Method and apparatus for reducing moisture content of cellulosic blanks

Abstract

A method and apparatus for reducing the moisture content of a fibrous blank are disclosed. The method comprises the following steps: providing a wet fibrous blank; -applying microwaves to the wet fibrous blank. The fibrous blank is provided in a microwave-transparent press mold (20).

Description

Technical Field

[0001] The invention relates to a method and a device for reducing the moisture content of a fibrous blank, in particular a method and a device for reducing the moisture content in a container or a fibrous closure element for a container according to the preamble of the independent claim. Background Art

[0002] WO 2012 / 139590 A1 discloses a fibrous blank in the form of a container. To produce such a container, so-called pulp is injected into an inverted mold and pressed against the corresponding wall layer by a flexible balloon in the mold and compressed accordingly. In the process, the pulp is compressed and heated to a temperature of about 180° C. in order to dry the container. It is also known to produce closure elements for containers from pulp.

[0003] Pulp is a mixture of fibers and water, in particular natural fibers such as hemp, cellulose or flax or mixtures thereof. The pulp may contain additives which improve the hardening of the compressed pulp or which influence the subsequent appearance or which generally change the properties of the pulp or of the subsequent container.

[0004] The above method is time-consuming and requires a lot of energy. Therefore, it has been suggested to improve it. WO 2018 / 020219A1 discloses another method for drying wet fibrous blanks. The blank here also refers to a container. Here, the wet pulp is also compacted in the mold with a flexible balloon. Next, the container pre-processed in this way together with the balloon located therein is demolded and placed on a conveyor belt. The balloon is removed from the cold-formed container. Next, microwaves are applied to the container to dry it. Before drying, the blank is very sensitive to forces and must be handled with great care. During the drying process, the container may be deformed, for example due to uneven drying or due to inconsistent wall thickness, or the container may be damaged due to external influences. Summary of the invention

[0005] The object of the present 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 which make it possible to dry wet fibrous blanks, in particular containers such as bottles, cups, bowls or plates or wet fibrous closure elements, with low energy consumption and in the process ensure that they remain dimensionally stable.

[0006] This object is achieved by the method and the device defined in the independent claims. Further embodiments are derived from the dependent claims.

[0007] A method for reducing the moisture content in a fibrous blank according to the invention, in particular a method for reducing the moisture content in a fibrous container or a closure element, comprises the following steps:

[0008] - providing a wet fibrous blank;

[0009] - Applying microwaves to the wet fibrous billet.

[0010] A fibrous blank is provided in a microwave-transmitting compression mold.

[0011] By providing the fibrous blank in a microwave-transparent pressing mold, the wet fibrous blank can be kept in the mold during the drying process, i.e. during the application of microwaves. This protects the container from external influences and avoids damage or deformation. By placing the wet fibrous blank in a microwave-transparent pressing mold, it is also achieved that the blank is exposed to microwaves on all sides and can then be dried on all sides. After this drying step, the moisture content of the wet fibrous blank is about 5% to 12%.

[0012] In the present method, the wet fibrous blank is usually formed according to methods known in the prior art. In other words, the pulp is poured into a porous mold or a solid mold with drainage channels, the input end of which is covered with a screen or has openings small enough to prevent the pulp fibers from penetrating, and the pulp fibers are deposited on the inner wall of the mold, thus forming a wall layer of the container. Once the wall layer thickness is sufficient, the alluvial deposition of the pulp is completed. The semi-finished product, i.e. the wet fibrous blank, is removed from the mold and placed in a pressing mold, microwave-proof so that it can be used in the pressing mold. At this point, the moisture content of the wet fibrous blank is about 75%.

[0013] The wet fibrous blank is removed from the casting mold using a suitable transfer device. Subsequently, the wet fibrous blank is placed in the open pressure mold. Preferably, the pressure mold is designed to consist of two parts. Here, it may be necessary to blow out and / or suck in the blank by means of negative pressure or overpressure for removal and insertion. For this transfer operation, purely mechanical grippers can also be used.

[0014] Typically, the compression mold can have an inner wall which has a better surface quality than the inner wall of the casting mold.

[0015] Preferably, after the fibrous blank is prepared, an expandable tool is placed in the fibrous blank. By expanding the expandable tool, the first step is to reduce the moisture content of the fibrous blank. At this time, the moisture content of the wet fibrous blank is about 50% to 60%.

[0016] At the same time, better surface properties can be achieved on the wet fibrous blank because, as mentioned above, a higher quality compression mold can be formed compared to an injection mold.

[0017] The expandable tool may be designed to remain expanded during the application of microwaves.

[0018] The wall pressure on the wet fibrous blank can be maintained. In addition, by retaining the expandable tool in the wet fibrous blank, the blank is supported from the inside and accidental deformation is avoided. In addition, this can also improve the surface quality of the blank.

[0019] Before the microwaves are applied, the fibrous blank can be placed in a microwave cavity which reflects the microwaves, in particular together with a pressing die.

[0020] This can enhance the effect of the microwaves. Microwaves that are not directly absorbed by the wet fibrous blanks are usually reflected on the inner walls of the microwave cavity, thereby increasing the probability that these microwaves hit the blanks that need to be dried.

[0021] It is well known that the excitation of microwaves can cause molecular vibrations, and heat is generated by such vibrations. For example, the natural frequency of water is 2.45 GHz. Therefore, microwaves are preferably generated at this frequency as well. In order to remove water or residual moisture from the wet fibrous blank, the water is preferably heated until it evaporates and accordingly escapes from the wet blank.

[0022] In order to accelerate the drying process, it can be provided that the press mold and / or the microwave cavity are preheated to a temperature higher than 60° C., but preferably lower than 160° C.

[0023] This also prevents the water escaping from the wet fibrous blank from condensing again in the immediate vicinity of the blank and condensing in the form of droplets.

[0024] For example, the heating can be carried out by conventional resistance heating. Additionally or alternatively, it is conceivable to blow in a corresponding heated fluid, such as air, so that the components reach the required temperature.

[0025] An additional or alternative method of preheating the mold can also be that the mold itself absorbs the microwave radiation partially in a targeted manner, up to a maximum of 5%, or by discharging the steam energy generated during drying toward the mold.

[0026] It can be designed to discharge moisture through strong exhaust. The moisture here can be water vapor, but it can also be liquid water.

[0027] By forced drainage, the moisture content inside the device can be kept low and condensation of the moisture or reheating of the moisture, for example by microwave radiation, can be avoided.

[0028] In order to better dry and / or evaporate the moisture in the wet fibrous blank, it can also be designed to rotate the blank during the application of microwaves.

[0029] In this way, the energy input to the wet fibrous blank is more uniform and overheating of local locations of the blank can be avoided.

[0030] It can be designed to apply microwaves to multiple blanks at the same time. To this end, it can be designed to put multiple blanks, especially multiple dies each having a blank, into the microwave cavity at the same time. This can shorten the cycle time and achieve more efficient use of microwaves.

[0031] The blanks can be rotated around their respective axes and / or around the same axis, which can improve the utilization efficiency of microwaves and input energy into the blanks more evenly.

[0032] Additionally or alternatively, it is also possible to consider designing one or more pressing dies that can simultaneously fill a plurality of blanks. This simplifies the device because if the blanks are located in a multi-cavity pressing die, each blank does not need to be operated separately.

[0033] A plurality of individual dies with blanks can be arranged in any spatial relationship to one another in the microwave cavity. This arrangement has no influence on the uniformity of the energy input.

[0034] Additionally or alternatively, it can be provided that a rotating element, a so-called stirrer, is arranged in particular inside the microwave cavity or at the transition from the waveguide to the microwave cavity and that the microwaves are swirled by means of this element. The stirrer can disrupt the static propagation of microwaves in the drying chamber, i.e. the microwave cavity, and minimize the microwave regions with higher intensity.

[0035] Such an arrangement also has a positive effect on uniform energy input.

[0036] Another way to improve quality is to time the microwave application according to the moisture content of the wet fibrous blank. Timing can reduce power consumption. Usually, the moisture content in the wet fibrous blank is low near the end of the drying process, and too much energy may cause the blank to overheat in certain places. This can be avoided by reducing the power.

[0037] Microwave-transparent stamps can be made from a range of materials including polyetherimide, polyimide, polyethylene, polyoxymethylene, polyetheretherketone, wood, polytetrafluoroethylene, ceramic, glass and polypropylene. Stamps can be designed to be porous, or solid with channels for moisture drainage, or designed with fine mesh materials.

[0038] Another aspect relates to a device for reducing the moisture content of a fibrous blank, in particular a device for reducing the moisture content of a fibrous blank according to the method described herein. The device has a microwave cavity for placing a wet fibrous container and at least one device for generating microwaves. In addition, the device also has a device for supplying a medium into the microwave cavity and discharging a medium from the microwave cavity. In particular, this involves the supply and discharge of compressed air and moisture.

[0039] By means of such an input device and a discharge device, a specific airflow can be formed inside the microwave cavity, whereby the moisture generated by applying microwaves can be discharged.

[0040] The device for generating microwaves can be connected to the microwave cavity by means of a waveguide.

[0041] By means of this connection, the device for generating microwaves can be arranged at a certain spatial distance from the microwave cavity, and the microwave radiation generated by the device can be introduced into the microwave cavity in a targeted manner.

[0042] Preferably, the waveguide has a rectangular cross section, wherein its longer side is generally oriented in the direction of the longitudinal axis of the microwave cavity. The longitudinal axis of the microwave cavity substantially coincides with the longitudinal axis of the fibrous blank or the container. The longitudinal axis is determined by the connection between the blank bottom and the blank or container gate.

[0043] It can be designed that a stirrer is arranged inside the microwave cavity, especially at the transition between the waveguide and the microwave cavity, and the microwaves are swirled by the stirrer.

[0044] Additionally or alternatively, openings connected to the microwave cavity may be arranged along the waveguide, and microwaves may propagate into the microwave cavity through these openings. This can reduce the structural size of the entire unit.

[0045] The device can have a cover plate for closing the microwave cavity. In this case, an exhaust opening can be arranged in the cover plate. Therefore, the opening is equivalent to a medium input and discharge device of the microwave cavity, in particular an input and discharge device for compressed air and moisture.

[0046] The cover plate can realize convenient sealing of the microwave cavity and accurate orientation of the exhaust port, so that a directional airflow can be generated in the device, that is, in the microwave cavity.

[0047] It can be designed to have multiple exhaust ports, which increases the capacity on the one hand and provides multiple airflows on the other.

[0048] Additionally or alternatively, the microwave cavity can be divided such that the microwave cavity consists of two identical housing parts or of housing parts of different size and shape.

[0049] Additionally or alternatively, the microwave cavity may have a base plate. A large number of openings are arranged in the base plate for supplying air to the microwave cavity. These openings thus serve as a medium input and discharge device for the microwave cavity, in particular an input and discharge device for compressed air and moisture.

[0050] The device for reducing the water content of the fiber container can be designed to have a plurality of devices for generating microwaves. Each of the plurality of devices for generating microwaves can be connected to the microwave cavity through a waveguide.

[0051] In this way, the various devices for generating microwaves can feed the generated microwave radiation into the microwave cavity at different locations. Each device can be controlled individually and emit microwave radiation at different powers. Accordingly, the drying of the blank can be carried out in a targeted manner, wherein, if necessary, microwaves can also be applied at different powers at different locations, so that the drying process can be carried out uniformly overall. In this case, uniform means that the wet fibrous container reaches a predetermined moisture content simultaneously over the entire container.

[0052] For this purpose, the waveguides may be arranged at different angles and / or at different heights along the longitudinal axis and / or the waveguides may have different orientations of the longer sides of their rectangular cross sections when arranged relative to the longitudinal axis.

[0053] Preferably, the device has a fixing device for the microwave-transparent die. In this way, the microwave-transparent die can be arranged inside the device, especially the microwave cavity.

[0054] It can be designed to apply microwaves to multiple blanks at the same time. To this end, the device can be designed to have multiple fixing devices so as to fix multiple dies in the microwave cavity at the same time. This can shorten the cycle time and achieve more efficient use of microwaves.

[0055] The fixing devices can be respectively designed to rotate around respective axes and / or around the same axis. This can improve the utilization efficiency of microwaves and can input energy into the blank more evenly.

[0056] Alternatively, it is also possible to consider designing a fixture that can fix a plurality of pressing dies or can fix a multi-cavity pressing die at the same time. This simplifies the device because if the pressing die is located in the microwave cavity, each pressing die does not need to be operated separately.

[0057] The blank can be configured as a container, in particular a bottle, a dish, a cup, a (coffee) capsule, a tray or a can. In addition, container closures can be processed by means of the method according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] A method for reducing the moisture content of wet fibrous raw materials and a corresponding device are explained with the aid of schematic diagrams. In the drawings:

[0059] Figure 1 : A device before applying microwaves;

[0060] Figure 2 : shows the period of microwave application Figure 1The device shown;

[0061] Figure 3 : Schematically shows other typical fibrous containers that can be produced using the method of the present invention;

[0062] Figure 4 : A typical fibrous bottle cap that can be produced using the method described in the present invention is shown by way of example. DETAILED DESCRIPTION

[0063] Figure 1 The device 200 for reducing the moisture content of a fibrous blank before applying microwaves is shown. In this example, the fibrous blank is a bottle-shaped container 100.

[0064] The device 200 has a microwave cavity 40 which is closed by a cover plate 41. An exhaust port 42 is provided in the cover plate 41, through which compressed air and / or moisture (e.g. water or water vapor) can be discharged. The microwave cavity 40 also has a bottom plate 43. A large number of openings 44 are arranged in the bottom plate, through which the supplied air can be introduced into the microwave cavity 40. The device 200 also has a device 50 for generating microwaves. In this example, the device 50 is designed as a magnetron. The device 50 for generating microwaves is connected to the microwave cavity 40 via a waveguide 51. The waveguide 51 is designed in a rectangular shape.

[0065] In the device 200, a die 20 is arranged in a microwave cavity 40. A wet fibrous container 100 is arranged inside the die 20. The container 100 has been taken out of a casting mold before being placed in the die 20, and the water content at this time is about 75%. After the wet fibrous container 100 is placed in the die 20, an expandable tool 30 is placed inside the wet fibrous container 100. Through the expansion of the expandable tool 30, the wall of the container 100 is pressed onto the inner wall of the die 20, and the water in the wet fibrous container 100 or the moisture therein is partially squeezed out therefrom. For this purpose, the die 20 is designed to be water-permeable. The water permeability can be achieved by porosity, alternatively, various channels or openings can be designed in the die. Water can also be discharged through the gaps or openings on the demolding portion of the die. The discharged water or the discharged moisture is discharged in Figure 1 The water droplets are shown in simplified form in FIG. These water droplets can drip onto the bottom plate 43 of the microwave cavity and be discharged through the opening 44. After this step, the water content of the fibrous container 100 is about 50%.

[0066] Figure 2 The wet fibrous container 100 is shown during the application of microwaves. Figure 1 That is, Figure 2The actual drying process is shown. Microwaves are generated in the device 50 for generating microwaves and are fed into the microwave cavity 40 via the waveguide 51. The water in the fibrous container 100 is heated by the microwaves, in other words, the molecules begin to vibrate. The water begins to evaporate and is discharged from the container 100 through the microwave-transparent die 20. Figure 2 In the figure, the expandable tool 30 is shown in an unexpanded state, but the expandable tool 30 can also remain in an expanded state during the process shown here. The moisture shown here by the wavy lines enters the microwave cavity 40. In order to prevent this moisture from condensing in the microwave cavity 40, air is blown in through the opening 44 in the bottom plate 43 of the microwave cavity 40. The blown air flows out of the microwave cavity 40 through the exhaust port 42. In this way, an air flow is formed inside the microwave cavity 40, and the moisture can be discharged from the microwave cavity 40 through this air flow.

[0067] In this example, the fixing device of the microwave-transparent die 20 is designed to be integral with the cover plate 41. However, it is also conceivable that the device 200 is designed to be composed of two parts, that is, two halves and, if necessary, a separate bottom plate. In this case, the die 20 can be fixed and pressed together by corresponding elements on each half of the device 200.

[0068] Figure 3 Other typical fibrous containers that can be produced using the methods described herein are shown by way of example. For example, container 100 can be seen, which is similar to Figure 1 and 2 The container 100 described is consistent. The container 100 is also bottle-shaped and additionally has a thread at the neck. The container 100 'is in the form of a bowl, while the container 100" is in the form of a cup.

[0069] Figure 4 A typical bottle cap 300 that may be produced using the methods described herein is shown schematically.

Claims

1. A method for reducing the moisture content of a fibrous blank, in particular a method for reducing the moisture content of a container (100, 100', 100") or a fibrous closure element (300) for a container (100), comprising the following steps: - providing a wet fibrous blank; - applying microwaves to the wet fibrous blank, It is characterized in that A wet fibrous blank is provided in a microwave-transmissive compression mold (20).

2. The method according to claim 1, characterized in that After the fibrous blank is provided, an expandable tool (30) is placed in the fibrous blank and reduces the water content of the fibrous blank by expansion.

3. The method according to any one of claims 1 to 2, characterized in that The expandable tool (30) remains in an expanded state during the application of microwaves.

4. The method according to any one of claims 1 to 3, characterized in that Before applying microwaves, the fibrous blank is placed in a microwave cavity (40) that reflects microwaves.

5. The method according to any one of claims 1 to 4, characterized in that The die (20) and / or the microwave cavity (40) are preheated to a temperature higher than 60°C and lower than 160°C.

6. The method according to any one of claims 1 to 5, characterized in that Remove moisture, especially water vapor, through strong exhaust ventilation.

7. The method according to any one of claims 1 to 5, characterized in that The fibrous blank was rotated during the application of microwaves.

8. The method according to any one of claims 1 to 7, characterized in that The microwaves are applied at a timed interval depending on the moisture content of the fibrous blank.

9. The method according to any one of claims 1 to 8, characterized in that The microwaves are vortexed by a stirrer, particularly in the microwave cavity (40).

10. The method according to any one of claims 1 to 9, characterized in that The microwave-transparent stamp (20) is made of one of the materials in the following table: polyetherimide, polyimide, polyethylene, polyoxymethylene, polyetheretherketone, wood, polytetrafluoroethylene, ceramic, glass, polypropylene.

11. A device (200) for reducing the moisture content of a fibrous blank, in particular a device for reducing the moisture content of a fibrous blank according to the method according to any one of claims 1 to 10, characterized in that: The device comprises a microwave cavity (40) for placing wet fibrous blanks and at least one device (50) for generating microwaves, wherein the device (200) comprises a device for adding and discharging a medium into and from the microwave cavity, in particular a device for adding and discharging compressed air and moisture.

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

13. The device (200) according to claim 11 or 12, characterized in that The device (200) comprises a cover (41) for closing the microwave cavity (40), wherein an air outlet (42) is arranged in the cover (41).

14. The device (200) according to any one of claims 11 to 13, characterized in that The microwave cavity (40) has a bottom plate (43), wherein the bottom plate (43) has a large number of openings (44) for applying air to the microwave cavity (40).

15. The device (200) according to any one of claims 11 to 14, characterized in that The device (200) comprises a plurality of devices (50) for generating microwaves, wherein each of the plurality of devices (50) for generating microwaves is connected to the microwave cavity (40) via a waveguide (51).

16. The device (200) according to claim 15, characterized in that The waveguide tube (51) is connected to the microwave cavity (40) at different angles.

17. The device (200) according to any one of claims 11 to 16, characterized in that The device comprises a fixing device for the microwave-transmitting die (20).

18. The device (200) according to claim 17, characterized in that The microwave-transparent stamp (20) is made from one of the materials in the following table: polyetherimide, polyimide, polyethylene, polyoxymethylene, polyetheretherketone, wood, ceramic, glass, polypropylene.

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