Method for coating a dried preform
Patent Information
- Application Number
- EP2023761543
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-08-30
- Filing Date
- 2023-08-28
- Publication Date
- 2025-07-09
AI Technical Summary
Fiber-based containers made from pulp are prone to softening and leakage when exposed to liquids, and the process of incorporating a plastic lining is complex and requires high plastic usage due to tolerance issues and inaccuracies in the production process.
A method involving applying a powder coating to the inside of a dried fiber-based container, followed by curing with infrared radiation to create a coherent film, which provides a seal and reduces plastic usage by allowing the container to be partially uncoated for easier recycling and improved accuracy in sealing.
The method creates a liquid-tight fiber-based container with reduced plastic usage, improved sealing accuracy, and enhanced durability, while allowing for easier recycling by maintaining an uncoated area for breakdown.
Smart Images
Figure 1.1
Abstract
Description
[0001] Method for coating a dried blank
[0002] The present invention relates to a method for coating a dried blank of a fiber-based pulp product.
[0003] Various containers for holding liquids are known from the state of the art. For example, glass bottles or plastic bottles for holding beverages have become well-known. Containers made of fiber-based materials have also been proposed.
[0004] A fiber-based container was proposed in WO 2012 / 139590 A1. To produce this container, so-called pulp is introduced into a mold and pressed against a corresponding wall using a flexible balloon in this mold, thereby compressing it accordingly.
[0005] Recently, at the same time as or after this compression step, the still wet blank is dried by applying energy so that a dried blank is ready for further processing.
[0006] Pulp is a mixture of fibers and water, particularly natural fibers such as hemp fibers, cellulose fibers, or flax fibers, or a mixture thereof. The pulp may contain additives, as disclosed, for example, in PCT / EP2019 / 076839, which, for example, improve the hardening of the compressed pulp, influence its subsequent appearance, or generally alter the properties of the pulp or the subsequent container.
[0007] With these containers, there is a risk that they could become softened by liquid stored in the container and, for example, become leaky, or that substances from the container could diffuse into the liquid. It has been proposed to provide such fiber-based containers with an inner layer of plastic, in particular to arrange a plastic bottle within the fiber-based container, which can assume corresponding barrier functions. The fiber-based container here therefore merely provides a shell for a thin-walled plastic container. Such a combination is known from WO 2018 / 167192 A1.
[0008] Typically, a fiber-based container is provided into which a plastic lining is inserted. This typically occurs in such a way that in a first step the fiber-based container is provided and in a second step a preform is inserted into this container. This preform is then inflated inside the fiber-based container until it touches an inner contour of the fiber-based container or is in contact with the inner contour of the fiber-based container. This inflation process typically takes place in a blow mold whose cavity corresponds to the outer contour of the fiber-based container. Since, in contrast to conventional blow molding processes, two separate elements have to be handled, this type of process is much more complicated because the preform has to be positioned and held relative to the fiber-based container and this in turn has to be positioned and held within the blow mold.
[0009] An exemplary process is described in EP 3 375 593 A1. EP 3 375 593 A1 describes a preform for producing a container which has extensions in its neck area which can be brought into engagement with a corresponding fibre-based container with the aim of the container and the preform remaining connected to one another. However, it has been found that this type of connection is prone to errors because the inner contour or the inner surface of the container is subject to varying degrees of deviation depending on the specific properties of the pulp from which the container is formed. This is particularly disadvantageous in the neck area because a suitable seal is required for clean pressing between the preform or the fibre-based container.Certain tolerance limits must be maintained between its extensions and the fiber-based container, but this is not always possible due to the varying process parameters and the potentially changing nature of the pulp. Furthermore, this type of production still requires a relatively large amount of plastic.
[0010] The object of the invention is to remedy one or more disadvantages of the prior art. In particular, a method is to be provided that makes it possible to form a fiber-based container in a liquid-tight manner and, in particular, reduces the use of plastics.
[0011] This object is achieved by the method described in the independent claim. Further advantageous embodiments emerge from the dependent patent claims.
[0012] A method according to the invention for coating a dried blank of a fiber-based product made of pulp, in particular a container or a fiber-based closure element for a container, comprises the steps:
[0013] - Providing the dried blank,
[0014] - Applying a powder coating to an inner side of the dried blank,
[0015] - Curing of the powder coating by exposure to infrared radiation so that a coherent film is created.
[0016] To apply infrared radiation to the powder coating, the radiation penetrates a wall of the dried blank during irradiation, particularly in the area inside the container, before hitting the powder coating. This allows the infrared source to be positioned outside the dried blank, while still allowing the powder coating inside the dried blank to be exposed to infrared radiation.
[0017] The penetration of the dried blank makes it possible in particular to bring the powder coating to a higher temperature level than the blank.
[0018] An additional or alternative aspect of the invention also relates to a method in which the blank and the powder coating are heated, in particular differently. The powder coating is heated to a higher temperature than the blank, in particular by infrared radiation penetrating a wall of the blank. In particular, the blank is heated essentially only by the heat radiation from the powder coating.
[0019] Preferably, the dried blank is provided with a prefabricated opening before the powder coating is applied.
[0020] By providing a prefabricated opening, a corresponding sealing plane or sealing surface can be created, which can interact with a corresponding closure, such as a lid. Furthermore, by providing a prefabricated opening, a fibrous or imprecise finish on the blank can be removed.
[0021] It is known that certain inaccuracies can arise during production of fiber-based containers. Due to the material properties of the pulp, an upper, final edge of the opening is subject to greater tolerances and is regularly fibrous. This is particularly disadvantageous because this forms an interface with container closures, for example, and this interface must be dimensionally accurate. During container production, the dried blank is preferably manufactured in such a way that a projection is provided in the area of an upper opening, which can be cut off after the blank has dried. By cutting off this projection, a correspondingly inaccurate or fibrous area of the dried blank can be removed.
[0022] It may be provided that the powder coating is additionally applied to the finished opening of the dried blank. This also allows the finished opening to be sealed.
[0023] Additionally, a powder coating can be applied to the outside of a neck area of the dried blank after assembly. The dried blank remains uncoated on its outside, at least in some areas.
[0024] By coating the outside of the neck area it can also be sealed and / or made more durable during use.
[0025] The uncoated area on the outside of the blank allows the product to be recycled. This uncoated area provides a surface where the product can be broken open or softened using water. This makes the product easier to recycle.
[0026] A meltable polymer can be applied as a powder coating. Polymers have advantageous properties and are easy to process.
[0027] The meltable polymer used is preferably a polyester such as polyethylene terephthalate (PET), polyethylene furanoate (PEF), polyethylene isosorbide terephthalate (PEIT), polylactide (PLA), polybutylene succinate (PBS), poly-ε-caprolactone (PCL), or polyhydroxyalkanoate (PHA), especially polyhydroxybutyrate (PHB). These polyesters are preferably bio-based. Ethylene-vinyl alcohol copolymer (EVOH) has also proven suitable.
[0028] To apply the powder coating, it can be electrostatically charged. In particular, a conductive mold encasing the dried blank can be charged with opposite polarity to the powder. The powder then deposits itself, particularly on the inside of the blank, and adheres there.
[0029] An infrared source for generating the infrared radiation is preferably arranged outside the dried blank.
[0030] This makes it possible to direct the infrared radiation in a targeted manner, at a specific distance and at a specific angle onto the dried blank and, in particular, at the corresponding distance and angle onto the powder coating. In the near infrared range, infrared radiation has a wavelength of 780 nm to 1400 nm, in the short-wave infrared range a wavelength of 1.4 pm to 3.0 pm, in the middle range a wavelength of 3.0 to 8.0 pm, in the long-wave range a wavelength of 8.0 pm to 15 pm and in the far range a wavelength of 15 pm to 1 mm.
[0031] The wavelength of the infrared radiation present is preferably between 1 pm and 10 pm, in particular between 2 pm and 7 pm. These wavelengths can be readily absorbed by polymers. The absorption capacity is particularly high in the short-wave range, preferably in the range from 2 pm to 7 pm. The proportion of higher-wave radiation, i.e., radiation in the long-range, is preferably less than 70%, in particular less than 50%, preferably less than 30%.
[0032] This ensures that the fiber-based blank is subjected to as little thermal stress as possible.
[0033] These are wavelength ranges that are not or only slightly absorbed by the wall of the dried blank.
[0034] In other words, these wavelengths allow the powder coating to be melted without radiating unnecessary energy into the dried blank.
[0035] To be exposed to infrared radiation, the dried blank can be conveyed through a furnace. The furnace in question is a device within which a plurality of infrared sources are arranged. These can, for example, be arranged along a congruent contour of the dried blank and spaced apart from it.
[0036] The emitted infrared radiation is preferably generated without a heat source. This makes it possible to reduce the effect on the fiber-based blank itself.
[0037] It may also be possible to install reflectors in the oven to redirect and / or reflect emitted infrared radiation.
[0038] It can also be provided to arrange different infrared sources along the length of the oven. For example, infrared sources which emit radiation with a wavelength of 6 pm can be arranged at the oven inlet to quickly heat up the powder coating. Infrared sources which emit radiation with a wavelength of 3 pm can be arranged downstream to keep the melting rate constant. While being exposed to the infrared radiation, the dried blank can be rotated about its longitudinal axis. The dried blank is therefore moved linearly through the oven while it rotates about its longitudinal axis. Accordingly, each area of a surface of the blank is guided past corresponding infrared sources so that the dried blank, and thus the powder coating, is evenly exposed to infrared radiation from all sides.
[0039] To prevent the dried blank from overheating, it can be cooled by a cooling air stream during exposure to infrared radiation. Overheating of the dried blank is avoided. Overheating of the dried blank would lead to fiber degeneration and a decrease in strength.
[0040] The infrared sources can, for example, be arranged at different heights along the conveying direction of the blank, so that they each act on different areas of the blank.
[0041] Alternatively or additionally, it may be possible to provide infrared sources of different power or to control the infrared sources, for example, based on a respective product profile, so that their power is adjusted depending on the product or the length of time the product is in the room.
[0042] Preferably, the dried blank is transparent in the wavelength range from 1 pm to 10 pm. This can be achieved by the chemical composition of the blank containing functional groups that cannot be excited in this wavelength range.
[0043] Due to the transparency in this wavelength range, the corresponding infrared radiation can penetrate the wall of the dried blank without unnecessarily heating it. Accordingly, the powder coating preferentially absorbs infrared radiation in the wavelength range from 1 pm to 10 pm. This means that the coating can be heated quickly.
[0044] The applied powder coating is thus subjected to energy, transforming the powder into a melt. The melting process creates a homogeneous film that provides a suitable seal. This film preferably extends from the inside over the finished opening to the outside of the neck, forming a continuous seal in this area.
[0045] It may be necessary to test the dried blank for leaks. This can prevent defective products from being sold.
[0046] After sealing, i.e., after melting the powder coating and subsequent cooling, a product can be filled into the dried blank, provided the dried blank is designed as a container. The dried blank can then be sealed with a closure. This creates a closed body for transporting and protecting liquid products. In particular, by sealing the packaging edge, a reliable seal can be created in this area using, for example, a suitable sealing cone or a sealing plane, for example made of a sealing material such as a liner.
[0047] The method according to the invention is explained using schematic figures. It shows:
[0048] Figure 1 : a powder coating process;
[0049] Figure 2: the drying step of the powder coating process; Figure 3: a leak test;
[0050] Figure 4 : the closing process;
[0051] Figure 5: shows, by way of example, further typical products which can be produced by means of the process according to the invention;
[0052] Figure 6: shows, by way of example, a typical fibre-based closure which can be produced by means of the method according to the invention;
[0053] Figure 7 : a representation of first absorption spectra;
[0054] Figure 8 : a representation of second absorption spectra;
[0055] Figure 9 : a representation of third absorption spectra .
[0056] Figure 1 shows a coating step. A dried and pre-finished blank 61 is fed to a powder coating system (not shown in detail here). In the next step, an electrostatically charged lance 35 is inserted into the finished blank 61. This is located in an oppositely charged casing (also not shown here). Due to the electrostatic charge of the applied powder, it adheres to the inner side 63 of the finished blank 61.
[0057] The now coated, finished blank 61 is transferred to an oven, as shown in Figure 2, and exposed to infrared radiation. This melts the powder coating, creating a continuous, homogeneous film. The blank 61 is thus sealed.
[0058] Subsequently, the blank 61 can be tested for leaks using a corresponding testing device 500, as shown in Figure 3. The blank 61 can then be sealed with a lid 300, as shown in Figure 4.
[0059] Figure 5 shows, by way of example, further typical fiber-based products that can be manufactured using the method described here. A container 100 in the shape of a bottle is shown. This container also has a thread on the bottle neck and essentially corresponds to a fiber-based product manufactured from a blank 61 according to Figures 1 to 4. The container 100' is in the shape of a bowl, and the container 100'' is in the shape of a cup.
[0060] Figure 6 shows an example of a typical fiber-based closure 300 that can be manufactured using the method described herein.
[0061] Figures 7 to 9 each show different comparisons of different absorption spectra of different materials.
[0062] In Figures 7 to 9, the dark solid line represents the emitted infrared power as a cumulative distribution function of an infrared source with a 3 pm peak and the light solid line represents the emitted infrared power as a cumulative distribution function of an infrared source with a 6 pm peak.
[0063] Figures 7 to 9 also show the absorption capacity, or rather the absorption spectrum, of the dried blank. The corresponding line is shown in fine dotted lines. It is evident that the blank exhibits increased absorption in the range around approximately 10 pm and from approximately 14 pm onwards.
[0064] In Figure 7, the dashed line represents the absorption capacity, or rather the absorption spectrum, of an EVOH powder coating. As can be seen, EVOH exhibits increased absorption in the range at approximately 3 pm, at approximately 3.5 pm, and in the range between 7 pm and 8 pm. It is therefore clear that radiation at these wavelengths is absorbed significantly better by EVOH than by the blank. The powder coating is therefore heated more quickly, until it melts, without the blank being heated as much.
[0065] In Figure 8, the dashed line shows the absorption capacity, or absorption spectrum, of a powder coating made of PHB. As can be seen, PHB exhibits increased absorption in the range around approximately 6 pm and in the range between 8 pm and 10 pm. It is therefore clear that radiation at these wavelengths is absorbed significantly better by PBH than by the blank. The powder coating is therefore heated more quickly, until it melts, without the blank being heated as much.
[0066] In Figure 9, the dashed line shows the absorption capacity, or absorption spectrum, of a powder coating made of PET-C, i.e., crystalline PET. As can be seen, PET-C exhibits increased absorption in the range around 6 pm and 8 pm. It is therefore clear that radiation at these wavelengths is absorbed significantly better by PET-C than by the blank. The powder coating is therefore heated more quickly, until it melts, without the blank being heated as much.
Claims
Patent claims 1. A method for coating a dried blank (61) of a fiber-based product made of pulp (40), in particular a container (100, 100', 100'') or a fiber-based closure element (300) for a container (100, 100', 100'' ) , comprising the steps - Providing the dried blank (61) , - Applying a powder coating to an inner side (63) of the dried blank (61) - Curing the powder coating by exposure to infrared radiation (81) so that a coherent film is formed, characterized in that the infrared radiation (81) penetrates a wall of the dried blank (61) during irradiation.
2. Method according to claim 1, characterized in that the dried blank (61) is provided with a prefabricated opening before the application of the powder coating.
3. Method according to claim 3, characterized in that the powder coating is additionally applied to the finished opening of the dried blank (61).
4. Method according to one of claims 2 to 3, characterized in that a powder coating is additionally applied to an outer side (64) of a neck region of the dried blank (61) after the finishing, wherein the dried blank (61) remains uncoated on its outer side at least in some regions.
5. Method according to one of claims 1 to 4, characterized in that a meltable polymer is applied as powder coating, in particular polyester such as Polyethylene terephthalate (PET), polyethylene furanoate (PEF), polyethylene isosorbide terephthalate (PEIT), polylactide (PLA), polybutylene succinate (PBS), poly-s-caprolactone (PCL) or polyhydroxyalkanoate (PHA), in particular polyhydroxybutyrate (PHB), whereby these polyesters are preferably bio-based, or ethylene-vinyl alcohol copolymer (EVOH). Method according to one of claims 1 to 5, characterized in that in order to apply the powder coating, the latter is electrostatically charged. Method according to one of claims 1 to 6, characterized in that an infrared source (80) for generating the infrared radiation (81) is arranged outside the dried blank (61). Method according to one of claims 1 to 7, characterized in that the wavelength of the infrared radiation (81) is between 1 pm and 10 pm, preferably between 2 pm and 7 pm.Method according to one of claims 1 to 8, characterized in that the dried blank (61) is conveyed through a furnace (85) for exposure to the infrared radiation (81). Method according to one of claims 1 to 9, characterized in that the dried blank (61) is rotated about its longitudinal axis during exposure to the infrared radiation (81). Method according to one of claims 1 to 10, characterized in that the dried blank (61) is cooled by a cooling air stream during exposure to the infrared radiation (81). Method according to one of claims 1 to 11, characterized in that the dried blank (61) is transparent in the wavelength range from 1 pm to 10 pm. Method according to one of claims 1 to 12, characterized in that the powder coating absorbs the infrared radiation (81) in the wavelength range from 1 pm to 10 pm. Method according to one of claims 1 to 13, characterized in that the dried blank (61) is tested for leaks. Method according to one of claims 1 to 14, characterized in that the dried blank (61) is a container (100), wherein a product is filled into the dried blank (61) and the dried blank is subsequently closed with a closure.