JP2015108052A - Epoxy resin composition, prepreg and fiber reinforced composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an epoxy resin composition providing a resin cured article excellent in handleability in the case of making a prepreg and achieving both of low thermal expansion rate and elastic modulus, a prepreg using the epoxy resin composition and a fiber reinforced composite material.SOLUTION: There is provided an epoxy resin composition containing [A] a tetra functional bisnaphthalene type epoxy resin, [B] a bisphenol type epoxy resin having an epoxy equivalent of 2000 or more, [C] an epoxy resin which is liquid at 25°C and [D] a curing agent and satisfying following conditions of (1) and (2). (1) [A] is 25 to 60 pts.mass, [B] is 10 to 35 pts.mass and [C] is 30 to 50 pts.mass based on 100 pts.mass of the total epoxy resin component. (2) [A]≥[B] in terms of pts.mass based on the total epoxy resin component.

Description

  The present invention relates to an epoxy resin composition preferably used as a matrix resin of a fiber reinforced composite material suitable for sports applications and general industrial applications, and a prepreg and a fiber reinforced composite material using the epoxy resin composition as a matrix resin.

  Epoxy resins are used in various applications such as electrical / electronic materials, fiber reinforced composite materials, paints, adhesives, etc. due to their excellent adhesiveness, heat resistance, chemical resistance, and the like.

  In particular, fiber reinforced composite materials composed of reinforced fibers and cured epoxy resins are widely used in aircraft, automobiles, and industrial applications because of their excellent mechanical properties.

  Epoxy resins are generally cured using curing agents and curing accelerators such as aliphatic amines, aromatic amines, acid anhydrides, phenols, etc. The coefficient of thermal expansion is as high as about 60-80 ppm / ° C. A resin having a large coefficient of thermal expansion generally has a large volume shrinkage upon curing, which causes voids and cracks in the cured epoxy resin and causes a decrease in strength of the cured epoxy resin. Also, when epoxy resin is used as a matrix resin for adhesives or fiber reinforced composite materials, only the epoxy resin cures and shrinks, resulting in residual stress in the vicinity of the interface between the cured epoxy resin and the adherend or reinforcing fiber. , The adhesiveness is lowered, or the epoxy resin becomes brittle.

  As a method of reducing the coefficient of thermal expansion, that is, a method of reducing volume shrinkage, a method of adding an inorganic filler to an epoxy resin can be mentioned. However, the addition of an inorganic filler to an epoxy resin often leads to an increase in the viscosity of the epoxy resin, that is, a decrease in fluidity. Such an increase in viscosity may worsen the handleability. For example, when an epoxy resin to which an inorganic filler is added is used as a matrix resin for a fiber reinforced composite material, the impregnation property of the epoxy resin between the reinforced fibers is reduced, and voids are generated in the fiber reinforced composite material. The strength of the reinforced composite material tends to decrease.

  Furthermore, it is known that the thermal expansion coefficient of the resin can be reduced by using a naphthalene type epoxy having a low coefficient of thermal expansion. However, since the viscosity of the naphthalene type epoxy at room temperature is extremely high, it is generally between the reinforcing fibers. In many cases, the impregnation property of the epoxy resin is lowered. In addition, when the resin composition is solid at room temperature and used as a prepreg, there is a drawback that handling properties such as roll-up property and formability are deteriorated.

  Examples of a method for reducing volume shrinkage without increasing the viscosity of the epoxy resin include a method using a monomer that suppresses volume shrinkage as a curing agent for the epoxy resin. Patent Documents 1 to 3 disclose a method of blending a cyclic ester. However, lactones that are not condensed to an aromatic or heteroaromatic skeleton used in these methods have not been sufficiently reduced in volume shrinkage or have low elasticity of cured epoxy resins.

  Patent Documents 4 and 5 show a method of reducing the residual stress of an epoxy resin by blending a polymer in the epoxy resin. In this method, although the residual strain of the epoxy resin around the polymer is reduced, the residual strain in the epoxy resin often becomes non-uniform, and generally, when a polymer is blended, the elastic modulus of the epoxy resin is lowered. There was a problem that there was something to do.

JP 2003-012764 A JP 2003-238659 A JP 2005-255767 A JP 2006-249395 A JP-A-8-027360

  The object of the present invention is to improve the drawbacks of the prior art, and have excellent handling properties when used as a prepreg, and an epoxy resin composition in which the fiber-reinforced composite material obtained by molding the prepreg has high mechanical properties, and Another object is to provide a prepreg and a fiber reinforced composite material using the epoxy resin composition.

  As a result of intensive studies to solve the above problems, the present inventors have found an epoxy resin composition having the following constitution, and have completed the present invention. That is, this invention consists of the following structures.

An epoxy resin composition comprising the following [A], [B], [C], and [D] in a content ratio that satisfies the following conditions (1) to (2).
[A] Tetrafunctional bisnaphthalene type epoxy resin [B] Bisphenol type epoxy resin having an epoxy equivalent of 2000 or more [C] Epoxy resin liquid at 25 ° C. [D] Curing agent (1) 100 parts by mass of all epoxy resin components [A] 25-60 parts by mass, [B] 10-35 parts by mass and [C] 30-50 parts by mass.
(2) With respect to parts by mass relative to all epoxy resin components, [A] ≧ [B].

  ADVANTAGE OF THE INVENTION According to this invention, while being excellent in the handleability when it is set as a prepreg, the fiber reinforced composite material obtained by shape | molding a prepreg has a high mechanical characteristic, and the prepreg using this epoxy resin composition And fiber reinforced composite materials can be provided.

  As a result of intensive studies to achieve the above object, the inventors have determined that the epoxy resin composition contains an epoxy resin [A], an epoxy resin [B], an epoxy resin [C], and a curing agent [D]. By blending at a specific blending ratio, it is excellent in moldability when used as a prepreg, and further a cured resin obtained by curing the epoxy resin composition is an epoxy resin [A] rich phase and an epoxy resin [B]. It has been found that a low thermal expansion coefficient and a high elastic modulus can be achieved by forming a fine phase separation structure including a rich phase.

  Here, even when the epoxy resins [A] to [C] are in a state of being uniformly compatible with each other before curing, the spinodal decomposition occurs in the curing process, and the epoxy resin [A] rich phase and the epoxy resin [ B] It is preferable to form a phase separation structure with the rich phase. Further, the phase separation structure period is more preferably 1 nm to 5 μm, and a more preferable phase separation structure period is 1 nm to 1 μm. In the curing process of the epoxy resin composition, the epoxy resin [C] functions as a compatibilizing agent for the epoxy resins [A] and [B].

  The cured product of the epoxy resin composition of the present invention includes an epoxy resin [A] rich phase and an epoxy resin [B] rich phase, and has a phase separation structure period of 1 nm to 5 μm. Is achieved. When the structural period is less than 1 nm or when the structural period exceeds 5 μm, the coefficient of thermal expansion is the same as the blending ratio of the epoxy resin [A] and the epoxy resin [B], and the coefficient of thermal expansion of the cured resin is Relatively high.

  In the present invention, the phase separation structure means a structure in which two or more phases including an epoxy resin [A] rich phase and an epoxy resin [B] rich phase are separated. Here, the epoxy resin [A] rich phase and the epoxy resin [B] rich phase refer to phases mainly composed of the epoxy resin [A] and the epoxy resin [B], respectively. Moreover, a main component means the component contained by the highest content rate in the said phase here. The phase separation structure may be a phase separation structure of three or more phases further including a phase mainly composed of components other than the epoxy resin [A] and the epoxy resin [B]. On the other hand, the state of being uniformly mixed at the molecular level is called a compatible state.

  The phase separation structure of the cured resin product can be observed with a scanning electron microscope or a transmission electron microscope. You may dye | stain with osmium etc. as needed. Dyeing can be performed by a usual method.

  In the present invention, the structural period of phase separation is defined as follows. The phase separation structure includes a two-phase continuous structure and a sea-island structure. When the phase separation structure is a biphasic continuous structure, draw three straight lines of a predetermined length on the micrograph, extract the intersection of the straight line and the phase interface, measure the distance between the adjacent intersections, These number average values are used as the structure period. The predetermined length is set as follows based on a micrograph. When the structural period is expected to be on the order of 0.01 μm (0.01 μm or more and less than 0.1 μm), a sample photograph was taken at a magnification of 20,000 times, and a length of 20 mm drawn on the photograph (1 μm on the sample) Is a predetermined length of a straight line. Similarly, when the phase separation structure period is expected to be on the order of 0.1 μm (0.1 μm or more and less than 1 μm), a photograph is taken at a magnification of 2,000 times and a length of 20 mm on the photograph (10 μm on the sample) (Length) is a predetermined length of a straight line. When the phase separation structure period is expected to be on the order of 1 μm (1 μm or more and less than 10 μm), a photograph is taken at a magnification of 200 times, and a length of 20 mm on the photograph (a length of 100 μm on the sample) is defined as a predetermined straight line length. To do. If the measured phase separation structure period is out of the expected order, the measurement is performed again at a magnification corresponding to the corresponding order.

  When the phase separation structure is a sea-island structure, three predetermined regions on the micrograph are selected at random, the island phase size in the region is measured, and the number average value of these is the structure period. The size of the island phase refers to the length of the shortest distance line drawn from the phase interface to one phase interface through the island phase. Even when the island phase is an ellipse, an indeterminate shape, or a circle or ellipse of two or more layers, the shortest distance passing through the island phase from the phase interface to one phase interface is defined as the island phase size. The predetermined area is set as follows based on a micrograph. When the phase separation structure period is expected to be on the order of 0.01 μm (0.01 μm or more and less than 0.1 μm), a photograph of the sample was taken at a magnification of 20,000 times, and an area of 4 mm square on the photograph (0 on the sample) .2 μm square area) is defined as a predetermined area. Similarly, when the phase separation structure period is expected to be on the order of 0.1 μm (0.1 μm or more and less than 1 μm), a photograph is taken at a magnification of 2,000 times, and a 4 mm square area on the photograph (2 μm square on the sample) Is defined as a predetermined area. When the phase separation structure period is expected to be on the order of 1 μm (1 μm or more and less than 10 μm), a photograph is taken at a magnification of 200 times, and an area of 4 mm square on the photograph (an area of 20 μm square on the sample) is defined as a predetermined area. If the measured phase separation structure period is out of the expected order, the measurement is performed again at a magnification corresponding to the corresponding order.

  Next, specific embodiments of the present invention will be described. The epoxy resin composition of the present invention is an epoxy resin composition containing an epoxy resin [A], an epoxy resin [B], an epoxy resin [C] and a curing agent [D], wherein [A] is a naphthalene type epoxy resin , [B] is a bisphenol type epoxy resin having an epoxy equivalent of 2000 or more, and [C] is a liquid epoxy at 25 ° C., and the epoxy resins [A] to [C] are based on 100 parts by mass of all epoxy resin components. [A] 25 to 60 parts by mass, [B] 10 to 35 parts by mass and [C] 30 to 50 parts by mass, and [A] ≧ [B] with respect to parts by mass relative to all epoxy resin components It is an epoxy resin composition.

  As epoxy resin [A], it is necessary to contain a tetrafunctional bisnaphthalene type epoxy resin 25-60 mass parts among 100 mass parts of all the epoxy resins. When the epoxy resin [A] is a bisnaphthalene type epoxy resin having a functional group number of less than 4 functional groups, the phase separation period becomes larger than 5 μm, and the thermal expansion coefficient of the cured resin becomes high. Alternatively, when it is not a bisnaphthalene type epoxy resin but a bifunctional naphthalene type epoxy resin, phase separation does not occur and the thermal expansion coefficient of the cured resin becomes high. Moreover, when content of epoxy resin [A] is less than 25 mass parts, a phase-separation period will become larger than 5 micrometers and the thermal expansion coefficient of a resin cured material will become high. When the content of the epoxy resin [A] exceeds 60 parts by mass, the viscosity of the epoxy resin composition at 25 ° C. becomes too high, and when the prepreg is produced using the epoxy resin composition, the flexibility of the prepreg is increased. It will be damaged, and handling properties, such as winding property to a roll and moldability, will deteriorate. In order to have sufficient handleability when used as a prepreg, it is necessary that the resin composition has fluidity at 25 ° C.

  As a commercial item of such an epoxy resin [A], “EPICLON (registered trademark)” HP-4700 (manufactured by DIC Corporation) can be mentioned.

  The epoxy resin composition of the present invention needs to contain 10 to 35 parts by mass of 100 parts by mass of the total epoxy resin of bisphenol type epoxy resin having an epoxy equivalent of 2000 or more as the epoxy resin [B]. When the epoxy equivalent of the epoxy resin [B] is less than 2000, the phase separation period is larger than 5 μm, and the thermal expansion coefficient of the cured resin product is increased. Moreover, when content of epoxy resin [B] is less than 10 mass parts, phase separation does not generate | occur | produce, the viscosity of an epoxy resin composition becomes high, and a void arises in resin hardened | cured material. When the content of the epoxy resin [B] exceeds 35 parts by mass, phase separation does not occur and the thermal expansion coefficient of the cured resin product is increased.

  The epoxy resin [B] is selected from bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol AD type epoxy resins, bisphenol S type epoxy resins, and halogen-substituted products, alkyl-substituted products, hydrogenated products, and the like. An epoxy resin can be preferably used. Examples of such commercially available epoxy resin [B] include “jER (registered trademark)” 1007, 1009P, 1010P, 4002P, 4004P, 4007P, 4110P, 40010P (above, manufactured by Mitsubishi Chemical Corporation). Among them, a resin having a number average molecular weight of about 3000 to 5000 is preferably used because of a good balance of heat resistance, elastic modulus, and toughness. In addition, the number average molecular weight as used in the field of this invention is the value calculated | required in polystyrene conversion by melt | dissolving the epoxy resin to measure in tetrahydrofuran (THF), measuring with a gel permeation chromatograph (GPC).

  The mixing ratio of [A] and [B] needs to be [A] ≧ [B]. When [A] ≧ [B] is not satisfied, phase separation does not occur, and the thermal expansion coefficient of the resin cured product becomes high.

  In this embodiment, it is necessary to use an epoxy resin that is liquid at 25 ° C. as 30 to 50 parts by mass of 100 parts by mass of the total epoxy resin as the epoxy resin [C]. When the compounding quantity of epoxy resin [C] is less than 30 mass parts, and epoxy resin [C] is not liquid at 25 degreeC, the viscosity of an epoxy resin composition may become high. In this case, in the prepreg manufacturing process, the epoxy resin composition is less likely to be impregnated between the reinforcing fibers, and it may be difficult to improve the fiber content of the prepreg. Moreover, when the viscosity of the epoxy resin composition at 25 ° C. is high, the handleability in the case of using a prepreg as described above may deteriorate.

  The curing agent [D] is not particularly limited as long as it cures an epoxy resin, and amines such as aromatic amines and alicyclic amines, acid anhydrides, polyaminoamides, organic acid hydrazides, isocyanates And the like.

  An amine curing agent is preferable because it is excellent in mechanical properties and heat resistance of the obtained resin cured product. As the amine curing agent, diaminodiphenyl sulfone and diaminodiphenylmethane which are aromatic amines, dicyandiamide or a derivative thereof which is an aliphatic amine, hydrazide compounds, and the like are used. Examples of such commercially available dicyandiamide include DICY-7 and DICY-15 (manufactured by Mitsubishi Chemical Corporation). The dicyandiamide derivative is obtained by bonding various compounds to dicyandiamide, and includes a reaction product with an epoxy resin, a reaction product with a vinyl compound or an acrylic compound.

  Furthermore, it is preferable to blend dicyandiamide or a derivative thereof as a curing agent [D] as a powder into the epoxy resin composition from the viewpoints of storage stability at room temperature and viscosity stability during prepreg formation. When dicyandiamide or a derivative thereof is blended into a resin as a powder, 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 pressing in the prepreg manufacturing process, if the average particle diameter is 10 μm or less, the resin impregnation property inside the fiber bundle is good.

  Moreover, it is preferable that the total amount of hardening | curing agent [D] contains the quantity from which an active hydrogen group becomes the range of 0.6-1.0 equivalent with respect to the epoxy group of all the epoxy resin components contained in an epoxy resin composition. . When the amount of the active hydrogen group falls within this range, a cured resin product having an excellent balance of heat resistance, elastic modulus, and plastic deformation ability can be obtained.

  Each curing agent may be used in combination with a curing accelerator [E] or other epoxy resin curing agent. Examples of the curing accelerator to be combined include ureas, imidazoles, and Lewis acid catalysts.

  Examples of the urea compound include N, N-dimethyl-N ′-(3,4-dichlorophenyl) urea, toluene bis (dimethylurea), 4,4′-methylenebis (phenyldimethylurea), and 3-phenyl-1 , 1-dimethylurea and the like can be used. Examples of commercially available urea compounds include DCMU99 (manufactured by Hodogaya Chemical Co., Ltd.), “Omicure (registered trademark)” 24, 52, and 94 (manufactured by CVC Specialty Chemicals, Inc.).

  Examples of commercially available imidazoles include 2MZ, 2PZ, and 2E4MZ (manufactured by Shikoku Kasei Co., Ltd.). Lewis acid catalysts include boron trifluoride / piperidine complex, boron trifluoride / monoethylamine complex, boron trifluoride / triethanolamine complex, boron trichloride / octylamine complex, etc. Is mentioned.

  Among these, a urea compound is preferably used from the balance between storage stability and catalytic ability. As for the compounding quantity of this urea compound, 1-3 mass parts is preferable with respect to 100 mass parts of all the epoxy resin components contained in an epoxy resin composition. By controlling the compounding amount of the urea compound within this range, a cured resin product having an excellent balance of elastic modulus, heat resistance and toughness can be obtained.

  Next, other components will be described. In the epoxy resin composition of the present invention, an epoxy resin other than the epoxy resins [A] to [C] is used for the purpose of adjusting the viscoelasticity and improving the workability or the elastic modulus and heat resistance of the cured resin. It can add in the range which does not lose the effect of invention. These may be used in combination of not only one type but also a plurality of types. Specifically, phenol novolac type epoxy resin, cresol novolac epoxy resin, resorcinol type epoxy resin, phenol aralkyl type epoxy resin, dicyclopentadiene type epoxy resin, epoxy resin having biphenyl skeleton, isocyanate modified epoxy resin, anthracene type epoxy resin Polyethylene glycol type epoxy resin, N, N′-diglycidylaniline, liquid bisphenol A type epoxy resin, and the like.

  In addition, the epoxy resin composition of the present invention impairs the effects of the present invention in order to control viscoelasticity and improve mechanical properties such as tack and drape characteristics of prepreg and impact resistance of fiber reinforced composite materials. As long as there is no epoxy resin, thermoplastic resin soluble in epoxy resin, organic particles such as rubber particles and thermoplastic resin particles, inorganic particles, and the like can be blended.

  As the thermoplastic resin soluble in the epoxy resin, a thermoplastic resin having a hydrogen bondable functional group that can be expected to improve the adhesion between the resin and the reinforcing fiber is preferably used. Examples of the hydrogen bondable functional group include an alcoholic hydroxyl group, an amide bond, a sulfonyl group, and a carboxyl group.

  Examples of the thermoplastic resin having an alcoholic hydroxyl group include polyvinyl acetal resins such as polyvinyl formal and polyvinyl butyral, polyvinyl alcohol, and phenoxy resins. Examples of the thermoplastic resin having an amide bond include polyamide, polyimide, polyamideimide, and polyvinylpyrrolidone. Examples of the thermoplastic resin having a sulfonyl group include polysulfone. Here, polyamide, polyimide and polysulfone may have a functional group such as an ether bond and a carbonyl group in the main chain. The polyamide may have a substituent on the nitrogen atom of the amide group. Examples of the thermoplastic resin having a carboxyl group include polyester, polyamide, and polyamideimide.

  For preparing the epoxy resin composition of the present invention, a kneader, a planetary mixer, a three-roll extruder, a twin-screw extruder, or the like is preferably used.

  Next, the fiber reinforced composite material will be described. The fiber-reinforced composite material containing the cured product of the epoxy resin composition of the present invention as a matrix resin can be obtained by impregnating the epoxy resin composition of the present invention into a reinforcing fiber and then curing.

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

  The method for producing the fiber-reinforced composite material of the present invention is not particularly limited, but includes a prepreg lamination molding method, a resin transfer molding method, a resin film infusion method, a hand layup method, a sheet molding compound method, and a filament winding method. , Pultrusion method, etc.

  Among these, the prepreg laminate molding method is preferable because the obtained fiber-reinforced composite material is excellent in rigidity and strength.

  A preferred prepreg includes the epoxy resin composition of the present invention and reinforcing fibers. Such a prepreg can be obtained by impregnating the reinforcing fiber substrate with the epoxy resin composition of the present invention. Examples of the impregnation method include a wet method and a hot melt method (dry method).

  In the wet method, after immersing the reinforcing fiber in a solution in which the epoxy resin composition is dissolved in a solvent such as methyl ethyl ketone or methanol, the reinforcing fiber is pulled up, and the solvent is evaporated from the reinforcing fiber using an oven or the like. This is a method of impregnating a reinforcing fiber. The hot melt method is a method in which a reinforcing fiber is impregnated directly with an epoxy resin composition whose viscosity is reduced by heating, or a film in which an epoxy resin composition is coated on a release paper is prepared, and then both sides of the reinforcing fiber are prepared. Alternatively, it is a method of impregnating a reinforcing fiber with a resin by overlapping the film from one side and heating and pressing.

  In the prepreg lamination molding method, as a method of applying heat and pressure, 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.

  The 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, general industrial applications, and aerospace applications. More specifically, in sports applications, it is preferably used for golf shafts, fishing rods, tennis or badminton rackets, hockey sticks, ski poles, and the like. In addition, in general industrial applications, structural materials for moving bodies such as automobiles, bicycles, ships and railway vehicles, drive shafts, leaf springs, windmill blades, pressure vessels, flywheels, paper rollers, roofing materials, cables, and repair reinforcement materials Etc. are preferably used.

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

  The components [A] to [E] used in this example and the comparative example are as follows.

<Epoxy resin [A]>
Tetrafunctional bisnaphthalene type epoxy resin ("EPICLON (registered trademark)" HP-4700, epoxy equivalent: 165, manufactured by DIC Corporation)
-Bifunctional bisnaphthalene type epoxy resin ("EPICLON (registered trademark)" HP-4770, epoxy equivalent: 204, manufactured by DIC Corporation)
-Bifunctional naphthalene type epoxy resin ("EPICLON (registered trademark)" HP-4032, epoxy equivalent: 136, manufactured by DIC Corporation).

<Epoxy resin [B]>
-Bisphenol F type epoxy resin ("jER (registered trademark)" 4010P, epoxy equivalent: 4400, manufactured by Mitsubishi Chemical Corporation)
-Bisphenol F type epoxy resin ("jER (registered trademark)" 4007P, epoxy equivalent: 2270, manufactured by Mitsubishi Chemical Corporation)
-Bisphenol F type epoxy resin ("jER (registered trademark)" 4005P, epoxy equivalent: 1075, manufactured by Mitsubishi Chemical Corporation).

<Epoxy resin [C]>
Liquid bisphenol F type epoxy resin (“EPICLON (registered trademark)” 830, epoxy equivalent: 172, manufactured by Mitsubishi Chemical Corporation).

<Curing agent [D]>
Dicyandiamide (curing agent, DICY7, manufactured by Mitsubishi Chemical Corporation).

<Curing accelerator [E]>
DCMU99 (3- (3,4-dichlorophenyl) -1,1-dimethylurea, curing accelerator, manufactured by Hodogaya Chemical Co., Ltd.)

  Various physical properties were measured by the following methods. These physical properties were measured in an environment at a temperature of 23 ° C. and a relative humidity of 50% unless otherwise specified.

(1) Preparation of epoxy resin composition In a beaker, a predetermined amount of components other than the curing agent and the curing accelerator are added, the temperature is raised to 150 ° C. while kneading, and the mixture is kneaded for 1 hour at 150 ° C. A viscous liquid was obtained. After the viscous liquid was cooled to 60 ° C. while being kneaded, a predetermined amount of a curing agent and a curing accelerator was added and further kneaded to obtain an epoxy resin composition. Tables 1 and 2 show the compounding ratios of the examples and comparative examples.

(2) Property of epoxy resin composition The resin composition obtained in the above (1) was placed in a beaker, stored in a thermostatic bath at 25 ° C, and the property after 3 hours was observed. It stirred using the spatula and the presence or absence of fluidity | liquidity was determined. Classification was carried out according to whether it was liquid and fluid, liquid but viscous and poorly fluid, or solid. The case where it was liquid was A, the case where it was viscous and poor in fluidity was B, the case where it was solid was C, A and B were passed, and C was rejected.

(3) Elastic modulus of cured resin The epoxy resin composition was preheated at 70 ° C., then defoamed in a vacuum, and set to a thickness of 2 mm using a 2 mm thick “Teflon (registered trademark)” spacer. In a mold, it was cured at a temperature of 130 ° C. for 90 minutes to obtain a plate-shaped resin cured product having a thickness of 2 mm. From this cured resin, a test piece having a width of 10 mm and a length of 60 mm was cut out, an Instron universal testing machine (manufactured by Instron) was used, the span was set to 32 mm, the crosshead speed was set to 100 mm / min, and JIS K7171 (1994). According to the above, three-point bending was performed and the elastic modulus was measured. The average value of the values measured with the number of samples n = 5 was taken as the elastic modulus value.

(4) Measurement of coefficient of thermal expansion of epoxy component of resin cured product The epoxy resin composition was preheated at 70 ° C., defoamed in vacuum, and 6 mm thick with a 6 mm thick “Teflon (registered trademark)” spacer. And cured for 90 minutes at a temperature of 130 [deg.] C. to obtain a cured resin sheet having a thickness of 6 mm. This cured resin product was cut out to a width of 10 mm and a length of 10 mm with a diamond cutter to obtain a test piece. Using a thermomechanical analyzer (TMA T-60: manufactured by Shimadzu Corp.), the test piece was heated from 40 ° C. to 180 ° C. at a heating rate of 5 ° C./min, and the linear thermal expansion coefficient at 50 to 100 ° C. was measured.

(5) Measurement of structural period After the resin cured product obtained in (4) was dyed, it was cut into thin sections and a transmission electron image was obtained under the following conditions using a transmission electron microscope (TEM). As the staining agent, OsO ₄ and RuO ₄ were properly used according to the resin composition so that the morphology was sufficiently contrasted.
Apparatus: H-7100 transmission electron microscope (manufactured by Hitachi, Ltd.)
Acceleration voltage: 100 kV
Magnification: 10,000 times The structure period of [A] rich phase and [B] rich phase was observed from the transmission electron image. Depending on the type and ratio of each component, the phase separation structure of the resin cured product forms a biphasic continuous structure or a sea-island structure, and thus was measured as follows.

  When the phase separation structure is a biphasic continuous structure, draw three straight lines of a predetermined length on the micrograph, extract the intersection of the straight line and the phase interface, measure the distance between the adjacent intersections, These number average values were used as the structure period. The predetermined length is set as follows based on a micrograph. When the structural period is expected to be on the order of 0.01 μm (0.01 μm or more and less than 0.1 μm), a sample photograph was taken at a magnification of 20,000 times, and a length of 20 mm drawn on the photograph (1 μm on the sample) Was defined as a predetermined straight line length. Similarly, when the phase separation structure period is expected to be on the order of 0.1 μm (0.1 μm or more and less than 1 μm), a photograph is taken at a magnification of 2,000 times and a length of 20 mm on the photograph (10 μm on the sample) The length) is a predetermined length of the straight line. When the phase separation structure period is expected to be on the order of 1 μm (1 μm or more and less than 10 μm), a photograph is taken at a magnification of 200 times, and a length of 20 mm on the photograph (a length of 100 μm on the sample) did. If the measured phase separation structure period was out of the expected order, it was measured again at a magnification corresponding to the corresponding order.

  When the phase separation structure was a sea-island structure, three predetermined regions on the micrograph were selected at random, the island phase size in the region was measured, and the number average value of these was the structure period. The size of the island phase refers to the length of the shortest distance line drawn from the phase interface to one phase interface through the island phase. Even when the island phase is an ellipse, an indeterminate shape, or a circle or ellipse of two or more layers, the shortest distance passing through the island phase from the phase interface to one phase interface is defined as the island phase size. The predetermined region is set as follows based on a micrograph. When the phase separation structure period is expected to be on the order of 0.01 μm (0.01 μm or more and less than 0.1 μm), a photograph of the sample was taken at a magnification of 20,000 times, and an area of 4 mm square on the photograph (0 on the sample) .2 μm square area) was defined as a predetermined area. Similarly, when the phase separation structure period is expected to be on the order of 0.1 μm (0.1 μm or more and less than 1 μm), a sample photograph is taken at a magnification of 2,000 times, and a 4 mm square region (sample) The upper 2 μm square area) was defined as a predetermined area. When the phase separation structure period is expected to be on the order of 1 μm (1 μm or more and less than 10 μm), a photograph was taken at a magnification of 200 times, and an area of 4 mm square on the photograph (an area of 20 μm square on the sample) was defined as a predetermined area. If the measured phase separation structure period was out of the expected order, it was measured again at a magnification corresponding to the corresponding order.

Example 1
30 parts by mass of “EPICLON (registered trademark)” HP-4700 as the epoxy resin [A], 30 parts by mass of “jER (registered trademark)” 4007P as the epoxy resin [B], and “EPICLON (registered) as the epoxy resin [C]” Trademark) "830" 40 parts by mass, DICY7 as curing agent [D] in an amount of 1.0 equivalent of active hydrogen groups with respect to the epoxy groups of all epoxy resin components, and 3 parts by mass of DCMU99 as curing accelerator Thus, an epoxy resin composition was prepared. The resulting epoxy resin composition was heated at 2.5 ° C./min and cured at 130 ° C. for 90 minutes. The obtained cured resin formed a fine phase separation structure and exhibited a low coefficient of thermal expansion. The results are shown in Table 1.

(Examples 2-6, Comparative Examples 1-8)
An epoxy resin composition was prepared in the same manner as in Example 1 except that the composition was changed to the compositions shown in Tables 1 and 2. The evaluation results are shown in Tables 1 and 2. Each of the epoxy resin compositions of each example has fluidity at 25 ° C., and is considered to be excellent in handleability when used as a prepreg. Moreover, the obtained resin cured product showed a low coefficient of thermal expansion derived from a fine phase separation structure.

  Since the epoxy resin composition of Comparative Example 1 used a bifunctional bisnaphthalene type epoxy resin instead of the epoxy resin [A], the resulting resin cured product had a phase separation of 5 μm or more, The coefficient of thermal expansion was high.

  Since the epoxy resin composition of Comparative Example 2 used a bifunctional naphthalene type epoxy resin instead of the epoxy resin [A], the obtained cured resin was uniform without phase separation, and had a coefficient of thermal expansion. Showed a high value.

  Since the epoxy resin composition of Comparative Example 3 did not use the epoxy resin [B] and used an epoxy resin having an epoxy equivalent of less than 2000, the obtained resin cured product had a structural period of 5 μm or more although it was phase-separated. The coefficient of thermal expansion showed a high value.

  In the epoxy resin composition of Comparative Example 4, since the blending amount of the epoxy resin [A] is less than the blending amount of [B], the obtained resin cured product has a phase separation of 5 μm or more, and heat The expansion coefficient showed a high value.

  Since the epoxy resin [B] of the epoxy resin composition of Comparative Example 5 was less than 10 parts by mass with respect to all the epoxy resins, the properties of the resin composition at 25 ° C. were solid, and the handleability when used as a prepreg deteriorated. did.

  In the epoxy resin composition of Comparative Example 6, since the blending amount of the epoxy resin [C] was less than 30 parts by mass, the viscosity of the epoxy resin composition was increased, and a large amount of voids were observed in the cured resin, The expansion coefficient could not be measured.

  Since the epoxy resin composition of Comparative Example 7 contained more than 50 parts by mass of the epoxy resin [C], the obtained cured resin was uniform without phase separation and had a high coefficient of thermal expansion. showed that.

  Although the epoxy resin composition of Comparative Example 8 does not contain the epoxy resin [B] and the blending amount of the epoxy resin [A] is more than 60 parts by mass, the elastic modulus and thermal expansion coefficient of the cured resin are excellent, The properties of the resin composition at 25 ° C. were solid, and there was a problem in handleability when used as a prepreg.

Claims (5)

An epoxy resin composition comprising the following components [A], [B], [C], and [D] in a content ratio that satisfies the following conditions (1) to (2).
[A] Tetrafunctional bisnaphthalene type epoxy resin [B] Bisphenol type epoxy resin having an epoxy equivalent of 2000 or more [C] Epoxy resin liquid at 25 ° C. [D] Curing agent (1) 100 parts by mass of all epoxy resin components [A] 25-60 parts by mass, [B] 10-35 parts by mass, and [C] 30-50 parts by mass. (2) With respect to parts by mass relative to all epoxy resin components, [A] ≧ [B].   The epoxy resin composition according to claim 1, wherein the constituent element [D] is dicyandiamide or a derivative thereof.   The epoxy resin composition of Claim 1 or 2 containing a hardening accelerator as component [E].   A prepreg comprising the epoxy resin composition according to claim 1 and reinforcing fibers.   A fiber-reinforced composite material obtained by curing the prepreg according to claim 4.