Highly toughened thermosetting resin composition

Abstract

The present disclosure provides a curable resin composition containing a thermosetting resin, a toughening agent component containing a multi-stage polymer and a thermoplastic toughener, and a curing agent. The curable resin composition can be combined with reinforcing fibers and then cured to form a fiber-reinforced composite having a high glass transition temperature and excellent mechanical properties. The fiber-reinforced composite can be used in a variety of applications, such as transportation applications, including aerospace vehicles, aircraft, marine vehicles, and land vehicles.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 62 / 979,815, filed February 21, 2020, the entire contents of which are expressly incorporated herein by reference.

[0002] Technical Field The present disclosure relates generally to curable resin compositions having high glass transition temperatures and improved toughness resistance. Specifically, the present disclosure relates to curable resin compositions containing a thermosetting resin, a toughener component containing a multi-stage polymer and a thermoplastic toughener, and a curing agent. The present disclosure also relates to the use of the curable resin compositions that can be cured in the presence of reinforcing fibers to form fiber-reinforced composites, and to aerospace structural components made from the fiber-reinforced composites. [Background technology]

[0003] Thermosetting materials, such as cured epoxy resins, are known for their heat and chemical resistance. While they also exhibit good mechanical properties, they often lack toughness and tend to be very brittle. This is especially true when their crosslink density or monomer functionality enhances these two features. Attempts have been made to strengthen or toughen epoxy resins and other thermosetting materials, such as bismaleimide resins, benzoxazine resins, cyanate ester resins, epoxy vinyl ester resins, and unsaturated polyester resins, by incorporating various toughening agents into them.

[0004] Such tougheners can be compared with one another based on their structural, morphological, or thermal properties. The structural backbone of the toughener can be aromatic, aliphatic, or both. Aromatic tougheners, such as polyetheretherketone or polyimide, exhibit reasonable improvements in toughness, i.e., compression after impact, and, due to the aromatic structure of the toughener, provide thermoset materials with low water uptake when subjected to high-temperature, high-humidity environments. In contrast, aliphatic tougheners, such as nylon (also known as polyamide), exhibit significant improvements in compression after impact, but provide thermoset materials with higher than desired water uptake when subjected to high-temperature, high-humidity environments, which can lead to reduced compressive strength and modulus. Other tougheners, such as core-shell polymers, can provide thermoset materials with good damage resistance. However, these tougheners tend to adversely affect the processability and glass transition temperature of thermoset materials.

[0005] Certain toughening agents that have recently become available for use in thermosetting resin compositions are multi-stage polymers, such as those described in U.S. Patent Nos. 5,629,999; 5,7 ... and 5,729,999. While such toughening agents have been found to disperse readily in the thermosetting matrix, resulting in a uniform distribution, the cured products can still lack adequate toughness, particularly when cured at the elevated temperatures during resin infusion processing associated with primary structural applications.

[0006] Therefore, there is a need to further improve upon the state of the art by utilizing novel toughener components with thermosetting materials that, upon curing, enable the cured product to exhibit high glass transition temperatures and high compression after impact. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2016 / 102666 [Patent Document 2] International Publication No. 2016 / 102658 [Patent Document 3] International Publication No. 2016 / 102682 [Patent Document 4] International Publication No. 2017 / 211889 [Patent Document 5] International Publication No. 2017 / 220793 [Patent Document 6] International Publication No. 2018 / 002259 [Patent Document 7] International Publication No. 2019 / 012052 Summary of the Invention

[0008] The present disclosure generally provides curable resin compositions comprising (a) a thermosetting resin, (b) a toughening agent component comprising a multi-stage polymer and a thermoplastic toughening agent, and (c) a curing agent. The present disclosure also provides fiber-reinforced resin compositions comprising a reinforcing fiber and the curable resin composition of the present disclosure. The fiber-reinforced resin compositions can be cured to form fiber-reinforced composites that can be used in a variety of applications, such as transportation applications (including aerospace, aircraft, marine, and land vehicles, as well as automotive, rail, long-haul, and military industries), building / construction applications, or other commercial applications. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present disclosure generally provides a curable resin composition comprising (a) a thermosetting resin, (b) a toughening agent component comprising a multi-stage polymer and a thermoplastic toughener, and (c) a curing agent. While the curable resin composition can be used alone, it can also be combined with reinforcing fibers to form a fiber-reinforced resin composition that is cured to form a fiber-reinforced composite. It has unexpectedly been discovered that the combination of the multi-stage polymer and the thermoplastic toughener acts synergistically, resulting in an observed toughening effect greater than would be expected from the combined toughening effects of the multi-stage polymer and the thermoplastic toughener. For example, it has been surprisingly discovered that the combination of the multi-stage polymer and the thermoplastic toughener may enable composites to exhibit chemical and mechanical properties particularly suited for primary and secondary aerospace structural applications and for structural materials for other moving objects, including cars, boats, and rail vehicles. In particular, the fiber-reinforced composites exhibit higher compression after impact (CAI) when compared to fiber-reinforced composite particles containing the multi-stage polymer or thermoplastic toughener alone, and also exhibit glass transition temperatures of at least 190°C.

[0010] The following terms shall have the following meanings:

[0011] The terms "cure," "cured," or similar terms, "curing," or "cure," refer to the hardening of a thermosetting resin by chemical crosslinking. The term "curable" means that the composition is capable of being subjected to conditions that will cause it to assume a cured or thermoset state or condition.

[0012] The term "multi-stage polymer" refers to a polymer formed in a sequential manner by a multi-stage polymerization process. The multi-stage polymerization process can be a multi-stage emulsion polymerization process, in which a first polymer is the first stage polymer and a second polymer is the second stage polymer (i.e., the second polymer is formed by emulsion polymerization in the presence of the first emulsion polymer).

[0013] The term "(meth)acrylic polymer" refers to a polymer that contains 50% or more by weight of (meth)acrylic monomers, based on the total weight of the polymer.

[0014] The term "(meth)acrylic" as used herein refers to all types of acrylic and methacrylic monomers.

[0015] The term "comprising" and its derivatives are not intended to exclude the presence of any additional components, steps, or procedures, whether or not they are disclosed herein. For the avoidance of doubt, all compositions claimed herein through the use of the term "comprising" may include any additional additives or compounds, unless specified to the contrary. In contrast, the term "consisting essentially of," when it appears herein, excludes from the scope of the succeeding recitation any other component, step, or procedure, excepting those that are not essential to operability, and the term "consisting of," when used, excludes any component, step, or procedure not specifically delineated or listed. The term "or," unless otherwise stated, refers to the recited members individually as well as in any combination.

[0016] The articles "a" and "an" are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, "an epoxy resin" means one epoxy resin or multiple epoxy resins.

[0017] Phrases such as "in one embodiment," "according to one embodiment," and the like generally mean that the particular feature, structure, or characteristic that follows the phrase is included in at least one aspect of the disclosure, and may also be included in multiple embodiments of the disclosure. Importantly, such phrases do not necessarily refer to the same embodiment.

[0018] When the specification uses "may," "can," "could," or "might" to describe that a component or feature is included or has a certain characteristic, it does not require that the particular component or feature be included or have the characteristic.

[0019] The term "about," as used herein, allows for a degree of variability in values or ranges; for example, the variation may be within 10%, within 5%, or within 1% of the stated value or stated range limit.

[0020] Values expressed in range format should be interpreted in a flexible manner to include not only the numerical values specified as the limits of the range, but also to include all individual numerical values or subranges subsumed within the range, as if each numerical value and subrange were specifically written out. For example, a range such as 1 to 6 should be interpreted as specifically disclosing subranges such as 1 to 3, 2 to 4, 3 to 6, etc., as well as individual numbers within that range, e.g., 1, 2, 3, 4, 5, and 6. This is true regardless of the broadness of the range.

[0021] The terms "preferred" and "preferably" refer to embodiments that may provide certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or different circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the present disclosure.

[0022] In accordance with a first embodiment, the present disclosure provides a curable resin composition generally comprising: (a) a thermosetting resin; (b) a toughening agent component comprising a multi-stage polymer and a thermoplastic toughening agent; and (c) a curing agent.

[0023] In one embodiment, the thermosetting resin can be an epoxy resin, a bismaleimide resin, a benzoxazine resin, a cyanate ester resin, a phenolic resin, a vinyl ester resin, or a mixture thereof. In one particular embodiment, the thermosetting resin is an epoxy resin.

[0024] Generally, any epoxy-containing compound is suitable for use as the epoxy resin of the present disclosure, such as those disclosed in U.S. Patent No. 5,476,748, which is incorporated herein by reference. According to one embodiment, the epoxy resin is selected from difunctional epoxy resins (i.e., having two epoxide groups), trifunctional epoxy resins (i.e., having three epoxide groups), tetrafunctional epoxy resins (i.e., having four epoxide groups), and mixtures thereof.

[0025] Non-limiting examples of difunctional epoxy resins include bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, tetrabromobisphenol A diglycidyl ether, propylene glycol diglycidyl ether, butylene glycol diglycidyl ether, ethylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, polytetramethylene glycol diglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, bisphenol A polyethylene glycol diglycidyl ether, bisphenol A polypropylene glycol diglycidyl ether, 3,4-epoxycyclohexylmethylcarboxylate, hexahydrophthalic acid diglycidyl ester, methyltetrahydrophthalic acid diglycidyl ester, and mixtures thereof. In some embodiments, the difunctional epoxy resin may be modified with a monofunctional reactive diluent, such as, for example, p-tertiary butylphenol glycidyl ether, cresyl glycidyl ether, 2-ethylhexyl glycidyl ether, and C8-C 14 These include, but are not limited to, glycidyl ethers.

[0026] Non-limiting examples of trifunctional epoxy resins include: triglycidyl ether of para-aminophenol, triglycidyl ether of meta-aminophenol, dicyclopentadiene-based epoxy resins, N,N,O-triglycidyl-4-amino-m- or -5-amino-o-cresol-type epoxy resins, and 1,1,1-(triglycidyloxyphenyl)methane-type epoxy resins.

[0027] Non-limiting examples of tetrafunctional epoxy resins include: N,N,N',N'-tetraglycidylmethylenedianiline, N,N,N',N'-tetraglycidyl-m-xylylenediamine, tetraglycidyldiaminodiphenylmethane, sorbitol polyglycidyl ether, pentaerythritol tetraglycidyl ether, tetraglycidyl bisaminomethylcyclohexane, and tetraglycidyl glycoluril.

[0028] Examples of commercially available epoxy resins that can be used include Araldite® PY 306 epoxy resin (unmodified bisphenol-F based liquid epoxy resin), Araldite® MY 721 epoxy resin (tetrafunctional methylenedianiline based epoxy resin), Araldite® MY 0510 epoxy resin (trifunctional para-aminophenol based epoxy resin), Araldite® GY 6005 epoxy resin (bisphenol-A based liquid epoxy resin modified with a monofunctional reactive diluent), Araldite® 6010 epoxy resin (bisphenol-A based liquid epoxy resin), Araldite® MY 06010 epoxy resin (trifunctional meta-aminophenol based epoxy resin), Araldite® GY 285 epoxy resin (unmodified bisphenol-F based liquid epoxy resin), and Araldite® EPN. 1138, 1139, and 1180 epoxy resins (epoxy phenol novolac resins), Araldite® ECN 1273 and 9611 epoxy resins (epoxy cresol novolac resins), Araldite® GY 289 epoxy resin (epoxy phenol novolac resin), Araldite® PY 307-1 epoxy resin (epoxy phenol novolac resin), and mixtures thereof.

[0029] In one embodiment, the amount of epoxy resin present in the curable resin composition can be from about 10% to about 90% by weight, or from about 20% to about 75% by weight, or from about 30% to about 60% by weight, or from about 40% to about 50% by weight, based on the total weight of the curable resin composition. In another embodiment, the amount of epoxy resin present in the curable resin composition can be from about 50% to about 95% by weight, or from about 65% to about 90% by weight, based on the total weight of the curable resin composition.

[0030] In yet another embodiment, the epoxy resin can be comprised of at least one trifunctional or tetrafunctional epoxy resin or a mixture thereof, and optionally at least one difunctional epoxy resin. In such embodiments, the trifunctional epoxy resin can be present in the curable resin composition in an amount of about 25 wt % to about 50 wt %, or about 35 wt % to 45 wt %, based on the total weight of the curable resin composition, and the tetrafunctional epoxy resin can be present in the curable resin composition in an amount of about 1 wt % to 20 wt %, or about 5 wt % to about 15 wt %, based on the total weight of the curable resin composition.

[0031] According to another embodiment, the thermosetting resin is a benzoxazine resin. The benzoxazine resin can be any curable monomer, oligomer, or polymer having at least one benzoxazine moiety. That is, in one embodiment, the benzoxazine can be represented by the general formula (1):

[0032] [ka] wherein b is an integer from 1 to 4; each R is independently hydrogen, a substituted or unsubstituted C-C 20 Alkyl groups, substituted or unsubstituted C2-C 20 Alkenyl groups, substituted or unsubstituted C6-C 20 Aryl groups, substituted or unsubstituted C2-C 20 Heteroaryl groups, substituted or unsubstituted C4-C20 Carbocyclic groups, substituted or unsubstituted C2-C 20 heterocyclic group, or a C3-C8 cycloalkyl group; each R1 is independently hydrogen, C1-C 20 Alkyl groups, C2-C 20 Alkenyl group, or C6-C 20 aryl group; and Z is a direct bond (when b=2), a substituted or unsubstituted C-C 20 Alkyl groups, substituted or unsubstituted C6-C 20 Aryl groups, substituted or unsubstituted C2-C 20 Heteroaryl groups include O, S, S=O, O=S=O, and C=O. Substituents include hydroxy, C1-C 20 Alkyl groups, C2-C 10 Alkoxy group, mercapto, C3-C8 cycloalkyl group, C6-C 14 Heterocyclic group, C6-C 14 Aryl groups, C6-C 14 Heteroaryl groups include, but are not limited to, halogen, cyano, nitro, nitrone, amino, amido, acyl, oxyacyl, carboxyl, carbamate, sulfonyl, sulfonamido, and sulfuryl.

[0033] In certain embodiments within formula (1), the benzoxazine can be represented by formula (1a):

[0034] [ka] wherein Z is a direct bond, CH, C(CH), C=O, O, S, S=O, O=S=O, and

[0035] [ka] is selected from Each R is independently hydrogen, C1-C 20 Alkyl, aryl, or C6-C 14 is an aryl group; and R1 is defined as above.

[0036] In another embodiment, the benzoxazine can be encompassed by the following general formula (2):

[0037] [ka] In the formula, Y is C1-C 20 Alkyl groups, C2-C 20 alkenyl group, or substituted or unsubstituted phenyl; and each R is independently hydrogen, halogen, C-C 20 Alkyl groups, C2-C 20 Alkenyl group, or C6-C 20 Suitable substituents for phenyl are as described above.

[0038] In certain embodiments within formula (2), the benzoxazine can be represented by formula (2a):

[0039] [ka] wherein each R2 is independently C1-C 20 Alkyl or C2-C 20 Alkenyl groups, each of which is optionally substituted or interrupted by one or more of O, N, S, C=O, COO, and NHC=O, and C-C 20 an aryl group; and each R is independently hydrogen, C-C 20 Alkyl or C2-C 20 alkenyl groups, each of which is optionally substituted or interrupted by one or more O, N, S, C=O, COOH, and NHC=O, or C-C 20 It is an aryl group.

[0040] Alternatively, the benzoxazine can be encompassed by the following general formula (3):

[0041] [ka] wherein p is 2; W is selected from biphenyl, diphenylmethane, diphenylisopropane, diphenylsulfide, diphenylsulfoxide, diphenylsulfone, and diphenylketone; and R 1 is defined as above.

[0042] Benzoxazines are commercially available from several sources, including Huntsman Advanced Materials Americas LLC, Georgia Pacific Resins Inc., and Shikoku Chemicals Corporation.

[0043] Benzoxazines can also be obtained by reacting a phenolic compound, such as bisphenol A, bisphenol F, or phenolphthalein, with an aldehyde, such as formaldehyde, and a primary amine under conditions that remove water. The molar ratio of the phenolic compound to the aldehyde reactant can be about 1:3 to 1:10, or about 1:4 to 1:7. In yet another embodiment, the molar ratio of the phenolic compound to the aldehyde reactant can be about 1:4.5 to 1:5. The molar ratio of the phenolic compound to the primary amine reactant can be about 1:1 to 1:3, or about 1:1.4 to 1:2.5. In yet another embodiment, the molar ratio of the phenolic compound to the primary amine reactant can be about 1:2.1 to 1:2.2.

[0044] Examples of primary amines include aromatic mono- or diamines, aliphatic amines, cycloaliphatic amines, and heterocyclic monoamines, such as aniline, o-, m-, and p-phenylenediamine, benzidine, 4,4'-diaminodiphenylmethane, cyclohexylamine, butylamine, methylamine, hexylamine, allylamine, furfurylamine, ethylenediamine, and propylenediamine. The amines may be substituted at each carbon with C1-C8 alkyl or aryl. In one embodiment, the primary amines are represented by the general formula R a NH2, wherein Ra R is allyl, unsubstituted or substituted phenyl, unsubstituted or substituted C1-C8 alkyl, or unsubstituted or substituted C3-C8 cycloalkyl. a Suitable substituents for the group include, but are not limited to, amino, C1-C4 alkyl, and allyl. In some embodiments, one to four substituents may be present in R a In one particular embodiment, R a is phenyl.

[0045] According to one embodiment, the benzoxazine may be present in the curable composition in an amount ranging from about 10% to about 90% by weight, based on the total weight of the curable composition. In another embodiment, the benzoxazine may be present in the curable composition in an amount ranging from about 60% to about 90% by weight, based on the total weight of the curable composition.

[0046] The curable resin composition also includes a toughening component that includes a multi-stage polymer and a thermoplastic toughening agent.

[0047] Multi-stage polymers (e.g., those described in WO2016 / 102411 and WO2016 / 102682, the contents of which are incorporated herein by reference) have at least two stages differing in their polymer composition, with the first stage forming a core and the second or all subsequent stages forming a shell, respectively. Multi-stage polymers can be in the form of polymer particles, particularly spherical particles. These polymer particles are also called core-shell particles, with the first stage forming a core and the second or all subsequent stages forming a shell, respectively. In one embodiment, the polymer particles can have a weight average particle size of 20 nm to 800 nm, or 25 nm to 600 nm, or 30 nm to 550 nm, or 40 nm to 400 nm, or 75 nm to 350 nm, or 80 nm to 300 nm. The polymer particles can be agglomerated to provide a polymer powder.

[0048] That is, the polymer particles can have a multilayer structure comprising at least one layer (or stage) (A) comprising polymer (A1) having a glass transition temperature below about 10° C., and at least another layer (or stage) (B) comprising polymer (B1) having a glass transition temperature above about 30° C. In some embodiments, polymer (B1) is the outer layer of the polymer particle. In other embodiments, stage (A) comprising polymer (A1) is the first stage, and stage (B) comprising polymer (B1) is grafted to stage (A) comprising polymer (A1).

[0049] As described above, the polymer particles can be obtained by a multi-stage process, for example, a process including two, three, or more stages. The polymer (A1) having a glass transition temperature of less than about 10° C. in the layer (A) is never produced in the last stage of the multi-stage process. This means that the polymer (A1) is never present in the outer layer of the particle. Therefore, the polymer (A1) having a glass transition temperature of less than about 10° C. in the layer (A) is either present in the core of the polymer particle or in one of the inner layers.

[0050] In some embodiments, polymer (A1) having a glass transition temperature of less than about 10°C of layer (A) is produced during the first stage of a multi-stage process for forming the core of the polymer particle having a multi-layer structure and / or before polymer (B1).

[0051] In another embodiment, the polymer (B1) having a glass transition temperature greater than about 30° C. is produced during the final stage of a multi-stage process that forms the outer layer of the polymer particles. Additional intermediate layer(s) may be present, resulting from intermediate stage(s).

[0052] In one embodiment, at least a portion of polymer (B1) in layer (B) is grafted to the polymer made in the preceding layer. When there are only two steps (A) and (B), each comprising polymer (A1) and polymer (B1), a portion of polymer (B1) is grafted to polymer (A1). In some embodiments, at least 50% by weight of polymer (B1) is grafted.

[0053] According to one embodiment, the polymer (A1) is a (meth)acrylic polymer.

[0054] In a further embodiment, polymer (A1) comprises a comonomer(s) that are copolymerizable with alkyl acrylates, so long as polymer (A1) has a glass transition temperature of less than about 10° C. The comonomer(s) of polymer (A1) can be selected from (meth)acrylic monomers and / or vinyl monomers. The (meth)acrylic monomers can be selected from C1 to C 12 In yet another embodiment, polymer (A1) comprises a C1-C4 alkyl (meth)acrylate monomer and a C1-C8 alkyl acrylate monomer. Most preferably, the monomers of polymer (A1) are selected from methyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, tert-butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and mixtures thereof, so long as polymer (A1) has a glass transition temperature of less than about 10°C.

[0055] In another embodiment, the polymer (A1) is crosslinked (i.e., a crosslinking agent is added to the other monomer(s)). The crosslinking agent may have at least two groups that allow polymerization.

[0056] In one specific embodiment, polymer (A1) is a homopolymer of butyl acrylate. In another specific embodiment, polymer (A1) is a copolymer of butyl acrylate and at least one crosslinker. The crosslinker may be present in an amount of less than 5% by weight of the copolymer.

[0057] In yet another embodiment, the polymer (A1) having a glass transition temperature of less than about 10° C. is a silicone rubber-based polymer. The silicone rubber can be, for example, polydimethylsiloxane.

[0058] In yet another embodiment, polymer (A1) having a glass transition temperature of less than about 10° C. comprises at least 50% by weight of polymer units derived from isoprene or butadiene, and stage (A) is the innermost layer of the polymer particle. In other words, stage (A) comprising polymer (A1) is the core of the polymer particle. By way of example, core polymer (A1) can be made of an isoprene homopolymer or a butadiene homopolymer, an isoprene-butadiene copolymer, a copolymer of isoprene and up to 98% by weight of a vinyl monomer, and a copolymer of butadiene and up to 98% by weight of a vinyl monomer. The vinyl monomer can be styrene, alkylstyrene, acrylonitrile, alkyl (meth)acrylate, or butadiene or isoprene. In one embodiment, the core is a butadiene homopolymer.

[0059] The polymer (B1) can be made of a homopolymer or a copolymer containing a monomer with a double bond and / or a vinyl monomer. Preferably, the polymer (B1) is a (meth)acrylic polymer. Preferably, the polymer (B1) is a C1-C 12 The polymer (B1) comprises at least 70% by weight of monomers selected from alkyl (meth)acrylates. Even more preferably, the polymer (B1) comprises at least 80% by weight of C1-C4 alkyl methacrylate monomers and / or C1-C8 alkyl acrylate monomers. Most preferably, the acrylic or methacrylic monomers of the polymer (B1) are selected from methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and mixtures thereof, so long as the polymer (B1) has a glass transition temperature of at least about 30°C. Advantageously, the polymer (B1) comprises at least 70% by weight of monomer units derived from methyl methacrylate.

[0060] In another embodiment, the multi-stage polymer as described above has an additional stage, which is a (meth)acrylic polymer (P1). The primary polymer particles according to this embodiment will have a multi-layer structure comprising at least one stage (A) comprising a polymer (A1) having a glass transition temperature below about 10° C., at least one stage (B) comprising a polymer (B1) having a glass transition temperature above about 30° C., and at least one stage (P) comprising a (meth)acrylic polymer (P1) having a glass transition temperature between about 30° C. and about 150° C. Preferably, the (meth)acrylic polymer (P1) is not grafted to either polymer (A1) or (B1).

[0061] The (meth)acrylic polymer (P1) can have a weight average molecular weight Mw of less than about 100,000 g / mol, or less than about 90,000 g / mol, or less than about 80,000 g / mol, or less than about 70,000 g / mol, advantageously less than about 60,000 g / mol, more advantageously less than about 50,000 g / mol, and even more advantageously less than about 40,000 g / mol.

[0062] The (meth)acrylic polymer (P1) can have a weight average molecular weight Mw of greater than about 2000 g / mol, or greater than about 3000 g / mol, or greater than about 4000 g / mol, or greater than about 5000 g / mol, advantageously greater than about 6000 g / mol, more advantageously greater than about 6500 g / mol, even more advantageously greater than about 7000 g / mol, and most advantageously greater than about 10,000 g / mol.

[0063] The weight average molecular weight Mw of the (meth)acrylic polymer (P1) can be about 2000 g / mol to about 100,000 g / mol, or about 3000 g / mol to about 90,000 g / mol, or about 4000 g / mol to about 80,000 g / mol, preferably about 5000 g / mol to about 70,000 g / mol, more preferably about 6000 g / mol to about 50,000 g / mol, and most preferably about 10,000 g / mol to about 40,000 g / mol.

[0064] Preferably, the (meth)acrylic polymer (P1) is a copolymer containing a (meth)acrylic monomer. Even more preferably, the (meth)acrylic polymer (P1) is a copolymer containing a C1 to C 12 The (meth)acrylic polymer (P1) comprises at least 50% by weight of monomers selected from alkyl (meth)acrylates. Advantageously, the (meth)acrylic polymer (P1) comprises at least 50% by weight of monomers selected from C1-C4 alkyl methacrylate monomers and C1-C8 alkyl acrylate monomers and mixtures thereof. More advantageously, the (meth)acrylic polymer (P1) comprises at least 50% by weight of polymerized methyl methacrylate, even more advantageously at least 60% by weight, and most advantageously at least 65% by weight of polymerized methyl methacrylate.

[0065] In one embodiment, the (meth)acrylic polymer (P1) comprises 50% to 100% by weight of methyl methacrylate, or 80% to 100% by weight of methyl methacrylate, or 80% to 99.8% by weight of methyl methacrylate, and 0.2% to 20% by weight of a C1-C8 alkyl acrylate monomer. Advantageously, the C1-C8 alkyl acrylate monomer is selected from methyl acrylate, ethyl acrylate, or butyl acrylate.

[0066] In another embodiment, the (meth)acrylic polymer (P1) comprises 0.01% to 50% by weight of the functional monomer. Preferably, the (meth)acrylic polymer (P1) comprises 0.01% to 30% by weight of the functional monomer, more preferably 1% to 30% by weight, even more preferably 2% to 30% by weight, and advantageously 3% to 30% by weight of the functional monomer.

[0067] In one embodiment, the functional monomer is selected from glycidyl (meth)acrylate, acrylic acid or methacrylic acid, amides derived from acrylic acid or methacrylic acid, such as dimethylacrylamide, 2-methoxyethyl acrylate or methacrylate, 2-aminoethyl acrylate or methacrylate, which may be optionally quaternized, acrylate or methacrylate monomers bearing phosphonate or phosphate groups, alkylimidazolidinone (meth)acrylates, and polyethylene glycol (meth)acrylates. Preferably, the polyethylene glycol group of the polyethylene glycol (meth)acrylate has a molecular weight in the range of 400 g / mol to 10,000 g / mol.

[0068] The toughening agent component also includes a thermoplastic toughener. Any suitable thermoplastic polymer can be used as the thermoplastic toughener. Typically, the thermoplastic toughener can be added to the thermosetting resin prior to the addition of the curing agent as particles that dissolve in the resin upon heating. Once the thermoplastic toughener has substantially dissolved in the hot resin, the resin can be cooled and the remaining ingredients (e.g., curing agent and multi-stage polymer) can be added and mixed with the cooled resin blend.

[0069] Examples of thermoplastic toughening agents may include any of the following thermoplastic polymers, alone or in combination: polysulfone, polyethersulfone, polyetherimide, polyamide (PA), poly(phenylene) oxide (PPO), poly(ethylene oxide) (PEO), phenoxy, poly(methyl methacrylate) (PMMA), poly(vinylpyrrolidone) (PVP), poly(ether ether ketone) (PEEK), poly(styrene) (PS), and polycarbonate (PC).

[0070] According to one embodiment, the thermoplastic toughening agent is polyethersulfone. Non-limiting examples of polyethersulfone include particulate polyethersulfone commercially available from Sumitomo Chemicals under the trademark Sumnikaexcel® polyethersulfone, and those commercially available from Solvay Chemicals under the trademarks Veradel® and Virantage® polyethersulfone. Densified polyethersulfone particles can also be used. The shape of the polyethersulfone is not particularly important, as the polyethersulfone can be dissolved during the formation of the curable resin composition. Densified polyethersulfone particles can be made according to the teachings of U.S. Pat. No. 4,945,154, the contents of which are hereby incorporated by reference. Densified polyethersulfone particles can also be used, such as those sold by Hexcel Corporation under the trademark HRI-1. In some embodiments, the average particle size of the polyethersulfone is less than 100 microns to promote and ensure complete dissolution of the polyethersulfone in the thermosetting resin.

[0071] According to one embodiment, the amount of the toughening agent component present in the curable resin composition is less than about 25 wt%, based on the total weight of the curable resin composition. In another embodiment, the amount of the toughening agent component present in the curable resin composition is less than about 22.5 wt%, or less than about 20 wt%, or less than about 17.5 wt%, or less than about 15 wt%, based on the total weight of the curable resin composition. According to another embodiment, the amount of the toughening agent component present in the curable resin composition is at least about 1 wt%, or at least about 5 wt%, or at least about 7.5 wt%, based on the total weight of the curable resin composition. In yet another embodiment, the amount of the toughening agent component present in the curable resin composition is from about 1 wt% to about 25 wt%, or from about 5 wt% to about 20 wt%, or from about 7 wt% to about 16 wt%, based on the total weight of the curable resin composition.

[0072] According to another embodiment, the amount of multi-stage polymer present in the curable resin composition is from about 3 wt % to about 20 wt %, or from about 5 wt % to about 15 wt %, or from about 7 wt % to about 13 wt %, based on the total weight of the curable resin composition. In yet another embodiment, the amount of thermoplastic toughening agent present in the curable resin mixture is from about 0.1 wt % to about 10 wt %, or from about 0.1 wt % to about 7 wt %, or from about 0.1 wt % to about 5 wt %, based on the total weight of the curable resin composition.

[0073] Curing of the curable resin composition can be achieved by adding any chemical material(s) known in the art for curing thermosetting resins. Such materials, which are compounds having reactive moieties capable of reacting with reactive groups in thermosetting resins, are referred to herein as "hardeners," including materials known to those skilled in the art as curing agents, curatives, activators, catalysts, or accelerators. Some hardeners promote curing through catalytic action, while others participate directly in the thermosetting resin reaction and become incorporated into the thermoplastic polymer network formed by condensation, chain extension, and / or crosslinking of the thermosetting resin. Depending on the hardener, heat may or may not be required for significant reaction to occur. Curing agents for thermosetting resins include, but are not limited to, aromatic amines, cyclic amines, aliphatic amines, alkylamines, polyetheramines, including those derived from polypropylene oxide and / or polyethylene oxide, 9,9-bis(4-amino-3-chlorophenyl)fluorene (CAF), acid anhydrides, carboxylic acid amides, polyamides, polyphenols, cresol and phenol novolac resins, imidazoles, guanidines, substituted guanidines, substituted ureas, melamine resins, guanamine derivatives, tertiary amines, Lewis acid complexes such as boron trifluoride and boron trichloride, and polymercaptans. Any epoxy-modified amine, Mannich-modified, or Michael-modified addition products of the above curing agents can also be used. All of the above curing agents can be used alone or in any combination.

[0074] In one embodiment, the curing agent is a polyfunctional amine. As used herein, the term "polyfunctional amine" refers to an amine having at least two primary and / or secondary amino groups in the molecule. For example, the polyfunctional amine can be an aromatic polyfunctional amine having two amino groups bonded to benzene in any one of ortho, meta, and para positions, such as phenylenediamine, xylenediamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, and 3,5-diaminobenzoic acid; an aliphatic polyfunctional amine such as ethylenediamine and propylenediamine; or an acyclic polyfunctional amine such as 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, 1,3-bispiperidylpropane, and 4-aminomethylpiperazine. These polyfunctional amines can be used alone or in mixtures thereof.

[0075] Examples of aromatic amines include 1,8-diaminonaphthalene, m-phenylenediamine, diethylenetoluenediamine, diaminodiphenyl sulfone, diaminodiphenylmethane, diaminodiethyldimethyldiphenylmethane, 4,4'-methylenebis(2,6-diethylaniline), 4,4'-methylenebis(2-isopropyl-6-methylaniline), 4,4'-methylenebis(2,6-diisopropylaniline), 4,4'-[1,4-phenylenebis(1-methyl-ethylaniline)] Indene)]bisaniline, 4,4'-[1,3-phenylenebis(1-methyl-ethylindene)]bisaniline, 1,3-bis(3-aminophenoxy)benzene, bis-[4-(3-aminophenoxy)phenyl]sulfone, bis-[4-(4-aminophenoxy)phenyl]sulfone, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, and bis(4-amino-2-chloro-3,5-diethylphenyl)methane. Furthermore, aromatic amines can also include heterocyclic polyfunctional amine adducts as disclosed in U.S. Pat. Nos. 4,427,802 and 4,599,413, both of which are incorporated herein by reference in their entirety.

[0076] Examples of cyclic amines include, but are not limited to, bis(4-amino-3-methyldicyclohexyl)methane, diaminodicyclohexylmethane, bis(aminomethyl)cyclohexane, N-aminoethylpyrazine, 3,9-bis(3-aminopropyl)-2,4,8,10-tetraoxaspiro(5,5)undecane, m-xylenediamine, isophoronediamine, menthenediamine, 1,4-bis(2-amino-2-methylpropyl)piperazine, N,N'-dimethylpiperazine, pyridine, picoline, 1,8-diazabicyclo[5,4,0]-7-undecene, benzylmethylamine, 2-(dimethylaminomethyl)-phenol, 2-methylimidazole, 2-phenylimidazole, and 2-ethyl-4-methylimidazole.

[0077] Examples of aliphatic amines include, but are not limited to, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 3-(dimethylamino)propylamine, 3-(diethylamino)propylamine, 3-(methylamino)propylamine, tris(2-aminoethyl)amine; 3-(2-ethylhexyloxy)propylamine, 3-ethoxypropylamine, 3-methoxypropylamine, 3-(dibutylamino)propylamine, and tetramethyl-ethylenediamine; ethylenediamine; 3,3′-iminobis(propylamine), N-methyl-3,3′-iminobis(propylamine); allylamine, diallylamine, triallylamine, polyoxypropylenediamine, and polyoxypropylenetriamine.

[0078] Examples of alkylamines include, but are not limited to, methylamine, ethylamine, propylamine, isopropylamine, butylamine, sec-butylamine, t-butylamine, n-octylamine, 2-ethylhexylamine, dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, di-sec-butylamine, di-t-butylamine, di-n-octylamine, and di-2-ethylhexylamine.

[0079] Examples of acid anhydrides include cyclohexane-1,2-dicarboxylic anhydride, 1-cyclohexene-1,2-dicarboxylic anhydride, 2-cyclohexene-1,2-dicarboxylic anhydride, 3-cyclohexene-1,2-dicarboxylic anhydride, 4-cyclohexene-1,2-dicarboxylic anhydride, 1-methyl-2-cyclohexene-1,2-dicarboxylic anhydride, 1-methyl-4-cyclohexene-1,2-dicarboxylic anhydride, 3-methyl-4-cyclohexene-1,2-dicarboxylic anhydride, 4-methyl-4-cyclohexene-1,2-dicarboxylic anhydride, dodecenylsuccinic anhydride, succinic anhydride, 4-methyl-1-cyclohexene-1,2-dicarboxylic anhydride, Examples of suitable anhydrides include, but are not limited to, carboxylic anhydride, phthalic anhydride, hexahydrophthalic anhydride, methylnadic anhydride, dodecenylsuccinic anhydride, tetrahydrophthalic anhydride, maleic anhydride, pyromellitic anhydride, trimellitic anhydride, benzophenonetetracarboxylic dianhydride, bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride, methylbicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride, bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride, dichloromaleic anhydride, chlorendic anhydride, tetrachlorophthalic anhydride, and any derivatives or adducts thereof.

[0080] Examples of imidazoles include imidazole, 1-methylimidazole, 2-methylimidazole, 2-ethylimidazole, 2-isopropylimidazole, 2-n-propylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-isopropyl-2-methylimidazole, and 1-cyanoethyl-2-methylimidazoline. methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-phenylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 1,2-phenyl-4-methyl-5-hydroxymethylimidazole, 1-dodecyl-2-methylimidazole, and 1-cyanoethyl-2-phenyl-4,5-di(2-cyanoethoxy)methylimidazole.

[0081] Examples of substituted guanidines include methylguanidine, dimethylguanidine, trimethylguanidine, tetramethylguanidine, methylisobiguanidine, dimethylisobiguanidine, tetramethylisobiguanidine, hexamethylisobiguanidine, heptamethylisobiguanidine, and cyanoguanidine (dicyandiamide). Representative examples of guanamine derivatives include alkylated benzoguanamine resin, benzoguanamine resin, or methoxymethylethoxymethylbenzoguanamine. Examples of substituted ureas include p-chlorophenyl-N,N-dimethylurea (monuron), 3-phenyl-1,1-dimethylurea (fenuron), or 3,4-dichlorophenyl-N,N-dimethylurea (diuron).

[0082] Examples of tertiary amines include trimethylamine, tripropylamine, triisopropylamine, tributylamine, tri-sec-butylamine, tri-t-butylamine, tri-n-octylamine, N,N-dimethylaniline, N,N-dimethyl-benzylamine, pyridine, N-methylpiperidine, N-methylmorpholine, N,N-dimethylaminopyridine, and morpholine derivatives such as bis(2-(2,6-dimethyl-4-morpholino) Examples of heterocyclic compounds having an amidine bond include, but are not limited to, bis(2-(2,6-dimethyl-4-morpholino)ethyl)-(2-(2,6-diethyl-4-morpholino)ethyl)amine, tris(2-(4-morpholino)ethyl)amine, and tris(2-(4-morpholino)propyl)amine, diazabicyclooctane (DABCO), and the like, as well as heterocyclic compounds having an amidine bond such as diazabicyclooctane (DABCO).

[0083] Amine-epoxy adducts are well known in the art and are described, for example, in U.S. Pat. Nos. 3,756,984, 4,066,625, 4,268,656, 4,360,649, 4,542,202, 4,546,155, 5,134,239, 5,407,978, and 5,407,978. Nos. 5,543,486, 5,548,058, 5,430,112, 5,464,910, 5,439,977, 5,717,011, 5,733,954, 5,789,498, 5,798,399, and 5,801,218, each of which is incorporated herein by reference in its entirety. Such amine-epoxy adducts are the product of the reaction between one or more amine compounds and one or more epoxy compounds. Preferably, the adducts are solids that are insoluble in epoxy resins at room temperature but become soluble upon heating, functioning as accelerators to increase the cure rate. While any type of amine can be used (heterocyclic amines and / or amines having at least one secondary nitrogen atom are preferred), imidazole compounds are particularly suitable. Illustrative examples of imidazoles include 2-methylimidazole, 2,4-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, etc. Other suitable amines include, but are not limited to, piperazine, piperidine, pyrazole, purine, and triazole. Any type of epoxy compound can be employed as the other starting material of the adduct, including monofunctional epoxy compounds and multifunctional epoxy compounds, such as those previously described with respect to the epoxy resin component.

[0084] In one embodiment, the curable resin composition of the present disclosure may contain the curing agent in an amount of about 10% to about 60% by weight, about 20% to about 50% by weight, or about 30% to about 50% by weight, based on the total weight of the curable resin composition. In another embodiment, the curable resin composition of the present disclosure may contain the curing agent in an amount of about 5% to about 50% by weight, about 10% to about 45% by weight, or about 20% to about 40% by weight, based on the total weight of the curable resin composition.

[0085] In yet another embodiment, the curable resin composition includes 4,4'-methylene-bis-(3-chloro-2,6-diethyl-aniline) as the curing agent in an amount of about 30% to about 55% by weight or about 40% to about 50% by weight, based on the total weight of the curable resin composition. In yet another embodiment, the curing agent includes about 25 to about 100 parts of 4,4'-methylene-bis-(3-chloro-2,6-diethyl-aniline) and 0 to about 75 parts of an aromatic amine or an aliphatic amine, based on 100 parts of the curing agent.

[0086] In yet another embodiment, the curable resin composition may also contain one or more other additives that are useful with respect to the additive's intended application. For example, useful optional additives include diluents, stabilizers, surfactants, flow modifiers, mold release agents, matting agents, degassing agents, thermoplastic particles (e.g., carboxyl-terminated liquid butadiene acrylonitrile rubber (CTBN), acrylic-terminated liquid butadiene acrylonitrile rubber (ATBN), epoxy-terminated liquid butadiene acrylonitrile rubber (ETBN), elastomeric liquid epoxy resin (LER) adducts, and preformed core-shell rubbers), cure initiators, cure inhibitors, wetting agents, processing aids, fluorescent compounds, UV stabilizers, antioxidants, impact modifiers, corrosion inhibitors, tackifiers, high-density particulate fillers (e.g., various natural clays, e.g., kaolin, bentonite, montmorillonite or modified montmorillonite, attapulgate, and Buckminsterfuller's earth), and the like. earth); other natural or naturally occurring materials, such as mica, calcium carbonate, and aluminum carbonate; various oxides, such as ferric oxide, titanium dioxide, calcium oxide, and silicon dioxide (e.g., sand); various man-made materials, such as precipitated calcium carbonate; and various waste materials, such as ground blast furnace slag), conductive particles (e.g., silver, gold, copper, nickel, aluminum, and conductive grade carbon and carbon nanotubes), and mixtures thereof.

[0087] When present, the additive may be included in the curable resin composition in an amount of at least about 0.5 wt%, or at least 2 wt%, or at least 5 wt%, or at least 10 wt%, based on the total weight of the curable resin composition. In other embodiments, the additive may be included in the curable resin composition in an amount of about 30 wt% or less, or 25 wt% or less, or 20 wt% or less, or 15 wt% or less, based on the total weight of the curable resin composition.

[0088] The curable resin composition can be prepared, for example, by premixing the individual components and then mixing the premixes, or by mixing all of the components together using conventional equipment, such as a stirred vessel, a stirring rod, a ball mill, a sample mixer, a static mixer, a high shear mixer, or a ribbon blender.

[0089] That is, according to another embodiment, the curable resin composition of the present disclosure can be prepared by mixing together about 10 wt % to about 90 wt % of a thermosetting resin, about 1 wt % to about 25 wt % of a toughening agent component, and about 10 wt % to about 60 wt % of a curing agent, where the wt % are based on the total weight of the curable resin composition.

[0090] A thermoset can be formed from the curable resin composition of the present disclosure by mixing the thermosetting resin, toughening agent component, and curing agent in the proportions described above and then curing the curable resin composition. In some embodiments, it may generally be necessary to heat the composition at an elevated temperature to achieve rapid curing. In molding processes, such as those for making fiber-reinforced composites, the curable resin composition may be introduced into a mold, which may be preheated along with any reinforcing fibers and / or inserts present in the mold. Curing temperatures can range, for example, from about 60°C up to about 190°C. When a long gel time (at least 30 seconds, preferably at least 40 seconds) is desired, the curing temperature preferably does not exceed 130°C. When both a long gel time and a short demold time are desired, suitable curing temperatures may be from about 80°C to about 120°C, preferably 95-120°C, and particularly 105-120°C. In some embodiments, it may be suitable to continue curing until the resulting composite achieves a glass transition temperature above the cure temperature. The glass transition temperature at demolding may be at least about 100°C, or at least about 110°C, or at least about 115°C, or even at least about 120°C. Demolding times at cure temperatures of about 95°C to about 120°C, particularly about 105°C to about 120°C, are typically 350 seconds or less, preferably 300 seconds or less, and more preferably 240 seconds or less.

[0091] Thus, for the production of high-performance composites and prepregs, reinforcing fibers can be combined with a curable resin composition to form a fiber-reinforced resin composition, which can then be cured. The curable resin composition can be combined with the reinforcing fibers according to any of the known prepreg manufacturing techniques. The reinforcing fibers can be fully or partially impregnated with the curable resin composition. In an alternative embodiment, the curable resin composition may be applied to the reinforcing fibers as a separate layer that is proximate to and in contact with the reinforcing fibers, but does not substantially impregnate the reinforcing fibers. Prepregs are typically coated on both sides with a protective film and rolled up for storage and transportation at temperatures maintained well below room temperature to avoid premature curing. Any other prepreg manufacturing process and storage / transportation system can be used if desired.

[0092] Suitable reinforcing fibers include, but are not limited to, fibers having high tensile strength, e.g., greater than 500 ksi (or 3447 MPa). Useful fibers for this purpose include carbon or graphite fibers, glass fibers, and fibers formed from silicon carbide, alumina, boron, quartz, and the like, as well as fibers formed from organic polymers such as polyolefins, poly(benzothiazoles), poly(benzimidazoles), polyarylates, poly(benzoxazoles), aromatic polyamides, polyaryl ethers, and the like, as well as mixtures of two or more of these fibers. Preferably, the fibers are selected from glass fibers, carbon fibers, and aromatic polyamide fibers. Reinforcing fibers can be used in the form of discontinuous or continuous ropes made from multiple filaments, as continuous unidirectional or multidirectional tapes, or as woven, noncrimped, or nonwoven fabrics. Weaves can be selected from plain, satin, or twill weaves. A crimp-free fabric can have multiple plies and fiber directions.

[0093] The reinforcing fibers may be sized or unsized and may be present in an amount of about 5% to about 35% by weight, preferably at least 20% by weight, based on the total weight of the fiber-reinforced resin composition. For structural applications, it is preferred to use continuous fibers, such as glass or carbon fibers, in an amount of 30% to 70% by volume, more particularly 50% to 70% by volume, based on the total volume of the fiber-reinforced resin composition.

[0094] To form a fiber-reinforced composite, multiple curable, flexible prepreg plies can be arranged on a tool in a layup sequence to form a prepreg layup. The prepreg plies within the layup may be oriented at a selected angle relative to each other, such as 0°, +45°, 90°, etc. Prepreg layups can be manufactured by, but are not limited to, manual layup, automated layup (ATL), advanced fiber placement (AFP), and filament winding techniques.

[0095] Each prepreg is comprised of a sheet or layer of reinforcing fibers at least a portion of whose volume is impregnated with a curable resin composition. In one embodiment, the prepreg has a fiber volume fraction of about 0.50 to 0.60, based on the total volume of the prepreg.

[0096] Prepregs useful in the manufacture of aerospace structures are generally resin-impregnated sheets of unidirectional reinforcing fibers, typically carbon fibers, often referred to as "tapes," "unidirectional tapes," or "unitapes." The prepregs may be fully or partially impregnated. The curable resin composition that impregnates the reinforcing fibers may be in a partially cured or uncured state.

[0097] Typically, prepregs are in a pliable or flexible form that allows for easy layup and molding in three-dimensional configurations, followed by curing into the final fiber-reinforced composite part. This type of prepreg is particularly suitable for the manufacture of load-bearing structural parts, such as aircraft wings, fuselages, bulkheads, and control surfaces. Key properties of cured prepregs are high strength and stiffness combined with reduced weight.

[0098] As noted above, curing of prepreg lay-ups is generally carried out at elevated temperatures, typically up to about 190°C, preferably in the range of about 170°C to about 190°C, accompanied by the use of elevated pressures, typically up to 10 bar (1 MPa), preferably 3 bar (0.3 MPa) to 7 bar (0.7 MPa), to suppress the deforming effects of leaking gases or to suppress void formation. Preferably, the cure temperature is achieved by heating at a rate of up to 5°C / min, e.g., 2°C / min to 3°C / min, and maintained for the required period of up to 9 hours, preferably up to 6 hours, e.g., 2 hours to 4 hours. The use of a catalyst in the curable resin composition may permit even lower cure temperatures. Pressure can be released throughout, and the temperature reduced by cooling at a rate of up to 5°C / min, e.g., 3°C / min. Post-curing can be carried out at temperatures ranging from about 190°C to about 350°C and atmospheric pressure, employing appropriate heating rates.

[0099] That is, according to one embodiment, a process for making a fiber-reinforced composite is generally provided, the process comprising: (i) contacting reinforcing fibers with a curable resin composition in a mold to coat and / or impregnate the reinforcing fibers; and (ii) curing the coated and / or impregnated reinforcing fibers at a temperature of at least about 60°C, or at least about 120°C to about 190°C.

[0100] The coating and / or impregnation can be achieved by either a wet method or a hot melt method. In the wet method, the curable resin composition is first dissolved in a solvent to reduce the viscosity, and then the coating and / or impregnation of the reinforcing fibers is achieved, and the solvent is evaporated using an oven or the like. In the hot melt method, the coating and / or impregnation can be achieved by directly coating and / or impregnating the reinforcing fibers with the curable resin composition, which is heated to reduce the viscosity. Alternatively, a coating of the curable resin composition can be first prepared on a release paper or the like, and then the coating can be placed on one or both sides of the reinforcing fibers, and the coating and / or impregnation can be achieved by applying heat and pressure.

[0101] In yet another embodiment, a method for producing a fiber-reinforced composite with a RIM system is generally provided, the process comprising the steps of: a) introducing a fiber matrix containing reinforcing fibers into a mold; b) injecting a curable resin composition into the mold; c) impregnating the fiber matrix with the curable resin composition; and d) heating the impregnated fiber matrix at a temperature of at least about 60°C or at least about 120°C for a period of time to produce an at least partially cured fiber-reinforced composite; and e) optionally subjecting the partially cured fiber-reinforced composite to a post-cure operation at a temperature of from about 100°C to about 350°C.

[0102] In an alternative embodiment, the present disclosure generally provides a method for producing a fiber-reinforced composite in a VaRTM system, the process comprising the steps of: a) introducing a fiber matrix containing reinforcing fibers into a mold; b) injecting a curable resin composition into the mold; c) creating a vacuum within the mold; d) maintaining the mold at about this vacuum; e) impregnating the fiber matrix with the curable resin composition; f) heating the impregnated fiber matrix at a temperature of at least about 60°C or at least about 120°C for a period of time sufficient to produce an at least partially cured fiber-reinforced composite; and e) optionally subjecting the at least partially cured fiber-reinforced composite to a post-cure operation at a temperature of from about 100°C to about 350°C.

[0103] The process of the present invention is useful for making a wide variety of fiber-reinforced composites, including various aerospace structures as well as automotive, rail, and marine structures. Examples of aerospace structures include primary and secondary aerospace structural materials (wings, fuselages, bulkheads, flaps, ailerons, cowls, fairings, interior trim, etc.), rocket engine cases, and structural materials for satellites. Examples of automotive structures include vertical and horizontal body panels (fenders, door skins, hoods, roof skins, decklids, tailgates, etc.) and chassis components for cars and trucks. [Example]

[0104] Various curable resin compositions were prepared and then cured. Various thermal and mechanical properties were measured according to techniques known to those skilled in the art. The results are shown in Tables 1 and 2:

[0105] [Table 1]

[0106] [Table 2]

[0107] The results show that the compression after impact (CAI) and glass transition temperature of Inventive Example 3 exceed those of Examples 1 and 2, thus demonstrating the synergistic effect of the toughening agent component containing the multi-stage polymer and thermoplastic toughener.

[0108] While the making and using of various embodiments of the invention have been described above in detail, it should be understood that the invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention.

Claims

1. 1. A curable resin composition comprising: (a) a thermosetting resin; (b) a toughening agent component comprising a multi-stage polymer having at least two stages, the multi-stage polymer differing in polymer composition, wherein a first stage forms a core and a second or any subsequent stages form shells, respectively; and a thermoplastic toughening agent; and (c) a curing agent, wherein the multi-stage polymer is in the form of polymer particles, the polymer particles having a multi-layer structure comprising at least one layer (or stage) (A) comprising a polymer (A1) having a glass transition temperature of less than 10° C., and at least another layer (or stage) (B) comprising a polymer (B1) which is a (meth)acrylic polymer; the toughening agent component comprises 5% to 15% by weight of the multi-stage polymer and 0.1% to 10% by weight of the thermoplastic toughening agent; Curable resin composition.

2. The curable resin composition according to claim 1 , wherein the thermosetting resin is an epoxy resin.

3. 3. The curable resin composition of claim 2, wherein the epoxy resin is selected from difunctional epoxy resins, trifunctional epoxy resins, tetrafunctional epoxy resins, and mixtures thereof.

4. The curable resin composition of claim 1 , wherein the thermoplastic toughening agent is a polyethersulfone.

5. The curable resin composition of claim 1, wherein the curing agent comprises 4,4'-methylene-bis-(3-chloro-2,6-diethyl-aniline).

6. A fiber-reinforced resin composition comprising reinforcing fibers and the curable resin composition according to claim 1.

7. 7. The fiber-reinforced resin composition according to claim 6, wherein the reinforcing fibers are selected from graphite fibers, glass fibers, fibers made of silicon carbide, fibers made of alumina, fibers made of boron, fibers made of quartz, fibers made of organic polymers, and mixtures thereof.

8. 8. The fiber reinforced resin composition of claim 7, wherein the reinforcing fibers are present in an amount of 5% to 35% by weight, based on the total weight of the fiber reinforced resin composition.

9. 1. A method for producing a fiber-reinforced composite, comprising the steps of: (i) contacting reinforcing fibers with the curable resin composition of claim 1 to coat and / or impregnate the reinforcing fibers; and (ii) curing the coated and / or impregnated reinforcing fibers at a temperature of at least 60°C. The method comprising:

10. 1. A method for producing a fiber-reinforced composite in a RIM system, comprising the steps of: a) introducing a fiber matrix containing reinforcing fibers into a mold; b) injecting the curable resin composition of claim 1 into the mold; c) impregnating the fiber matrix with the curable resin composition; and d) heating the impregnated fiber matrix at a temperature of at least 60°C for a period of time to produce an at least partially cured fiber-reinforced composite; and e) optionally subjecting the partially cured fiber-reinforced composite to a post-cure operation at a temperature of from 100°C to 350°C. The method comprising:

11. 1. A method for producing a fiber-reinforced composite with a VaRTM system, comprising the steps of: a) introducing a fiber matrix containing reinforcing fibers into a mold; b) injecting the curable resin composition of claim 1 into the mold; c) reducing the pressure within the mold; d) maintaining the mold at about said reduced pressure; e) impregnating the fiber matrix with the curable resin composition; f) heating the impregnated fiber matrix at a temperature of at least 60°C for a period of time to produce an at least partially cured fiber-reinforced composite; and e) optionally subjecting the at least partially cured fiber-reinforced composite to a post-cure operation at a temperature of from 100°C to 350°C. The method comprising:

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