JP7322709B2 - Epoxy resin curing agent, epoxy resin composition and its cured product, and fiber reinforced composite - Google Patents

Description

The present invention provides 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 comprising a cured product of the epoxy resin composition and reinforcing fibers. Regarding materials.

BACKGROUND ART Carbon fiber reinforced composite materials (hereinafter also referred to as “CFRP (Carbon Fiber Reinforced Plastics)”) have a very high modulus of elasticity, strength, and light weight, and are attracting attention as metal substitute materials. Demand for CFRP is expected to accelerate, especially for automobile structural materials, wind power generation blades, pressure vessels, and aerospace applications. Demand for carbon fibers used in CFRP and matrix resins such as epoxy resins is also expected to increase. increasing in recent years.

By the way, since the molding method of CFRP is different for automobile structural material use, wind turbine blade use, pressure vessel use, and aerospace use, the characteristics required for the matrix resin for CFRP also differ depending on the use.
For example, wind turbine blades have come to be molded by infusion molding, Va-RTM (Vacuum Assist Resin Transfer Molding) or Light-RTM. In these methods, for example, reinforcing fibers are placed in advance in a mold consisting of an upper mold using a film or FRP and a lower mold, the inside of this mold is evacuated, and an epoxy resin composition serving as a matrix resin is applied. It is filled under normal pressure to impregnate the reinforcing fibers, and then the epoxy resin is cured and molded.
In molding by infusion molding, Va-RTM method, and Light-RTM method, due to the characteristics of the molding method, it is usually necessary to fill the mold with an epoxy resin composition in which an epoxy resin and an epoxy resin curing agent are mixed. takes several tens of minutes. Therefore, epoxy resin compositions used in these molding methods are required to have low viscosity and long pot life. As epoxy resin curing agents, isophoronediamine, polyamine compounds having a polyether skeleton, and the like are used.

Further, in CFRP for pressure vessel applications, molding by a filament winding method is used. The filament winding method is a method in which the outer surface of the liner is coated with reinforcing fiber yarns impregnated with a matrix resin such as an epoxy resin composition, and then the matrix resin is cured. 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, a fast-curing epoxy resin composition cannot be applied to the filament winding method.

On the other hand, CFRP for automotive structural materials is formed by the high-cycle RTM method. This is an improvement over the conventional RTM method.
The conventional RTM method is one of closed mold molding using a pair of upper and lower molds. After placing a fiber reinforced preform in the mold and sealing the mold by clamping, epoxy resin is injected from the injection hole. In this method, a resin such as a composition is injected into a mold to impregnate the fiber-reinforced preform, the resin is cured, and the mold is released. However, with the conventional RTM method, several hours are required for molding (preform placement, resin impregnation, resin curing, and mold release). The RTM method is used.

Molding technology based on the high-cycle RTM method greatly shortens the time required for placing the fiber-reinforced preform, impregnating the resin, curing the resin, and demolding, shortening the total molding time to about 10 minutes. It is. 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 closed. Reduce pressure. Next, the epoxy resin, which is the main ingredient of the epoxy resin composition, and the epoxy resin curing agent are pumped in a mist state from separate tanks to the mixing head, and after collision mixing, they are immediately injected into the mold to impregnate the carbon fibers. to cure the epoxy resin. The epoxy resin composition after impingement mixing is injected under high pressure through a plurality of injection holes in order to increase the speed of filling the mold and impregnating the carbon fibers.

It is known to use general-purpose N-aminoethylpiperazine (AEP), isophoronediamine (IPDA), or a mixture thereof as an epoxy resin curing agent used in conventional epoxy resin compositions for the RTM method ( See, for example, Patent Literature 1 and Non-Patent Literature 1).

Japanese Patent Publication No. 9-507262

Ogawa, "Regarding RIM Molding Based on Epoxy Resin," Thermosetting Resin, 1986, Vol. 7, No. 2, p. 87-99

The epoxy resin curing agent used for molding by the high-cycle RTM method and the epoxy resin composition containing the curing agent and the epoxy resin must be fast-curing, have a low viscosity, and have a long pot life. In addition, it is desired that the cured product has a high glass transition temperature (Tg) and good heat resistance.
However, while AEP is fast-curing and has a low initial viscosity, there is a problem that the pot life is short and the cured product of the obtained epoxy resin composition has a low Tg. Further, IPDA has a long pot life and the Tg of the cured product of the obtained epoxy resin composition is relatively high, but there is a problem that the curing speed is slow and the initial viscosity is high. Even if AEP and IPDA were mixed in order to improve their shortcomings, satisfactory performance was not obtained as an epoxy resin curing agent used in molding by the high cycle RTM method or the like.

An object of the present invention is to provide an epoxy resin composition that contains N-aminoethylpiperazine and/or isophoronediamine, which are widely used as epoxy resin curing agent components, has fast curing and low viscosity, and has a pot life and Provided are an epoxy resin curing agent capable of improving the heat resistance of a cured product, an epoxy resin composition containing the same, a cured product thereof, and a fiber-reinforced composite material containing the cured product of the epoxy resin composition and reinforcing fibers. That's what it is.

As a result of intensive studies to solve the above problems, the present inventors have found that an epoxy resin curing agent containing at least one compound selected from the group consisting of N-aminoethylpiperazine and isophoronediamine and bis(aminomethyl)cyclohexane. It was found that the above problems could be solved by

That is, the present invention relates to the following [1] to [9].
[1] An epoxy resin curing agent containing at least one compound (A) selected from the group consisting of N-aminoethylpiperazine and isophoronediamine and bis(aminomethyl)cyclohexane (B).
[2] Curing epoxy resin according to [1] above, wherein the mass ratio of component (A) to component (B) satisfies 0.575<(A)/[(A)+(B)]<1. agent.
[3] The epoxy resin curing agent according to [1] or [2] above, wherein the component (A) is N-aminoethylpiperazine.
[4] The epoxy resin curing agent according to any one of [1] to [3] above, wherein the component (B) is 1,3-bis(aminomethyl)cyclohexane.
[5] The epoxy resin curing agent according to any one of [1] to [4] above, wherein the total content of components (A) and (B) is 50% by mass or more.
[6] An epoxy resin composition containing the epoxy resin curing agent according to any one of [1] to [5] above and an epoxy resin.
[7] A cured product of the epoxy resin composition described in [6] above.
[8] A fiber-reinforced composite material comprising a cured epoxy resin composition according to [6] above and reinforcing fibers.
[9] The fiber-reinforced composite material according to [8] above, wherein the reinforcing fibers are carbon fibers.

According to the present invention, while using N-aminoethylpiperazine and isophorone diamine, which are widely used as epoxy resin curing agent components, as epoxy resin curing agents, CFRP such as automotive structural materials and building materials are produced by the high cycle RTM method. It is possible to provide an epoxy resin curing agent and an epoxy resin composition that can be produced efficiently.
Since the epoxy resin composition has a long pot life, workability is good. In addition, when used as a matrix resin for FRP such as CFRP, it has excellent impregnating properties for reinforcing fibers and is fast-curing, so it can be released from the mold in a short time, resulting in FRP production. can improve sexuality. Furthermore, the obtained FRP has good heat resistance.

[Epoxy resin curing agent]
The epoxy resin curing agent of the present invention comprises at least one compound (A) selected from the group consisting of N-aminoethylpiperazine (AEP) and isophoronediamine (IPDA), and bis(aminomethyl)cyclohexane (B). contains.
The present invention improves various properties derived from AEP and IPDA by blending bis(aminomethyl)cyclohexane in epoxy resin curing agents containing AEP and IPDA, which are widely used as epoxy resin curing agent components, The present inventors have found that the obtained epoxy resin composition achieves rapid curability, low viscosity and long pot life, and that the heat resistance of the cured product can be improved.

<(A) Component>
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 are economically efficient.
As a performance of an epoxy resin curing agent, AEP has the advantage of being fast curing and having a low viscosity, and improving the toughness of the cured product of the resulting epoxy resin composition. IPDA also has the advantage of prolonging the pot life of the resulting epoxy resin composition and increasing the heat resistance of the cured product. Considering these characteristics, at least one compound selected from the group consisting of AEP and IPDA can be appropriately selected as the component (A) used in the present invention depending on the desired performance and application.
When AEP and IPDA are used in combination, the content ratio is not particularly limited. For example, AEP and IPDA may be used in a mass ratio of 1/99 to 99/1, preferably 5/95 to 95/5. can be done.
In the case of an epoxy resin curing agent used for molding by a high cycle RTM method or the like, the component (A) is N-aminoethylpiperazine or N-aminoethylpiperazine and isophorone because of its fast curing and low viscosity. It is preferably a mixture of diamines, more preferably N-aminoethylpiperazine.

<(B) Component>
The epoxy resin curing agent of the present invention contains a predetermined amount of bis(aminomethyl)cyclohexane as component (B). As a result, the epoxy resin composition containing the epoxy resin curing agent containing the component (A) can achieve rapid curability, low viscosity, and a long pot life, and can also improve the heat resistance of the cured product. Methyl)cyclohexane includes 1,2-bis(aminomethyl)cyclohexane, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, and one of these alone , or two or more thereof can be used in combination. Among these, 1,3-bis(aminomethyl)cyclohexane is preferred.
Bis(aminomethyl)cyclohexane may be cis-isomer, trans-isomer, or a mixture thereof. When bis(aminomethyl)cyclohexane is a mixture of cis and trans isomers, the cis/trans molar ratio is preferably 5/95 to 95/5, more preferably 10/90 to 90/10. .

The epoxy resin curing agent of the present invention preferably has a mass ratio of component (A) to component (B) that satisfies 0.575<(A)/[(A)+(B)]<1. When the mass ratio (A) / [(A) + (B)] is 1, that is, when the component (B) is not contained, the resulting epoxy resin composition has fast curing, low viscosity, long pot life, or a cured product It becomes impossible to achieve either of the high heat resistance of Moreover, when the mass ratio (A)/[(A)+(B)] exceeds 0.575, the proportion of AEP or IPDA in the epoxy resin curing agent is high, which is economical. In addition, it becomes easier to express various properties derived from AEP or IPDA.
From the viewpoint of obtaining rapid curability, low viscosity, long pot life, and high heat resistance of the cured product in the resulting epoxy resin composition, the mass ratio (A)/[(A)+( B)] is preferably 0.95 or less, more preferably 0.90 or less, still more preferably 0.85 or less, and more preferably 0.85 or less from the viewpoint of expressing various properties derived from AEP or IPDA. It is 60 or more, more preferably 0.65 or more, even more preferably 0.70 or more, and still more preferably 0.75 or more.

The epoxy resin curing agent of the present invention may contain known curing agents other than the components (A) and (B), known curing accelerators, additives, solvents, and the like.
Examples of curing agents other than the components (A) and (B) include polyamine compounds having two or more amino groups in the molecule other than the components (A) and (B), and modified products thereof. be done. Examples of the polyamine compound include linear aliphatic polyamine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexamethylenediamine, 2-methylpentamethylenediamine, trimethylhexamethylenediamine; - Aromatic ring-containing aliphatic polyamine compounds such as xylylenediamine, m-xylylenediamine and p-xylylenediamine; 2-methylcyclohexane, 1,4-diamino-3,6-diethylcyclohexane, diaminodiethylmethylcyclohexane, 3,3′-dimethyl-4,4′-diaminodicyclohexylmethane, 3,3′,5,5′-tetra Polyamine compounds having an alicyclic structure such as methyl-4,4'-diaminodicyclohexylmethane and 4,4'-diaminodicyclohexylmethane; phenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, diethyltoluenediamine, 2,2'-diethyl Aromatic polyamine compounds such as -4,4'-methylenedianiline; polyamine compounds having a heterocyclic structure such as N,N'-bis(aminoethyl)piperazine; and polyether polyamine compounds. Examples of modified polyamine compounds include Mannich-modified products, epoxy-modified products, Michael adducts, Michael addition/polycondensation products, styrene-modified products, and polyamide-modified products of the above compounds. These can be used individually by 1 type or in combination of 2 or more types.
From the viewpoint of efficiently expressing the effects of the present invention, when the curing agent is contained, the content is preferably 50% by mass or less, more preferably 30% by mass, based on the total amount of the epoxy resin curing agent of the present invention. Below, more preferably 20% by mass or less, still more preferably 15% by mass or less, still more preferably 10% by mass or less, even more preferably 5% by mass or less, and even more preferably 1% by mass or less. Moreover, a lower limit is 0 mass %.

Examples of known curing accelerators include phenolic compounds such as bisphenol A and styrenated phenol and salts thereof; sulfonic acid compounds such as p-toluenesulfonic acid and methanesulfonic acid and salts or esters thereof; salicylic acid, benzoic acid and the like. and salts thereof; mercaptan-terminated polysulfide compounds; guanidine compounds; and alkanolamine compounds. These can be used individually by 1 type or in combination of 2 or more types.
From the viewpoint of efficiently expressing the effects of the present invention, when the curing accelerator is contained, the content is preferably 50% by mass or less, more preferably 30% by mass, based on the total amount of the epoxy resin curing agent of the present invention. % or less, 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 is 0.5% by mass or less. Moreover, a lower limit is 0 mass %.
The final content of the curing accelerator in the epoxy resin curing agent may be 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 mixing 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 the curing accelerator may be supplied with a concentration gradient during molding. and so on.

However, from the viewpoint of efficiently expressing the effects of the present invention, the total content of the components (A) and (B) is preferably 50% by mass or more relative to the total amount of the epoxy resin curing agent of the present invention. More preferably 70% by mass or more, still more preferably 80% by mass or more, still more preferably 85% by mass or more, still more preferably 90% by mass or more, still more preferably 95% by mass or more, particularly preferably 99% by mass or more (the upper limit is 100% by mass).

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 still more preferably 60 mPa·s or less at a temperature of 25°C. When the viscosity is 150 mPa·s or less at a temperature of 25° C., it is easy to mix with the epoxy resin, and the productivity is improved when used for FRP applications. Although the lower limit of the viscosity of the epoxy resin curing agent at a temperature of 25° C. is not particularly limited, it is preferably 10 mPa·s or more from the viewpoint of miscibility with the epoxy resin. The viscosity of the epoxy resin curing agent can be measured using an E-type viscometer.

The method for producing the epoxy resin curing agent of the present invention is not particularly limited, and can be appropriately selected according to the type of use, the apparatus used, the types and mixing ratios of the ingredients, and the like. For example, component (A), component (B), and, if necessary, other ingredients may be brought into contact and mixed at the same time, or some components constituting the epoxy resin curing agent may be supplied while providing a concentration gradient. , may be mixed. As will be described later, each component contained in the epoxy resin curing agent and the epoxy resin may be mixed together at the time of preparation of the epoxy resin composition.
From the viewpoint of avoiding the progress of gelation before use, it is preferable that the components contained in the epoxy resin curing agent are brought into contact with each other and mixed immediately before use. When the epoxy resin curing agent is prepared alone, the temperature when mixing each component contained in the epoxy resin curing agent is preferably 5 to 30°C, more preferably 10 to 25°C, from the viewpoint of suppressing viscosity increase. is. The mixing time is preferably 0.1 to 15 minutes, more preferably 0.2 to 10 minutes, still more preferably 0.5 to 5 minutes.

[Epoxy resin composition]
The epoxy resin composition of the present invention contains the epoxy resin curing agent of the present invention and an epoxy resin. As the epoxy resin, 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. , preferably an epoxy resin containing an aromatic ring or an alicyclic structure in the molecule, more preferably one or more selected from the group consisting of bisphenol A type epoxy resin and bisphenol F type epoxy resin, bisphenol A type epoxy resin is more preferred. Among them, an epoxy resin represented by the following general formula (1) is particularly preferable from the viewpoint of having a low viscosity and being able to secure the mechanical strength of the cured product.

(In Formula (1), R ¹¹ to R ¹⁴ 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. Plural R ¹¹ , a plurality of R ¹² , a plurality of R ¹³ , and a plurality of R ¹⁴ may all be the same or different.Y ¹ and Y ² each independently represent a single bond, —CH ₂ —, —CH( CH ₃ )— or —C(CH ₃ ) ₂ —, ^{R 15} is —CH ₂ CH(OH)—, or —CH(OH)CH ₂ —, m indicates the average number of repeating units, It is a number between 0 and 0.2.)
R ¹¹ to R ¹⁴ are preferably alkyl groups having 1 to 4 carbon atoms, more preferably at least one selected from the group consisting of methyl, ethyl, isopropyl and t-butyl groups.
Each of p, q, r, and s is preferably an integer of 0 to 2, more preferably 0 or 1, and more preferably all 0.
Y ¹ and Y ² are preferably —CH ₂ — or —C(CH ₃ ) ₂ —, more preferably —C(CH ₃ ) ₂ —.
In addition, m is preferably 0 to 0.15, more preferably 0.01 to 0.1, from the viewpoint of ensuring a low viscosity and the mechanical strength of the cured product.

In addition, the epoxy equivalent of the epoxy resin is preferably 300 g/equivalent or less, more preferably 220 g/equivalent or less, still more preferably 200 g/equivalent or less, from the viewpoint of achieving both low viscosity and fast curing properties of the epoxy resin composition. Even more preferably, it is 180 g/equivalent or less.
An epoxy resin may be used individually by 1 type, and may use 2 or more types together.

The epoxy resin composition of the present invention may further contain other components such as fillers, modifying components such as plasticizers, flow control components such as thixotropic agents, pigments, leveling agents, tackifiers, and elastomer fine particles. may be included depending on

The content of the epoxy resin curing agent in the epoxy resin composition of the present invention is 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 (active amine hydrogens in the epoxy resin curing agent number/number of epoxy groups in the epoxy resin) is preferably 1/0.8 to 1/1.2, more preferably 1/0.9 to 1/1.1, and still more preferably 1/1. be. The ratio may finally fall within the above range, and may be constant during molding of the epoxy resin composition, or may be varied during molding.

The viscosity of the epoxy resin composition of the present invention at a temperature of 40° C. is preferably 400 mPa·s or less, more preferably 350 mPa·s or less, still more preferably 300 mPa·s or less. A viscosity of 400 mPa·s or less at a temperature of 40° C. improves productivity when used for FRP applications. Although the lower limit of the viscosity of the epoxy resin composition at a temperature of 40 ° C. is not particularly limited, it suppresses the occurrence of turbulence in the mold due to an increase in the Reynolds number in FRP molding, and the turbulence of the reinforcing fibers. From the point of view, it is preferably 150 mPa·s or more. The viscosity of the epoxy resin composition can be measured using an E-type viscometer, specifically by the method described in Examples.

From the viewpoint of rapid curing, the epoxy resin composition of the present invention preferably has a gelation time at 80°C of 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. minutes or less. From the viewpoint of workability, the gelation time is preferably 0.5 minutes or longer, more preferably 1.0 minute or longer.
Also, 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. From the viewpoint of workability, the gelation time is preferably 0.2 minutes or longer, more preferably 0.5 minutes or longer.
The gelation time can be measured using a rheometer by the method described in Examples. Specifically, the storage elastic modulus G′ and loss elastic 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 distance between plates of 0.5 mm, The point where G' and G'' intersect is the gelation time.

The method for producing the epoxy resin composition of the present invention is not particularly limited, and it can be produced by mixing the epoxy resin curing agent, epoxy resin, and optionally other components using a known method and apparatus. The mixing order of each component contained in the epoxy resin composition is not particularly limited. After the epoxy resin curing agent is prepared, it may be mixed with the epoxy resin. Epoxy resin may be mixed at the same time.
From the viewpoint of avoiding the progress of gelation before use, it is preferable that the components contained in the epoxy resin composition are brought into contact with each other and mixed immediately before use. The temperature at which the components contained in the epoxy resin composition are mixed can be appropriately adjusted according to the viscosity of the epoxy resin. From the viewpoint of miscibility with the epoxy resin, the temperature is preferably 30° C. or higher, more preferably 50° C. or higher. The mixing time is preferably 0.1 to 15 minutes, more preferably 0.2 to 10 minutes, still more preferably 0.5 to 5 minutes. As an apparatus, for example, an apparatus exemplified in various molding methods described later can be used.

[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 above-described epoxy resin composition of the present invention by a known method. 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 also not particularly limited, and can be selected depending on 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. From the viewpoint of effectively exhibiting the effects of the present invention, the cured product of the present invention is preferably the matrix resin of the fiber-reinforced composite material described below.

The epoxy resin composition of the present invention has a cured product with a high glass transition temperature (Tg) from the viewpoint of improving the productivity of molded articles when used in fiber-reinforced composite materials and the like, and from the viewpoint of the heat resistance of molded articles. is preferred. When the cured product of the epoxy resin composition has a high Tg, it can be demolded without cooling the mold to a low temperature when used for a fiber-reinforced composite material, so that the molding cycle can be shortened. Also, the heat resistance of the molded product is improved.
For example, the epoxy resin composition of the present invention is cured at a temperature of 120° C. for 15 minutes, and a cured product obtained is measured using a differential scanning calorimeter at a temperature increase rate of 5° C./min. The Tg determined by scanning thermal analysis is preferably 100° C. or higher, more preferably 110° C. or higher, still more preferably 120° C. or higher, and even more preferably 123° C. or higher. Specifically, the Tg of the cured product can be measured by the method described in Examples.

[Fiber Reinforced Composite (FRP)]
The epoxy resin composition containing the epoxy resin curing agent of the present invention has the characteristics of rapid curing, low viscosity, long pot life, and high heat resistance of the cured product. is preferred, and it is particularly preferred for carbon fiber reinforced composites (CFRP).
The fiber-reinforced composite material contains a cured product of the 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. can. The FRP may further contain a foaming material in addition to the cured epoxy resin composition and reinforcing fibers.

Examples of reinforcing fibers include glass fibers, carbon fibers, boron fibers, aramid fibers, cellulose fibers, nanocellulose fibers and metal fibers. Reinforcing fibers may be used singly or in combination of two or more. Among these, carbon fiber is preferable from the viewpoint of the strength and lightness of the resulting composite material.
The carbon fiber used in CFRP may be produced using rayon, polyacrylonitrile (PAN), or the like as a raw material, or may be produced by spinning a pitch such as petroleum or coal as a raw material. Further, it is also possible to use a recycled product obtained by reusing carbon fiber offcuts or a recycled carbon fiber obtained by removing the resin from CFRP.

Either continuous fibers or non-continuous fibers can be used as the reinforcing fibers. When discontinuous fibers are used, the fiber length is preferably 1 mm or more, more preferably 3 mm or more, still more preferably 6 mm or more, as the average fiber length of the discontinuous fibers used, from the viewpoint of the strength of the obtained FRP. It is preferably 10 mm or more. In addition, the upper limit of the average fiber length of the discontinuous fibers used is preferably 500 cm or less, more preferably 300 cm or less, and even more preferably 100 cm or less, from the viewpoint of shaping properties. The average fiber length can be measured by visual observation, optical microscope, scanning electron microscope (SEM), or the like. 100 fibers can be randomly selected and the length measured to calculate the number-average average fiber length.

The average fiber diameter of the reinforcing fibers is preferably 1 to 100 μm, more preferably 3 to 50 μm, even more preferably 4 to 20 μm. When the average fiber diameter is within this range, processing is easy, and the resulting FRP has excellent elastic modulus and strength. The average fiber diameter can be measured by observation using a scanning electron microscope (SEM) or the like. By randomly selecting 50 or more fibers and measuring the length, the number-average average fiber diameter can be calculated.

The fineness of the reinforcing fibers is preferably 20 to 4,500 tex, more preferably 50 to 4,000 tex. When the fineness is within this range, impregnation with the epoxy resin composition is easy, and the resulting FRP has excellent elastic modulus and strength. The fineness can be obtained by obtaining the weight of long fibers of any length and converting it into the weight per 1,000 m. Reinforcing fibers having a filament number of about 500 to 60,000 can be preferably used.

Examples of the form of reinforcing fibers include various forms such as monofilaments or multifilaments arranged so as to intersect in one direction or alternately, fabrics such as knitted fabrics, nonwoven fabrics, and mats. Among these, the form of monofilament, cloth, non-woven fabric or mat is preferable, and the form of cloth is more preferable.

The foam material is not particularly limited, but examples include foam materials composed of resin materials such as polyvinyl chloride resin, polyurethane resin, polystyrene resin, polyolefin resin, acrylic resin, phenol resin, polymethacrylimide resin, and epoxy resin. be done.

The method for producing the fiber-reinforced composite material is not particularly limited, but since the epoxy resin curing agent and the epoxy resin composition of the present invention are fast-curing, the epoxy resin curing agent and the epoxy resin are mixed immediately before molding. After that, it is preferable to impregnate and cure the reinforcing fibers preferably within 10 minutes, more preferably within 5 minutes.
From this point of view, the method for producing a fiber-reinforced composite material includes a low-pressure RTM method, a medium-pressure RTM method, a high-pressure RTM method, a compression RTM method, a liquid compression molding method, a liquid laydown method, a spray laydown method, a surface RTM method, and a prepreg compression molding. method, wet compression molding (WCM) method, and Dynamic Fluid Compression Molding method. Among these molding methods, the low-pressure RTM method, the medium-pressure RTM method, or the high-pressure RTM method is preferable from the viewpoint of application to the high-cycle RTM method, and the medium-pressure RTM method or the high-pressure RTM method is more preferable. is more preferably a high pressure RTM method.
In this specification, "low pressure" in the low-pressure RTM method means that the pressure at the time of pumping and mixing the epoxy resin, which is the main ingredient of the epoxy resin composition, and the epoxy resin curing agent is less than 0.5 MPa. It means that Similarly, "medium pressure" in the medium pressure RTM method means that the above pressure is 0.5 MPa or more and less than 7 MPa, and "high pressure" in the high pressure RTM method means that the above pressure is 7 MPa or more and 20 MPa or less.
Since the epoxy resin composition of the present invention is fast-curing and has low viscosity, it can be quickly filled into a mold and impregnated into reinforcing fibers, and can be rapidly cured, thereby significantly shortening the molding time. Therefore, the epoxy resin curing agent and epoxy resin composition of the present invention are particularly suitable for the above molding method. In addition, by using the molding method described above, medium to large-sized FRPs for automotive structural materials and building materials can be produced with good productivity by applying the epoxy resin curing agent and the epoxy resin composition of the present invention. .

In the high-pressure RTM method, it is preferable to use an impingement mixer as a device for mixing the epoxy resin, which is the main ingredient of the epoxy resin composition, and the epoxy resin curing agent. For example, reinforcing fibers are placed in a pair of upper and lower molds, which are then sealed, and the pressure inside the molds is reduced. Next, the epoxy resin, which is the main ingredient of the epoxy resin composition, and the epoxy resin curing agent are filled in separate tanks, each of which is discharged from very small holes (orifices) at high speed, and placed in the mixing chamber of an impingement mixer. Collision mix. The epoxy resin composition thus prepared is injected into a mold under high pressure to impregnate the reinforcing fibers, and then the epoxy resin is cured.

In the low-pressure RTM method, it is preferable to use a dynamic mixer as a device for mixing the epoxy resin, which is the main ingredient of the epoxy resin composition, and the epoxy resin curing agent. A dynamic mixer has a cylindrical high-speed rotating body with an uneven surface. For example, the epoxy resin, which is the main ingredient of the epoxy resin composition, and the epoxy resin curing agent are filled in separate tanks, and each liquid is fed to a dynamic mixer to mix the two liquids of the main ingredient and the curing agent by the rotating body. . The epoxy resin composition thus prepared 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 compounding ratio of the epoxy resin and the epoxy resin curing agent is greatly different, and from the viewpoint of equipment cost and space saving of the equipment.
In the medium-pressure RTM method, it is preferable to use a static mixer as a device for mixing the epoxy resin, which is the main ingredient of the epoxy resin composition, and the epoxy resin curing agent. A static mixer is a tubular reactor incorporating one or more static mixers consisting of multiple mixing elements. For example, an epoxy resin, which is the main ingredient of the epoxy resin composition, and an epoxy resin curing agent are filled in separate tanks, and the respective tanks are fed to a static mixer. By passing the two liquids of the main agent and the curing agent through the twisted elements of the static mixer, the two liquids are mixed by the action of division, conversion, inversion, and the like. The epoxy resin composition thus prepared 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 pumped into the mold and in terms of equipment costs.

When the FRP contains a foaming material in addition to the cured epoxy resin composition and the reinforcing fiber, the reinforcing fiber and the foaming material can be arranged in the mold and the FRP can be manufactured in the same manner as described above. can.

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 method, the liquid laydown method, and the WCM method, after casting the epoxy resin composition on the reinforcing fiber (on the reinforcing fiber and the foaming material when the FRP further includes a foaming material), it is reinforced by heating and compressing. The epoxy resin is cured while being impregnated into the fiber. The Dynamic Fluid Compression Molding method is an improved method of the LCM method, the liquid laydown method, and the WCM method, and is characterized by reducing the pressure inside the mold during heat compression.

In FRP molding, the temperature at which the epoxy resin composition is injected into the mold or impregnated into the reinforcing fibers is preferably 30 to 120°C, more preferably 50 to 100°C. When the epoxy resin curing agent and the epoxy resin are supplied from separate tanks and mixed immediately before molding, the temperature at which the epoxy resin curing agent and the epoxy resin are mixed can be set individually. The temperature at which the epoxy resin curing agent is mixed is preferably 5 to 30°C, more preferably 10 to 25°C, from the viewpoint of suppressing an increase in viscosity. The temperature at which the epoxy resin is mixed can be adjusted according to the viscosity of the epoxy resin. The temperature may be constant during molding or may be varied during molding.
The impregnation time of the reinforcing fiber with the epoxy resin composition is preferably 0.1 to 15 minutes, more preferably 0.2 to 10 minutes, and still more preferably 0.5 to 5 minutes, from the viewpoint of moldability and productivity. is.
The ejection speed when the epoxy resin composition is injected into the mold is preferably 5 to 400 g/s, more preferably 10 to 100 g/s, and still more preferably 20 to 60 g/s, from the viewpoint of moldability and productivity. . The speed may be constant during molding or may be varied during molding.

The curing temperature of the epoxy resin composition is preferably 50 to 200°C, more preferably 80 to 150°C, still 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 curing of the epoxy resin will proceed sufficiently, and the resulting FRP will have excellent mechanical properties. Further, if the temperature is 200° C. or less, the cost for adjusting the mold temperature can be reduced. The curing time of the epoxy resin composition is preferably 0.1 to 15 minutes, more preferably 0.2 to 10 minutes, still more preferably 0.5 to 5 minutes, from the viewpoint of moldability and productivity.

Using the epoxy resin curing agent or the epoxy resin composition of the present invention, FRP can be produced with high productivity by the molding method described above. The fiber-reinforced composite material of the present invention is preferably a structural material for automobiles or a building material, particularly a structural material for automobiles. Automotive structural materials include bumpers, spoilers, cowlings, front grills, garnishes, bonnets, trunk lids, fender panels, door panels, roof panels, instrument panels, door trims, quarter trims, roof linings, pillar garnishes, deck trims, and tonneau boards. , package trays, dashboards, console boxes, kicking plates, switch bases, seat back boards, seat frames, armrests, sun visors, intake manifolds, engine head covers, engine undercovers, oil filter housings, etc.

EXAMPLES 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 carried out according to the following methods.

(viscosity)
The viscosity of the epoxy resin composition was measured at 40° C. and 80° C. using an E-type viscometer “TVE-22H viscometer cone plate type” (manufactured by Toki Sangyo Co., Ltd.). In the measurement at 80°C, the measurement was started immediately after the epoxy resin composition was prepared by mixing the epoxy resin and the epoxy resin curing agent, and the measured value was read every 30 seconds to confirm the change in viscosity over time.
The lower the viscosity at 40° C. and the viscosity after 30 seconds at 80° C., the lower the initial viscosity, the higher the fillability during molding, and the better the moldability. In addition, it shows that the pot life is longer as the viscosity changes less over time in the measurement at 80° C. and the lower the viscosity is maintained.

(Gelling time)
Measurement was performed at 80°C and 120°C using a rheometer "ARES-G2" (manufactured by TA Instruments). The epoxy resin composition is filled between aluminum plates heated to 80 ° C. (or 120 ° C.), the temperature is 80 ° C. (or 120 ° C.), the frequency is 1 Hz, and the distance between the plates is 0.5 mm. The rate G'' was measured and the point where G' and G'' intersected was taken as the gelation time. A shorter gelation time indicates a faster curing property.

(Glass transition temperature (Tg))
The Tg of the cured product of the epoxy resin composition was measured using a differential scanning calorimeter "DSC 6200" (manufactured by Seiko Instruments Inc.) for the epoxy resin composition cured by heating at 120°C for 15 minutes. It was determined by performing differential scanning calorimetry from 30 to 250°C at a temperature rate of 5°C/min.

Examples 1-7 and Comparative Examples 1-3 (Preparation of epoxy resin curing agent and epoxy resin composition)
(A) components N-aminoethylpiperazine (AEP, manufactured by Tosoh Corporation) and isophoronediamine (IPDA, manufactured by EVONIK), and component (B) 1,3-bis(aminomethyl)cyclohexane (1, 3-BAC, manufactured by Mitsubishi Gas Chemical Co., Ltd., cis/trans ratio = 77/23) were blended in parts by mass shown in Table 1 and mixed to obtain an epoxy resin curing agent.
Furthermore, this epoxy resin curing agent and a bisphenol A liquid epoxy resin ("jER825", manufactured by Mitsubishi Chemical Corporation) as a main agent are combined with the number of active amine hydrogens in the epoxy resin curing agent and the epoxy resin as a main agent. An epoxy resin composition was prepared by blending and mixing so that the number of epoxy groups in the mixture was equimolar.
The obtained epoxy resin curing agent and epoxy resin composition were evaluated by the methods described above. Table 1 shows the results. The epoxy resin jER825 is represented by the following structural formula, and has an epoxy equivalent weight of 175 g/equivalent and m=0.035.

In the above formula, R ¹⁵ is -CH ₂ CH(OH)- or -CH(OH)CH ₂ -.

As shown in Table 1, the epoxy resin compositions of Examples 1 to 3 maintained rapid curability as compared with the epoxy resin composition of Comparative Example 1 using only AEP, which is the component (A), as the epoxy resin curing agent. At the same time, the viscosity was lowered, the pot life was extended, and the heat resistance of the cured product was improved. In addition, compared to the epoxy resin composition of Comparative Example 2 using only IPDA, which is the component (A), as the epoxy resin curing agent, the epoxy resin compositions of Examples 4 to 6 maintained a pot life while maintaining a low temperature. The viscosity was increased, and the curing speed and the heat resistance of the cured product were improved.
Compared with the epoxy resin composition of Comparative Example 3, the epoxy resin composition of Example 7 was improved in viscosity, pot life, curing speed and heat resistance of the cured product.

Example 8 (Production of CFRP)
The epoxy resin composition of Example 1 was subjected to hand lay-up molding at room temperature to form a carbon fiber fabric (“CO6343” manufactured by Toray Industries, Inc., T300 plain weave cloth, 3K, 198 g/m ² , 0.25 mm thickness, 4 ply). was impregnated with to produce a CFRP substrate. Subsequently, the CFRP substrate was placed on upper and lower aluminum molds preheated to 120° C. in an oven, the molds were quickly closed, and the epoxy resin composition was cured by heating for 3 minutes to obtain CFRP. The obtained CFRP was able to be easily released from the upper and lower aluminum molds, confirming that the curing of the epoxy resin composition progressed in a short time. In addition, there were no defects due to low impregnation of the epoxy resin composition into carbon fibers, and the appearance was good.

According to the present invention, while using N-aminoethylpiperazine and isophorone diamine, which are widely used as epoxy resin curing agent components, as epoxy resin curing agents, CFRP such as automotive structural materials and building materials are produced by the high cycle RTM method. It is possible to provide an epoxy resin curing agent and an epoxy resin composition that can be produced efficiently.
Since the epoxy resin composition has a long pot life, workability is good. In addition, when used as a matrix resin for FRP such as CFRP, it has excellent impregnating properties for reinforcing fibers and is fast-curing, so it can be released from the mold in a short time, resulting in FRP production. can improve sexuality. Furthermore, the obtained FRP has good heat resistance.

Claims (7)

containing at least one compound (A) selected from the group consisting of N-aminoethylpiperazine and isophoronediamine, and bis(aminomethyl)cyclohexane (B), the sum of the components (A) and (B) Epoxy having a content of 70% by mass or more and a mass ratio of the component (A) to the component (B) satisfying 0.575<(A)/[(A)+(B)]≦0.75 Resin hardener. 2. The epoxy resin curing agent according to claim 1, wherein the component (A) is N-aminoethylpiperazine. 3. The epoxy resin curing agent according to claim 1, wherein the component (B) is 1,3-bis(aminomethyl)cyclohexane. An epoxy resin composition comprising the epoxy resin curing agent according to any one of claims 1 to 3 and an epoxy resin. A cured product of the epoxy resin composition according to claim 4 . A fiber-reinforced composite material comprising a cured product of the epoxy resin composition according to claim 4 and reinforcing fibers. 7. The fiber reinforced composite according to claim 6 , wherein said reinforcing fibers are carbon fibres.