# US 8,772,391 B2 · Co-curable, conductive surfacing films for lightning strike and electromagnetic interference shielding of thermoset composite materials

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- Number: US 8,772,391 B2
- Document ID: US8772391B2
- Status: Granted
- Kind: B2
- Application number: 13/714,506
- Filed: 2012-12-14
- Published: 2013-04-25
- Granted: 2014-07-08
- Earliest claimed: 2009-02-16
- Assignees: Cytec Technology Corp.
- Applicants: Cytec Technology Corp.
- Inventors: Junjie Jeffrey Sang; Dalip Kumar Kohli
- Web page: https://patentgrep.com/patent/US8772391B2

## CPC

- C09D 5/24: Electrically-conducting paints {(conductive materials H01B1/00)}
- B82Y 30/00: Nanotechnology for materials or surface science, e.g. nanocomposites
- C09D 163/00: Coating compositions based on epoxy resins; Coating compositions based on derivatives of epoxy resins
- H01B 1/22: the conductive material comprising metals or alloys
- H01B 1/24: the conductive material comprising carbon-silicon compounds, carbon or silicon
- C08K 3/10: Metal compounds
- Y10S 977/742: Carbon nanotubes, CNTs
- Y10S 977/762: Nanowire or quantum wire, i.e. axially elongated structure having two dimensions of 100 nm or less
- Y10T 156/10: Methods of surface bonding and/or assembly therefor
- Y10T 428/249921: Web or sheet containing structurally defined element or component
- Y10T 428/252: Glass or ceramic [i.e., fired or glazed clay, cement, etc.] [porcelain, quartz, etc.]
- Y10T 428/254: Polymeric or resinous material
- Y10T 428/256: Heavy metal or aluminum or compound thereof
- Y10T 428/268: Monolayer with structurally defined element
- Y10T 428/27: Web or sheet containing structurally defined element or component, the element or component having a specified weight per unit area [e.g., gms/sq cm, lbs/sq ft, etc.]
- Y10T 428/273: of coating
- C09D: COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR (cosmetics A61K; processes for applying liquids or other fluent materials to surfaces, in general, B05D; staining wood B27K5/02; glazes or vitreous enamels C03C; natural resins, French polish, drying-oils, driers, turpentine, per se, C09F; polishing compositions other than French polish, ski waxes C09G; adhesives or use of materials as adhesives C09J; materials for sealing or packing joints or covers C09K3/10; materials for stopping leaks C09K3/12; processes for the electrolytic or electrophoretic production of coatings C25D)
- B82Y: SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- H01B: CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES (selection for magnetic properties H01F1/00; waveguides H01P {; printed circuits H05K})
- C08K: Use of inorganic or non-macromolecular organic substances as compounding ingredients (paints, inks, varnishes, dyes, polishes, adhesives C09)
- Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

Embodiments of the present disclosure present electrically conductive, thermosetting compositions for use in surfacing films and adhesives. The surfacing films possess enhanced electrical conductivity, comparable to metals, without the use of embedded metal screens or foils. Such surfacing films may be incorporated into composite structures (e.g., prepregs, tapes, and fabrics), for example, by co-curing, as an outermost surface layer. In particular, compositions formed using silver flakes as conductive fillers are found to exhibit very high electrical conductivity. For example, compositions including greater than 45 wt. % silver flake exhibit resistivities less than about 55 mΩ/sq. In this manner, the surfacing films as an outermost conductive layer may provide lighting strike protection (LSP) and electromagnetic interference (EMI) shielding when used in applications such as aircraft components.

## Claims

### Claim 1

A composite structure comprising an electrically conductive surfacing film formed on a composite substrate,
wherein the surfacing film is capable of providing lightning strike protection and electromagnetic interference shielding, has an electrical resistivity of less than 500 mΩ/sq, a film weight in the range of 0.01-0.15 psf (pounds per square foot), and is formed from a curable thermosetting composition comprising:
a. at least one multifunctional epoxy resin;
b. at least one curing agent selected from the group consisting of: aromatic primary amines, bisureas, boron trifluoride complexes, and dicyandiamide;
c. at least one toughening agent having a functional group selected from epoxy groups, carboxylic acid groups, amino groups and hydroxyl groups capable of reacting with other components of the composition;
d. non-conductive fillers;
e. conductive additives in an amount greater than about 35 wt. %, based on the total weight of the composition.

### Claim 2 (depends on 1)

The composite structure of claim 1, wherein the composite substrate is a prepreg layup comprising a plurality of prepreg layers, each of said prepreg layers comprising reinforcing fibers impregnated with a matrix resin.

### Claim 3 (depends on 1)

The composite structure of claim 1, wherein said at least one multifunctional epoxy resin comprises a combination of Diglycidylether of Bisphenol A and at least one of Tetraglycidylether methylenedianiline and Diglycidylether of Tetrabromo Bisphenol A.

### Claim 4 (depends on 1)

The composite structure of claim 1, wherein said at least one curing agent is selected from the group consisting of: dicyandiamide, Bisureas, 4,4′-Methylene bis-(phenyl dimethylurea), 4,4′-diaminodiphenyl sulfone (4,4′-DDS), and BF3.

### Claim 5 (depends on 1)

The composite structure of claim 1, wherein said thermosetting composition further comprises non-conductive fillers.

### Claim 6 (depends on 1)

The composite structure of claim 1, wherein said non-conductive fillers comprise ceramic microspheres.

### Claim 7 (depends on 1)

The composite structure of claim 1, wherein said at least one toughening agent is selected from the group consisting of: carboxylated nitriles, carboxyl-terminated butadiene acrylonitrile (CTBN), carboxyl-terminated polybutadiene (CTB), polyether sulfone, polyether ether ketone (PEEK), polyetherketoneketone (PEKK), liquid rubber, and core/shell rubber particles.

### Claim 8 (depends on 1)

The composite structure of claim 1, wherein said thermosetting composition further comprises ceramic microspheres and fumed silica, and
said at least one multifunctional epoxy resin comprises a combination of Diglycidylether of Bisphenol A, Tetraglycidylether methylenedianiline, and Diglycidylether of Tetrabromo Bisphenol A,
said at least one curing agent comprises dicyandiamide and bisureas, and
said at least one toughening agent comprises carboxylated nitrile and either carboxyl-terminated butadiene acrylonitrile (CTBN) or carboxyl-terminated polybutadiene (CTB).

### Claim 9 (depends on 1)

The composite structure of claim 1, wherein said curable thermosetting composition further comprises a chain extension agent selected from the group consisting of: bisphenol A, tetrabromo bisphenol A (TBBA), bisphenol Z, tetramethyl bisphenol A (TMBP-A), and bisphenol fluorines.

### Claim 10 (depends on 1)

The composite structure of claim 1, wherein said thermosetting composition further comprises a UV stabilizer selected from the group consisting of: butylated hydroxytoluene (BHT), 2-hydroxy-4-methoxy-benzophenone, 2,4-Bis(2,4-dimethylphenyl)-6-(2-hydroxy-4-octyloxyphenyl)-1,3,5-triazine, 3,5-Di-tert-butyl-4-hydroxybenzoic acid, n-hexadecyl ester, titanium dioxide, ultra-fine zinc oxide, and carbon black.

### Claim 11

An electrically conductive surfacing film capable of providing lightning strike protection and electromagnetic interference shielding, said surfacing film comprising silver flakes distributed substantially uniformly throughout the film in a substantially interconnected, lamellar configuration, and formed from a curable thermosetting composition comprising:
a. at least one multifunctional epoxy resin;
b. at least one curing agent selected from the group consisting of: aromatic primary amines, bisureas, boron trifluoride complexes, and dicyandiamide;
c. at least one toughening agent having a functional groups selected from epoxy groups, carboxylic acid groups, amino groups and hydroxyl groups capable of reacting with other components of the composition; and
d. silver flakes in an amount greater than about 35 wt. %, based on the total weight of the composition;
e. ceramic microspheres; and
f. fumed silica,
wherein said surfacing film has an electrical resistivity of less than 500 mΩ/sq, a film weight in the range of 0.01-0.15 psf (pounds per square foot), and less than about 1 wt. % of volatile content.

### Claim 12 (depends on 11)

The electrically conductive surfacing film of claim 11, wherein the curable thermosetting composition comprises:
a. a combination of Diglycidylether of Bisphenol A and at least one of Tetraglycidylether methylenedianiline and Diglycidylether of Tetrabromo Bisphenol A;
b. at least one curing agent selected from the group consisting of: dicyandiamide, bisureas, 4,4′-diaminodiphenyl sulfone (4,4-DDS), and BF3;
c. at least one toughening agent selected from the group consisting of: carboxylated nitriles, carboxyl-terminated butadiene acrylonitrile (CTBN), carboxyl-terminated polybutadiene (CTB), polyether sulfone, and core/shell rubber particles; and
d. silver flakes in an amount greater than about 35 wt. %, based on the total weight of the composition;
e. ceramic microspheres; and
f. fumed silica.