Method for coating dry parisons

Abstract

The present disclosure relates to a method for coating a dry parison (61) of a fibre-based product made of pulp (40), comprising the steps of:-providing a dry parison (61),-applying a powder coating on an inner side (63) of the dry parison (61),-curing the powder coating by applying infrared radiation (81), thereby forming a coherent film. During radiation, the infrared radiation (81) penetrates through the wall of the dry parison (61).

Description

Technical Field

[0001] The present invention relates to a method for coating a dry parison of a fiber-based product made of paper pulp. Background Art

[0002] Different containers for containing liquids are known in the prior art. For example, glass bottles or plastic bottles for containing beverages are known. Containers made of fiber-based materials have also been proposed.

[0003] A fibrous container is proposed in WO 2012 / 139590 A1. To produce such a container, a so-called paper pulp is introduced into a mold and is pressed against the corresponding walls and compressed accordingly by means of a flexible balloon in the mold.

[0004] Recently, simultaneously with or after this compression step, the still wet parison is dried by applying energy, thereby providing a dry parison for further processing.

[0005] Pulp is a mixture of fibers and water, in particular natural fibers such as hemp, cellulose or flax or mixtures thereof. If necessary, the pulp has additives, such as those known from PCT / EP2019 / 076839, which, for example, improve the hardening of the compressed pulp or influence the subsequent appearance or generally change the properties of the pulp or the subsequent container.

[0006] With these containers there is the risk that the container softens due to the liquid stored in it and, for example, leaks, or that substances diffuse from the container into the liquid.

[0007] It has been proposed to provide such fiber-based containers with an inner layer made of plastic, in particular to arrange a plastic bottle inside the fiber-based container, which plastic bottle can assume a corresponding barrier function. The fiber-based container thus only provides a sheath for a thin-walled plastic container. Such a combination is known from WO 2018 / 167192 A1.

[0008] Therefore, a fiber-based container is usually provided, into which the plastic liner is introduced. This usually takes the form that in a first step a fiber-based container is provided and in a second step a preform is introduced into the container. Subsequently, the preform is blown up in the fiber-based container until it touches or comes into contact with the inner contour of the fiber-based container. This blowing process usually takes place in a blow mould, the mould cavity of which corresponds to the outer contour of the fiber-based container. Unlike the conventional blow moulding process, this process has to deal with two separate elements and is therefore much more complicated, since the preform has to be positioned and held relative to the fiber-based container, which in turn has to be positioned and held in the blow mould.

[0009] An exemplary process is described, for example, in EP 3 375 593 A1. EP 3 375 593 A1 describes a preform for container production which has extensions in its neck region which can engage with corresponding fiber-based containers in order to keep the container and the preform connected to each other. 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 can produce deviations of different sizes, depending on the specific properties of the pulp forming the container. This is particularly disadvantageous in the neck region, because in order to achieve a clean compression between the preform or its extension and the fiber-based container, certain tolerance limits must be observed, which is not always possible due to different process parameters and the changing pulp properties. In addition, such production still requires relatively large amounts of plastic. Summary of the invention

[0010] The object of the present invention is to obviate one or more disadvantages of the prior art and in particular to provide a method which enables the formation of 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 are given in the dependent claims.

[0012] A method according to the invention for coating a dry parison of a fiber-based product made of paper pulp, in particular a container or a fiber-based closing element for a container, comprises the following steps:

[0013] - providing a dry parison,

[0014] - Apply powder coating to the inside of the dry preform,

[0015] - Curing of the powder coating by applying infrared radiation, thus forming a coherent film.

[0016] In order to subject the powder coating to infrared radiation, during the irradiation process, in particular in the region of the interior of the container, the infrared radiation penetrates the wall of the dry preform before striking the powder coating.

[0017] This means that the infrared source can be arranged outside the dry parison, but the powder coating inside the dry parison can be exposed to the infrared radiation.

[0018] Throughdrying the preform in particular enables the powder coating to reach a higher temperature level than the preform.

[0019] An additional or alternative aspect of the invention also relates to a method, in which the preform and the powder coating are heated differently, in particular, the powder coating is heated to a higher temperature than the preform, in particular by infrared radiation penetrating the wall of the preform. In particular, the preform is heated substantially only via heat radiation from the powder coating.

[0020] Preferably, the assembly opening is provided on the dry preform before the powder coating is applied.

[0021] By providing the assembly opening, a corresponding sealing plane or sealing surface can be provided, which can interact with a corresponding closure (e.g., lid). In addition, by providing the assembly opening, a fibrous or inaccurate closure of the parison can be for example removed at the same time.

[0022] It is known that for fiber-based containers, certain tolerances may occur during the production process. Due to the material properties of the pulp, the upper closing edge of the opening is subject to greater tolerances and is often fibrous. This is particularly disadvantageous because this edge, for example, forms an interface with respect to the container closure and the dimensions of this interface must be precise.

[0023] Preferably, during the production of the container, the dry parison is produced in such a way that a projection is provided in the region of the top opening, which projection can be separated after the parison is dried. By separating the projection, corresponding inaccurate or fibrous regions of the dry parison can be removed.

[0024] It can be proposed that a powder coating is additionally applied to the assembly opening of the dry preform. This way the assembly opening can also be sealed.

[0025] Additionally, a powder coating can be applied to the outside of the neck region of the dry preform after assembly, wherein the dry preform remains uncoated at least partially on its outside.

[0026] By coating the outside of the neck area, it may also be made sealed and / or more durable during use.

[0027] The uncoated area on the outside of the parison allows the product to be recycled. The uncoated area provides an active surface to break up or soften the product with water. This makes the product easier to recycle.

[0028] Fusible polymers can be used as powder coatings. Polymers have superior properties and are easy to process.

[0029] As fusible polymers, polyesters are preferably used, such as polyethylene terephthalate (PET), polyethylene furanoate (PEF), polyisosorbide terephthalate (PEIT), polylactide (PLA), polybutylene succinate (PBS), polycaprolactone (PCL) or polyhydroxyalkyl esters (PHA), especially polyhydroxybutyrate (PHB). These polyesters are preferably bio-based. Ethylene-vinyl alcohol copolymers (EVOH) have also proven to be suitable.

[0030] In order to apply the powder coating, it can be electrostatically charged. In particular, it can be provided that the conductive mold surrounding the dry preform is charged with a charge opposite to the polarity of the powder. The powder will be deposited, in particular, on the inside of the preform and adhere there.

[0031] The infrared source for generating the infrared radiation is preferably arranged outside the drying preform.

[0032] This allows the infrared radiation to be directed at a specific distance and angle onto the dry preform, in particular onto the powder coating, in a targeted manner. The infrared radiation has a wavelength of 780 nm to 1400 nm in the near infrared range, 1.4 μm to 3.0 μm in the short wave infrared range, 3.0 μm to 8.0 μm in the medium wave range, 8.0 μm to 15 μm in the long wave range and 15 μm to 1 mm in the far wave range.

[0033] The wavelength of the infrared radiation in the present invention is preferably between 1 μm and 10 μm, especially between 2 μm and 7 μm. These wavelengths can be well absorbed by polymers. In particular, the absorption capacity is particularly high in the short-wave range, preferably in the range of 2 μm to 7 μm.

[0034] Preferably, the proportion of higher-wavelength radiation, ie radiation in the long-wave range, is less than 70%, in particular less than 50%, preferably less than 30%.

[0035] This ensures that the fiber-based preform is subjected to the least possible thermal stress.

[0036] In turn, these wavelength ranges are not absorbed or are only slightly absorbed by the walls of the dry parison. In other words, these wavelengths can melt the powder coating but do not radiate energy unnecessarily into the dry parison.

[0037] In order to apply infrared radiation, the dried preforms can be conveyed through an oven. The oven of the invention is a device in which a plurality of infrared sources are arranged. These infrared sources can be arranged, for example, along the contour of the dried preforms and at a certain distance from the preforms.

[0038] The emitted infrared radiation is preferably infrared radiation generated without a heat source. This can reduce the impact on the fiber-based parison itself.

[0039] In this case, it can also be provided that a reflector is installed in the oven, which deflects and / or reflects the emitted infrared radiation.

[0040] It can also be proposed to arrange different infrared sources along the length of the oven. For example, an infrared source emitting radiation with a wavelength of 6 μm can be arranged at the inlet of the oven to quickly heat the powder coating. An infrared source emitting radiation with a wavelength of 3 μm can be arranged downstream to keep the melting rate constant.

[0041] During the application of infrared radiation, the dry parison can be rotated about its longitudinal axis. The dry parison is moved linearly through the oven while rotating about its longitudinal axis. Thus, each area of ​​the parison surface is guided past a corresponding infrared source, so that the dry parison and the powder coating are uniformly exposed to the infrared radiation from all sides.

[0042] In order that the dry preform does not overheat, it can be provided that it is cooled by a cooling air flow during the application of the infrared radiation. This avoids overheating of the dry preform. Overheating of the dry preform would lead to denaturation of the fibers and a loss of strength.

[0043] For example, the infrared sources can be arranged at different heights along the conveying direction of the preforms, so that each of these infrared sources acts on a different area of ​​the preforms.

[0044] Alternatively or additionally, it can be provided that infrared sources of different powers are provided or that the infrared sources are adjusted, for example, depending on the respective product profile, so that the power of the infrared source can be adjusted depending on the product or the residence time of the product.

[0045] The dried preform is preferably transparent in the wavelength range of 1 μm to 10 μm. This can be achieved by providing the chemical composition of the preform with functional groups that cannot be excited in this specific wavelength range.

[0046] Due to the transparency in this wavelength range, the corresponding infrared radiation can penetrate the walls of the dry preform without heating them unnecessarily.

[0047] Accordingly, the powder coating preferably absorbs infrared radiation in the wavelength range of 1 μm to 10 μm. The coating can thus be heated rapidly.

[0048] Thus, the applied powder coating is supplied with energy and the powder is converted into a melt. A uniform film is formed by melting, thereby providing a corresponding seal. Preferably, the film extends from the inside through the assembly opening to the outer area of ​​the neck and forms a continuous seal in this area.

[0049] It can be provided that the dried preforms are tested for leaks. This can prevent defective products from being sold.

[0050] After sealing, i.e. after melting of the powder coating and subsequent cooling, the dry preform can be filled with the product, provided that the dry preform is designed as a container. The dry preform can then be closed in connection with a closure. Accordingly, a closure for transporting and protecting liquid products is formed. In particular, by sealing the assembly edge, a reliable seal can be produced in this area, for example with a corresponding sealing cone or sealing surface (for example made of a sealing material such as a cushion). BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The method according to the invention is explained on the basis of the schematic drawings. In the drawings:

[0052] Figure 1 : Powder coating process;

[0053] Figure 2 : Drying step of the powder coating process;

[0054] Figure 3 : Leak test;

[0055] Figure 4 : Closing process;

[0056] Figure 5 : other representative products that can be produced by the method of the present invention are shown by way of example;

[0057] Figure 6 : A representative fiber-based closure member that can be produced by the method of the present invention is shown by way of example;

[0058] Figure 7 : Graphical representation of the first absorption spectrum;

[0059] Figure 8 : Illustration of the second absorption spectrum;

[0060] Fig. 9 : Graphic representation of the third absorption spectrum. DETAILED DESCRIPTION

[0061] Figure 1 The coating step is shown. The dried assembled preform 61 is fed to a powder coating device (not shown here). In a subsequent step, an electrostatically charged spray gun 35 is introduced into the assembled preform 61. The preform is located in an oppositely charged housing, also not shown here. The electrostatic charge of the sprayed powder causes it to adhere to the inner side 63 of the assembled preform 61.

[0062] like Figure 2 As shown, the coated assembled preform 61 is now transferred to an oven and exposed to infrared radiation. This causes the powder coating to melt, thereby forming a continuous, uniform film. The preform 61 is thereby sealed.

[0063] The parison 61 can then be tested for leakage using a corresponding testing device 500, such as Figure 3 shown.

[0064] The parison 61 can then be closed with a cover 300, such as Figure 4 shown.

[0065] Figure 5 Other representative fiber-based products that can be produced by the method described herein are shown by way of example. For example, the container 100 is shown in the shape of a bottle. In addition, the container has threads on the neck and substantially corresponds to the fiber-based product according to Figures 1 to 4 The fiber-based product is made of the parison 61. The container 100' is in the shape of a disk, while the container 100" is in the shape of a cup.

[0066] Figure 6 A representative fiber-based closure element 300 that can be produced using the presently described method is shown by way of example.

[0067] Figures 7 to 9 Different comparisons of different absorption spectra of different materials are shown respectively.

[0068] exist Figures 7 to 9 In the figure, the dark solid line represents the cumulative distribution function of the infrared emission power as a peak infrared source at 3 μm, and the light solid line represents the cumulative distribution function of the infrared emission power as a peak infrared source at 6 μm.

[0069] Figures 7 to 9 The absorption capacity or absorption spectrum of the dried preform is also shown. The corresponding lines are shown with fine dots. It can be seen that the absorption of the preform increases in the region of about 10 μm and in the region starting from about 14 μm.

[0070] exist Figure 7 In the graph, the dotted line shows the absorption capacity or absorption spectrum of a powder coating made of EVOH. It can be seen that EVOH absorbs increasing amounts in the region of about 3 μm, about 3.5 μm and in the region between 7 μm and 8 μm. It can therefore be seen that EVOH absorbs radiation of these wavelengths significantly better than the preform. As a result, the powder coating can be heated to melting more quickly, while the preform is not heated to the same extent.

[0071] exist Figure 8 In the graph, the dotted line shows the absorption capacity or absorption spectrum of a powder coating made of PHB. It can be seen that PHB absorbs increasing amounts in the region of about 6 μm and in the region between 8 μm and 10 μm. It can therefore be seen that PBH absorbs radiation of these wavelengths significantly better than the preform. As a result, the powder coating can be heated to melting faster, while the preform is not heated to the same extent.

[0072] exist Fig. 9 In the graph, the dotted line shows the absorption capacity or absorption spectrum of a powder coating made of PET-C (i.e. crystalline PET). It can be seen that PET-C has an increased absorption in the region of about 6 μm and about 8 μm. It can therefore be seen that PET-C absorbs radiation of these wavelengths significantly better than the preform. As a result, the powder coating can be heated to melting more quickly, while the preform is not heated to the same extent.

Claims

1. A method for coating a dry parison (61) of a fiber-based product made of pulp (40), in particular a container (100, 100', 100") or a fiber-based closing element (300) for a container (100, 100', 100"), the method comprising the following steps: - providing the dried parison (61), - applying a powder coating on the inside (63) of the dried preform (61), - curing the powder coating by applying infrared radiation (81) to form a coherent film, It is characterized in that During irradiation, the infrared radiation (81) penetrates the wall of the drying parison (61).

2. The method according to claim 1, characterized in that Prior to applying the powder coating, a mounting opening is provided on the dry preform (61).

3. The method according to claim 3, characterized in that: In addition, the powder coating is applied to the assembly opening of the dry preform (61).

4. The method according to any one of claims 2 to 3, characterized in that After assembly, a powder coating is additionally applied to the outer side (64) of the neck region of the dry preform (61), wherein the dry preform (61) remains at least partially uncoated on its outer side.

5. The method according to any one of claims 1 to 4, characterized in that A fusible polymer is applied as a powder coating, in particular a polyester such as polyethylene terephthalate (PET), polyethylene furanoate (PEF), polyisosorbide terephthalate (PEIT), polylactide (PLA), polybutylene succinate (PBS), polycaprolactone (PCL) or polyhydroxyalkylates (PHA), in particular polyhydroxybutyrate (PHB), wherein the polyester is preferably bio-based, or ethylene vinyl alcohol copolymer (EVOH).

6. The method according to any one of claims 1 to 5, characterized in that To apply the powder coating, it is electrostatically applied.

7. The method according to any one of claims 1 to 6, characterized in that An infrared source (80) for generating the infrared radiation (81) is arranged outside the drying parison (61).

8. The method according to any one of claims 1 to 7, characterized in that The wavelength of the infrared radiation (81) is preferably between 1 μm and 10 μm, in particular between 2 μm and 7 μm.

9. The method according to any one of claims 1 to 8, characterized in that The dried preforms (61) are conveyed through an oven (85) to apply the infrared radiation (81).

10. The method according to any one of claims 1 to 9, characterized in that During the application of the infrared radiation (81), the drying parison (61) is rotated about its longitudinal axis.

11. The method according to any one of claims 1 to 10, characterized in that During the exposure of the dry preform (61) to the infrared radiation (81), the dry preform is cooled by a cooling air flow.

12. The method according to any one of claims 1 to 11, characterized in that The dried parison (61) is transparent in the wavelength range of 1 μm to 10 μm.

13. The method according to any one of claims 1 to 12, characterized in that The powder coating absorbs the infrared radiation (81) in the wavelength range of 1 μm to 10 μm.

14. The method according to any one of claims 1 to 13, characterized in that The dried parison (61) is subjected to a leak test.

15. The method according to any one of claims 1 to 14, characterized in that The dry preform (61) is a container (100) into which a product is filled and which is closed in connection with a closure.

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