Method for manufacturing article at least partially made of cellulosic fibres and article at least partially made of cellulosic fibres

Abstract

A method for manufacturing an article (62) at least partially made of cellulosic fibres, the method comprising the steps of: a. Inserting a cellulose pulp (20) comprising cellulosic fibres and water into a mixing chamber; b. Applying a high shear mixing action to the cellulose pulp (20) using a high shear mixer (28) such that a foam mixture comprising cellulose fibres, water and air bubbles is produced; c. Inserting the foam mixture into the mold cavity (334); d. Moulding the article (62) by heating the foam mixture contained in the mould cavity.

Description

Technical Field

[0001] According to the preambles of the independent claims, the invention relates to a method for producing an article at least partially made of cellulose fibers and to an article at least partially made of cellulose fibers. Background Art

[0002] WO2021 / 262467 A1 discloses protective packaging and a method for preparing the same. More specifically, it discloses producing a foam made of wood fiber, a binder, a surfactant and water. The foam is placed in an oven and heated using microwaves. EP2841649 B1 relates to a fiber web of paper using a foam comprising water and cellulose fibers. Summary of the invention

[0003] The object of the present invention is to provide a method for producing an article at least partially made of cellulose fibers and to provide an article at least partially made of cellulose fibers which has a three-dimensional shape and is low in weight.

[0004] This object is achieved by a method for producing an article at least partially made of cellulose fibers and an article at least partially made of cellulose fibers, the method and the article having the features of the independent claims. Further embodiments are given in the dependent claims.

[0005] The method according to the present invention allows the production of products comprising an inner core part and an outer skin part, wherein the density of the cellulose fiber material in the inner core part is lower than the density of the cellulose fiber material in the outer skin part. Therefore, this product has a relatively high stiffness of the outer skin part, but at the same time has a relatively low-density inner core part. The term "low density" of the inner core part includes zero density (i.e., voids) and a density that is not zero density but is significantly lower than the outer skin part. In short, the product according to the present invention has a relatively low weight. In addition, since the product is molded, it has a defined and desired three-dimensional shape.

[0006] The articles produced by the method of the invention also have the following characteristics: improved softness of the surface created by the low density, which prevents sensitive products from being scratched during their transportation. In addition, using the method of the invention, the cycle time required to produce the articles is shorter than that of the prior art methods. Finally, the method of the invention allows the production of articles with relatively thick parts and relatively thin other parts, all in the same manufacturing process. For example, in the same article, the thickness can vary by a factor of 5, more preferably by a factor of 10.

[0007] More specifically, the present invention proposes a method for manufacturing an article made of cellulose fibers. For example, the cellulose fibers can be obtained from paper, preferably from used paper. It should be noted that the term "paper" includes cartons, cardboard, etc., and can be a product made from an assembly of natural fibers (such as softwood, hardwood, flax, hemp and cotton), in which fibers of different lengths can be mixed. Preferably, the paper is provided in the form of a paper sheet. The method comprises a first step, as a first step, a cellulose pulp comprising cellulose fibers and water is inserted into a mixing chamber, such as a mixing volume or a mixing container. The cellulose pulp can be obtained by a previous pulping step, in which the above-mentioned paper sheet is combined with a large amount of water to separate the fibers from each other, so that a cellulose pulp slurry ("cellulose pulp") is produced.

[0008] In a subsequent step of the method of the present invention, a high shear mixer is used to apply high shear mixing to the cellulose pulp. For example, such a high shear mixer may include an external fixed cylindrical stator and an internal rotatable rotor. The outer surface of the rotor is very close to the inner surface of the stator, with only a very small radial gap between the two surfaces, and the rotor rotates at a very high speed. This results in applying high shear to the cellulose pulp between the inner surface of the stator and the outer surface of the rotor. The application of high shear mixing produces a foam mixture including cellulose fibers, water and bubbles.

[0009] High shear is very important to produce dispersion of the fibers in the foam and ultimately to obtain a fiber network. High intensity energy is required to overcome the adhesion forces between the cellulose fibers. This high energy input can best be provided by a high shear mixer.

[0010] In a further subsequent step of the method according to the invention, the foam mixture is inserted into the mold cavity. This method step can be similar to method steps known from other molding techniques, such as injection molding, in which an injection nozzle is arranged in the wall of the mold in order to inject the foam mixture into the mold cavity.

[0011] In another subsequent step of the method of the invention, the article is molded by heating the foam mixture contained in the mold cavity. Again, this method step can be similar to known molding methods. For example, heat can be applied to the foam mixture by heating the mold surface of the mold and / or by blowing hot gas into the mold cavity. The purpose of the heating step is mainly to remove any residual liquid water and humidity from the foam mixture so that the cellulose fibers can adhere to each other mainly through natural hydrogen bonds. This produces a solid, dry, three-dimensional molded body made at least partially of cellulose fibers.

[0012] In another embodiment, water is at least partially drained from the foam mixture before or during step d (heating step). This reduces the amount of water in the foam mixture contained in the cavity. Only a minimum amount of water remains, allowing a water film to be maintained around the bubbles of the foam. By doing so, the final quality of the article is improved.

[0013] In another embodiment of the present invention, water is partially discharged through at least a portion of the wall surrounding the mold cavity. For example, a plurality of discharge holes can be provided in the wall, which are large enough to allow water to pass through and small enough to prevent the entry of cellulose fibers. Preferably, the discharge holes are provided at the bottom of the mold so that the water can be discharged by gravity. This other embodiment significantly reduces the amount of water in the form of steam that must be removed in the subsequent steps of the manufacturing process, thereby reducing the energy and cycle time required to produce the article. However, it should be understood that in most applications, the water contained in the foam cannot be completely removed by drainage, so it is necessary to remove the remaining water and moisture in the form of steam by heating, which also requires a breathable mold wall. It should be understood that the discharge holes can also be located on the side of the mold, for example, in the case where the mold rotates around the axis of rotation, thereby generating a centrifugal force that causes the water to leave the mold cavity in the direction of the centrifugal force.

[0014] In another embodiment, the gas pressure difference between the volume inside the mold cavity and outside the mold cavity is controlled at least temporarily. Preferably, the gas pressure difference is of the type in which the gas pressure inside the mold cavity is higher than the gas pressure outside the mold cavity. This can be achieved by applying an overpressure inside the mold cavity or by applying suction outside the mold cavity. For example, the suction can be applied through the above-mentioned discharge holes in the mold wall.

[0015] This type of pressure difference helps to expel the remaining water and push the cellulosic fiber material toward the wall of the mold, so that the density of the material near the wall of the mold becomes higher than the density of the material far from the wall of the mold. This results in the final product comprising an inner core portion and an outer skin portion, wherein the density of the cellulosic fiber material in the inner core portion is lower than the density of the cellulosic fiber material in the outer skin portion.

[0016] In another embodiment herein, the air permeability of the first wall portion of the mold cavity is different from the air permeability of the second wall portion. For example, the number of vents per surface area in the wall of the mold can be different from one wall portion to another. This allows the manufacture of an article having a density of the first area of ​​the outer skin portion that is different from the density of the second area of ​​the outer skin portion.

[0017] In another embodiment, an object is inserted into the mold cavity before step d, which includes that the object may be inserted before step c. The object may be a plastic film (e.g., comprising PE) in the form of, for example, a plastic bag, which is airtight and / or liquid-tight. This allows the manufacture of an article comprising an airtight and / or liquid-tight cavity and an outer wall made of cellulose fibers and having a buffering capacity. As another example, the object may be an article to be transported, and the object is protected from environmental hazards, such as mechanical impacts, by the cellulose fiber article. Thus, the article made of cellulose fibers contains the article to be transported.

[0018] In another embodiment, the foam mixture contained in the mold cavity is heated by high frequency electromagnetic radiation. This is a very effective method of heating the foam mixture without the need to insert hot gas or steam into the mold cavity. With the method of the present invention, heating by electromagnetic radiation is possible because even after the above-mentioned discharge step, the foam mixture still contains sufficient humidity to allow heating by electromagnetic radiation (such as microwaves). In addition, it has been observed that drying the foam of the pulp at a high frequency causes the bubbles in the core of the material to expand. As a result, the cellulose fibers are pushed against the air permeable surface of the mold.

[0019] In another embodiment, surfactants, pigments and / or additives (e.g., affecting thermal properties) are added to the cellulose pulp before or during step b (high shear mixing). This allows the cellulose pulp to be designed and adapted to the specific needs of the product to be manufactured. More specifically, the product can obtain a desired color and / or desired thermal insulation properties. In addition, surfactants can reduce the surface tension of water and thus reduce the internal cohesion of water. This allows the physical properties of the foam to be adjusted according to the requirements of the specific application. Another additive can improve the bonding between fibers. Another additive can migrate to the surface to produce a soft touch. The advantage of the proposed technology is the ability to mix short fibers with longer fibers. The short fibers migrate to the surface to provide a soft touch, while the longer fibers provide the desired mechanical properties through effective entanglement of the fibers.

[0020] In another embodiment, the mold has an elevated temperature at least partially when the foam mixture is inserted. This helps to create a skin portion in the molded article that has a much higher density than the core portion. In addition, this helps to remove liquid water from the foam mixture.

[0021] As described above, the present invention allows the manufacture of an article made of a nonwoven cellulosic fibrous material, the article comprising an inner core portion and an outer sheath portion, wherein the density of the cellulosic fibrous material in the inner core portion is lower than the density of the cellulosic fibrous material in the outer sheath portion.

[0022] With such an article, the density gradient in the transient region between the core portion and the skin portion is preferably below about 5000 kg / m³·cm, preferably below about 1500 kg / m³·cm. This means that the density of the article produced according to the invention provides a fairly smooth density change from the inner core portion to the outer skin portion. This increases the overall stability of the article of the invention and provides excellent cushioning properties.

[0023] In another embodiment, the density of the first area of ​​the outer skin portion is different from the density of the second area of ​​the outer skin portion. As described above, this can be achieved by having a mold that has different air permeabilities when viewed in the transverse direction. Thus, an article having these features has skin portions adjacent to each other that have different densities and therefore different stiffness and / or different tactile properties.

[0024] In another embodiment, the article comprises a film material. In another embodiment herein, the film material forms a closable or closed cavity inside the article. As described above, therefore, such an article can form a type of bottle or container with an outer soft cushioning wall.

[0025] In another embodiment, the thickness of the skin portion is at least 5 mm. Thus, the articles and methods of the present invention can have a skin of considerable thickness that provides excellent stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Embodiments of the present invention will now be described with reference to the accompanying drawings. Figure 1 is a flow chart of a method for making an article made at least in part from cellulose fibers; Figure 2 is Figure 1 Schematic diagram of a high shear mixing device used in the method; Figure 3 is used Figure 1 A front view of a first embodiment of an article manufactured by the method; Figure 4 is similar to Figure 3 A view of a second embodiment of an article of manufacture; Figure 5 yes Figure 4 A schematic cross-sectional side view of an article of; Figure 6 It is shown Figure 4 A graph of the density of an article along its transverse extension; Figure 7 yes Figure 3 A schematic cross-sectional side view of an article of; Figure 8 It is shown Figure 3 A graph of the density of an article along its transverse extension; Fig. 9 is a schematic cross-sectional side view of another embodiment of an article; Fig.10 is a schematic cross-sectional side view of another embodiment of an article; and Fig.11 is a schematic cross-sectional side view of another embodiment of an article.

[0027] In the following, functionally equivalent elements and parts will be denoted by the same reference numerals in different embodiments and figures. DETAILED DESCRIPTION

[0028] The method for manufacturing an article made of cellulose fibers starts at the start block 10. In functional block 12, cellulose fibers and water provided in functional block 14 are brought together to form an initial cellulose pulp. In functional block 16, the initial cellulose pulp is refined by adding further components, such as surfactants, pigments and / or additives, the latter, for example, influencing the thermal properties of the cellulose pulp. These further components are provided in functional block 18. As a result of the refining step in block 16, a cellulose pulp slurry is obtained in functional block 20.

[0029] In the subsequent functional block 22, the pulp 20 is inserted into a mixing chamber provided in the functional block 24. Thereafter, a high shear mixing action is applied to the cellulose pulp 20 in the functional block 26 using a high shear mixer provided in the functional block 28. By means of this high shear mixing action, a foam mixture comprising cellulose fibers, water and air bubbles is obtained in the functional block 30.

[0030] Subsequently, in functional block 32, the foam mixture 30 is inserted into a mold cavity, which is provided in functional block 34. Optionally, an object may have been inserted into the mold cavity 34 before the foam mixture 30 is inserted into the mold cavity 34, such an object being provided in functional block 36. The object may be an object protected by an article made of cellulose fibers, or the object may include an airtight and / or fluid-tight plastic film, for example in the form of a bag, forming the inner surface of the cavity. The plastic film may be solid / rigid so as to provide a defined shape of the cavity.

[0031] Subsequently, the liquid water contained in the foam mixture 30 is drained in a functional block 38. Preferably, the water is at least initially drained by gravity. To allow the water to drain by gravity, the wall of the mold may include a large number or a plurality of drain openings that are large enough to allow the water to pass through, but small enough to prevent the cellulosic fibers from entering. The drain openings are preferably arranged in the lower part of the mold.

[0032] In functional step 40, a gas pressure difference between the interior of mold cavity 34 and the exterior of mold cavity 34 is at least temporarily applied. For example, a negative pressure or suction may be applied outside mold cavity 34 so that, on the one hand, water is drawn out of mold cavity 34 and, on the other hand, cellulose fibers within mold cavity 34 move toward and press against the inner wall of mold cavity 34. The air permeability of the first wall portion of mold cavity 34 may be different from the air permeability of the second wall portion. The air permeability may be provided at least in part by the above-mentioned vent.

[0033] In functional step 42, the foam mixture 30 in the mold cavity 34 is heated by applying high frequency electromagnetic radiation, such as microwaves. The high frequency electromagnetic radiation is provided in functional block 44. It will be appreciated that the material of the walls of the mold must be chosen such that it can be penetrated by the high frequency electromagnetic radiation.

[0034] The heating step 42 increases the temperature of the foam mixture 30 within the mold cavity 34, which causes the water in the foam mixture 30 to evaporate and leave the mold cavity 34 through the above-mentioned drain port. This leads to a drying step 46, in which the cellulose fibers adhere to each other mainly through hydrogen bonds. Finally, the mold is opened in functional block 48, and the method ends in functional block 50.

[0035] Figure 2 The high shear mixing device provided in the functional block 28 described above is shown in more detail. In the present exemplary embodiment, the high shear mixing device 28 may include an outer fixed cylindrical stator 52 and an inner rotatable rotor 54. The rotor 54 includes a plurality of radially extending rotor blades 56. The radially outer surface 58 of the rotor blades 56 is very close to the inner surface of the stator 52, with only a very small radial gap between the two surfaces. The rotor 54 rotates around the rotation axis 60 at a very high rotational speed. This results in a high shear action being applied to the cellulose pulp 20 within the gap and produces the above-mentioned foam mixture 30 including cellulose fibers, water and bubbles.

[0036] pass Figure 1 The product 62 obtained by the method described in Figure 3 or Figure 4 The article 62 is at least partially made of cellulose fibers 64 and includes an inner core portion 66 and an outer sheath portion 68. The density of the material formed of cellulose fibers 64 in the inner core portion 66 is lower than the density of the material formed of cellulose fibers 64 in the outer sheath portion 68.

[0037] exist Figure 3 In the article 62, the outer skin portion 68 has a relatively large thickness, which may be 5 mm or more. Figure 3 and 4In those embodiments, the density of the material formed by the cellulose fibers 64 in the inner core portion 68 is very low, such as close to zero. Or, in other words, in Figure 3 and 4 In the inner core portion 68 of the article 64, there is almost no material formed by the cellulose fibers 64. However, there may be a transient region 70 between the inner core portion 66 and the outer skin portion 68, and within the transient region 70, the density of the material formed by the cellulose fibers 64 gradually increases from the inner core portion 66 to the outer skin portion 68.

[0038] like Figure 5 In the embodiment schematically shown, the thickness of the outer skin portion 68 is relatively low, for example, one tenth of a millimeter, and the thickness of the transient region 70 can be equally relatively low, for example, a few millimeters. In this case, the density gradient 72 ( Figure 6 ) may be in the order of magnitude between 1000 kg / m³·cm and 2000 kg / m³·cm, lower than about 5000 kg / m³·cm, preferably lower than about 1500 kg / m³·cm, for example 1200 kg / m³·cm.

[0039] for Figure 7 An embodiment of Figure 5 The thickness of the transient region 70 is relatively high compared to the transient region 70 of FIG. Figure 8 ) can be in the order of magnitude between 100 kg / m³·cm and 500 kg / m³·cm, for example 200 kg / m³·cm.

[0040] exist Figure 1 In the method of FIG. 1 , functional block 32 is described, wherein an object 36 is inserted into a mold cavity 34 prior to inserting the foam mixture 30 . Fig. 9 0 represents an example of a final molded article 62 made of cellulose fibers 64 and including an object 36. In this embodiment, the object 36 is completely surrounded by the article 62 and is therefore protected by the article 62 from mechanical impacts that may occur, for example, during transportation of the object 36 and the article 62. When the object 36 reaches its destination, the article 62 made of cellulose fibers 64 can be easily broken / opened to remove the article 62 from its envelope.

[0041] exist Fig.10 In the embodiment of FIG. 3 , the object 36 is formed of a plastic film in the form of a solid / rigid hemisphere.

[0042] In with Figure 5 An embodiment similar to Fig.11 In the embodiment of FIG. 6 , the inner core portion 66 also includes a plurality of cellulose fibers 64 and thus has a density that is substantially greater than zero.

Claims

1. A method for manufacturing an article (62) at least partially made of cellulose fibers (64), the method comprising the following steps: a. Inserting a cellulose pulp (20) comprising cellulose fibers and water into a mixing chamber (24); b. Subjecting the cellulose pulp (20) to high-shear mixing using a high-shear mixer (28) such that a foam mixture (30) comprising cellulose fibers, water, and air bubbles is produced; c. Inserting the foam mixture (30) into a mold cavity (34); d. Molding the article (62) by heating the foam mixture (30) accommodated within the mold cavity (34).

2. The method according to claim 1, wherein, prior to or during step d, at least part of the water is discharged from the foam mixture (30).

3. The method according to claim 2, wherein, at least part of the water is partially discharged through at least part of the wall of the mold cavity (34).

4. The method according to any one of the preceding claims, wherein, a gas pressure difference is at least temporarily applied between the interior and the exterior of the mold cavity (34).

5. The method according to claim 4, wherein, the gas permeability of a first wall portion of the mold cavity (34) is different from the gas permeability of a second wall portion.

6. The method according to any one of the preceding claims, wherein, an object (36) is inserted into the mold cavity (34) prior to step d.

7. The method according to any one of the preceding claims, wherein, the foam mixture (30) accommodated within the mold cavity (34) is heated by electromagnetic radiation, preferably by high-frequency electromagnetic radiation.

8. The method according to any one of the preceding claims, wherein, prior to or during step b, a surfactant, a pigment, and / or an additive affecting thermal properties is added to the cellulose pulp (20).

9. The method according to any one of the preceding claims, wherein, when the foam mixture (30) is inserted, the mold has an elevated temperature at least locally.

10. An article (62) at least partially made of cellulose fibers (64), characterized in that, the article (62) comprises a core portion (66) and a skin portion (68), wherein the density of the material formed by the cellulose fibers (64) in the core portion (66) is lower than the density of the material formed by the cellulose fibers (64) in the skin portion (68).

11. The article (62) according to claim 10, wherein, the density gradient in the transient region between the core portion (66) and the skin portion (68) is lower than about 5000 kg / m³·cm, preferably lower than about 1500 kg / m³·cm.

12. The article (62) according to any one of claims 10 to 11, wherein, the density of a first region of the skin portion (68) is different from the density of a second region of the skin portion (68).

13. The article (62) according to any one of claims 10 to 12, wherein, The article (62) includes an object (36) having a membrane material.

14. The article (62) according to claim 13, wherein, the membrane material forms a closable or closed cavity within the article (62).

15. The article (62) according to any one of claims 10 to 14, wherein, the outer skin portion (68) has a thickness of at least 5 mm.

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