Pulp for producing a fiber-based preform

Abstract

The invention relates to a pulp for producing a fiber-based preform, in particular using a method for reducing the water content in the fiber-based preform, in particular in a container or a fiber-based closure element for a container. The pulp contains water and fibers. The pulp contains at least one additive that is microwave-radiation-sensitive.

Description

[0001] Pulp for the production of a fiber-based blank

[0002] The present invention relates to a pulp for producing a fiber-based blank, in particular using a method for reducing the water content in the fiber-based blank. The blank is in particular a container or a closure element for a container.

[0003] The invention also relates to a container made of pulp.

[0004] 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.

[0005] Pulp is a mixture of fibers and water, especially natural fibers such as hemp fibers, cellulose fibers or flax fibers or a mixture thereof.

[0006] 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 deform, for example, due to uneven drying or a non-uniform layer thickness, or it may be damaged by external influences. The moisture content in the blank can vary within the blank. Accordingly, microwave radiation has a non-uniform effect on the blank.

[0007] It is therefore an object of the invention to remedy at least one of the disadvantages of the prior art. In particular, a pulp for producing a fiber-based blank, in particular using a method for reducing the water content in the fiber-based blank, is to be provided, which makes it possible to generate heat uniformly using microwave radiation, in particular regardless of the water content during the drying process.

[0008] This object is achieved by the compositions and methods defined in the independent patent claims. Further embodiments emerge from the dependent patent claims.

[0009] A pulp according to the invention for producing a fiber-based blank, in particular a container or a fiber-based closure element for a container, comprises water and fibers. In addition to these two components, the pulp contains at least one additive that is sensitive to microwave radiation.

[0010] The pulp is particularly intended for use in a process for reducing the water content in a fiber-based blank, in particular in a container or a fiber-based closure element for a container. Materials that are sensitive to microwave radiation are materials whose molecules are caused to vibrate under the influence of microwave radiation.

[0011] The addition of an additive which is sensitive to microwave radiation makes it possible to produce a fibre-based blank and, accordingly, a fibre-based container by means of a process for reducing the water content which uses microwave radiation in at least one drying step.

[0012] A pulp as described here makes it possible to dry a fiber-based blank produced therefrom with microwave radiation, even if the blank has a relatively low and / or uneven moisture content.

[0013] Particularly during the drying process, the water content decreases, so the drier the fiber-based blank is and thus the further the drying process progresses, the fewer water molecules resonate and generate heat by absorbing the microwave power. This can unnecessarily prolong the drying step, and on the other hand, there is a risk of the fiber-based blank overheating at certain points.

[0014] Preferably, the aggregate is present in a mass fraction such that, at a water mass fraction of 30%, the power absorbed by the aggregate is higher than that absorbed by the water. In other words, the absorption shifts from the water to the aggregate during the drying process.

[0015] A method for reducing the water content in a fiber-based blank comprises in particular the following steps:

[0016] - Providing a wet fiber-based blank,

[0017] - Exposing the wet fiber-based blank to microwaves. Preferably, the at least one additive is polar. Polar substances exhibit a magnetic orientation. Such substances exhibit increased interaction with microwave radiation.

[0018] The aggregate is preferably selected from a list of aggregates comprising silicon ceramic, chitosan, kaolin, CaCOa, gypsum, lime, TiOa, AI2O3, aluminum silicate fibers and carbon nanotubes or a combination thereof.

[0019] The mass fraction of the aggregate is in particular between 0.1 % and 20 % .

[0020] This ensures that even with a low water content there are enough molecules that can be set into vibration.

[0021] The fibers of the pulp are preferably selected from a list of fibers comprising hemp fibers, cellulose fibers, jute fibers, cotton fibers, bamboo fibers, bioplastic fibers and recycled fibers or a combination thereof.

[0022] These are easy to obtain and are of consistent quality. Furthermore, these fibers can absorb water and / or the additives themselves, so that when exposed to microwaves, heat can be generated not only between the fibers but also within them.

[0023] Preferably, the mass fraction of fibers in the pulp is between 0.5% and 4%, especially between 1% and 1.5%. It goes without saying that the weight specifications relating to the pulp refer to the state of the pulp before it is introduced into the mold.

[0024] A further aspect relates to a method for reducing the water content in a fiber-based blank, in particular in a container or a fiber-based closure element for a container. The method comprises the steps

[0025] - Providing pulp with an additive, in particular a pulp as described herein

[0026] - Forming a wet fiber-based blank,

[0027] - Exposure of the wet fiber-based blank to microwaves.

[0028] 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 wall of a blank, for example a container, 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. At this point, the wet fiber-based blank has a water content of approximately 75%.

[0029] The fiber-based blank can then preferably be provided in a microwave-permeable press mold.

[0030] By providing the fiber-based blank in a microwave-permeable press 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 against external influences and damage or deformation is prevented. By providing the wet fiber-based blank within the microwave-permeable press mold, it can also be achieved that it is accessible to the microwaves from all sides and drying can therefore be accomplished from all sides. After this drying step, the wet fiber-based blank has a water content of approximately 5% to 12%. This is particularly suitable if the blank is in the shape of a container, for example a bottle.

[0031] For blanks with smaller dimensions such as closures or with a substantially flat extension or lower requirements for dimensional stability, the drying process can also take place outside of a press mold.

[0032] The wet fiber-based blank is removed from the mold using a suitable transfer device. The wet fiber-based blank is then placed into the open mold or, for example, placed on a conveyor belt. 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.

[0033] Preferably, after the fiber-based blank has been prepared in the press mold, 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%.

[0034] It can be provided that the expandable tool remains in the expanded state during the application of microwaves.

[0035] Pressure can be maintained on the wall of the wet fiber-based blank. Furthermore, the expandable tool remains inside the wet fiber-based blank, providing internal support and preventing unwanted deformation.

[0036] It is generally known that microwave excitation can cause molecules to vibrate, generating heat. Water, for example, can be excited very effectively with microwaves at a frequency of 2.45 GHz.

[0037] In order to remove the water or the residual moisture from the wet fiber-based blank, the water is preferably heated until it evaporates and is accordingly removed from the wet blank.

[0038] The more water that escapes from the wet blank, the weaker the interaction. This interaction can be improved by the addition of the additive. In the present process, the molecules of the additive also vibrate and heat the blank evenly, so that the water evaporates evenly from the blank.

[0039] The fiber-based blank can be rotated during microwave exposure, particularly around its own axis. This allows for more efficient use of the microwaves and a more uniform energy input into the blank.

[0040] The microwaves can be applied in a timed manner depending on the water content of the wet fiber-based blank. The power can be reduced by the timed operation. Typically, towards the end of the drying process, the water content in the wet fiber-based blank is lower and too high a level of energy can lead to the blank overheating in certain areas. This can be prevented by reducing the power. The additive still ensures that sufficient energy is introduced into the blank to evaporate the residual moisture, even if the power is reduced. In particular, the microwaves can be applied in a timed manner depending on the composition of the pulp. The composition of the pulp can, or will, change during the drying process. Accordingly, the timing of the microwaves can also change over time.

[0041] The pulp is stored in a storage bin. The additive can be added to the pulp from the beginning or mixed into the pulp stream when the pulp is removed from the storage bin.

[0042] It may be provided, for example, that at the beginning of the introduction of the pulp into the casting mould it is introduced without any additive, so that for example the surface of the blank is essentially free of additive and the additive is only added later so that it lies within the built-up wall.

[0043] Typically, however, an essentially homogeneous distribution is preferred.

[0044] A further aspect relates to a container made from pulp, in particular made from a pulp as described herein. The container is preferably produced using a process as described herein. The container comprises water, fibers, and at least one additive, wherein the additive is sensitive to microwave radiation. This makes it possible to adjust the container to a specific water content in a prior process.

[0045] The mass fraction of water is preferably less than 8%. This makes the container stable and dimensionally stable.

[0046] The mass fraction of the aggregate in the container is preferably between 0.1% and 20%, in particular between 1% and 10%. This ensures that it does not impair the strength and / or quality of the container.

[0047] Another aspect concerns the use of a microwave-sensitive additive in a pulp for producing a fiber-based blank to improve the interaction of microwave radiation and pulp.

[0048] Figure 1: A device for reducing the water content in a fiber-based blank before exposure to microwaves;

[0049] Figure 2: the device according to Figure 1 during exposure to microwaves;

[0050] 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;

[0051] Figure 4 shows an example of a typical fiber-based closure that can be produced by means of the method according to the invention.

[0052] 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. The blank was produced from a pulp containing water, fibers, and 5% of the aggregate.

[0053] 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.

[0054] 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.

[0055] 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%.

[0056] 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.

[0057] Even if some of the moisture has already been dissipated, the molecules of the aggregate continue to vibrate, so that heat is still generated in the container 100. This results in the container being heated evenly or remaining warm, even if some of the moisture has already evaporated and, in terms of humidity, the container is dry in some areas.

[0058] In the present case, a holding device for the microwave-permeable press mold 20 is designed as an integral component of the lid 41. However, it is also conceivable that, for example, the device 200 is designed in two parts, i.e. consists of two halves and optionally of a separate base. In this case, for example, the press mold 20 can be held and pressed together by corresponding elements on the respective halves of the device 200. Figure 3 shows, by way of example, further typical fiber-based containers which can be produced by means of the method described here and from the pulp described here. A container 100 can be seen which 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, the container 100'' is in the shape of a cup.

[0059] Figure 4 shows an example of a typical fiber-based closure 300 that can be produced by the method described herein and from the pulp described herein.

Claims

Patent claims 1. Pulp for producing a fiber-based blank, in particular using a method for reducing the water content in the fiber-based blank, in particular in a container (100, 100', 100'') or a fiber-based closure element (300) for a container (100), wherein the pulp comprises water and fibers, characterized in that the pulp contains at least one additive which is sensitive to microwave radiation.

2. Pulp according to claim 1, characterized in that the at least one additive is polar.

3. Pulp according to claim 1 or 2, wherein the additive is selected from a list of additives comprising silicon ceramic, chitosan, kaolin, CaCOa, gypsum, lime, TiOa, Al2O3, aluminum silicate fibers and carbon nanotubes or a combination thereof.

4. Pulp according to one of claims 1 to 3, characterized in that the mass fraction of the additive is between 0.1% and 20%.

5. Pulp according to one of claims 1 to 4, wherein the fibers are selected from a list of fibers comprising hemp fibers, cellulose fibers, flax fibers, jute fibers, cotton fibers, bamboo fibers, bioplastic fibers and recycled fibers or a combination thereof.

6. Pulp according to one of claims 1 to 5, characterized in that the mass fraction of fibers in the pulp is between 0.5% and 4%, in particular between 1% and 1.5%.

7. 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 pulp with an additive, in particular pulp according to one of claims 1 to 7 - Forming a wet fiber-based blank, - Exposure of the wet fiber-based blank to microwaves.

8. The method according to claim 7, characterized in that the fiber-based blank is rotated during the exposure to microwaves.

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

10. Method according to one of claims 7 to 9, characterized in that the microwaves are applied in a timed manner depending on the composition of the pulp.

11. Container made from pulp, in particular from a pulp according to one of claims 1 to 7, preferably in a process according to one of claims 8 to 10, characterized in that the container comprises water, fibers and at least one additive, wherein the additive is sensitive to microwave radiation.

12. Container according to claim 11, characterized in that the mass fraction of water is less than 8%.

13. Container according to claim 11 or 12, characterized in that the mass fraction of the additive is between 0.1% and 20%, in particular between 1% and 10%.

14. Use of a microwave-sensitive additive in a pulp for producing a fiber-based blank for Improving the interaction of microwave radiation and pulp .

Images