Two-part epoxy resin composition, cured resin object, fiber-reinforced composite material, and method for producing fiber-reinforced composite material

Abstract

The present invention provides a two-part epoxy resin composition comprising: a main ingredient composition which comprises an epoxy resin (a) having at least one oxazolidone ring structure and an epoxy resin (b) having at least three glycidyl groups and has a viscosity at 120°C of 200 mPa·s or less; and a hardener composition including an aromatic polyamine (d) and having a viscosity at 120°C of 200 mPa·s or less. The two-part epoxy resin composition is characterized by including core / shell rubber particles (g) and in that, when the main ingredient composition is mixed with the hardener composition so that the equivalent ratio (H / E) of the active hydrogen equivalent (H) of the whole hardener to the epoxy equivalent (E) of all the epoxy resins is any value in the range of 0.8-1.2, then the mixture has a minimum viscosity of 200 mPa·s or less at a temperature in the range of 90-120°C.

Description

Two-component epoxy resin composition, cured resin product, fiber-reinforced composite material, and method for producing fiber-reinforced composite material.

[0001] The present invention relates to a two-component epoxy resin composition, a resin cured product obtained by curing the same, a fiber-reinforced composite material, and a method for producing a fiber-reinforced composite material. More specifically, the present invention relates to a two-component epoxy resin composition, a resin cured product, and a fiber-reinforced composite material that is low viscosity and particularly suitable for resin transfer molding (RTM) methods, as well as a method for producing a fiber-reinforced composite material.

[0002] Fiber-reinforced composite materials are lightweight, high-strength, and highly rigid, making them suitable for a wide range of applications, including sports and leisure activities such as fishing rods and golf shafts, as well as industrial applications such as automobiles and aircraft. Known methods for molding composite materials using thermosetting resins as the matrix resin include resin transfer molding (RTM), in which a liquid resin composition is impregnated into a reinforcing fiber substrate placed in a mold, and then the resin composition is cured to obtain the fiber-reinforced composite material, and methods for molding prepregs (intermediate substrates) that have been pre-impregnated with resin and formed into sheets.

[0003] In recent years, the RTM (Reinforced Polymer) method has attracted particular attention as a low-cost and highly productive manufacturing method for fiber-reinforced composite materials, as it involves fewer steps in the manufacturing process and does not require expensive equipment such as autoclaves. The resin composition used in the RTM method mainly consists of epoxy resin and a curing agent, and may include other additives as needed. Aromatic polyamines are used as curing agents to obtain resin cured products and fiber-reinforced composite materials with high mechanical properties.

[0004] In epoxy resin compositions used in the RTM method, it is necessary to prevent solid matter in the resin composition from being filtered out by the reinforcing fiber base material when impregnating the epoxy resin composition into the reinforcing fiber base material. For this reason, it is common practice to pre-dissolve the curing agent and additives in the epoxy resin. An epoxy resin composition in which the curing agent and additives are pre-dissolved in the epoxy resin is called a one-component epoxy resin composition. In one-component epoxy resin compositions, because the curing agent is dissolved in the epoxy resin, the reaction between the epoxy resin and the curing agent proceeds relatively easily, which has the problem of shortening the shelf life of the epoxy resin composition. For this reason, one-component epoxy resin compositions had to be stored frozen to suppress the reaction between the epoxy resin and the curing agent, and were not easy to handle.

[0005] To address this challenge, a two-component epoxy resin composition is being investigated, in which the epoxy resin and curing agent are mixed immediately before use. A two-component epoxy resin composition consists of a main component composition containing epoxy resin as the main component and a curing agent composition containing a curing agent as the main component, and is obtained by mixing these two components immediately before use.

[0006] In two-component epoxy resin compositions, the main component composition and the curing agent composition are mixed immediately before use, making ease of mixing crucial. While it is possible to use the same curing agent for a one-component epoxy resin composition as the curing agent for a two-component epoxy resin composition, the curing agents used in one-component epoxy resin compositions are usually solids, which can easily lead to poor mixing with the main component composition. To suppress poor mixing between the main component composition and the curing agent composition, it is desirable that both the main component composition and the curing agent composition have low viscosity.

[0007] Epoxy resin compositions using liquid aromatic polyamines as curing agents are described in Patent Documents 1 and 2. However, the epoxy resin compositions described in Patent Documents 1 and 2 use a large amount of solid epoxy resin, and there is room for improvement in terms of uniformity of mixing with the curing agent composition and the properties of the resulting cured resin.

[0008] Special table No. 2016-501922 Japanese Patent Application Publication No. 11-171974

[0009] The object of the present invention is to solve the problems of the prior art described above and to provide an epoxy resin composition that has low viscosity, can be suitably used in the RTM method, and has excellent rapid curing properties. Furthermore, a further object of the present invention is to provide a resin cured product and a fiber-reinforced composite material that have excellent heat resistance and mechanical properties.

[0010] As a result of their investigations to solve the above problems, the present inventors have found that the above problems can be solved by using an epoxy resin composition containing an oxazolidone ring structure and an epoxy resin containing at least three glycidyl groups, in combination with an aromatic polyamine compound and core-shell type rubber particles, and have completed the present invention.

[0011] The present invention, which achieves the above-mentioned problems, is described below.

[0012] [1] A two-component epoxy resin composition comprising: a main component composition comprising an epoxy resin (a) having at least one oxazolidone ring structure and an epoxy resin (b) having at least three glycidyl groups, wherein the main component composition and the curing agent composition comprising an aromatic polyamine (d), wherein the curing agent composition comprises an aromatic polyamine (d), wherein the curing agent composition comprises core-shell type rubber particles (g), and when the main component composition and the curing agent composition are mixed such that the equivalent ratio (H / E) of the epoxy equivalent (E) of the total epoxy resin to the active hydrogen equivalent (H) of the total curing agent is any equivalent ratio within the range of 0.8 to 1.2, the minimum viscosity of the mixture shown in the range of 90 to 120°C is 200 mPa·s or less.

[0013] [2] The two-component epoxy resin composition according to [1], wherein the epoxy resin (a) is a reaction product of a bisphenol A type epoxy resin and an aromatic diisocyanate.

[0014] [3] The two-component epoxy resin composition according to [1] or [2], wherein the epoxy resin (b) is triglycidyl-m-aminophenol, triglycidyl-p-aminophenol, or tetraglycidyl-4,4'-diaminodiphenylmethane.

[0015] [4] The two-component epoxy resin composition according to any one of [1] to [3], wherein the aromatic polyamine (d) is diethyltoluenediamine.

[0016] [5] A two-component epoxy resin composition according to any one of [1] to [4], wherein the curing agent composition further comprises an alicyclic polyamine (e).

[0017] [6] The two-component epoxy resin composition according to [5], wherein the alicyclic polyamine (e) is isophoronediamine, N-(3-aminopropyl)cyclohexylamine, or 4,4'-methylenebis(cyclohexylamine).

[0018] [7] The two-component epoxy resin composition according to any one of [1] to [6], wherein the core component of the core-shell type rubber particles (g) is a polymer of one or more monomers selected from conjugated diene monomers and aromatic vinyl compounds, or a silicone resin.

[0019] [8] The two-component epoxy resin composition according to any one of [1] to [7], wherein the shell component of the core-shell type rubber particles (g) is a polymer of one or more monomers selected from (meth)acrylic acid esters and aromatic vinyl compounds.

[0020] [9] The two-component epoxy resin composition according to any one of [1] to [8], wherein the content of the epoxy resin (a) relative to the total mass of the main component composition is 5 to 30% by mass.

[0021]

[10] A two-component epoxy resin composition according to any one of [1] to [9], wherein the degree of curing of the resin cured product obtained by heating a mixture of the main component composition and the curing agent composition, obtained by heating the mixture at 180°C for 15 minutes such that the equivalent ratio (H / E) of the epoxy equivalent (E) of the total epoxy resin to the active hydrogen equivalent (H) of the total curing agent is any equivalent ratio within the range of 0.8 to 1.2, reaches 80% or more.

[0022]

[11] A cured resin product characterized by being formed by curing a two-component epoxy resin composition described in any of [1] to

[10] .

[0023]

[12] The resin cured product according to

[11] , wherein the content of the core-shell type rubber particles (g) is 1.0 to 5.0% by mass.

[0024]

[13] A fiber-reinforced composite material characterized by comprising a resin cured product as described in

[11] or

[12] and a reinforcing fiber substrate.

[0025]

[14] The fiber-reinforced composite material according to

[13] , wherein the reinforcing fiber base material is made of carbon fibers.

[0026]

[15] A method for producing a fiber-reinforced composite material, characterized by compounding a reinforcing fiber substrate with a two-component epoxy resin composition described in any of [1] to

[10] and curing the compound.

[0027]

[16] A method for producing a fiber-reinforced composite material, characterized by mixing the main component composition and the curing agent composition of a two-component epoxy resin composition described in any of [1] to

[10] , impregnating the mixture into a reinforcing fiber substrate placed in a mold, and curing it.

[0028] The present invention provides an epoxy resin composition having low viscosity and rapid curing properties. It also provides a cured resin product and a fiber-reinforced composite material having heat resistance and high mechanical properties.

[0029] The following describes the two-component epoxy resin composition, cured resin product, and fiber-reinforced composite material of the present invention. Fiber-reinforced composite material may be abbreviated as "FRP," and carbon fiber reinforced composite material as "CFRP." Unless otherwise specified, all physical properties are those obtained at 25°C and atmospheric pressure. In this specification, an epoxy resin composition refers to an uncured or semi-cured material, and after the epoxy resin composition has cured, it is referred to as a cured body or cured resin product. In this specification, a numerical value of x to y means that the value is greater than or equal to x and less than or equal to y, and if only y has a unit, it means that x also has the same unit. In this specification, a two-component epoxy resin composition means a composition in which the epoxy resin and curing agent are separated. Core-shell type rubber particles and other components may be mixed into the main component composition or into the curing agent composition, but they may also be mixed separately without being pre-mixed into these main component or curing agent compositions. In such cases, the epoxy resin composition may consist of three or more components, but as long as the epoxy resin and the curing agent are separated, it shall be included in the two-component epoxy resin composition of the present invention.

[0030] 1. Two-component epoxy resin composition The two-component epoxy resin composition of the present invention comprises: a main component composition comprising an epoxy resin (a) having at least one oxazolidone ring structure and an epoxy resin (b) having at least three glycidyl groups, and having a viscosity of 200 mPa·s or less at 120°C; and a curing agent composition comprising an aromatic polyamine (d), and having a viscosity of 200 mPa·s or less at 120°C, wherein the two-component epoxy resin composition comprises core-shell type rubber particles (g), and when the main component composition and the curing agent composition are mixed such that the equivalent ratio (H / E) of the epoxy equivalent (E) of the total epoxy resin of the main component composition and the active hydrogen equivalent (H) of the total curing agent of the curing agent composition is any equivalent ratio within the range of 0.8 to 1.2, the minimum viscosity of the mixture is 200 mPa·s or less. Furthermore, in the case of a formulation in which core-shell type rubber particles are dispersed in epoxy resin, the epoxy equivalent of the epoxy resin is added to the total epoxy equivalent (E) of the epoxy resin (the same applies hereinafter).

[0031] The two-component epoxy resin composition of the present invention is such that when the main component composition and the curing agent composition are mixed so that the equivalent ratio (H / E) of the epoxy equivalent (E) of all the epoxy resins in the main component composition and the active hydrogen equivalent (H) of all the curing agents in the curing agent composition is any equivalent ratio within the range of 0.8 to 1.2, the minimum viscosity of the mixture (hereinafter, also simply referred to as the "uncured mixture") is 200 mPa·s or less. That is, it means that there is an equivalent ratio within the range of H / E of 0.8 to 1.2 such that the minimum viscosity of the uncured mixture is 200 mPa·s or less. When the minimum viscosity exceeds 200 mPa·s, it becomes difficult to impregnate the epoxy resin composition into the reinforcing fiber base material. The minimum viscosity is preferably 150 mPa·s or less, more preferably 140 mPa·s or less, still more preferably 130 mPa·s or less, and particularly preferably 120 mPa·s or less. The lower limit of the minimum viscosity is not particularly limited, but generally it is 5 mPa·s or more, and preferably 10 mPa·s or more. Here, the minimum viscosity means the minimum value of the viscosities shown in the range of 90 to 120°C among the viscosities measured while heating the main component composition and the curing agent composition to 90°C in advance, mixing them at a predetermined ratio, and then raising the temperature to 120°C within 15 minutes. After the main component composition and the curing agent composition are mixed, due to the partial curing reaction, the viscosity of the mixture begins to increase, so the minimum viscosity is not necessarily the viscosity at 120°C.

[0032] The uncured mixture of the two-component epoxy resin composition of the present invention preferably has a pot life at 120°C of 300 seconds or more, more preferably 600 seconds or more, and still more preferably 900 seconds or more. If the pot life is too short, the reaction is too fast, and depending on the size of the molded product, gelation of the epoxy resin composition may occur before the injection into the mold during RTM is completed. Also, there is a possibility that the amount of waste increases because it cannot be used up within the usage time. The pot life is preferably 5 hours or less, more preferably 3 hours or less, still more preferably 2 hours or less, and particularly preferably 90 minutes or less. If the pot life is too long, the curing time becomes long and the production efficiency tends to decrease.

[0033] When the heat generation start temperature S obtained from the intersection of the tangent line on the low temperature side of the heat generation peak in the differential scanning calorimetry curve obtained by performing differential scanning calorimetry at a heating rate of 20 (°C / min) and the baseline is used, it is preferable to satisfy the relationship of the following mathematical formula (1): -20 ≤ S - 180 ≤ 100... Mathematical formula (1)

[0034] More preferably, S - 180 (the value obtained by subtracting 180 from S) is 5 to 100, and even more preferably 10 to 30. When the value of S - 180 is less than -20, the pot life of the epoxy resin composition is not sufficient, and gelation of the epoxy resin composition may occur before the injection of the resin into the mold during RTM is completed. When S - 180 exceeds 100, the time required until the completion of curing becomes long, and the rapid curing property is impaired, which is not preferable.

[0035] The inflection point on the low temperature side of the heat generation peak in the differential scanning calorimetry curve obtained by performing differential scanning calorimetry at a heating rate of 20 (°C / min) means the point where the heat generation peak has the maximum gradient. The point where the heat generation peak has the maximum gradient can be obtained directly from the obtained differential scanning calorimetry curve or by processing with analysis software. In the present invention, the heat generation start temperature S means the intersection of the baseline and the tangent line at the maximum gradient point of the heat generation peak.

[0036] It is preferable that the temperature at which the degree of curing obtained from the integral value of the heat generation peak in the differential scanning calorimetry curve obtained by performing differential scanning calorimetry at a heating rate of 20 (°C / min) of the uncured mixture of the two-component epoxy resin composition of the present invention reaches 95 (%) is 320°C or lower, more preferably 310°C or lower, and even more preferably 300°C or lower. When the temperature at which the degree of curing reaches 95 (%) exceeds 320°C, the time required until the completion of curing becomes long, and the rapid curing property may be impaired.

[0037] The temperature at which the degree of curing reaches 95%, as determined from the integral value of the curing exothermic peak in the differential scanning calorimetry curve, is the temperature at which the reaction rate of the curing reaction reaches 95%, obtained by dividing the curing exothermic peak by reaction fraction. The reaction fraction can be calculated based on the area of ​​the curing exothermic peak.

[0038] To adjust the exothermic onset temperature S and the temperature at which the degree of curing reaches 95%, one can refer to the description in the present invention's examples or to the differential scanning calorimetry curves of several epoxy resin compositions with different compositions, and adjust the amount of each component, without requiring excessive trial and error.

[0039] The uncured mixture of the two-component epoxy resin composition of the present invention is preferably cured to 80% or more, more preferably 90% or more, and particularly preferably 95% or more, when heated from 25°C to 180°C at a rate of 100°C / min, held at 180°C for 15 minutes, and then cooled to 25°C at a rate of 100°C / min, and held at 25°C for 20 minutes (see the examples described below). If the curing degree is less than 80%, the rapid curing properties are poor, and the productivity of cured resin products and fiber-reinforced composite materials tends to decrease.

[0040] 1-1. Main component composition The main component composition of the two-component epoxy resin composition of the present invention contains, as essential components, an epoxy resin (a) having at least one oxazolidone ring structure and an epoxy resin (b) having at least three glycidyl groups. The viscosity of this main component composition at 120°C must be 200 mPa·s or less.

[0041] The viscosity of the main component composition at 120°C is 200 mPa·s or less, preferably 150 mPa·s or less, more preferably 140 mPa·s or less, even more preferably 130 mPa·s or less, and particularly preferably 120 mPa·s or less. If the viscosity is 200 mPa·s or less, it is easy to handle and easy to mix uniformly with the curing agent composition. The lower limit of the viscosity at 120°C is not particularly limited, but is generally 30 mPa·s or more, and preferably 50 mPa·s or more. Here, viscosity at 120°C refers to the minimum viscosity measured during the process of preheating the main component composition to 90°C and raising it to 120°C within 15 minutes. Since the main component composition does not harden (thicken) on its own, the minimum viscosity can be considered as the viscosity at 120°C.

[0042] 1-1-1. Epoxy resin (a) Epoxy resin (a) is an epoxy resin having at least one oxazolidone ring structure. As such an epoxy resin, an epoxy resin represented by the following chemical formula (1), which is a reaction product of a bisphenol A type epoxy resin and an aromatic diisocyanate, can be preferably used.

[0043]

[0044] However, in chemical formula (1), R １ The structure is represented by the following chemical formula (2), and R ２ is a substituent having 6 to 20 carbon atoms. n is an integer greater than or equal to 1.

[0045]

[0046] However, in chemical formula (2), R ３ is, -CH ２ -, -CH(CH ３ )-,-C(CH ３ ) ２ -, -SO ２ - is a base chosen from among. m is a non-negative integer.

[0047] Examples of commercially available epoxy resins (a) having at least one oxazolidone ring structure include AER4152 (trade name) from Asahi Kasei E-Materials Corporation, D.E.R. 858 (trade name) and D.E.R. 6508 (trade name) from Olin Corporation, and EPICLON TSR-400 (trade name) from DIC Corporation.

[0048] The proportion of epoxy resin (a) in the total epoxy resin is preferably 3 to 35% by mass, more preferably 5 to 33% by mass, even more preferably 8 to 30% by mass, and particularly preferably 10 to 25% by mass. If it is less than 3% by mass, it tends to be difficult to sufficiently increase the toughness of the resulting cured resin. If it exceeds 35% by mass, the viscosity tends to increase, and the impregnation and handling properties may decrease. In addition, the degree of curing and Tg of the resulting cured resin tend to decrease.

[0049] 1-1-2. Epoxy resin (b) Epoxy resin (b) is an epoxy resin containing at least three glycidyl groups. Examples of such epoxy resins include tetrafunctional glycidylamine type epoxy resins such as tetraglycidyl-4,4'-diaminodiphenylmethane, tetraglycidyl-4,4'-diaminodiphenylsulfone, tetraglycidyl-3,3'-diaminodiphenylsulfone, tetraglycidyl-4,4'-diaminodiphenyl ether, tetraglycidyl-3,4'-diaminodiphenyl ether, and tetraglycidyl-4,4'-diamino-3,3'-diethyldiphenylmethane; and trifunctional epoxy resins such as triglycidyl-m-aminophenol, triglycidyl-p-aminophenol, and triglycidyl isocyanurate. Among these, it is preferable to use tetraglycidyl-4,4'-diaminodiphenylmethane, triglycidyl-m-aminophenol, or triglycidyl-p-aminophenol. These epoxy resins may be used individually, or they may be used in combination as a mixture.

[0050] The proportion of epoxy resin (b) in the total epoxy resin is preferably 65 to 97% by mass, more preferably 67 to 95% by mass, even more preferably 70 to 92% by mass, and particularly preferably 75 to 90% by mass. If it is less than 65% by mass, the viscosity tends to increase, which may reduce impregnation and handling properties. In addition, the degree of curing and glass transition temperature (Tg) of the resulting resin cured product tend to decrease.

[0051] 1-1-3. Other Epoxy Resins The main component of the two-component epoxy resin composition of the present invention contains, as essential components, an epoxy resin (a) having at least one oxazolidone ring structure and an epoxy resin (b) having at least three glycidyl groups, but may also contain other epoxy resins. As other epoxy resins, for example, monofunctional epoxy resins can be used. By using a monofunctional epoxy resin in combination, the reactivity of the epoxy resin composition can be mitigated and the pot life can be extended. Furthermore, since monofunctional epoxy resins do not form crosslinking sites in the curing reaction, the crosslinking density of the cured product can be moderately reduced, which can improve the toughness and impact resistance of the cured product. In addition, by using a low-viscosity monofunctional epoxy resin, the viscosity of the entire main component composition can be reduced, which can improve the mixability and impregnation properties. Among these, epoxy resins containing aromatic groups are preferred, and epoxy resins having a glycidyl ether structure are preferred. Alicyclic epoxy resins can also be suitably used. Specific examples include phenyl glycidyl ether, cresyl glycidyl ether, butyl glycidyl ether, or glycidyl neodecanoate. These epoxy resins may have non-reactive substituents, such as aromatic ring structures, as needed. Examples of non-reactive substituents include alkyl groups such as methyl, ethyl, and isopropyl groups, aromatic groups such as phenyl groups, alkoxyl groups, aralkyl groups, and halogen groups such as chlorine and bromine.

[0052] Other epoxy resins that can be used include, for example, bifunctional epoxy resins. In particular, including a bifunctional epoxy resin with low viscosity can reduce the viscosity of the epoxy resin composition, improve resin impregnation into the reinforcing fiber substrate, extend the pot life, and potentially increase the design flexibility of the mold used in the RTM method. Furthermore, by using a combination of bifunctional epoxy resins, it may be possible to obtain resin cured products and fiber-reinforced composite materials that improve resin impregnation into the reinforcing fiber substrate while maintaining heat resistance and high modulus of elasticity.

[0053] As the bifunctional epoxy resin, an aromatic epoxy resin is preferred. Examples of bifunctional epoxy resins include N,N-diglycidylaniline and its derivatives, diglycidyl-o-toluidine, diglycidyl-m-toluidine, diglycidyl-p-toluidine, diglycidyl-xylidine, diglycidyl-mesidine, diglycidyl-anisidine, diglycidyl-phenoxyaniline, diglycidyl-naphthylamine, and their derivatives. In particular, diglycidylaniline, diglycidyl-o-toluidine, diglycidyl-m-toluidine, diglycidyl-p-toluidine, and diglycidyl-phenoxyaniline are preferred, and diglycidylaniline or diglycidyl-o-toluidine are more preferred. The epoxy resin preferably has a diglycidylamino group. By using an epoxy resin having a diglycidylamino group, a sufficient pot life can be obtained.

[0054] As a bifunctional epoxy resin, it is also preferable to use an epoxy resin having a polycyclic aromatic hydrocarbon skeleton. Examples of polycyclic aromatic hydrocarbon skeletons include naphthalene skeletons and anthracene skeletons, with naphthalene skeletons being preferred from the viewpoint of the physical properties of the cured resin. The polycyclic aromatic hydrocarbon skeleton may have substituents in addition to the glycidyl group. Examples of monomers having a naphthalene skeleton include 1,6-bis(glycidyloxy)naphthalene, 1,5-bis(glycidyloxy)naphthalene, 2,6-bis(glycidyloxy)naphthalene, 2,7-bis(glycidyloxy)naphthalene, 2,2'-bis(glycidyloxy)-1,1'-binaphthalene, and 2,7-bis(glycidyloxy)-1-[2-(glycidyloxy)-1-naphthylmethyl]naphthalene. By using these bifunctional epoxy resins, it may be possible to reduce the viscosity of the epoxy resin composition and improve the heat resistance of the cured resin. Furthermore, when using an epoxy resin having a polycyclic aromatic hydrocarbon skeleton as a bifunctional epoxy resin, the crosslinking density of the cured product does not increase excessively, and the decrease in toughness of the cured resin may be suppressed. Specifically, examples include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenol novolac type epoxy resin, and cresol novolac type epoxy resin.

[0055] The main component of the two-component epoxy resin composition of the present invention preferably does not contain a dissolved curing agent component, and more preferably does not contain any curing agent component at all. If a dissolved curing agent component is present in the main component composition, its storage stability may be reduced.

[0056] 1-2. Curing Agent Composition The curing agent composition of the two-component epoxy resin composition of the present invention contains liquid aromatic polyamine (d) as an essential component. The viscosity of this curing agent composition at 120°C must be 200 mPa·s or less. By including aromatic polyamine (d) as an essential component, the viscosity of the epoxy resin composition can be reduced to a viscosity that can be handled during casting in the RTM method.

[0057] The viscosity of the curing agent composition at 120°C is 200 mPa·s or less, preferably 150 mPa·s or less, more preferably 100 mPa·s or less, even more preferably 50 mPa·s or less, and particularly preferably 10 mPa·s or less. If the viscosity is 200 mPa·s or less, the handling property is high, and it becomes easy to uniformly mix with the main agent composition. The lower limit of the viscosity at 120°C is not particularly limited, but generally it is 0.1 mPa·s or more, and preferably 0.5 mPa·s or more. Here, the viscosity at 120°C means the minimum value of the viscosity measured in the process of preheating the curing agent composition to 90°C and then raising the temperature to 120°C within 15 minutes. Since the curing agent composition does not cure (thicken) alone, this minimum value of the viscosity can be regarded as the viscosity at 120°C. The curing agent composition is preferably a liquid at 25°C. Being a liquid at 25°C means having fluidity at 25°C, including the case of being in a paste state. Specifically, it means that the viscosity at 25°C is 90,000 mPa·s or less.

[0058] 1-2-1. Aromatic polyamine (d) As the aromatic polyamine (d), a phenylenediamine derivative or a 4,4'-diaminodiphenylmethane derivative that is a liquid at 25°C can be used. Specifically, the compounds represented by the following chemical formulas (3) or (4) are exemplified.

[0059]

[0060] However, in Chemical Formula (3), R １ to R ４ are each independently any one of a hydrogen atom, an aliphatic substituent, a halogeno group, an alkoxy group or a thioalkoxy group, and at least one substituent is either an aliphatic substituent having 1 to 6 carbon atoms or a thioalkoxy group.

[0061]

[0062] However, in Chemical Formula (4), R ５ to R ６ are each independently any one of an aliphatic substituent, a methoxy group, an alkoxy group or a thioalkoxy group.

[0063] More specific compounds represented by the above chemical formulas (3) or (4) include the compounds represented by the following chemical formulas (5) to (9). Diethyltoluenediamine represented by chemical formulas (5) and (6) is particularly preferred. These may be used individually or in combination.

[0064]

[0065]

[0066]

[0067]

[0068]

[0069] The total amount of curing agent contained in the epoxy resin composition of the present invention is an amount suitable for curing all the epoxy resins blended in the epoxy resin composition in a short time, and is appropriately adjusted depending on the type of epoxy resin and curing agent used. Specifically, it is preferable that the equivalent ratio (H / E) of the active hydrogen equivalent H (g / eq) of the curing agent to the epoxy equivalent E (g / eq) of the epoxy resin is 0.8 to 1.2. If the equivalent ratio (H / E) is outside the range of 0.8 to 1.2, curing failure may occur.

[0070] The content of aromatic polyamine (d) in the curing agent composition is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 90% by mass or more, based on the total mass of the curing agent. If the content of aromatic polyamine (d) is below the lower limit, it may be difficult for the epoxy resin composition to maintain a liquid state at room temperature, which may hinder RTM (Return to Manufacturing). In addition, the mechanical properties such as heat resistance, elastic modulus, and fracture toughness of the resulting cured resin may be insufficient.

[0071] 1-2-2. Other curing agents The epoxy resin composition of the present invention may contain curing agents other than aromatic polyamine (d). Examples of other curing agents include alicyclic polyamine (e), aliphatic polyamine, various isomers of aromatic amine curing agents, aminobenzoic acid esters, and acid anhydrides, and the inclusion of alicyclic polyamine (e) is particularly preferred.

[0072] Examples of alicyclic polyamines (e) include isophoronediamine, N-(3-aminopropyl)cyclohexylamine, 4,4'-methylenebis(cyclohexylamine), 1,3-bisaminomethylcyclohexane, norbornenediamine, 1,2-diaminocyclohexane, N-aminoethylpiperazine, and 1,4-bis(2-amino-2-methylpropyl)piperazine and cyclohexylenediamine.

[0073] When using alicyclic polyamines, the amount added is preferably 1 to 20% by mass, more preferably 3 to 15% by mass, and particularly preferably 5 to 12% by mass, based on the total mass of the curing agent.

[0074] Examples of aliphatic polyamines include diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, trimethylhexamethylenediamine, and 2-methylpentamethylenediamine. Examples of aminobenzoic acid esters include trimethylene glycol di-p-aminobenzoate and neopentyl glycol di-p-aminobenzoate. Cured products and fiber-reinforced composite materials cured using these curing agents tend to have high tensile elongation. Examples of acid anhydrides include 1,2,3,6-tetrahydrophthalic anhydride, hexahydrophthalic anhydride, and 4-methylhexahydrophthalic anhydride. When these curing agents are used, the pot life of the resin composition can be extended, and a cured resin product with a balanced electrical, chemical, and mechanical property can be obtained.

[0075] In the present invention, when two or more curing agents are mixed to form a curing agent composition, it is preferable that the curing agent composition becomes a uniform liquid when heated to a temperature of 200°C or lower, and that a uniform liquid state is maintained thereafter at room temperature. The period during which a uniform liquid state is maintained at room temperature is preferably one week or more, more preferably three weeks or more, and particularly preferably one month or more. If the period during which a uniform liquid state is maintained at room temperature is less than one week, it becomes difficult to handle the curing agent composition as a substantially liquid, and poor mixing with the main component composition is likely to occur.

[0076] 1-3. Core-shell type rubber particles The two-component epoxy resin composition of the present invention contains core-shell type rubber particles. Core-shell type rubber particles in the present invention are formed by coating part or all of the surface of a particulate core component, which is mainly composed of a crosslinked rubber-like polymer or elastomer, with a shell component of a different type from the core component.

[0077] Core components constituting core-shell type rubber particles include polymers of one or more monomers selected from conjugated diene monomers and aromatic vinyl compounds, or silicone resins. In particular, cross-linked polybutadiene, obtained by polymerizing butadiene, a conjugated diene monomer, is suitable for use as a core component because it exhibits excellent improvement in fracture toughness at extremely low temperatures.

[0078] The shell component constituting the core-shell type rubber particle is preferably graft polymerized onto the core component and chemically bonded to the polymer constituting the core component. The components constituting such a shell component are polymers polymerized from one or more types selected from, for example, (meth)acrylic acid ester compounds and aromatic vinyl compounds. (Meth)acrylic acid ester compounds refer to acrylic acid ester compounds and / or methacrylic acid ester compounds. Acrylic acid ester compounds refer to compounds having an acrylic acid ester structure and their derivatives, and examples include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, t-butyl acrylate, n-hexyl acrylate, and cyclohexyl acrylate. Methacrylic acid ester compounds refer to compounds having a methacrylic acid ester structure and their derivatives, for example, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, n-hexyl methacrylate, and cyclohexyl methacrylate. Aromatic vinyl compounds refer to compounds having a polymerizable vinyl structure, for example, styrene, α-methylstyrene, divinylbenzene, and compounds in which their aromatic rings are substituted with various functional groups such as alkyl groups and halogen atoms. Furthermore, it is preferable that the shell component has a functional group that reacts with the epoxy resin composition of the present invention in order to stabilize the dispersion state. Examples of such functional groups include hydroxyl groups, carboxyl groups, and epoxy groups.

[0079] There are no particular limitations on the core-shell type rubber particles that can be applied to the epoxy resin composition of the present invention, and those manufactured by well-known methods can be used. As a masterbatch in which core-shell type rubber particles are dispersed in epoxy resin, "KaneAce" (registered trademark), which is commercially available from Kaneka Corporation, can be suitably used.

[0080] Core-shell type rubber particles are preferable if their average particle diameter is in the range of 1 to 500 nm in volume average particle diameter, because when the epoxy resin composition of the present invention is impregnated into carbon fibers or a fabric mainly composed of carbon fibers, the core-shell polymer particles are less likely to be filtered out by the carbon fibers or other fibers contained in the fabric, and the dispersion state does not change. A value of 10 to 300 nm is even more preferable.

[0081] The core-shell type rubber particles may be mixed with the main component composition and / or the curing agent composition of the two-component epoxy resin composition, or they may be mixed separately.

[0082] The average degree of polymerization of the core-shell type rubber particles is preferably 4,000 to 40,000.

[0083] The two-component epoxy resin composition of the present invention is preferably formulated so that the content of core-shell type rubber particles is 0.5 to 5.0% by mass, more preferably 0.5 to 4.5% by mass, and particularly preferably 1.0 to 4.0% by mass, based on the total mass of the epoxy resin composition.

[0084] 1-4. Other Optional Components The epoxy resin composition of the present invention may contain thermosetting resins other than the epoxy resins described above. Examples of thermosetting resins other than epoxy resins include vinyl ester resins, benzoxazine resins, bismaleimide resins, bismaleimide-triazine resins, and thermosetting polyurethanes.

[0085] In addition to the core-shell type rubber particles described above, the epoxy resin composition of the present invention may also contain thermoplastic resins and oligomers that can be used as raw materials for thermoplastic resins as components dissolved in the epoxy resin composition. Thermoplastic resins and oligomers improve the fracture toughness and impact resistance of the resulting fiber-reinforced composite material. Such thermoplastic resins and oligomers may be dissolved in the epoxy resin composition during the curing process. Specific examples of thermoplastic resins include polyethersulfone, polysulfone, polyetherimide, polycarbonate, thermoplastic polyurethane, polyether polyol, polyester polyol, acrylic resin, and acrylic block copolymer. Specific examples of oligomers include polyether polyol and polyester polyol. These may be used individually or in combination of two or more.

[0086] The thermoplastic resin is preferably a polyethersulfone or polysulfone with a weight-average molecular weight (Mw) in the range of 8,000 to 100,000, as measured by gel permeation chromatography. A weight-average molecular weight (Mw) of 8,000 or more ensures sufficient impact resistance of the resulting FRP, while a weight-average molecular weight (Mw) of 100,000 or less allows for the creation of an epoxy resin composition with good handling properties without significantly increasing viscosity. The molecular weight distribution of the thermoplastic resin is preferably uniform, and the polydispersity (Mw / Mn), which is the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn), is preferably 1 to 10, and more preferably 1.1 to 5.0.

[0087] The thermoplastic resin may also preferably have reactive groups that react with the epoxy resin or functional groups that form hydrogen bonds. Such a thermoplastic resin can improve the dissolution stability during the curing process of the epoxy resin. Furthermore, it can impart fracture toughness, chemical resistance, heat resistance, and humid heat resistance to the fiber-reinforced composite material obtained after curing. Preferred reactive groups that react with the epoxy resin include hydroxyl groups, carboxyl groups, imino groups, and amino groups. Using polyethersulfone with hydroxyl group termini is preferable because it provides particularly excellent impact resistance, fracture toughness, and solvent resistance to the resulting fiber-reinforced composite material. The content of the thermoplastic resin in the epoxy resin composition is adjusted as appropriate according to the viscosity. When a thermoplastic resin is included, from the viewpoint of impregnation into the reinforcing fiber substrate, the content of 0.1 to 10 parts by mass, and more preferably 0.5 to 5 parts by mass, is preferred per 100 parts by mass of epoxy resin in the epoxy resin composition. By including 0.1 parts by mass or more, the resulting fiber-reinforced composite material exhibits sufficient fracture toughness and impact resistance. By having a content of 10 parts by mass or less, the viscosity of the epoxy resin composition does not increase significantly, making it easy to impregnate the reinforcing fiber substrate, and improving various physical properties of the resulting fiber-reinforced composite material.

[0088] The thermoplastic resin may also preferably contain a reactive aromatic oligomer having an amine-terminated group (hereinafter also simply referred to as "aromatic oligomer"). During heat curing, the epoxy resin composition undergoes a high molecular weight increase due to the curing reaction between the epoxy resin and the curing agent. This increase in molecular weight expands the two-phase region, causing the aromatic oligomer dissolved in the epoxy resin composition to undergo reaction-induced phase separation. This phase separation forms a two-phase structure within the matrix resin, where the cured epoxy resin and the aromatic oligomer are co-continuous. Furthermore, because the aromatic oligomer has an amine-terminated group, it also reacts with the epoxy resin. Since each phase in this co-continuous two-phase structure is strongly bonded to each other, solvent resistance is also improved. This co-continuous structure absorbs external impacts to the fiber-reinforced composite material, suppressing crack propagation. As a result, fiber-reinforced composite materials made using an epoxy resin composition containing a reactive aromatic oligomer having an amine-terminated group have high impact resistance and fracture toughness. Known polysulfones and polyethersulfones having amine-terminated groups can be used as the aromatic oligomer. The amine terminal group is a primary amine (-NH ２ ) Preferably, the oligomer is an end group. When an aromatic oligomer is incorporated into an epoxy resin composition, the aromatic oligomer preferably has a weight-average molecular weight of 8,000 to 40,000 as measured by gel permeation chromatography. A weight-average molecular weight of 8,000 or more provides a high effect in improving the toughness of the matrix resin. Furthermore, a weight-average molecular weight of 40,000 or less provides processing advantages such as easier impregnation of the resin composition into the reinforcing fiber substrate without the viscosity of the resin composition becoming too high. Commercially available aromatic oligomers such as "Virantage DAMS VW-30500 RP (registered trademark)" (manufactured by Solvay Specialty Polymers) can preferably be used.

[0089] The thermoplastic resin is preferably in particulate form before being incorporated into the epoxy resin composition. Particulate thermoplastic resin can be uniformly incorporated and dissolved in the resin composition.

[0090] The epoxy resin composition of the present invention may contain other additives, such as conductive particles, flame retardants, inorganic fillers, and internal mold release agents. Examples of conductive particles include conductive polymer particles such as polyacetylene particles, polyaniline particles, polypyrrole particles, polythiophene, polyisothianaphthene particles, and polyethylenedioxythiophene particles, as well as carbon particles, carbon fiber particles, metal particles, and particles in which a core material made of an inorganic or organic material is coated with a conductive substance. Examples of flame retardants include phosphorus-based flame retardants. Phosphorus-based flame retardants can be any substance containing a phosphorus atom in their molecule, and examples include organophosphorus compounds such as phosphate esters, condensed phosphate esters, phosphazene compounds, polyphosphates, and red phosphorus. Examples of inorganic fillers include kaolinite, hydrated magnesium silicate, aluminum borate, calcium carbonate, silicon carbonate, silicon nitride, potassium titanate, basic magnesium sulfate, zinc oxide, graphite, calcium sulfate, magnesium borate, magnesium oxide, and silicate minerals. Silicate minerals are particularly preferred. A commercially available silicate mineral is THIXOTROPIC AGENT DT 5039 (manufactured by Huntsman Japan Co., Ltd.). Examples of internal release agents include metal soaps, plant waxes such as polyethylene wax and carnauba wax, fatty acid ester-based release agents, silicone oils, animal waxes, and fluorinated nonionic surfactants. When these internal release agents are incorporated, the amount is preferably 0.1 to 5 parts by mass, and more preferably 0.2 to 2 parts by mass, per 100 parts by mass of the epoxy resin. Within this range, the release effect from the mold is particularly favorably exhibited. Examples of commercially available internal mold release agents include MOLD WIZ (registered trademark) INT1846 (manufactured by AXEL PLASTICS RESEARCH LABORATORIES INC.), Licowax S, Licowax P, Licowax OP, Licowax PE190, Licowax PED (manufactured by Clariant Japan), and stearyl stearate (SL-900A, manufactured by Riken Vitamin Co., Ltd.).

[0091] 2. Method for Manufacturing the Epoxy Resin Composition The two-component epoxy resin composition of the present invention is prepared by first preparing a main component composition and a curing agent composition, and then mixing the main component composition and the curing agent composition immediately before use. The core-shell type rubber particles may be mixed in advance with the main component composition and / or the curing agent composition, or they may be mixed separately.

[0092] Conventional mixing machinery and equipment can be used. Specific examples include roll mills, planetary mixers, kneaders, extruders, Banbury mixers, mixing vessels equipped with stirring blades, and horizontal mixing tanks. Mixing of each component can be carried out in air or under an inert gas atmosphere. When mixing in air, it is preferable to do so in an atmosphere where temperature and humidity are controlled. For example, it is preferable to mix at a temperature controlled to 30°C or lower, or in a low-humidity atmosphere with a relative humidity of 50% RH or lower.

[0093] 2-1. Method for Producing the Main Component Composition The main component composition is prepared by mixing an epoxy resin (a) having at least one oxazolidone ring structure, an epoxy resin (b) having at least three glycidyl groups, and, if necessary, core-shell type rubber particles or other optional components. The order of mixing these components does not matter. The main component composition may be in a single-liquid state in which each component is uniformly mixed, or in a slurry state in which some components are dispersed as solids. Any conventionally known method may be used to produce the main component composition. The mixing temperature is, for example, 40 to 200°C, preferably 50 to 100°C, and more preferably 50 to 90°C. If the temperature exceeds the upper limit, the self-polymerization reaction of the epoxy resin may proceed partially, reducing its impregnation into the reinforcing fiber substrate, or the physical properties of the cured resin product produced using the obtained main component composition may decrease. If the temperature is below the lower limit, the viscosity of the main component composition may be high, making mixing substantially difficult.

[0094] 2-2. Method for Producing the Curing Agent Composition The curing agent composition is prepared by mixing aromatic polyamine (d) as an essential component with core-shell type rubber particles and other optional components as needed. The state of this curing agent composition may be a single liquid state in which each component is uniformly mixed, or a slurry state in which some components are dispersed as solids. Any conventionally known method may be used to produce the curing agent composition. The mixing temperature is, for example, 25 to 200°C, preferably 25 to 150°C, and more preferably 50 to 120°C. If the temperature exceeds the upper limit, the added components may decompose due to thermal stress. On the other hand, if the temperature is below the lower limit, it becomes difficult to dissolve solid curing agent components in aromatic polyamine (d), making it difficult to obtain a liquid curing agent composition.

[0095] 3. Cured Resin A cured resin is obtained by curing the epoxy resin composition of the present invention. The resulting cured resin may have the following properties.

[0096] The degree of curing of the resin cured product is preferably 80% or higher, more preferably 90% or higher, and particularly preferably 95% or higher. Here, the degree of curing is as described above.

[0097] The glass transition temperature (dry-Tg) of the cured resin in its dry state is preferably 160°C or higher, more preferably 175°C or higher, even more preferably 190°C or higher, and particularly preferably 200°C or higher. It is preferable that the glass transition temperature (dry-Tg) in its dry state is above the lower limit temperature, as this allows the cured resin and fiber composite materials to exhibit sufficient mechanical properties even in high-temperature environments.

[0098] The glass transition temperature (wet-Tg) of the resin cured product at saturated water absorption is preferably 110°C or higher, more preferably 125°C or higher, even more preferably 140°C or higher, and particularly preferably 155°C or higher. It is preferable that the glass transition temperature (wet-Tg) at saturated water absorption is above the lower limit temperature, as this allows the resin cured product and fiber composite material to exhibit sufficient mechanical properties even in a humid environment.

[0099] The room-temperature dry flexural modulus (RTD-FM) of the cured resin, measured in accordance with JIS K 7171, is preferably 2.80 GPa or higher, and more preferably 2.90 to 4.0 GPa. Exceeding the lower limit results in a fiber-reinforced composite material obtained using the epoxy resin composition of the present invention exhibiting superior mechanical properties.

[0100] The content of core-shell type rubber particles (g) in the cured resin is preferably 0.5 to 5.0% by mass, more preferably 0.5 to 4.5% by mass, and particularly preferably 1.0 to 4.0% by mass.

[0101] 4. Fiber-reinforced composite material The fiber-reinforced composite material of the present invention is formed by compounding a resin cured product obtained by curing an epoxy resin composition with a reinforcing fiber substrate.

[0102] Examples of reinforcing fibers for the base material include carbon fibers, glass fibers, aramid fibers, silicon carbide fibers, polyester fibers, ceramic fibers, alumina fibers, boron fibers, metal fibers, mineral fibers, rock fibers, and slug fibers. Among these reinforcing fibers, carbon fibers, glass fibers, and aramid fibers are preferred. Carbon fibers are more preferred because they have good specific strength and specific modulus, and a lightweight and high-strength fiber-reinforced composite material can be obtained. Among carbon fibers, polyacrylonitrile (PAN) carbon fibers are particularly preferred because they have excellent tensile strength.

[0103] When PAN-based carbon fibers are used as reinforcing fibers, their tensile modulus is preferably 100 to 600 GPa, more preferably 200 to 500 GPa, and particularly preferably 230 to 450 GPa. The tensile strength is preferably 2,000 to 10,000 MPa, and more preferably 3,000 to 8,000 MPa.

[0104] When carbon fibers are used as reinforcing fibers, the diameter of the carbon fibers is preferably 4 to 20 μm, and more preferably 5 to 10 μm. By using such carbon fibers, the mechanical properties of the resulting fiber-reinforced composite material can be improved.

[0105] In the present invention, it is preferable that the reinforcing fibers are treated with a sizing agent. In this case, the amount of sizing agent attached is preferably 0.01 to 10% by mass, more preferably 0.05 to 3.0% by mass, and particularly preferably 0.1 to 2.0% by mass, relative to the mass of the reinforcing fibers to which the sizing agent is attached. A larger amount of sizing agent tends to result in stronger interfacial adhesion between the reinforcing fibers and the matrix resin. On the other hand, a smaller amount of sizing agent tends to result in superior interlaminar toughness of the resulting composite material.

[0106] For the reinforcing fiber base material, it is preferable to use a reinforcing fiber sheet in which reinforcing fibers are formed into a sheet. Examples of reinforcing fiber sheets include sheets in which many reinforcing fibers are aligned in one direction, bidirectional woven fabrics such as plain weave and twill weave, multiaxial woven fabrics, nonwoven fabrics, mats, knits, braids, and paper made by papermaking with reinforcing fibers. Among these, it is preferable to use a unidirectional aligned sheet, bidirectional woven fabric, or multiaxial woven fabric base material in which reinforcing fibers are formed into a sheet as continuous fibers, because this can yield a fiber-reinforced composite material with superior mechanical properties. Bidirectional woven fabrics and multiaxial woven fabric base materials may be made by laminating and stitching together multiple unidirectional aligned sheets. In this case, in order to improve the interlaminar toughness of the resulting fiber-reinforced composite material, a nonwoven fabric layer of thermoplastic resin may be placed on one side of the unidirectional aligned sheet before lamination to form a woven fabric. Examples of thermoplastic resin nonwoven fabric layers include nonwoven fabric layers made of polyester resin fibers, polyamide resin fibers, polyethersulfone resin fibers, polysulfone resin fibers, polyetherimide resin fibers, polycarbonate resin fibers, and mixtures thereof. The basis weight and number of layers of the unidirectional drawn sheet can be appropriately set according to the application of the fiber-reinforced composite material. For example, the basis weight of the unidirectional drawn sheet can be 100 to 300 g / m². ２ Preferably 150 to 250 g / m ２ The thickness of each layer of the unidirectional aligned sheet of the reinforcing fiber base material is preferably 0.01 to 3 mm, and more preferably 0.05 to 1.5 mm.

[0107] The reinforced fiber substrate according to the present invention may contain a binder resin or inorganic particles. Using a binder resin can improve the handling properties of the reinforced fiber substrate. There are no particular restrictions on the resin material used as the binder resin; thermosetting resins such as epoxy resins and vinyl ester resins, thermoplastic resins such as polyamides and polyethersulfones, and mixtures thereof can be used as appropriate. Inorganic particles can improve the elastic modulus and strength of the reinforced fiber substrate. These binder resins and inorganic particles may be used by scattering them as powder and fixing them by sintering, or they may be formed into sheets or nonwoven fabrics and laminated onto the reinforced fiber substrate. Alternatively, they may be pre-attached to each filament constituting the reinforced fiber substrate of the present invention.

[0108] The fiber-reinforced composite material provided by the present invention preferably has a post-impact compressive strength (CAI, impact energy 30.5 J) of 170 MPa or more, and more preferably 190 to 400 MPa, as measured in accordance with ASTM D7136.

[0109] The fiber-reinforced composite material provided by the present invention preferably has a room-temperature dry perforated compressive strength (RTD-OHC) of 300 MPa or more, more preferably 310 to 450 MPa, and particularly preferably 320 to 400 MPa, as measured in accordance with SACMA SRM3.

[0110] 5. Method for Manufacturing Fiber-Reinforced Composite Materials The fiber-reinforced composite material of the present invention is manufactured by compounding a reinforcing fiber substrate with the epoxy resin composition of the present invention and then curing it, or by curing it while compounding. Examples of compounding methods include resin transfer molding (RTM method), hand lay-up method, filament winding method, and pultrusion method. Examples of methods for manufacturing fiber-reinforced composite materials using the epoxy resin composition of the present invention include known molding methods such as the RTM method, autoclave molding method, and press molding method. The epoxy resin composition of the present invention is particularly suitable for the RTM method. The RTM method is a method for obtaining a fiber-reinforced composite material by impregnating a reinforcing fiber substrate placed in a mold with a liquid epoxy resin composition and curing it. In the present invention, the mold used in the RTM method may be a closed mold made of a rigid material, or a combination of an open mold made of a rigid material and a flexible film (bag). In the latter case, the reinforcing fiber substrate can be placed between the open mold made of a rigid material and the flexible film. For rigid materials, metals such as steel and aluminum, fiber-reinforced plastics, wood, and gypsum can be used. For flexible film materials, polyamide, polyimide, polyester, fluororesin, and silicone resin can be used. When a closed mold of a rigid material is used in the RTM method, the epoxy resin composition is usually injected under pressure into the clamped mold. In this case, a suction port may be provided in addition to the injection port and connected to a vacuum pump for suction. Alternatively, the epoxy resin composition may be injected using only atmospheric pressure without the use of special pressurizing means by suction. This method is suitable because it allows for the manufacture of large components by providing multiple suction ports. When an open mold of a rigid material and a flexible film are used in combination in the RTM method, the epoxy resin composition may be injected using only atmospheric pressure without the use of special pressurizing means by suction. To achieve good impregnation with injection at atmospheric pressure alone, it is effective to use a resin diffusion medium. Furthermore, it is preferable to apply a gel coat to the surface of the rigid material prior to the placement of the reinforcing fiber substrate.

[0111] In the RTM method, the epoxy resin composition is impregnated into the reinforcing fiber substrate, and then heat curing is performed. From the viewpoint of productivity, it is preferable that the mold is preheated. The mold temperature (curing temperature) during heat curing is generally selected to be the same as or higher than the mold temperature (preheating temperature) when the epoxy resin composition is injected. The preheating temperature and curing temperature of the mold are preferably 100 to 200°C, more preferably 125 to 180°C, and particularly preferably 140 to 180°C.

[0112] The heat curing time is preferably 1 minute to 20 hours. After heat curing is complete, the fiber-reinforced composite material is removed by demolding. The obtained fiber-reinforced composite material may then be heated at a higher temperature for post-curing. The temperature for this post-curing is preferably 150 to 200°C, and the time is preferably 1 minute to 4 hours. The impregnation pressure when impregnating the reinforcing fiber substrate with the epoxy resin composition by the RTM method is appropriately determined considering the viscosity and resin flow of the resin composition. A specific impregnation pressure is, for example, 0.001 to 10 MPa, preferably 0.01 to 1 MPa.

[0113] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The components and evaluation methods used in these examples and comparative examples are described below.

[0114] <Evaluation Method> The evaluations performed on the examples and comparative examples are as follows.

[0115] (1) Characteristics of the epoxy resin composition (1-1) Preparation of the epoxy resin composition The epoxy resins [a] to [c] and resin particles [g] were mixed in the proportions shown in Table 1 to obtain the main component composition. Separately, the curing agents [d] to [f] were mixed in the proportions shown in Table 1 to obtain the curing agent composition. This resulted in obtaining a two-component epoxy resin composition.

[0116] (1-2) Viscosity and Pot Life The viscosity of the main component composition and curing agent composition prepared in (1-1) was measured using a Type B viscometer "TVB-15M" manufactured by Toki Sangyo Co., Ltd., preheated to 120°C. The main component composition and curing agent composition were each preheated to 90°C, and the viscosity was measured while raising the temperature to 120°C within 15 minutes. The minimum viscosity value shown within 15 minutes of the start of measurement was taken as the viscosity measurement value. The viscosity of the epoxy resin composition was measured using a Type B viscometer "TVB-15M" manufactured by Toki Sangyo Co., Ltd., preheated to 120°C. The main component composition and curing agent composition were each preheated to 90°C, and after mixing them in the proportions shown in Table 1, the viscosity was measured while raising the temperature to 120°C within 15 minutes. The minimum viscosity value shown within the range of 90 to 120°C within 15 minutes of the start of measurement was taken as the minimum viscosity. The pot life was defined as the time it took for the viscosity of the epoxy resin composition to reach 200 mPa·s after heating to 120°C.

[0117] (1-3) Degree of curing Differential scanning calorimetry (DSC measurement) (heating rate: 20°C / min) was performed on the epoxy resin composition prepared in (1-1) by mixing the main component composition and the curing agent composition in the proportions shown in Table 1 to obtain the total heat generation. DSC measurement was performed separately on the same epoxy resin composition. First, the temperature was raised from 25°C to 180°C at a rate of 100°C / min, held at 180°C for 15 minutes, then cooled down to 25°C at a rate of 100°C / min, and held at 25°C for 20 minutes. Subsequently, this epoxy resin composition (cured resin) was reheated from 25°C to 350°C at a rate of 10°C / min. The heat generation during curing was obtained from the heat generation during the reheating from 25°C to 350°C. From the total heat generation value and the heat generation during curing value, the degree of curing was calculated according to the following formula. Degree of curing [%] = (Total heat generation [J / g] - Heat generation during curing [J / g]) / Total heat generation [J / g] × 100

[0118] (1-4) Difference between exothermic onset temperature and curing temperature The epoxy resin composition prepared in (1-1) and the curing agent composition were mixed in the proportions shown in Table 1, and DSC measurement (heating rate: 20°C / min) was performed. The exothermic onset temperature was obtained from the intersection of the baseline and the tangent at the inflection point on the low-temperature side of the curing exothermic peak. The difference between the obtained exothermic onset temperature and the curing temperature (180°C) when curing the resin composition was calculated.

[0119] (1-5) Difference between the temperature at which the degree of curing reaches 95% (determined from the integral value of the exothermic peak) and the curing temperature. The epoxy resin composition prepared in (1-1) and the curing agent composition were mixed in the proportions shown in Table 1, and DSC measurements (heating rate: 20°C / min) were performed. The obtained exothermic peak was integrated with respect to temperature, and the temperature at which the cumulative amount of the total heat generated reached 95% was defined as the temperature at which the degree of curing reached 95%. The difference between the temperature at which the degree of curing reached 95% (determined from the integral value of the exothermic peak) and the curing temperature (180°C) was calculated.

[0120] (2) Characteristics of the cured resin product (2-1) Preparation of the cured resin plate The epoxy resin composition prepared in (1-1) and the curing agent composition were mixed in the proportions shown in Table 1. The mixture was degassed in a vacuum for 60 minutes and then poured into a stainless steel mold set to a thickness of 4 mm using a 4 mm thick Teflon® resin spacer. The mixture was heated and cured at 180°C for 15 minutes as shown in Table 1 to obtain a cured resin plate with a thickness of 4 mm.

[0121] (2-2) Glass transition temperature (dry-Tg) Measurement was performed according to the method compliant with SACMA 18R-94. Using the resin cured plate obtained in (2-1) above, a resin test piece with dimensions of 50 mm × 6 mm × 2 mm was prepared. Using the UBM Rheogel-E4000 dynamic viscoelasticity measuring device, the storage modulus E' of the resin test piece was measured from 50°C to the rubber elastic region under the conditions of a measurement frequency of 1 Hz, a heating rate of 5°C / min, and a strain of 0.0167%, with a distance of 30 mm between the chucks. Log E' was plotted against temperature, and the temperature obtained from the intersection of the approximate straight line of the flat region of log E' and the approximate straight line of the region where E' transitions was recorded as the glass transition temperature (dry-Tg).

[0122] (2-3) Glass transition temperature after water absorption (wet-Tg) Measurement was performed according to the method in accordance with SACMA 18R-94. Using the resin cured plate obtained in (2-1) above, resin test pieces with dimensions of 50 mm × 6 mm × 2 mm were prepared. Using a pressure cooker (ESPEC, HASTEST PC-422R8), the prepared resin test pieces were subjected to water absorption treatment at 121°C for 24 hours. Using a dynamic viscoelasticity measuring device "Rheogel-E4000" manufactured by UBM, the storage modulus E' of the water-treated resin test pieces was measured from 50°C to the rubber elastic region with a measurement frequency of 1 Hz, a heating rate of 5°C / min, and a strain of 0.0167%, with a distance of 30 mm between the chucks. Log E' was plotted against temperature, and the temperature obtained from the intersection of the approximate straight line of the flat region of log E' and the approximate straight line of the region where E' undergoes a transition was recorded as the glass transition temperature (wet-Tg).

[0123] (2-4) Room temperature dry resin flexural modulus (RTD-FM) The test was conducted in accordance with JIS K7171. Using the resin cured plate obtained in (2-1) above, a resin test specimen with dimensions of 80 mm × 10 mm × 4 mm (thickness h) was prepared. Under an ambient temperature of 25°C, with a support distance L of 16 × h mm, a bending test was performed at a test speed of 2 mm / min, and the bending strength and flexural modulus were measured.

[0124] (3) Characteristics of Fiber-Reinforced Composite Materials (3-1) Preparation of Fiber-Reinforced Composite Materials Carbon fiber multiaxial fabrics 1, 2, 3, and 4, as described in <Components> below, were each cut to 300 mm x 300 mm, and a total of 16 sheets were stacked on a 500 mm x 500 mm release-treated aluminum plate so that the angle of the reinforcing fibers was [(+45 / -45)(0 / 90)(-45 / +45)(90 / 0)] [(+45 / -45)(0 / 90)(-45 / +45)(90 / 0)] [(0 / 90)(+45 / -45)(90 / 0)(-45 / +45)] [(0 / 90)(+45 / -45)(90 / 0)(-45 / +45)] to form an NCF laminate. The carbon fiber fabric 1 described in the <Components> section below is cut to 300 mm x 300 mm and placed on a 500 mm x 500 mm release-treated aluminum plate with the angle of the reinforcing fibers set to [(+45 / -45) / (0 / 90)]. ４ｓA total of 16 sheets were stacked to form a woven laminate. Furthermore, on top of this laminate, "Release Ply C" (manufactured by AIRTECH), a peel cloth with mold release properties, and "Resin Flow 90HT" (manufactured by AIRTECH), a resin diffusion substrate, were laminated. After that, hoses for forming the resin injection port and resin discharge port were placed, the whole thing was covered with nylon bag film, sealed with sealant tape, and the inside was evacuated. Subsequently, the aluminum plate was heated to 120°C, the pressure inside the bag was reduced to 5 torr or less, and then the epoxy resin composition prepared in (1-1) above, and the main component composition and curing agent composition were mixed in the proportions shown in Table 1 were heated to 100°C and injected into the vacuum system through the resin injection port. The injected epoxy resin composition filled the bag and impregnated the laminate. The temperature was then raised to a curing temperature of 180°C and maintained at that temperature for 15 minutes to obtain a carbon fiber reinforced composite material (CFRP).

[0125] (3-2) Compressive Strength After Impact (CAI) The CFRP obtained in (3-1) above was cut to dimensions of 101.6 mm in width and 152.4 mm in length to obtain a specimen for the Compressive Strength After Impact (CAI) test. The test was carried out in accordance with ASTM D7136. An impact energy of 30.5 J was applied to this specimen using a drop-weight impact tester (DynaTup, Instron). After impact, the damaged area of ​​the specimen was measured using an ultrasonic flaw detection tester (SDS3600, HIS3 / HF, Krautkramer). The strength test was conducted by attaching one strain gauge to each side of the impacted specimen, 25.4 mm from the top and 25.4 mm from each side, and similarly attaching one to the back side, for a total of four strain gauges per specimen. Then, the test was performed using a testing machine (Shimadzu Autograph) with a crosshead speed of 1.27 mm / min, applying a load until the specimen fractured.

[0126] (3-3) Room temperature dry perforated compressive strength (RTD-OHC) The CFRP obtained in (3-1) above was cut to dimensions of 38.1 mm in width and 304.8 mm in length, and a hole with a diameter of 6.35 mm was drilled in the center of the test piece to obtain a test piece for the room temperature dry perforated compressive strength (RTD-OHC) test. The test was carried out in accordance with SACMA SRM3 at an ambient temperature of 25°C, and the room temperature dry perforated compressive strength was calculated from the maximum point load.

[0127] <Ingredients> The ingredients used in the examples and comparative examples are as follows:

[0128] (Epoxy resin [a]): Epoxy resin having an oxazolidone skeleton; D.E.R. 858: Oxazolidone-modified epoxy resin, registered trademark, manufactured by Olin Corporation; EPICLON TSR-400: Oxazolidone-modified epoxy resin, registered trademark, manufactured by DIC Corporation.

[0129] (Epoxy resin [b]): Liquid epoxy resin having three or more glycidyl groups - Araldite MY 721: Tetraglycidyl-4,4'-diaminodiphenylmethane (hereinafter abbreviated as "4,4'-TGDDM"), registered trademark, manufactured by Huntsman Ltd. - Araldite MY 610: Triglycidyl-m-aminophenol (hereinafter abbreviated as "TG-mAP"), registered trademark, manufactured by Huntsman Ltd.

[0130] (Epoxy resin [c]): Liquid bisphenol-type epoxy resin - EpoTohto YD-8125: Bisphenol A-diglycidyl ether (hereinafter abbreviated as "DGEBA"), registered trademark, manufactured by Nippon Steel & Sumitomo Metal Chemical Co., Ltd. - EpoTohto YDF-170: Bisphenol F-diglycidyl ether (hereinafter abbreviated as "DGEBF"), registered trademark, DGEBF, manufactured by Nippon Steel & Sumitomo Metal Chemical Co., Ltd.

[0131] (Hardening agent [d]): Aromatic amine type liquid hardening agent - Primacure DETDA 80: Diethyltoluenediamine (hereinafter abbreviated as "DETDA"), registered trademark, manufactured by TriiSO LLC.

[0132] (Curing agent [e]): Alicyclic diamine type liquid curing agent - IPDA: Isophorone diamine (cis- and trans-mixture) - CPDA: N-(3-aminopropyl)cyclohexylamine - PACM: bis-(p-diaminocyclohexyl)methane

[0133] (Hardening agent [f]): Other hardening agents / DETA: Diethylenetriamine

[0134] (Resin particles [g]): Core-shell type rubber particle-containing epoxy resin - KaneAce MX-136: Liquid masterbatch in which core-shell type rubber particles are dispersed at 25% by mass in epoxy resin (DGEBF), core-shell type rubber particles / epoxy resin (DGEBF) = 25 / 75, manufactured by Kaneka Corporation - KaneAce MX-154: Liquid masterbatch in which core-shell type rubber particles are dispersed at 40% by mass in epoxy resin (DGEBA), mixture of core-shell type rubber particles / epoxy resin (DGEBA) = 40 / 60, manufactured by Kaneka Corporation

[0135] (Carbon Fiber Strands) ・Carbon Fiber 1: “Tenax®” HTS45 E23 12K 800tex (Carbon fiber strand, tensile strength 4.5 GPa, tensile modulus 240 GPa, sizing agent adhering amount 1.3 mass%, manufactured by Teijin Limited) ・Carbon Fiber 2: “Tenax®” HTA40 E13 6K 400tex (Carbon fiber strand, tensile strength 4.1 GPa, tensile modulus 240 GPa, sizing agent adhering amount 1.3 mass%, manufactured by Teijin Limited)

[0136] (Carbon fiber multilayer fabric) ・Carbon fiber multiaxial fabric 1: 194 g / m² of carbon fibers 1 aligned in one direction per layer ２ It is made into a sheet, two sheets are laminated at an angle of (+45 / -45) and stitched together (total weight of carbon fiber on a woven base material of 388 g / m²). ２ ). ・Carbon fiber multiaxial fabric 2: 194 g / m² of carbon fibers 1 aligned in one direction per layer ２ The material is formed into a sheet, and two sheets are layered at an angle of (-45 / +45) and stitched together (total weight of carbon fiber on a woven base fabric: 388 g / m²). ２ ). ・Carbon fiber multiaxial fabric 3: 194 g / m² of carbon fibers 1 aligned in one direction per layer２ It is made into a sheet, two sheets are laminated at an angle of (0 / 90) and stitched together (total weight of carbon fiber on a woven base material of 388 g / m²). ２ ). ・Carbon fiber multiaxial fabric 4: 194 g / m² of carbon fibers 1 aligned in one direction per layer ２ It is made into a sheet, two sheets are laminated at a (90 / 0) angle and stitched together (total weight of carbon fiber on a woven base material of 388 g / m²). ２ ). (Carbon fiber fabric) ・Carbon fiber fabric 1: Using carbon fiber 2 as the warp and weft threads, with a fiber weight of 375 g / m ２ Made from five layers of satin weave

[0137]

[0138]

[0139] Comparative Examples 1-3 did not use epoxy resin (a) having an oxazolidone ring structure, resulting in low CAI or RTD-OHC. Comparative Example 4 had too much epoxy resin having an oxazolidone ring structure, resulting in excessively high viscosity of the main component composition and low RTD-FM. Comparative Example 5 used an aliphatic diamine instead of an alicyclic diamine, resulting in extremely high reactivity. The minimum viscosity of the resin composition after mixing became too high to measure, making molding difficult. Comparative Example 6 did not use epoxy resin (b) containing at least three glycidyl groups, resulting in low Tg and RTD-FM.

Claims

1. A two-component epoxy resin composition comprising: a main component composition comprising an epoxy resin (a) having at least one oxazolidone ring structure and an epoxy resin (b) having at least three glycidyl groups, wherein the main component composition and the curing agent composition comprising an aromatic polyamine (d), wherein the curing agent composition comprises an aromatic polyamine (d), wherein the curing agent composition comprises core-shell type rubber particles (g), and when the main component composition and the curing agent composition are mixed such that the equivalent ratio (H / E) of the epoxy equivalent (E) of the total epoxy resin to the active hydrogen equivalent (H) of the total curing agent is any equivalent ratio within the range of 0.8 to 1.2, the minimum viscosity of the mixture shown in the range of 90 to 120°C is 200 mPa·s or less.

2. The two-component epoxy resin composition according to claim 1, wherein the epoxy resin (a) is a reaction product of a bisphenol A type epoxy resin and an aromatic diisocyanate.

3. The two-component epoxy resin composition according to claim 1 or 2, wherein the epoxy resin (b) is triglycidyl-m-aminophenol, triglycidyl-p-aminophenol, or tetraglycidyl-4,4'-diaminodiphenylmethane.

4. The two-component epoxy resin composition according to claim 1 or 2, wherein the aromatic polyamine (d) is diethyltoluenediamine.

5. The two-component epoxy resin composition according to claim 1 or 2, wherein the curing agent composition further comprises an alicyclic polyamine (e).

6. The two-component epoxy resin composition according to claim 5, wherein the alicyclic polyamine (e) is isophoronediamine, N-(3-aminopropyl)cyclohexylamine, or 4,4'-methylenebis(cyclohexylamine).

7. The two-component epoxy resin composition according to claim 1 or 2, wherein the core component of the core-shell type rubber particles (g) is a polymer of one or more monomers selected from conjugated diene monomers and aromatic vinyl compounds, or a silicone resin.

8. The two-component epoxy resin composition according to claim 1 or 2, wherein the shell component of the core-shell type rubber particles (g) is a polymer of one or more monomers selected from (meth)acrylic acid esters and aromatic vinyl compounds.

9. The two-component epoxy resin composition according to claim 1 or 2, wherein the content of the epoxy resin (a) relative to the total mass of the main component composition is 5 to 30% by mass.

10. The two-component epoxy resin composition according to claim 1 or 2, wherein the degree of curing of the resin cured product obtained by heating a mixture of the main component composition and the curing agent composition, obtained by heating the mixture at 180°C for 15 minutes such that the equivalent ratio (H / E) of the epoxy equivalent (E) of the total epoxy resin to the active hydrogen equivalent (H) of the total curing agent is any equivalent ratio within the range of 0.8 to 1.2, reaches 80% or more.

11. A cured resin product characterized by being obtained by curing the two-component epoxy resin composition described in claim 1 or 2.

12. The resin cured product according to claim 11, wherein the content of the core-shell type rubber particles (g) is 1.0 to 5.0% by mass.

13. A fiber-reinforced composite material characterized by comprising a resin cured product according to claim 11 and a reinforcing fiber substrate.

14. The fiber-reinforced composite material according to claim 13, wherein the reinforcing fiber base material is a reinforcing fiber base material made of carbon fibers.

15. A method for producing a fiber-reinforced composite material, characterized by compounding a reinforcing fiber substrate with the two-component epoxy resin composition described in claim 1 or 2 and curing the compound.

16. A method for producing a fiber-reinforced composite material, characterized by mixing the main component composition and the curing agent composition of the two-component epoxy resin composition according to claim 1 or 2, impregnating a reinforcing fiber substrate placed in a mold with the mixture, and curing it.

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