Method for producing prepreg and prepreg

Abstract

A prepreg production method according to one aspect of the present invention comprises: obtaining an impregnated fiber-reinforced material by impregnating a fiber-reinforced material with a liquid epoxy resin composition which is a precursor material for a matrix; and increasing the viscosity of the liquid epoxy resin composition in the impregnated fiber-reinforced material. An epoxy resin, an epoxy curing agent, a thickening agent, and a radical-polymerizable liquid monomer are blended in the liquid epoxy resin composition, and increase of the viscosity is conduced such that the epoxy curing agent and the radical-polymerizable liquid monomer remain in the matrix.

Description

[Technical Field]

[0001] The present invention relates primarily to a method for producing a prepreg and to the prepreg. [Background technology]

[0002] Fiber-reinforced plastics (FRP) are lightweight materials with excellent mechanical properties that are suitable for parts of various transportation equipment, including automobiles, ships, railway vehicles, manned aircraft, and unmanned aerial vehicles, and their importance has been increasing in recent years. One method for efficiently manufacturing FRP products is compression molding prepregs such as sheet molding compounds (SMCs). Prepregs are intermediate materials that have a structure in which fiber reinforcement is impregnated with a matrix made of an uncured thermosetting resin composition.

[0003] SMC is produced by impregnating a random mat type fiber reinforcement material with a liquid thermosetting resin composition, and then thickening the thermosetting resin composition. In order to put epoxy resin-based SMCs into practical use, the following techniques for thickening epoxy resin compositions have been proposed. A thermoplastic resin powder that becomes soluble in epoxy resin when heated is mixed with epoxy resin (Patent Document 1). Polyol and polyisocyanate are mixed with epoxy resin (Patent Document 2). Styrene and maleic anhydride are mixed with an epoxy resin together with a radical polymerization initiator (Patent Document 3). A relatively small amount of carboxylic acid anhydride is mixed into the epoxy resin (Patent Document 4). A relatively small amount of an amine compound is blended into the epoxy resin (Patent Document 5). Furthermore, a technique has been proposed in which an amine or carboxylic acid anhydride that exhibits a thickening effect at temperatures below 40°C and thickening particles that exhibit a thickening effect at temperatures above 45°C are mixed into an epoxy resin in order to suppress excessive flow of SMC during press molding (Patent Document 6). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-181245 [Patent Document 2] Japanese Patent Publication No. 4-88011 [Patent Document 3] Japanese Patent Publication No. 59-68321 [Patent Document 4] International Publication No. 1998 / 022527 [Patent Document 5] Japanese Patent Publication No. 6-166742 [Patent Document 6] Japanese Patent Application Publication No. 2019-167429 Summary of the Invention [Problem to be solved by the invention]

[0005] A primary object of the present invention is to provide an SMC that contains an epoxy resin in a matrix and that is flexible at room temperature but is resistant to squeezing of the matrix from the fiber reinforcement when heated and pressurized. In this specification, problems that can be solved by each embodiment of the present invention may be explicitly or implicitly disclosed. [Means for solving the problem]

[0006] One aspect of the present invention provides a method for producing a prepreg comprising a fiber reinforcement and a matrix. The method includes: impregnating a fiber reinforcement with a liquid epoxy resin composition, which is a precursor material for the matrix, to obtain an impregnated fiber reinforcement; and thickening the liquid epoxy resin composition in the impregnated fiber reinforcement. The liquid epoxy resin composition contains an epoxy resin, an epoxy curing agent, a thickener, and a radical-polymerizable liquid monomer, and the thickening is performed so that the epoxy curing agent and the radical-polymerizable liquid monomer remain in the matrix.

[0007] In another aspect of the present invention, there is provided a prepreg comprising a fiber reinforcement material and a matrix. The matrix is ​​an epoxy resin composition containing an epoxy curing agent and a radically polymerizable liquid monomer. The epoxy resin composition is thickened with a thickener so that the viscosity is 2,000 Pa·s or more and 20,000 Pa·s or less at 25°C. [Effects of the Invention]

[0008] According to a preferred embodiment of the present invention, there is provided an SMC that contains an epoxy resin in a matrix, and that is flexible at room temperature but is difficult to squeeze out of the matrix from the fiber reinforcement when heated and pressurized. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of an SMC manufacturing apparatus. [Figure 2] FIG. 2 is a graph showing a typical viscosity-temperature curve obtained by measuring the viscosity of a thickened product obtained by thickening a liquid epoxy resin composition while increasing the temperature. [Figure 3] FIG. 3 is a schematic bottom view of a ribbed hat channel. [Figure 4] FIG. 4 is a schematic cross-sectional view of the ribbed hat channel of FIG. 3 taken along line AA. [Figure 5] Figure 5 shows the arrangement of SMC when the mold was charged with SMC in the molding experiment of the ribbed hat channel. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail. The viscosity of the liquid epoxy resin composition or its thickened product referred to in the following description refers to the viscosity measured using a rheometer under the conditions of an oscillatory mode, an angular velocity of 10 rad / s, a constant stress of 300 Pa, a plate diameter of 25 mm, and a plate distance of 0.5 mm. In the following description, the liquid epoxy resin composition may be abbreviated as LERC.

[0011] 1. Prepreg manufacturing method One embodiment of the present invention relates to a method for producing a prepreg comprising a fiber reinforcement and a matrix. The method according to the embodiment comprises the following three steps. (i) A step of preparing a LERC as a precursor material of the matrix, which is a mixture of an epoxy resin, an epoxy curing agent, a thickener, and a radical polymerizable liquid monomer. (ii) impregnating a fiber reinforcement with said LERC to obtain an impregnated fiber reinforcement. (iii) thickening the LERC in the impregnated fiber reinforcement to complete the prepreg. Hereinafter, steps (i) to (iii) will also be referred to as steps (i) to (iii), respectively.

[0012] [Step (i)] In step (i), the LERC is prepared by mixing multiple components including an epoxy resin, an epoxy curing agent, a thickener, and a radically polymerizable liquid monomer. Unlike varnishes, LERC is solvent-free and does not require solvent removal before thickening.

[0013] The LERC is liquid at room temperature, and its initial viscosity is preferably 15 Pa s or less, more preferably 10 Pa s or less, and even more preferably 5 Pa s or less at 25° C. There is no particular lower limit to the initial viscosity of the LERC, but it can be, for example, 0.1 Pa s or more, 0.2 Pa s or more, or 0.5 Pa s or more at 25° C. The initial viscosity refers to the viscosity measured within 5 minutes of preparation. The viscosity of the LERC increases over time due to the action of the thickener. When the LERC is kept at 25°C for 6 to 15 days after preparation, the viscosity at 25°C is preferably 2000 Pa·s or more, more preferably 3000 Pa·s or more, even more preferably 4000 Pa·s or more, and is preferably 20000 Pa·s or less, more preferably 10000 Pa·s or less, even more preferably 8000 Pa·s or less.

[0014] Details of each component contained in LERC will be explained later.

[0015] [Step (ii)] In step (ii), an impregnated fiber reinforcement is formed by impregnating the fiber reinforcement with the LERC prepared in step (i). When the viscosity of the LERC is within the above-mentioned preferred range, the LERC can be impregnated with the fiber reinforcement material in a room at a temperature suitable for work of 17°C to 28°C without heating.

[0016] Suitable examples of the fiber reinforcement material include carbon fiber, glass fiber, and aramid fiber, of which carbon fiber is the most preferred due to its low specific gravity and high strength.

[0017] Examples of the form of the fiber reinforcement include, but are not limited to, random mat, woven fabric, nonwoven fabric, and non-crimp fabric. Random mats are formed by cutting continuous fiber bundles with a chopper into short fiber bundles, which are then scattered and piled up on a carrier film. SMC is a type of prepreg that uses random mats as fiber reinforcement.

[0018] When SMC is produced, an impregnated random mat is typically formed using an SMC production apparatus having the basic configuration shown in Figure 1. The procedure can be briefly explained as follows.

[0019] A continuous fiber bundle 10, which is the raw material for the random mat, is drawn out from a fiber package P and sent to a chopper 1. The continuous fiber bundle 10 is a carbon fiber bundle consisting of, for example, 1,000 to 100,000 filaments per bundle, and may be partially split.

[0020] The continuous fiber bundle 10 is cut by a chopper 1 into short fiber bundles 20. The fiber length of the short fiber bundles 20 is, for example, in the range of 5 mm to 100 mm, and can typically be about 1.3 cm (0.5 inches), about 2.5 cm (1 inch), about 3.8 cm (1.5 inches), about 5.1 cm (2 inches), etc.

[0021] The short fiber bundles 20 fall onto the first carrier film 51 traveling below the chopper 1 and are deposited thereon, thereby forming a random mat 30. Before the random mat 30 is deposited, a first resin paste 41 is applied to the surface of the first carrier film 51 by a first coater 2a equipped with a doctor blade, to form a first resin paste layer 41L.

[0022] Following the formation of the random mat 30, the first carrier film 51 and the second carrier film 52 are bonded together with the random mat 30 sandwiched therebetween to form a laminate 60. Prior to the bonding, a second resin paste 42 is applied to the surface of the second carrier film 52 by a second coater 2b equipped with a doctor blade to form a second resin paste layer 42L.

[0023] The formed laminate 60 is pressed by the impregnation machine 3, whereby the random mat 30 is impregnated with the first resin paste 41 and the second resin paste 42 to form an impregnated random mat. The impregnated random mat is wound up on a bobbin. Instead of winding it up on a bobbin, the impregnated random mat may be folded and stored in a container.

[0024] The material of the first carrier film 51 and the second carrier film 52 is, for example, polyolefin such as polyethylene or polypropylene, polyvinylidene chloride, polyvinyl chloride, or polyamide.

[0025] The basis weight of the random mat 30 and the thicknesses of the first resin paste layer 41L and the second resin paste layer 42L are set in consideration of the basis weight and fiber content of the SMC to be manufactured. Typical SMC has a basis weight of 500 to 3500 g / m 2 the fiber content is in the range of 40 to 75 mass %, and the thickness is in the range of 1 to 4 mm, particularly 1.5 to 3 mm.

[0026] In the procedure for producing the impregnated random mat described above, the LERC prepared in step (i) is used as the first resin paste 41 and the second resin paste 42 . It is advantageous for the viscosity of the LERC not to be too low in order to form the first resin paste layer 41L and the second resin paste layer 42L to a uniform thickness in a room at a temperature of 17° C. or higher and 28° C. or lower. From this perspective, the viscosity of the LERC at 25° C. is preferably 0.1 Pa s or higher, more preferably 0.2 Pa s or higher, and even more preferably 0.5 Pa s or higher.

[0027] [Step (iii)] In step (iii), the LERC in the impregnated fiber reinforcement obtained in step (ii) is thickened to complete the prepreg. In other words, the LERC in the impregnated fiber reinforcement is the LERC that has permeated the fiber reinforcement. The matrix in the prepreg is a thickened version of the LERC. The LERC after thickening, i.e., the prepreg matrix, still maintains its ability to cure based on the reaction of epoxy groups. This is because at least some of the epoxy groups contained in the epoxy resin blended into the LERC remain in the matrix. All or part of the epoxy curing agent and radically polymerizable liquid monomer blended into the LERC also remain in the prepreg matrix.

[0028] Whether the epoxy group, epoxy curing agent, and radical polymerizable liquid monomer remain in the matrix depends on the following: 1 This can be confirmed using known analytical techniques such as H-NMR (proton NMR), HPLC (high performance liquid chromatography), and IR (infrared spectroscopy). For example, the components contained in the matrix 1 If a H-NMR spectrum is obtained and a peak due to the proton of the epoxy group is observed, it can be determined that the epoxy group remains. Regarding the radical polymerizable liquid monomer, if it has a vinyl group, for example, the proton of the vinyl group is 1 H-NMR peaks can be used for the determination.

[0029] The epoxy curing agent, which has low solubility in LERC, remains mostly insoluble in the matrix. Since a matrix normally does not harden in the absence of an epoxy hardener, if the matrix has the property of being hardened by heating, it can be assumed that the epoxy hardener blended into its precursor, LERC, remains in the matrix.

[0030] The thickening of the LERC in step (iii) is preferably carried out by holding the impregnated fiber reinforcement at a predetermined thickening temperature, which is lower than the temperature at which the finished prepreg is used to compression mold an FRP product, i.e., the prepreg curing temperature, and can be, for example, 80°C or lower, 70°C or lower, 60°C or lower, 50°C or lower, 40°C or lower, or 30°C or lower. The thickening rate generally decreases as the thickening temperature decreases.

[0031] When a radical polymerization initiator is blended into the LERC, the viscosity increasing temperature is set to a temperature lower than the 10-hour half-life temperature of the radical polymerization initiator, for example, by 10° C. or more, preferably by 20° C. or more, and more preferably by 30° C. or more. This is because the radically polymerizable liquid monomer is not substantially polymerized in step (iii). When a plurality of radical polymerization initiators are blended into the LERC, the viscosity increasing temperature is set to a temperature that is, for example, 10°C or more, preferably 20°C or more, and more preferably 30°C or more lower than the 10-hour half-life temperature of the radical polymerization initiator having the lowest 10-hour half-life temperature.

[0032] When producing SMC as a prepreg, the impregnated random mat is sandwiched between two carrier films, and the viscosity of the LERC is increased until the low viscosity LERC does not adhere to the surface of the carrier film when the carrier film is peeled off from the impregnated random mat. The two carrier films used in the production of SMC are not removed after the impregnation in step (ii) is completed, but serve as protective films for the impregnated random mat and the completed prepreg, and are usually only removed when the prepreg is used to manufacture FRP products.

[0033] The thickening time when thickening at a predetermined thickening temperature can be set so that, when a LERC having the same composition as the LERC used for impregnation in step (ii) is placed in a container and maintained at the same temperature as the thickening temperature, the viscosity at 25°C is preferably 2000 Pa·s or more, more preferably 3000 Pa·s or more, even more preferably 4000 Pa·s or more, and preferably 20000 Pa·s or less, more preferably 10000 Pa·s or less, even more preferably 8000 Pa·s or less. By setting the thickening time in this manner, it is possible to obtain an SMC that can be cleanly peeled off from the carrier film in a room at a temperature of 17 to 28°C and that exhibits appropriate flexibility (which can also be said to have good drapeability).

[0034] The thickening time is not limited, and for example, step (iii) may take longer than two weeks. However, in order to detect any thickening defect early, the thickening time is preferably shorter, preferably within two weeks, more preferably within one week, and even more preferably within four days.

[0035] In step (iii), the LERC thickens mainly due to the action of the thickener. Partial polymerization of the radical polymerizable liquid monomer may contribute to thickening, but this is not the role expected of a radical polymerizable liquid monomer. The radical polymerizable liquid monomer remains in the matrix and acts like a plasticizer, imparting flexibility to the prepreg.

[0036] [Liquid epoxy resin composition] Below, each component to be blended into the LERC prepared in step (i) will be explained.

[0037] [Epoxy resin] As is well known to those skilled in the art, an epoxy resin is a thermosetting resin made of a compound having an epoxy group (hereinafter sometimes referred to as an "epoxy compound"), and is usually a mixture containing two or more compounds.

[0038] For example, bisphenol A epoxy resin is a mixture of compounds represented by the following general formula (a) with different n's, and is solid at room temperature when the average n in the mixture is 1.8 or greater. Commercially available general liquid bisphenol A epoxy resins are mixtures containing, as the main component, the compound where n = 0 in the following formula (a), i.e., bisphenol A diglycidyl ether, and containing small amounts of components where n = 1, and the average n is approximately 0.1 to 0.2. Highly purified bisphenol A diglycidyl ether is known to crystallize at room temperature.

[0039] [ka]

[0040] A mixture obtained by mixing two commercially available epoxy resins is also an epoxy resin. If one of the two commercially available epoxy resins is solid and the other is liquid, whether the mixture will be solid or liquid depends on the mixing ratio and the composition of each commercially available epoxy resin. Generally, the higher the mixing ratio of the liquid, the higher the probability that the mixture will be liquid.

[0041] The total amount of epoxy resins blended into the LERC is, for example, 50 wt% or more of the entire liquid epoxy resin composition, and may also be 60 wt% or more, 65 wt% or more, 70 wt% or more, 75 wt% or more, etc. The viscosity of the blended epoxy resins greatly affects the viscosity of the LERC.

[0042] There are no limitations on the type of epoxy resin that can be blended into the LERC, and various types of epoxy resins can be used, including bisphenol-type epoxy resins, naphthalene-type epoxy resins, biphenyl-type epoxy resins, novolac-type epoxy resins, glycidylamine-type epoxy resins, epoxy resins with an oxazolidone ring structure, alicyclic epoxy resins, and aliphatic epoxy resins. When mixing a plurality of epoxy resins with different viscosities, the viscosity of the mixture generally decreases as the lower viscosity resin is mixed at a higher mixing ratio.

[0043] In a preferred embodiment, the LERC is blended with a bisphenol-based epoxy resin, such as bisphenol A epoxy resin or bisphenol F epoxy resin. Some commercially available bisphenol-based epoxy resins have a low viscosity of 5 Pa·s or less at 25°C. The LERC may contain 50 wt% or more, 60 wt% or more, 65 wt% or more, 70 wt% or more, or 75 wt% or more of the total epoxy resins contained therein as bisphenol-type epoxy resins. Bisphenol-type epoxy resins, especially bisphenol A-type epoxy resins, have the advantages of relatively small shrinkage during curing and relatively good heat resistance of the cured product.

[0044] Examples of commercially available bisphenol A type epoxy resins include, but are not limited to, "jER" (registered trademark) 826, jER827, jER828, jER834, and jER1001 (all manufactured by Mitsubishi Chemical Corporation), "Epiclon" (registered trademark) 850 (manufactured by DIC Corporation), and "Epotohto" (registered trademark) YD-128 (manufactured by Nippon Steel Chemical & Material Co., Ltd.).

[0045] [Epoxy hardener] As the epoxy curing agent, it is preferable to use a latent curing agent. Latent hardeners are solids that have low solubility in epoxy resins at room temperature, but when heated, they melt or dissolve in epoxy resins and function as hardeners. When a properly selected latent curing agent is used, the onset temperature of the viscosity-temperature curve of the LERC can exceed 90° C. As a result, the effect of the epoxy curing agent on the thickening of the LERC in step (iii) is reduced, making it easier to control the thickening and improving the storage stability of the finished prepreg.

[0046] Various imidazoles, dicyandiamide and boron trifluoride-amine complexes are typical examples of latent hardeners. Imidazoles are compounds having an imidazole ring, and include substituted imidazoles in which the hydrogen atoms of imidazole are substituted with substituents, as well as imidazolium salts and imidazole complexes.

[0047] Suitable examples of the substituted imidazole that functions as a latent curing agent include substituted imidazoles having an aromatic ring, which may be a heteroaromatic ring, in the molecule, such as 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2-phenyl-4-methylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-phenyl-4-benzyl-5-hydroxymethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-para-toluyl-4-methyl-5-hydroxymethylimidazole, 2-para-toluyl-4,5-dihydroxymethylimidazole, 2-meta-toluyl-4-methyl-5-hydroxymethylimidazole, 2-meta-toluyl-4,5-dihydroxymethylimidazole and 1-cyanoethyl-2-phenylimidazole.

[0048] Imidazolium salts such as 1-cyanoethyl-2-ethyl-4-methylimidazolium trimellitate, 1-cyanoethyl-2-undecylimidazolium trimellitate, and 1-cyanoethyl-2-phenylimidazolium trimellitate are also suitable examples of imidazole-based latent curing agents.

[0049] Suitable examples of the imidazole-based latent curing agent also include isocyanuric acid adducts of various substituted imidazoles such as 2-phenylimidazole, 2-methylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, and 2-phenyl-4-methyl-5-hydroxymethylimidazole, and in particular, isocyanuric acid adducts of substituted imidazoles having a triazine ring such as 2,4-diamino-6-(2'-methylimidazolyl-(1'))-ethyl-s-triazine, 1-(4,6-diamino-s-triazin-2-yl)ethyl-2-undecylimidazole, and 2,4-diamino-6-[2-(2-ethyl-4-methyl-1-imidazolyl)ethyl]-s-triazine.

[0050] Amine adducts are also suitable examples of latent curing agents. Amine adducts are polymerized by reacting imidazole and / or tertiary amine with epoxy resin and / or isocyanate, and have relatively low solubility in epoxy resin.

[0051] The latent curing agents may be used singly or in combination of two or more. When dicyandiamide is used as the latent curing agent, urea derivatives such as 4,4'-methylenebis(phenyldimethylurea) and 2,4-bis(3,3-dimethylureido)toluene can be preferably used as the curing accelerator. In addition to the latent curing agent, the LERC may contain an epoxy curing agent other than the latent curing agent.

[0052] [Thickener] The thickener is a component that increases the viscosity of the LERC in step (iii). The thickening caused by the thickener affects the viscosity characteristics of the matrix when the completed prepreg is heated, which in turn affects the quality of the FRP product obtained by compression molding the prepreg.

[0053] FIG. 2 is a graph showing a typical viscosity-temperature curve obtained by measuring the viscosity of a thickened product obtained by thickening a liquid epoxy resin composition while increasing the temperature. As can be seen from Figure 2, when the prepreg is heated in the mold, the viscosity of the matrix initially decreases and then begins to increase as the curing reaction begins due to the action of the epoxy curing agent. The temperature at which the viscosity of the matrix changes from decreasing to increasing can exceed 90°C by using a latent curing agent.

[0054] Meanwhile, the flow of prepreg in the mold occurs before the viscosity of the matrix increases, i.e., when the temperature reaches only about 70–80°C. If the viscosity of the matrix is ​​too low at this temperature range, the fiber reinforcement will not flow with the matrix and will be squeezed out of the fiber reinforcement. This results in a poor uniformity of the fiber content in the molded FRP product, and in severe cases, the formation of areas that contain no fiber at all.

[0055] This problem is likely to occur when prepregs are produced using LERCs containing epoxy resins made from epoxy compounds with aromatic rings in their structure, such as bisphenol-type epoxy resins. Such LERCs thicken to a sufficiently high viscosity near room temperature with just a small amount of thickener. However, if the viscosity is optimized near room temperature, only a thickened product with a significantly reduced viscosity can be obtained when heated to 70°C. The present inventors speculate that this is due to the high temperature dependence of intermolecular interactions in epoxy compounds with aromatic rings.

[0056] The inventors have discovered that, ignoring for the moment the fact that the viscosity of the matrix becomes too high near room temperature, the solution to this problem alone is to increase the amount of thickener added to sufficiently increase the viscosity of LERC at 70°C. The 70°C viscosity is the viscosity at 70°C measured by holding LERC at 25°C to thicken it to a viscosity in the range of 2000 to 8000 Pa·s at 25°C, and then increasing the temperature at a rate of 2°C / min.

[0057] Based on the above findings, it is preferable to determine the amount of thickener in the LERC so that the viscosity of the LERC at 70°C is 10 Pa s or more, preferably 20 Pa s or more, further 30 Pa s or more, or even 50 Pa s. The amount of thickener may be an amount that results in a viscosity of 100 Pa s or more, 200 Pa s or more, or 300 Pa s or more at 70°C.

[0058] Adding a thickener to LERC so that the viscosity at 70°C is sufficiently high also has the added benefit of reducing the amount of flash that forms when the finished prepreg is compression molded into an FRP product. To prevent the fluidity of the prepreg from decreasing too much in the temperature range of 70 to 80°C, the amount of thickener in the LERC should be determined so that the viscosity at 70°C does not exceed 1000 Pa·s.

[0059] In step (iii), the radically polymerizable liquid monomer may remain in the LERC thickened by the action of the thickener because the thickener does not use radical polymerization as a thickening mechanism. The compounds that are components of the thickener do not undergo radical polymerization themselves, but rather react with the epoxy compound and / or other compounds that are blended into the LERC to produce compounds with higher molecular weights, thereby thickening the LERC.

[0060] Suitable examples of thickeners include carboxylic acid anhydrides, amine compounds, and polyisocyanates. These thickeners exhibit relatively good thickening properties even at temperatures below 30° C. Polyisocyanates are preferably blended into the LERC together with polyols.

[0061] Examples of carboxylic acid anhydrides that can be used as thickeners include methyltetrahydrophthalic anhydride and methylhexahydrophthalic anhydride. These carboxylic acid anhydrides have low viscosities of less than 0.5 Pa·s at 25°C, so they also function to lower the viscosity of LERC for a while after preparation. Other carboxylic acid anhydrides can also be used as thickeners.

[0062] The carboxylic acid anhydride is preferably blended into the LERC together with a tertiary amine. The tertiary amine catalyzes the reaction between the carboxylic acid anhydride and the epoxy compound, promoting thickening of the LERC. The tertiary amine may be a glycidyl amine.

[0063] Thickening by carboxylic acid anhydrides occurs by forming bonds with epoxy compounds, so when LERC thickens, the carboxylic acid anhydrides in the LERC are consumed.

[0064] Examples of amine compounds that can be preferably used as thickeners include, but are not limited to, isophoronediamine, bis(4-aminocyclohexyl)methane, and 1,3-bis(aminomethyl)cyclohexane. For amine compounds that can be used as thickeners, reference may be made to the aforementioned Patent Documents 5 and 6.

[0065] Thickening by amine compounds occurs by forming a bond between the amine compound and the epoxy compound. Therefore, when the LERC thickens, the amine compound added as a thickener in the LERC is consumed.

[0066] Examples of polyisocyanates that can be preferably used as thickeners include, but are not limited to, diisocyanates having an aromatic ring in the molecular structure, such as bis(4-isocyanatophenyl)methane and toluene diisocyanate.

[0067] Examples of polyols that can be formulated into the LERC with the polyisocyanate include, but are not limited to, ethylene glycol, polyethylene glycol, isosorbide, neopentyl glycol, cyclohexanediol, cyclohexanedimethanol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, and 1,6-hexanediol.

[0068] Thickening by polyisocyanates occurs when polyisocyanates form bonds with epoxy compounds or polyols that are blended together, so when LERCs thicken, the polyisocyanates in the LERCs are consumed.

[0069] [Radical polymerizable liquid monomer] Suitable radically polymerizable liquid monomers have a viscosity at 25°C of, for example, 1 Pa·s or less, preferably 0.5 Pa·s or less, and more preferably 0.25 Pa·s or less, and act as a plasticizer in the matrix of the completed prepreg. That is, they enhance the flexibility at room temperature of the matrix made of LERC thickened with a thickener in an amount sufficient to increase the viscosity at 70°C, thereby improving the drapeability of the prepreg.

[0070] Despite its effect of lowering the viscosity of the matrix, the radical polymerizable liquid monomer does not substantially reduce the room temperature strength and modulus of elasticity of the FRP obtained by curing the prepreg, and this is not limited to when a radical polymerization initiator is blended with the radical polymerizable liquid monomer to the LERC.

[0071] Suitable examples of the radically polymerizable liquid monomer are (meth)acrylate and allyl ester, and (meth)acrylate is more preferred in terms of rapid reaction. In situations where odor is not a problem, styrene can also be used as the radical polymerizable liquid monomer. There is a patent document (WO 2018 / 070076) that states that radical polymerizable monomers having a flash point of 100°C or higher as measured by the Cleveland Open Method have particularly little odor, and this can be referenced. The smaller the molecular weight of a radically polymerizable liquid monomer, the more likely it is to volatilize. Therefore, in order to reduce the odor of the LERC and the completed prepreg and to increase stability, it is desirable that the molecular weight of the radically polymerizable liquid monomer is not too small. From this perspective, the molecular weight of the radically polymerizable liquid monomer is preferably 150 or more, more preferably 200 or more.

[0072] The radical polymerizable liquid monomer may be monofunctional or polyfunctional. Examples of monofunctional (meth)acrylates include, but are not limited to, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, phenyl methacrylate, benzyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, tetrahydrofurfuryl methacrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, 1,3-butanediol dimethacrylate, ethylene glycol dimethacrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, benzyl acrylate, cyclohexyl acrylate, isobornyl acrylate, tetrahydrofurfuryl acrylate, 2-hydroxyethyl acrylate, and hydroxypropyl acrylate.

[0073] A polyfunctional radically polymerizable liquid monomer is, in other words, a compound having two or more ethylenically unsaturated groups per molecule. Compared to monofunctional monomers, polyfunctional monomers are less likely to remain unreacted when the prepreg is cured, and have the advantage of less likely to impair the heat resistance of the FRP obtained by curing the prepreg. Suitable examples of the polyfunctional radically polymerizable liquid monomer include, but are not limited to, polyfunctional (meth)acrylates and diallyl phthalates.

[0074] Suitable examples of polyfunctional (meth)acrylates include, but are not limited to, difunctional monomers such as dimethylol-tricyclodecane dimethacrylate, neopentyl glycol dimethacrylate, 1,6-hexanediol dimethacrylate, dimethylol-tricyclodecane diacrylate, neopentyl glycol diacrylate, and 1,6-hexanediol diacrylate, and trifunctional monomers such as trimethylolpropane trimethacrylate and trimethylolpropane triacrylate.

[0075] The amount of the radically polymerizable liquid monomer is determined so that the prepreg completed after the thickening in step (iii) has an appropriate degree of flexibility. In practice, the amount of the radically polymerizable liquid monomer to be blended may be determined so that when a LERC having the same composition as the LERC used for impregnation in step (ii) is placed in a container and allowed to thicken under the same temperature and time conditions as those used in step (iii), the viscosity at 25°C is preferably 2000 Pa s or more, more preferably 3000 Pa s or more, even more preferably 4000 Pa s or more, and preferably 20000 Pa s or less, more preferably 10000 Pa s or less, even more preferably 8000 Pa s or less. The radical polymerizable liquid monomer to be blended into the LERC may be one type or two or more types.

[0076] [Radical polymerization initiator] To prevent the heat resistance of the FRP obtained by curing the prepreg from being impaired, it is desirable to minimize the amount of unreacted radically polymerizable liquid monomer remaining in the FRP. From this perspective, it is preferable to incorporate a radical polymerization initiator into the LERC. The amount of radical polymerization initiator in the LERC may be appropriately determined, for example, within the range of 0.05 to 1.5% in molar ratio relative to the radically polymerizable liquid monomer.

[0077] Considering that the desired molding time in compression molding is 10 minutes or less, or even 5 minutes or less, in order to polymerize the radically polymerizable liquid monomer during molding, it is preferable that the 1-minute half-life temperature of the radical polymerization initiator be equal to or lower than the temperature at which the FRP product is molded from the prepreg. The one-minute half-life temperature is the temperature at which the half-life of a radical polymerization initiator when thermally decomposed at a certain temperature is one minute. Since the molding temperature in compression molding is usually 130°C or higher, it is particularly preferable that the radical polymerization initiator has a one-minute half-life temperature of 130°C or lower.

[0078] As mentioned above, when the prepreg is heated in the mold, the viscosity of the matrix initially decreases, and then begins to increase once the curing reaction begins due to the action of the epoxy curing agent. In a preferred example, by initiating polymerization of the radical polymerizable liquid monomer before the increase in viscosity of the matrix due to the action of the epoxy curing agent begins, the reaction rate of the radical polymerizable liquid monomer can be increased and the amount of unreacted radical polymerizable liquid monomer remaining in the FRP obtained by curing the prepreg can be effectively reduced.

[0079] In LERC, a radical polymerization initiator is added so that the polymerization of the radically polymerizable liquid monomer begins before the viscosity increase caused by the action of the epoxy curing agent. The viscosity of the thickened product is increased to a range of 2000 to 8000 Pa·s by holding the product at 25°C. When the viscosity of the thickened product is measured while the temperature is increased at a rate of 2°C / min, the temperature at which the viscosity changes from decreasing to increasing is lower than that of LERC prepared and thickened in the same manner except that no radical polymerization initiator is added.

[0080] When the prepreg matrix contains a radical polymerization initiator, the amount of flash produced when the prepreg is used to compression mold an FRP product is reduced. This is thought to be because the viscosity of the matrix increases more quickly as the radically polymerizable liquid monomer polymerizes during molding. This effect is particularly pronounced when the matrix is ​​formed from LERC, which has a viscosity at 90°C higher than that at 70°C due to the addition of a radical polymerization initiator.

[0081] The 90°C viscosity is the viscosity at 90°C measured by holding LERC at 25°C to thicken it to a viscosity in the range of 2000 to 8000 Pa·s at 25°C, and then increasing the temperature at a rate of 2°C / min.

[0082] From the viewpoint of storage stability of the completed prepreg, the 10-hour half-life temperature of the radical polymerization initiator is preferably 60° C. or higher, more preferably 70° C. or higher, and even more preferably 80° C. or higher. The 10-hour half-life temperature is the temperature at which the half-life of the radical polymerization initiator when thermally decomposed at a constant temperature is 10 hours.

[0083] To improve the storage stability of the prepreg, a polymerization inhibitor can be added to the LERC along with the radical polymerization initiator. Suitable examples of the polymerization inhibitor include, but are not limited to, quinones, including hydroquinone, benzoquinone, and their various derivatives, and nitroso compounds. Typical examples of nitroso compounds are nitrosophenols such as p-nitrosophenol and 2-methyl-4-nitrosophenol, and N-nitroso compounds such as N-nitrosodiphenylamine and N-nitrosophenylhydroxyamine. A particularly preferred polymerization inhibitor is N-nitrosophenylhydroxylamine aluminum salt ([C6H5N(NO)O]3Al), which is a type of N-nitroso compound.

[0084] If the amount of polymerization inhibitor added is too small, the storage stability of the prepreg will not be sufficiently improved. Conversely, if the amount of polymerization inhibitor added is too large, the action of the radical polymerization initiator will be inhibited. Taking these factors into consideration, the amount of polymerization inhibitor added can be determined, for example, from the range of 0.02% to 25% in molar ratio relative to the radical polymerizable liquid monomer.

[0085] For sheet-like prepregs such as SMC, storage stability can be improved by using atmospheric oxygen as a polymerization inhibitor instead of or in addition to adding the aforementioned polymerization inhibitor to LERC. To achieve this, it is preferable to use a polyolefin film with high oxygen permeability, such as a polyethylene film or polypropylene film, as a protective film to protect the surface of the sheet-like prepreg.

[0086] Suitable examples of radical polymerization initiators include dilauroyl peroxide [116°C; 62°C], 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate [124°C; 65°C], t-hexylperoxy-2-ethylhexanoate [133°C; 70°C], t-butylperoxy-2-ethylhexanoate [134°C; 72°C], 1,1-di(t-hexylperoxy)-3,3,5-trimethylcyclohexane [147°C; 87°C], and 1,1-di(t-hexylperoxy)-cyclohexane [149°C; 87°C]. The two temperatures listed in parentheses after each compound name are the 1-minute half-life temperature and the 10-hour half-life temperature, respectively.

[0087] From the viewpoint of reducing the VOC (Volatile Organic Compound) content of FRP products molded from the finished prepreg, the compound represented by the chemical formula R is preferred as a radical polymerization initiator. 1 C(=O)OOC(=O)R 2 Diacyl peroxides represented by the formula R 1 and R 2 and diacyl peroxides, each of which is a hydrocarbon group having 10 or more carbon atoms and which may have a substituent. 1 and R 2 may be the same or different. Suitable examples of such diacyl peroxides include, but are not limited to, dilauroyl peroxide and distearoyl peroxide.

[0088] 2. Prepreg Another embodiment of the present invention relates to a prepreg comprising a fiber reinforcement and a matrix. The prepreg according to the embodiment is a prepreg produced by the production method described above, and therefore, its matrix is ​​an epoxy resin composition thickened with a thickener, and contains an epoxy curing agent and a radically polymerizable liquid monomer. For suitable examples of materials and forms of the fiber reinforcing material contained in the prepreg according to the embodiment, please refer to the previous section.

[0089] The prepreg according to the embodiment may be SMC, in which case it contains a random mat as a fiber reinforcement material. The random mat is preferably made of carbon fiber bundles, and may further be made of only carbon fiber bundles, but is not limited thereto. The fiber length of the carbon fiber bundles is, for example, within the range of 5 mm to 100 mm. When the prepreg according to the embodiment is SMC, typically, the basis weight is 500 to 3500 g / m 2 the fiber content is in the range of 40 to 75 mass %, and the thickness is in the range of 1 to 4 mm, particularly 1.5 to 3 mm.

[0090] The matrix of the prepreg according to the embodiment is a thickened LERC containing a plurality of components including an epoxy resin, an epoxy curing agent, a thickener, and a radical polymerizable liquid monomer, and at least a portion of the epoxy groups of the epoxy resin, at least a portion of the epoxy curing agent, and at least a portion of the radical polymerizable liquid monomer remain within the matrix. The total amount of epoxy resins blended into the LERC is, for example, 50 wt% or more of the entire LERC, and may be 60 wt% or more, 65 wt% or more, 70 wt% or more, 75 wt% or more, etc.

[0091] In a preferred embodiment, the LERC contains a bisphenol-based epoxy resin, such as a bisphenol A-based epoxy resin or a bisphenol F-based epoxy resin. The bisphenol-based epoxy resin may account for 50 wt% or more, 60 wt% or more, 65 wt% or more, 70 wt% or more, or 75 wt% or more of the total epoxy resin contained in the LERC.

[0092] The epoxy curing agent blended into the LERC preferably contains a latent curing agent. See the previous section for specific examples of latent curing agents. Suitable examples of thickeners to be incorporated into the LERC include carboxylic acid anhydrides, amine compounds, and polyisocyanates. Polyisocyanates are preferably incorporated into the LERC together with polyols. See the previous section for specific examples of these thickeners.

[0093] The radically polymerizable liquid monomer contained in the matrix of the prepreg according to the embodiment has a viscosity at 25°C of, for example, 1 Pa s or less, preferably 0.5 Pa s or less, and more preferably 0.25 Pa s or less, and acts as a plasticizer in the matrix, i.e., it increases the flexibility of the matrix at room temperature and, in turn, improves the drapeability of the prepreg.

[0094] Suitable examples of the radically polymerizable liquid monomer are (meth)acrylate and allyl ester, and (meth)acrylate is more preferred in terms of rapid reaction. The radically polymerizable liquid monomer may be monofunctional or polyfunctional. Compared to monofunctional monomers, polyfunctional monomers have the advantage that they are less likely to remain unreacted when the prepreg is cured, and therefore are less likely to impair the heat resistance of the FRP obtained by curing the prepreg. Suitable examples of the polyfunctional radically polymerizable liquid monomer include, but are not limited to, polyfunctional (meth)acrylates and diallyl phthalates.

[0095] For specific examples of radical polymerizable liquid monomers, see the previous section. In order to reduce odor and improve stability of the prepreg, it is desirable that the molecular weight of the radical polymerizable liquid monomer is not too small. From this viewpoint, the molecular weight of the radical polymerizable liquid monomer is preferably 150 or more, more preferably 200 or more.

[0096] The prepreg according to the embodiment preferably further contains a radical polymerization initiator in the matrix. The one-minute half-life temperature of the radical polymerization initiator is preferably equal to or lower than the temperature at which an FRP product is molded from the prepreg. Because the molding temperature in compression molding is usually 130°C or higher, radical polymerization initiators having a one-minute half-life temperature of 130°C or lower are particularly preferred. The 10-hour half-life temperature of the radical polymerization initiator is preferably 60°C or higher, more preferably 70°C or higher, and even more preferably 80°C or higher.

[0097] For specific examples of radical polymerization initiators, see the previous section. The radical polymerization initiator contained in the matrix of the prepreg according to the embodiment is preferably not a photoradical polymerization initiator. From the viewpoint of reducing the VOC content of FRP products molded from prepregs, the preferred radical polymerization initiator is a compound represented by the chemical formula R 1 C(=O)OOC(=O)R 2 Diacyl peroxides represented by the formula R 1 and R 2and diacyl peroxides, each of which is a hydrocarbon group having 10 or more carbon atoms and which may have a substituent. 1 and R 2 may be the same or different. Suitable examples of such diacyl peroxides include, but are not limited to, dilauroyl peroxide and distearoyl peroxide.

[0098] The prepreg according to the embodiment may further contain a polymerization inhibitor in addition to the radical polymerization initiator in the matrix. For specific examples of polymerization inhibitors, please refer to the previous section. When the prepreg according to the embodiment is a sheet-like prepreg such as SMC, storage stability can be improved by using atmospheric oxygen as a polymerization inhibitor instead of or in addition to adding a polymerization inhibitor to the matrix. To this end, it is preferable to use a polyolefin film with high oxygen permeability, such as a polyethylene film or a polypropylene film, as a protective film to protect the surface of the sheet-like prepreg.

[0099] In the prepreg according to the embodiment, the viscosity of the matrix at 25°C is preferably 2000 Pa s or more, more preferably 3000 Pa s or more, and even more preferably 4000 Pa s or more. The viscosity of the matrix at 25°C is also preferably 20000 Pa s or less, more preferably 10000 Pa s or less, and even more preferably 8000 Pa s or less. The viscosity of the matrix can be considered to be the viscosity of the matrix when LERC, which is a matrix precursor, is placed in a container and thickened under the same conditions as those used for thickening when producing prepreg.

[0100] When the LERC is kept at 25°C for 6 to 15 days after preparation, the viscosity at 25°C is preferably 2000 Pa·s or more, more preferably 3000 Pa·s or more, even more preferably 4000 Pa·s or more, and is preferably 20000 Pa·s or less, more preferably 10000 Pa·s or less, even more preferably 8000 Pa·s or less.

[0101] The prepreg according to the embodiment contains a compound having an epoxy group and an epoxy curing agent in a matrix. When the prepreg is heated, the epoxy curing agent acts to react with the compound having an epoxy group, curing the matrix and producing FRP. As a molding method for producing an FRP product from the prepreg according to the embodiment, press molding (also called compression molding) is preferably used, but is not limited to this. For example, molding methods other than press molding, such as autoclave molding, can also be used.

[0102] The molding temperature when molding an FRP product from the prepreg according to the embodiment is preferably 130°C or higher. The molding temperature is also preferably 180°C or lower, more preferably 160°C or lower, and even more preferably 150°C or lower.

[0103] 3. Summary of embodiments Embodiments of the present invention include the following. [Embodiment 1] A method for producing a prepreg comprising a fiber reinforcement material and a matrix, the method comprising: impregnating the fiber reinforcement material with a liquid epoxy resin composition that is a precursor material of the matrix to obtain an impregnated fiber reinforcement material; and thickening the liquid epoxy resin composition in the impregnated fiber reinforcement material, wherein the liquid epoxy resin composition contains an epoxy resin, an epoxy curing agent, a thickener, and a radical polymerizable liquid monomer, and the thickening is carried out so that the epoxy curing agent and the radical polymerizable liquid monomer remain in the matrix. [Embodiment 2] 2. The method according to embodiment 1, wherein the matrix contains epoxy groups. [Embodiment 3] The method according to embodiment 1 or 2, wherein the thickening step comprises maintaining the impregnated fiber reinforcement at a predetermined temperature for a predetermined time, and the viscosity of the liquid epoxy resin composition maintained at the predetermined temperature for the predetermined time is at least 2000 Pa s, preferably at least 3000 Pa s, more preferably at least 4000 Pa s, and at most 20000 Pa s, preferably at most 10000 Pa s, more preferably at most 8000 Pa s, at 25° C. The viscosity is measured using a rheometer in an oscillatory mode at an angular velocity of 10 rad / s, with a constant stress of 300 Pa, a plate diameter of 25 mm, and a plate distance of 0.5 mm. [Embodiment 4] The method according to any one of embodiments 1 to 3, wherein the liquid epoxy resin composition has a viscosity of 2000 Pa·s or more, preferably 3000 Pa·s or more, more preferably 4000 Pa·s or more, and 20000 Pa·s or less, preferably 10000 Pa·s or less, more preferably 8000 Pa·s or less, at 25° C. when kept at 25° C. for 6 to 15 days after preparation. The viscosity is measured using a rheometer in an oscillatory mode under the conditions of an angular velocity of 10 rad / s, a constant stress of 300 Pa, a plate diameter of 25 mm, and a plate distance of 0.5 mm. [Embodiment 5] 5. The method according to any one of embodiments 1 to 4, wherein the matrix is ​​softened by the radically polymerizable liquid monomer. [Embodiment 6] The method according to any one of embodiments 1 to 5, wherein the radically polymerizable liquid monomer comprises a (meth)acrylate. [Embodiment 7] The method according to embodiment 6, wherein the (meth)acrylate comprises a multifunctional (meth)acrylate. [Embodiment 8] The method according to embodiment 7, wherein the multifunctional (meth)acrylate comprises a difunctional (meth)acrylate. [Embodiment 9] The method according to any one of embodiments 1 to 8, wherein the radical polymerizable liquid monomer comprises a radical polymerizable liquid monomer having a molecular weight of 150 or more, preferably 200 or more. [Embodiment 10] The method according to any one of embodiments 1 to 9, wherein the viscosity of the liquid epoxy resin composition measured within 5 minutes after preparation is 15 Pa s or less, preferably 10 Pa s or less, and more preferably 5 Pa s or less at 25° C. The viscosity is measured using a rheometer in an oscillatory mode under the conditions of an angular velocity of 10 rad / s, a constant stress of 300 Pa, a plate diameter of 25 mm, and a plate distance of 0.5 mm. [Embodiment 11] The method according to any one of embodiments 1 to 10, wherein the liquid epoxy resin composition is maintained at 25°C immediately after preparation to thicken the composition so that the viscosity at 25°C is in the range of 2000 to 8000 Pa s, and the viscosity of the thickened composition is measured at 70°C while raising the temperature at a rate of 2°C / min. The viscosity is measured using a rheometer in an oscillatory mode under the conditions of an angular velocity of 10 rad / s, a constant stress of 300 Pa, a plate diameter of 25 mm, and a plate distance of 0.5 mm. [Embodiment 12] The method according to any one of embodiments 1 to 11, wherein a radical polymerization initiator is further blended into the liquid epoxy resin composition. [Embodiment 13] The method of embodiment 12, wherein the radical polymerization initiator comprises a radical polymerization initiator having a 1 minute half-life temperature of 130° C. or less. [Embodiment 14] The method according to embodiment 12 or 13, wherein the liquid epoxy resin composition is maintained at 25°C immediately after preparation to thicken the composition so that the viscosity at 25°C is in the range of 2000 to 8000 Pa s, and the viscosity of the thickened composition is measured while increasing the temperature at a rate of 2°C / min, and the first temperature is the temperature at which the viscosity starts to increase from a decrease. The method also includes: a control epoxy resin composition prepared in the same manner as the liquid epoxy resin composition except that the radical polymerization initiator is not added; the control epoxy resin composition is thickened in the same manner as the liquid epoxy resin composition to obtain a thickened composition; and the second temperature is the temperature at which the viscosity of the thickened composition starts to increase from a decrease from a decrease. The first temperature is lower than the second temperature. The viscosity is measured using a rheometer in an oscillatory mode at an angular velocity of 10 rad / s, a constant stress of 300 Pa, a plate diameter of 25 mm, and a plate distance of 0.5 mm. [Embodiment 15] The method according to any one of embodiments 12 to 14, wherein the liquid epoxy resin composition is kept at 25°C immediately after preparation to thicken the composition so that the viscosity at 25°C is in the range of 2000 to 8000 Pa s, and the viscosity of the thickened composition is measured while raising the temperature at a rate of 2°C / min, such that the viscosity at 90°C is higher than the viscosity at 70°C. The viscosity is measured using a rheometer in an oscillatory mode under the conditions of an angular velocity of 10 rad / s, a constant stress of 300 Pa, a plate diameter of 25 mm, and a plate distance of 0.5 mm. [Embodiment 16] The method according to any one of embodiments 12 to 15, wherein the radical polymerization initiator has a 10-hour half-life temperature of 60° C. or higher. [Embodiment 17] 17. The method according to any one of embodiments 12 to 16, wherein the thickening step involves maintaining the impregnated fiber reinforcement at a temperature that is at least 10° C. lower, preferably at least 20° C. lower, more preferably at least 30° C. lower than the 10-hour half-life temperature of the radical polymerization initiator. [Embodiment 18] The radical polymerization initiator is represented by the chemical formula R 1 C(=O)OOC(=O)R2 and R 1 and R 2 wherein each of the following is a hydrocarbon group having 10 or more carbon atoms which may have a substituent. [Embodiment 19] The method according to any one of embodiments 11 to 18, wherein the liquid epoxy resin composition further comprises a polymerization inhibitor. [Embodiment 20] 20. The method according to any one of embodiments 1 to 19, wherein the epoxy resin comprises a bisphenol-type epoxy resin. [Embodiment 21] 21. The method according to any one of embodiments 1 to 20, wherein the epoxy curing agent comprises a latent curing agent. [Embodiment 22] The method of embodiment 21, wherein the latent curing agent comprises one or more curing agents selected from the group consisting of imidazoles, dicyandiamide, boron trifluoride-amine complexes, and amine adducts. [Embodiment 23] 23. The method according to any one of embodiments 1 to 22, wherein the thickener comprises a compound that is not radically polymerizable. [Embodiment 24] 24. The method according to any one of the preceding embodiments, wherein the thickener comprises a compound that reacts with a compound having an epoxy group to produce a compound with a higher molecular weight. [Embodiment 25] 25. The method according to any one of embodiments 1 to 24, wherein the thickening agent comprises a carboxylic acid anhydride. [Embodiment 26] The method of embodiment 25, wherein the liquid epoxy resin composition is formulated with a tertiary amine. [Embodiment 27] 25. The method according to any one of embodiments 1 to 24, wherein the thickener comprises an amine compound. [Embodiment 28] 25. The method according to any one of embodiments 1 to 24, wherein the thickener comprises a polyisocyanate. [Embodiment 29] The method according to embodiment 28, wherein the liquid epoxy resin composition is blended with a polyol. [Embodiment 30] 30. The method according to any one of embodiments 1 to 29, wherein the fiber reinforcement comprises carbon fiber. [Embodiment 31] 31. The method according to any one of embodiments 1 to 30, wherein the prepreg is a sheet molding compound. [Embodiment 32] A prepreg produced by the method according to any one of the first to thirty embodiments. [Embodiment 33] A sheet-like prepreg produced by the method according to any one of embodiments 12 to 19, using a polyolefin film, which may be a polyethylene film or a polypropylene film, as a protective film for protecting the surface. [Embodiment 34] A prepreg comprising a fiber reinforcement material and a matrix, the matrix being an epoxy resin composition containing an epoxy curing agent and a radically polymerizable liquid monomer, the epoxy resin composition having a viscosity increased with a thickener to a viscosity of 2000 Pa·s or more, preferably 3000 Pa·s or more, more preferably 4000 Pa·s or more, and 20000 Pa·s or less, preferably 10000 Pa·s or less, more preferably 8000 Pa·s or less at 25°C. The viscosity is measured using a rheometer in an oscillatory mode under the conditions of an angular velocity of 10 rad / s, a constant stress of 300 Pa, a plate diameter of 25 mm, and a plate distance of 0.5 mm. [Embodiment 35] 35. A prepreg according to embodiment 34, wherein the matrix is ​​softened by the radically polymerizable liquid monomer. [Embodiment 36] 36. A prepreg according to embodiment 34 or 35, wherein the radical polymerizable liquid monomer comprises a radical polymerizable liquid monomer having a molecular weight of 150 or more, preferably 200 or more. [Embodiment 37] 37. The prepreg according to any one of embodiments 34 to 36, wherein the radical polymerizable liquid monomer comprises a (meth)acrylate. [Embodiment 38] 38. The prepreg according to embodiment 37, wherein the (meth)acrylate comprises a polyfunctional (meth)acrylate. [Embodiment 39] 39. The prepreg according to embodiment 38, wherein the multifunctional (meth)acrylate comprises a difunctional (meth)acrylate. [Embodiment 40] 40. The prepreg according to any one of embodiments 34 to 39, wherein the matrix further comprises a radical polymerization initiator. [Embodiment 41] 41. The prepreg of embodiment 40, wherein the radical polymerization initiator comprises a radical polymerization initiator having a one-minute half-life temperature of 130° C. or less. [Embodiment 42] 42. The prepreg according to embodiment 40 or 41, wherein the radical polymerization initiator has a 10-hour half-life temperature of 60° C. or higher. [Embodiment 43] The radical polymerization initiator is represented by the chemical formula R 1 C(=O)OOC(=O)R 2 and R 1 and R 2 43. The prepreg according to any one of embodiments 40 to 42, comprising a diacyl peroxide, each of which is a hydrocarbon group having 10 or more carbon atoms which may have a substituent. [Embodiment 44] 44. The prepreg according to any one of embodiments 40 to 43, wherein the radical polymerization initiator is not a photoradical polymerization initiator. [Embodiment 45] 40. The prepreg according to any one of embodiments 34 to 39, wherein the matrix does not contain a radical polymerization initiator. [Embodiment 46] 45. The prepreg according to any one of embodiments 40 to 44, wherein the matrix further contains a polymerization inhibitor. [Embodiment 47] The prepreg according to any one of embodiments 34 to 46, wherein a bisphenol-type epoxy resin is blended into the epoxy resin composition. [Embodiment 48] 48. The prepreg according to any one of embodiments 34 to 47, wherein the epoxy curing agent comprises a latent curing agent. [Embodiment 49] 49. The prepreg of embodiment 48, wherein the latent curing agent comprises one or more curing agents selected from the group consisting of imidazoles, dicyandiamide, boron trifluoride-amine complexes, and amine adducts. [Embodiment 50] 50. A prepreg according to any one of embodiments 34 to 49, wherein the fiber reinforcement comprises carbon fiber. [Embodiment 51] 51. The prepreg according to any one of embodiments 34 to 50, wherein the fiber reinforcement is a random mat. [Embodiment 52] 52. The prepreg according to any one of embodiments 34 to 51, which is in a sheet form and has a surface protected with a polyolefin film, which may be a polyethylene film or a polypropylene film. [Embodiment 53] The prepreg according to any one of embodiments 34 to 52, which is a sheet molding compound. [Embodiment 54] 54. The prepreg according to any one of embodiments 34 to 53, having a thickness in the range of 1 to 4 mm, and optionally in the range of 1.5 to 3 mm.

[0104] 4. Experimental Results The experiments conducted by the present inventors will be described below.

[0105] [Initial Viscosity of Liquid Epoxy Resin Composition] The initial viscosity of the liquid epoxy resin composition was measured in oscillatory mode using a rheometer manufactured by Thermo Fisher Scientific (product name: HAAKE MARS 40, both "HAAKE" and "MARS" are registered trademarks) under the following conditions: temperature 25°C, angular velocity 10 rad / s, constant stress 300 Pa, plate diameter 25 mm, and distance between plates 0.5 mm. Approximately 0.5 mL of a freshly prepared liquid epoxy resin composition was loaded into the rheometer by mixing the materials in a room at a temperature of approximately 25°C, and measurements were started after confirming that the plate temperature had reached 25°C. In all measurements, the time from preparation of the epoxy resin composition to the start of measurements was 5 minutes or less.

[0106] [Viscosity of thickened liquid epoxy resin composition at elevated temperatures] The prepared liquid epoxy resin composition was kept at 25°C to thicken it to a viscosity in the range of 2000 to 8000 Pa·s at 25°C. The viscosity of the thickened product was measured using a Thermo Fisher Scientific rheometer (product name: HAAKE MARS 40) while raising the temperature from 30°C to 100°C at a rate of 2°C / min. The measurement mode was vibration mode, and the conditions were an angular velocity of 10 rad / s, a constant stress of 300 Pa, a plate diameter of 25 mm, and a distance between plates of 0.5 mm.

[0107] [Strength, Elastic Modulus, and Glass Transition Temperature of Cured Resin] The liquid epoxy resin composition immediately after preparation was vacuum degassed and then poured into a 2 mm gap formed between two 4 mm thick glass plates using a spacer. The liquid epoxy resin composition sandwiched between the two glass plates was then placed in a hot air circulating thermostatic chamber preheated to 70°C, and the temperature inside the chamber was increased at a rate of 10°C / min from 70°C to 140°C until the surface temperature of the glass plates reached 140°C. The chamber was then heated for an additional 30 minutes to maintain the surface temperature at 140°C, thereby curing the liquid epoxy resin composition and producing a 2 mm thick resin plate. DMA test specimens measuring 60 mm long and 12.7 mm wide were cut from the resin plate.

[0108] The strength, elastic modulus (storage flexural modulus E') and glass transition temperature (E'-Tg) were measured by performing dynamic viscoelastic analysis of the DMA specimen in a three-point bending mode using a TA Instruments DMA Q800. The measurement conditions were a temperature rise rate of 5°C / min, a frequency of 1 Hz, a strain of 0.05%, and a temperature of 25 to 250°C. E'-Tg is the temperature at the intersection of the approximate line of the flat region in a graph plotting the storage flexural modulus E' against temperature and the approximate line of the region where logE' drops sharply on the graph.

[0109] [VOC evaluation of cured resin] A VOC test piece measuring 50 mm in length and 10 mm in width was cut out from a 2 mm thick resin plate prepared to obtain a DMA test piece, or from a 2 mm thick resin plate prepared in the same manner. The VOC test piece was placed in a 20 mL glass vial, sealed, and heated at 120°C for 5 hours. The VOCs contained in the gas inside the glass vial were then quantified using a gas chromatograph mass spectrometer. When converting the area of ​​the peaks appearing on the total ion chromatogram into the amount of VOC, the calibration curve of toluene was used for each peak for convenience.

[0110] [Material preparation] The materials shown in Table 1 below were prepared.

[0111] [Table 1]

[0112] Epoxy resin 1 is a bisphenol A type epoxy resin with a nominal viscosity of 9 to 11 Pa·s at 25°C. Epoxy resin 2 is a glycidylamine-type epoxy resin with a nominal viscosity of 1.6 to 2.6 Pa·s at 25°C. Curing agent 1 is an amine adduct-type latent curing agent having a melting point of 59°C. Curing agent 2 is an imidazole-based latent curing agent having a melting point of 253°C. The thickener is a carboxylic acid anhydride with a nominal viscosity of 50-80 mPa·s at 25°C. The radically polymerizable liquid monomer is a bifunctional acrylate with a nominal viscosity of 130 to 170 mPa·s at 25°C. Radical polymerization initiator 1 is an organic peroxide-based polymerization initiator having a 1-minute half-life temperature of 124°C and a 10-hour half-life temperature of 65°C. Radical polymerization initiator 2 is an organic peroxide-based polymerization initiator having a 1-minute half-life temperature of 175°C and a 10-hour half-life temperature of 116°C. The plasticizer is a phosphate ester with a nominal viscosity of 12 mPa·s at 25°C.

[0113] [Experiment 1] The following materials were mixed in the following ratios in a room at a temperature of about 25°C to obtain composition 1. Epoxy resin 1 95 parts by weight Epoxy resin 2 5 parts by weight Hardener 1 4 parts by weight Hardener 2 4 parts by weight Thickener 11 parts by weight

[0114] The initial viscosity of Composition 1 was 7 Pa·s. Composition 1 was kept at 25°C for 7 days to thicken the mixture to a viscosity of 4000 Pa·s at 25°C. The viscosity of this thickened mixture was then measured at elevated temperatures, and was found to be 3 Pa·s at 70°C and 0.8 Pa·s at 90°C. The cured product of Composition 1 had a strength of 120 MPa, an elastic modulus of 3.0 GPa, and a glass transition temperature of 154°C. The VOC evaluation result for the cured product of Composition 1 was 2.5 ppm (toluene equivalent).

[0115] [Experiment 2] Composition 2 was prepared in the same manner as in Experiment 1, except that the blending ratio of the thickener was changed from 11 parts by weight to 20 parts by weight per 100 parts by weight of the epoxy resin. The initial viscosity of Composition 2 was 7 Pa·s. Composition 2 was kept at 25°C for 5 days to thicken the mixture to a viscosity of more than 20,000 Pa·s at 25°C. The viscosity of this thickened mixture was then measured at elevated temperatures, and was found to be 110 Pa·s at 70°C and 70 Pa·s at 90°C.

[0116] [Experiment 3] Composition 3 was prepared in the same manner as in Experiment 2, except that 30 parts by weight of plasticizer was added to 100 parts by weight of the epoxy resin. The initial viscosity of Composition 3 was 1 Pa·s. Composition 3 was kept at 25°C for 16 days to thicken the mixture to a viscosity of 2200 Pa·s at 25°C. The viscosity of this thickened mixture was then measured at elevated temperatures, and was found to be 30 Pa·s at 70°C and 10 Pa·s at 90°C. The cured product of Composition 3 had a strength of 74 MPa, an elastic modulus of 1.9 GPa, and a glass transition temperature of 135°C.

[0117] [Experiment 4] Composition 4 was prepared in the same manner as in Experiment 2, except that 30 parts by weight of a radically polymerizable liquid monomer was additionally blended with 100 parts by weight of the epoxy resin. The initial viscosity of Composition 4 was 2 Pa·s. Composition 4 was kept at 25°C for 15 days to thicken the mixture to a viscosity of 4900 Pa·s at 25°C. The viscosity of this thickened mixture was then measured at elevated temperatures, and was found to be 100 Pa·s at 70°C and 30 Pa·s at 90°C. The cured product of Composition 4 had a strength of 135 MPa, an elastic modulus of 2.9 GPa, and a glass transition temperature of 130°C. The VOC evaluation result for the cured product of Composition 4 was 4.7 ppm (toluene equivalent).

[0118] [Experiment 5] Composition 5 was prepared in the same manner as in Experiment 4, except that 0.54 parts by weight of radical polymerization initiator 1 was additionally blended with 100 parts by weight of the epoxy resin. The initial viscosity of Composition 5 was 2 Pa·s. Composition 5 was kept at 25°C for 8 days to produce a thickened product with a viscosity of 4900 Pa s at 25°C. The viscosity of this thickened product was then measured at elevated temperatures, and was found to be 35 Pa s at 70°C and 130 Pa s at 90°C. In other words, when the temperature of the thickened product of Composition 5 was increased, the viscosity changed from decreasing to increasing at temperatures below 90°C. The cured product of Composition 5 had a strength of 138 MPa, a modulus of elasticity of 3.2 GPa, and a glass transition temperature of 144°C. The VOC evaluation result for the cured product of Composition 5 was 9.8 ppm (toluene equivalent).

[0119] [Experiment 6] Composition 6 was prepared in the same manner as in Experiment 4, except that 0.53 parts by weight of radical polymerization initiator 2 was additionally blended with 100 parts by weight of the epoxy resin. The initial viscosity of Composition 6 was 2 Pa·s. Composition 6 was kept at 25°C for 15 days to thicken the mixture to a viscosity of 6000 Pa·s at 25°C. The viscosity of this thickened mixture was then measured at elevated temperatures, and was found to be 130 Pa·s at 70°C and 45 Pa·s at 90°C. The cured product of Composition 6 had a strength of 131 MPa, a modulus of elasticity of 3.1 GPa, and a glass transition temperature of 133°C. The VOC evaluation result for the cured product of Composition 6 was 11.9 ppm (toluene equivalent).

[0120] Table 2 shows the formulations of Compositions 1 to 6, as well as the initial viscosity and post-curing properties of each composition measured in Experiments 1 to 6.

[0121] [Table 2]

[0122] [Experiment 7] A random mat formed from partially split continuous carbon fiber bundles with 15,000 filaments per bundle was impregnated with Composition 1 to produce a fiber mat with a thickness of approximately 2 mm and a basis weight of 1,800 g / m. 2 An SMC with a fiber content of 58% by weight was prepared. When forming the random mat, the carbon fiber bundles were cut to a fiber length of 2.5 cm. The thickening temperature and thickening time of the matrix after impregnation were 25°C and 5 days, respectively. Two pieces of this SMC were cut to 275 mm x 275 mm and placed on top of each other in a mold heated to a constant temperature of 130°C. After holding for 30 seconds, the mold was clamped. Compression was performed at a pressure of 4 MPa for 10 minutes to form an FRP plate measuring 300 mm x 300 mm x 2 mm. The weight of the flash generated during molding was 31.4 g, which was 11% of the total weight of the SMC used, 281 g.

[0123] Furthermore, the same SMC was compression molded to produce a ribbed hat channel 100 shown in Figures 3 and 4. The ribbed hat channel 100 has an elongated top plate 102, a pair of side walls 104 extending along the longitudinal direction of the top plate 102, flanges 106 extending outward from the lower edges of each side wall, a first rib 111 protruding from the top plate 102 and extending in the longitudinal direction of the top plate 102, and a second rib 112 protruding from the top plate 102 and the side walls 104 and extending in the lateral direction of the top plate 102.

[0124] The dimensions of the ribbed hat channel 100 were 430 mm in length, 72 mm in overall width, 10 mm in flange width, 25 mm in height, 2 mm in thickness, and 10 mm in rib height. Both the first rib 111 and the second rib 112 had a rib thickness of 2.5 mm at the position farthest from the top plate 102. Due to the provision of a draft angle, the rib thickness at the base of the top plate 102 was 3 mm for the first rib 111 and 3.5 mm for the second rib 112. The molding conditions were 130°C, 280 kN, and 10 minutes.

[0125] When charging the mold with SMC, three sheets of SMC cut to 420 mm × 95 mm and two sheets of SMC cut to 420 mm × 40 mm were placed between the male mold 200 and the female mold 300 as shown in Figure 5. In other words, no SMC was placed inside the groove 201 provided in the male mold 200, and a portion of the SMC placed outside the groove flowed into the groove, forming the first rib 111 and the second rib 112. The SMC exhibited good flexibility and could be easily bent by hand without heating. It was also easy to bend the three SMC sheets cut to 420 mm x 95 mm to fit the shape of the convex portion of the male mold 200. When the fabricated ribbed hat channel 100 was observed, it was found that in both the first rib 111 and the second rib 112, there were several areas near the edges that were not filled with carbon fiber and consisted only of cured resin.

[0126] [Experiment 8] An SMC was prepared in the same manner as in Experiment 7, except that Composition 2 was used instead of Composition 1. The resulting SMC did not have good flexibility, and it took a long time to cut it compared to the SMC obtained in Experiment 7. It was also difficult to bend it by hand without heating. When an FRP plate was molded from the SMC produced using this composition 2 in the same manner as in Experiment 7, the weight of the resulting flash was 3.1 g, which was 1% of the weight of the SMC used, 288 g. Furthermore, a ribbed hat channel 100 was molded from SMC made using this composition 2 in the same manner as in Experiment 7, and when observed, it was found that there were almost no areas in either the first rib 111 or the second rib 112 that consisted only of cured resin and were not filled with carbon fiber.

[0127] [Experiment 9] An SMC was prepared in the same manner as in Experiment 7, except that Composition 4 was used instead of Composition 1. The flexibility of the obtained SMC was equivalent to that of the SMC obtained in Experiment 7. An FRP plate was molded from the SMC produced using this composition 4 in the same manner as in Experiment 7, and the weight of the resulting flash was 10.2 g, which was 4% of the weight of the SMC used, 283 g. Furthermore, a ribbed hat channel 100 was molded from SMC made using this composition 4 in the same manner as in Experiment 7, and when observed, it was found that there were almost no areas in either the first rib 111 or the second rib 112 that consisted only of cured resin and were not filled with carbon fiber.

[0128] [Experiment 10] An SMC was prepared in the same manner as in Experiment 7, except that Composition 5 was used instead of Composition 1. The flexibility of the obtained SMC was equivalent to that of the SMC obtained in Experiment 7. An FRP plate was molded from the SMC produced using this composition 5 in the same manner as in Experiment 7, and the weight of the resulting flash was 2.1 g, which was 1% of the weight of the SMC used, 284 g. Furthermore, a ribbed hat channel 100 was molded from SMC made using this composition 5 in the same manner as in Experiment 7, and when observed, it was found that there were almost no parts in either the first rib 111 or the second rib that consisted only of cured resin and were not filled with carbon fiber.

[0129] [Experiment 11] An SMC was prepared in the same manner as in Experiment 7, except that Composition 6 was used instead of Composition 1. The flexibility of the obtained SMC was equivalent to that of the SMC obtained in Experiment 7. An FRP plate was molded from the SMC produced using this composition 6 in the same manner as in Experiment 7, and the weight of the resulting flash was 8.3 g, which was 3% of the weight of the SMC used, 284 g. Furthermore, a ribbed hat channel 100 was molded from SMC made using this composition 6 in the same manner as in Experiment 7, and when observed, it was found that there were almost no areas in either the first rib 111 or the second rib 112 that consisted only of cured resin and were not filled with carbon fiber.

[0130] [Experiment 12] Composition 5 was prepared in the same manner as in Experiment 5, except that a polymerization initiator, dilauroyl peroxide (PERLOYL (registered trademark) L, NOF Corporation), having a 1-minute half-life temperature of 116°C and a 10-hour half-life temperature of 62°C was blended in at a ratio of 0.79 parts by weight per 100 parts by weight of epoxy resin, instead of radical polymerization initiator 1. The VOC evaluation result for the cured product of Composition 5 was 3.3 ppm (toluene equivalent).

[0131] [Experiment 13] Composition 1 was kept at 25°C for 6 days to thicken the mixture to a viscosity of 3800 Pa·s at 25°C. The viscosity of this thickened mixture was then measured at elevated temperatures, and was found to be 3 Pa·s at 70°C and 1 Pa·s at 90°C.

[0132] [Experiment 14] Composition 4 was kept at 25°C for 6 days to thicken the material to a viscosity of 5700 Pa·s at 25°C. The viscosity of this thickened material was then measured as the temperature increased, and was found to be 60 Pa·s at 70°C and 60 Pa·s at 90°C.

[0133] [Experiment 15] Composition 6 was kept at 25°C for 6 days to thicken the mixture to a viscosity of 5600 Pa·s at 25°C. The viscosity of this thickened mixture was then measured at elevated temperatures, and was found to be 47 Pa·s at 70°C and 36 Pa·s at 90°C.

[0134] [Experiment 16] Composition 7 was prepared in the same manner as in Experiment 5, except that the blending ratio of the thickener was changed from 20 parts by weight to 19 parts by weight per 100 parts by weight of the epoxy resin. The initial viscosity of Composition 7 was 2 Pa·s. Composition 7 was kept at 25°C for 6 days to thicken the mixture to a viscosity of 3,400 Pa·s at 25°C. The viscosity of this thickened mixture was then measured at elevated temperatures, and was found to be 23 Pa·s at 70°C and 90 Pa·s at 90°C.

[0135] Furthermore, an SMC was prepared in the same manner as in Experiment 7, except that Composition 7 was used instead of Composition 1. The flexibility of the obtained SMC was equivalent to that of the SMC obtained in Experiment 7. An FRP plate was molded from the SMC produced using this composition 7 in the same manner as in Experiment 7, and the weight of the resulting flash was 2.1 g, which was 0.8% of the weight of the SMC used, 281 g.

[0136] [Experiment 17] Composition 8 was prepared in the same manner as in Experiment 6, except that the blending ratio of the thickener was changed from 20 parts by weight to 19 parts by weight per 100 parts by weight of the epoxy resin. The initial viscosity of Composition 8 was 2 Pa·s. Composition 7 was kept at 25°C for 6 days to thicken the mixture to a viscosity of 3600 Pa·s at 25°C. The viscosity of this thickened mixture was then measured at elevated temperatures, and was found to be 24 Pa·s at 70°C and 15 Pa·s at 90°C.

[0137] Furthermore, an SMC was prepared in the same manner as in Experiment 7, except that Composition 8 was used instead of Composition 1. The flexibility of the obtained SMC was equivalent to that of the SMC obtained in Experiment 7. An FRP plate was molded from the SMC produced using this composition 8 in the same manner as in Experiment 7, and the weight of the resulting flash was 11.3 g, which was 4% of the weight of the SMC used, 282 g.

[0138] [Experiment 18] Composition 9 was prepared in the same manner as in Experiment 5, except that the blending ratio of the thickener was changed from 20 parts by weight to 18 parts by weight per 100 parts by weight of the epoxy resin. This composition 9 was kept at 25°C for 7 days or 14 days to thicken it, and then the remaining epoxy groups and vinyl groups were measured. 1 It was investigated by H-NMR analysis. Specifically, 30 mg of thickened composition 9 and 10 mg of an internal standard reagent (1,2,4,5-tetrachloro-3-nitrobenzene, manufactured by Sigma-Aldrich) were mixed with 0.8 ml of deuterated DMSO to obtain a solution, which was placed in an NMR tube with a diameter of 0.5 mm and analyzed under the following conditions: 1 H-NMR spectrum was measured.

[0139] Equipment: JEOL JNM-ECS400 FT-NMR Magnet: JEOL JMTC-400 / 54 / SS Measurement temperature: 35℃ Spin: 15Hz Number of times accumulated: 8 times x sweep: 20 ppm x points:32768 x angle:90° Relaxation delay: 50 seconds

[0140] For the epoxy group of epoxy resin 1 (bisphenol type epoxy resin), attention was focused on the peak at 2.78 to 2.85 ppm derived from the proton of the epoxy group. For the epoxy group of epoxy resin 2 (N,N,N',N'-tetraglycidyl-m-xylylenediamine), attention was focused on the peak at 3.01 to 3.07 ppm derived from the proton of the epoxy group. Regarding the vinyl group, attention was focused on the peak at 6.07 to 6.2 ppm derived from the proton of the vinyl group.

[0141] As a result of the measurement, it was found that both epoxy groups and vinyl groups remained in both Composition 9 kept at 25°C for 7 days and Composition 9 kept at 25°C for 14 days. Composition 9, which had been kept at 25°C for 14 days, did not dissolve completely (30 mg) in 0.8 ml of deuterated DMSO, making accurate quantification difficult. However, it contained epoxy and vinyl groups in amounts far exceeding trace amounts. From this, it was inferred that the majority of the radically polymerizable liquid monomer (dimethylol-tricyclodecane diacrylate) remained without polymerizing even after Composition 9 had thickened.

[0142] Furthermore, Composition 9 was kept at 25°C for 7 days or 14 days to thicken it, and the amount of the thickener (3 or 4-methyl-1,2,3,6-tetrahydrophthalic anhydride) remaining therein was evaluated by FT-IR spectroscopy. Specifically, in the FT-IR spectrum of Composition 9 obtained by the ATR method (attenuated total reflection method), the peak at 1780 cm attributable to the carboxylic acid anhydride was -1 and the peak at 1510 cm due to the benzene ring. -1 The area ratio of the peaks was calculated and used as an index of the remaining amount of thickener. As a result of the measurement, a small amount of thickener remained in Composition 9 stored at 25°C for 7 days, but no thickener remained in Composition 9 stored at 25°C for 14 days.

[0143] While the present invention has been described above with reference to specific embodiments, these embodiments are presented as examples and do not limit the scope of the present invention. Each embodiment described in this specification can be modified in various ways within the scope of the effects of the invention, and can be combined with features described in other embodiments within the scope of feasibility. [Industrial Applicability]

[0144] The invention disclosed in this specification can be suitably used in the manufacture of FRP parts used in various types of transportation equipment, including automobiles, ships, railway vehicles, manned aircraft, and unmanned aircraft. [Explanation of symbols]

[0145] 1. Chopper 2a First coating machine 2b Second coating machine 3 Impregnation machine 10 Continuous fiber bundle 20 Short fiber bundle 30 Random Mat 41 Daiichi Resin Paste 41L First resin paste layer 42 Second resin paste 42L Second resin paste layer 51 Daiichi Carrier Film 52 Secondary Carrier Film 60 laminate 100 Ribbed Hat Channel 102 Top plate 104 Side wall 106 flange 111 First Rib 112 Second Rib 200 male type 201 Groove 300 female mold P Package

Claims

1. A method for producing a prepreg comprising a fiber reinforcement material and a matrix, the method comprising the steps of: impregnating the fiber reinforcement material with a liquid epoxy resin composition which is a precursor material of the matrix, thereby obtaining an impregnated fiber reinforcement material; and thickening the liquid epoxy resin composition in the impregnated fiber reinforcement material, wherein the liquid epoxy resin composition contains an epoxy resin, an epoxy curing agent, a thickener, and a radical polymerizable liquid monomer, and the thickening is carried out so that the epoxy curing agent and the radical polymerizable liquid monomer remain in the matrix, the thickener comprises a carboxylic acid anhydride, an amine compound, or a polyisocyanate; the epoxy curing agent is a latent curing agent containing one or more curing agents selected from the group consisting of imidazoles, dicyandiamide, boron trifluoride-amine complexes, and amine adducts; The amount of thickener blended is an amount such that the viscosity of the thickened product at 70°C is 10 Pa s or more and 1000 Pa s or less when the viscosity is measured while raising the temperature at a rate of 2°C / min by holding the liquid epoxy resin composition at 25°C immediately after preparation so that the viscosity is increased to a range of 2000 to 8000 Pa s at 25°C (the viscosity is measured using a rheometer under the conditions of an oscillation mode, an angular velocity of 10 rad / s, a constant stress of 300 Pa, a plate diameter of 25 mm, and a distance between plates of 0.5 mm).

2. 2. The method according to claim 1, wherein the thickening step comprises maintaining the impregnated fiber reinforcement at a predetermined temperature for a predetermined time, and the viscosity of the liquid epoxy resin composition maintained at the predetermined temperature for the predetermined time is 2,000 Pa s or more and 20,000 Pa s or less at 25°C (wherein the viscosity is measured using a rheometer under the conditions of an oscillation mode, an angular velocity of 10 rad / s, a constant stress of 300 Pa, a plate diameter of 25 mm, and a plate distance of 0.5 mm).

3. 2. The method according to claim 1, wherein the liquid epoxy resin composition has a viscosity of 2,000 Pa s or more and 20,000 Pa s or less at 25°C when kept at 25°C for 6 days or more and 15 days or less after preparation (wherein the viscosity is measured using a rheometer under the conditions of an oscillation mode, an angular velocity of 10 rad / s, a constant stress of 300 Pa, a plate diameter of 25 mm, and a plate distance of 0.5 mm).

4. The method of claim 1 , wherein the matrix is ​​softened by the radically polymerizable liquid monomer.

5. The method according to any one of claims 1 to 4, wherein the radical polymerizable liquid monomer comprises a radical polymerizable liquid monomer having a molecular weight of 150 or more.

6. The method according to any one of claims 1 to 4, wherein a radical polymerization initiator is further blended into the liquid epoxy resin composition.

7. 7. The method of claim 6, wherein the liquid epoxy resin composition is maintained at 25°C immediately after preparation to thicken the composition so that the viscosity at 25°C falls within the range of 2000 to 8000 Pa s, and the viscosity of the thickened composition is measured while increasing the temperature at a rate of 2°C / min, and the temperature at which the viscosity starts to increase from a decrease is defined as the first temperature; and a control epoxy resin composition, prepared in the same manner as the liquid epoxy resin composition except that the radical polymerization initiator is not blended, is thickened in the same manner as the liquid epoxy resin composition to obtain a thickened composition, and the viscosity of the thickened composition is measured while increasing the temperature at a rate of 2°C / min, and the temperature at which the viscosity starts to increase from a decrease is defined as the second temperature; wherein the first temperature is lower than the second temperature; (wherein the viscosity is measured using a rheometer in an oscillation mode at an angular velocity of 10 rad / s, under a constant stress of 300 Pa, with a plate diameter of 25 mm and a plate distance of 0.5 mm).

8. 7. The method according to claim 6, wherein the liquid epoxy resin composition is kept at 25°C immediately after preparation to thicken the liquid epoxy resin composition so that the viscosity at 25°C is in the range of 2000 to 8000 Pa s, and the viscosity of the thickened liquid is measured while raising the temperature at a rate of 2°C / min, and the viscosity at 90°C is higher than the viscosity at 70°C (wherein the viscosity is measured using a rheometer under the conditions of an oscillation mode, an angular velocity of 10 rad / s, a constant stress of 300 Pa, a plate diameter of 25 mm, and a plate distance of 0.5 mm).

9. The radical polymerization initiator is represented by the chemical formula R １ C(=O)OOC(=O)R ２ and R １ and R ２ The method according to claim 6, wherein each of the groups is a hydrocarbon group having 10 or more carbon atoms which may have a substituent.

10. The method according to claim 6, wherein the liquid epoxy resin composition further contains a polymerization inhibitor.

11. The method according to any one of claims 1 to 4, wherein the epoxy resin comprises a bisphenol-type epoxy resin.

12. The method of any one of claims 1 to 4, wherein the prepreg is a sheet molding compound.

13. A prepreg comprising a fiber reinforcement material and a matrix, wherein the matrix is ​​an epoxy resin composition containing an epoxy curing agent and a radical polymerizable liquid monomer, and the epoxy resin composition is thickened using a thickener; the thickener comprises a carboxylic acid anhydride, an amine compound, or a polyisocyanate; the epoxy curing agent is a latent curing agent containing one or more curing agents selected from the group consisting of imidazoles, dicyandiamide, boron trifluoride-amine complexes, and amine adducts; The amount of thickener blended is such that the viscosity of the liquid epoxy resin composition, which is the matrix precursor material, is increased to a range of 2000 to 8000 Pa s at 25°C by keeping the composition at 25°C immediately after preparation, and the viscosity of the thickened composition is measured while raising the temperature at a rate of 2°C / min, so that the viscosity at 70°C is 10 Pa s or more and 1000 Pa s or less (the viscosity is measured using a rheometer under the conditions of an oscillation mode, an angular velocity of 10 rad / s, a constant stress of 300 Pa, a plate diameter of 25 mm, and a plate distance of 0.5 mm).

14. 14. The prepreg according to claim 13, wherein the epoxy resin composition has been thickened so that its viscosity is 2,000 Pa s or more and 20,000 Pa s or less at 25°C (wherein the viscosity is measured using a rheometer under the conditions of a vibration mode, an angular velocity of 10 rad / s, a constant stress of 300 Pa, a plate diameter of 25 mm, and a plate distance of 0.5 mm).

15. The prepreg according to claim 13, wherein the matrix is ​​softened by the radical polymerizable liquid monomer.

16. The prepreg according to any one of claims 13 to 15, wherein the radical polymerizable liquid monomer comprises a radical polymerizable liquid monomer having a molecular weight of 150 or more.

17. The prepreg according to any one of claims 13 to 15, wherein the radically polymerizable liquid monomer comprises a (meth)acrylate.

18. The prepreg according to any one of claims 13 to 15, wherein the matrix further contains a radical polymerization initiator.

19. The radical polymerization initiator is represented by the chemical formula R １ C(=O)OOC(=O)R ２ and R １ and R ２ The prepreg according to claim 18, comprising a diacyl peroxide in which each of the above is a hydrocarbon group having 10 or more carbon atoms which may have a substituent.

20. The prepreg according to any one of claims 13 to 15, wherein a bisphenol-type epoxy resin is blended into the epoxy resin composition.

21. The prepreg according to claim 18, which is in the form of a sheet and has a surface protected with a polyolefin film.

22. 16. The prepreg according to any one of claims 13 to 15, having a thickness in the range of 1 to 4 mm.

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