Curable epoxy resin composition having a high glass transition point

Abstract

The present invention relates to a curable epoxy resin composition comprising an alkyl-substituted aromatic epoxy resin and a bisalicyclic amine curing agent, which curable epoxy resin composition exhibits favorable chemical and physical characteristics when cured. The present invention relates to the use of such a curable resin composition that can be cured in the presence of reinforcing fibers to form fiber-reinforced composites used in various applications such as transportation applications (including aerospace vehicles, aircraft, ships, and land vehicles, as well as the automotive industry, railway industry, heavy vehicle industry, and military industry), construction / construction applications, or other commercial applications, and also relates to aerospace structural parts made from such fiber-reinforced composites.

Description

Technical Field

[0001] Cross - reference to related applications This application claims priority to U.S. Provisional Application No. 63 / 356,135, filed Jun. 28, 2023. The application(s) is / are incorporated herein by reference.

[0002] Field of the invention The present invention is directed to a curable epoxy resin composition comprising an alkyl-substituted aromatic epoxy resin and a bisalicyclic amine curing agent, which, upon curing, exhibits favorable chemical and physical characteristics. Specifically, the cured epoxy resin composition of the present invention exhibits a high glass transition temperature. The present invention relates to the use of such curable resin compositions that can be cured in the presence of reinforcing fibers to form fiber-reinforced composites for use in a variety of applications such as transportation applications (including aerospace vehicles, aircraft, ships, and land vehicles, as well as the automotive, railroad, heavy vehicle, and military industries), construction / construction applications, or other commercial applications, and to aerospace structural components made from such fiber-reinforced composites.

Background Art

[0003] Curable resin compositions containing epoxy resins are used in many processes to form structural composites. In particular, curable resin compositions containing aromatic epoxy and amine components that achieve a high glass transition temperature are used to form structural composites that can withstand deformation and loss of mechanical properties in high-temperature applications. Structural composites used in high-temperature applications can include primary and secondary aerospace structural materials (such as wings, fuselages, bulkheads, flaps, ailerons, cowls, fairings, interiors, etc.), rocket motor cases, and structural composites for satellites. Examples of automotive structural composites include vertical and horizontal body panels (such as fenders, door skins, hoods, roof skins, deck lids, tailgates, and the like), as well as automotive and truck chassis members.

[0004] To form a structural composite, such compositions can be used in molding processes including those known as resin transfer molding (RTM), vacuum assisted resin transfer molding (VARTM), Seeman composite resin infusion molding process (SCRIMP), reaction injection molding (RIM) process, and liquid compression molding (LCM). In each of these processes, the curable resin composition is applied to a reinforcing agent and cured in the presence of the reinforcing agent. Thereafter, a composite having a continuous polymer phase (formed from the cured resin) in which the reinforcing agent is dispersed is formed.

[0005] By using the various processes described above, a wide range of products can be produced. For example, by using molding processes (such as RTM, VARTM, SCRIMP, RIM, and LCM), high-strength parts useful in, for example, automotive and aircraft components can be produced. In the RTM process, the VARTM process, and the SCRIMP process, a woven fiber preform or a mat fiber preform is inserted into a mold cavity, the mold is closed, resin is injected into the mold, and the resin is cured to form a part. In the RIM process, a woven fiber preform or a mat fiber preform can be inserted into the mold in advance as described above, or can be injected into the mold together with the curable resin composition. In the LCM process, the reaction mixture is applied directly to a fiber preform or a fiber laminate by spraying or coating the reaction mixture as a "band" of the system supplied through a wide slit die having a width of 1 cm to 50 cm or more without injection.

[0006] Although this is also true for many other manufacturing processes, the economics of such composite manufacturing processes are highly dependent on the utilization rate. For molding processes, the utilization rate is often expressed in terms of "cycle time". Cycle time refers to the time required to produce composite parts in a mold and to prepare the mold for making the composite parts. Cycle time directly affects the number of composite parts that can be made in a mold per unit time. As the cycle time increases, the overhead costs per part produced (especially equipment and labor) increase, resulting in an increase in manufacturing costs. For these reasons, it is often desirable to shorten the cycle time.

[0007] When a curable composition having a high glass transition point is used in the above molding process, the dominant factor in the cycle time is the time required for the resin to cure. To cure a resin composition containing aromatic epoxy and amine components (also called amine curing agents) that achieve a glass transition point above 200°C, it is well known to use a high curing temperature in the range of 180°C to 220°C. Furthermore, to achieve the targeted high glass transition point, post-curing treatment at a temperature higher than the curing temperature is often required after curing such a type of resin composition.

[0008] Furthermore, in the case of such resin compositions containing aromatic epoxy and amine curing agents, an increase in the glass transition is often achieved when both the epoxy and the curing agent contain more aromatic molecular structures (in contrast to aliphatic). Patent Document 1, Patent Document 2, and Patent Document 3 describe different combinations of aromatic epoxy resins and aromatic amine components, and the curing temperatures of these combinations range from 180°C to 220°C to achieve a glass transition point of 200°C to 280°C.

[0009] On the one hand, such resin compositions having a high glass transition point often require a long curing time, especially when higher temperatures are needed for post-curing treatment. Therefore, there is a need for a curable epoxy composition used for forming a structural composite that can withstand deformation and loss of mechanical properties in high-temperature applications, and can obtain its high glass transition point during its own molding process (i.e., without requiring an additional post-curing step).

[0010] Furthermore, structural composites for high-temperature applications such as engines and nacelle members including cowlings or thrust reversers, and the leading edges of wings or rockets, must maintain their properties under high thermal and mechanical stresses. Therefore, in order to safely operate at temperatures of 170 °C or higher using a structural composite made from a cured epoxy composition and avoid component breakage of the structural composite when exposed to high-temperature stresses and mechanical stresses, it is the goal for the cured epoxy composition to have a glass transition point of at least 300 °C.

[0011] To achieve a glass transition point of at least 300 °C, the curing temperature or post-curing temperature typically has to be at least 200 °C, and often has to be above 220 °C, so the curing time is longer than that of classical epoxy resins which are usually cured at 180 °C. In fact, it is widely known that it is difficult to achieve a glass transition point that is at least 100 °C higher than the maximum curing temperature or post-curing temperature. There is a further need for a curable epoxy composition having all of the above-described properties and achieving a high glass transition point using a conventional curing temperature (i.e., a curing temperature of 180 °C).

[0012] Furthermore, when performing a standard curing cycle using a liquid molding process such as the above-described VARTM, it is widely known that it is difficult to achieve a high glass transition temperature. Since the standard vacuum bag material used in VARTM is not suitable for a curing cycle that requires a high curing temperature above 200 or 220 °C, special process materials including a release film, a sealant tape, a breather, and a vacuum bag are required. Furthermore, the high curing temperature affects the thermal management in the mold, fibers, resin, and process materials. At a high curing temperature, it becomes impossible to appropriately release the heat generated during the curing process, resulting in heat generation or a change in the curing temperature required to achieve a cured epoxy composition having a high glass transition temperature. Such heat generation or heat management errors during the high curing temperature can lead to the rejection or non-conformance of the final part. There is a further need for a curable epoxy composition having all of the above-described properties that can achieve a high glass transition temperature when cured using a liquid molding process such as VARTM at a standard curing temperature of 180 °C.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

[0014] The present invention relates to (a) an alkyl-substituted aromatic epoxy resin of the general formula (I):

Chemical Formula

Chemical formula

[0015] When the above components are provided in the composition, upon curing, unexpectedly, a cured epoxy resin having a high glass transition temperature of at least 300 °C is given.

Mode for Carrying Out the Invention

[0016] As used herein, the term "comprising" and derivatives thereof are not intended to exclude the presence of any additional component, step, or procedure, whether or not it is disclosed herein. For the sake of avoiding any doubt, all compositions claimed herein through the use of the term "comprising" may include any additional additive, adjuvant, or compound, unless there is a contradictory description. In contrast, the term "consisting essentially of" as used herein excludes any other component, step, or procedure from the scope of any subsequent description, except for those that are not essential for practicability. The term "consisting of" when used excludes any component, step, or procedure not specifically described or enumerated. The term "or" refers to the listed members individually or in any combination, unless otherwise stated.

[0017] The articles "a" and "an" are used herein to refer to one or more (i.e., at least one) of the grammatical objects of the article. By way of example, "an epoxy" means one epoxy or more than one epoxy.

[0018] Phrases such as "in one embodiment", "according to one embodiment", and the like generally mean that the particular feature, structure, or property following such phrase is included in at least one embodiment of the present invention and may also be included in multiple embodiments of the present invention. Importantly, such phrases do not necessarily refer to the same embodiment.

[0019] When the present specification contains descriptions such as "may", "can", "could", or "might" that a component or feature may be included or have a characteristic, it is not necessary for that specific component or feature to be included or have that characteristic.

[0020] The present disclosure generally relates to novel epoxy resin compositions comprising an alkyl-substituted aromatic epoxy resin and a bisalicyclic amine curing agent, and structural composites obtained from such compositions. Surprisingly, certain combinations of an alkyl-substituted aromatic epoxy resin and a bisalicyclic amine curing agent have been found to provide an epoxy resin exhibiting an improved glass transition temperature (e.g., a glass transition temperature of at least about 300° C.) at conventional curing temperatures without substantial loss of toughness. By using such properties, a significantly improved composition according to the present invention can generally be defined. As used herein, the phrase “glass transition temperature” (abbreviated “Tg”) means the temperature at which the mechanical properties of a material (e.g., a cured resin) change abruptly due to internal movement of the polymer chains forming the material. As used herein, the term “curing agent” means a component that reacts with an epoxy resin to enable the epoxy composition to cure into a solid material (i.e., a cured epoxy composition). According to the present invention, the bisalicyclic amine curing agent is different from an amine catalyst, and such amine catalysts can also affect the curing of the epoxy composition, but can affect it by a different mechanism than the bisalicyclic amine curing agent.

[0021] According to certain embodiments, a particular combination of an alkyl-substituted bisaromatic glycidylamine and an (alkyl-substituted) biscyclohexylamine curing agent provides an epoxy resin composition for forming a cured epoxy resin exhibiting an improved glass transition temperature upon curing. As used herein, the term “improved glass transition temperature” is intended to refer to an increase in the glass transition temperature of a cured epoxy resin through the application of the present disclosure as compared to a conventional resin. Further, the terms “epoxy resin composition” or “curable epoxy resin composition” are intended to refer to an uncured composition that cures upon curing to become a “cured epoxy resin” or “cured product”. The term “curable” means that the composition can be subjected to conditions that render it in a cured state.

[0022] According to one embodiment, in the alkyl-substituted aromatic epoxy resin of general formula (I), 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-, a straight-chain or branched alkyl having 1 to 6 carbon atoms, a substituted or unsubstituted aromatic residue, or a substituted or unsubstituted heterocycle. Examples of straight-chain or branched alkyl 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-. Examples of substituted cycloalkyl include methylcyclopropane group, methylcyclopentane group, methylcyclohexane group, methylcyclopentene group, and methylcyclohexene group, preferably, methylcyclopropane group, methylcyclopentane group, and methylcyclohexane group. Examples of substituted or unsubstituted aromatic residues include methoxybenzyl group, methylbenzyl group, and fluorenyl group. Examples of substituted or unsubstituted heterocycles include furfuryl group, picolinyl group, pyrimidyl group, thienyl group, and indolyl group.

[0023] According to one embodiment, in the alkyl-substituted aromatic epoxy resin of general formula (I), R and R1 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 having 1 to 6 carbon atoms.

[0024] According to one embodiment, in the bisalicyclic amine curing agent of general formula (II), 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-, a linear or branched alkyl having 1 to 6 carbon atoms, or a substituted or unsubstituted cycloalkyl.

[0025] According to one embodiment, in the bisalicyclic amine curing agent of general formula (II), R4 and R5 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 having 1 to 6 carbon atoms.

[0026] According to one embodiment, the curable epoxy resin composition comprises (a) an alkyl-substituted aromatic epoxy resin of general formula (I), wherein R and R1 are each independently methyl, ethyl, or isopropyl, R2 and R3 are each independently hydrogen, methyl, ethyl, or isopropyl, X is a linear or branched alkyl having 1 to 6 carbon atoms, the alkyl-substituted aromatic epoxy resin, and (b) a bisalicyclic amine curing agent of general formula (II), wherein R4 and R5 are each, independently, hydrogen, methyl, ethyl, or isopropyl, R6 and R7 are each, independently, hydrogen, methyl, ethyl, or isopropyl, Y is a linear or branched alkyl having 1 to 6 carbon atoms, a bisalicyclic amine curing agent, and comprises.

[0027] In a preferred embodiment, in the alkyl-substituted aromatic epoxy resin of general formula (I), R and R1 are each, independently, methyl, ethyl, or isopropyl, R2 and R3 are each, independently, hydrogen, methyl, ethyl, or isopropyl, and X is -CH2-.

[0028] In a preferred embodiment, in the bisalicyclic amine curing agent of general formula (II), R4 and R5 are each, independently, hydrogen, methyl, ethyl, or isopropyl, R6 and R7 are each, independently, hydrogen, methyl, ethyl, or isopropyl, and Y is -CH2-.

[0029] Advantageously, the curable epoxy resin composition (a) an alkyl-substituted aromatic epoxy resin of general formula (I), wherein R and R1 are each, independently, methyl, ethyl, or isopropyl, R2 and R3 are each, independently, hydrogen, methyl, ethyl, or isopropyl, X is -CH2-, an alkyl-substituted aromatic epoxy resin, and (b) a bisalicyclic amine curing agent of general formula (II), wherein R4 and R5 are each, independently, hydrogen, methyl, ethyl, or isopropyl, R6 and R7 are each, independently, hydrogen, methyl, ethyl, or isopropyl, Y is -CH2-, a bisalicyclic amine curing agent, and comprises.

[0030] In another preferred embodiment, in the alkyl-substituted aromatic epoxy resin of general formula (I), R and R1 are each ethyl, R2 and R3 are each hydrogen, and X is -CH2-.

[0031] In another preferred embodiment, in the bisalicyclic amine curing agent of general formula (II), R4 and R5 are each independently hydrogen, methyl, or ethyl, R6 and R7 are each hydrogen, and Y is -CH2-.

[0032] More preferably, the curable epoxy resin composition (a) An alkyl-substituted aromatic epoxy resin of general formula (I), wherein R and R1 are each ethyl, R2 and R3 are each hydrogen, -X is -CH2-, and an alkyl-substituted aromatic epoxy resin, and (b) A bisalicyclic amine curing agent of general formula (II), wherein R4 and R5 are each hydrogen, methyl, or ethyl, R6 and R7 are each hydrogen, Y is -CH2-, and a bisalicyclic amine curing agent, and comprises.

[0033] For example, the alkyl-substituted aromatic epoxy resin of general formula (I) is N,N’,N’-tetraglycidyl-4,4’-diamino-3,3’-diethyldiphenylmethane. The CAS number is 130728-76-6. N,N,N’,N’-tetraglycidyl-4,4’-diamino-3,3’-diethyldiphenylmethane is commercially available from Huntsman Advanced Materials under the brand name Araldite®.

[0034] For example, the bisalicyclic amine curing agent of general formula (II) is 4,4'-methylenebis(2-methylcyclohexylamine). The CAS number is 6864-37-5. Another example of the bisalicyclic amine curing agent is 4,4'-methylenebis(cyclohexylamine). The CAS number is 1761-7-3. 4,4'-methylenebis(2-methylcyclohexylamine) is commercially available from Huntsman Advanced Materials under the brand name Aradur (registered trademark). 4,4'-methylenebis(cyclohexylamine) is commercially available from BASF under the brand name Dicykan (registered trademark).

[0035] In a preferred embodiment, the curable epoxy resin composition contains the alkyl-substituted aromatic epoxy resin of formula (I) above in an amount of about 5% to about 95% by weight, preferably about 10% to about 90% by weight, more preferably about 15% to about 85% by weight, based on the total weight of the epoxy resin composition. contains the bisalicyclic amine curing agent of formula (II) above in an amount of about 5% to about 95% by weight, preferably about 10% to about 90% by weight, more preferably about 15% to about 85% by weight, based on the total weight of the epoxy resin composition.

[0036] Advantageously, the curable epoxy resin composition contains the alkyl-substituted aromatic epoxy resin of formula (I) above in an amount of about 40% to about 80% by weight, preferably about 50% to about 80% by weight, more preferably about 60% to about 80% by weight, based on the total weight of the epoxy resin composition, and contains the bisalicyclic amine curing agent of formula (II) above in an amount of about 20% to about 60% by weight, preferably about 20% to about 50% by weight, more preferably about 20% to about 40% by weight, based on the total weight of the epoxy resin composition.

[0037] In one embodiment, the curable epoxy resin composition may optionally contain a catalyst, and such catalysts include imidazoles (such as 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole); tertiary amines (such as triethylamine, tripropylamine, N,N-dimethyl-1-phenylmethanamine, 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.

[0038] If desired, the curable epoxy resin composition may be optionally mixed prior to curing with one or more conventional additives such as stabilizers, reinforcing agents, extenders, fillers, reinforcing agents, pigments, dyes, plasticizers, tackifiers, accelerators, non-reactive diluents, or any mixture thereof. Stabilizers that can be used include phenothiazine itself or C-substituted phenothiazines having 1 to 3 substituents or N-substituted phenothiazines having 1 substituent (e.g., 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 quinine and catechol, copper naphthenate, zinc-dimethyldithiocarbonate, and phosphotungistic acid hydrate. Reinforcing agents, extenders, reinforcing agents, fillers, accelerators, and pigments that can be used include, for example: poly(ethersulfone), nylon, core-shell rubber, phenoxy, coal tar, bitumen, glass fiber, boron fiber, carbon fiber, cellulose, polyethylene powder, polypropylene powder, mica, asbestos, quartz powder, gypsum, antimony trioxide, bentone, silica aerogel ("aerosil"), lithopone, barite, titanium dioxide, eugenol, dicumyl peroxide, isoeugenol, carbon black, graphite, and iron powder. It is also possible to add other additives (e.g., flame retardants, flow control agents (such as silicone), cellulose acetate butyrate, polyvinyl butyrate, wax, stearate, and the like).

[0039] The present invention also relates to a process for forming a fiber-reinforced epoxy composite material, the process comprising a) mixing the above alkyl-substituted aromatic epoxy resin and the above bisalicyclic amine curing agent to form the curable epoxy resin composition of the present disclosure; b) transferring the resulting curable epoxy resin composition into a mold containing reinforcing fibers; c) Curing the obtained epoxy resin composition in a mold at a conventional curing temperature to form a fiber-reinforced composite material in which reinforcing fibers are embedded in a polymer matrix formed by curing the obtained epoxy resin composition; d) Demolding the fiber-reinforced composite material; comprises.

[0040] The polymer matrix is formed from the curable epoxy resin composition of the present disclosure by mixing an alkyl-substituted aromatic epoxy resin and a bisalicyclic amine curing agent in the aforementioned ratios and curing the resulting mixture. One or both of the components can be preheated, if desired, before mixing them with each other. The preheating step is often carried out to reduce the viscosity of the components and achieve complete mixing of both components in a short time. In general, it is necessary to heat the mixture to a high temperature to achieve rapid curing. In a molding process such as the process for making the molded composite material described below, the curable epoxy resin composition is introduced into a mold that can be preheated together with any reinforcing fibers and / or inserts contained within the mold. The curing temperature can be, for example, from about 90°C to about 190°C or from about 100°C to about 190°C or from about 110°C to about 190°C. In yet another embodiment, the curing temperature is controlled by the starting point of the reaction measured by differential scanning calorimetry (DSC). The starting point of the reaction is defined as the temperature at which a sufficient exothermic reaction occurs in the curable system, resulting in less heat being required to maintain the heat flow relative to the reference. This curing start temperature can be, for example, from about 130°C to about 190°C or, more preferably, from about 140°C to about 190°C. If the starting temperature exceeds 190°C, it is impossible to achieve rapid low-temperature curing, and if the temperature is below 120°C, it becomes impossible to take sufficient time to improve the quality and inject the components.

[0041] In one embodiment, it is preferred to continue curing until the resulting polymer matrix reaches a glass transition temperature above the curing temperature. Advantageously, the polymer matrix achieves a glass transition temperature of at least 300°C.

[0042] In another embodiment, the glass transition point at the time of release is preferably at least 130 °C, or at least 150 °C, or even at least 180 °C, or even at least 200 °C. An advantage of the present disclosure is that such a glass transition point can be obtained with a short curing time. This makes it possible to shorten the cycle time.

[0043] In one embodiment, the curable epoxy resin composition exhibits a degree of cure of about 85% or more when cured at the aforementioned temperature. In yet another embodiment, the curable epoxy resin composition exhibits a degree of cure of about 90% or more or 95% or more when cured at the aforementioned temperature. In yet another embodiment, it may be desirable to further cure the composite material at another stage (such as in a heating oven) after release to reach a degree of cure of over 90% or even over 95%.

[0044] As described above, the curable epoxy resin composition of the present disclosure is particularly useful in making fiber-reinforced composite materials by curing the system in the presence of reinforcing fibers. According to the present disclosure, such composites are generally made by mixing the above alkyl-substituted aromatic epoxy resin and the above bisalicyclic amine curing agent 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 the reinforcing fibers.

[0045] The reinforcing fibers are thermally stable and have a decomposition temperature such that the reinforcing fibers do not decompose or melt during the curing process. Suitable fiber materials may include, for example, glass, quartz, polyamide resin, aramid, boron, carbon, straw, hemp, sisal, cotton, bamboo, and gel-spun polyethylene fibers.

[0046] The reinforcing fibers can be provided in the form of short (0.5 - 15 cm) fibers, long (over 15 cm) fibers, or continuous rovings. The fibers can, if desired, be provided in the form of a mat or other preform, and such mats or preforms can, in some embodiments, be formed by entangling, weaving, and / or sewing the fibers, or can be formed by using an adhesive binder to bond the fibers together. The preform can be close to the size and shape of the final composite material (or a part thereof that requires reinforcement). Mats of continuous or chopped fibers can, if necessary, be laminated and typically compressed together using tackifiers to form preforms of various thicknesses.

[0047] Tackifiers suitable for the preparation of preforms include polymers that are softenable by heat (such as those described in U.S. Patent Nos. 4,992,228, 5,080,851, and 5,698,318, etc.). The tackifier should be compatible and / or reactive with the polymer phase of the composite so that good adhesion between the polymer and the reinforcing fibers occurs. The tackifier can include other components (such as one or more catalysts, thermoplastic polymers, rubbers, or other modifiers).

[0048] On the surface of the fibers, sizing or other useful coatings can be applied before it is introduced into the mold. Sizing often promotes adhesion between the cured resin and the fiber surface.

[0049] The composite material can be formed in a mold. In such a case, the reinforcing fibers can be introduced into the mold before the introduction of the curable epoxy resin composition. This is often done when fiber preforms are used. The fiber preform is placed in the 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 voids, and then cures to form the composite material.

[0050] Alternatively, fibers (including preforms) can be placed into an open mold, and a curable epoxy resin composition can be sprayed, poured, or injected onto and into the preform and mold. After the mold is filled in this manner, the mold is closed and the epoxy resin composition is cured. An example of this type of process is gap compression resin transfer molding, in which the mold containing the fibers remains open and the gap can be, for example, 10% to 100% or more of the original hole thickness. The gap allows for a reduction in flow resistance, which facilitates filling of the mold and promotes penetration of the curable epoxy resin composition around and between the fibers.

[0051] Short fibers can be introduced into the mold together with the curable epoxy resin composition. Such short fibers can be blended, for example, with an alkyl-substituted aromatic epoxy resin or a bisalicyclic amine hardener (or both) prior to the formation of the curable epoxy resin composition. Alternatively, the short fibers can be added to the curable epoxy resin composition simultaneously with the mixing of the alkyl-substituted aromatic epoxy resin and the bisalicyclic amine hardener, or after mixing but before the curable epoxy resin composition is introduced into the mold.

[0052] Alternatively, the short fibers can be sprayed into the mold. In such a case, the curable epoxy resin composition can also be sprayed into the mold simultaneously with or after the spraying of the short fibers. If the fibers and the curable epoxy resin composition are sprayed simultaneously, they can be mixed together before spraying. Alternatively, the fibers and the curable epoxy resin composition can be sprayed into the mold separately but simultaneously. The sprayed materials can be spread and / or leveled using a doctor blade or similar device prior to closing and curing the mold. In a particularly targeted process, long fibers are chopped to reduce their length, and the chopped fibers are sprayed into the mold simultaneously with or immediately after the spraying of the curable epoxy resin composition. Mesh materials often function as flow promoters.

[0053] A wet compression process can be used, in which case the curable epoxy resin composition is applied directly to the fiber preform or fiber laminate by spraying or coating the curable epoxy resin composition as a "band" of the system that is supplied through a wide slit die having a width of 1 cm to 50 cm or more without injection. Sufficient material is applied to reach the desired fiber volume content in the final composite. The curable epoxy resin composition can be applied to the fibers inside or outside the open mold. Alternatively, after wetting the fiber layer with the curable epoxy resin composition, a second fiber layer is placed on the wet surface, and the curable epoxy resin composition can be applied to the intermediate layer of the stack by sandwiching a resin layer between the two fiber layers. The fiber mat can be made from a non-crimp fiber stack, a woven fabric, a random fiber stack, or a preform. When the curable epoxy resin composition is applied to the fibers outside the mold, the curable epoxy resin composition is typically applied at a somewhat lower temperature to prevent premature curing and maintain the viscosity of the curable epoxy resin composition so that it does not drip from the fibers before the fibers are transferred into the mold. Then, the wet preform is placed into the lower half of the hot mold, the mold is closed, and the material is cured under pressure.

[0054] The composite material made in accordance with the present disclosure can have a fiber content of at least 40 volume% or at least 50 volume%, up to 60 volume%, or even up to 70 volume%.

[0055] The mold can include one or more inserts in addition to the reinforcing fibers. Such inserts can function as a reinforcement, can function as a flow promoter, and in some cases can be present for lightweighting purposes. Examples of such inserts can be, for example, various polymer materials (such as polyethylene, polypropylene, another polyolefin, polyurethane, polystyrene, polyamide, polyimide, polyester, polyvinyl chloride, and the like), various types of composite materials, and the like that do not deform or decompose at the temperature to which they are exposed during the molding step, such as wood, plywood, metal, foam or non-foam.

[0056] The reinforcing fibers and core material (if present) can be encapsulated in a bag or film (such as those commonly used in vacuum-assisted processes).

[0057] The mold and preform (and any other inserts if present) can be heated to the curing temperature or some other useful elevated temperature before bringing them into contact with the reaction mixture. The mold surface can be treated with an external release agent that can be solvent or water-based.

[0058] Mixing the alkyl-substituted aromatic epoxy resin and bisalicyclic amine hardener of the curable epoxy resin composition, and the specific equipment used to transfer the composition into the mold is not considered essential to the present disclosure. The required condition is that the curable epoxy resin composition can be transferred into the mold before it reaches a high viscosity or generates a significant amount of gel. The process of the present disclosure is applicable to methods and equipment of RTM, VARTM, RFI, gap compression resin transfer molding, and SCRIMP processing (in some cases, equipment modified to meet the heating requirements at various stages of the process), as well as other methods such as wet compression.

[0059] The mixing device used for mixing the epoxy component and the hardening component (and any optional components that are mixed together at this point) can be of any type that can obtain a highly uniform reaction mixture. Various types of mechanical mixers and stirrers can be used. Preferred types of mixers are two types: static mixers and impingement mixers.

[0060] In some embodiments, the mixing and dispensing apparatus is an impingement mixer. This type of mixer is typically used in so-called reaction injection molding processes to form polyurethane and polyurea moldings. The alkyl-substituted aromatic epoxy resin and the bisalicyclic amine hardener (and other additives mixed at this point) are fed under pressure into a mixing head where they are rapidly mixed together. The operating pressure in high-pressure machines can range from 1,000 to 29,000 psi or more (6.9 to 200 Mpa or more), although low-pressure machines can operate at significantly lower pressures. The resulting curable epoxy resin composition is then preferably passed through a static mixing device for further additional mixing and then transferred into the mold cavity. The static mixing device can be designed to be integrated into the mold. This has the advantage of allowing the static mixing device to be easily opened for cleaning.

[0061] In certain embodiments, the alkyl-substituted aromatic epoxy resin and the bisalicyclic amine hardener are mixed as described above by feeding them under pressure into the mixing head. Impingement mixing can be used. The operating pressures of the incoming alkyl-substituted aromatic epoxy resin stream and the bisalicyclic amine hardener stream can range from somewhat low values (e.g., about 1 to about 6.9 MPa) or high values (e.g., 6.9 to 200 Mpa, etc.). The resulting curable epoxy resin composition is then introduced into the mold at somewhat low operating pressures (up to 5 MPa or up to about 1.035 Mpa, etc.). In such embodiments, the curable epoxy resin composition is typically passed through a static mixer before entering the mold. The pressure loss between the mixing head and the injection port into the mold often occurs, at least in part, through such a static mixer. One preferred apparatus for carrying out the process is a reaction injection molding machine (such as those commonly used for processing large polyurethane and polyurea moldings).

[0062] In other embodiments, the curable epoxy resin composition is sprayed into a mold after being mixed as described above. In the spray zone, the temperature is maintained so that the temperature of the hot curable epoxy resin composition is maintained as described above.

[0063] The mold is typically a metal mold, but can be a ceramic or polymer composite, and the requirements are whether the mold can withstand the pressure and temperature conditions of the molding process. The mold includes one or more inlets in liquid communication with the mixer(s) through which the reaction mixture is introduced. The mold may include an outlet for venting gas during injection of the curable epoxy resin composition.

[0064] The mold is typically held in a press or other device that allows it to be opened and closed and applies pressure to the mold to keep it closed during the filling and curing operations. The mold or press is provided with means capable of heating or cooling.

[0065] In some embodiments of the above-described process, the molded composite is demolded within 200 minutes, preferably within 150 - 180 minutes, more preferably within 100 - 150 minutes after the curable epoxy resin composition is introduced into the mold. In such a process, the curable epoxy resin composition introduced flows around and between the reinforcing fibers, fills the mold, and then cures in the mold to form a polymer having a glass transition temperature of at least 300 °C, preferably within 90 minutes, more preferably within 30 - 60 minutes after the reaction mixture is introduced into the mold.

[0066] The process of the present disclosure is useful in making a wide variety of composite materials, including various types of aerospace and automotive parts. Examples of aerospace parts include those described above, and for automobiles, it includes vertical and horizontal body panels, chassis members of automobiles and trucks, and so-called "body-in-white" structure members.

[0067] In other embodiments, the curable epoxy resin composition can be used as a coating for forming a resin-coated substrate, as an adhesive for bonding one or more similar or dissimilar substrates together, or as a sealant for encapsulating electronic components.

Examples

[0068] Table 1 below shows the cure start points of various curable resin systems measured by differential scanning calorimetry (DSC) according to ASTM E2160 and the glass transition points by dynamic mechanical analysis (DMA) according to ASTM D5418. Comparative Examples 1 to 7 are combinations of an alkyl-substituted aromatic epoxy resin and different types of amine curing agents. Inventive Examples 1 and 2 are combinations of an alkyl-substituted aromatic epoxy resin and a bisalicyclic amine curing agent. In Table 1, the epoxy content and amine content in the composition are represented as weight percentages based on the total weight of the composition. The results of the comparative examples demonstrate that these curable epoxy resin compositions do not achieve an improved high glass transition point when cured at conventional curing temperatures.

Table 1-1

Table 1-2

Table 1-3

Claims

1. (a) An alkyl-substituted aromatic epoxy resin of the general formula (I): 【Chemical 1】 and a bisalicyclic amine curing agent of the general formula (II): wherein R and R １ are each independently methyl, ethyl, or isopropyl, R ２ and R ３ are each, independently, hydrogen, methyl, ethyl, or isopropyl, X is O−, −S−, −CO−, −C(=O)O−, −NHCO−, −SO ２ −, linear or branched alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted aromatic residue, or substituted or unsubstituted heterocycle, the alkyl-substituted aromatic epoxy resin, and wherein the bisalicyclic amine curing agent is represented by the formula (II): [Chemical Formula 2] and a curable epoxy resin composition comprising the same. In the formula, R ４ and R ５ are each independently hydrogen, methyl, ethyl, or isopropyl, R ６ and R ７ are each, independently, hydrogen, methyl, ethyl, or isopropyl, Y is -O-, -S-, -CO-, -C(=O)O-, -NHCO-, -SO ２ -, a linear or branched alkyl, or a substituted or unsubstituted cycloalkyl, the bisalicyclic amine curing agent, and

2.

3. In the alkyl-substituted aromatic epoxy resin of the general formula (I), R and R １ are each independently methyl, ethyl, or isopropyl, R ２ and R ３ are each independently hydrogen, methyl, ethyl, or isopropyl, and X is —O—, —S—, —CO—, —C(═O)O—, —NHCO—, —SO ２ —, a linear or branched alkyl having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl, a substituted or unsubstituted aromatic residue, or a substituted or unsubstituted heterocycle. The curable epoxy resin composition according to claim 1.

4. In the alkyl-substituted aromatic epoxy resin of the general formula (I), R and R １ are each independently methyl, ethyl, or isopropyl, and R ２ and R ３ are each independently hydrogen, methyl, ethyl, or isopropyl, and X is a linear or branched alkyl having 1 to 6 carbon atoms. The curable epoxy resin composition according to claim 1.

5. In the alkyl-substituted aromatic epoxy resin of the general formula (I), R and R １ are each independently methyl, ethyl, or isopropyl, R ２ and R ３ are each independently hydrogen, methyl, ethyl, or isopropyl, and X is -CH ２ -, The curable epoxy resin composition according to claim 1.

6. In the alkyl-substituted aromatic epoxy resin of the general formula (I), R and R １ are each ethyl, R ２ and R ３ are each hydrogen, and X is -CH ２ -, the curable epoxy resin composition according to claim 1.

7. In the bisalicyclic amine curing agent of the general formula (II), R ４ and R ５ are each independently hydrogen, methyl, ethyl, or isopropyl, R ６ and R ７ are each independently hydrogen, methyl, ethyl, or isopropyl, and Y is —O—, —S—, —CO—, —C(═O)O—, —NHCO—, —SO ２ —, a linear or branched alkyl having 1 to 6 carbon atoms, or a substituted or unsubstituted cycloalkyl. The curable epoxy resin composition according to claim 1.

8. In the bisalicyclic amine curing agent of the general formula (II), R ４ and R ５ are each independently hydrogen, methyl, ethyl, or isopropyl, and R ６ and R ７ are each independently hydrogen, methyl, ethyl, or isopropyl, and Y is a linear or branched alkyl having 1 to 6 carbon atoms. The curable epoxy resin composition according to claim 1.

9. In the bisalicyclic amine curing agent of the general formula (II), R ４ and R ５ are each independently hydrogen, methyl, ethyl, or isopropyl, R ６ and R ７ are each independently hydrogen, methyl, ethyl, or isopropyl, and Y is -CH ２ -, The curable epoxy resin composition according to claim 1.

10. In the bisalicyclic amine curing agent of the general formula (II), R ４ and R ５ are each independently hydrogen, methyl, or ethyl, R ６ and R ７ are each hydrogen, and Y is -CH ２ -, The curable epoxy resin composition according to claim 1.

11. The curable epoxy resin composition according to claim 1, wherein the alkyl-substituted aromatic epoxy resin of formula (I) as claimed in claim 1 is contained in an amount of about 5% by weight to about 95% by weight, preferably about 10% by weight to about 90% by weight, more preferably about 15% by weight to about 85% by weight, based on the total weight of the epoxy resin composition; the bisalicyclic amine curing agent of formula (II) as claimed in claim 1 is contained in an amount of about 5% by weight to about 95% by weight, preferably about 10% by weight to about 90% by weight, more preferably about 15% by weight to about 85% by weight, based on the total weight of the epoxy resin composition.

12. The curable epoxy resin composition according to claim 1, wherein the alkyl-substituted aromatic epoxy resin of formula (I) as claimed in claim 1 is contained in an amount of about 40% by weight to about 80% by weight, preferably about 50% by weight to about 80% by weight, more preferably about 60% by weight to about 80% by weight, based on the total weight of the epoxy resin composition; the bisalicyclic amine curing agent of formula (II) as claimed in claim 1 is contained in an amount of about 20% by weight to about 60% by weight, preferably about 20% by weight to about 50% by weight, more preferably about 20% by weight to about 40% by weight, based on the total weight of the epoxy resin composition.

13. The curable epoxy resin composition according to claim 1, which exhibits a degree of cure of about 80% or more when cured at a temperature of about 130°C to about 190°C.

14. A process for forming a fiber-reinforced epoxy composite material, comprising: a) mixing an alkyl-substituted aromatic epoxy resin and a bisalicyclic amine curing agent to form a curable epoxy resin composition; b) transferring the obtained curable epoxy resin composition into a mold containing reinforcing fibers; c) curing the obtained epoxy resin composition in the mold at a conventional curing temperature to form a fiber-reinforced composite material in which the reinforcing fibers are embedded in a polymer matrix formed by curing the obtained epoxy resin composition; d) demolding the fiber-reinforced composite material.

15.

14. A fiber-reinforced composite material produced according to the method described in Claim 13.

Images