JP2010265371A - Epoxy resin composition, prepreg, and carbon fiber-reinforced composite material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a prepreg for obtaining a carbon fiber-reinforced composite material suitable for airplane application, ship application, sport application and the other general industrial application in an epoxy resin composition having excellent curing properties, heat resistance and dynamic characteristics, to provide a method for producing the prepreg, to provide the carbon fiber-reinforced composite material obtained from the prepreg, and to provide a method for producing the same. <P>SOLUTION: In the epoxy resin composition containing, as constituent components, an epoxy resin [A], dicyandiamide or its derivative [B] and an imidazole derivative [C], the component [A] includes 35 to 70 pts.mass phenol novolak type epoxy resin and 40 to 20 pts.mass bisphenol A type epoxy resin solid at 25°C based on 100 pts.mass total epoxy resin and the bisphenol A type epoxy resin in the total epoxy resin has an average epoxy equivalent of ≤400. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an epoxy resin composition excellent in curability, heat resistance and mechanical properties. The present invention also relates to a prepreg for obtaining a carbon fiber reinforced composite material suitable for aircraft use, marine use, sports use and other general industrial uses, and a method for producing the same, and a carbon fiber reinforced composite material obtained from the prepreg and its It relates to a manufacturing method.

  Fiber reinforced composite materials consisting of epoxy resins and other thermosetting resins and reinforcing fibers, especially carbon fiber reinforced composite materials using carbon fibers, are used for golf clubs, tennis rackets, fishing rods, etc. due to their light weight and excellent mechanical properties. It is used in a wide range of applications such as sports equipment, structural materials for aircraft and vehicles, reinforcing materials for concrete structures, medical equipment such as X-ray equipment and wheelchairs, and electrical and electronic equipment such as laptop computers and mobile phones.

  The properties required of the epoxy resin composition and carbon fiber reinforced composite material used for such applications are of course excellent in physical properties of the molded product such as heat resistance and impact resistance, but at the same time at room temperature. It is excellent in storage stability and has a high curing rate at a specific curing temperature.

  As a method for improving the curability of the epoxy resin composition, it is common to increase the amount of the curing agent and the curing accelerator. In such a method, although the curing speed is increased, heating in the adjustment step of the epoxy resin composition is performed. There was a problem that the reaction progressed or the storage stability of the produced prepreg deteriorated. Further, when the amount of the curing agent and the curing accelerator is increased, the cured product tends to become brittle, and there is a problem that the mechanical properties are deteriorated.

  In order to solve such a problem, a technique using dicyandiamide as a curing agent of an epoxy resin composition and DCMU (3,4-dichlorophenyl-1,1-dimethylurea) as a curing accelerator is disclosed (for example, Patent Document 1). . However, this technique has a problem that sufficient curability is not obtained and the heat resistance of the cured product is low. Further, although techniques using various compounds such as dicyandiamide as a curing agent and aminourea compounds and imidazole derivatives as a curing accelerator have been disclosed, sufficient heat resistance and curability have not been obtained (for example, patent documents) 2). Patent Document 3 discloses a technique using dicyandiamide as a curing agent and 2,4′-toluenebis (3,3-dimethylurea) as a curing accelerator, but sufficient heat resistance is obtained. In addition, since a high molecular weight compound is blended in the matrix resin, there is a problem that the impregnation property of the epoxy resin composition into the carbon fiber is poor.

Japanese Patent Laid-Open No. 8-34864 JP 2000-319619 A International Publication No. 2005-029882 Pamphlet

  The present invention solves such problems in the prior art and provides an epoxy resin composition excellent in curability, heat resistance and mechanical properties. The present invention also relates to a prepreg for obtaining a carbon fiber reinforced composite material suitable for sports, aircraft, construction and other general industrial uses, and a method for producing the same, and a carbon fiber reinforced composite material obtained from the prepreg and a method for producing the same. It is to provide.

  The epoxy resin composition of the present invention has the following configuration in order to achieve the above object.

  That is, an epoxy resin composition containing an epoxy resin [A], dicyandiamide and its derivative [B], and an imidazole derivative [C], wherein the component [A] is phenol based on 100 parts by mass of the total epoxy resin. 35 to 70 parts by mass of a novolac type epoxy resin, 40 to 20 parts by mass of a bisphenol A type epoxy resin solid at 25 ° C., and the average epoxy equivalent of the bisphenol A type epoxy resin in all epoxy resins is 400 or less It is an epoxy resin composition.

  According to a preferred embodiment of the epoxy resin composition of the present invention, the component [C] is 2-phenyl-4-methyl-5-hydroxymethylimidazole.

  According to a preferred embodiment of the epoxy resin composition of the present invention, the epoxy resin composition does not substantially contain a compound having a weight average molecular weight of 12,000 or more.

  The prepreg of the present invention is composed of the above epoxy resin composition and carbon fiber.

  According to a preferred embodiment of the prepreg of the present invention, carbon fiber is impregnated with the epoxy resin composition by a solvent method.

  The carbon fiber reinforced composite material of the present invention is obtained by heat-curing the above prepreg.

  According to a preferred embodiment of the carbon fiber reinforced composite material of the present invention, the prepreg is produced using a press molding method.

  According to the present invention, an epoxy resin composition having excellent curability, heat resistance and mechanical properties can be obtained.

  Hereinafter, the epoxy resin composition of the present invention, the prepreg and its production method, and the carbon fiber reinforced composite material and its production method will be described.

  In the present invention, the “epoxy resin composition” includes epoxy resin [A], dicyandiamide and its derivative [B], and imidazole derivative [C].

  The epoxy resin composition of the present invention comprises 35 to 70 parts by mass of a phenol novolac type epoxy resin, 40 to 20 parts by mass of a bisphenol A type epoxy resin solid at 25 ° C. with respect to 100 parts by mass of the total epoxy resin, and The epoxy resin [A] whose average epoxy equivalent of the bisphenol A type epoxy resin in all epoxy resins is 400 or less, dicyandiamide and its derivative [B], and imidazole derivative [C] are comprised.

  Component [A] in the present invention is an epoxy resin, and 35 to 70 parts by mass of a phenol novolac type epoxy resin and 40 to 20 of a bisphenol A type epoxy resin solid at 25 ° C. with respect to 100 parts by mass of all epoxy resins. Including all parts by mass, the average epoxy equivalent of the bisphenol A type epoxy resin in all epoxy resins is 400 or less.

  The phenol novolac-type epoxy resin used in the present invention can impart fast curability and high heat resistance to the cured resin by blending a predetermined amount. That is, the compounding quantity of the phenol novolac type epoxy resin used for this invention is 35-70 mass parts with respect to 100 mass parts of all the epoxy resins, More preferably, it is 35-60 mass parts. When the amount is less than 35 parts by mass, sufficient curability and heat resistance may not be obtained. Moreover, when this compounding quantity exceeds 70 mass parts, resin cured | curing material may become weak.

  Further, the phenol novolac type epoxy resin used in the present invention is represented by the following formula (I).

(Wherein R represents a hydrogen atom or a methyl group, and each R may be the same as or different from each other, and n represents an integer of 0 or more).

  Component [A] in the present invention is such that the compounding amount of the component of n ≧ 1 in the epoxy resin represented by the above formula (I) is 28 to 60 parts by mass with respect to 100 parts by mass of the total epoxy resin. Is more preferable, and it is 28-50 mass parts. If the blending amount is less than 28 parts by mass, sufficient curability and heat resistance may not be obtained. Moreover, when this compounding quantity exceeds 60 mass parts, resin cured | curing material may become weak or a tack may not be obtained. In the present invention, the upper limit of the n value in the compound represented by formula (I) is preferably 15. If this value exceeds 15, tack and drape may be insufficient when a prepreg is formed.

  Commercially available phenol novolac epoxy resins include “jER (registered trademark)” 152, “jER (registered trademark)” 154 (manufactured by Japan Epoxy Resin Co., Ltd.), and “Epicron (registered trademark)” N-740. "Epiclon (registered trademark)" N-770, "Epiclon (registered trademark)" N-775 (manufactured by DIC Corporation), PY307, EPN1179, EPN1180 (manufactured by Huntsman Advanced Materials), YDPN638 YDPN638P (above, manufactured by Toto Kasei Co., Ltd.), DEN431, DEN438, DEN439 (above, manufactured by Dow Chemical Co., Ltd.), EPR600 (manufactured by Bakerite), EPPN-201 (manufactured by Nippon Kayaku Co., Ltd.) .

  The bisphenol A type epoxy resin that is solid at 25 ° C. used in the present invention can impart a suitable tack to the prepreg by blending a predetermined amount. That is, the blending amount of the bisphenol A type epoxy resin solid at 25 ° C. used in the present invention is 40 to 20 parts by mass, more preferably 40 to 25 parts by mass with respect to 100 parts by mass of all epoxy resins. . When this compounding quantity exceeds 40 mass parts, sclerosis | hardenability and heat resistance may be insufficient, or a tack may not be obtained. Moreover, when this compounding quantity is less than 20 mass parts, it may become a tack excess.

  Here, solid at 25 ° C. means that the glass transition temperature or melting point of the epoxy resin is 25 ° C. or higher. The glass transition temperature is a midpoint temperature determined based on JIS K7121 (1987) using a differential scanning calorimeter (DSC), and the melting point is a melting peak temperature determined based on JIS K7121 (1987).

  The bisphenol A type epoxy resin solid at 25 ° C. used in the present invention preferably has an epoxy equivalent of 300 to 1500, more preferably 350 to 1200. When such an epoxy equivalent is less than 300, a suitable tack may not be obtained when a prepreg is obtained. Moreover, when this compounding quantity exceeds 1500, sclerosis | hardenability and heat resistance may be insufficient.

  Commercially available products of bisphenol A type epoxy resin solid at 25 ° C. include “jER (registered trademark)” 1001, “jER (registered trademark)” 1002, “jER (registered trademark)” 1003, and “jER (registered trademark)”. 1003F, “jER (registered trademark)” 1004, “jER (registered trademark)” 1004FS, “jER (registered trademark)” 1004F, “jER (registered trademark)” 1004AF, “jER (registered trademark)” 1055, “jER (registered trademark)” Registered trademark) "1005F," jER (registered trademark) "1006FS," jER (registered trademark) "1007," jER (registered trademark) "1007FS," jER (registered trademark) "1008," jER (registered trademark) "1009 (Made by Japan Epoxy Resin Co., Ltd.), “Epototo (registered trademark)” YD-011, “Epototo (registered trademark) “YD-012,“ Epototo (registered trademark) ”YD-013,“ Epototo (registered trademark) ”YD-014,“ Epototo (registered trademark) ”YD-017,“ Epototo (registered trademark) ”YD-019,“ Epototo (registered trademark) "YD-020N", "Epototo (registered trademark)" YD-020H (above, Toto Kasei Co., Ltd.), "Epicron (registered trademark)" 1050, "Epicron (registered trademark)" 3050, "Epicron (Registered trademark) “4050”, “Epiclon (registered trademark)” 7050 (above, manufactured by DIC Corporation), EP-5100, EP-5400, EP-5700, EP-5900 (above, manufactured by ADEKA Corporation), DER-661, DER-663U, DER-664, DER-667, DER-668, DER-669 (above, manufactured by Dow Chemical Company) And the like.

  The average epoxy equivalent of the bisphenol A type epoxy resin in all the epoxy resins used in the present invention is 400 or less. When the average epoxy equivalent exceeds 400, the molecular weight of the epoxy resin is often relatively large, and it takes a high temperature and a long time for dissolution in the preparation process of the epoxy resin composition, and the curability and heat resistance are reduced. Or a suitable prepreg may not be obtained.

  Component [B] in the present invention is dicyandiamide or a derivative thereof, and is a component necessary for curing the epoxy resin composition. Dicyandiamide hardly dissolves in the epoxy resin at 25 ° C., but dissolves when heated to 100 ° C. or more and reacts with the epoxy group. That is, it is a latent curing agent that has stability in resin preparation step, step of impregnating carbon fiber with epoxy resin composition, and subsequent storage, and changes to a highly active state by receiving a thermal history during curing. .

  In the component [B] in the present invention, the equivalent of active hydrogen contained in dicyandiamide with respect to 1 equivalent of epoxy group contained in the epoxy resin is preferably in the range of 0.5 to 1.2, more preferably 0.6. It is the range of -1.1. When the equivalent is less than 0.5, curing may be insufficient and heat resistance may be reduced. Moreover, when this equivalent exceeds 1.2, the mechanical property of the carbon fiber reinforced composite material obtained may fall.

  As a commercial item of dicyandiamide, Dicy-7, Dicy-15 (above, Japan Epoxy Resin Co., Ltd. product) etc. are mentioned.

  Component [C] in the present invention is an imidazole derivative and is a component necessary for enhancing the curing activity of the dicyandiamide curing agent. Dicyandiamide alone requires about 170 to 180 ° C. for curing, whereas an epoxy resin composition using such a combination can be cured at 60 to 150 ° C.

  Examples of imidazole derivatives include 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-phenylimidazole, 2-phenyl-4-methyl. Imidazole, 1-benzyl-2-phenylimidazole, 1-benzyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecyl- Imidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazolium trimellitate, 1-cyanoethyl-2-undecylimidazolium trimellitate, 1-cyanoethyl-2-pheny Imidazolium trimellitate, 2,4-diamino-6- (2'-methylimidazolyl- (1 '))-ethyl-S-triazine, 2,4-diamino-6- (2'-undecylimidazolyl) ) -Ethyl-S-triazine, 2,4-diamino-6- (2'-ethyl-4-methylimidazolyl- (1 '))-ethyl-S-triazine, 2,4-diamino-6- (2' Methylimidazolyl- (1 ′))-ethyl-S-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-methylimidazole isocyanuric acid adduct, 1-cyanoethyl-2-phenyl-4,5-di (2-cyanoethoxy) methylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydride Such as carboxymethyl methylimidazole.

  Among them, 2-phenyl-4-methyl-5-hydroxymethylimidazole is used as component [C] in that the reaction exothermic peak is sharp, the calorific value is large, the curability at a specific temperature is excellent, and the heat resistance can be improved. Is preferably used.

  As a commercial item of 2-phenyl-4-methyl-5-hydroxymethylimidazole, “CUREZOLE (registered trademark)” 2P4MHZ (manufactured by Shikoku Kasei Kogyo Co., Ltd.) and the like can be mentioned.

  The compounding amount of the component [C] in the present invention is preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the epoxy resin. When the amount is less than 0.5 parts by mass, curability may be insufficient. Moreover, when this compounding quantity exceeds 5 mass parts, when the storage stability of an epoxy resin composition is not obtained, reaction advances with the heat history received in the process of manufacturing a prepreg, and tack and drape property fall. There is a case.

  These imidazole derivatives may be used alone or in combination of two or more.

  The epoxy resin composition in the present invention preferably contains substantially no compound having a weight average molecular weight of 12,000 or more, and more preferably contains substantially no compound having a weight average molecular weight of 10,000 or more. The “substantially free” described here means that the compounding amount of a compound having a weight average molecular weight of 12,000 or more, or a compound having a weight average molecular weight of 10,000 or more, relative to 100 parts by mass of all epoxy resins is 0.00. It represents less than 5 parts by mass.

  When such a compound is blended, the viscosity of the epoxy resin composition becomes high and impregnation into the carbon fiber becomes difficult, and when it is used as a prepreg, suitable tack and draping properties may not be obtained.

  A weight average molecular weight here refers to the polystyrene conversion weight average molecular weight obtained by GPC (gel permeation chromatography). As a method for measuring the weight average molecular weight, two “Shodex (registered trademark)” 80M (manufactured by Showa Denko) and one Shodex 802 (manufactured by Showa Denko) were used in a column, and 0.3 μL of a sample was injected. A method of obtaining the sample holding time measured at 1 mL / min by converting it into a molecular weight using the holding time of the polystyrene calibration sample can be used. In addition, when a some peak is observed by liquid chromatography, the objective component can be isolate | separated and molecular weight conversion can be performed about each peak.

  In addition, it is preferable that it is substantially not contained in the epoxy resin composition in this invention, As a specific example of the above-mentioned compound, polyamide, polyamideimide, polyaramide, polyarylene oxide, polyarylate, polyimide, polyethylene terephthalate, polyether Imide, polyether terephthalate, polyether imide, polyether ether ketone, polyether sulfone, polycarbonate, polyvinyl acetate, polystyrene, polysulfone, polyphenylene oxide, polyphenylene sulfide, polypropylene, polybenzimidazole, polymethyl methacrylate, polyvinyl formal, polyvinyl Examples include acetal, polyvinyl butyral, and phenoxy resin. Among these, the weight average molecular weight is 12000 or more. Things, to weight average molecular weight of 10000 or more compounds.

The structure and compounding ratio of the compound contained in the epoxy resin composition can be specified by the following method. That is, the epoxy resin composition was extracted with chloroform and then methanol with ultrasonic extraction to extract an epoxy resin, a curing agent, and a curing accelerator, and the obtained extract was analyzed for bisphenol A from IR and ¹ H-NMR spectra. Type epoxy resin, phenol novolac type epoxy resin, curing agent, curing accelerator structure can be specified, and using the chloroform extract thus obtained, the mobile phase is chloroform / acetonitrile. By measuring the HPLC and comparing the peak intensity ratio of the obtained chromatograph with the peak intensity ratio of known epoxy resin commercial products, the compounding ratio of each compound can be specified.

(Tg of cured resin)
It is preferable that the glass transition temperature of the hardened | cured material formed by hardening | curing the epoxy resin composition of this invention is 90-250 degreeC, More preferably, it is 100-220 degreeC. When the glass transition temperature is less than 90 ° C., the heat resistance of the cured resin becomes insufficient, and the carbon fiber reinforced composite material may be deformed when used in a high temperature environment. When the glass transition temperature exceeds 250 ° C., the cured resin tends to be brittle, and the tensile strength and impact resistance of the carbon fiber reinforced composite material may be lowered. Here, the glass transition temperature is 12.7 mm in width, 45 mm in length, and 2 mm in thickness as a test piece, using a dynamic viscoelasticity measuring apparatus ARES (manufactured by TA Instruments Japan), with a frequency of 1 Hz, Measured by raising the temperature at 5 ° C./min, the glass transition temperature is a tangent line drawn at the point where the slope of the staircase change portion becomes the maximum, and the base line on the low temperature side from the step change portion due to the glass transition of G ′ This means the extrapolated glass transition start temperature.

(Bending elastic modulus of cured resin)
It is preferable that the bending elastic modulus measured according to JIS K7171 (1999) of the hardened | cured material formed by hardening | curing the epoxy resin composition of this invention exists in the range of 2.5-5GPa, More preferably, it is 3-5GPa. Such a cured resin product is obtained by heating the epoxy resin composition at a temperature increase rate of 25 ° C. to 1.5 ° C./min, and then curing it at a temperature of 150 ° C. for 5 minutes. When the flexural modulus of the cured resin is less than 2.5 GPa, sufficient strength of the carbon fiber reinforced composite material may not be obtained. The higher the flexural modulus, the better. However, when the flexural modulus increases, the flexural deflection tends to decrease. In the present invention, if the flexural modulus exceeds 5 GPa, a suitable flexural flexure amount may not be obtained. .

(Gelification time of cured resin)
The epoxy resin composition of the present invention is preferably cured in a short time in applications where it is desired that it can be produced in a large amount in a short time. Specifically, the gelation time at the molding temperature is 3 minutes or less. preferable. Further, for the purpose of improving productivity, it is desirable to gel in a shorter time. The gelation time of an epoxy resin composition here can be measured as follows. That is, the epoxy resin composition is sampled as a 2 cm ³ sample, put into a die heated to 150 ° C. using a curastometer, and a torque that imparts to the die an increase in viscosity as the sample progresses by applying torsional stress. The time until the torque reaches 0.005 N · m after the start of measurement is defined as the gel time.

  In the epoxy resin composition of the present invention, if necessary, in addition to the above components, organic particles such as thermosetting resins other than [A] to [C], rubber particles and thermoplastic resin particles, curing acceleration One or more agents, flame retardants, pigments, and silane coupling agents can be contained, but the compounds blended in addition to [A] to [C] are solvent insolubles having a particle size of 1 μm or more. It is preferable that it does not contain substantially. In addition, “substantially free” described here represents that the blending amount of the solvent insoluble matter having a particle diameter of 1 μm or more is less than 0.5 parts by mass with respect to 100 parts by mass of all epoxy resins. . Further, the “solvent” described here represents a diluting solvent used in the solvent method described later.

  That is, the epoxy resin composition of the present invention preferably contains substantially no solvent insolubles having a particle size of 1 μm or more in the step of impregnating the carbon fiber with the epoxy resin composition. This is because the solvent insoluble matter on the surface of the prepreg remains locally without passing through the prepreg, so that the prepreg may have insufficient tack and drape properties or the strength characteristics of the carbon fiber reinforced composite material may be deteriorated.

(Prepreg)
The prepreg using the epoxy resin composition of the present invention desirably uses carbon fibers as reinforcing fibers. By using carbon fiber, the fiber reinforced composite material can exhibit excellent strength and impact resistance.

  In the present invention, carbon fibers of any type can be used depending on the application, and those having a tensile strength of 1 GPa to 9 GPa are preferably used. In view of the high tensile strength of carbon fiber and the impact resistance when a composite material is used, the tensile strength is preferably as high as possible, and more preferably 2 GPa to 9 GPa.

  Carbon fibers preferably used usually have a tensile elastic modulus of about 150 GPa to 1000 GPa. However, using carbon fibers having a high tensile elastic modulus provides a high elastic modulus when used as a fiber-reinforced composite material. Connected. The tensile strength and elastic modulus of carbon fiber here mean the strand tensile strength and the strand tensile elastic modulus measured according to JIS R7601 (1986).

  The carbon fibers used in the present invention are classified into polyacrylonitrile-based, rayon-based and pitch-based carbon fibers. Among these, polyacrylonitrile-based carbon fibers having high tensile strength are preferably used. The polyacrylonitrile-based carbon fiber can be produced, for example, through the following steps. A spinning dope containing polyacrylonitrile obtained from a monomer containing acrylonitrile as a main component is spun by a wet spinning method, a dry wet spinning method, a dry spinning method, or a melt spinning method. The spun coagulated yarn can be made into a precursor through a spinning process, and then carbon fiber can be obtained through processes such as flame resistance and carbonization.

  Examples of the form of carbon fiber in the prepreg using the epoxy resin composition of the present invention include long fibers aligned in one direction, bi-directional woven fabric, multiaxial woven fabric, non-woven fabric, mat, knit, braided string, etc. It is not limited to this. The long fiber here means a single fiber or a fiber bundle substantially continuous for 10 mm or more.

  A so-called unidirectional prepreg using long fibers aligned in one direction has a high fiber strength direction and a high strength utilization rate in the fiber direction because the fibers are less bent. Further, when the unidirectional prepreg is formed after a plurality of prepregs are laminated in an appropriate laminated configuration, the elastic modulus and strength of each surface of the carbon fiber reinforced composite material can be freely controlled.

  Further, a fabric prepreg using various fabrics is also a preferable embodiment because a material having low strength and elastic anisotropy can be obtained, and a pattern of a fiber fabric floats on the surface and is excellent in design. It is also possible to form a carbon fiber reinforced composite material using multiple types of prepregs, for example, both unidirectional prepregs and woven prepregs.

(Prepreg manufacturing method)
Next, a production method suitable for obtaining a prepreg using the epoxy resin composition of the present invention will be described.

  The prepreg using the epoxy resin composition of the present invention is desirably formed by impregnating the above-mentioned epoxy resin composition into carbon fibers. Examples of the impregnation method include a hot melt method and a solvent method.

  The above hot melt method is a method of impregnating carbon fiber directly with an epoxy resin composition for which the viscosity has been lowered by heating, or a resin film in which an epoxy resin composition is once coated on release paper or the like, Next, the resin film is overlapped from both sides or one side of the carbon fiber, and the carbon fiber is impregnated with the epoxy resin composition by heating and pressing.

  In the above solvent method, the epoxy resin composition is diluted with a solvent to form a solution, which is impregnated into carbon fiber, and then the solvent is evaporated using a hot air dryer or the like to obtain a prepreg. At this time, it is preferable to remove the solvent remaining in the prepreg as much as possible in order to avoid the generation of voids during molding and the deterioration of the strength characteristics of the carbon fiber reinforced composite material.

  Specific examples of the solvent for dilution used in the solvent method include organic solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, methanol, toluene, xylene, dimethyl sulfoxide, N, N-dimethylacetamide, and methyl cellosolve. These organic solvents may be used as a mixture thereof or as a mixture with water. Moreover, when adjusting an epoxy resin composition, you may mix and use an organic solvent and an epoxy resin previously, or may use the commercial item of an organic solvent containing epoxy resin.

(Viscosity of solution)
The solution obtained by diluting the epoxy resin composition with a solvent is preferably adjusted so that the viscosity at 30 ° C. is 10 to 50000 mPa · s in order to facilitate the impregnation of the epoxy resin composition into carbon fibers. Is 10 to 25000 mPa · s. If the viscosity is less than 10 mPa · s, the resin flow becomes large, or if a large amount of dilution solvent is added, the solvent volatilizes during resin adjustment, making it difficult to control the viscosity, or drying and removing the solvent. It may take a long time to decrease the productivity, and the solvent remaining in the epoxy resin composition may cause voids in the molded product to deteriorate the strength characteristics of the carbon fiber reinforced composite material. On the other hand, when the viscosity exceeds 50000 mPa · s, voids may be generated in the carbon fiber reinforced composite material which can be difficult to impregnate the carbon fiber with the epoxy resin composition. The viscosity at 30 ° C. here is an E-type viscometer equipped with a standard cone rotor (1 ° 34 ′ × R24) according to “Method of measuring viscosity with cone-plate rotational viscometer” in JIS Z8803 (1991) ( It means the viscosity measured at a rotational speed of 50 revolutions / minute using Tokimec Co., Ltd. (TVE-30H).

  From the above viewpoint, the blending amount of the solvent when diluting the epoxy resin composition with the solvent is preferably 30 to 150 parts by mass, more preferably 30 to 100 parts by mass with respect to 100 parts by mass of the total epoxy resin. Part.

(Carbon fiber reinforced composite material)
In the present invention, in order to form a carbon fiber reinforced composite material using a prepreg, a method of heating and curing the epoxy resin composition while applying pressure to the laminate after the prepreg is laminated can be preferably used.

  Examples of methods for heat-curing the epoxy resin composition while applying pressure include a press molding method, an autoclave molding method, a bagging molding method, a wrapping tape method, and an internal pressure molding method. Among the above molding methods, the press molding method is particularly preferably used because the equipment cost is low, the operation is simple, the molding is possible in a short time, and the mass productivity is excellent.

  The temperature at which the carbon fiber reinforced composite material is molded depends on the type of curing agent contained in the epoxy resin composition, but a temperature of 80 to 220 ° C. is usually preferable. If the molding temperature is too low, sufficient rapid curability may not be obtained. Conversely, if the molding temperature is too high, warping due to thermal strain may be likely to occur.

  Moreover, as a pressure which shape | molds a carbon fiber reinforced composite material with a press molding method, although it changes with thickness of prepreg, Wf, etc., the pressure of 0.1-1 Mpa is preferable normally. If the molding pressure is too low, heat may not be sufficiently transmitted to the inside of the prepreg, resulting in uncured locally or warping. On the other hand, if it is too high, the resin will flow out before being cured, and voids may be generated in the carbon fiber reinforced composite material, or the desired Wf may not be obtained.

(Tg of carbon fiber reinforced composite material)
The glass transition temperature after molding of the carbon fiber reinforced composite material produced using the prepreg using the epoxy resin composition of the present invention is preferably 130 to 250 ° C, more preferably 140 to 220 ° C. . When the glass transition temperature is less than 130 ° C., deformation may occur when the carbon fiber reinforced composite material is demolded after press molding. Moreover, when this glass transition temperature exceeds 250 degreeC, the tensile strength and impact resistance of a carbon fiber reinforced composite material may become low. As for the glass transition temperature here, a test piece having a mass of 10 mg is cut from the carbon fiber reinforced composite material after molding, and a differential scanning calorimeter Pyris DSC (manufactured by PerkinElmer Instruments Co., Ltd.) is used according to JIS K7121 (1987). Means a glass transition temperature at the midpoint of the portion where the DSC curve shows a step-like change when heated at 40 ° C./min in a nitrogen atmosphere.

  Hereinafter, the epoxy resin composition, prepreg, and carbon fiber reinforced composite material of the present invention will be described more specifically with reference to examples. The components used in the examples are the following (1), the preparation method of the epoxy resin composition for carbon fiber reinforced composite material is the following (2), the preparation method of the prepreg is the following (6), and the measurement method of each physical property Are shown in the following (3) to (5), (7), (8). These measurements were performed in an environment at a temperature of 23 ° C. and a relative humidity of 50% unless otherwise specified.

(1) Each resin and carbon fiber epoxy resin (component [A])
“JER (registered trademark)” 1001 (bisphenol A type epoxy resin solid at 25 ° C., epoxy equivalent (EEW): 475 g / eq, manufactured by Japan Epoxy Resins Co., Ltd.)
"JER (registered trademark)" 1004 (bisphenol A type epoxy resin solid at 25 ° C, epoxy equivalent (EEW): 975 g / eq, manufactured by Japan Epoxy Resins Co., Ltd.)
"JER (registered trademark)" 154 (phenol novolac type epoxy resin, epoxy equivalent (EEW): 178 g / eq, in the above formula (I), ratio of n ≧ 1: 83%, manufactured by Japan Epoxy Resins Co., Ltd.)
"JER (registered trademark)" 828 (bisphenol A type epoxy resin that is liquid at 25 ° C, epoxy equivalent (EEW): 189 g / eq, manufactured by Japan Epoxy Resins Co., Ltd.).

Curing agent Dicyandiamide (component [B])
-Dicy-7 (made by Japan Epoxy Resin Co., Ltd.).

Curing accelerator Imidazole derivative (component [C])
"Cureazole (registered trademark)" 2P4MHZ (2-phenyl-4-methyl-5-hydroxymethylimidazole, manufactured by Shikoku Chemicals Co., Ltd.).

Other curing accelerators, DCMU-99 (3,4-dichlorophenyl-1,1-dimethylurea, manufactured by Hodogaya Chemical Co., Ltd.)
"OMICURE" (registered trademark) 24 (2,4'-toluenebis (3,3-dimethylurea), manufactured by PTI Japan)
Solvent / Methyl ethyl ketone (Wako Pure Chemical Industries, Ltd.)
-Methanol (manufactured by Wako Pure Chemical Industries, Ltd.).

Carbon fiber "Treka (registered trademark)" T700SC-12000 (tensile strength 4.9 GPa, tensile elastic modulus 230 GPa, manufactured by Toray Industries, Inc.).

(2) Preparation of epoxy resin composition A predetermined amount of epoxy resin shown in Table 1 is added to the kneader, and the mixture is kneaded and heated to a temperature of 130 ° C to completely dissolve the solid components. A preparation was obtained. While kneading was continued, the temperature was lowered to a temperature of 50 to 60 ° C., and a predetermined amount shown in Table 1 was added to dicyandiamide and a curing accelerator, followed by stirring for 30 minutes so as to uniformly disperse to obtain an epoxy resin composition.

(3) Gelation time of the epoxy resin composition 2 cm ³ was prepared from the epoxy resin composition as a sample, and a curastometer V type (manufactured by Nigo Shoji Co., Ltd.) was used at 150 ° C. in order to follow the curing. The gelation time was measured at the temperature of The time when the torque reached 0.005 N · m after the start of measurement was defined as the gel time.

(4) Glass transition temperature of cured resin After defoaming the uncured epoxy resin composition in a vacuum, in a mold set to a thickness of 2 mm by a 2 mm thick “Teflon (registered trademark)” spacer The temperature was increased at a temperature increase rate of 25 ° C. to 1.5 ° C./min, and then cured at a temperature of 150 ° C. for 5 minutes to obtain a cured resin having a thickness of 2 mm. A test piece having a width of 12.7 mm and a length of 45 mm was cut out from the cured resin, and a dynamic viscoelasticity measuring device ARES (manufactured by TA Instruments Japan) was used, with a frequency of 1 Hz, a temperature of 25 to 250 ° C., and 5 ° C./min. The temperature was measured by raising the temperature. The glass transition temperature is the intersection of the base line on the lower temperature side of the step change portion due to the glass transition of G ′ and the tangent drawn at the point where the gradient of the step change portion is maximum, that is, the extrapolated glass transition start temperature The transition temperature was used.

(5) Measurement of resin flexural modulus A test piece having a width of 10 mm and a length of 60 mm was cut out from the cured resin obtained in (4) above, and the span length was measured using an Instron universal testing machine (Instron). Was set to 32 mm and 2.5 mm / min, and three-point bending was performed according to JIS K7171 (1999) to obtain a flexural modulus. The number of samples was set to n = 5, and the average value was compared.

(6) Preparation of prepreg After immersing a carbon fiber plain weave fabric in a solution obtained by adding the solvent shown in Table 1 to the epoxy resin composition obtained in (2) above and diluting, 50 to 50- A solvent was removed by heat treatment at 130 ° C. to obtain a prepreg having a Wf of 67%.

(7) Tack of prepreg The tack value of the prepreg obtained in (6) above was determined using a tack tester (PICMA tack tester II: manufactured by Toyo Seiki Co., Ltd.), and an 18 × 18 mm cover glass with a force of 3.9 N for 5 seconds. It was measured by the resistance when it was pressure-bonded to a prepreg, pulled at a rate of 30 mm / min, and peeled off. The measurement was performed twice immediately after prepreg production (initial stage) and 24 hours later. Moreover, tackiness was evaluated in the following three stages. The number of measurements was n = 7, and the average value of 5 points excluding the top 2 points was evaluated.
(Circle): A tack value is 3N or more and 20N or less, and shows moderate adhesiveness.
X: Tack value is 0N or more and less than 3N, or larger than 20N, and there is no adhesiveness or adhesiveness is too strong.

(8) Glass transition temperature of carbon fiber reinforced composite material The prepreg obtained in (6) above is molded by heating press at a temperature of 150 ° C. for 5 minutes under a pressure of 0.6 MPa. Got. A sample having a mass of 10 mg was cut from the obtained carbon fiber reinforced composite material to prepare a sample, and the glass transition temperature was measured using a differential scanning calorimeter (DSC) according to JIS K7121 (1987). The measurement conditions were a nitrogen atmosphere, a rate of temperature increase of 40 ° C./min, and the midpoint glass transition temperature of the portion where the DSC curve showed a step change. As a differential scanning calorimeter, Pyris DSC (manufactured by Perkin Elmer Instruments) was used.

  Table 1 shows the blending amounts and evaluation results of the components of Examples 1 to 5 and Comparative Examples 1 to 6. The numbers of the epoxy resin composition and the solvent in Table 1 represent parts by mass.

Example 1
As shown in Table 1, using “jER (registered trademark)” 154 as a phenol novolac type epoxy resin and “jER (registered trademark)” 1001 as a solid bisphenol A type epoxy at 25 ° C., the average epoxy of bisphenol A type epoxy resin An epoxy resin composition, a diluted solution thereof, a prepreg, and a carbon fiber reinforced composite material were prepared so that the equivalent weight was 343. When the characteristics were evaluated, the gelation time of the epoxy resin composition was 119 seconds and gelled within 3 minutes, and the Tg, flexural modulus and prepreg tack were also good. The Tg of the carbon fiber reinforced composite material also had sufficient heat resistance at 145 ° C. and could be removed from the mold.

(Example 2)
An epoxy resin composition, a diluted solution thereof, a prepreg, and a carbon fiber reinforced composite material were produced in the same manner as in Example 1 except that the blending amount of “jER (registered trademark)” 154 was increased from 35 parts by weight to 50 parts by weight. . When the characteristics were evaluated, the gelation time of the epoxy resin composition was 107 seconds. Further, the Tg of the carbon fiber reinforced composite material had a sufficient heat resistance of 152 ° C. and could be removed from the mold.

(Example 3)
Except that "jER (registered trademark)" 1001 and "jER (registered trademark)" 1004 were used as the solid bisphenol A type epoxy resin at 25 ° C, and the average epoxy equivalent of the bisphenol A type epoxy resin was 382, In the same manner as in Example 1, an epoxy resin composition, a diluted solution thereof, a prepreg, and a carbon fiber reinforced composite material were produced. When the characteristics were evaluated, the gelation time, Tg, flexural modulus, and prepreg tack of the epoxy resin composition were good. Further, the Tg of the carbon fiber reinforced composite material had a sufficient heat resistance of 150 ° C. and could be removed from the mold.

Example 4
Except that the amount of “jER (registered trademark)” 154 was increased to 65 parts by mass and the amount of “jER (registered trademark)” 1001 was decreased to 20 parts by mass, the epoxy resin composition, its diluted solution, A prepreg and a carbon fiber reinforced composite material were prepared. When the characteristics were evaluated, the gelation time of the epoxy resin composition was as fast as 97 seconds, and the Tg of the cured epoxy resin and the Tg of the carbon fiber reinforced composite material were also high.

(Example 5)
An epoxy resin composition, a diluted solution thereof, a prepreg, and a carbon fiber reinforced composite material were produced in the same manner as in Example 1 except that the amount of the imidazole derivative and 2P4MHZ was increased from 2 parts by mass to 5 parts by mass. When the characteristics were evaluated, the gelation time of the epoxy resin composition was as fast as 95 seconds, and the Tg of the cured epoxy resin and the Tg of the carbon fiber reinforced composite material were also high.

(Comparative Example 1)
Using 30 parts by mass of “jER (registered trademark)” 154 and 32 parts by mass of “jER (registered trademark)” 1004, an epoxy resin composition and diluted solution thereof so that the average epoxy equivalent of bisphenol A type epoxy resin is 548 A prepreg and a carbon fiber reinforced composite material were prepared. When the characteristics were evaluated, the gelation time was as slow as 145 seconds, and the Tg of the carbon fiber reinforced composite material was 120 ° C., and deformation was observed during demolding.

(Comparative Example 2)
An epoxy resin composition, a diluted solution thereof, a prepreg, and a carbon fiber reinforced composite material were prepared in the same manner as in Example 1 except that the amount of “jER (registered trademark)” 154 was reduced to 20 parts by mass. When the characteristics were evaluated, the Tg of the carbon fiber reinforced composite material was 118 ° C., and deformation was observed during demolding.

(Comparative Example 3)
An epoxy resin composition, a dilute solution, a prepreg and a carbon fiber reinforced composite material containing only a phenol novolac type epoxy resin and a bisphenol A type epoxy resin which is solid at 25 ° C. and liquid at 25 ° C. Produced. When the characteristics were evaluated, the Tg of the carbon fiber reinforced composite material was 121 ° C., and deformation was observed during demolding.

(Comparative Example 4)
Using 10 parts by weight of “jER (registered trademark)” 154, 30 parts by weight of “jER (registered trademark)” 1001, and 30 parts by weight of “jER (registered trademark)” 1004, the average epoxy equivalent of bisphenol A type epoxy resin is An epoxy resin composition, a diluted solution thereof, a prepreg, and a carbon fiber reinforced composite material were produced in the same manner as in Example 1 except that 546 was achieved. When the characteristics were evaluated, the gelation time was 235 seconds, and no gelation occurred within 3 minutes. Moreover, since there were many compounding quantities of a solid bisphenol A type epoxy resin at 25 degreeC, the tack of the prepreg was insufficient.

(Comparative Example 5)
An epoxy resin composition, a diluted solution thereof, a prepreg, and a carbon fiber reinforced composite material were produced in the same manner as in Example 1 except that DCMU-99 was used as a curing accelerator. When the characteristics were evaluated, the gelation time was as slow as 287 seconds, the Tg of the carbon fiber reinforced composite material was 87 ° C., and demolding was not possible.

(Comparative Example 6)
An epoxy resin composition, a diluted solution thereof, a prepreg, and a carbon fiber reinforced composite material were prepared in the same manner as in Example 1 except that “Omicure (registered trademark)” 24 was used as a curing accelerator. When the characteristics were evaluated, the Tg of the carbon fiber reinforced composite material was 129 ° C., and deformation was observed during demolding.

Claims (7)

An epoxy resin composition containing an epoxy resin [A], dicyandiamide and its derivative [B], and an imidazole derivative [C] as constituent components, wherein the component [A] is 100 parts by mass of the total epoxy resin, 35 to 70 parts by mass of phenol novolac type epoxy resin, 40 to 20 parts by mass of bisphenol A type epoxy resin solid at 25 ° C., and the average epoxy equivalent of bisphenol A type epoxy resin in all epoxy resins is 400 or less An epoxy resin composition characterized by being. The epoxy resin composition according to claim 1, wherein the component [C] is 2-phenyl-4-methyl-5-hydroxymethylimidazole. The epoxy resin composition according to claim 1 or 2, which does not substantially contain a compound having a weight average molecular weight of 12,000 or more. The prepreg comprised from the epoxy resin composition and carbon fiber of Claims 1-3. A method for producing a prepreg in which carbon fiber is impregnated with the epoxy resin composition according to claim 1, wherein the method for impregnation is a solvent method. A carbon fiber reinforced composite material obtained by curing the epoxy resin composition constituting the prepreg according to claim 4. It is a manufacturing method of the carbon fiber reinforced composite material which shape | molds the prepreg of Claim 4, Comprising: The manufacturing method of the carbon fiber reinforced composite material whose said shaping | molding is press molding.