Device for coating fibre-based hollow bodies

Abstract

The invention relates to a device (11) for coating fibre-based hollow bodies (17) with a barrier layer, comprising an electrically conductive mould (13) with a first port for receiving the body (17) and comprising a spray lance (15) with a second port, which spray lance (15) can be introduced into the body (17). A power source can be connected to the first and the second port, as a result of which an electric voltage can be realized between the mould (13) and the spray lance (15). An electrically conductive and compressible compensation element (19) is arranged on the inner side of the mould.

Description

[0001] Device for coating fiber-based hollow bodies

[0002] Field of the invention

[0003] The invention relates to a device for coating fiber-based hollow bodies according to the preamble of claim 1 and to a fiber-based closure according to the preamble of claim 15.

[0004] State of the art

[0005] Fibre materials have gained new importance as packaging materials in recent years due to their particularly sustainable nature. Advances in wet forming technology for components with undercuts, such as containers and bottles, are opening up new fields of application. Other new technologies, such as the dry forming of fibre mats, are enabling new fibre-based bodies, such as closures. These products compete with previously known products that are predominantly made of plastic. One disadvantage of fibre-based materials is that they are not intrinsically protected against external media such as water or steam, as is the case with plastics. Therefore, for many applications it is necessary to protect the formed fibres in a further process step and to provide the product with barrier properties.There are several technical solutions for applying such a barrier, whereby a distinction must be made between the medium from which the barrier is intended to protect the fiber-based body and whether the intended protection is for the contents or the shape of the fiber-based body. External protection can be achieved by incorporating chemical additives, e.g., AKD (alkyl ketene dimer), which is well-known in the fiber industry and makes fiber surfaces hydrophobic. However, this additive does not provide a barrier to water vapor or other gases, allowing them to penetrate unhindered and thus not adequately protecting the contents.

[0006] Coatings for fiber-based containers are known from the prior art, which have a powder coating on the inside of their shell. The powder coating is applied to the shell using an electrostatic high-voltage process. This allows the shell to be equipped with a barrier layer. However, fiber-based bodies have the peculiarity of having relatively large manufacturing tolerances compared to plastic bodies. Therefore, fiber-based bodies with an electrostatic coating have the disadvantage that the charge area is not uniform, and accordingly, the coating can have varying thicknesses and even gaps.

[0007] Object of the invention

[0008] The disadvantages of the described prior art give rise to the object of creating a device which improves the coating process described above.

[0009] Description

[0010] The stated object is achieved in a device for coating fiber-based hollow bodies with a barrier layer by the features stated in the characterizing portion of patent claim 1. Further developments and / or advantageous embodiments are the subject of the dependent patent claims.

[0011] The invention is preferably characterized in that an electrically conductive and compressible compensating element is arranged on the inside of the mold. Since the manufacturing tolerances of fiber-based hollow bodies are relatively high due to their manufacturing process, it is likely that the inside of the mold will not fully and precisely adhere to the outside of the hollow body. This can interrupt the electrical charge, leading to a patchy and uneven coating. The flexibility of the electrically conductive and compressible compensating element ensures that the outer surfaces of the body, whose corresponding inner surfaces are to be coated, are in full contact with the compensating element. Defects and irregularities in the coating are therefore reliably prevented.

[0012] In a particularly preferred embodiment of the invention, the compensating element is an electrically conductive foam and / or an electrically conductive 3D-printed filament body. The foam is typically used together with an additional support element, while the filament body serves as both the support element and the electrical conductor. The foam is preferably a polyurethane foam coated with copper and nickel.

[0013] 3D printing enables an extremely precise surface while maintaining high flexibility. The filament body can only be produced using 3D printing, as it must be built up in layers to create the intertwined filaments. The intertwined filaments ensure the compressibility and flexibility of the filament body. The filament body is intended for components where the contour of the mold does not allow for the adhesive bonding of the conductive foam.

[0014] In another particularly preferred embodiment, the mold consists of a plurality of electrically conductive segments, allowing the body to be coated to be enclosed within the segments. This allows an electrical charge to be present on all surfaces of the hollow body, which are to be coated evenly and seamlessly. The segments are preferably made of aluminum, as this metal has high electrical conductivity. The segments can also be free of the foam or filament body. This is preferred for interfaces of the hollow body that require force transmission and screw fastening.

[0015] The combination of compensating element and segments allows the hollow body to be fully enclosed by the mold while simultaneously maintaining electrical voltage on all surfaces to be coated. These features must work together for the device to function reliably.

[0016] It has proven useful for the mold to have several side segments, a base segment, and a shoulder segment. This allows the hollow body to be easily inserted into the mold and, after the mold is closed, remains in full contact with the segments.

[0017] The mold advantageously has a neck segment and a dividing segment, with the dividing segment adjoining the neck segment. The neck segment and the dividing segment form the boundary edge between the coated and uncoated areas on the outer surface of the neck thread. The neck segment is the contacting component and is therefore responsible for potential equalization. The dividing segment does not touch the outer surface of the bottle. This segment results in a "sharper" boundary edge of the coating. The fiber-based hollow body can optionally also be coated externally on the end or sealing surface as well as on the thread. The coating usually ends directly behind the end of the thread.

[0018] It is advantageous if the dividing segment and the neck segment are free of the compensating element. At this point in the hollow body, the aluminum segment without the compensating element is preferred because it offers better conductivity than foam and filament bodies and allows for a coating that, thanks to its improved adhesion, can withstand higher loads. This prevents the coating from peeling off at interfaces that transmit force and interfaces that require screwing.

[0019] As already mentioned above, it is advantageous if the coating area on the body can be defined by the dividing segment. This ensures that the coating has a precise demarcation from the uncoated part of the hollow body.

[0020] The invention is also preferably characterized in that the segments can be transferred, like a casting mold, from an open position, in which the body can be inserted into the mold, to a closed position, in which the body can be completely enclosed by the segments. This makes the device ideal for the series production of fiber-based hollow bodies. The increased manufacturing tolerances of the hollow bodies in a production series are compensated for by the compensating element.

[0021] In a further preferred embodiment of the invention, the surfaces of the segments that are covered with the compensating element or are free of it define a coating area in the closed position of the mold. This allows the entire interior to be coated particularly homogeneously, thinly, and without gaps.

[0022] It is preferred if the side segments are covered with foam, as the foam can be bonded to the contour of the side segment with an electrically conductive adhesive, thus adhering to the segment. The foam exhibits good conductivity and good compensation properties.

[0023] It is preferable if the base segment is covered with the filament body, as the foam does not stick to the base segment. This is because the base segment and also the shoulder segment usually have a contour that cannot be reproduced using foam alone. Radii, edges, and other 3D shapes can only be reproduced using very thin, elastic materials. However, foam must generally be about 5 mm thick because, on the one hand, it has a balancing function and, on the other hand, the copper-nickel coating is not elastic. Accordingly, the filament body is a suitable replacement for the foam on contours where the foam does not stick.

[0024] The spray lance can conveniently be inserted into the mold through the shoulder segment, since the filling or pouring opening of the fiber-based hollow body is also located there. In a further preferred embodiment of the invention, the spray lance is designed such that the polymer powder is electrically charged as it flows through the spray lance, with the segments being chargeable in the opposite direction to the polymer powder. This attracts the powder particles to the inside of the hollow body, where potential equalization occurs. The spray lance can be designed like a "corona gun."

[0025] Due to the advantages outlined above, the device is particularly well suited for fiber-based bottles and closures, as the compensating element can compensate for manufacturing tolerances and complex geometric shapes.

[0026] A further aspect of the invention relates to a fiber-based closure comprising a cover plate and a cylindrical casing adjoining the cover plate and having an internal thread. The inside of the cover plate and the casing can be particularly advantageously coated with a polymer powder using the present device. Firstly, the barrier layer is applied over the entire surface evenly. Secondly, the polymer coating increases the rigidity in this area. This can increase the maximum tightening torque of the closure. In addition, at the friction surfaces, e.g. the thread, fibers are prevented from being released from the surface due to the surfaces moving against one another, which would impair the function of the closure when used multiple times.

[0027] Further advantages and features will become apparent from the following description of an embodiment of the invention with reference to the schematic representations. These are not to scale:

[0028] Figure 1: a sectional view of a device for coating fiber-based hollow bodies with a mold, the mold being open;

[0029] Figure 2: a sectional view of the device in a partially closed

[0030] Position of the mold;

[0031] Figure 3: a sectional view of the device in a closed position of the mold; Figure 4: a detailed view of the mold from Figure 3 and

[0032] Figure 5: a perspective view of the device with the mold and a spray lance

[0033] Figure 5 shows a device for coating fiber-based hollow bodies, which comprises an electrically conductive mold 13 and a spray lance 15 and is designated overall by the reference numeral 11. The mold 13 functions like a casting mold, wherein mold segments can be moved between an open position (Figure 1) and a closed position (Figure 3). In the open position, a hollow body, for example a fiber-based bottle 17, can be inserted into the mold 13. In the context of this application, a fiber-based hollow body is understood to mean that the hollow body is formed from compressed pulp, which forms a dimensionally stable shell and encloses an interior space. Pulp is typically understood to be a mixture of water, fibers (in particular paper fibers) and a binder.

[0034] The mold 13 and the spray lance 15 have a first and a second electrical connection, respectively, to which an electrical voltage can be applied. Since the mold 13 is made of an electrically conductive material, for example aluminum, the charge can act on the hollow body or the bottle 17, even though the fibers are non-conductive. The more precisely the mold 13 fits against the bottle, the more even the coating of the interior will be. To coat the inside of the bottle 17, an electrical voltage is applied to the first and second connection. A polymer powder blown through the spray lance 15, for example, is positively charged. Once the mold 13 is negatively charged, the powder particles adhere to the inside of the bottle 17. The bottle 17 is then removed from the mold 13, and in a subsequent step, the powder is melted using thermal energy.The thermal energy can be introduced in the form of convective or radiant energy. The powder forms a homogeneous layer in the melt and solidifies during the subsequent cooling process.

[0035] Typically, fiber-based hollow bodies have a relatively large manufacturing tolerance compared to plastic bodies. On the other hand, the mold 13 must fit snugly and as precisely as possible against the hollow body over its entire surface in order to generate a charge field that replicates the interior of the hollow body as accurately as possible. To achieve this precise fit of the mold 13 against bottles 17, which differ in their dimensions due to the material, an electrically conductive and compressible compensating element 19 is arranged on the interior of the mold 13. This compensating element 19 fits snugly against the outer contour of the bottle 17, as it can be compressed to a greater or lesser extent. The coating is therefore particularly homogeneous and thin, adapting to the geometry of the hollow body on the interior. Even complex shapes, such as the threads of a fiber-based twist cap, can be precisely coated.

[0036] The mold 13 consists of a plurality of electrically conductive segments, whereby the body to be coated can be enclosed by the segments. The mold 13 preferably has a plurality of side segments 21, a base segment 23, and a shoulder segment 25. The segments can be lined with an electrically conductive foam 19a or with an electrically conductive 3D-printed filament body 19b. The filaments are intertwined plastic fibers that are compressible or flexible and electrically conductive. For components to which the contour does not allow the conductive foam to be adhered, the use of the filament body 19b is advantageous. Using the 3D printing process, the filament body 19b can be manufactured with the highest manufacturing tolerances and in complex shapes.

[0037] Segments, such as the side segments 21, can be lined with an electrically conductive foam 19a. The conductivity and compensating behavior of the conductive foam are higher than that of the filament body. The foam is used on all segments where it can be glued to the contour.

[0038] The fiber-based bottle 17 is inserted with its shoulder 27 into the shoulder segment 25 (Figure 1). Figure 2 shows the fixing of the bottle 17 between the shoulder and the base segment 25, 23. The fixing of the bottle 17 takes place by moving the base segment 23 vertically onto the base 29. After closing the base segment 23, the side segments 21 are closed, whereby the bottle is completely surrounded by segments. Preferably, four side segments 21 are provided, which are moved first in a vertical direction and then in a radial direction in order to cover the jacket of the bottle 31. The inner surfaces of the side segments 21 are covered with the electrically conductive foam 19a. After closing the segments, the surfaces of the segments covered with the compensating element 19 define a coating area in the closed position of the mold 13 (Figure 3). That isAll surfaces of the bottle 17 which are provided with the compensating element 19 (foam 19a or filament body 19b) can be coated over the entire surface, evenly and without gaps with the electrically charged polymer powder.

[0039] Following the shoulder segment 25, the mold 13 has a neck segment 33. The neck segment 33 and an adjoining dividing segment 35 are closed by two pneumatic grippers. The neck segment is the contacting component responsible for potential equalization.

[0040] Following the neck segment 33 is the dividing segment 35. The neck segment 33 ensures a coating at the transition between the shoulder 27 and the neck 33. The dividing segment 35 enables a clean separation or a "sharper boundary edge" on the neck of the bottle 37 between the coating zone and the outer mouth area, which is not coated. Neither the neck segment 33 nor the dividing segment 35 have a compensating element for the production of the interfaces. These two segments are made of aluminum and therefore have good conductivity.

[0041] Figure 5 shows the spray lance 15 before it is retracted through the shoulder segment 25 into the interior of the bottle 17. The spray lance can be designed as a "corona gun." Upon exiting the spray lance 15, the polymer powder is charged with the countercharge of the electrically conductive compensating element 19. This allows the powder to adhere to the inner surfaces of the bottle to be coated.

[0042] The 3D-printed filament body 19b and in particular the foam 19a allow geometrically complex shapes to be coated with a thin and uniformly thick polymer layer. Furthermore, the polymer layer is completely closed to create a reliable barrier layer. Therefore, the device 11 is also suitable for coating the inside of a fiber-based twist lock. In the process, the internal thread of the lock is also completely coated. By using a polymer powder that adheres flat to the geometric shapes, the stiffness in this area is also increased. This can increase the maximum tightening torque of the lock. Additionally, a polymer layer is applied to the friction surfaces, e.g.The thread prevents fibers from being released from the surface due to the movement of the surfaces against each other, thus impairing the function of the fastener when used repeatedly. Key:

[0043] 11 Device

[0044] 13 Shape

[0045] 15 spray lance

[0046] 17 Fiber-based bottle, fiber-based hollow body

[0047] 19 Compensating element

[0048] 19a electrically conductive foam

[0049] 19b electrically conductive 3D-printed filament body

[0050] 21 page segments

[0051] 23 Ground segment

[0052] 25 shoulder segment

[0053] 27 Shoulder of the bottle

[0054] 29 Bottom of the bottle

[0055] 31 Coat of the bottle

[0056] 33 neck segment

[0057] 35 division segment

[0058] 37 Neck of the bottle

Claims

Device (11) for coating fiber-based bodies (17) with a barrier layer comprising - an electrically conductive mold (13) with a first terminal for receiving the body (17), - a spray lance (15) for dispensing a polymer powder with a second connection, which spray lance (15) can be placed at a distance from the body (17), wherein - a power source can be connected to the first and second terminals, whereby an electrical voltage can be realized between the mold (13) and the spray lance (15), characterized in that an electrically conductive and compressible compensating element (19) is arranged on the inside of the mold. Device according to claim 1, characterized in that the compensating element is an electrically conductive foam (19a) and / or an electrically conductive 3D-printed filament body (19b). Device according to claim 1 or 2, characterized in that the mold (13) consists of a plurality of electrically conductive segments (21, 23, 25, 33, 35), whereby the body to be coated (17) is separated from the segments (21, 23, 25, 33, 35). Device according to claim 3, characterized in that the mold has a plurality of side segments (21), a base segment (23), and a shoulder segment (25). Device according to claim 3 or 4, characterized in that the mold has a neck segment (33) and a dividing segment (35), wherein the dividing segment (35) adjoins the neck segment (33). Device according to claim 5, characterized in that the dividing segment (35) and the neck segment (33) are free of the compensating element (19).

7. Device according to claim 5 or 6, characterized in that the coating area on the body (17) can be limited by the dividing segment (35).

8. Device according to one of claims 3 to 7, characterized in that the segments (21, 23, 25, 33, 35) can be transferred in the manner of a casting mold from an open position, in which the body (17) can be inserted into the mold, into a closed position, in which the body (17) is separated from the segments (21,23,25,33,35) can be completely enclosed.

9. Device according to one of claims 3 to 8, characterized in that the surfaces of the segments (21, 23, 25, 33, 35) which are covered with the compensating element or are free of it, define a coating area in the closed position of the mold (13).

10. Device according to one of claims 4 to 9, characterized in that the side segments (21) are covered with foam (19a). 11 . Device according to one of claims 4 to 10, characterized in that the base segment (23) is covered with the filament body (19b).

12. Device according to one of the preceding claims, characterized in that the spray lance (15) can be inserted into the mold (13) through the shoulder segment (25).

13. Device according to one of the preceding claims, characterized in that the spray lance (15) is designed such that the polymer powder is electrically charged when flowing through the spray lance (15), wherein the segments (21, 23, 25, 33, 35) are chargeable in the opposite direction to the polymer powder.

14. Use of the device (11) according to one of the preceding claims for coating fiber-based containers, in particular fiber-based bottles (17) and fiber-based closures.

15. Having fiber-based closure - a cover plate and - a cylindrical shell connected to the cover plate with an internal thread, characterized in that at least the inside of the cover plate and the casing is coated with a device (11) according to claims 1 to 13.

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