Method and device for reducing the water content in a fibre-based blank

Abstract

The invention relates to a method and device for reducing the water content in a fibre-based blank. The method comprises the steps of - providing a wet fibre-based blank, - subjecting the wet fibre-based blank to microwaves. The fibre-based blank is provided in a microwave-permeable press mould (20).

Description

[0001] Method and device for reducing the water content in a fiber-based blank

[0002] The present invention relates to a method and a device for reducing the water content in a fiber-based blank, in particular a container or in a fiber-based closure element for a container according to the preamble of the independent claims.

[0003] A fiber-based blank in the form of a container was disclosed in WO 2012 / 139590 A1. To produce this container, so-called pulp is injected into an upside-down mold and pressed against a corresponding wall using a flexible balloon in this mold, thereby compressing it accordingly. The pulp is compressed and heated to a temperature of approximately 180°C to dry the container. It is also known to produce closure elements for containers from pulp.

[0004] Pulp is a mixture of fibers and water, especially natural fibers such as hemp fibers, cellulose fibers, or flax fibers, or a mixture thereof. The pulp may contain additives that, 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.

[0005] The aforementioned process is time-consuming and energy-intensive. It has therefore already been proposed to improve it. WO 2018 / 020219 A1 discloses another process for drying wet, fiber-based blanks. Here, too, the blanks are containers. Here, the wet pulp is also pressed together inside the mold using a flexible balloon. The pre-processed container is then demolded together with the balloon inside and placed on a conveyor belt. The balloon is removed from the cold-formed container. The container is then exposed to microwaves to dry it. Before drying, the blank is very sensitive to the effects of force and must be handled very carefully.During the drying process, the container may become deformed, for example due to uneven drying or a non-uniform layer thickness, or it may be damaged by external influences.

[0006] The object of the invention is to remedy at least one of the disadvantages of the prior art. In particular, a method and a device are to be provided that enable wet fiber-based blanks, in particular containers such as bottles, cups, bowls or trays, or wet fiber-based closure elements, to be dried with low energy consumption while ensuring that they retain their dimensionally stable.

[0007] This problem is solved by the methods and devices defined in the independent patent claims. Further embodiments emerge from the dependent patent claims.

[0008] A method according to the invention for reducing the water content in a fiber-based blank, in particular in a fiber-based container or closure element, comprises the steps:

[0009] - Providing a wet fiber-based blank,

[0010] - Exposure of the wet fiber-based blank to microwaves.

[0011] The fiber-based blank is provided in a microwave-transparent press form.

[0012] By placing the fiber-based blank in a microwave-transparent mold, the wet fiber-based blank can remain within the mold during the drying process, i.e., while it is being exposed to microwaves. The container is thus protected from external influences and damage or deformation is prevented. By placing the wet fiber-based blank within the microwave-transparent mold, it can also be achieved that it is accessible to the microwaves from all sides, thus allowing drying from all sides. After this drying step, the wet fiber-based blank has a water content of approximately 5% to 12%.

[0013] In the present process, the wet fiber-based blanks are typically formed as already known in the art. In other words, pulp is introduced into a porous mold or a solid mold with water-draining channels whose entrances are covered with sieves or whose openings are small enough that the pulp fibers cannot penetrate, and the pulp fibers are washed onto the inner wall of the mold so that a container wall is built up. As soon as the wall is sufficiently thick, the washing of the pulp is stopped. The now available semi-finished product, i.e. the wet fiber-based blank, is removed from the mold and placed in the microwave-permeable press mold and thus made available in the press mold. At this point, the wet fiber-based blank has a water content of approximately 75%.

[0014] The wet fiber-based blank is removed from the mold using a suitable transfer device. The wet fiber-based blank is then inserted into the open mold. The mold is preferably constructed in two parts. Blowing and / or suction using negative or positive pressure may be necessary for removal and insertion. Purely mechanical grippers can also be used for this transfer.

[0015] Typically, the press mold may have an inner wall that is designed with a higher surface quality than the inner wall of the casting mold.

[0016] Preferably, after the fiber-based blank has been prepared, an expandable tool is inserted into the fiber-based blank. By expanding the expandable tool, the water content of the fiber-based blank can be reduced in a first step. At this point, the wet fiber-based blank has a water content of approximately 50%-60%.

[0017] At the same time, a surface with improved properties can be created on the wet fiber-based blank because, as already explained, the press mold can be designed with a higher quality than the casting mold.

[0018] It can be provided that the expandable tool remains in the expanded state during the application of microwaves.

[0019] Pressure can be maintained on the wall of the wet fiber-based blank. Furthermore, the expandable tool remaining inside the wet fiber-based blank provides internal support, preventing unwanted deformation. This also improves the surface quality of the blank.

[0020] The fiber-based blank can be placed in a microwave-reflecting microwave chamber before exposure to microwaves, in particular together with the press mold.

[0021] This can increase the effectiveness of the microwaves. Microwaves that are not directly absorbed by the wet fiber-based blank are typically reflected off the interior walls of the microwave chamber, increasing the likelihood that these microwaves will also reach the blank being dried.

[0022] It is generally known that microwave excitation can cause molecules to vibrate, and that this vibration generates heat. Water, for example, has a natural frequency of 2.45 GHz. Microwaves are therefore preferably generated at this frequency. To remove water or residual moisture from the wet fiber-based blank, the water is preferably heated until it evaporates and is then released from the wet blank.

[0023] In order to accelerate the drying process, it can be provided that the mold and / or the microwave chamber is preheated to a temperature which is higher than 60 ° C but preferably lower than 160 ° C.

[0024] This also prevents the moisture escaping from the wet fiber-based blank from condensing again in the immediate vicinity of the blank and precipitating as drops.

[0025] Heating can be achieved, for example, using conventional resistance heaters. Additionally or alternatively, it is conceivable to blow in a suitably heated fluid, such as air, so that the respective elements reach the desired temperature.

[0026] An additional or alternative way to preheat the mold could, for example, be through deliberate partial absorption in the mold itself, on the order of a maximum of 5% of the microwave radiation, or through the transfer of energy to the mold from the steam generated during drying. It may be possible to remove the moisture through a forced air flow. This moisture can be either water vapor or water in its liquid form.

[0027] By forced removal, the humidity within the device can be kept low and condensation of the moisture or reheating of the moisture, for example of water droplets by microwave radiation, can be prevented.

[0028] In order to improve the drying and / or evaporation of moisture from the wet fiber-based blank, it may also be provided to rotate it during exposure to microwaves.

[0029] The energy input into the wet fiber-based blank is thus more uniform and overheating of individual parts of the blank can be avoided.

[0030] It may be possible to expose several blanks to microwaves simultaneously. For this purpose, several blanks, in particular several molds each containing one blank, may be introduced into the microwave chamber simultaneously. This reduces cycle time and enables more efficient use of the microwaves.

[0031] The blanks can be rotated around their own axis and / or around a common axis. This allows for more efficient use of the microwaves and a more even energy input into the blanks.

[0032] Additionally or alternatively, it would also be conceivable to provide one or more molds that can accommodate multiple blanks simultaneously. This simplifies the device, since not every blank needs to be handled individually when it is in a multiple mold. It has been determined that several individual molds, including blanks, can be arranged in any spatial arrangement in the microwave chamber. This arrangement has no influence on the uniformity of the energy input.

[0033] Additionally or alternatively, a rotating element, a so-called stirrer, may be provided, particularly within the microwave chamber or at the transition from a waveguide to the microwave chamber, to swirl the microwaves. A stirrer can disrupt the static propagation of the microwaves within the drying chamber, i.e., the microwave chamber, and minimize areas of high microwave intensity.

[0034] Such an arrangement also has a positive effect in terms of a uniform energy input.

[0035] Another way to improve quality is to apply microwaves in a timed fashion depending on the water content of the wet fiber-based blank. This timed fashion allows for a reduction in power. Typically, toward the end of the drying process, the water content in the wet fiber-based blank is lower, and excessive energy can cause the blank to overheat in certain areas. This can be prevented by reducing the power.

[0036] The microwave-transparent mold can be made of a material selected from the list of materials including PEI, PI, PE, POM, PEEK, wood, PTFE, ceramic, glass, and PP. The mold can be porous or solid with water-draining channels or made of a fine-mesh material.

[0037] A further aspect relates to a device for reducing the water content in a fiber-based blank, in particular for reducing the water content in a fiber-based blank according to a method as described here. The device has a microwave chamber for introducing a wet fiber-based container and at least one device for generating microwaves. The device also has a device for supplying and removing media from the microwave chamber. In particular, this involves the supply and removal of compressed air and moisture.

[0038] By means of such supply and removal devices it is possible to generate a specific air flow within the microwave chamber with which moisture, which is produced by exposure to microwaves, can be removed.

[0039] The device for generating microwaves can be connected to the microwave chamber by means of a waveguide.

[0040] This connection allows the device for generating microwaves to be arranged at a spatial distance from the microwave chamber and allows the microwave radiation generated by this device to be introduced into the microwave chamber in a targeted manner.

[0041] The waveguide preferably has a rectangular cross-section, with its longer side typically aligned in the direction of a longitudinal axis of the microwave chamber.

[0042] The longitudinal axis of the microwave chamber essentially corresponds to the longitudinal axis of the fiber-based blank or container. This is determined by a connection between a bottom of the blank and a pouring opening of the blank or container.

[0043] It may be provided to provide a stirrer within the microwave chamber, in particular at the transition between the waveguide and the microwave chamber, and to swirl the microwaves with this.

[0044] Additionally or alternatively, openings can be provided along the waveguide, which are connected to the microwave chamber and through which the microwaves can propagate into the microwave chamber. This allows for a reduced size of the entire unit.

[0045] The device may have a lid for closing the microwave chamber. In this case, an exhaust air opening may be arranged in the lid. This opening thus corresponds to a device for supplying and removing a medium from the microwave chamber, in particular compressed air and moisture.

[0046] A lid allows for easy closure of the microwave chamber and precise alignment of the exhaust air opening so that a targeted air flow can be generated within the device, i.e. within the microwave chamber.

[0047] It may be possible to provide multiple exhaust air openings. This increases capacity and allows for multiple airflows.

[0048] Additionally or alternatively, the microwave chamber may be divided so that the microwave chamber consists of two identical housing parts or of housing parts of different sizes and shapes.

[0049] The microwave chamber may additionally or alternatively have a floor. A plurality of openings are arranged in the floor for supplying air to the microwave chamber. These openings thus correspond to a device for supplying and removing a medium from the microwave chamber, in particular compressed air and moisture.

[0050] It can be provided that the device for reducing the water content in a fiber-based container has a plurality of devices for generating microwaves. Each of the plurality of devices for generating microwaves can be connected to the microwave chamber by a waveguide. The individual devices for generating microwaves can thus introduce the microwave radiation they generate into the microwave chamber at different points. At the same time, each of the devices can be controlled separately and emit microwave radiation at a different power level. The drying of the blank can be carried out in a correspondingly targeted manner, with different power levels being applied to it at different points if necessary, so that the drying process is uniform overall.Uniformly means in this case that the wet fiber-based container reaches a predefined water content, which is achieved simultaneously across the entire container.

[0051] For this purpose, it can be provided that the waveguides are arranged at different angles, and / or along the longitudinal axis at different heights and / or in relation to the longitudinal axis with different orientations of the longer side of the respective rectangular cross-section of the waveguide.

[0052] The device preferably comprises a holding device for a microwave-transparent mold. The microwave-transparent mold can thus be arranged within the device, in particular within the microwave chamber.

[0053] It may be possible to apply microwaves to several blanks simultaneously. For this purpose, the device may be provided with several holding devices to hold several molds in the microwave chamber simultaneously. This reduces cycle time and enables more efficient use of the microwaves.

[0054] The holding devices can each be configured to rotate about their own axis and / or about a common axis. This allows for more efficient use of the microwaves and enables a more uniform energy input into the blanks. Alternatively, it would also be conceivable to provide a holding device that can hold several molds simultaneously or a multiple mold. This simplifies the device, since each mold does not have to be manipulated individually when it is in the microwave chamber.

[0055] A blank can be designed as a container, in particular as a bottle, bowl, cup, (coffee) capsule, tray, or can. Furthermore, it is possible to produce closures for containers using the method according to the invention.

[0056] The process for reducing the water content in a wet fiber-based blank and a corresponding device are explained using schematic figures. It shows:

[0057] Figure 1 : A device before exposure to microwaves;

[0058] Figure 2: the device according to Figure 1 during exposure to microwaves;

[0059] Figure 3 : shows, by way of example, further typical fiber-based containers which can be produced by means of the method according to the invention;

[0060] Figure 4 shows an example of a typical fiber-based closure that can be produced by means of the method according to the invention.

[0061] Figure 1 shows a device 200 for reducing the water content in a fiber-based blank prior to exposure to microwaves. The fiber-based blank is a container 100 in the form of a bottle.

[0062] The device 200 has a microwave chamber 40 which is closed with a lid 41. In the lid 41 there is an exhaust air opening 42 through which compressed air and / or moisture, such as water or water vapor, can be discharged. The microwave chamber 40 also has a floor 43. In the floor there are a plurality of openings 44 through which supply air can be introduced into the microwave chamber 40. The device 200 also has a device 50 for generating microwaves. In the present case this is designed as a magnetron. The device 50 for generating microwaves is connected to the microwave chamber 40 by a waveguide 51. The waveguide 51 is rectangular.

[0063] In the device 200, a mold 20 is arranged within the microwave chamber 40. A wet fiber-based container 100 is arranged within the mold 20. This container was taken from a casting mold before being introduced into the mold 20 and currently has a water content of approximately 75%. After the wet fiber-based container 100 was introduced into the mold 20, an expandable tool 30 was introduced into the interior of the wet fiber-based container 100.

[0064] By expanding the expandable tool 30, the wall of the container 100 is pressed onto the inner wall of the mold 20 and the water or moisture contained in the wet fiber-based container 100 is partially pressed out. For this purpose, the mold 20 is designed to be permeable to water. The water permeability can be achieved with porosity; alternatively, individual channels or openings can be provided in the mold. The water can also be drained off through gaps or openings at the separation point of the mold. The escaping water or moisture is represented stylized as water droplets in the illustration according to Figure 1. These water droplets can drip onto the floor 43 of the microwave chamber and be discharged through the openings 44. After this step, the fiber-based container 100 has a water content of approximately 50%.Figure 2 shows the device according to Figure 1 during the exposure of the wet fiber-based container 100 to microwaves. Figure 2 therefore shows the actual drying process. In the device 50 for generating microwaves, microwaves are generated accordingly, which are introduced into the microwave chamber 40 through the waveguide 51. The microwaves heat up the moisture located in the fiber-based container 100; in other words, the molecules begin to vibrate. The moisture begins to evaporate and exits the container 100 through the microwave-permeable mold 20. In Figure 2, the expandable tool 30 is shown in the non-expanded state; however, it is possible for the expandable tool 30 to remain expanded even during the process shown here. The moisture, represented here stylized by wavy lines, enters the microwave chamber 40.To prevent this moisture from condensing in the microwave chamber 40, air is blown in through the openings 44 in the floor 43 of the microwave chamber 40. This blown-in air flows out of the microwave chamber 40 through the exhaust air opening 42. This creates a flow within the microwave chamber 40 through which the moisture can be removed from the microwave chamber 40.

[0065] In the present case, a holding device for the microwave-transparent mold 20 is formed as an integral component of the lid 41. However, it is also conceivable that, for example, the device 200 is formed in two parts, i.e., consists of two halves and, if appropriate, a separate base. In this case, the mold 20 can, for example, be held and pressed together by corresponding elements on the respective halves of the device 200.

[0066] Figure 3 shows, by way of example, further typical fiber-based containers that can be produced using the method described here. A container 100 can be seen that corresponds to the container 100 from the description of Figures 1 and 2. This container 100 is also in the shape of a bottle and additionally has a thread on the bottle neck. The container 100' is in the shape of a bowl, and the container 100'' is in the shape of a cup.

[0067] Figure 4 shows an example of a typical fiber-based closure 300 that can be manufactured using the method described herein.

Claims

Patent claims 1. Method for reducing the water content in a fiber-based blank, in particular in a container (100, 100' , 100'' ) or a fiber-based closure element (300) for a container (100) , comprising the steps - Providing a wet fiber-based blank, - Exposure of the wet fiber-based blank to microwaves, characterized in that the wet fiber-based blank is provided in a microwave-permeable press mold (20).

2. Method according to claim 1, characterized in that after the provision of the fiber-based blank, an expandable tool (30) is introduced into the fiber-based blank and the water content of the fiber-based blank is reduced by expansion.

3. Method according to one of claims 1 to 2, characterized in that the expandable tool (30) remains in the expanded state during exposure to microwaves.

4. Method according to one of claims 1 to 3, characterized in that the fiber-based blank is placed in a microwave-reflecting microwave chamber (40) before being subjected to microwaves.

5. Method according to one of claims 1 to 4, characterized in that the press mold (20) and / or the microwave chamber (40) is preheated to a temperature higher than 60°C and lower than 160°C.

6. Method according to one of claims 1 to 5, characterized in that moisture, in particular water vapor, is removed by a forced airflow. I. Method according to one of claims 1 to 5, characterized in that the fiber-based blank is rotated during exposure to microwaves.

8. Method according to one of claims 1 to 7, characterized in that the microwaves are applied in a timed manner depending on the water content of the fiber-based blank.

9. Method according to one of claims 1 to 8, characterized in that the microwaves, in particular within the microwave chamber (40), are swirled with a stirrer.

10. Method according to any one of claims 1 to 9, characterized in that the microwaveable press mold (20) is made of a material from the list comprising: PEI, PI, PE, POM, PEEK, wood, PTFE, ceramic, glass, PP. II. Device (200) for reducing the water content in a fiber-based blank, in particular according to a method according to one of claims 1 to 10, characterized in that the device has a microwave chamber (40) for introducing a wet fiber-based blank and at least one device (50) for generating microwaves, wherein the device (200) has a device for supplying and removing media from the microwave chamber, in particular for supplying and removing compressed air and moisture.

12. Device (200) according to claim 11, characterized in that the at least one device (50) for generating microwaves is connected to the microwave chamber by means of a waveguide (51).

13. Device (200) according to claim 11 or 12, characterized in that the device (200) has a cover (41) for The microwave chamber (40) is closed, wherein a vent opening (42) is arranged in the lid (41). The device (200) according to any one of claims 11 to 13, characterized in that the microwave chamber (40) has a base (43), wherein the base (43) has a plurality of openings (44) for supplying air to the microwave chamber (40). The device (200) according to any one of claims 11 to 14, characterized in that the device (200) has several microwave-generating devices (50), wherein each of the several microwave-generating devices (50) is connected to the microwave chamber (40) by a waveguide (51). The device (200) according to claim 15, characterized in that the waveguides (51) are connected to the microwave chamber (40) at different angles.Device (200) according to any one of claims 11 to 16, characterized in that the device has a holding device for a microwave-permeable press mold (20). Device (200) according to claim 17, characterized in that the microwave-permeable press mold (20) is made of a material from the list comprising: PEI, PI, PE, POM, PEEK, wood, PTFE, ceramic, glass, PP.

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