[0167] In step S50, the coating processes are controlled and synchronized to ensure optimal adhesion of the coating film 700 to the substrate 200.

[0168] Fig. Figure 9 schematically represents a computer program product 900 comprising an executable program code 950 configured to perform the method according to the second aspect of the present invention.

[0169] The system and method according to the invention are thus based on a simultaneous wet-on-wet multi-layer application and offer new possibilities for the production of substrates with multi-layer barriers. It is therefore particularly suitable for the production of specialty papers. By combining a blade coater with a curtain coater or a roll coater with a curtain coater, a higher degree of smoothness can be achieved in the multi-layer application. Furthermore, the required installation space for a barrier coating application system is reduced, since the multi-layer application technology reduces the number of coating and drying stations, thereby correspondingly lowering the required building length and thus the investment costs. Reference sign 100 System 200 substrate 210 paper web 230 transport system 250 roller 300 control unit 400 Pre-coating 450 first coating material 500 squeegee elements 530 Spreading knives 532 first order page 534 second order page 570 squeegee roll 700 coating film 750 second coating material 770 third coating material 790 fourth coating material 800 first order processing device 850 second order device 870 Curtain order head 890 integrated application device 900 computer program product 950 program code QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 03 / 049871 A1

[0030] DE 10 2008 040 584 A1

[0031] DE 10 2011 007 026 A1

[0032] EP 1 964 971 A2

[0033] WO 23222299 A1

[0104]

Claims

[1] System (100) for multilayer coating of a moving substrate (200), in particular a fibrous web such as a paper web (210), in particular for producing one or more barrier layers, comprising a first application device (800) for applying a first coating material (450) as a pre-coating (400) to the substrate (200); a second application device (850) with a doctor blade element (500) and a curtain application head (870), wherein the application device (400) is configured such that the doctor blade element (500) smooths the pre-coating (400) and the curtain application head (870) applies at least one layer of a second coating material (750) wet-on-wet to the pre-coating (400) of the substrate (200) to produce a coating film (700);a transport system (230) with at least one roller (250) for supporting and guiding the substrate (200) past the first application device (800) and the second application device (850). [2] System (100) according to claim 1, wherein the squeegee element (500) is designed as a coating knife (530) or as a squeegee roller (570). [3] System (100) according to one of the preceding claims, wherein the application of the second coating material (750) takes place immediately after the doctor blade element (500). [4] System (100) according to claim 3, wherein the second coating material (750) is brought into contact with the doctor blade element (500) before being applied to the pre-coating (400). [5] System (100) according to one of the preceding claims, wherein an integrated application device (890) is provided which combines the functions of the first application device (800) and the second application device (850). [6] System (100) according to one of the preceding claims, wherein the curtain application head (870) comprises several reservoirs for the second coating material (750) and a third coating material (770) and / or a fourth coating material (790), arranged such that the different coating materials (750, 770, 790) can be applied simultaneously wet-on-wet in a multi-layer curtain application to the substrate (200) to enable multi-layer coating in a single operation. [7] System (100) according to one of the preceding claims, wherein the second application device (850) or the integrated application device (890) is designed for applying barrier layers, in particular against the permeation of gases such as water vapor and oxygen and / or liquids and / or against UV radiation, for the production of specialty papers with specific barrier properties. [8] System (100) according to one of the preceding claims, wherein a control unit (300) is provided for controlling and synchronizing the coating processes on the first application device (800) and on the second application device (850), and the control unit (300) is configured to monitor and adjust the coating parameters such as the viscosity and temperature of the coating materials (450, 750, 770, 790) in real time, wherein the control unit (300) uses measurement data from sensors and, in particular, artificial intelligence algorithms to monitor and adjust the coating parameters. [9] System (100) according to any of the preceding claims, wherein the coating materials (450, 750, 770, 790) have a solids concentration between 5 and 60%, in particular between 15 and 40%. [10] System (100) according to any of the preceding claims, wherein the temperature of the coating materials (450, 750, 770, 790) is in a range of 20 to 30°C or optionally in a range of 50 to 60°C. [11] Application device (850) for a system (100) for multi-layer coating of a moving substrate (200), in particular a fibrous web or a paper web (210), in particular for producing one or more barrier layers, comprising a doctor blade element (500) and one or more storage containers for a second coating material (750) and / or a third coating material (770) and / or a fourth coating material (790), wherein the storage containers are arranged such that the different coating materials (750, 770, 790) can be applied simultaneously wet-on-wet in a guided multi-layer curtain application past the doctor blade element (500) onto the substrate (200) to enable multi-layer coating in a single operation.

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