Prepregs, fiber-reinforced composites, fiber-reinforced composite tubular bodies, golf club shafts and fishing rods

Abstract

The present invention addresses the problem of providing: a prepreg which comprises a resin composition and has excellent elastic modulus and heat resistance and also has excellent appearance including weather resistance and transparency; and a fiber-reinforced composite material, a tubular body made of a fiber-reinforced composite material, a golf club shaft and a fishing rod in each of which the prepreg is used and each of which has excellent mechanical properties, heat resistance and appearance. As a solution for the problem, a prepreg is provided, which comprises reinforcing fibers and a resin composition, in which the resin composition comprises the components [A] to [D] mentioned below and satisfies the requirements (1) to (5) mentioned below. Component [A]: a novolac-type epoxy resin; component [B]: an oxazolidone-type epoxy resin; component [C]: one or both of a sorbitol-type epoxy resin and a glycerol-type epoxy resin; and component [D]: dicyandiamide. Requirement (1): the content of the component [A] is 20 to 50 parts by mass relative to 100 parts by mass that is the total amount of all of the epoxy resins. Requirement (2): the content of the component [B] is 10 to 40 parts by mass relative to 100 parts by mass that is the total amount of all of the epoxy resins. Requirement (3): the content of the component [C] is 10 to 40 parts by mass relative to 100 parts by mass that is the total amount of all of the epoxy resins. Requirement (4): the component [B] and the component [C] are contained in a total amount of 40 parts by mass or more in 100 parts by mass that is the total amount of all of the epoxy resins. Requirement (5): a component [E] that is a glycidylamine-type epoxy resin is not contained or, if contained, the component [E] is contained in an amount of 10 parts by mass or less relative to 100 parts by mass that is the total amount of all of the epoxy resins.

Description

[Technical Field]

[0001] The present invention relates to prepregs, fiber-reinforced composite materials, and tubular bodies made of fiber-reinforced composite materials, which are suitably used in fiber-reinforced composite materials for aerospace, general industrial, and sports applications, and also to golf club shafts and fishing rods made using said tubular bodies made of fiber-reinforced composite materials. [Background technology]

[0002] Fiber-reinforced composite materials, which use carbon fibers, aramid fibers, and other reinforcing fibers, are widely used in structural materials for aircraft and automobiles, as well as in sports and general industrial applications such as tennis rackets, golf club shafts, fishing rods, bicycles, and housings, due to their high specific strength and specific modulus of elasticity. Thermosetting resins are primarily used as resin compositions for these fiber-reinforced composite materials from the viewpoint of heat resistance and productivity, and epoxy resins are particularly preferred from the viewpoint of mechanical properties such as adhesion to reinforcing fibers.

[0003] In recent years, the application of fiber-reinforced composite materials to applications such as golf club shafts, fishing rods, and bicycles, where further weight reduction is required, necessitates improvements in various physical properties. For example, to achieve excellent bending strength in tubular bodies such as golf club shafts and fishing rods, the fiber-reinforced composite material used requires high strength in both the fiber direction and the non-fiber direction, which is greatly influenced by the strength and elastic modulus of the epoxy resin itself used as the matrix resin. Furthermore, high heat resistance is required to withstand the processing heat when fiber-reinforced composite materials are processed into final products. In addition, there is an increasing trend to use the cross-weave of the reinforcing fibers as a design element by applying a clear coating to the surface of the fiber-reinforced composite material. Therefore, in addition to the excellent mechanical properties and heat resistance of the cured epoxy resin, the weather resistance and transparency of the cured product are also becoming increasingly important.

[0004] Patent Document 1 describes a composition combining oxazolidone-type epoxy resin and novolac-type epoxy resin, which allows for both mechanical properties and heat resistance to be achieved. Patent Document 2 describes a prepreg that uses an epoxy resin composition with a parallel light transmittance of 30% or more, resulting in no clouding due to moisture absorption and an excellent appearance for fiber-reinforced composite materials. Furthermore, Patent Document 3 describes a toupreg that incorporates a dissolution accelerator such as sorbitol-type epoxy resin to reduce defects caused by undissolved dicyandiamide used as a curing agent, resulting in a resin composition with excellent fracture strain and transparency. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2020 / 080474 [Patent Document 2] Japanese Patent Publication No. 2003-261744 [Patent Document 3] Japanese Patent Publication No. 2020-158594 [Overview of the project] [Problems that the invention aims to solve]

[0006] When using the technology described in Patent Document 1, while elastic modulus and heat resistance can be achieved simultaneously, no consideration is given to appearance, such as weather resistance and transparency, and a superior appearance cannot be consistently obtained. Furthermore, when using the technology described in Patent Document 2, although resin cured products with excellent transparency and molded products without clouding due to moisture absorption can be obtained, the elastic modulus of the resin cured product is low, and superior mechanical properties cannot necessarily be obtained in fiber-reinforced composite materials. Moreover, Patent Document 2 does not consider weather resistance at all, and there is room for improvement in terms of weather resistance as well. In Patent Document 3, although resin cured products with excellent transparency can be obtained, the elastic modulus and heat resistance of the resin cured product are low, and superior mechanical properties and heat resistance cannot necessarily be obtained in fiber-reinforced composite materials. Furthermore, Patent Document 3 also does not consider weather resistance at all, and superior weather resistance cannot be consistently obtained.

[0007] Therefore, the object of the present invention is to provide a prepreg made of a resin composition that is excellent in elastic modulus and heat resistance, as well as excellent in appearance such as weather resistance and transparency, and a fiber-reinforced composite material, a tubular body made of fiber-reinforced composite material, a golf club shaft, and a fishing rod using the prepreg that are excellent in mechanical properties, heat resistance, and appearance. [Means for solving the problem]

[0008] 1. A prepreg comprising reinforcing fibers and a resin composition, wherein the resin composition comprises the following components [A] to [D] and satisfies the following conditions (1) to (5). Ingredients [A]: Novolac epoxy resin Ingredients [B]: Oxazolidone-type epoxy resin Ingredients [C]: Either or both sorbitol-type epoxy resin and glycerol-type epoxy resin. Ingredient [D]: Dicyandiamide Condition (1): The content of component [A] is 20 to 50 parts by mass per 100 parts by mass of the total epoxy resin. Condition (2): The content of component [B] is 10 to 40 parts by mass per 100 parts by mass of the total epoxy resin. Condition (3): The content of component [C] is 10 to 40 parts by mass per 100 parts by mass of the total epoxy resin. Condition (4): Of 100 parts by mass of the total epoxy resin, components [B] and [C] together make up 40 parts by mass or more. Condition (5): Component [E]: Does not contain glycidylamine-type epoxy resin, or if it does, it is 10 parts by mass or less per 100 parts by mass of the total epoxy resin. 2. The prepreg according to item 1 above, which does not contain the above-mentioned component [E], or if it does contain it, in an amount of 1 part by mass or less per 100 parts by mass of the total epoxy resin. 3. Component [F]: A prepreg according to 1 or 2 above, comprising a compound having a boiling point of 130°C or higher and a molecular weight m of 50 to 250, which does not have an epoxy group in its molecule and does not have the ability to cure epoxy resins. 4. As the thermoplastic resin, a prepreg according to any one of 1 to 3 above, containing component [G]: phenoxy resin. 5. A fiber reinforced composite material obtained by curing the prepreg according to any one of 1 to 4 above. 6. A tubular body made of a fiber reinforced composite material, obtained by molding the prepreg according to any one of 1 to 4 above. 7. A golf club shaft using the tubular body made of the fiber reinforced composite material according to 6 above. 8. A fishing rod using the tubular body made of the fiber reinforced composite material according to 6 above.

Advantages of the Invention

[0009] According to the present invention, a prepreg made of a resin composition excellent in elastic modulus, heat resistance, and also excellent in appearance such as weather resistance and transparency, and a fiber reinforced composite material, a tubular body made of a fiber reinforced composite material, a golf club shaft, and a fishing rod excellent in mechanical properties, heat resistance, and appearance, using the prepreg can be obtained.

Modes for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described in detail.

[0011] The prepreg of the present invention contains a resin composition and reinforcing fibers. It is preferably composed of a resin composition and reinforcing fibers. The resin composition contains components [A] to [D] as essential components.

[0012] Component [A] in the present invention is a novolac type epoxy resin. By containing component [A], the elastic modulus and heat resistance of the resin cured product are improved without deteriorating the weather resistance, and a fiber reinforced composite material having excellent mechanical properties, heat resistance, and appearance can be obtained.

[0013] It is necessary to contain 20 to 50 parts by mass of component [A] with respect to 100 parts by mass of the total epoxy resin contained in the resin composition. Regarding the lower limit, it is preferably 25 parts by mass or more, more preferably 30 parts by mass or more. Regarding the upper limit, it is preferably 45 parts by mass or less, more preferably 40 parts by mass or less. By containing component [A] within this range, the transparency of the resin cured product is excellent, and the balance of mechanical properties, heat resistance, and appearance is good.

[0014] Also, in order to obtain a good balance between the flexural modulus and heat resistance of the resin cured product, for the novolac type epoxy resin, the softening point is preferably 50°C or higher, more preferably 60°C or higher for the lower limit. Regarding the above softening point, the upper limit is preferably 120°C or lower, more preferably 110°C or lower.

[0015] Examples of component [A] include phenol novolac type epoxy resin and cresol novolac type epoxy resin.

[0016] Examples of commercially available products of phenol novolac type epoxy resin include "jER (registered trademark)" 152, 154 (manufactured by Mitsubishi Chemical Corporation), EPPN-201 (manufactured by Nippon Kayaku Co., Ltd.), "EPICLON (registered trademark)" N-740, N-770 (softening point: 70°C), N-775 (softening point: 75°C, manufactured by DIC Corporation), etc.

[0017] Examples of commercially available products of cresol novolac type epoxy resin include "EPICLON (registered trademark)" N-660 (softening point: 66°C), N-665 (softening point: 70°C), N-670 (softening point: 73°C), N-673 (softening point: 78°C), N-680 (softening point: 87°C), N-690 (softening point: 93°C), N-695 (softening point: 95°C, manufactured by DIC Corporation), etc.

[0018] In this invention, component [B] is an oxazolidone-type epoxy resin. By including component [B], it is possible to improve the heat resistance of the cured resin without impairing weather resistance. Furthermore, by including component [B], the dissolution of component [D], dicyandiamide, can be promoted, improving the transparency of the cured resin. In other words, by including component [B], a fiber-reinforced composite material with excellent heat resistance and appearance can be obtained.

[0019] The resin composition must contain 10 to 40 parts by mass of component [B] per 100 parts by mass of total epoxy resin. The lower limit is preferably 15 parts by mass or more, and more preferably 20 parts by mass or more. The upper limit is preferably 35 parts by mass or less, and more preferably 30 parts by mass or less. If the content of component [B] is above the lower limit, the heat resistance and transparency of the cured resin product will be excellent, and if it is below the upper limit, the flexural modulus of the cured resin product will not be impaired. In other words, by including component [B] within this range, a good balance of transparency, heat resistance, and flexural modulus of the cured resin product is achieved.

[0020] Commercially available components [B] include AER4152, AER4151 (both manufactured by Asahi Kasei E-Materials Corporation), “DER (registered trademark)” 852, 858 (both manufactured by Dow Chemical Ltd.), TSR-400 (manufactured by DIC Corporation), ACR1348 (manufactured by ADEKA Corporation), etc.

[0021] In this invention, component [C] is either a sorbitol-type epoxy resin or a glycerol-type epoxy resin, or both. If both sorbitol-type and glycerol-type epoxy resins are included, they are collectively referred to as component [C]. These may be used individually or in combination. The inclusion of component [C] improves the flexural modulus of the cured resin without impairing weather resistance. Furthermore, because component [C] has hydroxyl groups in its molecular structure, it is highly polar, promoting the dissolution of dicyandiamide, which is component [D], and improving the transparency of the cured resin. In short, the inclusion of component [C] yields a fiber-reinforced composite material with excellent flexural modulus and appearance.

[0022] The resin composition must contain 10 to 40 parts by mass of component [C] per 100 parts by mass of total epoxy resin. Preferably, the lower limit is 15 parts by mass or more, and more preferably 20 parts by mass or more. Preferably, the upper limit is 35 parts by mass or less, and more preferably 30 parts by mass or less. If the component [C] content is above the lower limit, the flexural modulus and transparency of the cured resin are excellent, and if it is below the upper limit, the heat resistance of the cured resin is not impaired. In other words, including component [C] within this range results in a good balance of transparency, heat resistance, and flexural modulus of the cured resin.

[0023] Examples of glycerol-type epoxy resins for component [C] include monoglycerol-type epoxy resins, diglycerol-type epoxy resins, and polyglycerol-type epoxy resins.

[0024] Commercially available sorbitol-type epoxy resins include "Denacol®" EX-612, EX-614, EX-614B, and EX-622 (all manufactured by Nagase ChemteX Corporation).

[0025] Commercially available glycerol-type epoxy resins include "Denacol®" EX-313 and EX-314 (both manufactured by Nagase ChemteX Co., Ltd.). Commercially available diglycerol-type epoxy resins include "Denacol®" EX-421 (manufactured by Nagase ChemteX Co., Ltd.), and commercially available polyglycerol-type epoxy resins include "Denacol®" EX-512 and EX-521 (both manufactured by Nagase ChemteX Co., Ltd.).

[0026] Condition (4) in the present invention requires that the total content of component [B] and component [C] be 40 parts by mass or more per 100 parts by mass of the total epoxy resin. The lower limit is preferably 45 parts by mass or more, and more preferably 50 parts by mass or more. The upper limit is 80 parts by mass or less, which is the sum of the upper limits of each component in conditions (2) and (3), but is preferably 70 parts by mass or less, and more preferably 60 parts by mass or less. By setting the total content of component [B] and component [C] per 100 parts by mass of the total epoxy resin within the above range, the transparency of the cured resin is dramatically improved, and a fiber-reinforced composite material with an excellent appearance (improved opacity) can be obtained.

[0027] Condition (5) in the present invention is that the glycidylamine-type epoxy resin, which is component [E], is either not included, or if it is included, it is 10 parts by mass or less per 100 parts by mass of the total epoxy resin. Furthermore, if component [E] is included, it is more preferable that it be 5 parts by mass or less, and even more preferable that it be 1 part by mass or less. By limiting the amount of component [E] to 10 parts by mass or less, a fiber-reinforced composite material with excellent weather resistance can be obtained without hindering the improvement of the weather resistance of the cured resin product.

[0028] Examples of glycidylamine-type epoxy resins of component [E] include glycidylamine-type epoxy resins having aromatic rings, aliphatic glycidylamine-type epoxy resins, diaminodiphenylmethane-type epoxy resins, diaminodiphenylsulfone-type epoxy resins, aminophenol-type epoxy resins, metaxylenediamine-type epoxy resins, and 1,3-bisaminomethylcyclohexane-type epoxy resins.

[0029] Commercially available diaminodiphenylmethane-type epoxy resins include ELM434 (manufactured by Sumitomo Chemical Co., Ltd.), "Araldite®" MY720, MY721, MY9512, MY9663 (all manufactured by Huntsman Advanced Materials Co., Ltd.), "Epotote®" YH-434 (manufactured by Nippon Steel Chemical & Material Co., Ltd.), and "jER®" 604 (manufactured by Mitsubishi Chemical Corporation).

[0030] Examples of commercially available diaminodiphenylsulfone-type epoxy resins include TG3DAS (manufactured by Mitsui Chemicals Fine, Inc.).

[0031] Commercially available aminophenol-type epoxy resins include ELM120 and ELM100 (both manufactured by Sumitomo Chemical Co., Ltd.), "jER®" 630 (manufactured by Mitsubishi Chemical Corporation), and "Araldite®" MY0500, MY0510, MY0600, and MY0610 (all manufactured by Huntsman Advanced Materials Co., Ltd.).

[0032] A commercially available example of a metaxylenediamine-type epoxy resin is "TETRAD®" -X (manufactured by Mitsubishi Gas Chemical Company, Inc.).

[0033] A commercially available example of a 1,3-bisaminomethylcyclohexane type epoxy resin is "TETRAD®" -C (manufactured by Mitsubishi Gas Chemical Company, Inc.).

[0034] Other epoxy resins may be appropriately blended into the resin composition used in the present invention, as long as they do not impair the effects of the present invention. Specifically, examples include bisphenol type, isocyanuric acid type, dicyclopentadiene type, hydantoin type, trimethylolpropane type, pentaerythritol type, trishydroxyphenylmethane type, and tetraphenyloleethane type epoxy resins.

[0035] Among them, commercially available bisphenol A type epoxy resins include "jER(registered trademark)" 825, 828, 834, 1001, 1002, 1003, 1003F, 1004, 1004AF, 1005F, 1006FS, 1007, 1009, 1010 (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 Co., Ltd.), and "DER(registered trademark)" -331, 332 (both manufactured by Dow Chemical Ltd.).

[0036] Commercially available bisphenol F type epoxy resins include "Araldite®" GY282 (manufactured by Huntsman Advanced Materials Co., Ltd.), "jER®" 806, 807, 4005P, 4007P, 4010P (all manufactured by Mitsubishi Chemical Corporation), "EPICLON®" 830 (manufactured by DIC Corporation), and "Epotote®" YD-170 (manufactured by Nippon Steel Chemical & Material Co., Ltd.).

[0037] Component [D] in the present invention is dicyandiamide. Dicyandiamide is excellent in that it imparts high mechanical properties and heat resistance to the cured epoxy resin product, and is widely used as a curing agent for various epoxy resins. Furthermore, it can be suitably used because it provides excellent weather resistance and storage stability to the epoxy resin composition. Examples of commercially available dicyandiamides include DICY7 and DICY15 (both manufactured by Mitsubishi Chemical Corporation).

[0038] Furthermore, in this invention, the balance of mechanical properties, heat resistance, and transparency of the cured resin is excellent, so the content of component [D] is preferably 4 to 12 parts by mass per 100 parts by mass of the total epoxy resin. The lower limit is more preferably 5 parts by mass or more, and the upper limit is even more preferably 10 parts by mass or less.

[0039] The resin composition used in the prepreg of the present invention preferably contains phenoxy resin as component [G], from the viewpoint of controlling the viscosity of the resin composition and the tack of the prepreg. Phenoxy resin can improve the viscosity of the resin composition and the tack of the prepreg without impairing the weather resistance of the cured resin product, and is therefore preferably included in order to produce a prepreg with excellent handling properties.

[0040] Commercially available phenoxy resins include "Phenotote®" YP-50, YP-50S, and YP-70 (all manufactured by Nippon Steel Chemical & Material Co., Ltd.).

[0041] The resin composition used in the prepreg of the present invention may contain a curing accelerator from the viewpoint of controlling the curing speed. Examples of curing accelerators include urea compounds and imidazole compounds, and urea compounds are particularly preferred from the viewpoint of storage stability of the resin composition.

[0042] 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 PTI Japan Co., Ltd.).

[0043] The resin composition used in the present invention preferably contains a compound [F] which has a boiling point of 130°C or higher and a molecular weight m of 50 to 250, does not have an epoxy group in its molecule, and does not possess the ability to cure epoxy resins, in order to achieve a high elastic modulus of the cured resin. Here, 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 not included in component [F]. Here, "does not possess the ability to cure epoxy resins" means that it does not chemically react with epoxy resins and does not participate in the self-polymerization of epoxy resins.

[0044] Component [F] is thought to exist in the voids of the crosslinked structure formed by the reaction of epoxy resin and dicyandiamide, without being incorporated into the crosslinked structure, and to maintain this state even after the epoxy resin hardens. This is thought to result in a higher elastic modulus of the resulting cured resin. Surprisingly, by incorporating component [F], a cured resin with not only a high elastic modulus but also high elongation and high strength can be obtained.

[0045] Furthermore, having a boiling point of component [F] of 130°C or higher, more preferably 180°C or higher, suppresses the volatilization of component [F] during the curing of the resin composition, resulting in resin cured products and fiber-reinforced composite materials with excellent mechanical properties. Setting the boiling point of component [F] within this range is also preferable because it suppresses the generation of voids and the deterioration of mechanical properties in the resulting fiber-reinforced composite materials. While there is no particular upper limit to the boiling point of component [F], the boiling points of compounds commonly used in this invention are often 400°C or lower.

[0046] Component [F] is preferably present in 1 to 15 parts by mass, more preferably in 2 to 10 parts by mass, and more preferably in 3 to 6 parts by mass, per 100 parts by mass of the total epoxy resin.

[0047] The molecular weight m of component [F] is 50 to 250, more preferably 70 to 120. By setting the molecular weight of component [F] within this range, component [F] is appropriately retained in the voids of the crosslinked structure formed by the reaction of epoxy resin and dicyandiamide, resulting in a cured product with excellent elastic modulus, strength, and elongation.

[0048] In the present invention, component [F] is preferably a compound having at least one functional group selected from the group consisting of an amide group, a ketone group, and a hydroxyl group in its molecule. When component [F] has such a highly polar functional group in its molecule, strong intermolecular interactions act between the hydroxyl groups in the crosslinked structure formed from the epoxy resin and dicyandiamide and component [F], making it easier for component [F] to be properly retained in the voids of the crosslinked structure, thus providing particularly excellent improvements in elongation and strength. Furthermore, when component [F] has such a highly polar functional group, it can promote the dissolution of dicyandiamide, which is component [D], and improve the transparency of the cured resin product.

[0049] Examples of such components [F] 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.

[0050] Preferred reinforcing fibers for 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.

[0051] 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.

[0052] 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.

[0053] The carbon fibers preferably have a tensile modulus in the range of 200 to 440 GPa. The tensile modulus of carbon fibers is influenced by the crystallinity of the graphite structure constituting the carbon fibers; the higher the crystallinity, the higher the modulus. This range is preferable because it allows for a high level of balance between the stiffness and strength of the carbon fiber reinforced composite material. A more preferable modulus is in the range of 230 to 400 GPa, and even more preferably in the range of 260 to 370 GPa. Here, the tensile modulus of carbon fibers is a value measured according to JIS R7601 (2006).

[0054] 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.

[0055] 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.

[0056] 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.

[0057] The fiber-reinforced composite material or fiber-reinforced composite tubular body of the present invention can be manufactured, for example, by laminating the prepreg of the present invention described above in a predetermined form and curing the resin by applying pressure and heat. The method of applying heat and pressure here can be press molding, autoclave molding, bagging molding, wrapping tape method, internal pressure molding, etc.

[0058] 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 tubular bodies such as golf club shafts and fishing rods.

[0059] When the resin composition according to the present invention is used, the cured product has excellent mechanical properties, weather resistance, and transparency, and therefore the fiber-reinforced composite tubular body of the present invention exhibits excellent bending strength, weather resistance, and appearance.

[0060] 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 in structures such as automobiles, ships, and railway vehicles. In sports applications, it is suitably used in golf club shafts, fishing rods, and tennis and badminton rackets. Among these, the tubular body made of fiber-reinforced composite material of the present invention can be suitably used in golf club shafts and fishing rods.

[0061] The upper and lower limits of the numerical ranges described above can be combined in any way unless otherwise specified. [Examples]

[0062] 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.

[0063] <Materials used in the examples and comparative examples> (1) Reinforced fiber "Toreca (registered trademark)" T1100G-24K (24,000 fibers, tensile modulus: 324 GPa, density: 1.8 g / cm³) 3 (Manufactured by Toray Industries, Inc.) (2) Epoxy resin • Components [A]: Novolac-type epoxy resin [A]-1 “EPICLON(registered trademark)” N-775 (phenol novolac type epoxy resin, epoxy equivalent: 189, manufactured by DIC Corporation) [A]-2 “EPICLON(registered trademark)” N-695 (cresol novolac type epoxy resin, epoxy equivalent: 214, manufactured by DIC Corporation) • Components [B]: Oxazolidone-type epoxy resin [B]-1 “DER (registered trademark)” 858 (epoxy equivalent: 400, manufactured by Dow Chemical Ltd.) • Components [C]: Sorbitol-type epoxy resin, glycerol-type epoxy resin [C]-1 “Denacol (registered trademark)” EX-614B (sorbitol-type epoxy resin, epoxy equivalent: 173, manufactured by Nagase ChemteX Co., Ltd.) [C]-2 “Denacol (registered trademark)” EX-512 (polyglycerol-type epoxy resin, epoxy equivalent: 168, manufactured by Nagase ChemteX Corporation) • Components [E]: Glycidylamine-type epoxy resin [E]-1 "Araldite®" MY0600 (aminophenol-type epoxy resin, epoxy equivalent: 118, manufactured by Huntsman Advanced Materials Co., Ltd.) • Components [H]: Other epoxy resins [H]-1 “EPICLON(registered trademark)” 830 (Bisphenol F type epoxy resin, epoxy equivalent: 172, manufactured by DIC Corporation) [H]-2 “Denacol (registered trademark)” EX-411 (pentaerythritol-type epoxy resin, epoxy equivalent: 229, manufactured by Nagase ChemteX Corporation) (3) Component [D]: Dicyandiamide [D]-1 DICY7 (Dicyandiamide, manufactured by Mitsubishi Chemical Corporation) (4) Component [F]: A compound having a boiling point of 130°C or higher and a molecular weight m of 50 to 250, which does not contain an epoxy group in its molecule and does not have the ability to cure epoxy resins. [F]-1 2-Pyrrolidone (Boiling point: 245℃, Molecular weight m: 85, Manufactured by Tokyo Chemical Industry Co., Ltd.) [F]-2 1,2-Propanediol (Boiling point: 188°C, Molecular weight m: 76, Manufactured by Tokyo Chemical Industry Co., Ltd.) (5) Component [G]: Phenoxy resin [G]-1 “Phenotote (registered trademark)” YP-70 (manufactured by Nippon Steel Chemical & Material Co., Ltd.) (6) Curing accelerator DCMU99 (3-(3,4-dichlorophenyl)-1,1-dimethylurea, manufactured by Hodogaya Chemical Co., Ltd.).

[0064] <Method for preparing resin compositions> (1) Preparation of the hardener master Ten parts by mass of epoxy resin (which is liquid at room temperature and consists of [C]-1, [C]-2, [H]-1, and [H]-2) were prepared (10 parts by mass per 100 parts by mass of all epoxy resins). Dicyandiamide, which is component [D], was added to each of these and kneaded at room temperature. The mixture was passed through a three-roll mill twice to prepare a curing agent master.

[0065] (2) Preparation of resin composition The remaining 90 parts by mass of epoxy resin, excluding the 10 parts by mass of liquid epoxy resin used in (1) above, were placed in a beaker. While kneading, the temperature was raised to 150°C, then component [G]: phenoxy resin was added, and the mixture was heated and kneaded at 150°C for 1 hour to dissolve it. Next, while continuing to knead, the temperature was lowered to 55-65°C, then the curing agent master prepared in (1) above, component [F] in the components and amounts shown in the table, and the curing accelerator were added, and the mixture was kneaded at the same temperature for 30 minutes to obtain the resin composition. Tables 1 to 5 show the compositions of each example and comparative example.

[0066] <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.

[0067] Furthermore, for visual evaluation, the curing reaction was carried out in a mold set to a thickness of 1 mm using a 1 mm thick "Teflon®" spacer, to obtain a 1 mm thick plate-shaped cured resin product.

[0068] <Prepreg preparation method> The resin composition prepared according to the above <Method for preparing the resin composition> is applied to release paper using a knife coater, and the resin basis weight is 31 g / m².2 Two resin films were prepared. Next, the fiber weight was 125 g / m². 2 The above-mentioned resin film was placed on each of the two sides of a sheet of reinforcing fibers (the above-mentioned "Torayca (registered trademark)" T1100G-24K) arranged in one direction, and the resin composition was impregnated by heating and pressurizing under conditions of a temperature of 110°C and a maximum pressure of 2 MPa to obtain a prepreg.

[0069] <Various Evaluation Methods> (1) Three-point bending measurement of cured resin From the 2 mm thick resin cured material prepared according to the above <Method for Preparing Resin Cured Materials>, test pieces measuring 10 mm in width and 60 mm in length were cut out. Using an Instron universal testing machine (manufactured by Instron), with a span of 32 mm, a crosshead speed of 2.5 mm / min, and a sample size of n=6, three-point bending was performed according to JIS K7171 (1994). The average value of the elastic modulus of each test piece was used as the flexural modulus of the resin cured material.

[0070] (2) Measurement of glass transition temperature of cured resin A test specimen measuring 12.7 mm in width and 55 mm in length was cut from a 2 mm thick resin cured material prepared according to the above-described method for preparing cured resin. A viscoelasticity analyzer (ARES, manufactured by T.A. Instruments) was used to measure the glass transition temperature of this specimen under conditions of a torsional vibration frequency of 1.0 Hz and a heating rate of 5.0 °C / min, within a temperature range of 40 to 250 °C. The glass transition temperature was then determined. The glass transition temperature was defined as the temperature at the intersection of the tangent line in the glassy state and the tangent line in the transition state on the storage modulus G' curve.

[0071] (3) Evaluation of the transparency of the cured resin product A 1mm thick resin cured object, prepared according to the above <Method for Preparing Resin Cured Objects>, was placed on a piece of paper with writing on it, and a person with visual acuity of approximately 1.0, as measured using a Landolt ring, checked the transparency of the resin cured object. A indicated that the writing was clearly legible, as before the resin cured object was placed; B indicated that it was faintly legible; and C indicated that the writing was illegible.

[0072] (4) Weather resistance test of the resin cured product From the resin cured product with a thickness of 1 mm prepared according to the above <Method for producing resin cured product>, test pieces with a width of 37 mm and a length of 68 mm were cut out. Using an accelerated weather resistance tester (Super Xenon Weather Meter SX-75, manufactured by Suga Test Instruments Co., Ltd.) for this test piece, with an intensity of 180 W / m 2 , black panel temperature of 63 °C, and humidity of 50% RH, irradiation for 102 minutes without water injection, and an intensity of 180 W / m 2 , with a tank temperature of 28 °C and humidity of 99% RH, irradiation for 18 minutes while injecting water were taken as one cycle, and a weather resistance test was repeated 12 times (i.e., 24 hours).

[0073] The evaluation of weather resistance was carried out by measuring the color difference (ΔE) of the cured product before and after the weather resistance test using a multi-source spectrophotometer MSC-P (manufactured by Suga Test Instruments Co., Ltd.). The tristimulus values (L * , a * , b * ) were obtained by the reflection method under the optical conditions of D65 light source, 10° field of view, and d / 8 excluding regular reflection light. Using the differences in tristimulus values (ΔL * , Δa * , Δb * ) before and after the weather resistance test, the color difference (ΔE) was calculated by the following formula (I).

[0074] ΔE = {(ΔL * ) 2 + (Δa * ) 2 + (Δb * ) 2} 1 / 2 ···(I).

[0075] (5) Weather resistance test of the fiber reinforced composite material Twenty plies of prepreg prepared using the method described above were laminated with the fiber direction aligned. The material was heated in an autoclave under a pressure of 0.7 MPa from 30°C to 90°C at a rate of 1.7°C / min, held at 90°C for 60 minutes, then heated to 135°C at a rate of 2.0°C / min and molded at 135°C for 120 minutes to produce a 2 mm thick unidirectional CFRP board. A test piece measuring 37 mm wide and 68 mm long was cut from the board. This test piece was placed outdoors in a location without a roof and not shaded while the sun was out, and left for two months to conduct a weather resistance test. The test pieces before and after the weather resistance test were placed side by side, and 10 subjects were asked about the difference in color. If 8 or more subjects answered "no change in color" or "no change in color," it was marked as "○," and if 3 or more subjects answered "there is a change in color," it was marked as "×."

[0076] <Example 1> A resin composition was prepared using the following epoxy resins: 35 parts by mass of “EPICLON®” N-775 as component [A], 25 parts by mass of “DER®” 858 as component [B], 20 parts by mass of “Denacol®” EX-614B as component [C], 20 parts by mass of “EPICLON®” 830 as other epoxy resin (component [H]), 5.8 parts by mass of DICY7 as dicyandiamide as component [D], 3 parts by mass of “Phenotote®” YP-70 as phenoxy resin as component [G], and 3 parts by mass of DCMU99 as a curing accelerator, according to the above <Method for preparing the resin composition>.

[0077] A cured resin product was prepared from the obtained resin composition according to the <Method for Preparing Cured Products>. The flexural modulus, glass transition temperature, transparency, and weather resistance (color difference ΔE) of this cured resin product were measured. The flexural modulus was 4.0 GPa, the glass transition temperature was 140°C, the transparency was A, and the color difference ΔE was 6.7, indicating that the physical properties and appearance of the cured resin product were good.

[0078] Furthermore, a prepreg was prepared from the obtained resin composition according to the <Prepreg Preparation Method>, and measured according to "(5) Weather Resistance of Fiber-Reinforced Composite Materials" in <Various Evaluation Methods>. The weather resistance of the fiber-reinforced composite material was found to be good.

[0079] <Examples 2-14> Except for the changes in composition shown in Table 1, the resin cured product and prepreg were prepared in the same manner as in Example 1. For each example, the flexural modulus, glass transition temperature, transparency, weather resistance (color difference ΔE) of the resin cured product, and the weather resistance of the fiber-reinforced composite material were as shown in Table 1, and all were good.

[0080] <Comparative Example 1> The compositions shown in Table 2 were used to prepare the cured resin and prepreg using the same method as in Example 1. The results of the physical property evaluation are shown in Table 1 (the same applies to the following comparative examples). The transparency and weather resistance of the cured resin and the weather resistance of the fiber-reinforced composite material were good. However, the content of component [A] was less than 20 parts by mass in 100 parts by mass of total epoxy resin, and condition (1) was not met, so the flexural modulus and glass transition temperature of the cured resin were lower than in Example 5.

[0081] <Comparative Example 2> The compositions shown in Table 3 were used to prepare the cured resin and prepreg using the same method as in Example 1. The flexural modulus, glass transition temperature, and weather resistance of the cured resin, as well as the weather resistance of the fiber-reinforced composite material, were good. However, the content of component [A] exceeded 50 parts by mass in 100 parts by mass of the total epoxy resin, failing to meet condition (1), resulting in poorer transparency of the cured resin compared to Example 6.

[0082] <Comparative Example 3> The compositions shown in Table 4 were used to prepare the cured resin and prepreg using the same method as in Example 1. The flexural modulus, transparency, and weather resistance of the cured resin and the weather resistance of the fiber-reinforced composite material were good. However, the content of component [B] was less than 10 parts by mass per 100 parts by mass of total epoxy resin, and condition (2) was not met, resulting in a lower glass transition temperature compared to Example 8.

[0083] <Comparative Example 4> The resin cured product and prepreg were prepared using the composition shown in Table 2 and the same method as in Example 1. The glass transition temperature, transparency, and weather resistance of the resin cured product, and the weather resistance of the fiber-reinforced composite material were good. However, the content of component [B] exceeded 40 parts by mass in 100 parts by mass of total epoxy resin, failing to meet condition (2), resulting in a lower flexural modulus of the resin cured product compared to Example 5. <Comparative Example 5> The compositions shown in Table 2 were used to prepare the cured resin and prepreg using the same method as in Example 1. The glass transition temperature, transparency, and weather resistance of the cured resin, as well as the weather resistance of the fiber-reinforced composite material, were good. However, the content of component [C] was less than 10 parts by mass per 100 parts by mass of the total epoxy resin, and condition (3) was not met, resulting in a lower flexural modulus compared to Example 5.

[0084] <Comparative Example 6> The compositions shown in Table 4 were used to prepare the cured resin and prepreg using the same method as in Example 1. The flexural modulus, transparency, and weather resistance of the cured resin and the weather resistance of the fiber-reinforced composite material were good. However, the content of component [C] exceeded 40 parts by mass in 100 parts by mass of the total epoxy resin, failing to meet condition (3), resulting in a lower glass transition temperature of the cured resin compared to Example 8.

[0085] <Comparative Example 7> The compositions shown in Table 3 were used to prepare the cured resin and prepreg using the same method as in Example 1. The flexural modulus, glass transition temperature, and weather resistance of the cured resin, as well as the weather resistance of the fiber-reinforced composite material, were good. However, the combined content of components [B] and [C] was less than 40 parts by mass per 100 parts by mass of total epoxy resin, failing to meet condition (4), resulting in poorer transparency of the cured resin compared to Example 6.

[0086] <Comparative Example 8> The compositions shown in Table 4 were used to prepare the cured resin and prepreg using the same method as in Example 1. The flexural modulus, transparency, and weather resistance of the cured resin and the weather resistance of the fiber-reinforced composite material were good. However, the content of component [C] exceeded 40 parts by mass per 100 parts by mass of total epoxy resin, failing to meet condition (3), and the content of component [A] was less than 20 parts by mass, failing to meet condition (1). As a result, the glass transition temperature of the cured resin was lower than that of Example 9.

[0087] <Comparative Example 9, Comparative Example 10> The resin cured product and prepreg were prepared using the composition shown in Table 5 and the same method as in Example 1. The glass transition temperature, transparency, and weather resistance of the resin cured product, and the weather resistance of the fiber-reinforced composite material were good. However, because component [C] was not included and condition (3) was not met, the flexural modulus was lower than that of all examples.

[0088] <Comparative Example 11> The resin cured product and prepreg were prepared using the composition shown in Table 5 and the same method as in Example 1. The flexural modulus, glass transition temperature, and weather resistance of the resin cured product, as well as the weather resistance of the fiber-reinforced composite material, were good. However, because component [C] was not included and condition (3) was not met, the transparency was poorer compared to all examples.

[0089] <Comparative Example 12> The composition shown in Table 3 was used to prepare the cured resin and prepreg using the same method as in Example 1. The flexural modulus, glass transition temperature, and weather resistance of the cured resin, as well as the weather resistance of the fiber-reinforced composite material, were good. However, although component [C] was not included and instead a pentaerythritol-type epoxy resin (an aliphatic epoxy resin without hydroxyl groups) was included, this did not satisfy condition (3), resulting in poorer transparency compared to Example 6.

[0090] <Comparative Example 13> The resin cured product and prepreg were prepared using the composition shown in Table 3 and the same method as in Example 1. The flexural modulus, glass transition temperature, and transparency of the resin cured product were good. However, the content of component [E] exceeded 10 parts by mass in 100 parts by mass of total epoxy resin, failing to meet condition (5). As a result, the weather resistance of the resin cured product and the fiber-reinforced composite material were poorer compared to Example 6 and Example 10.

[0091] <Comparative Example 14> The resin cured product and prepreg were prepared using the composition shown in Table 2 and the same method as in Example 1. The glass transition temperature, transparency, and weather resistance of the resin cured product, and the weather resistance of the fiber-reinforced composite material were good. However, because component [D] was not included, the flexural modulus of the resin cured product was lower than that of Example 5.

[0092] <Comparative Example 15> The compositions shown in Table 3 were used to prepare the cured resin and prepreg using the same method as in Example 1. The flexural modulus, glass transition temperature, and weather resistance of the cured resin, as well as the weather resistance of the fiber-reinforced composite material, were good. However, the combined content of components [B] and [C] was less than 40 parts by mass per 100 parts by mass of total epoxy resin, failing to meet condition (4), resulting in poorer transparency of the cured resin compared to Example 6.

[0093] [Table 1]

[0094] [Table 2]

[0095] [Table 3]

[0096] [Table 4]

[0097] Table 5

Claims

1. A prepreg comprising reinforcing fibers and a resin composition, wherein the resin composition comprises the following components [A] to [D] and satisfies the following conditions (1) to (5). Ingredients [A]: Novolac-type epoxy resin Component [B]: Oxazolidone type epoxy resin Components [C]: Either or both sorbitol-type epoxy resin and glycerol-type epoxy resin. Ingredient [D]: Dicyandiamide Condition (1): The content of component [A] is 20 to 50 parts by mass per 100 parts by mass of the total epoxy resin. Condition (2): The content of component [B] is 10 to 40 parts by mass per 100 parts by mass of the total epoxy resin. Condition (3): The content of component [C] is 10 to 40 parts by mass per 100 parts by mass of the total epoxy resin. Condition (4): Of the 100 parts by mass of the total epoxy resin, components [B] and [C] together comprise at least 40 parts by mass. Condition (5): Component [E]: Does not contain glycidylamine-type epoxy resin, or if it does, it is 10 parts by mass or less per 100 parts by mass of the total epoxy resin.

2. The prepreg according to claim 1, which does not contain the aforementioned component [E], or if it does contain it, in an amount of 1 part by mass or less per 100 parts by mass of the total epoxy resin.

3. Furthermore, the prepreg according to claim 1, comprising component [F]: a compound having a boiling point of 130°C or higher and a molecular weight m of 50 or more and 250 or less, which does not have an epoxy group in its molecule and does not have the ability to cure epoxy resins.

4. The prepreg according to claim 1, comprising component [G]: phenoxy resin as the thermoplastic resin.

5. A fiber-reinforced composite material obtained by curing a prepreg according to any one of claims 1 to 4.

6. A tubular body made of fiber-reinforced composite material, obtained by molding a prepreg according to any one of claims 1 to 4.

7. A golf club shaft comprising a tubular body made of fiber-reinforced composite material as described in claim 6.

8. A fishing rod comprising a tubular body made of fiber-reinforced composite material as described in claim 6.

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