Prepreg and Fiber Reinforced Composite Material

Abstract

To provide a prepreg which is suitably usable for use of a fiber-reinforced composite material, and is excellent in heat resistance and moldability of a fiber-reinforced composite material in addition to an elastic modulus and strength.SOLUTION: A prepreg contains an epoxy resin composition which contains the following components [A] to [C] and satisfies the following condition (1), and a reinforcement fiber. [A]: epoxy resin, [B]: polyamine curing agent, and [C]: a cyclic compound which has a boiling point of 130°C or higher and is represented by general formula (I) or formula (II). (1): A mol number E of the epoxy group of the component [A] and a mol number C of the component [C] have a relation of 0.01≤C / E≤0.20. In the formulae, R1, R3 and R4 each independently represent a hydrogen atom or a methyl group, R2 is an alkyl group having 2 to 11 carbon atoms, and R5 is an alkyl group having 1 to 10 carbon atoms.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to prepregs and fiber-reinforced composite materials, which are suitably used for fiber-reinforced composite materials for aerospace applications, general industrial applications, sports applications, and the like.

Background Art

[0002] Fiber-reinforced composite materials using carbon fibers, aramid fibers, etc. as reinforcing fibers are widely used for structural materials such as aircraft and automobiles, and for sports and general industrial applications such as tennis rackets, golf shafts, fishing rods, bicycles, and casings, by utilizing their high specific strength and specific modulus of elasticity. As the resin composition used for this fiber-reinforced composite material, thermosetting resins are mainly used from the viewpoints of heat resistance and productivity, and among them, epoxy resins are preferably used from the viewpoint of mechanical properties such as adhesiveness to reinforcing fibers.

[0003] In recent years, in order to apply fiber-reinforced composite materials to applications that require further weight reduction, it is necessary to improve various physical properties. Therefore, in order to improve various mechanical properties of fiber-reinforced composite materials, an improvement in the elastic modulus, elongation, and strength of the epoxy resin used as the matrix resin has been required. However, cured epoxy resins having a high elastic modulus are generally brittle and tend to have a low elongation. For this reason, it has been a technical problem to improve the high elastic modulus and elongation at the same time.

[0004] In order to solve this problem, various studies have been made. For example, a method of improving the resin strength by blending an additive to reduce the remaining undissolved dicyandiamide used as a curing agent and causing it to be a defect has been studied (Patent Document 1). Further, a method of obtaining a fiber-reinforced plastic with extremely few voids and excellent mechanical properties by impregnating a composition containing an epoxy resin and a small amount of a solvent into reinforcing fibers by a hot melt method has been studied (Patent Document 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] When the technology of Patent Document 1 is used, the resulting cured resin and fiber-reinforced composite material have excellent mechanical properties, but there is a need to improve the balance with further heat resistance. When the technology of Patent Document 2 is used, a fiber-reinforced plastic with excellent impregnation properties can be obtained, but it is not particularly excellent in elastic modulus and heat resistance.

[0007] Therefore, an object of the present invention is to provide a prepreg that can be suitably used for fiber-reinforced composite material applications and is excellent in elastic modulus, strength, heat resistance, and moldability of the fiber-reinforced composite material.

Means for Solving the Problems

[0008] The present invention adopts the following configuration to solve such problems. That is, a prepreg containing an epoxy resin composition containing the following constituent elements [A] to [C] and satisfying the following condition (1), and reinforcing fibers. [A]: Epoxy resin [B]: Polyamine curing agent [C]: A cyclic compound represented by the general formula (I) or formula (II) having a boiling point of 130°C or higher (1): The molar number E of the epoxy group of the constituent element [A] and the molar number C of the constituent element [C] satisfy the relationship of 0.01 ≤ C / E ≤ 0.20.

[0009]

Chemical formula

[0010] In the formula, R1, R3, and R4 are each independently a hydrogen atom or a methyl group, R2 is an alkyl group having 2 to 11 carbon atoms, and R5 is an alkyl group having 1 to 10 carbon atoms.

[0011] Further, a fiber-reinforced composite material obtained by laminating and curing the prepreg of the present invention is provided.

Effect of the Invention

[0012] According to the present invention, a prepreg excellent in elastic modulus, strength, heat resistance, and moldability of a fiber-reinforced composite material, which can be suitably used for fiber-reinforced composite material applications, can be obtained.

Mode for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described in detail.

[0014] The prepreg of the present invention contains an epoxy resin composition and reinforcing fibers, and the epoxy resin composition used contains components [A] to [C] as essential components. In the present invention, the "component" means a compound contained in the composition. Further, when a plurality of numerical ranges such as an essential range, a preferable range, etc. are shown for a certain physical property, characteristic, or composition ratio, a combination of any upper limit value and any lower limit value in the plurality of ranges is also a preferable range (for example, for H / E described below, 0.30 or more and 1.10 or less can be taken as a preferable range).

[0015] Component [A] in the present invention is an epoxy resin. As the epoxy resin of component [A], those containing two or more epoxy groups in one molecule are preferable because the glass transition temperature of the cured product obtained by heat-curing the resin composition can be increased and the heat resistance can be improved. Further, an epoxy resin containing one epoxy group in one molecule may be blended. These epoxy resins may be used alone or in appropriate combination.

[0016] Examples of the epoxy resin of component [A] include epoxy resins such as diaminodiphenylmethane type, diaminodiphenylsulfone type, aminophenol type, bisphenol type, metaxylylenediamine type, 1,3-bisaminomethylcyclohexane type, isocyanurate type, hydantoin type, phenol novolak type, orthocresol novolak type, trishydroxyphenylmethane type, and tetraphenylol ethane type. Among them, due to the good balance of physical properties, diaminodiphenylmethane type, aminophenol type, and bisphenol type epoxy resins are particularly preferably used.

[0017] Examples of commercially available diaminodiphenylmethane type epoxy resins include ELM434 (manufactured by Sumitomo Chemical Co., Ltd.), "Araldite (registered trademark)" MY720 (manufactured by Huntsman Advanced Materials Co., Ltd.), "Araldite (registered trademark)" MY721 (manufactured by Huntsman Advanced Materials Co., Ltd.), "Araldite (registered trademark)" MY9512 (manufactured by Huntsman Advanced Materials Co., Ltd.), "Araldite (registered trademark)" MY9663 (manufactured by Huntsman Advanced Materials Co., Ltd.), and "Epotope (registered trademark)" YH-434 (manufactured by Tohto Kasei Co., Ltd.), "jER (registered trademark)" 630 (manufactured by Mitsubishi Chemical Corporation), etc.

[0018] Examples of commercially available diaminodiphenylsulfone type epoxy resins include TG3DAS (manufactured by Mitsui Chemicals Fine Co., Ltd.), etc.

[0019] Commercially available aminophenol type epoxy resins include ELM120 (manufactured by Sumitomo Chemical Co., Ltd.), ELM100 (manufactured by Sumitomo Chemical Co., Ltd.), "jER (registered trademark)" 630 (manufactured by Mitsubishi Chemical Corporation), "Araldite (registered trademark)" MY0500 (manufactured by Huntsman Advanced Materials Co., Ltd.), "Araldite (registered trademark)" MY0510 (manufactured by Huntsman Advanced Materials Co., Ltd.), "Araldite (registered trademark)" MY0600 (manufactured by Huntsman Advanced Materials Co., Ltd.), "Araldite (registered trademark)" MY0610 (manufactured by Huntsman Advanced Materials Co., Ltd.), and the like.

[0020] Commercially available bisphenol A type epoxy resins include "jER (registered trademark)" 825 (manufactured by Mitsubishi Chemical Corporation), "Epiclon (registered trademark)" 850 (manufactured by DIC Corporation), "Epotoate (registered trademark)" YD-128 (manufactured by Nippon Steel Chemical & Materials Co., Ltd.), and DER-331 and DER-332 (both manufactured by Dow Chemical Company), and the like.

[0021] Commercially available bisphenol F type epoxy resins include "Araldite (registered trademark)" GY282 (manufactured by Huntsman Advanced Materials), "jER (registered trademark)" 806, "jER (registered trademark)" 807, "jER (registered trademark)" 1750 (all manufactured by Mitsubishi Chemical Corporation), "Epiclon (registered trademark)" 830 (manufactured by DIC Corporation), and "Epotoate (registered trademark)" YD-170 (manufactured by Nippon Steel Chemical & Materials Co., Ltd.), and the like.

[0022] In addition, epoxy compounds other than those described above may be appropriately blended in the epoxy resin composition of the present invention.

[0023] Component [B] in the present invention is a polyamine curing agent. The polyamine curing agent has a plurality of amino groups (including two modes of amino groups) that can react with epoxy groups and functions as a curing agent. The polyamine curing agent undergoes an addition reaction with the epoxy resin, and in this case, hydroxyl groups are generated by the ring-opening of the epoxy groups. A strong intermolecular interaction occurs between the hydroxyl groups generated in the crosslinked structure of the cured epoxy resin and Component [C] described later, making it easier for Component [C] to be retained in the crosslinked structure, and an effect of improving the elastic modulus, strength, and elongation can be obtained.

[0024] Examples of the polyamine curing agent include aliphatic polyamines and aromatic polyamines. These polyamine curing agents may be used alone or may be used in appropriate combinations. Aromatic polyamines, especially aromatic diamines, are excellent as curing agents in that they can impart high mechanical properties and heat resistance to the cured epoxy resin.

[0025] Those classified as aromatic polyamines include diethyltoluenediamines such as 2,2'-diethyldiaminodiphenylmethane, 2,4-diethyl-6-methyl-m-phenylenediamine, 4,6-diethyl-2-methyl-m-phenylenediamine, and 4,6-diethyl-m-phenylenediamine; 4,4'-methylenebis(N-methylaniline), 4,4'-methylenebis(N-ethylaniline), 4,4'-methylenebis(N-sec-butylaniline), N,N'-di-sec-butyl-p-phenylenediamine, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 3,3'-diisopropyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-4,4'-diaminodiphenylmethane, 3,3'-diethyl-5,5'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-5,5'-dimethyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane, 3,3'-diisopropyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-5,5'-diisopropyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetra-t-butyl-4,4'-diaminodiphenylmethane, etc. Among them, 3,3'-diaminodiphenylsulfone and 4,4'-diaminodiphenylsulfone are preferably used because the cured products obtained therefrom have excellent mechanical properties. Also, from the point that the pot life can be effectively improved, it is a preferred embodiment to use a solid curing agent as the polyamine curing agent. It is preferable to contain at least one of 3,3'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, and dicyandiamide.

[0026] Examples of commercially available aromatic polyamines include Seika Cure S (manufactured by Wakayama Seika Kogyo Co., Ltd.), MDA-220 (manufactured by Mitsui Chemicals, Inc.), "jER Cure (registered trademark)" WA (manufactured by Mitsubishi Chemical Corporation), 3,3'-DAS (manufactured by Mitsui Chemicals, Inc.), "Lonzacure (registered trademark)" M-DEA (manufactured by Lonza Ltd.), "Lonzacure (registered trademark)" M-DIPA (manufactured by Lonza Ltd.), "Lonzacure (registered trademark)" M-MIPA (manufactured by Lonza Ltd.), and "Lonzacure (registered trademark)" DETDA 80 (manufactured by Lonza Ltd.).

[0027] Examples of commercially available dicyandiamide include DICY7 (manufactured by Mitsubishi Chemical Corporation) and DICY15 (manufactured by Mitsubishi Chemical Corporation).

[0028] Regarding the blending amount of the polyamine curing agent in the present invention, it is preferable that the ratio H / E of the number of moles H of the active hydrogen of the polyamine curing agent to the number of moles E of the epoxy groups of component [A] is 0.20 or more and 1.30 or less, more preferably 0.30 or more and 1.20 or less, and still more preferably 0.50 or more and 1.10 or less. By setting H / E within such a range, a crosslinked structure can be appropriately formed by the reaction between the epoxy resin and the polyamine curing agent, and a resin cured product excellent in strength and elongation can be obtained. In addition, by setting H / E to 0.50 or more and 1.10 or less, the amount of hydroxyl groups generated by the reaction between the epoxy resin and the polyamine curing agent becomes appropriate. As a result, component [C] described later is likely to be retained in the crosslinked structure, and an effect of improving the elastic modulus, strength, and elongation can be obtained.

[0029] In particular, when diaminodiphenyl sulfone is applied as component [B] in the present invention, the ratio ((total molar number of active hydrogens of at least one of the curing agents of 3,3'-diaminodiphenyl sulfone and 4,4'-diaminodiphenyl sulfone) / E) of the molar number E of the epoxy groups of component [A] to the total molar number of active hydrogens of at least one of 3,3'-diaminodiphenyl sulfone and 4,4'-diaminodiphenyl sulfone is preferably 0.50 or more and 1.30 or less. More preferably, it is 0.70 or more and 1.20 or less, and even more preferably 0.80 or more and 1.10 or less. By setting it in this way, the balance between the heat resistance and mechanical properties of the epoxy resin composition of the present invention can sometimes be improved.

[0030] Also, when dicyandiamide is applied as component [B] in the present invention, the total amount of dicyandiamide is preferably an amount such that the active hydrogen groups are 0.20 to 1.20 equivalents relative to the epoxy groups of the epoxy resin contained in the resin composition, more preferably an amount in the range of 0.30 to 1.00 equivalents, and most preferably an amount in the range of 0.50 to 0.80 equivalents. By setting the amount of active hydrogen groups within this range, an epoxy resin cured product excellent in the balance between heat resistance and mechanical properties can sometimes be obtained.

[0031] Component [C] is a cyclic compound represented by general formula (I) or (II) having a boiling point of 130°C or higher.

[0032]

Chemical formula

[0033] R1, R3, and R4 in general formulas (I) and (II) are each independently a hydrogen atom or a methyl group, R2 is an alkyl group having 2 to 11 carbon atoms, and R5 is an alkyl group having 1 to 10 carbon atoms.

[0034] Component [C] exists in the voids without being incorporated into the crosslinked structure formed by the reaction of the epoxy resin and the polyamine, and this state is maintained even after curing. As a result, the elastic modulus of the obtained cured epoxy resin becomes high. Moreover, surprisingly, by blending component [C], not only a high elastic modulus but also a cured epoxy resin having a high elongation and high strength can be obtained.

[0035] Further, the boiling point of component [C] is 130°C or higher, preferably 190°C or higher, and more preferably 210°C or higher, so that the volatilization of component [C] during the curing of the epoxy resin composition can be suppressed, and a fiber-reinforced composite material having excellent mechanical properties can be obtained. Furthermore, the generation of voids and the deterioration of mechanical properties in the obtained fiber-reinforced composite material can be suppressed. Also, from the viewpoint of compatibility with the epoxy resin and the curing agent, the boiling point of component [C] is preferably 400°C or lower. In the present invention, the boiling point is the value at normal pressure (101 kPa). Also, when the boiling point at normal pressure cannot be measured, the converted boiling point converted to 101 kPa using a boiling point conversion chart can be used.

[0036] The molecular weight m of component [C] is preferably 70 or more and 200 or less, more preferably 70 or more and 150 or less, and even more preferably 80 or more and 120 or less. By setting the molecular weight of component [C] within such a range, component [C] is appropriately retained in the voids of the crosslinked structure formed by the reaction of the epoxy resin and the polyamine, and a cured product excellent in elastic modulus, strength, and elongation can be obtained. Component [C] is a cyclic compound represented by the general formula (I) or (II), that is, an amide compound or a urea compound having a cyclic structure. Since the ring component [C] is an amide compound or a urea compound having high polarity, a strong intermolecular interaction acts between the alcoholic hydroxyl group in the crosslinked structure formed from component [A] and component [B] and component [C], and component [C] is likely to be appropriately retained in the voids of the crosslinked structure, so that an excellent effect of improving elongation and strength can be obtained. In addition, due to its cyclic structure, the cured product in a state where component [C] is retained in the crosslinked structure may have excellent heat resistance. Furthermore, due to its cyclic structure, the boiling point of the compound is likely to be high, and generation of voids due to volatilization during resin curing can be suppressed in some cases. It is preferable that in component [C], R1 in the general formula (I) is a hydrogen atom, or at least one of R3 or R4 in the general formula (II) is a hydrogen atom. By using the compound containing the above hydrogen atom, the intermolecular interaction described above becomes stronger in the crosslinked structure, and an especially excellent effect of improving elongation and strength can be obtained, and heat resistance and moldability are also likely to be excellent. The melting point of component [C] is preferably room temperature or higher and preferably 140 °C or lower. When the melting point is room temperature or higher, the viscosity of the epoxy resin composition does not decrease too much, and it is easy to handle as a prepreg. In addition, when the melting point is 140 °C or lower, the compatibility with the epoxy resin composition is good, and an excellent effect of improving elongation and strength can be easily obtained. In this specification, room temperature refers to 23 °C.

[0037] Also, component [C] may be a single compound or may be used by appropriately blending a plurality of compounds.

[0038] In the epoxy resin composition of the present invention, it is preferably important that the ratio C / E of the total number of moles E of epoxy groups contained in component [A] to the number of moles C of component [C] satisfying the above condition (1) is 0.01 or more and 0.20 or less, more preferably 0.07 or more and 0.20 or less, and even more preferably 0.07 or more and 0.13 or less. By setting C / E within such a range, component [C] is appropriately retained in the voids of the crosslinked structure formed by the reaction of the epoxy resin and the polyamine, and a cured product excellent in elastic modulus, strength, elongation, and heat resistance is easily obtained.

[0039] The epoxy resin composition used for the prepreg of the present invention may be blended with a curing accelerator from the viewpoint of controlling the curing rate. Examples of the curing accelerator include urea compounds and imidazole compounds, and urea compounds can be particularly preferably used from the viewpoint of the storage stability of the epoxy resin composition.

[0040] Examples of the urea compound include 3-(3,4-dichlorophenyl)-1,1-dimethylurea, 3-(4-chlorophenyl)-1,1-dimethylurea, phenyldimethylurea, and toluenebisdimethylurea. Commercially available products of aromatic urea compounds such as DCMU99 (manufactured by Hodogaya Chemical Co., Ltd.) and "Omicure (registered trademark)" 24 (manufactured by PTI Japan Co., Ltd.) can be used.

[0041] The epoxy resin composition used for the prepreg of the present invention may be blended with a thermoplastic resin. By blending a thermoplastic resin into the resin composition, control of the viscosity of the resulting resin composition, control of the tackiness of the prepreg, control of the fluidity of the resin composition when the prepreg is heat-cured, and improvement of the toughness that does not impair the heat resistance and elastic modulus of the resulting fiber-reinforced composite material are expected. As such a thermoplastic resin, a thermoplastic resin having a hydrogen-bonding functional group that has high compatibility with the epoxy resin and can improve the adhesion between the resin and the reinforcing fiber is preferably used.

[0042] Examples of the reinforcing fibers used in the prepreg of the present invention preferably include carbon fibers, graphite fibers, aramid fibers, glass fibers, etc., and carbon fibers are particularly preferred. The form and arrangement of the reinforcing fibers are not limited. For example, long fibers aligned in one direction, single tows, woven fabrics, knits, and fibrous structures such as braids are used. Two or more types of carbon fibers, glass fibers, aramid fibers, boron fibers, PBO fibers, high-strength polyethylene fibers, alumina fibers, silicon carbide fibers, etc. may be used in combination as the reinforcing fibers.

[0043] Specific examples of the carbon fibers include acrylic-based, pitch-based, and rayon-based carbon fibers, etc., and acrylic-based carbon fibers with particularly high tensile strength are preferably used.

[0044] As the form of the carbon fibers, twisted yarns, untwisted yarns, and non-twisted yarns can be used. However, in the case of twisted yarns, since the orientation of the filaments constituting the carbon fibers is not parallel, it may cause a decrease in the mechanical properties of the obtained carbon fiber reinforced composite material. Therefore, untwisted yarns or non-twisted yarns with a good balance between the moldability and strength characteristics of the carbon fiber reinforced composite material are preferably used.

[0045] The tensile elastic modulus of the carbon fibers is preferably 200 GPa or more and 440 GPa or less. The tensile elastic modulus of the carbon fibers is affected by the crystallinity of the graphite structure constituting the carbon fibers, and the higher the crystallinity, the higher the elastic modulus. This range is preferred because all of the rigidity and strength of the carbon fiber reinforced composite material are balanced at a high level. A more preferred elastic modulus is 230 GPa or more and 400 GPa or less, and even more preferably 260 GPa or more and 370 GPa or less. Here, the tensile elastic modulus of the carbon fibers is a value measured according to JIS R7608 (2008).

[0046] The prepreg of the present invention is in a form in which an epoxy resin composition is impregnated into reinforcing fibers in advance and can be manufactured by various known methods. For example, a prepreg can be manufactured by a hot melt method in which the resin composition is made to have a low viscosity by heating without using an organic solvent and then impregnated into the reinforcing fibers. The hot melt method is preferred because voids are less likely to occur in the molded product compared to the wet method using an organic solvent.

[0047] In the hot melt method, methods such as directly impregnating the reinforcing fibers with the resin composition whose viscosity has been lowered by heating, or first producing a release paper sheet with a resin film in which the resin composition has once been coated on a release paper or the like, and then overlapping the resin film from both sides or one side of the reinforcing fibers onto the reinforcing fiber side and impregnating the reinforcing fibers with the resin composition by heating and pressurizing can be used.

[0048] The content of the reinforcing fibers in the prepreg is preferably 30% by mass or more and 90% by mass or less. By setting it to 30% by mass or more, more preferably 35% by mass or more, and still more preferably 65% by mass or more, it is easy to obtain the advantages of a fiber-reinforced composite material excellent in specific strength and specific modulus. In addition, when molding the fiber-reinforced composite material, it is possible to suppress an excessive increase in the amount of heat generated during curing. On the other hand, by setting it to 90% by mass or less, more preferably 85% by mass or less, it is possible to suppress the generation of voids in the composite material due to poor impregnation of the resin. In addition, the tackiness of the prepreg can be maintained.

[0049] The fiber-reinforced composite material of the present invention can be manufactured, for example, by laminating the prepreg of the present invention described above in a predetermined form and applying pressure and heat to cure the resin. Here, methods for applying heat and pressure include a press molding method, an autoclave molding method, a bagging molding method, a wrapping tape method, an internal pressure molding method, etc.

[0050] The fiber-reinforced composite material of the present invention can be widely used in aerospace applications, general industrial applications, and sports applications. More specifically, in general industrial applications, it is preferably used for structures such as automobiles, ships, and railway vehicles. In sports applications, it is preferably used for golf shafts, fishing rods, and rackets for tennis and badminton.

Examples

[0051] Hereinafter, the present invention will be described with reference to examples. However, the scope of the present invention is not limited to these examples. The unit "part" of the composition ratio means parts by mass unless otherwise noted. In addition, the measurement of various properties (physical properties) was carried out under the environment of a temperature of 23 ° C and a relative humidity of 50% unless otherwise noted.

[0052] <Materials used in Examples and Comparative Examples> (1) Component [A]: Epoxy resin · "Araldite (registered trademark)" MY0600 (aminophenol type epoxy resin, epoxy equivalent: 118 g / eq, number of epoxy groups: 3, manufactured by Huntsman Advanced Materials Co., Ltd.).

[0053] (2) Component [B]: Polyamine curing agent · 3,3’-DAS (3,3’-diaminodiphenyl sulfone, active hydrogen equivalent: 62 g / eq, number of active hydrogens: 4, manufactured by Mitsui Chemicals Fine Co., Ltd.) · DICY7 (dicyandiamide, active hydrogen equivalent: 21 g / eq, number of active hydrogens: 4, manufactured by Mitsubishi Chemical Corporation).

[0054] (3) Component [C]: A cyclic compound represented by formula (I) or formula (II) having a boiling point of 130 ° C or higher, having no epoxy group in the molecule, and substantially having no curing ability for epoxy resin. · 2-pyrrolidone (boiling point: 245 ° C, melting point: 25 ° C, molecular weight m: 85 g / mol, manufactured by Tokyo Chemical Industry Co., Ltd.) · 2-imidazolidinone (boiling point: 279 ° C, melting point: 131 ° C, molecular weight m: 86 g / mol, manufactured by Tokyo Chemical Industry Co., Ltd.) ·N-Methylpyrrolidone (boiling point: 202 °C, melting point: -24 °C, molecular weight m: 99 g / mol, manufactured by Tokyo Chemical Industry Co., Ltd.) ·N,N'-Dimethylpropyleneurea (boiling point: 247 °C, melting point: -20 °C, molecular weight m: 128 g / mol, manufactured by Tokyo Chemical Industry Co., Ltd.).

[0055] (4) Other compounds ·DCMU99 (3-(3,4-dichlorophenyl)-1,1-dimethylurea, manufactured by Hodogaya Chemical Co., Ltd.) ·N-Methylformamide (boiling point: 180 °C, melting point: -5 °C, molecular weight m: 59 g / mol, manufactured by Tokyo Chemical Industry Co., Ltd.) ·N-Ethylacetamide (boiling point: 206 °C, melting point: -32 °C, molecular weight m: 73 g / mol, manufactured by Tokyo Chemical Industry Co., Ltd.) ·1,3-Dimethylurea (boiling point: 269 °C, melting point: 104 °C, molecular weight m: 88 g / mol, manufactured by Tokyo Chemical Industry Co., Ltd.) ·1,2-Propanediol (boiling point: 188 °C, melting point: -59 °C, molecular weight m: 76, manufactured by Tokyo Chemical Industry Co., Ltd.).

[0056] The epoxy resin compositions of each example were measured using the following measurement methods.

[0057] <Method for preparing epoxy resin composition> (1) Preparation of curing agent master Liquid component [A]: 10 parts by mass of epoxy resin (10 parts by mass with respect to 100 parts by mass of all epoxy resins) was prepared. Component [B]: Polyamine curing agent was added thereto, and kneaded at room temperature. The mixture was passed through a three-roll mill twice to prepare two kinds of curing agent master.

[0058] (2) Preparation of epoxy resin composition The liquid component [A] used in the above (1): 90 parts by mass of component [A] excluding 10 parts by mass of epoxy resin and component [C] were put into a beaker. After heating to the melting point of component [C] used + 10 °C, it was stirred until uniformly compatible. After cooling to room temperature, the curing agent master prepared in the above (1) was added and stirred well at the same temperature to obtain an epoxy resin composition.

[0059] <Various evaluation methods> (1) Three-point bending measurement of resin cured product After degassing the uncured epoxy resin composition in a vacuum, it was poured into a mold set to a thickness of 2 mm with a 2-mm-thick "Teflon (registered trademark)" spacer. Then, when 3,3'-DAS was used as the curing agent, it was heated from 130 °C at a rate of 1.7 °C / min, held at 125 °C for 5 hours, and then heated at a rate of 1.7 °C / min and cured at 225 °C for 2 hours. When DICY7 was used as the curing agent, it was heated from 30 °C at a rate of 1.7 °C / min, held at 90 °C for 60 minutes, and then heated at a rate of 2.0 °C / min and cured at 135 °C for 120 minutes to obtain a plate-shaped resin cured product with a thickness of 2 mm. From this resin cured product, test pieces with a width of 10 mm and a length of 60 mm were cut out. Using an Instron universal testing machine (manufactured by Instron), with a span of 32 mm, a crosshead speed of 2.5 mm / min, and the number of samples n = 6, the average values of the elastic modulus and elongation when performing three-point bending according to JIS K7171 (1994) were taken as the elastic modulus and elongation of the resin cured product, respectively.

[0060] (2) Glass transition temperature (Tg) measurement of resin cured product In the same manner as in (1), after producing a plate-shaped resin cured plate with a thickness of 2 mm, test pieces with a width of 12.7 mm and a length of 55 mm were cut out from the obtained resin cured plate, and the glass transition temperature was determined by the DMA method according to SACMA SRM18R-94. In the storage elastic modulus G' curve, the intersection temperature value of the tangent in the glass state and the tangent in the transition state was taken as the glass transition temperature. Here, it was measured at a heating rate of 5 °C / min and a frequency of 1 Hz.

[0061] (3) Molding property of fiber-reinforced composite material (CFRP) The epoxy resin composition prepared according to the above <Method for Preparing Epoxy Resin Composition> was applied onto release paper using a film coater to obtain a resin film with a basis weight of 66 g / m 2 . Two resin films were produced. A two-directional cross (2 / 2 twill weave, basis weight 198 g / m 2 ) made of carbon fiber "Torayca (registered trademark)" T300 (manufactured by Toray Industries, Inc.) was prepared. After laminating the above resin films on both sides of this, it was impregnated with heat and pressure from both sides using a prepreg machine to obtain a prepreg. The resin content of the prepreg was 40% by mass. After aligning the fiber directions of this woven prepreg and laminating 10 plies, it was covered with a nylon film so that there were no gaps, and this was heated and pressed at 130 °C and an internal pressure of 0.3 MPa in an autoclave for 2 hours to cure, thereby producing a fiber-reinforced composite material. Those with a void content of less than 1% and substantially no voids in the obtained fiber-reinforced composite material were designated as "A", those with a void content of 1% or more and less than 3% in the fiber-reinforced composite material and no resin-impregnated portions observable in the appearance of the fiber-reinforced composite material were designated as "B", and those with a void content of 3% or more in the fiber-reinforced composite material or resin-impregnated portions observable in the appearance were designated as "C". The void content in the above CFRP was calculated from the area ratio of voids in the fiber-reinforced composite material by observing a cross-section arbitrarily selected on a fiber-reinforced composite material polished smoothly with a surface polished smoothly using an inclined-type optical microscope.

[0062] <Examples 1 to 6, Comparative Examples 1 to 6> Resin compositions prepared by mixing components at the ratios shown in Tables 1 and 2 were prepared by the above method, and the glass transition temperature and three-point bending measurement of the resin cured product were carried out by the above method. Also, prepregs and CFRPs were produced by the above method, and the moldability of the CFRP was confirmed.

[0063] In all of Examples 1 to 6, the balance of the elastic modulus, elongation at break, and Tg was excellent, and the moldability was also excellent. When Comparative Examples 1 and 2 did not contain Component [C] and other compound [C'], the elastic modulus of the cured resin was inferior. When Comparative Examples 3 to 6 contained other compound [C'] instead of Component [C], although the elastic modulus of the cured resin was excellent, it was sometimes inferior in Tg and moldability compared to Examples 1 to 4 using the same curing agent.

[0064]

Table 1

[0065]

Table 2

Claims

1. A prepreg comprising an epoxy resin composition containing the following constituent elements [A] to [C] and satisfying the following conditions (1) and (2), and reinforcing fibers. [A]: Epoxy resin [B]: Polyamine curing agent [C]: A cyclic compound represented by the general formula (I) or formula (II) having a boiling point of 130°C or higher and a melting point of room temperature or higher (1): The molar number E of the epoxy groups of the constituent element [A] and the molar number C of the constituent element [C] are in the relationship of 0.01 ≦ C / E ≦ 0.

20. (2): The ratio H / E of the molar number H of the active hydrogen of the constituent element [B] to the molar number E of the epoxy groups of the constituent element [A] is in the relationship of 0.50 or more and 1.10 or less. 【Chemical Formula 1】 R in the formula １ , R ３ , R ４ are each independently a hydrogen atom or a methyl group, and R ２ is an alkyl group having 2 to 11 carbon atoms, and R ５ is an alkyl group having 1 to 10 carbon atoms

2. A fiber-reinforced composite material obtained by laminating and curing the prepreg according to Claim 1.

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