WO2018181849A1 - Epoxy resin composition for fiber-reinforced composite materials, fiber-reinforced composite material and molded body - Google Patents

Abstract

Provided is an epoxy resin composition for fiber-reinforced composite materials, which has a good balance between storage stability and impregnation ability during the production of a prepreg, and which enables the achievement of a molded article that has excellent mechanical characteristics. An epoxy resin composition for fiber-reinforced composite materials, which contains, as essential ingredients, (A) an epoxy resin, (B) dicyandiamide, (C) an imidazole-based curing assistant and (D) a core-shell rubber, and which is characterized in that the imidazole-based curing assistant (C) makes the epoxy resin composition have an exothermic onset temperature of 135°C or higher as determined by DSC at a heating rate of 10°C/minute. Also, an epoxy resin composition which contains, as essential ingredients, (A) an epoxy resin, (B) an epoxy resin curing agent and (C) an imidazole compound, and which is characterized in that: the epoxy resin (A) contains a liquid bisphenol A epoxy resin and/or a liquid bisphenol F epoxy resin, while having a viscosity (25°C) of from 1 Pa·s to 100 Pa·s (inclusive); and both of the epoxy resin curing agent (B) and the imidazole compound (C) are solids that have a melting point or a decomposition temperature of 200°C or higher, while having an average particle diameter (D50) of 2 μm or less.

Description

Epoxy resin composition for fiber reinforced composite material, fiber reinforced composite material and molded body

The present invention relates to a fiber reinforced composite material and an epoxy resin composition used therefor. The present invention relates to an epoxy resin composition that is excellent in winding property when a tow primreg is formed and can reduce the generation of voids, and a fiber-reinforced composite material using the same.

Conventionally, fiber-reinforced composite materials made of carbon fiber, glass fiber, and other reinforcing fibers and epoxy resins, phenol resins, and other thermosetting resins are lightweight, yet have mechanical properties such as strength and rigidity, heat resistance, and corrosion resistance. It has been applied to many fields such as aviation / space, automobiles, rail cars, ships, civil engineering and sports equipment. Especially in applications where high performance is required, 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 is used as a matrix resin. Of these, many epoxy resins are used that are particularly excellent in adhesion to carbon fibers. However, since epoxy resins (cured products) are generally brittle, that is, have low toughness and elongation, the mechanical properties of fiber reinforced composite materials using them as they are are not satisfactory.

As a method for improving the toughness and elongation of an epoxy resin, a method of blending a rubber component or a thermoplastic resin having excellent toughness has been tried. For example, it has been studied since the 1970s that the toughness of an epoxy resin is improved by adding a rubber component such as acrylonitrile-butadiene rubber containing a carboxyl group to the epoxy resin, and is well known. However, the rubber component causes a decrease in heat resistance and a decrease in elastic modulus, and it is necessary to add a large amount of the rubber component in order to obtain a sufficient toughness modification effect by the rubber component. For this reason, there existed a fault that the composite material which has a favorable physical property cannot be obtained because the heat resistance and mechanical characteristics inherent to the epoxy resin are lowered.

In addition, as a method of blending a thermoplastic resin with an epoxy resin, a thermoplastic resin such as polyethersulfone, polysulfone and polyetherimide is dissolved in the epoxy resin, or blended and dissolved in a fine powder. It is known that a fiber-reinforced composite material with improved impact resistance and excellent impact resistance can be obtained without impairing the mechanical properties of the epoxy resin. Reference 1).

However, in this method, it is necessary to add a large amount of these thermoplastic resins in order to obtain a sufficient toughness improving effect. As a result, the viscosity of the epoxy resin composition is significantly increased, resulting in a significant decrease in processability when obtaining a prepreg, a resin unimpregnated portion in the resulting prepreg, or a fiber reinforced composite obtained by curing the prepreg There is a drawback that voids occur in the material.

In response to this problem, a method using polymer particles substantially insoluble in an epoxy resin has been proposed. In particular, a method is proposed in which core-shell rubber particles covering part or all of the surface of the core part are blended by a method such as graft polymerization of a particulate core part mainly composed of a polymer and a polymer different from the core part. (For example, Patent Documents 2 and 3). It is known that this method can suppress an increase in viscosity of the epoxy resin composition and a decrease in Tg of the cured epoxy resin.

However, in order to obtain a sufficient toughness-improving effect, it is necessary to mix a large amount of core-shell rubber particles. As a result, the elastic modulus of the cured epoxy resin is lowered, and consequently the mechanical properties of the fiber-reinforced composite material are lowered. The problem remained.

As a means for supplementing them, there has also been proposed a technique in which a core-shell rubber and a long-chain epoxy resin having a large molecular weight are used in combination (Patent Document 4). However, the long-chain epoxy resin increases the viscosity of the composition, causes deterioration in storage stability, and is not satisfactory in improving toughness.

Epoxy resin is one of the resins classified as thermosetting resins. It has a strong adhesion to materials, and its use is widely used for paints, electronic materials, civil engineering / adhesion and others. In addition, fiber-reinforced composite materials combined with reinforcing fibers such as carbon fiber and glass fiber are lightweight, but have excellent mechanical properties such as strength and rigidity, heat resistance, and corrosion resistance. It is applied to many fields such as railway vehicles, ships, civil construction and sports equipment.

Examples of processing of fiber reinforced composite materials include autoclave method, pultrusion method, filament winding method, braiding method, resin transfer molding method, etc., but the processing method requires the shape of the target structure and required It is selected depending on productivity.

The filament winding method is a process of winding (winding) a carbon fiber bundle or other fiber bundle (filament) impregnated with epoxy resin or other curable resin into a mold called a mandrel. Thus, a composite material can be obtained. This method can be roughly divided into two methods, a dry method and a wet method.

The wet method is a method in which a resin impregnation tank is installed in the filament winding process between unwinding carbon fibers and winding them around a mandrel. While this method is simple as a process, since it is necessary to impregnate the resin in accordance with the winding speed, there is a problem that it is limited to a resin having low viscosity and excellent impregnation properties. In addition, since the basis weight varies, there are problems such as having to use extra resin, causing the resin to fall and become contaminated during the process, and shifting from the target location depending on the winding speed and angle. is there.

One dry method uses a tow prepreg in which carbon fiber is impregnated with a resin in advance. This process is divided into an impregnation step and a winding step, so that each can be carried out with high accuracy, but storage stability of the tow prepreg as an intermediate member is required. A resin having excellent storage stability is generally known to have a trade-off that sacrifices curing reactivity. This trade-off is a widely recognized issue in the industry.

As a technique for achieving both the storage stability and curing reactivity of an epoxy resin, a method using a powder curing agent or a curing accelerator (hereinafter referred to as a curing agent) is generally known. By adopting a solid curing agent or the like, the opportunity for the epoxy resin and the curing agent or the like to contact can be limited only to the solid-liquid interface. In addition, since a reaction occurs when the curing agent or the like is dissolved and diffused by heating, it is known as a technique capable of eliminating the trade-off.

When applying this technology to composite materials, applicability is completely different depending on the timing of molding and the timing of dissolution of particles such as a curing agent. That is, even when a large amount of powder is contained, when autoclave molding is performed, a cured product with few defects can be obtained, while the filament winding method has a problem of becoming a cured product with many defects such as voids. In particular, this problem tends to increase as the resin content (Rc) decreases.

Patent Document 5 describes an epoxy resin composition capable of achieving both storage stability and quick curing, and discloses a carbon fiber cloth prepreg having a resin content of 41% by weight in Examples. Patent Document 6 describes an accelerator combining a specific urea derivative and dicyandiamide, but there is no example of a fiber composite material. Patent Document 7 also describes a resin composition capable of achieving both storage stability and rapid curing, and discloses a glass fiber prepreg having a resin content of 66% by weight in Examples.
In any patent document, there is no description about the void reduction technique when the resin content is reduced.

Patent Document 8 discloses a composition containing an amine compound having an average particle size of 10 μm or less and a borate ester compound as an epoxy resin composition having good storage stability and curability. However, even if referring to Examples and the like, there is no description of the resin content when it is made a prepreg.

Japanese Patent Publication No. 6-43508 Japanese Patent Laid-Open No. 5-65391 JP 2003-277579 A Japanese Patent No. 5293629 JP 2004-075914 A Special Table 2007-504341 JP-T-2015-516497 JP-A-9-157498

The present invention provides an epoxy resin composition for a fiber-reinforced composite material that is excellent in mechanical properties of a molded product while achieving both impregnation and storage stability at the time of prepreg production, and in particular, storage of a tow prepreg used in a filament winding method. Disclosed is an epoxy resin composition for fiber-reinforced composite materials that can improve stability.
Another object of the present invention is to provide an epoxy resin composition used for a carbon fiber composite material, which has excellent storage stability and curing reactivity, and can reduce voids and other defects even at a low resin content Rc.

That is, the first present invention is an epoxy resin composition comprising an epoxy resin (A), dicyandiamide (B), an imidazole-based curing aid (C), and a core-shell rubber (D) as essential components. The fiber reinforced composite, wherein the curing aid (C) has an exothermic starting temperature of 135 ° C. or higher when the epoxy resin composition is measured by DSC at a temperature rising rate of 10 ° C./min. It is an epoxy resin composition for materials.

It is desirable that the epoxy resin composition for fiber-reinforced composite material according to the first aspect of the present invention satisfies any of the following.
1) 0.2 to 0.8 equivalent of dicyandiamide (B) with respect to the epoxy equivalent of epoxy resin (A), and 50 to 50 parts of imidazole curing aid (C) with respect to 100 parts by mass of dicyandiamide (B). Containing 250 parts by weight,
2) The epoxy resin (A) has two epoxy groups in one molecule, and the viscosity at 25 ° C. measured using an E-type viscometer is 1 to 50 Pa · s.
3) The imidazole curing aid (C) is 2,4-diamino-6- [2′-ethyl-4′-methylimidazolyl- (1 ′)]-ethyl-s-triazine isocyanuric acid adduct or 2-phenyl -4-methyl-5-hydroxymethylimidazole,
4) The volume average particle diameter of the core-shell rubber (D) is 1 to 500 nm.
5) The viscosity at 25 ° C. measured using an E-type viscometer is 1 to 50 Pa · s.

Another aspect of the first aspect of the present invention is a fiber-reinforced composite material obtained by blending reinforcing fibers into the epoxy resin composition. The volume content of the reinforcing fibers is preferably 30 to 75%.
Yet another embodiment of the present invention is a molded body obtained by molding and curing the fiber-reinforced composite material by a filament winding method.

In addition, as a result of intensive studies to solve the above-mentioned problems, the present inventors use a low-viscosity liquid epoxy resin as an epoxy resin, both as a curing agent and a curing accelerator blended in the epoxy resin. It has been found that by incorporating a solid having a high melting point etc. and an average particle size of not more than a certain value as an essential component, it is possible to sufficiently reduce voids, and the second invention is completed. It came to.

That is, the second aspect of the present invention is an epoxy resin composition comprising an epoxy resin (A), an epoxy resin curing agent (B), and an imidazole compound (C) as essential components, wherein the epoxy resin (A) is a liquid bisphenol. It contains an A-type epoxy resin and / or a liquid bisphenol F-type epoxy resin, has a viscosity (25 ° C.) of 1 Pa · s to 100 Pa · s, and the epoxy resin curing agent (B) and the imidazole compound (C) are both An epoxy resin composition having a melting point or a decomposition temperature of 200 ° C. or higher and an average particle size (D50) of 2 μm or less.

  In the second invention, the epoxy curing agent (B) may be dicyandiamide. The imidazole compound (C) can be a compound represented by the following formula (1) or formula (2). Moreover, it is preferable that the total amount of an epoxy hardening | curing agent (B) and an imidazole compound (C) shall be 10 weight% or less with respect to an epoxy resin composition.

The epoxy resin composition of the second present invention can contain a rubber component (D). The rubber component (D) is preferably rubber particles having a core-shell structure. It is also preferable to contain a small amount of a stabilizer.

Another aspect of the second present invention is a tow prepreg formed by impregnating carbon fiber (E) with the above epoxy resin composition. As carbon fiber (E), it is suitable that an average diameter is 7.5 micrometers or less.

Another aspect of the second present invention is a carbon fiber reinforced plastic obtained by molding and curing the tow prepreg.

It is a graph which shows the exothermic start temperature calculated | required from a DSC chart, and exothermic peak temperature.

Hereinafter, first, the first embodiment of the present invention will be described.

The epoxy resin composition for fiber-reinforced composite material according to the first aspect of the present invention (hereinafter also simply referred to as an epoxy resin composition) includes an epoxy resin (A), a dicyandiamide (B), an imidazole-based curing aid (C), and a core-shell rubber. (D) is an essential component. Hereinafter, epoxy resin (A), dicyandiamide (B), imidazole-based curing aid (C), and core-shell rubber (D) are respectively referred to as (A) component, (B) component, (C) component, and (D) component. Say.

The amount of the epoxy resin (A) used in the present invention is 40 to 75 parts by weight, preferably 40 to 70 parts by weight, more preferably 50 to 50 parts, out of a total of 100 parts by weight of the components (A) to (D). 70 parts by mass.
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, isophorone bisphenol type epoxy resin having two epoxy groups in one molecule. Bisphenol-type epoxy resins, halogens, alkyl-substituted products, hydrogenated products, high-molecular weight products having a plurality of repeating units as well as monomers, glycidyl ethers of alkylene oxide adducts, phenols, etc. Novolak type epoxy resins such as novolak type epoxy resin, cresol novolak type epoxy resin, bisphenol A novolak type epoxy resin, 3,4-epoxy-6-methylcyclohexylmethyl-3,4-e Cycloaliphatic epoxy resins such as xyl-6-methylcyclohexanecarboxylate, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 1-epoxyethyl-3,4-epoxycyclohexane, and trimethylol Aliphatic epoxy resins such as propane polyglycidyl ether, pentaerythritol polyglycidyl ether, polyoxyalkylene diglycidyl ether, phthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, glycidyl ester such as dimer acid glycidyl ester, Tetraglycidyldiaminodiphenylmethane, tetraglycidyldiaminodiphenylsulfone, triglycidylaminophenol, triglycidylaminocresol, tetraglycidylalkyl Glycidyl amines such as Rirenjiamin like can be used. Among these epoxy resins, an epoxy resin having two epoxy groups in one molecule is preferable from the viewpoint of viscosity increase rate, and a polyfunctional epoxy resin having more epoxy groups is not preferable. Among them, bisphenol F type epoxy resin is 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 measured using an E-type viscometer (cone plate type) at 25 ° C. in the range of 1 to 50 Pa · s, more preferably 5 to 30 Pa · s. More preferably, it is 6 to 25 Pa · s, particularly preferably 7 to 20 Pa · s. Accordingly, the resin has good impregnation into the reinforcing fiber, and the resin dripping hardly occurs after the impregnation. Moreover, several types of mixtures may be sufficient as an epoxy resin (A), and it is preferable that the viscosity of the mixture is the said range.

In the epoxy resin composition of the present invention, dicyandiamide (B) is used as a curing agent. Dicyandiamide is a solid curing agent at room temperature, hardly dissolves in epoxy resin at room temperature, but dissolves when heated to 180 ° C or higher, and has the property of having excellent storage stability at room temperature. It is a curing agent. The amount to be used is preferably in the range of 0.2 to 0.8 equivalents (calculated assuming that 1 mol of dicyandiamide is 4 equivalents) relative 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 equivalent 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 equivalent, unreacted dicyandiamide tends to remain, resulting in poor mechanical properties. There is a tendency.

The epoxy resin composition of the present invention can be produced by various known methods. For example, there is a method of kneading each component with a kneader. Moreover, you may knead | mix using a biaxial extruder. Dicyandiamide (B) is dispersed in each component in a solid state, but when all the components are kneaded at once, dicyandiamide may aggregate to cause poor dispersion. A poorly dispersed epoxy resin composition is not preferred because it causes uneven physical properties in the cured product or poor curing. Therefore, dicyandiamide is preferably used as a master batch by using a part of the epoxy resin, preliminarily kneading with three rolls.

The blending amount of the imidazole-based curing aid (C) contained in the epoxy resin composition of the present invention is preferably 50 to 250 parts by weight, more preferably 50 to 100 parts by weight with respect to 100 parts by weight of dicyandiamide (B). Part. When the amount of the imidazole-based curing aid is less than 50 parts by mass, it is difficult to express fast curability. When the amount is more than 250 parts by mass, the cured product tends to be brittle although there is no change in the fast curability.

As the imidazole-based curing aid (C), the DSC (differential scanning calorimetry) exothermic start temperature when the epoxy resin composition is used is 135 ° C. or higher in order to improve the suppression of viscosity increase rate (storage stability). Use something. The imidazole-based curing aid (C) preferably has an exothermic starting temperature of preferably 137 ° C. or higher, more preferably 140 ° C. or higher. When the heat generation starting 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. This DSC exothermic start temperature is outside the amount of heat generated per hour when the epoxy resin composition containing the imidazole-based curing aid (C) as a curing catalyst is subjected to DSC measurement at a temperature rising rate of 10 ° C / min. FIG. 1 shows the temperature obtained from the actual measurement values.
In FIG. 1, the amount of heat generation per hour is extrapolated, the intersection is defined as the heat generation start temperature, and the temperature indicating the maximum value of the heat generation amount is defined as the heat generation peak temperature.

Further, as the imidazole-based curing aid (C), the DSC exothermic peak temperature when used as an epoxy resin composition is preferably 145 ° C. to 160 ° C., more preferably 148 ° C. to suppress heat generation during curing. What is 155 degreeC is good. When the exothermic peak temperature of the imidazole-based curing aid (C) 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 fluidity improving effect is not sufficiently exhibited. On the other hand, if it exceeds 160 ° C., abnormal heat generation and decomposition of the resin itself occur due to the heat generated during curing. This DSC exothermic peak temperature is an exothermic peak temperature when DSC measurement is performed on an epoxy resin composition containing an imidazole-based curing aid (C) as a curing catalyst under a temperature rising rate of 10 ° C / min.

As the imidazole-based curing aid (C), 2,4-diamino-6- [2 ′] is used in order to further satisfy the heat resistance at the time of curing in addition to the impregnation property to the reinforcing fiber at the time of mixing in the present invention. -Ethyl-4'-methylimidazolyl- (1 ')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenyl-4-methyl-5-hydroxymethylimidazole is preferred. Moreover, as long as it becomes a composition in which exothermic peak temperature shows 145 degreeC or more, you may use another imidazole type compound in combination of 1 type, or 2 or more types as a part of hardening adjuvant component. For example, these other imidazole curing aids (C1) include 2-methylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 2-undecylimidazole. Imidazoles such as 2-heptadecyl imidazole, 2-phenyl imidazole, 2-phenyl-4-methyl imidazole, 2-phenyl 6-4 ', 5'-dihydroxymethyl imidazole, 1-cyanoethyl-2-ethyl-4methyl imidazole, etc. It is preferable to use a system compound. Further, as an imidazole compound containing a triazine ring, for example, 2,4-diamino-6- [2′-methylimidazolyl- (1 ′)]-ethyl-s-triazine, 2,4-diamino-6- [ 2'-undecylimidazolyl- (1 ')]-ethyl-s-triazine and the like.

Since the imidazole-based curing aid (C) is also solid, it tends to cause poor dispersion, so a part of the epoxy resin is used in the same way as dicyandiamide (B), pre-kneaded with three rolls, and used as a master batch It is preferable to do.

As the core-shell rubber (D), the surface of the particulate core component is obtained by graft polymerization of a shell component polymer different from the core component on the surface of a particulate core component mainly composed of a crosslinked rubbery polymer or elastomer. A part or the whole is coated with a shell component.

As the core component constituting the core-shell polymer, a polymer polymerized from one or more kinds selected from vinyl monomers, conjugated diene monomers, (meth) acrylate monomers, silicone resins, and the like can be used. A crosslinked rubber-like polymer composed of an aromatic vinyl monomer and a conjugated diene monomer, especially styrene and butadiene can be preferably used because of its high toughness improving effect.

The shell component constituting the core-shell polymer is preferably graft-polymerized to the above-described core component and chemically bonded to the polymer constituting the core component. As a component constituting such a shell component, for example, a polymer polymerized from one or more kinds selected from (meth) acrylic acid esters, aromatic vinyl compounds and the like can be used. When a crosslinked rubber-like polymer composed of styrene and butadiene is used as the core component, a mixture of methyl methacrylate as a (meth) acrylic ester and styrene as an aromatic vinyl compound can be suitably used.

In addition, it is preferable that a functional group that reacts with the epoxy resin composition of the present invention is introduced into the shell component in order to stabilize the dispersion state. Examples of such a functional group include a hydroxyl group, a carboxyl group, and an epoxy group, and an epoxy group is particularly preferable. As a method for introducing an epoxy group, there is a method in which, for example, 2,3-epoxypropyl methacrylate is used in combination with the shell component and graft polymerization is performed on the core component.

The core-shell polymer that can be applied to the epoxy resin composition of the present invention is not particularly limited as long as it is described above, and those manufactured by a known method can be used. However, the core-shell polymer is usually handled as a powder by pulverizing what is taken out as a lump, and the powder-like core-shell polymer is often dispersed again in the epoxy resin. It is difficult to disperse stably. Therefore, what can be handled in the state of the masterbatch finally disperse | distributed by the primary particle in the epoxy resin, without taking out from the manufacturing process of a core-shell polymer once at a lump is preferable. For example, polymerization is performed by a method described in JP-A-2004-315572, that is, a method in which a core-shell polymer is polymerized in an aqueous medium typified by emulsion polymerization, dispersion polymerization, and suspension polymerization. After obtaining a turbid liquid, water and a partially soluble organic solvent, for example, an ether solvent such as acetone or methyl ethyl ketone, are mixed, and then contacted with a water-soluble electrolyte such as sodium chloride or potassium chloride. For example, a method in which an organic resin layer and an aqueous layer are phase-separated, an epoxy resin is appropriately mixed with a core-shell polymer-dispersed organic solvent obtained by separating and removing the aqueous layer, and then the organic solvent is removed by evaporation. For example, “Kane Ace” commercially available from Kaneka Corporation can be suitably used as the core-shell polymer-dispersed epoxy masterbatch.

When applying the core-shell polymer to the epoxy resin composition of the present invention, the core-shell polymer preferably has an average particle size of 1 to 500 nm in terms of volume average particle size, and more preferably 3 to 300 nm. The volume average particle diameter can be measured using a nanotrack particle size distribution measuring apparatus (manufactured by Nikkiso). When the volume average particle size of the core-shell polymer used in the present invention is 1 nm or less, it is difficult to produce or becomes very expensive and cannot be used substantially. When the volume average particle size is 500 nm or more, In the prepreg manufacturing process, in the step of impregnating the epoxy resin composition, the reinforcing fibers present at a level of several thousand fibers are in a net-like state. Therefore, the reinforcing fibers are separated by filtration and dispersed in the tow prepreg. Since it may become uneven, it is not preferable.

The compounding amount of the core shell rubber (D) 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. If the blending amount is 0.5 parts by mass or more, the fracture toughness required for the fiber-reinforced composite material after molding can be easily obtained, and if the blending amount is 15 parts by mass or less, the resulting epoxy resin composition Since the increase in the viscosity of the product can be suppressed and the reinforcing fiber can be impregnated without difficulty, it is more suitable for a fiber-reinforced composite material.

The epoxy resin composition of the present invention may further contain other stabilizers, modifiers and the like. A preferred stabilizer is a boric acid compound represented by B (OR) ₃ (wherein R represents a hydrogen atom, an alkyl group or an aryl group). The compounding 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 weight, stability during storage cannot be ensured, and if it exceeds 10 parts by weight, the effect of inhibiting the curing reaction becomes larger, which leads to poor curing. Absent.

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

The epoxy resin composition of the present invention is produced by uniformly mixing the above components (A) to (D). The obtained epoxy resin composition for fiber-reinforced composite materials has good impregnation properties for reinforcing fibers, and resin dripping does not easily occur from the fibers even after the impregnation. Furthermore, the epoxy resin composition for fiber-reinforced composite material of the present invention is stable at room temperature of 23 ° C. and hardly changes in viscosity, and increases in viscosity after 72 hours under the conditions of a temperature of 40 ° C., an air atmosphere or an inert gas atmosphere. The rate is 20% or less, and not only can ensure stable impregnation into a reinforcing fiber during the production of a prepreg having a long impregnation step, but also the resin flowability deteriorates because it does not thicken during storage. Thus, a fiber-reinforced composite material having few voids during curing and excellent surface smoothness can be obtained.

The epoxy resin composition of the present invention can be blended with other curable resins. 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 epoxy resin composition of the present invention preferably has a viscosity measured using an E-type viscometer of 1 to 50 Pa · s / 25 ° C., more preferably 5 to 30 Pa · s / 25 ° C., and even 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 carbon fiber impregnation property deteriorates. If the viscosity is too low, precipitation of dicyandiamide or an imidazole curing aid is caused.

The epoxy resin composition of the present invention is suitably used for a toe 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 lower the viscosity, impregnated while immersing the reinforcing fiber bundle, and the like. A wet method in which an organic solvent is evaporated to form a tow prepreg, or the epoxy resin composition heated to a low viscosity without using an organic solvent is formed into a film on a roll or release paper, and then a reinforcing fiber bundle After being transferred to one side or both sides, a hot melt method in which pressure is applied by impregnation through a bending roll or a pressure roll, the epoxy resin composition is reduced in viscosity by heating, and impregnated while dipping a reinforcing fiber bundle Manufactured by the filament winding method, etc., and virtually no organic solvent remains in the tow prepreg There, high quality tow prepreg high productivity since it can be produced, can be preferably used a filament winding method. By using such a production method, a resin-impregnated tow prepreg can be obtained.

The reinforcing fiber used in the epoxy resin composition for fiber-reinforced composite material of the present invention is selected from glass fiber, aramid fiber, carbon fiber, boron fiber, etc., but in order to obtain a fiber-reinforced composite material having excellent strength It is preferable to use carbon fibers.

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

The epoxy resin composition of the present invention is a cured product in which a crosslinking reaction proceeds 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. Can be obtained. The heating condition may be one stage or may be a multistage condition in which a plurality of heating conditions are combined. In particular, assuming a high-pressure vessel filled with hydrogen gas or the like used in fuel cells, heating is performed 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.

Next, a second embodiment of the present invention will be described.

The epoxy resin composition of the second present invention contains an epoxy resin (A), an epoxy resin curing agent (B), and an imidazole compound (C) as essential components. Hereinafter, the epoxy resin (A), the epoxy resin curing agent (B), and the imidazole compound (C) are also referred to as the (A) component, the (B) component, and the (C) component, respectively.

The epoxy resin (A) is an epoxy resin containing a liquid bisphenol A type epoxy resin, a liquid bisphenol F type epoxy resin, or both, and having a viscosity at 25 ° C. of 1 Pa · s to 100 Pa · s.
This viscosity is a viscosity measured using an E-type viscometer (cone plate type) at 25 ° C. The preferred viscosity is 30 Pa · s or less, more preferably 15 Pa · s or less. Further, it is 4 Pa · s or more, more preferably 8 Pa · s or more. When the viscosity exceeds 100 Pa · s, the carbon fiber cannot be sufficiently impregnated, and voids are easily generated during filament winding molding. If it is less than 1 Pa · s, there is dripping at the time of threading or winding, unwinding at the time of winding, etc., which is not preferable.

The epoxy resin (A) is a liquid bisphenol A type epoxy resin, a liquid bisphenol F type epoxy resin, or a component containing both, but if the viscosity at 25 ° C. satisfies the above range, other liquid or solid epoxy resins May be contained.

Other epoxy resins include bisphenol E-type epoxy resins having two epoxy groups in one molecule, bisphenol S-type epoxy resins, bisphenol Z-type epoxy resins, isophorone bisphenol-type epoxy resins, and other bisphenol-type epoxy resins. Type epoxy resin halogens, alkyl-substituted products, hydrogenated products, high molecular weight compounds having a plurality of repeating units, not limited to monomers, glycidyl ethers of alkylene oxide adducts, phenol novolac type epoxy resins, cresol novolac type epoxy resins Novolak type epoxy resins such as bisphenol A novolak type epoxy resin, 3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexanecarboxylate, 3,4- Alicyclic epoxy resins such as poxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate and 1-epoxyethyl-3,4-epoxycyclohexane, trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, polyoxyalkylene diester Aliphatic epoxy resins such as glycidyl ether, diglycidyl phthalate, diglycidyl tetrahydrophthalate, glycidyl ester such as dimer acid glycidyl ester, tetraglycidyldiaminodiphenylmethane, tetraglycidyldiaminodiphenylsulfone, triglycidylaminophenol Glycidylamines such as triglycidylaminocresol and tetraglycidylxylylenediamine can be used. . These may be used alone or in combination of two or more.

The epoxy resin curing agent (B) is a solid epoxy resin curing agent having a melting point or a thermal decomposition temperature of 200 ° C. or higher. Because it is solid, it hardly dissolves in an epoxy resin at room temperature, but it can be a latent curing agent with excellent storage stability at room temperature, having the property of dissolving when heated to 100 ° C or higher and reacting with an epoxy group. .
As the epoxy resin curing agent, for example, dicyandiamide, dihydrazide compound, guanidine compound, diaminodiphenylsulfone and the like are preferably used. When using dicyandiamide, the blending amount should be 0.3 to 1.2 equivalents per mole of epoxy group of epoxy resin (A) (in the case of dicyandiamide, 1 mole is calculated as 4 equivalents). Is preferred. More preferably, it is 0.4 to 0.6 equivalent. If it is less than 0.3 equivalent, the crosslink density of the cured product is low and the fracture toughness tends to be low, and if it exceeds 1.2 equivalent, unreacted dicyandiamide tends to remain, so that the mechanical properties tend to deteriorate. From another viewpoint, it is preferably 1 to 15 wt%, more preferably 3 to 7 wt%, based on the epoxy resin composition.

The imidazole compound (C) acts as a curing accelerator, and in order to satisfy the heat resistance at the time of curing in addition to the impregnation property to the reinforcing fiber at the time of mixing, for example, 2-methylimidazole, 1,2- Dimethylimidazole, 2-ethyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-phenyl Imidazole compounds such as 6-4 ′, 5′-dihydroxymethylimidazole, 1-cyanoethyl-2-ethyl-4methylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole are preferably used. Furthermore, an imidazole compound containing a triazine ring can also be preferably used. For example, 2,4-diamino-6- [2′-methylimidazolyl- (1 ′)]-ethyl-s-triazine represented by the formula (2) 2,4-diamino-6- [2′-undecylimidazolyl- (1 ′)]-ethyl-s-triazine, 2,4-diamino-6- [2′-ethyl represented by the formula (1) -4'-methylimidazolyl- (1 ')]-ethyl-S-triazine isocyanuric acid adduct and the like. These may be used alone or in combination of two or more, and in particular, an imidazole compound represented by formula (1) or formula (2) is preferably used. It is not limited to the above as long as it is chemically stable and does not dissolve in the epoxy resin at room temperature.
The amount of the imidazole compound (C) used is preferably 0.01 to 7 parts by weight with respect to 100 parts by weight of the epoxy resin composition. More preferably, it is 1 to 5 parts by weight. When the amount exceeds 7 parts by weight, the powder component increases, which causes a problem that voids are likely to increase. When the amount is less than 0.01 parts by weight, there arises a problem that rapid curability cannot be realized.

The total addition amount of the epoxy resin curing agent (B) and the imidazole compound (C) is preferably 10% by weight or less with respect to the epoxy resin composition from the effect of reducing voids. More preferably, it is 1 to 5% by weight based on the epoxy resin composition.

Both the epoxy resin curing agent (B) and the imidazole compound (C) exhibit good impregnation properties when the average particle diameter D50 is 2 μm or less, preferably D90 is 3 μm or less. It becomes possible. However, when the particle size is too fine, specifically, when D90 is 1 μm or less, the storage stability may be significantly impaired. In that case, it can be technically improved by adding a Lewis acid such as tributyl borate. Since the hardener powder fits in the gaps between the carbon fibers during filament winding, the step of the carbon fibers inevitably generated in the filament winding process can be filled with the resin without inhibiting the seepage of the resin component from the tow prepreg. As a result, generation of voids can be suppressed even under low Rc conditions. Ideally, when the particle diameter of the curing agent or the like is set to (2 / √3-1) or less with respect to the diameter of the carbon fiber, the winding of the carbon is not affected. Therefore, D50 is preferably less than or equal to this diameter, and D90 is more preferably less than or equal to this diameter. Ideally, D100 is less than or equal to this diameter, but it is difficult to achieve this accurately, and storage stability deteriorates if the particle size becomes too fine. When D50 is larger than this diameter, sufficient resin seepage cannot be obtained in the filament winding process, and the steps of the carbon fibers cannot be filled with the resin. For this reason, air tends to remain, and voids may remain in the cured product.

Grinding of the curing agent or the like can be performed by, for example, a jet mill. The particle size distribution of the pulverized curing agent and the like can be evaluated using, for example, a Nikkiso Microtrac particle size distribution analyzer MT3300EXII. The dispersant is selected depending on the type of powder. In this specification, the dispersant is dispersed in 2-propanol and measured.

Since the curing agent and the like increase the surface area by reducing the particle size of the powder, there is a concern that the storage stability is lowered. In that case, the storage stability can be improved by a known and commonly used technique. Specific examples of the stabilizer include a method of adding a small amount of a Lewis acid such as tributyl borate, for example, 1.0 part by weight or less based on 100 parts by weight of the epoxy resin composition.

The epoxy resin composition of the present invention can contain a rubber component (D). As the rubber component, a copolymer using acrylonitrile and butadiene as raw materials is preferably used because of its excellent solubility in an epoxy resin. In particular, it is particularly preferable to use an epoxy resin such as a carboxyl group, an amino group or an epoxy group or one having a functional group capable of reacting with a curing agent thereof because the effect of improving the toughness of the cured product is great.
Further, particles containing a rubber component insoluble in epoxy resin can also be preferably used. Although crosslinked rubber particles themselves can be used, rubber particles having a core-shell structure in which the surfaces of epoxy resin-insoluble rubber particles are coated with a non-rubber component are particularly suitable. In this case, the component to be coated may be one that dissolves or swells in the epoxy resin, such as polymethyl methacrylate, but rather is preferable because the dispersion of the particles in the epoxy resin becomes good. When rubber particles having an epoxy resin insoluble core-shell structure are used, there is an advantage that the heat resistance of the cured resin is superior to that of a normal rubber component.

The addition of the rubber component has an effect of improving toughness and an effect of improving the tackiness of the prepreg, and the average particle diameter is preferably 1 to 500 nm, more preferably 3 to 300 nm in terms of volume average particle diameter.
The blending amount of the rubber component (D) such as core-shell rubber is preferably 0.5 to 15 parts by weight, more preferably 1 to 10 parts by weight, in 100 parts by weight of the epoxy resin composition. If the blending amount is 0.5 parts by weight or more, the fracture toughness required for the fiber-reinforced composite material after molding can be easily obtained, and if the blending amount is 15 parts by weight or less, the resulting fiber-reinforced composite Since the increase in the viscosity of the epoxy resin composition for materials is suppressed and the reinforcing fibers can be impregnated without difficulty, it is more suitable for fiber-reinforced composite materials.

In the epoxy resin composition of the present invention, an antifoaming agent and a leveling agent can be added as an additive for the purpose of improving the surface smoothness. These additives can be blended in an amount of 0.01 to 3 parts by weight, preferably 0.01 to 1 part by weight, based on 100 parts by weight of the entire resin composition. If the blending amount is less than 0.01 parts by weight, the effect of smoothing the surface does not appear, and if it exceeds 3 parts by weight, the additive causes bleeding on the surface, which is a factor that impairs smoothness. If necessary, pigments and other additives can be blended. However, in the epoxy resin composition of the present invention, the blending amount of the component (A) is 50 wt% or more, preferably 80 wt% or more so as to keep the liquid state as a whole. Note that the solvent is not treated as an additive.

The epoxy resin composition of the present invention can be blended with other curable resins. 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 epoxy resin composition of the present invention is produced by uniformly mixing the above components (A) to (C). The raw materials can be mixed by a known and conventional method. For example, a rotation and revolution type centrifugal stirring device may be used, or dispersion with a disper or the like may be performed, or roll dispersion may be performed. Other methods may be used, or these may be combined. However, when temperature rises, since a hardening | curing agent etc. melt | dissolve in an epoxy resin, storage stability deteriorates. Preferably, it is rapidly mixed under a condition of 40 ° C. or lower, desirably 30 ° C. or lower.

In the epoxy resin composition of the present invention, the component (A) is present in liquid form, and at least part of the component (B) and component (C) is present in powder form. Although a part of (B) component and (C) component may melt | dissolve in a liquid, it is controlled to such an extent that hardening of an epoxy resin does not fully advance. Therefore, it is useful as an epoxy resin composition used in the production of a prepreg or as an epoxy resin composition present in a prepreg.

The epoxy resin composition of the present invention is capable of producing a tow prepreg by a filament winding method or the like in which the viscosity is lowered by heating and impregnated while dipping a reinforcing fiber bundle, and there is substantially no organic solvent remaining in the tow prepreg. Therefore, a high-quality tow prepreg can be manufactured with high productivity. Examples of the reinforcing fiber bundle used here include carbon fibers, preferably carbon fibers having an average diameter of 7.5 μm or less, more preferably 6.5 μm or less, and particularly preferably 6.5 μm or less. When the average diameter is larger, the significant difference in the effect of the present invention becomes smaller.

The epoxy resin composition of the present invention is suitably used for a toe 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 lower the viscosity, impregnated while immersing the reinforcing fiber bundle, and then an oven or the like. Use a wet method to evaporate the organic solvent to make a tow prepreg, or heat and reduce the viscosity of the epoxy resin composition without using an organic solvent into a film on a roll or release paper, then one side of the reinforcing fiber bundle Alternatively, after being transferred to both sides, a hot melt method for impregnation by pressurizing by passing a bending roll or a pressure roll, a filament winding method for impregnating while impregnating a bundle of reinforcing fibers by reducing the viscosity of the epoxy resin composition by heating If an organic solvent is not used or a low boiling point solvent is used, the Organic solvent remains in the prepreg is substantially nil, since it can be produced high-quality tow prepreg has high productivity, can be preferably used a filament winding method. By using such a production method, a resin-impregnated tow prepreg can be obtained.

The epoxy resin composition of the present invention is useful as a fiber reinforced composite material, and the reinforcing fiber used here is selected from glass fiber, aramid fiber, carbon fiber, boron fiber, etc., but fiber reinforced with excellent strength In order to obtain a composite material, it is preferable to use carbon fibers.

For example, T700SC-12000-50C (diameter 7 μm, density 1.8 g / cm ³ , fineness 802 TEX), Toray T720SC-36000-50C (diameter 6 μm, density 1.8 g / cm ³ , fineness 1650 TEX) However, the present invention is not limited to these.

The tow prepreg of the present invention can be obtained by impregnating carbon fiber with the above epoxy resin composition. In this method, the carbon fiber may be immersed in a resin bath, or the resin applied to the drum may be transferred to the carbon fiber. In addition, it can obtain by a well-known and usual method.

In the molded body composed of the epoxy resin composition of the present invention and reinforcing fibers, the content of reinforcing fibers varies depending on the target material, but in order to achieve weight reduction in a vehicle-mounted high-pressure gas container, Rc is It is 18 to 28% by weight, preferably 20 to 26% by weight, more preferably 21 to 24% by weight. If Rc is lower than 18% by weight, voids are likely to increase. If it is higher than 28% by weight, the product weight increases.

The epoxy resin composition of the present invention is a cured product in which a crosslinking reaction proceeds 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. Can be obtained. The heating condition may be one stage or may be a multistage condition in which a plurality of heating conditions are combined. In particular, assuming a high-pressure vessel filled with hydrogen gas or the like used in fuel cells, heating is performed 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.

Hereinafter, the present invention will be described more specifically with reference to examples.

First, the first aspect of the present invention will be specifically described with reference to examples.
In the first invention, the following resin raw materials were used to obtain the resin compositions of the respective examples.

(A) Epoxy resin / liquid bisphenol F type epoxy resin: YDF-170 (manufactured by Nippon Steel & Sumikin Chemical) (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) (epoxy equivalent 184 to 194 g / eq, viscosity 11 to 15 Pa · s)
(B) Dicyandiamide / Dicyandiamide: DICYANEX 1400F (manufactured by AIRPRODUCT)
(C) Imidazole-based curing aid 2MZA-PW (manufactured by Shikoku Chemicals) 2,4-diamino-6- [2′-ethyl-4′-methylimidazolyl- (1 ′)]-ethyl-s-triazine 2MAOK-PW (manufactured by Shikoku Chemicals) 2,4-diamino-6- [2'-ethyl-4'-methylimidazolyl- (1 ')]-ethyl-s-triazine isocyanuric acid adduct 2P4MHZ-PW (Shikoku 2-Phenyl-4-methyl-5-hydroxymethylimidazole / PN-23J (Ajinomoto Fine-Techno)
・ PN-50J (Ajinomoto Fine Techno)
(D) Core shell rubber / MX-154 (manufactured by Kaneka): Epoxy masterbatch (core shell rubber compounding amount 40 wt%, BPA type epoxy resin compounding amount 60 wt%, average particle size 100 nm)

The measuring method is shown below.
(1) Epoxy equivalent: Measured according to JIS K 7236 standard. Specifically, using a potentiometric titrator, 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.
(2) Viscosity: Conforms to JIS K7117-1. Specifically, the viscosity at 25 ° C. of the pre-curing resin composition was measured with an E-type viscometer.
(3) Thickening rate: After standing in a hot air circulation oven at 40 ° C. for 3 days, the viscosity was measured according to JIS K7177-1.
(4) Reaction peak temperature: When the calorific value per time when the measurement was performed at a temperature rising condition of 10 ° C./min with a differential scanning calorimeter (EXSTAR6000 DSC6200, manufactured by SII Nanotechnology) It was expressed as a temperature.
(5) Reaction start temperature: Expressed by extrapolation of calorific value per hour when measurement was carried out under a temperature rising condition of 10 ° C./min with a differential scanning calorimeter (EXSTAR 6000 DSC6200 manufactured by SII Nanotechnology). .
(6) Tg: Expressed as a DSC extrapolated temperature when measured under a temperature rising condition of 10 ° C./min with a differential scanning calorimeter (EXSTAR 6000 DSC6200 manufactured by SII Nanotechnology).
(7) 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.
(8) Tensile modulus, tensile strength, tensile elongation: conforming to JIS K7161. Specifically, a universal material testing machine (Shimadzu Science Autograph AGS-H) was used. At room temperature, a dumbbell test piece having a length of 215 mm including the grip part, a width of 10 mm, and a thickness of 4 mm was measured with a chuck distance of 114 mm and a speed of 50 mm / min. Tensile tests were conducted and tensile strength, tensile modulus, and tensile elongation were determined from the obtained stress-strain diagram.

Reference Example An epoxy resin composition used for measurement of the exothermic onset temperature and reaction peak temperature of an imidazole-based curing aid was prepared as follows.
YD-128 (A) / dicyandiamide (B) / imidazole-based curing aid (C) was added and kneaded according to the formulation (wt%) shown in Table 1A to obtain an epoxy resin composition. Table 1A shows the measurement results of the exothermic start temperature and the exothermic peak temperature extrapolated from the calorific value per hour when the differential scanning calorimeter was used under the temperature rising condition of 10 ° C./min.

  

  

Examples 1A-4A, Comparative Examples 1A-8A
(1) Preparation of epoxy resin composition (A) Epoxy resin, (B) Dicyandiamide, (C) Imidazole-based curing aid and (D) Core shell rubber are added, and THINKY PLANETARY VACUUM MIXER (manufactured by Sinky) is used at 2000 rpm, 4 An epoxy resin composition having a composition (wt%) shown in Tables 1A and 2A was prepared by kneading for 6 minutes under a condition of 0.0 mmhg. (B) Dicyandiamide was pre-kneaded with a part of the epoxy resin, and (D) core-batch rubber was also used as a masterbatch dispersed in the epoxy resin during the production process of the core-shell polymer.

(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 heated to 150 ° C. at 3 / min in an oven at a temperature of 50 ° C. Thereafter, curing was performed for 45 minutes to prepare a plate of cured epoxy resin having a thickness of 4 mm. Next, the obtained cured epoxy resin plate was cut out and used for test analysis. The results are shown in Tables 2A and 3A.

 

 

 

 

Next, the second aspect of the present invention will be specifically described with reference to examples.
In the second aspect of the present invention, materials used in the examples and comparative examples are shown below. In order to obtain a resin composition, the following resin raw materials were used.

(A) Component / Liquid bisphenol F type epoxy resin: YDF-170 (manufactured by Nippon Steel & Sumikin Chemical) (epoxy equivalent 160 to 180 g / eq, viscosity 2 to 5 Pa · s)
Liquid bisphenol A type epoxy resin: YD-128 (manufactured by Nippon Steel & Sumikin Chemical) (epoxy equivalent 184 to 194 g / eq, viscosity 11 to 15 Pa · s)
-Core shell rubber-containing liquid BPA type epoxy resin: Kane Ace MX-154 (manufactured by Kaneka) (rubber content 40% by weight, epoxy equivalent 301 g / eq, viscosity 30 Pa · s-50 ° C.)
Component (B): Dicyandiamide: DICYANEX 1400F (decomposition temperature of 250 ° C. or higher; manufactured by AIRPRODUCT)
Diethylmethylbenzenediamine: Ecure 100 (liquid at room temperature; manufactured by Albemarle)
Component (C) 2,4-diamino-6- [2′-ethyl-4′-methylimidazolyl- (1 ′)]-ethyl-s-triazine isocyanuric acid adduct: 2MAOK-PW (decomposition temperature 250 ° C. or higher) ; Shikoku Chemical Industries)

Carbon fiber T7μm: Toray T700SC-12000-50C (diameter 7μm)
T6μm: Toray SC-36000-50C (diameter 6μm)

The measuring method is shown below.
Average particle size measurement:
Using 2-propanol as a dispersant, evaluation was performed using a Nikkiso Microtrac particle size distribution analyzer MT3300EXII.

viscosity:
According to JIS K7117-1, an E-type viscometer RE-85 manufactured by Toki Sangyo was used.

Storage stability:
Changes in viscosity were followed and evaluated. The condition is that 50 g of the resin composition is prepared, put in a 50 mL vial, the initial viscosity at 25 ° C., and the viscosity after storage for a predetermined time (24 h, 48 h, 96 h or 168 h) are measured, and the viscosity is increased. The rate was evaluated. The viscosity increase rate Z is a value calculated by the following equation from the viscosity V _Z after storage for a predetermined time at 25 ° C. and the initial viscosity Vi. The viscosity increase rate was determined for each of the storage times 24h, 48h, 96h or 168h.
Viscosity increase rate (%) = (V _Z / Vi−1) × 100
In addition, the storage stability as a whole was evaluated as ◎: excellent, ○: good, ×: not possible.

Curability (curing residual heat):
This was performed by differential scanning calorimetry (DSC). After encapsulating the resin composition in a sample pan, the temperature was raised to 300 ° C. at a rate of temperature increase of 10 ° C./min, and the reference curing heat value A was measured. Similarly, after enclosing the resin composition in a sample pan, the temperature is raised to a predetermined temperature (140 ° C., 150 ° C. or 160 ° C.) at a rate of 10 ° C./min, held for 30 minutes, and then rapidly cooled to room temperature. Thus, a cured product was obtained. These hardened | cured materials were heated up to 300 degreeC with the temperature increase rate of 10 degreeC / min, and the emitted-heat amount B was measured. The curing calorific value B of each obtained cured product was divided by the curing calorific value A of the resin composition serving as a reference, and the residual curing calorific value was determined by the following formula. It shows that sclerosis | hardenability is so favorable that residual hardening heat_generation | fever (%) is low.
Curing heat generation remaining amount (%) = B / A × 100
In addition, sclerosis | hardenability as a whole was evaluated by (double-circle): excellent, (circle): good, x: impossibility.

Resin content It calculated | required by the following calculations.
Resin content Rc = (carbon fiber g with resin-carbon fiber g) / carbon fiber with resin g

Void rate:
It calculated | required with the following formula | equation.
Void ratio = 1- (actual density) / (theoretical density)
Here, the measured density was evaluated by the Archimedes method.
The theoretical density was calculated by the following calculation.
Theoretical density = density of cured epoxy resin × Rc + density of carbon fiber × (1−Rc)

Example 1B
In a kneading vessel, MX-154 25 parts by weight, YDF-170 66.9 parts by weight, dicyandiamide (a finely pulverized product of DICYANEX 1400F, particle size D50 = 1.2 μm, D90 = 2.1 μm) 5.1 parts by weight, 2 MAOK (2 MAOK -PW finely pulverized product, particle size D50 = 1.2 μm, D90 = 2.3 μm) 3 parts by weight are mixed and dispersed to obtain an epoxy resin composition (C1), and evaluation of storage stability and residual heat generated by curing Went. The results are shown in Table 1B.

Example 2B
An epoxy resin composition (C2) was obtained and evaluated in the same manner as in Example 1B except that 0.3 parts by weight of tributyl borate was added as a stabilizer. The results are shown together in Table 1B.

Comparative Examples 1B-4B
With the composition shown in Table 1B, epoxy resin compositions (R1, R2, R3, R4) were obtained in the same manner as in Example 1B, and the physical properties were evaluated. The results are shown together in Table 1B.
In the table, the particle sizes of the curing agent and the imidazole compound are as follows.
Dicyandiamide (D50 = 2.5) has D50 = 2.5 μm, D90 = 4.7 μm, and dicyandiamide (D50 = 1.2) has D50 = 1.2 μm, D90 = 2.1 μm, 2MAOK (D50 = 3. 5) D50 = 3.5 μm, D90 = 5.5 μm, 2MAOK (D50 = 1.2) D50 = 1.2 μm, D90 = 2.3 μm.

 
注）＊１：測定不可、＊２：ゲル化

Note) * 1: Measurement not possible * 2: Gelation

Examples 3B-8B
The epoxy resin composition (C1) obtained in Example 1B was impregnated into a carbon fiber having a diameter of 6 μm or 7 μm to obtain a carbon fiber with a resin having a resin content Rc of 0.20 to 0.28. Further, the obtained carbon fiber with resin was wound around a pipe-shaped mandrel having a diameter of 140 mm while applying a back tension of 10 kN to obtain a laminate having a thickness of 6 mm by traverse and repeated lamination. It hardened | cured on the conditions of 120 degreeC x 2 hours +160 degreeC x 1 hour, the fiber reinforced plastic was obtained, and the void ratio was measured. The results are shown in Table 2B.

 

 

Comparative Examples 5B-16B
Except that the epoxy resin composition used was changed to the resin compositions (R1 to R4) of Comparative Examples 1B to 4B, carbon fibers with a resin and fiber reinforced plastic were obtained in the same manner as in Example 3B, and the void ratio was It was measured. The results are shown in Table 3B.

 

 

In the example of the second invention, the void ratio was reduced as compared with the comparative example. Moreover, although the void ratio tends to increase when the diameter of the carbon fiber is reduced, the example obtained a result in which the increase in the void ratio was suppressed as compared with the comparative example.

The result that the epoxy resin composition of Example 1B was a void rate close | similar to the epoxy resin composition of Comparative Example 4B was obtained. In the epoxy resin composition of Example 1B, the increase in viscosity was clearly suppressed as compared with Comparative Example 4B, and the storage stability was improved. Furthermore, the time required for the curing reaction was clearly shortened.

The epoxy resin composition of Example 1B is slightly lower in storage stability than the epoxy resin compositions of Comparative Examples 1B to 3B, but Example 2B in which only a small amount of tributyl borate was added to the system was used. The result that can be improved.

According to the present invention, an epoxy resin composition for a fiber-reinforced composite material is obtained that is excellent in impregnation during prepreg production and has both high storage stability and high fracture toughness and elongation. Also, to provide an epoxy resin composition for a fiber reinforced composite material which can suppress defects such as voids in a cured product while achieving both high storage stability and high curing reactivity and realizing a low resin content. Can do.
Therefore, it can be suitably used for various fiber-reinforced composite materials.

Claims (19)

An epoxy resin composition comprising an epoxy resin (A), dicyandiamide (B), an imidazole-based curing aid (C), and a core-shell rubber (D) as essential components, wherein the imidazole-based curing aid (C) is an epoxy An epoxy resin composition for fiber-reinforced composite materials, wherein the heat generation starting temperature is 135 ° C or higher when the resin composition is measured by DSC at a temperature rising rate of 10 ° C / min. 0.2 to 0.8 equivalent of dicyandiamide (B) is contained with respect to the epoxy equivalent of epoxy resin (A), and 50 to 250 parts by mass of imidazole curing aid (C) with respect to 100 parts by mass of dicyandiamide (B). The epoxy resin composition for fiber-reinforced composite materials according to claim 1, which is contained in a part. The fiber according to claim 1 or 2, wherein the epoxy resin (A) has two epoxy groups in one molecule, and the viscosity at 25 ° C measured using an E-type viscometer is 1 to 50 Pa · s. Epoxy resin composition for reinforced composite materials. The imidazole curing aid (C) is 2,4-diamino-6- [2′-ethyl-4′-methylimidazolyl- (1 ′)]-ethyl-s-triazine isocyanuric acid adduct or 2-phenyl-4 The epoxy resin composition for fiber-reinforced composite materials according to claim 1, which is -methyl-5-hydroxymethylimidazole. 2. The epoxy resin composition for fiber-reinforced composite material according to claim 1, wherein the core-shell rubber (D) has a volume average particle diameter of 1 to 500 nm. 2. The epoxy resin composition for fiber-reinforced composite materials according to claim 1, wherein the viscosity at 25 ° C. measured using an E-type viscometer is 1 to 50 Pa · s. A fiber-reinforced composite material comprising a reinforcing fiber mixed with the epoxy resin composition for fiber-reinforced composite material according to claim 1. The fiber-reinforced composite material according to claim 7, wherein the volume content of the reinforcing fiber is 30 to 75%. A molded product obtained by molding and curing the fiber-reinforced composite material according to claim 7 by a filament winding method. An epoxy resin composition comprising an epoxy resin (A), an epoxy resin curing agent (B), and an imidazole compound (C) as essential components,
The epoxy resin (A) contains a liquid bisphenol A type epoxy resin and / or a liquid bisphenol F type epoxy resin, and has a viscosity (25 ° C.) of 1 Pa · s to 100 Pa · s,
An epoxy resin composition characterized in that the epoxy resin curing agent (B) and the imidazole compound (C) are both solids having a melting point or a decomposition temperature of 200 ° C. or higher and an average particle diameter (D50) of 2 μm or less. The epoxy resin composition according to claim 10, wherein the epoxy resin curing agent (B) is dicyandiamide. The epoxy resin composition according to claim 10, wherein the imidazole compound (C) is a compound represented by the formula (1) or the formula (2).

The epoxy resin composition according to claim 10, further comprising a rubber component (D). The epoxy resin composition according to claim 10, wherein the total amount of the epoxy resin curing agent (B) and the imidazole compound (C) is 10% by weight or less based on the epoxy resin composition. The epoxy resin composition according to claim 10, wherein the rubber component (D) is a rubber particle having a core-shell structure. The epoxy resin composition according to claim 10 containing a stabilizer. A tow prepreg obtained by impregnating the carbon fiber (E) with the epoxy resin composition according to claim 10. The tow prepreg according to claim 17, wherein the carbon fiber (E) has an average diameter of 7.5 μm or less. A carbon fiber reinforced plastic obtained by molding and curing the tow prepreg according to claim 17.

Images