Epoxy resin curing agent, epoxy resin composition and cured product thereof, fiber-reinforced composite material, and blade for wind turbine

Abstract

The present invention aims to provide an epoxy resin curing agent comprising component (a1): polyether polyamine, component (a2): aliphatic polyamine having an alicyclic structure, and component (a3): aliphatic polyamine having an aromatic ring; and to provide an epoxy resin composition and its cured product, a fiber-reinforced composite material comprising the epoxy resin composition and reinforcing fibers, and a wind turbine blade.

Description

Technical Field

[0001] This invention relates to an epoxy resin curing agent, an epoxy resin composition and its cured form, a fiber-reinforced composite material comprising the epoxy resin composition and reinforcing fibers, and a wind turbine blade comprising the fiber-reinforced composite material. Prior Technology

[0002] Fiber-reinforced plastics (FRP) possess very high elastic modulus and strength, thus attracting attention as a metal alternative. Demand for FRP, particularly in automotive structural materials, wind turbine blades, pressure vessels, and aerospace applications, is expected to accelerate. The demand for reinforcing fibers and matrix resins such as epoxy resins used in FRP has also been increasing in recent years.

[0003] Furthermore, the molding methods for FRP differ depending on its application in automotive structural materials, wind turbine blades, pressure vessels, and aerospace. Consequently, the required properties of the matrix resin for FRP also vary depending on the application. For example, wind turbine blades are formed by injection molding, Va-RTM (vacuum-assisted resin transfer molding), or Light-RTM (light resin transfer molding). These methods involve, for instance, pre-positioning reinforcing fibers within a mold consisting of an upper and lower mold made of a thin film or FRP, evacuating the mold, filling it with an epoxy resin composition that forms the matrix resin at atmospheric pressure, impregnating the reinforcing fibers, and then allowing the epoxy resin to harden to form the blade. In molding processes using injection molding, Va-RTM, and Light-RTM, the process of filling an epoxy resin composition (obtained by mixing epoxy resin and epoxy resin hardener) into a mold typically takes several tens of minutes. Therefore, the epoxy resin composition used in these molding methods requires a long pot life.

[0004] It is also known that epoxy resin compositions used in wind turbine blades employ isophorone diamine, polyamine compounds with a polyether backbone, and other epoxy resin curing agents. For example, Patent Document 1 discloses an epoxy resin composition for vacuum-guided wind turbine blades that has low viscosity and high processing performance, comprising an epoxy resin with a predetermined composition and an epoxy resin composition containing, respectively, a polyetheramine curing agent D230, isophorone diamine IPDA and a tertiary amine accelerator K54 within predetermined ranges.

[0005] Furthermore, Patent Document 2 discloses an admixture containing an epoxy resin component and a curing agent; the epoxy resin component contains, within a predetermined range, one or more epoxy resins selected from the group of aromatic epoxy resins and / or cyclic aliphatic epoxy resins, cyclic carbonates having 1 to 10 carbon atoms, and one or more predetermined reactive diluents; the curing agent contains, within a predetermined range, one or more polyalkoxy polyamines, one or more other amines selected from the group of aromatic polyamines having at least 4 reactive NH functional groups within the primary and / or secondary amines having at least 3 carbon atoms, aryl aliphatic polyamines, cyclic aliphatic polyamines, heterocyclic polyamines, and aliphatic polyamines, and a predetermined catalyst; the ratio of the amine equivalent in the curing agent to the total amount of epoxy resin and cyclic carbonate in the epoxy resin component falls within a specific range. It also states that: In order to manufacture large fiber-reinforced components, especially rotor blades for wind power generation, the blend has sufficient flowability for the Va-RTM process, and the blend can be fully hardened in a short time and meets mechanical requirements (such as high tensile strength, elongation at break, flexural strength, and thermal stability required when using large fiber-reinforced components). [Previous Technical Documents] [Patent Literature]

[0006] [Patent Document 1] Chinese Invention Patent Application Publication No. 104151780 [Patent Document 2] Japanese Patent Publication No. 2015-511264 Summary of the Invention

[0007] [The problem that the invention aims to solve]

[0008] As mentioned above, epoxy resin compositions used in molding processes such as Va-RTM require a long pot life. Furthermore, for epoxy resin compositions used as the matrix resin in FRP, it is also important to obtain FRPs with high elasticity. Furthermore, for wind turbine blades used at sea, excellent salt water resistance is also desired. However, the technologies disclosed in Patent Documents 1 and 2 cannot meet all these required characteristics.

[0009] The objective of this invention is to provide an epoxy resin curing agent that provides an epoxy resin composition with a long pot life and suitable for forming highly elastic and salt-resistant wind turbine blades using methods such as Va-RTM; and to provide the epoxy resin composition and its cured form, a fiber-reinforced composite material comprising the cured form of the epoxy resin composition and reinforcing fibers, and a wind turbine blade. [Methods for solving problems]

[0010] The inventors have discovered that the above-mentioned problems can be solved by using an epoxy resin curing agent containing polyether polyamine, aliphatic polyamine having an alicyclic structure, and aliphatic polyamine having an aromatic ring. That is, the present invention relates to the following. [1] An epoxy resin curing agent comprising component (a1): polyether polyamine, component (a2): aliphatic polyamine having an alicyclic structure, and component (a3): aliphatic polyamine having an aromatic ring. [2] An epoxy resin composition comprising an epoxy resin and an epoxy resin curing agent as described in [1] above. [3] A cured epoxy resin composition is a cured epoxy resin composition as described in [2] above. [4] A fiber-reinforced composite material comprising a hardened epoxy resin composition as described in [3] above, and reinforcing fibers. [5] A wind turbine blade comprising the fiber-reinforced composite material as described in [4] above. [Effects of the Invention]

[0011] The epoxy resin curing agent of the present invention provides an epoxy resin composition with a long pot life and suitable for forming wind turbine blades using methods such as Va-RTM. Wind turbine blades obtained using this epoxy resin composition exhibit high elasticity and excellent salt water resistance. Implementation

[0012] [Epoxy Resin Hardener] The epoxy resin curing agent of the present invention contains polyether polyamine (a1), aliphatic polyamine having an alicyclic structure (a2), and aliphatic polyamine having an aromatic ring (a3). With the epoxy resin curing agent of the present invention having the above-described composition, it is possible to provide an epoxy resin composition that has a long service life and is suitable for forming highly elastic wind turbine blades with excellent salt water resistance using methods such as Va-RTM.

[0013] The reason why the epoxy resin hardener of the present invention achieves the above-mentioned effect is not yet clear, but it is speculated as follows. Polyether polyamine (a1) (hereinafter also referred to as "component (a1)") is a low-viscosity curing agent component that can achieve a long pot life. On the other hand, it tends to have a slow curing speed and a low curing Tg of the resulting epoxy resin composition, which leads to production problems such as difficulty in curing unless under high temperature conditions. Aliphatic polyamines (a2) with an alicyclic structure (hereinafter also referred to as "component (a2)") are also curing agents that can achieve a long service life. Compared with polyether polyamines (a1), component (a2) tends to have higher viscosity, which will increase the Tg of the cured epoxy resin composition and make it easier to achieve high elasticity. Furthermore, it is believed that the epoxy resin curing agent of the present invention, by containing an aliphatic polyamine (a3) ​​with an aromatic ring (hereinafter also referred to as "component (a3)"), suppresses the excessive reduction in curing speed caused by components (a1) and (a2) which can achieve a long service life, and by improving the crystallinity of the structure derived from component (a3), it can impart a salt water resistance improvement effect that cannot be achieved by components (a1) and (a2) alone.

[0014] <Ingredient (a1): Polyether polyamine> The epoxy resin curing agent of the present invention contains polyether polyamine as a component (a1). The polyether polyamine used in this invention, from the viewpoint of fulfilling its function as a component of epoxy resin curing agent, is preferably a compound having a polyether structure and two or more amine groups containing at least one active hydrogen atom. Furthermore, "amine group containing active hydrogen atom" refers to an amine group having at least one hydrogen atom directly bonded to the nitrogen atom of the amine group. Regarding polyether polyamines, chain polyether polyamines and cyclic polyether polyamines can be listed. Considering the low viscosity suitable for molding using the Va-RTM method, as well as availability and economy, component (a1) is preferably a chain polyether polyamine.

[0015] Considering the low viscosity suitable for molding using the Va-RTM method and the long shelf life, component (a1) is preferably a chain-like polyether diamine. Component (a1) is even more preferably a polyoxyalkylene diamine represented by the following general formula (1). H₂N-(R₁O)ₙR₂-NH₂(1) In formula (1), R1 is an alkyl group having 2 to 6 carbon atoms. n is the average number of repetitions of the (R1O) unit, and is a number greater than 1. Multiple R1s may be all the same or different. R2 is a divalent group having 2 to 12 carbon atoms.

[0016] In formula (1), R1 is preferably an alkyl group having 2 to 4 carbon atoms, more preferably an alkyl group having 2 to 3 carbon atoms. Specific examples of R1 include ethyl, propyl, trimethylene, tetramethylene, butyl, isobutyl, pentamethyl, hexamethylene, etc.; preferably selected from one or more of the group consisting of ethyl, propyl, trimethylene, tetramethylene, butyl, and isobutyl; more preferably selected from one or more of the group consisting of ethyl, propyl, and trimethylene; even more preferably selected from one or more of the group consisting of ethyl and propyl; and still more preferably propyl.

[0017] In equation (1), n ​​is the average number of repetitions of (R 1O) units. Considering the low viscosity suitable for molding using the Va-RTM method and the long service life, it is preferably 1.5~100, more preferably 1.5~50, even more preferably 2~30, even more preferably 2~20, even more preferably 2~10, and even more ideally 2~6.

[0018] In formula (1), R2 is preferably a divalent chain aliphatic group with 2 to 12 carbon atoms, more preferably 2 to 8 carbon atoms, and even more preferably 2 to 4 carbon atoms. Specific examples of R2 include ethyl, propyl, trimethylene, tetramethylene, butyl, isobutyl, pentamethylene, hexamethylene, heptamethylene, octamethylene, ethylhexyl, nonamethylene, decamethylene, undecamethylene, and dodecamethylene. Of these, R2 is preferably selected from one or more of the group consisting of ethyl, propyl, trimethylene, tetramethylene, butyl, isobutyl, pentamethyl, hexamethylene, heptamethyl, octamethyl and ethylhexyl; more preferably selected from one or more of the group consisting of ethyl, propyl, trimethylene, tetramethylene, butyl and isobutyl; even more preferably selected from one or more of the group consisting of ethyl, propyl and trimethylene; and still more preferably propyl.

[0019] Considering the viewpoints of having low viscosity suitable for molding using the Va-RTM method and achieving a long service life, component (a1) is preferably selected from one or more of the group consisting of polyoxyethylenediamine, polyoxypropylenediamine and polyoxyethylene ethyl-polyoxypropylenediamine; more preferably selected from one or more of the group consisting of polyoxypropylenediamine and polyoxyethylene ethyl-polyoxypropylenediamine; and even more preferably polyoxypropylenediamine. The average repeating number of oxyalkylene units in polyoxyethylenediamine, polyoxypropylenediamine, and polyoxyethylene ethyl-polyoxypropylenediamine is preferably 1.5 to 100, more preferably 1.5 to 50, even more preferably 2 to 30, even more preferably 2 to 20, even more preferably 2 to 10, and even more ideally 2 to 6, taking into account the viewpoints of having low viscosity suitable for molding by Va-RTM and achieving a long service life.

[0020] The component (a1) is even more preferably a polyoxyalkylene diamine represented by the following general formula (1-1). [Chemistry 1] In equation (1-1), n1, n2 and n3 are the average number of repetitions, n1+n3>1, and n2≧0. In formula (1-1), the sum of n1, n2 and n3 (n1+n2+n3) should be 1.5~100, more preferably 1.5~50, even more preferably 2~30, even more preferably 2~20, even more preferably 2~10, and even more ideally 2~6. In formula (1-1), n2 should preferably be 0~50, more preferably 0~30, even more preferably 0~20, and even more preferably 0.

[0021] The component (a1) is even more preferably polyoxypropylene diamine represented by the following general formula (1-2). [Chemistry 2] In equation (1-2), n is the average number of repetitions, which is a number greater than 1. In equation (1-2), considering the low viscosity suitable for molding using the Va-RTM method and the long service life, n is preferably 1.5~100, more preferably 1.5~50, even more preferably 2~30, even more preferably 2~20, even more preferably 2~10, and even more ideally 2~6.

[0022] Regarding the composition (a1), commercially available polyether polyamines can also be used. Examples of commercially available polyether polyamines include the JEFFAMINE D series (polyoxypropylene diamine, D-230, D-400, D-2000, D-4000) and the JEFFAMINE ED series (ED-600, ED-900, ED-2003) (all manufactured by HUNTSMAN).

[0023] <Component (a2): Aliphatic polyamine with an alicyclic structure> The epoxy resin curing agent of the present invention contains an aliphatic polyamine having an alicyclic structure as component (a2). Considering the goal of achieving a long service life, component (a2) is an aliphatic polyamine having an alicyclic structure and not containing an aromatic ring.

[0024] Component (a2) has at least one alicyclic structure, preferably one to three, more preferably one to two, and considering the low viscosity suitable for molding using the Va-RTM method, it is even more preferably only one.

[0025] Regarding the alicyclic structure of component (a2), examples include cycloalkane rings, cycloalkene rings, bicycloalkane rings, bicycloalkene rings, and tricycloalkane rings. Among these, cycloalkane rings are preferred, more preferably cycloalkane rings with 5 to 8 carbon atoms, and even more preferably cyclohexane rings.

[0026] Considering the need for a long service life and the need to obtain a hardened material with high Tg and high elasticity, component (a2) should preferably be an aliphatic polyamine having at least one amine group directly bonded to an alicyclic structure.

[0027] Considering the need to obtain a highly elastic hardened material, component (a2) should preferably be a diamine.

[0028] Specific examples of component (a2) include isophorone diamine, menthane diamine, norcamphene diamine, tricyclodecane diamine, adamantane diamine, 1,2-diaminocyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, 1,2-bis(aminomethyl)cyclohexane, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, 1,4-diamino-2-methylcyclohexane, 1,4-diamino-3,6-diethylcyclohexane, 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane (bis(4-amino-3-methylcyclohexyl)methane), 3,3',5,5'-tetramethyl-4,4'-diaminodicyclohexylmethane, 4,4'-diaminodicyclohexylmethane, etc., and one or more of these can be used. Of the above, considering the viewpoints of having low viscosity suitable for molding using the Va-RTM method, achieving a long pot life, and obtaining a hardened material with high Tg and high elasticity, component (a2) is preferably one or more selected from the group consisting of isophorone diamine, menthane diamine, norcamphene diamine, 1,2-diaminocyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, and 1,4-diamino-2-methylcyclohexane; more preferably one or more selected from the group consisting of isophorone diamine, menthane diamine, and norcamphene diamine; and even more preferably isophorone diamine.

[0029] <Ingredient (a3): Aliphatic polyamine with an aromatic ring> The epoxy resin curing agent of this invention contains an aliphatic polyamine with an aromatic ring as component (a3). Because component (a3) ​​has an aromatic ring, it imparts salt water resistance to the cured epoxy resin composition. Furthermore, component (a3) ​​is an aliphatic polyamine without amine groups directly bonded to the aromatic ring, thus easily achieving low viscosity suitable for molding using the Va-RTM method.

[0030] Component (a3) ​​has at least one aromatic ring, preferably one to three, more preferably one to two. Considering the low viscosity suitable for molding using the Va-RTM method, it is even more preferably to have only one.

[0031] Considering its low viscosity, suitable for molding using the Va-RTM method, component (a3) ​​is preferably a diamine. Component (a3) ​​is more preferably a diamine represented by the following general formula (2). [Chemistry 3] In formula (2), R11 and R12 are each independently an alkyl group having 1 to 6 carbon atoms.

[0032] In formula (2), R11 and R12 are each preferably alkyl groups having 1 to 4 carbon atoms, and more preferably alkyl groups having 1 to 3 carbon atoms. Specific examples of R11 and R12 include methylene, ethyl, propyl, trimethylene, tetramethylene, butyl, isobutyl, pentamethylene, hexamethylene, etc.; preferably one or more of the group consisting of ethyl, trimethylene, and tetramethylene; more preferably one or more of the group consisting of methylene, ethyl, and trimethylene; and even more preferably methylene.

[0033] Specific examples of component (a3) ​​include o-xylene diamine, m-xylene diamine (MXDA), p-xylene diamine (PXDA), 1,2-bis(aminoethyl)benzene, 1,3-bis(aminoethyl)benzene, 1,4-bis(aminoethyl)benzene, 1,2-bis(aminopropyl)benzene, 1,3-bis(aminopropyl)benzene, 1,4-bis(aminopropyl)benzene, etc., and one or more of these can be used. Of the above, considering the improvement of the salt water resistance of the cured epoxy resin composition, component (a3) ​​is preferably xylenediamine. Among xylenediamines, considering the improvement of the salt water resistance of the cured epoxy resin composition, it is preferable to select one or more from the group consisting of m-xylenediamine and p-xylenediamine. Considering the low viscosity suitable for molding using the Va-RTM method, it is preferable to use m-xylenediamine alone, or a mixture of m-xylenediamine and p-xylenediamine, and m-xylenediamine is even more preferable. When component (a3) ​​is a mixture of m-xylenediamine and p-xylenediamine, the mass ratio of m-xylenediamine to p-xylenediamine, considering both low viscosity and improved salt water resistance, is preferably 99 / 1 to 50 / 50, more preferably 99 / 1 to 60 / 40, and even more preferably 99 / 1 to 75 / 25.

[0034] Furthermore, at least a portion of the polyamines in components (a1) to (a3) ​​can also be modified for use. Examples of modifiers of the polyamines in components (a1) to (a3) ​​include Mannich modifiers, epoxy modifiers, Michael adducts, Michael adduct-polymers, styrene modifiers, and polyamide modifiers.

[0035] <Content> The content of components (a1) to (a3) ​​in the epoxy resin hardener of the present invention is, in view of providing an epoxy resin composition with a long service life and suitable for forming highly elastic and salt-resistant wind turbine blades using methods such as Va-RTM, as described below.

[0036] The content of component (a1) in the epoxy resin hardener is preferably 60-90% by mass, more preferably 65-85% by mass, and even more preferably 65-75% by mass. The content of component (a2) in the epoxy resin hardener is preferably 2-30% by mass, more preferably 5-25% by mass, and even more preferably 10-25% by mass. The content of component (a3) ​​in the epoxy resin hardener is preferably 1~25% by mass, more preferably 5~20% by mass, and even more preferably 5~15% by mass.

[0037] Furthermore, the ideal combination of the contents of components (a1) to (a3) ​​in the epoxy resin hardener is that the content of component (a1) is 60-90% by mass and the total content of components (a2) and (a3) ​​is 10-40% by mass; a more ideal combination is that the content of component (a1) is 65-85% by mass and the total content of components (a2) and (a3) ​​is 15-35% by mass; and an even more ideal combination is that the content of component (a1) is 65-75% by mass and the total content of components (a2) and (a3) ​​is 25-35% by mass.

[0038] The total content of components (a1) to (a3) ​​in the epoxy resin hardener is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and even less than 100% by mass.

[0039] The ratio of component (a3) ​​in the epoxy resin hardener to the total content of components (a2) and (a3), considering the improvement of the salt water resistance of the hardened epoxy resin composition, is expressed as a mass ratio [(a3) / {(a2)+(a3)}], preferably 0.15~0.70, more preferably 0.20~0.55, and even more preferably 0.25~0.45.

[0040] <Other Ingredients> The epoxy resin curing agent of the present invention may also contain conventional curing agents other than components (a1) to (a3). Regarding the hardeners other than components (a1) to (a3) ​​mentioned above, examples include polyamine compounds or their modified forms that have two or more amine groups within their molecules, other than components (a1) to (a3). Examples of such polyamine compounds include: chain-like aliphatic polyamine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexamethylenediamine, 2-methylpentamethylenediamine, and trimethylhexamethylenediamine; aromatic polyamine compounds such as phenylenediamine, diaminodiphenylmethane, diaminodiphenylmethane, and diethyltoluenediamine; and polyamine compounds with heterocyclic structures such as N-aminoethylpiperidine and N,N'-bis(aminoethyl)piperidine. Furthermore, regarding the modified forms of the polyamine compound, examples include Mannich modified forms, epoxy modified forms, Michael adducts, Michael adduct-polycondensates, styrene modified forms, and polyamide modified forms. These can be used individually or in combination of two or more.

[0041] From the viewpoint of effectively demonstrating the effects of the present invention, when the epoxy resin curing agent of the present invention contains curing agents other than components (a1) to (a3), the content of such curing agents relative to the total amount of the epoxy resin curing agent of the present invention is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, even more preferably 5% by mass or less, and even more preferably 1% by mass or less. Furthermore, the lower limit is 0% by mass.

[0042] [Epoxy Resin Composition] The epoxy resin composition of this invention contains epoxy resin and the aforementioned epoxy resin curing agent of this invention. In this specification, "epoxy resin" refers to the component used as the main agent in the epoxy resin composition.

[0043] <Epoxy Resin> Regarding epoxy resins, any epoxy resin containing glycidyl groups that can react with the active hydrogen in the epoxy resin curing agent of this invention can be used. From the viewpoint of obtaining a highly elastic cured product, epoxy resins containing aromatic rings or alicyclic structures within the molecule are preferable.

[0044] For epoxy resins containing an aromatic ring within the molecule, the resin is one containing at least one aromatic ring and at least two epoxy groups. The aforementioned aromatic ring can be a monocyclic or condensed ring, and examples include benzene rings, naphthalene rings, anthracene rings, and tetracene rings, but are not limited to these. Among these, benzene rings and naphthalene rings are preferred, and benzene rings are more preferred.

[0045] For ideal epoxy resins containing aromatic rings within their molecules, examples include: bisphenol A type epoxy resin, bisphenol E type epoxy resin, bisphenol F type epoxy resin, etc.; biphenol type epoxy resin; phenol-formaldehyde varnish type epoxy resin; resorcinol type epoxy resin, etc. Of the above, it is preferable to select one or more from the group consisting of bisphenol type epoxy resin and biphenol type epoxy resin. Considering the viewpoint of obtaining a highly elastic cured material, it is even more preferable to select an epoxy resin represented by the following general formula (3). [Chemistry 4] In formula (3), R31 to R34 are each independently an alkyl group with 1 to 6 carbon atoms, and p, q, r, and s are each independently an integer from 0 to 4. Multiple R31s, multiple R32s, multiple R33s, and multiple R34s may all be the same or different from each other. Y1 and Y2 are each independently a single bond, -CH2-, -CH(CH3)-, or -C(CH3)2-. R35 is -CH2CH(OH)- or -CH(OH)CH2-. m represents the average number of repeating units and is a number from 0 to 2.0. R 31 to R 34 are preferably alkyl groups having 1 to 4 carbon atoms, and are more preferably selected from one or more of the group consisting of methyl, ethyl, isopropyl and tributyl. It is better if p, q, r, and s are all integers between 0 and 2, even better if they are 0 or 1, and even better if they are all 0. Y1 and Y2 are preferably -CH2- or -C(CH3)2-, with -C(CH3)2- being even better. Furthermore, considering the viewpoint of obtaining a highly elastic hardened material, m is preferably 0~1.0, even better if it is 0.01~0.5, even better if it is 0.01~0.2, and even better if it is 0.01~0.15.

[0046] Of the above, the bisphenol A type epoxy resin represented by the following formula (3-1) is preferred. [Chemistry 5] In the above formula, R 35 and m are the same as before. Epoxy resin can be used alone or in combination with two or more types.

[0047] Considering the need for low-viscosity epoxy resin compositions suitable for molding using the Va-RTM method and for improved workability, epoxy resins can also contain more reactive diluents. Regarding reactive diluents, examples include low molecular weight compounds having at least one epoxy group, such as: aromatic monoepoxypropyl ethers like phenyl glycidyl ether and cresol glycidyl ether; alkyl monoepoxypropyl ethers like butyl glycidyl ether, hexyl glycidyl ether, octyl glycidyl ether, decyl glycidyl ether, lauryl glycidyl ether, and tetradecyl glycidyl ether; and diepoxypropyl ethers of aliphatic diols like 1,3-propanediol diepoxypropyl ether, 1,4-butanediol diepoxypropyl ether, neopentyl glycol diepoxypropyl ether, and 1,6-hexanediol diepoxypropyl ether. The above-mentioned reactive diluents can be used alone or in combination of two or more.

[0048] The epoxy equivalent of the epoxy resin, considering the low viscosity of the epoxy resin composition and the need to inhibit excessive reduction in curing speed, should preferably be 400 g / equivalent or less, more preferably 300 g / equivalent or less, even more preferably 250 g / equivalent or less, and still more preferably 220 g / equivalent or less. There is no particular limitation on the lower limit. When the epoxy resin contains bisphenol A type epoxy resin represented by the aforementioned formula (3-1), it is preferably 170 g / equivalent or more.

[0049] The viscosity of epoxy resin at 30°C, considering the viewpoint of obtaining a low-viscosity epoxy resin composition suitable for molding using the Va-RTM method, is preferably 20,000 mPa·s or less, more preferably 15,000 mPa·s or less, even more preferably 10,000 mPa·s or less, still more preferably 5,000 mPa·s or less, even more preferably 3,000 mPa·s or less, even more ideally 2,000 mPa·s or less, and even more suitablely 1,500 mPa·s or less. There is no particular limitation on the lower limit of the viscosity of epoxy resin at 30°C, and it is usually 5 mPa·s or more. The viscosity of epoxy resin can be measured using an E-type viscometer, specifically using the method described in the examples.

[0050] <Other Ingredients> The epoxy resin composition of the present invention may contain other components such as fillers, plasticizers and other modifying components, thixotropic agents and other flow modifiers, pigments, leveling agents, tackifiers, and elastomer microparticles, depending on the application.

[0051] <Content> The ratio of epoxy resin to epoxy resin curing agent in the epoxy resin composition of the present invention is the ratio of the number of active hydrogen atoms in the epoxy resin curing agent to the number of epoxy groups in the epoxy resin (number of active hydrogen atoms in the epoxy resin curing agent / number of epoxy groups in the epoxy resin), preferably 1 / 0.5 to 1 / 2, more preferably 1 / 0.75 to 1 / 1.5, and even more preferably 1 / 0.8 to 1 / 1.2. This ratio can ultimately be within the above range and can be kept constant during the molding of the epoxy resin composition, or it can be varied during molding.

[0052] In the epoxy resin composition, the total content of epoxy resin and epoxy resin hardener, from the viewpoint of achieving the effect of the present invention, is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and even less than 100% by mass.

[0053] Furthermore, considering the low viscosity suitable for molding using the Va-RTM method and the goal of achieving a long service life, it is preferable that the epoxy resin content in the epoxy resin composition is 65-85% by mass, the epoxy resin curing agent content is 15-35% by mass, and the total content of epoxy resin and epoxy resin curing agent in the epoxy resin composition is 80-100% by mass. More preferably, the epoxy resin content in the epoxy resin composition is 70-80% by mass, the epoxy resin curing agent content is 20-30% by mass, and the total content of epoxy resin and epoxy resin curing agent in the epoxy resin composition is 80-100% by mass.

[0054] <Viscosity> The viscosity of the epoxy resin composition of this invention at 30°C, considering the need for low viscosity suitable for molding using the Va-RTM method, is preferably 5,000 mPa·s or less, more preferably 3,000 mPa·s or less, even more preferably 2,000 mPa·s or less, still more preferably 1,000 mPa·s or less, still more preferably 800 mPa·s or less, and still most ideally 600 mPa·s or less. There is no particular limitation on the lower limit of the viscosity of the epoxy resin composition at 30°C, but it is generally 5 mPa·s or more. The viscosity of the epoxy resin composition can be measured using an E-type viscometer in the same way as the viscosity of the epoxy resin, specifically using the method described in the examples.

[0055] <Applicable Period> The epoxy resin composition of this invention has a long pot life. Specifically, at a temperature of 50°C, the time for the viscosity to reach 0.3 Pa·s is preferably 2500 seconds or more, more preferably 3000 seconds or more, and even more preferably 3200 seconds or more. The pot life of the epoxy resin composition can be determined specifically using the methods described in the examples.

[0056] <Preparation Method of Epoxy Resin Composition> There are no particular limitations on the preparation method of epoxy resin composition. Epoxy resin curing agent, epoxy resin, and other components as needed can be mixed and prepared using conventional methods and apparatus. There are also no particular limitations on the mixing order of the components contained in the epoxy resin composition. The epoxy resin curing agent can be prepared first and then mixed with the epoxy resin. Alternatively, the epoxy resin can be mixed simultaneously with components (a1) to (a3) ​​constituting the epoxy resin curing agent and other components. To avoid pre-gelation, it is advisable to bring all components of the epoxy resin composition into contact and mix them just before use. The mixing temperature should be appropriately adjusted according to the viscosity of the epoxy resin. To suppress viscosity increase, a temperature below 120°C is preferable, more preferably below 100°C. Considering the miscibility of the epoxy resin, a temperature above 30°C is preferable, more preferably above 50°C. Furthermore, the mixing time should preferably be between 0.1 and 15 minutes, more preferably between 0.2 and 10 minutes, and even more preferably between 0.5 and 5 minutes.

[0057] [Hardened material] The cured epoxy resin composition of the present invention (hereinafter also referred to as "the cured composition of the present invention") is obtained by curing the epoxy resin composition of the present invention using conventional methods. The curing conditions of the epoxy resin composition can be appropriately selected according to the application and form, and are not particularly limited. The form of the cured material of this invention is not particularly limited and can be selected according to the application. For example, when the epoxy resin composition is used as a coating, the cured material of the composition is usually in the form of a film. Furthermore, considering the viewpoint of effectively demonstrating the effects of this invention, the cured material of this invention is preferably the matrix resin of the fiber-reinforced composite material described later.

[0058] [Fiber-reinforced composite materials] The fiber-reinforced composite material (FRP, hereinafter also referred to as "composite material") of the present invention comprises a cured form of the aforementioned epoxy resin composition and reinforcing fibers. This fiber-reinforced composite material can be obtained by impregnating the aforementioned epoxy resin composition into the reinforcing fibers and then curing the composition.

[0059] <Reinforced Fibers> Examples of reinforcing fibers include glass fiber, carbon fiber, polyaramid fiber, boron fiber, and metal fiber. A single reinforcing fiber can be used alone, or two or more can be used in combination. Considering the application of the resulting composite material to wind turbine blades, it is preferable that the reinforcing fiber be selected from one or more fibers composed of glass fiber and carbon fiber. Carbon fiber can be manufactured from raw materials such as spunbond or polyacrylonitrile (PAN), or it can be manufactured by spinning from raw materials such as petroleum or coal pitch. In addition, it is also possible to use recycled carbon fiber obtained by reusing the surplus carbon fiber or recycled carbon fiber obtained by removing resin from carbon fiber reinforced composite (CFRP).

[0060] Regarding the morphology of reinforcing fibers, short fibers and continuous fibers can be listed, but considering the viewpoint of impregnating epoxy resin components and shaping composite materials using the Va-RTM method, continuous fibers are preferable. Furthermore, both continuous and short fibers can be used together. Examples of continuous fibers include: those simply formed by arranging monofilaments or multiple filaments in a unidirectional or intersecting manner; woven fabrics; nonwoven fabrics; or felts. Among these, monofilaments, fabrics, nonwoven fabrics, or felts are preferred, with fabrics being even more desirable.

[0061] The number of filaments in continuous fibers is usually in the range of 500 to 100,000, preferably 5,000 to 80,000, and more preferably 10,000 to 70,000.

[0062] The fineness of continuous fibers is preferably 20~4,500 tex, and even better if it is 50~4,000 tex. If the fineness is within this range, the impregnation system of the resin component is easy, and highly elastic composite materials can be easily obtained. Furthermore, the fineness can be obtained by calculating the weight of continuous fibers of any length and converting it to the weight per 1,000 m.

[0063] The average fiber diameter of the reinforcing fibers is preferably 1~100μm, more preferably 3~50μm, and even more preferably 4~20μm. When the average fiber diameter is within this range, the processing system is easy, and highly elastic composite materials can be easily obtained. Furthermore, the average fiber diameter of the reinforcing fiber is obtained by observing and measuring more than 50 randomly selected fibers using a scanning electron microscope (SEM) and calculating the average of the number of fibers.

[0064] In addition to the aforementioned epoxy resin components, hardened materials, and reinforcing fibers, fiber-reinforced composites may also include foamed materials. There are no particular limitations on the type of foamed material; examples include foamed materials composed of resins such as polyvinyl chloride resin, polyurethane resin, polystyrene resin, polyolefin resin, acrylic resin, phenolic resin, polymethacrylamide resin, and epoxy resin.

[0065] For fiber-reinforced composites, considering the goal of producing highly elastic composites, the fiber volume fraction (Vf) should ideally be 20% or higher, more preferably 30% or higher, and even more preferably 35% or higher. Furthermore, considering the formability, processability, and lightweight properties of the composite, it should ideally be 90% or lower, more preferably 80% or lower, even more preferably 70% or lower, and still even more preferably 60% or lower. The fiber volume content of the fiber-reinforced composite material is specifically obtained using the method described in the examples.

[0066] <Applications> The epoxy resin composition and fiber-reinforced composite of this invention are ideally suited for use in wind turbine blades. Furthermore, applications of the fiber-reinforced composite of this invention include automotive structural materials and building materials.

[0067] <Manufacturing Method of Fiber-Reinforced Composite Materials> There are no particular limitations on the manufacturing method of the fiber-reinforced composite material of the present invention. However, considering the viewpoint of avoiding the hardening of the epoxy resin composition during the manufacturing process, it is advisable to impregnate and harden the reinforcing fibers after mixing the epoxy resin hardener and epoxy resin just before molding. In particular, considering the viewpoint of manufacturing wind turbine blades made of fiber-reinforced composites, it is preferable to have a step in which the fiber-reinforced composite and the wind turbine blade are formed using the Va-RTM method. By using the epoxy resin curing agent and epoxy resin composition of the present invention, which have a long shelf life, and by manufacturing the composite using the Va-RTM method, wind turbine blades can be manufactured with good productivity.

[0068] The manufacture of composite materials using the Va-RTM method can be carried out, for example, through the following procedures. First, reinforcing fibers are placed in a pair of upper and lower molds and sealed to reduce pressure within the molds. Next, epoxy resin (the main component of the epoxy resin composition) and epoxy resin hardener are filled into separate tanks, conveyed to a mixer, and mixed. The epoxy resin composition prepared in this manner is then injected into the molds, impregnating the reinforcing fibers, and subsequently, the epoxy resin is cured.

[0069] In the above steps, the temperature at which the epoxy resin composition is injected into the mold or impregnated with the reinforcing fibers is preferably 30~120℃, more preferably 50~100℃. When the epoxy resin hardener and epoxy resin are supplied from separate tanks and mixed just before molding, the mixing temperature of the epoxy resin hardener and epoxy resin can also be set individually. The mixing temperature of the epoxy resin hardener, considering the need to suppress viscosity increase, is preferably 5~30℃, more preferably 10~25℃. Furthermore, the mixing temperature of the epoxy resin can be appropriately adjusted according to its viscosity, preferably 30~120℃, more preferably 50~100℃. These temperatures can be kept constant during molding or varied during molding. The impregnation time of the epoxy resin composition on the reinforcing fibers also varies depending on the shape of the fiber-reinforced composite material. However, considering the formability and productivity, it is advisable to use 10 to 120 minutes, and more preferably 10 to 60 minutes.

[0070] The curing temperature of the epoxy resin composition is preferably 50~200℃, more preferably 50~150℃, and even more preferably 50~120℃. The curing temperature can be kept constant or varied during molding. If the curing temperature is above 50℃, the epoxy resin will cure sufficiently; if it is below 200℃, the cost of adjusting the mold temperature can be reduced. The curing time of the epoxy resin composition can be appropriately selected according to the curing temperature, but considering moldability and productivity, it is preferably 0.5~24 hours, more preferably 1~18 hours.

[0071] Wind turbine blades Furthermore, the present invention provides a wind turbine blade comprising the aforementioned fiber-reinforced composite material. At least a portion of this wind turbine blade is constructed from a fiber-reinforced composite material comprising a hardened form of the aforementioned epoxy resin composition and reinforcing fibers, thus exhibiting high elasticity and excellent salt water resistance. When a portion of a wind turbine blade is constructed using the fiber-reinforced composite material of this invention, considering the need for salt water resistance, it is preferable that at least the outer surface of the wind turbine blade is constructed using the fiber-reinforced composite material. Alternatively, the wind turbine blade may also be constructed solely of the fiber-reinforced composite material of this invention. The wind turbine blade of the present invention can be formed, for example, using the Va-RTM method described in the manufacturing method of fiber-reinforced composite materials. Wind turbine blades can also be formed in a single process. Alternatively, they can be manufactured by forming two or more components made of fiber-reinforced composite materials and then bonding them together using adhesives. [Example]

[0072] The present invention is described in detail below with examples and comparative examples, but the present invention is not limited to the following examples. Furthermore, various measurements and evaluations are performed according to the following methods.

[0073] (Viscosity) The viscosity of the main component, epoxy resin, and epoxy resin components was measured at 30°C using a Type E viscometer, "TVE-22H type cone-plate viscometer" (manufactured by Toki Sangyo Co., Ltd.).

[0074] (Applicability period evaluation) The pot life of epoxy resin compositions is evaluated using the following methods. The viscosity of the epoxy resin composition was measured at 50°C using a rheometer (TA Instruments). Measurements were taken every 10 seconds, and the time taken for the viscosity to reach 0.3 Pa·s is shown in the table. A longer time to reach 0.3 Pa·s indicates a longer pot life.

[0075] (Fiber volume content in fiber-reinforced composites) The fiber volume content (Vf(%)) in fiber-reinforced composites is calculated using the following formula. Vf(%) = {Mass of reinforcing fiber (g) / Specific gravity of reinforcing fiber} ÷ [{Mass of reinforcing fiber (g) / Specific gravity of reinforcing fiber} + {Mass of solid components of impregnated epoxy resin composition (g) / Specific gravity of solid components of epoxy resin composition}] × 100

[0076] (Flexural strength and flexural modulus of fiber-reinforced composites) The fiber-reinforced composites obtained in the following examples were machined to produce test pieces of 80mm × 15mm × 2mm thickness, which were then used in the measurements. Using Autograph (manufactured by Shimadzu Corporation), in accordance with ISO 178, a bending test was conducted at room temperature (23°C) and a test speed of 5 mm / min to determine the bending strength and bending modulus.

[0077] (Retention rate of flexural strength after salt spray test) The fiber-reinforced composite test pieces used for flexural strength testing were placed in a salt spray tester (SUGA Testing Equipment Co., Ltd. "STP-90", tank temperature 35°C) and continuously sprayed with salt water (5% by mass) for one month. Next, the test pieces were dried at 60°C for 15 hours, and the flexural strength was measured using the same method as described above. Let the flexural strength before the salt spray test be A (MPa) and the flexural strength after the salt spray test be B (MPa), and the flexural strength retention rate be calculated using the following formula. A high flexural strength retention rate indicates excellent salt water resistance. Flexural strength retention rate (%) after salt spray test = B / A × 100

[0078] Examples 1-5 and Comparative Examples 1-3 (Preparation of epoxy resin curing agent and epoxy resin composition) The polyoxypropylene diamine (JEFFAMINE D-230, manufactured by HUNTSMAN) of component (a1), isophorone diamine (IPDA, manufactured by EVONIK) of component (a2), and xylene diamine (MXDA, manufactured by Mitsubishi Gas Chemical Co., Ltd.) of component (a3) ​​were blended and mixed in the proportions shown in the table to obtain an epoxy resin hardener. Furthermore, the epoxy resin curing agent and the bisphenol A type liquid epoxy resin "jER811" (manufactured by Mitsubishi Chemical Co., Ltd.) as the main agent are blended and mixed so that the ratio of the number of active hydrogens in the epoxy resin curing agent to the number of epoxy groups in the epoxy resin as the main agent (number of active hydrogens in the epoxy resin curing agent / number of epoxy groups in the epoxy resin) is 1 / 1, thereby preparing an epoxy resin composition.

[0079] (Manufacturing of fiber-reinforced composite materials) The prepared epoxy resin composition was impregnated into a 16cm × 16cm plain woven glass cloth (Yarn bundle "ERW320-554A", Central Glass Fiber (ply), 0.3mm thick) using Va-RTM molding at room temperature to create a prepreg. The prepreg was then thermocureed in a 60°C hot air dryer for 15 hours to produce a 2mm thick glass fiber reinforced composite. The volume fraction (Vf) of the glass fiber in this composite is shown in the table.

[0080] The epoxy resin compositions and composites obtained by the above method were evaluated using the same method. The results are shown in Table 1. Furthermore, the amount of each component listed in the table is the amount of the effective component. Furthermore, in this embodiment, if the pot life of the epoxy resin composition is 3200 seconds or more, and the flexural strength retention rate of the fiber-reinforced composite material after the salt spray test is 92% or more, it is determined that it can balance long pot life and salt water resistance.

[0081] [Table 1] Comparative example Example Example Example Example Comparative example Comparative example Example 1 1 2 3 4 2 3 5 Epoxy resin composition Main component: epoxy resin type jER811 jER811 jER811 jER811 jER811 jER811 jER811 jER811 Epoxy equivalent (g / equivalent) 186 186 186 186 186 186 186 186 Viscosity / mPa·s (30℃) 1100 1100 1100 1100 1100 1100 1100 1100 Blending amount (g) 77.7 78.0 78.2 78.5 78.7 79.2 76.3 76.6 hardener Composition (mass %) (a1)JEFFAMINE D-230 70 70 70 70 70 70 90 90 (a2)IPDA 30 25 20 15 10 0 10 5 (a3)MXDA 0 5 10 15 20 30 0 5 Mass ratio [(a3) / {(a2)+(a3)}] 0 0.17 0.33 0.5 0.67 1 0 0.5 Blending amount (g) 22.3 22.0 21.8 21.5 21.3 20.8 23.7 23.4 Number of active hydrogen atoms in the curing agent / Number of epoxy groups in the epoxy resin 1 / 1 1 / 1 1 / 1 1 / 1 1 / 1 1 / 1 1 / 1 1 / 1 Viscosity of epoxy resin composition / mPa·s (30℃) 530 - - - - 430 - - Total content (mass%) of main component epoxy resin + hardener 100 100 100 100 100 100 100 100 Evaluation results Applicable period Time (seconds) to reach 0.3 Pa·s (50℃) 3348 3324 3450 3318 3270 3072 4020 4152 Composite materials Reinforced Fibers type GF GF GF GF GF GF GF GF Fiber volume content Vf (%) 39 39 39 39 39 39 39 39 Evaluation results Bending strength (MPa) 392 435 428 398 397 402 452 422 Flexural modulus (GPa) 14 15 15 16 15 16 17 16 Flexural strength retention rate (%) after salt spray test 87.1 93.7 97.9 97.2 95.3 98.5 90.3 94.2

[0082] The ingredients used in the table are as follows. <Main component: epoxy resin> ･jER811: Bisphenol A type liquid epoxy resin "jER811", manufactured by Mitsubishi Chemical Co., Ltd., epoxy equivalent: 186g / equivalent, viscosity at 30°C: 1100mPa·s <Epoxy Resin Hardener Ingredients> (a1) JEFFAMINE D-230: Polyoxypropylene diamine "JEFFAMINE D-230" represented by the following general formula, manufactured by HUNTSMAN, where n=2.5 [Chemistry 6] (a2) IPDA: Isophorone diamine, manufactured by EVONIK ･(a3)MXDA: m-xylenediamine, manufactured by Mitsubishi Gas Chemical Co., Ltd. <Reinforced Fibers> •GF: Plain woven glass cloth, yarn bundle fabric "ERW320-554A", CENTRAL GLASS FIBER (ply) construction, unit weight: 320g / m², silane-based treatment, thickness 0.3mm

[0083] As shown in Table 1, the epoxy resin composition containing the epoxy resin hardener of the present invention has a long pot life. Furthermore, when the cured product of this epoxy resin composition is used as a fiber-reinforced composite material with a matrix resin, it exhibits higher elasticity and superior salt water resistance compared to Comparative Example 1. In contrast, the comparative examples of the present invention are the result of either a poor service life of the epoxy resin composition or poor salt water resistance of the fiber-reinforced composite material in which the cured epoxy resin composition is used as the matrix resin. [Industrial applicability]

[0084] The epoxy resin curing agent of the present invention provides an epoxy resin composition with a long pot life and suitable for forming wind turbine blades using methods such as Va-RTM. Wind turbine blades obtained using this epoxy resin composition exhibit high elasticity and excellent salt water resistance.

Claims

1. An epoxy resin curing agent comprising component (a1): polyether polyamine, component (a2): aliphatic polyamine having an alicyclic structure, and component (a3): aliphatic polyamine having an aromatic ring; wherein component (a3) ​​is xylenediamine, the content of component (a1) in the epoxy resin curing agent is 60-90% by mass, the total content of component (a2) and component (a3) ​​is 10-40% by mass, and the ratio of the content of component (a3) ​​in the epoxy resin curing agent to the total content of component (a2) and component (a3) ​​is expressed as a mass ratio [(a3) / {(a2)+(a3)}] which is 0.20-0.

55.

2. The epoxy resin hardener as claimed in claim 1, wherein, The component (a1) is polyoxypropylene diamine.

3. The epoxy resin hardener as requested in item 1 or 2, wherein, The component (a2) is isophorone diamine.

4. An epoxy resin composition comprising an epoxy resin and an epoxy resin curing agent as claimed in any one of claims 1 to 3.

5. The epoxy resin composition as claimed in claim 4, wherein, The epoxy resin content in the epoxy resin composition is 65-85% by mass, and the epoxy resin curing agent content is 15-35% by mass; the total content of the epoxy resin and the epoxy resin curing agent in the epoxy resin composition is 80-100% by mass.

6. A cured epoxy resin composition, which is a cured epoxy resin composition as claimed in any one of claims 4 or 5.

7. A fiber-reinforced composite material comprising a cured form of an epoxy resin composition as claimed in claim 6, and reinforcing fibers.

8. As in claim 7, the fiber-reinforced composite material, wherein, The reinforcing fiber is selected from one or more types of glass fiber and carbon fiber.

9. A wind turbine blade comprising a fiber-reinforced composite material as claimed in claim 7 or 8.