Composite sandwich panels

Abstract

The sandwich panel 162, 164, 166 comprises a thermoplastic foam core 102 with fabric layers 122, 124 on two faces 108, 110. Each fabric 122, 124 layer comprise reinforcement fibres (126, figure 2) and

Description

Field The present invention relates to a method of continuously producing a composite sandwich panel, a composite sandwich panel, and a method of recycling a composite sandwich panel. Background Composite sandwich panels are known. Composite sandwich panels consist of a lightweight core, with thin outer skin layers applied to each side of the core. Composite sandwich panels may find utility in applications where high strength, but low weight is required, such as for one or more elements of a wind turbine blade. For example, composite sandwich panels may be used to form a shear web of a wind turbine blade. One known way of applying the outer skin layers to the foam core includes laying up dry layers of glass or carbon fibres on top of the core. The dry layers are then infused with a liquid resin, which must be left to cure for a period. Alternatively, a "pre-preg" can be used for the outer skin layers, where the pre-preg comprises one or more fabric layers pre-impregnated with resin. The prepreg is laid on the core, then heated before being allowed to cure. Therefore, whether dry layers are infused with liquid resin or a pre-preg is used, the composite sandwich panel must be left to cure for a period after the outer skin layers have been applied to the core. This slows down the overall manufacturing process. The present inventors have attempted to address or at least mitigate the above-mentioned problems and have aimed to provide a method of continuously producing a composite sandwich panel in a highly efficient manner. The present inventors have also aimed to provide a composite sandwich panel which has a composition that promotes recyclability, and a method of recycling such a composite sandwich panel. Summary Accordingly, in a first aspect the present invention provides a method of continuously producing a composite sandwich panel according to claim 1 In a second aspect the present invention provides a composite sandwich panel according to claim 24. In a third aspect the present invention provides a wind turbine blade according to claim 37. In a fourth aspect the present invention provides a method of recycling a composite sandwich panel, according to claim 38. Brief description of drawings Figure 1 schematically shows a process flow of continuously producing a composite sandwich panel, according to an embodiment of the present invention; Figure 2 schematically shows first and second fibre materials of a fabric layer, according to an embodiment of the present invention; Figure 3 schematically shows a biaxially oriented fabric layer, according to an embodiment of the present invention; Figure 4 schematically shows a composite sandwich panel, according to an embodiment of the present invention; Figure 5 schematically shows a method of recycling a composite sandwich panel, according to an embodiment of the present invention. Detailed description Figure 1 schematically shows a process flow of continuously producing a composite sandwich panel, according to an embodiment of the present invention. According to the embodiment of Figure 1, the process takes place in a system or facility 100 for continuously producing sandwich panels. At step (a), the method comprises extruding an elongate thermoplastic foam panel 102 from an extrusion die 103 of an extruder 104. Solid particles 106 of a thermoplastic resin may be fed in to the extruder 104. As is well known to those skilled in the art, within the extruder the thermoplastic resin is melted and combined with a blowing agent, which may be a physical or chemical blowing agent, to form a molten body of cellular foam. The molten body of cellular foam is then extruded through the extrusion die 103 to form an elongate panel having a desired width and height. Various combinations of thermoplastic resins and blowing agents are well known to those skilled in the art for producing structural cellular foams having desired structure, composition and mechanical and thermodynamic properties. In some examples, the thermoplastic resin, and consequently the thermoplastic foam, comprises polyethylene terephthalate (PET or PETE), which may be composed of virgin PET (vPET) and / or recycled PET (rPET). Virgin PET is typically supplied as pellets. Recycled PET may be supplied as flakes recovered directly from the recycling process, or as pre-processed pellets. The thermoplastic foam panel 102 comprises a top face 108 and a bottom face 110. The thermoplastic foam panel 102 has first and second side edges 112 and 114, and a width W of the thermoplastic foam panel 102 extends between the first and second side edges 112 and 114. The thermoplastic foam panel 102 is extruded continuously in a longitudinal direction L away from the extrusion die 103. At step (b), the method comprises applying to each of the top and bottom faces 108,110 of the foam panel 102 a respective fabric material 116 and 118 at a fabric material applying station 120 that is downstream of the extrusion die 103, to form a top outer fabric layer 122 covering the top face 108 of the foam panel 102 and a bottom outer fabric layer 124 covering the bottom face 110 of the foam panel 102. The application of the top outer fabric layer 122 and the bottom outer fabric layer 124 occurs whilst the foam panel 102 is continuously extruded from the extrusion die 103, so that the foam panel forms a foam core which is sandwiched between the top and bottom outer fabric layers 122 and 124. Where it is said that the top outer fabric layer 122 covers the top face 108 of the foam panel 102, it will be understood that this may encompass fully covering the top face 108 or at least substantially covering the top face 108. Likewise, where it is said that the bottom outer fabric layer 124 covers the bottom face 110 of the foam panel 102, it will be understood that this may encompass fully covering the bottom face 110 or at least substantially covering the bottom face 110. According to some examples, the top outer fabric layer 122 and the bottom outer fabric layer 124 comprise the same fabric material, although it is not excluded that the top outer fabric layer 122 and the bottom outer fabric layer 124 could comprise different fabric materials. Nevertheless, for conciseness, where reference is made to the fabric material it will be understood that this encompasses both the material of the top outer fabric layer 122 and the bottom outer fabric layer 124, unless stated otherwise. In examples, the fabric material comprises a mixture of first and second fibre materials. Figure 2, which is a schematic cross-sectional view showing the first and second fibre materials "end-on", shows first fibre material 126 (represented by the shaded circles), and second fibre material 128 (represented by the non-shaded circles). In some examples the first fibre material 126 comprises a reinforcement fibre selected from glass, carbon fibre, aramid fibre or natural fibre, or any two or more thereof. In some examples the reinforcement fibre material comprises glass fibres. In some examples the second fibre material 128 comprises a thermoplastic fibre. In some examples, the second fibre material comprises polyester fibres, optionally polyethylene terephthalate (PET or PETE) fibres. According to some examples it may be considered that the first and second fibre materials 126,128 are comingled in a mixed roving within the fabric material, as shown in Figure 2. According to some examples, it may be considered that the first and second fibre materials 126,128 are intimately commingled. According to some examples, the first and second fibre materials 126, 128 are not twisted around each other in the fabric material. According to some examples, the first and second fibre materials 126,128 each comprise filaments (or rovings, each roving comprising a plurality of filaments) that longitudinally extend in the fabric material. In some examples the longitudinal axes of the rovings and / or filaments of the first and second fibre materials 126,128 are arranged parallel or approximately parallel to each other. In other words, in some examples there is parallel alignment of the first and second fibre materials 126, 128 in the mixed roving. According to some examples, the commingled first and second fibre materials 126,128 comprise a single mixed roving of uniform dispersion across a cross section of the fabric material. According to some examples, there is a homogenous distribution of the first and second fibre materials 126,128, in the mixed roving. This homogenous distribution helps to produce a fully wet-out matrix polymer with minimal or zero voids when the mixed roving is heated to a suitable temperature (which is explained in more detail below). According to some examples, a thread or yarn, schematically shown at 130, may be stitched through the fabric material to hold the first and second fibre materials 126,128 in place. The thread or yarn 130 may comprise a thermoplastic material, such as PET. According to some examples, the mixed roving comprises from 30 to 70 wt% of the first fibre material and from 70 to 30 wt% of the second fibre material, each being based on the total weight of the mixed roving. According to some examples, in the mixed roving the first fibre material has a Tow size of from 3K to 50K. For example, the first fibre material may have a Tow size of from 3k to 50k where the first fibre material comprises carbon fibre. In some examples the first fibre material has a TEX of from 150 to 650 TEX. For example, the first fibre material may have a TEX value of from 150 to 650 TEX where the first fibre material is a para-aramid or fibreglass. In some examples the first fibre material has an areal weight of from 200 to 500 g / m2 in the fabric material. According to some examples, the fabric material is non-woven. According to some examples, the fabric material comprises a non-crimp fabric material. According to some examples, the noncrimp fabric material comprises two or more fibre plies oriented multi-axially. According to some examples, the non-crimp fabric material comprises two or more fibre plies oriented biaxially. This is schematically shown in Figure 3, which shows a first ply or layer 130 and a second ply or layer 132. In the example of Figure 3, the first ply 130 is oriented at -45 degrees and the second ply 132 is oriented at +45 degrees, before they are overlaid with each other to form a multi-ply biaxial material as schematically shown at 134. In some examples the non-crimp fabric material comprises three or more fibre plies oriented triaxially. In some examples a thermoplastic stitching yarn is stitched through the fabric material, to join the plies. A stitching yarn is schematically shown at 136 in Figure 3. In some examples the thermoplastic stitching yarn 136 comprises a polyester, optionally polyethylene terephthalate. A commercially available example of the fabric material comprises or includes Synergex™ material (https: / / www.coats.com / en / products / composites / synergex / synergex). Referring back to Figure 1, in some examples the fabric material applying station 120 comprises a top supply roller 138 opposing the top face 108 of the foam panel and a bottom supply roller 140 opposing the bottom face 110 of the foam panel. The top supply roller 138 and the bottom supply roller 140 are arranged for holding respective rolls 142 and 144 of the fabric material. In some examples the fabric material applying station 120 comprises a top application roller 146 and a bottom application roller 148 for respectively applying the fabric material to the top and bottom faces 108,110 of the foam panel 102. In some examples the top and bottom application rollers 146, 148 are positioned in an opposing configuration to form a pair of pinch rollers. In some examples the top and bottom application rollers are free rolling. In some examples the top and bottom application rollers are rotationally driven for drawing the fabric material from the top and bottom supply rollers 138,140 respectively. At step (c) in Figure 1, the method of continuously producing the sandwich panel comprises, at a bonding station 150 that is downstream of the fabric material applying station 120, applying heat to the top and bottom outer fabric layers 116, 118 whilst the foam panel 102 is continuously extruded from the extrusion die 103. This causes the second fibre material 128 to at least partly melt so as to be bonded to the respective top or bottom face 108,110 of the foam core 102. This causes the top fabric layer 116 to be bonded to the top face 108 of the foam core 102, and causes the bottom fabric layer 118 to be bonded to the bottom face 110 of the foam core 102, to form a composite sandwich panel 152. In some examples the bonding station 150 comprises an upper heater 149 and a lower heater 151. In some examples "bonding" may also be referred to as "fusing" or "welding". Likewise, "bonded" may also be referred to as "fused" or "welded". According to some examples, step (c) comprises heating the top and bottom outer fabric layers to a temperature of 125 to 275 °C or to a temperature which is from 1 to 50 °C above the melting temperature of the second fibre material. Once the sandwich panel 152 has cooled, the second fibre material 128 solidifies, to form a solid bond between the fabric material and the foam core 102. According to the disclosed method of applying the fabric material to the foam core 102, there is no need to add liquid resin (or to supply the fabric material as a pre-preg which is then heated), for the purpose of adhering the fabric material to the foam core. Therefore, according to embodiments of the invention there is no need to go through a resin curing stage immediately following step (c). In some examples the method further comprises a step (d), which occurs after step (a) and before step (b), of trimming the top and bottom faces 108, 110 of the foam panel 102 at a trimming station 154. In some examples the trimming station 154 comprise an upper trimming machine 156 for trimming the top face 108 and a lower trimming machine 158 for trimming the lower face 110 of the foam core 102. Trimming the foam core 102 may help provide a consistent thickness of the foam core 102. In some examples, positions of the upper and / or lower trimming machines 156 and 158 may be adjusted, to allow fine control over the thickness of the foam core 102. In some examples the method further comprises a step (e), which occurs after step (c), of cutting the composite sandwich panel 152 with a cutting machine 160 into one or more sandwich panel sections. In Figure 1, the one or more sandwich panel sections are schematically shown at 162, 164,166. Each sandwich panel section has a length Lsp and a width Wsp. In some examples, the method comprises controlling the cutting machine 160 to control the length Lsp and / or width Wsp . In some examples, the cutting machine 160 comprises two or more cutting units, which may be in close proximity to each other or may be spaced apart. For example, one cutting unit may be used to control length Lsp and another cutting unit may be used to control width Wsp of each sandwich panel section. According to some examples, the method comprises a further step (f), which occurs after step (e), of supplying the one or more sandwich panel sections 162,164,166 to an assembly station 168 for assembling one or more parts of a wind turbine blade. By way of non-limiting example, shear webs for a wind turbine blade may be assembled at assembly station 168. That the composite sandwich panel is "continuously produced" will be understood to mean that the composite sandwich panel can be produced to any length so long as the constituent raw materials are supplied and the machinery such as extruder 104 and the fabric material applying station 120 are operational. It will therefore be understood that the phrase "continuously produced" refers to an extending length of composite sandwich panel being produced as the foam core 102 is extruded and the top and bottom outer fabric layers 122,124 are applied. The phrase "in a continuous manner" does not preclude that the process of producing the extending length of composite sandwich panel can be started and stopped (for example for maintenance or at the start / end of a shift). In practice, the main restriction to the overall length of composite sandwich panel that can be produced in the continuous manner is a length of the production facility. Figure 4 schematically shows a portion of a composite sandwich panel 452 formed by the above-described method. The composite sandwich panel 452 comprises a thermoplastic foam core 402 having opposite and first and second foam faces 408 and 410. The composite sandwich panel 452 comprises first and second fabric layers 422 and 424 respectively bonded to the first and second foam faces 408, 410 to form the composite sandwich panel 452. The first and second fabric layers 422, 424 each comprise a fabric material which comprises a mixture of first and second fibre materials 426 and 428. The first fibre material 426 comprises a reinforcement fibre selected from glass fibre, carbon fibre, aramid fibre or natural fibre, or any two or more thereof. The second fibre material 428 comprises a thermoplastic fibre. At least part of the second fibre material 428 is solidified from a melt formed in contact with the respective first or second face 408, 410, and thereby bonded to the respective first or second face 408, 410 of the foam core 402. Other features of the composite sandwich panel 452 are as described above in relation to Figures 1 to 3. The composite sandwich panel 452 is optimised for recyclability, because of the thermoplastic materials present in the thermoplastic foam core 402 and the thermoplastic second fibre material 428. Figure 5 is a flow chart schematically showing a method of recycling a composite sandwich panel, such as composite sandwich panel 452. At step 501, the method comprises providing a composite sandwich panel, such as composite sandwich panel 452. At step 502, the method comprises heating the composite sandwich panel to a temperature which is sufficient to melt the solidified thermoplastic materials in the core 402 and in the fabric layers 422 and 424 (i.e. to melt the thermoplastic fibres 428). At step 503, the method comprises separating off the thermoplastic materials while they are in a molten state. Any other thermoplastics materials present in the composite sandwich panel 452 (such as any thermoplastic yarns in the fabric layers 422 and 424) may also be collected at this stage. At step 504 the method comprises cooling the molten thermoplastic material until it solidifies into one or more portions of recycled thermoplastic material. The recycled thermoplastic material may undergo one or more further processing steps, such as breaking up the recycled thermoplastic material into granules or pellets. The examples described herein are to be understood as illustrative examples of embodiments of the invention. Further embodiments and examples are envisaged. Any feature described in relation to any one example or embodiment may be used alone or in combination with other features. In addition, any feature described in relation to any one example or embodiment may also be used in combination with one or more features of any other of the examples or embodiments, or any combination of any other of the examples or embodiments. 5 Various modifications to the preferred embodiments of the present invention, as defined by the appended claims, will be apparent to those skilled in the art.

Claims

25Claims1. A method of continuously producing a composite sandwich panel comprising the steps of:(a) extruding an elongate thermoplastic foam panel from an extrusion die of an5 extruder, the foam panel having a top face and a bottom face, the foam panel being extruded continuously in a longitudinal direction away from the extrusion die;(b) applying to each of the top and bottom faces of the foam panel a respective fabric material at a fabric material applying station that is downstream of the extrusion die to form a top outer fabric layer covering the top face of the foam panel and a bottom outer fabric layer covering10 the bottom face of the foam panel whilst the foam panel is continuously extruded from the extrusion die, so that the foam panel forms a foam core which is sandwiched between the top and bottom outer fabric layers, wherein the fabric material comprises a mixture of first and second fibre materials, wherein the first fibre material comprises a reinforcement fibre selected from glass fibre, carbon fibre, aramid fibre or natural fibre, or any two or more thereof, and the second fibre15 material comprises a thermoplastic fibre; and(c) at a bonding station that is downstream of the fabric material applying station, applying heat to the top and bottom outer fabric layers, whilst the foam panel is continuously extruded from the extrusion die so that the second fibre material at least partly melts so as to be bonded to the respective top or bottom face of the foam core to form a composite sandwich panel,20 wherein the first and second fibre materials are comingled in a mixed roving withinthe fabric material.

2. A method according to claim 1, wherein the thermoplastic foam comprises polyethylene terephthalate.

253. A method according to claim 1 or claim 2, wherein the first fibre material comprises glass fibres.

4. A method according to any of claims 1 to 3, wherein the second fibre material comprises30 polyester fibres.

5. A method according to claim 1, wherein the mixed roving comprises from 30 to 70 wt% of the first fibre material and from 70 to 30 wt% of the second fibre material, each being based on the14 01 25total weight of the mixed roving.5 6. A method according to claim 1 or claim 5, wherein in the mixed roving the first fibre materialcomprises a Tow size of from 3k to 50k.

7. A method according to any one of claims 1 to 6, wherein the first fibre material has an areal weight of from 200 to 500 g / m2 in the fabric material.

108. A method according to any of claims 1 to 7, wherein the fabric material is non-woven.

9. A method according to any of claims 1 to 8, wherein the fabric material comprises a noncrimp fabric material.15 10. A method according to any of claims 1 to 9, wherein the non-crimp fabric material comprisestwo or more fibre plies oriented multi-axially.

11. A method according to claim 10, wherein the non-crimp fabric material comprises two or more fibre plies oriented biaxially or three or more fibre plies oriented triaxially.2012. A method according to any of claim 1 to 11, wherein a thermoplastic yarn is stitched through the fabric material.

13. A method according to claim 8, wherein the thermoplastic yarn comprises a polyester.2514. A method according to any of claims 1 to 13, wherein step (c) comprises heating the top and bottom outer fabric layers to a temperature of 125 to 275 °C or to a temperature which is from 1 to 50 °C above the melting temperature of the second fibre material.14 01 2515. A method according to any of claims 1 to 14, wherein the fabric material applying station comprises a top supply roller opposing the top face of the foam panel and a bottom supply roller opposing the bottom face of the foam panel, the top supply roller and the bottom supply roller arranged for holding respective rolls of the fabric material.

16. A method according to any of claims 1 to 15, wherein the fabric material applying station comprises top and bottom application rollers for respectively applying the fabric material to the top and bottom faces of the foam panel.

17. A method according to claim 16, wherein the top and bottom application rollers are positioned in an opposing configuration to form a pair of pinch rollers.

18. A method according to claim 16 or claim 17, wherein the top and bottom application rollers are free-rolling.

19. A method according to claim 16 or claim 17, wherein the top and bottom application rollers are rotationally driven for drawing the fabric material from the top and bottom supply rollers respectively.

20. A method according to any of claims 1 to 19, wherein the method further comprises a step (d) which occurs after step (a) and before step (b), of trimming the top and bottom faces of the foam panel at a trimming station.

21. A method according to any of claim 1 to 20, further comprising a step (e) which occurs after step (c), of cutting the sandwich panel with a cutting machine into one or more sandwich panel sections.

22. A method according to claim 21, further comprising a step (f) which occurs after step (e), of supplying the one or more sandwich panel sections to an assembly station for assembling one or more parts of a wind turbine blade.

23. A composite sandwich panel comprising:14 01 25(a) a thermoplastic foam core having opposite and first and second foam faces; and(b) first and second fabric layers respectively bonded to the first and second foam facesto form the composite sandwich panel, wherein the first and second fabric layers each comprise a5 fabric material which comprises a mixture of first and second fibre materials, wherein the first fibre material comprises a reinforcement fibre selected from glass fibre, carbon fibre, aramid fibre or natural fibre, or any two or more thereof, and the second fibre material comprises a thermoplastic fibre, and wherein at least part of the second fibre material is solidified from a melt formed in contact with the respective first or second face and thereby bonded to the respective first or second10 face of the foam core,wherein the first and second fibre materials are comingled in a mixed roving in the fabric material.

24. A composite sandwich panel according to claim 23, wherein the thermoplastic foam core15 comprises polyethylene terephthalate.

25. A composite sandwich panel according to claim 23 or claim 24, wherein the first fibre material comprises glass fibres.20 26. A composite sandwich panel according to any of claims 23 to 25, wherein the mixed rovingcomprises from 30 to 70 wt% of the first fibre material and from 70 to 30 wt% of the second fibre material, each being based on the total weight of the mixed roving.

27. A composite sandwich panel according to any of claims 23 to 26, wherein in the mixed25 roving the first fibre material comprises a TEX value of from 150 to 650 TEX.

28. A composite sandwich panel according to any of claims 23 to 27, wherein the first fibre material has an areal weight of from 200 to 500 g / m2 in the fabric material.

29. A composite sandwich panel according to any of claims 23 to 28, wherein the fabric material14 01 25is non-woven.

30. A composite sandwich panel according to any of claims 23 to 29, wherein the fabric material 5 comprises a non-crimp fabric material.

31. A composite sandwich panel according to claim 30, wherein the non-crimp fabric material comprises two or more fibre plies oriented multi-axially.10 32. A composite sandwich panel according to claim 31, wherein the non-crimp fabric materialcomprises two or more fibre plies oriented biaxially or three or more fibre plies oriented triaxially.

33. A composite sandwich panel according to any of claims 23 to 32, comprising a thermoplastic yarn stitched through the fabric material.1534. A composite sandwich panel according to claim 33, wherein the thermoplastic yarn comprises polyethylene terephthalate.

35. A wind turbine blade comprising at least one sandwich panel according to any of claims 2320 to 34.Application No: GB2401039.9Claims searched: 1-38Examiner: Mr Robert BlackDate of search: 23 July 2024Patents Act 1977: Search Report under Section 17Documents considered to be relevant:Category Relevant to claims Identity of document and passage or figure of particular relevance X Y X = 24, 28 and 31; Y=l,2, 4,21-23, 30 and 37 WO 00 / 06375 Al (KEUM) See especially the abstract, page 5 lines 12-19, page 6 lines 3-32, page 8 lines 17-27, page 11 line 25 to page 12 line 5 and figure 4 X,Y X = 24, 28 and 31; Y 2,4 and 30 KR 201211619 A (RYU) See especially WPI abstract 2012-C18217, the EPODOC abstract, and paragraphs 0039 and 0043 Y 1 and 21 US 2007 / 0166526 Al (MYARD) See especially the abstract, and paragraphs 0003, 0042, 0065, 0072, 0076, 0079-0081, 0084, 0085, 0093, 0095-0098, 0100 and 0101 Y 2-4, 22, 23 and 37 US 2006 / 0257612 Al (RAKUTT) See especially figure 1, and paragraphs 0014, 0035, 0054, 0056 and 0061 Y 2-4 KR 201987715 A (HUVIS) See especially WPI abstract 2019-65434E, the EPODOC abstract, paragraphs 0088, 0125 and 0166, and claims 1, 10 and 11Categories:X Document indicating lack of novelty or inventive step A Document indicating technological background and / or state of the art. Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of same category. before the filing date of this invention. & Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:International Classification:Subclass Subgroup Valid From B32B 0005 / 24 01 / 01 / 2006 B29C 0048 / 00 01 / 01 / 2019 B32B 0005 / 08 01 / 01 / 2006 B32B 0005 / 18 01 / 01 / 2006 B32B 0027 / 12 01 / 01 / 2006 B32B 0037 / 04 01 / 01 / 2006 B32B 0038 / 00 01 / 01 / 2006

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