Lightning strike surfacing material

Abstract

There is provided a surfacing material comprising: a) a fibrous support layer having a first surface and an opposing second surface, a first edge and an opposing second edge, and first and second ends; and5 b) a lightning strike protection (LSP) layer having a first surface and an opposing second surface, a first edge and an opposing second edge, and first and second ends; wherein the first surface of the LSP layer contacts the second surface of the fibrous support layer, and the first edge of the LSP layer extends beyond the 10 first edge of the fibrous support layer. There is also provided methods for manufacturing a cured composite structure using the materials of the invention.

Description

[0001] LIGHTNING STRIKE SURFACING MATERIAL

[0002] The present invention relates to surfacing materials that provide a surface finish for composite structures including an integral lightning strike protection layer as well as methods of forming cured composite structures using the surfacing materials and cured composite structures produced using the surfacing materials. The present invention particularly relates to surfacing materials that provide an enhanced surface finish and / or that reduce the need for post-curing treatments such as gel coat removal, sanding and painting, especially, but not exclusively, for use in the aerospace and wind turbine industries.

[0003] Composite materials have well-documented advantages over traditional construction materials, particularly in providing excellent mechanical properties at very low material densities. As a result, the use of such composite materials has become widespread in many industries, including the aerospace, automotive, marine and wind turbine industries.

[0004] Prepregs or semipregs, comprising a fibre arrangement either fully or partially impregnated with a thermoplastic or thermocurable resin, such as epoxy resin, are widely used in the manufacture of composite structures. Typically, a number of plies of prepregs and / or semipregs are "laid up" as desired and the resulting assembly, or laminate, is placed in a mould and cured, usually by exposure to elevated temperatures, optionally under pressure, to produce a cured composite laminate. In an alternative manufacturing technique, a fibrous material is laid up, generally within an enclosure into which a liquid resin system can be infused to envelope the fibrous material, where it may then be cured to produce the finished article. In the infusion process the layers of fibre may be dry fibres or mixtures of dry fibres and prepregs and / or semipregs.

[0005] As the first layer deposited on a mould or tool during the laying up process will typically form the outer layer of the composite structure being formed, the first layer may sometimes comprise a "surfacing material", i.e. a layer of material that ensures the surface quality of the outer layer is sufficient for the intended use of the material. Surfacing materials may be used to enhance both the appearance and the environmental resistance of the surfacing material. Preferably, the surfacing material will be formed from a fibrous material so that it will be compatible with the underlying layers of fibres forming the composite.

[0006] Prepregs, semipregs, and dry fibre sheets, and the associated surfacing materials may generally by formed as very long materials, but are difficult to manufacture, store and / or transport as wide sheets, and are generally produced in the form of relatively long strips, i.e. with much longer lengths than widths. When relatively large materials are being produced therefore, for example aircraft fuselages or wings or wind turbine blades, the composite materials are laid up as parallel strips, with a continuous series of strips forming each layer. The strips may be laid down by hand, but in order to improve the efficiency and accuracy of the lay-up process, automated lay-up techniques have been developed. For such automated processes the prepregs, semipregs or dry fibre layers are often slit into tapes before being laid up in tape form.

[0007] As composite materials are generally built up from multiple layers of material, it is important that the layers are laid down accurately, and this is particularly critical when the layer that will form the outer layer of the composite is formed from a surfacing material, as any gaps in the surfacing material will reduce the quality of the appearance of the material and may compromise the integrity of the final product. Thus, it is particularly important to ensure that the first layer of material laid down does not include gaps between the individual strips of material forming the layer. Composite materials are therefore typically laid up with overlaps between the individual strips to ensure that there are no gaps in the layers.

[0008] It is important that certain components made from fibre reinforced composite materials are protected against lightning strikes. This is particularly important for components used in aerospace vehicles such as aircraft and helicopters, in particular aircraft fuselage, wing and tails, and large composite structures such as wind turbines, particularly wind turbine blades. As composite materials are made up from a laminate of a plurality of fibre layers, interleafed with resin layers, even if the fibre layers have some electrical conductivity (for example when the fibres comprise carbon fibres), the presence of the interleaf layers means that this is only exhibited in the plane of the laminate, and the electrical conductivity in the direction orthogonal to the surface of the laminate, the so-called z-direction, will be very low. This situation will be even worse in composites formed from fibres that have low conductivity, such as glass fibres, as there will be very little conductivity in any direction.

[0009] The lack of conductivity in one or more planes is generally accepted to contribute to the vulnerability of composite laminates to electromagnetic hazards, such as lightning strikes. A lightning strike can cause damage to the composite material which can be quite extensive, and could be catastrophic if occurring on an aircraft structure in flight or to a large wind turbine blade. A well-known method of addressing this problem is to include a conductive element, e.g. metallic mesh or foil, at or near the external surface of the composite material. Such a conductive layer (known as a lightning strike protective layer) is not necessarily required to cover the entire surface of a composite structure, for example in some wind turbine blades only the tips of the blades include this feature, but in many cases complete cover is required, for example in aeroplanes. Furthermore, where a lightning strike protective layer is present, it is important that it is continuous, because breaks in the path can lead to damage, for example due to resistive. Incorporating such an additional layer in a large composite structure can be very time consuming.

[0010] US2013 / 0328226 discloses the incorporation of a conductive layer in a composite, compression-moulded part, but this requires the application of the conductive layer to a mould surface as a separate processing step, and also results in the conductive layer forming the outer, environment facing, surface of the part, which can leave the conductive layer vulnerable to damage and reduces the quality of the surface.

[0011] An alternative, common way for such a conductive element to be applied during manufacturing is to deposit a layer of conductive material during the lay-up of a composite material, generally after the first, surfacing layer, has been laid down. Such laying down is difficult to do using automated processes as preferred conductive elements are thin metal foils, such as aluminium or copper foil, and these are not strong enough to be processed by automated slitting and tape lay-up, particularly when using automated fibre placement which provides greater stress on the foil during placement due to their placement on structures with complex shapes. Thus, special apparatus is required for automated lay-up of conductive elements. Alternatively, the conductive element may be laid down manually by skilled handlers, but this requires additional time and expertise. The addition of a conductive element also represents an additional step in the lay-up process, increasing the time required for the construction of the material and therefore the cost.

[0012] Consequently, the labour, equipment and time required to lay-down a conductive element whilst maintaining reasonable surface quality causes an increased cost and time burden on the manufacture of such structures, and ideally such conductive electromagnetic hazard protector elements would be incorporated as part of the standard materials used in the lay-up process, particularly as part of the surfacing layer and without the need for a separate surface layer deposition step. In practice however, incorporation of a conductive component into a prepreg or fabric material for inclusion in a layup process has not been practical on an industrial scale because when the material incorporating the conductive component is laid up with overlaps, the overlap prevents the creation of a continuous electrically conductive layer across the entire lay-up. This is because, when a section of surfacing material having a conductive material on one surface is laid down with a region overlapping an adjacent identical section of surfacing material, the conductive material in the overlapping section of surfacing material contacts the reverse side of the overlaid section of surfacing material, i.e. the resin or fibre side rather than the conductive material side, so that no conductive contact is made. This means that the electromagnetic hazard protector element will not function when included as part of conventional prepregs and fibre strips that are laid up in conventional laying up processes with overlap of the prepregs and fibre strips. US2012 / 0063050 discloses a method for producing a structure having a lightning strike protective layer by forming a number of lengths of lightning strike protection means, each comprising a lightning strike protection strip disposed on a reinforcement layer, and depositing the lightning strike protection means onto a structural layer by various methods, including automatic deposition. In some embodiments of the disclosed lightning strike protection means, the lightning strike protection strip may be wider than the associated reinforcement layer, so that when two of the lightning strike protection means are laid down next to each other, the lightning strike protection strip of one lightning strike protection means overlaps with the lightning strike protection strip of the adjacent lightning strike protection means, to improve electrical conduction between adjacent strips.

[0013] In general, the lightning strike protection strip will form the outer, environment-contacting surface of the structures produced by the methods disclosed in US2012 / 0063050, but a further aspects is stated to include providing a smooth finish to the lightning strike protection means. This may be achieved by embedding the lightning strike protection strip in a matrix material, applying a surface veil over the lightning strike protection strip and making smoothing passes over the lightning strike protection strip with the fibre placement, tape placement or other manufacturing equipment. However, these steps are all carried out after the deposition of the lightning strike protection means onto the structural layer, and therefore represent additional processing steps in the laying down procedure. Furthermore, there is no suggestion in US2012 / 0063050 that the surface veil should be applied in an offset arrangement with respect to the lightning strike protection strip.

[0014] WO2016 / 055421 also discloses a surfacing material for use in automatic tape laying devices, comprising a layer of reinforcement material and a conducting surface layer in contact with the reinforcement material, wherein the conducting surface layer extends beyond the surface of the reinforcement material, so that when strips of the surfacing material are laid down next to each other the conducting surface layer of one strip of surfacing material may contact and overlap with the conductive surface layer of an adjacent strip of surfacing material. In use, the conducting surfacing layer of the surfacing materials of WO2016 / 055421 form the outer, environment contacting surface of the structures into which they are formed, resulting in generally poor quality surfaces for such structures and potential loss of lightning strike protection due to environmental surface damage and / or the need to apply a protective surface layer as a separate processing step.

[0015] The present invention aims to obviate or at least mitigate the above described problems and / or to provide improvements generally.

[0016] According to the present invention there is provided a surfacing material comprising: a) a fibrous support layer having a first surface and an opposing second surface, a first edge and an opposing second edge, and first and second ends; and b) a lightning strike protection (LSP) layer having a first surface and an opposing second surface, a first edge and an opposing second edge, and first and second ends; wherein the first surface of the LSP layer contacts the second surface of the fibrous support layer, and the first edge of the LSP layer extends beyond the first edge of the fibrous support layer.

[0017] The present invention further provides a process for preparing a cured composite structure comprising: a) depositing a first portion of surfacing material according to the present invention on the surface of a mould or tool with the fibrous support layer closer to the surface of the mould or tool than the LSP layer; b) depositing a second portion of surfacing material according to the present invention on the surface of the mould or tool adjacent to and overlapping the first portion so that the first surface of the LSP layer of the second portion of surfacing material contacts the second surface of the LSP layer of the first portion of surfacing material; c) continuing to deposit portions of surfacing material according to the present invention in the same manner as the second portion, to form a continuous layer of surfacing material having a continuous electrical path across the entire layer; d) depositing further layers of fibrous reinforcement and / or resin on to the continuous layer of surfacing material to form an uncured composite material; and e) curing the uncured composite material to provide a cured composite structure having a continuous lightning strike protection layer across the structure.

[0018] The surfacing materials of the present invention enable the manufacture of cured composite materials having a continuous lightning strike protection layer across the structure without the need for a separate step for depositing the lightning strike component. Large scale production of such composite materials having a continuous LSP layer using automated means for laying down all, or the majority of, the components of the material is also facilitated by the invention. The invention therefore provides a significant reduction in the length and complexity of the manufacturing process of composite materials having a continuous lightning strike protection (LSP) layer adjacent to the surface by avoiding the need for a step of applying a separate lightning strike component, and this saving in time and complexity also represents a reduction in the cost of the manufacturing process.

[0019] In the surfacing materials of the present invention the first surface of the LSP layer contacts the second surface of the fibrous support layer, i.e. the LSP and the fibrous support layers are adjacent to each other and are generally not separated by any other component other than a possible resin layer as discussed herein. In certain embodiments of the present invention, the first surface of the LSP layer and the second surface of the fibrous support layer are connected together, for example by use of an adhesive or resin or by stitching.

[0020] In the surfacing materials of the present invention the first edge of the LSP layer extends beyond the first edge of the fibrous support layer, i.e. at least a portion of the LSP layer is not in contact with the fibrous support layer. The LSP layer may extend beyond one or more of the second edge, the first end and the second end of the fibrous support layer, but in preferred embodiments the LSP layer extends only beyond the first edge of the fibrous support layer. This reduces the amount of LSP material required to form the surfacing material and reduces the weight of the surfacing material, and also helps to create a relatively smooth layer when the surfacing layer is laid down overlapping adjacent portions of the surfacing material.

[0021] The extension of the first edge of the LSP layer beyond the first edge of the fibrous support layer may be intermittent or partial, i.e. the LSP layer may extend beyond only a section of the fibrous support layer or over only a number of sections, but preferably the LSP layer extends beyond substantially the whole of the first edge of the fibrous support layer. The length by which the first edge of the LSP layer extends beyond the first edge of the fibrous support layer will depend upon user requirements, but should not be so long as to make the surfacing material unstable or difficult to handle. In particular, the length of overlap of the first edge of the LSP beyond the first edge of the fibrous support layer will be from 1 to 150mm, preferably 5 to 100mm such as 50mm.

[0022] Whilst the LSP layer may extend beyond the fibrous support layer at one or both ends, or vice versa, generally the ends of the LSP layer and the fibrous support layer will be congruent, i.e. there will be little or no overlap of the materials at either end.

[0023] The LSP layer may cover the entire second surface of the fibrous support or may only partially cover the second surface, so long as a continuous layer of LSP material is formed when the surfacing material is laid up in overlap with another portion of the surfacing material. However, in some embodiments of the present invention, the second edge of the LSP layer may be offset from the second edge of the fibrous support layer. Offsetting the second edge of the LSP layer from the second edge of the fibrous support layer reduces the amount of LSP material used in the invention, resulting in cost savings and also a reduction in the weight of the surfacing material. In embodiments in which the second edge of the LSP layer is offset from the second edge of the fibrous support layer the length of the offset may be any convenient length so long as the LSP layer may be contacted by the LSP layer of a further portion of surfacing material laid down in overlap with the surfacing material in an automated lay-up process. In particular, the offset length should be less than the sum of the length by which the LSP layer extends beyond the first edge of the fibrous support layer and the length of overlap of two adjacent portions of surfacing material. In particular, the length of offset of the second edge of the LSP from the second edge of the fibrous support layer will be from 1 to 150mm, preferably 5 to 100mm such as 50mm. In particular embodiments of the invention, the length of the offset of the second edge of the LSP layer from the second edge of the fibrous support is equal to the length of the extension of the first edge of the LSP layer beyond the first edge of the fibrous support layer, i.e. the distance between the first and second edges of the LSP layer is the same as the distance between the first and second edges of the fibrous support layer, so that the LSP layer and the fibrous support layer have equal widths. This embodiment avoids the use of excessive LSP material, whilst ensuring that overlap of the LSP layers will occur at any length of overlap of the surfacing material.

[0024] In practice, the length of the overlap of the sections of surfacing material in a lay-up process will depend upon the apparatus used for the process. In particular, the length of overlap used will be selected so that a continuous layer of the fibrous support layer is laid down in an automated process, i.e. the overlap distance will be selected to be greater than the expected variation in the placement accuracy of an automated lay-up apparatus. However, the length of the overlap will generally be selected so as not to be so long as to require the use of excess surfacing material. In most lay-up processes the overlap distances will generally be from 1mm to 100mm.

[0025] The surfacing material of the present invention may be any suitable shape, but will generally be regular to enable automated production, such as square or rectangular. Preferably, the surfacing material of the present invention is rectangular with a generally regular cross cross-section, i.e. having a length that is greater than the width of the material, so that the first and second edges of the fibrous support and the LSP layers are longer than the respective first and second ends.

[0026] The surfacing material of the present invention is particularly useful for use in the manufacture of large composite materials, partly because automated laying down of materials is more important and cost effective in the manufacture of large composite parts, but also because of the greater waste in materials if faults in the manufacturing process lead to gaps in the surface layer and / or the LSP layer. In particular embodiments of the present invention, the length of the surfacing material is at least 5 times the width, up to many, many times greater. Particularly suitable lengths for the surfacing material of the present up to 500m, up to 1000m and up to 4000m. Particularly suitable widths for the surfacing material of the present invention up to 2m, such as 3mm to 50mm. The thickness of the surfacing materials of the present invention will depend on the number and nature of the layers incorporated therein, but will generally be negligible.

[0027] Lightning strike protective components for composite materials are well known, and suitable components generally comprise an electrically conductive layer. Any known lightning strike protective component may be used in the surfacing materials of the present invention, but electrically conductive layers, for example metal layers, are particularly suitable, and in order to reduce the weight / bulk of the surfacing materials, electrically conductive metal meshes or expanded foils are particularly preferred, for example copper or aluminium meshes or expanded foils.

[0028] The fibrous support layer incorporated in the surfacing materials of the present invention acts as a support to the LSP layer and assists in handling the surfacing material, and also prevents print-through from the LSP layer and / or any fibrous layers positioned above the surfacing material to the outer surface of materials incorporating the surfacing material after formation of a cured composite. Preferably, the fibrous support layer should be both resin and air permeable.

[0029] Any suitable material may be used to form the fibrous support layer, but in preferred embodiments of the invention the fibrous support layer comprises a non-woven fibre carrier. Suitable non-woven fibre carriers include components known as veils or fleeces.

[0030] The non-woven fibre carrier used in this embodiment of the invention may be formed from any suitable fibres, but preferably the non-woven fibre carrier comprises glass, carbon, polyester, polyamide or aramid (aromatic polyamide) fibres, or combinations thereof, more preferably glass fibres. The fibres of the non-woven fibre carrier may be bound together in any suitable manner, but preferably the fibres of the non-woven fibre carrier are bound with an organic binder. When present, any suitable amount of organic binder may be incorporated in the non-woven fibre carrier, such as 1 to 10%w / w.

[0031] The non-woven fibre carriers used in this embodiment of the present invention may be any suitable density, but should be robust enough to prevent print- through of underlying fibrous layers after formation of a cured composite, and also be able to withstand processing in the processes of the invention. Conversely, the non-woven fibre carrier should not be so heavy as to unnecessarily increase the weight of the surfacing material and composite materials produced therefrom. In preferred embodiments of the present invention the non-woven fibre carrier has an areal density of at least 10 g / m2and no more than 300 g / m2, preferably 20 to 200 g / m2, more preferably 30 to 90 g / m2, even more preferably 30 to 60 g / m2.

[0032] Suitable non-woven glass mats or fleeces are commercially available under the trade name Evalith® from Johns Manville, Denver, Colorado, USA, including but not limited to Evalith® ST-3022, S 4030 and S 5030, and under the trade name Changhai® from Taishan Fiberglass Inc., Economic Development Zone, Taian, Shandong, P.R. China, including but not limited to Changhai® S-SM30, S-SM50, S-HM30 and S-HM50.

[0033] In embodiments of the present invention in which the fibrous support layer comprises a non-woven fibre carrier it may also comprise further components, such as a layer of reinforcement fibres. The layer of reinforcement fibres may increase the robustness of the fibrous support layer and also assist in print- through prevention. The layer of reinforcement fibres is preferably contiguous with the non-woven fibre carrier (so that the non-woven fibre carrier does not overlap the layer of reinforcement fibres at either edge. When present, the layer of reinforcement fibres preferably directly contacts the non-woven fibre carrier, and is preferably located between the non-woven fibre carrier and the LSP layer. The reinforcement fibre included in the fibrous support layer may be any conventional fibre material, preferably glass fibre, and can be woven or a noncrimped fabric. The reinforcement fibre included in the fibrous support layer may be unidirectional or multi axial (e.g. biaxial), and may be any weight, but is preferably no more than 500 g / m2, more preferably 50 to 500 g / m2, most preferably 100 to 300 g / m2.

[0034] The fibrous support layers of the surfacing materials of the present invention preferably include a resin composition. The resin composition may be a separate layer to the fibrous component of the fibrous support, such as a non-woven fibre carrier, but preferably the resin composition partially or fully impregnates the fibrous component of the fibrous support layer. Preferably, the resin composition attaches the fibrous support layer to the LSP layer. In embodiments of the present invention in which the fibrous support layer comprises a non-woven fibre carrier and a layer of reinforcement fibres, the resin composition may attach the non-woven fibre carrier to the layer of reinforcement fibres.

[0035] The resin composition of the fibrous support layer may comprise a thermosetting resin or a thermoplastic resin. Any resin compositions used in thermoplastic compositions may be suitable for use as the resin composition of the fibrous support layer in the surfacing materials of the present invention, but preferably the resin composition comprises an epoxy resin or a blend of epoxy resins. Preferred epoxy resins for use in the present invention have Epoxy Equivalent Weight (EEW) in the range of 150 to 1,500, preferably in the range of 150 to 1,000, 150 to 750, or 150 to 500, such as 200 to 500. Preferably the resins of the fibrous support layer, when present, comprise a curing agent. Suitable resins include the M9 and M79 range of epoxy resins available from Hexcel Composites Limited, Duxford, Cambridgeshire, United Kingdom.

[0036] In particular embodiments of the surfacing materials of the present invention, the first surface of the fibrous support layer contacts a surface layer which provides an external mould- or tool-contacting surface of the surfacing material. The surface layer helps to provide an enhanced surface finish to materials incorporating the surfacing materials of the invention, and may also provide additional pre and post curing benefits, such as allowing the manufacture of cured composite materials in a mould without the use of a mould release agent and / or the manufacture of cured composite materials that are ready for use without the need for the application of a protective outer layer after curing, such as by painting. The surface layer may generally cover the entire first surface of the fibrous support layer, but may be offset from one or both edges and / or extend beyond one or both edges thereof. In particular embodiments, the surface layer has the same width as the fibrous support layer and is either a) congruent with both edges of the fibrous support layer or b) extends beyond the second edge of the fibrous support layer by a first distance and is offset from the first edge of the fibrous support layer by the same distance. Where the surface material is offset from and / or extends beyond the edges of the fibrous support layer the distance is generally from 1 to 150mm, preferably 5 to 100mm such as 50mm.

[0037] In a first aspect of the embodiment of the present invention in which the fibrous support layer contacts a surface layer, the surface layer comprises a non-woven fibre veil at least partially impregnated by a thermosetting resin composition. Preferably the thermosetting resin composition fully impregnates the nonwoven fibre veil and attaches the non-woven fibre veil to the first surface of the fibrous support layer and also forms the outer, mould- or tool-contacting surface of the surfacing material. Preferably, the thermosetting resin composition of the surface layer forms a continuous layer on the external mould- or tool- contacting surface of the surfacing material.

[0038] In the first aspect of the present invention, the thermosetting resin composition which at least partially impregnates the non-woven fibre veil may be any suitable resin, but preferably comprises an epoxy resin composition comprising a curing agent, such as any of the epoxy resin compositions discussed with respect to the resin compositions of the fibrous support. In a particular embodiment, the thermosetting resin composition of the surface layer comprises a rheology modifier. The term "rheology modifier" is used to refer to a compound or substance that is capable of imparting non-Newtonian rheological properties in materials such as resin composition. The rheology modifier causes the minimum viscosity of the resin under shear to be increased compared to the non-viscosity modified resin, and also causes the viscosity of the resin when not under shear to be increased by a greater amount compared to the non-rheology modified resin. This can be measured using a shear sweep viscosity method. Suitable conditions for a shear sweep viscosity method are 25mm parallel plates with a gap of 1mm set to provide a shear rate from 0.1 to 100s, and a temperature of 60°C. In the present invention, the rheology modifier is preferably selected such that when measured as set out above, the first resin composition has a viscosity at 60° and at 0.1s1of from 200 to lOOOPa.s; and a viscosity at 60°C and at 100s1of 25% or less of the viscosity at 0.1s1, with the proviso that the viscosity at 60°C and at 100s1is not less than 25Pa.s. A shear sweep viscosity method may be carried out using any viscometer adapted to provide the above conditions, for example using a TA HR-2 Discovery Hybrid Rheometer manufactured by TA Instruments, New Castle, Delaware, USA. Suitable rheology modifiers include treated and untreated grades of fumed silica, such as hydrophobic silica. Hydrophilic silica may also be used, but preferably in combination with a thixotrophy booster. Organophilic phyllosilicates may also be used. Suitable silicas include Aerosil® R 202, available from Evonik Resource Efficiency GmbH, Germany, and Cab-O- Sil® TS720, available from Cabot Corporation, Alpharetta, Georgia, USA. Suitable organophilic phyllosilicates include Garamite-7305, available from BYK (Altana Group). Suitable thixotropy boosters include those available under the trade name Rheobyk® from BYK-Chemie GmbH, Wesel, Germany. In an embodiment, the rheology modifier is a hydrophobic fumed silica, such as Aerosil® R202. The rheology modifier, optionally in combination with a thixotropy booster, may be present in an amount 1 to 20% by weight based on the total weight of the first resin composition, preferably 1 to 15% by weight, 1 to 12% by weight, 1 to 10% by weight, 2 to 10% by weight, 3 to 9 % by weight, 4 to 8% by weight, or any combination thereof, based on the total weight of the resin composition.

[0039] In the first aspect of the present invention, the non-woven fibre veil at least partially impregnated by the thermosetting resin composition may be any nonwoven material that is both air and resin permeable. Suitable non-woven fibre veils are lightweight, preferably less than 100g / m2, but are preferably robust enough to carry a layer of resin and to withstand processing in the processes of the invention and may comprise continuous fibres or discontinuous fibres. In preferred embodiments, the non-woven fibre veil is a thermoplastic fibre veil having an areal weight in the range 1 to 80g / m2, preferably wherein the fibres are bound together using an organic binder to impart structural integrity to the material. In a particular embodiment, the thermoplastic material comprises a polyester, or an aliphatic or semi-aromatic polyamide, such as nylon or polyester fibres. In another embodiment, the non-woven fibre veil comprises a veil formed of a blend of thermoplastic fibres, such as a blend of polyester and nylon fibres. The organic binder is typically present in an amount of 1 to 10% by weight based on the total weight of the first non-woven fibre carrier. The non-woven fibre veil acts as a support or carrier for the resin composition of the surface layer and controls the manner in which the resin composition interacts with the surface of a mould or tool in order to provide a good surface finish. In an embodiment, the non-woven fibre veil has an openness of between 1 to 10%, preferably 2 to 9%, and / or a mean open area of between 75 to 350 pm2. In preferred embodiments, the non-woven fibre veil has an areal weight in the range of 5 to 50 g / m2, more preferably from 10 to 40 g / m2. In an embodiment, the non-woven fibre veil has an air permeability of approximately 2,300 L / m2 / s at an applied pressure of 200Pa. The air permeability of the non-woven fibre veil may be measured by ASTM D737-18 - Standard Test Method for Air Permeability of Textile Fabrics. Suitable thermoplastic fibre veils include those commercially available under the trade name Optiveil® T2761-00 from Technical Fibre Products Limited, Burnside Mills, Kendal, Cumbria, United Kingdom.

[0040] In a second aspect of the embodiment of the present invention in which the fibrous support layer contacts a surface layer, the surface layer comprises an ultraviolet (UV) resistant polymer layer. Preferably the UV resistant polymer layer forms a continuous layer on the external mould- or tool- contacting surface of the surfacing material. In this aspect of the invention the UV resistant polymer layer is preferably non-removably attached to the first surface of the fibrous support layer, for example by means of a resin composition, which may be a resin composition which forms part of the fibrous support layer or a separate layer located between the fibrous support layer and the UV resistant polymer layer and linking the two together. The separate resin composition, if present, may comprise a thermocurable or a thermoplastic resin, preferably an epoxy resin.

[0041] In the second aspect of the invention, the UV resistant polymer layer preferably comprises a flexible film, preferably a polyurethane film, more preferably a polyurethane based thermoplastic film, such as a polycaprolactone-based aliphatic polyurethane film. Examples of suitable UV resistant polymer films include Argotec Thermoplastic Polyurethane (TPU) films, such as Argotec 46510-White, Argotec 46510-Clear and Argotec 49510, all available from Schweitzer-Mauduit International, Inc., Georgia, USA. Preferred UV resistant polymer layers have the UV resistant polymer layer have a Taber Abrasion resistance value of no more than 12mg / 500 cycles when measured according to ASTM D4060, preferably no more than 6mg / 500 cycles; and / or a softening point below 0°C, preferably below -10°C, more preferably below -40°C; and / or the surface of the UV resistant polymer layer which contacts the fibrous support layer has a surface energy of at least 30 dyn / cm, preferably at least 35 dyn / cm when tested by a standard method using Dyne test pens, as set out in ISO 8296.

[0042] In the second aspect of the invention, the change in the Yellowness Index of the UV resistant polymer layer is no more than 3.0 when tested according to ASTM D-4329 cycle B using a QUV weatherometer fitted with UVA 340 bulbs under a repeated cycle of 8 hours at 70 °C under UVA and 4 hours at 50°C water condensation (no UVA) for 2000 hours total; and / or the UV resistant polymer layer has a thickness of from 5 to 500pm, preferably from 25 to 250pm; and / or the thermocurable or thermoplastic resin layer has an areal weight of from 3 g / m2to 500 g / m2, preferably from 25 g / m2to 200 g / m2.

[0043] In a particular embodiment of the present invention, the surfacing material further comprises a fibrous reinforcement layer having a first surface and an opposing second surface, a first edge and an opposing second edge, and first and second ends; wherein the second surface of the LSP layer contacts the first surface of the fibrous reinforcement layer, and the second edge of the fibrous reinforcement layer is offset from the second edge of the LSP layer. This fibrous reinforcement layer may provide additional stability to the surfacing material and also reduces processing time when using the surfacing material to lay-up composite parts as it reduces the number of separate layers of fibrous reinforcement required in the lay-up and therefore laying up steps.

[0044] In this embodiment, the fibrous reinforcement layer is located on the second surface of the LSP layer, i.e. the opposite surface to the first surface (which contacts the fibrous support layer) but does not completely cover the second surface of the LSP layer. Specifically, the fibrous reinforcement layer is offset from the second edge of the LSP layer along the entire length of the surfacing material, so that a portion of the LSP layer adjacent to the second edge is not covered by the fibrous support. This means that when a first strip of surfacing material of the present invention comprising a fibrous reinforcement layer is laid up and a second strip of the same material is laid up in overlap with the first strip, a portion of the LSP layer of the second strip which extends beyond the fibrous support layer of the second strip will contact the exposed portion of the LSP layer of the first strip not covered by the fibrous reinforcement layer of the first strip, so that an electrically conductive connection is made between the two LSP layers and therefore between the two strips of surfacing material.

[0045] The first edge of the fibrous reinforcement layer may be contiguous with the first edge of the LSP layer or may extend beyond it, conveniently the first edge of the fibrous reinforcement layer may extend beyond the first edge of the LSP layer by the same length as the length of the offset of the second edge of the fibrous reinforcement layer from the second edge of the LSP layer, so that the fibrous reinforcement layer has the same width as the LSP layer. The length of the offset of the second edge of the fibrous reinforcement layer from the second edge of the LSP layer must be sufficient to allow contact between the exposed portion of the LSP layer and an overlapping portion of the LSP layer of an adjacent strip of surfacing material when laid down by an automated lay-up apparatus. In particular embodiments, the length of the offset of the second edge of the fibrous reinforcement from the second edge of the LSP layer will be from 1 to 150mm, preferably 5 to 100mm such as 50mm.

[0046] In this embodiment of the present invention, the fibrous reinforcement may be any fibrous reinforcement material used in composite manufacture, but preferably comprises glass, carbon or aramid fibres. The fibres of the fibrous reinforcement layer may be in any arrangement used in composite materials such as unidirectional or multiaxial, for example biaxial. The fibrous reinforcement layer may comprise non-crimped fabric.

[0047] In particular embodiments of the surfacing materials of the present invention comprising a fibrous reinforcement layer, the fibrous reinforcement may comprise dry fibres, i.e. the fibrous reinforcement layer does not comprise any resin component. Alternatively, the fibrous reinforcement layer may be partially or fully impregnated with a thermocurable or thermoplastic resin. The thermocurable or thermoplastic resin may be any resin used in composite resins, including the resins discussed with respect to other embodiments of the present invention, but is preferably an epoxy resin composition. Where the fibrous reinforcement layer comprises a thermocurable or thermoplastic resin the resin composition may assist in joining the surfacing material to the fibrous reinforcement layer and / or any subsequent layers applied in a lay-up after the surfacing material has been deposited on a mould or tool.

[0048] As set out herein, the present invention also provides a process for preparing cured composite structures. The cured composite structures prepared by the processes of the invention have a good quality surface finish and also comprise a lightning strike protection layer across the entire surface of the cured structure and close to the outer surface thereof.

[0049] The process of the present invention comprises laying down strips of the surfacing material of the invention in overlapping arrangement so that the exposed first surface of the LSP layer at the first edge of a strip of surfacing material comes into contact with the exposed second surface of the LSP layer at the second edge of a previously laid down strip of surfacing material. The laying down process may be carried out in any conventional manner, for example by use of an automated laydown apparatus such as by automated fiber placement (AFP) or automated tape laying (ATL) apparatus. Once a layer of the surfacing material of the present invention has been laid down, further layers of conventional composite components, such as unimpregnated fibre layers and / or partially of fully impregnated fibre layers (semipregs or prepregs). In conventional lay-up processes where a lightning strike protection layer is required this must be added separately, which can be time consuming, but the present invention removes the need for this step, resulting in significant time savings and savings in raw materials; the present invention therefore provides both time and cost savings compared to conventional lay-up processes using conventional components. Once laid down, the layers of composite materials including the surfacing materials of the present invention may be cured in conventional manner and then further processed as for standard cured composite materials, but the requirements for surfacing finishing steps, such as removing mould release agents, sanding and / or painting, may be reduced or even avoided entirely depending on the nature of the surface layer of the surfacing material of the present invention, and this may provide further savings in time and / or materials, and therefore costs.

[0050] The invention will now be described by way of example only and with reference to the accompanying drawings in which;

[0051] Figure 1 represents a cross-section of a surfacing material according to a first embodiment of the present invention;

[0052] Figure 2 represents a view from above of a length of surfacing material according to the first embodiment of the present invention;

[0053] Figure 3 represents a cross-section of a surfacing material according to a second embodiment of the present invention;

[0054] Figure 4 represent a cross-section of a surfacing material according to a third embodiment of the present invention;

[0055] Figure 5 represents the result of laying up two strips of prior art material each strip comprising a lightning strike protective layer and a contiguous reinforcement / surface layer in an overlapping arrangement;

[0056] Figure 6 represents the result of laying up two strips of surfacing material according to a first embodiment of the present invention in an overlapping arrangement;

[0057] Figure 7 represents the result of laying up two strips of surfacing material according to a second embodiment of the present invention in an overlapping arrangement; and

[0058] Figure 8 represents the result of laying up two strips of surfacing material according to a third embodiment of the present invention in an overlapping arrangement.

[0059] It should be noted that the drawings are representations only, and that the dimensions of the various components shown in the drawings are not to scale and are intended only to illustrate the relative arrangements of the various components. Figure 1 shows a representation of a surfacing material 1 in accordance with a first embodiment of the present invention. The surfacing material 1 comprises a fibrous support layer 3 having a first surface 5 and an opposing second surface 7. The fibrous support layer also has a first edge 9 and an opposing second edge 11, plus first and second ends 23 and 25 (see Figure 2). The surfacing material 1 also comprises a lightning strike protection (LSP) layer 13 having a first surface 15 and an opposing second surface 17. The LSP layer also has a first edge 19 and an opposing second edge 21, plus first and second ends 27 and 29 (see Figure 2).

[0060] As shown in Figure 1, the first surface 15 of the LSP layer 13 contacts the second surface 7 of the fibrous support layer 3, and the first edge 19 of the LSP layer 13 extends beyond the first edge 9 of the fibrous support layer 3 leaving a portion of the first surface 15 of the LSP layer 13 exposed. The length of the overlap of the LSP layer 13 beyond the first edge 9 of the fibrous support layer 3 may vary depending on the scale of the various components and the intended use of the surfacing material 1, but generally, the length of the overlap will be from 1 to 150 mm, more generally from 5 to 100mm, for example 50mm.

[0061] In the embodiment shown in Figure 1, the width of the LSP layer 13 is generally the same as the width of the fibrous support layer 3, so that the second edge 21 of the LSP layer 13 is offset from the second edge 11 of the fibrous support layer 3 by the same distance as the length of the overlap of the first edge 19 of the LSP layer 13 beyond the first edge 9 of the fibrous support layer 3. In alternative embodiments, the widths of the LSP layer 13 and fibrous support layer 3 may be different, so that whilst the overlap of the first edge 19 of the LSP layer 13 beyond the first edge 9 of the fibrous support layer 3 is maintained, the length of offset of the second edge 21 of the LSP layer 13 from the second edge 11 of the fibrous support layer 3 may vary. For example, the second edge 21 of the LSP layer 13 may be contiguous with the second edge 11 of the fibrous support layer 3, i.e. there is no offset between the edges, or the offset may be any length, but generally no more than 150mm, more generally between 5 and 100mm for example 50mm.

[0062] Figure 2 shows surfacing material 1 of Figure 1 from above. For illustration purposes the first and second ends 23 and 25 of the fibrous support layer 3 are shown slightly offset from the respective first and second ends 27 and 29 of the LSP layer 13, but in general the first end 23 of the fibrous support layer 3 will be contiguous with the first end 27 of the LSP layer 13, and the second end 25 of the fibrous support layer 3 will be contiguous with the second end 29 of the LSP layer. As shown in Figure 2, the length of the overlap of the first edge 19 of the LSP layer 13 beyond the first edge 9 of the fibrous support layer 3 is generally consistent along the entire length of the surfacing material 1.

[0063] The LSP layer 13 of the surfacing material 1 shown in Figures 1 and 2 may be, for example, a metal layer, such an electrically conductive metal mesh or expanded foil, for example a copper or aluminium mesh or expanded foil.

[0064] The fibrous support layer 3 of the surfacing material 1 shown in Figures 1 and

[0065] 2 may be any fibrous material suitable to act as a support to the LSP layer 13 and assists in handling the surfacing material 1, and also prevent print-through from the LSP layer 13 and / or any fibrous layers positioned above the surfacing material 1 to the outer surface of materials incorporating the surfacing material

[0066] 1 after formation of a cured composite. For example, the fibrous support layer

[0067] 3 may be a non-woven fibre carrier, such as a veil or fleece, for example a nonwoven glass mat or fleece having a density of in the range 30 to 60 g / m2.

[0068] In certain embodiments the fibrous support layer 3 of the surfacing material 1 may comprise only a single component, such as a non-woven fibre carrier, but in alternative embodiments the fibrous support layer 3 may comprise a nonwoven fibre carrier and a layer of reinforcement fibres, as discussed herein. When present, the layer of reinforcement fibres is preferably contiguous with the non-woven fibre carrier so that the non-woven fibre carrier does not overlap the layer of reinforcement fibres at either edge. When present, the layer of reinforcement fibres preferably directly contacts the non-woven fibre carrier, and is preferably located between the non-woven fibre carrier and the LSP layer 13. Thus, the fibrous support layer 3 shown in Figures 1 and 2 may comprise either a single non-woven fibre carrier layer or the combination of a non-woven fibre carrier and a layer of reinforcement fibres.

[0069] The fibrous support layer 3 of the surfacing material 1 shown in Figures 1 and

[0070] 2 may also include a resin composition as described herein. The resin composition may be in the form of a distinct separate layer to the fibrous component of the fibrous support layer 3, but preferably the resin partially or fully impregnates the fibrous components of the fibrous support and does not represent a separate layer.

[0071] Figure 3 shows a representation of a surfacing material 31 in accordance with a second embodiment of the present invention. The surfacing material 31 according to the second embodiment comprises a number of components that correspond to the components of the surfacing material 1 of the first embodiment shown in Figures 1 and 2, and identical numbering has been used to identify such components.

[0072] As shown in Figure 3, the surfacing material 31 of the second embodiment comprises a fibrous support layer 3 and an LSP layer 13 arranged in the same manner as for the surfacing material 1 of the first embodiment, i.e. the first surface 15 of the LSP layer 13 contacts the second surface 7 of the fibrous support layer 3, the first edge 19 of the LSP layer 13 extends beyond the first edge 9 of the fibrous support layer 3, and the second edge 21 of the LSP layer 13 is offset from the second edge 11 of the fibrous support layer 3. In addition, the surfacing material 31 of the second embodiment also comprises a surface layer 33 which contacts the second surface 5 of the fibrous support layer 3 and provides an external mould- or tool-contacting surface 35 of the surfacing material 31. The surface layer 33 may cover the entire first surface 5 of the fibrous support layer 3 or may be offset from one or both edges 9 and 11 and / or extend beyond one or both edges 9 and 11 of the fibrous support layer 3. The surface layer 33 may be a different width to the width of the fibrous support layer 3 or may have the same width as the fibrous support layer 3, and in the latter case may be either a) congruent with both edges 9 and 11 of the fibrous support layer 3 or b) extend beyond the second edge 11 of the fibrous support layer 3 by a first distance and be offset from the first edge 9 of the fibrous support layer 3 by the same distance, as shown in Figure 3. Where the surface material is offset from and / or extends beyond the edges of the fibrous support the distance is generally from 1 to 150mm, preferably 5 to 100mm such as 50mm. The surface layer 33 of the surfacing material 31 shown in Figure 3 may be any suitable material as discussed herein, such as a non-woven fibre veil (preferably a relatively light-weight non-woven veil) at least partially impregnated by a thermosetting resin composition optionally comprising a rheology modifier or an ultraviolet (UV) resistant polymer layer such as a flexible polyurethane film, for example a polycaprolactone-based aliphatic polyurethane film, which is preferably non-removably attached to the first surface 5 of the fibrous support layer 3, for example by means of a resin composition.

[0073] Figure 4 shows a representation of a surfacing material 37 in accordance with a third embodiment of the present invention. The surfacing material 37 according to the third embodiment comprises a number of components that correspond to the components of the surfacing materials 1 and 31 of the first and second embodiments shown in Figures 1, 2 and 3, and identical numbering has been used to identify such components.

[0074] As shown in Figure 4, the surfacing material 37 of the third embodiment comprises a fibrous support layer 3, an LSP layer 13 and a surface layer 33 arranged in the same manner as for the surfacing material 31 of the second embodiment, i.e. the first surface 15 of the LSP layer 13 contacts the second surface 7 of the fibrous support layer 3, the first edge 19 of the LSP layer 13 extends beyond the first edge 9 of the fibrous support layer 3, the second edge 21 of the LSP layer 13 is offset from the second edge 11 of the fibrous support layer 3; and the surface layer 33 contacts the second surface 5 of the fibrous support layer 3 and provides an external mould- or tool-contacting surface 35 of the surfacing material 37. In addition, the surfacing material 37 of the third embodiment also comprises a fibrous reinforcement layer 39 having a first surface 41 and an opposing second surface 43, a first edge 45 and an opposing second edge 47, and first and second ends (not shown). The fibrous reinforcement layer 39 is arranged so that the first surface 41 of the fibrous reinforcement layer 39 contacts the second surface 17 of the LSP layer 13 but does not completely cover the second surface 17 of the LSP layer 13, i.e. the second edge 47 of the fibrous reinforcement layer 39 is offset from the second edge 21 of the LSP layer 13 so that a portion of the second surface 17 of the LSP layer 13 is exposed. In an alternative version of this embodiment, the surface layer 33 may be omitted from the surfacing material 37 so that the second surface 5 of the fibrous support provides the external mould- or toolcontacting surface of the surfacing material 37.

[0075] In the surfacing material 37 of the third embodiment shown in Figure 4, the first edge 45 of the fibrous reinforcement layer 39 may be contiguous with the first edge 19 of the LSP layer 13 or may extend beyond it, for example the first edge 45 of the fibrous reinforcement layer 39 may extend beyond the first edge 19 of the LSP layer 13 by the same length as the length of the offset of the second edge 47 of the fibrous reinforcement layer 39 from the second edge 21 of the LSP layer 13, so that the fibrous reinforcement layer 39 has the same width as the LSP layer 13. The fibrous reinforcement layer 39 may be any fibrous reinforcement material used in composite manufacture as discussed herein, and the fibrous reinforcement layer 39 may comprise dry fibres or may be partially or fully impregnated with a thermocurable or thermoplastic resin.

[0076] Figure 5 represents the result of laying up two strips of prior art material 51 and 51A, each strip comprising a lightning strike protective layer 51, 51A and a contiguous reinforcement / surface layer 53, 53A. As shown, when a first such prior art strip 51 is laid up and a second such strip 51A is laid up in overlap with the first strip 51, the reinforcement surface layer 53A of the second strip contacts the LSP layer 13 of the first strip 51 but the LSP layer 13A of the second strip 51A does not contact the LSP layer 13 of the first strip 51, and therefore no conductive connection is made between the two strips, so that an effective lightning strike protective layer is not formed.

[0077] Figure 6 represents the result of laying up two strips of surfacing material according to the first embodiment of the present invention (designated 1 and 1A) in an overlapping arrangement. As shown, when a second strip of surfacing material as shown in Figure 1 1A is laid up in overlap with a first strip of the same material 1, the fibrous support layer 3A of the second strip 1A contacts the fibrous support layer 3 of the first strip 1, and the first surface 15A of the LSP layer 13A of the second strip 1A contacts the second surface 17 of the LSP layer 13 of the first strip 1, so that a conductive connection is made between the LSP layer 13A of the second strip 1A and the LSP layer 13 of the first strip 1 and an effective lightning strike protective layer is formed across the entire surface. Furthermore, it may be seen that, even if the degree of overlap is so large that that the fibrous support layer 3A of the second strip of surfacing material 1A contacts the LSP layer 13 of the first strip of surfacing material 1, the first surface 15A of the LSP layer 13A of the second strip 1A will contact the second surface 17 of the LSP layer 13 of the first strip 1 so that a conductive connection will still be made between the two strips 1, 1A and a functioning lightning strike layer will be formed across the entire surface.

[0078] Once sufficient strips of the surfacing material 1 of the first embodiment of the invention have been laid up to form a surface layer, additional layers of composite materials such as layers of NCF and / or prepregs, semipregs, etc. may be added to complete the uncured structure, and a cured structure may then be produced by standard procedures, such as infusion or curing etc. In this way, a finished product may be prepared without the need for a separate step of adding an LSP layer.

[0079] Figure 7 represents the result of laying up two strips of surfacing material according to the second embodiment of the present invention (designated 31 and 31A) in an overlapping arrangement. As shown, when a second strip of surfacing material as shown in Figure 3 31A is laid up in overlap with a first strip of the same material 31, the surface layer 33A of the second strip 31A contacts the surface layer 33 of the first strip 31, the fibrous support layer 3A of the second strip 31A contacts the fibrous support layer 3 of the first strip 31, and the first surface 15A of the LSP layer 13A of the second strip 31A contacts the second surface 17 of the LSP layer 13 of the first strip 31, so that a conductive connection is made between the LSP layer 13A of the second strip 31A and the LSP layer 13 of the first strip 31 and an effective lightning strike protective layer is formed across the entire surface. Furthermore, it may be seen that, even if the degree of overlap is so large that the surface layer 33A of the second strip 31A contacts the fibrous support layer 3 or even the LSP layer 13 of the first strip of surfacing material 31, the first surface 15A of the LSP layer 13A of the second strip 31A will contact the second surface 17 of the LSP layer 13 of the first strip 31 so that a conductive connection will still be made between the two strips 31, 31A, and a functioning lightning strike layer will be formed across the entire surface. As for the first embodiment, once sufficient strips of the surfacing material 31 of the second embodiment of the invention have been laid up to form a surface layer, additional layers of composite materials such as layers of NCF and / or prepregs, semipregs, etc. may be added to complete the uncured structure, and a cured structure may then be produced by standard procedures, such as infusion or curing etc. In this way, a finished product may be prepared having a high quality surface and a functioning lightning strike protection layer but without the need for a separate step of adding an LSP layer and / or a surfacing layer.

[0080] Figure 8 represents the result of laying up two strips of surfacing material according to the third embodiment of the present invention (designated 37 and 37A) in an overlapping arrangement. As shown, when a second strip of surfacing material as shown in Figure 4 37A is laid up in overlap with a first strip of the same material 37, the surface layer 33A of the second strip 37A contacts the surface layer 33 of the first strip 37, the fibrous support layer 3A of the second strip 37A contacts the fibrous support layer 3 of the first strip 37, the first surface 15A of the LSP layer 13A of the second strip 37A contacts the second surface 17 of the LSP layer 13 of the first strip 37, so that a conductive connection is made between the LSP layer 13A of the second strip 37A and the LSP layer 13 of the first strip 37 and an effective lightning strike protective layer is formed across the entire surface, and the fibrous reinforcement layer 39A of the second strip 37A contacts the fibrous reinforcement layer 39 of the first strip 37. Furthermore, it may be seen that, even if the degree of overlap is so large that the surface layer 33A of the second strip 37A contacts the fibrous support layer 3 or even the LSP layer 13 of the first strip of surfacing material 37, the first surface 15A of the LSP layer 13A of the second strip 37A will be positioned over an exposed section of the second surface 17 of the LSP layer 13 of the first strip 37 and will therefore come into contact with the second surface 17 of the LSP layer 13 of the first strip 31 once the area of the overlap of the two strips 37, 37A is pressed following the overlap so that a conductive connection will still be made between the two strips 37, 37A, and a functioning lightning strike layer will be formed across the entire surface.

[0081] As for the first embodiment, once sufficient strips of the surfacing material 37 of the third embodiment of the invention have been laid up to form a surface layer, additional layers of composite materials such as layers of NCF and / or prepregs, semipregs, etc. may be added to complete the uncured structure, and a cured structure may then be produced by standard procedures, such as infusion or curing etc. In this way, a finished product may be prepared having a high quality surface and a functioning lightning strike protection layer but without the need for a separate step of adding an LSP layer or a surfacing layer and also with one less layer of reinforcement fibre application.

[0082] EXAMPLES

[0083] Example 1

[0084] A surfacing material having the structure shown in Figure 3 was prepared. The lightning strike protection layer comprised an aluminium mesh (0.25mm thick, 325g / m2). The fibrous support layer comprised a non-woven glass veil having a density of 50g / m2(Evalith® S 5030 available from Johns Manville, Denver, Colorado, USA) in combination with a biaxial layer of fibre-glass reinforcement fibres (200g / m2), the layer of glass fibres being positioned between the LSP layer and the non-woven veil and the edges of the glass fibre layer aligning with the edges of the non-woven glass veil. The surfacing material also comprised a surface layer positioned on the face of the non-woven veil not in contact with the layer of glass fibres and comprising a light-weight non-woven thermoplastic veil (Optiveil® T2761-00, available from Technical Fibre Products Limited, Burnside Mills, Kendal, Cumbria, United Kingdom). The fibrous support and surface layer also comprised a thermosetting epoxy resin impregnating the materials at 35wt%. The resin comprised M79 epoxy resin, available from Hexcel Composites Limited, Duxford, Cambridgeshire, United Kingdom. The LSP layer, fibrous support layer and surface layers all had the same width, and the length of the overlap of the first edge of the LSP layer over the first edge of the fibrous support layer was 50mm, and the length of the overlap of the first edge of the fibrous support layer over the first edge of the surface layer was also 50mm. The lengths of the offset of the second edge of the LSP layer from the second edge of the fibrous support layer and the second edge of the fibrous support layer from the second edge of the surface layer were therefore also both 50mm. Example 2

[0085] A surfacing material having the structure shown in Figure 3 was prepared. The lightning strike protection layer comprised an aluminium mesh (0.25mm thick, 325g / m2). The fibrous support layer comprised a non-woven glass veil having a density of 50g / m2(Evalith® S 5030 available from Johns Manville, Denver, Colorado, USA). The surfacing material also comprised a surface layer positioned on the face of the non-woven veil not in contact with the lightning strike protection layer and comprising a light-weight non-woven thermoplastic veil (Optiveil® T2761-00, available from Technical Fibre Products Limited, Burnside Mills, Kendal, Cumbria, United Kingdom). The fibrous support and surface layer also comprised a thermosetting epoxy resin impregnating the materials at 50wt%. The resin comprised M79 epoxy resin, available from Hexcel Composites Limited, Duxford, Cambridgeshire, United Kingdom. The LSP layer, fibrous support layer and surface layers all had the same width, and the length of the overlap of the first edge of the LSP layer over the first edge of the fibrous support layer was 50mm, and the length of the overlap of the first edge of the fibrous support layer over the first edge of the surface layer was also 50mm. The lengths of the offset of the second edge of the LSP layer from the second edge of the fibrous support layer and the second edge of the fibrous support layer from the second edge of the surface layer were therefore also both 50mm.

[0086] Example 3

[0087] A surfacing material having the structure shown in Figure 3 was prepared. The lightning strike protection layer comprised an aluminium mesh (0.25mm thick, 325g / m2). The fibrous support layer comprised a non-woven glass veil having a density of 50g / m2(Evalith® S 5030 available from Johns Manville, Denver, Colorado, USA). The surfacing material also comprised a surface layer positioned on the face of the non-woven veil not in contact with the lightning strike protection layer and comprising a 0.05mm thick polycaprolactone-based aliphatic polyurethane film having a density of 65g / m2(Argotec 46510-White, available from Schweitzer-Mauduit International, Inc., Georgia, USA). The fibrous support and surface layer also comprised a thermosetting epoxy resin impregnating the materials at 50wt%. The resin comprised M79 epoxy resin, available from Hexcel Composites Limited, Duxford, Cambridgeshire, United Kingdom. The LSP layer, fibrous support layer and surface layers all had the same width, and the length of the overlap of the first edge of the LSP layer over the first edge of the fibrous support layer was 50mm, and the length of the overlap of the first edge of the fibrous support layer over the first edge of the surface layer was also 50mm. The lengths of the offset of the second edge of the LSP layer from the second edge of the fibrous support layer and the second edge of the fibrous support layer from the second edge of the surface layer were therefore also both 50mm.

[0088] Example 4

[0089] A surfacing material having the structure shown in Figure 4 was prepared. The material corresponded to the surfacing material of Example 1, but included a fibrous reinforcement layer attached to the surface of the lightning strike protective layer not in contact with the fibrous support. The fibrous reinforcement layer comprised a layer of LBB1200 glass fibres impregnated at 42wt% with an M79 epoxy resin. The fibrous reinforcement layer had the same width as the other layers and the length of the offset of the second edge of the fibrous reinforcement layer from the second edge of the LSP layer was 50mm, so that the length of the overlap of the first edge of the fibrous reinforcement layer over the first edge of the LSP layer was also 50mm.

[0090] Example 5

[0091] A surfacing material having the structure shown in Figure 4 was prepared. The material corresponded to the surfacing material of Example 2, but included a fibrous reinforcement layer attached to the surface of the lightning strike protective layer not in contact with the fibrous support. The fibrous reinforcement layer comprised a layer of LBB1200 glass fibres impregnated at 42wt% with an M79 epoxy resin. The fibrous reinforcement layer had the same width as the other layers and the length of the offset of the second edge of the fibrous reinforcement layer from the second edge of the LSP layer was 50mm, so that the length of the overlap of the first edge of the fibrous reinforcement layer over the first edge of the LSP layer was also 50mm.

[0092] Example 6

[0093] A surfacing material having the structure shown in Figure 4 was prepared. The material corresponded to the surfacing material of Example 3, but included a fibrous reinforcement layer attached to the surface of the lightning strike protective layer not in contact with the fibrous support. The fibrous reinforcement layer comprised a layer of LBB1200 glass fibres impregnated at 42wt% with an M79 epoxy resin. The fibrous reinforcement layer had the same width as the other layers and the length of the offset of the second edge of the fibrous reinforcement layer from the second edge of the LSP layer was 50mm, so that the length of the overlap of the first edge of the fibrous reinforcement layer over the first edge of the LSP layer was also 50mm.

[0094] Example 7

[0095] Strips of surfacing material according to Example 1 were laid up against a mould surface that had previously been treated with a mould release agent with the surface layer of each strip facing the mould surface. The strips were laid up so that the first edges of each strip overlapped the second edges of each preceding strip so that the first edge of the LSP layer of each applied strip contacted the exposed second edge of the LSP layer of the strip to which it was applied. Once the surface of the mould had been covered layers of standard NCF materials such as dry LBB1200 glass fibre or LBB1200 glass fibre impregnated at 42% with epoxy resin (such as M79 epoxy resin) were laid up to form an uncured composite structure. The uncured composite structure was then vacuum or infusion cured and removed from the mould for sanding and painting.

[0096] Example 8

[0097] Strips of surfacing material according to Example 2 were used to prepare a cured composite structure as in Example 7. After removal from the mould the structure was ready for sanding and painting.

[0098] Example 9

[0099] Strips of surfacing material according to Example 3 were used to prepare a cured composite structure as in Example 7, however, no mould release agent was applied to the mould before the lay-up of the surfacing material and the composite structure was ready for use immediately on removal from the mould i.e. no sanding or painting was required. Example 10

[0100] Strips of surfacing material according to Example 4 were used to prepare a cured composite structure as in Example 7. After removal from the mould the structure was ready for sanding and painting.

[0101] Example 11

[0102] Strips of surfacing material according to Example 5 were used to prepare a cured composite structure as in Example 7. After removal from the mould the structure was ready for sanding and painting.

[0103] Example 12

[0104] Strips of surfacing material according to Example 6 were used to prepare a cured composite structure as in Example 7, however, no mould release agent was applied to the mould before the lay-up of the surfacing material, and the composite structure was ready for us immediately on removal from the mould i.e. no sanding or painting was required.

[0105] Comparative Example 1

[0106] Strips of prior art surfacing material comprising a layer of aluminium mesh (0.25mm thick, 325g / m2) and a layer of fibrous support / surfacing material but in which there was no overlap or offset of the edges of the two layers (as shown in Figure 5) were used to prepare a surface layer on a mould. Additional layers of NCF were then added and used to form a cured composite structure as in Example 7.

[0107] Example 13 - Conductivity test

[0108] The composite structures prepared in Example 9 and Comparative Example 1 were tested for conductivity using a multimeter or continuity meter which was attached to opposite edges of the composite structures so that each connector was attached to the LSP layer of a different strip of surfacing material. For the material of Example 9 there was no reading in the mega Ohms or kilo Ohms range, and only a reading of 0.5 or 0.2 on the 200 Ohm scale, indicating that there was a very conductive path through the laminate. In comparison, when the structure of Comparative Example 1 was connected there was no evidence of a conductive path whatsoever, indicating that composite materials made using automated lay-up using prior art materials would not have an effective lightning strike protective layer across the entire surface.

[0109] Comparative Example 2

[0110] A composite structure having a functioning lightning strike layer was prepared using conventional materials and processes. A mould surface was prepared by application of Hexcel Clear gel coat which was gelled before addition of a glass fleece. Strips of an aluminium mesh (0.25mm thick, 325g / m2) were then applied in overlapping arrangement to form a complete layer followed by the addition of NCF layers and curing to form a composite material. After removal from the mould the structure was ready for sanding and painting. The cured composite material has a functioning lightning strike protective layer, but the time to prepare the material was length due to the need to carefully lay-up separate layers of surfacing material and LSP material.

[0111] Comparative Example 3

[0112] A composite structure having a functioning lightning strike layer was prepared using conventional materials and processes. A mould surface was prepared by application of a surface layer comprising a glass fleece and epoxy resin. Strips of an aluminium mesh (0.25mm thick, 325g / m2) were then applied in overlapping arrangement to form a complete layer followed by the addition of NCF layers and curing to form a composite material. After removal from the mould the structure was ready for sanding and painting. The cured composite material has a functioning lightning strike protective layer, but the time to prepare the material was length due to the need to carefully lay-up separate layers of surfacing material and LSP material.

[0113] A comparison of the time taken to prepare the materials of Examples 7 to 12 and Comparative Examples 2 and 3 is shown in Table 1 below. The time required is shown as relative to the time for Examples 10 to 12.

[0114] Table 1

[0115] As shown in Table 1, the use of surfacing materials according to the present invention allow the production of composite materials having good surface quality and functional lightning strike protection across the entire surface with a significant saving in processing / manufacturing time compared to the use of conventional materials and therefore also reduce associated production costs significantly.

Claims

CLAIMS:

1. A surfacing material comprising: a) a fibrous support layer having a first surface and an opposing second surface, a first edge and an opposing second edge, and first and second ends; and b) a lightning strike protection (LSP) layer having a first surface and an opposing second surface, a first edge and an opposing second edge, and first and second ends; wherein the first surface of the LSP layer contacts the second surface of the fibrous support layer, and the first edge of the LSP layer extends beyond the first edge of the fibrous support layer.

2. A surfacing material according to claim 1, wherein the surfacing material is an elongate material having a generally regular cross-section and having a length that is greater than the width of the material, and wherein the first and second edges of the fibrous support and the LSP layers are longer than the respective first and second ends.

3. A surfacing material according to claim 1 or claim 2, wherein the LSP layer is an electrically conductive layer, preferably a metal layer, more preferably a metal mesh.

4. A surfacing material according to any preceding claim, wherein the fibrous support layer comprises a non-woven fibre carrier, preferably wherein the nonwoven fibre carrier comprises glass, carbon, polyester, polyamide or aramid (aromatic polyamide) fibres, or combinations thereof, and / or wherein the fibres of the non-woven fibre carrier are bound together with an organic binder.

5. A surfacing material according to claim 4, wherein the non-woven fibre carrier has an areal density of at least 10 g / m2and no more than 300 g / m2, preferably 20 to 200 g / m2, more preferably 30 to 90 g / m2, even more preferably 30 to 60 g / m2.

6. A surfacing material according to claim 4 or claim 5, wherein the fibrous support layer further comprises a layer of reinforcement fibres.

7. A surfacing material according to any preceding claim wherein the fibrous support layer includes a resin composition, preferably wherein the resin composition partially or fully impregnates the fibrous support layer.

8. A surfacing material according to claim 7, wherein the resin composition comprises a thermosetting resin, preferably wherein the resin composition comprises a polyester resin, a polyurethane resin, a polyurethane / polyurea resin, a phenol-formaldehyde resin, a urea-formaldehyde resin, a vinyl ester resin, a cyanate ester resin, a polyimide resin or an epoxy resin, more preferably an epoxy resin composition.

9. A surfacing material according to any preceding claim, wherein the first surface of the fibrous support layer contacts a surface layer which provides an external mould- or tool-contacting surface of the surfacing material.

10. A surfacing material according to claim 9, wherein the surface layer comprises a non-woven fibre veil at least partially impregnated by a thermosetting resin composition.

11. A surfacing material according to claim 10, wherein the thermosetting resin composition of the surface layer forms a continuous layer on the external mould- or tool- contacting surface of the surfacing material.

12. A surfacing material according to claim 10 or claim 11, wherein the thermosetting resin composition of the surface layer is an epoxy resin composition.

13. A surfacing material according to any of claims 10 to 12, wherein the nonwoven fibre veil is a thermoplastic fibre veil, preferably having an areal weight in the range 1 to 80g / m2, preferably, wherein the non-woven fibre veil has an openness of 1 to 10% and / or a mean open area of between about 75 to 350pm2.

14. A surfacing material according to claim 9, wherein the surface layer comprises an ultraviolet (UV) resistant polymer layer.

15. A surfacing material according to claim 14, wherein the UV resistant polymer layer comprises a flexible film, preferably a polyurethane film, more preferably a polyurethane based thermoplastic film, such as a polycaprolactone-based aliphatic polyurethane film.

16. A surfacing material according to claim 14 or claim 15, wherein the UV resistant polymer layer has a Taber Abrasion resistance value of no more than 12mg / 500 cycles, preferably no more than 6mg / 500 cycles; and / or wherein the UV resistant polymer layer has a softening point below 0°C, preferably below - 10°C, more preferably below -40°C and / or wherein the surface of the UV resistant polymer layer which contacts the fibrous support has a surface energy of at least 30 dyn / cm, preferably at least 35 dyn / cm.

17. A surfacing material according to any of claims 14 to 16, wherein the change in the Yellowness Index of the UV resistant polymer layer is no more than 3.0 when tested according to ASTM D-4329 cycle B using a QUV weatherometer fitted with UVA 340 bulbs under a repeated cycle of 8 hours at 70 °C under UVA and 4 hours at 50°C water condensation (no UVA) for 2000 hours total; and / or wherein the UV resistant polymer layer has a thickness of from 5 to 500pm, preferably from 25 to 250pm; and / or wherein the UV resistant polymer layer comprises a thermoplastic film, preferably a polyurethane based thermoplastic film; and / or wherein the thermocurable or thermoplastic resin layer has an areal weight of from 3 g / m2to 500 g / m2, preferably from 25 g / m2to 200 g / m2.

18. A surfacing material according to any preceding claim further comprising a fibrous reinforcement layer having a first surface and an opposing second surface, a first edge and an opposing second edge, and first and second ends; wherein the first surface of the fibrous reinforcement layer contacts the second surface of the LSP layer, and the second edge of the fibrous reinforcement layer is offset from the second edge of the LSP layer.

19. A surfacing material according to claim 18, wherein the fibrous reinforcement layer comprises glass, carbon or aramid fibres.

20. A surfacing material according to claim 18 or claim 19, wherein the fibrous reinforcement layer comprises dry fibres.

21. A surfacing material according to claim 18 or claim 19, wherein the fibrous reinforcement layer is partially or fully impregnated with a thermocurable or thermoplastic resin.

22. A process for preparing a cured composite structure comprising: a) depositing a first portion of surfacing material according to any of claims 1 to 21 on the surface of a mould or tool with the fibrous support layer closer to the surface of the mould or tool than the LSP layer; b) depositing a second portion of surfacing material according to any of claims 1 to 21 on the surface of the mould or tool adjacent to and overlapping the first portion so that the first surface of the LSP layer of the second portion of surfacing material contacts the second surface of the LSP layer of the first portion of surfacing material; c) continuing to deposit portions of surfacing material according to any of claims 1 to 21 in the same manner as the second portion, to form a continuous layer of surfacing material having a continuous electrical path across the entire layer; d) depositing further layers of fibrous reinforcement and / or resin on to the continuous layer of surfacing material to form an uncured composite material; and e) curing the uncured composite material to provide a cured composite structure having a continuous lightning strike protection layer across the structure.

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