WO2025115600A1 - Epoxy resin composition and cured product thereof, prepreg, fiber-reinforced composite material, and fiber-reinforced composite material - Google Patents

Abstract

The present invention pertains to: an epoxy resin composition which contains epoxy resins (A) and an epoxy resin curing agent (B), and in which the epoxy resins (A) include a prescribed epoxy resin (A1) and an epoxy resin (A2) at a prescribed ratio, and the epoxy resin curing agent (B) contains resorcinol (B1); a cured product thereof; a prepreg using said epoxy resin composition; a fiber-reinforced composite material; and a high-pressure gas container.

Description

Epoxy resin composition and cured product thereof, prepreg, fiber-reinforced composite material, and fiber-reinforced composite material

The present invention relates to an epoxy resin composition and its cured product, a prepreg, a fiber-reinforced composite material, and a high-pressure gas cylinder containing the fiber-reinforced composite material.

In recent years, environmentally friendly natural gas vehicles (CNG vehicles) and fuel cell vehicles (FCVs) have become increasingly popular. Fuel cell vehicles are powered by fuel cells, so it is essential to develop hydrogen stations where hydrogen, the fuel used in fuel cell vehicles, can be compressed to high pressure and filled into the vehicles.
Steel tanks have been used so far as high-pressure gas storage tanks used in hydrogen stations for fuel cell vehicles, or as on-board fuel tanks for CNG vehicles, fuel cell vehicles, etc., but progress has been made in the development of lighter high-pressure gas storage tanks that use resin materials for the tank liner or outer layer. Reducing the weight of on-board fuel tanks has the advantage of improving the fuel efficiency of the vehicles that are equipped with them.

It is known that resins with gas barrier properties and fiber-reinforced composites (FRP) in which reinforcing fibers are impregnated with the resins are used as resin materials for high-pressure gas storage tanks. For example, Patent Document 1 discloses a method for manufacturing a pressure vessel having a liner and an outer layer of the liner, the outer layer being made of a composite material containing reinforcing fibers and a matrix resin, in which a filament winding method or tape winding method is used to form the outer layer by wrapping the composite material around the outer circumference of the liner.

The winding method can also be used when the matrix resin in the composite material is a cured product of a thermosetting resin rather than a thermoplastic resin. In this case, a continuous reinforcing fiber bundle impregnated with a thermosetting resin (tow prepreg) is wound around the outer periphery of the liner and then heated to harden and mold the material.
Prepregs using an epoxy resin composition as a matrix resin are also known. For example, Patent Document 2 discloses an epoxy resin composition containing an epoxy resin, a compound having two functional groups each having one active hydrogen that reacts with an epoxy group in the molecule, and a curing agent, and a prepreg and a fiber-reinforced composite material obtained by impregnating reinforcing fibers with the epoxy resin composition.

Furthermore, as an example of a thermosetting resin composition with gas barrier properties, Patent Document 3 discloses a composition that contains a meta-substituted aromatic resin and an additional aromatic epoxy resin as an oxygen barrier composition for electrical components, and has oxygen permeability below a specified value.

International Publication No. 2016/084475 JP 2002-284852 A Special Publication No. 2012-533643

The cured product of the thermosetting resin composition used in high-pressure gas cylinders for storing hydrogen gas is required to have high barrier properties against hydrogen gas and high heat resistance. Furthermore, from the perspective of improving the impact resistance of high-pressure gas cylinders, it is also desirable for the cured product to have a high elongation rate. However, with the technologies disclosed in Patent Documents 1 to 3, it was difficult to satisfy all of the above required properties.

The object of the present invention is to provide an epoxy resin composition capable of producing a cured product having high hydrogen gas barrier properties, heat resistance and elongation, the cured product, a prepreg using the epoxy resin composition, a fiber-reinforced composite material, and a high-pressure gas cylinder.

The present inventors have found that an epoxy resin composition using two specific epoxy resins as the main epoxy resin and further using an epoxy resin curing agent containing resorcinol can solve the above problems.
That is, the present invention relates to the following.
[1] An epoxy resin composition containing an epoxy resin (A) and an epoxy resin curing agent (B), wherein the epoxy resin (A) contains an epoxy resin (A1) and an epoxy resin (A2), the epoxy resin (A1) is an epoxy resin having a glycidyl group derived from a triphenylmethane type phenol, and the epoxy resin (A2) is an epoxy resin having a glycidyl group derived from bisphenol F (A2-1), an epoxy resin having a glycidyl group derived from bisphenol A (A2-2), or an epoxy resin having a glycidyl group derived from bisphenol B (A2-3). a mass ratio [(A1)/(A2)] of the epoxy resin (A1) to the epoxy resin (A2) in the epoxy resin (A) is 1/99 to 90/10, and the epoxy resin curing agent (B) contains resorcinol (B1).
[2] The epoxy resin composition according to [1], wherein the epoxy resin curing agent (B) further comprises an epoxy resin curing agent (B2) other than resorcinol (B1), and the epoxy resin curing agent (B2) comprises a phenol-based curing agent (B2-1) other than resorcinol (B1).
[3] The epoxy resin composition according to [2], wherein the phenol-based curing agent (B2-1) contains at least one selected from the group consisting of bisphenol F, bisphenol A, novolac-type phenol, and triphenylmethane-type phenol.
[4] The epoxy resin composition according to any one of [1] to [3], wherein a mass ratio [(A1)/(A2)] of the epoxy resin (A1) to the epoxy resin (A2) in the epoxy resin (A) is 5/95 to 70/30.
[5] The epoxy resin composition according to any one of [1] to [4], further comprising a curing accelerator (C), the curing accelerator (C) comprising at least one selected from the group consisting of imidazoles, tertiary amines, and phosphorus compounds.
[6] The epoxy resin composition according to any one of [1] to [5], further comprising a stress relaxation component (D).
[7] The epoxy resin composition according to any one of [1] to [6], further comprising a non-reactive diluent (E).
[8] The epoxy resin composition according to any one of [1] to [7], wherein a hydrogen gas permeability coefficient of a cured product of the epoxy resin composition at 23°C is 7.0 x 10 ^-11 [cc·cm/(cm ² ·s·cmHg)] or less.
[9] A cured product of the epoxy resin composition according to any one of [1] to [8].
[10] A prepreg comprising the epoxy resin composition according to any one of [1] to [8] and reinforcing fibers.
[11] The prepreg according to [10], wherein the reinforcing fibers are at least one selected from the group consisting of carbon fibers, glass fibers, and basalt fibers.
[12] The prepreg according to [10] or [11], wherein the prepreg is a tow prepreg or a tape prepreg.
[13] A fiber-reinforced composite material, which is a cured product of the prepreg according to any one of [10] to [12].
[14] A high-pressure gas cylinder comprising the fiber-reinforced composite material according to [13].

The present invention provides an epoxy resin composition capable of producing a cured product having high hydrogen gas barrier properties, heat resistance, and elongation, the cured product, a prepreg using the epoxy resin composition, a fiber-reinforced composite material, and a high-pressure gas container. The high-pressure gas container has high hydrogen gas barrier properties and is suitable as a container for storing high-pressure hydrogen gas.

[Epoxy resin composition]
The epoxy resin composition of the present invention is an epoxy resin composition containing an epoxy resin (A) and an epoxy resin curing agent (B), wherein the epoxy resin (A) contains an epoxy resin (A1) and an epoxy resin (A2), the epoxy resin (A1) is an epoxy resin having a glycidyl group derived from a triphenylmethane type phenol, the epoxy resin (A2) is at least one selected from the group consisting of an epoxy resin (A2-1) having a glycidyl group derived from bisphenol F, an epoxy resin (A2-2) having a glycidyl group derived from bisphenol A, an epoxy resin (A2-3) having a glycidyl group derived from a novolac type phenol, and an epoxy resin (A2-4) having a glycidyl group derived from a polyol having a naphthalene skeleton, the mass ratio [(A1)/(A2)] of the epoxy resin (A1) to the epoxy resin (A2) in the epoxy resin (A) is 1/99 to 90/10, and the epoxy resin curing agent (B) contains resorcinol (B1).
The epoxy resin composition of the present invention has the above-mentioned structure, and thus can produce a cured product having high hydrogen gas barrier properties, heat resistance and elongation.

In this specification, the hydrogen gas barrier property of the cured product of the epoxy resin composition is determined by the low hydrogen gas permeability coefficient, the heat resistance is determined by the high glass transition temperature (Tg), and the elongation is determined by the tensile elongation value. The hydrogen gas barrier property, heat resistance, and elongation of the cured product of the epoxy resin composition can be specifically evaluated by the method described in the examples.

The reason why the above-mentioned effects are obtained in the present invention is not clear, but is thought to be as follows.
An epoxy resin (A1) having a glycidyl group derived from a triphenylmethane-type phenol (hereinafter, also simply referred to as "epoxy resin (A1)" or "component (A1)") has a polymer structure in which a plurality of aromatic rings are spread two-dimensionally or three-dimensionally, and is therefore considered to exhibit high hydrogen gas barrier properties and high heat resistance.
Here, other epoxy resins, for example, epoxy resins having glycidyl groups derived from resorcinol, can also exhibit high hydrogen gas barrier properties. However, the cured product of the epoxy resin having glycidyl groups derived from resorcinol has a low glass transition temperature and cannot achieve high heat resistance. Furthermore, since the epoxy resin having glycidyl groups derived from resorcinol has a low epoxy equivalent and is fast curing, the pot life and shelf life of the resulting epoxy resin composition also tend to be short.
In contrast, when the epoxy resin (A1) is used as the epoxy resin (A) in the epoxy resin composition of the present invention, the cured product has high hydrogen barrier property and high heat resistance. Furthermore, since the epoxy equivalent of the epoxy resin (A1) is relatively high, it is considered that the pot life and shelf life of the epoxy resin composition can also be improved.

On the other hand, if the epoxy resin (A) consists only of the epoxy resin (A1), the elongation of the cured product of the resulting epoxy resin composition tends to be low. If the elongation of the cured product is low, the impact resistance of the cured product tends to be low, resulting in a problem that the product is not suitable for applications such as high-pressure gas containers.

Here, the epoxy resin (A2) (hereinafter also simply referred to as "epoxy resin (A2)" or "component (A2)") has a higher elongation of the cured product compared to the epoxy resin (A1), and is relatively likely to exhibit hydrogen gas barrier properties among epoxy resins. Furthermore, the epoxy resins (A2-1) to (A2-4) have high heat resistance because they have two or more ring structures in the molecule. Thus, in the present invention, it is believed that by using the epoxy resins (A1) and (A2) in combination in a predetermined mass ratio as the epoxy resin (A), a cured product with a high elongation can be obtained without significantly impairing the hydrogen gas barrier properties and heat resistance derived from the epoxy resin (A1).
Furthermore, in the present invention, by using resorcinol (B1) as the epoxy resin curing agent (B), it is believed that high hydrogen gas barrier properties derived from the resorcinol skeleton can be obtained, and furthermore, the pot life and shelf life can also be improved.

<Epoxy resin (A)>
The epoxy resin (A) used in the epoxy resin composition of the present invention comprises an epoxy resin (A1) and an epoxy resin (A2), the epoxy resin (A1) is an epoxy resin having a glycidyl group derived from a triphenylmethane type phenol, the epoxy resin (A2) is at least one selected from the group consisting of an epoxy resin (A2-1) having a glycidyl group derived from bisphenol F, an epoxy resin (A2-2) having a glycidyl group derived from bisphenol A, an epoxy resin (A2-3) having a glycidyl group derived from a novolac type phenol, and an epoxy resin (A2-4) having a glycidyl group derived from a polyol having a naphthalene skeleton, and the mass ratio [(A1)/(A2)] of the epoxy resin (A1) to the epoxy resin (A2) in the epoxy resin (A) is 1/99 to 90/10.

(Epoxy resin (A1))
The epoxy resin (A1) is an epoxy resin having a glycidyl group derived from a triphenylmethane type phenol. When the epoxy resin (A) contains the epoxy resin (A1), an epoxy resin composition capable of producing a cured product having high hydrogen gas barrier properties and heat resistance can be obtained.
The epoxy resin (A1) is an epoxy resin having a glycidyl group derived from a triphenylmethane type phenol. The triphenylmethane type phenol means a phenol compound containing a triphenylmethane skeleton, and the epoxy resin (A1) has a structure in which at least a part of the hydrogen atoms of the phenol hydroxyl groups in the triphenylmethane type phenol are replaced with glycidyl groups. Hereinafter, the epoxy resin having a glycidyl group derived from the triphenylmethane type phenol is also simply referred to as a "triphenylmethane type epoxy resin".
The epoxy resin (A1) can be used alone or in combination of two or more.
As the epoxy resin (A1), commercially available products such as EPICLON series "HP-7250" and "HP-7241" manufactured by DIC Corporation can be used.

The epoxy equivalent of the epoxy resin (A1) is preferably 120 g/equivalent or more, more preferably 150 g/equivalent or more, from the viewpoint of improving hydrogen gas barrier properties and heat resistance. Also, from the viewpoint of improving curability, it is preferably 800 g/equivalent or less, more preferably 500 g/equivalent or less, even more preferably 300 g/equivalent or less, and even more preferably 200 g/equivalent or less. When a mixture of two or more epoxy resins is used as the epoxy resin (A1), the epoxy equivalent of the epoxy resin (A1) means the epoxy equivalent of the mixture.

The content of epoxy resin (A1) in epoxy resin (A) is preferably 1.0 to 90 mass%, more preferably 2.0 to 80 mass%, even more preferably 3.0 to 70 mass%, even more preferably 3.0 to 60 mass%, even more preferably 3.0 to 50 mass%, even more preferably 4.0 to 45 mass%, even more preferably 5.0 to 35 mass%, even more preferably 6.0 to 30 mass%, even more preferably 10 to 30 mass%, and even more preferably 15 to 30 mass%. If the content of epoxy resin (A1) in epoxy resin (A) is within the above range, the cured product of the obtained epoxy resin composition is likely to exhibit high hydrogen gas barrier properties and heat resistance, and a decrease in elongation can be suppressed.

(Epoxy resin (A2))
The epoxy resin (A2) is at least one selected from the group consisting of epoxy resins (A2-1) having a glycidyl group derived from bisphenol F, epoxy resins (A2-2) having a glycidyl group derived from bisphenol A, epoxy resins (A2-3) having a glycidyl group derived from a novolac-type phenol, and epoxy resins (A2-4) having a glycidyl group derived from a polyol having a naphthalene skeleton. It is believed that by including the epoxy resin (A2) in the epoxy resin (A), a cured product having a high elongation can be obtained without significantly impairing the hydrogen gas barrier properties and heat resistance derived from the epoxy resin (A1).

[Epoxy resin (A2-1)]
The epoxy resin (A2-1) is an epoxy resin having a glycidyl group derived from bisphenol F. The epoxy resin (A2-1) is preferably bisphenol F diglycidyl ether or an oligomer thereof. The epoxy resin (A2-1) may be solid or liquid at room temperature (25° C.).
The epoxy resin (A2-1) can be used alone or in combination of two or more.

From the viewpoint of obtaining an epoxy resin composition having a long pot life and shelf life and capable of achieving high heat resistance, elongation, and hydrogen gas barrier property, the epoxy equivalent of the epoxy resin (A2-1) is preferably 100 g/equivalent or more, more preferably 120 g/equivalent or more, and even more preferably 150 g/equivalent or more. From the viewpoint of improving curability, the epoxy equivalent is preferably 1200 g/equivalent or less, more preferably 1100 g/equivalent or less, and even more preferably 1050 g/equivalent or less.
In addition, when a mixture of two or more epoxy resins is used as the epoxy resin (A2-1), the epoxy equivalent of the epoxy resin (A2-1) means the epoxy equivalent of the mixture. The same applies to the epoxy resins described below.

As the epoxy resin (A2-1), commercially available products such as "jER806", "jER806H", "jER807", "jER4005P", "jER4007P", and "jER4010P" manufactured by Mitsubishi Chemical Corporation can be used.

[Epoxy resin (A2-2)]
The epoxy resin (A2-2) is an epoxy resin having a glycidyl group derived from bisphenol A. The epoxy resin (A2-2) is typically bisphenol A diglycidyl ether or an oligomer thereof. The epoxy resin (A2-2) may be solid or liquid at room temperature (25° C.).
The epoxy resin (A2-2) can be used alone or in combination of two or more.

The epoxy equivalent of the epoxy resin (A2-2) is preferably 100 g/equivalent or more, more preferably 120 g/equivalent or more, and even more preferably 150 g/equivalent or more, from the viewpoint of obtaining an epoxy resin composition that has a long pot life and shelf life and can achieve high heat resistance, elongation, and hydrogen gas barrier properties. Also, from the viewpoint of improving curability, it is preferably 1200 g/equivalent or less, more preferably 1000 g/equivalent or less, even more preferably 800 g/equivalent or less, even more preferably 600 g/equivalent or less, even more preferably 500 g/equivalent or less, even more preferably 400 g/equivalent or less, even more preferably 300 g/equivalent or less, and even more preferably 250 g/equivalent or less.

As the epoxy resin (A2-2), commercially available products such as "jER825", "jER827", "jER828", "jER834", and "jER1001" manufactured by Mitsubishi Chemical Corporation can be used.

[Epoxy resin (A2-3)]
The epoxy resin (A2-3) is an epoxy resin having a glycidyl group derived from a novolac phenol. The epoxy resin (A2-3) is typically a resin synthesized using a novolac phenol and epichlorohydrin. The novolac phenol referred to here includes phenol novolac, bisphenol A novolac, cresol novolac, etc., and is preferably phenol novolac.
From the viewpoint of improving handleability, the molecular weight of the epoxy resin (A2-3) is preferably 400 to 1500, more preferably 400 to 1000, and even more preferably 400 to 900. In addition, the melt viscosity (150° C.) of the epoxy resin (A2-3) is preferably 9.0 Pa·s or less, more preferably 6.0 Pa·s or less, and even more preferably 3.0 Pa·s or less, and from the viewpoint of improving heat resistance, it is preferably 0.1 Pa·s or more, more preferably 0.3 Pa·s or more.
The epoxy resin (A2-3) can be used alone or in combination of two or more.

The epoxy equivalent of the epoxy resin (A2-3) is preferably 100 g/equivalent or more, more preferably 120 g/equivalent or more, and even more preferably 150 g/equivalent or more, from the viewpoint of obtaining an epoxy resin composition that has a long pot life and shelf life and can achieve high heat resistance, elongation, and hydrogen gas barrier properties. Also, from the viewpoint of improving curability, it is preferably 500 g/equivalent or less, more preferably 400 g/equivalent or less, even more preferably 300 g/equivalent or less, even more preferably 250 g/equivalent or less, and even more preferably 200 g/equivalent or less.

As the epoxy resin (A2-3), commercially available products such as EPICLON series "N730A", "N740", "N770", "N775", and "N865" manufactured by DIC Corporation can be used.

[Epoxy resin (A2-4)]
The epoxy resin (A2-4) is an epoxy resin having a glycidyl group derived from a polyol having a naphthalene skeleton. The polyol having a naphthalene skeleton may have one or more naphthalene skeletons, and is preferably a polyol having one or two naphthalene skeletons.
From the viewpoint of obtaining an epoxy resin composition having a long pot life and shelf life and capable of achieving high hydrogen gas barrier properties, the number of glycidyl groups in the epoxy resin (A2-4) is preferably 2 to 4, and more preferably 2 to 3.

The epoxy equivalent of the epoxy resin (A2-4) is preferably 100 g/equivalent or more, more preferably 120 g/equivalent or more, and even more preferably 130 g/equivalent or more, from the viewpoint of obtaining an epoxy resin composition that has a long pot life and shelf life and can achieve high heat resistance, elongation, and hydrogen gas barrier properties. Also, from the viewpoint of improving curability, it is preferably 500 g/equivalent or less, more preferably 400 g/equivalent or less, even more preferably 300 g/equivalent or less, even more preferably 250 g/equivalent or less, and even more preferably 200 g/equivalent or less.

（式中、ｎは１～３である。）

（式中、ｍ１は０～２、ｍ２は０～２であり、ｍ１とｍ２の合計は０～３である。）
　一般式（Ａ２－４－１）において、ｎは好ましくは１又は２であり、より好ましくは１である。
　一般式（Ａ２－４－２）において、ｍ１は好ましくは０又は１、ｍ２は好ましくは０又は１であり、ｍ１とｍ２の合計は、好ましくは０～２、より好ましくは０である。 The epoxy resin (A2-4) is preferably an epoxy resin represented by the following general formula (A2-4-1) or (A2-4-2).

(In the formula, n is 1 to 3.)

(In the formula, m1 is 0 to 2, m2 is 0 to 2, and the sum of m1 and m2 is 0 to 3.)
In formula (A2-4-1), n is preferably 1 or 2, and more preferably 1.
In formula (A2-4-2), m1 is preferably 0 or 1, m2 is preferably 0 or 1, and the sum of m1 and m2 is preferably 0 to 2, more preferably 0.

More specifically, the epoxy resin (A2-4) may be any of those represented by the following formulas (A2-4-3) to (A2-4-6).

The epoxy resin (A2-4) may be one or more of different types. Among the above, from the viewpoint of obtaining an epoxy resin composition that has a long pot life and shelf life and can achieve high heat resistance, elongation, and hydrogen gas barrier properties, the epoxy resin (A2-4) preferably contains an epoxy resin represented by the above general formula (A2-4-1), and more preferably contains an epoxy resin represented by the above formula (A2-4-3).
The content of the epoxy resin represented by general formula (A2-4-1) in the epoxy resin (A2-4) is preferably 50 mass% or more, more preferably 60 mass% or more, even more preferably 70 mass% or more, still more preferably 80 mass% or more, and still more preferably 90 mass% or more, and is 100 mass% or less.

As the epoxy resin (A2-4), commercially available products such as EPICLON series "HP-4032SS" (epoxy resin represented by formula (A2-4-3)), "HP-4700", "HP-4710" (all epoxy resins represented by formula (A2-4-6)), "EXA-4750" (epoxy resin represented by formula (A2-4-5)), "HP-4770" (epoxy resin represented by formula (A2-4-4)), "HP-5000", "HP-9900-75M", and "HP-9500" manufactured by DIC Corporation can be used.

From the viewpoint of obtaining an epoxy resin composition that has a long pot life and shelf life and can achieve high heat resistance, elongation, and hydrogen gas barrier properties, the epoxy resin (A2) preferably contains at least one selected from the group consisting of epoxy resins (A2-1), (A2-2), and (A2-3), more preferably contains epoxy resin (A2-3), even more preferably contains epoxy resin (A2-1) or (A2-2) and epoxy resin (A2-3), and even more preferably contains epoxy resin (A2-1) and epoxy resin (A2-3).

When the epoxy resin (A2) contains the epoxy resin (A2-3), the content of the epoxy resin (A2-3) in the epoxy resin (A2) is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and even more preferably 60% by mass or more and 100% by mass or less, from the viewpoint of obtaining an epoxy resin composition that has a long pot life and shelf life and can achieve high heat resistance, elongation, and hydrogen gas barrier properties.

When the epoxy resin (A2) contains the epoxy resin (A2-1) or (A2-2) and the epoxy resin (A2-3), the total content of the epoxy resins (A2-1) and (A2-2) in the epoxy resin (A2) is preferably 2.0% by mass or more, more preferably 3.0% by mass or more, and even more preferably 5.0% by mass or more, from the viewpoint of obtaining an epoxy resin composition that has a long pot life and shelf life and can achieve high heat resistance, elongation, and hydrogen gas barrier properties, and is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, and even more preferably 10% by mass or less, from the viewpoint of obtaining an epoxy resin composition that can achieve higher hydrogen gas barrier properties.

The epoxy equivalent of the epoxy resin (A2) is preferably 120 g/equivalent or more, more preferably 150 g/equivalent or more, from the viewpoint of obtaining an epoxy resin composition that has a long pot life and shelf life and can achieve high heat resistance, elongation, and hydrogen gas barrier properties. Also, from the viewpoint of improving curability, it is preferably 800 g/equivalent or less, more preferably 500 g/equivalent or less, even more preferably 300 g/equivalent or less, and even more preferably 250 g/equivalent or less.

The content of epoxy resin (A2) in epoxy resin (A) is preferably 10 to 99 mass%, more preferably 20 to 98 mass%, even more preferably 30 to 97 mass%, even more preferably 40 to 97 mass%, even more preferably 50 to 97 mass%, even more preferably 55 to 96 mass%, even more preferably 65 to 95 mass%, even more preferably 70 to 94 mass%, even more preferably 70 to 90 mass%, and even more preferably 70 to 85 mass%. If the content of epoxy resin (A2) in epoxy resin (A) is within the above range, an epoxy resin composition that has a longer pot life and shelf life and can achieve high heat resistance, elongation, and hydrogen gas barrier properties can be obtained.

The mass ratio of epoxy resin (A1) to epoxy resin (A2) in epoxy resin (A) [(A1)/(A2)] is 1/99 to 90/10, preferably 2/98 to 80/20, more preferably 3/97 to 70/30, even more preferably 5/95 to 70/30, still more preferably 5/95 to 60/40, still more preferably 5/95 to 50/50, still more preferably 5/95 to 40/60, still more preferably 5/95 to 30/70, still more preferably 10/90 to 30/70, still more preferably 15/85 to 30/70, still more preferably 20/80 to 30/70, from the viewpoint of obtaining an epoxy resin composition that has a long pot life and shelf life and can achieve high heat resistance, elongation, and hydrogen gas barrier properties.

The epoxy resin (A) may contain an epoxy resin other than the epoxy resin (A1) and the epoxy resin (A2). Examples of the epoxy resin other than the epoxy resin (A1) and the epoxy resin (A2) include an epoxy resin having an aminoglycidyl group, an epoxy resin having a glycidyloxy group derived from a polyol having no aromatic ring, etc. Examples of the polyol having no aromatic ring include a chain aliphatic polyol that may contain an ether bond, an aliphatic polyol having an alicyclic structure, etc.
However, from the viewpoint of exhibiting high hydrogen gas barrier property, the total content of the epoxy resin (A1) and the epoxy resin (A2) in the epoxy resin (A) is preferably 70 mass% or more, more preferably 80 mass% or more, even more preferably 90 mass% or more, and still more preferably 95 mass% or more and 100 mass% or less.

In addition, from the viewpoint of obtaining a cured product of an epoxy resin composition having a longer pot life and shelf life and high heat resistance, the epoxy resin (A) used in the present invention preferably has a content of an epoxy resin having a glycidyl group derived from resorcinol of 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, even more preferably 2% by mass or less, and even more preferably less than 1% by mass.

The epoxy equivalent of the epoxy resin (A) is preferably 100 g/equivalent or more, more preferably 120 g/equivalent or more, and even more preferably 150 g/equivalent or more, from the viewpoint of obtaining an epoxy resin composition that has a long pot life and shelf life and can achieve high heat resistance, elongation, and hydrogen gas barrier properties. Also, from the viewpoint of improving curability, it is preferably 1200 g/equivalent or less, more preferably 1000 g/equivalent or less, even more preferably 800 g/equivalent or less, even more preferably 600 g/equivalent or less, even more preferably 500 g/equivalent or less, even more preferably 400 g/equivalent or less, even more preferably 300 g/equivalent or less, and even more preferably 250 g/equivalent or less.

<Epoxy Resin Curing Agent (B)>
The epoxy resin curing agent (B) used in the epoxy resin composition of the present invention contains resorcinol (B1), which is believed to achieve high hydrogen gas barrier properties and improve pot life and shelf life.

(Resorcinol (B1))
Resorcinol (B1) is a 1,3-dihydroxybenzene.
The content of resorcinol (B1) in the epoxy resin curing agent (B) is, from the viewpoint of improving the hydrogen gas barrier property, pot life and shelf life, preferably 30 mass% or more, more preferably 40 mass% or more, even more preferably 50 mass% or more, still more preferably 70 mass% or more, still more preferably 80 mass% or more, still more preferably 85 mass% or more, still more preferably 90 mass% or more, and 100 mass% or less.

(Epoxy resin curing agent (B2))
The epoxy resin curing agent (B) may further contain an epoxy resin curing agent (B2) as an epoxy resin curing agent other than resorcinol (B1) within a range that does not impair the effects of the present invention. Examples of the epoxy resin curing agent (B2) include compounds having two or more groups having active hydrogen capable of reacting with the epoxy groups in the epoxy resin (A).
From the viewpoint of suppressing deterioration of pot life, shelf life, heat resistance, elongation, and hydrogen gas barrier property, the epoxy resin curing agent (B2) preferably contains a phenol-based curing agent (B2-1) other than resorcinol (B1).

[Phenol-based curing agent (B2-1) other than resorcinol (B1)]
The phenol-based curing agent (B2-1) may be any phenol compound having two or more phenolic hydroxyl groups, but from the viewpoint of suppressing deterioration in pot life, shelf life, heat resistance, elongation, and hydrogen gas barrier properties, it preferably contains at least one selected from the group consisting of bisphenol F, bisphenol A, novolac-type phenols, and triphenylmethane-type phenols, and more preferably contains at least one selected from the group consisting of novolac-type phenols and triphenylmethane-type phenols.

Examples of novolak-type phenols used as the phenol-based curing agent (B2-1) include phenol novolak, bisphenol A novolak, cresol novolak, etc., which may be used alone or in combination of two or more. Among these, phenol novolak is preferred from the viewpoints of suppressing the decrease in pot life, shelf life, heat resistance, elongation, and hydrogen gas barrier property.
The triphenylmethane type phenol means a phenol compound having a triphenylmethane skeleton (excluding those corresponding to the epoxy resin (A1)).

From the viewpoint of improving heat resistance, the softening point of the novolac phenol is preferably 70 to 250°C, more preferably 75 to 240°C, even more preferably 75 to 200°C, even more preferably 75 to 120°C, and even more preferably 75 to 100°C. The softening point can be measured, for example, by a thermomechanical analyzer (TMA).

The hydroxyl group equivalent of the phenolic curing agent (B2-1) is usually 90 g/equivalent or more, preferably 95 g/equivalent or more, and from the viewpoint of improving curing properties, is preferably 160 g/equivalent or less, more preferably 150 g/equivalent or less, even more preferably 130 g/equivalent or less, and even more preferably 120 g/equivalent or less.

Commercially available products can also be used as the phenol-based hardener (B2-1). For example, examples of novolac-type phenols include the PHENOLITE series "TD-2131", "TD-2106", "TD-2093Y", and "TD-2090" (all phenol novolacs), "VH-4150", "VH-4170", and "KH-6021" (all bisphenol A novolacs), "KA-1160", "KA-1163", and "KA-1165" (all cresol novolacs) manufactured by DIC Corporation. Examples of triphenylmethane-type phenols include "S-TPM-105" manufactured by JFE Chemical Corporation.

The epoxy resin curing agent (B2) may contain other epoxy resin curing agents, such as dihydrazide curing agents, in addition to the phenolic curing agent (B2-1). However, from the viewpoint of suppressing the deterioration of pot life, shelf life, heat resistance, elongation, and hydrogen gas barrier properties, the content of the phenolic curing agent (B2-1) in the epoxy resin curing agent (B2) is preferably 70 mass% or more, more preferably 80 mass% or more, even more preferably 90 mass% or more, and even more preferably 95 mass% or more and 100 mass% or less.

<Curing Accelerator (C)>
From the viewpoint of improving curability, the epoxy resin composition of the present invention preferably further contains a curing accelerator (C).
From the viewpoint of improving curability, the curing accelerator (C) preferably contains at least one selected from the group consisting of imidazoles, tertiary amines, and phosphorus compounds.
Examples of the imidazoles include 1-cyanoethyl-2-ethyl-4-methylimidazole, 2-ethyl-4-methylimidazole, and the like.
Examples of the tertiary amines include tertiary amines or salts thereof that can accelerate the curing of resorcinol (B1) and the phenol-based curing agent (B2-1), such as 1,8-diazabicyclo[5.4.0]-undecene-7 (DBU), 1,5-diazabicyclo[4.3.0]-nonene-5 (DBN), tris(dimethylaminomethylphenol), and the like.
Examples of the phosphorus compound include phosphine compounds such as triphenylphosphine, and phosphonium salts such as tetraphenylphosphonium tetraphenylborate.

The curing accelerator (C) may be used alone or in combination with two or more other types. From the viewpoint of improving curability, the curing accelerator (C) preferably contains at least one selected from the group consisting of imidazoles and tertiary amines, more preferably contains imidazoles, and even more preferably contains 2-ethyl-4-methylimidazole.

<Stress relaxation component (D)>
The epoxy resin composition of the present invention may further contain a stress relaxation component (D) for the purposes of suppressing an excessive increase in elastic modulus of the cured product and reducing the occurrence of cracks.
Examples of the stress relaxation component (D) include elastomer particles such as silicone-based elastomer particles, butyl acrylate-based elastomer particles, polyetheramine-based elastomer particles, other rubber particles, etc. Liquid rubber components such as epoxidized polybutadiene can also be used.
Commercially available stress relaxation components include Kane Ace B series, FM series, M series, and MX series manufactured by Kaneka Corporation, and liquid epoxidized polybutadiene Epolead PB3600 and Epolead PB4700 manufactured by Daicel Corporation.

<Non-reactive diluent (E)>
The epoxy resin composition of the present invention may further contain a non-reactive diluent (E) for the purposes of improving the ease of incorporation of the curing accelerator (C) and improving the tensile stress of the cured product, etc. "Improving the ease of incorporation of the curing accelerator (C)" means that by dissolving the curing accelerator (C) in the non-reactive diluent (E) in advance to prepare a solution, and then incorporation of the solution in the epoxy resin composition, it becomes possible to uniformly dissolve or disperse even a small amount of the curing accelerator (C) in the composition.

The non-reactive diluent (E) may be at least one selected from the group consisting of benzyl alcohol, furfuryl alcohol, tetrahydrofurfuryl alcohol, and aromatic hydrocarbon formaldehyde resins.
Among the above, the aromatic hydrocarbon formaldehyde resin is a resin obtained by reacting an aromatic hydrocarbon with formaldehyde, and examples thereof include toluene formaldehyde resin obtained by reacting toluene with formaldehyde, xylene formaldehyde resin obtained by reacting xylene with formaldehyde, mesitylene formaldehyde resin obtained by reacting mesitylene with formaldehyde, and pseudocumene formaldehyde resin obtained by reacting pseudocumene with formaldehyde. Among these, the aromatic hydrocarbon formaldehyde resin preferably contains xylene formaldehyde resin from the viewpoints of improving the ease of blending the curing accelerator (C), improving the tensile stress of the cured product, and maintaining various physical properties other than the tensile stress of the cured product.
Commercially available aromatic hydrocarbon formaldehyde resins include, for example, xylene formaldehyde resins (hereinafter also simply referred to as "xylene resins") manufactured by Fudow Co., Ltd., such as "NIKANOL Y-50", "NIKANOL Y-100", "NIKANOL Y-300", "NIKANOL Y-1000", "NIKANOL L", "NIKANOL LL", "NIKANOL LLL", "NIKANOL G", "NIKANOL H", and "NIKANOL H-80".

Among the above, from the viewpoints of improving the ease of blending the curing accelerator (C), improving the tensile stress of the cured product, and maintaining various physical properties other than the tensile stress of the cured product, the non-reactive diluent (E) preferably contains at least one selected from the group consisting of benzyl alcohol and aromatic hydrocarbon formaldehyde resins, and more preferably contains at least one selected from the group consisting of benzyl alcohol and xylene formaldehyde resins.

<Solvent>
The epoxy resin composition of the present invention may further contain a solvent from the viewpoint of lowering the viscosity of the composition and enhancing the impregnation property into the reinforcing fibers. Examples of the solvent include organic solvents other than the non-reactive diluent (E).
Examples of the solvent include alcohol-based solvents such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, 2-butoxyethanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, and 1-propoxy-2-propanol; ester-based solvents such as ethyl acetate and butyl acetate; ketone-based solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ether-based solvents such as diethyl ether and diisopropyl ether; and hydrocarbon-based solvents such as toluene. Among these, one or more types can be used.
From the viewpoint of the solubility of the components contained in the epoxy resin composition and the ease of removing the solvent, the solvent is preferably at least one selected from the group consisting of alcohol-based solvents, ester-based solvents, ketone-based solvents, and hydrocarbon-based solvents having 8 or less carbon atoms, and more preferably at least one selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, ethyl acetate, methyl ethyl ketone, methyl isobutyl ketone, and toluene.

<Content>
The content ratio of the epoxy resin (A) to the epoxy resin curing agent (B) in the epoxy resin composition of the present invention is such that the functional group equivalent ratio of the epoxy resin (A) to the epoxy resin curing agent (B) [(B)/(A)] is preferably 0.5 to 2.0, more preferably 0.75 to 1.5, and even more preferably 0.8 to 1.2.
In this specification, unless otherwise specified, the functional group equivalent ratio [(B)/(A)] means (the number of active hydrogen atoms in the epoxy resin curing agent (B)/the number of epoxy groups in the epoxy resin (A)).

The content of the epoxy resin (A) in the epoxy resin composition is preferably 40 to 95 mass%, more preferably 50 to 90 mass%, even more preferably 60 to 85 mass%, and still more preferably 65 to 80 mass%.
When the epoxy resin composition contains water or the solvent, the content of the epoxy resin (A) in 100% by mass of the solid content of the epoxy resin composition is preferably 40 to 95% by mass, more preferably 50 to 90% by mass, even more preferably 60 to 85% by mass, and still more preferably 65 to 80% by mass. Note that the "solid content of the epoxy resin composition" means the amount excluding water and the solvent in the epoxy resin composition.
The content of the epoxy resin curing agent (B) in the epoxy resin composition is preferably 5.0 to 60 mass%, more preferably 10 to 50 mass%, even more preferably 15 to 40 mass%, and still more preferably 20 to 35 mass%.
When the epoxy resin composition contains water or the solvent, the content of the epoxy resin curing agent (B) in 100% by mass of the solid content of the epoxy resin composition is preferably 5.0 to 60% by mass, more preferably 10 to 50% by mass, even more preferably 15 to 40% by mass, and still more preferably 20 to 35% by mass.

When the epoxy resin composition contains a curing accelerator (C), the content of the curing accelerator (C) in the epoxy resin composition is, from the viewpoint of improving curability, preferably 0.01 to 10 parts by mass, more preferably 0.01 to 5 parts by mass, even more preferably 0.05 to 1 part by mass, and even more preferably 0.05 to 0.5 parts by mass, per 100 parts by mass of the total amount of the epoxy resin (A) and the epoxy resin curing agent (B).

From the viewpoint of effectively exerting the effects of the present invention, the total content of the epoxy resin (A), epoxy resin curing agent (B), and curing accelerator (C) in the epoxy resin composition of the present invention is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more and 100% by mass or less. When the epoxy resin composition contains water or the solvent, the total content of the epoxy resin (A), epoxy resin curing agent (B), and curing accelerator (C) in 100% by mass of the solid content of the epoxy resin composition is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more and 100% by mass or less.

When the epoxy resin composition contains a stress relaxation component (D), the content of the stress relaxation component (D) in the epoxy resin composition is preferably 1.0 to 30 parts by mass, more preferably 3.0 to 20 parts by mass, even more preferably 5.0 to 15 parts by mass, and even more preferably 8.0 to 12 parts by mass, per 100 parts by mass of the total amount of the epoxy resin (A) and the epoxy resin hardener (B).

When the epoxy resin composition contains a non-reactive diluent (E), the content of the non-reactive diluent (E) in the epoxy resin composition is preferably 0.1 to 20 parts by mass, more preferably 0.2 to 15 parts by mass, even more preferably 0.3 to 10 parts by mass, still more preferably 0.3 to 7 parts by mass, even more preferably 0.3 to 5 parts by mass, even more preferably 0.4 to 3 parts by mass, and even more preferably 0.5 to 2 parts by mass, per 100 parts by mass of the total amount of the epoxy resin (A) and the epoxy resin curing agent (B), from the viewpoints of improving the ease of blending the curing accelerator (C), improving the tensile stress of the cured product, and maintaining various physical properties other than the tensile stress of the cured product.

When the epoxy resin composition contains a solvent, the content is not particularly limited, but from the viewpoint of reducing the viscosity of the epoxy resin composition, the content is preferably 5 mass% or more, more preferably 10 mass% or more, and even more preferably 15 mass% or more in the epoxy resin composition. Also, from the viewpoint of ease of removing the solvent, the content is preferably 95 mass% or less, more preferably 90 mass% or less, even more preferably 80 mass% or less, and even more preferably 70 mass% or less.

The epoxy resin composition of the present invention may be a solvent-free epoxy resin composition. Specifically, the content of the solvent in the epoxy resin composition may be less than 5% by mass, preferably less than 2% by mass, more preferably less than 1% by mass, and even more preferably less than 0.1% by mass.

The epoxy resin composition of the present invention is preferably a non-aqueous epoxy resin composition. Specifically, the water content in the epoxy resin composition is preferably less than 5% by mass, more preferably less than 2% by mass, even more preferably less than 1% by mass, and even more preferably less than 0.1% by mass. However, the non-aqueous epoxy resin composition referred to here means an epoxy resin composition in which the amount of water intentionally blended is small, and does not exclude the inclusion of water that has been unintentionally mixed in.

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, reactive diluents, pigments, leveling agents, tackifiers, and flame retardants depending on the application.

<Hydrogen gas permeability coefficient>
The cured product of the epoxy resin composition of the present invention exhibits high hydrogen gas barrier properties. The hydrogen gas permeability coefficient of the cured product of the epoxy resin composition of the present invention at 23°C is preferably 7.0 x ^10-11 [cc cm/( ^cm2 -s-cmHg)] or less, more preferably 6.0 x ^10-11 [cc cm/( ^cm2 -s-cmHg)] or less, even more preferably 5.0 x ^10-11 [cc cm/( ^cm2 -s-cmHg)] or less, and still more preferably 3.5 x ^10-11 [cc cm/( ^cm2 -s-cmHg)] or less.
The hydrogen gas permeability coefficient of the cured product of the epoxy resin composition is measured in accordance with JIS K 7126-1 under dry conditions at 23° C. (23° C., humidity 0%). Specifically, it can be measured by the method described in the examples.

<Glass transition temperature>
From the viewpoint of high heat resistance, the glass transition temperature (Tg) of the cured product of the epoxy resin composition of the present invention is preferably 100° C. or higher, more preferably 105° C. or higher, even more preferably 110° C. or higher, and still more preferably 115° C. or higher. The upper limit of the glass transition temperature is not particularly limited, but may be, for example, 200° C. or lower.
The glass transition temperature of the cured product of the epoxy resin composition can be measured using a dynamic viscoelasticity measuring device, specifically, by the method described in the examples.

<Tensile elongation>
The tensile elongation of the cured product of the epoxy resin composition of the present invention is preferably 3.0% or more, more preferably 3.5% or more, even more preferably 3.8% or more, and still more preferably 4.0% or more, from the viewpoint of improving impact resistance, etc. The upper limit of the tensile elongation is not particularly limited, but from the viewpoint of improving mechanical strength, it may be, for example, 10% or less.
The tensile elongation of the cured product of the epoxy resin composition can be measured in accordance with JIS K7161-1:2014 and JIS K7161-2:2014, specifically by the method described in the examples.

<Pot life>
The epoxy resin composition of the present invention has a long pot life (workable time). For example, the pot life of the epoxy resin composition at 23° C. is preferably 3 hours or more, more preferably 6 hours or more, even more preferably 12 hours or more, and still more preferably 24 hours or more. The pot life of the epoxy resin composition can be specifically measured by the method described in the Examples.

<Shelf life>
The epoxy resin composition of the present invention has a long shelf life. For example, the shelf life of the epoxy resin composition at 0° C. is preferably 7 days or more, more preferably 14 days or more, and even more preferably 30 days or more. The shelf life of the epoxy resin composition can be specifically measured by the method described in the Examples.

The method for preparing the epoxy resin composition of the present invention is not particularly limited, and the epoxy resin (A), the epoxy resin curing agent (B), and other components as necessary can be mixed and prepared using a known method and device. The order of mixing the components contained in the epoxy resin composition is also not particularly limited, and the components (A1) and (A2) constituting the epoxy resin (A) may be mixed and then mixed with other components, or the components (A1), (A2) constituting the epoxy resin (A) and other components may be mixed simultaneously to prepare the epoxy resin composition.
From the viewpoint of preventing gelation from proceeding before use, it is preferable to contact and mix the components contained in the epoxy resin composition immediately before use. The temperature when mixing the components contained in the epoxy resin composition can be appropriately adjusted depending on the viscosity of the epoxy resin, but from the viewpoint of suppressing an increase in viscosity, it is preferably 120° C. or less, more preferably 100° C. or less, and from the viewpoint of miscibility with the epoxy resin, it is preferably 20° C. or more, more preferably 25° C. or more. 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.

[Cured product]
The cured product of the epoxy resin composition of the present invention (hereinafter, simply referred to as "cured product of the present invention") is obtained by curing the above-mentioned epoxy resin composition of the present invention by a known method. The curing conditions of the epoxy resin composition are appropriately selected depending on 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 application of the epoxy resin composition is a coating material, the cured product of the composition is usually in the form of a film. From the viewpoint of effectively exerting the effects of the present invention, the cured product of the present invention is preferably a matrix resin of a fiber-reinforced composite material described below.

[Prepreg]
The prepreg of the present invention includes the epoxy resin composition and reinforcing fibers. More specifically, the prepreg of the present invention is obtained by impregnating reinforcing fibers with the epoxy resin composition.

<Reinforced Fiber>
Examples of the form of the reinforcing fiber used in the prepreg include short fiber, long fiber, and continuous fiber. Among these, from the viewpoint of producing a high-pressure gas container by a filament winding method or a tape winding method using the obtained prepreg, long fiber or continuous fiber is preferred, and continuous fiber is more preferred.
In this specification, short fibers refer to fibers having a fiber length of 0.1 mm or more and less than 10 mm, long fibers refer to fibers having a fiber length of 10 mm or more and 100 mm or less, and continuous fibers refer to fiber bundles having a fiber length of more than 100 mm.

The continuous fibers may be in the form of a tow, a sheet, a tape, etc., and the continuous fibers constituting the sheet or tape may be unidirectional (UD) materials, woven fabrics, nonwoven fabrics, etc.
From the viewpoint of producing a high-pressure gas container by a filament winding method or a tape winding method using a prepreg, the shape of the continuous fibers is preferably a tow or tape, more preferably a tow. The number of continuous fiber bundles (filament number) constituting a tow is preferably 3K to 50K, more preferably 6K to 40K, from the viewpoint of easily obtaining high strength and high elastic modulus.

In the case of continuous fibers, the average fiber length of the continuous fiber bundle is not particularly limited, but from the viewpoint of molding processability, it is preferably 1 to 10,000 m, more preferably 100 to 10,000 m.
The average fineness of the continuous fiber bundle is preferably 50 to 2000 tex (g/1000 m), more preferably 200 to 1500 tex, and even more preferably 500 to 1500 tex, from the viewpoint of moldability and the viewpoint of facilitating obtaining high strength and high elastic modulus.
The average tensile modulus of the continuous fiber bundle is preferably 50 to 1000 GPa.

Examples of the material of the reinforcing fiber include inorganic fibers such as carbon fiber, glass fiber, basalt fiber, metal fiber, boron fiber, and ceramic fiber; and organic fibers such as aramid fiber, polyoxymethylene fiber, aromatic polyamide fiber, polyparaphenylene benzobisoxazole fiber, and ultra-high molecular weight polyethylene fiber. Among these, inorganic fibers are preferred from the viewpoint of obtaining high strength. Since the reinforcing fiber is lightweight, has high strength, and has a high elastic modulus, the reinforcing fiber is preferably at least one selected from the group consisting of carbon fiber, glass fiber, and basalt fiber, and is more preferably carbon fiber from the viewpoint of strength and light weight.
Examples of carbon fibers include polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, etc. Carbon fibers made from plant-derived raw materials such as lignin and cellulose can also be used.

The reinforcing fibers may be treated with a treatment agent, such as a surface treatment agent or a sizing agent.
The surface treatment agent is preferably a silane coupling agent, for example, a silane coupling agent having a vinyl group, a silane coupling agent having an amino group, a silane coupling agent having an epoxy group, a silane coupling agent having a (meth)acrylic group, a silane coupling agent having a mercapto group, etc.

Examples of the bundling agents include urethane-based bundling agents, epoxy-based bundling agents, acrylic-based bundling agents, polyester-based bundling agents, vinyl ester-based bundling agents, polyolefin-based bundling agents, polyether-based bundling agents, and carboxylic acid-based bundling agents, and among these, one or more of these may be used in combination. Examples of bundling agents that combine two or more types include urethane/epoxy-based bundling agents, urethane/acrylic-based bundling agents, and urethane/carboxylic acid-based bundling agents.

The amount of the treatment agent is preferably 0.001 to 5% by mass, more preferably 0.1 to 3% by mass, and even more preferably 0.5 to 2% by mass relative to the reinforcing fiber, from the viewpoint of improving the interfacial adhesion with the cured product of the epoxy resin composition and further improving the strength and impact resistance of the resulting prepreg and composite material.

Commercially available products can also be used as reinforcing fibers. Commercially available continuous carbon fibers (tows) include, for example, Toray Industries, Inc.'s Torayca (registered trademark) yarns "T300", "T300B", "T400HB", "T700SC", "T800SC", "T800HB", "T830HB", "T1000GB", "T100GC", "M35JB", "M40JB", "M46JB", "M50JB", "M55J", "M55JB", "M60JB", "M30SC", and "Z600"series; and TENAX (registered trademark) "HTA40" series, "HTS40" series, "HTS45" series, and "HTS45P12" series manufactured by Teijin Limited. carbon fiber tows of the "STS40" series, "UTS50" series, "ITS50" series, "ITS55" series, "IMS40" series, "IMS60" series, "IMS65" series, "IMS65P12" series, "HMA35" series, "UMS40" series, "UMS45" series, "UMS55" series, and "HTS40MC" series manufactured by Mitsubishi Chemical Corporation; and the like.
In addition, examples of commercially available continuous carbon fibers other than tow include Toray Industries, Inc.'s TORAYCA (registered trademark) cloth "CO6142", "CO6151B", "CO6343", "CO6343B", "CO6347B", "CO6644B", "CK6244C", "CK6273C", "CK6261C", "UT70" series, "UM46" series, "BT70" series, "T300" series, "T300B" series, "T400HB" series, "T700SC" series, "T800SC" series, "T800HB" series, "T1000GB" series, "M35JB" series, and "M40 JB series, M46JB series, M50JB series, M55J series, M55JB series, M60JB series, M30SC series, and Z600GT series; carbon fiber fabrics such as PYROFIL (registered trademark) TR3110M, TR3523M, TR3524M, TR6110HM, TR6120HM, TRK101M, TRK510M, TR3160TMS, TRK979PQRW, TRK976PQRW, TR6185HM, and TRK180M manufactured by Mitsubishi Chemical Corporation; and the like.

<Content>
The content of the reinforcing fibers in the prepreg of the present invention is in a range in which the volume fraction of the reinforcing fibers in the prepreg is preferably 0.10 or more, more preferably 0.20 or more, even more preferably 0.30 or more, and even more preferably 0.40 or more, from the viewpoint of obtaining high strength and high elastic modulus. Also, from the viewpoint of hydrogen gas barrier property, impact resistance, and moldability, the content is preferably 0.85 or less, more preferably 0.80 or less, and even more preferably 0.70 or less.
The volume fraction _Vf1 of the reinforcing fibers in the prepreg can be calculated from the following formula.
Vf ₁ = {mass (g) of reinforcing fiber/specific gravity of reinforcing fiber} ÷ [{mass (g) of reinforcing fiber/specific gravity of reinforcing fiber} + {mass (g) of solid content of impregnated epoxy resin composition/specific gravity of solid content of epoxy resin composition}]

In addition, from the viewpoint of obtaining the effects of the present invention, the total content of the solids and reinforcing fibers in the epoxy resin composition constituting the prepreg of the present invention is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, and 100% by mass or less.

<Prepreg shape and manufacturing method>
The shape of the prepreg varies depending on the form of the reinforcing fibers used. From the viewpoint of producing high-pressure gas containers by the filament winding method or tape winding method, the prepreg of the present invention is preferably a tow prepreg or a tape prepreg.
Among tape prepregs, the prepreg of the present invention is preferably a unidirectional (UD) tape. Unidirectional tape (hereinafter also referred to as "UD tape") is particularly suitable for use in the tape winding method. The UD tape may be cut into small pieces for use.
In addition, when continuous fibers in the form of unidirectional (UD) material, woven fabric, nonwoven fabric, etc. are used, a prepreg in the form of a sheet can also be formed.

The method for producing the prepreg is not particularly limited, and it can be produced according to a conventional method. For example, the prepreg can be obtained by impregnating the reinforcing fiber with an epoxy resin composition containing an epoxy resin (A), an epoxy resin curing agent (B), and other components used as necessary, and then subjecting the reinforcing fiber to a drying process to remove the solvent.

The method of impregnating the reinforcing fiber with the epoxy resin composition is not particularly limited, and a known method can be used as appropriate depending on the form of the reinforcing fiber, etc. For example, when producing a tow prepreg, a method can be mentioned in which a continuous fiber bundle unwound from a roll is immersed in a resin bath filled with the above-mentioned epoxy resin composition, and after impregnation with the composition, the bundle is pulled up from the resin bath. Then, a step of removing excess epoxy resin composition using a squeeze roll or the like can be performed.
The impregnation with the epoxy resin composition can be carried out under pressurized or reduced pressure conditions, if necessary.

Then, if necessary, the reinforcing fibers impregnated with the epoxy resin composition are subjected to a drying process to remove the solvent. There are no particular restrictions on the drying conditions in the drying process, but it is preferable that the conditions are such that the solvent can be removed and the curing of the epoxy resin composition does not proceed excessively. From this perspective, for example, the drying temperature can be selected in the range of 30 to 120°C, and the drying time can be selected in the range of 10 seconds to 5 minutes.

The prepreg obtained through the drying process can be wound up once to form a prepreg product, or it can be dried without being wound up and then continuously used to manufacture fiber-reinforced composite materials. In particular, when making a tape- or sheet-shaped prepreg product, it is preferable to wind it up to form a roll-shaped product.

[Fiber-reinforced composite materials]
The fiber reinforced composite material (FRP, hereinafter also simply referred to as "composite material") of the present invention is a cured product of the prepreg, and contains a cured product of the epoxy resin composition and reinforcing fibers. The fiber reinforced composite material of the present invention has high hydrogen barrier properties due to the inclusion of a cured product of the epoxy resin composition. The prepreg, epoxy resin composition, reinforcing fibers, and preferred embodiments thereof used in the production of the composite material are the same as those described above.

The content of the reinforcing fibers in the fiber-reinforced composite is preferably in a range such that the volume fraction of the reinforcing fibers in the fiber-reinforced composite is 0.10 or more, more preferably 0.20 or more, even more preferably 0.30 or more, and even more preferably 0.40 or more, from the viewpoints of obtaining high strength and high elastic modulus, and is preferably in a range of 0.85 or less, more preferably 0.80 or less, and even more preferably 0.70 or less, from the viewpoints of hydrogen gas barrier property, impact resistance, and moldability.
The volume fraction Vf of the reinforcing fibers in the fiber-reinforced composite material can be calculated from the following formula.
Vf={mass (g) of reinforcing fiber/specific gravity of reinforcing fiber}÷[{mass (g) of reinforcing fiber/specific gravity of reinforcing fiber}+{mass (g) of cured product of epoxy resin composition/specific gravity of cured product of epoxy resin composition}]

<Method of manufacturing fiber reinforced composite material>
The composite material can be produced by premolding the prepreg into a desired shape and then curing the prepreg. For example, when the composite material of the present invention is applied to a molded article having a hollow shape such as a pipe, a shaft, a cylinder, or a tank, the composite material can be produced by molding the tow prepreg by a filament winding method, a braiding method, a 3D printer method, or the like.
In the filament winding method, specifically, a tow prepreg is wound around the outer surface of a balloon, mandrel, or liner, and then heat cured to produce a composite material of a desired shape.
In the braiding method, for example, a balloon or a mandrel is used to braid the tow prepreg into a unidirectional or braided structure by a braider to form a prepreg, and then the prepreg is heated and cured. Note that in the braiding method, the tow prepreg can also be braided and formed without using a balloon or a mandrel.

When using sheet-shaped prepregs such as unidirectional (UD) materials, woven fabrics, and nonwoven fabrics, a composite material can be produced by placing one or more prepregs in a mold and heating and curing them under vacuum or pressurized conditions.

The method of curing the prepreg in the manufacture of the composite material is not particularly limited, and is carried out by a known method at a temperature and for a time sufficient to cure the epoxy resin composition contained in the prepreg. The prepreg curing conditions depend on the thickness of the prepreg and the composite material to be formed, but for example, the curing temperature can be selected in the range of 10 to 180°C and the curing time in the range of 5 minutes to 200 hours, and from the viewpoint of productivity, the curing temperature is preferably 80 to 180°C and the curing time in the range of 10 minutes to 5 hours.

From the viewpoint of manufacturing using tow prepregs, the composite material of the present invention is suitable for use in hollow molded articles such as pipes, shafts, gas cylinders, tanks, and cylinders (cylinders whose both ends are closed by two disks). Since the composite material has excellent hydrogen gas barrier properties, it is particularly suitable as a material for forming high-pressure gas containers.

[High pressure gas cylinder]
The high pressure gas container of the present invention contains the fiber reinforced composite material. It is sufficient that at least a part of the high pressure gas container of the present invention is made of the fiber reinforced composite material. For example, in the case of a high pressure gas container having a liner and an outer layer provided so as to cover the outer surface of the liner, at least one of the liner and the outer layer may be made of the fiber reinforced composite material. In addition, in the case of a linerless high pressure gas container, the entire container may be made of the fiber reinforced composite material.

Specific examples of high-pressure gas containers containing fiber-reinforced composite materials include: (1) a configuration having a metal liner and an outer layer made of the fiber-reinforced composite material of the present invention; (2) a configuration having a resin liner and an outer layer made of the fiber-reinforced composite material of the present invention; (3) a configuration having a liner made of the fiber-reinforced composite material of the present invention and an outer layer made of a material other than the fiber-reinforced composite material; and (4) a configuration consisting only of a container made of the fiber-reinforced composite material of the present invention (linerless).

Examples of the metal used in the "metallic liner" in (1) above include light alloys such as aluminum alloys and magnesium alloys.

The resin used in the "resin liner" in (2) above is not particularly limited as long as it is a resin having excellent hydrogen gas barrier properties and pressure resistance, and examples of such resins include thermoplastic resins, cured products of thermosetting resins, cured products of photocurable resins, etc. Among these, thermoplastic resins are preferred from the viewpoint of ease of molding the liner.
Examples of the thermoplastic resin include polyamide resins, polyester resins, polyolefin resins, polyimide resins, polycarbonate resins, polyetherimide resins, polyamideimide resins, polyphenylene etherimide resins, polyphenylene sulfide resins, polysulfone resins, polyethersulfone resins, polyarylate resins, liquid crystal polymers, polyetheretherketone resins, polyetherketone resins, polyetherketoneketone resins, polyetheretherketoneketone resins, polybenzimidazole resins, and the like. These may be used alone or in combination of two or more.
From the viewpoint of hydrogen gas barrier properties and pressure resistance, among the thermoplastic resins, at least one selected from the group consisting of polyamide resins and polyolefin resins is preferred, and polyamide resins are more preferred.
In addition, from the viewpoint of improving impact resistance, the resin liner may contain the above-mentioned stress relaxation component.

The "outer layer made of a material other than the fiber-reinforced composite material" in (3) above is preferably an outer layer made of a fiber-reinforced composite material other than the fiber-reinforced composite material of the present invention, from the viewpoint of improving reinforcement.

In the above embodiments (1) to (3), the outer layer can be formed so as to cover the outer surface of the main body portion of the liner without any gaps.
The outer layer may be provided directly on the outer surface of the liner, or may be provided on one or more other layers provided on the outer surface of the liner. For example, an adhesive layer may be provided between the liner and the outer layer to improve adhesion between the liner and the outer layer.

When the high-pressure gas container is of the above-mentioned embodiment (1) or (2), the thickness of the outer layer made of the fiber-reinforced composite material of the present invention can be appropriately selected according to the capacity, shape, etc. of the high-pressure gas container, but from the viewpoint of imparting high hydrogen gas barrier properties and impact resistance, it is preferably 100 μm or more, more preferably 200 μm or more, and even more preferably 400 μm or more, and from the viewpoint of miniaturization and weight reduction of the high-pressure gas storage tank, it is preferably 80 mm or less, more preferably 60 mm or less.

When the high-pressure gas container is of the above-mentioned embodiment (3), the thickness of the liner made of the fiber-reinforced composite material of the present invention can be appropriately selected according to the capacity, shape, etc. of the high-pressure gas container, but from the viewpoint of hydrogen gas barrier properties and pressure resistance, it is preferably 100 μm or more, more preferably 200 μm or more, and even more preferably 400 μm or more, and from the viewpoint of miniaturization and weight reduction of the high-pressure gas container, it is preferably 60 mm or less, more preferably 40 mm or less.

When the high-pressure gas container is of the above embodiment (4), the thickness of the container made of the fiber-reinforced composite material of the present invention can be appropriately selected depending on the capacity, shape, etc. of the high-pressure gas container, but from the viewpoint of hydrogen gas barrier properties and pressure resistance, it is preferably 1 mm or more, more preferably 2 mm or more, and even more preferably 5 mm or more, and from the viewpoint of miniaturization and weight reduction of the high-pressure gas container, it is preferably 80 mm or less, more preferably 60 mm or less.

The content of the reinforcing fibers in the liner, outer layer or high-pressure gas container made of the fiber-reinforced composite material of the present invention is preferably in a range such that the volume fraction of the reinforcing fibers is 0.10 or more, more preferably 0.20 or more, even more preferably 0.30 or more, and even more preferably 0.40 or more, from the viewpoint of obtaining high strength and high elastic modulus. Also, from the viewpoint of hydrogen gas barrier property, impact resistance and moldability, the volume fraction is preferably in a range such that the volume fraction is 0.85 or less, more preferably 0.80 or less, even more preferably 0.75 or less, and even more preferably 0.70 or less.
The volume fraction of the reinforcing fibers can be calculated in the same manner as described above.

Among the above, from the viewpoint of light weight and the requirement for high hydrogen barrier properties for fiber-reinforced composite materials, the high-pressure gas container is preferably in the above-mentioned form (2), (3) or (4), and more preferably in the form (3) or (4).

The high-pressure gas container may further include components such as a nozzle and a valve that are made of a material other than the fiber-reinforced composite material. In addition, the surface of the high-pressure gas container may be formed with any layer such as a protective layer, a paint layer, or a rust-preventing layer.

The gas to be stored in the high-pressure gas container may be any gas that is in a gaseous state at 25°C and 1 atm, and examples of such gas include hydrogen, oxygen, carbon dioxide, nitrogen, argon, LPG, alternative fluorocarbons, methane, etc. Among these, hydrogen is preferred from the viewpoint of the effectiveness of the present invention.

<Manufacturing method of high pressure gas cylinder>
As a method for producing the high pressure gas container of the present invention, the above-mentioned methods for producing fiber reinforced composite materials can be appropriately used depending on the form of the reinforcing fiber or prepreg used. When a high pressure gas container is produced using a tow prepreg, the tow prepreg can be molded by a filament winding method, a braiding method, a 3D printer method, or the like to produce the high pressure gas container.
When the high-pressure gas container is in the above embodiment (1) or (2), the tow prepreg is wound around the outer surface of the metal or resin liner by a filament winding method, and then the tow prepreg is heated and cured to form an outer layer made of a fiber-reinforced composite material, thereby manufacturing the high-pressure gas container.
When the high-pressure gas container has the above embodiment (3) or (4), the tow prepreg is formed into a container shape by a filament winding method, a braiding method, a 3D printer method, or the like, and then heated and cured, thereby producing a high-pressure gas container.

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. Measurements and evaluations in the examples were performed using the following methods.

<Hydrogen gas permeability coefficient [cc cm/(cm ² s cmHg)]>
The epoxy resin composition prepared in each example was poured into a mold (120 mm x 120 mm x 1 mm) coated with a mold release agent (Chemtrend Japan Co., Ltd.'s "Kemlease AF-7 EZ"), and heat cured for 2 hours under conditions of 80 to 160°C to produce a plate-shaped molded body with a thickness of 1 mm. From this plate-shaped molded body, a circular test piece with a thickness of 1 mm and a diameter of 20 mm was prepared. For the test piece, the hydrogen gas permeability coefficient [cc cm/(cm2·s·cmHg)] at 23°C was measured by a differential pressure method using a gas permeability measuring device (GTR-30X manufactured by GTR Tech Co., Ltd.) in accordance with JIS K 7126-1:2006 ( ²³ °C, humidity 0%).

<Glass transition temperature (Tg)>
The epoxy resin composition prepared in each example was molded into a flat plate of 200 mm × 200 mm × 2 mm thickness, and cured by heating at 120° C. for 30 minutes and then at 160° C. for 2 hours to produce a cured product. A rectangular piece measuring 50 mm × 10 mm × 2 mm thickness was cut out from the cured product to prepare a dynamic viscoelasticity (DMA) measurement sample.
The above sample was subjected to DMA bending measurement under the following conditions using a rotational rheometer "ARES G2" (manufactured by TA Instruments). The peak top value of tan δ, plotted on the vertical axis and the measurement temperature on the horizontal axis, was taken as the Tg of the cured product. The higher the glass transition temperature (Tg) of the cured product, the more excellent the heat resistance.
(Measurement conditions)
Measurement mode: bending DMA measurement Measurement temperature: 30 to 180°C
Heating rate: 5° C./min

<Tensile stress, tensile elongation, tensile modulus>
The epoxy resin composition prepared in each example was molded into a flat plate of 200 mm × 200 mm × 2 mm thickness, and cured by heating at 120° C. for 30 minutes and then at 160° C. for 2 hours to produce a cured product. A rectangular piece measuring 180 mm × 15 mm × 2 mm thickness was cut out from the cured product to prepare a tensile test specimen.
Using the test piece, a tensile test was performed under the following conditions (N=3) in accordance with JIS K7161-1:2014 and JIS K7161-2:2014 using a precision universal testing machine ("Autograph AGX-plus" manufactured by Shimadzu Corporation), and the tensile stress, tensile elongation, and tensile modulus were calculated from the following formulas. The length of the test piece at break was calculated from the displacement of the load cell at break.
(Measurement conditions)
Distance between grippers: 115 mm
Distance between gauge lines: 75mm
Load cell (tensile force): 1 kN
Tensile speed: 1 mm/min (tensile direction: longitudinal direction of test piece)
(calculation formula)
Tensile stress (MPa)=load at break of test piece (N)/initial cross-sectional area of test piece (mm ² )
Tensile elongation (%)=(length of test piece at break−initial length of test piece)/(initial length of test piece)×100
Tensile modulus (GPa)=elastic modulus gradient (N/mm)×initial test piece length (mm)/initial test piece cross-sectional area (mm ² )×10 ⁻³
The elastic modulus gradient here means the slope of the stress-strain curve corresponding to the two points where the tensile strain (the value obtained by dividing the increase in the gauge length by the gauge length) is 0.05% and 0.25%.

<Pot life>
After measuring the initial viscosity at 23°C of the epoxy resin composition prepared in each example, 10 g of the epoxy resin composition was placed in a plastic cup (diameter 46 mm) and stored at 23°C. The time [h] until the viscosity of the epoxy resin composition became at least twice the initial viscosity was measured and shown in the table. In the table, those whose pot life exceeded 24 hours are indicated as ">24". The longer the time, the better the pot life.
The viscosity of the epoxy resin composition was measured using a rotational rheometer "ARES G2" (manufactured by TA Instruments) in the measurement mode: rotational mode, using a 25 mm circular plate.

<Shelf life>
10 g of the epoxy resin composition prepared in each example was placed in a plastic cup (diameter 46 mm) and stored at 0°C. After a certain period of time had elapsed, the epoxy resin composition was returned to room temperature (23°C) and visually observed for fluidity. The number of days (days) until the composition began to lose fluidity after storage at 0°C is shown in the table. In the table, those whose shelf life exceeded 30 days are indicated as ">30". The longer the time, the better the shelf life.

Example 1 (Preparation and Evaluation of Epoxy Resin Composition)
As the epoxy resin (A), a triphenylmethane type epoxy resin (DIC Corporation's "HP-7241", epoxy equivalent: 172 g/equivalent) was used as component (A1), and bisphenol A diglycidyl ether (Mitsubishi Chemical Corporation's "jER828", epoxy equivalent: 186 g/equivalent), a phenol novolac type epoxy resin (DIC Corporation's "N730A", epoxy equivalent: 176 g/equivalent), and a phenol novolac type epoxy resin (DIC Corporation's "N740", epoxy equivalent: 183 g/equivalent) were used as component (A2). As the epoxy resin curing agent (B), resorcinol was used as component (B1). In addition, 2-ethyl-4-methylimidazole (Tokyo Chemical Industry Co., Ltd.) was used as the curing accelerator (C). These were blended and mixed in the parts by mass shown in Table 1 to obtain an epoxy resin composition. The functional group equivalent ratio [(B)/(A)] of the epoxy resin (A) to the epoxy resin curing agent (B) was 1/1.
The epoxy resin compositions thus obtained were evaluated by the methods described above, and the results are shown in Table 1.

Examples 2 to 13 and Comparative Examples 1 to 5
Epoxy resin compositions were prepared and evaluated in the same manner as in Example 1, except that the types and amounts of the epoxy resin (A), epoxy resin curing agent (B), and curing accelerator (C) were changed as shown in Tables 1 to 3. The results are shown in Tables 1 to 3.

Examples 14 to 15
Epoxy resin compositions were prepared and evaluated in the same manner as in Example 1, except that the types and amounts of epoxy resin (A), epoxy resin curing agent (B), and curing accelerator (C) were changed as shown in Table 2, and that when these were blended, the component shown in Table 2 was also blended and mixed as a stress relaxation component (D). The results are shown in Table 2.

Examples 16 to 17
The types and amounts of the epoxy resin (A), epoxy resin curing agent (B), and curing accelerator (C) were changed as shown in Table 2. In addition, a solution was prepared by dissolving the curing accelerator (C) in the non-reactive diluent (E) shown in Table 2, and the epoxy resin (A) and the epoxy resin curing agent (B) were mixed with the solution, and the epoxy resin compositions were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

The components listed in the table are as follows.
<Epoxy resin (A)>
(A1-1) Triphenylmethane type epoxy resin (HP-7241): "HP-7241" manufactured by DIC Corporation, epoxy equivalent: 172 g/equivalent (A2-1-1) Bisphenol F diglycidyl ether (jER807): "jER807" manufactured by Mitsubishi Chemical Corporation, epoxy equivalent: 168 g/equivalent (A2-1-2) Bisphenol F diglycidyl ether oligomer (jER4005P): "jER4005P" manufactured by Mitsubishi Chemical Corporation, epoxy equivalent: 1026 g/equivalent, oligomer type (A2-2-1) Bisphenol A diglycidyl ether (jER828): "jER828" manufactured by Mitsubishi Chemical Corporation, epoxy equivalent: 186 g/equivalent (A2-2-2) Bisphenol A diglycidyl ether oligomer (jER1001): "jER1001" manufactured by Mitsubishi Chemical Corporation, epoxy equivalent: 483 g/equivalent, oligomer type (A2-3-1) Phenol novolac type epoxy resin (N730A): "N730A" manufactured by DIC Corporation, epoxy equivalent: 176 g/equivalent (A2-3-2) Phenol novolac type epoxy resin (N740): "N740" manufactured by DIC Corporation, epoxy equivalent: 183 g/equivalent (A2-3-3) Phenol novolac type epoxy resin (N770): "N770" manufactured by DIC Corporation, epoxy equivalent: 188 g/equivalent, melt viscosity at 150°C: 0.48 Pa·s
(A2-4-1) Naphthalene epoxy resin (HP-4032SS): "HP-4032SS" manufactured by DIC Corporation, epoxy resin represented by formula (A2-4-3), epoxy equivalent: 142 g/equivalent

<Epoxy Resin Curing Agent (B)>
(B1) Resorcinol: "Resorcin" manufactured by Sumitomo Chemical Co., Ltd.
(B2-1-1) Triphenylmethane type phenol: "S-TPM-105" manufactured by JFE Chemical Corporation, hydroxyl value equivalent: 99 g/equivalent (B2-1-2) Novolak type phenol: "TD-2131" manufactured by DIC Corporation, hydroxyl value equivalent: 104 g/equivalent, softening point: 78 to 82°C

<Curing Accelerator (C)>
2-Ethyl-4-methylimidazole: manufactured by Tokyo Chemical Industry Co., Ltd.

<Stress relaxation component (D)>
Kane Ace MX-136: Core-shell rubber particle dispersed epoxy resin masterbatch, Kaneka Corporation "Kane Ace MX-136", epoxy type Bis-F type, particle polybutadiene/silicone, particle content 25%
Epolead PB4700: Epoxidized polybutadiene, "Epolead PB4700" manufactured by Daicel Corporation, molecular weight 2000 to 3500

<Non-reactive diluent (E)>
Xylene resin: xylene formaldehyde resin, "NIKANOL Y-300" manufactured by Fudow Co., Ltd., viscosity at 25°C: 285 mPa·s, hydroxyl equivalent: 2,805 g/equivalent (hydroxyl value: 20 mgKOH/g)
Benzyl alcohol: Tokyo Chemical Industry Co., Ltd.

It can be seen from Tables 1 and 2 that the cured products of the epoxy resin compositions of this Example all achieved a hydrogen gas permeability coefficient of 7.0 (×10 ⁻¹¹ cc·cm/cm ² ·sec·cmHg) or less, a glass transition temperature of 100°C or more, and a tensile elongation of 3.0% or more. Furthermore, the pot life and shelf life of the epoxy resin compositions were also good. In contrast, the cured products of the epoxy resin compositions of Comparative Examples 1 to 5 listed in Table 3 were inferior in either hydrogen gas barrier property, glass transition temperature, or tensile elongation.
Regarding the cured products of the epoxy resin compositions of Examples 14 and 15, by adding the stress relaxation component (D), the tensile stress and tensile modulus were lowered while maintaining the same hydrogen gas barrier property, glass transition temperature, and tensile elongation values as compared to the other Examples, and a stress relaxation effect was observed.
In addition, the cured products of the epoxy resin compositions of Examples 16 and 17, which contained the non-reactive diluent (E), were found to have improved tensile strength compared to Example 6.

According to the present invention, it is possible to provide an epoxy resin composition capable of producing a cured product having high hydrogen gas barrier properties, heat resistance and elongation, the cured product thereof, a prepreg using the epoxy resin composition, a fiber-reinforced composite material, and a high-pressure gas container. The high-pressure gas container has high hydrogen gas barrier properties and is suitable as a container for storing high-pressure hydrogen gas.

Claims (14)

An epoxy resin composition comprising an epoxy resin (A) and an epoxy resin curing agent (B),
The epoxy resin (A) contains an epoxy resin (A1) and an epoxy resin (A2),
The epoxy resin (A1) is an epoxy resin having a glycidyl group derived from a triphenylmethane type phenol,
the epoxy resin (A2) is at least one selected from the group consisting of an epoxy resin (A2-1) having a glycidyl group derived from bisphenol F, an epoxy resin (A2-2) having a glycidyl group derived from bisphenol A, an epoxy resin (A2-3) having a glycidyl group derived from a novolac phenol, and an epoxy resin (A2-4) having a glycidyl group derived from a polyol having a naphthalene skeleton,
a mass ratio [(A1)/(A2)] of the epoxy resin (A1) to the epoxy resin (A2) in the epoxy resin (A) is 1/99 to 90/10;
The epoxy resin composition, wherein the epoxy resin curing agent (B) comprises resorcinol (B1). The epoxy resin composition according to claim 1, wherein the epoxy resin curing agent (B) further comprises an epoxy resin curing agent (B2) other than resorcinol (B1), and the epoxy resin curing agent (B2) comprises a phenol-based curing agent (B2-1) other than resorcinol (B1). The epoxy resin composition according to claim 2, wherein the phenol-based curing agent (B2-1) includes at least one selected from the group consisting of bisphenol F, bisphenol A, novolac-type phenol, and triphenylmethane-type phenol. The epoxy resin composition according to any one of claims 1 to 3, wherein the mass ratio [(A1)/(A2)] of the epoxy resin (A) to the epoxy resin (A1) is 5/95 to 70/30. The epoxy resin composition according to any one of claims 1 to 4, further comprising a curing accelerator (C), the curing accelerator (C) comprising at least one selected from the group consisting of imidazoles, tertiary amines, and phosphorus compounds. The epoxy resin composition according to any one of claims 1 to 5, further comprising a stress relaxation component (D). The epoxy resin composition according to any one of claims 1 to 6, further comprising a non-reactive diluent (E). 8. The epoxy resin composition according to claim 1, wherein a cured product of the epoxy resin composition has a hydrogen gas permeability coefficient of 7.0×10 ⁻¹¹ [cc·cm/(cm ² ·s·cmHg)] or less at 23° C. A cured product of the epoxy resin composition according to any one of claims 1 to 8. A prepreg comprising the epoxy resin composition according to any one of claims 1 to 8 and reinforcing fibers. The prepreg according to claim 10, wherein the reinforcing fibers are at least one selected from the group consisting of carbon fibers, glass fibers, and basalt fibers. The prepreg according to claim 10 or 11, wherein the prepreg is a tow prepreg or a tape prepreg. A fiber-reinforced composite material that is a cured product of the prepreg according to any one of claims 10 to 12. A high pressure gas bottle comprising the fiber reinforced composite material of claim 13.