Lightning-protective permeable material and its use in resin infusion processes

Abstract

To provide a method of forming a permeable lightning strike protection (LSP) material that can be incorporated into a resin infusion process such as RTM and VARTM.SOLUTION: A method of forming a permeable material 10 includes: (i) distributing a particulate or powder binder onto a first nonwoven veil 11 to form a first binder-containing nonwoven veil; (ii) laminating the first binder-containing nonwoven veil to one side of a porous electrically conductive layer 12 having openings through the thickness thereof; and (iii) laminating a reinforcement textile on the opposite side of the porous electrically conductive layer. The reinforcement textile includes a second nonwoven veil bonded to a layer of unidirectional fibers. Either the second nonwoven veil or the layer of unidirectional fibers is adjacent to the electrically conductive layer during the lamination in the step (iii).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates generally to materials for providing lightning strike protection (LSP) to composite parts. [Brief explanation of the drawings]

[0002] [Figure 1] 1 illustrates a permeable LSP material that can be incorporated into a resin infusion process, according to one embodiment. [Figure 2] 1 illustrates a permeable LSP material according to another embodiment. [Figure 3] 1 illustrates a permeable LSP material according to yet another embodiment. [Figure 4] 1 illustrates a permeable LSP material according to yet another embodiment. [Figure 5] 1 illustrates an exemplary closed mold RTM process. [Figure 6] 1 illustrates an exemplary VARTM method. [Figure 7] 1 illustrates another exemplary VARTM method. [Figure 8] FIG. 1 is a top view of a transmissive LSP structure fabricated in accordance with one embodiment. [Figure 9] 1 illustrates a cross-sectional view of a cured composite panel with embedded LSP material manufactured according to one embodiment. [Figure 10] 1 illustrates a cross-sectional view of a cured composite panel with embedded LSP material manufactured in accordance with another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0003] Fiber-reinforced polymer matrix composites (PMCs) are high-performance structural materials composed of reinforcing fibers impregnated in a polymer matrix. PMC materials are commonly used in applications requiring resistance to aggressive environments, high strength, and / or light weight. Examples of such applications include aircraft components, such as tails, wings, fuselages, and propellers, automobiles, ship hulls, and bicycle frames.

[0004] Materials used in the manufacture of aerospace component parts, such as fuselages and wings, must have specific properties that protect the parts from damage or hazards caused by common environmental events. Lightning is an example of a common environmental event that can cause severe damage and / or punch-through to component parts if such parts are not sufficiently conductive and are not grounded through the aircraft. If lightning strikes an aircraft wing component during flight, the event can cause dangerous surge currents in addition to causing severe physical damage to the component itself. Surge currents are of particular concern because they may eventually come into contact with fuel tanks and cause an explosion.

[0005] To provide lightning strike protection (LSP) to composite parts made from PMC materials, various methods have been used to increase the electrical conductivity of the composite part. A traditional method for imparting LSP to component parts in the aerospace industry is to incorporate metal mesh, screen, expanded metal foil, or woven wire mesh into the composite part.

[0006] Such LSP materials can be incorporated into composite parts during their manufacture. Composite parts can be manufactured using a variety of methods, one of which is the prepreg process. Prepreg is typically a sheet of reinforcing fiber impregnated with a matrix resin, such as an epoxy-based resin. To form a composite part, the prepreg is cut to size and laid up on a mold. Metal LSP materials can be incorporated as a single conductive layer between the prepreg layup and the outer surface film, or by embedding a conductive layer into the surface film. In aerospace applications, such surface films are often incorporated into composite parts to improve their surface quality. The surface film is typically an epoxy-based film and can be co-cured with the prepreg layup during the manufacture of the composite part. Once in place, the prepreg layup, along with the conductive layer and surface film, is vacuum-bagged and heat-cured under pressure to produce the final composite part. Prepreg molding into composite parts offers the advantages of ease of use and high reliability. However, they also suffer from the drawback of having limited drapeability (ie, ability to drape).

[0007] Resin infusion processes, such as resin transfer molding (RTM) and vacuum-assisted resin transfer molding (VARTM), have been used to produce composite parts with more complex shapes. During the RTM process, a dry preform is placed in a sealed mold cavity, and liquid resin is injected into the cavity under pressure. A dry preform is a molded structure containing layers of dry reinforcing fiber and / or fabric plies, which may be held together with a small amount of binder. The mold containing the preform is often placed under vacuum, which removes any air trapped within the preform and speeds the RTM process. Once the liquid resin fills the mold cavity, it hardens, resulting in the formation of a hardened composite part. VARTM is similar to RTM, except that single-sided tooling is typically used. Typically, the VARTM process involves enclosing a preform on a tool surface in a vacuum bag, which is a flexible, fluid-impermeable cover; drawing a vacuum between the tool and the bag, thereby compressing the bag against the preform; and introducing liquid resin into the vacuum bag through one or more resin supply lines or conduits. Such resin infusion processes are particularly useful for producing complex shaped structures that are difficult to fabricate using traditional prepreg technology.

[0008] Traditionally, dry preforms for forming composite parts by liquid resin infusion are made by manual layup operations, in which overlapping layers of dry fibrous material are laid up on a tool that substantially defines the shape of the composite part. The layers of fibrous material may be in the form of a nonwoven or woven fabric, e.g., a non-crimped fabric (NCF), which is not pre-impregnated with resin. While laying up the layers on the tool, operators must be careful to allow them to take the shape of the tool without causing wrinkles or bridging. Furthermore, to incorporate an LSP conductive material integrated by the resin infusion process, typically a single conductive layer, such as an expanded metal foil, is placed on the tool surface before laying up the dry preform, and then the entire assembly is infused with resin. The resin-infused preform is then cured together with a metal foil to form a cured composite part with the LSP metal layer embedded therein. Because expanded metal foil is a very delicate material, such manual operations are tedious and time-consuming, and are prone to distortion and wrinkling, which can alter the final surface quality.

[0009] It would be desirable to form dry preform layups by automated layup processes, such as automated tape layup (ATL) and automated fiber layup (AFP), and to incorporate LSP materials into such automated processes to increase manufacturing speed, efficiency, and quality, thereby reducing manufacturing costs.

[0010] Disclosed herein is a permeable LSP material that can be incorporated into resin infusion processes, particularly VARTM. The permeable LSP material can be in the form of a strip or continuous tape that can be used in automated lamination processes such as ATL and AFP. In some embodiments, the LSP material is configured to provide protection against lightning strikes, electrostatic discharge (ESD), and electromagnetic interference (EMI) as well as improve the surface quality of the final composite structure.

[0011] 1, LSP material 10 is a permeable material comprised of at least the following components: (a) a nonwoven veil 11 of randomly arranged fibers; (b) a porous conductive layer 12 having openings through its thickness; and (c) a resin material 13 discontinuously distributed throughout nonwoven veil 11 and between nonwoven veil 11 and conductive layer 12. Porous conductive layer 12 is adhered to one side of nonwoven veil 11 due to the presence of resin material 13 therebetween. Porous conductive layer 12 faces or contacts a preform into which resin is infused during the manufacture of a composite part.

[0012] With respect to the resin material, "discontinuously" means that the resin material does not form a continuous resin film covering the major surface of the nonwoven veil or the major surface of the conductive layer in a manner that prevents fluids, liquids, or air from flowing through the thickness of the veil or the thickness of the conductive layer. The resin material is distributed so that the resin-containing nonwoven veil remains porous and most (i.e., more than half) or all of the openings in the conductive layer are not completely blocked. Therefore, liquids, particularly liquid resins used in RTM and VARTM, can flow through the thickness of the LSP material during resin infusion and form a fully embedded LSP solution. Additionally, air initially trapped in the initial dry preform can escape during the outgassing process (a process in which the dry preform is heated to remove volatiles and moisture trapped in the preform).

[0013] In another embodiment shown in FIG. 2, a porous conductive layer 12 (described with reference to FIG. 1) is sandwiched between two nonwoven veils 11 and 14, and a resin material 13 is discontinuously distributed throughout the nonwoven veils 11, 14, and the conductive layer 12. The discontinuous presence of the resin material is as described with reference to FIG. 1. While some of the resin material can penetrate the openings (or holes) in the conductive layer 12, the resin material does not completely fill all of the openings. As a result, the laminate structure shown in FIG. 2 remains porous and fluid-permeable, allowing liquid resin to easily flow through. In this embodiment, one of the resin-containing veils (11, 14) contacts the preform into which the resin is infused during the production of a composite part.

[0014] In the embodiment shown in Figures 1 and 2, each nonwoven fabric veil (11, 14) containing no resin material is a thin, lightweight structure with a basis weight ranging from 3 to 50 gsm or 4 to 15 gsm. "gsm" stands for g / m 2Each nonwoven veil may be composed of continuous or chopped fibers made from glass, carbon, or polymers such as thermoplastic polymers. The nonwoven veils may be composed of different types of fibers, i.e., fibers of different materials. Suitable thermoplastic fibers include those made from polyamides (aliphatic polyamides (PA), cycloaliphatic polyamides, aromatic polyamides, polyphthalamides (PPA), ether or ester block polyamides (PEBAX, PEBA)), polyphenylene sulfide (PPS), polyetherimide (PEI), polyimide (PI), polyamideamide (PAI), polysulfones such as polyarylsulfones (such as polyethersulfone (PES), polyethersulfone-etherethersulfone (PES:PEES), polyetherethersulfone (PEES)), polyaryletherketones (PAEK) (such as polyetherketone (PEK), polyetheretherketone (PEEK)), polyurethanes such as thermoplastic polyurethanes, polycarbonates, polyacetals, polyphenylene oxides (PPO), polyesters, polyethers, polyethernitriles, polybenzimidazoles, liquid crystal polymers (LCPs), and combinations and copolymers thereof.

[0015] In the embodiment shown in FIGS. 1 and 2, the porous conductive layer 12 (without the resin material) may be an expanded metal foil, metal screen, or metal mesh, preferably having a basis weight in the range of about 50 gsm to 850 gsm, or 60 gsm to 350 gsm, or 60 gsm to 195 gsm. The conductive layer may be a perforated metal foil (sheet form) having holes through its thickness and a thickness in the range of 3 μm to 300 μm. The holes may have any suitable cross-sectional shape, such as circular or oval. Suitable metals may be selected from copper, aluminum, bronze, titanium, alloys, and combinations thereof. In one embodiment, the porous conductive layer is a perforated copper foil having a thickness in the range of 10 μm to 75 μm, or a basis weight in the range of 60 gsm to 350 gsm.

[0016] In the embodiment shown in Figure 1, the resin material 13 is present in an amount ranging from 20 gsm to 75 gsm, or from 25 gsm to 50 gsm. In the embodiment shown in Figure 2, the total amount of resin material in the LSP material is from 40 gsm to 150 gsm, or from 50 gsm to 100 gsm. The resin material is a curable resin that includes one or more thermosetting resins. The composition of the resin material is described in more detail below.

[0017] In another embodiment, illustrated by FIG. 3, the LSP material described with reference to FIG. 1 is bonded to a reinforcing textile 15. The reinforcing textile 15 is composed of a layer of unidirectional (UD) reinforcing fibers 15a attached to a nonwoven veil 15b. The UD reinforcing fibers 15a shown in FIG. 3 are bonded to the perforated conductive layer 12. Alternatively, the veil surface 15b of the reinforcing textile 15 may be bonded to the perforated conductive layer 12. The reinforcing textile 15 functions as a reinforcement material to prevent the "accordion" effect that occurs when slitting a wide LSP material into narrow tapes or when automated laying of LSP tapes. The "accordion" effect refers to the tape wrinkling or bunching. The reinforcing textile 15 also functions as the first reinforcing layer during the automated laying process to form the preform. Therefore, the application of the LSP material and the first or last reinforcing ply is performed in one step rather than two separate steps, thereby reducing overall processing time.

[0018] In yet another embodiment illustrated by Figure 4, the LSP material described with reference to Figure 2 is adhered to a reinforcing textile 15. Reinforcing textile 15 is as described for Figure 3. Again, either UD fiber 15a or veil 15b may be in contact with resin-containing veil 13.

[0019] In the embodiment shown in Figures 3 and 4, the reinforcing textile 15 will come into contact with the preform that will be infused with resin during the manufacture of the composite part.

[0020] In the configurations of Figures 3 and 4, resin material 13 can be replaced with a binder that is solid at temperatures up to 50°C and has a softening point in the range of 65°C to 125°C as measured by differential scanning calorimetry (DSC). This solid binder includes a blend of an epoxy resin and a thermoplastic polymer, but does not include a catalyst or crosslinker that is active above 65°C. When such a solid binder is used, the amount of binder in the LSP multilayer structure shown in Figure 3 or 4 can range from 5 gsm to 20 gsm total.

[0021] The multilayer LSP material described with reference to Figures 1-4 may be in the form of a flexible tape that is lightweight and configured for automated layup processes such as ATL and AFP. Due to its flexibility and light weight, such LSP tape can be laid down at significantly faster speeds than conventional resin-impregnated prepreg tapes. The LSP tape may have a width of about 0.125 inches to about 12 inches (or about 3.17 mm to about 305 mm). In some embodiments, the LSP tape has a width of about 0.125 inches to about 1.5 inches (or about 3.17 mm to about 38.1 mm), or about 0.25 inches to about 0.50 inches (or about 6.35 mm to about 12.77 mm). In other embodiments, the LSP tape has a width of about 6 inches to about 12 inches (or about 152 mm to about 305 mm). The length of the tape may be continuous or very long relative to its width, for example, at least 10 times its width, and in some cases 100 to 100,000 times its width. In continuous form, the surface tape may be wound into a roll for storage prior to its application in an automated process.

[0022] ATL and AFP are methods that use computer-guided robotics to lay continuous tapes onto a forming surface (e.g., a mandrel) to form composite structures or fiber preforms. The ATL / AFP process involves dispensing one or more tapes in parallel onto the tool surface to form layers of a desired width and length, and then stacking additional layers on top of the previous layers to obtain a layup with a desired thickness. Subsequent tapes may be oriented at different angles relative to the preceding tape. ATL / AFP systems typically include a robotically controlled head for dispensing and compressing the tape directly onto the tool surface.

[0023] Resin materials The resin material in the LSP material of the present disclosure is tacky at room temperature (20°C-25°C), thereby imparting a tacky surface to one or both sides of the LSP material. The term "tacky" as used with respect to a resin material means that it is tacky to the touch and easily adheres to another surface. The tackiness of the resin material allows the LSP material to stay reliably in place when placed on a tool surface or laminated onto another substrate, such as a dried fiber preform, without the application of heat. Such tackiness is advantageous in automated lamination processes, such as ATL and AFP.

[0024] The adhesive resin materials described in various embodiments herein, particularly with reference to Figures 1 and 2, are formed from a curable resin composition that includes one or more thermosetting resins. Examples of suitable thermosetting resins include, but are not limited to, epoxies, phenolic resins, cyanate esters, bismaleimides, benzoxazines (such as polybenzoxazines), unsaturated polyesters, vinyl ester resins, and combinations thereof.

[0025] In a preferred embodiment, the curable resin composition comprises one or more epoxy resins and at least one curing agent. Epoxy resins include monofunctional and multifunctional epoxies. Multifunctional epoxy resins (or polyepoxides) contain two or more epoxy functional groups in one molecule.

[0026] Examples of suitable polyfunctional epoxy resins include polyglycidyl ethers prepared by reacting epichlorohydrin or epibromohydrin with polyphenols in the presence of alkali. Suitable polyphenols include, for example, resorcinol, pyrocatechol, pyrocatechin, hydroquinone, bisphenol A (bis(4-hydroxyphenyl)-2,2-propane), bisphenol F (bis(4-hydroxyphenyl)methane), bis(4-hydroxyphenyl)-1,1-isobutane, 4,4'-dihydroxybenzophenone, bis(4-hydroxyphenyl)-1,1-ethane, and 1,5-hydroxynaphthalene.

[0027] Also included are polyglycidyl ethers of polyalcohols. Such polyalcohols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,4-butylene glycol, triethylene glycol, 1,5-pentanediol, 1,6-hexanediol, and trimethylolpropane. Still other epoxy resins include polyglycidyl esters of polycarboxylic acids, such as the reaction products of glycidol or epichlorohydrin with aliphatic or aromatic polycarboxylic acids, such as oxalic acid, succinic acid, glutaric acid, terephthalic acid, or dimer fatty acids.

[0028] Other epoxides may include those derived from the epoxidation products of olefinically unsaturated alicyclic compounds or derived from natural fats and oils.

[0029] Also included are liquid epoxy resins which are the reaction products of bisphenol A or bisphenol F with epichlorohydrin. These epoxy resins are liquid at room temperature and generally have an epoxy equivalent weight (g / eq) of about 150 to about 480 as measured by ASTM D-1652.

[0030] Particularly suitable are epoxy novolac resins which are polyglycidyl derivatives of phenol-formaldehyde novolac or cresol-formaldehyde novolac having the following chemical structure: TIFF0007721721000001.tif35170 (wherein n=0-5 and R=H or CH3). When R=H, the resin is a phenolic novolac resin. When R=CH3, the resin is a cresol novolac resin. The former are commercially available as DEN™ 428, DEN™ 431, DEN™ 438, DEN™ 439, and DEN™ 485 from Dow Chemical Co. The latter are commercially available as ECN1235, ECN1273, and ECN1299 from Ciba-Geigy Corp. Other suitable novolacs that can be used include SU-8 from Celanese Polymer Specialty Co. In a preferred embodiment, the epoxy novolac resin has a viscosity of 4000 to 10,000 mPa·s at 25° C. and an epoxide equivalent weight (EEW) of about 190 g / eq to about 235 g / eq as measured by ASTM D-1652.

[0031] Particularly suitable multifunctional epoxy resins are tetrafunctional aromatic epoxy resins having four epoxy functional groups and at least one glycidyl amine group per molecule. Examples include the following chemical structure: TIFF0007721721000002.tif34170 is a tetraglycidyl ether of methylenedianiline. The amine groups in the structure are shown in the para- or 4,4' position of the aromatic ring structure; however, it should be understood that other isomers such as 2,1', 2,3', 2,4', 3,3', and 3,4' are possible alternatives. Examples of commercially available tetrafunctional epoxy resins are Araldite® MY9663, MY9634, MY9655, MY-721, MY-720, and MY-725 supplied by Huntsman Advanced Materials.

[0032] Another particularly suitable multifunctional epoxy resin is a trifunctional epoxy resin, such as a triglycidyl ether of aminophenol. Specific examples of commercially available trifunctional epoxy resins are Araldite® MY0510, MY0500, MY0600, MY0610 supplied by Huntsman Advanced Materials.

[0033] Another suitable trifunctional epoxy resin is a tris-(hydroxylphenyl)-methane based epoxy, such as that supplied by Huntsman Advanced Materials, having the following chemical structure: TACTIX® 742 resin with TIFF0007721721000003.tif56170.

[0034] The curable resin composition has a high T g and may be formulated to produce high crosslink densities. In some embodiments, a combination of an epoxy novolac resin and a non-novolac multifunctional epoxy resin (especially a trifunctional and / or tetrafunctional epoxy) is used. The relative amounts of epoxy novolac resin and non-novolac multifunctional epoxy resin may be varied, but the amount of epoxy novolac resin is preferably within the range of about 80 to about 100 parts per 100 parts of non-novolac multifunctional epoxy resin. The combination of epoxy novolac resin and multifunctional epoxy resin in the specified ratios provides the desired high T g and contributes to the crosslink density when cured.

[0035] Multifunctional epoxide resins may be cured with various amine-based latent curing agents, which are activated at elevated temperatures (e.g., temperatures above 150°F (65°C)). Examples of suitable curing agents include dicyandiamide (DICY), diaminodiphenylsulfone (4,4'-DDS or 3,3'-DDS), 4,4'-methylene-bis(3-chloro-2,6-diethylaniline) (MCDEA), guanamine, guanidine, aminoguanidine, and derivatives thereof. Compounds from the imidazole and amine complex classes may also be used. In one embodiment, the curing agent is dicyandiamide. In another embodiment, the curing agent is 4,4'-methylene-bis(3-chloro-2,6)-diethylaniline (MCDEA). The amine-based curing agent is present in an amount ranging from about 1% by weight to about 5% by weight, based on the total weight of the resin composition.

[0036] A cure accelerator may be used with the amine-based curing agent to accelerate the curing reaction between the epoxy resin and the amine-based curing agent. Suitable cure accelerators may include alkyl- and aryl-substituted ureas (such as aromatic or cycloaliphatic dimethylureas) and bis-ureas based on toluenediamine or methylenedianiline. One example of a bis-urea is 4,4'-methylenebis(phenyldimethylurea), commercially available as Omicure® U-52 or CA152 from CVC Chemicals, which is a suitable accelerator for dicyandiamide. Another example is 2,4-toluenebis(dimethylurea), commercially available as Omicure® U-24 or CA150 from CVC Chemicals. The cure accelerator may be present in an amount ranging from about 0.5 wt % to about 3 wt %, based on the total weight of the resin composition.

[0037] As used herein, the terms "cure" and "curing" refer to the irreversible solidification of a prepolymeric substance or resin or monomer caused by heating at elevated temperatures, exposure to ultraviolet light and radiation, or chemical additives. The term "curable" means capable of being cured into a solidified material.

[0038] The curable resin composition may further contain one or more toughening agents. The toughening agents may be selected from thermoplastic polymers, elastomers, core-shell rubber particles, pre-reacted adducts that are reaction products of epoxy resins, bisphenols, and elastomeric polymers, as well as combinations thereof. In some embodiments, a combination of two different toughening agents from this group is used. The amount of toughening agent(s) may be, in total, from about 1% to about 30% by weight, and in some cases from about 10% to about 20% by weight, based on the total weight of the resin composition.

[0039] For the pre-reacted adduct, suitable epoxy resins include the diglycidyl ether of bisphenol A, the diglycidyl ether of tetrabromobisphenol A, the hydrogenated diglycidyl ether of bisphenol A, or the hydrogenated diglycidyl ether of bisphenol F. Cycloaliphatic epoxies are also suitable and include compounds containing at least one cycloaliphatic group and at least two oxirane rings per molecule. Specific examples include diepoxides of cycloaliphatic alcohols, the following structure: and hydrogenated bisphenol A, represented by TIFF0007721721000004.tif25170. An example of such a cycloaliphatic epoxy resin is EPALLOY® 5000 (a cycloaliphatic epoxy prepared by hydrogenating bisphenol A diglycidyl ether) available from CVC Thermoset Specialties. Other cycloaliphatic epoxides suitable for use in the pre-reacted adduct may include EPONETX™ cycloaliphatic epoxy resins, such as EPONETX™ Resin 1510, supplied by Momentive Specialty Chemicals.

[0040] The bisphenol in the pre-reacted adduct functions as a chain extender for linear or cycloaliphatic epoxy compounds. Suitable bisphenols include bisphenol A, tetrabromobisphenol A (TBBA), bisphenol Z, and tetramethylbisphenol A (TMBP-A).

[0041] Suitable elastomers for forming the pre-reacted adduct include, but are not limited to, liquid elastomers such as amine-terminated butadiene acrylonitrile (ATBN), carboxyl-terminated butadiene acrylonitrile (CTBN), and carboxyl-terminated butadiene (CTB). Fluorocarbon elastomers, silicone elastomers, and styrene-butadiene polymers are also possible. In embodiments, the elastomer used in the pre-reacted adduct is ATNB, CTBN, or CTB.

[0042] Suitable thermoplastic toughening agents include polyarylsulfone polymers such as polyethersulfone (PES), polyetherethersulfone (PEES), etc. In some embodiments, the toughening agent is a copolymer of PES and PEES, which is described in U.S. Pat. No. 7,084,213.

[0043] The reinforcing component may be core-shell rubber (CSR) particles having a particle size of 300 nm or less. CSR particles may be either core-shell particles, with a soft core surrounded by a hard shell. Preferred CSR particles are particles having a polybutadiene or butadiene-acrylonitrile rubber core and a polyacrylate shell. Commercial sources of CSR particles include Kane Ace™ MX 411 (a suspension of 25 wt. % CSR particles in MY 721 epoxy resin) and Kane Ace™ MX 120 (containing 25% to 37 wt. % CSR particles dispersed in DER™ 331 resin), and Dow Chemical Co.'s Paraloid™ EXL-2691 (methacrylate-butadiene-styrene CSR particles with an average particle size of approximately 200 nm).

[0044] Ceramic microspheres may be added to the curable resin composition. They may be hollow or solid ceramic microspheres. In one embodiment, hollow ceramic microspheres made from an inert silica-alumina ceramic material are used. Microspheres having diameters ranging from about 0.1 μm to about 20 μm, preferably from about 1 μm to about 15 μm, have been found to be particularly suitable. Examples of commercially available ceramic microspheres particularly suitable for use in the resin film composition are sold by Zeelan Industries, Inc. under the trade name Zeeospheres®, e.g., G-200, G210, and W-200. These are thick-walled, odorless, and light gray hollow silica-alumina spheres. In some embodiments, the amount of ceramic microspheres may be in the range of about 20 wt% to about 40 wt%, or about 25 wt% to about 35 wt%, based on the total weight of the resin composition. In other embodiments, the amount of ceramic microspheres may be in the range of about 3 wt% to about 15 wt%, or about 5 wt% to about 10 wt%.

[0045] To control the flow of the resin composition and prevent agglomeration therein, inorganic fillers in particulate form (e.g., powder) are added to the resin composition as rheology-modifying components. Suitable inorganic fillers that may be used in the resin film composition include talc, mica, calcium carbonate, alumina, and fumed silica. In one embodiment, hydrophobic fumed silica (e.g., Cab-O-Sil® TS-720) is used as the inorganic filler. The amount of inorganic filler may be in the range of about 1 wt % to about 5 wt %, based on the total weight of the resin composition.

[0046] The curable resin composition may further contain one or more optional additives that affect one or more of the mechanical, electrical, optical, and thermal properties of the cured or uncured resin material. Such additives include, but are not limited to, ultraviolet (UV) stabilizers, color pigments, and dyes. When such additives are used, their total amount is less than about 5 wt. %, based on the total weight of the resin composition.

[0047] For purposes of this specification, discontinuous resin distribution can be achieved, for example, by film lamination. For the embodiment of FIG. 1, the resin material can be applied by (i) preparing an assembly of porous conductive layers (e.g., a metal mesh as the top layer, a nonwoven veil as the middle layer, and a thin resin film as the bottom layer); and (ii) applying heat and pressure to the assembly, for example, with a heated roller, so that the resin film becomes flowable and spreads over the entire veil and the conductive layer, including the interface between the veil and the conductive layer. Alternatively, the resin film can be an intermediate layer in the assembly in step (i). Because of the small amount of resin used, such lamination does not produce a continuous resin surface on the resulting laminate, which is porous and permeable to fluids such as liquids and volatile substances. For the embodiment of FIG. 2, the lamination process is the same, but the assembly includes a porous conductive layer between two nonwoven veils and two outer resin films, with each resin film on the outer surface of each veil.

[0048] Alternatively, a nonwoven veil is placed in contact with a resin film, then heat is applied to reduce the viscosity of the resin, and a vacuum is applied to pull the resin through the veil. The resin spreads throughout the veil but does not form a continuous surface or continuous film on the veil, so the resulting resin-infused veil remains porous. The porous resin-infused veil is then laminated to a porous conductive layer to produce the configuration shown in Figure 1. For the configuration of Figure 2, a second resin-infused veil, made in the same manner, is laminated to the opposite side of the porous conductive layer.

[0049] As another example, the resin material can be distributed by spray coating. The nonwoven veil and porous conductive layer are separately spray-coated with a resin solution and then dried to remove the solvent. The resin-coated veil and the resin-coated conductive layer are then laminated together to produce the configuration shown in Figure 1. For the configuration shown in Figure 2, a second resin-coated veil, prepared in the same manner, is laminated on the opposite side of the resin-coated conductive layer. Spray coating does not create a continuous resin surface on the veil or conductive layer. Therefore, the resin-coated veil and the resin-coated conductive layer remain porous and permeable to liquids. Alternatively, only the nonwoven veil is coated with the resin solution before the veil is laminated to the porous conductive layer.

[0050] For spray coating, the resin solution may have a solids content of 10% to 30% solids. The resin solution composition may include one or more thermosetting resins in dispersed solid form, at least one curing agent, and a solvent. The thermosetting resin and curing agent are as described above for the resin material. The solvent may be selected from organic solvents such as methyl ethyl ketone (MEK), acetone, dimethylacetamide, and N-methylpyrrolidone. Optionally, a thermoplastic polymer may be added to the resin solution as a toughening agent in an amount of up to 10 to 40 parts per 100 parts total thermosetting resin (all thermosetting resins combined). Parts are measured by weight.

[0051] solid binder For the configurations shown in Figures 3 and 4, a solid binder may be used in place of the curable resin material disclosed above. This solid binder may be dispensed in particulate form, e.g., as a powder, onto the veil and / or porous conductive layer and subsequently laminated. The term "particulate form" in this context means the form of discrete particles. The particles can have any shape, such as flakes or other non-spherical shapes. The resulting laminate is then bonded to a reinforcing textile, which itself contains a small amount of binder.

[0052] As disclosed above, the binder is solid at temperatures up to 50°C and has a softening point in the temperature range of 65°C to 125°C as measured by differential scanning calorimetry (DSC), and comprises a blend of an epoxy resin and a thermoplastic polymer, but does not contain a catalyst or crosslinker active at temperatures above 65°C. The epoxy resin can be selected from those disclosed for the curable resin composition. The thermoplastic polymer in the epoxy-thermoplastic blend can be a polyarylsulfone polymer that is soluble in the epoxy resin. Such polyarylsulfone polymers comprise ether-linked repeating units and optional thioether-linked repeating units, which units are: -(Ph-A-Ph)n- and optionally -(Ph)a- wherein A is CO or SO2, Ph is phenylene, n=1-2 and can be a fractional number, and a=1-4 and can be a fractional number, provided that when a is greater than 1, the phenylenes are linearly linked by a single chemical bond or a divalent group other than -CO- or -SO2-, or fused together directly or by a cyclic moiety selected from the group consisting of alkyl groups, (hetero)aromatics, cyclic ketones, cyclic amides, imides, cyclic imines, and combinations thereof.

[0053] The polyarylsulfone may comprise repeating units of -(PhSO2Ph)-, which are present in the polyarylsulfone in a proportion such that on average there are at least two of said units -(PhSO2Ph)- consecutively in each polymer chain present.

[0054] Preferably, the polyarylsulfone is a copolymer comprising the following units: X-Ph-SO2-Ph-X-PhSO2Ph (“PES”) (I) and X-(Ph) a -X-PhSO2Ph("PEES")(II) (wherein X is O or S and may be different for each unit, and a is 1 to 4).

[0055] This method of making a solid binder material can be found in US Pat. No. 8,927,662, assigned to Cytec Technology Corp., the contents of which are incorporated herein by reference.

[0056] reinforced textile In the embodiment of Figures 3 and 4, the reinforcing textile 15 is a dry, fluid-permeable material comprising a nonwoven veil bonded to at least one side of a layer of unidirectional (UD) fibers and a small amount of binder sufficient to bind the UD fibers to the veil. The total amount of binder in the reinforcing textile is about 15% by weight or less, e.g., 0.1% to 15% by weight, based on the total weight of the reinforcing textile. The UD fibers and nonwoven veil constitute more than 80% by weight of the total weight of the reinforcing textile. The binder in the reinforcing textile does not form a continuous film on the nonwoven veil or throughout the UD fibers. Therefore, the reinforcing textile is porous and permeable to the liquid resin used in resin infusion.

[0057] UD fibers are aligned parallel in the same direction with spaces between adjacent fibers. Suitable UD fibers include glass fibers, carbon (including graphite) fibers, and aramid fibers (e.g., Kevlar).

[0058] The nonwoven veil is composed of randomly arranged fibers, which may include thermoplastic or carbon fibers, or a combination of carbon and thermoplastic fibers. The fiber length may vary from 1 / 8 inch (0.32 cm) to 2 inches (5.08 cm). The basis weight of the nonwoven veil in this embodiment is preferably 10 gsm or less, for example, 2 to 10 gsm.

[0059] For nonwoven veils composed of thermoplastic fibers, the fibers can be made from a thermoplastic material selected from polyamides (such as aliphatic polyamides, cycloaliphatic polyamides, and aromatic polyamides); polyphthalamides; polyamideimides; polyimides; polyetherimides; polyesters; polyphenylene oxides; polyurethanes; polyacetals; polyolefins; polyarylsulfones (such as polyethersulfones and polyetherethersulfones); polyaryletherketones (PAEKs) (such as polyetheretherketones (PEEK) and polyetherketoneketones (PEKK)); poly(phenylene sulfide); liquid crystal polymers (LCPs); phenoxy; acrylics; acrylates; and mixtures and copolymers thereof. Furthermore, the nonwoven veil can be composed of two different types of fibers, i.e., fibers having different thermoplastic compositions.

[0060] Suitable binders for reinforced textiles include uncrosslinked, partially or fully crosslinked polyurethanes or modified polyurethane polymers; partially or fully crosslinked copolymers of polyhydroxyethers and polyurethanes; epoxies that are uncrosslinked, partially or fully crosslinked, or modified epoxies; and uncrosslinked, partially or fully crosslinked poly(hydroxyether) resins.

[0061] The binder for use in the reinforcing textile may be the same solid binder comprised of an epoxy resin and a thermoplastic polymer as disclosed above with reference to the configurations of FIGS.

[0062] In one embodiment, the binder is an aqueous dispersion containing (i) a copolymer of a polyhydroxyether and a polyurethane, (ii) a crosslinker, and, optionally, (iii) a catalyst. The crosslinker may be an aminoplast crosslinker, such as an aminoplast crosslinker of the methoxyalkylmelamine class. Catalysts include, but are not limited to, proton-donating acids (such as carboxylic acids, phosphoric acids, acidic alkyl phosphate esters, sulfonic acids, disulfonic acids, etc.) and / or Lewis acids (such as aluminum chlorides, bromides, or halides, ferric halides, boron trihalides, etc.), as well as many others in both categories known to those skilled in the art.

[0063] An exemplary method for applying the binder includes applying the binder in particulate or liquid form to a layer of spread UD fibers and / or a nonwoven veil; bonding the nonwoven veil to at least one side of the fibrous layer. In another exemplary method, the binder is added during the manufacture of the nonwoven veil. The resulting veil, including the binder, is then bonded to the UD fiber layer.

[0064] According to one embodiment, a method for producing a reinforced textile includes applying a first binder in powder form to a dry fibrous web of spread UD fibers (e.g., carbon fibers) and / or a nonwoven veil (e.g., composed of carbon fibers and / or thermoplastic fibers); bonding the nonwoven veil to at least one side of the fibrous web to form a laminate; applying a second binder in the form of a liquid composition to the laminate, for example by dip coating; and drying the binder-treated laminate in an oven.

[0065] Use in resin infusion processes The LSP materials disclosed herein are configured for use in resin infusion processes such as RTM and VARTM. Typically, the LSP material is applied to the outer surface of a fiber preform in the shape of a composite part, and the assembled assembly is infused with resin. After the resin-infused preform is cured to form a cured composite structure, the LSP material becomes an integral part of the cured structure.

[0066] For the LSP material shown in Figure 1, the LSP material is placed over the preform to be infused with resin, with the resin-containing veil 11 being the outermost layer, prior to infusion of the resin. For the LSP material shown in Figure 2, either one of the resin-containing veils (11 or 14) can be in contact with the preform to be infused with resin. For the LSP materials shown in Figures 3 and 4, the reinforcing textile 15 is in contact with the preform to be infused with resin.

[0067] The preforms disclosed herein consist of an assembly or layup of multiple layers of dry reinforcing fibers. The layers of reinforcing fibers in the preform may be any type of textile known in the art for producing composite materials. Examples of suitable fabric types or configurations include, but are not limited to, all woven fabrics, including plain weave, twill weave, satin weave, spiral weave, and unidirectional weave; all multiaxial fabrics (examples of which include warp knit fabrics and non-crimped fabrics (NCF)); knitted fabrics; braided fabrics; all nonwoven fabrics (examples of which include nonwoven mats and felts composed of chopped and / or continuous fiber filaments); and combinations of the aforementioned fabric types. In certain applications, the preform may include a porous foam or honeycomb core between two stacks of fibrous layers.

[0068] Reinforcing fibers for the preform may be made from materials selected from, but not limited to, glass (including electroglass or E-glass), carbon (including graphite), aramid, polyamide, high modulus polyethylene (PE), polyester, poly-p-phenylene-benzoxazole (PBO), boron, quartz, basalt, ceramic, and combinations thereof.

[0069] Preforms can be manufactured by automated layup processes, such as ATL or AFP, in which multiple fiber tapes are laid side by side to form fiber layers of desired dimensions and then laid in the same manner to form a layup of desired thickness. The LSP material of the present disclosure can be incorporated into such automated layup processes to form the first layer on the tool surface before the fiber layers are laid, or can be incorporated as the final layer after the preform layup is formed.

[0070] FIG. 5 illustrates an exemplary closed-mold RTM process in which an assembly of a dried fiber preform 50 (fiber layer layup) and LSP material 51 is placed in a closed mold cavity 52 of a molding tool, and then resin is injected into the cavity under pressure. The mold cavity 52 is defined by two or more die parts, such as an upper die part 52a and a lower die part 52b shown in FIG. 5. At least one of the die parts includes a temperature control mechanism for regulating the temperature of the molding tool. The mold cavity 52 is in fluid communication with a resin infusion line (not shown) and is connected to a vacuum source via a vacuum line (not shown). The resin infusion line and vacuum line are positioned so that resin flows through the thickness of the LSP material 51 and preform 50. The LSP material 51 may be according to any one of the embodiments shown in FIGS. 1-4. During operation, the molding tool is clamped closed, heated, and evacuated, after which liquid resin is injected under pressure through the resin line into the mold cavity 52. After the preform is infused, the mold cavity is heated while maintaining high pressure to cure the infused preform, thereby forming a cured, solidified composite structure incorporating the LSP material. After curing, the mold tool is opened and the cured composite structure is removed from the mold tool.

[0071] FIG. 6 illustrates an exemplary VARTM process in which an assembly of fiber preform 60 and LSP material 61 is enclosed between a single-sided molding tool 62 and a flexible, gas-impermeable sheet or "vacuum bag" 63. Vacuum bag 63 is sealed to tool 62 by sealing element 64. The enclosed vacuum bag is in communication with a resin supply line (not shown), which may include a series of conduits, and a vacuum line (not shown). A resin distribution mesh 65 is disposed between preform 60 and tool 62 and contacts the resin supply line to enhance distribution of resin to the preform. In an alternative embodiment, LSP material 61, instead of preform 60, contacts resin distribution mesh 65.

[0072] During VARTM operation, a relative vacuum is drawn between the tool 62 and the vacuum bag 63, thereby compressing the bag against the LSP material / preform assembly. Liquid resin is introduced into the vacuum bag via a resin supply line. Multiple separate resin supply lines may be used to facilitate complete wetting or infusion of the entire preform with the liquid resin. The vacuum and resin supply lines are strategically positioned relative to one another so that the resin can be infused through the thickness of the LSP material / preform assembly to saturate the entire assembly. In this regard, a vacuum source may be provided on one side of the assembly, and resin is introduced on the opposite side, as shown in FIG. 6.

[0073] FIG. 7 illustrates another exemplary VARTM method in which an assembly of a preform 70 and an LSP material 71 is enclosed between a molding tool 72 and a flexible, gas-permeable membrane 73. The gas-permeable membrane 73 contains small pores throughout, allowing gas to pass through but not liquid resin. The gas-permeable membrane 73 is surrounded by an outer, gas-impermeable cover or vacuum bag 74. Sealing elements 76 are provided to seal the gas-permeable membrane 73 and vacuum bag 74 to the tool 72. A resin distribution mesh 75 is disposed between the preform 70 and the tool 72 and contacts the resin supply line to enhance resin distribution to the preform 70. In an alternative embodiment, the LSP material 71 contacts the resin distribution mesh 75 instead of the preform 70. A vacuum source is connected to the space between the gas-permeable membrane 73 and the vacuum bag 74.

[0074] During operation, a vacuum is drawn from the space between vacuum bag 74 and tool 72, thereby compressing the bag against the LSP material / preform assembly. Liquid resin is introduced to the LSP material / preform assembly via a resin supply line and with the aid of resin distribution mesh 75. Due to the vacuum pressure, the resin is pulled through the thickness of the LSP material / preform assembly, but gas permeable membrane 73 prevents the resin from flowing into the space between gas permeable membrane 73 and vacuum bag 74.

[0075] It should be understood that Figures 5-7 are merely illustrative of how the LSP materials of the present disclosure may be used in a Resin Infusion process, and the use of the LSP materials disclosed herein is not limited to any particular configuration of either RTM or VARTM. [Example]

[0076] Example 1 FIG. 8 is a top view image (magnification ×50) showing a permeable LSP structure formed by laminating a 10 gsm nonwoven glass veil and a 26 gsm epoxy-based resin film under vacuum and heat in a first step, and then laminating the resin-infused veil to a 73 gsm expanded copper foil (or copper mesh) under vacuum and heat.

[0077] Example 2 A permeable LSP material was formed by combining 195 gsm expanded copper foil (ECF), two glass veils (10 gsm each), and two SM905C epoxy-based films (50 gsm each) so that the ECF was sandwiched between the two glass veils and the epoxy-based films were the outermost layers, followed by lamination of the assembly under vacuum and heat. A dry preform was formed by laying up 16 plies of NCF fabric (268 gsm each) arranged in a quasi-isotropic symmetric layup. The LSP material was placed on the dry preform, and the entire assembly was infused with an epoxy-based resin composition at 90 °C in a VaRTM setup. The preform was fully infused in 3 minutes, using approximately 136 g of resin. The resin-infused preform was cured at 180 °C for 120 minutes to form a cured composite panel.

[0078] FIG. 9 shows a cross section of a cured composite panel with embedded LSP material.

[0079] Example 3 A permeable LSP material was formed as described in Example 2, except that 73 gsm ECF was used. The LSP material was placed onto a dry preform composed of 16 plies of NCF (268 gsm each), and the entire assembly was infused with an epoxy-based resin composition at 90°C in a VaRTM setup. The preform was fully infused in 3 minutes, and approximately 134 g of resin was used. The resin-infused preform was cured at 180°C for 120 minutes to form a cured composite panel.

[0080] FIG. 10 shows a cross section of a cured composite panel with embedded LSP material.

Claims

1. (i) distributing a particulate or powdered binder onto a first nonwoven veil to form a first binder-containing nonwoven veil; (ii) laminating a first binder-containing nonwoven veil to one side of a porous conductive layer having openings through its thickness; (iii) laminating a reinforcing textile to the opposite surface of the porous conductive layer; 1. A method of forming a permeable material comprising: The method of claim 1, wherein the reinforcing textile comprises a second nonwoven veil bonded to a layer of unidirectional fibers, and either the second nonwoven veil or the layer of unidirectional fibers is adjacent to the conductive layer during lamination in step (iii).

2. (i) distributing a binder in particulate or powder form onto a first nonwoven veil and a second nonwoven veil to form a first binder-containing nonwoven veil and a second binder-containing nonwoven veil; (ii) laminating said first binder-containing nonwoven veil to one side of a porous conductive layer having openings through its thickness; (iv) laminating the second binder-containing nonwoven veil to the opposite side of the porous conductive layer; (v) laminating a reinforcing textile to the second binder-containing nonwoven veil; 1. A method of forming a permeable material comprising: The method of claim 1, wherein the reinforcing textile comprises a third nonwoven veil bonded to a layer of unidirectional fibers, and either the third nonwoven veil or the layer of unidirectional fibers is adjacent to the second nonwoven veil containing a binder during lamination in step (v).

Images