Prepreg and fiber-reinforced composite material

Abstract

The purpose of the present invention is to provide a prepreg which has excellent handleability even during winding work on an object having a portion on which pressure is difficult to apply, such as a multi-stage tapered mandrel.　Specifically, provided is a prepreg obtained by impregnating reinforcing fibers with a matrix resin, wherein the matrix resin has a storage elastic moduli at 25°C of 10.0×104 Pa or less at an angular frequency of 1 Hz and 2.5×103 Pa or greater at an angular frequency of 0.01 Hz.

Description

Prepregs and fiber-reinforced composite materials

[0001] This invention relates to a prepreg with excellent handling properties that can be applied to sports applications, general industrial applications, and the like.

[0002] Fiber-reinforced composite materials, consisting of reinforcing fibers and matrix resin, are lightweight, high-strength, and highly rigid, making them widely used in sports, aerospace, and general industrial applications. In sports applications, reinforcing fiber composite materials are often molded into tubular shapes for use in golf club shafts, fishing rods, and bicycle frames. A widely known method involves wrapping prepreg around a core material such as a mandrel, curing the prepreg by heating, and then removing the core material to obtain a tubular shape.

[0003] In this type of molding method, the handling of the prepreg is important. If it is not handled well, gaps may form between the core material such as a mandrel and the prepreg due to peeling or lifting, requiring manual correction before heating. Patent document 1 proposes a method to improve the handling of the prepreg by placing a resin layer with relatively high viscosity at room temperature on the surface of the prepreg.

[0004] Japanese Patent Publication No. 2010-229211

[0005] The method described in Patent Document 1 is suitable when sufficient pressure can be applied to wrap the prepreg. However, when wrapping prepreg around complex-shaped multi-stage tapered mandrels or other objects with areas where pressure is difficult to apply, the prepreg may not adhere properly, leading to peeling or lifting, and potentially degrading the quality of the molded product.

[0006] Therefore, the present invention aims to provide a prepreg that offers excellent handling properties, even in winding operations involving materials with areas that are not easily subjected to pressure, such as multi-stage tapered mandrels.

[0007] To solve the aforementioned problems, the present invention has the following configuration.

[0008] 1. A prepreg comprising reinforcing fibers impregnated with a matrix resin, wherein the storage modulus of the matrix resin at 25°C is 10.0 × 10⁻⁶ at an angular frequency of 1 Hz. ４ When Pa is less than or equal to 0.01 Hz and the angular frequency is 0.01 Hz, then 2.5 × 10 ３ 1. A prepreg having a viscosity of Pa or higher. 2. The prepreg according to 1 above, wherein the matrix resin contains an epoxy resin. 3. The prepreg according to 1 or 2 above, wherein the matrix resin has a viscosity of 70 Pa·s or less at 75°C and a viscosity of 15 Pa·s or less at 100°C. 4. The prepreg according to any one of 1 to 3 above, wherein the matrix resin contains a thermoplastic resin with a weight-average molecular weight of less than 80,000 and a thermoplastic resin with a weight-average molecular weight of 80,000 or more. 5. The prepreg according to 1 or 3 above, wherein the matrix resin contains an epoxy resin, a thermoplastic resin with a weight-average molecular weight of less than 80,000 and a thermoplastic resin with a weight-average molecular weight of 80,000 or more. 6. The prepreg according to 4 or 5 above, wherein the thermoplastic resin with a weight-average molecular weight of 80,000 or more is an acrylic resin. 7. 5. The prepreg according to 5 or 6 above, wherein the matrix resin is 5 to 15 parts by mass of a thermoplastic resin with a weight-average molecular weight of less than 80,000 and a thermoplastic resin with a weight-average molecular weight of 80,000 or more, per 100 parts by mass of epoxy resin. 8. The prepreg according to any one of 1 to 7 above, wherein the reinforcing fibers are carbon fibers, and in a winding performance evaluation performed by winding the prepreg around a two-stage tapered mandrel having a predetermined shape and material such that the carbon fiber direction is at a 90° (hoop) angle with respect to the axial direction of the mandrel, there is no winding delamination for 9 hours from the completion of winding. 9. A fiber-reinforced composite material obtained by curing the prepreg according to any one of 1 to 8 above.

[0009] This invention provides a prepreg with excellent handling properties for winding operations on materials with areas that are not easily subjected to pressure, such as multi-stage tapered mandrels, thereby improving the quality of molded products.

[0010] A rolling table used when wrapping prepreg around a mandrel.

[0011] The reinforcing fibers of the present invention can be selected as appropriate according to the required strength, as long as they are commonly used as reinforcing fibers. For example, chemical fibers such as carbon fibers, glass fibers, Kevlar®, boron fibers, silicon carbide fibers, or nylon, natural fibers, metal fibers such as alumina fibers, etc., can be used, and these can be combined, or combined with other organic fibers.

[0012] Among these, carbon fiber is particularly preferred because it has a high tensile modulus of elasticity among reinforcing fibers. The carbon fiber is not particularly limited; pitch-based carbon fiber, polyacrylonitrile-based carbon fiber, etc., can be used, and two or more of these fibers may be mixed and used. Among these, polyacrylonitrile-based carbon fiber is preferred because it is easy to obtain a prepreg with high tensile strength.

[0013] The matrix resin used in the prepreg of the present invention is not particularly limited as long as it is a thermosetting resin that undergoes a crosslinking reaction upon heating to form at least partially a three-dimensional crosslinked structure. Examples of such thermosetting resins include epoxy resins, unsaturated polyester resins, vinyl ester resins, benzoxazine resins, phenolic resins, urea resins, melamine resins, and thermosetting polyimide resins. Modified versions thereof and resins blended from two or more types can also be used. Furthermore, these thermosetting resins may self-cur upon heating, or they may cure by reacting with a curing agent or curing accelerator. An epoxy resin composition mainly composed of epoxy resin is preferred because it offers an excellent balance of heat resistance, mechanical properties, and adhesion to carbon fibers.

[0014] The epoxy resin is not particularly limited, and one or more can be selected and used from among bisphenol-type epoxy resins, amine-type epoxy resins, phenol novolac-type epoxy resins, cresol novolac-type epoxy resins, resorcinol-type epoxy resins, phenol aralkyl-type epoxy resins, naphthol aralkyl-type epoxy resins, dicyclopentadiene-type epoxy resins, epoxy resins having a biphenyl skeleton, isocyanate-modified epoxy resins, tetraphenylethane-type epoxy resins, triphenylmethane-type epoxy resins, diglycidylaniline derivatives, etc.

[0015] Here, bisphenol-type epoxy resin refers to a bisphenol compound in which two phenolic hydroxyl groups have been glycidylated, and examples include bisphenol A type, bisphenol F type, bisphenol AD ​​type, bisphenol S type, or halogen, alkyl substituted, and hydrogenated versions of these bisphenols. Furthermore, not only monomers but also high molecular weight compounds having multiple repeating units can be suitably used. In the present invention, it is preferable to use two or more types of bisphenol-type epoxy resins, and a combination of bisphenol A type and bisphenol F type is particularly preferred, and among these, it is preferable to use two or more types of bisphenol A with different epoxy equivalents. In this case, for example, a combination of epoxy equivalents of 400 to 800 g / eq (e.g., YD-011, manufactured by Kokuto Chemical Co., Ltd., YD-012, manufactured by Kokuto Chemical Co., Ltd.) and epoxy equivalents of 1300 to 3000 g / eq (e.g., YD-017, manufactured by Kokuto Chemical Co., Ltd.) can be mentioned.

[0016] In the matrix resin of the present invention, a curing agent is preferably used to improve the curability of the prepreg. The curing agent is not particularly limited, but may include amines such as aromatic amines and alicyclic amines, phenolic resins, dicyandiamides or their derivatives, acid anhydrides, polyaminoamides, organic acid hydrazides, and isocyanates.

[0017] Furthermore, in sports applications such as golf shafts, fishing rods, and bicycles, curing at low temperatures and in a short time is required, so curing accelerators are preferably used. Examples of curing accelerators include urea compounds, tertiary amines and their salts, imidazoles and their salts, triphenylphosphine or its derivatives, metal carboxylate salts, Lewis acids, Brønsted acids and their salts.

[0018] The matrix resin of the present invention may contain a thermoplastic resin, inorganic particles, or inorganic fillers. As the thermoplastic resin, it can be a thermoplastic resin soluble in epoxy resin, or organic particles such as rubber particles and thermoplastic resin particles. As the thermoplastic resin soluble in epoxy resin, a thermoplastic resin having hydrogen bonding functional groups that can be expected to improve the adhesion between the resin and the reinforcing fibers is preferably used. Examples of thermoplastic resins soluble in epoxy resin and having hydrogen bonding functional groups include thermoplastic resins having alcoholic hydroxyl groups, thermoplastic resins having amide bonds, and thermoplastic resins having sulfonyl groups.

[0019] The storage modulus of the matrix resin used in the prepreg of the present invention at 25°C is 10.0 × 10⁻⁶ at an angular frequency of 1 Hz. ４ When Pa is less than or equal to 0.01 Hz and the angular frequency is 0.01 Hz, then 2.5 × 10 ３ It is Pa or higher. The storage modulus at an angular frequency of 1 Hz is 10.0 × 10⁻⁶. ４ By keeping the pressure below Pa, the adhesion at the moment the prepreg is wrapped around the mandrel is improved, suppressing peeling and lifting. The storage modulus at an angular frequency of 0.01 Hz is 2.5 × 10⁻⁶. ３ By setting the pressure to Pa or higher, the adhesion after winding the prepreg onto the mandrel can be maintained for a long time. Furthermore, the storage modulus of the matrix resin at 25°C is 7.0 × 10⁻⁶ at an angular frequency of 1 Hz. ４ It is preferable that it be Pa or less, and when the angular frequency is 0.01 Hz, it is 2.8 × 10⁻⁶. ３It is preferably at least Pa. This allows a state free of peeling and lifting to be maintained for a long time. Furthermore, since excessive adhesive force during handling of the prepreg can be suppressed, at an angular frequency of 1 Hz, 3.5 × 10 ４ It is preferably at least Pa, and at an angular frequency of 0.01 Hz, 2.0 × 10 ４ It is preferably at most Pa. The storage modulus of the matrix resin as referred to herein refers to the storage modulus G' obtained by measurement using a dynamic viscoelasticity measuring apparatus (for example, ARES G2: manufactured by TA Instrument), using a parallel plate, maintaining the temperature at 25°C, setting an angular frequency of 0.01 Hz or 1 Hz, and setting the thickness of the matrix resin between the parallel plates to 1 mm.

[0020] The matrix resin used in the prepreg of the present invention preferably has a viscosity at 75°C of 70 Pa·s or less from the viewpoint of processability, and further preferably has a viscosity at 100°C of 15 Pa·s or less. By setting the viscosity at 75°C to 70 Pa·s or less, it becomes possible to uniformly coat the resin composition onto release paper or the like. A more preferable viscosity at 75°C is 65 Pa·s or less, and even more preferably 60 Pa·s or less. On the other hand, those having a viscosity at 75°C of 5 Pa·s or more can generally be used. In addition, by setting the viscosity at 75°C to 30 Pa·s or less, the affinity between the resin and the adherend is improved, and the storage modulus of the matrix resin at 25°C is 7.0 × 10 at an angular frequency of 1 Hz ４ exceeds Pa, 10.0 × 10 ４Even in the range of Pa or less, more favorable effects can be obtained. Furthermore, by setting the viscosity at 100°C to 15 Pa·s or less, the impregnation of the epoxy resin composition into the reinforcing fibers is improved, thereby improving the processability of the prepreg. A more favorable viscosity at 100°C is 12 Pa·s or less, and even more preferably 9 Pa·s or less. On the other hand, a viscosity of 1 Pa·s or more at 100°C can be commonly used. The viscosity referred to here is the viscosity η obtained by measuring the viscosity using a dynamic viscoelasticity measuring device (e.g., ARES G2: manufactured by TA Instrument, Inc.) with parallel plates, simple heating at a heating rate of 2°C / min, angular frequency of 0.5 Hz, and a thickness of the epoxy resin composition between parallel plates of 1 mm. ＊ It refers to.

[0021] The prepreg manufacturing method of the present invention is preferably obtained by pressure-impregnating reinforcing fibers with a matrix resin. Examples of pressure-impregnation methods include the hot-melt method. The hot-melt method is a method of directly impregnating a fibrous substrate made of reinforcing fibers with a resin composition whose viscosity has been reduced by heating, or a method of first preparing a film by coating the resin composition on a release paper or the like, then placing the film on both sides or one side of the fibrous substrate made of reinforcing fibers, and impregnating the fibrous substrate made of reinforcing fibers with the matrix resin by heating and pressurizing. The hot-melt method is preferable because it results in virtually no residual solvent in the prepreg.

[0022] The method for manufacturing a film coated on release paper or the like is not particularly limited. Examples include spraying a fixed amount of resin onto the release paper or the like using a spraying device, or coating by controlling the coating amount while discharging a fixed amount of resin using a knife coater, die coater, lip coater, or gravure coater. As for methods for preparing a resin film in advance, a method of applying a resin composition to a release sheet as described above using the above-mentioned coater, or a method using a reverse roll coater or top-feed reverse roll coater that controls the coating amount by the roll rotation speed and the clearance between rolls can also be used.

[0023] In the matrix resin used in the prepreg of the present invention, when an epoxy resin is used as the main component, it is preferable to use the aforementioned thermoplastic resin soluble in epoxy resin. Furthermore, it is preferable to use two or more thermoplastic resins with different weight-average molecular weights as thermoplastic resins soluble in epoxy resin. The content of the thermoplastic resin soluble in epoxy resin is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, and on the other hand, preferably 15 parts by mass or less, and more preferably 12 parts by mass or less, when the total amount of epoxy resin is 100 parts by mass.

[0024] When using two or more thermoplastic resins with different weight-average molecular weights, it is preferable that each thermoplastic resin has a weight-average molecular weight of 5,000 to 2,000,000. When the weight-average molecular weight is 5,000 or higher, sufficient compatibility with epoxy resins can be achieved. Furthermore, when the weight-average molecular weight is 2,000,000 or lower, the viscosity can be appropriately adjusted, and as a result, it can be kept within a predetermined viscosity range.

[0025] More preferably, the matrix resin contains a thermoplastic resin with a weight-average molecular weight of less than 80,000 and a thermoplastic resin with a weight-average molecular weight of 80,000 or more. When the matrix resin contains a thermoplastic resin with a weight-average molecular weight of 80,000 or more as a thermoplastic resin soluble in epoxy resin, it becomes easier to achieve the above-mentioned range of storage modulus for the matrix resin by combining it with other compounds. On the other hand, when the matrix resin contains a thermoplastic resin with a weight-average molecular weight of less than 80,000, it becomes easier to achieve the above-mentioned range of viscosity for the matrix resin. Including a thermoplastic resin with a weight-average molecular weight of less than 80,000 and a thermoplastic resin with a weight-average molecular weight of 80,000 or more tends to make it easier to achieve both the range of storage modulus and the range of viscosity. The mass blending ratio of the thermoplastic resin with a weight-average molecular weight of less than 80,000 is preferably in the range of 0.5 to 15, more preferably 0.8 to 12, and even more preferably 0.9 to 12, when the thermoplastic resin with a weight-average molecular weight of 80,000 or more is set to 1.

[0026] For thermoplastic resins with a weight-average molecular weight of less than 80,000, a more preferred range for the weight-average molecular weight is less than 70,000, even more preferably less than 60,000, while it is preferable that it is 5,000 or more. For thermoplastic resins with a weight-average molecular weight of 80,000 or more, a more preferred range for the weight-average molecular weight is 90,000 or more, even more preferably 100,000 or more, while it is preferable that it is 2,000,000 or less. However, the content of thermoplastic resins with a weight-average molecular weight of 1,000,000 or more and 2,000,000 or less is preferably 0.5 to 1.5 parts by mass when the total amount of epoxy resin is 100 parts by mass.

[0027] While there are no particular limitations on thermoplastic resins with a weight-average molecular weight of less than 80,000, acetal resins are preferred. Other examples include polysulfone resins and polyethersulfone resins. Polymers that make up acetal resins include polyvinyl acetal, polyvinyl formal, and polyvinyl butyral. Examples of commercially available acetal resins include "Eslec®" K, KS-10 (both manufactured by Sekisui Chemical Co., Ltd.), "Sumika Excel®" 2603MP, 5003P (both manufactured by Sumitomo Chemical Co., Ltd.), and "Vinirec®" K, L, H (both manufactured by JNC Corporation).

[0028] While there are no particular limitations on thermoplastic resins with a weight-average molecular weight of 80,000 or more, acrylic resins are preferred. Other examples include polyvinyl acetal resins. Acrylic resins have high compatibility with epoxy resins and are suitably used for viscoelasticity control. Polymers constituting acrylic resins include polyacrylates and polymethacrylates, as well as polyacrylonitrile and polyacrylamide. More specifically, polymethyl methacrylate is suitably used, and copolymers containing two or more acrylates or methacrylates as monomers are also suitable. Homopolymers such as polyacrylates and polymethacrylates may be used in combination with the copolymers mentioned above. Examples of commercially available acrylic resins include "Dianal®" BR-85, 88, 108 (all manufactured by Mitsubishi Chemical Corporation), "Matsumoto Microsphere®" M (manufactured by Matsumoto Oil & Fat Pharmaceutical Co., Ltd.), and "Nanostrength®" M22N, M52N (both manufactured by Arkema Inc.).

[0029] The weight-average molecular weight referred to here is the converted molecular weight using standard polystyrene, obtained by GPC (gel permeation chromatography). An example of specific measurement conditions is shown in Example (4) Measurement of Weight-Average Molecular Weight.

[0030] The fiber mass content in the prepreg of the present invention is preferably 60% or more, more preferably 63% or more. Furthermore, such fiber mass content is preferably 85% or less, more preferably 80% or less.

[0031] The fiber basis weight in the prepreg of the present invention is preferably 46 g / m². ２ The above is preferable to 50 g / m ２ That concludes the explanation. Furthermore, the fiber mass content is preferably 300 g / m². ２ The following, and more preferably 250 g / m² ２ The following applies:

[0032] When the reinforcing fibers of the prepreg of the present invention are carbon fibers, in the winding property evaluation in which the prepreg is wound around a two-stage tapered mandrel having a predetermined shape and material such that the carbon fiber direction is 90° (hoop) relative to the axial direction of the mandrel, it is preferable that no winding peeling occurs within 9 hours after the completion of winding. With regard to the specific evaluation conditions for this winding property evaluation, they are as set forth in (5) Winding Property Evaluation in the Examples. The predetermined shape of the above-mentioned two-stage tapered mandrel is: a tip diameter of Φ6.4 to 8.3 mm, a taper angle on the tip side of 0.2°, a rear end diameter of Φ14.3 to 15.1 mm, a taper angle on the rear end side of 0.4°, and an axial length of 1400 mm. The predetermined material refers to that specified in JIS G3109:2020. The expression "no winding peeling" herein means that the distance of the lift of the prepreg from the mandrel used for evaluation in the direction perpendicular to the mandrel surface is within 3 mm. It is more preferable that the distance is within 1 mm.

[0033] The fiber-reinforced composite material according to the present invention is obtained by curing the above-described prepreg, and can be used as a molded article in sports applications such as golf shafts, fishing rods, and bicycles. In addition, the mandrel according to the present invention is a multi-stage tapered mandrel, which can be suitably used for winding applications targeting a mandrel in which the taper angle is not the same across all stages, or a mandrel having a different taper angle for each stage, and improves the quality of the fiber-reinforced composite material as a molded product. The number of stages of such a mandrel is preferably 2 to 4, and the preferred range of the taper angle is 0.1 to 0.6°.

[0034] The upper and lower limits of the numerical ranges described above can be arbitrarily combined unless otherwise specified.

[0035] Hereinafter, the present invention will be described in detail by way of examples. The present invention is not limited to the following examples.

[0036] The matrix resins and reinforcing fibers used in the examples and comparative examples are as follows.

[0037] <Epoxy Resin> ・Bisphenol A type epoxy resin (YD-011, manufactured by Kokuto Chemical Co., Ltd.) ・Bisphenol A type epoxy resin (YD-012, manufactured by Kokuto Chemical Co., Ltd.) ・Bisphenol A type epoxy resin (YD-017, manufactured by Kokuto Chemical Co., Ltd.) ・Bisphenol A type epoxy resin (jER828, manufactured by Mitsubishi Chemical Corporation) ・Bisphenol F type epoxy resin ("EPICLON (Registered Trademark)" 830, manufactured by DIC Corporation) ・Phenol novolac type epoxy resin ("EPICLON (Registered Trademark)" N740, manufactured by DIC Corporation) ・Aminophenol type epoxy resin (PA-808, manufactured by Kokuto Chemical Co., Ltd.) ・Isocyanuric acid type epoxy resin ("TEPIC (Registered Trademark)"-S, manufactured by Nissan Chemical Corporation)

[0038] <Curing Agent> ・Dicyandiamide (DICY7, manufactured by Mitsubishi Chemical Corporation)

[0039] <Curing Accelerator> ・3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU99, manufactured by Hodogaya Chemical Co., Ltd.)

[0040] <Thermoplastic Resin> ・Polyvinyl acetal ("S-Lec (Registered Trademark)" KS-10, manufactured by Sekisui Chemical Co., Ltd., weight average molecular weight: 17,000 g / mol) ・Polyvinyl formal ("Vinylec (Registered Trademark)" K, manufactured by JNC Corporation, weight average molecular weight: 54,000 g / mol) ・M-B-M copolymer ("Nanostrength (Registered Trademark)" M22N: B is butyl acrylate, M is a copolymer of methyl methacrylate and a polar functional group-containing monomer, manufactured by Arkema Inc., weight average molecular weight: 100,000 g / mol) ・Polymethyl methacrylate ("Matsumoto Microsphere (Registered Trademark)" M, manufactured by Matsumoto Yushi-Seiyaku Co., Ltd., weight average molecular weight: 1,000,000 g / mol)

[0041] <Reinforcing Fiber> ・Carbon fiber ("TORAYCA (Registered Trademark)" T800SC-24K, manufactured by Toray Industries, Inc., tensile elastic modulus: 294 GPa, tensile strength: 5880 MPa). ・Carbon fiber ("TORAYCA (Registered Trademark)" M60JB-6K, manufactured by Toray Industries, Inc., tensile elastic modulus: 588 GPa, tensile strength: 3820 MPa).

[0042] (1) Preparation of prepregs An epoxy resin composition was obtained by melting and kneading epoxy resin and thermoplastic resin in the mass parts listed in Table 1, then cooling, and adding a curing agent and a curing accelerator. An epoxy resin film was prepared by applying the obtained epoxy resin composition onto release paper using a coater. A unidirectional prepreg was prepared by pressure impregnating carbon fibers with the epoxy resin film.

[0043] (2) Measurement of Storage Modulus A dynamic viscoelasticity measuring device (ARES G2: manufactured by TA Instrument Co.) was used to measure the storage modulus at a measurement temperature of 25°C using parallel plates with a diameter of 25 mm, with a thickness of 1 mm of epoxy resin composition between the parallel plates, and an angular frequency of 0.01 Hz or 1 Hz.

[0044] (3) Viscosity measurement Using a dynamic viscoelasticity measuring device (ARES G2: manufactured by TA Instrument Co., Ltd.), parallel plates with a diameter of 25 mm were used, the thickness of the epoxy resin composition between the parallel plates was set to 1 mm, the angular frequency was set to 0.5 Hz, and the temperature was simply increased at a heating rate of 2 °C / min to measure the viscosity when the measurement temperature was 75 °C or 100 °C.

[0045] (4) Measurement of weight-average molecular weight The weight-average molecular weight was measured using GPC. One Shodex K-80M, one Shodex K-806M, and one Shodex K-802 (manufactured by Showa Denko Corporation) were used, and 0.3 mL of each thermoplastic resin sample was injected. Measurement was performed under conditions of a flow rate of 1 mL / min. The retention time of the obtained samples was converted to the weight-average molecular weight based on the retention time of a calibration sample using polystyrene.

[0046] (5) Evaluation of Wrapping Properties A prepreg was set on a two-stage tapered mandrel (shape: tip diameter Φ8.3 mm, taper angle at the tip side 0.2°, end diameter Φ15.1 mm, taper angle at the end side 0.4°, axial length 1400 mm, material: JIS G3109:2020) so that the carbon fiber direction was 90° (hoop) with respect to the axial direction of the mandrel, and wrapping was performed using the rolling table shown in Figure 1. The presence or absence of unwinding was checked 9 hours after the completion of wrapping. Specifically, the rolling table, as shown in Figure 1, consists of a lower rolling table, an upper rolling table, and a cylinder shaft that moves the upper rolling table up and down relative to the lower rolling table. The following classifications were made based on the amount of unwinding. If the wrapping properties were judged to be good, A or B was written in the table. On the other hand, if the distance of the prepreg lift perpendicular to the mandrel surface (hereinafter referred to as prepreg lift) exceeded 3 mm and delamination was confirmed, C was indicated in the table.

[0047] A: Prepreg lift is less than 1 mm B: Prepreg lift is 1 mm or more and 3 mm or less C: Prepreg lift is more than 3 mm

[0048] <Example 1> An epoxy resin composition was prepared by mixing the components shown in Table 1, and then formed into an epoxy resin film. Next, as shown in Table 3, 75 g / m ２ A unidirectional prepreg with a fiber mass content of 76% was prepared by laminating an epoxy resin film onto carbon fiber T800SC-24K having a basis weight and then applying pressure to impregnate it with a resin composition. The storage modulus of the epoxy resin composition at 25°C was 3.6 × 10⁻⁶ at an angular frequency of 1 Hz. ４ Pa, when angular frequency is 0.01 Hz, is 2.7 × 10 ３ The viscosity was Pa. Furthermore, the viscosity at 75°C was 73 Pa·s, and the viscosity at 100°C was 10 Pa·s. The prepreg's wrapability was evaluated and found to be good (B).

[0049] <Examples 2-19> An epoxy resin composition was prepared by mixing the components shown in Table 1, and then formed into an epoxy resin film. Next, the epoxy resin film was laminated onto each carbon fiber having a predetermined basis weight as shown in Table 3, and the resin composition was impregnated by pressing to produce a unidirectional prepreg having a predetermined fiber mass content as shown in Table 3. The storage modulus at 25°C and the viscosity at the predetermined temperature of the epoxy resin composition are as shown in Table 3. The winding properties of the prepreg were evaluated, and as shown in Table 3, both were good.

[0050] <Comparative Example 1> An epoxy resin composition was prepared by mixing the components shown in Table 2, and then formed into an epoxy resin film. Next, the epoxy resin film was laminated onto each carbon fiber having a predetermined basis weight as shown in Table 4, and the resin composition was impregnated by pressing to produce a unidirectional prepreg having a predetermined fiber mass content as shown in Table 4. The storage modulus at 25°C and the viscosity at a predetermined temperature of the epoxy resin composition are as shown in Table 4, with the storage modulus at 25°C being low at an angular frequency of 0.01 Hz. As a result of evaluating the winding properties of the prepreg, dewinding was confirmed as shown in Table 4.

[0051] <Comparative Example 2> An epoxy resin composition was prepared by mixing the components shown in Table 2, and then formed into an epoxy resin film. Next, the epoxy resin film was laminated onto each carbon fiber having a predetermined basis weight as shown in Table 4, and the resin composition was impregnated by pressing to produce a unidirectional prepreg having a predetermined fiber mass content as shown in Table 4. The storage modulus at 25°C and viscosity at a predetermined temperature of the epoxy resin composition are as shown in Table 4, with the storage modulus at 25°C being higher at an angular frequency of 1 Hz. As a result of evaluating the winding properties of the prepreg, dewinding was confirmed as shown in Table 2.

[0052] <Comparative Example 3> An epoxy resin composition was prepared by mixing the components shown in Table 2, and then formed into an epoxy resin film. Next, the epoxy resin film was laminated onto each carbon fiber having a predetermined basis weight as shown in Table 4, and the resin composition was impregnated by pressing to produce a unidirectional prepreg having a predetermined fiber mass content as shown in Table 4. The storage modulus at 25°C and the viscosity at the predetermined temperature of the epoxy resin composition are as shown in Table 4, with the storage modulus at 25°C and the viscosity at 75°C and 100°C being high at an angular frequency of 1 Hz. As a result of evaluating the winding properties of the prepreg, dewinding was confirmed as shown in Table 2.

[0053] <Comparative Example 4> An epoxy resin composition was prepared by mixing the components shown in Table 2, and then formed into an epoxy resin film. Next, the epoxy resin film was laminated onto each carbon fiber having a predetermined basis weight as shown in Table 4, and the resin composition was impregnated by pressing to produce a unidirectional prepreg having a predetermined fiber mass content as shown in Table 4. The storage modulus at 25°C and the viscosity at a predetermined temperature of the epoxy resin composition are as shown in Table 4, with the storage modulus at 25°C being low at an angular frequency of 0.01 Hz. As a result of evaluating the winding properties of the prepreg, dewinding was confirmed as shown in Table 2.

[0054]

[0055]

[0056]

[0057]

[0058] 1. Rolling table 2. Lower rolling table 3. Upper rolling table 4. Cylinder shaft

Claims

1. A prepreg comprising reinforcing fibers impregnated with a matrix resin, wherein the storage modulus of the matrix resin at 25°C is 10.0 × 10⁻⁶ at an angular frequency of 1 Hz. ４ When Pa is less than or equal to 0.01 Hz and the angular frequency is 0.01 Hz, then 2.5 × 10 ３ A prepreg with a pressure of Pa or higher.

2. The prepreg according to claim 1, wherein the matrix resin contains an epoxy resin.

3. The prepreg according to claim 1, wherein the matrix resin has a viscosity of 70 Pa·s or less at 75°C and a viscosity of 15 Pa·s or less at 100°C.

4. The prepreg according to claim 1, wherein the matrix resin comprises a thermoplastic resin having a weight-average molecular weight of less than 80,000 and a thermoplastic resin having a weight-average molecular weight of 80,000 or more.

5. The prepreg according to claim 1, wherein the matrix resin comprises an epoxy resin, a thermoplastic resin with a weight-average molecular weight of less than 80,000, and a thermoplastic resin with a weight-average molecular weight of 80,000 or more.

6. The prepreg according to claim 4, wherein the thermoplastic resin having a weight-average molecular weight of 80,000 or more is an acrylic resin.

7. The prepreg according to claim 5, wherein the matrix resin is 5 to 15 parts by mass of a total of a thermoplastic resin with a weight-average molecular weight of less than 80,000 and a thermoplastic resin with a weight-average molecular weight of 80,000 or more, per 100 parts by mass of epoxy resin.

8. The prepreg according to claim 1 or 3, wherein the reinforcing fibers are carbon fibers, and in a winding performance evaluation performed by winding the prepreg around a two-stage tapered mandrel having a predetermined shape and material such that the direction of the carbon fibers is 90° (hoop) with respect to the axial direction of the mandrel, there is no unwinding for 9 hours from the completion of winding.

9. A fiber-reinforced composite material obtained by curing a prepreg according to any one of claims 1 to 7.

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