High temperature surface treatment films for composite substrates

Abstract

Disclosed is a high temperature surface treatment film formed from a curable resin composition containing: (i) at least one bismaleimide (BMI) monomer; (ii) at least one comonomer that reacts with the BMI monomer; (iii) a pre-reaction adduct that enhances film-forming properties and improves toughness; (iv) inorganic microspheres; and (v) a flow control agent in the form of a particulate inorganic filler that is not microspheres.

Description

DETAILED DESCRIPTION

[0001] Fiber-reinforced polymer matrix composites (PMC) are high-performance structural materials that are typically used in applications that require resistance to corrosive environments, high strength, and / or low weight. Examples of such applications include aircraft components (e.g., tail, wing, fuselage, and propeller), high-performance automobiles, boat hulls, and bicycle frames. Composite structural parts for aerospace applications typically include surface treatment films to provide required performance characteristics to composite structures before painting. Such surface treatment films are used to improve the surface quality of structural parts while reducing labor, time, and cost. During the manufacture of structural parts, surface treatment films are typically co-cured with PMC materials. Such surface treatment films are also typically combined with lightning protection (LSP) materials to provide an integrated solution with both surface treatment and LSP.

[0002] Currently, most surface treatment films for aerospace applications are formed from epoxy-based resin compositions containing epoxy resin as a thermosetting resin component. Such epoxy-based surface treatment films can be co-cured with epoxy-based composite substrates at a temperature in the range of 121°C-176°C (or 250°F-350°F). The resulting epoxy-based surface treatment films typically have a glass transition temperature (Tg) of about 350°F (about 176°C) or less. g After co-curing, the resulting cured surface treatment film eliminates surface defects (such as pinholes and pits) on the composite substrate.

[0003] Surface treatment materials used in aerospace applications often include epoxy resins because they produce good mechanical properties, achieve a wide service temperature range, and allow for easy application during part manufacturing. The maximum service temperature is defined as the highest temperature at which a material can be used for a long time without significant changes in properties or decomposition. Epoxy-based surface treatment materials cannot be used in extreme environments such as high temperature applications above about 180°C. Therefore, their maximum service temperature is about 180°C and cannot be used in higher temperature applications common in aerospace applications.

[0004] Where aerospace applications require service temperatures that exceed the capabilities of epoxy resins, bismaleimide (BMI) resins are used. Current BMI-based composites can be used at service temperatures ranging from 149°C to 265°C and can provide excellent mechanical properties (such as long-term microcracking resistance at such service temperatures). BMI resins can be initially cured at relatively low temperatures (e.g., 350°F or 176°C) and then post-cured at elevated temperatures (e.g., 450°F-510°F or 232°C-265°C) to complete the polymerization reaction and produce a highly cross-linked network with a high glass transition temperature. There remains a need for surface treatment materials that can be co-cured with BMI-based composites. Such surface treatment materials must be able to withstand the post-curing conditions of the BMI resin.

[0005] Disclosed herein is a surface treatment film for PMC that can be used at high use temperatures above 176°C and, in addition, can be co-cured with high temperature thermosetting composite materials (such as BMI-based composite materials). The surface treatment film is referred to herein as "HT surface treatment film".

[0006] The HT surface treatment film is formed from a curable resin composition containing: (i) at least one bismaleimide (BMI) monomer; (ii) at least one comonomer that reacts with the BMI monomer; (iii) a pre-reacted adduct that enhances film-forming properties and improves toughness; (iv) inorganic microspheres or microcapsules that improve the surface smoothness of the film; and (v) a flow control agent in the form of a particulate inorganic filler that is not a microsphere or microcapsule. The curable resin composition may further contain a pigment or dye to add color to the HT surface treatment film.

[0007] The combination of the one or more BMI monomers and the one or more comonomers constitutes greater than 45%, in some embodiments greater than 50%, by weight of the total weight of the curable resin composition. In preferred embodiments, the curable resin composition does not contain any epoxy resin other than the epoxy resin used to form the pre-reacted adduct.

[0008] After curing, the cured HT surface treated film has a glass transition temperature (T ) greater than 176° C. (eg, 270° C. to 300° C. (or 518° F. to 572° F.)). g The cured HT surface treatment film may be used at a use temperature greater than 176°C (or >350°F), for example, 200°C (392°F) to 265°C (510°F).

[0009] As used herein, the term "cure" or "curing" refers to the irreversible hardening of a prepolymer material or resin precursor 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 hardened material.

[0010] Bismaleimide (BMI)

[0011] BMI monomers are typically prepared by the reaction of maleic anhydride or substituted maleic anhydride with a suitable diamine. Both aromatic and aliphatic diamines are suitable for preparing BMI. The curable resin composition of the HT surface treatment film may contain both aromatic and aliphatic BMI monomers.

[0012] A eutectic mixture of two or more different bismaleimide monomers may be used. By using such a mixture, the melting point of the bismaleimide component is greatly reduced relative to the melting point of the individual bismaleimide monomers.

[0013] Suitable BMI monomers include, but are not limited to: 4,4-bismaleimido-diphenylmethane (BMI-H); 2,2-bismaleimidotoluene-m-xylylene bismaleimide (MXBI); p-xylylene bismaleimide; 1,6-hexamethylenediamine bismaleimide (HMDA-BMI); 1,2-bis(maleimido)ethane; 1,4-bis(maleimido)butane; 2,2-bis(maleimido)butane [4-(4-Maleimidophenoxy)-phenyl]propane; N,N'-(1,3-phenylene)bismaleimide; N,N'-(1,4-phenylene)bismaleimide; 4,4-bismaleimidodiphenyl ether; bismaleimidomethyl ether; bis(4-maleimidophenyl)sulfone; N,N'-4,4'-3,3'-dichloro-diphenylmethane-bismaleimide; N-phenylmaleimide.

[0014] Comonomer

[0015] The bismaleimide monomer reacts with a comonomer to improve processability, impart toughness and produce a highly crosslinked network. Suitable comonomers are selected from allyl compounds, aromatic amines and acryl benzophenone (or acryl phenol ether compounds).

[0016] Suitable allyl compounds are characterized by the presence of two or more allyl or methallyl groups per aromatic nucleus. Preferred allyl compounds include: 2,2'-diallyl bisphenol A or o,o'-diallyl bisphenol A (available from Huntsman as 5292B and from Evonik Corp. TM124 is commercially available); diallyl ether of bisphenol A; 2,2'-diallyl-4,4'-bisphenol; 3'-allyl-4'hydroxyacetophenone; diallyl phthalate; triallyl isocyanurate; triallyl cyanurate; and triallyl trimellitate.

[0017] Preferred aromatic amines include: 4,4'-methylenedianiline (MDA); 4,4'-diaminodiphenyl sulfone (DDS); m- or p-phenylenediamine (PD).

[0018] Propylene benzophenone (or propenylphenol ether compound) is in liquid form at room temperature and is characterized by having two or more propenylphenoxy groups per aromatic nucleus. An example of a suitable propenyl benzophenone is 4,4'-bis(o-propenylphenoxy)benzophenone (available from Evonik as TM123 is commercially available), which reacts with BMI to form a tough and temperature-resistant polymer network.

[0019] Pre-reacted adduct

[0020] One disadvantage of BMI resins is their brittleness. The presence of the pre-reacted adduct improves the film-forming properties of the BMI-based curable composition and the flexibility (or draping ability) of the BMI-based film. The presence of the pre-reacted adduct also improves the toughness and microcracking resistance of the cured BMI polymer.

[0021] In one embodiment, the pre-reaction adduct is a reaction product of a difunctional epoxy resin, epoxy dicyclopentadiene (DCPD) and an elastomer. In another embodiment, the pre-reaction adduct is a reaction product of core-shell rubber (CSR) particles, one or more multifunctional epoxy resins, epoxy dicyclopentadiene (DCPD) and an elastomer. Multifunctional epoxy resins include difunctional, trifunctional and tetrafunctional epoxy resins. The reaction is preferably carried out in the presence of a accelerator (e.g., triphenylphosphine).

[0022] A multifunctional epoxy resin refers to a polyepoxide having two or more epoxy functional groups per molecule. A difunctional epoxy resin refers to a polyepoxide having two epoxy functional groups per molecule, a trifunctional epoxy resin refers to a polyepoxide having three epoxy functional groups per molecule, and a tetrafunctional epoxy resin refers to a polyepoxide having four epoxy functional groups per molecule.

[0023] Suitable difunctional epoxy resins for forming the pre-reacted adduct include diglycidyl ethers of bisphenol A (e.g., Epon from Hexion). TM828 (liquid epoxy resin), DER 331 and DER 661 (solid epoxy resins) supplied by Dow Chemical Co., and Tactix 123 and DER 661 (solid epoxy resins) supplied by Huntsman Advanced Materials. 184). Additional difunctional epoxy resins used to form the pre-reacted adduct may include diglycidyl ether of bisphenol F, diglycidyl ether of bisphenol S, diglycidyl ether of bisphenol Z, diglycidyl ether of tetrabromobisphenol A, and diepoxides of hydrogenated bisphenol A.

[0024] Suitable trifunctional epoxy resins for forming the pre-reacted adduct include triglycidyl ethers of aminophenols. Specific examples of commercially available trifunctional epoxy resins are supplied by Huntsman Advanced Materials. MY0510, MY 0500, MY 0600, MY 0610.

[0025] Suitable tetrafunctional aromatic epoxy resins are polyepoxides having at least one glycidylamine group. An example is the tetraglycidyl ether of methylenedianiline having the following general chemical structure:

[0026]

[0027] The amine group in the structure is shown in the para or 4,4' position of the aromatic ring structure, however, it is understood that other isomers (such as 2,1', 2,3', 2,4', 3,3', 3,4') are possible alternatives. An example of a commercially available tetrafunctional epoxy resin is supplied by Huntsman Advanced Materials. MY 9663, MY 9634, MY 9655, MY-721, MY-720, MY-725.

[0028] The epoxy dicyclopentadiene (DCPD) is a dicyclopentadiene based epoxy resin and a multifunctional hydrocarbon epoxy novolac having the chemical formula / structure:

[0029]

[0030] in

[0031] n=1 to 3.

[0032] The CSR particles used to form the pre-reacted adduct may have a particle size of 300 nm or less. The particle size may be measured, for example, by laser diffraction techniques using a Malvern Mastersizer 2000 instrument. The CSR particles may be any core-shell particles in which a soft core is surrounded by a hard shell. Preferred CSR particles are those having a polybutadiene rubber core or a butadiene-acrylonitrile rubber core and a polyacrylate shell. However, CSR particles having a hard core surrounded by a soft shell may also be used. The CSR particles may be supplied as a suspension containing 25%-40% by weight of CSR particles dispersed in a liquid epoxy resin, such as Kane Ace available from Kaneka Corporation. TM MX 120, MX 125 or MX 156 (in DER TM 331 epoxy resin contains 25%-37% CSR particles by weight).

[0033] The elastomer used to form the pre-reacted adduct is preferably an elastomeric polymer with carboxyl or amine functional groups. Suitable elastomers used to form the pre-reacted adduct include, but are not limited to, rubbers, such as, for example, amine-terminated butadiene acrylonitrile (ATBN), carboxyl-terminated butadiene acrylonitrile (CTBN), carboxyl-terminated butadiene (CTB), fluorocarbon elastomers, silicone elastomers, styrene-butadiene polymers. In an embodiment, the elastomer used to form the pre-reacted adduct is CTBN or CTB.

[0034] In one embodiment, the pre-reacted adduct is formed by reacting a difunctional epoxy resin and epoxy dicyclopentadiene (DCPD) with an elastomeric polymer (preferably having carboxyl or amine groups) in the presence of a catalyst such as triphenylphosphine (TPP) at about 300°F (or 148.9°C) to link the epoxy resin and elastomer chains and form a high viscosity film-forming, high molecular weight epoxy-based pre-reacted adduct. The pre-reacted adduct is then mixed with the remaining components of the curable composition for forming the HT surface treatment film.

[0035] In another embodiment, the pre-reacted adduct is formed by reacting a suspension of CSR particles in a liquid difunctional epoxy resin with DCPD, an elastomer, and optionally a trifunctional or tetrafunctional epoxy resin in the presence of a catalyst as described above. The presence of CSR particles provides additional toughness to the cured surface treatment film. This enhanced toughness is advantageous when working with the inherently brittle BMI resin. The presence of the trifunctional or tetrafunctional epoxy resin increases the strength of the cured surface treatment film and further increases its T g .

[0036] The amount of the pre-reacted adduct in the curable composition is about 8% to 30% by weight based on the total weight of the curable composition.

[0037] Inorganic microspheres

[0038] Microspheres or microspherical capsules are added to the curable composition to improve the surface smoothness of the surface treatment film. Such microspheres are small, spherical, hollow bodies. Each microsphere has a shell encapsulating a hollow core. Inorganic microspheres can be made of various materials (including glass, silicon dioxide (SiO2) and ceramics). It has been found that microspheres with a diameter ranging from about 0.1 μm to about 20 μm and preferably from about 1 μm to about 15 μm are particularly suitable.

[0039] In a preferred embodiment, the inorganic microspheres are hollow ceramic microspheres, such as microspheres made of an inert silica-alumina ceramic material. These ceramic microspheres can have a crush strength in excess of 60,000 psi, a dielectric constant of about 3.7-4.6, a softening point in the range of 1000°C-1100°C (or 1832°F-2012°F), and a particle size in the range of 0.1 micron to 50 microns, or 1 to 50 microns. The high softening point of the ceramic microspheres makes them non-adsorbent to solvents, non-flammable, and highly resistant to chemicals. An example of commercially available ceramic microspheres particularly suitable for use in surface treatment film compositions is available from Zeelan Industries, Inc. under the trade name These microspheres are hollow silica-alumina spheres that have thick walls, are odorless, and are light gray in color.

[0040] The amount of inorganic microspheres is at least 3% by weight based on the total weight of the curable composition. For example, the amount of ceramic microspheres by weight percentage can be in the range of about 5% to about 15%, or about 10% to about 30%, or about 20% to about 40% by weight based on the total weight of the curable composition.

[0041] Flow Control Agents

[0042] Inorganic fillers in the form of particles different from inorganic microspheres or microspherical capsules can be added to the curable composition as flow control agents or rheology modifying components to control the flow of the resin composition and prevent the agglomeration of components therein. Filler particles include powders and particles of any shape. Suitable inorganic fillers that can be used in the curable composition include talc, mica, calcium carbonate, aluminum oxide and silicon dioxide. In one embodiment, hydrophobic fumed silica (e.g., Cab-O-Sil TS-720) is used as an inorganic filler. The amount of the flow control agent can be in the range of about 0.5% to about 5% by weight based on the gross weight of the curable resin composition.

[0043] Optional Additives

[0044] Pigments and / or dyes known in the art for adding color to the resin system can be added to the curable composition. Examples of pigments and / or dyes include, but are not limited to, iron oxide red, chrome green, carbon black, and titanium dioxide. In an embodiment, titanium dioxide (white) pigment is added to the resin composition. In another embodiment, carbon black pigment is added. Such pigments / dyes can be added in an amount of 0.5% to 10% by weight based on the gross weight of the curable composition.

[0045] Exemplary Embodiments

[0046] Some examples of curable compositions for forming the HT surface treatment films of the present disclosure are shown below.

[0047]

[0048] The amounts in the above examples are weight percent (wt %) based on the total weight of the entire composition.

[0049] In one embodiment, the pre-reaction is formed by reacting the following components in weight percent (wt %):

[0050] 1-5wt% carboxylated nitrile elastomer;

[0051] 1-5wt% CTBN or CTB elastomer;

[0052] 1-15 wt% epoxy dicyclopentadiene (DCPD);

[0053] 5-15wt% diglycidyl ether of bisphenol A;

[0054] 1-2 wt% accelerator (preferably triphenylphosphine).

[0055] In another embodiment, the pre-reaction is formed by reacting the following components in weight percent (wt %):

[0056] 1-5wt% carboxylated nitrile elastomer;

[0057] 5-15wt% of a liquid difunctional epoxy resin (e.g. MX 120, MX156) containing 25-40wt% CSR particles;

[0058] 1-15 wt% epoxy dicyclopentadiene (DCPD);

[0059] 1-15wt% trifunctional epoxy resin (e.g., MY510) or tetrafunctional epoxy resin (e.g., MY 721, MY9663);

[0060] 1-2 wt% accelerator (preferably triphenylphosphine).

[0061] Manufacturing methods and applications

[0062] In order to form a surface treatment film, the components of the curable composition are added to a mixing container and blended at room temperature (23°C-25°C) using a solution process. One or more organic solvents can be added to promote the mixing and film formation of each component. Possible solvents include methyl ethyl ketone (MEK), acetone, N-methyl pyrrolidone (NMP), ethanol, dioxolane and propylene carbonate. A conventional film-forming process is then used to form a surface treatment film from the curable composition. Depending on the intended use, the resulting surface treatment film can have an area weight of 0.01 to 0.045psf (or 48gsm to 220gsm).

[0063] In order to facilitate the handling of the surface treatment film, a carrier can be embedded in the film. The carrier can be selected from a fiber sheet made of thermoplastic polymer fibers or carbon fibers, a metal mesh or foil, a nonwoven mat, a random mat, a knitted carrier, a metal-coated carbon fiber veil, etc.

[0064] The surface treatment film can be combined with a conductive layer to impart lightning strike protection (LSP). The conductive layer can be selected from various expanded metal meshes or foils used as surface treatments and lightning strike protection for aircraft composite parts. The metal meshes or foils can include expanded metal meshes or foils and metal-coated fiber mats.

[0065] The curable composition for forming the HT surface treatment film can be applied to one or both surfaces of the conductive layer using conventional coating techniques to form a double-layer or triple-layer structure. Alternatively, a prefabricated surface treatment film is laminated to one side of the conductive layer to form a double-layer structure, or two prefabricated surface treatment films are laminated to both side surfaces of the conductive layer to form a triple-layer structure. The conductive layer can also be embedded in the surface treatment film.

[0066] The HT surface treatment films disclosed herein can be co-cured with fiber-reinforced BMI-based composite substrates at a temperature in the range of 300°F-380°F (or 148°C-193°C). For BMI-based composite substrates, post-curing is required to impart high temperature properties. This post-curing can occur at a temperature range of greater than 350°F (176.66°C) and up to 510°F (265°C).

[0067] The fiber-reinforced BMI-based composite substrate is composed of reinforcing fibers impregnated with or embedded in a matrix resin. The matrix resin includes one or more BMI resins and optionally one or more epoxy resins. The composite substrate can be in the form of a prepreg monolayer or a prepreg stack. The prepreg monolayer is composed of reinforcing fibers in the form of fabric or directional aligned continuous fibers impregnated with resin. These directional aligned fibers can be unidirectional or multidirectional fibers. The prepreg stack is composed of a plurality of prepreg monolayers arranged in a stacking order.

[0068] Generally speaking, an uncured HT surface treatment film can be applied to a fiber-reinforced composite substrate in an uncured or partially cured state and then co-cured to form a fully cured composite structure bonded to the thermosetting (hardened) surface treatment film. After curing, the surface treatment film is the outermost layer of the composite structure.

[0069] The resulting surface treated film is highly cross-linked, with high T as discussed above. g The cured surface treatment film provides a directly paintable surface without surface defects such as pinholes, pits or pores. If the surface treatment film is additionally combined with a metal mesh, foil or metal-coated fiber mat, the surface will also have sufficient lightning protection properties.

[0070] Compared to the glass transition temperature of current epoxy-based surface treatment films on the market today, the HT surface treatment film of the present disclosure has a higher glass transition temperature (T g ). As compared with the T of about 180°C of the existing epoxy-based surface treatment films g In contrast, a T greater than 215°C (e.g., up to 300°C) g is achievable, depending on which BMI comonomer is used.

[0071] The thermal stability of the cured HT surface treatment film as measured by thermogravimetric analysis (TGA) has been found to be 330° C.-390° C. as defined by the temperature at 5% weight loss. In comparison, the thermal stability of current epoxy-based surface treatment films on the market is about 270° C.-285° C. as defined by the temperature at 5% weight loss.

[0072] Examples

[0073] The following examples are used to give specific embodiments of HT surface treatment films formed according to the present disclosure, but are not intended to limit the scope of the present disclosure in any way.

[0074] Example 1

[0075] The curable resin composition for forming the HT surface treatment film was prepared based on the formulation shown in Table 1. The amounts shown in Table 1 are weight percentages (wt%) based on the total weight of the entire composition. Table 1A shows the components used to form the pre-reacted adduct in Table 1. Before being incorporated into the curable resin composition of Table 1, the components shown in Table 1A were pre-reacted to form a pre-reacted adduct. The amounts in Table 1A are expressed in weight percentages (wt%) based on the total weight of all components of the adduct.

[0076] In Table 1, BMI-H refers to N,N'-(4,4'-diphenylmethane)bismaleimide.

[0077] Table 1

[0078] Components wt% Pre-reacted adducts (Table 1A) 13 Diallyl(Matrimid 5292B) 25 BMI-H 32 Zeeospheres G200 18 TiO2 9 Carbon Black 1 Fumed Silica (Cabosil TS 720) 2 total 100

[0079] Table 1A - Pre-reacted Adducts

[0080] Components wt% Accelerator (triphenylphosphine) 0.23 Diglycidyl ether of bisphenol A (DER 331) 54.6 Tactix 556 27.7 Nitrile rubber elastomer (Nipol 1072) 5.93 CTB 11.54 total 100

[0081] The pre-reacted adduct was prepared by mixing the components in Table 1A and heating the mixture to 300°F (or 148.9°C) for one hour.

[0082] The resin composition is prepared by adding the components disclosed in Table 1 to a mixing vessel and mixing the components using a high shear laboratory mixer. BMI-H resin and diallyl comonomer are added first. MEK is added as a solvent to the BMI resin and comonomer mixture to adjust the rheology and solid content of the mixture. Subsequently, the pre-reacted adduct is added to the mixing vessel. Zeeospheres, fumed silica and carbon black are further added to the mixer. Additional MEK solvent is added to control the viscosity of the composition to about 90wt% solids. The components of the composition are mixed at 2000rpm for 50 minutes. The temperature of the composition during mixing is maintained at 75°F (23°C). Additional MEK is added to achieve 90wt% solids.

[0083] In order to form the surface treatment film, the prepared resin composition is filtered, degassed and deposited as a resin film. The filtration is carried out through a nylon mesh screen. Degassing is carried out so that the solid content of the composition is about 90wt%. The filtered and degassed composition is then coated on a film coating machine as a film with a film weight of 0.020psf (or 97.6gsm), and then dried to realize a film with a volatile content less than 1%.

[0084] Example 2

[0085] The curable resin composition for forming the HT surface treatment film was prepared based on the formulation shown in Table 2. The formulation of the pre-reaction adduct is disclosed in Table 2A. The amounts in the table are expressed in weight percent (wt%).

[0086] Table 2

[0087]

[0088] Table 2A - Pre-reacted Adducts

[0089]

[0090]

[0091] The pre-reacted adduct was prepared by mixing the components in Table 2A and heating the mixture to 300°F (or 148.9°C) for one hour.

[0092] The resin composition was prepared by adding the components disclosed in Table 2 to a mixing container and mixing the components using a high shear laboratory mixer. The mixing conditions were as described in Example 1. The resulting resin composition after mixing had a solid content of 85 wt%. A resin film was formed from the resin composition by the film forming method described in Example 1. The dried resin film had a film weight of 0.045 psf (or 220 gsm).

[0093] Example 3

[0094] The curable resin composition for forming the HT surface treatment film was prepared based on the formulation shown in Table 3. The formulation of the pre-reaction adduct is disclosed in Table 3 A. The amounts in the table are expressed in weight percent (wt %).

[0095] Table 3

[0096] Components wt% Pre-reacted adducts (Table 2A) 12.1 Dipropylene (TM 123) 24.7 MXBI 24.7 Zeeospheres W200 26 TiO2 10 Black Dye 1 Fumed Silica (Cabosil TS 720) 1.5 total 100

[0097] Table 3A - Pre-reacted Adducts

[0098] Components wt% Accelerator (triphenylphosphine) 0.25 Diglycidyl ether of bisphenol A (DER 331) 34.7 Tactix 556 9.1 Tactix 756 17.35 Nitrile rubber elastomer (Nipol 1072) 17.1 CTB 21.5 total 100

[0099] The pre-reacted adduct was prepared by mixing the components in Table 3A and heating the mixture to 300°F (or 148.9°C) for one hour.

[0100] The resin composition was prepared by adding the components disclosed in Table 3 to a mixing container and mixing the components using a high shear laboratory mixer. The mixing conditions were as described in Example 1. The resulting resin composition after mixing had a solid content of 95 wt%. A resin film was formed from the resin composition by the film forming method described in Example 1. The dried resin film had a film weight of 0.015 psf (or 73 gsm).

[0101] Example 4

[0102] The curable resin composition for forming the HT surface treatment film was prepared based on the formulation shown in Table 4. The formulation of the pre-reaction adduct is disclosed in Table 4A. The amounts in the table are expressed in weight percent (wt%).

[0103] Table 4

[0104] Components wt% Pre-reacted adducts (Table 2A) 15.5 Diamine (4,4-diaminodiphenyl sulfone (DDS) 20 HMDA BMI 32 Zeeospheres G200 20 TiO2 8 Carbon Black 2 Fumed Silica (Cabosil TS 720) 2.5 total 100

[0105] Table 4A - Pre-reacted Adducts

[0106] Components wt% Accelerator (triphenylphosphine) 0.19 Diglycidyl ether of bisphenol A (EPON 828) 39.3 Tactix 556 13.51 Tactix 756 7.1 Nitrile rubber elastomer (Nipol 1472) 20.5 CTBN 19.4 total 100

[0107] The pre-reacted adduct was prepared by mixing the components in Table 4A and heating the mixture to 300°F (or 148.9°C) for one hour.

[0108] The resin composition was prepared by adding the components disclosed in Table 4 to a mixing container and mixing the components using a high shear laboratory mixer. The mixing conditions were as described in Example 1. The resulting resin composition after mixing had a solid content of 95 wt%. A resin film was formed from the resin composition by the film forming method described in Example 1. The dried resin film had a film weight of 0.030 psf (or 146 gsm).

[0109] Example 5

[0110] The curable resin composition for forming the HT surface treatment film was prepared based on the formulation shown in Table 5. The formulation of the pre-reaction adduct is disclosed in Table 5A. The amounts in the table are expressed in weight percent (wt%).

[0111] Table 5

[0112]

[0113] Table 5A - Pre-reacted Adducts

[0114] Components wt% Nipol 1072 (nitrile rubber elastomer) 8.8 Triphenylphosphine 0.2 Kaneka MX 120 resin containing 25wt% CSR 60.2 Tactix 556 10.5 Tactix 756 10.5 CTBN 9.8 total 100

[0115] The pre-reacted adduct was prepared by mixing the components in Table 5A and heating the mixture to 300°F (or 148.9°C) for one hour.

[0116] The resin composition was prepared by adding the components disclosed in Table 5 to a mixing container and mixing the components using a high shear laboratory mixer. The mixing conditions were as described in Example 1. The resulting resin composition after mixing had a solid content of 90 wt%. A resin film was formed from the resin composition by the film forming method described in Example 1. The dried resin film had a film weight of 0.010 psf (or 49 gsm).

[0117] Example 6

[0118] The curable resin composition for forming the HT surface treatment film was prepared based on the formulation shown in Table 6. The formulation of the pre-reaction adduct is disclosed in Table 6A. The amounts in the table are expressed in weight percent (wt%).

[0119] Table 6

[0120] Components wt% Pre-reaction adduct (Table 6A) 17 Matrimid 5292B (Huntsman Corporation) 21.5 BMI H 31.5 Zeeospheres G210 25 Carbon Black 2 Fumed Silica (Cabosil TS 720) 3 total 100

[0121] Table 6A

[0122] Components wt% Nipol 1472 (nitrile rubber elastomer) 16.02 Triphenylphosphine 0.18 Kaneka MX 257 resin containing 37wt% CSR 32.4 MY0510 19.1 Tactix 556 11.7 CTBN 20.6 total 100

[0123] The pre-reacted adduct was prepared by mixing the components in Table 6A and heating the mixture to 300°F (or 148.9°C) for one hour.

[0124] The resin composition was prepared by adding the components disclosed in Table 6 to a mixing container and mixing the components using a high shear laboratory mixer. The mixing conditions were as described in Example 1. The resulting resin composition after mixing had a solid content of 90 wt%. A resin film was formed from the resin composition by the film forming method described in Example 1. The dried resin film had a film weight of 0.040 psf (or 195 gsm).

[0125] Example 7

[0126] The curable resin composition for forming the HT surface treatment film was prepared based on the formulation shown in Table 7. The formulation of the pre-reaction adduct is disclosed in Table 7A. The amounts in the table are expressed in weight percent (wt%).

[0127] Table 7

[0128] Components wt% Pre-reaction adduct (Table 7A) 15 TM 124-Ether (Bisphenol A bisallyl ether) 22 HMDA BMI 31 Zeeospheres G200, G210, W200 28 TiO2 1 Carbon black or black dye 1 Flow control agent (Cabosil TS 720) 2 total 100

[0129] Table 7A

[0130] Components wt% Nipol 1072 (nitrile rubber elastomer) 11.5 Triphenylphosphine 0.2 Kaneka MX 156 with 25wt% CSR 16.7 MY 721 43.3 Tactix 756 13.3 CTB 15 total 100

[0131] In Table 7, HMDA BMI refers to 1,6-hexamethylenediamine bismaleimide.

[0132] The pre-reacted adduct was prepared by mixing the components in Table 7A and heating the mixture to 300°F (or 148.9°C) for one hour.

[0133] The resin composition was prepared by adding the components disclosed in Table 7 to a mixing container and mixing the components using a high shear laboratory mixer. The mixing conditions were as described in Example 1. The resulting resin composition after mixing had a solid content of 85 wt%. A resin film was formed from the resin composition by the film forming method described in Example 1. The dried resin film had a film weight of 0.020 psf (or 98 gsm).

[0134] Example 8

[0135] Properties of Cured Surface Treatment Films

[0136] Each resin film prepared in Examples 1-7 was spread into a mold and cured using the following autoclave cure cycle: 3°F / min (about 2°C / min) ramp to 350°F (176.7°C); hold at 350°F for 360 min; followed by post cure at 440°F (226.7°C) for 360 minutes.

[0137] Thermomechanical analysis (TMA) was used to determine the T of each cured resin sample using a TA Instruments TMA Q400 at a ramp rate of 10°C / min from room temperature to 350°C. g Thermal stability was determined by thermogravimetric analysis (TGA) of each cured resin sample using a TGA Q50 (TA Instruments) ramping to 500°C at 10°C / min. Thermal stability was defined as the 5% weight loss of the cured material. The results of TMA and TGA are reported in Table 8.

[0138] Table 8

[0139]

[0140] The results in Table 8 demonstrate the high temperature properties and stability of the cured BMI-based surface treatment films. Such properties confirm that these BMI-based surface treatment films are suitable for use at high temperatures (>180°C) and in extreme environments. The cured resins of Examples 1-7 exhibited T values ​​ranging from 227.53°C to 310.10°C. g values, all of which are much higher than the common T values ​​of conventional epoxy-based surface treatment membrane materials. g Such conventional epoxy-based surface treatment film materials typically have a T of about 177°C or less. g . T of BMI-based surface treatment membranes gThe thermal stability also demonstrates the ability of these films to be co-cured with BMI-based composites, which can sometimes have a post-cure temperature of 275° C. or higher. The TGA (especially the 5% weight loss of the cured material) is also much higher than that of conventional epoxy-based surface treatment films, which typically occurs between about 280° C. and about 290° C. Therefore, the BMI-based surface treatment films of Examples 1-7 can more easily withstand temperature shocks in higher temperature environments.

Claims

1. A surface treatment film formed from a curable resin composition, the curable resin composition comprising: a) at least one bismaleimide (BMI) monomer; b) at least one comonomer that reacts with the BMI monomer; c) pre-reacted adduct; d) inorganic microspheres or microcapsules, each having a hollow core; and e) Inorganic particles that are not microspheres or microcapsules; The pre-reacted adduct is a reaction product of a difunctional epoxy resin, epoxy dicyclopentadiene (DCPD) and one or more elastomers.

2. A surface treatment film formed from a curable resin composition, the curable resin composition comprising: a) at least one bismaleimide (BMI) monomer; b) at least one comonomer that reacts with the BMI monomer; (iii) c) pre-reacted adduct; d) inorganic microspheres, each of which has a hollow core; and e) inorganic fillers in the form of particles other than microspheres; in, The pre-reacted adduct is the reaction product of core-shell rubber (CSR) particles, one or more multifunctional epoxy resins, epoxydicyclopentadiene (DCPD), and one or more elastomers.

3. The surface treatment film according to claim 2, wherein: The pre-reacted adduct is the reaction product of core-shell rubber (CSR) particles, a difunctional epoxy resin, dicyclopentadiene (DCPD), an elastomer, and optionally a trifunctional or tetrafunctional epoxy resin.

4. The surface treatment film according to any one of the preceding claims, wherein The comonomer is selected from the group consisting of allyl compounds, aromatic amines and acryl benzophenone.

5. The surface treatment film according to claim 4, wherein: The comonomer is selected from: 2,2'-diallylbisphenol A or o,o'-diallylbisphenol A; diallyl ether of bisphenol A; 2,2'-diallyl-4,4'-bisphenol; 3'-allyl-4'hydroxyacetophenone; diallyl phthalate; triallyl isocyanurate; triallyl cyanurate; triallyl trimellitate; 4,4'-methylenedianiline (MDA); 4,4'-diaminodiphenyl sulfone (DDS); m- or p-phenylenediamine (PD); and 4,4'-bis(o-propenylphenoxy)benzophenone.

6. The surface treatment film according to any one of claims 1, 3 to 5, wherein The difunctional epoxy resin is selected from the group consisting of diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F, diglycidyl ether of bisphenol S, diglycidyl ether of bisphenol Z, diglycidyl ether of tetrabromobisphenol A and diepoxide of hydrogenated bisphenol A, preferably diglycidyl ether of bisphenol A or F.

7. The surface treatment film according to any one of claims 3 to 6, wherein A trifunctional epoxy resin is included in the reaction to form the pre-reacted adduct, and the trifunctional epoxy resin is a triglycidyl ether of aminophenol.

8. The surface treatment film according to any one of claims 3 to 6, wherein A tetrafunctional aromatic epoxy resin is included in the reaction to form the pre-reacted adduct, and the tetrafunctional aromatic epoxy resin is a tetraglycidyl ether of methylene dianiline.

9. The surface treatment film according to any one of claims 2 to 8, wherein The CSR particles used to form the pre-reacted adduct have a particle size of 300 nm or less as measured by laser diffraction techniques, preferably each CSR particle has a polybutadiene rubber core or a butadiene-acrylonitrile rubber core and a polyacrylate shell.

10. The surface treatment film according to any one of the preceding claims, wherein The elastomer used to form the pre-reacted adduct contains carboxyl or amine functional groups.

11. The surface treatment film according to any one of claims 1 to 9, wherein The elastomer used to form the pre-reacted adduct is selected from: amine-terminated butadiene acrylonitrile (ATBN), carboxyl-terminated butadiene acrylonitrile (CTBN), carboxyl-terminated butadiene (CTB), fluorocarbon elastomers, silicone elastomers and styrene-butadiene polymers; preferably, CTBN or CTB.

12. The surface treatment film according to any one of claims 1, 4 and 5, wherein The pre-reaction is formed by reacting the following components in weight percent (wt %): 1-5wt% carboxylated nitrile elastomer; 1-5wt% CTBN or CTB elastomer; 1-15 wt% epoxy dicyclopentadiene (DCPD); 5-15wt% diglycidyl ether of bisphenol A; 1-2 wt% promoter, preferably triphenylphosphine.

13. The surface treatment film according to any one of claims 2 to 5, wherein The pre-reaction is formed by reacting the following components in weight percent (wt %): 1-5wt% carboxylated nitrile elastomer; 5-15 wt% of a liquid bifunctional epoxy resin containing 25-40 wt% of CSR particles; 1-15 wt% epoxy dicyclopentadiene (DCPD); 1-15wt% trifunctional or tetrafunctional epoxy resin; 1-2 wt% promoter, preferably triphenylphosphine.

14. A surface treatment film according to any one of the preceding claims, wherein: The combination of the one or more BMI monomers and the one or more comonomers constitutes greater than 45% by weight of the total weight of the curable resin composition.

15. The surface treatment film according to any one of the preceding claims, wherein: The amount of the pre-reacted adduct in the curable composition is from about 8% to about 30% by weight based on the total weight of the curable resin composition.

16. A surface treatment film according to any one of the preceding claims, wherein: The amount of the inorganic microspheres is about 10 to about 30% by weight based on the total weight of the curable resin composition.

17. A surface treatment film according to any one of the preceding claims, wherein: These inorganic microspheres are made of glass, silica or ceramics and preferably have a diameter in the range of about 0.1 μm to about 20 μm.

18. A surface treatment film according to any one of the preceding claims, wherein: The amount of the inorganic filler is about 0.5% to about 5% by weight based on the total weight of the curable resin composition.

19. A surface treatment film according to any one of the preceding claims, wherein: These inorganic fillers are made of materials selected from the group consisting of talc, mica, calcium carbonate, alumina, and silica, preferably fumed silica.

20. The surface treatment film according to any one of the preceding claims, wherein: The curable resin composition further comprises a color pigment or dye.

21. A composite structure comprising: a composite substrate comprising reinforcing fibers impregnated with or embedded in a curable matrix resin; and a surface treatment film according to any one of claims 1 to 20 in contact with the outer surface of the composite substrate, The curable matrix resin of the composite substrate comprises one or more bismaleimide (BMI) monomers.

22. A composite structure comprising: A surface treatment film according to any one of claims 1 to 20 formed on a prepreg stack of a plurality of prepreg single layers, Each prepreg monolayer comprises reinforcing fibers impregnated with or embedded in a curable matrix resin, and the matrix resin comprises one or more bismaleimide (BMI) monomers.

23. A conductive surface treatment material comprising a conductive layer laminated to one side of the surface treatment film according to any one of claims 1 to 20 or embedded therein.

24. A method for forming a composite structure, the method comprising: forming a prepreg layup of a plurality of prepreg monolayers, each prepreg monolayer comprising reinforcing fibers impregnated with or embedded in a curable matrix resin; bringing the surface treatment film according to any one of claims 1 to 20 into contact with the prepreg stack; co-curing the surface treatment material and the prepreg layup to form a cured composite structure; as well as The cured composite structure is removed from the molding tool.

25. The method according to claim 24, wherein: Co-cure is carried out at an initial temperature in the range of 300°F-380°F (or 148°C-193°C), followed by post-cure at a temperature above the initial temperature, and the higher temperature is greater than 350°F (or greater than 176°C) and up to 510°F (or 265°C).

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