Epoxy resin curing agents, epoxy resin compositions and their cured products, and fiber-reinforced composite materials

Abstract

Provided are: an epoxy resin curing agent containing a compound (A) of at least one selected from the group consisting of N-aminoethylpiperazine and isophoronediamine, and a norbornadiamine (B); an epoxy resin composition containing the same; and a fiber-reinforced composite material including a cured product of the epoxy resin composition, and a reinforcing fiber.

Description

[Technical Field]

[0001] The present invention relates to an epoxy resin curing agent, an epoxy resin composition containing the epoxy resin curing agent and an epoxy resin, a cured product thereof, and a fiber-reinforced composite material containing the cured product of the epoxy resin composition and reinforcing fibers. [Background technology]

[0002] Among fiber-reinforced composite materials (hereinafter also called "FRP (Fiber Reinforced Plastics)"), carbon fiber reinforced plastics (CFRP) are attracting attention as a metal substitute material due to their extremely high modulus of elasticity, strength, and lightweight properties. Demand for CFRP is expected to accelerate, particularly in automotive structural materials, wind turbine blades, pressure vessels, and aerospace applications. Consequently, the demand for carbon fibers and matrix resins such as epoxy resins used in CFRP has also increased in recent years.

[0003] Incidentally, since the molding methods for FRP differ for automotive structural materials, wind turbine blades, pressure vessels, and aerospace applications, the required properties for the matrix resin used in FRP also differ depending on the application. For example, wind turbine blades are now being molded using infusion molding, Va-RTM (Vacuum Assist Resin Transfer Molding), or Light-RTM methods. In these methods, for example, reinforcing fibers are pre-placed in a mold consisting of an upper mold made of film or FRP and a lower mold. The mold is then vacuumed, and an epoxy resin composition, which will serve as the matrix resin, is filled at atmospheric pressure to impregnate the reinforcing fibers. Subsequently, the epoxy resin is cured to form the mold. In infusion molding, Va-RTM, and Light-RTM molding methods, due to the characteristics of these molding methods, it usually takes several tens of minutes to fill the mold with the epoxy resin composition, which is a mixture of epoxy resin and epoxy resin curing agent. Therefore, the epoxy resin composition used in these molding methods is required to have low viscosity and a long pot life. Isophorone diamine and polyamine compounds with a polyether skeleton are used as epoxy resin curing agents.

[0004] Furthermore, in the case of FRP used for pressure vessels, molding is performed using the filament winding method. The filament winding method involves covering the outer surface of a liner with reinforcing fiber yarns impregnated with a matrix resin such as an epoxy resin composition, and then curing the matrix resin. If the epoxy resin composition used in this method has a short pot life and is fast-curing, the epoxy resin will harden before molding. Therefore, fast-curing epoxy resin compositions cannot be used in the filament winding method.

[0005] In contrast, FRP used for automotive structural materials is molded using the high-cycle RTM method. This is an improvement over the conventional RTM method. Conventional RTM (Return to Molding) is a closed-mold molding method that uses a pair of upper and lower molds. In this method, a fiber-reinforced preform is placed inside the mold, the mold is clamped and sealed, and then a resin such as an epoxy resin composition is injected into the mold through an injection hole to impregnate the fiber-reinforced preform. After the resin hardens, the mold is demolded. However, conventional RTM requires several hours for molding (from preform placement to resin impregnation, resin hardening, and demolding), so the more productive high-cycle RTM method is used in the production of FRP for automotive structural materials.

[0006] The high-cycle RTM molding technology significantly reduces the placement time of the fiber-reinforced preform, the resin impregnation time, the resin curing time, and the demolding time. In the high-cycle RTM method, in the process from resin impregnation to curing, for example, in the high-pressure RTM method, which is a type of high-cycle RTM method, reinforcing fibers are placed in a pair of upper and lower molds and sealed, and the inside of the mold is depressurized. Next, the epoxy resin, which is the main component of the epoxy resin composition, and the epoxy resin curing agent are pumped in a mist state from separate tanks to a mixing head, and after collision mixing, are quickly injected into the mold to impregnate the reinforcing fibers and cure the epoxy resin. The epoxy resin composition after collision mixing is injected at high pressure from multiple injection holes to increase the filling speed into the mold and the impregnation speed into the reinforcing fibers.

[0007] It is known that N-aminoethylpiperazine (AEP), isophoronediamine (IPDA), or mixtures thereof are commonly used as epoxy resin curing agents in epoxy resin compositions for conventional RTM methods (see, for example, Patent Document 1 and Non-Patent Document 1). [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Special Publication No. 9-507262 [Non-patent literature]

[0009] [Non-Patent Document 1] Ogawa, "On RIM Molding Centered on Epoxy Resins," Thermosetting Resins, 1986, Vol. 7, No. 2, pp. 87-99. [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] In an epoxy resin curing agent used for molding by a high-cycle RTM method or the like, and an epoxy resin composition containing the curing agent and an epoxy resin, it is desired that the composition has low viscosity, rapid curing properties, a long pot life, and a high glass transition temperature (Tg) of the cured product and good heat resistance. When the Tg of the cured product is high, it is possible to release the mold without cooling it to a low temperature after molding by a high-cycle RTM method or the like, which is also advantageous in terms of shortening the molding cycle.

[0011] However, although AEP has rapid curing properties and a low initial viscosity, it has a problem of a short pot life and a low Tg of the cured product of the obtained epoxy resin composition. Also, IPDA has a long pot life and a relatively high Tg of the cured product of the obtained epoxy resin composition, but has problems of a slow curing rate and a high initial viscosity. Even when these are mixed to improve the respective drawbacks of AEP and IPDA, sufficient satisfactory performance as an epoxy resin curing agent used for molding by a high-cycle RTM method or the like could not be obtained.

[0012] In the high-cycle RTM method, since the epoxy resin and the epoxy resin curing agent are mixed and then immediately injected into the mold, the pot life of the epoxy resin curing agent and the epoxy resin composition is not so highly regarded. On the other hand, from the viewpoint of productivity, it is important that the impregnation property into the reinforcing fiber and the filling rate into the mold are high, the curing is rapid, and the mold can be released in a short time after curing. Therefore, an epoxy resin composition having low viscosity, rapid curing properties, and a high Tg of the cured product is desired.

[0013] The problem of the present invention is to provide an epoxy resin curing agent that can provide an epoxy resin composition containing N-aminoethylpiperazine and / or isophoronediamine, which are widely used as an epoxy resin curing agent component, having low viscosity, rapid curing properties, and a high Tg of the cured product, an epoxy resin composition containing the same and its cured product, and a fiber-reinforced composite material including the cured product of the epoxy resin composition and a reinforcing fiber.

Means for Solving the Problems

[0014] The present inventors have found that the above problems can be solved by an epoxy resin curing agent containing at least one compound selected from the group consisting of N-aminoethylpiperazine and isophoronediamine and norbornanediamine. That is, the present invention relates to the following. [1] An epoxy resin curing agent containing at least one compound (A) selected from the group consisting of N-aminoethylpiperazine and isophoronediamine and norbornanediamine (B). [2] The epoxy resin curing agent according to [1] above, wherein the component (A) contains N-aminoethylpiperazine. [3] The epoxy resin curing agent according to [2] above, wherein the mass ratio of the component (A) to the component (B) satisfies 0.15 ≦ {(A) / [(A)+(B)]} < 1. [4] The epoxy resin curing agent according to any one of [1] to [3] above, wherein the total content of the component (A) and the component (B) is 50% by mass or more. [5] An epoxy resin composition containing the epoxy resin curing agent according to any one of [1] to [4] above and an epoxy resin. [6] A cured product of the epoxy resin composition according to [5] above. [7] A fiber reinforced composite material containing the cured product of the epoxy resin composition according to [6] above and a reinforcing fiber. [8] The fiber reinforced composite material according to [7] above, wherein the reinforcing fiber is a carbon fiber. [Effects of the Invention]

[0015] According to the present invention, while using N-aminoethylpiperazine or isophoronediamine which is generally used as an epoxy resin curing agent component as an epoxy resin curing agent, it is possible to provide an epoxy resin curing agent and an epoxy resin composition capable of producing CFRP for automotive structural materials and building materials with high productivity by a high cycle RTM method or the like. [Embodiments for Carrying out the Invention]

[0016] [Epoxy Resin Curing Agent] The epoxy resin curing agent of the present invention contains at least one compound (A) selected from the group consisting of N-aminoethylpiperazine (AEP) and isophoronediamine (IPDA) (hereinafter also referred to as "component (A)") and norbornanediamine (B) (NBDA, hereinafter also referred to as "component (B)"). The present invention has found that by incorporating norbornanediamine into an epoxy resin curing agent containing AEP and IPDA, which are commonly used as epoxy resin curing agent components, various properties derived from AEP and IPDA can be improved, resulting in a low viscosity and rapid curing of the resulting epoxy resin composition, and also improving the cured product Tg.

[0017] <Component (A): At least one compound selected from the group consisting of N-aminoethylpiperazine and isophoronediamine> The epoxy resin curing agent of the present invention contains, as component (A), at least one compound selected from the group consisting of N-aminoethylpiperazine (AEP) and isophoronediamine (IPDA). These compounds are widely used as epoxy resin curing agent components and offer excellent cost-effectiveness. As for the performance of epoxy resin curing agents, AEP has the advantage of low viscosity and rapid curing, and improves the toughness of the cured epoxy resin composition. IPDA, on the other hand, has the advantage of extending the pot life of the resulting epoxy resin composition and increasing the cured product Tg. Considering these characteristics, at least one compound selected from the group consisting of AEP and IPDA can be appropriately selected as component (A) used in the present invention, depending on the desired performance and application.

[0018] When used as an epoxy resin curing agent for molding by methods such as high-cycle RTM, component (A) is preferably N-aminoethylpiperazine because it has low viscosity and is fast-curing. Specifically, component (A) is preferably N-aminoethylpiperazine, or a mixture of N-aminoethylpiperazine and isophoronediamine, and more preferably N-aminoethylpiperazine.

[0019] If component (A) is a mixture of AEP and IPDA, there are no particular restrictions on the content ratio. For example, AEP and IPDA can be used in a mass ratio of 1 / 99 to 99 / 1, preferably 5 / 95 to 95 / 5. From the viewpoint of low viscosity and rapid curing properties of the resulting epoxy resin composition, the mass ratio of AEP to IPDA is more preferably 10 / 90 to 95 / 5, even more preferably 20 / 80 to 95 / 5, even more preferably 30 / 70 to 95 / 5, and even more preferably 40 / 60 to 95 / 5.

[0020] <Ingredient (B): Norbornanediamine> The epoxy resin curing agent of the present invention contains norbornanediamine as component (B). This makes it possible to achieve low viscosity and rapid curing properties in an epoxy resin composition containing an epoxy resin curing agent containing component (A), and to improve the cured product Tg. In the present invention, norbornanediamine can be 2,5-diaminomethylbicyclo[2.2.1]heptane, 2,6-diaminomethylbicyclo[2.2.1]heptane, or a mixture thereof. When a mixture of 2,5-diaminomethylbicyclo[2.2.1]heptane and 2,6-diaminomethylbicyclo[2.2.1]heptane is used, there are no particular restrictions on the mixing ratio, and it can be selected within any range.

[0021] The mass ratio of component (A) to component (B) in the epoxy resin curing agent of the present invention can be selected within any range such that the mass ratio (A) / [(A)+(B)] is greater than 0 and less than 1, depending on the desired performance and application. When component (A) contains N-aminoethylpiperazine, it is preferable that the mass ratio of component (A) to component (B) is 0.15 ≤ {(A) / [(A)+(B)]} < 1 from the viewpoint of low viscosity and rapid curing properties of the resulting epoxy resin composition, as well as improved cured product Tg. When component (A) contains AEP, if the mass ratio (A) / [(A)+(B)] is 0.15 or more and less than 1, compared to the case where the mass ratio (A) / [(A)+(B)] is 1, the resulting epoxy resin composition will have improved cured product Tg and a longer pot life while achieving rapid curing properties. When component (A) contains AEP, the mass ratio (A) / [(A)+(B)] is more preferably 0.20 or higher, even more preferably 0.30 or higher, even more preferably 0.40 or higher, even more preferably 0.50 or higher, and even more preferably 0.60 or higher, from the viewpoint of rapid curing and improved economic efficiency due to a high proportion of component (A). From the viewpoint of improving cured product Tg and obtaining a long pot life, it is preferably 0.99 or lower, more preferably 0.95 or lower, even more preferably 0.90 or lower, and even more preferably 0.85 or lower.

[0022] When component (A) is isophorone diamine, it is preferable that the mass ratio of component (A) to component (B) satisfies 0 < {(A) / [(A)+(B)]} ≤ 0.85 from the viewpoint of low viscosity and rapid curing of the resulting epoxy resin composition, as well as improved cured product Tg. When component (A) is IPDA, if the mass ratio (A) / [(A)+(B)] is greater than 0 and 0.85 or less, the curing speed and cured product Tg are improved without significantly reducing the pot life of the resulting epoxy resin composition compared to the case where the mass ratio (A) / [(A)+(B)] is 1. When component (A) is isophorone diamine, the mass ratio (A) / [(A)+(B)] is preferably 0.01 or higher, more preferably 0.05 or higher, even more preferably 0.10 or higher, and even more preferably 0.12 or higher, from the viewpoint of obtaining a long pot life and improving economic efficiency due to a high proportion of component (A). From the viewpoint of rapid curing of the resulting epoxy resin composition, improved cured product Tg, and release properties of the cured product when the epoxy resin composition is used as a molding material, it is more preferably 0.75 or lower, even more preferably 0.70 or lower, even more preferably 0.60 or lower, even more preferably 0.50 or lower, even more preferably 0.40 or lower, even more preferably 0.30 or lower, and even more preferably 0.25 or lower. Note that when both the gelation rate and Tg of the cured product of the epoxy resin composition are high, the release properties of the cured product are good.

[0023] The epoxy resin curing agent of the present invention may contain known curing agents other than components (A) and (B), as well as known curing accelerators, additives, solvents, etc. Other curing agents besides components (A) and (B) include polyamine compounds having two or more amino groups in the molecule, or modified versions thereof, other than components (A) and (B). Examples of such polyamine compounds include chain-like aliphatic polyamine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexamethylenediamine, 2-methylpentamethylenediamine, and trimethylhexamethylenediamine; aromatic ring-containing aliphatic polyamine compounds such as o-xylylenediamine, m-xylylenediamine, and p-xylylenediamine; mensendiamine, norbornanediamine, tricyclodecanediamine, adamantanediamine, diaminocyclohexane, 1,4-diamino-2-methylcyclohexane, 1,4-diamino-3,6-diethylcyclohexane, and diaminodi Examples include polyamine compounds having an alicyclic structure such as ethylmethylcyclohexane, 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane (bis(4-amino-3-methylcyclohexyl)methane), 3,3',5,5'-tetramethyl-4,4'-diaminodicyclohexylmethane, and 4,4'-diaminodicyclohexylmethane; aromatic polyamine compounds such as phenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, diethyltoluenediamine, and 2,2'-diethyl-4,4'-methylenedianiline; polyamine compounds having a heterocyclic structure such as N,N'-bis(aminoethyl)piperazine; and polyether polyamine compounds. Modified forms of these polyamine compounds include Mannich modified products, epoxy modified products, Michael adducts, Michael adduct-polycondensates, styrene modified products, and polyamide modified products of the above compounds. These can be used individually or in combination of two or more.

[0024] From the viewpoint of efficiently exhibiting the effects of the present invention, if the curing agent is included, its content is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, even more preferably 15% 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, relative to the total amount of the epoxy resin curing agent of the present invention. The lower limit is 0% by mass. For example, from the viewpoint of obtaining rapid curing properties, the content of 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane (bis(4-amino-3-methylcyclohexyl)methane) is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, even more preferably 15% 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, based on the total amount of the epoxy resin curing agent of the present invention.

[0025] Known curing accelerators include phenolic compounds such as bisphenol A and styrene-phenol and their salts; sulfonic acid compounds such as p-toluenesulfonic acid and methanesulfonic acid and their salts or esters; carboxylic acid compounds such as salicylic acid and benzoic acid and their salts; mercaptan-terminated polysulfide compounds; guanidine compounds; and alkanolamine compounds. These can be used individually or in combination of two or more. From the viewpoint of effectively exhibiting the effects of the present invention, if the curing accelerator is included, its content is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, even more preferably 15% by mass or less, even more preferably 10% by mass or less, even more preferably 5% by mass or less, even more preferably 1% by mass or less, and even more preferably 0.5% by mass or less, relative to the total amount of the epoxy resin curing agent of the present invention. The lower limit is 0% by mass. The content of the curing accelerator in the epoxy resin curing agent should ultimately fall within the above range, and the concentration of the curing accelerator may be appropriately varied during the preparation or use of the epoxy resin curing agent. For example, the blending ratio of the curing accelerator to the epoxy resin curing agent may be constant during the molding of the epoxy resin composition containing the curing agent, or it may be varied during molding by supplying the curing accelerator with a concentration gradient.

[0026] However, from the viewpoint of effectively exhibiting the effects of the present invention, the total content of component (A) and component (B) 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 85% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more, relative to the total amount of the epoxy resin curing agent of the present invention. The upper limit of the total content of component (A) and component (B) relative to the total amount of the epoxy resin curing agent of the present invention is 100% by mass.

[0027] The epoxy resin curing agent of the present invention preferably has a viscosity of 150 mPa·s or less, more preferably 100 mPa·s or less, and even more preferably 60 mPa·s or less at a temperature of 25°C. A viscosity of 150 mPa·s or less at 25°C facilitates mixing with epoxy resin, improving productivity when used in FRP applications. There is no particular lower limit to the viscosity of the epoxy resin curing agent at 25°C, but from the viewpoint of miscibility with epoxy resin, it is preferably 10 mPa·s or more. The viscosity of the epoxy resin curing agent can be measured using an E-type viscometer, specifically by the method described in the examples.

[0028] There are no particular limitations on the method for preparing the epoxy resin curing agent of the present invention, and it can be appropriately selected depending on the form of use, the equipment used, the type and proportion of the components to be blended, etc. For example, component (A), component (B), and other components to be blended as needed may be brought into contact and mixed simultaneously, or some of the components constituting the epoxy resin curing agent may be supplied and mixed while creating a concentration gradient. Furthermore, as will be described later, the epoxy resin composition may be prepared by simultaneously mixing each component contained in the epoxy resin curing agent with the epoxy resin.

[0029] [Epoxy resin composition] The epoxy resin composition of the present invention contains the epoxy resin curing agent and epoxy resin of the present invention. Any epoxy resin having a glycidyl group that reacts with the active amine hydrogen in the epoxy resin curing agent of the present invention can be used as the epoxy resin, but from the viewpoint of excellent mechanical strength of the cured product, it is preferable to use an epoxy resin that contains an aromatic ring or alicyclic structure in its molecule.

[0030] An epoxy resin containing an aromatic ring in its molecule can be any resin containing at least one aromatic ring and at least two epoxy groups. The aromatic ring may be a monoring or a fused ring, and examples include, but is not limited to, a benzene ring, a naphthalene ring, anthracene ring, and a tetracene ring. Among these, a benzene ring and a naphthalene ring are preferred, and a benzene ring is more preferred.

[0031] Preferred epoxy resins containing aromatic rings in their molecules include, for example, bisphenol-type epoxy resins such as bisphenol A-type epoxy resin, bisphenol E-type epoxy resin, and bisphenol F-type epoxy resin; biphenol-type epoxy resins; phenol novolac-type epoxy resins; and resorcinol-type epoxy resins. Among the above, at least one selected from the group consisting of bisphenol-type epoxy resins and biphenol-type epoxy resins is more preferred, and from the viewpoint of low viscosity and ensuring the mechanical strength of the cured product, the epoxy resin represented by the following general formula (1) is even more preferred. [Chemical formula] (In formula (1), R 1 ~R 4 are each independently an alkyl group having 1 to 6 carbon atoms, and p, q, r, and s are each independently an integer of 0 to 4. A plurality of R 1 , a plurality of R 2 , a plurality of R 3 , and a plurality of R 4 may all be the same or different from each other. Y 1 and Y 2 are each independently a single bond, -CH2-, -CH(CH3)-, or -C(CH3)2-. R 5 is -CH2CH(OH)- or -CH(OH)CH2-. m represents the average number of repeating units and is a number from 0 to 0.2.) R 1 ~R 4 is preferably an alkyl group having 1 to 4 carbon atoms, and at least one selected from the group consisting of a methyl group, an ethyl group, an isopropyl group, and a t-butyl group is more preferable.) p, q, r, and s are preferably all integers of 0 to 2, more preferably 0 or 1, and even more preferably all 0.) Y 1 and Y 2 are preferably -CH2- or -C(CH3)2-, and more preferably -C(CH3)2-.) Also, from the viewpoint of ensuring low viscosity and mechanical strength of the cured product, m is preferably from 0 to 0.15, and more preferably from 0.01 to 0.1.)

[0032] Among the above, more preferably, it is a bisphenol A type epoxy resin represented by the following formula (1-1). [Chemical formula] In the above formula, R 5 and m are the same as described above.)

[0033] An epoxy resin containing an alicyclic structure within its molecule can be any resin containing at least one alicyclic structure and at least two epoxy groups. The number of carbon atoms in the ring member of the alicyclic structure is preferably 5 to 20, more preferably 5 to 12, even more preferably 5 to 10, even more preferably 5 to 8, and even more preferably 6. The alicyclic structure may be saturated or unsaturated, and may be monocyclic or polycyclic. The alicyclic structure may also have substituents. Examples of substituents include alkyl groups having 1 to 8 carbon atoms, hydroxyl groups, and alkoxy groups having 1 to 8 carbon atoms. Examples of such alicyclic structures include, but are not limited to, cycloalkane rings, cycloalkene rings, bicycloalkane rings, bicycloalkene rings, and tricycloalkane rings. Among these, cycloalkane rings are preferred, more preferably cycloalkane rings having 5 to 8 carbon atoms, and even more preferably cyclohexane rings.

[0034] From the viewpoint of weather resistance of the cured product, among epoxy resins containing an alicyclic structure in the molecule, it is preferable to use an epoxy resin that contains an alicyclic structure but does not contain an aromatic ring.

[0035] Preferred epoxy resins containing an alicyclic structure within the molecule include, for example, epoxy resins obtained by the reaction of epichlorohydrin with at least one selected from the group consisting of polyols having an alicyclic structure, polyamines having an alicyclic structure, and compounds having an alicyclic structure and having both a hydroxyl group and an amino group. Examples of polyols having an alicyclic structure include dihydroxycyclohexane, bicyclohexanediol, 2,2-bis(4-hydroxycyclohexyl)propane, and bis(4-hydroxycyclohexyl)methane. Examples of polyamines having an alicyclic structure include bis(aminomethyl)cyclohexane and diaminodicyclohexylmethane. Examples of compounds having an alicyclic structure and containing both a hydroxyl group and an amino group include aminocyclohexanol.

[0036] Furthermore, hydrogenated epoxy resins obtained by hydrogenating epoxy resins containing the aforementioned aromatic rings are also preferred.

[0037] From the viewpoint of low viscosity, rapid curing, mechanical strength and weather resistance of the cured product, and availability, epoxy resins containing an alicyclic structure in the molecule are more preferably those represented by the following general formula (2). [ka] (In formula (2), R 11 ~R 14 Each of these is an alkyl group having 1 to 6 carbon atoms, and each of t, u, v, and w is an integer from 0 to 4. 11 , multiple R 12 , multiple R 13 , and multiple R 14 They may all be the same, or they may be different from one another. 3 and Y 4 Each of these is independently a single bond, -CH2-, -CH(CH3)-, or -C(CH3)2-. 15 (This is -CH2CH(OH)- or -CH(OH)CH2-. n represents the average number of repeating units, a number between 0 and 0.2.) R 11 ~R 14 It is preferably an alkyl group having 1 to 4 carbon atoms, and more preferably at least one selected from the group consisting of a methyl group, an ethyl group, an isopropyl group, and a t-butyl group. t, u, v, and w are preferably integers between 0 and 2, more preferably 0 or 1, and even more preferably all 0. Y 3 and Y 4 It is preferably -CH2- or -C(CH3)2-, and more preferably -C(CH3)2-. Furthermore, from the viewpoint of achieving low viscosity and ensuring the mechanical strength of the cured product, n is preferably 0 to 0.15, and more preferably 0.01 to 0.1.

[0038] The epoxy resin represented by the general formula (2) may be obtained by the reaction of a polyol having an alicyclic structure with epichlorohydrin, or it may be a hydrogenated epoxy resin obtained by hydrogenating the epoxy resin represented by the general formula (1).

[0039] When the epoxy resin represented by the general formula (2) is a hydrogenated epoxy resin, the hydrogenation rate is preferably close to 100% from the viewpoint of obtaining a cured product with excellent weather resistance, but it is sufficient to be 50% or more, preferably 70-100%, more preferably 80-100%, even more preferably 90-100%, and even more preferably 95-100%.

[0040] Among the above, a hydrogenated bisphenol A type epoxy resin represented by the following formula (2-1) is more preferable. [ka] In the above formula, R 15 And n are the same as above.

[0041] As for the epoxy resin, from the viewpoint of low viscosity and mechanical strength of the cured product, at least one selected from the group consisting of the epoxy resin represented by general formula (1) and the epoxy resin represented by general formula (2) is preferred, and at least one selected from the group consisting of the epoxy resin represented by formula (1-1) and the epoxy resin represented by formula (2-1) is more preferred.

[0042] Furthermore, the epoxy equivalent of the epoxy resin is preferably 400 g / equivalent or less, more preferably 300 g / equivalent or less, even more preferably 250 g / equivalent or less, and even more preferably 220 g / equivalent or less, from the viewpoint of achieving both low viscosity and rapid curing properties of the epoxy resin composition. Epoxy resin may be used alone or in combination of two or more types.

[0043] The epoxy resin composition of the present invention may further contain, depending on the application, other components such as fillers, plasticizers and other modifying components, thixotropes and other flow-adjusting components, pigments, leveling agents, tackifiers, and elastomer fine particles.

[0044] The amount of epoxy resin curing agent in the epoxy resin composition of the present invention is such that the ratio of the number of active amine hydrogens in the epoxy resin curing agent to the number of epoxy groups in the epoxy resin (number of active amine hydrogens in the epoxy resin curing agent / number of epoxy groups in the epoxy resin) is 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 only needs to be within the above range in the end, and may be constant during molding of the epoxy resin composition or may be varied during molding.

[0045] The viscosity of the epoxy resin composition of the present invention at a temperature of 80°C is preferably 500 mPa·s or less, more preferably 400 mPa·s or less, even more preferably 200 mPa·s or less, even more preferably 100 mPa·s or less, and even more preferably 50 mPa·s or less. When the viscosity of the epoxy resin composition at 80°C is 500 mPa·s or less, productivity is improved when used in FRP applications. There is no particular lower limit to the viscosity of the epoxy resin composition at 80°C, but it is preferably 5 mPa·s or more in order to suppress turbulence in the mold caused by an increase in the Reynolds number during FRP molding, which can lead to disorder in the reinforcing fibers. In addition, it is preferable that the epoxy resin composition of the present invention has an initial viscosity within the above range after mixing the epoxy resin curing agent and the epoxy resin and allowing 30 seconds to pass at a temperature of 80°C. The viscosity of the epoxy resin composition can be measured using an E-type viscometer, specifically by the method described in the examples.

[0046] From the viewpoint of rapid curing, the epoxy resin composition of the present invention has a gelation time at a temperature of 80°C that is preferably 30 minutes or less, more preferably 25 minutes or less, even more preferably 20 minutes or less, and even more preferably 15 minutes or less. From the viewpoint of workability, the gelation time is preferably 0.5 minutes or more, and more preferably 1.0 minute or more. Furthermore, the gelation time at a temperature of 120°C is preferably 10 minutes or less, more preferably 8.0 minutes or less, even more preferably 5.0 minutes or less, and even more preferably 3.0 minutes or less. Also, from the viewpoint of workability, the gelation time is preferably 0.2 minutes or more, more preferably 0.5 minutes or more. The above gelation time can be measured using a rheometer in the manner described in the examples. Specifically, the storage modulus G' and loss modulus G'' of the epoxy resin composition are measured using a rheometer at a temperature of 80°C or 120°C, a frequency of 1 Hz, and a plate-to-plate distance of 0.5 mm, and the point where G' and G'' intersect is defined as the gelation time.

[0047] There are no particular restrictions on the method for preparing the epoxy resin composition of the present invention. It can be prepared by mixing an epoxy resin curing agent, an epoxy resin, and other components as needed using known methods and apparatus. There are no particular restrictions on the mixing order of the components contained in the epoxy resin composition. The epoxy resin curing agent may be prepared and then mixed with the epoxy resin, or the epoxy resin may be prepared by simultaneously mixing component (A), component (B), and other components that constitute the epoxy resin curing agent with the epoxy resin. From the viewpoint of avoiding gelation before use, it is preferable to bring the components of the epoxy resin composition into contact and mix them immediately before use. The temperature when mixing the components of the epoxy resin composition can be appropriately adjusted according to the viscosity of the epoxy resin, but from the viewpoint of suppressing viscosity increase, it is preferably 120°C or lower, more preferably 100°C or lower, and from the viewpoint of miscibility of the epoxy resin, it is preferably 20°C or higher, more preferably 25°C or higher. The mixing time is preferably in the range of 0.1 to 15 minutes, more preferably 0.2 to 10 minutes, and even more preferably 0.3 to 5 minutes. As for the apparatus, for example, the apparatus exemplified in the various molding methods described later can be used.

[0048] [Cured product] The cured product of the epoxy resin composition of the present invention (hereinafter also simply referred to as "the cured product of the present invention") is obtained by curing the epoxy resin composition of the present invention described above by a known method. The curing conditions for the epoxy resin composition are appropriately selected according to the application and form, and are not particularly limited. The form of the cured product of the present invention is not particularly limited and can be selected according to the application. For example, when the epoxy resin composition is used as a paint, the cured product of the composition is usually in the form of a film. However, from the viewpoint of effectively exhibiting the effects of the present invention, it is preferable that the cured product of the present invention be the matrix resin of the fiber-reinforced composite material described later.

[0049] The epoxy resin composition of the present invention is preferable to have a high glass transition temperature (Tg) of the cured product, from the viewpoint of improving the productivity of molded products when used in fiber-reinforced composite materials and the like, and from the viewpoint of the heat resistance of the molded product. When the Tg of the cured product of the epoxy resin composition is high, when used in fiber-reinforced composite materials and the like, the mold can be released without cooling the mold to a low temperature, thus shortening the molding cycle. In addition, the heat resistance of the molded product is also improved. For example, the epoxy resin composition of the present invention has a cured product that is cured at 120°C for 15 minutes. The cured product is then subjected to differential scanning calorimeter analysis from 30 to 250°C at a heating rate of 5°C / min. The Tg is preferably 100°C or higher, more preferably 110°C or higher, even more preferably 114°C or higher, even more preferably 115°C or higher, and even more preferably 120°C or higher. The Tg of the cured product can be specifically measured by the method described in the examples.

[0050] [Fiber-reinforced composite material] The fiber-reinforced composite material (FRP) of the present invention comprises a cured epoxy resin composition and reinforcing fibers, and can be obtained by impregnating the reinforcing fibers with the epoxy resin composition and then curing the composition. Examples of reinforcing fibers include glass fibers, carbon fibers, boron fibers, and metal fibers. One type of reinforcing fiber may be used alone, or two or more types may be used in combination. Among these, carbon fibers are preferred from the viewpoint of strength and lightness of the resulting composite material. That is, the fiber-reinforced composite material of the present invention is preferably a carbon fiber reinforced composite material (CFRP) comprising a cured product of the epoxy resin composition and carbon fibers.

[0051] The carbon fibers used in CFRP may be manufactured from raw materials such as rayon or polyacrylonitrile (PAN), or they may be manufactured by spinning pitch from petroleum or coal. Furthermore, recycled carbon fibers made from recycled carbon fiber scraps or recycled carbon fibers obtained by removing resin from CFRP can also be used. Carbon fibers can take various forms, such as simply monofilaments or multifilaments arranged in one direction or alternately in an intersecting pattern, fabrics such as knitted or woven materials, nonwoven fabrics, or mats. Of these, monofilaments, fabrics, nonwoven fabrics, or mats are preferred, with fabrics being more preferred.

[0052] The average fiber diameter of the carbon fibers is preferably 1 to 100 μm, more preferably 3 to 50 μm, and even more preferably 4 to 20 μm. When the average fiber diameter is within this range, processing is easy, and the resulting CFRP has excellent elastic modulus and strength. The average fiber diameter can be measured by observation using a scanning electron microscope (SEM). The average fiber diameter can be calculated by randomly selecting 50 or more fibers, measuring their lengths, and averaging the number of fibers.

[0053] The fineness of the carbon fiber is preferably 20 to 4,500 tex, and more preferably 50 to 4,000 tex. Within this fineness range, impregnation with the epoxy resin composition is easy, resulting in a composite material with excellent elastic modulus and strength. The fineness can be determined by calculating the weight of a long fiber of any length and converting it to the weight per 1,000 m. Typically, carbon fibers with approximately 500 to 60,000 filaments are preferably used.

[0054] In addition to the cured epoxy resin composition and reinforcing fibers, the FRP may further contain a foaming agent. There are no particular restrictions on the foaming agent, but examples include foaming agents made from resin materials such as polyvinyl chloride resin, polyurethane resin, polystyrene resin, polyolefin resin, acrylic resin, phenolic resin, polymethacrylimide resin, and epoxy resin.

[0055] <Method for manufacturing fiber-reinforced composite materials> There are no particular limitations on the method for producing the fiber-reinforced composite material of the present invention, but since the epoxy resin curing agent and epoxy resin composition of the present invention are fast-curing, it is preferable to mix the epoxy resin curing agent and the epoxy resin immediately before molding, and then impregnate and cure the reinforcing fibers in a shorter time. From this viewpoint, the method for producing the fiber-reinforced composite material of the present invention preferably includes a step of molding by low-pressure RTM, medium-pressure RTM, high-pressure RTM, compression RTM, liquid compression molding, liquid laydown, spray laydown, surface RTM, prepreg compression molding, wet compression molding (WCM), or dynamic fluid compression molding (DFCM). Among these molding methods, from the viewpoint of application to a high-cycle RTM method, the low-pressure RTM, medium-pressure RTM, or high-pressure RTM method is preferred, the medium-pressure RTM or high-pressure RTM method is more preferred, and from the viewpoint of molding speed, the high-pressure RTM method is even more preferred. In this specification, "low pressure" in the low-pressure RTM method refers to a pressure of less than 0.5 MPa when pumping and mixing the epoxy resin, which is the main component of the epoxy resin composition, with the epoxy resin curing agent. Similarly, "medium pressure" in the medium-pressure RTM method refers to a pressure of 0.5 MPa or more and less than 7 MPa, and "high pressure" in the high-pressure RTM method refers to a pressure of 7 MPa or more and 20 MPa or less. In the above molding method, the epoxy resin, which is the main component, and the epoxy resin curing agent can be mixed and used immediately before molding. Furthermore, the resulting epoxy resin composition has low viscosity and is fast-curing, allowing for quick filling into the mold and impregnation into the reinforcing fibers, and rapid curing, thus significantly reducing molding time. Therefore, the epoxy resin curing agent and epoxy resin composition of the present invention are particularly suitable for the above molding method. Moreover, by using the above molding method, medium to large FRPs for automotive structural materials and building materials can be manufactured with high productivity by applying the epoxy resin curing agent and epoxy resin composition of the present invention.

[0056] In the high-pressure RTM method, it is preferable to use an impact mixing mixer as the device for mixing the epoxy resin, which is the main component of the epoxy resin composition, with the epoxy resin curing agent. For example, reinforcing fibers are placed in a pair of upper and lower molds and sealed, and the inside of the molds is depressurized. Next, the epoxy resin, which is the main component of the epoxy resin composition, and the epoxy resin curing agent are filled into separate tanks, and each is discharged at high speed through a very small hole (orifice) and mixed by impact in the mixing chamber of the impact mixing mixer. The epoxy resin composition prepared in this way is injected into the mold under high pressure to impregnate the reinforcing fibers, and then the epoxy resin is cured.

[0057] In the low-pressure RTM method, it is preferable to use a dynamic mixer as the device for mixing the epoxy resin, which is the main component of the epoxy resin composition, with the epoxy resin curing agent. The dynamic mixer is equipped with a cylindrical high-speed rotating body having an uneven surface. For example, the epoxy resin and the epoxy resin curing agent are filled into separate tanks, and each is sent to the dynamic mixer to mix the two liquids, the main component and the curing agent, by the rotating body. The epoxy resin composition prepared in this way is injected into a mold to impregnate the reinforcing fibers, and then the epoxy resin is cured. The low-pressure RTM method is advantageous when the mixing ratio of epoxy resin and epoxy resin curing agent differs significantly, and also in terms of equipment cost and space saving of the equipment. In the medium-pressure RTM method, it is preferable to use a static mixer as the device for mixing the epoxy resin, which is the main component of the epoxy resin composition, with the epoxy resin curing agent. A static mixer is a tubular reactor incorporating one or more stationary mixers consisting of numerous mixing elements. For example, the epoxy resin and the epoxy resin curing agent are filled into separate tanks and each is sent to a static mixer. By passing the two liquids, the epoxy resin and the epoxy resin curing agent, through the twisted elements of the static mixer, the two liquids are mixed through actions such as division, conversion, and inversion. The epoxy resin composition prepared in this way is injected into a mold to impregnate the reinforcing fibers, and then the epoxy resin is cured. The medium-pressure RTM method is advantageous in that the epoxy resin composition can be pressure-fed into the mold and in terms of equipment cost.

[0058] If the FRP further includes a foaming agent in addition to the cured epoxy resin composition and reinforcing fibers, the reinforcing fibers and foaming agent can be placed in the mold and the FRP can be manufactured in the same manner as described above.

[0059] The epoxy resin curing agent and epoxy resin composition of the present invention can also be suitably used in liquid compression molding (LCM), liquid laydown, and wet compression molding (WCM) methods. In the LCM, liquid laydown, and WCM methods, the epoxy resin composition is cast onto the reinforcing fibers (or onto the reinforcing fibers and foaming material if the FRP further contains foaming material), and then heated and compressed to cure the epoxy resin while impregnating the reinforcing fibers. Dynamic Fluid Compression Molding (DFCM) is an improved method of the LCM, liquid laydown, and WCM methods, characterized by reducing the pressure inside the mold during heating and compression.

[0060] In FRP molding, the temperature at which the epoxy resin composition is injected into the mold or impregnated into the reinforcing fibers is preferably 20 to 120°C, more preferably 25 to 100°C. When the epoxy resin curing agent and epoxy resin are supplied from separate tanks and mixed immediately before molding, the mixing temperatures of the epoxy resin curing agent and epoxy resin can be set individually. From the viewpoint of suppressing viscosity increase, the mixing temperature of the epoxy resin curing agent is preferably 5 to 30°C, more preferably 10 to 25°C. The mixing temperature of the epoxy resin can be appropriately adjusted according to the viscosity of the epoxy resin, but is preferably 20 to 120°C, more preferably 25 to 100°C. The above temperatures may be constant during molding or may be varied during molding. The impregnation time of the epoxy resin composition into the reinforcing fibers is preferably 0.1 to 15 minutes, more preferably 0.2 to 10 minutes, and even more preferably 0.3 to 5 minutes, from the viewpoint of moldability and productivity. The discharge rate when injecting the epoxy resin composition into the mold is preferably 5 to 400 g per second, more preferably 10 to 100 g per second, and even more preferably 20 to 60 g per second, from the viewpoint of moldability and productivity. The above rate may be constant during molding or may be varied during molding.

[0061] The curing temperature of the epoxy resin composition is preferably 50 to 200°C, more preferably 80 to 150°C, and even more preferably 100 to 150°C. The curing temperature may be constant during molding or may be varied during molding. If the curing temperature is 50°C or higher, the epoxy resin will cure sufficiently, and the resulting FRP will have excellent mechanical properties. If the temperature is 200°C or lower, the cost of adjusting the mold temperature will be low. The curing time of the epoxy resin composition can be appropriately selected according to the curing temperature, etc., but from the viewpoint of moldability and productivity, it is preferably 0.1 to 15 minutes, more preferably 0.2 to 10 minutes, and even more preferably 0.5 to 5 minutes.

[0062] Using the epoxy resin composition of the present invention, FRP can be manufactured productively by the molding method described above. The fiber-reinforced composite material of the present invention is preferably used as an automotive structural material or building material, and in particular as an automotive structural material. Examples of automotive structural materials include bumpers, spoilers, cowlings, front grilles, garnishes, bonnets, trunk lids, fender panels, door panels, roof panels, instrument panels, door trims, quarter trims, roof linings, pillar garnishes, deck trims, tonneau boards, package trays, dashboards, console boxes, kicking plates, switch bases, seat backboards, seat frames, armrests, sun visors, intake manifolds, engine head covers, engine undercovers, oil filter housings, and the like. [Examples]

[0063] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. Various measurements and evaluations were performed according to the following methods.

[0064] (viscosity) Using an E-type viscometer, the "TVE-22H type viscometer, cone plate type" (manufactured by Toki Sangyo Co., Ltd.), the viscosity of the epoxy resin curing agent was measured at 25°C, and the viscosity of the epoxy resin composition was measured at 80°C. For the viscosity measurement of the epoxy resin composition at 80°C, measurement was started after mixing the epoxy resin and epoxy resin curing agent, and the measured value was read every 30 seconds to confirm the change in viscosity over time. For epoxy resin compositions, a lower viscosity after 30 seconds at 80°C indicates lower initial viscosity, better filling properties during molding, and thus better moldability. Furthermore, a smaller change in viscosity over time at 80°C and the maintenance of low viscosity indicate a longer pot life.

[0065] (Gelation time) Measurements were performed at 80°C and 120°C using a rheometer "ARES-G2" (manufactured by TA Instruments). An epoxy resin composition was filled between aluminum plates heated to 80°C or 120°C. The storage modulus G' and loss modulus G'' were measured at 80°C or 120°C, a frequency of 1 Hz, and a plate-to-plate distance of 0.5 mm. The point where G' and G'' intersected was defined as the gelation time. A shorter gelation time indicates faster curing.

[0066] (Glass transition temperature (Tg)) The Tg of the cured epoxy resin composition was determined by performing differential scanning thermal analysis on an epoxy resin composition cured by heating at 120°C for 15 minutes, using a differential scanning calorimeter "DSC 6200" (manufactured by Seiko Instruments Inc.) at a heating rate of 5°C / min from 30 to 250°C.

[0067] (Mold releasability) The epoxy resin composition is molded by hand lay-up molding at room temperature to produce carbon fiber fabric (Toray Industries, Inc.'s "CO6343", T300 plain weave cloth, warp and weft filament count: 3K, fabric weight: 198g / m²). 2A CFRP substrate was prepared by impregnating a 0.25 mm thick, 4-ply material. Subsequently, the CFRP substrate was placed in an aluminum upper and lower mold preheated to 120°C in an oven, the mold was quickly closed, and the release properties after 6 minutes were evaluated according to the following criteria. A: Easily demoldable B: Removable C: Not suitable for mold release.

[0068] Examples 1-9 and Comparative Examples 1-3 (Preparation of epoxy resin curing agents and epoxy resin compositions) An epoxy resin curing agent was obtained by mixing components (A), N-aminoethylpiperazine (AEP, manufactured by Tosoh Corporation) and isophorone diamine (IPDA, manufactured by EVONIK), and component (B), norbornanediamine (NBDA, manufactured by Mitsui Chemicals, Inc.), in the parts by mass shown in Table 1. Furthermore, this epoxy resin curing agent and the main component, a bisphenol A type liquid epoxy resin ("jER825", manufactured by Mitsubishi Chemical Corporation), were blended and mixed so that the ratio of the number of active amine hydrogens in the epoxy resin curing agent to the number of epoxy groups in the main component epoxy resin (number of active amine hydrogens in the epoxy resin curing agent / number of epoxy groups in the epoxy resin) was 1 / 1, thereby preparing an epoxy resin composition. The obtained epoxy resin curing agent and epoxy resin composition were evaluated using the method described above. The results are shown in Table 1. Note that the epoxy resin jER825 is a bisphenol A type epoxy resin represented by the following formula (1-1), with an epoxy equivalent of 175 g / equivalent and m = 0.035.

[0069] [ka]

[0070] In the above formula, R 5 It is -CH2CH(OH)- or -CH(OH)CH2-.

[0071] [Table 1]

[0072] As shown in Table 1, compared to the epoxy resin composition of Comparative Example 1, which used only AEP (component (A)) as the epoxy resin curing agent, the epoxy resin compositions of Examples 1 to 3 maintained rapid curing properties while improving the cured product Tg and extending the pot life. Furthermore, compared to the epoxy resin composition of Comparative Example 2, which used only IPDA (component (A)) as the epoxy resin curing agent, the epoxy resin compositions of Examples 4 to 8 were able to improve the curing speed and cured product Tg without significantly reducing the pot life. In addition, the cured products of the epoxy resin compositions of Examples 4 to 6 had particularly good release properties. This is thought to be due to the high gelation rate and Tg of the cured products of the epoxy resin compositions. Compared to the epoxy resin composition of Comparative Example 3, the epoxy resin composition of Example 9 showed improvements in pot life, curing speed, and cured product Tg.

[0073] Example 10 (Manufacturing of CFRP) The epoxy resin composition of Example 1 was hand-laid up at room temperature to produce a carbon fiber fabric (Toray Industries, Inc.'s "CO6343", T300 plain weave cloth, warp and weft filament count: 3K, fabric weight: 198g / m²). 2 A CFRP substrate was prepared by impregnating a 0.25 mm thick, 4-ply (CFRP) material. Next, the CFRP substrate was placed in an aluminum upper and lower mold preheated to 120°C in an oven, the mold was quickly closed, and the epoxy resin composition was cured by heating for 3 minutes to obtain CFRP. The obtained CFRP could be easily released from the aluminum upper and lower mold, confirming that the curing of the epoxy resin composition proceeded in a short time. Furthermore, there were no defects due to low impregnation of the epoxy resin composition into the carbon fibers, and the appearance was good. [Industrial applicability]

[0074] According to the present invention, it is possible to provide an epoxy resin curing agent and an epoxy resin composition that can efficiently produce CFRP for automotive structural materials and building materials by high-cycle RTM or the like, while using N-aminoethylpiperazine and isophoronediamine, which are commonly used as epoxy resin curing agent components, as epoxy resin curing agents.

Claims

1. An epoxy resin curing agent containing isophoronediamine, or a mixture of N-aminoethylpiperazine and isophoronediamine (A), and norbornanediamine (B), An epoxy resin curing agent wherein the mass ratio of component (A) to component (B) satisfies 0.60 ≤ {(A) / [(A) + (B)]} < 1.

2. The epoxy resin curing agent according to claim 1, wherein the component (A) is a mixture of N-aminoethylpiperazine and isophoronediamine.

3. The epoxy resin curing agent according to claim 1 or 2, wherein the total content of component (A) and component (B) is 50% by mass or more.

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

5. A cured product of the epoxy resin composition according to claim 4.

6. A fiber-reinforced composite material comprising a cured product of the epoxy resin composition according to claim 5 and reinforcing fibers.

7. The fiber-reinforced composite material according to claim 6, wherein the reinforcing fiber is carbon fiber.

Images