CH720862A2 - pulp for producing a fiber-based blank - Google Patents

Abstract

A pulp for producing a fiber-based blank is disclosed, in particular using a method for reducing the water content in the fiber-based blank, in particular in a container (100) or a fiber-based closure element for a container. The pulp comprises water and fibers. The pulp contains at least one additive that is sensitive to microwave radiation.

Description

[0001] 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. The invention also relates to a container made from pulp.

[0002] 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 introduced into an upside-down mold by injection and pressed against a corresponding wall in this mold using a flexible balloon and compressed accordingly. The pulp is pressed together and heated to a temperature of around 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 fibres and water, in particular natural fibres such as hemp fibres, cellulose fibres or flax fibres or a mixture thereof.

[0004] The aforementioned method is time-consuming and energy-intensive. It has therefore already been proposed to improve it. WO 2018/020219 A1 discloses another method for drying wet, fiber-based blanks. Here, too, the blanks are containers. Here, the wet pulp is also pressed together with a flexible balloon inside the mold. 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. The blank is very sensitive to force before drying and must be handled very carefully. During the drying process, the container can deform, for example due to uneven drying or caused by a non-uniform layer thickness, or it can be damaged by external influences. The moisture content in the blank can vary within the blank. The microwave radiation therefore has an uneven effect on the blank.

[0005] 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 independently of the water content during the drying process.

[0006] This object is achieved by the compositions and methods defined in the independent patent claims. Further embodiments emerge from the dependent patent claims.

[0007] 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.

[0008] The pulp is particularly intended for use in 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.

[0009] Substances that are sensitive to microwave radiation are substances whose molecules are caused to vibrate by the influence of microwave radiation.

[0010] 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 using a process for reducing the water content which uses microwave radiation in at least one drying step.

[0011] A pulp as described herein makes it possible to dry a fibre-based blank produced therefrom with microwave radiation, even if it has a relatively low and/or uneven moisture content.

[0012] In particular, during the drying process the water content becomes lower and lower, so that the drier the fiber-based blank is and thus the further the drying process has progressed, the fewer water molecules resonate and generate heat by absorbing the power of the microwaves. On the one hand, this can unnecessarily prolong the drying step, and on the other hand there is a risk that the fiber-based blank will overheat in certain places.

[0013] Preferably, the aggregate is present in a mass fraction that allows the power absorbed by the aggregate to be higher than the power absorbed by the water at a mass fraction of water of 30%. In other words, absorption shifts from the water to the aggregate during the drying process.

[0014] A method for reducing the water content in a fiber-based blank comprises in particular the following steps: - providing a wet fiber-based blank, - exposing the wet fiber-based blank to microwaves.

[0015] Preferably, the at least one additive is polar. Materials that are polar have a magnetic orientation. Such materials have an increased interaction with microwave radiation.

[0016] The aggregate is preferably selected from a list of aggregates comprising silicon ceramic, chitosan, kaolin, CaCO3, gypsum, lime, TiO2, Al2O3, aluminum silicate fibers and carbon nanotubes or a combination thereof.

[0017] The mass fraction of the aggregate is in particular between 0.1% and 20%.

[0018] This ensures that even at low water content there are enough molecules that can be set into vibration.

[0019] 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.

[0020] These are easy to obtain and are of uniform quality. In addition, these fibers can absorb water and/or the additives themselves, so that when irradiated with microwaves, heat can be generated not only between the fibers but also within the fibers.

[0021] Preferably, the mass fraction of the fibers in the pulp is between 0.5% and 4%, in particular between 1% and 1.5%. It goes without saying that the weight information with respect to the pulp refers to the state of the pulp before it is introduced into the mold.

[0022] 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 of - providing pulp with an additive, in particular a pulp as described here - forming a wet fiber-based blank, - exposing the wet fiber-based blank to microwaves.

[0023] In the present process, the wet fiber-based blanks are typically formed as already known in the prior art. In other words, pulp is introduced into a porous mold or into a solid mold with water-draining channels, the entrances of which 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. The wet fiber-based blank has a water content of approximately 75% at this point.

[0024] The fiber-based blank can then preferably be provided in a microwave-permeable mold.

[0025] By providing the fiber-based blank in a microwave-permeable 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 mold, it can also be achieved that it is accessible to the microwaves from all sides and drying can therefore be carried out from all sides. After this drying step, the wet fiber-based blank has a water content of approximately 5% to 12%. This is particularly useful if the blank is in the shape of a container, for example a bottle.

[0026] 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 a press mold.

[0027] The wet fiber-based blank is removed from the mold using a suitable transfer device. The wet fiber-based blank is then placed in the opened mold or, for example, placed on a conveyor belt. Blowing out 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.

[0028] Preferably, after the fiber-based blank has been provided in the press mold, an expandable tool is introduced 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. The wet fiber-based blank has a water content of approximately 50% - 60% at this point.

[0029] It can be provided that the expandable tool remains in the expanded state during the application of microwaves.

[0030] Pressure on the wall of the wet fiber-based blank can be maintained. In addition, by keeping the expandable tool inside the wet fiber-based blank, the blank is supported from the inside and undesirable deformation is prevented.

[0031] It is generally known that molecules can be excited to vibrate by means of microwaves and that this vibration generates heat. Water, for example, can be excited very well with microwaves at a frequency of 2.45 GHz.

[0032] In order to remove the water or residual moisture from the wet fiber-based blank, the water is preferably heated until it evaporates and diffuses accordingly from the wet blank.

[0033] The more water diffuses out of the wet blank, the less interaction there is. This interaction can be improved by 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.

[0034] The fiber-based blank can be rotated during exposure to microwaves, in particular around its own axis. This enables more efficient use of the microwaves and enables a more uniform energy input into the blank.

[0035] 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 places. This can be prevented by reducing the power. The additive still ensures that enough energy is introduced into the blank to evaporate the residual moisture, even if the power is reduced.

[0036] 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.

[0037] The pulp is provided in a storage container. It is also possible to add the additive to the pulp from the beginning or to mix it into the pulp stream when the pulp is removed from the storage container.

[0038] It may be provided, for example, that at the beginning of the introduction of the pulp into the mold, 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 comes to lie within the built-up wall.

[0039] Typically, however, a substantially homogeneous distribution is preferred.

[0040] A further aspect relates to a container made from pulp, in particular made from a pulp as described here. The container is preferably made in a process as described here. 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.

[0041] The mass fraction of water is preferably less than 8%. The container is thus stable and dimensionally stable.

[0042] 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.

[0043] A further aspect relates to the use of a microwave-sensitive additive in a pulp for producing a fibre-based blank to improve the interaction of microwave radiation and pulp. Figure 1: A device for reducing the water content in a fibre-based blank before exposure to microwaves; Figure 2: the device according to Figure 1 during exposure to microwaves; Figure 3: examples of further typical fibre-based containers that can be produced using the method according to the invention; Figure 4 examples of a typical fibre-based closure that can be produced using the method according to the invention.

[0044] Figure 1 shows a device 200 for reducing the water content in a fiber-based blank before exposure to microwaves. The fiber-based blank is in the present case a container 100 in the form of a bottle. The blank was made from a pulp which comprises water, fibers and 5% of the aggregate.

[0045] 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 base 43. A plurality of openings 44 are arranged in the base 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.

[0046] 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 was taken from a 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. 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 in the wet fiber-based container 100, or the moisture therein, is partially pressed out of it. 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 through gaps or openings at the separation point of the mold. The escaping water, or the escaping moisture, is shown in the representation according to Figure 1 in a stylized manner by water drops. These water drops 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%.

[0047] Figure 2 shows the device according to Figure 1 during the application of microwaves to the wet fiber-based container 100. 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 in the fiber-based container 100, in other words, the molecules start to vibrate. The moisture starts 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, but it is possible that the expandable tool 30 remains expanded during the process shown here. The moisture, shown 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.

[0048] Even if some of the moisture has already been removed, the molecules of the additive continue to vibrate, so that heat is still generated in the container 100. This means that it is heated evenly or remains warm, even if some of the moisture has already diffused out and, in relation to the moisture, the container is dry in some areas.

[0049] In the present case, a holding device for the microwave-permeable 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, if necessary, a separate base. In this case, for example, the mold 20 can be held and pressed together by corresponding elements on the respective halves of the device 200.

[0050] Figure 3 shows, by way of example, further typical fiber-based containers that can be produced using the method described here and from the pulp 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 also has a thread on the bottle neck. The container 100' is in the shape of a bowl, the container 100'' in the shape of a cup.

[0051] Figure 4 shows an example of a typical fiber-based closure 300 that can be produced using the method described herein and from the pulp described herein.

Claims (14)

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, CaCO3, gypsum, lime, TiO2, 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, - exposing 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 application of 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 10 or 11, 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 fibre-based blank to improve the interaction of microwave radiation and pulp.