Prepreg

Abstract

A prepreg which contains at least the constituents (A) to (D) described below, and has a structure comprising a first layer that is obtained by impregnating the constituent (A) with a first resin composition that contains the constituents (B) and (C), and second layers that are formed on both surfaces of the first layer, while being formed of a second resin composition that contains the constituents (B) to (D). The average fiber diameter of the carbon fibers of the constituent (A) is from 6 μm 9 μm; and the content of a bifunctional amine-type epoxy resin (B1) in a total of 100 parts by mass of the epoxy resin of the constituent (B) is 15 parts by mass or more but less than 40 parts by mass. (A) Carbon fibers (B) An epoxy resin (C) A curing agent (D) Thermoplastic resin particles The present invention provides a prepreg which forms a carbon fiber composite material that has excellent tensile strength, heat resistance and impact resistance, while being suitable as a structural material for airframes; and this prepreg is excellent in terms of impregnation ability during the production and conveyability in an automatic stacking device.

Description

[Technical Field]

[0001] The present invention relates to a prepreg for producing a carbon fiber composite material. [Background technology]

[0002] Fiber-reinforced composite materials, consisting of reinforcing fibers and a matrix resin, have traditionally been used in numerous fields, including aerospace, automobiles, railway vehicles, ships, civil engineering and construction, and sporting goods, due to their excellent mechanical properties, such as strength and rigidity, as well as heat and corrosion resistance, while remaining lightweight. In particular, applications requiring high heat resistance require fiber-reinforced composite materials using continuous reinforcing fibers. A common method is to use prepregs, which are sheet-shaped intermediate substrates in which reinforcing fibers are impregnated with an uncured thermosetting resin composition. In this method, molded fiber-reinforced composite materials are obtained by laminating prepregs and then curing the thermosetting resin composition by heating. Carbon fibers, which have excellent specific strength and specific modulus, are preferred as reinforcing fibers. Thermosetting resins, particularly epoxy resins, are often used as matrix resins because of their strong adhesion to carbon fibers, high heat resistance, high modulus, and low cure shrinkage. In recent years, carbon fiber-reinforced composite materials (CFRPs) have attracted attention as structural materials for aircraft, particularly those requiring lightweight construction, due to their high specific strength and specific rigidity.

[0003] Examples of prepreg lamination methods include the hand layup method, the automated tape layup (ATL) method, and the automated fiber placement (AFP) method, but when manufacturing large composite materials such as those for aircraft, automated lamination methods such as the ATL method and the AFP method, which have superior productivity to the hand layup method, are used (see, for example, Patent Document 1). Among these, the AFP method is a technique for laminating slit tape prepregs (hereinafter simply referred to as slit tape), which are prepregs cut into tape-like shapes in the fiber direction, and is suitable for manufacturing parts with a relatively large number of curved surfaces, such as aircraft fuselages, and has become a method that has been widely used in recent years because it has a good material yield.

[0004] In the AFP method, to improve lamination efficiency, approximately ten to several dozen narrow slit tapes, 3 to 13 mm wide, are passed through a guide roll, converged at a machine head, and laminated onto a substrate. During this process, the guide roll and the slit tape rub against each other, causing resin to adhere to the guide roll, and the unimpregnated fibers contained in the subsequently passing slit tape adhere to the resin on the guide roll and are pulled, resulting in a problem of reduced processability of the slit tape in subsequent processes.

[0005] To prevent the unimpregnated fibers in the slit tape from adhering to the resin on the guide roll and being pulled, it is necessary to reduce the amount of unimpregnated fibers in the slit tape. One possible approach to this is to adjust the viscoelasticity of the matrix resin to improve its ability to impregnate the carbon fibers. One possible way to improve impregnation is to use a large amount of liquid epoxy resin to lower the viscosity of the matrix resin.

[0006] For aircraft structural materials, improved material strength and durability are required, so liquid multifunctional aromatic epoxy resins, which can produce cured resins with high crosslink density, have been used favorably. However, while the extensive use of liquid multifunctional aromatic epoxy resins allows for the design of resins with high elastic modulus and high heat resistance, they tend to result in cured resins with low deformation capacity and low toughness.

[0007] In response to this, methods have been tried, such as blending rubber components or thermoplastic resins with excellent toughness to form a phase-separated structure with the epoxy resin (for example, Patent Document 2). Patent Document 3 also considers a method of improving toughness while lowering viscosity by blending a large amount of thermoplastic resin with a small molecular weight.

[0008] In addition, in Patent Document 4, the impregnation of the matrix resin is improved by increasing the opening property of the carbon fiber bundles during the production of the prepreg. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Special Publication No. 2008-517810 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-139662 [Patent Document 3] International Publication No. 2012 / 051045 [Patent Document 4] Japanese Patent Application Laid-Open No. 2000-309021 Summary of the Invention [Problem to be solved by the invention]

[0010] In the method described in Patent Document 2, the resin viscosity is high, which causes a problem in impregnation into carbon fibers during prepreg production. In addition, in the method described in Patent Document 3, there is a problem in that the viscosity of the matrix resin cannot be sufficiently reduced. In the method described in Patent Document 4, the carbon fiber basis weight is 35 g / m 2 The technology was essentially targeted at the following prepregs and was not suitable for use in prepregs for aircraft applications.

[0011] In view of the above background art, an object of the present invention is to provide a prepreg that provides a carbon fiber composite material excellent in tensile strength, heat resistance, and impact resistance, and that exhibits excellent impregnation properties during prepreg production and excellent transportability of the prepreg in an automatic laminating device. [Means for solving the problem]

[0012] The present invention employs the following means to solve the above problems: A prepreg comprising at least the following components [A] to [D], in which a first layer formed by impregnating the component [A] with a first resin composition containing components [B] and [C] and a second layer formed on both sides of the first layer and made of a second resin composition containing components [B] to [D] are adjacent to each other, in which the average fiber diameter of the carbon fibers of the component [A] is 6 μm or more and 9 μm or less, and the content of the bifunctional amine-type epoxy resin [B1] in the component [B] is 15 parts by mass or more but less than 40 parts by mass out of 100 parts by mass of the total amount of epoxy resin. [A] Carbon fiber [B] Epoxy resin [C] Hardener [D] Thermoplastic resin particles Hereinafter, a resin composition containing at least the components [B] to [D] may be simply referred to as a "resin composition." [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a prepreg that is an intermediate substrate for obtaining CFRP that is excellent in tensile strength, heat resistance, and impact resistance and is suitable as a structural material for aircraft fuselage.Furthermore, it is possible to provide a prepreg that is excellent in the impregnation of carbon fibers with a resin composition during the prepreg manufacturing process and in the transportability of the prepreg. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in more detail below.

[0015] Examples of carbon fibers for the component [A] include polyacrylonitrile-based and pitch-based carbon fibers, and polyacrylonitrile-based carbon fibers (PAN) with particularly high tensile strength are preferably used.

[0016] The average fiber diameter of the carbon fibers of the component [A] used in the present invention is 6 μm or more and 9 μm or less. By setting the average fiber diameter within this range, impregnation of the carbon fibers with the matrix resin during the prepreg production process is facilitated, and the unimpregnated regions in the carbon fiber layer in the prepreg can be effectively reduced. Therefore, during the process of transporting the prepreg using a slitting device or an AFP device, the generation of fluff due to the carbon fibers in the unimpregnated regions can be suppressed, improving the transportability of the prepreg. Furthermore, even during the process of sufficiently impregnating the unimpregnated regions of the carbon fibers in the prepreg during prepreg molding with the matrix resin, the fluidity of the matrix resin can be increased, reducing the risk of voids occurring in the CFRP. This is thought to be because, when the fiber volume fraction is the same, the prepreg of the present invention can have larger flow paths for the matrix resin during the matrix resin impregnation process compared to prepregs using carbon fibers whose average fiber diameter is not within the above range. Furthermore, by setting the average fiber diameter to 9 μm or less, concerns about uneven flame retardancy in the fiber cross-sectional direction are reduced. Therefore, the tensile strength of the resulting CFRP can be increased, and in addition, the drapeability of the resulting prepreg is also excellent. On the other hand, by making the average fiber diameter 6 μm or more, more preferably 7 μm or more, the above-mentioned impregnation is excellent and the tensile strength of the resulting CFRP can also be increased. Note that the average fiber diameter is measured by the following method, and refers to the arithmetic average obtained by measuring the diameter of multiple single fibers.

[0017] The average fiber diameter can be measured from a cross-sectional observation image of the CFRP obtained from the prepreg. When the carbon fibers in the prepreg are continuous fibers aligned in one direction (hereafter referred to as unidirectional prepreg), 16 plies of the unidirectional prepreg are quasi-isotropically laminated in a [+45° / 0° / -45° / 90°]2s configuration, and then heated in an autoclave at a temperature of 180°C for 2 hours under a pressure of 6 kg / cm. 2The CFRP is produced by molding at a temperature increase rate of 1.5°C / min. The resulting CFRP sample is cut perpendicular to the 90° carbon fiber layer (the same direction as the carbon fiber direction in the 0° carbon fiber layer) to obtain a cross section. Prepregs other than unidirectional prepregs, such as prepregs in which the carbon fibers are woven or in which short fibers are uniformly dispersed, can be laminated in any configuration. After producing the CFRP under the same conditions as above, the sample is cut in any direction (perpendicular to the fiber direction in the case of woven prepregs) to obtain a cross section. The resulting cross section is observed using a laser microscope (e.g., VHX-5000, manufactured by Keyence Corporation). Images of the carbon fiber layer (90° layer) perpendicular to the cutting direction of the sample are analyzed using image analysis software (e.g., Image-Pro Premier, manufactured by Nippon Rover Co., Ltd.) to calculate the diameter of the single fiber. One hundred single fibers are selected from the cross-sectional image, and their diameters are measured. The arithmetic mean is calculated to obtain the average fiber diameter.

[0018] The average fiber diameter can also be measured from a cross-sectional observation image of the prepreg itself. Similar to the method for obtaining a cross-section from CFRP described above, the prepreg is cut with a sharp blade in a direction perpendicular to the carbon fibers or in any other direction, and the resulting cross-section is observed under a scanning electron microscope (SEM). The resulting cross-section is analyzed using image analysis software in the same manner as above to calculate the diameter of the individual fibers. The average fiber diameter can be calculated by selecting 100 individual fibers from the cross-sectional image, measuring their diameters, and calculating the arithmetic mean.

[0019] In either case, if 100 single fibers are not enough to obtain the arithmetic mean, 200 or 300 single fibers may be selected to obtain the arithmetic mean of their diameters.

[0020] The form and arrangement of the carbon fibers in the prepreg of the present invention are not limited, and examples thereof include continuous fibers aligned in one direction, single tows, plain weave, satin weave, twill weave, and other woven fabrics, knits, nonwoven fabrics, mats, and braids. Among these, continuous fibers aligned in one direction and woven fabrics such as plain weave, satin weave, and twill weave are preferred. Here, continuous fibers refer to fibers having an average length of 10 mm or more.

[0021] The carbon fiber used in the present invention preferably has a tensile modulus in the range of 200 to 440 GPa. This range is preferable because the rigidity and strength of the CFRP are well balanced at a high level. The lower limit of the modulus is more preferably 230 GPa or more, and even more preferably 250 GPa or more. The upper limit of the modulus is more preferably 400 GPa or less, and even more preferably 370 GPa or less.

[0022] The tensile elongation of the carbon fiber is preferably in the range of 0.8 to 3.0%. If the tensile elongation of the carbon fiber is low, the tensile strength and impact resistance of the resulting CFRP tend to decrease. Furthermore, if the tensile elongation exceeds 3.0%, the tensile modulus of the carbon fiber tends to decrease. The lower limit of the tensile elongation of the carbon fiber is more preferably 1.0% or more, and even more preferably 1.2% or more. The upper limit of the tensile elongation of the carbon fiber is more preferably 2.5% or less, and even more preferably 2.3% or less.

[0023] Here, the tensile modulus and tensile elongation of the carbon fiber are values ​​measured in accordance with JIS R7601 (2006).

[0024] The carbon fiber used in the present invention preferably has a filament count in the range of 1,000 to 50,000 in one fiber bundle. If the filament count is less than 1,000, the fiber arrangement tends to be meandering, which may result in a decrease in strength. From the viewpoint of suitability particularly for aerospace applications, the lower limit of the filament count is more preferably 2,500 or more, and the upper limit is more preferably 40,000 or less.

[0025] The properties and number of the carbon fibers may fall within a range that combines any of the upper limits and any of the lower limits described above.

[0026] The component [B] in the present invention is an epoxy resin, which is the basis for the mechanical properties of CFRP and the handleability of prepreg. The epoxy resin in the present invention means a compound having one or more epoxy groups in one molecule.

[0027] In the present invention, the component [B] includes a difunctional amine-type epoxy resin [B1]. The difunctional amine-type epoxy resin as the component [B1] refers to a glycidylamine-type epoxy resin containing two epoxy groups per molecule. For example, diglycidylaniline, its halogen-substituted, alkyl-substituted, aralkyl-substituted, allyl-substituted, alkoxy-substituted, aralkoxy-substituted, aryloxy-substituted, and hydrogenated products can be used.

[0028] As the diglycidyl aniline, GAN (N,N-diglycidyl aniline, manufactured by Nippon Kayaku Co., Ltd.) and "TOREP (registered trademark)" A-204E (N,N-diglycidyl-p-phenoxyaniline, manufactured by Toray Fine Chemicals Co., Ltd.) can be preferably used. As the diglycidyl toluidine, GOT (N,N-diglycidyl-o-toluidine, manufactured by Nippon Kayaku Co., Ltd.) can be preferably used.

[0029] The bifunctional amine epoxy resin component [B1] reduces the rubber-state modulus of the cured matrix resin. By reducing the rubber-state modulus of the cured matrix resin, the CFRP obtained by curing the prepreg exhibits excellent tensile strength. Conventional methods for reducing the rubber-state modulus include using long-chain epoxies with a high epoxy equivalent (such as bisphenol A epoxy resins or bisphenol F epoxy resins) and epoxies with rigid skeletons, such as dicyclopentadiene epoxy and biphenyl epoxy. The former significantly reduces the modulus and heat resistance of the matrix resin, making it unsuitable for aircraft applications. On the other hand, the latter, while reducing crosslink density through the rigid skeleton within the molecule, exhibits a high modulus and high heat resistance due to the rigid skeleton. Therefore, from the perspective of mechanical properties, they are known to be suitable resins for aircraft applications.

[0030] When comparing the resin impregnation properties of carbon fibers with an average fiber diameter of less than 6 μm, commonly used in aircraft applications, during prepreg preparation, between a resin composition containing a bifunctional amine-type epoxy resin (component [B1]) and a resin composition containing an epoxy resin with a rigid skeleton, such as a dicyclopentadiene-type epoxy resin, there is little difference at the same viscosity, and it is difficult to achieve high resin impregnation with either. However, in the prepreg of the present invention, by combining the carbon fibers with an average fiber diameter of 6 μm to 9 μm (component [A]) and the resin composition containing the component [B1], a synergistic effect is achieved, significantly improving resin impregnation properties during prepreg preparation. Specifically, when carbon fibers with an average fiber diameter of 6 μm or more are impregnated with the resin composition containing [B1] of the present invention and the resin composition containing the rigid skeleton-containing epoxy resin, the resin composition containing [B1] exhibits a greater improvement in impregnation properties when the viscosities are comparable. In particular, from the perspective of improving impregnation properties, it is preferable that the carbon fibers of component [B] have an average fiber diameter of 7 μm or more.

[0031] The reason why the resin composition containing the component [B1] has good impregnation properties is presumably due to the fact that the molecular structure of the component [B1] is such that intermolecular interactions are unlikely to occur and that it has good affinity with the surface environment of the carbon fiber. In the case of carbon fibers with a diameter of less than 6 μm, which cannot ensure large flow paths for the matrix resin during the matrix resin impregnation process during prepreg production, impregnation with the resin is difficult in the first place, so there is no difference in impregnation properties regardless of the resin composition used. However, in the case of carbon fibers with an average fiber diameter of 6 μm or more, which can ensure large flow paths, it is presumed that when a resin composition containing the component [B1] is used as the matrix resin, the resin is more easily impregnated into the finer details.

[0032] In the present invention, the content of the difunctional amine-type epoxy resin as component [B1] is 15 parts by mass or more and less than 40 parts by mass per 100 parts by mass of the total amount of the epoxy resin as component [B]. By setting the content of component [B] within this range, it is possible to achieve a balance between the mechanical properties such as tensile strength and the heat resistance of the resulting CFRP. The content of the difunctional amine-type epoxy resin as component [B1] is more preferably 25 parts by mass or more and 35 parts by mass or less per 100 parts by mass of the total amount of the epoxy resin as component [B].

[0033] In the resin composition of the present invention, the epoxy resin as component [B] may contain an epoxy resin other than the component [B1]. Examples of such epoxy resins include, but are not limited to, bisphenol-type epoxy resins such as bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, bisphenol AD-type epoxy resins, and bisphenol S-type epoxy resins; brominated epoxy resins such as tetrabromobisphenol A diglycidyl ether; and trifunctional or higher polyfunctional glycidylamine-type epoxy resins.

[0034] Here, the term "polyfunctional glycidylamine epoxy resin" refers to a glycidylamine epoxy resin containing three or more epoxy groups in one epoxy resin molecule. Examples include tetraglycidyldiaminodiphenylmethane, triglycidylaminophenol, tetraglycidylxylylenediamine, and their halogen-substituted, alkyl-substituted, aralkyl-substituted, allyl-substituted, alkoxy-substituted, aralkoxy-substituted, aryloxy-substituted, and hydrogenated products.

[0035] Examples of tetraglycidyldiaminodiphenylmethane that can be used include Sumiepoxy (registered trademark) ELM434 (manufactured by Sumitomo Chemical Co., Ltd.), YH434L (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.), jER (registered trademark) 604 (manufactured by Mitsubishi Chemical Corporation), and Araldite (registered trademark) MY720 and MY721 (manufactured by Huntsman Advanced Materials). Examples of triglycidylaminophenol and its alkyl-substituted derivatives that can be used include Sumiepoxy (registered trademark) ELM100 and ELM120 (manufactured by Sumitomo Chemical Co., Ltd.), Araldite (registered trademark) MY0500, MY0510, and MY0600 (manufactured by Huntsman Advanced Materials), and jER (registered trademark) 630 (manufactured by Mitsubishi Chemical Corporation). As tetraglycidylxylylenediamine and its hydrogenated products, "TETRAD (registered trademark)"-X, "TETRAD (registered trademark)"-C (manufactured by Mitsubishi Gas Chemical Company, Inc.), etc. can be used.

[0036] When a trifunctional or higher polyfunctional glycidylamine epoxy resin is used as the epoxy resin of component [B] of the present invention, the content is preferably 30 to 85 parts by mass per 100 parts by mass of the total amount of epoxy resins of component [B]. By setting the content within this range, the heat resistance, impact resistance, and tensile strength of the resulting CFRP can be balanced.

[0037] The epoxy resin of component [B] of the present invention may contain an epoxy resin that is solid at 25°C. However, from the viewpoint of impregnation properties, the content thereof is preferably 5 parts by mass or less when the total amount of the epoxy resin of component [B] is taken as 100 parts by mass.

[0038] The curing agent, which is the component [C] of the present invention, may be any compound having an active group capable of reacting with the epoxy resin, such as an amino group or an acid anhydride group.

[0039] The component [C] is preferably an aromatic amine compound, and from the viewpoints of heat resistance and mechanical properties, an aromatic amine compound having 1 to 4 phenyl groups in the molecule is preferred. Furthermore, since imparting flexibility to the molecular skeleton improves the resin's elastic modulus and contributes to improved mechanical properties, an aromatic amine compound in which at least one phenyl group contained in the skeleton of the curing agent is a phenyl group having an amino group at the ortho- or meta-position is preferred. Furthermore, from the viewpoint of heat resistance, an aromatic polyamine compound in which two or more phenyl groups have an amino group at the para-position is preferably used. Specific examples of such aromatic amines include metaphenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, metaxylylenediamine, (p-phenylenemethylene)dianiline, and various derivatives such as alkyl-substituted derivatives of these, as well as isomers with different amino group positions.

[0040] Among these, when used in structural components of aircraft and the like, 4,4'-diaminodiphenyl sulfone or 3,3'-diaminodiphenyl sulfone is preferred from the viewpoint of obtaining a cured product that has excellent heat resistance and elastic modulus, and furthermore, exhibits little decrease in heat resistance due to linear expansion coefficient and moisture absorption. These aromatic amine compounds may be used alone or in combination of two or more. Furthermore, when mixed with other components, the aromatic amine compounds may be in either powder or liquid form, or a mixture of both powder and liquid aromatic amine compounds may be used.

[0041] Commercially available aromatic amine compounds include Seikacure-S (manufactured by Seika Corporation), MDA-220 (manufactured by Mitsui Chemicals, Inc.), "LONZACURE (registered trademark)" M-DIPA (manufactured by Lonza), and "LONZACURE (registered trademark)" M-MIPA (manufactured by Lonza) and 3,3'-DAS (manufactured by Mitsui Chemicals, Inc.).

[0042] When an aromatic amine compound is used as component [C], its content can be expressed in terms of heat resistance and mechanical properties as the ratio of the total number of active hydrogens (H) in the aromatic amine to the total number of epoxy groups (E) in the epoxy resin (component [B]), known as H / E. An H / E ratio of 0.6 or higher is preferred because it achieves a sufficient degree of curing and improves the heat resistance of the cured product. On the other hand, an H / E ratio of 1.3 or lower is preferred because it reduces the unreacted portion of the curing agent and improves heat resistance.

[0043] In the present invention, a curing accelerator may be further contained within a range that does not impair the heat resistance and thermal stability of the resin composition. Examples of curing accelerators include tertiary amines, Lewis acid complexes, onium salts, imidazole compounds, urea compounds, hydrazide compounds, and sulfonium salts. The content of the curing accelerator needs to be adjusted appropriately depending on the type used, but is 10 parts by mass or less, preferably 5 parts by mass or less, per 100 parts by mass of the total epoxy resin. When the curing accelerator is contained within this range, temperature unevenness is less likely to occur when molding the CFRP, which is preferable.

[0044] The component [D] of the present invention is thermoplastic resin particles. The inclusion of thermoplastic resin particles can improve the Mode II interlaminar toughness and impact resistance of the resulting CFRP. There are no particular limitations on the thermoplastic resin used for the thermoplastic resin particles as long as it achieves the effects of the present invention. However, from the viewpoint of imparting stable adhesive strength and impact resistance to the resulting CFRP, it is preferable for the thermoplastic resin to retain its shape in the epoxy resin composition. Here, "retaining its shape" means that when an epoxy resin composition containing dispersed thermoplastic resin particles [D] is heat-cured, the thermoplastic resin particles [D] do not substantially dissolve in the epoxy resin composition. "Substantially not dissolving" refers to, for example, a state in which, when the thermoplastic resin particles [D] in the cured resin are observed using a transmission electron microscope, the size of the thermoplastic resin particles [D] does not substantially shrink from the size before heat-curing, and a clear interface can be observed between the thermoplastic resin particles [D] and the matrix resin. The thermoplastic resin used for the thermoplastic resin particles [D] is preferably a resin selected from polyamide, polyamideimide, and polyphenylene ether. Among polyamides, polyamide 12, polyamide 11, polyamide 6, polyamide 66, polyamide 6 / 12 copolymers, polyamides formed into a semi-IPN (polymer interpenetrating network) structure in the epoxy compound described in Example 1 of JP-A-1-104624 (semi-IPN polyamides), and polyamide copolymers having an alicyclic ring such as cyclohexane in the molecular skeleton are preferably used. The shape of the thermoplastic resin particles may be spherical, non-spherical, or porous, but spherical thermoplastic resin particles are preferred because they do not reduce the flow properties of the resin composition and therefore have excellent viscoelasticity, are free of stress concentration points, and provide high impact resistance. Although the thermoplastic resin particles are not spherical, examples that can be used include Orgasol (registered trademark) 1002D, 2001UD, 2001EXD, 2002D, 3202D, 3501D, and 3502D (all manufactured by Arkema), Grilamid (registered trademark) TR90 (manufactured by Ms. Welke), and TROGAMID (registered trademark) CX7323, CX9701, and CX9704 (manufactured by Evonik).These thermoplastic resin particles may be used alone or in combination. Commercially available polyetherimide products include "Ultem (registered trademark)" 1000, "Ultem (registered trademark)" 1010, and "Ultem (registered trademark)" 1040 (all manufactured by SABIC Innovative Plastics).

[0045] In the present invention, the resin composition may contain a thermoplastic resin other than the thermoplastic resin particles of the component [D]. The thermoplastic resin other than the thermoplastic resin particles of the component [D] controls the fluidity of the matrix resin when the prepreg is heat-cured, and improves the impact resistance and mode I interlaminar toughness (G IC ) is included for the purpose of improving the adhesiveness between the matrix resin and the carbon fiber. In this case, the thermoplastic resin is preferably soluble in the epoxy resin of component [B]. It is preferable to use a thermoplastic resin having a hydrogen-bonding functional group, as this is expected to improve the adhesiveness between the matrix resin and the carbon fiber. Examples of the hydrogen-bonding functional group include an alcoholic hydroxyl group, an amide bond, a sulfonyl group, a carboxyl group, and a carbonyl group.

[0046] In the present invention, the term "soluble in epoxy resin" refers to a temperature range in which a homogeneous phase is formed when the thermoplastic resin is mixed with the epoxy resin of component [B] and heated and stirred. The temperature range in which a homogeneous phase is formed can be confirmed by mixing the thermoplastic resin with the epoxy resin and heating and stirring for several hours, e.g., about 2 hours, at a temperature below the glass transition temperature of the thermoplastic resin. Forming a homogeneous phase refers to a state in which no phase separation is visible to the naked eye. Furthermore, improved compatibility suppresses the formation of a phase-separated structure between the epoxy resin and the thermoplastic resin during the curing process, resulting in CFRP of consistent quality regardless of the curing conditions. Furthermore, this broadens the range of possible curing conditions and also suppresses structural differences between different locations, even when molding thick products, improving quality stability.

[0047] Examples of thermoplastic resins having an alcoholic hydroxyl group include polyvinyl acetal resins such as polyvinyl formal and polyvinyl butyral; polyvinyl alcohol; and phenoxy resins.

[0048] Examples of thermoplastic resins having an amide bond include polyamide, polyimide, polyamideimide, and polyvinylpyrrolidone.

[0049] Examples of the thermoplastic resin having a sulfonyl group include polysulfone and polyethersulfone.

[0050] Examples of thermoplastic resins having a carboxyl group include polyester, polyamide, polyamideimide, etc. The carboxyl group may be present in either the main chain or the terminal, or both.

[0051] Examples of the thermoplastic resin having a carbonyl group include aromatic polyether ketones such as polyether ether ketones.

[0052] Of the above, polyamide, polyimide and polysulfone may further have a functional group such as an ether bond or a carbonyl group in the main chain. Furthermore, polyamide may have a substituent on the nitrogen atom of the amide group.

[0053] Commercially available thermoplastic resins that are soluble in epoxy resins and have hydrogen-bonding functional groups include polyvinyl acetal resins such as "Mowital (registered trademark)" (manufactured by Kuraray Co., Ltd.) and "Vinylec (registered trademark)" K (manufactured by JNC Corporation); polyvinyl alcohol resins such as "Denka Poval (registered trademark)" (manufactured by Denka Co., Ltd.); polyamide resins such as "Macromelt (registered trademark)" (manufactured by Henkel) and "Amilan (registered trademark)" CM4000 (manufactured by Toray Industries, Inc.); polyimides such as "Ultem (registered trademark)" (manufactured by SABIC Innovative Plastics), "Aurum (registered trademark)" (manufactured by Mitsui Chemicals, Inc.), and "Vespel (registered trademark)" (manufactured by DuPont); polyether ether ketone polymers such as "Victrex (registered trademark)" (manufactured by Victrex); and polysulfones such as "UDEL (registered trademark)" (manufactured by Solvay Advanced Materials). Polymers Co., Ltd.); polyvinylpyrrolidone such as "Ruviscol (registered trademark)" (BASF).

[0054] Another suitable example of the thermoplastic resin soluble in the epoxy resin is a thermoplastic resin having a polyaryl ether skeleton. Use of the thermoplastic resin having a polyaryl ether skeleton makes it possible to control the tackiness of the resulting prepreg, control the fluidity of the matrix resin when the prepreg is heat-cured, and impart toughness to the resulting carbon fiber-reinforced composite material without impairing its heat resistance or elastic modulus.

[0055] Examples of thermoplastic resins having a polyaryl ether skeleton include polysulfone, polyphenylsulfone, polyethersulfone, polyetherimide, polyphenylene ether, polyetheretherketone, polyetherethersulfone, etc. These thermoplastic resins having a polyaryl ether skeleton may be used alone or in combination of two or more.

[0056] Among these, polysulfone or polyethersulfone (hereinafter sometimes referred to as PES) is preferred from the viewpoints of solubility in epoxy resin, heat resistance, solvent resistance, and toughness.

[0057] PES has ether bonds and sulfone bonds in the main chain, which control the tackiness of the prepreg, control the fluidity of the matrix resin when the prepreg is heat-cured, and are less likely to impair the heat resistance and elastic modulus of the resulting CFRP, and improve tensile strength, impact resistance, and Mode I interlaminar toughness (G IC ) and is included for the purpose of improving the

[0058] Commercially available PES products include "Virantage (registered trademark)" VW-10700RFP (weight average molecular weight 21,000 g / mol) and "Virantage (registered trademark)" VW-10200RFP (weight average molecular weight 46,500 g / mol) (both manufactured by Solvay Advanced Polymers, Inc.). Another product having a weight average molecular weight similar to that of "Virantage (registered trademark)" VW-10200RFP is "Sumikaexcel (registered trademark)" PES5003P (manufactured by Sumitomo Chemical Co., Ltd.).

[0059] The content of the thermoplastic resin other than component [D] is preferably 5 parts by mass or more relative to 100 parts by mass of the total epoxy resin of component [B], thereby improving the mechanical properties of the CFRP, such as tensile strength, impact resistance, and mode I interlaminar toughness. On the other hand, it is preferable to set the content of the thermoplastic resin other than component [D] to 40 parts by mass or less, since this can prevent the resin composition from becoming too viscous and improve process stability in processes such as resin composition production, resin film formation, and prepreg formation. This is also preferable in terms of the handleability of the prepreg, such as tackiness.

[0060] The resin composition used in the prepreg of the present invention may contain coupling agents; inorganic fillers such as silica gel, carbon black, clay, carbon nanotubes, carbon particles, and metal powder; and flame retardants such as red phosphorus and phosphate esters, as long as the effects of the present invention are not impaired. In particular, the inclusion of conductive particles such as carbon particles as component [E] dramatically improves the conductivity of CFRP, making it preferable in terms of lightning resistance in aircraft applications. The amount of conductive particles in component [E] is preferably 1 part by mass or more per 100 parts by mass of the total epoxy resin in component [B]. By maintaining the amount in this range, the resulting CFRP has excellent conductivity. The upper limit of the amount is preferably 30 parts by mass or less. The conductivity of CFRP can be determined as volume resistivity in the thickness direction, and is preferably 300 Ωcm or less, more preferably 35 Ωcm or less, and even more preferably 20 Ωcm or less. When conductive particles are used, a method of incorporating conductive particles, such as that described in International Publication No. 2012 / 124450, can be used. The particle size of the carbon particles can be measured by applying a light scattering method using, for example, Partica LA-950V2 manufactured by Horiba Ltd. or MT3300II manufactured by Microtrac.

[0061] The heat resistance of the CFRP obtained by curing the prepreg of the present invention depends on the glass transition temperature of the cured resin obtained by curing the resin composition. To obtain a CFRP with excellent heat resistance, the glass transition temperature of the cured resin obtained by curing the resin composition used in the prepreg at 180°C for 2 hours (120 minutes) is preferably 180°C or higher, and more preferably 185°C or higher. A glass transition temperature of 180°C or higher ensures excellent mechanical properties of the CFRP under high-temperature, high-humidity conditions. The glass transition temperature here refers to the temperature at the inflection point of the storage modulus G' obtained by measuring a cured resin composition plate cut to a specified size using a dynamic viscoelasticity measuring device (e.g., ARES G2, manufactured by TA Instruments) at a heating rate of 5°C / min and a frequency of 1 Hz.

[0062] To increase the glass transition temperature of the cured resin, it is preferable to use a trifunctional or higher polyfunctional glycidylamine-type epoxy resin as the epoxy resin component [B]. In particular, it is preferable to contain 50 parts by mass or more of a trifunctional or higher polyfunctional glycidylamine-type epoxy resin per 100 parts by mass of the total epoxy resin component [B], since this makes it easier to keep the glass transition temperature of the cured resin within the above range. Furthermore, as mentioned above, it is preferable to use diaminodiphenyl sulfone as the component [C], since this can increase the glass transition temperature of the cured resin and makes it easier to keep the glass transition temperature of the cured resin within the above range. 4,4'-Diaminodiphenyl sulfone is particularly preferable.

[0063] The prepreg of the present invention has a carbon fiber mass per unit area (weight per unit area) of 70 to 1,000 g / m 2 It is preferable that the mass of the carbon fiber is 70 g / m 2 When the carbon fiber mass is 250 g / m or more, the weight per unit area of ​​the carbon fiber in the width direction of the obtained prepreg tends to be uniform even when there is unevenness in the degree of opening of the carbon fiber bundles. 2 If the thickness is more than this, the number of laminated sheets required to obtain a predetermined thickness during CFRP molding is reduced, which is more preferable since the lamination efficiency during CFRP molding is increased.

[0064] The mass ratio of carbon fiber in the prepreg is preferably 50 mass % or more and 80 mass % or less, since this allows for both the light weight of the CFRP and the reduction of voids due to molding.

[0065] The prepreg of the present invention can be produced by various known methods, such as a hot melt method in which an epoxy resin film is laid on the surface of a carbon fiber sheet in which carbon fiber bundles are arranged in a sheet form, and the film is impregnated under pressure and heat.

[0066] As a method for producing the prepreg of the present invention by the hot melt method, a multi-stage impregnation hot melt method is preferred, in which the resin composition is impregnated in multiple stages by heating and pressurizing the carbon fibers of the component [A] from both sides or one side. In the multi-stage impregnation hot melt method, the number of times the resin composition is impregnated into the carbon fibers of the component [A] is not limited, but the more times it is impregnated, the higher the production costs. Therefore, a so-called two-stage impregnation hot melt method is preferably used, in which the resin composition is impregnated in two stages by heating and pressurizing the carbon fibers of the component [A] from both sides or one side.

[0067] When using the two-stage impregnation hot melt method, first, a resin film made of a first resin composition is impregnated from both sides of the carbon fibers to obtain a primary prepreg. Then, a resin film made of a second resin composition is impregnated from both sides of the primary prepreg to obtain a prepreg. When the resin film made of the second resin composition is impregnated into the primary prepreg, the unimpregnated carbon fibers in the prepreg are pressed through the resin film, which can result in variations in the arrangement of the carbon fibers in the unimpregnated regions. When molding the resulting prepreg, areas where the carbon fibers are sparsely arranged can form wide flow paths, which can increase the fluidity of the matrix resin during molding. From this perspective, the two-stage impregnation hot melt method is also preferred.

[0068] The coefficient of variation of the average distance between carbon fibers in the first layer of the CFRP obtained by curing the prepreg of the present invention is preferably 16% or more and less than 50%. It is more preferably 16% or more and 30% or less, and even more preferably 16% or more and 25% or less. A coefficient of variation of 16% or more is preferable because it can increase the fluidity of the matrix resin during molding. A coefficient of variation of less than 50% is preferable because it makes the carbon fiber layer less likely to crack and ensures impact resistance. Furthermore, cracks in the carbon fiber layer refer to the presence of a portion where the second layer on one side of the first layer is continuous with the second layer on the other side in a portion of the carbon fiber layer with few carbon fibers.

[0069] The coefficient of variation of the average distance between carbon fibers is measured by the following method: In the case of unidirectional prepreg, 16 plies of unidirectional prepreg are quasi-isotropically laminated in a [+45° / 0° / -45° / 90°] 2s configuration, and then heated in an autoclave at a temperature of 180°C for 2 hours under a pressure of 6 kg / cm. 2 The CFRP is produced by molding at a temperature rise rate of 1.5°C / min. Prepregs other than unidirectional prepregs may be laminated in any configuration, and the CFRP is produced under the same conditions as above. The obtained CFRP sample is cut in the 0° direction to obtain a cross section. Using a laser microscope (e.g., VHX-5000, manufactured by Keyence Corporation), the carbon fiber layer (90° layer) perpendicular to the cutting direction of the sample is observed at a magnification of 200x and a field of view of 100 μm × 150 μm. For example, in the case of a prepreg using carbon fibers with an average fiber diameter of 7 μm, approximately 450 carbon fibers are included in the cross-sectional image within this field of view. Using image analysis software (e.g., Image-Pro Premier, manufactured by Nippon Rover Co., Ltd.), the distance between the carbon fiber and the closest carbon fiber is determined as the inter-carbon fiber distance. This distance is measured for all carbon fibers included in the field of view, and the average value and coefficient of variation are calculated.

[0070] To ensure that the coefficient of variation of the average distance between carbon fibers in the first layer of the CFRP obtained by curing the prepreg of the present invention falls within the above range, it is preferable to use carbon fibers with an average fiber diameter of 6 μm or more and 9 μm or less as component [A]. If the average fiber diameter of the carbon fibers is less than 6 μm, sufficient resin flow may not occur during the production of the prepreg, and the coefficient of variation of the average distance between carbon fibers may not fall within the above range. Furthermore, to ensure that the coefficient of variation of the average distance between carbon fibers falls within the above range, it is preferable that the minimum viscosity of the first resin composition is 1.0 Pa s or less. The minimum viscosity of the first resin composition will be described later.

[0071] The prepreg produced as described above has a structure in which a first layer is formed by impregnating carbon fibers of component [A] with a first resin composition containing components [B] and [C] but not component [D], and second layers are formed adjacent to both sides of the first layer, each composed of a second resin composition containing components [B] to [D]. Using a multi-stage method, as described above, allows carbon fibers to be impregnated with different resin compositions in stages, thereby imparting different viscoelastic properties to the first resin composition constituting the first layer and the second resin composition constituting the second layer. This makes it possible to impart to the prepreg the properties required for impregnation during prepreg production and prepreg molding, the tackiness of the resulting prepreg, and the processability of the prepreg in an automated lamination machine, without being limited by the type of components of the resin composition or the amount of each component, which is industrially advantageous.

[0072] The width of the prepreg is not particularly limited; it may be a wide width of approximately several tens of centimeters to 2 meters, or it may be in the form of a tape with a width of several millimeters to several tens of millimeters. The width can be selected depending on the application. In recent years, to streamline the prepreg lamination process, machines called ATL and AFP, which automatically laminate narrow-width prepregs or prepreg tapes, have become widely used, and it is preferable to select a width that is compatible with these machines. Narrow-width prepregs with widths of approximately 7.5 cm, 15 cm, or 30 cm are often used in ATL, while prepreg tapes of approximately 3 mm to 25 mm are often used in AFP. There are no particular limitations on the method for obtaining prepregs of the desired width; a method of producing wide-width prepregs of approximately 1 m to 2 m and then slitting them to narrow widths can be used. Furthermore, to simplify or eliminate the slitting process, prepreg tapes, such as towpregs, can also be produced to the desired width from the beginning.

[0073] When a prepreg tape is transported in a slitting device or an AFP device, it may pass over small-diameter rolls or over folded-back locations where the prepreg tape is significantly bent. If the prepreg tape is too stiff, it may not be able to conform to the shape of the tape at these significantly bent locations, resulting in problems such as the prepreg tape deviating from the desired transport path or breaking at the splice. Here, "splicing" refers to joining multiple prepreg tapes together in the longitudinal direction by crimping or other methods. For this reason, it is preferable that the prepreg be soft, i.e., have good drapeability. While the prepreg can be softened by adjusting the modulus of elasticity of the carbon fiber or the type of sizing agent used, in the present invention, this is achieved by using component [A] carbon fibers with an average fiber diameter of 6 μm to 9 μm. If the average fiber diameter is too large, the prepreg's rigidity increases and its drapeability deteriorates. If the average fiber diameter of the carbon fibers used in the prepreg is 9 μm or less, the prepreg has good shape conformability and can reduce problems such as breakage at splices. The average fiber diameter of the carbon fibers is more preferably 7 μm or more and 8 μm or less.

[0074] Furthermore, prepregs using the bifunctional amine-type epoxy resin component [B1] exhibit superior drapeability compared to prepregs using epoxy resins with rigid skeletons, such as dicyclopentadiene-type epoxy resins. The drapeability of prepregs is believed to be influenced by the storage modulus of the matrix resin impregnated into the first layer. When rigid-skeleton epoxy is used, the rigid skeleton portions interact with each other, resulting in a high storage modulus. However, when component [B1] is used, the intermolecular interactions are weak, resulting in a low storage modulus, presumably resulting in better drapeability.

[0075] The storage modulus G' of the first resin composition at 25°C measured at an angular frequency of 3.14 rad / s is 5.0 × 10 3 Pa or more 5.0×10 4 Pa or less, and 3 Over 3.0 x 10 4It is more preferable that the G' at 25°C of the first resin composition is within the above range, the first resin composition exhibits excellent drapeability while satisfying high impregnation properties, and therefore the handling properties in an automatic lamination device are particularly excellent.

[0076] In order to set the storage modulus G' of the first resin composition within the above range, it is preferable to reduce the amount of epoxy resin that is solid at 25°C in the first resin composition and to incorporate a thermoplastic resin that is soluble in the epoxy resin. The amount of the epoxy resin that is solid at 25°C in the first resin composition is preferably 10 parts by mass or less per 100 parts by mass of the total amount of epoxy resins as component [B] in the first resin composition. The amount of the thermoplastic resin that is soluble in the epoxy resin is preferably in the range of 6 to 12 parts by mass per 100 parts by mass of the total amount of the first resin composition.

[0077] The drapeability of a prepreg is measured using the deflection angle, which can be measured using the following method. One end of a prepreg cut to a width of 12.7 mm and a length of 400 mm is fixed to a horizontal table, with the prepreg extending 200 mm beyond the edge of the table, and the deflection angle of the prepreg is measured 10 minutes later. The deflection angle of the prepreg is then measured by the angle formed by the horizontal extension of the prepreg fixed to the table and the line connecting the free end of the prepreg and the base of the extending part of the prepreg.

[0078] In this case, if the measured deflection angle is preferably in the range of 10° or more and 17° or less, and more preferably 12° or more and 16° or less, the prepreg has good shape conformability and can reduce problems such as breakage at the splice portion of the prepreg tape.

[0079] In the prepreg of the present invention, the tackiness of the prepreg is reduced, which is preferable because it is possible to sufficiently reduce adhesion of the resin composition in the prepreg to guide rolls when the prepreg is transported.

[0080] The tackiness is measured by the tack value between the prepreg and the metal, as determined by the following method. The tack value between the prepreg and the metal can be determined by pressing a 10 mm square aluminum plate attached to the weight of a tack tester (e.g., a handy tack tester manufactured by Imada Co., Ltd.) with double-sided tape against the surface of the prepreg for 0.1 seconds with a load of 0.5 kg, and then measuring the force applied when the aluminum plate is pulled up at a speed of 100 mm / min. If the tack value is 0.5 N or less, the resin adhesion to the guide roll during transport in the AFP device is small, resulting in excellent transportability. A tack value of 0.1 N or more and 0.4 N or less is even more preferable.

[0081] In order to set the tack value within the above range, the storage modulus G' of the second resin composition present in the surface layer of the prepreg at 20°C measured at an angular frequency of 77 rad / s must be 2.0 × 10 7 It is preferable that G' is 2.0×10 Pa or more. 7 Pa or more 2.0×10 8 Pa or less. The above G' is 2.0 × 10 7 When the second resin composition has a G' value of 2.0 × 10 Pa or more, the resin composition is less likely to deform when it comes into contact with the guide roll during transport, the contact area with the guide roll does not increase, cleaning frequency is reduced, and productivity is improved, which is preferable. 8 If the pressure is less than or equal to 100 Pa, resin powder is less likely to be generated on the surface of the prepreg when it rubs against a guide roll during transport, which is preferable because cleaning frequency can be reduced.

[0082] In order to set the storage modulus G' of the second resin composition within the above range, it is preferable to blend a thermoplastic resin soluble in epoxy resin into the second resin composition. The blending amount of the thermoplastic resin soluble in epoxy resin is preferably 14 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the total amount of the second resin composition.

[0083] The prepreg of the present invention preferably has an impregnation rate measured using the water pick-up (WPU) method of 5.0% or less, more preferably 3.0% or less, and even more preferably 2.0% or less. When the impregnation rate measured using the WPU method is 5.0% or less, the amount of carbon fiber in the unimpregnated regions of the prepreg to which the resin composition does not adhere can be reduced, and adhesion of fluff to the blade during slitting and to the guide rolls during prepreg transport in AFP can be suppressed.

[0084] The impregnation rate referred to here is measured using the WPU method as follows. Five 100 mm x 100 mm squares of prepreg are cut at equal intervals across the width of the prepreg, with two sides at 0° and 90° angles, to prepare test pieces. The mass W1 of each test piece is measured. The test piece is positioned so that the fibers contained in the test piece are oriented vertically, and an area 5 mm from the end (i.e., a 100 mm x 5 mm area) is immersed in water for 5 minutes. After wiping off any moisture adhering to the surface of the test piece with a cloth or the like, the mass W2 is determined. The average of the (W2 - W1) / W1 values ​​determined for the five test pieces, expressed as a percentage, is the impregnation rate measured using the WPU method.

[0085] In the prepreg of the present invention, the minimum viscosity of the first resin composition is preferably 1.0 Pa·s or less. The lower limit of the minimum viscosity is more preferably 0.01 Pa·s or more, and even more preferably 0.1 Pa·s or more. The upper limit of the minimum viscosity is more preferably 0.5 Pa·s or less. By using carbon fibers having an average fiber diameter of 6 μm or more and 9 μm or less as component [A] and further setting the minimum viscosity of the first resin composition to 1.0 Pa·s or less, the impregnation ability of the prepreg can be improved, and the carbon fiber mass per unit area, which was difficult to impregnate with resin using conventional technology, can be reduced to 250 g / m 2Since the above prepregs are also easily impregnated, the generation of fluff from carbon fibers in unimpregnated regions can be suppressed during the process of transporting the prepreg tape in a slitting device or AFP device, resulting in excellent transportability of the prepreg.Furthermore, since the fluidity of the first resin composition can be increased during prepreg molding, voids in the resulting CFRP can be reduced, which is preferable because it prevents a decrease in the mechanical strength of the CFRP.

[0086] In order to set the minimum viscosity of the first resin composition within the above range, it is preferable to use diaminodiphenyl sulfone as the component [C] in the first resin composition. It is also preferable not to add too much epoxy resin-soluble thermoplastic resin to the first resin composition. The amount of epoxy resin-soluble thermoplastic resin is preferably 16 parts by mass or less per 100 parts by mass of the total first resin composition. In order to set the lower limit of the minimum viscosity within the above range, it is preferable to add 6.5 parts by mass or more per 100 parts by mass of the total first resin composition.

[0087] The CFRP obtained by curing the prepreg of the present invention can be produced, for example, by a so-called hot and pressure molding method in which the above-mentioned prepreg of the present invention is laminated in a predetermined form and shaped by heating and pressure while curing the resin. Examples of the hot and pressure molding method that can be used include press molding, autoclave molding, bagging molding, wrapping tape molding, and internal pressure molding.

[0088] When the prepreg of the present invention is used, the temperature at which CFRP is molded is preferably in the range of 150° C. to 220° C. By setting the molding temperature within this temperature range, sufficient curing properties can be obtained.

[0089] The pressure when molding CFRP using the autoclave molding method varies depending on the thickness of the prepreg, the volume content of the carbon fiber, etc., but is preferably in the range of 0.1 to 1 MPa. By keeping the molding pressure within this range, the resulting CFRP is free of defects such as voids and has little dimensional variation such as warping.

[0090] The CFRP obtained by curing the prepreg of the present invention has excellent tensile strength properties, heat resistance, and impact resistance.

[0091] Such tensile strength characteristics can be evaluated by measuring 0° tensile strength. As described in JIS K7017 (1999), the 0° direction of CFRP refers to the fiber direction of a unidirectional fiber-reinforced composite material as the axial direction, with the axial direction defined as the 0° axis and the direction perpendicular to the axis defined as 90°. A 0° tensile test is performed at room temperature (23°C) in accordance with JIS K7073 (1988). In the present invention, the tensile strength of CFRP is evaluated by the tensile strength utilization factor. The tensile strength utilization factor (%) is the value calculated by dividing the 0° tensile strength of CFRP by (carbon fiber strand strength × fiber volume content) × 100. A high tensile strength utilization factor indicates that the CFRP maximizes the performance of the carbon fiber. Therefore, a high tensile strength utilization factor indicates excellent tensile strength characteristics. The tensile strength utilization factor of CFRP is preferably 85% or higher, and more preferably 90% or higher.

[0092] The impact resistance of CFRP can be evaluated by its compressive strength after impact (hereinafter abbreviated as CAI). CFRP obtained by curing the prepreg of the present invention preferably has a CAI of 250 MPa or more after applying an impact energy of 6.7 J per mm of test piece thickness according to JIS K 7089 (1996). A CAI in this range is preferable because it can be applied to a wide range of structural components, such as aircraft.

[0093] A prepreg tape containing the prepreg of the present invention, and a carbon fiber composite material obtained by curing the prepreg of the present invention or the prepreg tape of the present invention can also be preferably used for structural members of aircraft, for example. [Example]

[0094] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. The unit "parts" used in the composition ratios means parts by mass unless otherwise noted. Furthermore, measurements of various characteristics (physical properties) were carried out in an environment of 23°C and 50% relative humidity unless otherwise noted.

[0095] <Raw materials used in the examples and comparative examples> (1) Component [A] Carbon fiber Carbon fiber 1: Acrylonitrile copolymer was polymerized using dimethyl sulfoxide (DMSO) as a solvent to obtain a spinning solution. The obtained spinning solution was first discharged into the air from a spinneret, passed through a space, and then coagulated using a dry-wet spinning method in which it was introduced into a coagulation bath consisting of an aqueous DMSO solution to obtain a coagulated fiber. The obtained coagulated fiber was washed with water, stretched in a warm water bath, coated with a silicone-based oil, and stretched again to obtain a carbon fiber precursor fiber bundle.

[0096] The obtained carbon fiber precursor fiber bundle was heat-treated in air at 250°C using a hot air circulation oven to obtain a flame-resistant fiber bundle. The obtained flame-resistant fiber bundle was pre-carbonized in a nitrogen atmosphere at a temperature of 300 to 800°C, and then carbonized in a nitrogen atmosphere at a maximum temperature of 1300°C to obtain carbon fiber 1 with a total of 24,000 filaments, a specific gravity of 1.8, and an average fiber diameter of 7µm.

[0097] Carbon fiber 2: Produced in the same manner as carbon fiber 1, except that the average fiber diameter was changed by reducing the amount of spinning solution discharged from the spinneret. Carbon fiber 2 was obtained with a total of 24,000 filaments, a specific gravity of 1.8, and an average fiber diameter of 5 μm. Carbon fiber 3: Produced in the same manner as carbon fiber 1, except that the average fiber diameter was changed by increasing the amount of spinning solution discharged from the spinneret. Carbon fiber 3 was obtained with a total of 24,000 filaments, a specific gravity of 1.8, and an average fiber diameter of 10 μm.

[0098] Carbon fiber 4: Produced in the same manner as carbon fiber 1, except that the average fiber diameter was changed by reducing the amount of spinning solution discharged from the spinneret. Carbon fiber 4 was obtained with a total of 24,000 filaments, a specific gravity of 1.8, and an average fiber diameter of 6 μm.

[0099] (2) Component [B1] Difunctional amine-type epoxy resin GAN (N-diglycidylaniline, manufactured by Nippon Kayaku Co., Ltd.) TOREP (registered trademark) A-204E (N,N-diglycidyl-p-phenoxyaniline, manufactured by Toray Fine Chemicals Co., Ltd.) GOT (N,N-diglycidyl-o-toluidine, manufactured by Nippon Kayaku Co., Ltd.)

[0100] (3) Epoxy resin other than component [B1] "Sumiepoxy (registered trademark)" ELM434 (N,N,N',N'-tetraglycidyldiaminodiphenylmethane, manufactured by Sumitomo Chemical Co., Ltd.) "EPICLON (registered trademark)" 830 (bisphenol F epoxy resin, manufactured by DIC Corporation) "Araldite (registered trademark)" MY0510 (N,N,O-triglycidyl-p-aminophenol type epoxy resin, manufactured by Huntsman Advanced Materials, Inc.) "Araldite (registered trademark)" MY0600 (N,N,O-triglycidyl-m-aminophenol type epoxy resin, manufactured by Huntsman Advanced Materials Co., Ltd.) "EPICLON" HP-7200L (dicyclopentadiene type epoxy, manufactured by DIC Corporation).

[0101] (4) Component [C] Hardener Seikacure-S (4,4'-DDS, manufactured by Seika Corporation) 3,3'-DAS (3,3'-DDS, manufactured by Mitsui Chemicals Fine Co., Ltd.).

[0102] (5) Component [D] Thermoplastic resin particles Polyamide particles 1: Epoxy-modified polyamide particles (mode diameter 14 μm, sphericity 97) were obtained using a method similar to that used in the examples (e.g., Examples 1 and 2) of WO 2012 / 124450. The raw materials were transparent polyamide (Grilamid® TR55, manufactured by M-Chemie Japan), epoxy resin (jER® 828, manufactured by Mitsubishi Chemical Corporation), and curing agent (Tomide® #296, manufactured by T&K Toka Co., Ltd.). The particle size was measured using a Microtrac MT3300II (light source 780 nm, 3 mW, wet cell (medium: water)).

[0103] (6)Thermoplastic resin "Virantage (registered trademark)" VW-10700RFP (PES, manufactured by Solvay Advanced Polymers, weight-average molecular weight 21,000 g / mol) · “Virantage (registered trademark)” VW-10200RFP (PES, manufactured by Solvay Advanced Polymers Co., Ltd., weight average molecular weight 46,500 g / mol).

[0104] (7) Conductive particles Conductive particles "Mitsubishi (registered trademark)" conductive carbon black #3230B (primary particle diameter 23 nm (arithmetic mean diameter determined by observing carbon black particles under an electron microscope), manufactured by Mitsubishi Chemical Corporation) Carbon particles "Nikabeads (registered trademark)" ICB2020 (average particle size: 20 μm, manufactured by Nippon Carbon Co., Ltd.).

[0105] <Various evaluation methods> (8) Preparation of resin composition The epoxy resin of component [B] and the thermoplastic resin described in (6) were kneaded, heated to 150°C or higher, and stirred for 1 hour to dissolve the thermoplastic resin, yielding a transparent viscous liquid. After lowering the temperature of this liquid while kneading, the curing agent of component [C] described in (4) was added and further kneaded to obtain a first resin composition.

[0106] Furthermore, after obtaining the transparent viscous liquid, the temperature of this liquid was lowered while kneading, and then the thermoplastic resin particles of the component [D] described in (5) were added and kneaded, and then the component [C] was further added and kneaded to obtain a second resin composition.

[0107] When the conductive particles of the component [E] described in (7) were contained, [E] was added to both the first resin composition and the second resin composition at the same time as the component [B].

[0108] The composition ratios of the resin compositions of the examples and comparative examples are as shown in Tables 1 to 5.

[0109] (9) Measurement of the minimum viscosity of the resin composition The minimum viscosity of the resin composition was measured using a dynamic viscoelasticity analyzer, ARES-G2 (manufactured by TA Instruments). Using flat parallel plates with a diameter of 40 mm as the upper and lower measuring jigs, the resin composition was placed between the upper and lower jigs with a distance of 1 mm. The dynamic viscoelasticity was measured while increasing the temperature at an angular frequency of 10 rad / s and a rate of 2.0°C / min, and the minimum viscosity was determined.

[0110] (10) Measurement of storage modulus G' of second resin composition The storage modulus G' of the second resin composition was measured using a dynamic viscoelasticity analyzer, ARES-G2 (manufactured by TA Instruments). Flat parallel plates with a diameter of 8 mm were used as the upper and lower measuring jigs. The resin composition was placed between the upper and lower jigs at a distance of 0.5 mm. Dynamic viscoelasticity was measured while the temperature was increased at an angular frequency of 77 rad / s and a heating rate of 2.0°C / min. The storage modulus G' at a temperature of 20°C was read from the G' curve obtained by the temperature increase measurement.

[0111] (11) Measurement of glass transition temperature of cured resin For the first resin composition and the second resin composition used in each of the Examples and Comparative Examples, resin compositions for measuring the glass transition temperature were prepared by blending only the constituent elements [B] and [C] from the constituent elements used in each of the Examples in the proportions shown in Tables 1 to 3.

[0112] The resin composition for measuring the glass transition temperature was poured into a mold, heated from 30°C at a rate of 1.5°C / min in a hot air dryer, and then heated and cured at 180°C for 2 hours to produce a 2 mm thick cured resin plate.

[0113] A test piece measuring 12.7 mm in width and 55 mm in length was cut out from the prepared resin-cured plate, and the glass transition temperature was determined by the DMA method in accordance with SACMA SRM18R-94.

[0114] The glass transition temperature was determined as the temperature at which the tangent line in the glassy state intersected the tangent line in the transition state in the storage modulus G' curve. Measurements were performed at a heating rate of 5.0°C / min and a frequency of 1 Hz.

[0115] (12) Prepreg preparation In this example, the prepreg was produced using the two-stage impregnation method as follows: The first resin composition and the second resin composition produced in (8) above were each uniformly applied onto a release paper coated with silicone, to form a first resin film (resin mass 35 g / m 2 ) and second resin film (resin mass 35 g / m 2 Carbon fibers uniformly aligned in one direction were sandwiched between two sheets of the first resin film, and heated and pressed using a press roll to obtain a primary prepreg in which the carbon fibers were impregnated with the first resin composition, which was mainly used as the base of the first layer (carbon fiber mass per unit area: 268 g / m 2Both release papers were peeled off from the obtained primary prepreg. Next, the primary prepreg was sandwiched between two sheets of second resin film, and heated and pressed using a press roll to obtain a prepreg in which the primary prepreg was impregnated with the second resin composition, which would mainly serve as the base of the second layer (carbon fiber mass per unit area: 268 g / m 2 , resin content 34% by mass. In all Examples and Comparative Examples, the heating and pressing conditions during the preparation of the first prepreg and the preparation of the second prepreg, and the line speed for the prepreg preparation were the same.

[0116] (13) Evaluation of prepreg impregnation rate (water pick-up method) Five test pieces were prepared by cutting the prepreg into squares measuring 100 mm in width and 100 mm in length at equal intervals across the width of the prepreg. The mass W1 of each test piece was measured. The test piece was positioned so that one side of the test piece was oriented vertically, and a 5 mm area from the end (i.e., a 100 mm x 5 mm area) was immersed in water for 5 minutes. After wiping off the water adhering to the surface of the test piece with a cloth or the like, the mass W2 was determined. The average value of the (W2 - W1) / W1 values ​​determined for the five test pieces was expressed as a percentage and used as the impregnation rate. An impregnation rate of 5% or less was considered acceptable.

[0117] (14) Tack measurement between prepreg and metal The tack between the prepreg and the metal was determined by pressing a 10 mm square aluminum plate attached with double-sided tape to the weight part of a handy tack tester (manufactured by Imada Co., Ltd.) against the surface of the prepreg with a load of 0.5 kg for 0.1 seconds, and then measuring the force applied when the aluminum plate was pulled up at a rate of 100 mm / min. The measurement was carried out in an environment with a temperature of 25°C and a humidity of 50% RH. A tack value of 0.5 N or less was considered to be acceptable.

[0118] (15) Evaluation of drapeability of prepreg One end of a prepreg cut to a width of 12.7 mm and a length of 400 mm was fixed to a horizontal table, with the prepreg extending 200 mm longitudinally from the edge of the table. The deflection angle of the prepreg after 10 minutes was used as an index of drapeability. The deflection angle of the prepreg was defined as the angle formed by a horizontal extension of the prepreg fixed to the table and a line connecting the free end of the prepreg and the base of the protruding part of the prepreg. A deflection angle of 10° or more was considered to be acceptable.

[0119] (16) Evaluation of tensile strength utilization rate of CFRP The unidirectional prepreg was cut to the specified size, and four sheets were laminated in one direction. Then, they were placed in an autoclave at a temperature of 180°C for 2 hours under a pressure of 6 kg / cm. 2 CFRP was produced by molding under conditions of a temperature rise rate of 1.5°C / min. The obtained CFRP was cut to a width of 12.7 mm and a length of 230 mm, and glass fiber reinforced plastic tabs measuring 1.2 mm and 50 mm in length were attached to both ends to obtain test specimens. This test specimen was subjected to a 0° tensile test in accordance with JIS K7073 (1988) using an Instron universal testing machine. The measurement temperature was room temperature (23°C).

[0120] The tensile strength utilization rate (%) was calculated by the formula: 0° tensile strength of CFRP / (strand strength of carbon fiber × fiber volume content) × 100. The fiber volume content was measured in accordance with ASTM D 3171 (2004).

[0121] (17) Compression after impact (CAI) measurement of CFRP 16 plies of unidirectional prepreg were laminated quasi-isotropically in a [+45° / 0° / -45° / 90°] 2s configuration, and then heated in an autoclave at 180°C for 2 hours under a pressure of 6 kg / cm. 2 CFRP was produced by molding under conditions of a temperature rise rate of 1.5°C / min. Samples measuring 150mm long x 100mm wide were cut out from the obtained CFRP, and a falling weight impact of 6.7J / mm was applied to the center of the sample in accordance with SACMA SRM 2R-94 to determine the compressive strength after impact.

[0122] (18) Measurement method for electrical conductivity in the thickness direction of CFRP 16 plies of unidirectional prepreg were laminated quasi-isotropically in a [+45° / 0° / -45° / 90°] 2s configuration, and then heated in an autoclave at 180°C for 2 hours under a pressure of 6 kg / cm. 2 CFRP was produced by molding under conditions of 1.5°C / min heating rate. A 40mm x 40mm sample was cut from the obtained CFRP. After polishing and removing the resin layers on both surfaces, conductive paste N-2057 (Shoei Chemical Co., Ltd.) was applied to both surfaces to a thickness of approximately 70µm using a bar coater. The paste was cured for 30 minutes in a hot air oven adjusted to 180°C to obtain a sample for conductivity evaluation. The resistance in the thickness direction of the obtained sample was measured using the four-terminal method using an Advantest R6581 digital multimeter. The measurement was performed six times, and the average value was taken as the volume resistivity (Ωcm) in the thickness direction of the CFRP.

[0123] (19) Measurement of the average value and coefficient of variation of the distance between carbon fibers 16 plies of unidirectional prepreg were laminated quasi-isotropically in a [+45° / 0° / -45° / 90°] 2s configuration, and then heated in an autoclave at 180°C for 2 hours under a pressure of 6 kg / cm. 2 CFRP was produced by molding under conditions of 1.5°C / min heating rate. The obtained CFRP sample was cut in the 0° direction to obtain a cross section. Using a laser microscope (VHX-5000: manufactured by Keyence Corporation), the carbon fiber layer (90° layer) perpendicular to the cutting direction of the sample was observed at 200x magnification with a field of view of 100 μm × 150 μm. Five cross-sectional images were obtained, and the distance between each carbon fiber was measured for all carbon fibers included in the field of view using the software Image-Pro Premier (manufactured by Nippon Rover Co., Ltd.), and the average value and coefficient of variation of the distance between carbon fibers were calculated.

[0124] Example 1 A first resin composition was prepared in the composition ratios shown in Table 1 according to the above "(8) Preparation of Resin Composition" using GAN as the component [B1], Sumiepoxy (registered trademark) ELM434 as the epoxy resin for the component [B] other than the component [B1], Seikacure-S as the component [C], and Virantage (registered trademark) VW-10700RFP as the thermoplastic resin. Next, a second resin composition was prepared in the composition ratios shown in Table 1 according to the above "(8) Preparation of Resin Composition" using the same components as the first resin composition and polyamide particles 1 as the component [D].

[0125] Furthermore, carbon fiber 1 was used as the carbon fiber of the component [A], and a prepreg was produced using the first resin composition and the second resin composition prepared above in accordance with the above-mentioned "(12) Production of prepreg" (carbon fiber mass 268 g / m 2 , resin content 34% by mass).

[0126] As shown in Table 1, by adjusting the average fiber diameter of the carbon fiber in component [A] to an appropriate range, the impregnation rate, prepreg deflection angle, and tack value measured using the WPU method all passed the test. This resulted in a prepreg with excellent shape conformability and reduced fuzz generation during prepreg transfer. Furthermore, because the resin impregnation during prepreg molding was also excellent, voids were not generated in the CFRP, resulting in a CFRP with excellent heat resistance, tensile strength utilization, and impact resistance. Furthermore, when the cross section of the resulting CFRP was observed, the average interfiber distance in the first layer was 0.15 μm, and the coefficient of variation for the interfiber distance was 20%. Areas where the carbon fibers were densely and sparsely spaced were clearly visible. It is believed that the sparsely spaced carbon fiber arrangement provided a path for the matrix resin to penetrate, resulting in high impregnation.

[0127] (Comparative Examples 1 and 2) Prepregs were prepared in the same manner as in Example 1 using the compositions and composition ratios shown in Table 1.

[0128] In Comparative Example 1, the average fiber diameter of the carbon fibers was small, so the impregnation and deflection angle of the obtained prepreg were both unacceptable, and the handleability during transportation of the prepreg was poor. When the cross section of the obtained CFRP was observed, the coefficient of variation of the distance between the carbon fibers in the first layer was 12%, and there were few areas where the carbon fibers were densely and sparsely arranged.

[0129] In Comparative Example 2, the average fiber diameter of the carbon fibers was too large, so that although the impregnation ability passed, the deflection angle of the prepreg was unacceptable, resulting in a prepreg with poor shape conformability.

[0130] Example 2 With the composition ratio shown in Table 1, the basis weight of the resin film was 32 g / m for both the first resin film and the second resin film. 2 A prepreg was obtained in the same manner as in Example 1 except that the carbon fiber mass was 268 g / m 2 , resin content 32% by mass).

[0131] As shown in Table 1, by setting the average fiber diameter of the carbon fiber in component [A] within an appropriate range, impregnation passed the test, despite the low resin content. The prepreg deflection angle and tack strength also passed the test. A prepreg with excellent shape conformability was obtained, with reduced fuzz generation during prepreg transport. Furthermore, due to the high impregnation rate, a CFRP with excellent impact resistance and no voids was obtained. Furthermore, when the cross section of the resulting CFRP was observed, the coefficient of variation in the distance between carbon fibers in the first layer was 20%, and areas where the carbon fibers were densely and sparsely arranged were confirmed. It is believed that the sparsely arranged carbon fiber areas ensured impregnation paths for the matrix resin, resulting in high impregnation.

[0132] Example 18 A prepreg was obtained in the same manner as in Example 1, except that carbon fibers having an average fiber diameter of 6 μm were used as the component [A] (carbon fiber mass: 268 g / m 2, resin content 34% by mass). As shown in Table 1, by setting the average fiber diameter of the carbon fiber of component [A] within an appropriate range, the impregnation, prepreg deflection angle, and tack strength all passed the test. A prepreg with excellent shape conformability was obtained, with reduced fuzz generation during prepreg transport. When the cross section of the obtained CFRP was observed, the coefficient of variation of the distance between carbon fibers in the first layer was 16%, and areas where the carbon fibers were densely arranged and areas where they were sparsely arranged were confirmed. It is thought that the sparsely arranged carbon fiber areas ensured impregnation paths for the matrix resin, resulting in high impregnation.

[0133] (Comparative Example 3) Prepregs were produced in the same manner as in Example 2, with the composition ratios shown in Table 1. In Comparative Example 3, the average fiber diameter of the carbon fibers was small, resulting in an unacceptable impregnation rate. Because of the poor impregnation rate, fluffing occurred during prepreg transport, and voids were also generated in the CFRP, resulting in an insufficient CAI for the resulting CFRP. When the cross section of the resulting CFRP was observed, the coefficient of variation of the distance between carbon fibers in the first layer was 11%, and there were few areas where the carbon fibers were densely and sparsely arranged.

[0134] (Comparative Examples 10 to 12) A first resin composition was prepared in the composition ratios shown in Table 2 according to the above "(8) Preparation of Resin Composition" using Sumiepoxy (registered trademark) ELM434, EPICLON HP7200L, and EPICLON 830 as the epoxy resins for component [B], without using the bifunctional amine-type epoxy resin for component [B1], and Seikacure-S as the component [C] and Virantage (registered trademark) VW-10700RFP as the thermoplastic resin. Next, a second resin composition was prepared in the composition ratios shown in Table 2 according to the above "(8) Preparation of Resin Composition" using the same components as the first resin composition and polyamide particles 1 as the component [D].

[0135] Furthermore, a prepreg was produced in accordance with the above-mentioned "(12) Production of prepreg" using the carbon fiber according to Table 2 as the carbon fiber of the component [A] and the first and second resin compositions prepared above (carbon fiber mass 268 g / m 2 , resin content 34% by mass).

[0136] It can be seen that the impregnation improvement effect of Comparative Example 11 is smaller than that of Comparative Example 10, compared to the improvement in impregnation ability of Example 1 compared to Comparative Example 1. It can be seen that it is important to include a bifunctional amine-type epoxy resin as the component [B1] rather than a dicyclopentadiene-type epoxy resin as the matrix resin.

[0137] Examples 3 to 6 Prepregs were prepared in the same manner as in Example 1, using the composition ratios shown in Table 3. The amount of component [B1], bifunctional amine-type epoxy resin, was varied. In all Examples, the prepreg impregnation, deflection angle, and tack value all passed the test. In all Examples, prepregs were obtained that had excellent shape conformability and suppressed fluffing during prepreg transport. Furthermore, because all Examples had favorable compositions, CFRPs were obtained that had an excellent balance between heat resistance and tensile strength utilization rate.

[0138] Comparative Example 4 A prepreg was produced in the same manner as in Example 1 using the composition ratios shown in Table 3. The impregnation, deflection angle, and tack value of the prepreg itself were acceptable, but the tensile strength utilization rate of the obtained CFRP was insufficient because the blending amount of the bifunctional amine-type epoxy resin, component [B1], was small.

[0139] (Comparative Examples 5 and 6) A prepreg was produced in the same manner as in Example 1 using the composition ratios shown in Table 3. The impregnation, deflection angle, and tack value of the prepreg itself were acceptable, but the amount of the bifunctional amine-type epoxy resin (component [B1]) blended was too high, so the glass transition temperature of the cured resin was low and the heat resistance of the resulting CFRP was insufficient.

[0140] (Examples 7 and 8) Prepregs were prepared in the same manner as in Example 1, using the composition ratios shown in Table 4. The impregnation, deflection angle, and tack value of the prepregs themselves were acceptable. A prepreg with excellent shape conformability was obtained, with reduced fluff generation during prepreg transport. Because the bifunctional amine-type epoxy resin of component [B1] was used in an appropriate amount, a CFRP with an excellent balance between heat resistance and tensile strength utilization rate was obtained.

[0141] (Comparative Example 7) A prepreg was produced in the same manner as in Example 1 using the composition ratio shown in Table 4. Since the bifunctional amine-type epoxy resin, component [B1], was not included, the tensile strength utilization rate of the obtained CFRP was low.

[0142] (Comparative Example 8) A resin composition was prepared using the composition ratio of the second resin composition of Example 1 in Table 1 by the method described above in "(8) Preparation of Resin Composition." A prepreg was prepared using the one-stage impregnation method described below, rather than the method described above in "(12) Preparation of Prepreg." That is, the prepared resin composition was uniformly applied onto a release paper coated with silicone, and a resin film (resin mass 70 g / m) was formed. 2 Carbon fibers uniformly aligned in one direction were sandwiched between two resin films, and heated and pressed using a press roll to obtain a prepreg in which the carbon fibers were impregnated with the resin composition (carbon fiber mass: 268 g / m 2 , resin content 34% by mass. At this time, carbon fiber 1 was used as the carbon fiber of component [A].

[0143] The impregnation rate of the produced prepreg was high at 9% (failure), and the prepreg had poor transportability. Furthermore, when the cross section of the obtained CFRP was observed, the coefficient of variation of the distance between carbon fibers was low at 9%. The carbon fibers were uniformly arranged, with no sparse carbon fiber arrangements that would serve as impregnation channels, which is thought to have resulted in insufficient impregnation. Furthermore, due to the low impregnation rate, voids were observed in the CFRP, and the CAI was insufficient at 201 MPa.

[0144] (Examples 10 to 13) Prepregs were prepared in the same manner as in Example 1 using the composition ratios shown in Table 5. By setting the average fiber diameter of the carbon fiber component [A] within an appropriate range and setting the minimum viscosity of the first resin composition and the storage modulus G' of the second resin composition within appropriate ranges, the impregnation, deflection angle, and tack value of the prepreg were all acceptable. Therefore, when the obtained prepreg was transported, adhesion of fuzz was suppressed, and resin adhesion to the guide roll during prepreg transport was also small. In particular, in Example 13, the minimum viscosity of the first resin composition was low and the G' of the second resin composition was appropriately high, resulting in a well-balanced impregnation and tack, and excellent handleability during prepreg transport.

[0145] (Examples 14 and 15) Prepregs were prepared in the same manner as in Example 1, using the composition ratios shown in Table 6. The prepreg's impregnation, deflection angle, and tack value were all acceptable. Therefore, when the obtained prepreg was transported, adhesion of fuzz was suppressed, and resin adhesion to the guide roll during prepreg transport was also small. In these examples, conductive particles were added, so the volume resistivity in the thickness direction of the obtained CFRP was 30 Ωcm in Example 14 and 25 Ωcm in Example 15. On the other hand, Example 1, which did not contain conductive particles, had a volume resistivity of 950 Ωcm, demonstrating improved conductivity compared to Example 1. Therefore, when this material is applied to aircraft, it is expected that lightning resistance will be improved. Furthermore, the handleability of the obtained prepreg and the mechanical properties of the CFRP were both good.

[0146] Example 16 A resin composition was prepared in the same manner as in Example 14, except that carbon black was added, and a prepreg was obtained. The impregnation property, deflection angle, and tack value of the prepreg were all acceptable. Therefore, when the obtained prepreg was transported, adhesion of fuzz was suppressed, and resin adhesion to the guide roll during prepreg transport was also small. Furthermore, similar to Example 14, favorable properties were obtained. Furthermore, the volume resistivity in the thickness direction of the CFRP was 14 Ω cm.

[0147] Example 17 The carbon fiber 1 was used as the carbon fiber of the component [A] in the same composition ratio as in Example 1 of Table 1, and the carbon fiber mass was 540 g / m 2 , resin mass of the first resin film 70 g / m 2 , the resin mass of the second resin film is 70 g / m 2 A prepreg was produced in the same manner as in Example 1, except that the following conditions were met: The prepreg had an impregnation rate of 4% (acceptable) and a deflection angle, which is an indicator of drapeability, of 12° (acceptable). Because the impregnation rate was small and the resin impregnation was good when the prepreg was molded, no voids were generated in the CFRP, and the drapeability, which is an indicator of shape conformability, was good. The tensile strength utilization rate of the obtained CFRP was 90%, and the mechanical properties were also excellent.

[0148] (Comparative Example 9) A prepreg was produced in the same manner as in Example 17, using carbon fiber 2 as the carbon fiber of component [A] in the same composition ratio as in Comparative Example 1 in Table 1. Because carbon fiber with a small average fiber diameter was used and the carbon fiber mass of the prepreg was large, the impregnation rate was high at 10% (failure). Voids were observed in the obtained CFRP, and the CAI was insufficient at 187 MPa.

[0149] [Table 1]

[0150] [Table 2]

[0151] [Table 3]

[0152] [Table 4]

[0153] [Table 5]

[0154] Table 6

Claims

1. A prepreg comprising at least the following components [A] to [D]: The structure is such that a first layer is formed by impregnating a component [A] with a first resin composition containing components [B] and [C], and a second layer is formed on both sides of the first layer and is made of a second resin composition containing components [B] to [D], and the first layer is adjacent to the second layer, the carbon fibers of component [A] have an average fiber diameter of 6 μm or more and 9 μm or less, the carbon fiber mass per unit area of ​​the carbon fiber of component [A] is 250 g / m 2 or more; the content of the bifunctional amine-type epoxy resin [B1] is 15 parts by mass or more and less than 40 parts by mass out of 100 parts by mass of the total amount of epoxy resins in the component [B], A prepreg further comprising polyethersulfone, wherein the content of polyethersulfone is 17.2 parts by mass or more and 40 parts by mass or less per 100 parts by mass of the total amount of the epoxy resins that are the component [B]: [A] Carbon fiber [B] Epoxy resin [C] Curing agent [D] Thermoplastic resin particles.

2. 2. The prepreg according to claim 1, wherein the carbon fibers of component [A] have an average fiber diameter of 7 μm or more.

3. The prepreg according to claim 1 or 2, wherein the first resin composition has a minimum viscosity of 1.0 Pa·s or less.

4. The storage modulus G' of the second resin composition measured at 20°C and 77 rad / s is 2.0 × 10 ７ The prepreg according to claim 1 or 2, wherein the modulus is 100 Pa or more.

5. 3. The prepreg according to claim 1, wherein one end of the prepreg cut to a width of 12.7 mm and a length of 400 mm is fixed to a horizontal desk so that the prepreg protrudes 200 mm from the edge of the desk, and the deflection angle of the prepreg after 10 minutes is in the range of 10° or more and 17° or less.

6. 3. The prepreg according to claim 1, wherein the coefficient of variation of the average distance between the carbon fibers in the first layer of CFRP obtained by curing the prepreg is 16% or more and less than 50%.

7. 3. The prepreg according to claim 1, wherein a resin composition for glass transition temperature measurement is prepared by blending only the component [B] and the component [C] out of the components constituting the first resin composition and the second resin composition, and the epoxy resin composition for glass transition temperature measurement is cured at a temperature of 180°C for 2 hours to obtain a cured resin product having a glass transition temperature of 180°C or higher.

8. 3. The prepreg according to claim 1, further comprising 1 part by mass or more of conductive particles as component [E] per 100 parts by mass of the total amount of epoxy resins as component [B].

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