TWI881061B - Epoxy resin compositions, prepregs and fiber reinforced composites - Google Patents

Abstract

The subject of the present invention is to provide an epoxy resin composition having excellent elastic modulus, strength and viscosity, and a prepreg and a fiber-reinforced composite material using the epoxy resin composition. The present invention is an epoxy resin composition comprising the following components [A] to [C], wherein 100% by mass of component [A] comprises 20% by mass to 40% by mass of an isocyanuric acid-type epoxy resin as component [A-1]. [A]: Epoxy resin [B]: Dicyandiamide [C]: Polyurethane having a weight average molecular weight of 15,000 to 25,000

Description

Epoxy resin compositions, prepregs and fiber reinforced composites

The present invention relates to an epoxy resin composition, a prepreg using the epoxy resin composition, and a fiber-reinforced composite material.

Fiber-reinforced composite materials using carbon fiber or polyaramid fiber as reinforcing fiber are widely used in structural materials such as aircraft and automobiles, or sports and general industrial uses such as tennis rackets, golf clubs, fishing rods, bicycles, and frames, etc., due to their high specific strength and specific elastic modulus. As a manufacturing method for fiber-reinforced composite materials, there are two methods that can be used: a method of stacking a plurality of sheets of a prepreg formed by impregnating an uncured resin composition into reinforcing fibers and then heat-curing them; or a resin transfer molding method in which a liquid resin is poured into the reinforcing fibers arranged in a mold and then heat-cured. Among these manufacturing methods, the method using a prepreg has the advantage of easily obtaining a high-performance fiber-reinforced composite material, because the orientation of the reinforcing fibers can be strictly controlled and the design freedom of the laminate structure is high. As the resin composition used for the prepreg, thermosetting resins are mainly used from the perspective of heat resistance or productivity. Among them, epoxy resins are preferably used from the perspective of mechanical properties such as adhesion to the reinforcing fibers. In addition, in order to obtain excellent mechanical properties or heat resistance of the cured product, dicyandiamide is often used as a curing agent.

In recent years, fiber-reinforced composite materials have been used in golf clubs, fishing rods, bicycles, automotive components, industrial components, etc., which need to be further lightweight, and various physical properties need to be improved. For example, for prepregs used in cylindrical molded bodies such as golf clubs or fishing rods, high viscosity is required on the surface to prevent the prepreg from rolling off when forming into a cylindrical shape. As mentioned above, the viscosity of the prepreg will affect the viscosity characteristics of the resin composition used in combination with the reinforcing fiber. In order to show good viscosity, it is necessary to adjust the viscosity of the resin composition to a certain value or above by mixing thermoplastic resins with epoxy resins.

Furthermore, in order to exhibit excellent bending strength in the cylindrical molded body, the fiber-reinforced composite material used needs to have high compressive strength or tensile strength, and therefore, it is necessary to improve the elastic modulus or strength of the epoxy resin used. Here, as a method for making the epoxy resin exhibit excellent elastic modulus, patent documents 1 and 2 disclose a method of mixing isocyanuric acid-type epoxy resin.

Furthermore, when fiber-reinforced composite materials are applied to various purposes, the use of prepregs using fiber fabric substrates on the surface and using fabric patterns as designs has increased, and the base resin, in addition to requiring viscosity or mechanical properties of the cured product, has also become required to have low coloring of the cured product or the appearance quality of the fiber-reinforced composite material. [Prior art literature] [Patent literature]

Patent document 1: Japanese Patent Publication No. 2017-20004 Patent document 2: International Publication No. 2017/047225

[Problems to be solved by the invention]

However, in the resin composition used in Patent Document 1, the strength of the epoxy resin cured product is sometimes impaired due to the blending of the thermoplastic resin. In addition, in the resin composition used in Patent Document 2, the strength of the epoxy resin cured product is sometimes impaired due to the blending of the thermoplastic resin. As mentioned above, it has been extremely difficult to combine the excellent viscosity of the prepreg with the elastic modulus and strength of the resin. In addition, in Patent Document 1 or Patent Document 2, no consideration is given to the appearance quality of the obtained resin cured product or fiber-reinforced composite material.

The subject of the present invention is to provide an epoxy resin composition having an excellent elastic modulus or strength of a cured product, a prepreg having high viscosity using the epoxy resin composition, and a fiber-reinforced composite material having excellent appearance quality. [Means for solving the subject]

The present invention adopts the following means to solve the problem. That is, the present invention is an epoxy resin composition, which is an epoxy resin composition comprising the following components [A] to [C], wherein 100% by mass of component [A] comprises 20% by mass or more and 40% by mass or less of an isocyanuric acid type epoxy resin as component [A-1]; [A]: epoxy resin, [B]: dicyandiamide, [C]: polysulfone having a weight average molecular weight of 15,000 or more and 25,000 or less.

Furthermore, the present invention is a prepreg composed of the epoxy resin composition of the present invention and reinforcing fibers.

Furthermore, the present invention is a fiber-reinforced composite material, which comprises a cured product of the epoxy resin composition of the present invention and reinforcing fibers. [Effect of the invention]

According to the present invention, an epoxy resin composition having excellent elastic modulus or strength of a cured product, a prepreg having high viscosity using the epoxy resin composition, and a fiber-reinforced composite material having excellent appearance quality can be obtained.

[Form used to implement the invention]

The present invention is described in detail below. In the present invention, "above" means the same as or greater than the numerical value indicated therein. Also, "below" means the same as or less than the numerical value indicated therein.

The resin composition of the present invention contains constituents [A] to [C] as essential components. In the present invention, "constituent" means a compound contained in the composition.

The component [A] in the present invention is an epoxy resin. The epoxy resin can obtain thermosetting properties.

The epoxy resin as component [A] may have one epoxy group in one molecule, but it is preferred to have two or more epoxy groups in one molecule because the glass transition temperature of the cured product obtained by heating and curing the resin composition becomes higher and the heat resistance becomes higher. Such epoxy resins may be used alone or in combination.

Examples of the epoxy resin of component [A] include diaminodiphenylmethane type, diaminodiphenylsulfone type, aminophenol type, bisphenol type, meta-xylene diamine type, 1,3-bisaminomethylcyclohexane type, isocyanurate type, hydantoin type, phenol novolac type, o-cresol novolac type, trishydroxyphenylmethane type, and tetraphenylethane type epoxy resins.

Examples of commercially available bisphenol A type epoxy resins include EPON (registered trademark) 825 (manufactured by Mitsubishi Chemical Co., Ltd.), EPICLON (registered trademark) 850 (manufactured by DIC Co., Ltd.), EPOTOHTO (registered trademark) YD-128 (manufactured by NIPPON STEEL Chemical & Material Co., Ltd.), and DER-331 or DER-332 (manufactured by Dow Chemical Co., Ltd.).

Examples of commercially available bisphenol F-type epoxy resins include: “Araldite (registered trademark)” GY282 (manufactured by Huntsman Advanced Materials Co., Ltd.), “jER (registered trademark)” 806, “jER (registered trademark)” 807, “jER (registered trademark)” 1750 (all manufactured by Mitsubishi Chemical Co., Ltd.), “EPICLON (registered trademark)” 830 (manufactured by DIC Co., Ltd.), and “EPOTOHTO (registered trademark)” YD-170 (manufactured by NIPPON STEEL Chemical & Material Co., Ltd.).

It is important that the component [A] contains an isocyanuric acid type epoxy resin as the component [A-1]. The isocyanuric acid type epoxy resin has an isocyanuric acid skeleton in the molecule, and the elastic modulus of the cured product can be increased by the resin.

As for the content of the component [A-1], it is important that the component [A-1] is included in an amount of 20 mass % or more and 40 mass % or less in 100 mass % of the component [A]. By setting the content of the component [A-1] to 20 mass %, an epoxy resin cured product having an excellent modulus of elasticity can be obtained. Furthermore, by setting the content of the component [A-1] to 40 mass % or less, precipitation of the component [A-1] in the epoxy resin composition and unevenness can be suppressed, and precipitation of the component [A-1] after curing and loss of strength can be suppressed, and the appearance quality of the obtained fiber-reinforced composite material is also excellent. Furthermore, by setting the blending amount of the constituent element [A-1] to 30 mass % or more and 35 mass % or less, the elastic modulus and strength of the obtained epoxy resin cured product are particularly well balanced.

The component [A-1] is preferably a trifunctional isocyanuric acid type epoxy resin. If the component [A-1] is a trifunctional epoxy resin having three epoxy groups in the molecule, a cured epoxy resin having a particularly good balance between elastic modulus and strength can be obtained.

As commercially available isocyanuric acid epoxy resins, for example, "TEPIC (registered trademark)"-S (trifunctional), "TEPIC (registered trademark)"-G (trifunctional), "TEPIC (registered trademark)"-L (trifunctional), "TEPIC (registered trademark)"-HP (trifunctional), "TEPIC (registered trademark)"-VL (trifunctional), "TEPIC (registered trademark)"-UC (hexafunctional), "TEPIC (registered trademark)"-PAS B22 (2.2 functional), "TEPIC (registered trademark)"-PAS B26L (2.6 functional), (both manufactured by Nissan Chemical Industries, Ltd.), "Araldite (registered trademark)" PT9810 (3 functional) (manufactured by Huntsman Advanced Materials Co., Ltd.), etc. These may be used alone or in combination.

The component [A] preferably contains 20% by mass to 60% by mass of a trifunctional or higher-functional glycidylamine-type epoxy resin as the component [A-2] in 100% by mass of the component [A]. By containing 20% by mass to 60% by mass, more preferably 30% by mass to 40% by mass of the component [A-2], the obtained epoxy resin cured product has a particularly excellent balance in elastic modulus and strength.

Examples of the trifunctional or higher glycidylamine type epoxy resin include diaminodiphenylmethane type, diaminodiphenylsulfone type, and aminophenol type epoxy resins, etc. These may be used alone or in combination.

Commercially available products of diaminodiphenylmethane-based 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.), EPOTOHTO (registered trademark) YH-434 (manufactured by NIPPON STEEL Chemical & Material Co., Ltd.), and jER (registered trademark) 604 (manufactured by Mitsubishi Chemical Co., Ltd.).

Examples of commercially available diaminodiphenylsulfonium epoxy resins include TG3DAS (manufactured by MITSUI FINE CHEMICAL Co., Ltd.).

Commercially available products of 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 Co., Ltd.), "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.), and "Araldite (registered trademark)" MY0610 (manufactured by Huntsman Advanced Materials Co., Ltd.).

The component [A] preferably contains 10% by mass or more and 40% by mass or less of a bisphenol-type epoxy resin in a solid state at 25°C as the component [A-3] in 100% by mass of the component [A]. By containing 10% by mass or more, more preferably 30% by mass or more of the component [A-3], the resin viscosity of the resin composition at 25°C becomes high, and the viscosity of the obtained prepreg is excellent. In addition, by setting the content of the component [A-3] to 40% by mass or less, not only the elastic modulus of the obtained epoxy resin cured product is excellent, but also the appearance quality of the obtained fiber-reinforced composite material is excellent.

Examples of commercially available products of component [A-3] include: "jER (registered trademark)" 1001 (manufactured by Mitsubishi Chemical Co., Ltd.), "jER (registered trademark)" 1002 (manufactured by Mitsubishi Chemical Co., Ltd.), "jER (registered trademark)" 1003 (manufactured by Mitsubishi Chemical Co., Ltd.), "jER (registered trademark)" 1004 (manufactured by Mitsubishi Chemical Co., Ltd.), "jER (registered trademark)" 1007 (manufactured by Mitsubishi Chemical Co., Ltd.), "jER ( "jER (registered trademark)" 1009 (manufactured by Mitsubishi Chemical Co., Ltd.), "jER (registered trademark)" 1010 (manufactured by Mitsubishi Chemical Co., Ltd.), "jER (registered trademark)" 4004P (manufactured by Mitsubishi Chemical Co., Ltd.), "jER (registered trademark)" 4005P (manufactured by Mitsubishi Chemical Co., Ltd.), "jER (registered trademark)" 4007P (manufactured by Mitsubishi Chemical Co., Ltd.), "jER (registered trademark)" 4010P (manufactured by Mitsubishi Chemical Co., Ltd.), etc. These may be used alone or in combination.

In addition, the component [A] preferably contains 60% by mass or more of a component that is solid at 25°C in 100% by mass of the component [A]. By containing 60% by mass or more of a component that is solid at 25°C, the resin viscosity of the epoxy resin composition at 25°C becomes appropriate, and the viscosity of the obtained prepreg is excellent.

The epoxy resin composition of the present invention contains dicyandiamide as a component [B]. Dicyandiamide is excellent in terms of imparting high mechanical properties and heat resistance to the epoxy resin cured product, and functions as a curing agent that forms the main skeleton of the epoxy resin cured product. In addition, the storage stability of the epoxy resin composition containing dicyandiamide is also excellent.

Commercially available products of dicyandiamide include DICY7 (manufactured by Mitsubishi Chemical Co., Ltd.) and DICY15 (manufactured by Mitsubishi Chemical Co., Ltd.).

The content of dicyandiamide in the epoxy resin composition of the present invention is preferably set to an amount in which the active hydrogen groups of dicyandiamide are 0.2 equivalents or more and 1.2 equivalents or less relative to the total number of epoxy groups of the component [A]. By setting the dicyandiamide to 0.2 equivalents or more and 1.2 equivalents or less, more preferably 0.3 equivalents or more and 1.0 equivalents or less, and even more preferably 0.4 equivalents or more and 0.7 equivalents or less relative to the active hydrogen groups of the epoxy groups, a cured epoxy resin having a particularly excellent balance between heat resistance and mechanical properties can be obtained.

The epoxy resin composition of the present invention contains a polymer having a weight average molecular weight of 15000 to 25000 as a component [C]. In the present invention, the component [C] is required in order to improve the viscosity of the prepreg without compromising the elastic modulus or strength of the epoxy resin cured product and the appearance quality of the cured product.

The above is because: the constituent element [A-1], which is an essential component of the present invention, has a highly polar isocyanuric acid skeleton and therefore tends to have a lower compatibility with thermoplastic resins than other epoxy resins such as glycidyl type. Therefore, when polyvinyl formaldehyde or polyether sulfone having a weight average molecular weight of more than 25,000 is mixed as a viscosity adjuster in order to make the viscosity of the epoxy resin composition appropriate, the epoxy resin and the thermoplastic resin will be highly phase-separated after curing, resulting in a significant decrease in the resin strength.

The inventors of the present invention have found that if a polymer having a weight average molecular weight of 25,000 or less is used as a thermoplastic resin, the thermoplastic resin has excellent compatibility with the epoxy resin containing the component [A-1], and the epoxy resin composition does not undergo phase separation but forms a uniform phase, or a fine phase separation structure in which the epoxy resin and the thermoplastic resin are each the main component can be formed without compromising the elastic modulus or strength of the epoxy resin cured product. Furthermore, if the weight average molecular weight of the polymer is set to 25,000 or less, the viscosity change caused by dissolving in the epoxy resin can be suppressed from becoming too large, and the handling property of the resin can be prevented from deteriorating during the production of the prepreg. In addition, the obtained fiber-reinforced composite material will be excellent in appearance quality. In addition, by setting the weight average molecular weight of the polymer to 15,000 or more, even if it is a trace amount of the blending amount, the viscosity of the epoxy resin can be adjusted, and the viscosity of the prepreg can be improved without compromising the elastic modulus or strength of the epoxy resin cured product. Furthermore, if the weight average molecular weight of the constituent element [C] is 15,000 or more and 22,000 or less, the balance of the elastic modulus and strength of the cured product, the viscosity of the prepreg, and the appearance quality of the fiber-reinforced composite material becomes good, which is preferred.

Examples of commercially available products of the component [C] include: “Virantage (registered trademark)” VW-10700RFP (manufactured by Solvay Advanced Polymers Co., Ltd.) and “SUMIKAEXCEL (registered trademark)” PES2603P (manufactured by Sumitomo Chemical Industries, Ltd.).

The content of the component [C] in the epoxy resin composition of the present invention is preferably 2 parts by mass to 15 parts by mass, more preferably 5 parts by mass to 12 parts by mass, and even more preferably 8 parts by mass to 12 parts by mass, relative to 100 parts by mass of the component [A]. By setting the blending amount of the component [C] within this range, the components [A], [B], and [C] can be prevented from being highly phase-separated after curing, and the obtained resin cured product has particularly excellent elastic modulus, strength, and lightness index L ^* , and the viscosity of the prepreg is also particularly excellent.

The epoxy resin composition of the present invention may contain a thermoplastic resin other than the component [C] within the range not impairing the physical properties.

The epoxy resin composition of the present invention may also contain a curing accelerator from the viewpoint of controlling the curing rate. Examples of the curing accelerator include urea compounds and imidazole compounds. From the viewpoint of the storage stability of the epoxy resin composition, urea compounds are particularly preferably used.

Examples of the urea compound include aromatic urea compounds such as 3-(3,4-dichlorophenyl)-1,1-dimethylurea, 3-(4-chlorophenyl)-1,1-dimethylurea, phenyldimethylurea, and toluene dimethylurea. Among them, toluene dimethylurea is preferred because the epoxy resin composition obtained has excellent rapid curing properties and strength.

As commercially available products of the aromatic urea compound, for example, DCMU99 (manufactured by Hodogaya Chemical Industry Co., Ltd.), "Omicure (registered trademark)" U-24M (manufactured by CVC Thermoset Specialties), which is toluenebisdimethylurea, and the like can be used.

The epoxy resin composition of the present invention is preferably a cured product having a thickness of 2 mm and held at 90°C for 60 minutes and then cured at 135°C for 120 minutes, and the lightness index L ^* in the L ^* a ^* b ^* color system by a transmission method is preferably 15 or more, more preferably 20 or more, and even more preferably 30 or more. When the lightness index L ^* of the cured product is within this range, the coloring of the surface of the obtained fiber-reinforced composite material or the coloring of the resin accumulation portion existing in the pinhole of the fiber fabric substrate becomes inconspicuous, and the fiber-reinforced composite material is excellent in appearance quality.

The lightness index L ^* of the cured resin can be controlled by changing the type or blending ratio of each component contained in the resin composition and the weight average molecular weight of the constituent [C]. As a method for increasing the value of L*, the following methods can be exemplified: reducing the blending amount of the constituent [A-1], reducing the blending amount of the constituent [A-3], reducing the blending amount of the constituent [C], and reducing the weight average molecular weight of the constituent [C].

The epoxy resin composition of the present invention has excellent elastic modulus, strength and elongation, and is suitable as a base resin of a fiber-reinforced composite material. That is, the fiber-reinforced composite material of the present invention comprises a cured product of the epoxy resin composition of the present invention and reinforcing fibers.

Methods for obtaining fiber-reinforced composite materials include: hand-lamination method, RTM method, filament winding molding method, extrusion molding method, etc., methods of impregnating the resin composition into the reinforcing fiber in the molding step, or methods of forming the prepreg formed by impregnating the resin composition into the reinforcing fiber by autoclave method or pressure molding method. Among them, based on the ability to precisely control the configuration of the fiber and the ratio of the resin, and to maximize the properties of the composite material, it is preferred to pre-prepare the prepreg composed of the epoxy resin composition and the reinforcing fiber. That is, the prepreg of the present invention is composed of the epoxy resin composition of the present invention and the reinforcing fiber.

As the reinforcing fiber used in the prepreg and fiber-reinforced composite material of the present invention, preferably: carbon fiber, graphite fiber, polyaramide fiber, glass fiber, etc., especially carbon fiber. There is no limitation on the shape or arrangement of the reinforcing fiber, and fiber structures such as long fibers bundled in one direction, single filament bundles, woven fabrics, knitted fabrics, and braids can be used. As the reinforcing fiber, two or more types of carbon fiber or glass fiber, polyaramide fiber, boron fiber, PBO fiber, high-strength polyethylene fiber, alumina fiber, and silicon carbide fiber can also be used in combination.

Specifically, the carbon fiber includes acrylic, asphalt, and rayon carbon fibers, and acrylic carbon fibers having high tensile strength are particularly preferred.

As the form of carbon fiber, twisted yarn, untwisted yarn, untwisted yarn, etc. can be used. However, in the case of twisted yarn, the orientation of the filaments constituting the carbon fiber is not parallel, which may cause the mechanical properties of the obtained carbon fiber reinforced composite material to decrease. Therefore, it is better to use untwisted yarn or untwisted yarn with a good balance between the formability and strength properties of the carbon fiber reinforced composite material.

Carbon fiber preferably has a tensile modulus of 200 GPa to 440 GPa. The tensile modulus of carbon fiber is affected by the crystallinity of the graphite structure constituting the carbon fiber. The higher the crystallinity, the higher the modulus of elasticity. If it is within this range, the rigidity and strength of the carbon fiber reinforced composite material are both high-grade and balanced, so it is better. A more preferable modulus of elasticity is 230 GPa to 400 GPa, and a more preferable modulus of elasticity is 260 GPa to 370 GPa. Here, the tensile modulus of carbon fiber is a value measured in accordance with JIS R7608 (2008).

The prepreg of the present invention can be manufactured by various well-known methods. For example, the prepreg can be manufactured by a hot melt method in which the resin composition is heated to reduce the viscosity and impregnated into the reinforcing fiber without using an organic solvent.

In addition, the hot melt method can be used: a method in which the resin composition whose viscosity is reduced by heating is directly impregnated into the reinforcing fiber; or a method in which a release paper sheet with a resin film is first prepared by temporarily applying the resin composition on a release paper, etc., and then the resin film is superimposed on the reinforcing fiber side from both sides or one side of the reinforcing fiber, and the resin composition is impregnated into the reinforcing fiber by heating and pressurizing.

The content of 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 even more preferably 65% by mass or more, it is easier to obtain the advantages of fiber-reinforced composite materials with excellent specific strength and specific elastic modulus. In addition, during the forming of the fiber-reinforced composite material, the heat generated during curing can be suppressed from becoming too high. On the other hand, by setting it to 90% by mass or less, and more preferably 85% by mass or less, the generation of pores in the composite material caused by poor impregnation of the resin can be suppressed. In addition, the viscosity of the prepreg can be maintained.

The fiber-reinforced composite material of the present invention can be manufactured by, for example, laminating the prepreg of the present invention in a predetermined shape, and applying pressure and heat to harden the resin. Here, the method of applying heat and pressure can be a pressure molding method, an autoclave molding method, a bagging molding method, a wrapping tape method, an internal pressure molding method, etc.

The fiber-reinforced composite material of the present invention can be widely used in aerospace applications, general industrial applications, and sports applications. More specifically, the general industrial applications are suitable for use in structures such as automobiles, ships, and railway locomotives. The sports applications are suitable for use in golf clubs, fishing rods, tennis or badminton rackets. [Example]

The present invention is described in detail below based on the embodiments. However, the scope of the present invention is not limited to the embodiments. In addition, the unit "part" of the composition ratio means mass part unless otherwise specified. In addition, the measurement of various characteristics (physical properties) is carried out in an environment of temperature 23°C and relative humidity 50% unless otherwise specified.

<Various evaluation methods> The epoxy resin composition of each example was measured using the following measurement methods.

(1) Three-point bending test of cured resin The uncured resin composition was degassed in a vacuum and then heated from 30°C at a rate of 1.7°C/min in a mold with a 2mm thick "Teflon (registered trademark)" spacer. After being kept at 90°C for 60 minutes, the temperature was raised at a rate of 2.0°C/min and cured at 135°C for 120 minutes to obtain a 2mm thick plate-shaped cured resin. A test piece having a width of 10 mm and a length of 60 mm was cut out from the cured resin, and an Instron universal testing machine (manufactured by Instron Corporation) was used with a span of 32 mm, a crosshead speed of 2.5 mm/min, and a sample number of n=6. The average values of the strength and the modulus of elasticity when three-point bending was carried out in accordance with JIS K7171 (1994) were respectively determined as the flexural strength and the flexural modulus of the cured resin.

(2) Viscosity measurement of resin composition The viscosity of the resin composition was measured using a dynamic viscoelasticity device ("ARES"-G2 manufactured by TA Instruments Japan). The epoxy resin composition was set up in a torsion mode (measurement frequency: 0.5 Hz) using parallel plates with a diameter of 25 mm as the upper and lower measuring jigs so that the distance between the upper and lower jigs was 1 mm. The temperature was raised from 20°C to 30°C at a speed of 1°C/min, and the complex viscoelastic coefficient at 25°C was defined as the viscosity of the resin composition at 25°C.

(3) Measurement of lightness index of cured resin The uncured resin composition was degassed in a vacuum, and then heated from 30°C at a rate of 1.7°C/min in a mold set to a thickness of 2 mm with a 2 mm thick "Teflon (registered trademark)" spacer. After being kept at 90°C for 60 minutes, the temperature was raised at a rate of 2.0°C/min, and heated and cured at 135°C for 120 minutes to obtain a 2 mm thick plate-shaped cured resin. A test piece with a width of 10 mm and a length of 60 mm was cut out from the cured resin, and the lightness index L ^* was measured by the transmission method using a multi-light source spectrophotometer MSC-P (manufactured by Suga Test Instruments).

(4) Evaluation of the adhesion of prepregs The adhesion between overlapping prepregs at 25°C was evaluated using the following four stages: A to D. A: Very strong adhesion, excellent handling during lamination B: Strong adhesion, excellent handling during lamination C: Weak adhesion, but no problem with handling during lamination D: Very weak adhesion, easy to peel off during lamination, insufficient handling.

<Materials used in the examples and comparative examples> (1) Constituent element [A-1]: isocyanuric acid type epoxy resin ・"TEPIC (registered trademark)"-S (trifunctional isocyanuric acid type epoxy resin, epoxy equivalent: 100 g/eq, solid at 25°C, manufactured by Nissan Chemical Industries, Ltd.) ・"TEPIC (registered trademark)"-PAS B26L (2.6-functional isocyanuric acid type epoxy resin, epoxy equivalent: 138 g/eq, liquid at 25°C, manufactured by Nissan Chemical Industries, Ltd.)

(2) Constituent [A-2]: Trifunctional or higher epoxy propylamine type epoxy resin ・"Araldite (registered trademark)" MY0500 (aminophenol type epoxy resin, epoxy equivalent: 118 g/eq, liquid at 25°C, manufactured by Huntsman Advanced Materials (Co., Ltd.)) ・"Araldite (registered trademark)" MY0600 (aminophenol type epoxy resin, epoxy equivalent: 118 g/eq, liquid at 25°C, manufactured by Huntsman Advanced Materials (Co., Ltd.)) ・"Araldite (registered trademark)" MY721 (aminophenol type epoxy resin, epoxy equivalent: 120 g/eq, liquid at 25°C, manufactured by Huntsman Advanced Materials (Co., Ltd.)

(3) Constituent [A-3]: Bisphenol type epoxy resin in a solid state at 25°C ・"jER (registered trademark)" 4004P (bisphenol F type epoxy resin, epoxy equivalent: 880 g/eq, solid at 25°C, manufactured by Mitsubishi Chemical Co., Ltd.).

(4) Constituent elements not included in the above [A]: Epoxy resin ・“jER (registered trademark)” 828 (bisphenol F type epoxy resin, epoxy equivalent: 189 g/eq, liquid at 25°C, manufactured by Mitsubishi Chemical Co., Ltd.).

(5) Constituent [B]: dicyandiamide ・DICY7 (dicyandiamide, manufactured by Mitsubishi Chemical Co., Ltd.).

(6) Constituent [C]: Polyether sulphate having a weight average molecular weight of 15,000 to 25,000 ・"Virantage (registered trademark)" VW-10700RFP (polyether sulphate, weight average molecular weight: 21,000, manufactured by Solvay Advanced Polymers Co., Ltd.) ・"SUMIKAEXCEL (registered trademark)" PES2603P (polyether sulphate, weight average molecular weight: 16,000, manufactured by Sumitomo Chemical Industries, Ltd.)

(7) Constituent [C’]: Other thermoplastic resins ・“Virantage (registered trademark)” VW-30500RP (polysulfone, weight average molecular weight: 14,000, manufactured by Solvay Advanced Polymers Co., Ltd.) ・“SUMIKAEXCEL (registered trademark)” PES5003P (polyether sulfone, weight average molecular weight: 47,000, manufactured by Sumitomo Chemical Industries, Ltd.) ・“VINYLEC (registered trademark)” K (polyvinyl formaldehyde, weight average molecular weight: 50,000, manufactured by JNC Co., Ltd.)

(8) Curing accelerators ・"Omicure (registered trademark)" U-24M (2,4-toluenebis(dimethylurea), manufactured by CVC Thermoset Specialties) ・DCMU99 (3-(3,4-dichlorophenyl)-1,1-dimethylurea, manufactured by Hodogaya Chemical Industry Co., Ltd.)

(9) Carbon fiber: TORAYCA (registered trademark) T1100G-24K (fiber count: 24,000, tensile modulus: 324 GPa, density: 1.8 g/cm ³ , manufactured by Toray Co., Ltd.).

<Example 1> (Preparation of resin composition) The resin composition was prepared using the following method.

In a kneading device, 35 parts of "TEPIC (registered trademark)"-S as component [A-1], 35 parts of "Araldite (registered trademark)" MY0500 as component [A-2], 30 parts of "jER (registered trademark)" 4004P as component [A-3], and 10 parts of "Virantage (registered trademark)" VW-10700RP as component [C] were added, and the temperature was raised to 150°C while kneading. After kneading at 150°C for 60 minutes, the temperature was lowered to 55-65°C, and 7 parts of DICY7 as component [B] and 2 parts of "Omicure (registered trademark)" U-24M as a curing accelerator were added, and kneading was continued for 30 minutes to obtain a resin composition.

At this time, out of 100 mass % of the component [A], the component that is solid at 25° C. accounts for 65 mass %.

The obtained resin composition was subjected to a three-point bending test, and the results showed that the elastic modulus was 4.7 GPa and the strength was 190 MPa. Compared with Comparative Examples 2, 3, and 4 (without the addition of the constituent element [C]) described below, it was possible to obtain excellent elastic modulus and strength. In addition, the resin viscosity was 1.8×10 ⁵ Pa·s, which is a viscosity suitable for prepreg use. In addition, the lightness index L ^* was 23, and the appearance quality was also excellent.

(Preparation of prepreg) The resin composition obtained above was applied to release paper using a knife coater to prepare two resin films with a resin basis weight of 21g/ ^m2 . Then, for carbon fibers arranged in one direction in a sheet-like manner with a fiber basis weight of 125g/ ^m2 , the two obtained resin films were overlapped from both sides of the carbon fibers, heated and pressurized at a temperature of 110°C and a maximum pressure of 1MPa, and impregnated with an epoxy resin composition to obtain a prepreg. The viscosity evaluation of the prepared prepreg was judged to be A, and the handling of the prepreg was extremely good.

<Examples 2 to 13> The resin composition and prepreg were obtained in the same manner as in Example 1 except that the blending was performed according to the blending ratios in Tables 1 to 2.

The various measurement results of the embodiments are shown in Tables 1 and 2. As in Examples 2 to 13, when the resin composition is changed, the elastic modulus, strength and appearance quality of the cured resin are excellent, and the viscosity of the prepreg is not a problem in terms of handling.

<Comparative Examples 1 to 6> The resin composition and prepreg were obtained in the same manner as in Example 1 except that the blending was performed according to the blending ratio in Table 2.

Comparative Example 1 does not contain any material equivalent to component [C]. Comparison between Comparative Example 1 and Example 1 shows that by adding component [C], the viscosity of the resin can be prevented from being too low, and the viscosity of the prepreg can be improved.

Comparative Example 2 is a mixture of "Virantage (registered trademark)" VW-30500RP instead of component [C]. "Virantage (registered trademark)" VW-30500RP does not meet the requirement of a weight average molecular weight of 15,000 or more and 25,000 or less. Comparison between Example 1 and Comparative Example 2 shows that the strength of the cured resin is dramatically improved by setting the weight average molecular weight of component [C] to 15,000 or more and 25,000 or less.

Comparative Example 3 is a mixture of "SUMIKAEXCEL (registered trademark)" PES5003P instead of component [C]. "SUMIKAEXCEL (registered trademark)" PES5003P does not meet the requirement of a weight average molecular weight of 15,000 or more and 25,000 or less. Comparison between Example 1 and Comparative Example 3 shows that the strength of the cured resin is dramatically improved by setting the weight average molecular weight of component [C] to 15,000 or more and 25,000 or less. In addition, the lightness index L ^* of the cured resin in Comparative Example 3 is 10, and the color change is obvious.

Comparative Example 4 is a mixture of "VINYLEC (registered trademark)" K instead of component [C]. Comparison between Example 1 and Comparative Example 4 shows that the strength of the cured resin is dramatically improved by using component [C] as a polymer having a weight average molecular weight of 15,000 to 25,000.

In Comparative Example 5, the blending ratio of component [A-1] to component [A] is 15 mass %. Comparing Example 1 with Comparative Example 5, it can be seen that the elastic modulus or strength of the resin is excellent by including 20 mass % or more and 40 mass % or less of component [A-1] in 100 mass % of component [A].

Comparative Example 6 is a 45% by mass blend ratio of constituent [A-1] to constituent [A]. If the resulting resin composition is left at room temperature, a large amount of solid components will precipitate and solidify, making it unsuitable as a base resin for prepregs, and the resin viscosity or prepreg viscosity cannot be measured. Comparing Example 1 with Comparative Example 6, it can be seen that by including constituent [A-1] in an amount of 20% by mass or more and 40% by mass or less in 100% by mass of constituent [A], the strength or lightness index L ^* of the resin is excellent.

[Table 1] Embodiment 1 Embodiment 2 Embodiment 3 Embodiment 4 Embodiment 5 Embodiment 6 Embodiment 7 Embodiment 8 Embodiment 9 Embodiment 10 Components [A-1] (mass) “TEPIC®”-S 35 25 25 25 25 35 35 35 38 30 “TEPIC®”-PAS B26L - - 10 10 10 - - - - - Components [A-2] (mass) "Araldite®" MY0500 35 40 35 25 25 30 30 35 - 55 "Araldite®" MY0600 - - - 10 - - - - 15 - "Araldite®" MY721 - - - - 10 - - - - - Components [A-3] (mass) “jER®” 4004P 30 35 30 30 30 35 35 15 27 15 Constituent [A] (mass) "jER®"828 - - - - - - - 15 20 - Component [B] (mass) DICY7 7 7 7 7 7 7 7 8 7 9 Constituent [C] (mass) "Virantage®" VW-10700RFP 10 10 10 10 10 3 6 16 12 14 "SUMIKAEXCEL®" PES2603P - - - - - - - - - - Other thermoplastic resins [C'] (parts by mass) "Virantage®" VW-30500RP - - - - - - - - - - "SUMIKAEXCEL®" PES5003P - - - - - - - - - - "VINYLEC®" K - - - - - - - - - - Hardening accelerator (mass) "Omicure®" U-24M 2 2 2 2 2 2 2 2 2 2 DCMU99 - - - - - - - - - - The amount of the component [A] that is solid at 25°C (mass %) 65 60 55 55 55 70 70 50 65 45 Characteristics of resin composition Flexural modulus of hardened material (GPa) 4.7 4.6 4.7 4.8 4.5 4.8 4.7 4.5 4.5 4.8 Bending strength of hardened material (MPa) 190 188 192 191 192 193 190 185 186 182 Viscosity (Pa・s) 1.8×10 ⁵ 1.7×10 ⁵ 1.5×10 ⁵ 1.6×10 ⁵ 1.7×10 ⁵ 3.1×10 ⁴ 4.4×10 ⁴ 1.3×10 ⁵ 1.7×10 ⁵ 3.5×10 ⁴ Lightness index L* of hardened material twenty three 31 twenty three twenty two twenty two 37 32 15 18 twenty four Prepreg properties Viscosity A A A A A C B A A B

[Table 2] Embodiment 11 Embodiment 12 Embodiment 13 Comparison Example 1 Comparison Example 2 Comparison Example 3 Comparison Example 4 Comparison Example 5 Comparative Example 6 Components [A-1] (mass) “TEPIC®”-S 35 25 35 35 35 35 35 15 45 “TEPIC®”-PAS B26L - 10 - - - - - - - Components [A-2] (mass) "Araldite®" MY0500 35 35 35 35 35 35 35 30 30 "Araldite®" MY0600 - - - - - - - - - "Araldite®" MY721 30 - - - - - - - - Components [A-3] (mass) “jER®” 4004P - 30 30 30 30 30 30 40 25 Constituent [A] (mass) "jER®"828 - - - - - - - 15 - Component [B] (mass) DICY7 10 7 7 7 7 7 7 5 8 Constituent [C] (mass) "Virantage®" VW-10700RFP 18 10 - - - - - 10 10 "SUMIKAEXCEL®" PES2603P - - 10 - - - - - - Other thermoplastic resins [C'] (parts by mass) "Virantage®" VW-30500RP - - - - 15 - - - - "SUMIKAEXCEL®" PES5003P - - - - - 8 - - - "VINYLEC®" K - - - - - - 8 - - Hardening accelerator (mass) "Omicure®" U-24M 2 - 2 2 2 2 2 2 2 DCMU99 - 3 - - - - - - - The amount of the component [A] that is solid at 25°C (mass %) 35 55 65 65 65 65 65 55 70 Characteristics of resin composition Flexural modulus of hardened material (GPa) 4.9 4.6 4.7 4.8 4.4 4.8 4.8 3.8 5.0 Bending strength of hardened material (MPa) 184 180 192 202 162 148 156 172 138 Viscosity (Pa・s) 3.3×10 ⁴ 1.6×10 ⁵ 1.6×10 ⁵ 6.2×10 ³ 1.8×10 ⁵ 1.1×10 ⁵ 8.3×10 ⁴ 9.9×10 ⁴ - Lightness index L* of hardened material 16 twenty two twenty two 62 25 10 55 twenty one 11 Prepreg properties Viscosity B A A D A A A A -

without.

without.

without.

Claims (8)

An epoxy resin composition comprising the following components [A] to [C], wherein 100% by mass of component [A] comprises 20% by mass to 40% by mass of an isocyanuric acid-type epoxy resin as component [A-1], and the epoxy resin composition comprises 2% by mass to 15% by mass of component [C] relative to 100% by mass of component [A]; [A]: epoxy resin, [B]: dicyandiamide, [C]: polysulfide having a weight average molecular weight of 15,000 to 25,000. The epoxy resin composition of claim 1, wherein the epoxy resin composition is kept at 90°C for 60 minutes and then cured at 135°C for 120 minutes, and the lightness index L ^* of the cured product having a thickness of 2 mm in the L ^* a ^* b ^* color system measured by a transmission method is 15 or more. The epoxy resin composition of claim 1 or 2, wherein the component [A-1] is a trifunctional isocyanuric acid type epoxy resin. The epoxy resin composition of claim 1 or 2, wherein 100% by mass of component [A] contains 20% by mass or more and 60% by mass or less of trifunctional or higher epoxypropylamine-type epoxy resin as component [A-2]. The epoxy resin composition of claim 1 or 2, wherein 100% by mass of component [A] contains 10% by mass to 40% by mass of component [A-3], which is a bisphenol-type epoxy resin in a solid state at 25°C. For example, in the epoxy resin composition of claim 1 or 2, 100% by mass of the component [A] contains 60% by mass or more of a component that is solid at 25°C. A prepreg, which is composed of an epoxy resin composition as described in any one of claims 1 to 6 and reinforcing fibers. A fiber-reinforced composite material comprising a cured product of an epoxy resin composition as described in any one of claims 1 to 6 and reinforcing fibers.