Molding materials and fiber-reinforced composite materials

Abstract

To provide a fiber-reinforced composite material that possesses excellent impact resistance and tensile properties, and a molding material for obtaining the same. [Solution] A molding material comprising an epoxy resin composition containing the following components [A] and [B], and carbon fibers satisfying the following condition [a]. [A]: Bifunctional aniline epoxy resin [B]: Aliphatic amine curing agent [a]: Surface specific oxygen concentration O / C is 0.02 or higher and less than 0.08.

Description

[Technical Field]

[0001] This invention relates to aerospace components, UAM components, molding materials preferably used in general industrial applications, and fiber-reinforced composite materials using the same. [Background technology]

[0002] Epoxy resins are widely used as matrix resins in fiber-reinforced composite materials, taking advantage of their excellent heat resistance, adhesive properties, and mechanical strength. Fiber-reinforced composite materials are manufactured by integrating reinforcing fibers and matrix resin. Manufacturing methods include lamination molding of prepregs that have been pre-impregnated with reinforcing fibers and matrix resin, and injecting low-viscosity matrix resin into a shaped reinforcing fiber substrate and then thermosetting it. The method using prepregs is widely used in industrial and aerospace fields because it exhibits high mechanical properties, but it has the disadvantage of being time-consuming in the manufacturing process, including the preparation and shaping of the prepregs.

[0003] In recent years, there has been a growing demand for high productivity in structural materials for aircraft, UAMs, automobiles, and other applications. This has created a need for technologies that enable the high-speed production of large composite material components and to obtain fiber-reinforced composite materials with high mechanical properties and heat resistance. Therefore, there is a growing demand for fiber-reinforced composite materials that can be molded using injection molding methods such as resin transfer molding (RTM) and exhibit excellent properties.

[0004] In injection molding, two-component epoxy resin compositions are often used from the viewpoint of moldability. A two-component epoxy resin composition consists of an epoxy main liquid containing epoxy resin as the main component and a curing agent liquid containing a curing agent as the main component, and is obtained by mixing the two liquids immediately before use. In contrast, an epoxy resin composition in which all components, including the main liquid and curing agent, are mixed into one is called a one-component epoxy resin composition.

[0005] When applying fiber-reinforced composite materials to structural material applications such as aircraft and UAM, impact resistance is highly regarded. Generally, in order to improve impact resistance, methods to improve the toughness of the matrix resin are often adopted. At the same time, it is necessary to improve the adhesion between the matrix resin and the reinforcing fibers. To improve the adhesion between the matrix resin and the reinforcing fibers, the reinforcing fibers are often electrochemically treated to introduce functional groups such as hydroxyl groups and carboxyl groups on the surface. However, when the matrix resin cures, it does not react efficiently with the functional groups on the surface of the reinforcing fibers, resulting in the problem that the adhesion between the matrix resin and the reinforcing fibers is not improved and the impact resistance is low. In addition, if the reinforcing fibers are electrochemically treated too much, the strength of the reinforcing fibers decreases, and the tensile properties of the fiber-reinforced composite material also decrease, which is also a problem.

[0006] Patent Document 1 describes a technique for enhancing the toughness of a cured resin by using an epoxy resin composition containing a bisphenol A type epoxy resin and an alicyclic amine curing agent having a specific structure.

[0007] Patent Document 2 describes a technique for enhancing the toughness of a cured resin by blending cellulose nanofibers into an epoxy resin composition.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] The epoxy resin composition described in Patent Document 1 has high toughness in its cured product, but its high reactivity prevents it from forming a good interface with the reinforcing fibers when used as a matrix resin in fiber-reinforced composite materials, resulting in insufficient impact resistance. Furthermore, the tensile properties of the fiber-reinforced composite material were also insufficient. The epoxy resin composition described in Patent Document 2 has high viscosity due to the inclusion of cellulose nanofibers, making it unsuitable for resin injection molding such as RTM. Furthermore, when used as a matrix resin for fiber-reinforced composite materials, its fatigue resistance was insufficient. In addition, there is no suggestion or mention of the tensile properties of the fiber-reinforced composite material.

[0010] The present invention aims to provide a molding material that improves upon the shortcomings of the prior art, and a fiber-reinforced composite material using the same. [Means for solving the problem]

[0011] As a result of diligent research to solve the above problems, the inventors of the present invention have discovered a molding material and a fiber-reinforced composite material having the following configurations, and have completed the present invention. That is, the present invention has the following configurations. [1] A molding material comprising an epoxy resin composition containing the following components [A] and [B], and carbon fibers satisfying the following condition [a]. [A]: Bifunctional aniline epoxy resin [B]: Aliphatic amine curing agent [a]: Surface specific oxygen concentration O / C is 0.02 or higher and less than 0.08. [2] The molding material according to [1], wherein the carbon fibers further satisfy the following condition [b-1]. [b-1]: The cross-sectional shape is substantially circular. [3] The molding material according to [1], wherein the carbon fibers further satisfy the following condition [b-2]. [b-2]: The cross-sectional shape is flattened. [4] Gelation time t when epoxy resin composition is cured at 80°C gel and vitrification time t glass ratio t glass / t gelA molding material according to any of [1] to [3], wherein the ratio is 1.8 or more and 5.0 or less. [5] A molding material according to any one of [1] to [4], wherein the epoxy resin composition contains 10% to 50% by mass of component [A] out of 100% by mass of the total epoxy resin. [6] A molding material according to any one of [1] to [5], wherein the epoxy resin composition contains 1 to 10 parts by mass of core-shell type rubber particles as component [C] per 100 parts by mass of the total epoxy resin. [7] A molding material according to any one of [1] to [6], wherein the epoxy resin composition comprises a trifunctional or more aniline-type epoxy resin as component [D]. A fiber-reinforced composite material obtained by curing any of the molding materials described in [8], [1], to [7]. [9] The fiber-reinforced composite material according to [8], wherein the fiber volume content Vf is 55% or more and 65% or less. [Effects of the Invention]

[0012] According to the present invention, by using an epoxy resin composition containing specific components and a molding material consisting of carbon fibers that meet specific conditions, a fiber-reinforced composite material possessing excellent impact resistance and tensile properties can be obtained. [Modes for carrying out the invention]

[0013] The molding material is one aspect of the present invention. The molding material of the present invention consists of an epoxy resin composition containing specific components and carbon fibers that satisfy specific conditions.

[0014] In the molding material of the present invention, the epoxy resin composition needs to contain a bifunctional aniline-type epoxy resin as component [A]. By containing component [A], the time from the completion of gelation to the completion of vitrification in the curing reaction of the epoxy resin composition can be lengthened. During the time from the completion of gelation to the completion of vitrification, the reaction between the epoxy resin and the surface functional groups of the reinforcing fibers progresses. Therefore, by lengthening this time, the interface between the matrix resin and the reinforcing fibers in the obtained fiber-reinforced composite material can be made good, and a fiber-reinforced composite material excellent in impact resistance can be obtained.

[0015] Here, regarding the time from the completion of gelation to the completion of vitrification in the curing reaction, the value obtained by dividing the vitrification time (t glass ) of the epoxy resin composition at 80°C by the gelation time (t gel ), that is, t glass / t gel can be used as an index for evaluation. The larger t glass / t gel is, the larger the proportion of the time from the completion of gelation to the completion of vitrification in the time required for the curing reaction. Preferably, it is 1.8 or more, more preferably 2.0 or more, and even more preferably 2.2 or more. By this, a fiber-reinforced composite material excellent in impact resistance can be obtained. Also, it is preferable that t glass / t gel is 5.0 or less because the balance between potentiality and rapid curing property is excellent.

[0016] In the present invention, using a dynamic viscoelasticity measuring device, the time until the complex viscosity η * reaches 1.0×10 4 Pa·s is defined as the gelation time (t gel ), and the time until it reaches 5.0×10 6 Pa·s is defined as the vitrification time (t glass ).

[0017] Moreover, since component [A] is a liquid with a low viscosity at room temperature of 25°C, it can be suitably used for injection molding methods such as the RTM method.

[0018] In the molding material of the present invention, the epoxy resin composition preferably contains component [A] in an amount of 10% to 50% by mass, more preferably 20% to 50% by mass, and even more preferably 20% to 40% by mass, of 100% by mass of the total epoxy resin. Within this range, a fiber-reinforced composite material with superior impact resistance can be obtained without impairing heat resistance. Here, "total epoxy resin" refers to all epoxy resins contained in the epoxy resin composition.

[0019] The component [A] is diglycidylaniline or a derivative thereof, and commercially available products that can be used include GAN (diglycidylaniline), GOT (diglycidyl-o-toluidine) (both manufactured by Nippon Kayaku Co., Ltd.), and "TOREP®" A-204E (diglycidyl-p-phenoxyaniline) (manufactured by Toray Fine Chemicals Co., Ltd.).

[0020] In the molding material of the present invention, the epoxy resin composition must contain an aliphatic amine curing agent as component [B]. By including component [B], the epoxy resin composition exhibits excellent reactivity at curing temperatures of 100°C or lower, which can be controlled by hot water. Furthermore, since component [B] is a low-viscosity liquid at room temperature of 25°C, it can be suitably used in injection molding methods such as RTM.

[0021] Furthermore, from the viewpoint of heat resistance and strength of the cured resin, component [B] is preferably an aliphatic amine curing agent having a ring structure in its structure. Specific examples of such aliphatic amine curing agents having a ring structure in their structure include isophorone diamine, 1,3-bisaminomethylcyclohexane, bis(4-aminocyclohexyl)methane, norbornene diamine, 1,2-diaminocyclohexane, 4,4'-methylenebis(2-methylcyclohexylamine), and m-xylenediamine. Among these, isophorone diamine is preferred because it has superior heat resistance and strength.

[0022] Commercially available isophorone diamines such as "VESTAMIN®" IPD (manufactured by Evonik), "Baxxodur®" EC201 (manufactured by BASF), and "Aradur®" 22962 (manufactured by Huntsman) can be used.

[0023] In the molding material of the present invention, the epoxy resin composition may contain an aromatic amine curing agent for the purpose of improving heat resistance or adjusting reactivity, to the extent that the effects of the present invention are not lost.

[0024] In the molding material of the present invention, the epoxy resin composition preferably contains 1 to 10 parts by mass, and more preferably 3 to 6 parts by mass, of core-shell type rubber particles as component [C] per 100 parts by mass of the total epoxy resin. By including component [C] within this range, the fracture toughness can be increased without impairing the elastic modulus of the resin cured product obtained by curing the epoxy resin composition in the molding material of the present invention, and the compression properties and impact resistance of the fiber-reinforced composite material obtained by curing the molding material containing such epoxy resin composition are improved.

[0025] Commercially available products containing such component [C] include "KaneAce®" MX-125, "KaneAce®" MX-150, "KaneAce®" MX-154, "KaneAce®" MX-257, "KaneAce®" MX-267, "KaneAce®" MX-414, "KaneAce®" MX-416, "KaneAce®" MX-451 (all manufactured by Kaneka Corporation), "PARALOID®" EXL-2655, "PARALOID®" EXL-2668 (both manufactured by Dow Chemical Co., Ltd.), etc.

[0026] In the molding material of the present invention, the epoxy resin composition preferably contains a trifunctional or tetrafunctional aniline-type epoxy resin as component [D]. Component [D] is more preferably a trifunctional or tetrafunctional aniline-type epoxy resin. Including such component [D] can further enhance the heat resistance of the cured resin product obtained by curing the epoxy resin composition in the molding material of the present invention.

[0027] Specific examples of trifunctional aniline-type epoxy resins containing such component [D] include aminophenol-type epoxy resins such as triglycidyl-m-aminophenol and triglycidyl-p-aminophenol.

[0028] Examples of commercially available triglycidyl-m-aminophenol or triglycidyl-p-aminophenol include "SumiEpoxy®" ELM100, "SumiEpoxy®" ELM120 (both manufactured by Sumitomo Chemical Co., Ltd.), "Arraldite®" MY0500, "Arraldite®" MY0510, "Arraldite®" MY0600 (all manufactured by Huntsman), and "jER®" 630 (manufactured by Mitsubishi Chemical Corporation).

[0029] Specific examples of tetrafunctional aniline-type epoxy resins of such component [D] include diamine-type epoxy resins such as tetraglycidyldiaminodiphenylmethane, tetraglycidyldiaminodiphenylsulfone, and tetraglycidylxylylenediamine.

[0030] Examples of commercially available tetraglycidyldiaminodiphenylmethane include "SumiEpoxy®" ELM434, "SumiEpoxy®" ELM434VL (both manufactured by Sumitomo Chemical Co., Ltd.), YH434L (manufactured by Nippon Steel Chemical & Material Co., Ltd.), "jER®" 604 (manufactured by Mitsubishi Chemical Corporation), "Arraldite®" MY720, and "Arraldite®" MY721 (both manufactured by Huntsman).

[0031] Examples of commercially available tetraglycidyldiaminodiphenyl sulfone include TG3DAS (manufactured by Konishi Chemical Industry Co., Ltd.).

[0032] Examples of commercially available tetraglycidylxylylenediamine include "TETRAD®"-X and "TETRAD®"-C (both manufactured by Mitsubishi Gas Chemical Company, Inc.).

[0033] In the molding material of the present invention, the epoxy resin composition may use an epoxy resin different from components [A] and [D] as component [E], as long as the effects of the present invention are not lost. Component [E] may also be referred to as "other epoxy resin".

[0034] Examples of component [E] include, for example, bisphenol A type epoxy resin and bisphenol F type epoxy resin. These may be used individually or in combination.

[0035] Examples of commercially available bisphenol A type epoxy resins include "Epotote®" YD-128, "Epotote®" YD-8125 (both manufactured by Nippon Steel Chemical & Material Co., Ltd.), "jER®" 828, and "jER®" 825 (both manufactured by Mitsubishi Chemical Corporation).

[0036] Examples of commercially available bisphenol F type epoxy resins include "EPICLON®" 830 (manufactured by DIC Corporation), "jER®" 806, and "jER®" 807 (all manufactured by Mitsubishi Chemical Corporation).

[0037] In the molding material of the present invention, the carbon fiber must have a surface specific oxygen concentration (O / C) of 0.02 or more and less than 0.08, and preferably 0.02 or more and less than 0.05. Here, the surface specific oxygen concentration is determined by X-ray photoelectron spectroscopy, where O 1s Peak area [O 1s ] and C 1s Peak area [C 1s From ], surface specific oxygen concentration O / C = ([O1s ] / [C 1s This is determined by calculating ]) / (sensitivity correction value). Being within this range results in excellent tensile properties for fiber-reinforced composite materials using such carbon fibers. According to conventional technology, a low O / C ratio can lead to weak adhesion between the epoxy resin and carbon fibers, potentially resulting in low impact resistance. However, the epoxy resin composition in the molding material of the present invention contains the above-mentioned component [A], so that chemical bonds are efficiently formed between the epoxy resin and the carbon fiber surface during the curing reaction, resulting in exceptionally excellent impact resistance. A means for setting the surface specific oxygen concentration O / C within the above range is, for example, to change the amount of electricity during the electrolytic oxidation treatment.

[0038] In the molding material of the present invention, having a substantially circular cross-section of carbon fibers is one preferred embodiment because it allows for a higher fiber volume content Vf in the fiber-reinforced composite material obtained by curing such molding material.

[0039] Here, the cross-sectional shape of a carbon fiber can be indicated by the ratio of the major axis R to the minor axis r (r / R) of the cross-section of a single filament, measured using an optical microscope. The major axis R refers to the diameter of the circumscribed circle of the cross-sectional shape of the single filament, and the minor axis r refers to the diameter of the inscribed circle of the cross-sectional shape of the single filament. A cross-sectional shape is considered substantially circular if r / R is 0.9 or greater, and a cross-sectional shape is considered flat if r / R is less than 0.9.

[0040] According to conventional techniques, increasing the fiber volume content Vf of a fiber-reinforced composite material using injection molding methods such as RTM requires increasing the reinforcing fiber filling rate in the molding material, which may result in longer injection times. However, the epoxy resin composition in the molding material of the present invention contains components [A] and [B], resulting in a low-viscosity liquid state, which allows for injection in a short time without any problems.

[0041] Furthermore, in the molding material of the present invention, having a flattened cross-section of carbon fibers is a preferred embodiment because it increases the surface area of ​​the interface between the matrix resin and carbon fibers in the fiber-reinforced composite material obtained by curing the molding material, thereby further enhancing the impact resistance of the fiber-reinforced composite material.

[0042] According to conventional techniques, when using carbon fibers with a flattened cross-section in injection molding methods such as RTM, the injection time may be prolonged. However, the epoxy resin composition in the molding material of the present invention contains components [A] and [B], resulting in a low-viscosity liquid state, which allows for injection in a short time without any problems.

[0043] Fiber-reinforced composite materials represent one aspect of the present invention. The fiber-reinforced composite material of the present invention is a fiber-reinforced composite material obtained by curing the molded material of the present invention, and is preferred because it possesses excellent impact resistance and tensile properties. Here, impact resistance can be evaluated using post-impact compressive strength (CAI) as an indicator. That is, the higher the CAI, the better the impact resistance. CAI can be measured according to JIS K 7089:1996. Furthermore, tensile properties can be evaluated using tensile fracture strength measured according to ASTM D3039 as an indicator.

[0044] Furthermore, in the fiber-reinforced composite material of the present invention, the fiber volume content Vf is a value measured in accordance with ASTM D3171 (1999), and is preferably 55% or more and less than 65%, which can further increase the specific strength and specific modulus of the fiber-reinforced composite material.

[0045] Because such fiber-reinforced composite materials possess excellent impact resistance and tensile properties, they can be suitably used in a wide range of structural materials, including aircraft and UAM components such as fuselages, main wings, tail wings, control surfaces, fan blades, propeller blades, fairings, cowlings, doors, seats, and interior materials; spacecraft components such as motor cases and main wings; satellite components such as structures and antennas; automobile components such as outer panels, chassis, aerodynamic components, and seats; railway vehicle components such as structures and seats; and ship components such as hulls and seats. [Examples]

[0046] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the examples described.

[0047] The components used in this embodiment and the evaluation method are as follows. Unless otherwise specified, the evaluation was performed with n=1.

[0048] (1) Raw materials for epoxy resin The following raw materials were used to obtain the epoxy resin composition of the example.

[0049] Ingredients [A]: Bifunctional aniline epoxy resin • [A]-1 GAN (Diglycidylaniline, manufactured by Nippon Kayaku Co., Ltd.) • [A]-2 “TOREP (registered trademark)” A-204E (Diglycidyl-p-phenoxyaniline, manufactured by Toray Fine Chemicals Co., Ltd.).

[0050] Ingredients [B]: Aliphatic amines • "VESTAMIN®" IPD (isophorone diamine, manufactured by Evonik).

[0051] Ingredients [C]: Core-shell type rubber particles • "KaneAce (registered trademark)" MX-154 (a mixture of 60% by mass of bisphenol A type epoxy resin (corresponding to component [E]) and 40% by mass of butadiene-based core-shell type rubber particles (corresponding to component [C]), manufactured by Kaneka Corporation).

[0052] Ingredients [D]: Trifunctional or higher aniline-type epoxy resin • [D]-1 “SumiEpoxy (registered trademark)” ELM434 (tetraglycidyldiaminodiphenylmethane, manufactured by Sumitomo Chemical Co., Ltd.) • [D]-2 “jER(registered trademark)” 630 (triglycidyl-p-aminophenol, manufactured by Mitsubishi Chemical Corporation).

[0053] Ingredients [E]: Other epoxy resins • “Epotote (registered trademark)” YD-128 (Bisphenol A type epoxy resin, manufactured by Nippon Steel Chemical & Material Co., Ltd.).

[0054] (2) Preparation of epoxy resin composition A predetermined amount of components [A], [B], [C], [D], and [E] were placed in a stainless steel beaker and mixed in a planetary mixer for 3 minutes to obtain an epoxy resin composition. The composition of the epoxy resin composition is shown in Tables 1 to 4.

[0055] (3) Ratio of gelation time to vitrification time at 80°C glass / t gel Evaluation The epoxy resin composition obtained in (2) Preparation of epoxy resin composition above was placed on the stage of a thermosetting measurement device ATD-1000 (manufactured by Alpha Technologies Co., Ltd.) that had been preheated to 80°C, and dynamic viscoelasticity measurements were performed at a frequency of 1.0 Hz and a strain of 1.0%. At this time, the complex viscosity η * is 1.0 × 10 3 The time it takes to reach Pa·s is the gelation time t gel , 5.0×10 6 The time it takes to reach Pa·s is called the vitrification time t. glass The ratio of gelation time to vitrification time t glass / t gel The result was calculated.

[0056] (4) Evaluation of the glass transition temperature Tg of the cured resin The epoxy resin composition obtained in (2) Preparation of Epoxy Resin Composition above was degassed in a vacuum, and then pre-cured at 80°C for 2 hours in a mold set to a thickness of 2 mm using a 2 mm thick "Teflon®" spacer, followed by curing at 150°C for 4 hours to obtain a 2 mm thick cured resin product. A test piece measuring 12.7 mm in width and 45 mm in length was cut from this cured resin product, and the test piece was set in a solid torsion jig with a chunk distance of 30 mm using a dynamic viscoelasticity measuring device ARES-G2 (manufactured by TA Instruments Inc.). Measurements were taken in the temperature range of 40 to 260°C at a heating rate of 5°C / min, a frequency of 1 Hz, and a strain of 0.08%. In this case, the glass transition temperature Tg was defined as the temperature at the intersection of the tangent line drawn to the glassy state and the tangent line drawn to the glass transition region in the obtained graph of storage modulus and temperature.

[0057] (5) Evaluation of the fracture toughness value K1c of the cured resin The epoxy resin composition obtained in (2) above was degassed in a vacuum, and then pre-cured at 80°C for 2 hours in a mold set to a thickness of 6 mm using a 6 mm thick "Teflon®" spacer, followed by curing at 150°C for 4 hours to obtain a 6 mm thick cured resin product. The obtained cured resin product was processed into the test specimen shape described in ASTM D5045-99, and then the SENB test was performed according to ASTM D5045-99. In this case, the sample size n=16, and the average value was adopted as the K1c value.

[0058] (6) Measurement of the surface specific oxygen concentration (O / C) of carbon fibers The surface specific oxygen concentration (O / C) was determined by X-ray photoelectron spectroscopy according to the following procedure.

[0059] First, the carbon fiber bundles to be measured were cleaned of sizing agents and other contaminants using a solvent, then cut into approximately 5mm lengths, spread out on a stainless steel sample support stand, and measured under the following conditions. • Photoelectron escape angle: 90 degrees ·X-ray source: MgKα1,2 • Vacuum level inside sample chamber: 1 × 10⁻⁶ -8 Torr Next, in order to correct for the peak caused by charging during measurement, C 1S The binding energy value BE of the main peak was adjusted to 284.6 eV.

[0060] C 1s Peak area [C 1s ] is calculated by drawing a baseline line in the range of 282 to 296 eV, O 1s Peak area [O 1s This was determined by drawing a straight baseline in the range of 528 to 540 eV.

[0061] The surface specific oxygen concentration O / C is the above O 1s Peak area [O 1s ], C 1s Peak area [C 1s The ratio of ] and the device-specific sensitivity correction value were used to determine the following formula. O / C=([O 1s ] / [C 1s ]) / (sensitivity correction value) In this study, the ESCA-750 (manufactured by Shimadzu Corporation) was used as the measuring device, and the device's specific sensitivity correction value was set to 2.85. The number of test samples was n=3, and the average value was adopted.

[0062] (7) Measurement of the average fiber diameter of carbon fibers The carbon fiber bundles to be measured were embedded in embedding epoxy resin, polished perpendicular to the fibers using sandpaper, and then observed in cross-section at 1,000x magnification using an optical microscope. Twenty single filaments were randomly selected from the field of view, and their major axis R and minor axis r were measured. The average values ​​of these values ​​were calculated, and the average fiber diameter was defined as {(average value of R) + (average value of r)} / 2. Furthermore, if (average value of r) / (average value of R) was 0.9 or greater, it was judged to be substantially circular, and if it was less than 0.9, it was judged to be flattened.

[0063] (8) Fabrication of carbon fibers Carbon fibers [I] to [IV] were produced by the following manufacturing methods.

[0064] <Carbon fiber[I]> Using a copolymer consisting of 99.4 mol% acrylonitrile and 0.6 mol% methacrylic acid, acrylic precursor fibers with a single fiber fineness of 0.08 tex and 12,000 filaments were obtained by wet-dry spinning.

[0065] This acrylic precursor fiber was heated in air at 240-280°C with a draw ratio of 1.05 to convert it into a flame-resistant fiber. Further heating was performed in a nitrogen atmosphere at a temperature range of 300-900°C with a heating rate of 200°C / min and a draw ratio of 1.10, followed by firing to 1,400°C to promote carbonization. The resulting carbon fiber had a basis weight of 0.50 g / m and a density of 1.80 g / cm³. 3 That was the case.

[0066] Next, an aqueous solution of ammonium bicarbonate with a concentration of 1.0 mol / L was used as the electrolyte, and the carbon fibers were subjected to electrolytic oxidation treatment in a 1 C / g· cell. Subsequently, the carbon fibers after this electrolytic oxidation treatment were washed with water and dried in air at 150°C to obtain carbon fiber [I].

[0067] The carbon fiber [I] had a surface specific oxygen concentration (O / C) of 0.03, an average fiber diameter of 5.5 μm, and a cross-sectional shape with an r / R ratio of 0.95, which was substantially circular.

[0068] <Carbon fiber[II]> Except for using a 2.5 C / g· tank for the electrolytic oxidation treatment, carbon fiber [II] was prepared under the same conditions as carbon fiber [I] to obtain carbon fiber [II].

[0069] The carbon fiber [II] had a surface specific oxygen concentration (O / C) of 0.07, an average fiber diameter of 5.5 μm, and a cross-sectional shape with an r / R ratio of 0.95, which was substantially circular.

[0070] <Carbon fiber[III]> Except for using a 30 C / g· tank for the electrolytic oxidation treatment, carbon fiber [III] was prepared under the same conditions as carbon fiber [I], and carbon fiber [III] was obtained.

[0071] The carbon fiber [III] had a surface specific oxygen concentration (O / C) of 0.18, an average fiber diameter of 5.5 μm, and a cross-sectional shape with an r / R ratio of 0.95, which was substantially circular.

[0072] <Carbon fiber [IV]> The spinning method for the acrylic precursor fibers was changed to a wet spinning method. The single fiber fineness of the obtained acrylic precursor fibers was 0.09 tex. Except for using a 2 C / g· bath for the electrolytic oxidation treatment, carbon fibers [IV] were obtained under the same conditions as carbon fibers [I]. The basis weight of the obtained carbon fibers was 0.50 g / m and the density was 1.80 g / cm³. 3 That was the case.

[0073] The carbon fiber [IV] had a surface specific oxygen concentration (O / C) of 0.04, an average fiber diameter of 5.4 μm, and a flattened cross-sectional shape with an r / R ratio of 0.80.

[0074] (9) Preparation of reinforced fiber substrate The carbon fibers obtained in the above (8) carbon fiber preparation are arranged in one direction and sewn together with stitching thread, resulting in a basis weight of 190 g / m². 2 A reinforced fiber base material was obtained. For the stitching thread, a 56dtex polyester yarn consisting of 24 filaments with a melting point Tma of 260°C was used. The knitted structure was a 1×1 modified tricot knit with a stitch length of 2.3 mm and a gauge length of 5 mm.

[0075] (10) Preparation of nonwoven fabric A nonwoven fabric made of "UBESTA®" 3014U (polyamide 12, manufactured by UBE Corporation) was prepared by the melt-blown method. The basis weight of the obtained nonwoven fabric was 7 g / m². 2 The average fiber diameter was 8 μm.

[0076] (11) Fabrication of fiber-reinforced composite materials and evaluation of tensile fracture strength In a mold having a plate-shaped cavity measuring 400 mm × 400 mm × 1.1 mm, six layers of the reinforcing fiber substrate obtained in (9) above, cut to 395 mm × 395 mm, were stacked with the carbon fiber direction aligned and the nonwoven fabric obtained in (10) above, with one layer in between, and then the mold was clamped using a press device. Next, the temperature was maintained at 80°C, the pressure was reduced to atmospheric pressure -0.1 MPa using a vacuum pump, and the epoxy resin composition obtained in (2) above, which had been preheated to 40°C, was injected at a pressure of 0.2 MPa. After 2 hours, the mold was opened and demolded, and then left to stand in a hot air oven at 150°C for 4 hours to obtain a fiber-reinforced composite material with the target fiber volume content Vf of 58%.

[0077] Furthermore, the tensile breaking strength of the obtained fiber-reinforced composite material was measured according to ASTM D3039. A sample size of n=5 was used, and the average value was adopted.

[0078] (12) Fabrication of fiber-reinforced composite materials and evaluation of post-impact compressive strength (CAI) In a mold having a plate-shaped cavity measuring 400 mm × 400 mm × 4.4 mm, the reinforced fiber substrate obtained in the above (9) preparation of the reinforced fiber substrate was cut to 395 mm × 395 mm, and with the carbon fiber direction set to 0°, 12 sheets of the nonwoven fabric obtained in the above (10) preparation of the nonwoven fabric were layered 3 times, alternating between each layer (45° / 0° / -45° / 90°), and then 12 sheets of the nonwoven fabric were layered 3 times, alternating between each layer (90° / -45° / 0° / 45°), and then the mold was clamped with a press device. Next, the temperature was maintained at 80°C, the pressure was reduced to atmospheric pressure -0.1 MPa using a vacuum pump, and the epoxy resin composition obtained in the above (2) preparation of the epoxy resin composition, which had been preheated to 40°C, was injected at a pressure of 0.2 MPa. After 2 hours, the mold was opened and demolded, and the material was then left to stand in a 150°C hot air oven for 4 hours to obtain a fiber-reinforced composite material with a target fiber volume content Vf of 58%.

[0079] Furthermore, the post-impact compressive strength (CAI) of the obtained fiber-reinforced composite material was measured in accordance with JIS K 7089:1996. A sample size of n=5 was used, and the average value was adopted as the CAI value.

[0080] The following describes the sample preparation method and measurement results for each example.

[0081] (Example 1) An epoxy resin composition was prepared using 10 parts by mass of GAN (component [A]), 82.5 parts of "Epotote®" YD-128 (component [E]), 5 parts by mass of "Kaneace®" MX-157 (component [C] and 7.5 parts by mass of component [E]), and 23.8 parts by mass of "VESTAMIN®" IPD (component [B]) according to the above (2) Preparation of epoxy resin composition.

[0082] Regarding this epoxy resin composition, the ratio of gelation time to vitrification time at 80°C as described in (3) above. glass / t gel According to the evaluation of t glass / t gel When evaluated, it showed a favorable reactivity of 1.95. Furthermore, when the Tg was evaluated according to the evaluation of the glass transition temperature Tg of the cured resin above (4), it showed good heat resistance of 157°C. In addition, when the K1c was evaluated according to the evaluation of the fracture toughness value K1c of the cured resin above (5), it showed 0.95 MPa·m. 0.5 It showed good toughness.

[0083] Regarding the properties of the fiber-reinforced composite material, a fiber-reinforced composite material was fabricated using carbon fibers [I] prepared according to (8) above for carbon fiber production, and according to (11) above for fiber-reinforced composite material production and evaluation of tensile fracture strength. The tensile fracture strength was evaluated and found to be excellent at 1,410 MPa.

[0084] Furthermore, a fiber-reinforced composite material was fabricated according to the above (12) Fabrication of Fiber-Reinforced Composite Material and Evaluation of Post-Impact Compressive Strength (CAI), and the CAI was evaluated, showing an excellent value of 192 MPa.

[0085] (Examples 2-7) The epoxy resin compositions were prepared and evaluated using the same method as in Example 1, except that the resin compositions were changed as shown in Table 1.

[0086] The t of the epoxy resin composition of each example glass / t gel When evaluated, the values ​​were favorable, ranging from 1.91 to 3.05. Furthermore, when the Tg and K1c of the epoxy resin compositions of each example were evaluated, good physical properties were obtained at all levels.

[0087] Furthermore, fiber-reinforced composite materials were fabricated using the same method as in Example 1, and the tensile breaking strength of the fiber-reinforced composite materials of each example was evaluated and found to be excellent, ranging from 1,350 to 1,400 MPa. In addition, the CAI was excellent, ranging from 173 to 205 MPa.

[0088] (Comparative Example 1) The epoxy resin composition was prepared and evaluated in the same manner as in Example 1, except that the resin composition was changed as shown in Table 1. glass / t gel When evaluated, it was found to be 1.71, which falls outside the favorable range.

[0089] Furthermore, when a fiber-reinforced composite material was fabricated using the same method as in Example 1, and its tensile breaking strength was evaluated, it was excellent at 1,390 MPa, but its CAI was inferior at 155 MPa.

[0090] (Examples 8-14) Except for changing the resin composition as shown in Table 2 and replacing carbon fiber with carbon fiber [II], fiber-reinforced composite materials were prepared and evaluated using the same method as in Example 1.

[0091] The tensile breaking strength of the fiber-reinforced composite materials in each example was evaluated and showed excellent values ​​of 1,310 to 1,370 MPa. Furthermore, the CAI (Critical Impact Intensity) was also excellent, ranging from 182 to 213 MPa.

[0092] (Comparative Example 2) Except for changing the resin composition as shown in Table 2, the fiber-reinforced composite material was prepared and evaluated using the same method as in Example 7.

[0093] When the tensile fracture strength of this fiber-reinforced composite material was evaluated, it was excellent at 1,350 MPa, but the CAI (Critical Impact Intensity) was inferior at 165 MPa.

[0094] (Examples 15-21) Fiber-reinforced composite materials were prepared and evaluated using the same method as in Example 1, except that the resin composition was changed as shown in Table 3 and carbon fiber was replaced with carbon fiber [IV].

[0095] The tensile breaking strength of the fiber-reinforced composite materials in each example was evaluated and showed excellent values ​​of 1,320 to 1,380 MPa. Furthermore, the CAI (Critical Impact Intensity) was also excellent, ranging from 176 to 206 MPa.

[0096] (Comparative Example 3) Fiber-reinforced composite materials were prepared and evaluated using the same method as in Example 13, except that the resin composition was changed as shown in Table 3.

[0097] When the tensile fracture strength of this fiber-reinforced composite material was evaluated, it was excellent at 1,360 MPa, but the CAI (Computer-Aided Strength) was inferior at 160 MPa.

[0098] (Comparative Examples 4-11) Fiber-reinforced composite materials were prepared and evaluated using the same method as in Example 1, except that the resin composition was changed as shown in Table 4 and carbon fiber was replaced with carbon fiber [III].

[0099] While the CAI of each comparative example fiber-reinforced composite material was excellent at 180-226 MPa, its tensile breaking strength was inferior at 1,220-1,280 MPa.

[0100] [Table 1]

[0101] [Table 2]

[0102] [Table 3]

[0103] [Table 4] Note that the units for each component in Tables 1 to 4 above are parts by mass. [Industrial applicability]

[0104] The fiber-reinforced composite material obtained by curing the molding material of the present invention possesses excellent impact resistance and tensile properties, making it suitable for use in aerospace components, UAM components, and general industrial structural components.

Claims

1. A molding material comprising an epoxy resin composition containing the following components [A] and [B], and carbon fibers satisfying the following condition [a]. [A]: Bifunctional aniline epoxy resin [B] Aliphatic amine curing agent [a]: Surface specific oxygen concentration O / C is 0.02 or higher and less than 0.

08.

2. The molding material according to claim 1, wherein the carbon fibers further satisfy the following condition [b-1]. [b-1]: The cross-sectional shape is substantially circular.

3. The molding material according to claim 1, wherein the carbon fibers further satisfy the following condition [b-2]. [b-2]: The cross-sectional shape is flattened.

4. Gelation time t when an epoxy resin composition is cured at 80°C ｇｅｌ and vitrification time t ｇｌａｓｓ ratio t ｇｌａｓｓ / t ｇｅｌ A molding material according to any one of claims 1 to 3, wherein the ratio is 1.8 or more and 5.0 or less.

5. The molding material according to any one of claims 1 to 3, wherein the epoxy resin composition contains 10% to 50% by mass of component [A] out of 100% by mass of the total epoxy resin.

6. The molding material according to any one of claims 1 to 3, wherein the epoxy resin composition contains 1 to 10 parts by mass of core-shell type rubber particles as component [C] per 100 parts by mass of the total epoxy resin.

7. The molding material according to any one of claims 1 to 3, wherein the epoxy resin composition comprises a trifunctional or more aniline-type epoxy resin as component [D].

8. A fiber-reinforced composite material obtained by curing the molding material according to any one of claims 1 to 3.

9. The fiber-reinforced composite material according to claim 8, wherein the fiber volume content Vf is 55% or more and 65% or less.

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