JP2024046878A - Epoxy resin composition, prepreg and fiber-reinforced composite material - Google Patents

Abstract

[Problem] The present invention aims to provide an epoxy resin composition which, when cured, can give a resin cured product having excellent flame retardancy, mechanical properties and heat resistance, and a prepreg and a fiber-reinforced composite material having excellent fire resistance, each of which uses the epoxy resin composition. [Solution] The epoxy resin composition containing an epoxy resin which achieves the above-mentioned object contains [A] a glycidylamine-type epoxy resin having two or less functional groups and having at least one ring structure having four or more members, [B] an epoxy resin having three or more functional groups, [C] a phosphorus-based flame retardant selected from the group consisting of phosphorus-based compounds having a specific structure and red phosphorus, and [D] a filler made of a metal hydroxide, in which each of components [A] and [B] is contained in a predetermined amount relative to 100 parts by mass of the total epoxy resin, and the ratio of the content of component [D] to the content of phosphorus atoms in the resin composition is within a specific range. [Selected Figure] None

Description

The present invention relates to an epoxy resin composition, a prepreg, and a fiber-reinforced composite material with excellent fire resistance.

In composite materials that use carbon fiber, glass fiber, etc. as reinforcing fibers and thermosetting resins such as epoxy resin and phenol resin as matrix resin, intermediate substrates in which the reinforcing fibers are impregnated with resin, so-called prepregs, are used in a wide range of applications, from sports and leisure goods such as fishing rods and tennis and badminton rackets to various industrial equipment, civil engineering and construction, and the aerospace industry. However, the thermosetting resins used in most composite materials are flammable and can cause fires, so flame-retardant composite materials are required, especially in structural materials for aircraft and vehicles, to prevent accidents caused by ignition and combustion. In electronic and electrical equipment, materials that are flame-retardant are also required to prevent internal heat generation that can cause ignition and combustion of housings and parts, leading to accidents.

Methods for making composite materials flame retardant include promoting char formation in the matrix resin to suppress the diffusion of decomposition gases when the resin is thermally decomposed, suppressing heat generation when the resin is burned, or promoting heat dissipation in the thickness direction to suppress heat accumulation on the surface of the burning area.

To promote char formation in matrix resins, additives that make the material less flammable, so-called flame retardants, are often added. Phosphorus compounds are commonly used as flame retardants, and several phosphorus compounds are used industrially. Phosphorus compounds are converted to polyphosphoric acid, which has a dehydrating carbonization effect, during combustion, and it is believed that this promotes char formation. Flame retardant techniques using such phosphorus compounds include a technique in which additive flame retardants such as red phosphorus and phosphate esters are added to epoxy resin compositions, and a technique in which phosphorus atoms are introduced into the crosslinking structure of the resin by using reactive flame retardants that contain phosphorus atoms in the molecule and react with the resin.

In addition, heat absorbing agents are often added as a means of suppressing heat generation during combustion of the matrix resin. Metal hydroxides are commonly used as heat absorbing agents and are used industrially.

Patent Document 1 reports a technology for obtaining a material that has excellent viscosity stability and char formation promotion effects as well as excellent mechanical properties, by using a flame retardant technology that uses a resin composition that contains a reactive diluent having a specific structure and an amine-based curing agent that contains a phosphorus atom and has a specific structure.

Patent Document 2 reports a technology for obtaining a fire-resistant resin that contains a specific epoxy resin and red phosphorus and aluminum hydroxide as flame retardants.

Patent document 3 introduces a technology that adds an inorganic filler near the outermost layer of one of the laminates to obtain a laminate with excellent flame retardancy and mechanical properties.

International Publication No. 2019/082595 International Publication No. 2021/153644 International Publication No. 2022/154041

However, when using the epoxy resins described in these patent documents with phosphorus-based flame retardants and inorganic fillers, it was difficult to obtain a cured resin that satisfied all of the following requirements: flame retardancy, mechanical properties, and heat resistance.

The present invention aims to solve the above problems, that is, to provide an epoxy resin composition that can give a resin cured product with excellent flame retardancy, mechanical properties, and heat resistance, as well as a prepreg and a fiber-reinforced composite material with excellent fire resistance that use the epoxy resin composition.

In order to achieve the above object, the epoxy resin composition of the present invention has the following constitutions 1 to 7.
1. An epoxy resin composition comprising the following components [A] to [D], wherein, relative to 100 parts by mass of a total amount of epoxy resin, the composition contains 10 to 50 parts by mass of component [A] and 50 to 90 parts by mass of component [B], and the ratio of the mass content (%) of component [D] to the phosphorus atom content (%) in the resin composition is 1 or more.
[A] A glycidyl amine type epoxy resin having one or more ring structures of four or more members and having two or less functional groups; [B] An epoxy resin having three or more functional groups; [C] A phosphorus-based flame retardant selected from phosphorus-based compounds represented by the following general formula (1) or (2) or red phosphorus; [D] A filler made of a metal hydroxide.

(In general formula (1), R ¹ represents a hydrocarbon group having 1 to 4 carbon atoms. In general formula (2), R ² represents a hydrogen atom or an amino group.)
2. The resin cured product obtained by curing at 180°C for 2 hours was
2. The epoxy resin composition according to 1 above, having a char formation rate of 20% or more and less than 50%, a flexural modulus of 5 GPa or more and less than 7 GPa, and a glass transition temperature of 180°C or more and less than 210°C at 600°C in air.
3. The epoxy resin composition according to the above item 1 or 2, wherein component [D] is a filler made of aluminum hydroxide.
4. The epoxy resin composition according to any one of 1 to 3 above, wherein component [C] is a phosphorus-based flame retardant represented by general formula (1) or (2).
5. The epoxy resin composition according to any one of 1 to 4 above, wherein component [A] has a structure represented by the following general formula (3) or (4):

(In the general formula (3), ^R3 represents one selected from a hydrogen atom, an aliphatic hydrocarbon group having 1 to 4 carbon atoms, an alicyclic hydrocarbon group having 3 to 6 carbon atoms, an aromatic hydrocarbon group having 6 to 10 carbon atoms, a halogen atom, an acyl group, a trifluoromethyl group, and a nitro group. m represents an integer of 1 to 4. X represents a hydrogen atom or a substituent having a ring structure having four or more members.)

(In general formula (4), ^R4 represents one selected from a hydrogen atom, an aliphatic hydrocarbon group having 1 to 4 carbon atoms, an alicyclic hydrocarbon group having 3 to 6 carbon atoms, an aromatic hydrocarbon group having 6 to 10 carbon atoms, a halogen atom, an acyl group, a trifluoromethyl group, and a nitro group. n represents an integer of 1 to 4. Y represents a hydrogen atom or a substituent having a ring structure having four or more members.)
6. The epoxy resin composition according to any one of 1 to 5 above, further comprising a component [E] a thermoplastic resin.
7. The epoxy resin composition according to any one of 1 to 6 above, further comprising component [F] particles containing a thermoplastic resin as a main component.

The prepreg or fiber-reinforced composite material of the present invention has the following constitution 8 or 9 to 10, respectively.
8. A prepreg obtained by impregnating reinforcing fibers with the epoxy resin composition according to any one of 1 to 7 above.
9. A fiber-reinforced composite material obtained by curing the prepreg according to 8 above.
10. A fiber-reinforced composite material comprising a cured resin obtained by curing the epoxy resin composition according to any one of 1 to 7 above, and reinforcing fibers.

The present invention makes it possible to provide an epoxy resin composition that can be cured to give a resin cured product that has excellent flame retardancy, mechanical properties, and heat resistance, as well as a prepreg and a fiber-reinforced composite material that has excellent fire resistance using the epoxy resin composition.

The epoxy resin composition of the present invention contains [A] a glycidylamine type epoxy resin having two or less functional groups and having at least one ring structure having four or more members, [B] an epoxy resin having three or more functional groups, [C] a phosphorus-based flame retardant selected from the phosphorus-based compounds represented by the above general formula (1) or (2) or red phosphorus, and [D] a filler made of a metal hydroxide.

Component [A] is a glycidylamine type epoxy resin having one or more ring structures of four or more members and having two or less functionalities. In particular, it is preferable that component [A] is represented by the above general formula (3) or (4), since excellent flame retardancy and mechanical properties can be obtained.

Specific examples of component [A] include monoamine-type epoxy resins such as N,N-diglycidylaniline, N,N-diglycidyl-4-phenoxyaniline, N,N-diglycidyl-o-toluidine, N,N-diglycidyl-m-toluidine, N,N-diglycidyl-p-toluidine, N,N-diglycidyl-2,3-xylidine, N,N-diglycidyl-2,4-xylidine, and N,N-diglycidyl-3,4-xylidine, and imide-type epoxy resins such as N-glycidylphthalimide and N-glycidyl-4-methylphthalimide. Among them, monoamine-type epoxy resins are particularly preferred because they have excellent heat resistance, and many of them are liquid, so they can be used as reactive diluents, and it is relatively easy to control the viscosity of the resin composition to an appropriate range when an inorganic filler is added, and excellent resin impregnation is easily obtained. These epoxy resins of component [A] may be used alone or in combination of two or more types.

The content of component [A] in the present invention is 10 to 50 parts by mass per 100 parts by mass of the total amount of epoxy resin. A content of 20 to 40 parts by mass is preferable because it provides high mechanical properties and heat resistance.

The component [B] used in the present invention is an epoxy resin having three or more functionalities, preferably three or four functionalities.
Specific examples of component [B] include the following epoxy resins. That is, trifunctional epoxy resins include aminophenol-type epoxy resins such as N,N,O-triglycidyl-m-aminophenol, N,N,O-triglycidyl-p-aminophenol, and N,N,O-triglycidyl-4-amino-3-methylphenol. Tetrafunctional epoxy resins include diamine-type epoxy resins such as N,N,N',N'-tetraglycidyl-4,4'-methylenedianiline, N,N,N',N'-tetraglycidyl-2,2'-diethyl-4,4'-methylenedianiline, and N,N,N',N'-tetraglycidyl-m-xylylenediamine. Among them, tetrafunctional diamine-type epoxy resins have four glycidyl groups in one molecule, and therefore can provide a cured product with high heat resistance and elastic modulus. Therefore, they are suitable for use in aerospace applications.
The content of component [B] in the present invention is 50 to 90 parts by mass relative to 100 parts by mass of the total amount of the epoxy resin. A content of 60 to 80 parts by mass is preferred from the viewpoint of ensuring excellent heat resistance and mechanical properties.

Component [C] of the present invention is a phosphorus-based flame retardant. Examples of such compounds include phosphorus-based compounds having a structure represented by the above general formula (1) or general formula (2), which also act as amine-based curing agents. Alternatively, red phosphorus may be used. Adding such a phosphorus-based flame retardant to an epoxy resin composition promotes char formation.

Regarding the phosphorus-based compound represented by the general formula (1) or (2), when one of these is used, it is preferable since a cured product having excellent mechanical properties such as bending strength can be obtained.
It represents a hydrocarbon group having 1 to 4 carbon atoms.

In general formula (1), R ¹ represents a hydrocarbon group having 1 to 4 carbon atoms, but if the number of carbon atoms in R ¹ is reduced, the hydrophobicity of the amine-based curing agent having the structure represented by general formula (1) decreases, and the moisture absorption resistance of the obtained cured resin may decrease. Therefore, the number of carbon atoms in R ¹ is preferably 4.

The red phosphorus of component [C] in the present invention may be not only untreated red phosphorus, but also red phosphorus whose surface is coated with a metal hydrate and a resin to enhance stability. Examples of metal hydrates include aluminum hydroxide, magnesium hydroxide, zinc hydroxide, and titanium hydroxide. There are no particular limitations on the type and amount of coating of the resin, but the resin is preferably a phenolic resin, an epoxy resin, or polymethyl methacrylate, which has a high affinity with the epoxy resin used in the present invention. In addition, in order to suppress the generation of phosphine gas during kneading at high temperatures, the amount of coating is preferably 1% by mass or more relative to the red phosphorus. The greater the amount of coating, the better in terms of stability, but it is preferable that the amount of coating does not exceed 30% by mass from the viewpoint of flame retardancy.

Examples of amine-based curing agents having a structure represented by general formula (1) include bis(4-aminophenyl)methylphosphine oxide, bis(3-aminophenyl)methylphosphine oxide, bis(2-aminophenyl)methylphosphine oxide, bis(4-aminophenyl)ethylphosphine oxide, bis(3-aminophenyl)ethylphosphine oxide, bis(2-aminophenyl)ethylphosphine oxide, bis(4-aminophenyl)n-propylphosphine oxide, bis(3-aminophenyl)n-propylphosphine oxide, bis(4-aminophenyl)isopropylphosphine oxide, bis(3-aminophenyl)isopropylphosphine oxide, bis(4-aminophenyl)n-butylphosphine oxide, bis(3-aminophenyl)n-butylphosphine oxide, bis(4-aminophenyl)isobutylphosphine oxide, and bis(3-aminophenyl)isobutylphosphine oxide. Among these, bis(3-aminophenyl)n-butylphosphine oxide is preferably used because of its excellent mechanical properties, flame retardancy, and wet heat resistance. Examples of amine-based curing agents having a structure represented by general formula (2) include tris(4-aminophenyl)phosphine oxide, tris(3-aminophenyl)phosphine oxide, tris(2-aminophenyl)phosphine oxide, bis(4-aminophenyl)phenylphosphine oxide, bis(3-aminophenyl)phenylphosphine oxide, etc. Among these, tris(3-aminophenyl)phosphine oxide or bis(3-aminophenyl)phenylphosphine oxide is preferably used because of its excellent mechanical properties and heat resistance, and the latter of these two compounds is more preferably used.

In the present invention, the content of component [C] is preferably 1 to 10 parts by mass, and more preferably 3 to 6 parts by mass, per 100 parts by mass of the total epoxy resin, in the case of red phosphorus, from the viewpoint of ensuring the viscosity stability of the resin composition and the flame retardancy and mechanical properties of the resulting cured product and fiber-reinforced composite material. Also, in the case of a phosphorus-based flame retardant selected from amine-based curing agents having a structure represented by general formula (1) or (2), the content is preferably 10 to 100 parts by mass, and more preferably 25 to 100 parts by mass, per 100 parts by mass of the total epoxy resin, in the case of red phosphorus, from the viewpoint of ensuring the viscosity stability of the resin composition and the flame retardancy and mechanical properties of the resulting cured product and fiber-reinforced composite material.

In the present invention, the phosphorus atom content in the epoxy resin composition is preferably 0.1 to 5.0% by mass, and the resulting cured product and fiber-reinforced composite material can have both flame retardancy and mechanical properties. The phosphorus atom content is preferably 0.5 to 4.0% by mass. The phosphorus atom content (mass%) here is calculated by mass (g) of phosphorus atoms in the entire epoxy resin composition / mass (g) of the entire epoxy resin composition × 100. When component [C] is red phosphorus, the mass of phosphorus atoms is the mass% of phosphorus atoms in red phosphorus. When component [C] is an amine-based curing agent having the structure of the above formula (1) or (2), the mass of phosphorus atoms per molecule is calculated from the atomic weight of phosphorus atoms, and this is multiplied by the number of molecules of the compound of component [C] contained in the entire epoxy resin composition calculated from the number of moles.

As described above, the epoxy resin composition according to the present invention can contain a phosphorus-based compound having a structure represented by general formula (1) or (2) of component [C] as an amine-based curing agent, but can also contain other curing agents. Since red phosphorus cannot act as a curing agent, it is particularly preferable to use a curing agent other than the phosphorus compound of general formula (1) or (2) when red phosphorus is used as component [C]. The curing agent here is a curing agent for epoxy resins and is a compound having an active group that can react with epoxy groups. Examples of such curing agents include dicyandiamide, aromatic polyamines, aminobenzoic acid esters, various acid anhydrides, phenol novolac resins, cresol novolac resins, polyphenol compounds, imidazole derivatives, aliphatic amines, tetramethylguanidine, thiourea adduct amines, carboxylic acid anhydrides such as methylhexahydrophthalic anhydride, carboxylic acid hydrazides, carboxylic acid amides, polymercaptans, and Lewis acid complexes such as boron trifluoride ethylamine complexes. Among these, when aromatic polyamines are used as curing agents, it becomes easier to obtain epoxy resin cured products with good heat resistance. In particular, among aromatic polyamines, by using various isomers of diaminodiphenyl sulfone, such as 4,4'-diaminodiphenyl sulfone and 3,3'-diaminodiphenyl sulfone, it becomes easier to obtain epoxy resin cured products with good heat resistance.

The content of the curing agent other than the above component [C] is preferably 90 parts by mass or less per 100 parts by mass of the total amount of the curing agent, including the curing agent of component [C] and the curing agent other than component [C], since this makes it easier to ensure the flame retardancy of the resulting cured product and fiber-reinforced composite material.

Component [D] of the present invention is a filler made of a metal hydroxide, which decomposes during combustion and exerts an endothermic effect, which is thought to suppress heat generation due to combustion. Examples of metal hydroxides include aluminum hydroxide, magnesium hydroxide, zinc hydroxide, titanium hydroxide, and tin hydroxide. From the viewpoint of endothermic effect, aluminum hydroxide is preferred.

Component [D] can usually be in the form of particles, and although there are no particular limitations on the particle size, from the viewpoint of flame retardancy and dispersibility, the average diameter calculated from the arithmetic mean is preferably 0.8 to 10.0 μm, and more preferably 0.8 to 3.0 μm. Such particle size is measured by laser scattering particle size distribution measurement. Depending on the composition of the epoxy resin composition, from the viewpoint of the balance between flame retardancy and tackiness, the content of component [D] is preferably 5 to 60 parts by mass, more preferably 10 to 55 parts by mass, and even more preferably 15 to 50 parts by mass per 100 parts by mass of the total epoxy resin.

The ratio of the mass % of component [D] in the total amount of the resin composition to the phosphorus atom content (%) determined above (hereinafter, the mass ratio represented by [D]/P; the same applies below) is 1 or more. Note that the phosphorus atom content in this case is not particularly limited to the preferred range described above. This makes it possible to suppress the decomposition of char at the early stage of combustion due to the endothermic heat absorbed during the thermal decomposition of component [D], thereby more effectively promoting the formation of char by phosphorus. In addition, it is preferable that [D]/P is less than 25 in order to balance the char formation by phosphorus and the endothermic effect of the metal hydroxide.

The epoxy resin composition of the present invention preferably has a char generation rate of 20% or more and less than 50% at 600°C in air for the resin cured product obtained by curing at a temperature of 180°C for 2 hours. More preferably, the char generation rate is 30% or more and less than 50%. When the char generation rate is within this range, the thermal diffusion of the decomposition gas is sufficiently suppressed, and a fiber-reinforced composite material with excellent fire resistance can be obtained. Here, the char generation rate at 600°C in air refers to the remaining rate of thermal decomposition residue when the temperature reaches 600°C when heated from room temperature at a heating rate of 10°C/min in an air atmosphere using a thermogravimetric measuring device.

The epoxy resin composition of the present invention preferably has a flexural modulus of 5 GPa or more and less than 7 GPa for the resin cured product obtained by curing under the above conditions. More preferably, it is 5.5 GPa or more and less than 7 GPa. If it is in this range, a fiber-reinforced composite material with excellent compression properties can be obtained.

Furthermore, the epoxy resin composition of the present invention preferably has a glass transition temperature of 180°C or higher and lower than 210°C for the resin cured product obtained by curing under the above conditions. More preferably, it is 190°C or higher and lower than 210°C. When it is in this range, a fiber-reinforced composite material with excellent heat resistance can be obtained.

In the present invention, in order to control the tackiness of the resulting prepreg, control the fluidity of the resin when the epoxy resin composition is impregnated into the reinforcing fiber, and impart toughness to the resulting fiber-reinforced composite material, a thermoplastic resin (component [E]) can be dissolved in the epoxy resin composition and used. The thermoplastic resin of component [E] may be any compound that is soluble in the epoxy resin used at room temperature, but a thermoplastic resin composed of a polyaryl ether skeleton is preferred. Specific examples include polysulfone, polyphenylsulfone, polyethersulfone, polyetherimide, polyphenylene ether, polyetheretherketone, and polyetherethersulfone. These thermoplastic resins composed of a polyaryl ether skeleton may be used alone or in combination as appropriate. Among them, polyethersulfone and polyetherimide are preferably used because they can impart toughness to the resulting fiber-reinforced composite material without reducing the heat resistance and mechanical properties.

In order to improve the impact resistance of the resulting fiber-reinforced composite material, the epoxy resin composition according to the present invention preferably contains particles (thermoplastic resin particles) mainly composed of a thermoplastic resin as component [F]. Unlike component [E], such thermoplastic resin particles are insoluble in other components of the epoxy resin composition, and exist as particles even when the epoxy resin composition is made into a prepreg and further into a fiber-reinforced composite material.

As the thermoplastic resin particles, polyamide is most preferable, and among polyamides, polyamide 12, polyamide 6, polyamide 11, polyamide 66, polyamide 6/12 copolymer, and polyamides semi-IPNed with the epoxy compound described in Example 1 of JP-A-1-104624 (semi-IPN polyamides) provide particularly good adhesive strength with epoxy resins. Here, IPN is an abbreviation for Interpenetrating Polymer Network, a type of polymer blend. The blend component polymers are crosslinked polymers, and each of the different crosslinked polymers is partially or entirely entangled with each other to form a multiple network structure. Semi-IPN is a structure in which a double network structure is formed by crosslinked polymers and linear polymers. Semi-IPNed thermoplastic resin particles can be obtained, for example, by dissolving a thermoplastic resin and a thermosetting resin in a common solvent, mixing them uniformly, and then reprecipitation. By using particles made of epoxy resin and semi-IPN polyamide, excellent heat resistance and impact resistance can be imparted to the prepreg. The shape of these thermoplastic resin particles may be spherical, non-spherical, or porous, but spherical particles are preferred because they do not reduce the flow characteristics of the resin, have excellent viscoelasticity, have no starting point for stress concentration, and provide high impact resistance. Commercially available polyamide particles include SP-500, SP-10, TR-1, TR-2, 842P-48, and 842P-80 (all manufactured by Toray Industries, Inc.), and Orgasol (registered trademark) 1002D, 2001UD, 2001EXD, 2002D, 3202D, 3501D, and 3502D (all manufactured by Arkema). These polyamide particles may be used alone or in combination.

The epoxy resin composition of the present invention can be blended with a coupling agent, thermosetting resin particles, or inorganic fillers such as silica gel, carbon black, clay, carbon nanotubes, graphene, carbon particles, or metal powder, within the scope of the invention.

The prepreg of the present invention is formed by impregnating reinforcing fibers with the epoxy resin composition of the present invention. In other words, the above-mentioned epoxy resin composition is used as a matrix resin, and this epoxy resin composition is composited with reinforcing fibers. Preferred examples of reinforcing fibers include carbon fibers, graphite fibers, aramid fibers, and glass fibers. Of these, carbon fibers are particularly preferred from the viewpoint of mechanical properties.

The prepreg of the present invention can be manufactured by various known methods, such as the wet method and the hot melt method. Among them, the hot melt method is preferred because it is easy to achieve the effects of the present invention.

In the prepreg of the present invention, the weight of the reinforcing fiber is preferably 100 to 1000 g/m ^2. If the weight of the reinforcing fiber is less than 100 g/m ² , the number of layers needs to be increased to obtain a predetermined thickness when molding the fiber-reinforced composite material, and the lamination work may become complicated. On the other hand, if it exceeds 1000 g/m ² , the drapeability of the prepreg tends to deteriorate. In addition, the fiber mass content is preferably 40 to 90 mass%, more preferably 50 to 80 mass%. If the fiber mass content is less than 40 mass%, the ratio of the resin is too high, so that the advantage of the excellent mechanical properties of the reinforcing fiber cannot be utilized, and the heat generation during curing of the fiber-reinforced composite material may be too high. In addition, if the fiber mass content exceeds 90 mass%, impregnation of the resin occurs poorly, and the obtained fiber-reinforced composite material may have many voids.

The prepreg of the present invention may be in the form of a unidirectional (UD) prepreg, a woven fabric prepreg, or a nonwoven fabric such as a sheet molding compound.

The first aspect of the fiber-reinforced composite material of the present invention is obtained by curing the prepreg of the present invention. Such a fiber-reinforced composite material can be obtained, for example, by laminating the prepreg of the present invention in a predetermined form, and then applying heat and pressure to cure the resin. Here, known methods such as autoclave molding, press molding, bagging molding, wrapping tape method, and internal pressure molding can be used as the method for applying heat and pressure.

A second embodiment of the fiber-reinforced composite material of the present invention includes a resin cured product obtained by curing the epoxy resin composition of the present invention, and reinforcing fibers. Such a fiber-reinforced composite material can be obtained by a method in which a reinforcing fiber substrate is directly impregnated with a liquid epoxy resin and cured, without using a prepreg. Specifically, such a fiber-reinforced composite material can be obtained by, for example, a resin transfer molding method, a filament winding method, a pultrusion method, a hand layup method, or the like.

The upper and lower limits of the numerical ranges described above can be combined in any way.

The present invention will be described below with reference to examples, but the present invention is not limited to these examples.
The materials used in the examples and comparative examples of the present invention are shown below.

<Component [A]: Difunctional or less glycidylamine-type epoxy resin having one or more four-membered or larger ring structures>
N,N-diglycidylaniline (GAN, manufactured by Nippon Kayaku Co., Ltd.)
N-glycidylphthalimide (Denacol (registered trademark) EX-731, manufactured by Nagase ChemteX Corporation)
N,N-diglycidyl-o-toluidine (GOT, manufactured by Nippon Kayaku Co., Ltd.)
<Difunctional or lower epoxy resin other than component [A]>
Liquid bisphenol A epoxy resin ("jER (registered trademark)" 828, manufactured by Mitsubishi Chemical Corporation)
Liquid bisphenol F type epoxy resin ("Epc (registered trademark)" 830, manufactured by DIC Corporation)
Solid bisphenol A epoxy resin ("jER (registered trademark)" 1001, manufactured by Mitsubishi Chemical Corporation)
1,4-butanediol diglycidyl ether (Denacol (registered trademark) EX-214L, manufactured by Nagase ChemteX Corporation)
<Component [B]: Tri- or higher functional epoxy resin>
Tetraglycidyldiaminodiphenylmethane ("Araldite (registered trademark)" MY721, manufactured by Huntsman Advanced Materials)
Phenol novolac type epoxy resin ("jER (registered trademark)" 154, manufactured by Mitsubishi Chemical Corporation)
<Component [C]: Red phosphorus>
Red phosphorus ("Nova Red (registered trademark)" 120UF, manufactured by Rinkagaku Kogyo Co., Ltd.).

<Component [C]: Phosphorus-based compound having a structure represented by general formula (2) (amine-based curing agent)>
Bis(3-aminophenyl)phenylphosphine oxide (BAPP0, manufactured by Katayama Chemical Industry Co., Ltd.).
<Curing agents other than component [C]>
4,4'-diaminodiphenyl sulfone (Seikacure S, manufactured by Wakayama Seika Kogyo Co., Ltd.)
-Dicyandiamide (Dicy7T, manufactured by Mitsubishi Chemical Corporation).

<Component [D]: Filler composed of metal hydroxide>
Aluminum hydroxide (C-301N, manufactured by Sumitomo Chemical Co., Ltd.)
<Component [E]: Thermoplastic resin>
Polyethersulfone ("VIRANTAGE (registered trademark)" VW-10700RFP, manufactured by Solvay Advanced Polymers)
Polyvinyl formal ("Vinylec (registered trademark) K, manufactured by JNC Corporation).
<Other additives>
2,4'-toluenebis(3,3-dimethylurea) ("Omicure (registered trademark)" 24)
(1) Method for preparing an epoxy resin composition After the components other than the curing agent shown in Tables 1 and 2 were charged into a kneading device, the temperature was raised to 140° C. or higher and kneading was performed under heat. The temperature was then lowered to 80° C. or lower, and the curing agent of component [C] and the curing agents other than component [C] shown in Tables 1 and 2 were added and stirred to obtain an epoxy resin composition.

(2) Measurement of char formation rate of cured resin The measurement of char formation rate by thermogravimetry (TGA) was carried out as follows.

The epoxy resin composition prepared in (1) was degassed in a vacuum, and then cured under the prescribed curing conditions in a mold set so that a 2 mm or 3 mm thick "Teflon (registered trademark)" spacer was inserted to limit the thickness of the resulting cured product to 2 mm or 3 mm, to obtain a cured epoxy resin product having a thickness of 2 mm or 3 mm. Flame retardancy was evaluated using a thermogravimetric analyzer TG-DSC (PerkinElmer STA6000 system). A test piece of about 10 mg was cut out from the cured epoxy resin product and simply heated at a heating rate of 10°C/min in air, and the char generation rate (%) at 600°C was used as an index of flame retardancy. The char generation rate here is a value expressed as (mass (g) of thermal decomposition residue at 600°C)/(mass (g) of cured epoxy resin product before heating)×100.
(3) Evaluation of heat generation properties of cured resin Heat generation properties were evaluated using a cone calorimeter test device, Cone Calorimeter C3 (manufactured by Toyo Seiki Seisakusho, Ltd.) Test pieces measuring 100 mm x 100 mm square were cut out from the 3 mm thick cured epoxy resin products prepared in (2) and tested with a heater radiation amount of 50 kW/ ^m2 . The maximum heat generation rate (kW/ ^m2 ) within 5 minutes was used as an index of flame retardancy.
(4) Evaluation of Mechanical Properties of Cured Resin Products Evaluation of mechanical properties of cured resin products was carried out as follows.
The 2 mm thick epoxy resin cured product prepared in (2) was cut into a test piece having a size of 10 mm x 60 mm square, and a three-point bending test was performed based on JIS K7171 (2006) to evaluate the mechanical properties. The bending test was performed using an Instron 5565 universal testing machine (manufactured by Instron Corporation) under the conditions of a crosshead speed of 2.5 mm/min, a span length of 40 mm, an indenter diameter of 10 mm, and a fulcrum diameter of 4 mm, to measure the flexural modulus.
(5) Evaluation of heat resistance of cured resin The 2 mm thick cured epoxy resin prepared in (2) was cut into test pieces measuring 12.7 mm × 45 mm square, and the glass transition temperature was measured by dynamic mechanical analysis (DMA) in accordance with ASTM 7028-07.

(Examples 1 to 9, Comparative Examples 1 to 3)
Epoxy resin compositions were prepared by the above (1) method for preparing an epoxy resin composition using the ratios (parts by mass) of each component shown in Tables 1 and 2. Comparative Example 4 was cured at 130°C for 90 minutes, while the other examples were cured at 180°C for 2 hours. The cured resins were evaluated for char generation rate, mechanical properties, and heat resistance according to the above (2), (4), or (5). Examples 1 and 2 and Comparative Examples 1 and 2 were also evaluated for heat generation properties according to the above (3). The evaluation results are shown in Tables 1 and 2.

Claims (10)

The epoxy resin composition comprises the following components [A] to [D], wherein the composition contains 10 to 50 parts by mass of component [A] and 50 to 90 parts by mass of component [B] relative to 100 parts by mass of a total amount of epoxy resins, and the ratio of the mass content (%) of component [D] to the phosphorus atom content (%) in the resin composition is 1 or more.
[A] A glycidyl amine type epoxy resin having one or more ring structures of four or more members and having two or less functional groups; [B] An epoxy resin having three or more functional groups; [C] A phosphorus-based flame retardant selected from phosphorus-based compounds represented by the following general formula (1) or (2) or red phosphorus; [D] A filler made of a metal hydroxide.

(In general formula (1), R ¹ represents a hydrocarbon group having 1 to 4 carbon atoms. In general formula (2), R ² represents a hydrogen atom or an amino group.) The resin cured product obtained by curing at 180°C for 2 hours was
2. The epoxy resin composition according to claim 1, which has a char formation rate of 20% or more and less than 50% at 600°C in air, a flexural modulus of 5 GPa or more and less than 7 GPa, and a glass transition temperature of 180°C or more and less than 210°C. The epoxy resin composition according to claim 1 or 2, wherein component [D] is a filler made of aluminum hydroxide. The epoxy resin composition according to claim 1, wherein component [C] is a phosphorus-based flame retardant represented by general formula (1) or (2). 2. The epoxy resin composition according to claim 1, wherein the component [A] has a structure represented by the following general formula (3) or (4):

(In the general formula (3), ^R3 represents one selected from a hydrogen atom, an aliphatic hydrocarbon group having 1 to 4 carbon atoms, an alicyclic hydrocarbon group having 3 to 6 carbon atoms, an aromatic hydrocarbon group having 6 to 10 carbon atoms, a halogen atom, an acyl group, a trifluoromethyl group, and a nitro group. m represents an integer of 1 to 4. X represents a hydrogen atom or a substituent having a ring structure having four or more members.)

(In the general formula (4), ^R4 represents one selected from a hydrogen atom, an aliphatic hydrocarbon group having 1 to 4 carbon atoms, an alicyclic hydrocarbon group having 3 to 6 carbon atoms, an aromatic hydrocarbon group having 6 to 10 carbon atoms, a halogen atom, an acyl group, a trifluoromethyl group, and a nitro group. n represents an integer of 1 to 4. Y represents a hydrogen atom or a substituent having a ring structure having four or more members.) The epoxy resin composition according to claim 1, further comprising component [E] a thermoplastic resin. The epoxy resin composition according to claim 1, further comprising component [F] particles whose main component is a thermoplastic resin. A prepreg obtained by impregnating reinforcing fibers with the epoxy resin composition according to claim 1. A fiber-reinforced composite material obtained by curing the prepreg according to claim 8. A fiber-reinforced composite material comprising a cured resin obtained by curing the epoxy resin composition according to claim 1 and reinforcing fibers.