Curable resin composition and tow prepreg using the same

Abstract

To provide a curable resin composition which has such viscosity as to have good impregnation property into reinforcement fibers, is excellent in viscosity stability in an impregnation process and tow prepreg storage, has high strength of a molding obtained by curing, and is suitably used as a matrix resin of a fiber-reinforced composite material.SOLUTION: A curable resin composition contains an epoxy resin (A) which is liquid at 25°C, an oxazolidone type epoxy resin (B), dicyandiamide or a derivative thereof (C) and a solid curing accelerator (D) as essential components, wherein viscosity at 100°C of the oxazolidone type epoxy resin (B) is 8 Pa s or less, the blending amount of the oxazolidone type epoxy resin (B) is 10-35 pts.mass with respect to 100 pts.mass of the total of the component (A) and the component (B), and viscosity of the curable resin composition at 25°C is within a range of 4-40 Pa s.SELECTED DRAWING: None

Description

Technical Field

[0006]

[0001] The present invention relates to an epoxy resin composition that can obtain high strength upon curing and a prepreg using the same.

Background Art

[0002] Fiber reinforced composite materials are composed of reinforcing fibers such as glass fibers, aramid fibers, and carbon fibers, and thermosetting matrix resins such as unsaturated polyester resins, vinyl ester resins, epoxy resins, phenolic resins, benzoxazine resins, cyanate resins, and bismaleimide resins. They are lightweight and excellent in mechanical properties such as strength, corrosion resistance, and fatigue resistance, so they are widely applied as structural materials for aircraft, automobiles, civil engineering, and sports goods.

[0003] Manufacturing methods of fiber reinforced composite materials include an autoclave molding method, a press molding method using a prepreg in which a thermosetting matrix resin is impregnated into reinforcing fibers in advance, and a wet lay-up molding method, a pultrusion molding method, a filament winding molding method, an RTM method, etc. that include a step of impregnating a liquid matrix resin into reinforcing fibers and a molding step by thermosetting.

[0004] One of the filament winding molding methods is a dry method using a prepreg in which resin is impregnated into reinforcing fibers in advance. Since the dry method is excellent in shortening the winding speed and the stability of the resin ratio, it has an advantage in high productivity and quality stabilization of fiber reinforced composite materials, and is particularly applied as one of the manufacturing methods of high-pressure gas tanks.

[0005] In the dry method, in order to improve the quality of the prepreg, a matrix resin having a preferable viscosity range and a small viscosity increase rate is used to ensure stable impregnation property and handling property during winding. In addition, for the molded body after curing, in order to increase the rigidity and strength of the fiber reinforced composite material, the matrix resin is desired to have a high elastic modulus and strength, and high heat resistance from the viewpoint of long-term reliability.

[0006] Examples of curing agents for epoxy resin matrix resins include liquid polyamines, solid polyamines, liquid acid anhydrides, hydrazide compounds, imidazole compounds, and boron complex compounds. Liquid polyamines and liquid acid anhydrides have low viscosity and yield resin compositions with excellent impregnation properties, but their high viscosity increase rate makes them unsuitable for tow prepreg matrix resins. Therefore, solid polyamines such as dicyandiamide and diaminodiphenyl sulfone are often used as curing agents to reduce the viscosity increase rate of the matrix resin.

[0007] Patent documents 1 and 2 describe using and adding aliphatic epoxy resin as a method to reduce the viscosity of the matrix resin. However, these methods result in a decrease in heat resistance.

[0008] While studies using oxazolidone-type epoxy resins obtained by reacting epoxy resins with isocyanate compounds have been described in Patent Documents 3-5, etc., as a method for increasing the strength of matrix resins, studies on reducing the viscosity of the resin composition have been insufficient.

[0009] One method for increasing the strength of a matrix resin is to enhance its elasticity by using a polyfunctional epoxy resin. While this method can increase strength and Tg, it leads to an increase in viscosity and a decrease in toughness due to the high crosslinking density (Patent Document 6).

[0010] For fiber-reinforced composite materials, particularly matrix resins for tow prepregs, there is a need for a method that exhibits low viscosity, excellent impregnation properties, a low viscosity increase rate, and achieves high strength and heat resistance after curing. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Application Publication No. 11-302507 [Patent Document 2] Japanese Patent Publication No. 2019-189750 [Patent Document 3] Patent No. 4674988 [Patent Document 4] Japanese Patent Publication No. 2009-112626 [Patent Document 5] Patent No. 6073284 [Patent Document 6] Japanese Patent Publication No. 2016-148022 [Overview of the project] [Problems that the invention aims to solve]

[0012] The present invention aims to provide a resin composition that can be used as a matrix resin for tow prepregs, which has low viscosity, excellent impregnation properties into reinforcing fibers, and can produce fiber-reinforced composite materials with excellent strength and heat resistance in the molded product obtained after curing. [Means for solving the problem]

[0013] As a result of studies conducted to solve the aforementioned problems, the present inventors discovered that a specific epoxy resin composition containing oxazolidone-type epoxy resin as an essential component can be used to obtain a resin composition that exhibits excellent impregnation into reinforcing fibers and high strength upon curing, thus completing the present invention.

[0014] In other words, the present invention relates to a curable resin composition comprising a liquid epoxy resin (A) at 25°C, an oxazolidone-type epoxy resin (B), a dicyandiamide or a derivative thereof (C), and a solid curing accelerator (D) as essential components, wherein the viscosity of the oxazolidone-type epoxy resin (B) at 100°C is 8 Pa·s or less, the amount of oxazolidone-type epoxy resin (B) blended is 5 to 25 parts by mass per 100 parts by mass of the total of components (A) and (B), and the viscosity of the curable resin composition at 25°C is in the range of 4 to 40 Pa·s.

[0015] The above-mentioned oxazolidone-type epoxy resin (B) is obtained by reacting a bisphenol-type epoxy resin with toluene diisocyanate or diphenylmethane diisocyanate.

[0016] The oxazolidone-type epoxy resin (B) is obtained by reacting a bisphenol A-type epoxy resin having an epoxy equivalent of 165 to 175 g / eq represented by the following general formula (1) with toluene diisocyanate.

Chemical formula

[0017] A preferred form of the prepreg in the present invention is that reinforcing fibers are blended at a volume content ratio of 48 to 72%.

[0018] Another form of the present invention is a fiber-reinforced composite material obtained by molding a prepreg in which reinforcing fibers are blended with the above resin composition by a filament winding molding method.

Advantages of the Invention

[0019] The curable resin composition of the present invention has a low viscosity and excellent impregnability to reinforcing fibers. A molded product obtained by curing a prepreg using this composition exhibits high strength and heat resistance, and is particularly suitable for use in a fiber-reinforced composite material obtained by a filament winding molding method.

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present invention will be described in detail. The curable resin composition of the present invention contains, as essential components, an epoxy resin (A) that is liquid at 25°C, an oxazolidone-type epoxy resin (B), dicyandiamide or its derivative (C), and a solid curing accelerator (D). Hereinafter, the epoxy resin (A) that is liquid at 25°C, the oxazolidone-type epoxy resin (B), dicyandiamide or its derivative (C), and the curing accelerator (D) are also referred to as component (A), component (B), component (C), and component (D), respectively.

[0021] The epoxy resin (A) that is liquid at 25°C is not particularly limited as long as it is an epoxy resin that is liquid at room temperature (25°C), but examples include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol E type epoxy resin, bisphenol S type epoxy resin, bisphenol Z type epoxy resin, isophorone bisphenol type epoxy resin, para-aminophenol type epoxy resin, or meta-aminophenol type epoxy resin. Preferably, it is a bisphenol A type epoxy resin or a bisphenol F type epoxy resin, and particularly preferably a combination of a bisphenol A type epoxy resin and a bisphenol F type epoxy resin, for example, a blend of 10 to 40 parts by weight of bisphenol A type epoxy resin and 40 to 80 parts by weight of bisphenol F type epoxy resin. The epoxy equivalent of epoxy resin (A) is preferably 90 to 250 g / eq, and more preferably 150 to 200 g / eq.

[0022] Oxazolidone-type epoxy resin (B) is obtained by reacting an epoxy resin with an isocyanate compound, where the oxazolidone structure is formed by an addition reaction between the epoxy group of the epoxy resin and the isocyanate group of the isocyanate compound. In this reaction, side reactions such as the self-polymerization of the isocyanate compound occur, so if the reactivity of the epoxy group and the isocyanate group, the molar ratio of epoxy group to isocyanate group, the type of catalyst, and the reaction temperature are not carefully considered, an increase in viscosity due to increased molecular weight caused by side reactions will occur.

[0023] The viscosity of component (B) of the present invention at 100°C is 8 Pa·s or less. If the viscosity at 100°C exceeds 8 Pa·s, the viscosity of the curable resin composition becomes high, impairing its impregnation into reinforcing fibers. Preferably, it is 3 Pa·s or less, more preferably 1 Pa·s or less.

[0024] The amount of component (B) contained in the curable resin composition is 10 to 35 parts by mass per 100 parts by mass of the total of components (A) and (B). If the amount of component (B) is less than 10 parts by mass, no improvement in strength is observed, and if the amount of component (B) exceeds 35 parts by mass, the viscosity of the curable resin composition increases, impairing its ability to impregnate the reinforcing fibers. More preferably, the amount is 15 to 30 parts by mass.

[0025] The curable resin composition of the present invention has a viscosity of 4 to 40 Pa·s at 25°C, as measured by an E-type viscometer. Within this range, impregnation into reinforcing fibers is good, and resin leakage during molding is suppressed, resulting in a good appearance for the resulting fiber-reinforced composite material. For practical use, a small viscosity increase rate is desirable; for example, the viscosity increase rate of the 25°C viscosity after 48 hours is preferably 120% or less, more preferably 105% or less.

[0026] Component (B) of the present invention is preferably obtained by reacting a bisphenol-type epoxy resin with toluene diisocyanate or diphenylmethane diisocyanate represented by the following structural formulas (2) and (3). [ka] [ka] Here, n is an integer greater than or equal to 0 or 1, and diphenylmethane diisocyanate is usually a mixture of monomers (n=0) and polymers (n≧1). These compounds exhibit excellent reactivity between epoxy groups and isocyanate groups, and can reduce the viscosity of the resulting oxazolidone-type epoxy resin while increasing the reaction selectivity of the oxazolidone structure.

[0027] Furthermore, in the present invention, it is preferable that component (B) be obtained by reacting a bisphenol A type epoxy resin represented by the following general formula (1) and having an epoxy equivalent of 165 to 175 g / eq with toluene diisocyanate, because this suppresses side reactions, increases the molar ratio of the oxazolidone structure, and reduces the viscosity of the oxazolidone type epoxy resin. [ka] (In the formula, n represents 0 or more, or 1.)

[0028] In the curable resin composition of the present invention, an epoxy resin other than the epoxy resin (A) or oxazolidone-type epoxy resin (B) that is liquid at 25°C may be included, as long as it is less than 20 parts by mass per 100 parts by mass of the total of components (A) and (B).

[0029] Other epoxy resins that can be used include, for example, glycidyl ethers of alkylene oxide adducts of bisphenol having two or more epoxy groups in one molecule, novolac-type epoxy resins such as phenol novolac-type epoxy resins, cresol novolac-type epoxy resins, and bisphenol A novolac-type epoxy resins, alicyclic epoxy resins such as 3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexanecarboxylate, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, and 1-epoxyethyl-3,4-epoxycyclohexane, glycidyl esters such as diglycidyl phthalate, diglycidyl tetrahydrophthalate, and glycidyl dimer acid, and glycidylamines such as tetraglycidyldiaminodiphenylmethane, tetraglycidyldiaminodiphenylsulfone, triglycidylaminophenol, triglycidylaminocresol, and tetraglycidylxylylenediamine. These epoxy resins may be used individually or in combination of two or more types.

[0030] The resin composition of the present invention uses dicyandiamide or a derivative thereof (C) as a curing agent. Dicyandiamide is a curing agent that is solid at room temperature and is hardly soluble in epoxy resin at room temperature, but dissolves when heated to 180°C or higher and reacts with epoxy groups, making it a latent curing agent with excellent storage stability at room temperature. As a derivative thereof, N-substituted dicyandiamide derivatives such as N-hexyldicyandiamide described in Japanese Patent Publication No. 11-119429 can be used.

[0031] The amount of dicyandiamide or its derivative (C) contained in the curable resin composition of the present invention is preferably such that the ratio (H / E) of the number of moles of active hydrogen groups contained in component (C) to the number of moles of epoxy groups in the total epoxy resin in the composition is 0.25 to 0.65, and more preferably 0.35 to 0.55. In another view, the amount of component (C) is preferably in the range of 3.0 to 8.0 parts by weight per 100 parts by weight of the total epoxy resin containing components (A) and (B).

[0032] The solid curing accelerator (D) is preferably one that promotes the reaction with component (C) and suppresses the viscosity increase rate of the mixed curable resin composition, and solid aromatic urea compounds or solid imidazole compounds are used. Examples of solid aromatic urea compounds include 3-(3,4-dichlorophenyl)-1,1-dimethylurea, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, N-phenyl-N',N'-dimethylurea, N-(4-chlorophenyl)-N',N'-dimethylurea, N-(3,4-dichlorophenyl)-N',N'-dimethylurea, N-(3,4-dichlorophenyl)-N',N'-dimethylurea, N-(3-chloro-4-ethylphenyl)-N', Examples include N'-dimethylurea, N-(3-chloro-4-methoxyphenyl)-N',N'-dimethylurea, N-(4-methyl-3-nitrophenyl)-N',N'-dimethylurea, 2,4-bis(N',N'-dimethylureido)toluene, methylene-bis(p-N',N'-dimethylureidophenyl), among which 3-(3,4-dichlorophenyl)-1,1-dimethylurea and 3-(3,4-dichlorophenyl)-1,1-dimethylurea are preferred. These can be used individually or in combination of two or more, and are not limited to those listed above as long as they are chemically stable and do not dissolve in epoxy resin at room temperature. As solid imidazole compounds, it is preferable to use imidazole compounds such as 2-methylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-phenyl-6-4′,5′-dihydroxymethylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, and 2-phenyl-4-methyl-5-hydroxymethylimidazole. Furthermore, imidazole compounds containing a triazine ring can also be preferably used, such as 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, and 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-S-triazine isocyanuric acid adduct. These can be used individually or in combination of two or more, and are not limited to those described above, as long as they are chemically stable and do not dissolve in epoxy resin at room temperature. The amount of component (D) used is preferably 0.1 to 7 parts by weight per 100 parts by weight of the total epoxy resin containing components (A) and (B). If it exceeds 7 parts by weight, the viscosity increase rate during storage of the curable resin composition will increase. If it is less than 0.1 parts by weight, the curing reaction will not be promoted. More preferably it is 1 to 5 parts by weight.

[0033] The curable resin composition of the present invention may contain defoaming agents and leveling agents as additives to improve surface smoothness. These additives can be added in an amount of 0.01 to 3 parts by mass, preferably 0.01 to 1 part by mass, per 100 parts by mass of the total resin composition.

[0034] The curable resin composition of the present invention is manufactured by uniformly mixing the above-mentioned components (A), (B), (C), (D), etc. The resulting resin composition has a viscosity in the range of 4 to 40 Pa·s, as measured using an E-type viscometer cone plate type at 25°C. Within this range, impregnation into reinforcing fibers is good, and resin leakage during molding is suppressed, resulting in a good appearance for the resulting fiber-reinforced composite material.

[0035] Furthermore, the curable resin composition of the present invention may also contain other curable resins. Examples of such curable resins include, but are not limited to, unsaturated polyester resins, curable acrylic resins, curable amino resins, curable melamine resins, curable urea resins, curable cyanate ester resins, curable urethane resins, curable oxetane resins, and curable epoxy / oxetane composite resins.

[0036] The curable resin composition of the present invention may contain coupling agents, conductive particles such as carbon particles or metal-plated organic particles, thermosetting resin particles, or inorganic fillers such as silica gel, nanosilica, alumina fibers, or clay, as well as conductive fillers. The conductivity of the resulting cured resin or fiber-reinforced composite material can be improved by using conductive particles or conductive fillers.

[0037] Examples of conductive fillers include carbon black, carbon nanotubes, fullerenes, and metal nanoparticles, which can be used individually or in combination. Among these, the inclusion of carbon nanotubes is particularly well-known for not only improving conductivity but also for increasing the impact strength of fiber-reinforced composite materials even at concentrations of less than 1 wt%, making it a suitable choice.

[0038] The curable resin composition of the present invention is impregnated into reinforcing fibers or bundles to form a tow prepreg. The method for forming the tow prepreg may be a known method. The tow prepreg thus obtained is suitably used in fiber-reinforced composite materials obtained by filament winding molding.

[0039] The method for processing the curable resin composition of the present invention into a tow prepreg to produce a fiber-reinforced composite material is not particularly limited, but it is preferably applied as a method for manufacturing a pressure vessel by the filament winding method. By winding the tow prepreg around a metal or resin liner and then heat-curing it, a molded product is obtained in which a layer of fiber-reinforced composite material is formed to cover the liner. After this, the liner may be removed if necessary. It is also preferably applied as a method for manufacturing a circular, hollow fiber-reinforced composite material, such as a shaft or roll-shaped molded body, by the filament winding method. A molded product is obtained by winding the tow prepreg around a metal or resin mandrel and heat-molding it, and the mandrel may be removed depending on the application.

[0040] The reinforcing fibers used in the tow prepreg of the present invention can be selected from glass fibers, aramid fibers, carbon fibers, boron fibers, etc., but carbon fibers are preferable in order to obtain a fiber-reinforced composite material that is lightweight and has excellent rigidity and strength.

[0041] In the tow prepreg composed of the curable resin composition and reinforcing fibers of the present invention, the volume content of the reinforcing fibers is preferably 48-72%, and more preferably in the range of 55-68%. This results in a molded article with fewer voids and a high volume content of reinforcing fibers, thus providing a molded material with excellent rigidity and strength.

[0042] In the present invention, it is more preferable that the cured product obtained by curing the curable resin composition at a temperature of 160°C for 1 hour has a flexural modulus of 2.8 GPa or higher as measured in accordance with JIS K7171, and a glass transition temperature (Tg) of 120°C or higher as measured in accordance with JIS K7121. [Examples]

[0043] Next, the present invention will be specifically described based on examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention. Unless otherwise specified, parts are expressed in parts by mass. The unit of epoxy equivalent is g / eq.

[0044] The abbreviations for each component used in the synthesis examples and examples are as follows. (A) component YD-128: Bisphenol A type epoxy resin, epoxy equivalent weight 187 (manufactured by Nippon Steel Chemical & Material) YD-8125: Bisphenol A type epoxy resin, epoxy equivalent weight 173 (manufactured by Nippon Steel Chemical & Material) YDF-170: Bisphenol F type epoxy resin, epoxy equivalent 170 (manufactured by Nippon Steel Chemical & Material) (B) Component YD-952: Oxazolidone type epoxy resin, epoxy equivalent 335 (manufactured by Nippon Steel Chemical & Material, viscosity at 100°C 54 Pa·s) (C) Component DICY: Dicyandiamide, active hydrogen equivalent 21 g / eq (D) Component DCMU: 3-(3,4-dichlorophenyl)-1,1-dimethylurea 2MZA:2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine

[0045] Synthesis Example 1 In a glass separable flask equipped with a stirrer, thermometer, condenser with fraction recovery tank, and nitrogen gas introduction device, 171 parts of YD-128 and 0.2 parts of tris-(2,6-dimethoxyphenyl)phosphine were charged, and the mixture was heated to 150°C while stirring. Next, 20 parts of toluene diisocyanate were added dropwise over 3 hours using a dropping funnel, and the reaction was carried out. The reaction temperature was then maintained at 160°C for another 3 hours, yielding 189 parts of an epoxy resin with an epoxy equivalent of 277, a viscosity of 1.4 Pa·s at 100°C, and an oxazolidone structure. This epoxy resin was designated OXA1.

[0046] Synthesis Example 2 In the same apparatus as in Synthesis Example 1, 149 parts of YD-128 and 0.2 parts of tetrabutylammonium bromide were charged and the temperature was raised to 140°C while stirring. Next, 15 parts of diphenylmethane diisocyanate were added in installments over 4 hours and the reaction was carried out. The reaction temperature was then maintained at 160°C and the reaction was carried out for 3 hours to obtain 160 parts of an epoxy resin having an oxazolidone structure with an epoxy equivalent of 240 and a viscosity of 1.5 Pa·s at 100°C. This epoxy resin was designated as OXA2.

[0047] Synthesis Example 3 In the same apparatus as in Synthesis Example 1, 199 parts of YD-8125 and 0.2 parts of tetrabutylammonium bromide were charged and the temperature was raised to 150°C while stirring. Next, 20 parts of toluene diisocyanate were added dropwise over 3 hours to carry out the reaction. The reaction temperature was then maintained at 160°C for another 3 hours to obtain 208 parts of an epoxy resin having an oxazolidone structure with an epoxy equivalent of 236 and a viscosity of 0.6 Pa·s at 100°C. This epoxy resin was designated as OXA3.

[0048] Example 1 (A) Component consisted of 17 parts YD-128 and 67 parts YDF-170, (B) component consisted of 18 parts OXA1, (C) component consisted of 5.7 parts DICY, and (D) component consisted of 3.4 parts DCMU. These were placed in a 150 mL plastic container and stirred for 5 minutes under reduced pressure using a vacuum mixer "Awatori Rentaro" (manufactured by Shinky Co., Ltd.) to obtain a curable resin composition.

[0049] Examples 2-11, Comparative Examples 1-3 A curable resin composition was prepared in the same manner as in Example 1, except that the raw materials used for components (A) to (D) were in the compositions listed in Tables 1 and 2.

[0050] (viscosity measurement) The viscosity at 25°C was measured using an E-type viscometer with a cone plate. A curable resin composition was prepared, and 0.8 mL of it was used for measurement. The viscosity value was recorded 90 seconds after the start of the measurement. The viscosity at 25°C was measured using an E-type viscometer with a cone plate. A curable resin composition was prepared, and 0.8 mL of it was used for measurement. The value obtained 90 seconds after the start of measurement was taken as the viscosity at 25°C. The prepared fiber-reinforced composite resin composition was also left to stand in a constant temperature water bath set at 40°C for 48 hours, and the viscosity at 25°C was measured similarly using an E-type viscometer with a cone plate, and the value obtained after 48 hours was taken as the viscosity at 25°C. Furthermore, the viscosity increase rate was calculated using the formula 100 × (viscosity at 25°C after 48 hours / viscosity at 25°C).

[0051] (Measurement of flexural modulus and flexural strength) The curable resin composition was poured into a 60mm x 240mm mold equipped with a 4mm thick spacer cut into a flat plate shape, and cured at 150°C for 2 hours to create a molded plate for measurement. This plate was then used for measuring the flexural modulus and flexural strength, as well as the fracture toughness, as described later. The resulting molded plate was cut to a size of 80 mm x 10 mm using a bench band saw, and bending tests were performed on the bending test specimens at a temperature of 23°C using a method compliant with JIS 7171, and the bending modulus of elasticity and bending strength were calculated.

[0052] (Measurement of glass transition temperature) The above molded plate was cut to a size of 2.5 mm x 2.5 mm using a bench band saw, and then polished to a thickness of approximately 0.8 mm using a belt disc sander. A differential scanning calorimeter was used to measure the temperature under a nitrogen atmosphere at a heating rate of 10°C / min. The glass transition temperature Tg was defined as the intersection point of the tangent line at the inflection point of the DSC curve and the tangent line in the temperature region 20-30°C lower than the inflection point where the inflection begins.

[0053] (Measurement of interlaminar shear delamination strength) The obtained curable resin composition was poured into a resin bath, and while threading Toray T700SC-12K carbon fiber (manufactured by Toray) through a roll coater at a rate of 2 m / min, 0.33 g of the curable resin composition was applied and impregnated per meter of carbon fiber. The material was then wound up using a bobbin traverse winder equipped with a plate-shaped mandrel until the laminate thickness reached 3 mm, obtaining a tow prepreg laminate. Subsequently, the plate-shaped mandrel was removed, and a flat section measuring 200 mm in length and 100 mm in width was cut from the tow prepreg laminate. This was then cured at 150°C for 2 hours using a vacuum press to form a 3 mm thick plate of carbon fiber reinforced composite material with a volume content of 62% and uniform fiber orientation in one direction. Using a milling machine, specimens were cut from a carbon fiber reinforced composite material sheet to a size of 21 mm in the fiber-parallel direction and 10 mm in the fiber-vertical direction, and these specimens were used for measuring fracture toughness. Interlaminar shear delamination tests were performed at a temperature of 23°C according to the method compliant with JIS K7078, and the interlaminar shear delamination strength was measured.

[0054] The results of each physical property and test are shown in Table 1 and Table 2, respectively.

[0055] [Table 1]

[0056] [Table 2]

Claims

1. A curable resin composition comprising a liquid epoxy resin (A) at 25°C, an oxazolidone-type epoxy resin (B), a dicyandiamide or a derivative thereof (C), and a solid curing accelerator (D) as essential components, wherein the oxazolidone-type epoxy resin (B) is obtained by reacting a bisphenol A type epoxy resin represented by the following general formula (1) with an epoxy equivalent of 165 to 175 g / eq with toluene diisocyanate, the viscosity of the oxazolidone-type epoxy resin (B) at 100°C is 8 Pa·s or less, the amount of oxazolidone-type epoxy resin (B) blended is 10 to 35 parts by mass per 100 parts by mass of the total of components (A) and (B), and the viscosity of the curable resin composition at 25°C is in the range of 4 to 40 Pa·s. 【Chemistry 1】

2. A tow prepreg characterized by being a curable resin composition according to claim 1, to which reinforcing fibers are blended in such a volume content as 48 to 72%.

3. A molded article obtained by forming the tow prepreg described in claim 2 by a filament winding molding method.

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