• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
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    • 专利摘要:
    electrically conductive coating material, pre-impregnated conductive tape, method for fabricating a composite structure, and, composite structure an electrically conductive coating material capable of providing sufficient conductivity to protect from lightning (lsp) and/or shielding from interference The conductive coating material is a multilayer structure having a very thin conductive layer (eg sheet of solid material) is a resin film formed at least one surface of the conductive layer. resin is formed epoxy novalac, a trifunctional expoxy resin or tetrafunctional ceramic microspheres, a latent amine based curing agent, particulate inorganic fillers and a hardening component. optionally, the resin film exhibits high tg as well as high resistance to paint extracting solutions. In addition, the conductive coating material is suitable for co-curing with fiber reinforced resin composite substrates.
    公开号:BR112015012619B1
    申请号:R112015012619-7
    申请日:2013-11-25
    公开日:2021-06-01
    发明作者:Dalip Kumar Kohli；Junjie Jeffrey Sang
    申请人:Cytec Industries Inc.；
    IPC主号:
    专利说明:

    FUNDAMENTALS OF THE TECHNIQUE
    [001] Fiber reinforced polymeric matrix composites (PMCs) are high performance structural materials that are commonly used in applications that require resistance to harsh environments, high strength, and/or light weight. Examples of these applications include aircraft components (eg, tails, wings, fuselages and propellers), high-performance automobiles, boat hulls, and bicycle frames.
    [002] Composite structural parts for aerospace applications typically include a coating film to provide the performance characteristics required for composite structures prior to painting. These coating films are used to improve the surface quality of structural parts while reducing labor, time and cost. The coating films are generally co-cured with the fiber reinforced polymeric matrix composite materials during the fabrication of the structural components. Conventional epoxy-based composite prepregs and coating films exhibit low resistance to electromagnetic energy (EME) events such as lightning (LS), electrostatic discharge (ESD), and electromagnetic interference (EMI) due to their insulating properties. The relatively high resistivity (low electrical conductivity) exhibited by epoxies inhibits the energy of a lightning from properly dissipating, resulting in surface perforation and delamination of the underlying composite structure. Additionally, the charge generated on the composite surface can remain for long periods of time, raising the risk of ESD in low relative humidity environments, which can damage electronic systems and the risk of ignition in the vapor space of fuel tanks. In addition, the low electrical conductivity of epoxy-based film coatings can inhibit the mobility of charge carriers, which can impair the composite structure's ability to provide EMI shielding. To minimize lightning damage on a composite structure, there is a need to increase the electrical conductivity of the composite structure to provide LS/EDS/EMI protection for composite aircraft parts. It is not desirable, however, to incorporate conductive material that will significantly increase the aircraft's overall weight. Furthermore, conventional film coatings are not very resistant to commercial paint extraction solutions, such as benzyl alcohol based solutions, for pickling purposes. These strippers can cause swelling and/or blistering of the surface film, thus making the repainting process more complicated. As such, there is a need for a multifunctional, conductive coating material that is lightweight, can withstand repeated paint pickling using conventional paint pickling solutions, and can also withstand exposure to ultraviolet (UV) radiation. SUMMARY
    [003] The present invention provides an electrically conductive coating material, which is a multilayer structure composed of a very thin conductive layer with a thickness equal to or less than 76.2 µm and a resin film formed on at least one surface of the conductive layer. The resin film is formed from an epoxy-based curable composition, wherein after curing, the cured resin layer has a glass transition temperature (Tg) of >180°C, and a surface pencil hardness. greater than 7H as measured per ASTM D3363.
    [004] The conductive coating material is co-curable with a fiber reinforced composite polymeric substrate at a temperature within the range of 250°F - 355°F (120°C - 180°C) to form a composite structure . In addition, the conductive coating material can be used to form narrow tapes that are suitable for use in automated tape placement (ATL) or automated fiber placement (AFP). BRIEF DESCRIPTION OF THE DRAWINGS
    [005] The features of this disclosure will be more easily understood from the following detailed description of the various aspects of the description taken in conjunction with the accompanying drawings which show different embodiments of the present description.
    [006] FIG. 1 schematically shows the assembly of a conductive tri-layer coating material according to an embodiment.
    [007] FIG. 2 schematically shows a composite structure having a tri-layer of conductive coating material thereon according to an embodiment. DETAILED DESCRIPTION
    [008] Disclosed herein is a multifunctional, electrically conductive coating material that is lightweight, capable of providing LS/EDS/EMI protection, can withstand repeated paint removal using conventional paint pickling solutions, and can also withstand exposure to ultraviolet (UV) radiation. Compared to conventional conductive laminates for LS/EDS/EMI protection, the conductive coating material described herein is able to provide significant weight savings - 50% -80% less weight compared to some conventional conductive laminates.
    [009] The conductive coating material is a multilayer structure that includes a very thin conductive layer and a curable resin film formed on at least one of the two opposing surfaces of the conductive layer. The conductive layer can be a solid sheet of metal or a layer or layer of carbon. Carbon in this context includes graphite. The conductive layer preferably has a resistivity of less than 10 mQ, more preferably less than 5 mQ. Furthermore, the conductive layer preferably has a thickness of <76.2 µm, preferably 3 µm - 38 µm. The resin film may have a film weight of less than 500 gsm, for example 50 - 150 gsm, per side. In one embodiment, the conductive coating material is a three-layer structure that includes a conductive layer sandwiched between two resin films. The two resin films can have the same resin composition or different resin compositions. In an embodiment of the three-layer structure, the conductive layer is a microthin sheet metal with a thickness of 3 µm - 5 µm, and the resin film formed on each side of the metal sheet has a film weight of 50 - 150 gsm. As examples, the metal layer/sheet can be formed from metals such as copper, aluminum, bronze, or alloys thereof.
    [0010] The conductive coating material can be manufactured by coating a curable liquid resinous composition to one or both surfaces of a conductive layer (eg, solid metal sheet) using conventional coating techniques.
    [0011] Alternatively, the conductive coating material can be manufactured by laminating a prefabricated resin film to one side of a conductive layer so as to form a bilayer structure, or laminating two prefabricated resin films onto opposing surfaces of the conductive layer to form a three-layer structure.
    [0012] FIG. 1 schematically illustrates how a three-layer conductive coating material can be manufactured according to an example. A first resin film 11, which is supported by a peelable release backing paper 12, is laminated onto one surface of a metal sheet 13, and a second resin film 14 is laminated onto the opposite surface of the metal sheet 13 to form a three-layer structure 20. The lamination process can be carried out with the application of pressure and heat. Release backing paper 12 can be peeled off after lamination. To form a two-layer structure, the second resin film 14 could be eliminated, and the sheet metal is supported by its own detachable carrier.
    The conductive coating material described herein was designed to be co-cured with a fiber reinforced composite polymeric substrate at a temperature above 65°C, more particularly within the range of 120°C-175°C. The fiber reinforced polymer composite substrate is composed of reinforcing fibers that have been impregnated or infused with a curable matrix resin. In some embodiments, the composite substrate can be a pre-impregnated layer or pre-impregnated stack. The pre-impregnated stack consists of a plurality of pre-impregnated layers arranged in a stacking sequence. Each pre-impregnated layer consists of reinforcing fibers in the form of a fabric or directionally aligned, the continuous fibers which have been impregnated/infused with a matrix resin, for example epoxy resin. Directionally aligned fibers can be unidirectional or multidirectional fibers. In general, the curable conductive coating material can be applied over a fiber reinforced polymeric composite substrate, which is in an uncured or partially cured state, followed by co-curing to form a fully cured composite structure having a hardened surface film. attached to this as the outermost layer.
    [0014] With reference to FIG. 2, to form a composite structure, the three-layer structure 20 is contacted with a composite substrate 30 such that the resin film 14 is in direct contact with the composite substrate 30. In one embodiment, the composite substrate 30 is a pre-prepared stack. In this embodiment, the paper backing 12 is removed and the resin film 11 is brought into contact with a tool surface, and then a plurality of pre-impregnated layers are defined above on resin film 14 in an array of stacking. The tool surface can be (for example, curved surface or any other three-dimensional configuration) flat or non-planar. Pre-impregnated layers can be sequentially stored, one on top of the other, on top of the tool. Alternatively, the pre-impregnated layers can be assembled in a different location and then later placed over the resin film 14. One or more core structures, eg foam or honeycomb structures, can be interposed between pre-impregnated stacking layers, as is known in the art. After volume reduction of the entire assembly under full vacuum, the entire assembly is then subjected to heat and pressure to cure the pre-impregnated stack and the resin films of the coating material to a final composite structure hardened to a selected shape. When the composite structure is removed from the molding tool, the resin film 11, which has been in contact with the surface of the tool, becomes the outermost layer of the composite structure.
    [0015] The assembly in FIG. 2 can be modified by removing the second resin film 14 so that the metal sheet 13 is in contact with the composite substrate.
    [0016] The conductive coating material can be used to form pre-impregnated continuous tapes suitable for use in an automated tape placement (ATL) or automated fiber placement (AFP) to form a curable composite structure having the coating material conductor as the outermost layers. For ATL/AFP application, the conductive coating material can be used as is or laminated with a pre-impregnated layer, which is composed of a curable resin matrix and fiber reinforcement in the form of unidirectional fibers or fabric. The conductive coating material or laminated prepreg layer is cut into narrow tapes of suitable AFP width (eg 3.17mm - 38.1mm, including 6.35mm -12.77mm), or ATL width (eg 152mm - 305mm).
    [0017] ATL and AFP are processes that use computer-guided robotics to secure one or more layers of fiber tape or tow to a mold surface (eg, a mandrel) to create a part or composite structure. Exemplary applications include aircraft wing surfaces and fuselages. The AFP/ATL process involves distributing one or more strands side-by-side over a mandrel surface to create a layer of desired width and length, and then additional layers are built on top of a previous layer to provide a stacked to a desired thickness. The AFP/ATL system is equipped with means to distribute and compress pre-impregnated tapes directly onto the chuck surface.
    [0018] AFP automatically places several individual pre-impregnated tows or narrow slit tapes (eg 3.17 mm - 38.1 mm) into a mandrel to generate a given total pre-impregnated bandwidth. Material placement is done at high speed, using a numerically controlled command placement head to dispense, squeeze, cut and restart each trailer during placement. ATL machine places pre-impregnated unidirectional tapes or continuous strips of fabric, which are wider than the single trailers or slit tape used in AFP. Typically, with both processes, the material is applied through a robotically controlled head, which contains the necessary mechanism for placing the material. AFP is traditionally used on very complex and smaller surfaces.
    [0019] Typical coating films for use with aerospace composite parts are often epoxy-based and are adversely affected when exposed to ultraviolet (UV) radiation and conventional alcohol-based paint strippers such as benzyl alcohol-based solutions. The multifunctional conductive coating material disclosed herein is designed to overcome these problems. For that purpose, the resin component of the resin film composition has been formulated so as to provide high Tg and high crosslink density. It was found that the combination of high Tg and high crosslink density makes the resin film highly resistant to alcohol based stripping solutions, such as benzyl alcohol based solutions. To achieve these properties, the resin film composition is based on a combination of certain multifunctional resins, a polymeric hardening component to harden the resin matrix, a latent amine-based latent curing agent, ceramic microspheres as one component barrier fluids, and particulate inorganic fillers as a rheology modification component. Multifunctional resins and ceramic microspheres constitute more than 35% by weight of the total composition, preferably more than 45% by weight. Multifunctional resins
    [0020] The resin film in the multilayer coating material is formed from a thermosetting composition containing at least two multifunctional epoxy resins, preferably one of which is an epoxy novolac resin having an epoxy functionality greater than one. The second epoxy resin is a multifunctional non-novolac epoxy resin, preferably tetra- or tri-functional (i.e., epoxy resin having three or four or epoxy functional groups per molecule).
    Suitable epoxy novolac resins include polyglycidyl derivatives of phenol-formaldehyde novolacs or cresol-formaldehyde novolacs having the following chemical structure (Structure I): Structure I
    where n = 0 to 5, and R = H or CH3. When R = H, the resin is a phenol novolac resin. When R = CH3 , the resin is a novolac cresol resin. The former is commercially available as DEN 428, DEN 431, DEN 438, DEN 439, and DEN 485 from Dow Chemical Co. The latter is commercially available as ECN 1235, ECN 1273, ECN 1299 and from Ciba-Geigy Corp. Other suitable novolacs that may be used include SU-8 from Celanese Polymer Specialty Co. In a preferred embodiment, the epoxy novolac resin has a viscosity of 4000-10,000 mPa 2 at 25°C and epoxide equivalent weight (EEW) of 190- 210 g/eq.
    [0022] A suitable tetrafunctional epoxy resin is an aromatic tetrafunctional epoxy resin having four epoxy tetra functional groups per molecule and at least one glycidyl amine group. As an example, the aromatic tetrafunctional epoxy resin may have the following general chemical structure (Structure II), namely methylene dianiline tetraglycidyl ether: Structure II

    [0023] The amine groups in Structure II are shown at the para- or 4,4' positions of the aromatic ring structures, however, it should be understood that other isomers such as 2.1', 2,3', 2,4 ', 3.3', 3.4', are possible alternatives. Suitable tetrafunctional aromatic epoxy resins include commercially available tetraglycidyl-4,4'-diaminodiphenylmethane as Araldite® MY 9663, MY 9634, MY 9655, MY-721, MY-720, MY-725 supplied by Huntsman Advanced Materials. Examples of trifunctional epoxy resins include aminophenol triglycidyl ether, for example Araldite® MY 0510, MY 0500, MY 0600, MY 0610 supplied by Huntsman Advanced Materials.
    [0024] In a preferred embodiment, the combination of novolac epoxy resin and multifunctional epoxy resin (trifunctional and/or tetrafunctional) constitutes at least 15% by weight based on the total weight of the resin film composition. In certain embodiments, the combination of epoxy novolac resin and multifunctional epoxy resins constitutes about 30% to about 60% by weight based on the total weight of the resin film composition, and in other embodiments, about 15% to about 25% by weight. The relative amounts of epoxy novolac resin and multifunctional epoxy resin can be varied, but it is preferred that the amount of epoxy novolac resin is in the range of 80-100 parts per 100 parts of multifunctional epoxy resin. The combination of epoxy novolac resin and multifunctional epoxy resin in the specified ratio contributes to the desired high Tg and crosslink density after adapted cure. polymeric hardening component
    [0025] To harden the resin matrix based on the blend of multifunctional resins discussed above, one or more polymeric toughening agents are added to the resin film composition. Polymeric toughening agents are selected from the group consisting of: (i) a pre-reacted adduct formed by the reaction of an epoxy resin, a bisphenol, and an elastomeric polymer; (ii) a copolymer of polyether sulfone (PES) and polyether ether sulfone (PEES); and (iii) the core-cladding rubber particles; and their combinations. In a preferred embodiment, a combination of two hardening agents from this group is used. The amount of curing agents, in total, is from about 10% to about 20% by weight based on the total weight of the surface film composition.
    With respect to the pre-reacted adduct, suitable epoxy resins include bisphenol A diglycidyl ether, tetrabromo bisphenol A diglycidyl ether, hydrogenated bisphenol A diglycidyl ether, or bisphenol F hydrogenated diglycidyl ether. Cycloaliphatic epoxies are also suitable. which include compounds that contain at least one cycloaliphatic group and at least two oxirane rings per molecule. Specific examples include cycloaliphatic alcohol diepoxide, hydrogenated Bisphenol A (Epalloy™ 5000, 5001 supplied by CVC Thermoset Specialties) represented by the following structure: Structure III

    [0027] An example of such a cycloaliphatic epoxy resin is EPALLOY® 5000 (a cycloaliphatic epoxy prepared by hydrogenation of diglycidyl ether of bisphenol A) available from CVC Thermoset Specialties. Other cycloaliphatic epoxides suitable for use in the pre-reacted adduct may include EPONEX cycloaliphatic epoxy resins, for example, EPONEX 1510 resin supplied by Momentive Specialty Chemicals.
    [0028] Bisphenol A in pre-reacted adducts functions as a linear or cycloaliphatic epoxy chain extending agent. Suitable bisphenols include bisphenol A, tetrabromo bisphenol A (TBBA), Bisphenol Z, and tetramethyl bisphenol A (TMBP-A).
    [0029] Suitable elastomers to form the pre-reacted adduct include, among others, rubbers such as butadiene, e.g., amine-terminated butadiene acrylonitrile (ATBN), carboxyl-terminated butadiene acrylonitrile (CTBN), carboxyl-terminated butadiene (CTB) ), fluorocarbon elastomers, silicone elastomers, styrene-butadiene polymers. In one embodiment, the elastomers used in the pre-reacted adduct is ATNB or CTBN.
    [0030] In one embodiment, the epoxy resin reacts with the bisphenol chain extending agent and the elastomer polymer in the presence of a catalyst, such as triphenyl phosphine (TPP), at about 300°F (or 148.9° C) for chain bonding to epoxy resins and to form a pre-reacted, high molecular weight, film-forming, epoxy resin pre-reacted adduct. The pre-reacted adduct is then mixed with the remaining components of the surface film composition.
    [0031] A second option for the polymeric hardening component is a thermoplastic hardening material which is a copolymer of polyether sulfone (PES) and polyether ether sulfone (PEES) with an average molecular weight of 8,000-14,000. In one embodiment, the hardener is poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene), which has a Tg of about 200°C, as measured by Differential Scanning Calorimetry (DSC).
    [0032] The third option for the polymeric hardening component is made up of core-cladding rubber particles with a particle size equal to or less than 300 nm. The core-cladding rubber particles (CSR) can be any of the core-cladding particles where a soft core is surrounded by a hard coating. Preferred RSE particles are those having a polybutadiene rubber core or butadiene-acrylonitrile rubber core and a polyacrylate core. RSE particles that have a hard core surrounded by a soft coating can also be used, however. CSR particles can be supplied as a 25-40 weight percent of dispersed CSR particles in a liquid epoxy resin. CSR particles with rubber cores and polyacrylate cores are commercially available from Kaneka Texas Corporation (Houston, Texas.) under the trade names Kane Ace MX. It is preferred, but not necessary, that the core-sheath rubber particles be added to the surface film composition as a suspension of particles in a suitable liquid epoxy resin. Kane Ace MX 411 is a 25% by weight suspension of MY 721 epoxy resin core-cladding rubber particles and is a suitable source of core-cladding rubber particles. Kane Ace MX 120, MX 125, or MX 156, which contains 25 -37% by weight of the same core-cladding rubber particles dispersed in DER 331 resin, is also a suitable source of core-cladding rubber particles. Another suitable source of core-cladding rubber particles such as MX 257, MX 215, MX 217 and MX 451 can also be used. Another commercial source of core-sheath rubber particles is ParaloidTM EXL-2691 from Dow Chemical Co. (methacrylate-butadiene-styrene CSR particles, with an average particle size of about 200 nm). Ceramic microspheres
    [0033] Ceramic microspheres are added to the resin film composition to improve the smoothness of the film surface. In one embodiment, hollow ceramic microspheres made of an inert silica-alumina ceramic material are used. Ceramic microspheres can have a crush strength of more than 413.69 mPa, a dielectric constant of about 3.7-4.6, a softening point in the range 1000-1100°C, and particle diameters ranging from 0.1 micron to 50 microns or 1-50 microns. The high softening point of ceramic microspheres allows them to be non-solvent absorbent, non-flammable and highly resistant to chemicals. Microspheres having diameters ranging from about 0.1 µm to about 20 µm, and preferably from about 1 µm to about 15 µm, have been found to be particularly suitable. An example of commercially available ceramic microspheres which are particularly suitable for use in the present resin film composition are sold by Zeelan Industries, Inc. under the trade name Zeeospheres®, for example, G-200, G210 and W-200. These are hollow silica-alumina spheres, with thick walls, odorless and light gray in color. In a preferred embodiment, the combination of multifunctional resins and ceramic microspheres comprises more than 50% by weight, preferably more than 60% by weight, of the resin film composition. In certain embodiments, the amount of ceramic microspheres is at least 20% by weight, preferably at least 25% or at least 30% by weight, based on the total weight of the resin film composition. In some embodiments, the amount of ceramic microspheres may be within the range of 20% > - 40% > by weight, or 25% - 35% by weight. In other embodiments, the amount of ceramic microspheres can be within the range of 3% to 15% by weight, or 5% - 10% by weight. Healing Agents
    [0034] Multifunctional epoxide resins can be cured by a variety of amine-based latent curing agents, which are activated at elevated temperatures (eg, temperature greater than 150°F (65°C)). Examples of suitable curing agents include dicyandiamide (DICY), guanamine, guanidine, aminoguanidine, and derivatives thereof. Compounds of the class of imidazole and amine complexes can also be used. In one embodiment, the curing agent is dicyandiamide. The amine-based curing agent is present in an amount within the range of 1% -5% by weight, based on the total weight of the resin film composition.
    [0035] A curing accelerator can be used in conjunction with the amine-based curing agent to promote the curing reaction between the epoxy resins and the amine-based curing agent. Suitable cure accelerators can include ureas substituted with alkyl and aryl (including aromatic urea or alicyclic dimethyl), and with bisureas based on toluenediamine or methylene dianiline. An example of bisurea is 4,4'-methylene bis (dimethyl phenyl urea), commercially available as Omicure U-52 or CA 152 from CVC Chemicals, which is a suitable accelerator for dicyandiamide. Another example is 2,4-toluene bis(dimethyl urea), commercially available as Omicure U-24 or CA 150 from CVC Chemicals. The cure accelerator may be present in an amount within the range of 0.5% - 3% by weight based on the total weight of the resin film composition. Flow Control Agents
    [0036] Inorganic fillers in particulate form (eg powder) are added to the resin film composition as a rheology modification component to control the flow of the resin composition and to prevent agglomeration therein. Suitable inorganic fillers that can be used in the resin film composition include talc, mica, calcium carbonate, alumina, and fumed silica. In one embodiment, hydrophobic fumed silica (eg, Cab-O-Sil TS-720) is used as an inorganic filler material. The amount of inorganic filler can be within the range of 1% - 5% by weight, based on the total weight of the resin film composition. Optional additives
    [0037] The resin film composition may further include one or more optional additives that affect one or more of the optical, mechanical, electrical, flame, and/or thermal properties of cured or uncured resin film. Additives may comprise materials that chemically react with the epoxy resins of the composite substrate that are in contact with the resin film or may be non-reactive with these. Such additives include, among others, ultraviolet (UV) stabilizers, pigments/dyes, and conductive materials. When these additives are used, their total amount is less than 5% by weight based on the total weight of the resin film composition.
    [0038] Examples of UV stabilizers that can be added to the resin composition include butylated hydroxytoluene (BHT); 2-hydroxy-4-methoxy-benzophenone (for example UV-9); 2,4-bis(2,4-dimethylphenyl)-6-(2-hydroxy-4-octyloxyphenyl)-1,3,5-triazine (for example, CYASORB® UV-1164 light absorber); 3,5-di-tert-butyl-4-hydroxybenzoic acid; n-hexadecyl ester (eg CYASORB® UV-2908 light stabilizer); Pentaerythritol tetrakis (3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (eg IRGANOX 1010) Liquid hindered amine light stabilizer from Ciba Specialty Chemicals such as 2-(2H-benzotriazole -2-yl)-4,6-ditertpentylphenol (eg TINUVIN 328), methyl 1,2,2,6,6-pentamethyl-4-piperidyl sebacate (eg TINUVIN 292). ,2,6,6-tetramethyl-1-(octyloxy)-4-piperidinyl ester (eg TINUVIN 123), can also be used as suitable UV stabilizers. In addition, nano-sized zinc oxide (n- ZnO), eg NanoSunGuard 3015, and titanium oxide nanoparticles (n-TiO2) can also be used as UV stabilizers.
    [0039] Pigments and/or dyes known in the art for adding color to resin systems can be added to the resin film composition. Examples of pigments and/or dyes include, among others, red iron oxide, green chromium, carbon black, and titanium oxide. In one embodiment, titanium oxide pigment (white) is added to the resin film composition. In another embodiment, carbon black pigment is added.
    [0040] Conductive materials in particulate form, for example particles or flakes, can also be added to the resin film composition to impart electrical conductivity to the final resin film. It has been found that the combination of the metal layer (or sheet) and resin films which have conductive particles or flakes distributed therein results in the conductivity property which is similar to the pure metal layer. For example, a surface resistivity of less than 20 mfl, in some cases 5 mQ, is possible for a multilayer structure having one or two conductive resin films combined with a metal/foil layer. Examples of suitable conductive materials include metals such as silver, gold, nickel, copper, aluminum, bronze, and their alloys, in the form of flakes or particles. Carbon-based materials such as carbon nanotubes (single wall nanotubes or multi-wall nanotubes), carbon nanofibers, and graphene can also be used as conductive additives to impart electrical conductivity to the resin film . Nanofibers can have diameters ranging from 70-200 nanometers and a length of about 50200 microns. The nanotubes can have an outer diameter of about 10 nanometers, a length of about 10,000 nanometers, and an aspect ratio (L/D) of about 1000. In addition, conductive additives can also include carbon black particles (such as from Printex XE2 DeGussa).
    [0041] In certain embodiments, conductive multilayer coating materials with the metal/foil layer combined with conductive resin films (conductive additives having dispersed therein) are capable of exhibiting similar metal conductivity that is 1-2 magnitude greater than than that of conductive resin films only. As such, the multi-layer conductive coating material provides uniform three-dimensionality, high conductivity just like metal, which would bring in a significant improvement to composite EME protection in both LSP and EMI shielding.
    [0042] Tables 1A and 1B show various modalities for the composition of resin film. Table 1A
    Table 1B


    [0043] In one embodiment, the resin film composition has the following formulation, in weight percentages based on the total weight of the composition: 20%-25% epoxy novolac phenol resin; 20%-25% tetrafunctional epoxy resin; 10%-15% pre-reacted adduct, 1%-3% PES-PEES copolymer, 25%-35% ceramic microspheres; 1%-5% amine-based latent curing agent; 0.5% - 3% cure accelerator; 1% - 3% inorganic fillers; and optionally 0.1-1% color pigment.
    [0044] In another embodiment, the resin film composition has the following formulation, in percentages by weight based on the total weight of the composition: 5%-15% epoxy novolac phenol resin; 5%-15% tetrafunctional epoxy resin; 10%-20% pre-reacted adduct, 1%-3% PES-PEES copolymer, 25%-35% ceramic microspheres; 1%-5% amine-based latent curing agent; 0.5%-3% cure accelerator; 1%-3% inorganic fillers; and, optionally, 45%-70% conductive additives, such as silver flakes or silver-copper flakes, carbon-based nano-sized materials discussed above.
    [0045] The resin film composition components can be added to a mixing vessel equipped for mixing, heating and/or cooling the components. In addition, one or more organic solvents can also be added to the mixture, as needed, to facilitate mixing of the components. Examples of such solvents may include, among others, methyl ethyl ketone (MEK), acetone, dimethylacetamide, and N-methylpyrrolidone. A resin film is subsequently formed from the resin film composition using conventional film forming processes.
    [0046] To facilitate resin film handling, the resin film composition is applied over a carrier. Non-limiting examples of the carrier may include fibrous sheets made of thermoplastic polymeric fibers or carbon fibers, non-woven mats, random mats, carriers, metal coated carbon webs, and the like. Examples of non-woven mats, fabric or mesh protectors may include carbon mats, polymer mats and carbon coated with metals, glass, or polymer glass veils. Non-woven mat, woven or mesh protection can be coated with copper, aluminum, silver, nickel and their alloys. After curing, the resulting cured resin film exhibits a high crosslink density, a high glass transition temperature (Tg) of > 180°C, as measured by DSC, a pencil hardness of 7H or greater according to ASTM D-3363. These properties allow the cured resin film to be highly resistant to conventional paint strippers (eg benzyl alcohol based paint strippers) as well as UV radiation and microcracks. It was found that, after being in contact with a benzyl alcohol-based pickling solution for 7 days at room temperature (20°C-25°C), the coating film exhibits fluid absorption of less than 0.5% , and the pencil hardness is not reduced by more than 2H pencil degrees. In addition, the cured resin film was shown to have a microcrack density of less than 0.3 cracks/in2 after being subjected to a 2000X thermal cycling test between -55°C and 71°C. The cured resin film still exhibits high adhesion to paint coatings commonly used for painting aerospace structures. The adhesion of resin film to the paint layer is such that the painted surface shows substantially 0% paint loss after having been subjected to an paint adhesion test in accordance with ASTM D3359 under a dry condition or wet condition ( after immersion in deionized water at 75°C for 7 days), with or without being subjected to 1000 KJ/m2 of exposure to UVA radiation. EXAMPLES
    [0047] The following examples serve to confer specific embodiments of materials for conductive coatings according to the present invention, but are not intended to limit the scope of the present invention in any way. Nine resin films were made based on the formulations (1-9) shown in Table 2. All values are in percent by weight. TABLE 2


    [0048] Each resin film was prepared by adding the components described in Table 2 into a mixing vessel and mixing the components using a laboratory high-speed shear mixer. Epoxy resins were added first. MEK was added as a solvent to the epoxy resin blend as needed in order to adjust the rheology and solids content of the composition. Subsequently, hardening agents (pre-reacted adduct and/or PES-PEES copolymer) were added to the epoxy resins. In certain coating films (Formulations 4 to 7), conductive additives (silver flakes or Ag-Cu flakes) were also added to the mixing vessel. Ceramic microspheres, fumed silica, and UV stabilizers (in some formulations) were further added to the mixing vessel. MEK solvent was added as needed to control the viscosity of the mixture above about 80% by weight solids and the composition components were mixed for about 50-70 minutes at about 1000-3000 rpm. The temperature of the composition was kept below about 71°C. Additional MEK was added as needed to inhibit the mix from increasing the mix shaft.
    The mixture was subsequently cooled to below about 49°C and curing agents (dicyandiamide (Dicy) and Bisurea) were added to the composition. The composition was then mixed until approximately homogeneous. The temperature of the mixture, during the addition of the curing agents, was kept below about 54°C.
    [0050] To form films on the resin surface from the above compositions, each composition was deformed, de-aerated, and deposited as a film. Deformation was carried out through EP-15 filtration media. De-aeration was carried out in such a way that the solids content of the composition was about 80% by weight. The deformed and deaerated composition was then coated as a film having a film weight of about 97.6-146.4 gsm by a film coating device, and then dried to achieve less than about 1% by weight of volatiles. A selected non-woven polyester or glass random mat carrier or conductive carrier was pressed into the resin film under light pressure to incorporate the carrier into the film.
    [0051] To form multi-layer conductive coating material the resin films formed from the resin compositions of Table 2 were combined several metal sheets to form a three-layer structure (as shown in FIG. 1) through a lamination process film/sheet at the proper temperature and pressure. Composite panels were then manufactured by combining the multi-layer conductive coating material with a pre-impregnated stack. For each panel, the three-layer conductive coating material was placed over a tool, followed by stacking of pre-impregnated layers (CYCOM 5276-1 from Cytec Industries Inc., pre-impregnated based on carbon/epoxy fibers) to form a stacked pre-impregnated. The stack pre-impregnated with the conductive coating material was then cured at a temperature of about 176.6°C for 2 hours under 551.58 kPa in an autoclave. Coating Film Evaluation
    [0052] The glass transition temperature (Tg) of the cured resin films was determined using a modulated DSC (TA 2910) or a mechanical thermal analyzer (TMA 2940, TA Instruments) under nitrogen ramping from 10°C/min to 30 °C - 230°C temperature range. Composite Laminate Panel Evaluation
    [0053] Composite panels coated with the multi-layer conductive coating material were inspected for surface appearance defects (wells, holes). Next, the composite panels were evaluated for their resistance to strippers, the adhesion of dry and wet paint, with or without UV exposure, and resistance to micro-cracks. Paint stripper resistance test
    [0054] The stripping resistance of unpainted coated composite panels, coated composite panels (2'' x 2'' sample size, with a thickness of 0.15mm) were measured by measuring the pickling fluid absorption and pencil hardness change on surface over the immersion period (up to 168 hours at room temperature) of the benzyl alcohol based etching solution (Cee Bee 2012A available from McGean or Turkish 1270-6 available from Henkel) used for the aerospace composite structure paint stripping process. The weight of each test panel was measured before and after immersed etching at intervals of 24 hours, 48 hours and up to 168 hours (7 days). The pickling fluid absorption (weight change over immersion time, expressed in % by weight) of the tested panel was measured at the same test intervals up to 168 hours (7 days) of immersion.
    [0055] The surface of each unpainted test panel was immersed in the benzyl alcohol-based pickling solution for up to 168 hours at room temperature, and then tested for pencil hardness during the change of immersion time accordingly to ASTM D3363. ASTM D3363 refers to a standard test method for determining the surface hardness of pigmented, clear organic coating film on a substrate. The pencil hardness scale is as follows: 6B (softer), 5B, 4B, 3B, 2B, B, HB, F, H, 2H, 3H, 4H, 5H, 6H, 7H, 8H, 9H (more difficult). The pencil hardness of the test panel was measured before and after immersion in the paint remover within the range of 24 hours, 48 hours and up to 168 hours (7 days). Pencil hardness that changes more than the 2H level over 24 hours of immersion is not considered to have good paint stripping resistance. Adhesion of dry and wet paint to paint with or without UV exposure
    [0056] Dry and wet scribe paint adhesion of painted composite panels (in the form of 3'' x 6'' sample size, 0.15mm thickness) performed with multi-layer conductive surface film, with or without exposure to UV rays before painting, was measured in accordance with ASTM D3359. ASTM D3359 refers to a standard test method for evaluating surface adhesion of substrate coating films by applying and removing pressure sensitive tape over cuts made in the film (cross-hatch scribe tape test). Cured test panels were exposed to zero (no UV), 200 kJ/m2 or 1000 kJ/m2 ultraviolet radiation (UV-A) in accordance with AATCC test method 16, Option 3. Instrument used for the testing of UV is a Xeno-Weather-o-meter, such as Atlas CI3000 Fadeo meter. Each surface of the test panel was prepared (cleaned, with and without sanding) and applied with an exterior decorative paint coat used in aerospace paint (epoxy paint primer followed by a polyurethane-based top coat). Subsequently, dry paint adhesion test was performed in accordance with ASTM D3359. To perform wet paint adhesion, the test panels were exposed to UV painted and then immersed in deionized water at 75°C for 7 days. Wet paint adhesion test was then conducted in accordance with ASTM D3359. Electrical conductivity measurements
    [0057] Test panels with conductive coating material were cut to form test coupons of about 15.24 x 12.7 cm and their conductivity or electrical surface resistivity (in Ohm/square, or milliohm/square) were measured using a four-point probe AVO® Ducter®Ohmmeter with low resistivity digital DLRO10X. Tables 3 and 4 show the surface properties and test results for test panels coated with three-layer coating materials (resin film/metal sheet/resin film) based on the resin film formulations to from Table 2 and a sheet of solid metal (copper or aluminum) as specified in Tables 3 and 4. TABLE 3
    TABLE 4

    [0058] As shown in Tables 3 and 4, the test panels exhibited excellent stripping resistance and high surface hardness (> 7H). These panels also exhibited excellent ink adhesion (10+ means 0% ink loss) under various test conditions (dry and wet, with or without exposure to UV rays).
    [0059] Referring to Table 3, composite panels coated with three-layer conductive coating materials (test panels, 1-2 and 5-7) have been shown to exhibit unexpected metal-like conductivity (less than 5 mQ/sq), which is 1 to 2 magnitude greater than conductive resin films alone (without sheet metal). As such, three-layer conductive coating materials provide three-dimensionally uniform high conductivity just like metals. The metal-like conductivity of these three-layer conductive coating materials allows them to provide good LSP protection and EMI shielding. Micro-crack resistance test
    [0060] The test panels described in Tables 3 and 4 were painted, and the microcrack resistance of painted test panels (in the form of 4'' x 6'' sample size, 0.15 mm thick) it was also measured. The painted test panels were thermally cycled between -55°C and 71°C up to 2000X cycles. The surface of each test panel after thermal cycling was examined under a microscope for the occurrence of micro-cracks after being exposed to 400X, 800X, 1200X, 1600X and 2000X thermal cycles. Crack density (number of surface paint cracks shown in the test panel size area) is used to measure the micro-crack strength of the coated composite test panel. The maximum crack length must be less than 2.54 millimeters. The micro-crack test results after 2000X thermal cycling are shown in Table 5. Table 5 - Thermal cycling test results

    [0061] As shown in Table 5, the multi-layer coated test panels, materials for conductive coatings show good micro-crack resistance, with crack density less than 0.00465 cracks/mm2.
    [0062] The terms "first", "second" and so on here do not denote any order, quantity, or importance, but are used to distinguish one element from another, and the terms "one" and "an" here do not denote a quantity limit, but instead denote the presence of at least one of the referenced item. The modifier “about” and “approximately” used in relation to a quantity is inclusive of all values, and has the meaning dictated by the context, (eg includes the degree of error associated with measuring a given quantity). The suffix "(s)" as used herein is intended to include both the singular and plural of the word it modifies, thus including one or more than the term (e.g., the metal(s) includes (in) one or more metals). The ranges disclosed herein are inclusive and independently combinable (e.g. ranges of "up to about 25% by weight, or more specifically about 5% by weight to about 20% by weight", is inclusive of all endpoints and intermediate values of ranges, for example, "1% by weight to 10% by weight" include 1%, 2%, 3%, etc.
    [0063] Although various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements contained therein can be made by those skilled in the art, and are within the scope of the invention. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope of the same. Therefore, it is intended that the invention is not limited to the particular embodiment disclosed as the best contemplated mode for carrying out this invention, but that the invention includes all embodiments that are within the scope of the appended claims.
    权利要求:
    Claims (15)
    [0001]
    1. Electrically conductive coating material capable of providing lightning protection or shielding from electromagnetic interference, the coating material being a multilayer structure, characterized by the fact that it comprises: (a) an electrically conductive layer having two opposite surfaces and a thickness of less than 76.2 µm and resistivity of less than 10 mfi; (b) a resin film formed on at least one surface of the conductive layer, wherein the resin film is formed from a curable composition comprising: an epoxy novolac resin having epoxy functionality of more than one; a trifunctional or tetrafunctional epoxy resin; ceramic microspheres; a latent amine-based curing agent; particulate inorganic fillers; and at least one hardening agent selected from the group consisting of: (i) a pre-reacted adduct formed by the reaction of an epoxy resin, a bisphenol, and an elastomer; (ii) a copolymer of polyether sulfone (PES) and polyether ether sulfone (PEES); (iii) core-cladding rubber particles (CSR); and combinations thereof, and after curing, the resin film has a glass transition temperature (Tg) > 180°C, and a surface pencil hardness greater than 7H as measured in accordance with ASTM D-3363.
    [0002]
    2. Electrically conductive coating material according to claim 1, characterized in that the resin film has a film weight in the range of 50 - 150 gsm (gram per m2).
    [0003]
    3. Electrically conductive coating material according to claim 1 or 2, characterized in that the conductive layer has a thickness within the range of 3 μm-38 μm; or by the fact that the conductive layer is a sheet of metal having a thickness within the range of 3 µm -5 µm.
    [0004]
    4. Electrically conductive coating material, according to any one of claims 1 to 3, characterized in that the metal sheet comprises the metal selected from copper, aluminum, bronze, or alloys thereof.
    [0005]
    5. Electrically conductive coating material according to any one of claims 1 to 4, characterized in that the resin film exhibits less than 0.5% fluid absorption and a hardness reduction of no more than 2H grades of pencil, after being in contact with a benzyl alcohol-based pickling solution for 7 days at room temperature within the range of 20°C-25°C.
    [0006]
    6. Electrically conductive coating material, according to any one of claims 1 to 5, characterized in that the resin film further comprises conductive particles or flakes distributed throughout the resin film.
    [0007]
    7. Electrically conductive coating material according to claim 6, characterized in that the conductive particles or flakes are formed from conductive materials selected from: silver, gold, aluminum, copper, bronze, carbon, and combinations of the same; or by the fact that the surface resistivity of the multilayer structure is less than 5 mQ.
    [0008]
    8. Electrically conductive coating material according to any one of claims 1 to 7, characterized in that two resin films are formed on opposite surfaces of the metal layer such that the metal layer is sandwiched between the two resin films.
    [0009]
    9. Electrically conductive coating material, according to claim 8, characterized in that the two resin films are different in composition; or by the fact that the two resin films are of the same composition.
    [0010]
    10. Electrically conductive coating material, according to any one of claims 1 to 9, characterized in that the first resin layer has a micro-crack density of less than 0.00465 cracks/mm2 after it has been subjected to a 2000X test of thermal cycling between -55°C and 71°C.
    [0011]
    11. Electrically conductive coating material, according to any one of claims 1 to 10, characterized in that the epoxy novolac resin in the curable composition has the following structure:
    [0012]
    12. Electrically conductive coating material according to any one of claims 1 to 11, characterized in that the at least one hardening agent of the thermosetting composition includes a pre-reacted adduct formed by the reaction of diglycidyl ether of tetrabromo bisphenol A , bisphenol A, and amine-terminated acrylonitrile butadiene (ATBn) or carboxy-terminated acrylonitrile butadiene elastomer (CTBN); and/or by the fact that the curable composition comprises the pre-reacted adduct and PES-PEES copolymer as hardening agents; and/or by the fact that ceramic microspheres are hollow microspheres made of silica-alumina ceramic material and having a particle size within the range of 1-50 microns; and/or by the fact that epoxy resins and ceramic microspheres constitute more than 35% by weight of the total weight of the thermosetting composition; and/or by the fact that the curable composition further comprises a bisurea as a curing accelerator.
    [0013]
    13. Conductive pre-impregnated tape suitable for automated tape application (ATL) or automated fiber positioning (AFP), characterized in that it is derived from electrically conductive coating material as defined in any one of claims 1 to 12, said pre-impregnated conductive tape having a width within the range of 152mm - 305mm or 3.17mm - 38.1mm.
    [0014]
    14. Method of manufacturing a composite structure, characterized in that it comprises: laying pre-impregnated tapes in an automated tape placement (ATL) or automated fiber placement (AFP) process, using an automatic system equipped with means to distribute and compact pre-impregnated tapes directly onto a molding surface to form a composite structure; incorporating the pre-impregnated conductive tape as defined in claim 13 in the ATL or AFP process so that the pre-impregnated conductive tape is positioned as an outermost layer in the final composite structure.
    [0015]
    15. Composite structure, characterized in that it comprises: a composite substrate comprising reinforcing fibers impregnated with a matrix resin; and the electrically conductive coating material as defined in any one of claims 1 to 12, formed on a surface of the composite substrate such that the metal layer is positioned between the resin film and the composite substrate.
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    同族专利:
    公开号 | 公开日
    CN104853910B|2017-03-22|
    BR112015012619A2|2017-07-11|
    WO2014088866A1|2014-06-12|
    MX357441B|2018-07-10|
    AU2013356422B2|2016-07-28|
    MX2015006452A|2015-08-14|
    EP2900468B1|2016-09-07|
    TWI584947B|2017-06-01|
    AU2013356422A1|2015-05-14|
    MY176165A|2020-07-24|
    US9620949B2|2017-04-11|
    CN104853910A|2015-08-19|
    CA2893646C|2020-08-11|
    US20140154496A1|2014-06-05|
    KR102123475B1|2020-06-26|
    RU2605131C1|2016-12-20|
    JP6176802B2|2017-08-09|
    TW201429704A|2014-08-01|
    US20170179706A1|2017-06-22|
    ES2604784T3|2017-03-09|
    CA2893646A1|2014-06-12|
    KR20150091480A|2015-08-11|
    JP2016508077A|2016-03-17|
    US10256618B2|2019-04-09|
    EP2900468A1|2015-08-05|
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    法律状态:
    2018-03-06| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|
    2018-03-13| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|
    2018-03-20| B06I| Publication of requirement cancelled [chapter 6.9 patent gazette]|Free format text: ANULADA A PUBLICACAO CODIGO 6.6.1 NA RPI NO 2462 DE 13/03/2018 POR TER SIDO INDEVIDA. |
    2019-12-10| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|
    2021-02-09| B06A| Patent application procedure suspended [chapter 6.1 patent gazette]|
    2021-05-04| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|
    2021-06-01| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 25/11/2013, OBSERVADAS AS CONDICOES LEGAIS. |
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