Epoxy resin compositions, prepregs, fiber-reinforced composite materials, fiber-reinforced composite tubular bodies

Abstract

The present invention aims to provide an epoxy resin composition that exhibits excellent tackiness and high elastic modulus and elongation in the cured resin product, a prepreg consisting of the epoxy resin composition and reinforcing fibers, and a fiber-reinforced composite material using the prepreg that has excellent mechanical properties. [Solution] An epoxy resin composition comprising the following components [A] and [B], and satisfying the following condition (1). Component [A]: A reaction product resulting from the reaction between the epoxy group in component a1 and the carboxyl group in component a2 of a polyfunctional epoxy resin (component a1) having a weight-average molecular weight of 1,000 or less and an aliphatic carboxylic acid (component a2) having a molecular weight of 230 or less. Ingredients [B]: Hardener Condition (1): The total content of component (a1) is 50 parts by mass or more per 100 parts by mass of the total epoxy resin.

Description

Technical Field

[0001] The present invention relates to an epoxy resin composition, a prepreg, and a fiber reinforced composite material, which are suitably used for fiber reinforced composite materials for aerospace applications, general industrial applications, sports applications, and the like.

Background Art

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

[0003] In recent years, in order to apply fiber reinforced composite materials to uses such as golf club shafts, fishing rods, bicycles, etc. that require further weight reduction, improvement of various physical properties has been demanded. For example, in order to exhibit excellent bending strength in tubular bodies such as golf club shafts and fishing rods, high fiber direction strength and non-fiber direction strength are required for the fiber reinforced composite material used, but they are greatly affected by the modulus of elasticity and elongation of the epoxy resin itself used as the matrix resin. In addition, for the prepreg used for a tubular body, high tackiness is required on the surface in order to prevent peeling of the prepreg when shaped into a tube. Since the viscosity characteristics of the resin composition used in combination with the reinforcing fibers affect the tackiness of such a prepreg, it is necessary to adjust the viscosity of the resin composition to a certain value or more in order to exhibit good tackiness.

[0004] [[ID=十九]] As a means for increasing the modulus of elasticity of an epoxy resin, there is a method of blending a polyfunctional epoxy resin having a low weight average molecular weight such as a trifunctional or higher functional epoxy resin having a nitrogen atom in the molecule, but the polyfunctional epoxy resin having a low weight average molecular weight has a problem that it has a low viscosity and cannot be blended in a large amount to exhibit high tackiness.

[0005] To address these challenges, Patent Document 1 explores improving viscosity by blending a thermoplastic resin with an epoxy resin. Furthermore, Patent Document 2 explores improving viscosity by pre-reacting an epoxy resin with a curing agent. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2021 / 177089 [Patent Document 2] Japanese Patent Application Publication No. 59-219320 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, the technology described in Patent Document 1 sometimes requires the incorporation of a certain amount of thermoplastic resin, which can sometimes reduce the elongation of the cured resin product. Furthermore, while the technology described in Patent Document 2 can improve viscosity, it can sometimes reduce the elongation of the cured resin product.

[0008] Therefore, the object of the present invention is to provide an epoxy resin composition that exhibits excellent tackiness and high elastic modulus and elongation in the cured resin product, a prepreg consisting of the epoxy resin composition and reinforcing fibers, and a fiber-reinforced composite material using the prepreg that has excellent mechanical properties. [Means for solving the problem]

[0009] 1. An epoxy resin composition comprising component [A] and component [B], and satisfying condition (1). Component [A]: A reaction product resulting from the reaction between the epoxy group in component a1 and the carboxyl group in component a2 of a polyfunctional epoxy resin (component a1) having a weight-average molecular weight of 1,000 or less and an aliphatic carboxylic acid (component a2) having a molecular weight of 230 or less. Ingredients [B]: Hardener Condition (1): The total content of component a1 is 50 parts by mass or more per 100 parts by mass of the total epoxy resin. 2. The epoxy resin composition according to item 1 above, wherein component [B] is either an amine curing agent or a phenol curing agent or both. 3. The epoxy resin composition according to item 2 above, wherein component [B] is an amine curing agent, which is either or both of dicyandiamide and diaminodiphenylsulfone. 4. The epoxy resin composition according to any one of 1 to 3 above, wherein the number of carboxyl groups contained in the molecular structure of component a2 is 1 to 2. An epoxy resin composition according to any one of the above 1 to 4, wherein the viscosity at 5.25℃ is 1,000 Pa·s or more. 6. A prepreg comprising the epoxy resin composition described in any of items 1 to 5 above and reinforcing fibers. 7. A fiber-reinforced composite material obtained by molding the prepreg described in 6 above. 8. A tubular body made of fiber-reinforced composite material, obtained by molding the prepreg described in 6 above. 9. Golf shafts, golf heads, fishing rods, badminton rackets, tennis rackets, pickleball paddles, or bicycle components manufactured using the prepregs described in item 6 above. 10. A component for a flying vehicle, manufactured using the prepreg described in item 6 above. [Effects of the Invention]

[0010] According to the present invention, it is possible to obtain an epoxy resin composition that exhibits excellent tackiness and high elastic modulus and elongation in the cured resin product, a prepreg consisting of the epoxy resin composition and reinforcing fibers, and a fiber-reinforced composite material with excellent mechanical properties using the prepreg. [Modes for carrying out the invention]

[0011] The present invention will be described in detail below.

[0012] The epoxy resin composition of the present invention comprises component [A] and component [B]. Hereafter, component [A] may be simply referred to as [A], and component [B] may be simply referred to as [B].

[0013] Component [A] in the present invention is a reaction product of a polyfunctional epoxy resin (component a1) having a weight-average molecular weight of 1,000 or less and an aliphatic carboxylic acid (component a2) having a molecular weight of 230 or less. The reaction product of a polyfunctional epoxy resin (component a1) having a weight-average molecular weight of 1,000 or less and an aliphatic carboxylic acid (component a2) having a molecular weight of 230 or less is a reaction between the epoxy group of the polyfunctional epoxy resin and the carboxyl group of the aliphatic carboxylic acid, and refers to a preliminary reaction that occurs before the epoxy resin used in the present invention hardens by reacting with component [B]: curing agent. Hereafter, component a1 may be referred to as (a1) and component a2 may be referred to as (a2).

[0014] (a1) used in the reactant of [A] is a polyfunctional epoxy resin having a weight-average molecular weight of 1,000 or less. Here, a polyfunctional epoxy resin refers to a compound containing three or more epoxy groups. Regarding the upper limit of epoxy groups, it is preferable that there be four or fewer from the viewpoint of balancing the elastic modulus and elongation of the cured resin. The weight-average molecular weight is a value measured as a polystyrene equivalent by gel permeation chromatography. (a1) is not particularly limited as long as it is a compound having a weight-average molecular weight of 1,000 or less and containing three or more epoxy groups.

[0015] By using (a1) as [A], the elastic modulus of the cured resin is increased, and a fiber-reinforced composite material with excellent mechanical properties can be obtained. The weight-average molecular weight of (a1) is preferably 300 or more at the lower limit and 900 or less at the upper limit. By setting the weight-average molecular weight of (a1) within the above range, a good balance between the elastic modulus and elongation of the cured resin can be achieved.

[0016] The total content of (a1) is 50 parts by mass or more, preferably 60 parts by mass or more, based on 100 parts by mass of the total epoxy resin. The upper limit is preferably 80 parts by mass or less. By containing (a1) within the above range, the elastic modulus of the cured resin becomes good. Here, the "total content of (a1)" includes (a1) that has not reacted with (a2), and is the total amount of "(a1) reacted with (a2)" and "(a1) not reacted with (a2)". In the present invention, 100 parts by mass of the total epoxy resin includes (a1) reacted with (a2). Examples of (a1) include epoxy resins such as diaminodiphenylmethane type, aminophenol type, metaxylenediamine type, 1,3-bisaminomethylcyclohexane type, sorbitol type, and glycerol type. Among them, a polyfunctional epoxy resin having three or more functional groups and having a nitrogen atom in the molecule is particularly preferably used because of the good balance between elastic modulus and elongation.

[0017] Examples of commercially available products of diaminodiphenylmethane type epoxy resin include ELM434 (manufactured by Sumitomo Chemical Co., Ltd.), "Araldite (registered trademark)" MY720, MY721, MY9512, MY9663 (manufactured by Huntsman Corporation), "jER (registered trademark)" 604 (manufactured by Mitsubishi Chemical Corporation), and the like.

[0018] Examples of commercially available products of aminophenol type epoxy resin include "jER (registered trademark)" 630 (manufactured by Mitsubishi Chemical Corporation), "Araldite (registered trademark)" MY0500, MY0510, MY0600, MY0610 (manufactured by Huntsman Corporation), and the like.

[0019] Examples of commercially available products of metaxylenediamine type epoxy resin include "TETRAD (registered trademark)"-X (manufactured by Mitsubishi Gas Chemical Company, Inc.).

[0020] Examples of commercially available products of 1,3-bisaminomethylcyclohexane type epoxy resin include "TETRAD (registered trademark)"-C (manufactured by Mitsubishi Gas Chemical Company, Inc.).

[0021] Commercially available sorbitol-type epoxy resins include "Denacol®" EX-612, EX-614, EX-614B, and EX-622 (all manufactured by Nagase ChemteX Corporation).

[0022] Commercially available glycerol-type epoxy resins include "Denacol®" EX-313, EX-314, EX-321, and EX-321L (all manufactured by Nagase ChemteX Corporation).

[0023] The reactant (a2) used in [A] is an aliphatic carboxylic acid with a molecular weight of 230 or less. Here, an aliphatic carboxylic acid is a carboxylic acid that does not have an aromatic ring, and includes linear aliphatic carboxylic acids, branched aliphatic carboxylic acids, and alicyclic carboxylic acids. (a2) is not particularly limited as long as it is an aliphatic carboxylic acid with a molecular weight of 230 or less.

[0024] (a2) is used in the resin composition by pre-reacting at least a portion, preferably all, of it with (a1). This improves the viscosity of the resin composition compared to using (a1) alone, resulting in an epoxy resin composition or prepreg with excellent tack properties. Furthermore, by using (a2) in the preliminary reaction, the elongation of the cured resin is increased, resulting in a fiber-reinforced composite material with excellent mechanical properties.

[0025] The lower limit of the molecular weight of (a2) is preferably 100 or more. The upper limit is preferably 210 or less, and more preferably 200 or less. By setting the molecular weight of (a2) within the above range, a good balance between the elastic modulus and elongation of the cured resin is achieved.

[0026] Furthermore, it is preferable that the number of carboxyl groups in (a2) be 1 to 2. By keeping the number of carboxyl groups within the above range, the effect of improving the elongation of the cured resin is enhanced, which is preferable.

[0027] The content of (a2) is preferably such that the ratio (H / E) of the total number of moles of carboxyl groups in (a2) (H) to the total number of moles of epoxy groups in (a1) (E) is 0.1 ≤ H / E ≤ 0.3. The lower limit is more preferably 0.15 or higher, and the upper limit is more preferably 0.25 or lower.

[0028] Examples of (a2) include, but are not limited to, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanediic acid, 1,4-cyclohexanedicarboxylic acid, and tricarbaryl acid. Among these, aliphatic dicarboxylic acids are preferred due to their good balance of elastic modulus and elongation, linear aliphatic dicarboxylic acids and alicyclic dicarboxylic acids are more preferred, and linear aliphatic dicarboxylic acids are particularly preferred.

[0029] [A] is obtained by pre-reacting (a1) and (a2) at a temperature of 100 to 180°C for 1 to 12 hours. At this time, it is preferable that all carboxyl groups contained in the molecule of (a2) react with the epoxy group of (a1). In the above reaction, (a1) and (a2) may be used individually or in combination of two or more types.

[0030] The resin composition in the present invention may contain (a1) that has not reacted with (a2) or epoxy resins other than (a1), as long as the effects of the present invention are not impaired. That is, the resin composition may contain the reactants of [A] and (a1). Specific examples of epoxy resins other than (a1) include bisphenol type, phenol novolac type, cresol novolac type, dicyclopentadiene type, and oxazolidone type epoxy resins. Among these, it is preferable to incorporate an epoxy resin that is solid at 25°C from the viewpoint of the tackiness of the epoxy resin composition and prepreg.

[0031] Commercially available bisphenol A type epoxy resins include "jER(registered trademark)" 825, 828, 834, 1001, 1003F, 1004F, 1005F, 1007FS, 1009F (all manufactured by Mitsubishi Chemical Corporation), "EPICLON(registered trademark)" 850 (manufactured by DIC Corporation), "Epotote(registered trademark)" YD-128 (manufactured by Nippon Steel Chemical & Material Corporation), and "DER(registered trademark)" -331, 332 (both manufactured by Olin Corporation).

[0032] Commercially available bisphenol F type epoxy resins include "Araldite®" GY282 (manufactured by Huntsman Co., Ltd.), "jER®" 806, 807, 4005P, 4007P, 4010P (all manufactured by Mitsubishi Chemical Corporation), "EPICLON®" 830 (manufactured by DIC Corporation), and "Epotote®" YDF-170, YDF2001, YDF2004 (manufactured by Nippon Steel Chemical & Material Co., Ltd.).

[0033] Commercially available phenol novolac type epoxy resins include "jER(registered trademark)" 152 and 154 (both manufactured by Mitsubishi Chemical Corporation), EPPN-201 (manufactured by Nippon Kayaku Co., Ltd.), and "EPICLON(registered trademark)" N-740, N-770, and N-775 (both manufactured by DIC Corporation).

[0034] Commercially available cresol novolac type epoxy resins include "EPICLON®" N-660, N-665, N-670, N-673, N-680, N-690, and N-695 (all manufactured by DIC Corporation).

[0035] Commercially available dicyclopentadiene-type epoxy resins include "EPICLON®" HP-7200, HP-7200L, HP-7200H, HP-7200HH, and HP-7200HHH (all manufactured by DIC Corporation).

[0036] Commercially available oxazolidone-type epoxy resins include “DER®” 858 (manufactured by Olin Co., Ltd.), TSR-400 (manufactured by DIC Corporation), and ACR1348 (manufactured by ADEKA Corporation).

[0037] The total content of (a1) that has not reacted with (a2), and epoxy resins other than (a1), is preferably 97 parts by mass or less, more preferably 95 parts by mass or less, and particularly preferably 90 parts by mass or less, per 100 parts by mass of the total epoxy resin. The preferred lower limit is preferably 50 parts by mass or more, and more preferably 60 parts by mass or more, per 100 parts by mass of the total epoxy resin.

[0038] In the present invention, component [B] is a curing agent. Examples of curing agents include amine curing agents, phenol curing agents, acid anhydride curing agents, and imidazole curing agents. These may be used individually or in combination of two or more. However, although (a2) also has the ability to cure epoxy resins, the curing agent as component [B] in the present invention does not contain compounds corresponding to (a2). By using a curing agent other than (a2), a good balance between the elastic modulus and elongation of the cured resin is achieved. Among these, either an amine curing agent or a phenol curing agent, or a combination of both an amine curing agent and a phenol curing agent, is preferred because it provides a good balance between the elastic modulus and elongation.

[0039] Examples of amine curing agents include aromatic amines such as diaminodiphenylmethane, diaminodiphenylsulfone, and diethylmethylbenzenediamine, as well as aliphatic amines such as dicyandiamide and isophoronediamine. Examples of phenol curing agents include bisphenol A, bisphenol F, bisphenol S, bisphenol AD, bisphenol Z, dihydroxynaphthalene, and dihydroxybenzophenone. Among these, dicyandiamide and diaminodiphenylsulfone, or both, are more preferably used because they provide excellent storage stability and curability of the resulting resin composition, and a good balance between the elastic modulus and elongation of the cured resin.

[0040] Specific examples of diaminodiphenyl sulfones include 3,3'-diaminodiphenyl sulfone and 4,4'-diaminodiphenyl sulfone.

[0041] Examples of commercially available 3,3'-diaminodiphenylsulfone include 3,3'-DAS (manufactured by Mitsui Chemicals Fine, Inc.).

[0042] Examples of commercially available 4,4'-diaminodiphenylsulfone include Seika Cure S (manufactured by Wakayama Seika Kogyo Co., Ltd.).

[0043] Commercially available dicyandiamide products include DICY7 (manufactured by Mitsubishi Chemical Corporation) and DICY15 (manufactured by Mitsubishi Chemical Corporation).

[0044] The resin composition in the present invention may contain a curing accelerator from the viewpoint of controlling the curing speed. While not limited to curing accelerators, examples include urea compounds and imidazole compounds, and urea compounds are particularly preferred from the viewpoint of storage stability of the resin composition.

[0045] Examples of urea compounds include 3-(3,4-dichlorophenyl)-1,1-dimethylurea, 3-(4-chlorophenyl)-1,1-dimethylurea, phenyldimethylurea, and toluenebisdimethylurea. Commercially available aromatic urea compounds include DCMU99 (manufactured by Hodogaya Chemical Co., Ltd.) and “Omicure®” 24 (manufactured by Huntsman Corporation).

[0046] The resin composition in the present invention may contain a thermoplastic resin, provided that it does not impair the effects of the present invention. By incorporating a thermoplastic resin into the resin composition, it is possible to control the viscosity of the resin composition, the tackiness of the prepreg, and the fluidity of the resin composition when the prepreg is heat-cured, without impairing the heat resistance of the fiber-reinforced composite material. Preferably, such a thermoplastic resin is one that is compatible with epoxy resins and has hydrogen-bonding functional groups that can improve the adhesion between the resin and the reinforcing fibers. Examples of hydrogen-bonding functional groups include alcoholic hydroxyl groups, amide bonds, sulfonyl groups, and carboxyl groups.

[0047] Examples of thermoplastic resins having alcoholic hydroxyl groups include polyvinyl acetal resins such as polyvinyl formal and polyvinyl butyral, polyvinyl alcohol, and phenoxy resins. Examples of thermoplastic resins having amide bonds include polyamides, polyimides, polyamideimides, and polyvinylpyrrolidones. Examples of thermoplastic resins having sulfonyl groups include polysulfones. Polyamides, polyimides, and polysulfones may have functional groups such as ether bonds and carbonyl groups in their main chains. Polyamides may have substituents on the nitrogen atom of the amide group. Examples of thermoplastic resins having carboxyl groups include polyesters, polyamides, and polyamideimides. The thermoplastic resins having any of the functional groups are not limited to the compounds described above.

[0048] When a thermoplastic resin is blended into a resin composition, the amount blended is preferably 1 part by mass or more and 15 parts by mass or less per 100 parts by mass of the total epoxy resin. The lower limit is preferably 3 parts by mass or more, the upper limit is preferably 10 parts by mass or less, and more preferably 8 parts by mass or less. It is preferable to blend the resin within the above range because it provides a good balance between the elastic modulus and elongation of the cured resin. The resin composition in the present invention may contain certain low molecular weight compounds as additives, to the extent that they do not impair the effects of the present invention. Here, "certain low molecular weight compounds" refers to compounds with a boiling point of 130°C or higher, a molecular weight m of 50 to 250, that do not contain epoxy groups in their molecule, and that do not possess the ability to cure epoxy resins. Compounds such as amines and phenols that can undergo addition reactions with epoxy resins, acid anhydrides that can copolymerize with epoxy resins, imidazoles that can act as initiators for the self-polymerization reaction of epoxy resins, aromatic urea compounds, and tertiary amine compounds are compounds that possess the ability to cure epoxy resins and are therefore not included in the low molecular weight compounds described herein. Here, "not possessing the ability to cure epoxy resins" means that the compound does not chemically react with epoxy resins and does not participate in the self-polymerization of epoxy resins.

[0049] The low molecular weight compound described above is thought to exist in the voids of the crosslinked structure formed by the reaction of epoxy resin and curing agent, without being incorporated into the crosslinked structure, and to maintain this state even after the epoxy resin has cured. This is thought to result in a higher elastic modulus of the resulting epoxy resin cured product. Furthermore, by incorporating the low molecular weight compound described above, an epoxy resin cured product with not only a high elastic modulus but also high elongation and high strength can be obtained.

[0050] Examples of such low molecular weight compounds include amides such as N-methylformamide, N-methylacetamide, 2-pyrrolidone, N-methylpropionamide, N-ethylacetamide, N-methylacetanilide, and N,N'-diphenylacetamide, as well as diols such as ethanediol, propanediol, butanediol, pentanediol, hexanediol, and heptanediol. These compounds may be used individually or in appropriate combinations.

[0051] The viscosity of the resin composition in the present invention at 25°C is preferably 1,000 Pa·s or more, more preferably 10,000 Pa·s or more, and even more preferably 25,000 Pa·s or more, in order to exhibit excellent tack in the epoxy resin composition and prepreg. The upper limit is preferably 1,000,000 Pa·s or less, and even more preferably 500,000 Pa·s or less. Here, viscosity refers to the complex viscosity η measured using a dynamic viscoelasticity measuring device (e.g., Rheometer RDA2 (manufactured by Rheometox), Rheometer ARES (manufactured by TA Instruments)) with a 40 mm diameter parallel plate, a frequency of 0.5 Hz, and a gap of 1 mm. * This refers to the following. Furthermore, tack refers to the adhesiveness of resin films and prepregs. Sufficiently high tack is desirable because it suppresses peeling when the prepreg is bonded to a mold or when prepregs are bonded to each other, resulting in excellent handling. Also, high adhesion between prepregs is desirable because it makes it less likely for voids to occur between laminated prepregs, resulting in a fiber-reinforced composite material with high mechanical properties.

[0052] Preferred reinforcing fibers for use in the prepreg and fiber-reinforced composite material of the present invention include carbon fibers, graphite fibers, aramid fibers, glass fibers, etc., with carbon fibers being particularly preferred. The form and arrangement of the reinforcing fibers are not limited; for example, fiber structures such as unidirectionally aligned long fibers, single tows, woven fabrics, knits, and braids can be used. Two or more types of carbon fibers, or glass fibers, aramid fibers, boron fibers, PBO fibers, high-strength polyethylene fibers, alumina fibers, and silicon carbide fibers may be used in combination as reinforcing fibers.

[0053] Examples of carbon fibers include acrylic, pitch, and rayon-based carbon fibers, with acrylic-based carbon fibers, which have particularly high tensile strength, being preferred.

[0054] While twisted, untwisted, and untwisted carbon fibers can be used, twisted fibers are not oriented parallel to each other, which can lead to a decrease in the mechanical properties of the resulting carbon fiber reinforced composite material. Therefore, untwisted or untwisted fibers, which offer a good balance between moldability and strength properties of the carbon fiber reinforced composite material, are preferred.

[0055] The carbon fibers preferably have a tensile modulus of 150 GPa or more and 800 GPa or less. This range is preferable because it provides a good balance of high levels of rigidity and strength in the carbon fiber reinforced composite material. A more preferable lower limit for the tensile modulus is 200 GPa or more, and even more preferably 230 GPa or more. A more preferable upper limit for the tensile modulus is 700 GPa or less, and even more preferably 600 GPa or less. Here, the tensile modulus of the carbon fibers is a value measured according to JIS R7608 (2007), and the resin formulation used is "Celoxide (registered trademark)" 2021P / boron trifluoride monoethylamine / acetone = 100 / 3 / 4 (parts by mass), and the curing condition is curing in an oven set to a temperature of 125°C for 30 minutes.

[0056] The prepreg of the present invention can be manufactured by various known methods. For example, the prepreg can be manufactured by a hot-melt method, in which the resin composition is heated to reduce its viscosity without using an organic solvent and then impregnated into reinforcing fibers.

[0057] In the hot melt method, methods can be used in which a resin composition whose viscosity has been reduced by heating is directly impregnated into the reinforcing fibers, or in which a release paper sheet with a resin film, which is first coated with the resin composition on a release paper or the like, is prepared, and then the resin film is placed on both sides or one side of the reinforcing fibers and the reinforcing fibers are impregnated with the resin composition by heating and pressurizing.

[0058] The fiber content in the prepreg is preferably 30-90% by mass, more preferably 35-85% by mass, and even more preferably 65-85% by mass. If the fiber content is too low, the amount of resin is too high, making it difficult to obtain the advantages of fiber-reinforced composite materials, such as superior specific strength and specific modulus. Also, when molding fiber-reinforced composite materials, the amount of heat generated during curing may become too high. On the other hand, if the fiber content is too high, resin impregnation may occur, and the resulting composite material may have many voids. It may also impair the tackiness of the prepreg.

[0059] The fiber-reinforced composite material of the present invention can be manufactured, for example, by laminating the prepregs of the present invention described above in a predetermined form and curing the resin by applying pressure and heat. Methods for applying heat and pressure include press molding, autoclave molding, bagging molding, wrapping tape molding, and internal pressure molding. The wrapping tape method is particularly preferred for forming tubular bodies made of fiber-reinforced composite materials. The wrapping tape method is a method for obtaining a cylindrical molded body by wrapping prepreg around a core such as a mandrel. Specifically, the method involves wrapping prepreg around a mandrel, wrapping a wrapping tape made of thermoplastic resin film around its outer circumference to fix the prepreg and apply pressure, heating and curing the resin in an oven, and then removing the core to obtain a cylindrical molded body. This method is suitable for producing rod-shaped bodies such as golf club shafts and fishing rods.

[0060] When a prepreg impregnated with the resin composition according to the present invention is used, it exhibits excellent tackiness, reducing delamination when shaped into a tubular form, and resulting in a product with fewer defects such as voids. Furthermore, when the resin composition according to the present invention is used, the cured product can exhibit excellent elastic modulus and elongation, so the fiber-reinforced composite material of the present invention exhibits high strength in both the fiber direction and the non-fiber direction, and the tubular body made of the fiber-reinforced composite material of the present invention can exhibit excellent bending strength.

[0061] The fiber-reinforced composite material or tubular body made of fiber-reinforced composite material of the present invention can be widely used in aerospace, general industrial, and sports applications. More specifically, in general industrial applications, it is suitably used as structural components for automobiles, ships, and railway vehicles, as well as exterior components for automobiles, ships, railways, and buildings. In sports applications, it is suitably used for golf club shafts, golf heads, fishing rods, tennis and badminton rackets, pickleball paddles, and bicycle components such as frames, rims, cranks, wheels, handlebars, pedals, and saddles. It is also suitably used as a component for flying objects, with specific examples of flying objects including aircraft, drones, and UAMs (Urban Air Mobility).

[0062] The upper and lower limits of the numerical ranges described above can be combined in any way unless otherwise specified. [Examples]

[0063] The present invention will be described in detail below with reference to examples. However, the scope of the present invention is not limited to these examples. The unit "parts" in the composition ratio refers to parts by mass unless otherwise noted. Furthermore, the measurements of various properties (physical properties) were performed under conditions of 23°C and 50% relative humidity unless otherwise noted. In the table, the units for the amount of each component are all parts by mass.

[0064] <Materials used in the examples and comparative examples> <Epoxy resin composition> (1) Component [A]: Reaction product of (a1) and (a2) (a1) Polyfunctional epoxy resin with a weight-average molecular weight of 1,000 or less (a1)-1 “Araldite (registered trademark)” MY0600 (aminophenol-type epoxy resin, epoxy equivalent: 106, weight-average molecular weight: 640, number of functional groups: 3, manufactured by Huntsman Co., Ltd.) (a1)-2 “Denacol (registered trademark)” EX-614B (sorbitol-type epoxy resin, epoxy equivalent: 173, weight-average molecular weight: 949, number of functional groups: 4, manufactured by Nagase ChemteX Corporation) (a2) Aliphatic carboxylic acids with a molecular weight of 230 or less Adipic acid (molecular weight: 146, manufactured by Tokyo Chemical Industry Co., Ltd.) Sebacic acid (molecular weight: 202, manufactured by Tokyo Chemical Industry Co., Ltd.) 1,4-Cyclohexanedicarboxylic acid (Molecular weight: 172, manufactured by Tokyo Chemical Industry Co., Ltd.) (2) Hardeners other than (a2) 3,3'-DAS (Molecular weight: 248, 3,3'-diaminodiphenylsulfone, manufactured by Mitsui Chemicals Fine, Inc.) Abitienoic acid (molecular weight: 302, manufactured by Tokyo Chemical Industry Co., Ltd.) Octadecanedioic acid (molecular weight: 314, manufactured by Tokyo Chemical Industry Co., Ltd.) (3) Epoxy resins other than (a1) “jER(registered trademark)” 4005P (Bisphenol F type epoxy resin, epoxy equivalent: 1075, manufactured by Mitsubishi Chemical Corporation) "EPICLON®" N-775 (phenol novolac type epoxy resin, epoxy equivalent: 189, manufactured by DIC Corporation) "EPICLON®" 830 (Bisphenol F type epoxy resin, epoxy equivalent: 172, manufactured by DIC Corporation) (4) Components [B]: Hardener DICY7 (Dicyandiamide, manufactured by Mitsubishi Chemical Corporation) (5) Other hardening agents Adipic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) (6) Curing accelerator DCMU99 (3-(3,4-dichlorophenyl)-1,1-dimethylurea, manufactured by Hodogaya Chemical Co., Ltd.) <Method for preparing resin compositions> Table 1 shows the composition of each example and comparative example. (1) Preparation of the hardener masterbatch In each example and comparative example, 10 parts by mass of "EPICLON®" 830, one of the epoxy resins that is liquid at room temperature from the components of each example shown in the table (10 parts by mass per 100 parts by mass of all epoxy resins contained in the epoxy resin composition; in Comparative Examples 2 and 6, a portion of "EPICLON®" 830) was prepared. Component [B], DICY7, was added to this in the amounts shown in the table, and the mixture was kneaded at room temperature. The mixture was passed through a three-roll mill twice to prepare a curing agent masterbatch. (2) Preparation of resin composition In Examples 1 to 5, the components corresponding to (a1) and (a2) from the components of each example shown in the table were placed in a beaker in their entirety, and the temperature was raised to 160°C while mixing. Then, the mixture was heated and mixed at 160°C for 1 hour to react (a1) and (a2) to obtain [A]. Next, while continuing to mix, the entire amount of epoxy resin other than (a1), excluding 10 mass of "EPICLON®" used in (1) above, was added and dissolved. Then, while continuing to mix, the temperature was lowered to 55-65°C, and the entire amount of the curing agent masterbatch and curing accelerator prepared in (1) above was added. The mixture was then kneaded at the same temperature for 30 minutes to obtain the epoxy resin composition.

[0065] However, since (a2) was not used in Comparative Example 1, the step of adding (a2) was omitted, and (a1) and the epoxy resin other than (a1) were added and dissolved, and the resin composition was prepared in the same manner as in Examples 1 to 5. In Comparative Example 3, the above curing agent masterbatch was not used, and in the same manner as in Examples 1 to 5, (a1) and (a2) were reacted, the entire amount of the epoxy resin other than (a1) was added, and then a portion of adipic acid, which is (a2), was used as a curing agent and added together with a curing accelerator to prepare the resin composition. In Comparative Examples 4, 5, or 8, 3,3'-DAS, abietic acid, or octadecanediic acid was used instead of (a2) and reacted with (a1) in the same procedure as in Examples 1 to 5. In Comparative Examples 6 and 7, after (1) preparation of the curing agent masterbatch, "EPICLON®" 830 or "EPICLON®" N-775 was used instead of (a1) and reacted with (a2) in the same procedure as in Examples 1 to 5. In all other cases, the resin composition was prepared in the same manner as in Examples 1 to 5. <Method for producing cured resin products> The resin composition prepared according to the above <Method for preparing the resin composition> was degassed in a vacuum, and then heated in a mold set to a thickness of 2 mm using a 2 mm thick "Teflon®" spacer. The temperature was raised from 30°C at a rate of 1.7°C / min until it reached 90°C, where it was held for 1 hour. After that, the temperature was raised at a rate of 2.0°C / min until it reached 135°C, where it was cured for 2 hours to obtain a 2 mm thick plate-shaped cured resin product. <Various Evaluation Methods> (1) Three-point bending measurement of cured resin From the 2mm thick resin cured material prepared according to the above <Method for Preparing Resin Cured Materials>, test pieces measuring 10mm in width and 60mm in length were cut out. Using an Instron universal testing machine (manufactured by Instron), with a span of 32mm, a crosshead speed of 2.5mm / min, and a sample size of n=6, three-point bending was performed according to JIS K7171 (1994). The average values ​​of the elastic modulus and deflection (elongation) at fracture were recorded in the "Resin Properties" column of the table as the flexural modulus and deflection at fracture of the resin cured material, respectively.

[0066] (2) Viscosity measurement of epoxy resin composition The viscosity of the epoxy resin composition was measured using a dynamic viscoelasticity analyzer (ARES-2KFRTN1-FCO-STD, manufactured by T.A. Instruments Co., Ltd.). A parallel plate with a diameter of 25 mm was used as the upper measuring fixture and a diameter of 40 mm as the lower measuring fixture. The epoxy resin composition was set so that the distance between the upper and lower fixtures was 1 mm, and the measurement was performed in torsion mode (measurement frequency: 0.5 Hz). The temperature was increased from 20°C to 60°C at a rate of 1°C / min. If the viscosity at 25°C was between 1,000 and 1,000,000 Pa·s, it was marked as "○", and if it was less than 1,000 Pa·s, it was marked as "×", and this was recorded in the "Viscosity (25°C)" column of the resin properties table.

[0067] <Example 1> A resin composition was prepared according to the above-mentioned method for preparing the resin composition, using 70 parts by mass of "Araldite®" MY0600 as (a1), 5 parts by mass of adipic acid as (a2), 20 parts by mass of "jER®" 4005P and 10 parts by mass of "EPICLON®" 830 as epoxy resins other than (a1), 8.0 parts by mass of DICY7 as component [B], and 3 parts by mass of DCMU99 as a curing accelerator.

[0068] A cured resin product was prepared from the obtained resin composition according to the <Method for Preparing Cured Resin Products>. The flexural modulus and deflection at fracture of this cured resin product were measured according to "(1) Three-point bending measurement of cured resin products" in <Various Evaluation Methods>. The flexural modulus was 4.4 GPa and the deflection at fracture was 6.9 mm, indicating that the elastic modulus and elongation of the cured resin product were good.

[0069] Furthermore, when the obtained resin composition was measured according to "(2) Viscosity measurement of epoxy resin composition" in "Various evaluation methods," the viscosity of the resin composition was found to be good.

[0070] <Examples 2-5> Except for the changes in composition shown in Table 1, the resin composition and cured resin product were prepared in the same manner as in Example 1. For each example, the flexural modulus of the cured resin product, the deflection at fracture, and the viscosity of the resin composition, measured according to <Various Evaluation Methods>, are shown in Table 1, and all were satisfactory.

[0071] <Comparative Example 1> The resin composition and resin cured product were prepared using the composition shown in Table 1 and the methods described in <Method for preparing the resin composition> and <Method for producing the resin cured product>. The results of the physical property evaluation are shown in addition to Table 1 (the same applies to the following comparative examples). The flexural modulus of the resin cured product was good. However, because (a2) was not included in the resin composition and [A], which is a reaction product of (a1) and (a2), was not included, the deflection at break of the resin cured product and the viscosity of the resin composition were lower compared to Example 1.

[0072] <Comparative Example 2> The resin composition and resin cured product were prepared using the composition shown in Table 1 and the methods described in <Method for preparing the resin composition> and <Method for producing the resin cured product>. The bending at fracture of the resin cured product and the viscosity of the resin composition were good. However, in the resin composition, the total content of (a1) was less than 50 parts by mass out of 100 parts by mass of the total epoxy resin, and condition (1) was not met, so the flexural modulus of the resin cured product was lower than that of Example 1 and Example 4.

[0073] <Comparative Example 3> The resin composition and cured resin product were prepared using the composition shown in Table 1 and the methods described in <Method for preparing the resin composition> and <Method for producing the cured resin product>. The viscosity of the resin composition was good. However, there were many undissolved adipic acid particles used as a curing agent, making it impossible to produce a cured resin product that could accurately acquire the resin properties.

[0074] <Comparative Example 4> The resin composition and resin cured product were prepared using the composition shown in Table 1 and the methods described in <Method for preparing the resin composition> and <Method for producing the resin cured product>. The flexural modulus of the resin cured product and the viscosity of the resin composition were good. However, because 3,3'-DAS, an amine curing agent, was used in the resin composition instead of (a2), the deflection at fracture of the resin cured product was lower than that of Example 1.

[0075] <Comparative Example 5> The resin composition and resin cured product were prepared using the composition shown in Table 1 and the methods described in <Method for preparing the resin composition> and <Method for producing the resin cured product>. The flexural modulus of the resin cured product and the viscosity of the resin composition were good. However, because abietic acid, a carboxylic acid with a molecular weight greater than 230, was used in the resin composition instead of (a2), the deflection at break of the resin cured product was lower than that of Example 1.

[0076] <Comparative Example 6> The resin composition and resin cured product were prepared using the composition shown in Table 1 and the methods described in <Method for preparing the resin composition> and <Method for producing the resin cured product>. The bending at fracture of the resin cured product and the viscosity of the resin composition were good. However, because the resin composition used a large amount of "EPICLON®" 830, a bifunctional epoxy resin with a weight-average molecular weight of 1,000 or less, instead of (a1), the flexural modulus of the resin cured product was lower than that of Example 1.

[0077] <Comparative Example 7> The resin composition and resin cured product were prepared using the composition shown in Table 1 and the methods described in <Method for preparing the resin composition> and <Method for producing the resin cured product>. The viscosity of the resin composition was good. However, because the resin composition used a large amount of "EPICLON®" N-775, a polyfunctional epoxy resin with a weight-average molecular weight greater than 1,000, instead of (a1), the flexural modulus and fracture deflection of the resin cured product were lower than those of Example 1.

[0078] <Comparative Example 8> The resin composition and resin cured product were prepared using the composition shown in Table 1 and the methods described in <Method for preparing the resin composition> and <Method for producing the resin cured product>. The bending at break of the resin cured product and the viscosity of the resin composition were good. However, because octadecanediic acid, a carboxylic acid with a molecular weight greater than 230, was used in the resin composition instead of (a2), the flexural modulus of the resin cured product was lower than that of Example 1.

[0079] [Table 1]

Claims

1. An epoxy resin composition comprising component [A] and component [B], and satisfying condition (1). Component [A]: A reaction product resulting from the reaction between the epoxy group in component a1 and the carboxyl group in component a2 of a polyfunctional epoxy resin (component a1) having a weight-average molecular weight of 1,000 or less and an aliphatic carboxylic acid (component a2) having a molecular weight of 230 or less. Ingredients [B]: Hardener Condition (1): The total content of component a1 is 50 parts by mass or more per 100 parts by mass of the total epoxy resin.

2. The epoxy resin composition according to claim 1, wherein component [B] is either an amine curing agent or a phenol curing agent or both.

3. The epoxy resin composition according to claim 2, wherein component [B] is an amine curing agent, which is either dicyandiamide or diaminodiphenylsulfone or both.

4. The epoxy resin composition according to claim 1, wherein the number of carboxyl groups contained in the molecular structure of component a2 is 1 to 2.

5. The epoxy resin composition according to claim 1, wherein the viscosity at 25°C is 1,000 Pa·s or more.

6. A prepreg comprising the epoxy resin composition and reinforcing fibers according to any one of claims 1 to 5.

7. A fiber-reinforced composite material obtained by molding the prepreg described in claim 6.

8. A tubular body made of fiber-reinforced composite material, obtained by molding the prepreg described in claim 6.

9. A golf shaft, golf head, fishing rod, badminton racket, tennis racket, pickleball paddle, or bicycle component made using the prepreg described in claim 6.

10. A component for a flying object, manufactured using the prepreg described in claim 6.

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