High-speed curing resin composition and composite material containing the same

Abstract

A composite material containing a thermosetting resin composition and a reinforcing fiber impregnated with the thermosetting resin composition. The thermosetting resin composition contains (a) a combination of a multifunctional epoxy resin; (b) 4,4'-methylenebis(2,6-xylidine) as a curing agent for the epoxy resin; and (c) a thermoplastic component, wherein the thermosetting resin composition is devoid of any catalyst or accelerator that reacts with the epoxy resin.

Description

[Modes for carrying out the invention]

[0001] Fiber-reinforced polymer composites have been used to manufacture load-bearing structures. High-performance structures, such as primary and secondary structures of aircraft and automobile body components, can be manufactured by laying up multiple layers of thermosetting prepregs on a mold surface, followed by compaction and curing. Each thermosetting prepreg consists of layers of reinforcing fibers impregnated with or embedded in a matrix resin containing a thermosetting resin, such as epoxy resin. Epoxy resins are used because of their known heat and chemical resistance.

[0002] The design of composite materials for use in aerospace structures typically takes into account the high-temperature / high-humidity performance of the cured material. High-temperature / high-humidity performance refers to the mechanical properties of the material when tested after prolonged exposure to relatively high temperature and high humidity conditions. In aircraft manufacturing, extreme environmental factors such as high temperature and high humidity levels must be considered, as aircraft may experience high temperatures for several hours, although humidity levels are unknown. Therefore, composite materials for aerospace applications are typically evaluated for use under high-temperature and high-humidity conditions.

[0003] With respect to prepregs, one characteristic of prepregs to be considered is their "out-life" or shelf life, which refers to the length of time that an uncured prepreg can be stored at room temperature (20°C to 25°C) and still retain sufficient tack and drape (or flexibility) to enable the manufacture of composite parts of acceptable quality from such prepregs. The "tack" of an uncured prepreg is a measure of its ability to adhere to itself and to the mold surface, and is a crucial factor during layup and molding operations, during which multiple layers of prepreg are laid up to form a laminate, which is then cured to form a composite part.

[0004] Typically, the fabrication of cured composite structures from thermosetting prepregs is a relatively lengthy process. The curing of the prepreg gray-up is often the major contributor to the total time required. Most prepregs used to manufacture large aerospace structures are typically cured in an autoclave, which is a large pressurized oven. In such scenarios, the curing cycle usually begins with a temperature ramp from ambient temperature to the desired curing temperature. The rate at which the temperature is ramped is typically 0.5°C / min to 2°C / min, and the final curing temperature is often around 180°C or higher. The dwell time (or holding time) at the final curing temperature is typically around 2 to 3 hours, followed by a process of cooling the cured material to room temperature at a rate of 2°C / min to 3°C / min. The total duration of the curing cycle is typically in the range of 7 to 12 hours. A slow heating ramp to the final curing temperature and a long dwell time at high temperatures are required to achieve a high degree of curing and desirable thermomechanical properties.

[0005] Higher ramp speeds are not always achievable or desirable when larger tools are required or when curing thick composite structures, as this can lead to uncontrolled heat generation or non-uniform curing across the entire thickness of the composite. Various attempts have been made to formulate epoxy prepregs that can be cured in an autoclave at temperatures below 180°C and with dwell times below 2 hours.

[0006] To reduce the curing temperature or the duration of the curing cycle, pre-reacting epoxy resins, catalysts, co-curers, or combinations thereof are typically combined with the main amine curing agent. The presence of pre-reacting epoxy, catalysts, or co-curers can have undesirable effects on the handling and processing capabilities of the prepreg under ambient conditions, such as tack, drape, storage time, and out-life. Alternatively, highly reactive aromatic curing agents, such as 4,4'-methylenedianiline, have been used in the past, but they are now classified by some government authorities as carcinogens and / or mutagenic substances and are therefore undesirable for future applications. Catalytic epoxy resin compositions that can be cured in less than 2 hours at temperatures below 180°C are suitable for high-temperature / high-humidity applications below 150°C. g It was found that it yields a cured material typically characterized by high temperature / high humidity, and has a tendency to absorb more moisture than cured epoxy materials cured by a standard 180°C / 2-hour curing cycle, resulting in a substantial decrease in high temperature / high humidity mechanical performance. g This refers to the glass transition temperature of a cured composite material that has been pre-conditioned for a long period of time at high relative humidity (e.g., 85%–95%) and elevated temperature (e.g., 70°C–90°C) until the sample reaches saturation. g This can be measured according to EN6032. Highly reactive catalyst epoxy resin compositions also have a tendency to generate localized uncontrolled heat when they are used to manufacture thick composite structures. Uncontrolled heat can make the manufacturing process unsafe or result in composite structures with non-uniform curing from the top to the center of the cured part. An intermediate dwell of variable duration, e.g., 0.5 to 2 hours, at a temperature of 100°C to 140°C can be used to mitigate such problems, but this would not be suitable for the purpose of further extending the duration of the curing cycle and adding catalyst to the resin composition.

[0007] Solutions to address the aforementioned problems related to curing cycles for processing thermosetting prepregs and the high-temperature / high-humidity performance of cured composite parts manufactured from such prepregs are disclosed herein. Such solutions include providing thermosetting resin compositions for producing composite materials, in particular fiber-reinforced prepregs, comprising combinations of different epoxy resins, an orthomethyl-substituted aromatic diamine as the main amine curing agent, one or more thermoplastic components, and optionally, several fillers. The term "main" amine curing agent means that such amine constitutes 50% or more of the total molar content of the amine in the thermosetting resin composition. In some embodiments, the orthomethyl-substituted aromatic diamine is the sole amine curing agent in the composition.

[0008] The epoxy resin in the thermosetting resin composition is preferably a polyfunctional epoxy resin having two or more epoxy groups per molecule.

[0009] The thermoplastic component of the thermosetting resin composition includes one or more reinforcing agents selected from thermoplastic polymers and thermoplastic particles. In some embodiments, a combination of thermoplastic polymers and thermoplastic particles is present in the resin composition.

[0010] Orthomethyl-substituted aromatic diamines (main amines) contain two primary amino groups and two methyl substituents at the ortho position of each amino group per molecule. Preferred aromatic diamines have the following chemical structure: [ka] It is a synonym for 4,4'-methylenebis(2,6-xylidine) and 4,4'-methylenebis(2,6-dimethylaniline), represented as [the formula shown].

[0011] Preferred aromatic diamines are crystalline solids with a melting point of 116°C, stable at ambient temperature and humidity, and do not cause any significant advancement of thermosetting resins, particularly epoxy resins, during the prepreg manufacturing process, which is typically carried out at temperatures in the range of 80°C to 130°C. Therefore, the presence of such aromatic diamines does not affect the tack, workability, shelf life, and moldability of the uncured prepreg. In this context, the term "moldability" refers to the ability of a material to conform to or drape onto a three-dimensional tool surface.

[0012] 4,4'-methylenebis(2,6-dimethylaniline) can be distinguished from 4,4'-methylenebis(2,6-diethylaniline) or 4,4'-methylenebis(2,6-diisopropylaniline) in that the methyl group at the ortho position of the primary amine is more electron-donating and less sterically hindrance than that of an ethyl or isopropyl group due to steric, inductive, and hyperconjugation effects. Although alkyl groups can all be considered weak electron-activating groups when they are at the ortho position of the amine group, they do not contribute significantly to the basicity of aromatic diamines due to the steric hindrance of the aliphatic group very close to the primary amine. Such effects are more pronounced in the case of bulky ethyl or 2-isopropyl groups (in the case of Lonzacure® M-DEA, M-MIPA, and M-DIPA aromatic amines).

[0013] In addition, since the ethyl and isopropyl groups each have only two or one hydrogen atom bonded to the α-carbon atom directly attached to the aromatic ring, in contrast to the methyl group which has three hydrogen atoms, the hyperconjugation effect in the ethyl or isopropyl group will be less than in the case of the methyl group, and will result in greater electron donation from the methyl group than in the ethyl or isopropyl group. The described effect determines the higher reactivity of primary aromatic amines containing a methyl group at the ortho position to epoxy resins, and therefore, higher reaction rates can be achieved at the composite level.

[0014] Finally, the presence of the 2,6-ortho substituent in this methylenedianiline molecule significantly reduces the safety and occupational health risks associated with the molecule's volatility and potential inhalation by operators. Therefore, the properties of the methylenedianiline molecule as a human hepatotoxicity and animal carcinogen are substantially reduced, thereby making this curing agent a more suitable compound for use in resin formulations and composites for aerospace applications.

[0015] In some embodiments, 4,4'-methylenebis(2,6-xylidine) is used in combination with another aromatic amine or a number of other aromatic amines, provided that the molar content of 4,4'-methylenebis(2,6-xylidine) is 50% or more of the total molar amount of all aromatic amines. Other aromatic amines that can be used in combination include 3,3'-diaminodiphenylsulfone (3,3'-DDS); 4,4'-diaminodiphenylsulfone (4,4'-DDS); 1,4-bis(4-aminophenoxy)-2-phenylbenzene; 1,3-bis(3-aminophenoxy)benzene; 4,4'-(m-phenylenediisopropylidene)dianiline; 4,4'-(p-phenylenediisopropylidene)dianiline; 2,2'-bis(4-(4-aminophenoxy)phenylpropane; 4,4'-bis(3-aminophenoxy)diphenylsulfone; 1,3-bis(3-aminophenoxy)benzene; and 4,4'-1,4-phenylenebis(1-methylethylindene)bisaniline.

[0016] The addition of relatively small amounts of other aromatic amines, particularly aromatic diamines, may affect the solubility and compatibility of certain reinforcing agents in / with the epoxy-amine resin matrix in both the uncured and cured states. For example, when a thermoplastic polymer (e.g., polyethersulfone) is used to improve the toughness of an epoxy resin matrix containing 4,4'-methylenebis(2,6-xylidine), the addition of relatively small amounts of a more compatible aromatic amine, such as 4,4' or 3,3'-diaminodiphenylsulfone, may contribute to the formation of a more uniform and less phase-separated blend during curing. In such scenarios, the size of the separated thermoplastic domains dispersed in the epoxy resin may be reduced, and in some cases, a more desirable morphology (e.g., a micronized morphology of thermoplastic domains smaller than 5 microns) may be achieved. During curing, a cured polymer matrix or composite component containing reinforcing fibers embedded in such a cured polymer matrix can generally be characterized as having a good balance of toughness / impact properties, high-temperature and high-humidity performance, and resistance to aggressive solvents.

[0017] In some embodiments, the thermosetting resin composition of the present disclosure comprises the following components: (A)(i) a combination of a bifunctional polyepoxide and (ii) a trifunctional polyepoxide and / or a tetrafunctional polyepoxide; (B) A curing agent component containing 4,4'-methylenebis(2,6-xylidine) as the main amine curing agent for polyepoxides; (C) Preferably, a reinforcing component comprising a combination of a thermoplastic polymer and thermoplastic particles. Includes, Here, the relative amounts of the components in weight percentage (W%) are 30-75 Wt% of A, 20-30 Wt% of B, and 5-40 Wt% of C, based on the total weight of the resin composition. With respect to component B, 4,4'-methylenebis(2,6-xylidine) may be the sole amine curing agent or may be used in combination with one or more other aromatic amines, preferably aromatic diamines. When a combination of amine curing agents is used for component B, the molar content of 4,4'-methylenebis(2,6-xylidine) is 50% or more of the total molar amount of all amines in the thermosetting resin composition.

[0018] The relative amounts of components A and B are such that the molar ratio of epoxy to amine is 0.9 to 1.1. This thermosetting resin composition lacks any catalyst or accelerator for reaction with the polyfunctional polyepoxide. Optionally, this resin composition may further contain inorganic fillers, such as conductive fillers, in an amount of 0.1 to 10% by weight based on the total weight of the resin composition.

[0019] In preferred embodiments, the thermosetting resin composition does not contain any catalyst or accelerator that reacts with the epoxy resin. Such catalysts or accelerators include bisurea, metal complexes with carboxylate ligands, boron trifluoride or complexes thereof, or any co-curing agents such as tertiary amines, imidazoles, phosphonium halides, and adducts with polyepoxides. Such tertiary amines include tris(dimethylaminomethyl)phenol and benzyldimethylamine. Epoxy resin compositions containing such tertiary amines lack storage stability and, in most cases, must be used within 24 hours after the addition of these co-curing agents (as accelerators), otherwise the mixture will begin to cure under normal storage conditions. Phosphonium halides include ethyltriphenylphosphonium iodide. Adducts with polyepoxides include (i) N-methyl-, N-(2-hydroxyethyl)-, N-octyl-, N-phenyl- and N-benzylpiperazine and N-methylhomopiperazine adducts with polyglycidyl ether of 4,4'-isopropylidenediphenol (bisphenol A); and (ii) imidazole adducts with monoperoxides, polyepoxides, or phenol / novolac resins, such as the 2-ethyl-4-methylimidazole adduct with glycidyl polyether of 2,2-bis(4-hydroxyphenyl)propane. The presence of such catalysts / accelerators and co-curing agents can result in undesirable effects on properties such as tack, drape, storage time, and shelf life of the uncured prepreg under ambient conditions.

[0020] For the purpose of manufacturing prepregs, the viscosity of the uncured thermosetting resin composition may be in the range of 50 to 1500 poise at 80°C or 1 to 500 poise at temperatures in the range of 120°C to 170°C.

[0021] A thermosetting prepreg may be manufactured by impregnating a layer of reinforcing fibers with a thermosetting resin composition disclosed herein, wherein the resin composition constitutes 30% to 80%, or 30% to 65%, preferably 40% to 50%, of the total volume of the prepreg.

[0022] The prepreg produced using the thermosetting resin composition of the present disclosure has a degree of cure of more than 85% and a glass transition temperature of 180°C or higher (more specifically, 180°C to 200°C) under dry conditions and 150°C or higher (more specifically, 150°C to 160°C) under high temperature / high humidity conditions (after conditioning at 70°C / 85% humidity for 2 weeks), as measured by EN6032 and can be cured at 160°C to 180°C for 15 to 120 minutes to produce a cured composite material of (T g ). In some embodiments, the curing is carried out at 160°C to 170°C for 15 to 60 minutes.

[0023] The degree of cure of the thermosetting resin composition or prepreg can be measured by differential scanning calorimetry (DSC). The thermosetting resin composition undergoes an irreversible chemical reaction during curing. When the components in the resin system cure, heat is generated by the resin and is monitored by the DSC instrument. The heat of cure can be used to determine the percent cure of the resin material. As an example, the following simple calculation can provide percent cure information: % cure = [ΔH 未硬化 - ΔH 硬化 / [ΔH 未硬化 × 100% where ΔH is the enthalpy generated by the uncured sample or the cured sample.

[0024] A suitable curing cycle for a prepreg or prepreg layup containing reinforcing fibers impregnated with the thermosetting resin composition of the present disclosure is as follows: a ramp from room temperature (20°C to 25°C) to 160°C at 1°C / min, a dwell at 160°C for 60 minutes, and a ramp down to 60°C at 3°C / min. The stability of the resin composition can allow for further shortening of the curing cycle duration by preheating the mold supporting the prepreg / prepreg layup to a temperature of 80°C to 90°C before ramping the temperature to 160 - 170°C at a ramp rate in the range of 0.5°C / min to 2°C / min.

[0025] Therefore, the total duration of the curing cycle can be reduced from the industry standard of 7-12 hours to 3-5 hours while achieving equivalent thermomechanical performance.

[0026] The thermosetting resin compositions of this disclosure are characterized by controlled reactivity and do not require an intermediate temperature dwell step (holding at a temperature in the range of 100°C to 140°C for 30 to 60 minutes) when thick composite parts (having a thickness of up to 56 mm) are cured using an industry standard temperature lamp of 0.5°C / min to 2°C / min.

[0027] Cured composite materials derived from using the thermosetting resin compositions of this disclosure are characterized by low water absorption, e.g., less than 1.5%, as measured by EN2378, and excellent thermomechanical properties under high temperature / high humidity conditions. Such thermomechanical properties refer to tensile strength of filled holes, as measured by EN6035, bolt bearing strength, as measured by EN6037, and post-impact compressive strength (CAI), as measured by EN6038.

[0028] As used herein, the terms “cure” and “curing” encompass the polymerization and / or crosslinking of polymer materials brought about by mixing of main components, heating at high temperatures, or exposure to ultraviolet and radiation.

[0029] thermosetting resin The thermosetting resin compositions of this disclosure are curable or thermosetting resin compositions. In preferred embodiments, curable thermosetting resin compositions include a combination of polyfunctional epoxy resins or polyepoxides. As used herein, the term “polyfunctional” epoxy resin is a resin having two or more functions. The term “polyepoxide” is used herein with the same meaning as “epoxy resin.” Preferred polyfunctional resins are bifunctional, trifunctional, and tetrafunctional epoxy resins, although epoxy resins having greater functionality, for example, five or six epoxy groups, may also be used. The term “polyfunctional” includes resins having non-integer functionality, for example, epoxyphenol novolac (EPN) resins.

[0030] Suitable epoxy resins include polyglycidyl derivatives of aromatic diamines, aromatic monoprimary amines, aminophenols, polyhydric phenols, polyhydric alcohols, and polycarboxylic acids. Examples of suitable epoxy resins include polyglycidyl ethers of bisphenols such as bisphenol A, bisphenol F, bisphenol C, bisphenol S, and bisphenol K; and polyglycidyl ethers of cresol and phenolic novolacs.

[0031] Suitable bifunctional epoxy resins include diglycidyl ethers of bisphenol F, bisphenol A (optionally brominated), glycidyl ethers of phenols and cresol epoxy novolacs, glycidyl ethers of phenol-aldehyde adducts, glycidyl ethers of aliphatic diols, diglycidyl ethers, diethylene glycol diglycidyl ethers, aromatic epoxy resins, aliphatic polyglycidyl ethers, epoxidized olefins, brominated resins, aromatic glycidylamines, heterocyclic glycidylimidines and amides, glycidyl ethers, fluorinated epoxy resins, or any combination thereof. The bifunctional epoxy resin is preferably selected from diglycidyl ether of bisphenol F (DGEBF), diglycidyl ether of bisphenol A (DGEBA), diglycidyl ether of dihydroxynaphthalene, or any combination thereof.

[0032] Suitable trifunctional epoxy resins include, for example, those based on phenols and cresol epoxy novolacs, glycidyl ethers of phenol-aldehyde adducts, aromatic epoxy resins, aliphatic triglycidyl ethers, dialiphatic triglycidyl ethers, aliphatic polyglycidyl ethers, epoxidized olefins, brominated resins, triglycidylaminophenols (including triglycidyl p-aminophenol (TGPAM) and triglycidyl m-aminophenol), aromatic glycidylamines, heterocyclic glycidylimidines and amides, glycidyl ethers, fluorinated epoxy resins, triglycidyl derivatives of hydroxylphenylmethane, or any combination thereof.

[0033] Suitable tetrafunctional epoxy resins include tetraglycidyldiaminodiphenylmethane (TGDDM); tetraglycidyl-bis(4-aminophenyl)-1,4-diisopropylbenzene; tetraglycidyl-bis(4-amino-3,5-dimethylphenyl)-1,4-isopropylbenzene, tetraglycidyl derivatives of hydroxyphenylethane, and tetraglycidyl-m-xylenediamine.

[0034] In a preferred embodiment, the bifunctional epoxy resin is used in combination with a trifunctional epoxy resin and / or a tetrafunctional epoxy resin.

[0035] Reinforcement Suitable toughening agents (i.e., tougheners) for use in thermosetting resin compositions include thermoplastic polymers that may exist in the form of particles. The term “particles” as used herein encompasses a variety of granular materials in various shapes, including but not limited to spherical and non-spherical particles. In some embodiments, thermoplastic toughening particles include particles that are substantially insoluble in the thermosetting resin composition during curing and remain as inconspicuous particles in the cured material after curing. Insoluble thermoplastic particles suitable for the purposes of this specification include particles of aliphatic polyamides (PA), alicyclic polyamides, aromatic polyamides, polyphthalamides (PPA); polyaryl ether ketones (PAEK), such as polyether ether ketones (PEEK) and polyether ether ketones (PEKK); polyphenylene sulfide (PPS), polyamide-imides, liquid crystal polymers (LCP), polyimides, copolymers thereof, and derivatives thereof. These toughening particles do not have conductive coatings such as metals.

[0036] Insoluble thermoplastic particles have been shown to be effective as interlayer reinforcing agents to avoid loss of high temperature / high humidity performance. Because these thermoplastic particles remain insoluble in the cured polymer matrix, they impart improved toughness, damage resistance, high temperature / high humidity performance, processability, microcracking resistance, and reduced solvent sensitivity to the cured polymer matrix.

[0037] Insoluble thermoplastic particles may be used in combination with soluble thermoplastic polymers as additional reinforcing agents. Such soluble thermoplastic polymers may be selected from polyarylsulfones (e.g., polyethersulfone (PES), polyetherethersulfone (PEES), PES-PEES copolymer), polyphenylene oxide (PPO), thermoplastic phenoxy resins, polysulfones, polyetherimides (PEI), and polyimides (PI). These soluble thermoplastic polymers may be added to the resin composition as solids (e.g., powders) that dissolve into the resin composition when the composition is heated during the preparation of the composition or during the impregnation of reinforcing fibers for forming a prepreg. As used herein, “dissolve” into the resin means to form a homogeneous or continuous phase with the resin.

[0038] The reinforcing agent may also be selected from elastomeric polymers having functional groups that can react with the polyfunctional epoxy resin during curing. Suitable functional groups include, but are not limited to, -COOH, -NH, -NH2, -OH, -SH, -CONH2, -CONH-, -NHCONH-, -NCO, -NCS, and oxirane or glycidyl groups. Exemplary elastomers include, without limitation, natural rubber, styrene-butadiene rubber, polyisoprene, polyisobutylene, polybutadiene, isoprene-butadiene copolymer, neoprene, nitrile rubber, butadiene-acrylonitrile copolymer, butyl rubber, butylnitrile rubber, polysulfide elastomer, acrylic elastomer, acrylonitrile elastomer, silicone rubber, polysiloxane, polyester rubber, diisocyanate-linked condensed elastomer, EPDM (ethylene-propylene diene rubber), chlorosulfonated polyethylene, fluorinated hydrocarbons, polybutyl acrylate-methyl methacrylate (MAM) copolymer, thermoplastic elastomers such as (AB) and (ABA) type block copolymers of styrene and butadiene or isoprene, and (AB)n type multisegment block copolymers of polyurethane or polyester.

[0039] In a preferred embodiment, a polyarylsulfone, such as polyethersulfone (PES), is used as a reinforcing agent. In another preferred embodiment, a combination of insoluble polyamide particles and a soluble polyarylsulfone, such as PES, is used as a reinforcing agent in a thermosetting resin composition.

[0040] The reinforcing components may be present in an amount ranging from 5 to 40% by weight, such as 5 to 23% by weight, based on the total weight of the thermosetting resin composition.

[0041] Other additives Optionally, the thermosetting resin compositions of the present disclosure may also contain one or more additives selected from rheology regulators, tackifiers, inorganic or organic fillers, stabilizers, inhibitors, pigments, dyes, flame retardants, reactive diluents, conductive fillers, and other additives well known to those skilled in the art for modifying the properties of the resin before or after curing.

[0042] If present, inorganic or organic fillers constitute about 0.1 to 10% by weight based on the total weight of the resin composition. In some embodiments, conductive fillers are added to the thermosetting resin composition. Generally, conductive fillers can have any suitable three-dimensional shape, such as spherical, elliptical, spheroidal, disc-shaped, tree-shaped, rod-shaped, disk, cube, or polyhedron.

[0043] Suitable conductive fillers for thermosetting resin compositions include, but are not limited to, carbon nanomaterials such as carbon nanotubes (CNTs), carbon nanofibers, carbon nanoneedles, carbon nanosheets, and carbon nanorods; carbon black, graphite nanoplatelets or nanodots; graphene, graphite; or combinations thereof with or without partial or complete metal coatings or other fullerene materials. The term "carbon nanomaterial," as used herein, refers to a material having at least one dimension smaller than about 0.1 micrometers (<100 nanometers) and consisting entirely or largely of carbon atoms arranged in a pentagonal or hexagonal or both configuration at the molecular scale.

[0044] Reinforcement fibers Suitable reinforcing fibers for producing high-performance composite materials and prepregs have high tensile strength, preferably above 500 ksi (i.e., 3447 MPa) as measured according to ASTM C1557-14. Fibers useful for this purpose include carbon fibers or graphite fibers, glass fibers and fibers formed from silicon carbide, alumina, boron, quartz, etc., as well as fibers formed from organic polymers such as polyolefins, poly(benzothiazole), poly(benzimidazole), polyarylate, poly(benzoxazole), aromatic polyamides, polyaryl ethers, etc., and mixtures having two or more such fibers. Preferably, the fibers are selected from glass fibers, carbon fibers, and aromatic polyamide fibers, such as fibers sold by DuPont Company under the trade name KEVLAR. The reinforcing fibers may be used as continuous unidirectional or multidirectional tapes, or as discontinuous fibers in the form of woven, uncrimped, or nonwoven fabrics. The weave may be selected from plain weave, satin weave, or twill weave styles. Non-crimped fabrics may have multiple layers and fiber orientations.

[0045] The reinforcing fibers may be in the form of a continuous tow, where each tow consists of numerous filaments, unidirectional or multidirectional fibers, tapes of unidirectional fibers, or nonwoven or woven fabrics. In a preferred embodiment, the reinforcing fibers for the prepreg are unidirectional carbon fibers. The term "unidirectional" refers to the unidirectional position of parallel, spaced-apart fibers, i.e., orientation in the same direction.

[0046] Manufacturing of prepregs and composite structures As used herein, the term “prepreg” refers to a sheet or layer of reinforcing fibers impregnated with a curable resin composition. The prepreg may be a fully impregnated prepreg or a partially impregnated prepreg. As used herein, the term “impregnation” refers to fibers subjected to an impregnation process, which either partially surrounds the fibers with the resin or completely embeds them in a bulk resin, also known as the “matrix resin.”

[0047] Generally, a layer of dry fibers can be impregnated with a curable resin by heating the curable resin to its molten state and introducing the molten curable resin onto and into the layer of dry fibers. A typical impregnation method is: (1) A step of continuously moving reinforcing fibers through a bath of solvated resin composition to completely or substantially wet out the fibers; followed by a step of applying heat to evaporate the solvent; or (2) A process of pressing the top resin film and / or bottom resin film toward the reinforcing fiber layer at a high temperature (hot melt technique) Includes.

[0048] To produce a prepreg layer, a resin film is first produced by coating a thermosetting resin composition of the present disclosure onto a release liner. Next, one or two such resin films are laminated onto one or both sides of a layer of reinforcing fibers with the help of heat and pressure to impregnate the fibers, thereby forming a fiber-reinforced resin layer (or prepreg layer) of a specific fiber basis weight (FAW) and resin content. If reinforcing particles with a particle size larger than the spacing between fiber filaments are present, they are filtered out during the lamination process and remain outside the fiber layer.

[0049] To form a composite structure, multiple prepreg layers may be laid up on a tool in a lamination sequence to form a “prepreg gray-up”. The prepreg layers in the lay-up may be arranged in a selected orientation relative to each other, for example, 0°, ±45°, 90°, etc. The prepreg gray-up may be manufactured by techniques including, but not limited to, manual lay-up, automated tape lay-up (ATL), advanced fiber placement (AFP), and filament winding. The prepreg gray-up is then cured according to the curing cycle disclosed herein. [Examples]

[0050] Example 1 Epoxy resin formulations (1a-1i) according to Table 1 below were prepared by pre-blending the epoxy components at 70°C, then polyethersulfone (PES) was added to form a mixture, which was then heated to 115°C until complete dissolution of the PES was achieved. The mixture was then cooled to 80°C, and polyamide particles and then amine curing agents were added and mixed until a homogeneous composition was obtained.

[0051] [Table 1]

[0052] DGEBPF is a bisphenol F-based epoxy. TGDDM is a tetraglycidyl diaminodiphenylmethane epoxy resin. TGPAP is a triglycidyl para-aminophenol epoxy resin. DGEBPA is a bisphenol A-based epoxy resin. 4,4'-DDS is 4,4'-diaminodiphenylsulfone. The polyamide particles had a melting point of approximately 250°C (as measured by DSC).

[0053] Each of the resulting formulations was then cast in a steel mold and cured in an oven according to one of the curing cycles described in Table 2 to form a resin plaque.

[0054] [Table 2]

[0055] A test coupon approximately 2 mm thick was then extracted from each of the cured resin plaques, and the cured resin plaques were started. g The Tg and EoC of the cured resin were measured at a frequency of 1 Hz according to EN6032 at the intersection of extrapolated tangents drawn from points on the storage modulus curve before and after the onset of the glass transition event. Wet coupons were pre-conditioned in a climatostatic chamber at 70°C and 85% humidity until saturated according to EN2823, and then tested by dynamic mechanical analysis (DMA). The degree of curing (EoC) of the cured resin was measured by differential scanning calorimetry (DSC), calculated as the ratio of reaction heats in J / g for the cured resin and uncured resin, respectively, and expressed as a percentage. DSC was performed at 10°C / min in the temperature range of -50°C to 350°C. The Tg and EoC data of the cured resin are reported in Table 3.

[0056] [Table 3]

[0057] As shown in Tables 2 and 3, the use of 4,4'-methylenebis(2,6-xylidine) as a single-component curing agent in resins 1a to 1h, cured at 160°C to 170°C for 30 to 60 minutes, resulted in Tg numbers equal to or better than those of resin 1i, which contains more conventional 4,4'-DDS and was cured at 180°C (higher temperature) for 2 hours (longer dwell time), under both dry and H / W conditions.

[0058] When resin 1i was cured at 160°C to 170°C for 30 to 60 minutes, the measured Tg was approximately 25°C to 35°C lower than that of resins 1a to 1h cured using 4,4'-methylenebis(2,6-xylidine). In addition, only a curing degree in the range of 71% to 76% was achieved using 4,4'-DDS, while all evaluated cured resins derived from compositions containing 4,4'-methylenebis(2,6-xylidine) as a curing agent achieved a conversion degree in the range of 85% to 91%.

[0059] Example 2 Resin compound 1a from Table 1 was cast onto release paper to form a resin film. Two such resin films were used to impregnate a layer of unidirectional carbon fiber (Teijin's IMS65E23-24K-830tex) to produce unidirectional (UD) prepregs with a fiber basis weight (FAW) of 268 gsm and a resin content of 34%.

[0060] Test panels were manufactured using UD prepregs. Each test panel was a laminate of prepreg layers. The test panels were manufactured according to EN2565 and cured in an autoclave according to curing cycle 1 described in Table 2 of Example 1. Thermomechanical tests were performed on the cured panels, and the results are reported in Table 4.

[0061] [Table 4]

[0062] In Table 4, AR represents "as received", while RT represents room temperature (about 25 °C). 70 °C / WET represents the conditioning process at a relatively high temperature (70 °C) and high humidity level (85%) to achieve saturation of the test coupon.

[0063] G ic is the measurement of the mode I interlaminar fracture toughness measured according to EN6033. ILSS is the apparent interlaminar shear strength measured according to EN2563. CSAI is the post-impact compressive strength measured after 30 joule impact and according to EN6038. FHT is the notched tensile strength as measured by EN6035. BBS is the bolt bearing strength measured by EN6037. Tg is the glass transition temperature measured by DMA and according to EN6032 for the cured test panel array. The degree of cure (EoC) of the test panel was measured by DSC and calculated as the ratio between the heat of reaction in J / g of the cured test panel and the uncured prepreg, respectively, and expressed as a percentage. The heat of reaction was measured using a temperature ramp experiment at a temperature rate of 10 °C / min from 50 °C to 350 °C.

[0064] As shown in Table 4, the cured panel reached a degree of cure of over [X]% and a high temperature / moisture (H / W) T of 155 °C when cured at 160 °C for 1 hour. g The cured panel also showed a high peel resistance of 546 J / m 2 and a damage tolerance of 215 MPa. Furthermore, no decrease in CSAI or FHT was observed after exposure to conditioning at 70 °C and 85% humidity for 2 weeks.A relatively low decrease in BBS and ILSS was also observed after exposure to such H / W conditions.

[0065] Example 3 The resin formulation 1h of Table 1 was deposited onto silicone release paper to form a film. The resulting resin film was used to impregnate a layer of unidirectional carbon fibers (SGL Sigrafil® C T50 4.4 / 255 E100) on a prepreg production line, which had a resin content of 35% and a weight of 190 g / m 2This produced a prepreg with a nominal fiber weight.

[0066] Test panels were manufactured using prepregs. Each test panel was a laminate of prepreg layers. The test panels were manufactured according to EN2565 and cured in an autoclave according to curing cycle 1 described in Table 2 of Example 1. Thermomechanical tests were performed on the cured panels, and the results are reported in Table 4.

[0067] [Table 5]

[0068] [Table 6]

[0069] Example 4 - Heat The heat generation of the prepreg described in Example 3 was evaluated by producing two laminates from the prepreg with nominal thicknesses of 30 mm (Panel 4.1) and 56 mm (Panel 4.2), respectively, and curing them in an autoclave. A thermocouple (TC2) was placed at the center of each laminate, while a second one (TC1) was placed in the same location but between the two top layers. Each prepreg laminate was cured according to curing cycle 1 disclosed in Table 2 of Example 1. The evaluation results are reported in Table 5.

[0070] [Table 7]

[0071] For a 30mm thick panel (Panel 4.1), the highest temperature officially recorded at the center of the interlayer (TC2) in the laminate was 166°C, while a highest temperature of 162.4°C was measured by the thermocouple between the top two layers (TC1). Therefore, a difference of less than 4°C in the highest values ​​was measured during the curing cycle. An average curing degree of 88% was achieved from the outer to the center of the cured laminate with a standard deviation of less than 1%.

[0072] Similarly, for a 56mm thick panel (Panel 4.2), the highest temperature officially recorded by TC2 was 168.4°C, a difference of just 7.7°C compared to the highest temperature read by TC1. An average curing degree of 89% was achieved from the outer to the center of the cured laminate with a standard deviation of less than 1%.

[0073] The experiments described herein demonstrate that when the amine curing agent, 4,4'-methylenebis(2,6-xylidine), is used in the matrix resin, thick composite structures up to 56 mm in thickness can be manufactured without requiring lengthy intermediate dwell times during the curing cycle, and without the generation of uncontrolled heat generation. The controlled curing resulted in a highly uniform degree of curing throughout the entire thickness of the laminate, and consequently, uniform thermomechanical properties.

Claims

1. A composite material comprising reinforcing fibers impregnated with a thermosetting resin composition, wherein the thermoplastic resin composition is (A) An epoxy resin component consisting of a combination of polyfunctional epoxy resins selected from bifunctional, trifunctional, and tetrafunctional polyepoxides; (B) A curing agent component comprising (i) 4,4'-methylenebis(2,6-xylidine) or (ii) 4,4'-methylenebis(2,6-xylidine) in combination with one or more other amine curing agents, wherein the molar content of 4,4'-methylenebis(2,6-xylidine) is 50% or more of the total molar amount of all amines in the thermosetting resin composition; (C) (i) a thermoplastic component consisting of a polyarylsulfone polymer, or (ii) a combination of polyamide particles and a polyarylsulfone polymer. It includes, The thermosetting resin composition lacks any catalyst or accelerator for reaction with the epoxy resin. The one or more other amine curing agents mentioned above are: 3,3'-diaminodiphenylsulfone (3,3'-DDS); 4,4'-diaminodiphenylsulfone (4,4'-DDS); 1,4-bis(4-aminophenoxy)-2-phenylbenzene; 1,3-bis(3-aminophenoxy)benzene; 4,4'-(m-phenylenediisopropylidene)dianiline; 4,4'-(p-phenylenediisopropylidene)dianiline; 2,2'-bis(4-(4-aminophenoxy)phenylpropane; 4,4'-bis(3-aminophenoxy)diphenylsulfone; 1,3-bis(3-aminophenoxy)benzene; and 4,4'-1,4-phenylenebis(1-methylethylindene)bisaniline Composite materials selected from.

2. The composite material according to claim 1, wherein the relative amounts of the components in the thermosetting resin composition, in terms of weight percentage (wt%), are as follows: 30 to 75% by weight of A, 20 to 30% by weight of B, and 5 to 40% by weight of C, based on the total weight of the thermosetting resin composition.

3. The composite material according to claim 1 or 2, wherein the polyfunctional epoxy resin is selected from glycidyl ethers of aminophenol and glycidyl ethers of diaminodiphenylmethane.

4. The epoxy resin component is (i) Trifunctional epoxy resins; and / or (ii) A tetrafunctional epoxy resin, (iii) Combined with a bifunctional epoxy resin A composite material according to any one of claims 1 to 3.

5. The composite material according to claim 4, wherein the trifunctional epoxy resin is selected from triglycidyl p-aminophenol (TGPAP) and triglycidyl m-aminophenol (TGMAP), the tetrafunctional epoxy resin is tetraglycidyl diaminodiphenylmethane (TGDDM), and the bifunctional epoxy resin is selected from bisphenol A epoxy resin and bisphenol F epoxy resin.

6. The composite material according to any one of claims 1 to 5, wherein the thermosetting resin composition further comprises 0.1 to 10% by weight of an inorganic filler based on the total weight of the thermosetting resin composition.

7. The composite material according to claim 6, wherein the inorganic filler is a conductive filler such as carbon black, carbon nanotubes, graphite, and graphene.

8. The composite material according to any one of claims 1 to 7, wherein the reinforcing fibers are in the form of continuous, unidirectionally aligned fibers or a woven fabric.

9. The composite material according to any one of claims 1 to 8, wherein the reinforcing fibers are carbon fibers.

10. The composite material according to any one of claims 1 to 9, wherein the thermosetting resin composition is in the form of a resin layer, and the reinforcing fibers are embedded in the resin layer.

11. A method for manufacturing composite parts, A step of forming one or more prepreg layers from a composite material according to any one of claims 1 to 10; The steps include: placing one or more prepreg layers on the tool surface; A process to manufacture a cured composite part with a curing degree of more than 85% by curing one or more prepreg layers at a temperature in the range of 160°C to 180°C for 15 to 120 minutes. A method for manufacturing composite components, including

12. The method according to claim 11, wherein curing is carried out at a temperature in the range of 160°C to 170°C for 15 to 60 minutes.

13. The cured composite component has a glass transition temperature (T) of 180°C or higher under dry conditions, as measured by EN6032. ｇ ) and after conditioning for two weeks at 70°C / 85% humidity, then under high temperature / high humidity conditions, T150°C or higher. ｇ The method according to claim 11 or 12, comprising:

14. The method according to claim 13, wherein the cured composite part has a glass transition temperature (Tg) of 180°C to 200°C under dry conditions and a Tg of 150°C to 160°C under high-temperature / high-humidity conditions after conditioning at 70°C / 85% humidity for two weeks, as measured by EN6032.

15. (A) An epoxy resin component consisting of a combination of polyfunctional epoxy resins selected from bifunctional, trifunctional, and tetrafunctional polyepoxides; (B) 4,4'-methylenebis(2,6-xylidine) as the sole curing agent for the polyfunctional epoxy resin; (C) Thermoplastic components and A thermosetting resin composition comprising, A thermosetting resin composition lacking any catalyst or accelerator for reaction with the epoxy resin.

16. A thermosetting resin composition, (A) An epoxy resin component consisting of a combination of polyfunctional epoxy resins selected from bifunctional, trifunctional, and tetrafunctional polyepoxides; (B) A curing agent component comprising 4,4'-methylenebis(2,6-xylidine) in combination with one or more other aromatic amines, wherein the molar content of 4,4'-methylenebis(2,6-xylidine) is 50% or more of the total molar amount of all amines in the thermosetting resin composition; (C) (i) a thermoplastic component consisting of a polyarylsulfone polymer, or (ii) a combination of polyamide particles and a polyarylsulfone polymer. Includes, The epoxy resin lacks any catalyst or accelerator for reaction, A thermosetting resin composition in which the catalyst or accelerator that reacts with the epoxy resin is selected from bisurea, a metal complex with a carboxylate ligand, boron trifluoride or a complex thereof, and a co-curing agent, wherein the co-curing agent is selected from adducts with tertiary amines, imidazoles, phosphonium halides, and polyepoxides.

17. The one or more other aromatic amines mentioned above are: 3,3'-diaminodiphenylsulfone (3,3'-DDS); 4,4'-diaminodiphenylsulfone (4,4'-DDS); 1,4-bis(4-aminophenoxy)-2-phenylbenzene; 1,3-bis(3-aminophenoxy)benzene; 4,4'-(m-phenylenediisopropylidene)dianiline; 4,4'-(p-phenylenediisopropylidene)dianiline; 2,2'-bis(4-(4-aminophenoxy)phenylpropane; 4,4'-bis(3-aminophenoxy)diphenylsulfone; 1,3-bis(3-aminophenoxy)benzene; and 4,4'-1,4-phenylenebis(1-methylethylindene)bisaniline A thermosetting resin composition according to claim 16, selected from the following.

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