JP7059000B2 - Curing method of epoxy resin composition - Google Patents

Description

The present invention relates to a method for curing an epoxy resin composition used for a fiber-reinforced composite material.

Conventionally, fiber-reinforced composite materials consisting of reinforced fibers such as carbon fiber and glass fiber and thermosetting resins such as epoxy resin and phenol resin have been lightweight, but have mechanical properties such as strength and rigidity, heat resistance, and corrosion resistance. Due to its excellent properties, it has been applied to many fields such as aerospace, automobiles, railroad vehicles, ships, civil engineering and construction and sporting goods. In particular, in applications where high performance is required, a fiber-reinforced composite material using continuous reinforcing fibers is used, carbon fibers having excellent specific strength and specific elasticity as reinforcing fibers, and heat-curing as a matrix resin. Epoxy resins having excellent adhesiveness to carbon fibers are often used. However, since the epoxy resin (cured product) is generally brittle, that is, it has a drawback of low toughness and elongation, the mechanical properties of the fiber-reinforced composite material using the epoxy resin (cured product) as it is are lowered, which is not satisfactory.

As a method for improving the toughness and elongation of an epoxy resin, a method of blending a rubber component having excellent toughness or a thermoplastic resin has been tried. For example, it has been studied since the 1970s that the toughness of an epoxy resin is improved by blending a rubber component such as acrylonitrile-butadiene rubber containing a carboxyl group with an epoxy resin, and it is generally well known. However, the rubber component causes a decrease in heat resistance and a decrease in elastic modulus, and in order to sufficiently obtain the toughness modifying effect of the rubber component, it is necessary to add a large amount of the rubber component. For this reason, there is a drawback that the inherent heat resistance and mechanical properties of the epoxy resin are deteriorated, and a composite material having good physical properties cannot be obtained.

Curing of the epoxy resin proceeds by addition polymerization or ring-opening polymerization accompanied by ring-opening of the epoxy ring using a curing agent or a catalyst (curing aid). As the curing agent, amines, acid anhydrides, dicyandiamides, phenols and the like are widely used, and they are appropriately selected and used according to the purpose and use.
Among them, dicyandiamide is known as a latent curing agent because it is a solid crystal having a melting point of 200 ° C. or higher, and is used in applications requiring storage stability. On the other hand, since it melts at 100 ° C. or higher and the curing reaction starts, the curing temperature becomes high, and when an epoxy resin is used in a fiber-reinforced composite material application, the toughness of the obtained cured product may not meet the required physical characteristics. be.

Further, when the epoxy resin composition is cured, an operation called precure is generally performed in which pre-curing is performed at a temperature equal to or lower than the planned curing temperature. This is a technique used to shorten the curing time in the mold, control the heat generation of the cured product, or reduce the tackiness by solidifying and facilitate handling (Patent Document 1). 2). However, the epoxy resin composition used for the fiber-reinforced composite material has not been studied, and the influence on the physical properties of the cured product at that time has not been mentioned.

Japanese Unexamined Patent Publication No. 10-279780 Japanese Unexamined Patent Publication No. 11-286026

The present invention provides a fiber-reinforced composite material having excellent impregnation property and storage stability during prepreg production and excellent mechanical properties of the molded product by performing precure under specific conditions during the production of the molded body. It provides a curing method of an epoxy resin composition for a fiber reinforced composite material which can be suitably used in a winding method.

That is, the present invention is a method for curing an epoxy resin composition containing an epoxy resin (A), a dicyandiamide (B) and an imidazole-based curing aid (C) as essential components, as the imidazole-based curing aid (C). When the epoxy resin composition is measured by DSC at a heating rate of 10 ° C./min, the epoxy resin composition is pre-cured at 90 ° C. to 140 ° C. using a material having a heat generation start temperature of 135 ° C. or higher. It is a curing method of an epoxy resin composition characterized by.

In the above curing method, precure is preferably performed at 90 ° C. to 140 ° C. for 30 to 180 minutes, and after precure, the main curing reaction is preferably performed at a temperature higher than the precure temperature for 30 to 120 minutes.

Another aspect of the present invention is an epoxy resin composition for a fiber-reinforced composite material containing an epoxy resin composition containing an epoxy resin (A), a dicyandiamide (B) and an imidazole-based curing aid (C) as essential components, and reinforcing fibers. A method for producing a fiber-reinforced composite material by curing the epoxy resin composition, which has a heat generation start temperature of 135 ° C. or higher when measured with a DSC at a temperature rise rate of 10 ° C./min. A method for producing a fiber-reinforced composite material, which comprises pre-curing an epoxy resin composition for a fiber-reinforced composite material at 90 ° C to 140 ° C. Further, it is a molded product obtained by the above-mentioned method for producing a fiber-reinforced composite material.

According to the curing method of the present invention, an epoxy resin cured product for a fiber-reinforced composite material, which has excellent impregnation property during prepreg production and has both high storage stability, high fracture toughness and elongation, can be obtained.

It is a graph which shows the heat generation start temperature and the heat generation peak temperature obtained from a DSC chart.

Hereinafter, embodiments of the present invention will be described in detail.
The curing method of the present invention is a method for curing an epoxy resin composition containing an epoxy resin (A), a dicyandiamide (B) and an imidazole-based curing aid (C) as essential components, and the epoxy resin composition is precure (precure). After preheating), curing is performed in two steps of main curing at a temperature higher than that of precure.
As the imidazole-based curing aid (C), an epoxy resin composition having a heat generation start temperature of 135 ° C. or higher when measured by differential scanning calorimetry (DSC) at a heating rate of 10 ° C./min is used. do.

When the epoxy resin, dicyandiamide, and imidazole are present in the epoxy resin composition, the curing reaction mainly proceeds synergistically between the reaction between the epoxy resin and imidazole and the reaction between the epoxy resin and dicyandiamide catalyzed by imidazole. Furthermore, since the reaction between the epoxy resin and dicyandiamide also proceeds, the reaction mechanism becomes very complicated.
Although the details are not clear, this curing reaction is a two-step curing of precure and main curing, and by controlling at a specific temperature and time, an epoxy resin cured product for fiber reinforced composite materials that achieves both high fracture toughness and elongation. Can be obtained.

Precure (pre-curing) suppresses heat generation during the main curing reaction and controls the complicated curing reaction of the present composition by temperature to promote the curing reaction having superior elongation and fracture toughness. To do. Precure should be heated at an arbitrary temperature of 90 to 140 ° C., preferably 100 to 130 ° C., more preferably 105 to 125 ° C., for any time in the range of 0.5 to 3 hours, preferably 0.5 to 2 hours. It is done by. The heating condition may be one step or a multi-step condition in which a plurality of heating conditions are combined. If the curing temperature is less than 90 ° C., the reaction is delayed, which is not preferable from the viewpoint of productivity, and similarly, the curing time exceeding 3 hours is also not preferable. Further, if the curing time is less than 0.5 hours, the effect of precure is not sufficiently exhibited, and if the curing temperature is higher than 140 ° C., the elongation of the cured product is lowered.

After pre-cure, the main curing is performed, and a desired cured product is obtained by a crosslinking reaction. In this curing, the crosslinking reaction is allowed to proceed by heating at an arbitrary temperature equal to or higher than the precure temperature, preferably at a temperature higher than 10 ° C. for an arbitrary time in the range of 0.5 to 2 hours, preferably 0.5 to 1 hour. To obtain a cured product. The main curing temperature is appropriately selected in a temperature range of 140 to 180 ° C., preferably 140 to 160 ° C., more preferably 145 to 155 ° C. The heating condition of the main curing may be one-step or a multi-step condition in which a plurality of heating conditions are combined, but a curing time of more than 2 hours is not preferable from the viewpoint of productivity.

The epoxy resin composition used in the curing method of the present invention contains an epoxy resin (A), dicyandiamide (B), and an imidazole-based curing aid (C) as essential components. Further, it is preferable to include a rubber component as the component (D). Hereinafter, the epoxy resin (A), the dicyandiamide (B), the imidazole-based curing aid (C), and the core-shell rubber (D) are used as the components (A), (B), (C), and (D), respectively. say.

The blending amount of the epoxy resin (A) used in the present invention is 40 to 75 parts by mass, preferably 40 to 70 parts by mass, and more preferably 50 to 50 parts by mass, out of a total of 100 parts by mass of the components (A) to (C). It is 70 parts by mass. When the component (D) is also included, the blending amount is the same with respect to a total of 100 parts by mass of the components (A) to (D).
As the epoxy resin, a bisphenol A type epoxy resin having two epoxy groups in one molecule, a bisphenol F type epoxy resin, a bisphenol E type epoxy resin, a bisphenol S type epoxy resin, a bisphenol Z type epoxy resin, and an isophoron bisphenol type epoxy resin. Bisphenol type epoxy resins such as, halogens, alkyl substituents, hydrogenated products of these bisphenol type epoxy resins, high molecular weight bodies having multiple repeating units not limited to monomers, glycidyl ethers as alkylene oxide adducts, and phenols. Novolak type epoxy resin such as novolak type epoxy resin, cresol novolak type epoxy resin, bisphenol A novolak type epoxy resin, 3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexanecarboxylate , 3,4-Epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 1-epoxyethyl-3,4-epoxycyclohexane and other alicyclic epoxy resins, trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl Aliper epoxy resins such as ethers and polyoxyalkylene diglycidyl ethers, phthalic acid diglycidyl esters, tetrahydrophthalic acid diglycidyl esters, glycidyl esters such as dimer acid glycidyl esters, tetraglycidyl diaminodiphenylmethane, tetraglycidyl diaminodiphenyl Glycidyl amines such as sulfone, triglycidylaminophenol, triglycidylaminocrezole, and tetraglycidylxylylene diamine can be used. Among these epoxy resins, an epoxy resin having two epoxy groups in one molecule is preferable from the viewpoint of the rate of increase in viscosity, and a polyfunctional epoxy resin having more epoxy groups is not preferable. Among them, the bisphenol F type epoxy resin is the most preferable. These may be used alone or in combination of two or more.

The epoxy resin (A) used in the present invention preferably has a viscosity in the range of 5 to 30 Pa · s, more preferably 6 to 25 Pa · s, measured using an E-type viscometer (cone plate type) at 25 ° C. , More preferably 7 to 20 Pa · s. As a result, the reinforcing fiber has good impregnation property, and the resin does not easily drip from the fiber even after impregnation. Further, the epoxy resin (A) may be a mixture of several kinds, and the viscosity of the mixture is preferably in the above range.

In the epoxy resin composition, dicyandiamide (B) is used as a curing agent. Diciandiamide is a solid curing agent at room temperature and hardly dissolves in epoxy resin at room temperature, but it dissolves when heated to 180 ° C or higher and has the property of reacting with epoxy groups. It has excellent storage stability potential at room temperature. It is a curing agent. The amount to be used is preferably 0.2 to 0.8 equivalents (calculated with 1 mol of dicyandiamide as 4 equivalents) with respect to the epoxy equivalent of the epoxy resin (A). More preferably, it is 0.2 to 0.5 equivalent. If it is less than 0.2 equivalents to the epoxy equivalent, the crosslink density of the cured product becomes low and the fracture toughness tends to be low, and if it exceeds 0.8 equivalents, unreacted dicyandiamide tends to remain, resulting in poor mechanical properties. There is a tendency.

The epoxy resin composition can be prepared by various known methods. For example, there is a method of kneading each component with a kneader. Further, kneading may be performed using a twin-screw extruder. The dicyandiamide (B) is dispersed in each component in a solid state, but when all the components are kneaded at once, the dicyandiamide may aggregate and cause dispersion failure. An epoxy resin composition with poor dispersion is not preferable because it causes uneven physical properties in the cured product and causes poor curing. Therefore, it is preferable to use a part of the epoxy resin for dicyandiamide, pre-knead it with three rolls, and use it as a masterbatch.

The blending amount of the imidazole-based curing aid (C) contained in the epoxy resin composition is preferably 50 to 250 parts by mass, more preferably 50 to 100 parts by mass with respect to 100 parts by mass of the dicyandiamide (B). .. When the amount of the imidazole-based curing aid is less than 50 parts by mass, it becomes difficult to develop the fast-curing property, and when the amount is more than 250 parts by mass, the fast-curing property does not change, but the cured product tends to be brittle.

As the imidazole-based curing aid (C), in order to suppress the viscosity increase rate (storage stability), the DSC (differential difference) when the epoxy resin compositions of (A), (B) and (C) are used. Scanning calorie analysis) Use a heat generation start temperature of 135 ° C or higher. It is preferably 137 ° C. or higher, more preferably 140 ° C. or higher. If the heat generation start temperature is lower than 135 ° C., not only the storage stability at room temperature is lowered, but also the curing reaction proceeds at the time of impregnation, and the effect of improving the fluidity is not sufficiently exhibited. The DSC heat generation start temperature is the condition that the epoxy resin compositions (A), (B) and (C) containing the imidazole-based curing aid (C) as a curing catalyst are heated at a heating rate of 10 ° C./min. It is a temperature represented by the extrapolation of the calorific value per hour when DSC measurement is performed, and FIG. 1 shows the measurement method.
In FIG. 1, for the epoxy resin compositions (A), (B) and (C), the heat generation amount per hour is extrapolated, the intersection thereof is defined as the heat generation start temperature, and the temperature indicating the maximum value of the heat generation amount. Was defined as the exothermic peak temperature.

Further, as the imidazole-based curing aid (C), in order to suppress heat generation during curing, the DSC heat generation peak temperature when the epoxy resin composition is used is preferably 145 ° C. to 160 ° C., more preferably 148 ° C. to It is preferable that the temperature is 155 ° C. If the exothermic peak temperature is lower than 145 ° C., not only the storage stability at room temperature is lowered, but also the curing reaction proceeds at the time of impregnation, and the effect of improving the fluidity is not sufficiently exhibited. Further, if the temperature exceeds 160 ° C., abnormal heat generation and decomposition of the resin itself occur due to heat generation during curing, which is not preferable. This DSC exothermic peak temperature is the exothermic peak temperature when the epoxy resin composition containing the imidazole-based curing aid (C) as a curing catalyst is measured by DSC at a heating rate of 10 ° C./min.

As an imidazole-based curing aid (C), in order to further satisfy the heat resistance at the time of curing in addition to the impregnation property of the epoxy resin composition into the reinforcing fibers, 2,4-diamino-6- [2'-ethyl -4'-Methylimidazolyl- (1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenyl-4-methyl-5-hydroxymethylimidazole is preferred. Further, as long as the composition has a composition showing an exothermic peak temperature of 145 ° C. or higher, one or a combination of two or more of other imidazole-based compounds may be used as a part of the curing aid component. For example, other imidazole-based curing aids (C1) include 2-methylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 1-benzyl-2-methylimidazole, and 2-undecylimidazole. , 2-Heptadecylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-phenyl6-4', 5'-dihydroxymethylimidazole, 1-cyanoethyl-2-ethyl-4methylimidazole and the like. It is preferable to use a system compound. Further, examples of the imidazole compound containing a triazine ring include 2,4-diamino-6- [2'-methylimidazolyl- (1')]-ethyl-s-triazine and 2,4-diamino-6- [. 2'-Undecylimidazolyl- (1')]-ethyl-s-triazine and the like can be mentioned.

Since the imidazole-based curing aid (C) is also solid, it tends to cause poor dispersion. It is preferable to do so.

When the core-shell rubber (D) is added to the essential components (A) to (C), the core-shell rubber (D) is a particulate core component containing a crosslinked rubber-like polymer or elastomer as a main component. A part or the whole of the surface of the particulate core component is coated with the shell component by graft-polymerizing a shell component polymer different from the core component on the surface.

The amount of the core-shell rubber (D) to be blended is preferably 0.5 to 15 parts by mass, more preferably 1 to 10 parts by mass in 100 parts by mass of the epoxy resin composition. When the blending amount is 0.5 parts by mass or more, the breaking toughness required for the fiber-reinforced composite material after molding can be easily obtained, and when the blending amount is 15 parts by mass or less, the obtained fiber-reinforced composite can be easily obtained. Since it suppresses the increase in viscosity of the epoxy resin composition for materials and can be impregnated into the reinforcing fibers without difficulty, it is more suitable for fiber-reinforced composite materials.

The epoxy resin composition may further contain other stabilizers, modifiers and the like. As a preferable stabilizer, a borate compound represented by B (OR) ₃ (where R represents a hydrogen atom, an alkyl group or an aryl group) is preferable. The blending amount of the boric acid compound is 0.01 to 10 parts by mass, preferably 0.1 to 3 parts by mass with respect to 100 parts by mass of the entire resin composition. If the amount added is less than 0.01 parts by mass, stability during storage cannot be ensured, and if it exceeds 10 parts by mass, the effect of inhibiting the curing reaction becomes greater and induces curing failure, which is preferable. not.

An antifoaming agent and a leveling agent can be added to the epoxy resin composition as an additive for the purpose of improving surface smoothness. These additives can be blended in an amount of 0.01 to 3 parts by mass, preferably 0.01 to 1 part by mass, based on 100 parts by mass of the entire resin composition. If the blending amount is less than 0.01 parts by mass, the effect of smoothing the surface does not appear, and if it exceeds 3 parts by mass, the additive causes bleed-out on the surface, which conversely causes deterioration of smoothness, which is not preferable. ..

The epoxy resin composition is prepared by uniformly mixing the above-mentioned components (A) to (C) and the like. This epoxy resin composition has good impregnation property into reinforcing fibers, and the resin is less likely to drip from the fibers even after impregnation. Further, the viscosity is stable at room temperature of 23 ° C. and there is almost no change in viscosity, and the viscosity increase rate after 72 hours is 20% or less under the conditions of a temperature of 40 ° C. and an air atmosphere or an inert gas atmosphere, and the impregnation step for a long time. Not only can the impregnation property of the reinforcing fibers be stable during the production of the prepreg having the above properties be ensured, but also the viscosity does not increase during storage. Excellent fiber reinforced composite material can be obtained.

Other curable resins may be added to the epoxy resin composition. Examples of such curable resins include unsaturated polyester resins, curable acrylic resins, curable amino resins, curable melamine resins, curable urea resins, curable cyanate ester resins, curable urethane resins, and curable oxetane resins. Examples thereof include, but are not limited to, a curable epoxy / oxetane composite resin.

The epoxy resin composition for a fiber-reinforced composite material used in the curing method of the present invention has a viscosity measured using an E-type viscometer preferably 5 to 30 Pa · s / 25 ° C, more preferably 6 to 25 Pa · s. / 25 ° C, particularly preferably 7 to 20 Pa · s / 25 ° C. If the viscosity is too high, the impregnation property into carbon fibers deteriorates, and if the viscosity is too low, dicyandiamide and imidazole-based curing aids are precipitated.

The method for curing an epoxy resin composition of the present invention is suitably used for a tow prepreg fiber reinforced composite material. The method for producing the tow prepreg used here is not particularly limited, but the epoxy resin composition is dissolved in an organic solvent such as methyl ethyl ketone or methanol to reduce the viscosity, impregnated while immersing the reinforcing fiber bundle, and then in an oven or the like. A wet method in which an organic solvent is evaporated to form a tow prepreg using an organic solvent, or the epoxy resin composition which has been heated to a low viscosity without using an organic solvent is formed into a film on a roll or a release paper, and then a reinforcing fiber bundle is formed. A hot melt method in which the epoxy resin composition is impregnated by applying pressure through a bending roll or a pressure roll after transfer to one or both sides of the epoxy resin composition, and the epoxy resin composition is impregnated while being immersed in a reinforcing fiber bundle. The filament winding method can be preferably used because it can be produced by a filament winding method or the like, there is virtually no organic solvent remaining in the tow prepreg, and a highly productive and high-quality tow prepreg can be produced. By using such a production method, a resin-impregnated tow prepreg can be obtained.

In the curing method of the epoxy resin composition of the present invention, the reinforcing fiber used together with the epoxy resin composition is selected from glass fiber, aramid fiber, carbon fiber, boron fiber and the like, and a fiber-reinforced composite material having excellent strength is used. It is preferable to use carbon fiber for obtaining.

In the molded body (fiber reinforced composite material) composed of the epoxy resin composition obtained by the curing method of the present invention and the reinforcing fibers, the volume content of the reinforcing fibers is preferably 30 to 75%, more preferably 45 to 75. %, In this range, a molded body having few voids and a high volume content of the reinforcing fibers can be obtained, so that a molding material having excellent strength can be obtained.

Hereinafter, the present invention will be described in more detail with reference to Examples. The following resin raw materials were used to obtain the resin compositions of each example.

(A) Epoxy resin / Liquid bisphenol F type epoxy resin: YDF-170 (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.)
(Epoxy equivalent 160-180 g / eq, viscosity 2-5 Pa · s)
-Liquid bisphenol A type epoxy resin: YD-128 (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.)
(Epoxy equivalent 184 to 194 g / eq, viscosity 11 to 15 Pa · s)
(B) dicyandiamide / dicyandiamide: DICYANEX1400F (manufactured by AIRPRODUCT)
(C) Imidazole-based curing aid, 2MAOK-PW (manufactured by Shikoku Chemicals Corporation)
(D) Core shell rubber MX-154 (manufactured by Kaneka Corporation): Epoxy masterbatch (core shell rubber compounding amount 40 wt%, BPA type epoxy resin compounded amount 60 wt%, average particle size 100 nm, manufactured by Kaneka Corporation)

The measurement method is shown below.
Epoxy equivalent: Measured according to JIS K 7236 standard. Specifically, a potentiometric titrator was used, tetrahydrofuran was used as a solvent, a brominated tetraethylammonium acetic acid solution was added, and a 0.1 mol / L perchloric acid-acetic acid solution was used.
Viscosity: According to JIS K7117-1. Specifically, the viscosity of the pre-cured resin composition at 25 ° C. was measured with an E-type viscometer.
Thickness increase rate: After allowing to stand in a hot air circulation type oven at 40 ° C. for 3 days, the measurement was carried out according to JIS K7177-1.
Reaction peak temperature: When the calorific value around the time is maximized when the measurement is performed with a differential scanning calorimetry device (EXSTAR6000 DSC6200 manufactured by SII Nanotechnology Co., Ltd.) under a temperature rise condition of 10 ° C./min. Expressed in temperature.
Reaction start temperature: It is expressed by extrapolation of the calorific value per hour when the measurement is performed under the heating condition of 10 ° C./min with a differential scanning calorimetry device (EXSTAR6000 DSC6200 manufactured by SII Nanotechnology Co., Ltd.).
Tg: Expressed as the temperature of the DSC extrapolation value when the measurement was performed with a differential scanning calorimetry device (EXSTAR6000 DSC6200 manufactured by SII Nanotechnology Co., Ltd.) under a temperature rise condition of 10 ° C./min.
Fracture toughness (K1c): According to ASTM E399. Specifically, a test piece having a width of 10 mm, a thickness of 4 mm, and a length of 50 mm was prepared, and measured at a room temperature of 23 ° C. and a crosshead speed of 0.5 mm / min.
Tensile elastic modulus, tensile strength, tensile elongation: JIS K7161 was applied. Specifically, a universal material testing machine (Autograph AGS-H manufactured by Shimadzu Science Co., Ltd.) was used. At room temperature, a dumbbell test piece having a total length of 215 mm, a width of 10 mm, and a thickness of 4 mm including the grip portion was subjected to a chuck spacing of 114 mm and a speed of 50 mm / min. The tensile strength, tensile elastic modulus, and tensile elongation were obtained from the obtained stress-strain diagram.

Reference Example The epoxy resin composition used for measuring the heat generation start temperature and the reaction peak temperature was prepared according to the following.
YD-128 (A) / dicyandiamide (B) / imidazole-based curing aid-2MAOK-PW (C) were added in a formulation (wt%) of 93.7 / 5.3 / 1, respectively, and kneaded to make an epoxy. It was made into a resin composition. The exothermic start temperature and exothermic peak temperature of the imidazole-based curing aid extrapolated from the calorific value around the time when the measurement was performed under the heating condition of 10 ° C./min with the differential scanning calorimeter were 143 ° C., respectively. It was 154 ° C.

Examples 1 to 7, Comparative Examples 1 and 2.
(1) Preparation of Epoxy Resin Composition YDF-170 (A) / DICYANEX1400F (B) / 2MAOK-PW (C) / MX-154 (D) were added to 69.7 / 5.3 / 3/25, respectively. The epoxy resin composition was prepared by adding by compounding (part by weight) and kneading with THINKY PLANETARY VACUUM MIXER (manufactured by Shinky Co., Ltd.) at 2000 rpm for 6 minutes under the condition of 4.0 mmhg. As (B) dicyandiamide, a pre-kneaded product with a part of the epoxy resin (A) was used, and (D) a masterbatch in which the core-shell rubber was also dispersed in the epoxy resin (A) in the process of producing the core-shell polymer was used. The rubber content of the adjusted epoxy resin composition was 10% by weight. The initial viscosity was 6.8 mPa · s / 25 ° C., the viscosity after 3 days at 40 ° C. was 7.2 mPa · s / 25 ° C., and the thickening rate was 5.9%.
The prepared epoxy resin composition had low viscosity and thickening rate, and was excellent in impregnation property and storage stability during prepreg production.

(2) Preparation of test piece The epoxy resin composition prepared in (1) above is heated to a temperature of 80 ° C., poured into a mold, and raised to a predetermined temperature in an oven at a temperature of 50 ° C. at 3 / min. After warming, it was cured under various conditions of pureer temperature / time and post-cure (main curing) temperature / time shown in Table 1 to prepare a plate of a cured epoxy resin having a thickness of 4 mm. Next, a plate of the obtained cured epoxy resin was cut out and used for test analysis. The results are also shown in Table 1.

Claims (1)

Epoxy resin (A), dicyandiamide (B) and imidazole-based curing aid (C) are used as essential components, and a solvent-free epoxy resin composition and an epoxy resin composition for a fiber-reinforced composite material containing reinforcing fibers are cured. A method for producing a fiber-reinforced composite material, in which an epoxy resin composition having a heat generation start temperature of 135 ° C. or higher when measured with a DSC at a temperature rise rate of 10 ° C./min is used to reinforce the fibers . A fiber characterized in that the epoxy resin composition for a composite material is pre-cured at 90 ° C. to 140 ° C. for 30 to 180 minutes, and after the pre-cure, the main curing reaction is carried out at a temperature 140 to 160 ° C. higher than the pre-cure temperature for 30 to 120 minutes. A method for manufacturing a reinforced composite material.

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