JP7215002B2 - Epoxy resin composition, prepreg and fiber reinforced composite - Google Patents

Description

TECHNICAL FIELD The present invention relates to an epoxy resin composition preferably used as a matrix resin for fiber-reinforced composite materials suitable for sports, aerospace, and general industrial applications, and prepregs and fiber-reinforced composites using this composition as the matrix resin. be.

Epoxy resins are suitably used as matrix resins for fiber-reinforced composite materials combined with reinforcing fibers such as carbon fibers, glass fibers, and aramid fibers, taking advantage of their high mechanical properties, heat resistance, and adhesiveness.

A sheet-like intermediate base material (prepreg) in which reinforcing fibers are impregnated with an epoxy resin is widely used for the production of fiber-reinforced composite materials. Molded products are obtained by laminating prepregs and curing the epoxy resin by heating, and are applied to various fields such as aircraft and sports. In recent years, the application to industrial applications such as automobiles has progressed, and fast-curing prepregs with a short curing time that emphasize mass production are attracting attention. Particularly in automobile applications, a method of preforming a fast-curing prepreg and then press-molding is often used.

On the other hand, fast-curing prepregs are made by increasing the reactivity of the epoxy resin used and shortening the curing time. is required.

Patent Literature 1 discloses an epoxy resin composition and a prepreg that use a specific aromatic urea as an accelerator and give a cured product excellent in rapid curing and heat resistance.

Patent Document 2 discloses an epoxy resin composition having an excellent curing speed and a glass transition temperature not exceeding 140°C.

Patent Document 3 discloses an epoxy resin composition containing dicyandiamide, aromatic urea and a boric acid ester and having excellent storage stability and mechanical properties.

JP 2003-128764 A Japanese translation of PCT publication No. 2016-500409 JP 2016-148020 A

Although the epoxy resin composition disclosed in Patent Document 1 has a relatively short curing time, it does not satisfy the cycle time required for, for example, mass-produced vehicles. In addition, since aromatic urea with high activity is used, the handleability may be impaired due to storage of the prepreg and progress of curing due to heat history during preforming.

The epoxy resin composition disclosed in Patent Document 2 is excellent in rapid curability, but has insufficient storage stability.

The epoxy resin composition disclosed in Patent Document 3 has excellent storage stability, but the curing time was not sufficient. In addition, there is no mention of handleability in the preforming process, which is important when molding prepregs.

Therefore, in the present invention, an epoxy resin composition that overcomes the drawbacks of the prior art, achieves both excellent rapid curing and storage stability, and is excellent in handleability in the preforming process, and the epoxy resin composition and a fiber-reinforced composite material obtained by curing the prepreg.

As a result of intensive studies aimed at solving the above problems, the inventors of the present invention have found an epoxy resin composition having the following constitution, and have completed the present invention. That is, the epoxy resin composition of the present invention has the following constitution.

An epoxy resin composition containing the following components [A], [B], [C] and [D] and satisfying the following conditions [a], [b] and [c].
[A]: epoxy resin [B]: dicyanamide [C]: aromatic urea [D]: borate ester [a]: 0.005 ≤ (content of component [D] / content of component [C]) ≤ 0.045
[b]: In dielectric measurement at 80°C, the time from the start of measurement until the cure index reaches 10% is 120 minutes or more.
[c]: In dielectric measurement at 150°C, the time from the start of measurement until the cure index reaches 70% is within 120 seconds.

Also, the prepreg of the present invention comprises the above epoxy resin composition and reinforcing fibers.

Furthermore, the fiber-reinforced composite material of the present invention is obtained by curing the prepreg.

By using the epoxy resin composition according to the present invention, it is possible to provide a prepreg and a fiber-reinforced composite material that achieve both rapid curing and storage stability, and are also excellent in handleability in the preforming process.

The epoxy resin composition of the present invention contains component [A] epoxy resin, component [B] dicyandiamide, component [C] aromatic urea compound, and component [D] borate ester as essential components. First, these constituent elements will be described.

(Component [A])
Component [A] in the present invention is an epoxy resin. For example, bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, bisphenol S-type epoxy resin, biphenyl-type epoxy resin, naphthalene-type epoxy resin, novolac-type epoxy resin, epoxy resin having a fluorene skeleton, co-polymerization of phenol compound and dicyclopentadiene. Epoxy resins made from polymers, glycidyl ether type epoxy resins such as diglycidylresorcinol, tetrakis(glycidyloxyphenyl)ethane, tris(glycidyloxyphenyl)methane, tetraglycidyldiaminodiphenylmethane, triglycidylaminophenol, triglycidylamino Glycidylamine-type epoxy resins such as cresol and tetraglycidylxylenediamine are included. Epoxy resins may be used alone or in combination.

Commercially available products of component [A] include "jER (registered trademark)" 152, 154, 180S (manufactured by Mitsubishi Chemical Corporation), "Epiclon (registered trademark)" N-740, N-770, N- 775, N-660, N-665, N-680, N-695, HP7200L, HP7200, HP7200H, HP7200HH, HP7200HHH (manufactured by DIC Corporation), PY307, EPN1179, EPN1180, ECN9511, ECN1273, ECN1285, ECN128 , ECN1299 (manufactured by Huntsman Advanced Materials Co., Ltd.), YDPN-638, YDPN-638P, YDCN-701, YDCN-702, YDCN-703, YDCN-704 (manufactured by Tohto Kasei Co., Ltd.), DEN431, DEN438, DEN439 (manufactured by Dow Chemical Co.) and the like.

(Component [B])
Component [B] in the present invention is dicyandiamide. Dicyandiamide is a compound represented by the chemical formula (H ₂ N) ₂ C═N—CN. Dicyandiamide is excellent in that it imparts high mechanical properties and heat resistance to cured resins, and is widely used as a curing agent for epoxy resins. Commercial products of such dicyandiamide include DICY7 and DICY15 (manufactured by Mitsubishi Chemical Corporation).

Incorporation of dicyandiamide [B] as a powder into the epoxy resin composition is preferable from the viewpoint of storage stability at room temperature and viscosity stability during prepreg production. Further, it is preferable to disperse dicyandiamide [B] in a part of the epoxy resin of component [A] in advance using a triple roll or the like, in order to make the epoxy resin composition uniform and to improve the physical properties of the cured product. .

When the dicyandiamide is powdered and blended with the resin, the average particle size is preferably 10 μm or less, more preferably 7 μm or less. For example, when the reinforcing fiber bundle is impregnated with the epoxy resin composition by heating and pressurizing in the prepreg manufacturing process, if the average particle diameter is 10 μm or less, the impregnating property of the resin into the inside of the fiber bundle will be good. The average particle size as used herein means a volume average, and can be measured by a laser diffraction particle size distribution analyzer.

Dicyandiamide [B], when used in combination with component [C] described below, can lower the curing temperature of the resin composition compared to the case where component [B] is blended alone. In the present invention, it is necessary to use component [B] and component [C] together in order to shorten the curing time.

(Component [C])
Component [C] in the present invention is aromatic urea.

Specific examples of aromatic urea compounds for component [C] include 3-(3,4-dichlorophenyl)-1,1-dimethylurea, 3-(4-chlorophenyl)-1,1-dimethylurea, and phenyldimethylurea. , toluenebisdimethylurea, and the like. In addition, commercially available aromatic urea compounds include DCMU99 (manufactured by Hodogaya Chemical Industry Co., Ltd.), "Omicure (registered trademark)" 24 (manufactured by PTI Japan Co., Ltd.), "Dyhard (registered trademark) )” UR505 (4,4′-methylenebis(phenyldimethylurea, manufactured by CVC) and the like.

(Component [D])
Component [D] in the present invention is a boric acid ester. By using the component [C] and the component [D] together, the reaction between the component [C] and the epoxy resin at the storage temperature is suppressed, so that the storage stability of the prepreg is remarkably improved. Although the mechanism is not clear, since the component [D] has Lewis acidity, the amine compound liberated from the component [C] and the component [D] interact with each other to reduce the reactivity of the amine compound. It is thought that there is no.

Specific examples of the boric acid ester of component [D] include trimethyl borate, triethyl borate, tributyl borate, tri-n-octyl borate, tri(triethylene glycol methyl ether) boric acid ester, tricyclohexyl borate, trimenthyl borate, and the like. Alkyl borates, aromatic borates such as tri-o-cresylborate, tri-m-cresylborate, tri-p-cresylborate, triphenylborate, tri(1,3-butanediol)biborate, tri(2 -methyl-2,4-pentanediol) biborate, trioctylene glycol diborate and the like.

A cyclic boric acid ester having a cyclic structure in the molecule can also be used as the boric acid ester. Cyclic borate esters include tris-o-phenylene bisborate, bis-o-phenylene pyroborate, bis-2,3-dimethylethylene phenylene pyroborate, bis-2,2-dimethyltrimethylene pyroborate, and the like. .

Examples of products containing such borate esters include "Cure Duct (registered trademark)" L-01B (Shikoku Chemical Industry Co., Ltd.), "Cure Duct (registered trademark)" L-07N (Shikoku Chemical Industry Co., Ltd.) ) (a composition containing 5 parts by mass of a boric acid ester compound), “Cure Duct (registered trademark)” L-07E (Shikoku Chemical Industry Co., Ltd.) (a composition containing 5 parts by mass of a boric acid ester compound), etc. be done.

The epoxy resin composition of the present invention satisfies the following condition [a].
[a]: 0.005≦(content of component [D]/content of component [C])≦0.045.

Regarding condition [a], when the value represented by the content of component [D]/content of component [C] in the epoxy resin composition is within the range of 0.005 to 0.045, rapid curing and storage A prepreg with excellent balance of stability and excellent handling in the preforming process can be obtained.

The preforming step in the present invention is a step of prefabricating a prepreg into a three-dimensional shape before press molding. Generally, in the preforming process, it is necessary to heat and soften the prepreg in order to obtain a preshaped body of arbitrary shape. If the ratio of the content of component [D]/the content of component [C] is less than 0.005, the prepreg will be hardened during the preforming process, the flexibility will be impaired, and the handleability will be poor. Moreover, when the content of component [D]/the content of component [C] exceeds 0.045, the curing time becomes insufficient. The content of component [C] or the content of component [D] is the amount of [C] borate ester or [D] borate ester per 100 parts by mass of the epoxy resin of component [A]. be.

The epoxy resin composition of the present invention satisfies the following condition [b].
[b]: In dielectric measurement at 80°C, the time from the start of measurement until the cure index reaches 10% is 120 minutes or longer.

When the cure index reaches 10% in 120 minutes or longer, the prepreg has excellent moldability in the preforming process. If the time is less than 120 minutes, the prepreg becomes difficult to handle during preforming. The cure index is an index representing the degree of curing of the resin, and satisfying the condition [b] indicates that the curing of the epoxy resin hardly progresses at the temperature of the preforming process (usually room temperature to 80°C) and the process is stable. means.

The epoxy resin composition of the present invention satisfies the following condition [c].
[c]: In dielectric measurement at 150°C, the time from the start of measurement until the cure index reaches 70% is within 120 seconds.

If the time to reach 70% cure index at 150° C. is within 120 seconds, it is excellent in rapid curability. If it exceeds 120 seconds, the molding cycle time becomes insufficient.

The cure index (curing degree) of the epoxy resin composition of the present invention can be obtained from the change in ion viscosity over time at a predetermined temperature using, for example, an MDE-10 cure monitor manufactured by Homometrix-Micromet. The ionic viscosity of the epoxy resin composition is lowest at the beginning of curing and saturated upon completion of curing. As an index related to the curing time, the time required for the cure index to reach 70% at 150° C. can be used to determine the rapid curability. Also, the time required for the cure index to reach 10% at 80° C. can be used to determine the stability in the preforming process.

Generally, there is a trade-off relationship between the storage stability of prepregs, the handling properties of preforms, and the curing speed. When the epoxy resin composition of the present invention simultaneously satisfies the conditions [a], [b], and [c], storage stability of the prepreg, handleability of the preform, and excellent curing speed can be achieved at the same time.

If the epoxy resin composition of the present invention takes 60 minutes or more until the ionic viscosity becomes the lowest, it exhibits even better handleability in the step of preforming a prepreg using the epoxy resin composition. preferable.

The epoxy resin composition of the present invention preferably satisfies the following condition [d].
[d]: 0.9≦(moles of active groups in component [A]/moles of active hydrogen in component [B])≦1.3.

Regarding condition [d], when the value represented by the number of moles of active groups in component [A]/the number of moles of active hydrogen in component [B] is in the range of 0.9 to 1.3, rapid curing and resin curing Good balance of mechanical properties.

The number of moles of active groups in component [A] is the sum of the number of moles of each epoxy resin active group, and is represented by the following formula.
Number of moles of active groups in component [A] = (mass of resin A/epoxy equivalent of resin A) + (mass of resin B/epoxy equivalent of resin B) + ... + (mass of resin W/epoxy equivalent of resin W) .

The active hydrogen mole number of component [B] is obtained by dividing the dicyandiamide mass by the active hydrogen equivalent of dicyandiamide, and is expressed by the following formula.
Mole number of active hydrogen in component [B]=mass of dicyandiamide/active hydrogen equivalent of dicyandiamide.

The epoxy resin composition of the present invention preferably satisfies the following condition [e].
[e]: 12≤(content of component [A]/content of component [C])≤26.

When [e] is in the range of 12 to 26, the balance between rapid curing, storage stability and preform handling is excellent.

In the epoxy resin composition of the present invention, the average epoxy equivalent of component [A] is preferably 350 g/eq or less. By making it 350 g/eq or less, rapid curability can be further improved.

The epoxy resin composition of the present invention is used for the purpose of adjusting the viscoelasticity, improving the tag and drape properties of the prepreg, and improving the mechanical properties and toughness of the resin composition, as long as the effects of the present invention are not lost. and a thermoplastic resin can be included as component [E]. As the thermoplastic resin, a thermoplastic resin soluble in epoxy resin, organic particles such as rubber particles and thermoplastic resin particles, inorganic particles such as silica, nanoparticles such as CNT and graphene, and the like can be selected.

Examples of thermoplastic resins soluble in epoxy resins include polyvinyl acetal resins such as polyvinyl formal and polyvinyl butyral, polyvinyl alcohol, phenoxy resins, polyamides, polyimides, polyvinylpyrrolidone, and polysulfones.

Examples of rubber particles include crosslinked rubber particles and core-shell rubber particles obtained by graft-polymerizing a different polymer on the surface of crosslinked rubber particles.

For the preparation of the epoxy resin composition of the present invention, kneading may be carried out using a machine such as a kneader, planetary mixer, three-roll and twin-screw extruder. You can mix by hand using a spatula or the like.

In obtaining a fiber-reinforced composite material using the epoxy resin composition obtained in the present invention, it is preferable to prepare a prepreg composed of the epoxy resin composition and the reinforcing fibers in advance. A prepreg is a form of material that allows precise control over the arrangement of fibers and the ratio of resin to maximize the properties of the composite material. A prepreg can be obtained by impregnating a reinforcing fiber base material with the epoxy resin composition of the present invention. As a method for impregnation, a hot melt method (dry method) or the like can be used. The hot-melt method is a method of directly impregnating reinforcing fibers with an epoxy resin composition whose viscosity has been reduced by heating, or a film is prepared by coating an epoxy resin composition on release paper or the like, and then both sides of the reinforcing fibers. Another method is to stack the films from one side and impregnate the reinforcing fibers with the resin by applying heat and pressure.

As a method for molding the laminated prepreg, for example, a press molding method, an autoclave molding method, a bagging molding method, a wrapping tape method, an internal pressure molding method, or the like can be appropriately used.

Next, the fiber-reinforced composite material will be explained. The fiber-reinforced composite material of the present invention is obtained by curing the prepreg of the present invention. More specifically, a fiber-reinforced composite material containing a resin cured product of the epoxy resin composition of the present invention as a matrix resin is obtained by laminating prepregs made of the epoxy resin composition of the present invention and then curing the laminate by heating. be able to.

The reinforcing fibers used in the present invention are not particularly limited, and glass fibers, carbon fibers, aramid fibers, boron fibers, alumina fibers, silicon carbide fibers and the like can be used. Two or more kinds of these fibers may be mixed and used. It is preferable to use carbon fiber from the viewpoint of obtaining a lightweight and highly rigid fiber-reinforced composite material.

A resin cured product of the epoxy resin composition of the present invention and a fiber-reinforced composite material containing reinforcing fibers are preferably used for sports applications, aerospace applications and general industrial applications. More specifically, in sports applications, it is preferably used for golf shafts, fishing rods, tennis and badminton rackets, hockey sticks, and ski poles. In aerospace applications, it is preferably used for aircraft primary structural materials such as main wings, tail wings and floor beams, and secondary structural materials such as interior materials. Furthermore, in general industrial applications, it is preferably used for structural materials such as automobiles, bicycles, ships and railroad vehicles. Among them, the prepreg composed of the epoxy resin composition and carbon fiber of the present invention has excellent storage stability, can be stored for a long time without the need for refrigeration, and is also excellent in rapid curing, so it requires a high cycle. Suitable for automotive parts. Moreover, the prepreg made of the epoxy resin composition of the present invention is suitably used for a molding method of curing by heating and pressurization, that is, press molding. A fiber-reinforced composite material can be obtained in a shorter time by placing the prepreg laminate in a preheated mold and pressing the laminate. In addition, by taking advantage of its excellent rapid curability, it is possible to suppress disordered orientation of fibers, which is often a problem in press molding, so that it is possible to improve the mechanical properties and design of molded products. In the present invention, there are no particular restrictions on the shape of the mold used for heating and pressing and the pressing mechanism. Since the prepreg made of the epoxy resin composition of the present invention has excellent stability in the preforming (preforming) step, it is also suitable for a molding process in which a mold is used to heat and press after preforming by heating. Used.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the description of these examples.

The components used in this embodiment are as follows.

<Materials used>
・ Component [A]: Epoxy resin [A]-1 “jER (registered trademark)” 828 (bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Corporation),
[A]-2 “jER (registered trademark)” 1007FS (bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Corporation),
[A]-3 “jER (registered trademark)” 1001 (bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Corporation),
[A]-4 “Epotec (registered trademark)” YD136 (bisphenol A type epoxy resin, manufactured by KUKDO),
[A]-5 “EPON (registered trademark)” 2005 (bisphenol A type epoxy resin, manufactured by Resolution Performance Products),
[A]-6 “jER (registered trademark)” 4010P (bisphenol F type epoxy resin, manufactured by Mitsubishi Chemical Corporation),
[A]-7 “jER (registered trademark)” 154 (phenol novolak type epoxy resin, average number of functional groups: 3.0/molecule, manufactured by Mitsubishi Chemical Corporation),
[A]-8 “Epotec (registered trademark)” YDPN-638 (phenol novolac type epoxy resin, average number of functional groups: 3.6/molecule, manufactured by Tohto Kasei Co., Ltd.).

• Component [B]: Dicyandiamide [B]-1 DICY7 (dicyandiamide, manufactured by Mitsubishi Chemical Corporation).

・ Component [C]: Aromatic urea [C]-1 “Omicure (registered trademark)” 24 (4,4′-methylenebis (phenyldimethylurea, manufactured by PTI Japan Co., Ltd.),
[C]-2 DCMU99 (3-(3,4-dichlorophenyl)-1,1-dimethylurea, manufactured by Hodogaya Chemical Industry Co., Ltd.),
[C]-3 “Dyhard®” UR505 (4,4′-methylenebis(phenyldimethylurea, manufactured by CVC).

• Component [D]: borate ester [D]-1 “Cure Duct (registered trademark)” L-07E (a composition containing 5 parts by mass of a borate ester compound, manufactured by Shikoku Kasei Kogyo Co., Ltd.).

・ Component [E]: Thermoplastic resin [E]-1 “Vinylec (registered trademark)” K (polyvinyl formal, manufactured by JNC Co., Ltd.),
[E]-2 “Sumika Excel (registered trademark)” PES3600P (polyethersulfone, manufactured by Sumitomo Chemical Co., Ltd.),
[E]-3 YP-50 (phenoxy resin, manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.).

<Method for preparing epoxy resin composition>
Predetermined amounts of components other than [B] dicyandiamide, [C] aromatic urea and [D] borate ester were placed in a stainless steel beaker, heated to 60 to 150° C., and appropriately kneaded until each component was compatible. After the temperature was lowered to 60° C., the [D] borate ester component was blended and kneaded. Separately, predetermined amounts of [A]-1 (“jER (registered trademark)” 828) and [B] dicyandiamide are added to a polyethylene cup, and the mixture is passed through the rolls twice using a triple roll to obtain a dicyandiamide master. was made. The main component prepared above and the dicyandiamide master were kneaded at 60°C or less so as to have a predetermined mixing ratio, and finally [C] aromatic urea was added and kneaded at 60°C for 30 minutes to obtain an epoxy resin composition. got stuff

<Method for Evaluating Flexural Modulus of Cured Epoxy Resin>
After defoaming the epoxy resin composition obtained according to <Method for preparing epoxy resin composition> in a vacuum, it was placed in a mold set to a thickness of 2 mm with a 2 mm thick “Teflon (registered trademark)” spacer. and 150° C. for 2 hours to obtain a plate-like cured resin product having a thickness of 2 mm. A test piece having a width of 10 mm and a length of 60 mm is cut out from this resin cured product, and an Instron universal testing machine (manufactured by Instron) is used to set the span to 32 mm and the crosshead speed to 10 mm/min. Three-point bending was performed according to and the bending elastic modulus was measured. At this time, the value measured with the number of samples n=6 was adopted as the value of the flexural modulus.

<Method for evaluating cure index of epoxy resin composition>
The curing time of the epoxy resin composition was measured using an MDE-10 cure monitor (manufactured by Homometrix-Micromet), and a sample of the epoxy resin composition obtained by the above method was placed on a press plate heated to 150°C or 80°C. The sample was allowed to stand still, and the increase in ionic viscosity with the progress of curing of the sample was converted into a cure index according to ASTM E2039, and the time to reach 70% and 10% was calculated.

<Evaluation method for minimum ion viscosity observation time of epoxy resin composition>
The minimum ionic viscosity of the epoxy resin composition was determined by using an MDE-10 cure monitor (manufactured by Homometrix-Micromet) and placing a sample of the epoxy resin composition obtained above on a press plate heated to 80°C. Then, the time until the ion viscosity started to rise was measured.

<Evaluation Method for Storage Stability of Epoxy Resin Composition>
The storage stability of the epoxy resin composition was evaluated by weighing 3 g of the initial epoxy resin composition obtained by the above method into an aluminum cup and placing it in a constant temperature and humidity chamber for 14 days under an environment of 40° C. and 75% RH. The amount of change in the glass transition temperature was defined as ΔTg=Ta−Tb, where Ta was the glass transition temperature after heating and Tb was the initial glass transition temperature, and the storage stability was determined by the value of ΔTg. The glass transition temperature was measured by weighing 3 mg of the epoxy resin after storage into a sample pan and using a differential scanning calorimeter (Q-2000: manufactured by TA Instruments) from -20°C to 150°C at 5°C/min. Measured at elevated temperature. The midpoint of the inflection point of the obtained exothermic curve was obtained as the glass transition temperature.

<Prepreg manufacturing method>
The epoxy resin composition prepared according to <Method for preparing epoxy resin composition> was applied onto release paper using a knife coater to prepare two resin films having a basis weight of 39 g/m ² . Next, two sheets of the obtained resin film were placed on carbon fiber “Torayca (registered trademark)” T700S-12K-60E (manufactured by Toray Industries, Inc., basis weight 150 g/m ² ) arranged in one direction in a sheet shape. Both sides of the fiber were overlapped and pressurized and heated at a temperature of 90° C. and a pressure of 2 MPa to impregnate the fiber with the epoxy resin composition to obtain a unidirectional prepreg.

<Press molding method for unidirectional fiber reinforced composite material>
The prepreg produced according to the above <Prepreg production method> was cut into a size of 240 mm square, the fiber direction was aligned, and 16 plies were laminated to produce a 240 mm square prepreg laminate.

The mold used for molding is a double-sided mold, and the lower mold has a concave shape, and has a width of 250 mm and a cavity of 25 mm. The upper mold has a convex shape, the convex portion is shaped to fill the cavity of the lower mold, and the material of the mold is SS400. With the double-sided mold heated to 150° C. and temperature controlled in advance, the prepreg laminate produced by the above method was placed in the center of the lower mold cavity, then the mold was closed and pressurized at a surface pressure of 3 MPa for 5 minutes. . After 5 minutes, the prepreg laminate was removed from the double-sided mold to obtain a unidirectional fiber-reinforced composite material.

<Evaluation method for bending strength of unidirectional fiber reinforced composite material>
From the laminate obtained according to the above <Press molding method for unidirectional fiber reinforced composite material>, a piece having a width of 15 mm and a length of 100 mm was cut, and an Instron universal testing machine (manufactured by Instron) was used to test JIS K7017 ( 1988). The bending strength was measured at a crosshead speed of 5.0 mm/min, a span of 80 mm, a thickness diameter of 10 mm, and a fulcrum diameter of 4 mm. The 0° bending strength was measured for six samples, converted values were calculated with a fiber mass content of 60% by mass, and the average was obtained as the 0° bending strength.

(Example 1)
[A] 35 parts by mass of "jER (registered trademark)" 828 as epoxy resin, 55 parts by mass of "jER (registered trademark)" 154 as epoxy resin, [B] 11.6 parts by mass of DICY7 as dicyandiamide, and [C] fragrance Using 4.0 parts by mass of "Omicure (registered trademark)" 24 as a group urea compound and 3.0 parts by mass of "Cure Duct (registered trademark)" L-07E as a mixture containing [D] borate ester, the above An epoxy resin composition was prepared according to <Method for preparing epoxy resin composition>. The content of [a] component [D]/the content of component [C] in this epoxy resin composition was 0.038. Condition [b] Time to reach 10% cure index at 80°C was measured according to <Evaluation method for cure index of epoxy resin composition> and was 217 minutes. Similarly, [c] Time to reach 70% cure index at 150°C. was measured to be 63 seconds. In addition, when the observation time of the minimum ionic viscosity at 80° C. was measured according to <Method for evaluating minimum ionic viscosity observation time of epoxy resin composition>, good stability was shown with 202 minutes. The ΔTg evaluated according to <Method for Evaluating Storage Stability of Epoxy Resin Composition> was 12° C., indicating good storage stability.

The flexural modulus of the cured product was evaluated according to <Method for evaluating the flexural modulus of the cured epoxy resin product> and found to be 3.8 GPa.

A prepreg is produced by the method described in <Method for producing prepreg>, and the fiber reinforced composite material produced according to <Method for press molding of unidirectional fiber reinforced composite material> is evaluated as <Bending strength of unidirectional fiber reinforced composite material. When the 0° bending strength was evaluated according to the evaluation method>, it showed a good value of 1671 MPa.

(Examples 2-6, Comparative Examples 8-16 )
An epoxy resin composition, a prepreg, and a fiber-reinforced composite material were produced in the same manner as in Example 1, except that the resin compositions were changed as shown in Tables 1 and 2, respectively. The content of [a] component [D]/the content of component [C] in these epoxy resin compositions is in the range of 0.005 to 0.045, and the time to reach 10% cure index [b] at 80°C is 120 minutes or more, [c] 70% curing index at 150°C was reached within 120 seconds.

As in Example 1, all of the obtained resin compositions were good in storage stability, observation time of the lowest ion viscosity at 80° C., and bending elastic modulus of the cured product. The 0° bending strength of the obtained fiber-reinforced composite material was also good.

(Comparative example 1)
[D] An epoxy resin composition, a prepreg, and a fiber-reinforced composite material were produced in the same manner as in Example 1, except that the boric acid ester was not added. The resin composition and evaluation results are as shown in Table 3. The content of [a] component [D]/the content of component [C] in this epoxy resin composition is 0, [b] the time to reach 10% cure index in dielectric measurement at 80 ° C. is 50 minutes, [c] 150 ° C. The time to reach 70% cure index was 71 seconds.

The observation time for the lowest ionic viscosity at 80°C was 31 minutes, and the ΔTg was 40°C. Although the curing speed was good, the stability was significantly insufficient. Moreover, the 0° bending strength of the fiber-reinforced composite material was as low as 1468 MPa.

(Comparative example 2)
[C] An epoxy resin composition, a prepreg, and a fiber-reinforced composite material were produced in the same manner as in Example 1, except that "Omicure (registered trademark)" 24 was reduced to 3 parts as aromatic urea. The resin composition and evaluation results are as shown in Table 3. The content of component [a] / content of component [C] in this epoxy resin composition is 0.050, [b] the time to reach 10% cure index at 80 ° C. is 233 minutes, [c] 150 ° C. The time to reach 70% cure index was 192 seconds.

Also, the observation time for the lowest ionic viscosity at 80° C. was 197 minutes, and the ΔTg was 15° C. The stability was good, but the curing speed was insufficient. Moreover, the 0° bending strength of the fiber-reinforced composite material was as low as 1492 MPa.

(Comparative Example 3)
[B] An epoxy resin composition, a prepreg, and a fiber-reinforced composite material were produced in the same manner as in Example 1, except that DICY7 was reduced to 6.3 parts as dicyandiamide. The resin composition and evaluation results are as shown in Table 3. The content of [a] component [D]/the content of component [C] in this epoxy resin composition is 0.050, [b] the time to reach 10% cure index at 80 ° C. is 240 minutes, [c] 150 ° C. The time to reach 70% cure index was 250 seconds.

Also, the observation time for the lowest ionic viscosity at 80° C. was 200 minutes, and the ΔTg was 15° C. The stability was good, but the curing speed was insufficient. Moreover, the 0° bending strength of the fiber-reinforced composite material was as low as 1422 MPa.

(Comparative Example 4)
[D] An epoxy resin composition, a prepreg, and a fiber-reinforced composite material were produced in the same manner as in Example 1, except that the amount of "Cure Duct (registered trademark)" L-07E was increased to 7 parts as the borate ester. bottom. The resin composition and evaluation results are as shown in Table 3. The resin composition and evaluation results are shown in Table 3. The content of [a] component [D]/the content of component [C] in this epoxy resin composition is 0.048, [b] the time to reach 10% cure index at 80 ° C. is 221 minutes, [c] 150 ° C. The time to reach 70% cure index was 152 seconds.

Also, the observation time for the lowest ionic viscosity at 80° C. was 199 minutes, and the ΔTg was 9° C. The stability was good, but the curing speed was insufficient. Moreover, the 0° bending strength of the fiber-reinforced composite material was as low as 1493 MPa.

(Comparative Example 5)
[D] An epoxy resin composition, a prepreg, and a fiber-reinforced composite material were produced in the same manner as in Example 1, except that the boric acid ester was not added. The resin composition and evaluation results are as shown in Table 3. The content of [a] component [D]/the content of component [C] in this epoxy resin composition is 0, [b] the time to reach 10% cure index at 80 ° C. is 45 minutes, The time to reach 70% index was 68 seconds.

Also, the observation time for the lowest ionic viscosity at 80° C. was 35 minutes, and the ΔTg was 49° C. The curing speed was good, but the stability was insufficient. Also, the 0° bending strength of the fiber-reinforced composite material was insufficient at 1398 MPa.

(Comparative Example 6)
An epoxy resin composition, a prepreg, and a fiber-reinforced composite were produced in the same manner as in Example 1, except that [B] DICY7 was reduced to 5 parts as dicyandiamide, and [D] boric acid ester was not added. Material was made. The resin composition and evaluation results are as shown in Table 3. The content of [a] component [D]/the content of component [C] in this epoxy resin composition is 0, [b] the time to reach 10% cure index at 80 ° C. is 59 minutes, [c] cure at 150 ° C. The index 70% reaching time was 261 seconds.

The observation time for the lowest ionic viscosity at 80° C. was 49 minutes, and the ΔTg was 29° C. The curing rate was good, but the stability was low. Moreover, the 0° bending strength of the fiber-reinforced composite material was as low as 1356 MPa.

(Comparative Example 7)
[C] An epoxy resin composition, a prepreg, and a fiber-reinforced composite material were produced in the same manner as in Example 1, except that the amount of DCMU99 as the aromatic urea was reduced to 3 parts. The resin composition and evaluation results are as shown in Table 3. The content of [a] component [D]/the content of component [C] in this epoxy resin composition is 0.050, [b] the time to reach 10% cure index at 80 ° C. is 241 minutes, [c] 150 ° C. The time to reach 70% cure index was 210 seconds.

Also, the observation time for the lowest ionic viscosity at 80° C. was 210 minutes, and the ΔTg was 9° C. The stability was good, but the curing speed was insufficient. In addition, the fiber-reinforced composite material had an insufficient 0° bending strength of 1455 MPa.

In addition, the unit of each component in the table is parts by mass.

By using the epoxy resin composition according to the present invention, it is possible to provide a prepreg excellent in both rapid curability and storage stability. Moreover, since it is stable against the heat history applied during the preforming process, it is suitably used as a matrix resin for fiber-reinforced composite materials that require complex shapes. In particular, it is preferably used for industrial applications requiring high cycle molding.

Claims (7)

An epoxy resin composition containing the following components [A], [B], [C] and [D] and satisfying the following conditions [a], [b], [c] and [e] .
[A]: epoxy resin [B]: dicyanamide [C]: aromatic urea [D]: borate ester [a]: 0.005 ≤ (content of component [D] / content of component [C]) ≤ 0.045
[b]: In dielectric measurement at 80°C, the time from the start of measurement until the cure index reaches 10% is 120 minutes or longer.
[c]: In dielectric measurement at 150°C, the time from the start of measurement until the cure index reaches 70% is within 120 seconds.
[e]: 16 ≤ (content of component [A] / content of component [C]) ≤ 26 2. The epoxy resin composition according to claim 1, wherein the time required to observe the lowest ionic viscosity in dielectric measurement at 80[deg.] C. is 60 minutes or longer. 3. The epoxy resin composition according to claim 1, which satisfies condition [d] below.
[d] 0.9 ≤ (moles of active groups in component [A]/moles of active hydrogen in component [B]) ≤ 1.3 4. The epoxy resin composition according to any one of claims 1 to 3 , wherein the average epoxy equivalent of component [A] is 350 g/eq or less. The epoxy resin composition according to any one of claims 1 to 4, comprising components [A], [B], [C] and [D]. A prepreg comprising the epoxy resin composition according to any one of claims 1 to 5 and reinforcing fibers. A fiber-reinforced composite material obtained by curing the prepreg according to claim 6 .