Method of manufacturing a composite element comprising willow tree and composite element made by such a method

Abstract

The invention relates to a method of manufacturing a composite element (1) comprising willow tree (2). The method comprises providing willow tree in the form of chips, powder, and / or wood-dust (3) which is mixed with a binder (5), such as a bio-resin, and preferably a release agent (6) in a mixer (4). When a homogeneous or substantially homogeneous mixture has been obtained, it is removed from the mixer and arranged in a press (11). The mixture is pressed into a shaped composite element which is allowed to solidity. The invention further relates to a composite element which may have a bowl-shaped overall cross-sectional shape, or which may be a floor panel, ceiling panel, wall panel, furniture panel, and piece of furniture. It also relates to an acoustic element comprising an acoustic batt (14) on which a row or array of composite elements have been arranged with a distance between neighbouring composite elements.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a method of manufacturing a composite element comprising willow tree, and in particular a method in which the willow tree is provided as chips, powder, and / or wood-dust which is mixed with a binder and optionally other constituents in a mixer before being pressed into a desired geometry.BACKGROUND OF THE INVENTION

[0002] It is well-known within the building industry to use chipboard comprising chips of wood which have been pressed into plates by use of suitable binders. Such plates are typically made from softwood and hardwood, which after debarking is cut into chips or planed into shavings. The wood chips or shavings are mixed with glue and then pressed together between metal plates or rollers and heated. Such known plates are typically characterized by having a layered structure with smaller chips or shavings near the outer surfaces than in the core of the plate.OBJECT OF THE INVENTION

[0003] It is an object of the present invention to provide a method of manufacturing a composite element based on a material that is an alternative to known materials typically used in the building industry.

[0004] It is an object of at least some embodiments of the present invention to provide a method of manufacturing a composite material which is more environmentally friendly than similar products made from other types of wood.

[0005] It is another object of at least some embodiments of the present invention to provide a method of manufacturing a composite element comprising willow tree and having sound-absorbing characteristics.

[0006] It is a further object of the present invention to provide an alternative to the prior art.SUMMARY OF THE INVENTION

[0007] The above-described object and several other objects are intended to be obtained in a first aspect of the invention by providing a method of manufacturing a composite element comprising willow tree, the method comprising: providing willow tree in the form of chips, powder, and / or wood-dust, mixing the willow tree with a binder, such as a bio-resin, and preferably a release agent in a mixer until a homogeneous or substantially homogeneous mixture has been obtained, moving the mixture from the mixer to a press, pressing the mixture into a shaped composite element, allowing the composite element to solidify, and optionally applying a finishing treatment, such as polishing, to the composite element after it has solidified.

[0008] An advantage of willow tree is that it shoots again from the stump, so it does not need to be replanted. It can typically be felled on a 4-8 years cycle, and it is therefore advantageous for use in the present invention. Within this time period, willow tree is considered to be the most COz-absorbing tree grown. The use of this tree for composite elements as according to the present invention will therefore limit the amount of CO 2 emitted into the atmosphere. There are many types of willow tree, and which one to use may depend e.g. on what is available. In embodiments based on bio-binders as will be described below, the fact that plants take in CO 2 from the atmosphere and store it during growth will further limit the amount of CO 2 emitted into the atmosphere.

[0009] In some embodiments of the invention, no further layers are added to the composite element, so that the mixture of willow tree and binder extends throughout the thickness. The composition of the composite element is preferably homogeneous throughout the thickness.

[0010] The step of allowing the composite element to solidify may comprise applying cooling, such as by a flow of cooling air, in order to speed-up the solidification. Alternatively, the solidification may take place at room temperature.

[0011] The size distribution of the chips, powder, and / or wood-dust may e.g. be so that a majority thereof has a longest dimension in the order of 10 mm. For some applications it will be advantageous to have a wide size distribution, i.e. with the willow tree having a wide variety of sizes, as that may facilitate a high packing density of the willow tree. As an example, a size distribution of willow tree which has been used during the development of the present invention was around 25 weight% down to 355µm, 50 weight% 1-3.5 mm, and 25 weight% 3.5-10mm. The size and size distribution for a given application may be determined based on the required mechanical properties of the composite element, such as the strength and the stiffness. In addition, the resulting appearance of the surface of the composite element may be taken into account. The average size and the size distribution of the willow tree will typically be determined by experimentation. In order to be able to use a desired size distribution, the willow tree may first be sorted into the different size ranges and then mixed in the relevant amounts.

[0012] In some embodiments of the invention, the binder is provided in liquid or viscous state. In other embodiments of the invention, the binder is provided in solid state, and the mixing process used for the mixing of the willow tree and the binder can be referred to as a thermo-kinetic process, because the mutual movement of the constituents results in the generation of heat. The resulting melting allows the binder to adhere to the willow tree and thereby form a coherent mixture which after solidification provides a material that has the required properties, such as strength and stiffness. For some types of binder and / or for some amounts of materials, it may be advantageous to pre-heat the binder before it is supplied to the mixer. For some embodiments of the invention, it may also be advantageous to use a heated mixing chamber, such as to supply heat to the chamber during the mixing. However, it should be ensured that the temperature does not become so high that it causes degradation of any of the constituents.

[0013] The binder may be a polymer as traditionally used for the manufacturing of chipboard. Alternatively, the binder may be a bio-resin. A bio-resin is a thermoplastic made from plant-based materials instead of petroleum products. Willow tree has a higher content of cellulose than other types of wood typically used for chipboard. At least a part of this cellulose acts as binder, and therefore the content of added binder may be lower than in traditional chipboard.

[0014] In some embodiments of the invention, the mixing is performed in a closed chamber comprising a rotor, and the closed chamber and / or the rotor rotates and thereby applies a rotational movement to the willow tree and the binder. The rotational speed of the closed chamber and / or the rotor may be controllable. When both the chamber and the rotor rotate, they typically rotate in opposite directions.

[0015] When the mixture is moved from the mixer, it is preferably in the form of a coherent, semi-solid, wet mat so that it can be handled as a unit. However, the scope of protections also covers embodiments in which the mixture is in the form of smaller parts and is to be moved e.g. in a container. The viscosity and coherence of the mixture should be so that it allows for the necessary handling thereof during the transfer from the mixer to the equipment used for the subsequent step of pressing. The mixing and pressing may take part in the same processing equipment or in two separate ones. The moving of the mixture may be performed manually, or it may be performed mechanically e.g. by mechanical grippers controlled as a part of the manufacturing equipment in an automated or semi-automated process. The transfer may also take place with a conveyor belt. However, any suitable way of handling the mixture is covered by the scope of protection.

[0016] The amount of willow tree may be 75-95 weight%, such as 80-92 weight%, such as around 90 weight%. To this is added at least binder and preferably also release agent. Other components may also be added as will be described below.

[0017] The step of providing the willow tree may comprise: dividing larger parts of willow tree, such as pieces of trunk and / or branches, into the form of chips, powder, and / or wood-dust, and / or drying the willow tree.

[0018] These two steps may take place just after each other, or there may be storage time in between. When the method comprises drying, this drying may take place before and / or after the step of dividing. Whether or not such drying is necessary may be determined based on measurements of the water content in the larger parts and / or the chips, powder, and / or wood-dust. In embodiments not comprising the step of dividing larger parts of willow three into chips, powder, and / or wood-dust, the willow tree will typically be provided in the form ready for mixing from a supplier different from the manufacturer of the composite elements.

[0019] In some embodiments of the invention, the willow tree comprises bark. This may give a special aesthetic effect, and the bark may also influence the mechanical properties, such as strength, stiffness, and / or hardness. Furthermore, it will imply that the process of removing the bark beforehand can be avoided and that there is less or no waste. For some applications, it may even be relevant to add additional bark, such as bark removed from willow tree used in other products.

[0020] One or more of the following constituents may be added to the composite material before or during the mixing: fire-retardant, UV-stabilizer, and colour pigments. The specific constituents will be determined based on the actual application of the composite element. When a fire-retardant is added during the mixing, the resulting composite element comprises the fire-retardant throughout the thickness and not just at the surface as with traditional chipboard. Hereby the fire-resistance will be higher.

[0021] The willow tree may be pre-heated before being fed to the mixer. The temperature and duration of such a pre-heating treatment would depend on a number of factors including the type of binder, the weight% of willow tree, the total amount of material in the mixer, and the duration of the mixing. On the one hand, it should be ensured that the positive effect of the pre-heating is obtained. On the other hand, it should be ensured that the pre-heating in combination with the additional heating, including from friction, does not damage the material or even cause a risk of fire.

[0022] The step of pressing may be performed: by a roller press, by arranging the mixture in a mould and applying pressure thereto by a piston, such as a hydraulic piston, and / or by an extruder, such as a piston extruder. Which method to use will depend mainly on the geometry and size of the composite element being manufactured. When both options are possible, the choice will typically depend on what is available. With a roller press it is possible to manufacture very long, such as endless, plates which are cut into desired lengths in a subsequent process step.

[0023] Some embodiments of the invention further comprise providing the composite element with holes, such as through-going holes, typically arranged in a pre-determined pattern. Such elements may e.g. find use as baffle plates or other sound-absorbing members of which some examples will be shown in the figures.

[0024] In embodiments comprising holes, the holes may be: circular holes with a diameter of 0.3-1.0 mm, such as 0.4-0.6 mm, such as 0.5 mm, circular holes with a diameter of 3-20 mm, such as 5-15 mm, such as 10-15 mm, or rectangular holes of 5x50mm, such as 5x30 mm. The holes may e.g. be made by drilling or laser cutting.

[0025] In embodiments comprising holes, there may be 120,000-150,000 holes / m 2< , such as 130,000-140,000 holes / m 2< , such as around 137,000 holes / m 2< . An advantage of using so small holes is that they will be invisible when viewed from a distance so that the element in which they are provided looks coherent. The number of holes will be determined as a combination of an assessment of the resulting acoustic properties and what is possible with the machines used for establishing the holes.

[0026] A method as described in any of the above embodiments may further comprise applying an acoustic batt to a surface of the composite element after it has solidified. Hereby the composite element can be provided with sound-absorbing properties both with and without the additional holes. An acoustic batt may e.g. be made from waste material from carpet manufacturing, or it may be made from or comprise willow tree. An acoustic batt may be provided with a fire-retardant composition.

[0027] A second aspect of the invention relates to a composite element manufactured by a method according to the first aspect of the invention.

[0028] In some embodiments of the invention according to the second aspect, the composite element has a circular circumference, a plane central region, and a bowl-shaped overall cross-sectional shape. An example of such an embodiment will be described in the figures.

[0029] The composite element may be selected from the following group: floor panel, ceiling panel, wall panel, furniture panel, and piece of furniture. At least when the composite element is in the form of a panel, it could also be referred to as a chipboard or a fibreboard.

[0030] A third aspect of the invention relates to an acoustic element comprising an acoustic batt on which a row or array of composite elements according to the second aspect of the invention has been arranged with a distance between neighbouring composite elements. An example of such an acoustic element will be shown and described in relation to the figures.

[0031] The first, second and third aspects of the present invention may be combined. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.BRIEF DESCRIPTION OF THE FIGURES

[0032] The method of manufacturing a composite element comprising willow tree as well as examples of such elements according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set. Figure 1 schematically illustrates an embodiment of a method of manufacturing a composite element according to the present invention. Figure 2 is a photo of a composite element manufactured by a method according to the invention. Figure 3 is a photo of an array of composite elements. Figures 4.A to 4.C schematically show one of the composite elements in figure 3. Figures 5.a to 5.C schematically show an alternative to the embodiment in figures 4.A to 4.C. Figures 6.A and 6.B schematically show an embodiment of a composite element in the form of a sound-absorbing panel. Figures 7.A and 7.B schematically show an acoustic element comprising a row of composite elements. DETAILED DESCRIPTION OF AN EMBODIMENT

[0033] Figure 1 schematically illustrates an embodiment of a method of manufacturing a composite element 1 according to the present invention. In the illustrated embodiment, larger parts of willow tree 2, such as pieces of trunk and / or branches, are divided into the form of chips, powder, and / or wood-dust 3 which may comprise bark, if desired. This step may take place at the same location as the remaining process. However, in alternative embodiments, the willow tree is provided from an external supplier and has been prepared at another location. Optionally the willow tree is dried before being transferred to the mixer 4. The willow tree is mixed with a binder 5 and preferably a release agent 6 in the mixer 4. The binder 5 may be blown into the mixer 4 while it is rotating to ensure an even distribution thereof. One or more of the following constituents may be added to the composite material before or during the mixing: fire-retardant 7, UV-stabilizer 8, and colour pigments 9; they are marked with dotted lines in the figure to illustrate that they are optional.

[0034] The mixing is continued until a homogeneous or substantially homogeneous mixture 10 has been obtained. The mixture 10 is then moved from the mixer 4 to a press 11 by which the mixture 10 is pressed into a shaped composite element 1. As mentioned above, the press 11 may be a roller press, a press in which the mixture is arranged in a mould 12 and pressure P is applied thereto e.g. by a piston, such as a hydraulic piston, or it may be by an extruder. Subsequently the composite element 1 is allowed to solidify. If relevant for the actual application, a finishing treatment, such as polishing, is applied to the composite element after it has solidified.

[0035] Figure 2 is a photo of the surface of a composite element 1 which has been manufactured by a method according to the invention. The unit of the scale is in cm. As seen from the photo, the willow tree in the form of chips, powder, and / or wood-dust having a wide range of sizes which allows for a close packing thereof.

[0036] Figure 3 is a photo of an array of sound-absorbing members 13 made from composite members in the form of composite elements 1 to which an acoustic batt 14 (see figure 4) has been applied after solidification of the composite elements 1. Each of these composite elements 1 has a circular circumference, a plane central region, and a bowl-shaped overall cross-sectional shape. This geometry of the composite element 1 will typically be obtained by arranging the mixture 10 in a mould 12 and applying a pressure P thereto by use of a piston. Before the acoustic batt 14 has been applied, the composite element 1 has been provided with holes 15, such as through-going holes, arranged in a pre-determined pattern. In the illustrated embodiment, the composite members as well as the holes are circular, but any suitable shape is covered by the scope of protection. The sound-absorbing members 13 may e.g. be arranged on a ceiling to improve the acoustics of a room. The illustrated composite elements 1 have been manufactured as part of the development of the present invention with a diameter of 600 mm and a height of 50 mm. An advantage of using such an array of sound-absorbing members 13 with a circular circumference compared to one larger panel or a plurality of square elements arranged abutting each other is that the un-covered regions between the composite members provide space for other types of installations, such as smoke detectors, sprinklers or lamps.

[0037] Figures 4.A to 4.C show one of the composite members 13 in figure 3. Figure 4.A is a front view, figure 4.B is a side view, and figure 4.C is a cross-sectional view. Figures 5.A to 5.C show an alternative embodiment in which the region 16 at the circumference is not provided with holes.

[0038] As described above, a composite element according to the present invention may be selected from the following group: floor panel, ceiling panel, wall panel, furniture panel, or piece of furniture. Figure 6.A-6.B show an example of a panel 17 in which the sound-absorbing effect has been obtained or improved by applying an acoustic batt 14 to a composite element 1. Figure 6.A is a front view, and figure 6.B is a side view. An actual panel, which has been tested during the development of the present invention, was provided with 0.5 mm through-going holes in an amount corresponding to 137.000 holes per m 2< . However, due to the small size, these holes are not visible in the figure.

[0039] Figures 7.A-7.B show and alternative type of sound-absorbing acoustic element 18 comprising an acoustic batt 14 on which a row of composite elements 1 with small holes have been arranged with a distance between neighbouring composite elements. The illustrated acoustic element 18 has been made with composite elements 1 of 30x600 mm and with a 10 mm thick acoustic batt. In alternative, not illustrated, embodiments, the composite elements have been arranged in an array.

[0040] Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Claims

1. Method of manufacturing a composite element (1) comprising willow tree (2), the method comprising: - providing willow tree (2) in the form of chips, powder, and / or wood-dust (3), - mixing the willow tree with a binder (5), such as a bio-resin, and preferably a release agent (6) in a mixer (4) until a homogeneous or substantially homogeneous mixture (10) has been obtained, - moving the mixture (10) from the mixer (4) to a press (11), - pressing the mixture (10) into a shaped composite element (1), - allowing the composite element (1) to solidify, and - optionally applying a finishing treatment, such as polishing, to the composite element (1) after it has solidified.

2. Method according to claim 1, wherein the amount of willow tree (2) is 75-95 weight%, such as 80-92 weight%, such as around 90 weight%.

3. Method according to claim 1 or 2, wherein the step of providing the willow tree (2) comprises: - dividing larger parts of willow tree, such as pieces of trunk and / or branches, into the form of chips, powder, and / or wood-dust (3), and / or - drying the willow tree.

4. Method according to any of the preceding claims, wherein the willow tree (2) comprises bark.

5. Method according to any of the preceding claims, wherein one or more of the following constituents are added to the composite material before or during the mixing: fire-retardant (7), UV-stabilizer (8), and colour pigments (9).

6. Method according to any of the preceding claims, wherein the willow tree (2) is pre-heated before being fed to the mixer (4).

7. Method according to any of the preceding claims, wherein the step of pressing is performed: - by a roller press, - by arranging the mixture (10) in a mould (12) and applying pressure (P) thereto by a piston, such as a hydraulic piston, and / or - by an extruder, such as a piston extruder.

8. Method according to any of the preceding claims, further comprising providing the composite element (1) with holes (15), such as through-going holes, arranged in a pre-determined pattern.

9. Method according to claim 8, wherein the holes (15) are: - circular holes with a diameter of 0.3-1.0 mm, such as 0.4-0.6 mm, such as 0.5 mm, - circular holes with a diameter of 3-20 mm, such as 5-15 mm, such as 10-15 mm, or - rectangular holes of 5x50mm, such as 5x30 mm.

10. Method according to claim 8, wherein there are 120,000-150,000 holes / m2, such as 130,000-140,000 holes / m2, such as around 137,000 holes / m2.

11. Method according to any of the preceding claims, further comprising applying an acoustic batt (14) to a surface of the composite element (1) after it has solidified.

12. Composite element (1) manufactured by a method according to any of the preceding claims.

13. Composite element (1) according to claim 12, having a circular circumference, a plane central region, and a bowl-shaped overall cross-sectional shape.

14. Composite element (1) according to claim 12, wherein the composite element is selected from the following group: floor panel, ceiling panel, wall panel, furniture panel, and piece of furniture.

15. Acoustic element (18) comprising an acoustic batt (14) on which a row or array of composite elements (1) according to claim 12 have been arranged with a distance between neighbouring composite elements (1).

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