JP2022154652A - epoxy resin composition - Google Patents

Abstract

To provide an epoxy resin composition having excellent mechanical properties required for many molded articles, such as Tg and toughness, particularly an epoxy resin composition suitable for fiber-reinforced composite materials.SOLUTION: An epoxy resin composition contains epoxy resin (A), urethane-modified epoxy resin (B), dicyandiamide (C), and core-shell rubber (D) as essential components. The content of the urethane-modified epoxy resin (B) is 10 pts.wt. or more relative to 100 pts.mass of the total of the (A)-(D) components.SELECTED DRAWING: None

Description

The present invention relates to curable epoxy resin compositions.

Conventionally, fiber-reinforced composite materials made of reinforcing fibers such as carbon fibers and glass fibers and thermosetting resins such as epoxy resins and phenolic resins are lightweight, yet have mechanical properties such as strength and rigidity, heat resistance, and corrosion resistance. Because of its superiority, it has been applied in many fields such as aerospace, automobiles, railroad vehicles, ships, civil engineering and construction, and sporting goods. In particular, for applications that require high performance, fiber-reinforced composite materials using continuous reinforcing fibers are used. Carbon fibers with excellent specific strength and specific elastic modulus are used as reinforcing fibers, and thermosetting resins are used as matrix resins. In particular, epoxy resins, which have excellent adhesion to carbon fibers, are widely used. However, epoxy resins (cured products) generally have the drawback of being brittle, that is, having low toughness and elongation. Therefore, the mechanical properties of fiber-reinforced composite materials using them as they are are unsatisfactory.

As a method for improving the toughness and elongation of epoxy resins, methods such as blending rubber components and thermoplastic resins with excellent toughness have been tried. For example, it has been studied since the 1970s and is generally well known that the toughness of epoxy resins is improved by blending them with rubber components such as acrylonitrile-butadiene rubbers containing carboxyl groups. However, the rubber component causes a decrease in heat resistance and elastic modulus, and a large amount of the rubber component must be blended in order to obtain a sufficient toughness-improving effect of the rubber component. As a result, the inherent heat resistance and mechanical properties of the epoxy resin are degraded, and a composite material having good physical properties cannot be obtained.

In addition, as a method of blending a thermoplastic resin with an epoxy resin, a thermoplastic resin such as polyethersulfone, polysulfone, or polyetherimide is dissolved in the epoxy resin, or blended in fine powder and dissolved in the epoxy resin. There is a method of uniformly dispersing the thermoplastic resin in the epoxy resin. Reference 1).

However, in this method, a large amount of these thermoplastic resins must be blended in order to obtain a sufficient toughness-improving effect. As a result, the viscosity of the epoxy resin composition significantly increases, resulting in a significant decrease in processability when obtaining the prepreg, the occurrence of resin-unimpregnated portions in the obtained prepreg, and the fiber-reinforced composite obtained by curing the prepreg. There were drawbacks such as the formation of voids in the material.

To address this problem, a method has been proposed in which polymer particles that are substantially insoluble in epoxy resin are used. Among them, a method of compounding core-shell rubber particles in which a part or the entire surface of the core portion is coated by a method such as graft polymerization of a particulate core portion mainly composed of a polymer and a polymer different from the core portion is proposed. (For example, Patent Documents 2 and 3). It is known that this method can suppress an increase in the viscosity of the epoxy resin composition and a decrease in the Tg of the cured epoxy resin composition.

However, it is necessary to incorporate a large amount of core-shell rubber particles in order to obtain a sufficient effect of improving toughness, and as a result, the elastic modulus of the cured epoxy resin decreases, which in turn causes a decrease in the mechanical properties of the fiber-reinforced composite. The problem still remained.

As a means for compensating for these problems, a method of using a core-shell rubber and a long-chain epoxy resin with a large molecular weight in combination has been proposed (Patent Document 4). However, the long-chain epoxy resin increases the viscosity of the composition, deteriorates storage stability, and improves toughness unsatisfactorily.

Recently, use in higher temperature environments has also been investigated for application in more severe environments. The functionality of cured epoxy resins varies greatly around the glass transition temperature (Tg). When the glass transition point is exceeded, a state called a rubber region occurs, and a decrease in elastic modulus occurs. Therefore, the Tg of the cured epoxy resin generally needs to be higher than the temperature of the environment in which it is handled.

Japanese Patent Publication No. 6-43508 JP-A-5-65391 JP-A-2003-277579 Patent No. 5293629

The present invention provides an epoxy resin composition that is excellent in mechanical properties such as Tg and toughness required for many molded articles, and is particularly suitable for fiber-reinforced composite materials.

Ｇ：グリシジル基
Ｒ：炭素数６～３０の有機基 That is, the present invention provides an epoxy resin composition comprising an epoxy resin (A), a urethane-modified epoxy resin (B), dicyandiamide (C), and a core-shell rubber (D) as essential components,
10 parts by weight or more of a urethane-modified epoxy resin (B) with respect to a total of 100 parts by weight of components (A) to (D),
In gel permeation chromatography (GPC) measurement, the urethane-modified epoxy resin (B) is characterized by containing 15 area % or more of the structure represented by the following general formula (1) in the urethane-modified epoxy resin (B). It is an epoxy resin composition.

G: glycidyl group R: organic group having 6 to 30 carbon atoms

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail.
The present invention comprises epoxy resin (A), urethane-modified epoxy resin (B), dicyandiamide (C), and core-shell rubber (D) as essential components. Hereinafter, epoxy resin (A), urethane-modified epoxy resin (B), dicyandiamide (C), and core-shell rubber (D) are also referred to as component (A), component (B), component (C), and component (D), respectively. .

The amount of the epoxy resin (A) used in the present invention is preferably 10 to 90 parts by mass, more preferably 20 to 70 parts by mass, and even more preferably 100 parts by mass in total of components (A) to (D). is 20 to 50 parts by weight.
Epoxy resins 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, and isophorone bisphenol type epoxy resin having two epoxy groups in one molecule. Bisphenol-type epoxy resins such as bisphenol-type epoxy resins, halogen, alkyl-substituted products, hydrogenated products of these bisphenol-type epoxy resins, high molecular weight products having multiple repeating units not limited to monomers, glycidyl ethers of alkylene oxide adducts, and phenol Novolak type epoxy resins such as novolak type epoxy resins, cresol novolak type epoxy resins, bisphenol A novolac type epoxy resins, and 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 Aliphatic epoxy resins such as ethers and polyoxyalkylene diglycidyl ethers, glycidyl esters such as diglycidyl phthalate, diglycidyl tetrahydrophthalate, and glycidyl dimer, tetraglycidyldiaminodiphenylmethane, tetraglycidyldiaminodiphenyl Glycidylamines such as sulfone, triglycidylaminophenol, triglycidylaminocresol, and tetraglycidylxylylenediamine can be used. These may be used individually by 1 type, or may be used in combination of 2 or more type.

ここで、Ｇはグリシジル基を示す。Ｒは炭素数６～３０の有機基、好ましくは炭素数６～１８の有機基を示す。 The urethane-modified epoxy resin (B) contains 15 area % or more of the structure represented by the following general formula (1) as measured by gel permeation chromatography (GPC). More preferably 20 area % or more, still more preferably 25 area % or more.

Here, G represents a glycidyl group. R represents an organic group having 6 to 30 carbon atoms, preferably an organic group having 6 to 18 carbon atoms.

A urethane-modified epoxy resin can be obtained by using a bisphenol A type (BPA type) epoxy resin and isocyanate as essential reaction raw materials.
In producing the urethane-modified epoxy resin, raw materials other than the BPA-type epoxy resin and isocyanate, such as various polyol compounds, can be used as long as they do not interfere with the present invention.

ここで、Ｇはグリシジル基を示す。
ＢＰＡ型エポキシ樹脂の成分調整は、蒸留などによってｎ＝０成分を一定量除去することが望ましい。 The bisphenol A type epoxy resin as a reaction raw material must contain 20 area % or more of a dimer (n=1) represented by the following structure (b2) as measured by GPC. It is preferably 30 area % or more, more preferably 35 area % or more, and still more preferably 40 area % or more.
The bisphenol A monomer (n=0) is preferably 50 area % or less, more preferably 40 area % or less. Other components, for example, by-products between n = 0 and n = 1 (chloromethyl, diol, α, β adducts, etc.), trimers (n = 2) or higher components , preferably 30 area % or less.

Here, G represents a glycidyl group.
It is desirable to adjust the components of the BPA-type epoxy resin by removing a certain amount of the n=0 component by distillation or the like.

The BPA type epoxy resin preferably has an epoxy equivalent weight of 180 to 350 g/eq. The hydroxyl equivalent is preferably 500-3000 g/eq, more preferably 800-2000 g/eq.

ここで、Ｒは炭素数６～３０の有機基、好ましくは６～１８の有機基を示す。
イソシアネートとしては、例えば、トルエンジイソシアネート（ＴＤＩ）、４，４’－ジフェニルメタンジイソシアネート（ＭＤＩ）、キシリレンジイソシアネート（ＸＤＩ）、水素化キシリレンジイソシアネート（ＨＸＤＩ）、イソホロンジイソシアネート（ＩＰＤＩ）、ナフタレンジイソシアネート等が挙げられる。
これらの内、低分子量で増粘性がなく低価格、安全性などの観点からＭＤＩやＴＤＩが好ましい。これらは１種を単独で用いても２種以上を組み合わせて用いてもよい。 Isocyanate as a reaction raw material is represented by the following structure (b1).

Here, R represents an organic group having 6 to 30 carbon atoms, preferably an organic group having 6 to 18 carbon atoms.
Examples of isocyanates include toluene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), hydrogenated xylylene diisocyanate (HXDI), isophorone diisocyanate (IPDI), naphthalene diisocyanate, and the like. be done.
Among these, MDI and TDI are preferable from the viewpoints of low molecular weight, low viscosity, low cost, and safety. These may be used individually by 1 type, or may be used in combination of 2 or more type.

The amount of the urethane-modified epoxy resin (B) is 10 parts by weight or more, more preferably 20 parts by weight or more, with respect to a total of 100 parts by weight of components (A) to (D). The improvement effect does not appear. The upper limit is preferably 70 parts by mass or less, more preferably 60 parts by mass or less.
The amount of the structure represented by the general formula (1) in the urethane-modified epoxy resin (B) can be determined by GPC, and is 15 area % or more, more preferably 20 area % or more in the urethane-modified epoxy resin (B). is. Lower values do not exhibit the effect of improving Tg and toughness. The upper limit is preferably 50 area % or less, more preferably 40 area % or less.

The urethane-modified epoxy resin (B) preferably has an epoxy equivalent of 180 to 350 g/eq, more preferably 200 to 300 g/eq.

Dicyandiamide (C) is used as a curing agent in the epoxy resin composition of the present invention. Dicyandiamide is a curing agent that is solid at room temperature. It is almost insoluble in epoxy resin at room temperature, but when heated to 180°C or higher, it dissolves and reacts with epoxy groups. Hardener. The amount to be used is preferably in the range of 0.2 to 0.8 equivalents (calculated on the assumption that 1 mol of dicyandiamide is 4 equivalents) relative to the epoxy equivalent. More preferably, it is 0.2 to 0.5 equivalents. If it is less than 0.2 equivalents relative to the epoxy equivalent, the crosslink density of the cured product tends to be low and fracture toughness tends to be low. There is a tendency.

The epoxy resin composition of the present invention contains core-shell rubber (D) as an essential component. The core-shell rubber (D) is blended in an amount of preferably 10 to 40 parts by weight, more preferably 20 to 30 parts by weight, per 100 parts by weight of components (A) to (D) in total.
As the core-shell rubber (D) applicable to the present invention, those produced by a well-known method can be used. However, the core-shell polymer is usually taken out in a lump and pulverized and treated as a powder, and the powdery core-shell polymer is often dispersed again in the epoxy resin. It is difficult to disperse stably at Therefore, it is preferable that the core-shell polymer can be handled in the form of a masterbatch in which the primary particles are dispersed in the epoxy resin without being taken out from the manufacturing process of the core-shell polymer. For example, the method described in JP-A-2004-315572, that is, the core-shell polymer is polymerized in an aqueous medium represented by emulsion polymerization, dispersion polymerization, and suspension polymerization, and the core-shell polymer is dispersed in a suspension. A turbid liquid is obtained, and the resulting suspension is mixed with an organic solvent that is partially soluble in water, such as an ether solvent such as acetone or methyl ethyl ketone, and then brought into contact with a water-soluble electrolyte such as sodium chloride or potassium chloride. Alternatively, an organic solvent layer and an aqueous layer may be phase-separated, the core-shell polymer-dispersed organic solvent obtained by separating and removing the aqueous layer may be appropriately mixed with an epoxy resin, and then the organic solvent may be removed by evaporation. For example, as the core-shell polymer-dispersed epoxy masterbatch, "Kane Ace (registered trademark)" commercially available from Kaneka Corporation can be suitably used.

The epoxy resin composition of the present invention can further contain a curing accelerator. Curing accelerators include crystalline imidazole compounds such as 2,4-diamino-6-[2`-methylimidazolyl-(1`)]-ethyl-s-triazine isocyanuric acid addition salt (2MA-OK) and 3- Urea compounds such as (3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) can be preferably used. The amount of the curing accelerator is preferably 10 to 100 parts by mass, more preferably 20 to 90 parts by mass, per 100 parts by mass of dicyandiamide (C). When the imidazole-based curing aid is less than 10 parts by mass, it becomes difficult to develop fast curing. It is in.

The epoxy resin composition of the present invention may further contain other stabilizers, modifiers and the like. Although it is not particularly limited as long as it improves storage stability, a borate ester compound, phosphoric acid, alkyl phosphate, p-toluenesulfonic acid, methyl p-toluenesulfonate, and the like may be blended. Preferred stabilizers include trimethylborate, triethylborate, _tri -n-propylborate, triisopropylborate, tri- -n-butylborate, tris(2-ethylhexyloxy)borane, triphenylborate, trimethoxyboroxine and the like. Commercially available boric acid ester compounds include, for example, "Cadact L-07N" (Shikoku Kasei Kogyo Co., Ltd.). As the alkyl phosphate, trimethyl phosphate, tributyl phosphate and the like can be used, but the alkyl phosphate is not limited to these. The storage stabilizer may be used singly or in combination, and tri-n-butylborate is preferred in consideration of storage stability. The blending amount of the stabilizer is 0.005 to 10 parts by mass, preferably 0.05 to 3 parts by mass, per 100 parts by mass of the entire resin composition. If the addition amount is less than 0.005 parts by mass, the stability during storage cannot be ensured. do not have.

An antifoaming agent and a leveling agent can be added to the epoxy resin composition of the present invention as additives 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, per 100 parts by mass of the entire resin composition. When the amount is less than 0.01 part by mass, the effect of smoothing the surface is not exhibited, and when the amount exceeds 3 parts by mass, the additive bleeds out on the surface, which adversely impairs the smoothness, which is not preferable. .

The epoxy resin composition of the present invention can also contain other curable resins. 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, curable oxetane resins, Examples include, but are not limited to, curable epoxy/oxetane composite resins.

The reinforcing fiber used in the epoxy resin composition of the present invention is selected from glass fiber, aramid fiber, carbon fiber, boron fiber, etc. Carbon fiber is used to obtain a fiber-reinforced composite material having excellent strength. is preferred.

In the molded article composed of the epoxy resin composition of the present invention and reinforcing fibers, the volume content of the reinforcing fibers is preferably 30 to 75%, more preferably 45 to 75%. Since a molded article having a small amount of reinforcing fibers and a high volume content of reinforcing fibers can be obtained, a molding material having excellent strength can be obtained.

The epoxy resin composition of the present invention is cured by heating at an arbitrary temperature of 80 to 180° C., preferably 135° C. or higher, for an arbitrary time in the range of 0.5 to 10 hours to promote a cross-linking reaction. can be obtained. The heating condition may be one step, or may be a multi-step condition combining a plurality of heating conditions. In particular, assuming a high-pressure container filled with hydrogen gas such as that used in fuel cells, it is heated at an arbitrary temperature in the range of 80 to 150 ° C. for an arbitrary time in the range of 0.5 to 5 hours. By curing, desired physical properties of the cured product can be obtained.

Epoxy resin compositions can be prepared by a variety of known methods. For example, there is a method of kneading each component with a kneader. Moreover, you may knead using a twin-screw extruder. Dicyandiamide (C) is dispersed in each component in a solid state, but when all the components are kneaded at once, dicyandiamide may aggregate and become poorly dispersed. An epoxy resin composition with poor dispersion is not preferable because it causes unevenness in physical properties in the cured product and poor curing. Therefore, it is preferable to use dicyandiamide as a masterbatch by using a part of the epoxy resin and pre-kneading the mixture with a triple roll.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. In order to obtain the resin composition of each example, the following resin raw materials were used.

(A) Epoxy resin/liquid bisphenol A type epoxy resin: YD-128 (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.)
(Epoxy equivalent 184 to 194 g / eq)
・ Liquid bisphenol F type epoxy resin: YDF-170 (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.)
(Epoxy equivalent 160-180g/eq)
(B) Urethane-modified epoxy resin/Developed product 1: General-purpose bisphenol A type epoxy resin from which a certain amount of n=0 component was removed by distillation (epoxy equivalent 262 g/eq, hydroxyl equivalent 915 g/eq, n=0 component: 30 area %, n = 1 component: 50 area %, other: 20 area %)
・ Developed product 2: General-purpose bisphenol F type epoxy resin with a certain amount of n = 0 component removed by distillation (epoxy equivalent 192 g / eq, hydroxyl equivalent 1500 g / eq, n = 0 component: 40 area%, n = 1 component : 40 area%, others: 20 area%)
・ MDI: diphenylmethane diisocyanate (manufactured by Tokyo Kasei)
・TDI: toluene diisocyanate (manufactured by Tokyo Chemical Industry Co., Ltd.)
(C) Dicyandiamide DICYANEX1400F: Dicyandiamide: (manufactured by AIRPRODUCT)
(D) Core shell rubber MX-154: epoxy masterbatch (manufactured by Kaneka Corporation)
(40 wt% core-shell rubber content, 60 wt% BPA type epoxy resin content)
・ 2MAOK: imidazole-based curing aid (manufactured by Shikoku Kasei Kogyo Co., Ltd.)
・DCMU: 3-(3,4-dichlorophenyl)-1,1-dimethylurea (manufactured by Tokyo Kasei)

The measurement method is shown below.
(Ratio of general formula (1) in epoxy resin)
The molecular weight distribution was measured using GPC and determined from the peak area %. Specifically, a column (TSKgelG4000HXL, TSKgelG3000HXL, TSKgelG2000HXL manufactured by Tosoh Corporation) in series with a main body (HLC-8220GPC manufactured by Tosoh Corporation) was used, and the column temperature was set to 40°C. Tetrahydrofuran was used as an eluent at a flow rate of 1 mL/min, and an RI (differential refractometer) detector was used.
(hydroxyl equivalent)
25 ml of dimethylformamide is placed in a 200 ml Erlenmeyer flask with a glass stopper, and a sample containing 11 mg/equivalent or less of hydroxyl groups is accurately weighed and dissolved. Add 20 ml of the 1 mol/L-phenylisocyanate toluene solution and 1 ml of the dibutyltinmalate catalyst solution with a pipette, shake well to mix, seal tightly, and react for 30 to 60 minutes. After completion of the reaction, 20 ml of a 2 mol/L-dibutylamine toluene solution is added, mixed well by shaking, and allowed to stand for 15 minutes to react with excess phenyl isocyanate. Then 30 ml of methyl cellosolve and 0.5 ml of bromcresol green indicator are added and the excess amine is titrated with a standardized methyl perchlorate solution of cellosolve. Since the indicator changes from blue to green to yellow, the point at which it first turned yellow was taken as the end point, and the hydroxyl group equivalent was determined using the following formulas i and ii.
Hydroxyl equivalent (g / eq) = (1000 × W) / C (SB) (i)
C: Concentration of methyl perchlorate cellosolve solution mol/L
W: sample amount (g)
S: Titration volume of methyl perchlorate cellosolve solution (ml)
B: Titration volume of methyl perchlorate cellosolve solution required for blank test during titration (ml)
C=(1000×W)/{121×(s−b)} (ii)
w: Amount of tris-(hydroxymethyl)-aminomethane sampled for standardization (g)
s: Titration volume of methyl perchlorate cellosolve solution required for titration of tris-(hydroxymethyl)-aminomethane (ml)
b: Titration volume of methyl perchlorate cellosolve solution required for blank test during standardization (ml)
(epoxy equivalent)
Measured according to JIS K 7236 standard. Specifically, a potentiometric titrator was used, tetrahydrofuran was used as a solvent, a tetraethylammonium bromide acetic acid solution was added, and a 0.1 mol/L perchloric acid-acetic acid solution was used.
(Glass transition temperature: Tg)
It was expressed as the temperature of the DSC extrapolated value when the measurement was performed with a differential scanning calorimeter (EXSTAR6000 DSC6200 manufactured by SII Nanotechnology Co., Ltd.) under the temperature rising condition of 10°C/min.
(Fracture toughness (K1c))
Conforms 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 modulus, tensile strength, tensile strain)
Complies with JIS K7161. 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 dimensions of 215 mm in total length including the gripping portion, 10 mm in width, and 4 mm in thickness was held at a chuck distance of 114 mm and a speed of 50 mm/min. Tensile strength, tensile modulus and tensile strain were obtained from the obtained stress-strain diagram.

合成例２
エポキシ樹脂（ｂ１）として開発品２を３００ｇ、ポリイソシアネート（ｂ２）としてトルエンジイソシアネートを１７ｇ仕込んだ以外は合成例１と同じ手順で反応を行い、樹脂２（Ｂ）を得た。反応が完結していることは、ＩＲ測定によりＮＣＯ基の吸収スペクトルが消失したことで確認した。エポキシ当量は２０４ｇ／ｅｑ、ＧＰＣより得られた下記構造の比率は２０面積％だった。

合成例３
ポリイソシアネート（ｂ２）としてジフェニルメタンジイソシアネートを４１ｇ仕込んだ以外は合成例１と同じ手順で反応を行い、樹脂３（Ｂ）を得た。反応が完結していることは、ＩＲ測定によりＮＣＯ基の吸収スペクトルが消失したことで確認した。エポキシ当量は２９５ｇ／ｅｑ、ＧＰＣより得られた下記構造の比率は３５面積％だった。

(Synthesis of urethane-modified epoxy resin)
Synthesis example 1
As the epoxy resin (b1), 300 g of developed product 1 was charged into a 500 ml four-necked separable flask equipped with a nitrogen inlet tube, a stirrer and a temperature controller, and stirred at room temperature for 15 minutes. Next, 29 g of toluene diisocyanate was charged as polyisocyanate (b2) and reacted at 120° C. for 2 hours to obtain Resin 1 (B). Completion of the reaction was confirmed by the disappearance of the NCO group absorption spectrum by IR measurement. The epoxy equivalent was 283 g/eq, and the ratio of the following structure obtained by GPC was 25 area %.

Synthesis example 2
A reaction was carried out in the same manner as in Synthesis Example 1 except that 300 g of developed product 2 as epoxy resin (b1) and 17 g of toluenediisocyanate as polyisocyanate (b2) were charged to obtain resin 2 (B). Completion of the reaction was confirmed by the disappearance of the NCO group absorption spectrum by IR measurement. The epoxy equivalent was 204 g/eq, and the ratio of the following structure obtained by GPC was 20 area %.

Synthesis example 3
A reaction was carried out in the same manner as in Synthesis Example 1 except that 41 g of diphenylmethane diisocyanate was charged as polyisocyanate (b2) to obtain Resin 3 (B). Completion of the reaction was confirmed by the disappearance of the NCO group absorption spectrum by IR measurement. The epoxy equivalent was 295 g/eq, and the ratio of the following structure obtained by GPC was 35 area %.

Example 1
(1) Preparation of epoxy resin composition YD-128 (A) / resin 1 (B) / DICYANEX1400F (C) / MX-154 (D) and 2MAOK, respectively, 45.6/25/4.4/25 /3 (parts by weight) and kneaded for 6 minutes at 2000 rpm and 4.0 mmhg using THINKY PLANETARY VACUUM MIXER (manufactured by THINKY Co., Ltd.) to prepare an epoxy resin composition. Dicyandiamide (B) was pre-kneaded with a part of the epoxy resin (A), and core-shell rubber (D) was a masterbatch dispersed in the BPA-type liquid epoxy resin during the core-shell polymer manufacturing process.
Examples 2-6, Comparative Examples 1-9
An epoxy resin composition was prepared in the same manner as in Example 1 according to the composition shown in Table 1.

(2) Preparation of test piece The epoxy resin composition prepared in (1) above is heated to a temperature of 80°C, poured into a preheated mold, heated to a predetermined temperature in an oven, and then A plate of cured epoxy resin having a thickness of 4 mm was produced. Next, a plate of the obtained cured epoxy resin was cut out and used for test analysis. The results are shown in Table 1 together.

Claims (4)

An epoxy resin composition comprising an epoxy resin (A), a urethane-modified epoxy resin (B), dicyandiamide (C), and a core-shell rubber (D) as essential components,
The urethane-modified epoxy resin (B) contains 10 parts by weight or more based on the total of 100 parts by weight of components (A) to (D), and the urethane-modified epoxy resin (B) is represented by the following general formula (1). An epoxy resin composition comprising 15 area % or more of the structure obtained by gel permeation chromatography (GPC) measurement.

(However, G represents a glycidyl group. R represents an organic group having 6 to 30 carbon atoms.) The urethane-modified epoxy resin (B) uses a BPA type epoxy resin and the following isocyanate (b1) as essential reaction raw materials, and the bisphenol A type epoxy resin contains 20 area % or more of the following structure (b2) in GPC measurement. The epoxy resin composition according to claim 1.

(However, G represents a glycidyl group. R represents an organic group having 6 to 30 carbon atoms.) A fiber-reinforced composite material comprising the epoxy resin composition according to claim 1 and reinforcing fibers blended therein. The fiber-reinforced composite material according to claim 3, wherein the volume content of the reinforcing fibers is 30-75%.