Curable epoxy resin composition with high glass transition temperature

Abstract

The present invention relates to curable epoxy resin compositions comprising an alkyl-substituted aromatic epoxy resin and a bis-alicyclic amine hardener, which exhibit preferred physicochemical properties when cured. The present invention also relates to the use of such curable resin compositions that can be cured in the presence of reinforcing fibers to form fiber-reinforced composite articles for use in a variety of applications, such as transportation applications including aerospace, aviation, navigation and land vehicles, and the like. The present invention relates to fiber-reinforced composite articles, including automotive, railway, passenger car and military industries, for construction / construction applications or other commercial applications, and to aerospace structural components made from the fiber-reinforced composite articles.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Application No. 63 / 356,135, filed on June 28, 2022. Said application is incorporated herein by reference. Technical Field

[0003] The present invention relates to a curable epoxy resin composition comprising an alkyl-substituted aromatic epoxy resin and a dicycloaliphatic amine hardener, which exhibits preferred physicochemical properties when cured. In particular, the cured epoxy resin composition of the present invention exhibits a high glass transition temperature. The present invention also relates to the use of such curable resin compositions, which can be cured in the presence of reinforcing fibers to form fiber-reinforced composite products, which are used in a variety of applications, such as for transportation applications (including aerospace, aviation, marine and land vehicles, and including automobiles, railways, buses and military industries), for construction / building applications or other commercial applications, and to aerospace structural components made of fiber-reinforced composite products. Background Art

[0004] Curable resin compositions containing epoxy resins have been used in many methods to form structural composites. In particular, curable resin compositions containing aromatic epoxy resins and amine components that realize high glass transition temperatures are used to form structural composites that can resist deformation and mechanical property loss in high temperature applications. Structural composites for high temperature applications can include structural composites of primary and secondary aerospace structural materials (wings, fuselages, bulkheads, flaps, ailerons, hoods, fairings, interior trims, etc.), rocket engine housings, and satellites. The example of automotive structural composites includes vertical and horizontal body panels (fenders, door skins, hoods, roof skins, deck covers, tailgates, etc.) and automobile and truck chassis components.

[0005] In order to form structural composite materials, this type of composition can be used in molding methods, and molding methods include those called resin transfer molding (RTM), vacuum assisted resin transfer molding (VARTM), Seeman composite resin infusion molding method (SCRIMP), reaction injection molding (RIM) method and liquid compression molding (LCM). In each of these methods, curable resin composition is applied to reinforcing agent, and solidified in the presence of this reinforcing agent. Then form a composite material with a continuous polymer phase (formed by cured resin) in which the reinforcing agent is dispersed.

[0006] The above-mentioned various methods can be used for producing a wide range of products. For example, molding methods (such as RTM, VARTM, SCRIMP, RIM and LCM) can be used for producing high-strength components that can be used in, for example, automobiles and aircraft components. In RTM, VARTM and SCRIMP methods, parts are formed by the following: the fiber preforms woven or tangled are inserted into the die cavity, the mold is closed, resin is injected into the mold and the resin is hardened. In the RIM method, the fiber preforms woven or tangled can be inserted into the mold in advance as described above, or can be injected into the mold together with curable resin composition. In the LCM method, reactive mixture is directly applied to fiber preforms or stacked bodies, without injection, but by spraying or by laying it as the "belt" of the system, by width, it is 1cm to 50cm or larger wide slit die to feed.

[0007] As is the case with many other manufacturing processes, the economics of these composite manufacturing processes depend primarily on the operating rate. For molding processes, the operating rate is usually expressed in terms of "cycle time". Cycle time refers to the time required to produce a composite part in a mold and prepare the mold to make the composite part. Cycle time directly affects the number of composite parts that can be made on the mold per unit time. Longer cycle times increase manufacturing costs because the indirect costs (facilities and labor, etc.) to produce each part are greater. For these reasons, it is generally desirable to reduce cycle time.

[0008] When using a curable composition with a high glass transition temperature in the above molding method, a major component of the cycle time is the amount of time required for the resin to cure. For curing resin compositions comprising an aromatic epoxy resin and an amine component (also known as an amine hardener), which achieve a high glass transition temperature of more than 200 degrees, it is well known to use high curing temperatures of 180°C to 220°C. In addition, after curing of this type of resin composition, a post-curing treatment at a temperature higher than the curing temperature is usually required to achieve the targeted high glass transition temperature.

[0009] In addition, in the case of such resin compositions comprising an aromatic epoxy resin and an amine hardener, a higher glass transition temperature is generally obtained when both the epoxy resin and the hardener contain more aromatic (as opposed to aliphatic) molecular structures. WO2021083583, WO2019177131 and US20210292545 describe different combinations of aromatic epoxy resins and aromatic amine components, wherein the curing temperature of the combination is 180°C to 220°C to achieve a glass transition temperature of 200°C to 280°C.

[0010] However, such resin compositions having high glass transition temperatures generally require long curing times, especially if post-curing treatments at higher temperatures are required. Therefore, there is a need for a curable epoxy composition for forming structural composites that is able to resist deformation and loss of mechanical properties in high temperature applications, wherein its high glass transition temperature is obtained during the molding process itself (i.e., without the need for an additional post-curing step).

[0011] In addition, structural composites must maintain their properties under high thermal and mechanical stresses in high temperature applications such as engine and nacelle components (including engine cowlings or thrust reversers), and in the leading edges of wings or rockets. Therefore, the goal is to have a cured epoxy composition with a glass transition temperature of at least 300°C to safely operate with structural composites made from the cured epoxy composition at temperatures of 170°C or higher and avoid partial failure of the structural composite when exposed to high thermal and mechanical stresses.

[0012] In order to achieve a glass transition temperature of at least 300° C., the curing or post-cure temperature must generally be at least 200° C., typically above 220° C., which results in longer curing times than typical epoxy resins that are typically cured at 180° C. In fact, it is well known that it is difficult to achieve a glass transition temperature that is at least 100° C. above the highest curing or post-cure temperature. There is also a need for a curable epoxy composition having all of the above properties, which achieves a high glass transition temperature at conventional curing temperatures (i.e., a curing temperature of 180° C.).

[0013] In addition, it is well known that when the conventional curing cycle is implemented using the liquid molding method of the above-mentioned VARTM, it is difficult to achieve a high glass transition temperature. The conventional vacuum bagging materials used in VARTM are not suitable for curing cycles requiring high curing temperatures higher than 200°C or 220°C, and therefore require special process materials including release films, sealing tapes, breathers and vacuum bags. In addition, high curing temperatures will affect the thermal management in molds, fibers, resins and process materials. High curing temperatures may prevent the heat generated during the curing process from being properly released, resulting in the need for heat release or changing the curing temperature to obtain a cured epoxy composition with a high glass transition temperature. These heat releases or improper heat management during high curing temperatures may result in the final component being scrapped or rejected. There is also a need for a curable epoxy composition with all of the above properties, which can achieve a high glass transition temperature when cured with a liquid molding method such as VARTM at a conventional curing temperature of 180°C. Summary of the invention

[0014] The present invention relates to a curable epoxy resin composition comprising:

[0015] (a) Alkyl-substituted aromatic epoxy resins of the general formula (I):

[0016]

[0017] in

[0018] - R and R1 are each independently methyl, ethyl or isopropyl,

[0019] - R2 and R3 are each independently hydrogen, methyl, ethyl or isopropyl,

[0020] -X is -O-, -S-, -CO-, -C(=O)O-, -NHCO-, -SO2-, linear or branched alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted aromatic residue, or substituted or unsubstituted heterocycle; and

[0021] (b) Bis-alicyclic amine hardener of general formula (II):

[0022]

[0023] in

[0024] - R4 and R5 are each independently hydrogen, methyl, ethyl or isopropyl,

[0025] - R6 and R7 are each independently hydrogen, methyl, ethyl or isopropyl,

[0026] -Y is -O-, -S-, -CO-, -C(=O)O-, -NHCO-, -SO2-, linear or branched alkyl, or substituted or unsubstituted cycloalkyl.

[0027] The above components, when provided in a composition, unexpectedly produce a cured epoxy resin that exhibits a high glass transition temperature of at least 300°C upon curing. DETAILED DESCRIPTION

[0028] If it appears in this article, 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 in this article. For the avoidance of any doubt, all compositions claimed herein by using the term "comprising" may include any additional additives, adjuvants or compounds unless otherwise specified. In contrast, if it appears in this article, the term "essentially consisting of excludes any other components, steps or procedures from the scope of any subsequent description, except those that are not necessary for operability; and if used, the term "consisting of excludes any components, steps or procedures that are not explicitly described or listed. Unless otherwise specified, the term "or" refers to the listed members individually and in any combination.

[0029] The articles "a" and "an" are used herein to refer to one or to more than one (ie, to at least one) of the grammatical object of the article. For example, "an epoxy resin" means one epoxy resin or more than one epoxy resin.

[0030] The expressions "in one embodiment", "according to one embodiment", etc. generally mean that the specific features, structures or characteristics following the expression are included in at least one embodiment of the present invention, and may be included in more than one embodiment of the present invention. Importantly, these expressions do not necessarily refer to the same embodiment.

[0031] If the specification states that a component or feature "may," "could," "might," or "might" be included or have a property, that particular component or feature is not required to be included or have that property.

[0032] The present invention generally relates to new epoxy resin compositions comprising an alkyl-substituted aromatic epoxy resin and a dicycloaliphatic amine hardener, and structural composite materials obtained using such compositions. It has been surprisingly found that a specific combination of an alkyl-substituted aromatic epoxy resin and a dicycloaliphatic amine hardener produces an epoxy resin that exhibits an improved glass transition temperature, such as a glass transition temperature of at least about 300° C., without a significant loss of toughness using conventional curing temperatures. This property can generally be used to define a significantly improved composition according to the present invention. As used herein, the expression "glass transition temperature" (abbreviated as "Tg") means a temperature at which the mechanical properties of a material (e.g., a cured resin) are radically changed due to the internal movement of the polymer chains forming the material. As used herein, the term "hardener" means a component that reacts with an epoxy resin to harden the epoxy composition into a solid material (i.e., a cured epoxy composition). According to the present invention, the dicycloaliphatic amine hardener is different from an amine catalyst, which can also affect the curing of the epoxy composition, but the mechanism is different from that of the dicycloaliphatic amine hardener.

[0033] According to a specific embodiment, a specific combination of an alkyl-substituted diaromatic glycidylamine and a (alkyl-substituted) dicyclohexylamine hardener provides an epoxy resin composition that forms a cured epoxy resin exhibiting an improved glass transition temperature after curing. As used herein, the term "improved glass transition temperature" is intended to refer to a cured epoxy resin whose glass transition temperature is increased over conventional resins by applying the present invention. In addition, the term "epoxy resin composition" or "curable epoxy resin composition" is intended to refer to an uncured composition that cures to a "cured epoxy resin" or "cured product" after curing. The term "curable" means that the composition is capable of being subjected to conditions that will impart a cured state to the composition.

[0034] According to one embodiment, the alkyl-substituted aromatic epoxy resin of formula (I) has:

[0035] - R and R1 are each independently methyl, ethyl or isopropyl,

[0036] - R2 and R3 are each independently hydrogen, methyl, ethyl or isopropyl,

[0037] -X is -O-, -S-, -CO-, -C(=O)O-, -NHCO-, -SO2-, a linear or branched alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aromatic residue, or a substituted or unsubstituted heterocycle.

[0038] Examples of linear or branched alkyl groups having 1 to 6 carbon atoms include -CH2-, -C(H)(CH3)-, -C(CH3)2-, -C(H)(CH2CH3)-, -C(H)(CH(CH3)2)-, -C(H)(CH2CH2CH3)-, -C(H)(CH2CH2CH2CH3)-, -C(H)(C(CH3)3)-, -C(H)(CH2CH2CH2CH2CH3)-, -C(H)(CH2C(H)(CH3)2)-, -C(H)(C(H)(CH3)CH2CH2CH3)-, -C(CH3)(CH2CH3)- , C(CH3)(CH2CH2CH3)-, -C(CH2CH3)(CH2CH3)-, -C(CH3)(CH(CH3)2)-, -C(CH3)(C(CH3)3)-, -C(CH2CH3)(C(H)(CH3)2)-, preferably -CH2-, -C(H)(CH3)-, -C(CH3)2-, -C(H)(CH2CH3)-, -C(H)(CH(CH3)2)-, more preferably -CH2-.

[0039] Examples of the substituted cycloalkyl group include methylcyclopropane, methylcyclopentane, methylcyclohexane, methylcyclopentene and methylcyclohexene groups, with methylcyclopropane, methylcyclopentane and methylcyclohexene groups being preferred.

[0040] Examples of the substituted or unsubstituted aromatic residue include a methoxybenzyl group, a methylbenzyl group and a fluorenyl group.

[0041] Examples of substituted or unsubstituted heterocyclic rings include furfuryl, picolinyl, pyrimidinyl, thienyl and indolyl groups.

[0042] According to one embodiment, R and R1 of the alkyl-substituted aromatic epoxy resin of general formula (I) are each independently methyl, ethyl or isopropyl, R2 and R3 are each independently hydrogen, methyl, ethyl or isopropyl, and X is a linear or branched alkyl group having 1 to 6 carbon atoms.

[0043] According to one embodiment, the dicycloaliphatic amine hardener of formula (II) has:

[0044] - R4 and R5 are each independently hydrogen, methyl, ethyl or isopropyl,

[0045] - R6 and R7 are each independently hydrogen, methyl, ethyl or isopropyl,

[0046] Y is -O-, -S-, -CO-, -C(=O)O-, -NHCO-, -SO2-, a linear or branched alkyl group having 1 to 6 carbon atoms, or a substituted or unsubstituted cycloalkyl group.

[0047] According to one embodiment, R4 and R5 of the dialicyclic amine hardener of general formula (II) are each independently hydrogen, methyl, ethyl or isopropyl, R6 and R7 are each independently hydrogen, methyl, ethyl or isopropyl, and Y is a linear or branched alkyl group having 1 to 6 carbon atoms.

[0048] According to one embodiment, the curable epoxy resin composition comprises:

[0049] (a) an alkyl-substituted aromatic epoxy resin of the general formula (I), wherein

[0050] - R and R1 are each independently methyl, ethyl or isopropyl,

[0051] - R2 and R3 are each independently hydrogen, methyl, ethyl or isopropyl,

[0052] - X is a linear or branched alkyl group having 1 to 6 carbon atoms; and

[0053] (b) a dialicyclic amine hardener of formula (II), wherein

[0054] - R4 and R5 are each independently hydrogen, methyl, ethyl or isopropyl,

[0055] - R6 and R7 are each independently hydrogen, methyl, ethyl or isopropyl,

[0056] -Y is a linear or branched alkyl group having 1 to 6 carbon atoms.

[0057] In a preferred embodiment, R and R1 of the alkyl-substituted aromatic epoxy resin of formula (I) are each independently methyl, ethyl or isopropyl, R2 and R3 are each independently hydrogen, methyl, ethyl or isopropyl, and X is -CH2-.

[0058] In a preferred embodiment, R4 and R5 of the dicycloaliphatic amine hardener of formula (II) are each independently hydrogen, methyl, ethyl or isopropyl, R6 and R7 are each independently hydrogen, methyl, ethyl or isopropyl, and Y is -CH2-.

[0059] Advantageously, the curable epoxy resin composition comprises:

[0060] (a) an alkyl-substituted aromatic epoxy resin of the general formula (I), wherein

[0061] - R and R1 are each independently methyl, ethyl or isopropyl,

[0062] - R2 and R3 are each independently hydrogen, methyl, ethyl or isopropyl,

[0063] -X is -CH2-; and

[0064] (b) a dialicyclic amine hardener of formula (II), wherein

[0065] - R4 and R5 are each independently hydrogen, methyl, ethyl or isopropyl,

[0066] - R6 and R7 are each independently hydrogen, methyl, ethyl or isopropyl,

[0067] -Y is -CH2-.

[0068] In another preferred embodiment, R and R1 of the alkyl-substituted aromatic epoxy resin of formula (I) are each ethyl, R2 and R3 are each hydrogen, and X is -CH2-.

[0069] In another preferred embodiment, R4 and R5 of the dicycloaliphatic amine hardener of formula (II) are each independently hydrogen, methyl or ethyl, R6 and R7 are each hydrogen, and Y is -CH2-.

[0070] More advantageously, the curable epoxy resin composition comprises:

[0071] (a) an alkyl-substituted aromatic epoxy resin of the general formula (I), wherein

[0072] - R and R1 are each ethyl,

[0073] - R2 and R3 are each hydrogen,

[0074] -X is -CH2-; and

[0075] (b) a dialicyclic amine hardener of formula (II), wherein

[0076] - R4 and R5 are independently hydrogen, methyl or ethyl,

[0077] - R6 and R7 are each hydrogen,

[0078] -Y is -CH2-.

[0079] For example, the alkyl-substituted aromatic epoxy resin of the general formula (I) is N,N,N',N'-tetraglycidyl-4,4'-diamino-3,3'-diethyldiphenylmethane, and its CAS number is 130728-76-6.

[0080] N,N,N',N'-tetraglycidyl-4,4'-diamino-3,3'-diethyldiphenylmethane The trade name is commercially available from Huntsman Advanced Materials.

[0081] For example, the dicycloaliphatic amine hardener of general formula (II) is 4,4'-methylenebis(2-methylcyclohexylamine). The CAS number is 6864-37-5. Another example of a dicycloaliphatic amine hardener is 4,4'-methylenebis(cyclohexylamine). The CAS number is 1761-7-3.

[0082] 4,4'-Methylenebis(2-methylcyclohexylamine) The trade name is commercially available from Huntsman Advanced Materials. 4,4'-Methylenebis(cyclohexylamine) is The trade name is commercially available from BASF.

[0083] In a preferred embodiment, the curable epoxy resin composition comprises:

[0084] - from about 5 wt % to about 95 wt %, preferably from about 10 wt % to about 90 wt %, and more preferably from about 15 wt % to about 85 wt % of an alkyl-substituted aromatic epoxy resin of the above formula (I), based on the total weight of the epoxy resin composition, and

[0085] - About 5 wt % to about 95 wt %, preferably about 10 wt % to about 90 wt %, and more preferably about 15 wt % to about 85 wt % of the above-mentioned bis-alicyclic amine hardener of formula (II), based on the total weight of the epoxy resin composition.

[0086] Advantageously, the curable epoxy resin composition comprises:

[0087] - about 40 wt % to about 80 wt %, preferably about 50 wt % to about 80 wt %, and more preferably about 60 wt % to about 80 wt % of the alkyl-substituted aromatic epoxy resin of the above formula (I), based on the total weight of the epoxy resin composition, and about 20 wt % to about 60 wt %, preferably about 20 wt % to about 50 wt %, and more preferably about 20 wt % to about 40 wt % of the dicycloaliphatic amine hardener of the above formula (II), based on the total weight of the epoxy resin composition.

[0088] In one embodiment, the curable epoxy resin composition may optionally contain a catalyst, including imidazoles such as 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole; tertiary amines such as triethylamine, tripropylamine, N,N-dimethyl-1-phenylmethylamine and 2,4,6-tris((dimethylamino)methyl)phenol and tributylamine; phosphonium salts such as ethyltriphenylphosphonium chloride, ethyltriphenylphosphonium bromide and ethyltriphenylphosphonium acetate; ammonium salts such as benzyltrimethylammonium chloride and benzyltrimethylammonium hydroxide and mixtures thereof.

[0089] If desired, the curable epoxy resin composition may optionally be mixed with one or more conventional additives prior to curing, such as stabilizers, tougheners, extenders, fillers, reinforcing agents, pigments, dyes, plasticizers, tackifiers, accelerators, non-reactive diluents, or any mixtures thereof.

[0090] Stabilizers that can be used include: phenothiazine itself or C-substituted phenothiazine with 1 to 3 substituents or N-substituted phenothiazine with one substituent, such as 3-methyl-phenothiazine, 3-ethyl-phenothiazine, 10-methyl-phenothiazine; 3-phenyl-phenothiazine, 3,7-diphenyl-phenothiazine; 3-chlorophenothiazine, 2-chlorophenothiazine, 3-bromophenothiazine; 3-nitrophenothiazine, 3-aminophenothiazine, 3,7-diaminophenothiazine; 3-sulfonyl-phenothiazine, 3,7-disulfonyl-phenothiazine, 3,7-dithiocyanatophenothiazine; substituted quinines and catechols, copper naphthenate, zinc dimethyldithiocarbonate and phosphotungstic acid hydrate. Tougheners, fillers, reinforcing agents, fillers, accelerators and pigments that can be used include, for example: poly(ethersulfone), nylon, core-shell rubber, phenoxylate, coal tar, asphalt, glass fiber, boron fiber, carbon fiber, cellulose, polyethylene powder, polypropylene powder, mica, asbestos, quartz powder, gypsum, antimony trioxide, bentonite, silica aerogel ("aerosil"), lithopone, barite, titanium dioxide, eugenol, dicumyl peroxide, isoeugenol, carbon black, graphite and iron powder. Other additives may also be added, such as flame retardants, flow control agents such as silicone, cellulose acetate butyrate, polyvinyl butyrate, wax, stearate, etc.

[0091] The present invention also relates to a method of forming a fiber reinforced epoxy composite material, comprising:

[0092] a) mixing the above alkyl-substituted aromatic epoxy resin and the above bis-alicyclic amine hardener to form the curable epoxy resin composition of the present invention;

[0093] b) transferring the resulting curable epoxy resin composition into a mold containing reinforcing fibers;

[0094] c) curing the obtained epoxy resin composition in a mold at a conventional curing temperature to form a fiber reinforced composite material, wherein reinforcing fibers are embedded in a polymer matrix formed by curing the obtained epoxy resin composition; and

[0095] d) demoulding the fiber reinforced composite material.

[0096] By mixing an alkyl-substituted aromatic epoxy resin and a dialicyclic amine hardener in the aforementioned ratio, and curing the resulting mixture, a polymer matrix is ​​formed by the curable epoxy resin composition of the present invention. If necessary, any one or both of the components can be preheated and then mixed with each other. A preheating step is generally implemented to reduce the viscosity of the component to achieve thorough mixing of the two components in a short period of time. It is generally necessary to heat the mixture to an elevated temperature to obtain rapid solidification. In a molding method such as the method for manufacturing a molded composite material described below, a curable epoxy resin composition is introduced into a mold, which can be preheated together with any reinforcing fibers and / or inserts (which can be included in the mold). The curing temperature can be, for example, about 90°C to about 190°C, or about 100°C to about 190°C, or about 110°C to about 190°C. In still other embodiments, the curing temperature is controlled by the reaction initiation measured by differential scanning calorimetry (DSC). The reaction initiation is defined as the temperature at which the curable system undergoes enough exothermic reaction so that less heat is required to maintain heat flow relative to a reference. The cure start temperature may be, for example, about 130° C. to about 190° C. or more preferably about 140° C. to about 190° C. Start temperatures above 190° C. do not allow for rapid low temperature cure, and temperatures below 120° C. do not allow sufficient time to infuse high quality parts.

[0097] In one embodiment, curing is preferably continued until the resulting polymer matrix reaches a glass transition temperature that exceeds the curing temperature. Advantageously, the polymer matrix reaches a glass transition temperature of at least 300°C.

[0098] In other embodiments, the glass transition temperature at demoulding is preferably at least 130° C., or at least 150° C., or even still at least 180° C., or further at least 200° C. An advantage of the present invention is that such a glass transition temperature can be obtained with a short curing time. This allows short cycle times.

[0099] In one embodiment, when solidified at the aforementioned temperature, the curable epoxy resin composition exhibits a degree of cure of about 85% or more. In yet other embodiments, when solidified at the aforementioned temperature, the curable epoxy resin composition exhibits a degree of cure of about 90% or more, or 95% or more. In still other embodiments, further curing the composite material in a separate stage (such as in a heating oven) after demoulding may be desirable, to reach a degree of cure higher than 90% or even higher than 95%.

[0100] As described above, the curable epoxy resin composition of the present invention is particularly useful for making fiber-reinforced composite materials by curing the system in the presence of reinforcing fibers. According to the present invention, these composite materials are generally made by mixing the above-mentioned alkyl-substituted aromatic epoxy resin and the above-mentioned bis-alicyclic amine hardener to form a curable epoxy resin composition, wetting the fibers with the curable epoxy resin composition, and then curing the epoxy resin composition at the aforementioned temperature in the presence of reinforcing fibers.

[0101] The reinforcing fibers are thermally stable and have a degradation temperature such that the reinforcing fibers do not degrade or melt during the curing process. Suitable fiber materials may include, for example, glass, quartz, polyamide resins, aramid, boron, carbon, wheat straw, hemp, sisal, cotton, bamboo, and gel-spun polyethylene fibers.

[0102] Reinforcing fibers can be provided in the form of staple fibers (0.5 to 15 cm), long fibers (greater than 15 cm) or continuous rovings. If desired, fibers can be provided in the form of pads or other preforms, which in some embodiments can be formed by entanglement, weaving and / or stitching fibers or by bonding the fibers together using a binder. The preform can be similar in size and shape to the final composite material (or the part thereof that needs to be enhanced). If desired, pads of continuous or shorter fibers can be stacked and pressed together, usually with the aid of a tackifier, to form preforms of varying thicknesses.

[0103] Suitable tackifiers for preparing preforms include heat-softenable polymers such as those described in U.S. Pat. Nos. 4,992,228, 5,080,851, and 5,698,318. The tackifier should be compatible and / or reactive with the polymer phase of the composite material so that there is good adhesion between the polymer and the reinforcing fibers. The tackifier may contain other components such as one or more catalysts, thermoplastic polymers, rubbers, or other modifiers.

[0104] A sizing agent or other applicable coating may be applied to the fiber surface before they are introduced into the mold. The sizing agent generally promotes adhesion between the cured resin and the fiber surface.

[0105] Composite materials can be formed in a mold. In this case, the reinforcing fibers can be introduced into the mold before the curable epoxy resin composition is introduced. This is usually the case when a fiber preform is used. The fiber preform is placed in a mold, the mold is closed, and then the curable epoxy resin composition is introduced into the mold, where it penetrates between the fibers in the preform, fills the cavity, and is then cured to form a composite material.

[0106] Alternatively, the fiber (including preform) can be deposited in an open mold, and curable epoxy resin composition can be sprayed into, poured or injected on the preform and in the mold. After filling the mold in this way, the mold is closed, and the epoxy resin composition is solidified. The example of this type method is gap compression resin transfer molding, in which the mold containing the fiber is kept open, and the gap can be 10% to 100% or more of the original cavity thickness, for example. The gap allows lower flow resistance, which makes the mold filling easier and promotes the penetration of curable epoxy resin composition around the fiber and between the fibers.

[0107] The staple fibers may be introduced into the mold together with the curable epoxy resin composition. Such staple fibers may be blended, for example, with an alkyl-substituted aromatic epoxy resin or a bis-cycloaliphatic amine hardener (or both) prior to forming the curable epoxy resin composition. Alternatively, the staple fibers may be added to the curable epoxy resin composition at the same time as or after the alkyl-substituted aromatic epoxy resin and the bis-cycloaliphatic amine hardener are mixed but before the curable epoxy resin composition is introduced into the mold.

[0108] Alternatively, staple fibers can be sprayed into the mold. In this case, curable epoxy resin composition can also be sprayed into the mold while or after the staple fibers are sprayed into the mold. When the fibers and curable epoxy resin composition are sprayed into simultaneously, they can be mixed together and then sprayed into. Alternatively, the fibers and curable epoxy resin composition can be separated but sprayed into the mold simultaneously. A scraper or similar device can be used to spread and / or level the material sprayed into, and then the mold is closed and cured. In a particularly attractive method, long fibers are cut into short lengths, and while or before the curable epoxy resin composition is sprayed into, chopped fibers are sprayed into the mold. The mesh material usually serves as a flow promoter.

[0109] Can use wet compression method, wherein curable epoxy resin composition is directly applied to fiber preform or stacked body, and need not by spraying or by injecting by laying it as the " belt " of system, feed by wider slit die, the width of this slit die can be 1cm to 50cm or larger.Apply enough materials, to reach the fiber volume content of expectation in final composite material.Curable epoxy resin composition can be applied to the fiber of opening die inside or this mold outside.Alternately by following curable epoxy resin composition is applied to the center layer of deposit: with curable epoxy resin composition moistening fiber layer, and then place the second fiber layer on the moistening surface, thereby resin layer is sandwiched between two fiber layers.Fiber mat can be made by non-curling fiber deposit, woven fabric, random fiber deposit or preform. If the curable epoxy resin composition is applied to the fibers outside the mold, it is usually applied at a slightly lower temperature to prevent premature curing and to maintain the viscosity of the curable epoxy resin composition so that it does not drip from the fibers before being transferred to the mold. The wetted preform is then placed in the lower half of the hot mold, the mold is closed, and the material is cured under compression.

[0110] Composite materials produced according to the invention may have a fiber content of at least 40% by volume, or at least 50% by volume, up to 60% by volume, or even up to 70% by volume.

[0111] In addition to the reinforcing fibers, the mold may also contain one or more inserts. Such inserts may act as reinforcements, may act as flow promoters, and in some cases may be present for weight reduction purposes. Examples of such inserts include, for example, wood, plywood, metal, various polymeric materials (which may be foamed or unfoamed, such as polyethylene, polypropylene, other polyolefins, polyurethanes, polystyrenes, polyamides, polyimides, polyesters, polyvinyl chloride, etc.), various types of composite materials, etc., which will not deform or degrade at the temperatures encountered during the molding step.

[0112] The reinforcing fibers and core material, if any, may be enclosed in a bag or film, such as those commonly used in vacuum-assisted processes.

[0113] The mold and preform (and any other inserts, if any) may be heated to the curing temperature or some other useful elevated temperature before contacting them with the reactive mixture. The mold surface may be treated with an external mold release agent, which may be solvent-based or water-based.

[0114] The specific equipment used to mix the alkyl-substituted aromatic epoxy resin and the bis-alicyclic amine hardener of the curable epoxy resin composition and transfer the composition to the mold is not considered critical in the present invention, as long as the curable epoxy resin composition can be transferred to the mold before it reaches high viscosity or produces a large amount of gel. The method of the present invention is suitable for RTM, VARTM, RFI, gap compression resin transfer molding and SCRIMP processing methods and equipment (in some cases, the equipment is modified to provide necessary heating at various stages of the method), as well as for other methods such as wet compression.

[0115] The mixing device used to mix the epoxy component and the curing component can be of any type that can produce a highly uniform reactive mixture (and any optional components that are also mixed at this time). Different types of mechanical mixers and agitators can be used. Two preferred types of mixers are static mixers and impingement mixers.

[0116] In some embodiments, the mixing and dispersing device is an impact mixer. This type of mixer is commonly used in so-called reaction injection molding methods to form polyurethane and polyurea molded products. The alkyl-substituted aromatic epoxy resin and the di-alicyclic amine hardener (and other additives mixed at this time) are pumped under pressure into the mixing head, where they are quickly mixed together. The operating pressure in the high-pressure machine can be 1000 to 29000psi or higher (6.9 to 200MPa or higher), although some low-pressure machines can be operated at significantly lower pressures. Then the resulting curable epoxy resin composition is preferably passed through a static mixing device to provide further additional mixing, and then transferred to the mold cavity. The static mixing device can be designed into the mold. This has the advantage of allowing the static mixing device to be easily opened for cleaning.

[0117] In certain specific embodiments, as just described, the alkyl-substituted aromatic epoxy resin and the di-alicyclic amine hardener are mixed by pumping them into a mixing head under pressure. Impact mixing can be used. The operating pressure of the alkyl-substituted aromatic epoxy resin and the di-alicyclic amine hardener stream entering can be a slightly lower value (e.g., about 1 to about 6.9 MPa) or a high value (such as 6.9 to 200 MPa). The resulting curable epoxy resin composition is then introduced into the mold at a slightly lower operating pressure (such as up to 5 MPa or up to about 1.035 MPa). In this embodiment, the curable epoxy resin composition is usually passed through a static mixer and then enters the mold. Some or all of the pressure drop between the mixing head and the mold injection port usually occurs through this static mixer. A preferred device for carrying out this process is a reaction injection molding machine, such as a device commonly used for processing large polyurethane and polyurea molded products.

[0118] In other embodiments, the curable epoxy resin composition is mixed as previously described and then sprayed into the mold.The temperature in the spraying zone is maintained so that the temperature of the heat-curable epoxy resin composition is maintained as previously described.

[0119] The mold is typically a metal mold, but it may also be a ceramic or polymer composite material, as long as the mold can withstand the pressure and temperature conditions of the molding process. The mold includes one or more inlets in fluid communication with the mixer, through which the reactive mixture is introduced. The mold may include vents to allow gas to escape when the curable epoxy resin composition is injected.

[0120] The mould is usually held in a press or other device which allows the mould to be opened and closed and pressure may be applied to the mould to hold it closed during the filling and curing operations. The mould or press is provided with means which may provide heating or cooling.

[0121] In some embodiments of the aforementioned method, after the curable epoxy resin composition is introduced into the mold, the molded composite material is demoulded in no more than 200 minutes, preferably 150 to 180 minutes, more preferably 100 to 150 minutes. In this method, the introduced curable epoxy resin composition flows around and between the reinforcing fibers and fills the mold, and then solidifies in the mold, preferably within 90 minutes after the reactive mixture is introduced into the mold, more preferably within 30 to 60 minutes to form a polymer with a glass transition temperature of at least 300°C.

[0122] The method of the present invention can be used to manufacture a variety of composite materials, including various types of aerospace and automotive parts. Examples of aerospace parts include those described above, while automotive parts include vertical and horizontal body panels, automobile and truck chassis components, and so-called "body in white" structural components.

[0123] In other embodiments, the curable epoxy resin composition may be used as a coating to form a resin-coated substrate, as an adhesive to bond one or more similar or dissimilar substrates together, or as an encapsulant to encapsulate an electronic component.

[0124] Example

[0125] Table 1 below describes the cure onset of various curable resin systems measured by differential scanning calorimetry (DSC) according to ASTM E2160 and the glass transition temperature measured by dynamic mechanical analysis (DMA) according to ASTM D5418. Comparative Examples 1 to 7 are combinations of alkyl-substituted aromatic epoxy resins with different types of amine hardeners. Inventive Examples 1 and 2 are combinations of alkyl-substituted aromatic epoxy resins with dicycloaliphatic amine hardeners. In Table 1, the content of epoxy resin and amine in the composition is expressed as weight percentage based on the total weight of the composition. The results of the comparative examples show that these curable epoxy resin compositions cannot achieve improved high glass transition temperatures when cured using conventional curing temperatures.

[0126] Table 1

[0127]

[0128]

[0129]

[0130] MY 722: N,N,N′,N′-tetraglycidyl-4,4′-diamino-diethyldiphenylmethane

[0131] 2954: 4,4'-Methylenebis(2-methylcyclohexylamine)

[0132] DAPI: 5(6)-amino-3-(4'-aminophenyl)-1,1,3-trimethylindane

[0133] 4,4'-DDS: 4,4'-diaminodiphenyl sulfone

[0134] MCDEA: 4,4'-methylenebis(3-chloro-2,6-diethylaniline)

[0135] M-MIPA: 4,4'-methylenebis(2-isopropyl-6-methylaniline)

[0136] 5200: Low viscosity non-MDA based liquid aromatic diamine

[0137] Although the various embodiments of making and using the present invention have been described in detail above, it should be understood that the present invention provides many applicable inventive concepts that can be implemented in a variety of specific situations. The specific embodiments discussed herein are only illustrations of specific modes of making and using the present invention, and do not limit the scope of the present invention.

Claims

1. A curable epoxy resin composition comprising: (a) Alkyl-substituted aromatic epoxy resins of the general formula (I): in - R and R1 are each independently methyl, ethyl or isopropyl, - R2 and R3 are each independently hydrogen, methyl, ethyl or isopropyl, -X is -O-, -S-, -CO-, -C(=O)O-, -NHCO-, -SO2-, linear or branched alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted aromatic residue, or substituted or unsubstituted heterocycle; and (b) Bis-alicyclic amine hardener of general formula (II): in - R4 and R5 are each independently hydrogen, methyl, ethyl or isopropyl, - R6 and R7 are each independently hydrogen, methyl, ethyl or isopropyl, -Y is -O-, -S-, -CO-, -C(=O)O-, -NHCO-, -SO2-, linear or branched alkyl, or substituted or unsubstituted cycloalkyl.

2. The curable epoxy resin composition according to claim 1, wherein R and R1 of the alkyl-substituted aromatic epoxy resin of general formula (I) are each independently methyl, ethyl or isopropyl, R2 and R3 are each independently hydrogen, methyl, ethyl or isopropyl, and X is -O-, -S-, -CO-, -C(=O)O-, -NHCO-, -SO2-, a linear or branched alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aromatic residue or a substituted or unsubstituted heterocycle.

3. The curable epoxy resin composition according to claim 1, wherein R and R1 of the alkyl-substituted aromatic epoxy resin of general formula (I) are each independently methyl, ethyl or isopropyl, R2 and R3 are each independently hydrogen, methyl, ethyl or isopropyl, and X is a linear or branched alkyl group having 1 to 6 carbon atoms.

4. The curable epoxy resin composition according to claim 1, wherein R and R1 of the alkyl-substituted aromatic epoxy resin of general formula (I) are each independently methyl, ethyl or isopropyl, R2 and R3 are each independently hydrogen, methyl, ethyl or isopropyl, and X is -CH2-.

5. The curable epoxy resin composition according to claim 1, wherein R and R1 of the alkyl-substituted aromatic epoxy resin of formula (I) are each ethyl, R2 and R3 are each hydrogen, and X is -CH2-.

6. The curable epoxy resin composition according to claim 1, wherein R4 and R5 of the dialicyclic amine hardener of general formula (II) are each independently hydrogen, methyl, ethyl or isopropyl, R6 and R7 are each independently hydrogen, methyl, ethyl or isopropyl, and Y is -O-, -S-, -CO-, -C(=O)O-, -NHCO-, -SO2-, a linear or branched alkyl group having 1 to 6 carbon atoms, or a substituted or unsubstituted cycloalkyl group.

7. The curable epoxy resin composition according to claim 1, wherein R4 and R5 of the bis-alicyclic amine hardener of formula (II) are each independently hydrogen, methyl, ethyl or isopropyl, R6 and R7 are each independently hydrogen, methyl, ethyl or isopropyl, and Y is a linear or branched alkyl group having 1 to 6 carbon atoms.

8. The curable epoxy resin composition according to claim 1, wherein R4 and R5 of the bis-alicyclic amine hardener of general formula (II) are each independently hydrogen, methyl, ethyl or isopropyl, R6 and R7 are each independently hydrogen, methyl, ethyl or isopropyl, and Y is -CH2-.

9. The curable epoxy resin composition according to claim 1, wherein R4 and R5 of the bis-alicyclic amine hardener of formula (II) are each independently hydrogen, methyl or ethyl, R6 and R7 are each hydrogen, and Y is -CH2-.

10. The curable epoxy resin composition according to claim 1, wherein the curable epoxy resin composition comprises: - from about 5 wt % to about 95 wt %, preferably from about 10 wt % to about 90 wt %, and more preferably from about 15 wt % to about 85 wt % of an alkyl-substituted aromatic epoxy resin of formula (I) according to claim 1, based on the total weight of the epoxy resin composition, and - About 5 wt % to about 95 wt %, preferably about 10 wt % to about 90 wt %, and more preferably about 15 wt % to about 85 wt % of the bis-alicyclic amine hardener of formula (II) according to claim 1, based on the total weight of the epoxy resin composition.

11. The curable epoxy resin composition according to claim 1, wherein the curable epoxy resin composition comprises: - from about 40% to about 80% by weight, preferably from about 50% to about 80% by weight, and more preferably from about 60% to about 80% by weight, of an alkyl-substituted aromatic epoxy resin of formula (I) according to claim 1, based on the total weight of the epoxy resin composition, and - About 20 wt % to about 60 wt %, preferably about 20 wt % to about 50 wt %, and more preferably about 20 wt % to about 40 wt % of the bis-alicyclic amine hardener of formula (II) according to claim 1, based on the total weight of the epoxy resin composition.

12. The curable epoxy resin composition of claim 1, wherein the curable epoxy resin composition exhibits a degree of cure of about 80% or more after being cured at a temperature of about 130°C to about 190°C.

13. A method of forming a fiber reinforced epoxy composite material comprising: a) mixing an alkyl-substituted aromatic epoxy resin and a bis-cycloaliphatic amine hardener to form a curable epoxy resin composition; b) transferring the resulting curable epoxy resin composition into a mold containing reinforcing fibers; c) curing the epoxy resin composition obtained in the mold at a conventional curing temperature to form a fiber-reinforced composite material, wherein the reinforcing fibers are embedded in a polymer matrix formed by curing the epoxy resin composition obtained; and d) demoulding the fiber-reinforced composite material.

14. A fiber-reinforced composite material produced according to the method of claim 13.

Images