Method for manufacturing tubular body of fiber-reinforced composite material, tubular body of fiber-reinforced composite material, golf club shaft, and fishing rod

Abstract

To provide a tubular body which is a fiber-reinforced composite material using reinforcing fibers and a matrix resin, is lightweight and has excellent static bending strength, and to provide a golf club shaft and a fishing rod using the same.SOLUTION: A method for manufacturing a fiber-reinforced composite tubular body obtained by laminating a plurality of prepregs containing reinforcing fibers and an epoxy resin composition and curing the laminated prepregs, wherein the plurality of laminated prepregs have a difference in tensile modulus of the reinforcing fibers contained therein of at most 10% and an average value of flexural moduli of the epoxy resin compositions contained therein as cured products thereof of 4.0 GPa or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a tubular body made of a fiber-reinforced composite material using reinforcing fibers and a matrix resin, a method for producing the same, and a golf club shaft and a fishing rod using the tubular body. [Background technology]

[0002] Fiber-reinforced composite materials, which use carbon fiber, aramid fiber, or other reinforcing fibers, are widely used in structural materials for aircraft and automobiles, as well as in sports and general industrial applications such as golf club shafts, fishing rods, bicycles, and housings, due to their high specific strength and specific modulus. Among these applications, sports applications are one in which an extremely low level of lightness is required.

[0003] This fiber-reinforced composite material is composed of reinforcing fibers and a matrix resin. The resin composition used for the matrix resin is mainly a thermosetting resin from the viewpoints of heat resistance and productivity, and among these, epoxy resin is preferably used from the viewpoint of mechanical properties such as adhesion to the reinforcing fibers.

[0004] Various methods are used to produce fiber-reinforced composite materials, but a widely used method uses prepregs, which are sheet-like intermediate substrates made of reinforcing fibers impregnated with a resin composition. A fiber-reinforced composite material can be obtained as a molded product by stacking multiple prepregs and then heating them. The prepreg method has the advantage of being able to precisely control the orientation of the reinforcing fibers and offering a high degree of freedom in designing the laminate structure, making it easy to obtain high-performance fiber-reinforced composite materials. Therefore, it is widely used in the molding of fiber-reinforced composite tubular bodies that pursue ultimate performance, such as golf club shafts and fishing rods.

[0005] The use of carbon fiber reinforced composite materials in tubular bodies such as golf club shafts and fishing rods has led to progress in weight reduction. However, a certain level of mechanical strength, particularly high static bending strength to withstand flexural deformation, is required as a prerequisite. To date, there has been a trend toward improving static bending strength by combining reinforcing fibers with matrix resins or by improving the performance of each.

[0006] For example, Patent Document 1 studies a fiber-reinforced composite tubular body having sufficient static bending strength by using a prepreg that combines carbon fiber with specific properties and an epoxy resin that exhibits an excellent flexural modulus after curing. Patent Document 2 studies a tubular composite material that exhibits excellent fracture strength by using a prepreg that uses a specific epoxy resin and a radically polymerizable monomer as the matrix resin. Patent Document 3 studies a golf club shaft in which the crosslink density of the epoxy resin component is controlled to enhance the effect of compounding with the reinforcing fiber, and the strength and modulus of the resin component are increased, thereby further improving mechanical strength. In addition, Patent Document 4 studies a method for suppressing delamination and improving the strength of a fiber-reinforced plastic tubular body by disposing a resin layer formed from an epoxy resin composition at least partially between the laminate layers of the prepreg. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-74009 [Patent Document 2] Japanese Patent Application Publication No. 2019-157056 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-012996 [Patent Document 4] Japanese Patent Application Laid-Open No. 2016-87460 Summary of the Invention [Problem to be solved by the invention]

[0008] When the techniques of Patent Document 1 or Patent Document 2 are used, sufficient bending properties of the tubular body made of fiber-reinforced composite material are obtained, but a higher level of bending strength is required. When the techniques of Patent Document 3 or Patent Document 4 are used, a higher level of bending strength is also required for the tubular body made of fiber-reinforced composite material.

[0009] Therefore, an object of the present invention is to provide a tubular body that is a fiber-reinforced composite material using reinforcing fibers and a matrix resin, which is lightweight and has excellent static bending strength, and a golf club shaft and a fishing rod that use the same. [Means for solving the problem]

[0010] The present invention employs the following means to solve the above problems. 1. A method for producing a tubular fiber-reinforced composite material body obtained by laminating and curing a plurality of prepregs containing reinforcing fibers and an epoxy resin composition, A method for producing a fiber-reinforced composite tubular body, wherein the difference in tensile modulus of the reinforcing fibers contained in each of the laminated prepregs is at most 10% or more, and the average flexural modulus of the epoxy resin composition contained in each prepreg when cured is 4.0 GPa or more. 2. In each prepreg, the reinforcing fibers are oriented in one direction, A method for producing a fiber-reinforced composite tubular body described in 1 above, in which each prepreg is laminated so that the reinforcing fibers are oriented in two or more directions of 0°, 90°, and ±45° relative to the axial direction of the tubular body. 3. A method for producing a fiber-reinforced composite tubular body according to claim 2, wherein the difference in tensile modulus of the reinforcing fibers contained in a prepreg in which the reinforcing fibers are oriented at ±45° to the axial direction of the tubular body and a prepreg in which the reinforcing fibers are oriented at 0° to the axial direction of the tubular body is at most 10% or more. 4. The method for producing a fiber-reinforced composite tubular body according to any one of 1 to 3 above, wherein the laminated prepregs each contain an epoxy resin composition that, when cured, has a standard deviation of flexural modulus of 0.3 GPa or less. 5. The method for producing a fiber-reinforced composite tubular body according to any one of the above 1 to 4, wherein the epoxy resin composition contained in at least one layer of the laminated prepregs contains the component [A']. Component [A']: At least one of glycidylamine type epoxy resin or isocyanuric acid type epoxy resin [Effects of the Invention]

[0011] According to the present invention, a tubular body that is made of a fiber-reinforced composite material using reinforcing fibers and a matrix resin and that is lightweight and has excellent static bending strength, as well as a golf club shaft and a fishing rod that use the same, can be obtained. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below.

[0013] The fiber-reinforced composite tubular body of the present invention is produced by laminating and curing a plurality of prepregs containing reinforcing fibers and an epoxy resin composition.

[0014] Preferred examples of the reinforcing fibers used in the prepreg of the present invention include carbon fibers, graphite fibers, aramid fibers, and glass fibers, with carbon fibers being particularly preferred. Specific examples of carbon fibers include acrylic, pitch, and rayon carbon fibers, with acrylic carbon fibers, which have particularly high tensile strength, being preferred. It is also possible to use a combination of two or more types of carbon fibers, glass fibers, aramid fibers, boron fibers, PBO fibers, high-strength polyethylene fibers, alumina fibers, and silicon carbide fibers as reinforcing fibers.

[0015] The carbon fibers may be in the form of unidirectionally aligned long fibers, a single tow, woven fabric, etc., and may be twisted yarn, untwisted yarn, non-twisted yarn, etc. In the case of twisted yarn, the filaments constituting the carbon fiber are not oriented parallel to one another, which can cause a decrease in the mechanical properties of the resulting carbon fiber reinforced composite material. Therefore, untwisted yarn or non-twisted yarn, which provide a good balance between the formability and strength properties of the carbon fiber reinforced composite material, is preferably used.

[0016] The reinforcing fibers of the present invention preferably have a tensile modulus of 200 to 500 GPa (i.e., 200 GPa or more and 500 GPa or less). Within this range, the stiffness and strength of the fiber-reinforced composite material are well balanced. The tensile modulus is more preferably 230 GPa or more and 400 GPa or less, and even more preferably 260 GPa or more and 400 GPa or less. Here, the tensile modulus of the reinforcing fibers is a value measured in accordance with JIS R7608 (2008).

[0017] Furthermore, the reinforcing fibers of the present invention preferably have a tensile strength of 4,000 to 8,000 MPa. If the tensile strength is in the range equal to or greater than the lower limit, the reinforcing fiber reinforced composite material is less likely to break upon impact. The higher the tensile strength, the more preferable it is, but at present, it is not necessarily easy to obtain reinforcing fibers with a tensile strength exceeding 8,000 MPa. However, if reinforcing fibers with higher tensile strength become more readily available in the future, they will be preferably applicable.

[0018] The epoxy resin composition used in each prepreg of the present invention preferably contains components [A] and [B]. In this invention, "component" refers to the individual compounds contained in the composition. Furthermore, with regard to certain physical properties, characteristics, or composition ratios, regardless of the characteristics of the resin composition, any upper limit value and any lower limit value of the numerical ranges listed below can be arbitrarily combined, or a single numerical range that is not combined, can be said to be a preferred range, unless otherwise specified.

[0019] The component [A] of the epoxy resin composition of the present invention is an epoxy resin. The component [A] preferably contains two or more epoxy groups per molecule, because this increases the glass transition temperature of the cured product obtained by heat-curing the resin composition and improves heat resistance. An epoxy resin containing one epoxy group per molecule may also be blended. These epoxy resins may be used alone or in combination.

[0020] Examples of epoxy resins for component [A] include glycidylamine-type epoxy resins such as diaminodiphenylmethane-type, diaminodiphenylsulfone-type, aminophenol-type, meta-xylenediamine-type, 1,3-bisaminomethylcyclohexane-type, and glycidylaniline-type; glycidyl ether-type epoxy resins such as bisphenol-type, phenol novolac-type, orthocresol novolac-type, trishydroxyphenylmethane-type, tetraphenylolethane-type, and oxazolidone-type; glycidyl ester-type epoxy resins such as terephthalic acid-type and phthalic acid-type; and isocyanuric acid-type epoxy resins. However, epoxy compounds other than those mentioned above may also be blended as appropriate.

[0021] The epoxy resin composition contained in at least one layer of the laminated prepregs preferably contains, as the component [A'] of the component [A] of the present invention, at least one of a glycidylamine-type epoxy resin and an isocyanuric acid-type epoxy resin, from the viewpoint of improving the bending strength of the fiber-reinforced composite tubular body. The component [A'] is preferably contained in 20 parts by mass or more, more preferably 30 parts by mass or more, of 100 parts by mass of the component [A]. By containing 20 parts by mass or more of the component [A'], the elastic modulus of the epoxy resin composition when cured is likely to be improved, and a high bending strength of the fiber-reinforced composite tubular body is likely to be obtained. Furthermore, from the viewpoint of the handleability of the prepreg, the component [A'] is preferably contained in 90 parts by mass or less, more preferably 80 parts by mass or less, of 100 parts by mass of the component [A].

[0022] The component [B] of the epoxy resin composition of the present invention is a polyamine curing agent, which has an amino group capable of reacting with an epoxy group and functions as a curing agent.

[0023] Examples of polyamine curing agents include aliphatic polyamines and aromatic polyamines. These polyamine curing agents may be used alone or in combination. Examples of aliphatic polyamines include chain aliphatic polyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and diethylaminopropylamine; cyclic aliphatic polyamines such as isophoronediamine and bis(4-aminocyclohexyl)methane; aliphatic aromatic polyamines such as orthoxylenediamine, metaxylenediamine, and paraxylenediamine; and dicyandiamide. Examples of aromatic polyamines include diethyltoluenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, and derivatives thereof.

[0024] In view of effectively improving the pot life of the resin composition, it is a preferred embodiment to use a solid curing agent, and it is particularly preferred to use at least one of dicyandiamide, 3,3'-diaminodiphenyl sulfone, and 4,4'-diaminodiphenyl sulfone.

[0025] The amount of polyamine curing agent used in the present invention is preferably such that the ratio H / E, where E is the number of moles of epoxy groups in component [A] and H is the number of moles of active hydrogen in the polyamine curing agent, is 0.20 or more and 1.30 or less, more preferably 0.30 or more and 1.20 or less, and even more preferably 0.50 or more and 1.10 or less. By keeping H / E within this range, a crosslinked structure can be appropriately formed by the reaction between the epoxy resin and the polyamine curing agent, and a cured resin product with excellent strength can be obtained.

[0026] The epoxy resin composition of the present invention may contain a curing accelerator as component [B'] in order to control the curing rate. Examples of the curing accelerator include urea compounds and imidazole compounds, and urea compounds are particularly preferred in terms of the storage stability of the epoxy resin composition.

[0027] The urea compound is preferably an aromatic urea compound, and examples thereof include 3-(3,4-dichlorophenyl)-1,1-dimethylurea, 3-(4-chlorophenyl)-1,1-dimethylurea, phenyldimethylurea, and toluenebisdimethylurea.

[0028] Furthermore, the epoxy resin composition according to the present invention preferably contains, as component [C], a compound having a boiling point of 180°C or higher and a molecular weight m of 50 to 250 g / mol, which does not contain an epoxy group in its molecule and is incapable of curing epoxy resins. In the present invention, a compound incapable of curing epoxy resins refers to a compound that is substantially unreactive with either epoxy resins or polyamine curing agents. Whether or not a compound is substantially reactive with epoxy resins and polyamine curing agents can be confirmed by differential scanning calorimetry (DSC) of a mixture of component [C] and epoxy resin, or component [C] and polyamine curing agent, in equimolar amounts. A Pyris1 DSC (manufactured by PerkinElmer) can be used as a measuring device. The mixture is placed in an aluminum sample pan and subjected to measurement at a heating rate of 10°C / min from 0°C to 150°C under a nitrogen atmosphere. The presence or absence of reactivity can be determined by observing whether or not a reaction exotherm is observed in the resulting DSC curve. However, if the above components contain a compound with a boiling point of less than 150°C, confirmation is made by observing whether or not reaction heat is generated between 0°C and the boiling point.

[0029] In the crosslinked structure formed by the reaction of the epoxy resin with the polyamine curing agent, the component [C] is not incorporated into the crosslinked structure but exists in the voids therein, and this state is maintained even after curing. By including the component [C], it is easy to obtain a cured epoxy resin product with an excellent elastic modulus. The component [C] may be a single compound or a suitable blend of multiple compounds.

[0030] Constituent element [C] is preferably a compound having at least one functional group selected from the group consisting of an alcoholic hydroxyl group, an amide group, a ketone group, an ether group, a sulfoxide group, an imide group, and an ester group in the molecule, and more preferably a compound having at least one functional group selected from the group consisting of an alcoholic hydroxyl group, an amide group, and a ketone group. When constituent element [C] has such a highly polar functional group in the molecule, strong intermolecular interactions occur between the hydroxyl groups in the crosslinked structure formed from constituent element [A] and constituent element [B], making it easier for constituent element [C] to be properly held in the voids of the crosslinked structure, resulting in a particularly excellent effect of improving the elastic modulus.

[0031] The boiling point of the component [C] is 180°C or higher. If the boiling point of the component [C] is lower than 180°C, the component [C] is likely to volatilize when the epoxy resin composition is cured, resulting in poor mechanical properties. From the viewpoint of suppressing the generation of voids and the deterioration of mechanical properties in the cured product, the boiling point of the component [C] is preferably 200°C or higher, and more preferably 230°C or higher. Furthermore, from the viewpoint of compatibility with the epoxy resin and the curing agent, the boiling point of the component [C] is preferably 400°C or lower. In the present invention, the boiling point is a value at normal pressure (101 kPa). Furthermore, if the boiling point at normal pressure cannot be measured, the converted boiling point converted to 101 kPa using a boiling point conversion chart can be used.

[0032] The molecular weight of the component [C] is preferably 50 to 250. If the molecular weight of the component [C] exceeds 250, the component [C] is less likely to be properly retained in the voids of the crosslinked structure formed by the reaction of the epoxy resin and the polyamine curing agent, and the resulting cured product may have a poor modulus of elasticity. From the viewpoint of obtaining a cured product with excellent flexural modulus and strength, the molecular weight of the component [C] is more preferably 150 or less, and even more preferably 120 or less. Furthermore, from the viewpoint of properly retaining the component [C] in the voids of the crosslinked structure, the molecular weight of the component [C] is more preferably 70 or more, and even more preferably 80 or more.

[0033] From the viewpoints of the elastic modulus of the cured product and the viscoelasticity of the resin composition, the component [C] is contained in an amount of preferably 2 to 12 parts by mass, more preferably 3 to 10 parts by mass, and even more preferably 3 to 8 parts by mass per 100 parts by mass of the component [A].

[0034] From the viewpoint of achieving excellent static bending strength for the tubular body of the present invention, one preferred embodiment is to use an epoxy resin composition containing component [C] in at least the prepreg used for the 0° layer of the tubular body described below.

[0035] Furthermore, from the viewpoint of controlling the viscoelasticity of the epoxy resin composition, the epoxy resin composition of the present invention preferably contains a thermoplastic resin as component [D].

[0036] Examples of thermoplastic resins that can be used as component [D] in the present invention include polyamide, polycarbonate, polyphenylene oxide, polyphenylene sulfide, polyamideimide, polyimide, polyetherimide, polysulfone, polyethersulfone, polyetherketone, polyetheretherketone, polyethernitrile, polyvinyl acetal, polyvinyl formal, etc. Among these, polyetherimide, polysulfone, polyethersulfone, polyvinyl acetal, and polyvinyl formal are preferred because they have good compatibility with epoxy resins and can easily produce uniform cured products.

[0037] From the viewpoint of tackiness during prepreg lamination, the content of component [D] is preferably 2 to 20 parts by mass, more preferably 3 to 15 parts by mass, and even more preferably 5 to 12 parts by mass, relative to 100 parts by mass of component [A].

[0038] The epoxy resin composition contained in each prepreg of the present invention preferably has a flexural modulus of 3.0 to 5.5 GPa, more preferably 4.0 to 5.2 GPa, and even more preferably 4.5 to 5.2 GPa, when cured. Such a cured product is obtained by heating the epoxy resin composition from room temperature to 130°C at a heating rate of 1.5°C / min, and then curing at 130°C for 2 hours. Using a prepreg containing an epoxy resin composition having a flexural modulus within the above range tends to improve the static bending strength of the resulting fiber-reinforced composite tubular body. The flexural modulus of the cured product is measured in accordance with JIS K7171 (2016).

[0039] The epoxy resin composition of the present invention can be formed into a sheet by various methods to produce an epoxy resin film. For example, a method can be used in which the epoxy resin composition is dissolved in an organic solvent such as acetone, methyl ethyl ketone, or methanol to reduce the viscosity, and then coated on release paper, and the organic solvent is then evaporated to obtain a resin film, or a method can be used in which the viscosity is reduced by heating without using an organic solvent, and then the composition is coated on release paper to obtain a resin film.

[0040] The weight of the resin film is 15 to 150 g / m 2 The weight of the resin film is preferably 15 to 150 g / m 2 By setting the resin content within this range, a sufficient amount of resin can be ensured in the prepreg when the reinforcing fibers are impregnated to form a prepreg, making it easier to ensure tackiness of the prepreg.

[0041] The prepreg according to the present invention is in the form of a reinforcing fiber impregnated with an epoxy resin composition in advance, and can be produced by various known methods. For example, the prepreg can be produced by a hot melt method in which a resin composition is heated to reduce its viscosity and then impregnated into the reinforcing fiber without using an organic solvent. The hot melt method is preferred because it is less likely to produce voids in the molded product than a wet method that uses an organic solvent.

[0042] As the hot melt method, a method in which a resin composition whose viscosity has been reduced by heating is directly impregnated into reinforcing fibers, or a method in which a resin film with release paper is first prepared by coating the resin composition on release paper or the like, and then the resin film side 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, can be used.

[0043] It should be noted that the prepregs according to the present invention are not limited to those in which the reinforcing fiber layer is completely impregnated with the epoxy resin composition, but those in which the reinforcing fiber layer is partially impregnated, more specifically, those in which the surface layer or the reinforcing fiber layer is partially impregnated so that the epoxy resin composition and the reinforcing fibers can be handled as a single unit, are also considered to be prepregs. In other words, those in which the reinforcing fiber layer is at least partially impregnated with the epoxy resin composition are considered to be prepregs according to the present invention.

[0044] Each prepreg according to the present invention has a reinforcing fiber weight per unit area of ​​30 to 150 g / m 2 It is more preferable that the density is 30 to 130 g / m 2 By setting the amount of reinforcing fibers within the above range, the drapeability of the prepreg and the number of layers to be laminated to obtain a predetermined thickness when molding a fiber-reinforced composite material are well balanced, and workability is improved.

[0045] The reinforcing fiber content in each prepreg is preferably 30 to 90% by mass. By setting the content to 30% by mass or more, more preferably 35% by mass or more, and even more preferably 60% by mass or more, it is easy to obtain the advantages of a fiber-reinforced composite material with excellent specific strength and specific modulus. Furthermore, by setting the fiber content within the above range, it is possible to prevent excessive heat generation during curing when molding into a fiber-reinforced composite material. On the other hand, by setting the content to 90% by mass or less, more preferably 85% by mass or less, it is easy to prevent the generation of voids in the composite material due to insufficient resin impregnation, and it is also easy to maintain the tack of the prepreg.

[0046] The fiber-reinforced composite tubular body of the present invention, particularly a golf club shaft or a fishing rod, is produced by laminating the prepreg of the present invention and then heat-curing the resin while applying pressure to the laminate.

[0047] Here, methods for applying heat and pressure include press molding, autoclave molding, bagging molding, wrapping tape molding, and internal pressure molding. Among these, the wrapping tape and internal pressure molding methods are preferably used. The wrapping tape method is a suitable method for winding a prepreg around a core such as a mandrel to form a tubular body made of a fiber-reinforced composite material. More specifically, the method involves winding the prepreg around a mandrel, wrapping a thermoplastic film around the outside of the prepreg to fix the prepreg and apply pressure, heat-curing the resin in an oven, and then removing the core to obtain a tubular body. The internal pressure molding method involves placing a preform, in which the prepreg is wound around an internal pressure-applying body such as a thermoplastic resin tube, in a mold, and then introducing high-pressure gas into the internal pressure-applying body to apply pressure while simultaneously heating the mold to form the body.

[0048] As described above, the fiber-reinforced composite tubular body of the present invention is preferably formed by laminating prepregs in such a way that the reinforcing fibers contained in each prepreg are oriented in one direction during lamination, and can be laminated and molded using various reinforcing layers, such as 0° layers obtained by laminating prepregs in a state in which the reinforcing fibers are oriented parallel or approximately parallel to the axial direction of the tubular body, ±45° layers obtained by laminating prepregs in a state inclined at 45° or approximately 45° relative to the axial direction of the tubular body, 90° layers obtained by laminating prepregs in a state in which the prepregs are orthogonal or approximately orthogonal to the axial direction of the tubular body, and various other reinforcing layers. In this case, the 0° layers are primarily responsible for the bending rigidity and bending strength of the tubular body, the ±45° layers are primarily responsible for the torsional rigidity and torsional strength, and the 90° layers are primarily responsible for the crushing rigidity and crushing strength.

[0049] The fiber-reinforced composite tubular body of the present invention ensures rigidity and strength against bending, torsion, and crushing, and from the viewpoint of obtaining a tubular body with particularly excellent static bending strength, it is preferable to laminate and mold each prepreg so as to have layers in which the reinforcing fibers are oriented in two or more of the following directions relative to the axial direction of the tubular body: 0° (0° layer), 90° (90° layer), and ±45° (±45° layer). It is more preferable to laminate and mold so as to have layers oriented in all three directions. In particular, to obtain a tubular body with excellent static bending strength, it is preferable to laminate and mold so as to include a 0° layer. Here, in the present invention, the +45° layer and the −45° layer are collectively referred to as the ±45° layer, and are layers oriented in a single direction.

[0050] The fiber-reinforced composite tubular body of the present invention is obtained by constructing and molding a laminate so that the difference in tensile modulus between the reinforcing fibers contained in each of the laminated prepregs is at most 10% or more. Since the mechanical properties, such as the tensile modulus and tensile strength, of the reinforcing fibers contained in the prepregs generally remain unchanged when the prepregs are formed into a tubular body, the difference in tensile modulus between the reinforcing fibers contained in each layer of the prepregs obtained using the prepregs is at most 10% or more. This laminate configuration facilitates achieving both high bending strength and high torsional rigidity or crushing rigidity for the tubular body. The difference in tensile modulus between the reinforcing fibers contained in each prepreg or the reinforcing fibers contained in each layer of the cured prepreg is calculated by comparing the fiber with the highest tensile modulus and the fiber with the lowest tensile modulus among the reinforcing fibers contained in all prepregs constituting the laminate or in all layers of the tubular body, taking the difference between the highest and lowest tensile modulus, and dividing by the lowest tensile modulus (unit: %).

[0051] In particular, from the viewpoint of ensuring torsional rigidity or crushing rigidity, it is preferable to use reinforcing fibers with a higher tensile modulus than the 0° layer in either the ±45° layer or the 90° layer. In particular, it is more preferable to use reinforcing fibers with a tensile modulus 10% or more higher than that of the 0° layer in the prepreg used for the ±45° layer, or even more preferable to use reinforcing fibers with a tensile modulus 10% or more higher than that of either the 0° layer or the 90° layer. The specific numerical value of the tensile modulus of the reinforcing fibers contained in the prepreg used for the ±45° layer is preferably 300 to 500 GPa, more preferably 340 to 480 GPa, and even more preferably 370 to 480 GPa. On the other hand, from the viewpoint of obtaining a tubular body with excellent static bending strength, it is preferable to use reinforcing fibers with a higher tensile strength than the ±45° layer or the 90° layer, or both, in the 0° layer. The tensile strength of the reinforcing fibers contained in the prepreg used in the 0° layer is preferably 5,000 to 8,000 GPa, and more preferably 5,800 to 8,000 GPa.

[0052] The multiple prepregs laminated during the production of the fiber-reinforced composite tubular body of the present invention each contain an epoxy resin composition that has an average flexural modulus of 4.0 GPa or more when cured. By laminating multiple such prepregs, a tubular body can be obtained in which the average flexural modulus of the epoxy resin cured product (the cured product of the epoxy resin composition without fibers) contained in each layer constituting the cured body is 4.0 GPa or more. If this average value is less than 4.0 GPa, the static bending strength of the resulting tubular body will be insufficient. Furthermore, from the perspective of improving the bending strength of the tubular body, the average flexural modulus of both the prepregs and the tubular body is preferably 4.4 GPa or more, and more preferably 4.7 GPa or more. While a higher average flexural modulus is preferable, epoxy resin compositions that produce cured products with flexural moduli exceeding 6.0 GPa are currently difficult to obtain, making 6.0 GPa the preferred upper limit. However, if epoxy resin compositions with higher average flexural moduli become readily available in the future, they will be suitable for use. As described above, the flexural modulus is measured in accordance with JIS K7171 (2016).

[0053] The average value of the bending modulus is a value obtained as a volume average value for the entire epoxy cured material contained in the tubular body, and the weight of the reinforcing fibers of each prepreg layer (or each layer of the tubular body) is expressed as W(i) [g / m 2 ], the mass content of the reinforcing fibers contained in each prepreg layer (or each layer of the tubular body) is Wf(i) [%], the specific gravity of the epoxy resin composition contained in each prepreg layer when cured (or the specific gravity of the cured resin contained in each layer of the tubular body) is d(i) [-], and the flexural modulus of the epoxy resin composition contained in each prepreg layer when cured (or the flexural modulus of the cured resin contained in each layer of the tubular body) is E(i) [GPa], where i represents the number of each prepreg layer (or each layer of the tubular body), it can be calculated using the following formula (1).

[0054]

number

[0055] Furthermore, the multiple prepregs laminated during the production of the tubular body have a standard deviation of flexural modulus of 0.3 GPa or less when the epoxy resin composition contained in each prepreg is cured. Using such prepregs, the standard deviation of flexural modulus of the cured resin contained in each layer constituting the fiber-reinforced composite tubular body of the present invention can be made 0.3 GPa or less. This standard deviation is determined as a standard deviation weighted by the volume fraction of each cured epoxy material relative to the total volume fraction of the cured epoxy material contained in the tubular body. Using E(ave.), where E is the average value of the flexural moduli when the epoxy resin composition is cured (or the average value of the flexural moduli for the cured materials contained in the tubular body), and the other symbols are the same as in Equation (1), it can be calculated using Equation (2) below.

[0056]

number

[0057] The present invention will be described below with reference to examples. However, the scope of the present invention is not limited to these examples. The unit "parts" in the composition ratios means parts by mass unless otherwise noted. Furthermore, measurements of various characteristics (physical properties) were carried out in an environment of a temperature of 23°C and a relative humidity of 50% unless otherwise noted.

[0058] <Materials used in Examples and Comparative Examples> (1) Carbon fiber "TORAYCA (registered trademark)" T800GC-24k (tensile modulus: 294 GPa, tensile strength: 5880 MPa, manufactured by Toray Industries, Inc.) "TORAYCA (registered trademark)" M40JB-12k (tensile modulus: 377 GPa, tensile strength: 4400 MPa, manufactured by Toray Industries, Inc.) "TORAYCA (registered trademark)" M30SC-12k (tensile modulus: 294 GPa, tensile strength: 5690 MPa, manufactured by Toray Industries, Inc.) (2) Epoxy resin Component [A]: Epoxy resin jER (registered trademark) 828 (liquid bisphenol A epoxy resin, epoxy equivalent: 189 g / eq, manufactured by Mitsubishi Chemil Corporation) jER (registered trademark) 1001 (solid bisphenol A epoxy resin, epoxy equivalent: 475 g / eq, manufactured by Mitsubishi Chemical Corporation) jER (registered trademark) 154 (phenolic novolac epoxy resin, epoxy equivalent: 178 g / eq, manufactured by Mitsubishi Chemical Corporation) "Araldite (registered trademark)" MY0600 (aminophenol type epoxy resin): epoxy equivalent weight 118g / eq, manufactured by Huntsman Japan Co., Ltd.) "TEPIC (registered trademark)"-S (isocyanuric acid type epoxy resin): epoxy equivalent 100g / eq, manufactured by Nissan Chemical Industries, Ltd. Component [B]: Polyamine hardener DICY7 (dicyandiamide, active hydrogen equivalent: 21g / eq, number of active hydrogen atoms: 4, manufactured by Mitsubishi Chemical Corporation).

[0059] Other components [B']: Curing accelerator DCMU99 (3-(3,4-dichlorophenyl)-1,1-dimethylurea, manufactured by Hodogaya Chemical Industry Co., Ltd.).

[0060] Component [C]: A compound having a boiling point of 180°C or higher and a molecular weight m of 50 to 250, which does not have an epoxy group in the molecule and does not have the ability to harden epoxy resins. N-Ethylacetamide (boiling point: 206°C, melting point: -32°C, molecular weight m: 87 g / mol, manufactured by Tokyo Chemical Industry Co., Ltd.) Component [D]: Thermoplastic resin "Vinylec (registered trademark)" K (Polyvinyl formal, manufactured by JNC Corporation) <Method for preparing epoxy resin composition> The amounts shown below are all based on 100 parts by mass of all epoxy resins.

[0061] (1) Preparation of hardener master Component [A]: 10 parts by mass of "jER (registered trademark)" 828 was prepared, and component [B]: DICY7 was added to this in the amounts shown in the table, and the mixture was kneaded at room temperature to form a mixture. The mixture was passed through a three-roll mill twice to prepare a curing agent masterbatch.

[0062] (2) Preparation of epoxy resin composition Excluding 10 parts by mass of the component [A]: "jER (registered trademark)" 828 used in (1), the remaining 90 parts by mass of component [A] and component [D] were placed in a beaker and heated to 150°C to achieve a uniform solution, followed by cooling to below 60°C. After cooling, the curing agent masterbatch and curing accelerator prepared in (1) and component [C] were added in the amounts shown in the table, and the mixture was thoroughly stirred at below 60°C to obtain epoxy resin compositions (compositions 1 to 3).

[0063] The epoxy resin compositions of each example were measured using the following measurement methods.

[0064] <Method for evaluating the type of cured epoxy resin> (1) Preparation of epoxy resin cured board The prepared uncured epoxy resin composition was degassed in a vacuum, and then cast into a mold set to a thickness of 2 mm, sandwiching a 2 mm Teflon (registered trademark) spacer between them. The temperature in the mold was then raised from 30°C to 130°C at a rate of 1.5°C / min, and the composition was cured at 130°C for 2 hours, yielding a 2 mm thick cured resin plate. (2) Three-point bending test of cured resin Test pieces 10 mm wide and 60 mm long (in the fiber orientation direction, the same as in (3)) were cut out from the cured resin plate obtained in (1). Three-point bending was performed using an Instron universal testing machine (manufactured by Instron) with a span of 32 mm, a crosshead speed of 2.5 mm / min, and sample number n = 6 according to JIS K7171 (2016). The average value of the modulus of elasticity at each point was taken as the bending modulus of the cured resin. (3) Measurement of specific gravity of cured resin A test piece measuring 12.7 mm wide and 55 mm long was cut out from the resin-cured plate obtained in (1), and its mass was measured in air and water at room temperature. The specific gravity was calculated using Archimedes' method. The number of samples was 6, and the average of the measured values ​​was used as the specific gravity.

[0065] <Prepreg manufacturing method> The resin composition was applied to release paper using a reverse roll coater to produce a resin film. Next, two resin films were placed on both sides of a sheet of unidirectionally aligned carbon fibers, and the sheet was heated and pressurized to impregnate the resin composition, producing a unidirectional prepreg.

[0066] <Evaluation method for fiber-reinforced composite tubular bodies> (1) Fabrication of fiber-reinforced composite tubular bodies A test tubular body was fabricated as follows: By the following steps (a) to (e), three layers of each unidirectional prepreg fabricated above were laminated (six layers in total) so that the fiber direction was alternately laminated at +45° and -45° to the axial direction of the tubular body, and then three layers of each other unidirectional prepreg were laminated on top of that so that the fiber direction was alternately laminated perpendicular (90°) and parallel (0°) to the axial direction of the tubular body (six layers in total), and a composite material tubular body with an inner diameter of 10 mm was then fabricated.

[0067] A stainless steel round bar with a diameter of 10 mm and a length of 1000 mm was used as the mandrel. This tubular body was not tapered and did not contain any reinforcing material. The average bending modulus of the cured epoxy resin contained in the tubular body was calculated using equation (1). (a) Two rectangular pieces measuring 105 mm long x 800 mm wide were cut from the unidirectional prepreg prepared above (with the fiber axis direction at 45° to the direction of the long side). These two prepregs were laminated together so that the fiber directions contained in each piece were perpendicular to each other, with a 16 mm (half the circumference of the mandrel) offset in the short side direction, but without any offset in the long side direction. (b) The two prepregs laminated in (a) were wound around a release-treated mandrel so that the long sides of the rectangular shape were aligned with the axial direction of the mandrel. This resulted in a total of six layers (three layers each at ±45° to the axial direction of the tubular body). (c) The unidirectional prepreg prepared above was cut into a rectangular shape measuring 115 mm long and 800 mm wide, with the long side running perpendicular to the fiber direction or the axial direction. These two prepregs were laminated onto the prepreg wound in (b) without shifting either the long or short sides, so that the fiber directions were perpendicular to each other. The prepreg was then wound around the mandrel, with the long side of the rectangle aligned with the mandrel axial direction, so that the fiber directions were perpendicular (90°) or parallel (0°) to the mandrel axial direction. (d) Furthermore, wrapping tape (heat-resistant film tape, width 10 mm) was wound from above with a tension of 3 kgf to cover the wound product, and the product was heat-molded in a curing oven at 130°C for 120 minutes. (e) After this, the mandrel was removed and the wrapping tape was removed to obtain a tubular body made of the composite material. (2) Bending test of tubular body Using the composite material tubular body (inner diameter 10 mm) obtained by step (1), a test piece 350 mm in length was cut out from the tubular body, and the bending strength was measured in accordance with the three-point bending test method described in "Certification Standards and Standard Verification Methods for Golf Club Shafts" (compiled by the Consumer Product Safety Association, approved by the Minister of International Trade and Industry No. 2087, 1993). Here, the distance between supports was 300 mm, and the test speed was 10 mm / min. Measurements were conducted on eight samples (n = 8), and the average value was taken as the bending strength. (3) Torsion test of tubular body Using the composite tubular body (inner diameter 10 mm) obtained by step (1), a test piece 350 mm in length was cut out from the tubular body and measured in accordance with the torsion test method described in "Certification Standards and Standard Verification Methods for Golf Club Shafts" (compiled by the Consumer Product Safety Association, approved by the Minister of International Trade and Industry No. 2087, 1993). Here, the test piece gauge length was 250 mm, and measurements were taken by holding a 50 mm range from both ends of the test piece with a fixing jig. The torsional rigidity can be calculated using the following formula; measurements were taken on eight samples (n = 8), and the average value was taken as the torsional rigidity. Torsional rigidity (N·m / deg.) = Breaking torque (N·m) / Torsion angle at break (deg.) <Reference examples 1~10> Prepregs A to J were produced from the epoxy resin compositions prepared by the above method by blending the reinforcing fibers and each component as shown in Table 1, so as to have the reinforcing fiber weight per unit area and reinforcing fiber content shown in Table 1. Furthermore, cured epoxy resin plates were produced by the above method using the epoxy resin compositions of each example, and the flexural modulus and specific gravity of each cured epoxy resin product were measured. Meanwhile, the produced prepregs A to J were combined to produce a tubular fiber-reinforced composite material.

[0068] <Examples 1 to 6 and Comparative Examples 1 to 4> In Examples 1 to 6 and Comparative Examples 1 to 3, fiber-reinforced composite tubular bodies were produced by the above method using prepregs for the 0°, 90°, and ±45° layers as shown in Table 2. As described in Examples 1 to 6, tubular bodies with excellent bending strength and torsional rigidity were obtained by increasing the average bending modulus of the cured epoxy resin contained in the tubular body and by laminating and molding prepregs produced using reinforcing fibers with tensile moduli differing by 10% or more.

[0069] When the average flexural modulus of the epoxy cured product contained in the tubular body was insufficient, as in Comparative Examples 1 and 2, the flexural strength of the tubular body was poor. In Comparative Example 3, the reinforcing fibers contained in the 0° layer, 90° layer, and ±45° layer prepregs all had a tensile modulus of 294 GPa, and the torsional rigidity of the tubular body was poor. In Comparative Example 4, the reinforcing fibers contained in the 0° layer, 90° layer, and ±45° layer prepregs all had a tensile modulus of 377 GPa, and the flexural strength of the tubular body was poor.

[0070] [Table 1]

[0071] [Table 2]

Claims

1. A method for producing a tubular fiber-reinforced composite material body obtained by laminating and curing a plurality of prepregs containing reinforcing fibers and an epoxy resin composition, A method for producing a fiber-reinforced composite material tubular body, wherein the difference in tensile modulus of reinforcing fibers contained in each of the laminated prepregs is at most 10% or more, and the average flexural modulus of the epoxy resin composition contained in each prepreg when cured is 4.0 GPa or more.

2. In each prepreg, the reinforcing fibers are oriented in one direction, 2. The method for producing a fiber-reinforced composite tubular body according to claim 1, wherein each prepreg is laminated so that the reinforcing fibers are oriented in two or more directions selected from the group consisting of a 0° direction, a 90° direction, and a ±45° direction relative to the axial direction of the tubular body.

3. 3. The method for producing a fiber-reinforced composite tubular body according to claim 2, wherein the difference in tensile modulus of reinforcing fibers contained in a prepreg in which the reinforcing fibers are oriented in directions of ±45° relative to the axial direction of the tubular body and a prepreg in which the reinforcing fibers are oriented in a direction of 0° is at most 10% or more.

4. 3. The method for producing a fiber-reinforced composite material tubular body according to claim 1, wherein the laminated prepregs each contain an epoxy resin composition that, when cured, has a standard deviation of flexural modulus of elasticity of 0.3 GPa or less.

5. 3. The method for producing a fiber-reinforced composite tubular body according to claim 1 or 2, wherein the epoxy resin composition contained in at least one layer of the plurality of laminated prepregs contains the component [A']. Component [A']: at least one of a glycidylamine type epoxy resin and an isocyanuric acid type epoxy resin

6. A tubular fiber-reinforced composite material body is formed by laminating and curing a plurality of prepregs containing reinforcing fibers and an epoxy resin composition, A fiber-reinforced composite material tubular body in which the cured product of multiple laminated prepregs has a maximum difference in tensile modulus of the reinforcing fibers contained in each layer of 10% or more, and the average flexural modulus of the cured epoxy resin contained in each layer is 4.0 GPa or more.

7. A golf club shaft using the fiber-reinforced composite material tubular body according to claim 6.

8. A fishing rod using the fiber-reinforced composite material tubular body according to claim 6.

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