Improvements in composite materials

Abstract

Use of a structure (22) in an automatic process for placing it in a mold, wherein the structure (22) comprises a core layer comprising a fibrous reinforcement (14, 38) and a curable resin (18, 40), and is provided with an outer layer (12, 36) that is free of curable resin, wherein the outer layer (12, 36) is made sticky by the curable resin (18, 40) as a result of placing the structure (22) in the mold.

Description

Technical field

[0001] The present invention relates to composite materials, in particular curable prepregs and semipregs, and especially those used in industrial applications, particularly in wind energy applications such as wind turbine rotor blades. In particular, the invention relates to the provision of prepregs and semipregs with a high fiber basis weight that can be processed in automated processing machines and that do not require manual placement during forming and curing. Furthermore, the invention relates to a method for producing such curable prepregs and semipregs and to methods for manufacturing articles therefrom, as well as to the manufactured articles, in particular articles with a high fiber content. background

[0002] Composite materials have well-documented advantages over traditional materials; in particular, they provide excellent mechanical properties at very low material densities. This has led to the increasing use of such materials, with applications ranging from industrial and sports and leisure to demanding aerospace components. Fiber-reinforced cured resins are an example of such materials, with the nature and type of fiber, the amount of fiber, and the nature of the resin being selected according to the application. Industrial applications require high strength and may necessitate high fiber loadings, which can make processing in automated machinery difficult, if not impossible.

[0003] Pregpregs, which comprise a fiber arrangement impregnated with a resin such as an epoxy resin, are widely used in the production of such composite materials. Typically, a number of layers of such prepregs are placed or laid down in a mold as required, and the resulting stack of prepregs is cured, typically by exposure to elevated temperatures, to produce a cured composite laminate. Automated processes for laying down and curing such prepregs are available.

[0004] A special type of prepreg is the so-called semipreg, which contains a fiber arrangement that has only been partially impregnated with resin, so that part of the fiber arrangement is left in a "dry" state.

[0005] Semipregs can lead to lower porosity in the final cured composite because the dry regions create a passageway through which trapped air can escape from the laminate. This is particularly important in wind energy applications, where cost constraints generally require molding and curing to take place outside of an autoclave and at lower pressures.

[0006] In typical automated lay-up machines that apply prepregs or semipregs, the prepregs or semipregs are automatically fed to a position where they are arranged in a stack and condensed by the application of heat and pressure. For the stack to be adequately formed under automated processing conditions, it is important that the prepregs or semipregs do not stick to the feeder and that they do not form deposits of fibrous fragments on it. At the same time, the prepregs or semipregs must contain sufficient resin to allow fiber impregnation during curing and also provide enough fibers to ensure the required strength in the finished cured item.To this day, this is generally difficult and particularly difficult when processing semipregs and prepregs with high fiber content for the production of high-strength industrial materials such as wind turbine structures like rotor blades and spars.

[0007] A common semipreg arrangement consists of a layer of curable resin in contact with one or two adjacent layers of fibers that remain essentially dry, with very little resin migrating into the neighboring fibers. Such semipregs are particularly useful as layers for forming parts of large load-bearing structures, such as spars for wind turbine rotor blades. Another common arrangement involves the curable resin in contact with an adjacent layer of essentially dry fibers and another adjacent layer of resin-impregnated fibers. At high fiber loadings, it has been necessary in industrial processing to apply the layers manually.

[0008] A common fiber arrangement is woven, biaxial, or triaxial, as such overlap and interaction of the fibers helps maintain the integrity of the semipreg. In wind energy applications, it is common for the fiber layers to have a high density, for example, 600 g / m². 2 Layer or typical of 600 g / m² 2 up to 1500 g / m² 2However, such semipregs are typically applied manually, as they are difficult to process in known types of automated laying machines. This is because such machines rely on a certain degree of adhesion between the layers in the stack, allowing the processed material to be laid down and adhere to the underlying surface. Semipregs are dry on the outside, and thus appear unable to be automatically laid down by known methods, as they lack the necessary surface tackiness. On the other hand, if prepregs or semipregs with sufficient surface tackiness are used, they can adhere to the automated processing equipment and form deposits on it.

[0009] Furthermore, such semipregs, especially the heavyweight variants (those with a high fiber content) used in industrial applications such as wind turbine structures, tend to generate significant amounts of fuzz from broken fibers. This fuzz can accumulate in any automated equipment and cause processing problems and defects in the final product. This is particularly true for woven or other overlapping fiber arrangements.

[0010] It is therefore highly desirable to develop a method for the automatic placement of semipregs, especially the heavy variants used in industrial applications such as wind energy structures.

[0011] US patent application US 2001 / 0031350 A1 relates to sandwich panel composite structures comprising fiber-reinforced closed-cell low-density material, fibrous skin reinforcements and resin, and in particular to improved structural configurations, improved resin infusion methods and methods for manufacturing them.

[0012] The international patent application PCT / GB99 / 03667, published as WO 00 / 27632 A1, relates to molding materials, in particular composite materials, which contain fibers in their structure that provide reinforcement in the molded product.

[0013] The European patent application EP 1 321 282 A1 is directed to a prepreg with a web-shaped fabric of filaments and partial impregnation with a resin.

[0014] The European patent application EP 1 338 406 A1 relates to composite materials or preforms made of resin and reinforcing fibers, in which the resin is only partially impregnated into the fibers.

[0015] US patent application US 2009 / 0258220 A1 relates to a system and a method for manufacturing integrated lightning protection material, wherein integrated metal-resin lightning protection material is placed on a composite structure.

[0016] US patent 4,696,707 relates to a method and apparatus for applying tapes for the manufacture of laminated articles from composite tape.

[0017] European patent application EP 0 313 155 A1 relates to the processing of sheet-shaped products, the “Sheet Moulding Composites” (SMC), and is directed in particular to a method for producing molded bodies in which a web-shaped product comprising thermosetting resin, fillers and fiber material is cut into a desired shape, placed in a mold and cured at elevated temperature and pressure.

[0018] The international patent application PCT / EP2011 / 003608, published as WO 2012 / 010293 A1, relates to composite materials, in particular curable prepregs and semipregs. Summary of the invention

[0019] The present invention therefore provides a structure suitable for automatic placement and comprising a core layer comprising a fibrous reinforcing layer and a curable resin, wherein the layer is provided on at least one surface with an outer layer which is substantially free of curable resin (i.e., substantially non-resin-impregnated), wherein the outer layer is made sticky by the curable resin as a result of the placement of the structure in the mold.

[0020] In a preferred embodiment, the fibrous reinforcing layer on both surfaces is provided with a layer that is essentially free of curable material.

[0021] The term "suitable for automated laying" means that the structure is an intermediate product that can subsequently be processed in an automated system for the production of fiber-reinforced articles. The structure is particularly suitable for automated stacking and curing of the stack to produce the desired fiber-reinforced article. Therefore, the invention relates to the production of a structure that avoids the problems associated with the automated processing of fibrous structures, especially prepregs and semipregs with high fiber content.

[0022] For automatic installation, the structure or laminate can be cut into sections of the desired size and automatically stacked and hardened.

[0023] According to a preferred aspect of the invention, the outer layer or layers, which are essentially free of curable resin, are porous layers, and in a particularly preferred embodiment, they are fibrous layers which may be woven or non-woven.

[0024] According to another preferred aspect of the invention, the fibers in the fibrous reinforcing layer of the structure or laminate according to the invention are unidirectional, although the invention can also be used with other fiber orientations.

[0025] According to a first point of view, the invention relates to a curable semipreg material comprising a layer of substantially non-flowable curable resin and a layer of substantially non-resin-impregnated unidirectional fibers, wherein the prepreg has on an outer surface a layer of porous, arc-shaped material and wherein the non-flowable, curable resin becomes flowable by the application of heat.

[0026] Such a semipreg can be successfully laid up automatically using known automated laying methods and equipment, such as those used for prepregs. The use of unidirectional fibers is preferred, as these are less prone to producing fuzz. Because the fibers do not overlap, the presence of the outer layer, which is preferably a porous layer, has the additional advantage of helping to maintain the fiber orientation and the integrity of the semipreg.

[0027] Although the semipreg is dry on its outer surface when fed to the automated application machine, it has been found that when it is directed to the head of the automated application machine, the application of heat can be used to cause the resin to become fluid and to migrate through one or both of the outer surface layers, thereby introducing the necessary tackiness at the time of application of the semipreg to allow automated processing.

[0028] The term "essentially non-flowable" means that the resin essentially remains in place at room temperature and does not migrate substantially into adjacent fibers. The term "essentially not resin-impregnated" means that, with the exception of those in direct contact with the resin layer, the fibers are essentially resin-free with very little resin impregnation.

[0029] Within the fibrous reinforcement layer there will typically be some degree of resin impregnation, although it is preferred that non-resin-impregnated fibers are in contact with the outer layer, which is a porous arc-shaped material.

[0030] According to a second aspect, the invention relates to a method for producing a curable semipreg material, the method comprising the stage of producing a sheet on porous material with unidirectional fibers laid on it, and providing a layer of substantially non-flowing curable resin, wherein the porous material is on an outer surface, and pressing the layers together to form a curable semipreg. In the curable prepreg or semipreg, the porous material remains unimpregnated with resin after the pressing process. Furthermore, in the method, the non-flowing curable resin is heated to a temperature at which it becomes flowable and then applied to the sheet or sheets.

[0031] The unidirectional fibers can form a continuous layer that is many fibers deep and essentially covers the entire outer layer, for example, a porous material. In a preferred arrangement, however, the unidirectional fibers are arranged, for example, on the porous material, as a multitude of longitudinal strips separated from each other by individual gaps.

[0032] Accordingly, according to a third aspect, the invention relates to a sheet made of porous material with a plurality of strips of unidirectional fibers laid on it.

[0033] Unidirectional fibers are typically supplied as a rope consisting of several thousand fibers and can be wound onto a spool for ease of handling. The rope might, for example, comprise 12,000 filaments or fibers and have an approximately rectangular cross-section. When wound onto a spool, lengths of many thousands of meters are possible.

[0034] In a particularly convenient method, the strips of unidirectional fibers are provided by laying a large number of ropes of unidirectional fibers on a surface of the outer layer, for example a porous material.

[0035] The strips of unidirectional fibers typically have the same width, and the width is preferably not greater than 60 mm, particularly not greater than 30 mm, and most preferably not greater than 15 mm.

[0036] The semipreg according to the invention preferably comprises a second layer of unidirectional fibers. In this embodiment, the fibers in the two layers are aligned such that they are unidirectional in the same direction.

[0037] According to one embodiment, the second layer of fibers is essentially not impregnated with resin and is typically in contact with a second outer layer, for example, a second porous sheet material, arranged on the other outer surface of the semipreg. According to another embodiment, the second layer of fibers may be impregnated with resin.

[0038] Preferably, both the first and second layers of fibers are provided as a plurality of longitudinal strips separated from each other by a discrete gap. Furthermore, it is preferred that the strips in each layer are aligned with a corresponding strip in the other layer, such that the resulting semipreg has opposing strips of aligned fibers and discrete gaps between adjacent strips of fibers.

[0039] The layer of essentially non-flowing curable resin can be brought into contact with the layer or layers of fibrous reinforcing material in various ways. However, its non-flowing nature at room temperature can cause processing difficulties. In this process, the essentially non-flowing curable resin is heated to a temperature at which it becomes flowable and is then applied to the sheet or sheets of fibrous reinforcing material in a conventional manner, for example, by roller transfer.

[0040] In a preferred method, however, the heated resin is directed to cooled rollers through which at least one sheet comprising fibrous reinforcement and the outer layer are passed. The resin thus flows onto the sheet, but is simultaneously cooled to a temperature at which it is essentially non-flowing. This limits the impregnation of any fibers on the sheet or sheets within the fibrous reinforcement layer to the degree necessary to bind the resin to the fibers and avoids excessive impregnation of the outer layer or layers.

[0041] In a preferred embodiment, the outer layer, for example a sheet of porous material with fibers laid on it, and the essentially non-flowing resin are simultaneously passed through a pair of rollers. These rollers can also provide the pressure required to produce a continuous semipreg according to the invention. The conditions on the rollers can be such that the resin impregnates the fibers, but leaves the outer layer, for example the porous material, essentially unimpregnated with resin.

[0042] In the embodiment where the semipreg comprises two outer arcs of porous material, both arcs, the fibrous material, and the substantially non-flowing resin are preferably guided simultaneously through the pair of rollers. The resin can be supplied at a point between the arcs under conditions such that it contacts the fibrous material without significant contact with the outer layers.

[0043] Once the semipreg according to the invention has been produced, it can be rolled onto a core to form a storage-stable semipreg that can be used as insert material in an automatic laying device, such as those commonly used for automatic laying of prepregs.

[0044] However, it is often desirable to have much narrower arcs of material. For example, when constructing a structure with a high degree of curvature, wide arcs of material can wrinkle and crease when attempting to conform to such areas of strong curvature. Narrower strips of material can conform to areas of strong curvature without suffering such difficulties.

[0045] When the semipreg or prepreg according to the invention has been produced, it can accordingly be cut into a plurality of strips in which the fibers are unidirectional and the cuts are aligned in accordance with the direction of the orientation of the fibers.

[0046] In a particularly preferred embodiment, the semipreg comprises unidirectional fibers arranged in a plurality of strips (with either one or two layers), and the cuts are positioned to be aligned with the edges of each strip of fibers. This produces a plurality of strips of the semipreg, and the material in the gaps between the strips can be discarded as waste.

[0047] According to a preferred embodiment, the semipreg according to the invention has a rectangular cross-section with a well-defined width and thickness. Because such a semipreg is produced by cutting from a wider sheet, each layer in the prepreg has the same width, thus providing the rectangular cross-section.

[0048] Typically, the width is no greater than 60 mm, preferably no greater than 30 mm, in particular no greater than 15 mm, preferably from 10 mm to 60 mm.

[0049] Once the narrow strips of semipreg have been produced, they can be wound onto a core material, for example by winding, and the dry nature of the outer layer prevents adjacent layers from sticking together.

[0050] As mentioned above, the outer material, which is preferably a sheet of porous material, helps to maintain the integrity of the semipreg by providing a continuous surface on the outside of the semipreg.

[0051] If the outer layer is a porous material, the porous material sheets are typically a continuous sheet held together by interlocking and / or overlapping fibers. Such fibers can be woven, knitted, or randomly distributed, for example, jet-bonded fleece or yarn lay-ups, although non-woven, e.g., randomly distributed, is preferred. Such a sheet is often referred to as a veil in the prior art.

[0052] Such a porous sheet can be characterized by the degree of openness of the sheet, i.e., by the percentage of an average surface area of ​​the sheet that consists of open holes. The porous sheets of the present invention typically have a degree of openness of 10% to 70%, preferably 20% to 80%, and particularly 30% to 70%. This helps to maintain a lightweight sheet and allows the free passage of the resin.

[0053] The material of the porous material can be selected from a wide range of materials, for example polyamides (PA: PA6, PA12, PA11, PA6.6, PA6.10, PA6.12 etc.).), copolyamides (CoPA), ether or ester block polyamides (PEBAX, PEBA), polyphthalamide (PPA), polyesters (polyethylene terephthalate (PET), polybutylene terephthalate (PBT)), copolyesters (CoPE), thermoplastic polyurethanes (TPU), polyacetals (polyoxymethylene, POM), polyolefins (polypropylene (PP), high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE)), polyethersulfones (PES), polysulfones (PSU), polyphenylenesulfones (PPSU), polyetherketones (PEEK), polyetherketoneketones (PEKK), poly(phenylene sulfates) (PPS) or polyetherimides (PEI), thermoplastic polyimides, liquid crystal polymers (LCP), phenoxy resins, block copolymers such as styrene-butadiene methyl methacrylate copolymers (SBM), Methyl methacrylate acrylate or butyl methyl methacrylate copolymers (MAM), or a mixture of fibers composed of these thermoplastic materials.

[0054] The intention is that the arches made of porous material will not be removed from the semipreg, and they will therefore remain in place during application and hardening, becoming part of the composite structure obtained at the end.

[0055] The semipregs according to the invention are suitable for many different applications, and they can be quite heavy or light depending on the application. However, the invention is particularly suitable for heavy-duty applications, for example, for semipregs suitable for the manufacture of wind energy structures, which tend to be heavier and preferably weigh between 400 and 1800 g / m². 2 , especially from 800 to 1500 g / m² 2 have.

[0056] The unidirectional fibers can include ruptured (i.e., broken by stretching), selectively discontinuous or continuous fibers, although continuous fibers are preferred.

[0057] The structural fibers can be made from many different materials, such as carbon, graphite, glass, metallized polymers, aramid, and mixtures thereof. Carbon and glass fibers are preferred.

[0058] The curable resin can be selected, for example, from epoxy, isocyanate, and acid anhydride resins. Preferably, the curable resin is an epoxy resin.

[0059] Suitable epoxy resins can include monofunctional, difunctional, trifunctional and / or tetrafunctional epoxy resins.

[0060] Suitable difunctional epoxy resins include, for example, those based on: diglycidyl ether of bisphenol F, diglycidyl ether of bisphenol A (possibly brominated), phenol and cresol epoxy novolaks, glycidyl ethers of phenol-aldehyde adducts, glycidyl ethers of aliphatic diols, diglycidyl ethers, diethylene glycol diglycidyl ethers, aromatic epoxy resins, aliphatic polyglycidyl ethers, epoxidized olefins, brominated resins, aromatic glycidylamines, heterocyclic glycidylimidines and amides, glycidyl ethers, fluorinated epoxy resins, glycidyl esters and any combinations thereof.

[0061] Difunctional epoxy resins may preferably be selected from diglycidyl ethers of bisphenol F, diglycidyl ethers of bisphenol A, diglycidyl dihydroxynaphthalene or any combination thereof.

[0062] Suitable trifunctional epoxy resins include, for example, those based on phenol and cresol epoxy novolaks, glycidyl ethers of phenol-aldehyde adducts, aromatic epoxy resins, aliphatic triglycidyl ethers, dialiphatic triglycidyl ethers, aliphatic polyglycidyl ethers, epoxidized olefins, brominated resins, triglycidylaminophenyls, aromatic glycidylamines, heterocyclic glycidylimines and amides, glycidyl ethers, fluorinated epoxy resins, or any combination thereof.

[0063] Suitable tetrafunctional epoxy resins include N,N,N'N'-tetraglycidyl-m-xyloldiamine (commercially available from Mitsubishi Gas Chemical Company under the name Tetrat-X and as Erisys GA-240 from CVC Chemicals) and N,N,N',N'-tetraglycidyl-methylenedianiline (e.g. MY721 from Huntsman Advanced Materials).

[0064] The curable resin may also comprise one or more curing agents. Suitable curing agents include anhydrides, in particular polycarboxylic anhydrides; amines, in particular aromatic amines, e.g., 1,3-diaminobenzene, 4,4'-diaminodiphenylmethane, and in particular the sulfones, e.g., 4,4'-diaminodiphenylsulfone (4,4'-DDS) and 3,3'-diaminodiphenylsulfone (3,3'-DDS), and the phenol-formaldehyde resins. Preferred curing agents are the aminosulfones, in particular 4,4'-DDS and 3,3'-DDS.

[0065] As mentioned above, the semipregs of the present invention are suitable for being laid using an automated laying device.

[0066] According to a fourth aspect, the invention therefore relates to a method for depositing a continuous length of semipreg as defined herein onto a substrate by means of an automated laying apparatus.

[0067] As mentioned above, the semipregs of the present invention are particularly suitable for forming structural components of a wind turbine. Preferably, the semipreg is laid down to form a structural component of a wind turbine.

[0068] The molded structures are typically hardened by exposing them to elevated temperatures. One suitable hardening method involves the so-called vacuum bag technique. This involves placing the component in an airtight bag and drawing a vacuum to induce a compression force of up to atmospheric pressure.

[0069] The invention will now be explained by way of example and with reference to the following figures, in which: Fig. 1 is a schematic representation of a method according to the invention; Fig. 2 is a schematic representation of another method according to the invention; Fig. 3 a perspective representative view of a part of a sheet made of porous material with a plurality of strips of unidirectional fibers laid on it according to the invention; Fig. Figure 4 is a perspective representative view of a hardenable semipreg material according to the invention.

[0070] We turn to the characters; Fig. Figure 1 shows a method according to the invention. A plurality of carbon fiber ropes (10) are fed from a spool frame (not shown), which comprises a plurality of spools (not shown), each of which carries one rope (10). A continuous sheet of porous material (12) is brought into contact with the ropes (10) such that they are laid on the porous sheet parallel to each other and equally spaced apart. The two porous sheets 12 with the unidirectional fibers laid on them are then guided simultaneously to a pair of rollers (16). Care is taken to ensure that the strips of fibers on each of the porous sheets are aligned with a corresponding strip of fibers on the opposite sheet.

[0071] A supply of heated, curable resin (18) is also provided, which is fed to the rollers (16) simultaneously with the porous sheets. The rollers (16) are cooled below room temperature, so that the heated curable resin (18) begins to cool as soon as it comes into contact with the sheets of porous material. This cooling causes the resin to become essentially non-flowable and remain sandwiched between the two sheets. Before reaching the essentially non-flowable state, a small amount of resin impregnates the fibers closest to it, forming a bond between the resin and the fibers.

[0072] The sheets (14) and the resin (18) are slightly compressed by the rollers (16) to produce a semipreg according to the invention.

[0073] The semipreg is then directed to a cutting point (20) where cutters are arranged to cut the semipreg along the edges of each strip of fibers.

[0074] According to the invention, this produces a plurality of thinner strips of semipreg (22). The areas of porous material and resin located between the parallel strips of fibers are discarded as waste.

[0075] Fig. 2 shows a method that corresponds to the one in Fig. The same reference numerals have been used when the same procedural features are employed.

[0076] In this process, only one porous material (12) is used, the other being replaced by a conventional release paper (24) coated with a curable resin. When the resin comes into contact with the multitude of strands (10) of fibers, these are impregnated with the resin to form a sheet of release paper with a multitude of resin-impregnated strips of unidirectional fibers (26).

[0077] The sheets (14) and (26) are fed to cooled rollers (16), and resin (18) is introduced between the sheets as described above. After passing through the rollers, the paper (28) is removed, leaving behind a sticky resin surface. The semipreg thus produced has a dry surface, provided by the porous material, and a sticky surface formed by the resin surface. The asymmetric semipreg is then fed to the cutting station (20) to produce, as described above, a multitude of strips of semipreg (30).

[0078] Fig. Figure 3 shows a perspective view of an arch made of porous material (14) with a plurality of strips of unidirectional fibers laid upon it. As can be seen, the porous material (32) has a plurality of strips of unidirectional fibers (34) laid upon it, which are arranged parallel to each other and each have the same width, for example 1.5 mm, 6.35 mm, 12.7 mm, 25.4 mm, 75 mm, 150 mm, 300 mm, 600 mm or 1200 mm. The fibers are arranged so that they are parallel to the length of the strip (34). As can be seen, the strips (34) are separated by evenly spaced gaps.

[0079] Fig. 4 is a perspective view of a strip of semipreg (22) according to the invention, as described in Fig. The process shown in 1 can be used to produce the product.

[0080] The strip (22) has a well-defined rectangular cross-section, although it is composed of several layers. The cross-section can, for example, have a width of 1.5 mm, 6.35 mm, 12.7 mm, 25.4 mm, 75 mm, 150 mm, 300 mm, 600 mm, or 1200 mm. The strip (22) comprises two outer arcs (36) of porous material, two layers of essentially non-resin-impregnated unidirectional fibers (38), and a central layer of essentially non-flowable, curable resin (40).

[0081] A length of the strip (22) can be wound onto a spool to form a coiled arrangement. The spool can then be inserted into an automated laying machine equipped with a heating device near the head. During the automated laying process, the heating device causes the resin to become fluid, thus providing the tackiness necessary for successful adhesion of the semipreg to the substrate.

Claims

[1] Use of a structure (22) in an automatic process for placing it in a mold, wherein the structure (22) comprises a core layer comprising a fibrous reinforcement (14, 38) and a curable resin (18, 40), and is provided with an outer layer (12, 36) that is free of curable resin, wherein the outer layer (12, 36) is made sticky by the curable resin (18, 40) as a result of placing the structure (22) in the mold. [2] Use according to claim 1, wherein the outer layer (12, 36) is a fibrous layer. [3] Use according to claim 1 or claim 2, wherein outer layers (12, 36) are arranged on opposite sides of the core layer. [4] Use according to claim 2 or claim 3, wherein the outer layer (12, 36) comprises a porous material. [5] Use according to any of the preceding claims, wherein the fibers (10) in the fibrous reinforcement (14, 38) are unidirectional. [6] Use according to any of the preceding claims, wherein the structure (22) is in the form of a strip or band (34) with a width in the range of 10 mm to 60 mm. [7] Use according to any one of the preceding claims, wherein the material of the outer layer (12, 36) is selected from the group consisting of polyamides (PA), copolyamides (CoPA), ether or ester block polyamides (PEBAX, PEBA), polyphthalamides (PPA), polyesters (polyethylene terephthalate (PET), polybutylene terephthalate (PBT)), copolyesters (CoPE), thermoplastic polyurethanes (TPU), polyacetals (polyoxymethylene (POM)), polyolefins (polypropylene (PP), high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE)), polyethersulfones (PES), polysulfones (PSU), polyphenylenesulfones (PPSU), polyetheretherketones (PEEK), polyetherketoneketones (PEKK), poly(phenylene sulfates) (PPS), or polyetherimides (PEI), thermoplastic polyimides, liquid crystalline polymers (LCP), phenoxy resins, block copolymers such as styrene-butadiene-methyl methacrylate copolymers (SBM),Methyl methacrylate-acrylate or butyl methyl methacrylate copolymers (MAM) or a mixture thereof. [8] Use according to any of the preceding claims, wherein the structure (22) comprises a curable semipreg comprising a layer of non-flowable, curable resin (18, 40) and a layer of non-resin-impregnated, unidirectional fibers (14, 38), wherein the semipreg has on an outer surface a layer of a porous, arc-shaped material (12, 36). [9] Structure (22) for use according to any of the preceding claims, wherein structure (22) comprises a curable semipreg comprising a layer of non-flowable, curable resin (18, 40) and a layer of non-resin-impregnated, unidirectional fibers (14, 38), wherein the non-resin-impregnated, unidirectional fibers (14, 38) are in contact with a porous, arc-shaped material (12, 36) on an outer surface of the semipreg and wherein the non-flowable, curable resin (18, 40) becomes flowable by the application of heat. [10] Structure (22) according to claim 9, comprising a second layer of unidirectional fibers (14, 38; 26), wherein the fibers in the two layers are oriented such that they are unidirectional in the same direction. [11] Structure (22) according to claim 10, wherein the second layer of unidirectional fibers (14, 38) is not impregnated with resin and is in contact with a second porous, arc-shaped material (12, 36) arranged on the other surface of the semipreg. [12] Structure (22) according to claim 10, wherein the second layer of unidirectional fibers (26) is impregnated with curable resin. [13] Structure (22) according to one of claims 10 to 12, wherein the unidirectional fibers (14, 38; 26) are arranged as a plurality of longitudinal strips (34) which are separated from each other by a discrete gap (32). [14] Structure (22) according to any one of claims 10 to 13, wherein the strips of unidirectional fibers (14, 38; 26) are of the same width, and the width is not greater than 60 mm. [15] Structure (22) according to any one of claims 10 to 14, wherein both the first and the second layer of fibrous reinforcement (14, 38; 26) are provided as a plurality of longitudinal strips (34) which are separated from each other by a discrete gap (32). [16] Structure (22) according to claim 15, wherein the strips (14, 38; 26) in each layer are aligned in accordance with a respective opposite strip (14, 38; 26) in the other layer. [17] Structure (22) according to any one of claims 9 to 16, which has a rectangular cross-section. [18] Structure (22) according to any one of claims 9 to 17, wherein the porous arc-shaped material (12, 36) is a continuous arc held together by interconnected and / or overlapping fibers. [19] Structure (22) according to claim 18, wherein the porous arc-shaped material (12, 36) has a degree of openness of 10% to 70%. [20] Fiber-reinforced structure comprising one or more structures (22) according to any one of claims 9 to 19, wherein the resin (18, 40) is cured. [21] Wind turbine structure made from a fiber-reinforced structure according to claim 20. [22] A method for producing a curable semipreg material (22) comprising the stage of producing a sheet of porous material (12, 36) with unidirectional fibers (14, 38) laid on it, and providing a layer of non-flowing curable resin (18, 40) wherein the porous material (12, 36) is on an outer surface, and pressing the layers together to form a curable semipreg (22) wherein the outer surface of the porous material (12, 36) is not impregnated with resin after pressing, and further comprising the method heating the non-flowing curable resin (18, 40) to a temperature at which it becomes flowable and then applying it to the sheet or sheets (14, 38). [23] Method according to claim 22, wherein the heated resin (18, 40) and the sheet or sheets (14, 38) are guided to cooled rollers (16), whereby the resin (18, 40) is cooled and becomes non-flowable. [24] Method according to claim 22 or claim 23, wherein the sheet of porous material with unidirectional fibers (14, 38) laid on it and the non-flowing resin (18, 40) are simultaneously passed through a pair of rollers (16). [25] Method according to any one of claims 22 to 24, wherein the semipreg (22), once it has been produced, is automatically cut into a plurality of strips (34), the sections being oriented in accordance with the direction of the orientation of the fibers (10). [26] Method according to claim 25, wherein the semipreg (22) comprises unidirectional fibers (10) arranged in a plurality of strips (34) (with one or two layers) and the cuts are positioned such that they are aligned in accordance with the edges of each strip of fibers (34). [27] Method according to claim 26, wherein the strips of unidirectional fibers (34) have been deposited onto a sheet of porous material (14) from a wound supply of strips of unidirectional fibers. [28] Method comprising the automatic deposit of a continuous length of structure (22) according to any one of claims 9 to 19 onto a substrate. [29] Automatic process in which a structure (22) comprising a core structure comprising a fibrous reinforcement (14, 38) and a curable resin (18, 40) is provided with an outer layer (12, 36) that is free of curable resin (18, 40), wherein the structure (22) is automatically placed in a mold and is compressed before or during the placement of the structure (22) in the mold to make the outer surface (12, 36) sticky. [30] Automatic method according to claim 29, wherein several layers of the structure (22) are automatically deposited as a stack in the mold. [31] Automatic method according to claim 29 or claim 30, wherein the structure (22) is heated to cause the resin to make the outer surface (12, 36) sticky. [32] Automatic method according to any one of claims 29 to 31, wherein the structure (22) is deposited to form a structural component of a wind turbine.

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