Prepreg, carbon fiber-reinforced composite material, and structure

Abstract

The present invention addresses the problem of providing a carbon fiber-reinforced composite material having both excellent impact resistance and electroconductivity in the thickness direction.　Provided is a carbon fiber-reinforced composite material comprising components [A], [B], and [C], said carbon fiber-reinforced composite material being constituted by a plurality of carbon fiber layers that contains components [A] and [B] and an interlayer resin layer that is disposed between adjacent carbon fiber layers and that contains components [B] and [C] but not component [A], wherein the component [C] contained in the interlayer resin layer satisfies a condition (Ic). The component [A] is carbon fibers. The component [B] is a matrix resin. The component [C] is conductive particles. The condition (Ic) is that, in a number-based particle size distribution of the component [C] obtained from a cross-section of the carbon fiber-reinforced composite material, ranges (a) and (b) each include at least one maximum. The range (a) is Df×1 / 6≤Dsp≤Dlp×2 / 3. The range (b) is Tr×1 / 5≤Dlp≤Tr. Dsp is the minimum number-based particle size [μm] indicating a maximum. Dlp is the maximum number-based particle size [μm] indicating a maximum. Df is the carbon fiber diameter [μm]. Tr is the interlayer thickness [μm].

Description

Prepregs, carbon fiber reinforced composite materials and structures

[0001] This invention relates to prepregs, carbon fiber reinforced composite materials, and structures using the carbon fiber composite material.

[0002] Traditionally, fiber-reinforced composite materials, consisting of reinforcing fibers and matrix resins, have been applied in numerous fields such as aerospace, automotive, railway vehicles, ships, civil engineering, and sports equipment, due to their lightweight nature and excellent mechanical properties such as strength and rigidity, as well as heat resistance and corrosion resistance. In particular, for applications requiring high heat resistance, fiber-reinforced composite materials using continuous reinforcing fibers are used, with carbon fiber (hereinafter sometimes abbreviated as "CF"), which has excellent specific strength and specific modulus, being used as the reinforcing fiber. Thermosetting resins, especially epoxy resins, which have excellent adhesion to CF, heat resistance, and modulus, and exhibit low curing shrinkage, are frequently used as the matrix resin. In recent years, as the use of carbon fiber reinforced composite materials (hereinafter sometimes abbreviated as "CFRP") has increased, the required properties have become even more stringent.

[0003] However, cured products of thermosetting resins such as epoxy resins generally have lower fracture toughness compared to thermoplastic resins. This leads to a problem of reduced impact resistance in CFRP. In particular, for aircraft structural components, excellent impact resistance is required against impacts such as tools dropped during assembly and hail during operation, so improving impact resistance has been a major challenge.

[0004] CFRP generally has a layered structure, and when subjected to impact, high stress is generated between the layers, causing cracks to form. To suppress crack formation, it is effective to increase the plastic deformation capacity of the epoxy resin, and one way to do this is to incorporate a thermoplastic resin that has excellent plastic deformation capacity.

[0005] Various studies have been conducted in the past regarding methods for incorporating thermoplastic resins. For example, as described in Patent Document 1, a method is known in which a high-toughness thermosetting resin, obtained by dissolving a thermoplastic resin in a thermosetting resin to increase its toughness, is used as the matrix resin.

[0006] Furthermore, as another means of improving impact resistance, a method is known in which thermoplastic resin fine particles are placed between layers that are prone to cracking, as described in Patent Document 2.

[0007] However, the technology described in Patent Document 2, while providing CFRP with high impact resistance, creates an insulating resin layer between the layers. As a result, it has the drawback of significantly reducing the conductivity in the thickness direction, which is one of the characteristics of CFRP. When CFRP is applied to aircraft structural members or wind turbine blade members, the conductive path during a lightning strike is limited to the direction of the carbon fibers, and the current dissipation capacity in the thickness direction and in directions perpendicular to the thickness direction and the fiber direction becomes low. As a result, the area struck by lightning is exposed to a localized high current, and the resin in that area evaporates, potentially causing overall delamination and a catastrophic decrease in the strength of the structural member.

[0008] One possible method for improving the conductivity of CFRP in the thickness direction is to incorporate metal particles or carbon particles into the matrix resin, as described in Patent Document 3. However, these documents do not mention anything about achieving both high impact resistance and conductivity, and it has been difficult to achieve both excellent impact resistance and conductivity in CFRP using the methods described in these documents.

[0009] In recent years, diligent research has been conducted to achieve both excellent impact resistance and conductivity in CFRP. For example, as described in Patent Documents 4 or 5, one method involves placing reinforcing materials to improve impact resistance and conductive particles to improve conductivity in the interlayer portion of CFRP. However, the effect of these methods on improving conductivity is not entirely satisfactory, and further improvements have been anticipated.

[0010] JP-A-62-297314 JP-A-1-104624 JP-A-8-34864 JP-A-2008-231395 International Publication No. 2012 / 124450

[0011] The methods described in Patent Document 3 and others do not mention anything about achieving both high impact resistance and conductivity, and it was difficult to achieve both excellent impact resistance and conductivity in CFRP using the methods described in these documents.

[0012] Furthermore, the methods described in Patent Document 4 or 5 did not sufficiently improve conductivity, and further improvement was expected.

[0013] Generally, increasing the amount of conductive particles in CFRP to further improve its conductivity reduces its impact resistance. Similarly, increasing the carbon fiber content to improve the conductivity of CFRP also reduces its impact resistance. On the other hand, increasing the amount of thermoplastic resin between layers to improve the impact resistance of CFRP increases the thickness of the insulating resin layer between layers, thus reducing conductivity. Thus, achieving both excellent conductivity and impact resistance simultaneously has been difficult with conventional technology.

[0014] Therefore, the object of the present invention is to provide CFRP that combines excellent conductivity and impact resistance.

[0015] The CFRP and prepreg of the present invention employ the following means to solve the above problems. [1] A carbon fiber reinforced composite material comprising the following components [A], [B] and [C], wherein the structure consists of a plurality of carbon fiber layers comprising components [A] and [B], and an interlayer resin layer disposed between adjacent carbon fiber layers that does not contain component [A] but contains components [B] and [C], and the component [C] contained in the interlayer resin layer satisfies condition (Ic). [A]: carbon fiber [B]: matrix resin [C]: conductive particles (Ic): in the number-based particle size distribution of component [C] obtained from the cross-section of the carbon fiber reinforced composite material, there is one or more maxima in the ranges of (a) and (b), respectively. (a): Df × 1 / 6 ≤ Dsp ≤ Dlp × 2 / 3 (b): Tr × 1 / 5 ≤ Dlp ≤ Tr Dsp: Minimum particle size referenced to show maximum [μm] Dlp: Maximum particle size referenced to show maximum [μm] Df: Carbon fiber diameter [μm] Tr: Interlayer thickness [μm] [2] The carbon fiber reinforced composite material according to [1], wherein in its cross-section, the ratio (Acp / Ar) of the area of ​​the component [C] (Acp) to the area of ​​the interlayer resin layer (Ar) is 0.05 or more and 0.30 or less. [3] The carbon fiber reinforced composite material according to [1] or [2], wherein in the number-based particle size distribution of component [C] obtained from its cross-section, the ratio (PTlpc / PTspc) of the peak height of the largest number-based particle size (PTlpc) to the peak height (PTspc) of the smallest number-based particle size (PTspc) that shows the maximum is 0.05 or more and 0.50 or less. [4] The carbon fiber reinforced composite material according to any one of [1] to [3], wherein component [B] is a cured product of a thermosetting resin. [5] The carbon fiber reinforced composite material according to [4], wherein the interlayer resin layer further contains component [D]. [D]: Thermoplastic particles [6] The carbon fiber reinforced composite material according to [5], wherein in its cross-section, the ratio (Atp / Ar) of the area of ​​component [D] (Atp) to the area of ​​the interlayer resin layer (Ar) is 0.10 or more and 0.50 or less. [7] A carbon fiber reinforced composite material according to any one of [1] to [6], wherein the constituent element [C] is carbon particles.[8] A carbon fiber reinforced composite material according to any one of [1] to [7], wherein in the interlayer resin layer within its cross-section, 50 to 80% of the number of constituent elements [C] are located within 25% of the average thickness of the interlayer resin layer in the thickness direction from the surface of the carbon fiber layer. [9] A structure obtained using the carbon fiber reinforced composite material according to any one of [1] to [8], wherein the shape is selected from the group consisting of a flat plate structure, a cylindrical structure, a box-shaped structure, a C-shaped structure, an H-shaped structure, an L-shaped structure, a T-shaped structure, an I-shaped structure, a Z-shaped structure, and a hat-shaped structure.

[10] A prepreg comprising a first layer containing the following constituent elements [A] and [B], and a second layer containing constituent elements [B] and [C] but not containing constituent element [A], wherein the second layer is adjacent to one or both sides of the first layer, and the constituent elements [C] included in the second layer satisfy condition (Ip). [A]: Carbon fiber [B]: Matrix resin [C]: Conductive particles (Ip): The particle number-based particle size distribution of component [C] has one or more maxima in the range of 1.5 μm or more and less than 10 μm, and in the range of 10 μm or more and less than 100 μm.

[11] The prepreg according to

[10] above, wherein component [C] satisfies condition (Ip) in addition to condition (IIp). (IIp): The particle number-based particle size distribution of component [C] has one or more maxima in the range of 3 μm or more and less than 8 μm, and in the range of 15 μm or more and less than 60 μm.

[12] The prepreg according to

[10] or

[11] , wherein, per 100 parts by mass of the total amount of matrix resin, the prepreg contains 1 to 15 parts by mass of conductive particles having a mode diameter in the range of 1.5 μm or more and less than 10 μm, and 1 to 10 parts by mass of conductive particles having a mode diameter in the range of 10 μm or more and less than 100 μm.

[13] The prepreg according to any one of

[10] to

[12] , wherein, in the component [C], the ratio (PTlpp / PTspp) of the peak height (PTlpp) of conductive particles having a mode diameter in the range of 10 μm or more and less than 100 μm to the peak height (PTspp) of conductive particles having a mode diameter in the range of 1.5 μm or more and less than 10 μm is 0.05 or more and 0.50 or less.

[14] A prepreg according to any one of

[10] to

[13] , wherein the component [B] is a thermosetting resin.

[15] The prepreg according to

[14] , further comprising a component [D] in the second layer. [D]: Thermoplastic particles

[16] The prepreg according to

[15] , wherein the component [D] is contained in an amount of 10 to 50 parts by mass per 100 parts by mass of thermosetting resin contained in the prepreg.

[17] The prepreg according to any one of

[10] to

[16] , wherein the component [C] is carbon particles.

[18] The prepreg according to any one of

[10] to

[17] , wherein in the second layer, 50 to 80% of the number of components [C] are located within 25% of the average thickness of the second layer from the surface of the first layer toward the surface of the prepreg.

[19] A carbon fiber reinforced composite material obtained by laminating and molding the prepregs according to any one of

[10] to

[18] .

[20] A structure obtained using the carbon fiber reinforced composite material described in

[19] above, wherein the shape is selected from the group consisting of a flat plate structure, a cylindrical structure, a box-shaped structure, a C-shaped structure, an H-shaped structure, an L-shaped structure, a T-shaped structure, an I-shaped structure, a Z-shaped structure, and a hat-shaped structure.

[0016] The present invention makes it possible to provide a carbon fiber reinforced composite material that combines excellent conductivity in the thickness direction with impact resistance. Because the carbon fiber composite material of the present invention combines excellent conductivity in the thickness direction with impact resistance, it can be widely used in applications such as aircraft structural components, wind turbine blades, automobile body panels, and computer applications such as IC trays and laptop casings, and can significantly improve the performance of the applied products.

[0017] This is a schematic cross-sectional view showing an example of a substructure in the CFRP of the present invention. This is a graph showing an example of the particle size distribution of conductive particles obtained from a cross-section of the CFRP of the present invention. This is a schematic cross-sectional view showing an example in which conductive particles in the CFRP of the present invention are concentrated near the surface of the carbon fiber layer in the interlayer resin layer. This is a graph showing an example of the particle size distribution obtained by a particle size distribution analyzer of conductive particles in the prepreg of the present invention. This is a schematic cross-sectional view showing an example of the prepreg of the present invention. This is a schematic cross-sectional view showing an example in which conductive particles in the prepreg of the present invention are concentrated near the surface of the first layer in the second layer.

[0018] The present invention will be described in more detail below.

[0019] A first aspect of the present invention is a carbon fiber reinforced composite material comprising the following components [A], [B] and [C], wherein the structure consists of a plurality of carbon fiber layers comprising components [A] and [B], and an interlayer resin layer disposed between adjacent carbon fiber layers, which does not contain component [A] but contains components [B] and [C], and the component [C] included in the interlayer resin layer satisfies condition (Ic). [A]: carbon fiber [B]: matrix resin [C]: conductive particles (Ic): in the number-based particle size distribution of component [C] obtained from the cross-section of the carbon fiber reinforced composite material, there is one or more maxima in the ranges of (a) and (b), respectively. (a): Df × 1 / 6 ≤ Dsp ≤ Dlp × 2 / 3 (b): Tr × 1 / 5 ≤ Dlp ≤ Tr Dsp: Minimum number reference particle size [μm] showing the maximum Dsp: Maximum number reference particle size [μm] Df: Carbon fiber diameter [μm] Tr: Interlaminar thickness [μm].

[0020] A second aspect of the present invention is a prepreg comprising a first layer containing the following components [A] and [B], and a second layer containing components [B] and [C] but not component [A], wherein the second layer is adjacent to one or both sides of the first layer, and the component [C] included in the second layer satisfies condition (Ip). [A]: carbon fiber [B]: matrix resin [C]: conductive particles (Ip): In the particle size distribution based on the number of components [C], there is one or more maxima in the range of 1.5 μm or more and less than 10 μm, and in the range of 10 μm or more and less than 100 μm.

[0021] The following describes each aspect, but since there are common elements among the components, they will also be explained together.

[0022] <Component [A]> In the CFRP of the present invention, the carbon fibers, which are component [A], preferably have a tensile modulus in the range of 200 to 440 GPa. Within this range, the CFRP achieves a high level of balance in terms of rigidity and strength. The tensile elongation of the carbon fibers is preferably in the range of 0.8 to 3.0%. Here, the above tensile modulus and tensile elongation are values ​​measured for carbon fiber strands in accordance with JIS R 7606:2000. Furthermore, the diameter of the carbon fibers is preferably in the range of 3 to 10 μm. Within this range, it is easier to obtain a CFRP in which both large-diameter and small-diameter conductive particles exist in the interlayer resin layer, without the small-diameter conductive particles among the conductive particles, which are component [C], entering the carbon fiber layer during molding. By having both large-diameter and small-diameter conductive particles in the interlayer resin layer in this way, a state is formed in which small-diameter conductive particles exist between the large-diameter conductive particles in the interlayer resin layer and the carbon fibers in the carbon fiber layer, thereby forming conductive paths.

[0023] Commercially available carbon fiber products include "Torayca" (registered trademark) T800G-24K, "Torayca" (registered trademark) T800S-24K, "Torayca" (registered trademark) T700G-24K, "Torayca" (registered trademark) T300-3K, and "Torayca" (registered trademark) T700S-12K (all manufactured by Toray Industries, Inc.).

[0024] <Component [B]> The CFRP of the present invention has a structure comprising a carbon fiber layer and an interlayer resin layer, the interlayer resin layer containing a matrix resin which is component [B] and conductive particles which are component [C]. A resin layer may also be present on the outermost surface of the CFRP. Furthermore, the prepreg of the present invention uses a resin composition containing a matrix resin which is component [B] and conductive particles which are component [C].

[0025] The type of matrix resin, which is component [B], is not limited. In prepregs, thermosetting resins and / or thermoplastic resins are mainly used, and in CFRP, cured thermosetting resins and / or thermoplastic resins are mainly used. When a thermosetting resin is used as the matrix resin of a prepreg, types that undergo a crosslinking reaction and harden on their own when heat or ultraviolet light is applied, or types that harden when heated after a curing agent is added, can be used. When a curing agent is added in this way, the entire mixture including the curing agent is referred to as the thermosetting resin, and its components are referred to as the thermosetting resin main component and the curing agent. For example, if such a thermosetting resin is an epoxy resin, its components are referred to as the epoxy resin main component and the curing agent. When the matrix resin of CFRP is a cured thermosetting resin, the cured thermosetting resin used when a thermosetting resin is used as the matrix resin of the prepreg can be used. Hereafter, descriptions of thermosetting resins shall apply to both thermosetting resins in prepregs and cured thermosetting resins in CFRP. The thermosetting resin used in the matrix resin in this invention is not particularly limited as long as it undergoes a crosslinking reaction upon heating to form a three-dimensional network structure, and resin compositions such as epoxy resins, phenolic resins, vinyl ester resins, and cyanate ester resins can be used. Two or more of these resin compositions may be mixed and used. Among these thermosetting resins, epoxy resins are preferred because they have an excellent balance of heat resistance, mechanical properties, and adhesion to carbon fibers. Furthermore, from the viewpoint of heat resistance and mechanical properties, epoxy resins containing a curing agent are preferred.

[0026] Specifically, epoxy resin main components include, but are not limited to, amine-based epoxy resin main components such as tetraglycidyldiaminodiphenylmethane (N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane), triglycidyl-p-aminophenol, triglycidyl-m-aminophenol, and various isomers of triglycidylaminocresol; phenol-based epoxy resin main components such as bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, bisphenol S-type epoxy resin, phenol novolac-type epoxy resin, and cresol novolac-type epoxy resin; and alicyclic epoxy resins as epoxy resin main components having carbon-carbon double bonds as precursors. Using an epoxy resin with an aromatic amine, such as tetraglycidyldiaminodiphenylmethane, as the main epoxy resin component yields a matrix resin with good heat resistance and good adhesion to reinforcing fibers, making it most suitable for the present invention. Furthermore, when a curing agent is added to the epoxy resin, a compound having an active group that can react with epoxy groups can be used as the curing agent. Preferably, compounds having an amino group, an acid anhydride group, or an azide group are suitable. Specifically, dicyandiamide, various isomers of diaminodiphenylsulfone, and aminobenzoic acid esters are suitable.

[0027] In the present invention, when a thermoplastic resin is used as the matrix resin, the thermoplastic resin is not particularly limited and may include polyester resins such as polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, polytrimethylene terephthalate (PTT) resin, polyethylene naphthalate (PENp) resin, and liquid crystal polyester; polyolefin resins such as polyethylene (PE) resin, polypropylene (PP) resin, and polybutylene resin; styrene resins; urethane resins; as well as polyoxymethylene (POM) resin, polyamide (PA) resin, polycarbonate (PC) resin, polymethyl methacrylate (PMMA) resin, and polyvinyl chloride. Examples of these resins include PVC resin, polyarylene sulfide (PAS) resin such as polyphenylene sulfide (PPS) resin, polyethersulfone (PES) resin, polyamide-imide (PAI) resin, polyetherimide (PEI) resin, polysulfone (PSU) resin, modified PSU resin, polyketone (PK) resin, polyetherketone (PEK) resin, polyetheretherketone (PEEK) resin, polyetherketoneketone (PEKK) resin, polyarylate (PAR) resin, polyethernitrile (PEN) resin, thermoplastic polyimide (PI) resin, polyphenylene ether (PPE) resin, modified PPE resin, and polyamide (PA) resin. These thermoplastic resins may also be copolymers or modified versions of the above-mentioned thermoplastic resins, and / or resins blended from two or more types.

[0028] <Component [C]> The conductive particles, which are component [C] used in the CFRP and prepreg of the present invention, can be any particles that behave as good electrically conductive particles, and are not limited to particles consisting solely of conductors. The volume resistivity of the conductive particles is preferably 10 Ωcm or less, more preferably 5 Ωcm or less, and even more preferably 1 Ωcm or less. By setting the volume resistivity within this range, conductive paths can be formed in the interlayer resin layer, thereby increasing conductivity in the thickness direction. Here, the volume resistivity can be calculated by setting the sample in a cylindrical cell having four probe electrodes, applying a pressure of 60 MPa to the sample, and measuring the thickness and resistance value of the sample.

[0029] Specific examples of such conductive particles include, but are not limited to, metal particles, metal oxide particles, metal-coated inorganic particles or organic polymer particles, polyacetylene particles, polyaniline particles, polypyrol particles, polythiophene particles, polyisothianaphthene particles, polyethylenedioxythiophene particles, or conductive polymer particles or carbon particles in which conductivity has been imparted to polyamide particles. Carbon particles and conductive polyamide particles (conductive polyamide particles) are particularly preferred.

[0030] Carbon particles are preferred because they do not pose a corrosion problem when used in aircraft. Crystalline carbon and amorphous carbon are preferred as carbon particles. Specific examples of amorphous carbon include "Bellpearl®" C-600, C-800, C-2000 (manufactured by Air Water Co., Ltd.), "NICABEADS®" ICB, PC, MC (manufactured by Nippon Carbon Co., Ltd.), Glassy Carbon (manufactured by Tokai Carbon Co., Ltd.), high-purity artificial graphite SG series, SGB series, SN series (manufactured by SEC Carbon Co., Ltd.), and spherical carbon (manufactured by Gun-ei Chemical Industry Co., Ltd.).

[0031] Conductive polyamide particles are preferred because they possess conductivity and simultaneously impart impact resistance to CFRP, a function of polyamide particles described later. Conductive polyamide particles are obtained by imparting conductivity to non-conductive polyamide particles, described later. The means for imparting conductivity to polyamide particles are not particularly limited, but include coating with a metal, conductive polymer, or conductive nanomaterial, or dispersion of a conductive polymer or conductive nanomaterial within the polyamide particles. Of these, from the viewpoint of achieving both conductivity and impact resistance, the method of coating with a metal or the method of dispersing particulate conductive nanomaterial inside the particles are preferred. The conductive nanomaterial is not particularly limited, but examples include carbon nanotubes, carbon black, and graphene. Preferably, conductive particles with an aspect ratio of 1.5 or less are used.

[0032] Furthermore, in addition to these conductive particles, conductive materials in forms other than particles, such as conductive fillers, short fibers, or the aforementioned conductive nanomaterials, can also be used in combination as needed.

[0033] <Forms of the constituent element [C] in CFRP and prepreg> Figure 1(a) is a schematic cross-sectional view showing an example of a partial structure in the CFRP 100 of the present invention. Specifically, to show the arrangement of conductive particles 2 in the interlayer resin layer 20 and carbon fibers 1 in the carbon fiber layers 10 on both sides of the interlayer resin layer 20, the figure shows a region cut from the cross-section of the CFRP, which includes the interlayer resin layers 20 on both sides of one carbon fiber layer 10 and a part of the carbon fiber layer 10 outside of it. In this schematic cross-sectional view, the carbon fibers 1, which are constituent element [A], and the conductive particles 2, which are constituent element [C], are shown by figures representing their cross-sections, while the matrix resin, which is constituent element [B], occupies the background area surrounding them and is not explicitly depicted. Furthermore, although the CFRP 100 in Figure 1(a) is a schematic representation of a commonly performed cross-lamination, the lamination form of the CFRP of the present invention is not limited to this.

[0034] The CFRP 100 of the present invention has a carbon fiber layer 10 containing components [A] and [B], and an interlayer resin layer 20 containing components [B] and [C] arranged between them. Typically, the outermost surface of the CFRP also has a resin layer.

[0035] In the present invention, CFRP can be obtained by laminating and molding a prepreg impregnated with a composition containing component [A] and component [B] to component [C]. In this case, since the prepreg has layers of matrix resin on the upper and lower surfaces of a CF sheet in which CF is arranged in a sheet-like manner, the laminate of the prepreg and the CFRP obtained therefrom have a carbon fiber layer containing the matrix resin and the CF sheet, and a resin layer sandwiched between adjacent carbon fiber layers. The thickness between adjacent carbon fiber layers and the thickness of the resin layer present between the carbon fiber layers are equivalent. In the present invention, conductive particles, which are component [C], are arranged in the resin layer present between adjacent carbon fiber layers (such resin layer is called the "interlayer resin layer"). The conductive particles arranged in the interlayer resin layer in this way form a portion that electrically connects the carbon fiber layers on both sides of the interlayer resin layer, thereby making the interlayer electrically conductive. This means that the conductive particles substantially connect to the carbon fiber layers present on both sides of the interlayer resin layer, forming conductive paths.

[0036] Figure 1(b) is a schematic cross-sectional view showing an example in which the matrix resin of component [B] of the CFRP of the present invention is a cured product of a thermosetting resin, and further includes thermoplastic resin particles as component [D], which will be described later. It is the same as in Figure 1(a), except that the thermoplastic resin particles of component [D] are dispersed in the matrix resin in the interlayer resin layer.

[0037] Figure 5(a) is a schematic cross-sectional view showing an example of the prepreg 110 of the present invention. Specifically, it shows the arrangement of carbon fibers 1 in the first layer 30 and conductive particles 2 in the second layer 40 adjacent to both sides thereof, and represents a cross-section of a prepreg composed of a second layer 40 adjacent to both sides of a single first layer 30. In this schematic cross-sectional view, the carbon fibers 1, which are component [A], and the conductive particles 2, which are component [C], are shown as figures representing their cross-sections, while the matrix resin, which is component [B], occupies the background area surrounding them.

[0038] The prepreg 110 of the present invention has a first layer 30 containing component [A] and component [B], and a second layer 40 containing component [B] and component [C] on one or both sides thereof. Note that a part of the resin composition contained in each layer may be mutually mixed into the adjacent layer. Fig. 5(a) shows an example having a structure in which the second layer 40 is adjacent to both sides of the first layer 30, but the form of the prepreg of the present invention is not limited thereto.

[0039] Fig. 5(b) is a schematic cross-sectional view showing an example in the case where the matrix resin of component [B] of the prepreg of the present invention is a thermosetting resin and further contains thermoplastic resin particles as component [D] to be described later. It is the same as Fig. 5(a) except that the thermoplastic resin particles of component [D] are dispersed in the matrix resin in the second layer.

[0040] <Particle size distribution of component [C] in CFRP> The conductive particles, which are component [C] used in the CFRP of the present invention, have one or more maxima in the range satisfying the following formulas (a) and (b) in the particle size distribution obtained from the cross section of the CFRP (the range satisfying formula (a) may be referred to as range a, and the range satisfying formula (b) may be referred to as range b). (a): Df × 1 / 6 ≤ Dsp ≤ Dlp × 2 / 3 (b): Tr × 1 / 5 ≤ Dlp ≤ Tr Dsp: The minimum number-based particle size [μm] having a maximum Dlp: The maximum number-based particle size [μm] having a maximum Df: Carbon fiber diameter [μm] Tr: Thickness [μm] of the interlayer resin layer Here, the particle size distribution in the present invention is a frequency distribution based on the number. Also, in the particle size distribution, the maximum means the position where the frequency becomes the maximum value in the number-based particle size distribution expressed as the frequency, which is Pspc and Plpc in Fig. 2. When there are two or more maxima in range a, the one with the higher peak height to be described later is Dsp, and when there are two or more maxima in range b, the one with the higher peak height is Dlp.

[0041] The meaning that the particle size distribution of the conductive particles, which are the constituent elements [C], has maxima in the range a and the range b is as follows. The conductive particles with a particle size in the range a, that is, conductive particles of Df × 1 / 6 or more, can be suppressed from entering between the CFs, and the conductive particles of Dlp × 2 / 3 or less can exist between the carbon fiber and the conductive particles in the particle size range of the range b. Also, in the particle size range of the range b, that is, conductive particles of Tr × 1 / 5 or more can form a conductive path between the CFs of the carbon fiber layers on both sides of the interlayer resin layer, and the conductive particles of Tr or less can form a conductive path without disturbing the fiber arrangement of the carbon fiber layer. Therefore, a conductive path can be formed while maintaining the mechanical properties. Furthermore, by having maxima in the ranges a and b respectively, a conductive path can be formed more efficiently by the above mechanism, and CFRP having high conductivity in the stacking direction can be obtained.

[0042] The above-mentioned particle size distribution of the conductive particles can be obtained by using in combination the conductive particles having a maximum in the range a (hereinafter sometimes abbreviated as "CPspc") and the conductive particles having a maximum in the range b (hereinafter sometimes abbreviated as "CP lpc"). Also, as described above, when the amount of CP lpc contained to improve conductivity is increased, the impact resistance may decrease. However, by using in combination the conductive particles of CPspc and CP lpc, that is, by using the conductive particles having one or more maxima in the above-mentioned ranges respectively, the amount of CP lpc contained can be suppressed, and the decrease in the compressive strength after impact (CAI), which will be described later, can be suppressed.

[0043] Regarding the number of maxima in the particle size distribution, there may be two or more in the range a, two or more in the range b, or two in each of the particle size ranges of both.

[0044] Methods for obtaining conductive particles with a predetermined particle size distribution include, for example, classifying a single conductive particle into a desired range, mixing two or more types of conductive particles with different particle size distributions, or, if necessary, classifying them after mixing. When using two or more types of conductive particles with different particle size distributions, the materials may be the same or different. If the desired particle size distribution for conductive particles has been obtained, classification may not necessarily be required.

[0045] The particle size distribution of conductive particles, which are component [C] used in the CFRP of the present invention, can be determined from a cross-sectional image of the CFRP. A cut sample of approximately 20 mm x 20 mm is obtained from the CFRP obtained by the molding method described later, embedded and cured with epoxy resin, and then the edge is polished. This polished surface is magnified 200 times or more using a laser microscope (e.g., digital microscope VHX-5000: manufactured by Keyence Corporation), and a photograph is taken so that one arbitrarily selected interlayer resin layer is within the field of view. From the obtained image, an image analysis software (e.g., ImageJ: Wayne Rasband, National Institutes of Health) is used to fit a perfect circle to the conductive particles present in the interlayer resin layer. The diameter of the fitted perfect circle is obtained and this is taken as the particle size of the conductive particle. This is done for each of 1000 arbitrarily selected particles. If the aspect ratio of conductive particles exceeds 1.5, an ellipse is used for fitting. The particle size detection range is set to 0 to 100 μm, and this range is divided into 1000 segments. A particle size distribution graph is obtained with particle size on the horizontal axis and relative frequency based on the number of particles on the vertical axis.

[0046] The carbon fiber diameter Df for defining range a can be determined as follows, assuming the carbon fibers are aligned in one direction. The polished surface of the CFRP obtained by the method described above is magnified 200 times or more using a laser microscope, and a photograph is taken so that a single carbon fiber layer of arbitrary choice is within the field of view. At this time, the polished surface perpendicular to the longitudinal direction of the carbon fiber is selected and photographed. Image analysis software is used to perform a circular fitting on the cross-section of the carbon fiber from the obtained image. The diameter of the fitted circle is obtained, and this is done for each of 1000 arbitrarily selected carbon fibers. The average value of the diameters is taken as the carbon fiber diameter Df.

[0047] The thickness of the interlayer resin layer for defining range b can be determined as follows: Using the image of the interlayer resin layer obtained by the method described above, parallel lines are drawn at each interface between the interlayer resin layer and the adjacent carbon fiber layer. The distance between these parallel lines between adjacent carbon fiber layers is measured at 20 or more randomly selected locations, and the average value of these measurements is taken as the average thickness of the interlayer resin layer.

[0048] <Particle Size Distribution of Component [C] in Prepreg> The conductive particles, which are component [C] used in the prepreg of the present invention, have, as condition (Ip), one or more maxima in the particle size distribution in the range of 1.5 μm or more and less than 10 μm, and one or more in the range of 10 μm or more and less than 100 μm. Here, the particle size distribution in the prepreg of the present invention is a frequency distribution based on the number of particles, similar to that in CFRP, and a maximum in the particle size distribution is the position where the frequency is at its maximum value in the particle size distribution based on the number of particles expressed as frequency. Figure 4 shows an example in which there is one maximum in each of the aforementioned particle size ranges, with the maximum in the range of 1.5 μm or more and less than 10 μm corresponding to Pspp, and the maximum in the range of 10 μm or more and less than 100 μm corresponding to Plpp.

[0049] Regarding condition (IIp), which is a narrower range than condition (Ip), the range in the particle size distribution of the conductive particles, which are component [C], where there is a maximum is preferably 2 μm or more and less than 8 μm for maximum Pspp, and more preferably 3 μm or more and less than 7 μm. Furthermore, for maximum Plpp, it is preferably 15 μm or more and less than 60 μm, and more preferably 18 μm or more and less than 50 μm. By setting the position of the maximum value for each to this range, it becomes easy to ensure that conductive particles with a maximum value on the smaller diameter side of component [C] are located between the carbon fibers, which are component [A], and conductive particles with a maximum value on the larger diameter side. As a result, the conductive particles and carbon fibers efficiently form conductive paths, making it possible to obtain CFRP with high conductivity in the lamination direction.

[0050] The particle size distribution of conductive particles as described above can be achieved by using two or more types of particles with different particle size distributions as the component [C], namely conductive particles with a mode diameter in the range of 1.5 μm to less than 10 μm (hereinafter sometimes abbreviated as "CPspp") and conductive particles with a mode diameter in the range of 10 μm to less than 100 μm (hereinafter sometimes abbreviated as "CPlpp"). In this way, by using two or more types of particles with different particle size distributions in combination, it becomes easy to efficiently form conductive paths. At this time, as mentioned above, increasing the amount of CPlpp contained in order to improve conductivity may reduce the impact resistance of CFRP. However, by using conductive particles of CPspp and CPlpp in combination, that is, by using conductive particles that each have one or more maxima in the aforementioned range, the amount of CPlpp contained can be suppressed, and the decrease in post-impact compressive strength (CAI) described later can be suppressed.

[0051] Regarding the number of maxima in the particle size distribution, there may be two or more in the range of 1.5 μm or more and less than 10 μm, or there may be two or more in the range of 10 μm or more and less than 100 μm, or there may be two in each particle size range.

[0052] Methods for obtaining conductive particles with a predetermined particle size distribution include, for example, classifying a single conductive particle into a desired range, mixing two or more types of conductive particles with different particle size distributions, or, if necessary, classifying them after mixing. When using two or more types of conductive particles with different particle size distributions, the materials may be the same or different. If the desired particle size distribution for conductive particles has been obtained, classification may not necessarily be required.

[0053] The particle size distribution of conductive particles, which are component [C] used in the prepreg of the present invention, can be obtained using a laser diffraction particle size analyzer (for example, SALD-2100: manufactured by Shimadzu Corporation). Conductive particles are added to distilled water so that the particle concentration of conductive particles is approximately 0.1% by mass, and a dispersion is obtained by ultrasonic treatment. The particle size distribution is measured from this dispersion using a laser diffraction particle size analyzer. The detection range for particle size is set to 0 to 100 μm, and this range is divided into 1000 segments. A particle size distribution graph is obtained with the particle size on the horizontal axis and the relative frequency based on the number of particles on the vertical axis. In addition, the mode diameter in the present invention is the particle size at which the relative frequency in the particle size distribution graph is maximized, and is rounded to the second decimal place.

[0054] <Content of constituent element [C] in CFRP> If the number of conductive particles that can be placed in the interlayer resin layer of CFRP is sufficiently large, the number of conductive particles necessary to connect the carbon fiber layers on both sides of the interlayer resin layer and exhibit conductivity will be secured. However, if the amount of particles is too large, problems with mechanical properties and process passability may occur, so there is a preferred range for the amount of particles that can be preferably placed. In terms of the content of constituent element [C] in CFRP, the ratio (Acp / Ar) of the area of ​​constituent element [C] (Acp) to the area of ​​the interlayer resin layer (Ar) in the cross-section of the CFRP is preferably 0.05 or more and 0.30 or less, and more preferably 0.10 or more and 0.25 or less. By keeping it within this range, conductivity can be exhibited in CFRP while maintaining CAI.

[0055] The area of ​​the conductive particles and the interlayer resin layer in this invention can be determined as follows. A cross-sectional image of the CFRP is obtained as described above, and a cross-sectional image of the interlayer resin layer is obtained from the obtained CFRP cross-sectional image that includes the minimum range in which 1000 conductive particles exist and includes the interface with the adjacent upper and lower carbon fiber layers. A circular or elliptical fitting is performed on the conductive particles present in the interlayer resin layer, and the area of ​​each cross-section is calculated, and the sum of these values ​​is taken as the area of ​​the conductive particles (Acp). In addition, the thickness of the interlayer resin layer is obtained from the above image as described above, and the area of ​​the interlayer resin layer (Ar) is obtained by multiplying it by the distance in the image width direction. Acp / Ar is calculated by dividing the obtained Acp by Ar.

[0056] In terms of the content of component [C], the ratio of the peak height of CPlpc (PTlpc) to the peak height of CPspc (PTspc) (PTlpc / PTspc) is preferably 0.05 or more and 0.50 or less, and more preferably 0.10 or more and 0.40 or less. If CPspc and CPlpc have two or more maxima, the one with the higher peak height is designated as PTspc and PTlpc, respectively. By setting the ratio within this range, it becomes easier for CPspc to exist between the carbon fibers and CPlpc, and conductive paths are efficiently formed, thereby obtaining CFRP with high conductivity in the lamination direction.

[0057] <Content of constituent element [Cp]> Similar to the content of constituent element [C] in CFRP, there may be a limit to the amount of particles that can be preferably arranged in the prepreg. When the total amount of matrix resin contained in the prepreg is 100 parts by mass, the CPspp is preferably 1 part by mass or more and 15 parts by mass or less, and more preferably 5 parts by mass or more and 13 parts by mass or less. By keeping it within this range, the resin composition can easily pass through the coater when creating the resin composition film described later, and the moldability of the resin composition film is improved. Furthermore, the CPlpp is preferably 1 part by mass or more and 10 parts by mass or less, and more preferably 2 parts by mass or more and 8 parts by mass or less. By keeping it within this range, conductivity can be expressed in CFRP while maintaining CAI.

[0058] <Ratio of Peak Heights of Component [C] in Prepreg> In the particle size distribution of component [C], the ratio of the peak height of CPlpp (PTlpp) to the peak height of CPspp (PTspp) (PTlpp / PTspp) is preferably 0.05 or more and 0.50 or less, and more preferably 0.10 or more and 0.40 or less. Here, the peak height in this invention is the value of the frequency of showing a maximum in the particle size distribution. If CPspp and CPlpp have two or more maxima, the one with the higher peak height is designated as PTspp and PTlpp, respectively. By setting the range to this, it becomes easy for CPspp to exist between the carbon fibers and CPlpp, and conductive paths are efficiently formed, so that a CFRP with high conductivity in the lamination direction can be obtained.

[0059] <Non-specific distribution of constituent element [C] in CFRP> In the CFRP of the present invention, one preferred embodiment is that the constituent element [C] is uniformly dispersed in the interlayer resin layer. However, in another preferred embodiment, the constituent element [C] may be unevenly distributed on the surface of the carbon fiber layer within the interlayer resin layer. An example of an uneven distribution on the surface of the carbon fiber layer within the interlayer resin layer is the embodiment in which the conductive particles present in the interlayer resin layer 20 in Figure 3(a) are unevenly distributed in region 21. As an example of an uneven distribution on the surface of the carbon fiber layer within the interlayer resin layer, an embodiment is in which 50 to 80% of the constituent element [C] in the interlayer resin layer are located within a range of 25%, more preferably 20%, and even more preferably 15% of the thickness of the interlayer resin layer in the thickness direction from the surface of the carbon fiber layer (hereinafter sometimes referred to as a specific range near the interface in the interlayer resin layer). By adopting this embodiment, conductive particles and carbon fibers efficiently form conductive paths, making it possible to obtain a CFRP with high conductivity in the lamination direction. Figure 3(b) is a schematic cross-sectional view showing an example in which the matrix resin of component [B] of the CFRP of the present invention is a cured product of a thermosetting resin, and further includes thermoplastic resin particles as component [D], which will be described later. It is the same as in Figure 3(a), except that the thermoplastic resin particles of component [D] are dispersed in the matrix resin in the interlayer resin layer.

[0060] The proportion of component [C] present in a specific range near the interface of the interlayer resin layer can be determined as follows. From the cross-sectional image obtained by the method described above, the number of conductive particles present in the interlayer resin layer and the coordinates of the particle centers are determined using image analysis software. When determining the center coordinates, if the particle shape on the cross-sectional photograph is a perfect circle or nearly a perfect circle and the aspect ratio is 1.5 or less, a perfect circle fitting can be used; if the aspect ratio exceeds 1.5, an ellipse fitting can be used. This is done for each of 1000 arbitrarily selected particles. Next, a line parallel to the surface of the carbon fiber layer is drawn from the surface of the carbon fiber layer at a depth of 25% of the average thickness of the interlayer resin layer near the surface in the thickness direction. The total number of conductive particles whose center coordinates exist between the surface of the carbon fiber layer and the parallel line (Nc1) and the total number of conductive particles whose center coordinates exist throughout the entire thickness of the interlayer resin layer (Nc2) are determined. By dividing Nc1 by Nc2, the proportion of conductive particles present in a specific range near the interface of the interlayer resin layer is calculated.

[0061] <Non-concentration of component [C] in the prepreg> In the prepreg of the present invention, one preferred embodiment is that component [C] is uniformly dispersed in the second layer. However, in another preferred embodiment, component [C] may be unevenly distributed in the second layer near the surface of the first layer. Figure 6(a) shows a schematic cross-sectional view illustrating an example in which conductive particles in the prepreg of the present invention are unevenly distributed in the second layer near the surface of the first layer. Figure 6(b) is a schematic cross-sectional view illustrating an example in which the matrix resin of component [B] of the prepreg of the present invention is a thermosetting resin, and further includes thermoplastic resin particles as component [D], which will be described later. It is the same as in Figure 6(a), except that the thermoplastic resin particles of component [D] are dispersed in the matrix resin in the second layer. One configuration in which the second layer is biased towards the surface of the first layer is one in which 50 to 80% of the constituent elements [C] in the second layer are located within an area (hereinafter sometimes referred to as the area near the inner surface of the second layer) that extends from the surface of the first layer (i.e., the inner surface of the second layer) toward the surface of the prepreg (i.e., the outer surface of the second layer) within 25%, more preferably within 20%, and even more preferably within 15% of the average thickness of the second layer. This configuration allows conductive particles and carbon fibers to efficiently form conductive paths, thereby obtaining a CFRP with high conductivity in the lamination direction.

[0062] The thickness of the second layer can be determined as follows.

[0063] (1) In the case of a prepreg using a thermosetting resin as the matrix resin, the prepreg is sandwiched between two smooth-surfaced polytetrafluoroethylene resin plates placed parallel to each other without applying any pressure to bring them into close contact, and the temperature is gradually raised to 150°C over 7 days to gel and harden, thereby producing a plate-shaped prepreg cured product. After hardening, it is cut in a direction perpendicular to the contact surface (thickness direction), the cross-section is polished, and then a photograph is taken using a laser microscope (for example, a digital microscope VHX-5000: manufactured by Keyence Corporation) at a magnification of 200 times or more so that the top and bottom surfaces of the prepreg cured product are within the field of view. Lines parallel to the longitudinal direction of the polytetrafluoroethylene resin plates are drawn on both sides of this cross-sectional photograph of the first layer. The distance between the polytetrafluoroethylene resin plates and the parallel lines is measured at 10 or more points on each side, for a total of 20 or more points on both sides, and the average value is taken as the average thickness of the second layer.

[0064] (2) In the case of a prepreg using a thermoplastic resin as the matrix resin, the prepreg is cut in the thickness direction, the cross-section is polished, and the average thickness is determined by measuring in the same manner as in (1).

[0065] The proportion of component [C] in a specific range near the inner surface of the second layer can be determined as follows. From the cross-sectional image of the prepreg obtained by the method described above, the number of conductive particles present in the second layer and the coordinates of the particle centers are determined using image analysis software. When determining the center coordinates, if the particle shape on the cross-sectional photograph is a perfect circle or nearly a perfect circle and the aspect ratio is 1.5 or less, a perfect circle fitting can be used; if the aspect ratio exceeds 1.5, an ellipse fitting can be used. This is done for each of 1000 arbitrarily selected particles. Image analysis software such as ImageJ (developed by Wayne Rasband, National Institutes of Health) can be used. Next, a line parallel to the surface of the first layer is drawn from the surface of the first layer, i.e., the inner surface of the second layer, toward the surface of the prepreg, i.e., the outer surface of the second layer, at a depth of 25% inside the average thickness of the second layer. The number of conductive particles whose center coordinates lie between the surface of the first layer and the parallel line (Np1) and the number of conductive particles whose center coordinates lie across the entire thickness of the second layer (Np2) are determined. By dividing Np1 by Np2, the proportion of conductive particles present in a specific area near the inner surface of the second layer is calculated. As described above, in the case of a prepreg with a thermosetting resin as the matrix resin, the cured prepreg is cured under very slow conditions, so the calculated value is considered to be the proportion present in a specific area near the inner surface of the second layer.

[0066] <Component [D]> In the CFRP of the present invention, if the matrix resin is a cured product of a thermosetting resin, thermoplastic particles, which are component [D], may be included in the interlayer resin layer. Similarly, in the prepreg of the present invention, if the matrix resin is a thermosetting resin, thermoplastic particles, which are component [D], may be included in the second layer. Such thermoplastic particles mainly consist of a thermoplastic resin, are non-conductive components, and preferably have a volume resistivity of more than 10 Ωcm. Polyamides and polyimides can be preferably used as such thermoplastic resins, with polyamide being the most preferred. By using polyamide particles, the interlayer toughness of the CFRP can be improved, and the impact resistance, such as CAI, which is important in aircraft applications described later, can be further improved. Suitable polyamides include nylon 12, nylon 11, nylon 6, nylon 66, nylon 6 / 12 copolymers, and nylon (semi-IPN nylon) that has been semi-IPN (polymer interpenetrating network structure) with the epoxy compound described in Example 1 of Japanese Patent Application Publication No. 01-104624. In molding, which involves applying pressure to a prepreg as described later, it is preferable for the polyamide particles to be crystalline, having a melting point above the molding temperature, as this makes it easier to obtain the desired interlayer thickness by preventing the polyamide particles from being crushed and maintaining their original particle shape.

[0067] To ensure that CAI is within a favorable range, the amount of component [D] in the CFRP is preferably such that the ratio (Atp / Ar) of the area of ​​component [D] (Atp) to the area of ​​the interlayer resin layer (Ar) in the cross-section of the CFRP is 0.10 or more and 0.50 or less, and more preferably 0.15 or more and 0.40 or less. Atp / Ar in this invention can be determined by the same method as Acp / Ar described above.

[0068] Furthermore, from the viewpoint of obtaining CFRP that combines excellent conductivity and impact resistance, it is preferable that the sum of the Acp / Ar and Atp / Ar ratios for the total content of constituent elements [C] and [D] is 0.15 to 0.70, more preferably 0.20 to 0.60, and even more preferably 0.30 to 0.50.

[0069] Furthermore, regarding the content of component [D] in the prepreg of the present invention, it is preferable that thermoplastic particles are present in amounts of 10 parts by mass or more when the mass of thermosetting resin contained in the prepreg is 100 parts by mass, while from the viewpoint of process passability, it is preferable that it is 50 parts by mass or less. More preferably, it is 11 parts by mass or more and 40 parts by mass or less, and even more preferably 12 parts by mass or more and 35 parts by mass or less.

[0070] <Addition of Thermoplastic Resin when the Matrix Resin is a Thermosetting Resin> In the present invention, when a thermosetting resin is used as the matrix resin, it is preferable to include a thermoplastic resin in addition to the component [D], and it is preferable that such a thermoplastic resin is compatible with the thermosetting resin used. The thermoplastic resin referred to here does not include thermoplastic particles, which are component [D] that remain in particulate form even in CFRP as described above. Thermosetting resins generally have the disadvantage of being brittle, but can be molded at low pressure by an autoclave. On the other hand, thermoplastic resins generally have the advantage of being tough, but are difficult to mold at low pressure by an autoclave. In other words, the two exhibit contradictory properties. However, by using a mixture of these, it is possible to balance physical properties and moldability in low-pressure molding by an autoclave. In the prepreg for obtaining the CFRP of the present invention, the thermoplastic resin dissolved in the thermosetting resin is preferably present in an amount of 5% by mass or more, and more preferably 10% by mass or more, when the total amount of the thermosetting resin composition excluding conductive particles and thermoplastic particles is taken as 100% by mass. From a process viewpoint, the upper limit is preferably 20% by mass or less.

[0071] As the thermoplastic resins mentioned above, polymers can be used that have bonds selected from carbon-carbon bonds, amide bonds, imide bonds, ester bonds, ether bonds, carbonate bonds, urethane bonds, urea bonds, thioether bonds, sulfone bonds, imidazole bonds, and carbonyl bonds in their main chain. Specifically, examples include polyacrylate, polyolefin, polyamide (PA), aramid, polyester, polycarbonate (PC), polyphenylene sulfide (PPS), polybenzimidazole (PBI), polyimide (PI), polyetherimide (PEI), polysulfone (PSU), polyethersulfone (PES), polyaryletherketone (PAEK), and polyamideimide (PAI). Examples of PAEK include polyetherketone (PEK), polyetherether-ketone (PEEK), and polyetherketoneketone (PEKK). In fields requiring heat resistance, such as aircraft applications, PPS, PES, PI, PEI, PSU, PEEK, PEKK, and PAEK are preferred. When epoxy resin is used as the thermosetting resin, PES is particularly preferred from the viewpoint of mechanical properties and compatibility with epoxy resin.

[0072] <Method for Manufacturing Prepregs> An example of a method for manufacturing the prepreg of the present invention will be described in detail. The prepreg of the present invention is preferably used to obtain the CFRP of the present invention. Prepregs are classified into cross prepregs, UD prepregs, etc., depending on the form of the reinforcing fiber base material used, but considering use in aircraft structural materials, it is preferable to use a UD prepreg, which is a so-called UD sheet in which CF is aligned in one direction as the form of the CF sheet. Of course, when using a cover prepreg to be attached to the surface of a structural material prepreg, or when using it for CFRP with complex shapes, CF woven fabric, in which CF is in a woven fabric form, can also be used. The following description will take a UD prepreg using a matrix resin mainly composed of thermosetting resin as an example. However, the present invention is not limited to such examples.

[0073] In this invention, it is preferable to use a two-stage impregnation method in which the matrix resin is impregnated in two stages in order to form orderly interlayers when CFRP is made and to control the number of conductive particles that connect multiple adjacent carbon fiber layers. The two-stage impregnation method will be explained using the case in which a thermoplastic resin dissolved in an epoxy resin, which is a thermosetting resin, is used as the matrix resin. First, for the prepreg intermediate material obtained by the first stage impregnation (hereinafter sometimes simply referred to as "prepreg intermediate material"), a primary resin composition is prepared by kneading using a combination of epoxy resin main agent, curing agent, and thermoplastic resin, and a primary resin composition film is produced by coating with this primary resin composition. After that, the CF bundles are aligned to form a UD sheet, the primary resin composition film is applied from above and below, and after preheating, pressure is applied with a nipple roll to impregnate the UD sheet with the primary resin composition and obtain the prepreg intermediate material. At this time, it is preferable to increase the degree of impregnation of the matrix resin in the prepreg intermediate material.

[0074] Next, in order to perform the second stage of impregnation, a secondary resin composition is prepared by adding conductive particles and, if necessary, thermoplastic particles to an epoxy resin main component, a curing agent, and a thermoplastic resin. The secondary resin composition is then coated to form a film, thereby producing a secondary resin composition film.

[0075] Then, a secondary resin composition film is applied to both the top and bottom surfaces of the prepreg intermediate material, and after preheating, it is laminated by pressurizing with a nipple roll. At this time, it is desirable to preheat sufficiently and ensure that the fluidity of the secondary resin composition is sufficiently maintained. After that, the prepreg is obtained by winding it up with a winding machine or the like.

[0076] Here, in order to distribute conductive particles in the second layer unevenly near the surface of the first layer, a secondary resin composition film can be made by attaching a resin composition film containing CPspp (hereinafter referred to as resin composition film 2c) to a resin composition film containing CPlpp (hereinafter referred to as resin composition film 2b). Specifically, for example, a resin composition is prepared by adding CPlpp to an epoxy resin main component, a curing agent, a thermoplastic resin, thermoplastic particles, and a resin composition film 2b is produced using a coater. Next, for example, a resin composition is prepared by adding CPspp to an epoxy resin main component, a curing agent, a thermoplastic resin, thermoplastic particles, and a resin composition film 2c is produced using a coater. A secondary resin composition film is produced by attaching the resin composition film 2c to the surface of the resin composition film 2b. As described above, a secondary resin composition film is applied to both the upper and lower surfaces of the prepreg intermediate material so that the resin composition film 2c is in contact with the prepreg intermediate material. After preheating, the material is pressed with a nipple roll and laminated to obtain a prepreg.

[0077] <Carbon Fiber Reinforced Composite Material (CFRP)> The CFRP of the present invention can be obtained by laminating two or more sheets of the prepreg of the present invention and molding it, and various known methods can be used as the method. For example, a method in which the obtained prepreg is cut to a predetermined size, a predetermined number of prepregs are laminated, and then heat-cured while applying pressure can be preferably used.

[0078] Methods for heat-molding laminated prepregs while applying pressure include press molding, autoclave molding, bagging molding, wrapping tape molding, and internal pressure molding, and are used appropriately depending on the application. Among these, autoclave molding is often applied to aircraft and spacecraft applications because it yields CFRP with excellent performance and stable quality.

[0079] The temperature for molding CFRP is set or adjusted as follows: (1) When the matrix resin of the prepreg is a thermosetting resin, molding with thermosetting resin proceeds through the flow of the uncured thermosetting resin due to heat and the fixing of the shape through curing by crosslinking of the thermosetting resin. In this case, the temperature for molding CFRP needs to be adjusted, for example, depending on the type of curing agent mixed into the epoxy resin. When an aromatic amine compound is used as the curing agent, molding is usually performed at a temperature in the range of 150 to 220°C. If the molding temperature is too low, sufficient curing may not be obtained, and conversely, if it is too high, warping due to thermal distortion may easily occur. (2) When the matrix resin of the prepreg is a thermoplastic resin, molding with thermoplastic resin proceeds through the softening or flow of the thermoplastic resin due to heat and the fixing of the shape through solidification by cooling. In this case, the temperature for molding CFRP needs to be adjusted, for example, depending on the thermal properties of the thermoplastic resin. If the thermoplastic resin is a crystalline resin, it is preferable to be above the melting point, and if it is an amorphous resin, it is preferable to be above the glass transition temperature. When PEKK is used as the thermoplastic resin, molding is usually performed at a temperature in the range of 340 to 380°C. If the molding temperature is too low, the fluidity of the resin will be poor, and unimpregnated areas may exist within the carbon fiber layer. Conversely, if the temperature is too high, thermal decomposition of the resin may occur.

[0080] The pressure used to mold CFRP using the autoclave molding method varies depending on the thickness of the prepreg and the volume content of the reinforcing fibers, but it is usually in the range of 0.1 MPa to 1 MPa. This allows for the production of CFRP that is free from defects such as voids and has minimal dimensional variations such as warping.

[0081] <Volume resistivity in the thickness direction> The volume resistivity in the thickness direction of the CFRP after laminating and molding the prepreg of the present invention in a specific configuration described later is 1.0 × 10 ３ It is preferable that the density be less than or equal to Ωcm, and more preferably 1.0 × 10⁻� ２The resistivity is less than or equal to Ωcm, and more preferably less than or equal to 6.7 × 10 Ωcm. By keeping it within this range, electrical damage such as lightning strikes and static electricity dissipation can be suppressed when CFRP is used as a component, and especially in the case of aircraft applications, it is possible to reduce the amount of metal mesh etc. provided on the surface of the component as a countermeasure against lightning strikes, which is also effective in reducing weight. On the other hand, if the volume resistivity of the interlayer resin layer located between adjacent carbon fiber layers is made very small, the manufacturing process will become complicated and the cost may increase significantly, so in reality, 1.0 × 10 －１ A density of Ωcm or greater is preferable.

[0082] The volume resistivity in the thickness direction can be measured by the following method. Specifically, a unidirectional prepreg is laid symmetrically, with the longitudinal direction of the carbon fibers set to 0°, and the pattern [+45° / 0° / -45° / 90°] repeated twice. This is then heated and pressurized in an autoclave, and a sample is cut from the resulting fiber-reinforced composite material panel. Subsequently, the structure of symmetrically laid layers of [+45° / 0° / -45° / 90°] repeated twice is then measured in the [+45° / 0° / -45° / 90°] direction. ２ｓ This is referred to as the composition. After completely removing the resin layers from both surfaces of the sample by polishing, conductive paste is applied to both sides to prepare a sample piece. The volume resistivity of the obtained sample piece is determined by measuring the resistance in the lamination direction using the four-terminal method with a digital multimeter, and this value is used as the conductivity in the thickness direction. Here, the heating and pressurizing conditions using the autoclave, as well as the dimensions of the sample, the curing conditions after applying the conductive paste, and the digital multimeter and conductive paste used are as described in section (7) Measurement of Volume Resistivity in the Thickness Direction of CFRP in the Examples.

[0083] <CAI (Compression Strength After Impact)> The CFRP of the present invention can have high impact resistance and high conductivity in the thickness direction. The impact resistance of the CFRP of the present invention can be measured using the Compression Strength After Impact (CAI), which is an important indicator of impact resistance in aircraft applications. The CFRP formed by laminating the prepreg of the present invention in a specific configuration described later is preferable if the compressive strength after applying an impact of 6.7 J / mm is 230 MPa or more, as this allows it to maintain its strength even after weak impacts such as dropping a tool or being hit by a pebble. It is even more preferable if the CAI is 260 MPa or more, and more preferably 270 MPa or more. There is no particular upper limit on the CAI value, and the higher the value, the greater the safety when the CFRP is applied as a structural member, but usually a value of 500 MPa is used. The method for measuring CAI is as described in section (8) Post-Impact Compressive Strength (CAI) of the Examples.

[0084] <Structure> The CFRP of the present invention can be used in shapes selected from flat plate structures, cylindrical structures, box-shaped structures, C-shaped structures, H-shaped structures, L-shaped structures, T-shaped structures, I-shaped structures, Z-shaped structures, and hat-shaped structures. By combining these structures, complex-shaped parts can be obtained, and the CFRP of the present invention can be suitably used in aircraft parts, which often use complex-shaped parts. For details on the above-mentioned shapes of structures, see, for example, "Structural Design of Aircraft," 5th edition, Torikai and Kuze, Japan Aeronautical Technology Association (2003). Such structures can be obtained, for example, by shaping prepregs as described in International Publication No. 2017 / 110991 (paragraph

[0084] ), International Publication No. 2016 / 043156 (paragraph

[0073] ), and International Publication No. 2019 / 031478 (paragraph

[0088] ). Furthermore, a structure having the desired shape can also be obtained by automatically laminating prepreg tape onto a mold having the desired shape and then curing it.

[0085] In aircraft manufacturing, the fuselage, wings, center wing, tail wing, etc., are formed by joining multiple of the above-mentioned structures. Bolts, rivets, and other fasteners, as well as adhesive films, are used as means of joining these structures. Furthermore, if the matrix resin of the prepreg is a thermosetting resin, a co-cure method can be used, in which multiple uncured or semi-cured prepreg laminates are joined together and then cured.

[0086] The upper and lower limits of the numerical ranges described above can be combined in any way unless otherwise specified.

[0087] Furthermore, when evaluating the cross-section of the CFRP using the method described above, if the evaluation results for an arbitrarily selected cross-section differ from those for other arbitrarily selected cross-sections, and one of them falls within the scope or preferred scope of the present invention, but the other does not, then the average of the evaluation results for three arbitrarily selected cross-sections shall be used to determine whether or not it falls within the scope.

[0088] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to these examples. The unit "parts" in composition ratios refers to parts by mass unless otherwise specified. Furthermore, the measurements of various properties (physical properties) were performed under conditions of 23°C and 50% relative humidity unless otherwise specified. Unless otherwise specified, the number of measurements (n) was 1.

[0089] <Raw Materials> (1) Carbon Fiber (CF) A CF bundle was used, consisting of 24,000 filaments per bundle of CF with a fiber diameter of 5.5 μm, having a tensile strength of 5.8 GPa and a tensile modulus of 280 GPa measured according to JIS R 7606:2000.

[0090] (2) Thermosetting resins: "SumiEpoxy®" ELM434 (tetraglycidyldiaminodiphenylmethane (TGDDM), manufactured by Sumitomo Chemical Co., Ltd.); "EPICLON®" 830 (bisphenol F-type epoxy resin, manufactured by DIC Corporation).

[0091] (3) Hardening agent: Seika Cure-S (4,4'-diaminodiphenylsulfone, manufactured by Seika Co., Ltd.).

[0092] (4) Thermoplastic resin (PES) - “Sumika Excel (registered trademark)” 5003P (polyethersulfone, manufactured by Sumitomo Chemical Co., Ltd.).

[0093] (5) Thermoplastic particles - 6 spherical polyamide particles (D50: 15 μm, sphericity 96%, manufacturing method described below) Referring to International Publication No. 2018 / 207728, 200 g of ε-caprolactam (manufactured by Toray Industries, Inc.), 800 g of polyethylene glycol (Wako Pure Chemical Industries, Ltd., Grade 1 polyethylene glycol 20,000, mass average molecular weight 18,600), and 1,000 g of water were added to a 3 L autoclave equipped with a helical ribbon-type stirring blade to form a homogeneous solution, which was then sealed and purged with nitrogen. Subsequently, the stirring speed of the stirring blade was set to 100 rpm and the temperature was raised to 240°C. During this time, after the system pressure reached 1 MPa, the pressure was controlled by slowly releasing water vapor to maintain the pressure at 1 MPa. After the temperature reached 240°C, the pressure was released at a rate of 0.02 MPa / min. Subsequently, the above temperature was maintained for 1 hour while flowing nitrogen to complete polymerization, and the slurry was discharged into a water bath containing 2,000 g of water to obtain a slurry. After dissolving the unreacted material in the water bath, the slurry was filtered, and 2,000 g of water was added to the filtered product and washed at 80°C. The slurry liquid after washing was filtered through a 200 μm sieve to remove aggregates. The filtrate from which the aggregates had been removed was filtered again, and the isolated filtered product was dried at 80°C for 12 hours to prepare 140 g of polyamide 6 powder. The melting point of the obtained powder was 218°C, the same as polyamide 6, and the crystallization temperature was 170°C.

[0094] (6) Conductive particles - Conductive particle A: "NICABEADS®" ICB-0120 (manufactured by Nippon Carbon Co., Ltd.), (component: carbon, mode diameter: 1.5 μm) - Conductive particle B: "NICABEADS®" ICB-0520 (manufactured by Nippon Carbon Co., Ltd.), (component: carbon, mode diameter: 3.0 μm) - Conductive particle C: "NICABEADS®" ICB-1020 (manufactured by Nippon Carbon Co., Ltd.), (component: carbon, mode diameter: 9.5 μm) - Conductive particle D: "NICABEADS®" ICB-2020 (manufactured by Nippon Carbon Co., Ltd.), (component: carbon, mode diameter: 17.3 μm) • Conductive particle E: Conductive particles obtained by classifying "NICABEADS®" ICB-2020 (manufactured by Nippon Carbon Co., Ltd.), (component: carbon, mode diameter: 28.1 μm).

[0095] The mode diameter of each conductive particle was obtained by (1) measurement of the particle size distribution of conductive particles, as described in the following <Various Evaluation Methods>.

[0096] <Various Evaluation Methods> (1) Measurement of Particle Size Distribution of Conductive Particles Conductive particles were added to distilled water so that the particle concentration of conductive particles was approximately 0.1 mass%, and a dispersion was prepared by ultrasonic treatment. A particle size distribution graph was obtained using a laser diffraction particle size analyzer (SALD-2100: manufactured by Shimadzu Corporation), with the horizontal axis representing particle size and the vertical axis representing relative frequency based on the number of particles.

[0097] (2) Preparation of thermosetting resin composition An epoxy resin main component and a thermoplastic resin (PES), which are thermosetting resins, were kneaded together, the temperature was raised to 150°C or higher, and the mixture was stirred for 1 hour to dissolve the PES in the epoxy resin main component and obtain a transparent viscous liquid. After the temperature of this liquid was lowered while kneading, a curing agent was added and the mixture was kneaded further to obtain a primary resin composition.

[0098] In addition, the same transparent viscosity liquid as described above was prepared separately, and after being cooled while being kneaded, the curing agent, thermoplastic particles, and conductive particles listed in <Raw Materials> were added and kneaded to obtain secondary resin composition 2a.

[0099] Furthermore, the same transparent viscosity liquid as described above was prepared separately, and after cooling while kneading, a curing agent, polyamide particles, and conductive particles were added and kneaded to obtain resin composition 2b. Similarly, resin composition 2c was obtained by adding a curing agent, polyamide particles, and conductive particles to a transparent viscosity liquid.

[0100] Table 1 shows the composition ratio of the obtained primary resin composition, Table 2 shows the composition ratio of secondary resin composition 2a, and Tables 3 and 4 show the composition ratios of resin composition 2b and resin composition 2c for secondary resins, respectively (the units in each table are parts by mass). Hereafter, resin composition 2b and resin composition 2c for secondary resins will be abbreviated as resin composition 2b and resin composition 2c, respectively.

[0101] (3) Preparation of a prepreg with uniformly dispersed conductive particles The primary resin composition and secondary resin composition 2a prepared in (2) were used to prepare the prepreg using a two-stage impregnation method as follows. The primary resin composition and secondary resin composition 2a prepared in (2) were uniformly applied to a silicone-coated release paper using a coater to form a primary resin composition film and a secondary resin composition film a, respectively. Then, CF uniformly aligned in one direction was sandwiched between the two primary resin composition films, and the mixture was heated and pressurized using a press roll to obtain a prepreg intermediate material in which the primary resin composition was sufficiently impregnated into the CF (the basis weight of the CF was 268 g / m²). ２ The resin content (Rc) was 17% by mass. Next, both release papers were peeled off the prepreg intermediate material. Then, the prepreg intermediate material was sandwiched between two secondary resin composition films a, and heated and pressurized using a press roll to impregnate the prepreg intermediate material with resin composition 2a and obtain a prepreg in which conductive particles were uniformly dispersed (CF basis weight 268 g / m²). ２ , Rc34% by mass).

[0102] Tables 5 and 6 indicate the presence of component [A] and the presence of one or more maxima within a predetermined range in the particle size distribution of conductive particles, respectively, with "Present" in the corresponding column, and "Absent" if the above are not present. The same applies to the prepregs prepared in (4).

[0103] (4) Preparation of a prepreg with unevenly distributed conductive particles Using the primary resin composition prepared in (2), a prepreg intermediate material was obtained in the same manner as in (3). Next, in the same manner as in (3), the resin composition 2b and resin composition 2c prepared in (2) were uniformly applied with a coater onto a silicone-coated release paper to obtain resin composition film 2b and resin composition film 2c. The resin composition film 2c was attached to the surface of the resin composition film 2b, from which the release paper on one side had been peeled off, and the release paper on the side of resin composition film 2c was peeled off to obtain a secondary resin composition film b. Then, the secondary resin composition film b was applied to both the upper and lower surfaces of the prepreg intermediate material so that the side of resin composition film 2c was in contact with the prepreg intermediate material, and heated and pressurized in the same manner as in (3) so that the resin composition 2b and resin composition 2c impregnated the prepreg intermediate material, and a prepreg with unevenly distributed conductive particles was obtained.

[0104] (5) Evaluation of the distribution of conductive particles in the prepreg The prepregs prepared in (3) and (4) were pressed between two parallel, smooth-surfaced polytetrafluoroethylene resin plates without applying any pressure, and the temperature was gradually increased to 150°C over seven days to gel and harden, producing a plate-shaped hardened material. After hardening, the prepregs were cut in a direction perpendicular to the contact surface (thickness direction), the cross-sections were polished, and the images were photographed using a VHX-5000 at a magnification of 200x or more, so that the top and bottom surfaces of the prepregs were within the field of view. Lines parallel to the longitudinal direction of the polytetrafluoroethylene resin plates were drawn on both sides of the first layer in these cross-sectional photographs. The distance between the polytetrafluoroethylene resin plates and the parallel lines was measured at 10 or more points on each side of the first layer, for a total of 20 or more points on both sides, and the average value was taken as the average thickness of the second layer. From the above cross-sectional images, the number of conductive particles present in the second layer and the coordinates of the centers of each particle were determined using image analysis software. ImageJ (developed by Wayne Rasband, National Institutes of Health) was used as the image analysis software. Circular fitting was used to determine the center coordinates. This was done for each of 1000 arbitrarily selected particles. Next, a line parallel to the surface of the first layer was drawn from the surface of the first layer toward the surface of the prepreg at a depth of 25% of the average thickness of the second layer. The number of all conductive particles whose center coordinates exist between the surface of the first layer and this parallel line (Np1) and the number of all conductive particles whose center coordinates exist across the entire thickness of the second layer (Np2) were determined. By dividing Np1 by Np2, the proportion of conductive particles present in a specific area near the inner surface of the second layer was calculated and defined as the proportion present in that specific area near the inner surface of the second layer.

[0105] (6) Evaluation of the peak height ratio of conductive particles in the prepreg From the particle size distribution obtained in (5), the peak height of CPspp (PTspp), which is the number-based frequency of CPspp, and the peak height of CPlpp (PTlpp), which is the number-based frequency of CPlpp, are calculated. The peak height ratio of conductive particles, PTlpp / PTspp, is calculated by dividing the obtained PTlpp by PTspp.

[0106] (7) Measurement of volume resistivity in the thickness direction of CFRP The longitudinal direction of the CF contained in the prepreg prepared in (3) and (4) is set to 0°, and [+45° / 0° / -45° / 90°] ２ｓ The materials were laminated in a configuration to form a pseudo-isotropic pre-laminate with a total of 16 plies. The obtained pre-laminate was set in an autoclave and heated at a pressure of 0.6 MPa from room temperature to 180°C at a rate of 1.7°C per minute, and cured at 180°C for 2 hours to obtain CFRP. A 40 mm x 40 mm sample was cut from the obtained CFRP, and after polishing off the resin layer on both surfaces, conductive paste "Do-Tite®" D-550 (manufactured by Fujikura Chemical Co., Ltd.) was applied to both sides to a thickness of approximately 70 μm using a bar coater, and cured in a hot air oven adjusted to a temperature of 120°C for 1 hour to obtain a sample for conductivity evaluation. The resistance in the thickness direction of the obtained sample was measured using the four-terminal method with an Advantest R6451A 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.

[0107] (8) Compressive strength after impact (CAI) The prepreg prepared in (3) and (4) is subjected to [+45° / 0° / -45° / 90°] ２ｓ A CFRP (carbon fiber reinforced polymer) was fabricated by laminating 16 plies in a pseudo-isotropic manner and molding it in an autoclave at a temperature of 180°C for 2 hours at a pressure of 0.6 MPa and a heating rate of 1.7°C / min. A 150 mm x 100 mm sample was cut from this CFRP, and a drop weight impact of 6.7 J / mm was applied to the center of the sample according to SACMA SRM 2R-94. A compression fracture test was then performed to determine the post-impact compressive strength (CAI). Measurements were performed on five samples cut from one CFRP panel, and the average value was taken as the post-impact compressive strength.

[0108] (9) Measurement of particle size distribution of conductive particles in CFRP A cut sample of approximately 20 mm x 20 mm was obtained from the CFRP prepared in (7), embedded and cured with epoxy resin, and the edge was polished. The polished surface was magnified more than 200 times using a VHX-5000, and a photograph was taken so that one arbitrarily selected interlayer resin layer was within the field of view. From the obtained image, a perfect circle was fitted to the conductive particles present in the interlayer resin layer using image analysis software. The diameter of the fitted circle was obtained and this was taken as the particle size of the conductive particles. This was done for each of 1000 arbitrarily selected particles. The particle size detection range was set to 0 to 100 μm, and this range was divided into 1000 parts. A particle size distribution graph was obtained with the particle size on the horizontal axis and the relative frequency based on the number of particles on the vertical axis.

[0109] The carbon fiber diameter for defining range a was determined as follows: The polished surface of the CFRP obtained by the method described above was magnified to more than 200 times using a laser microscope, and a photograph was taken so that one arbitrarily selected carbon fiber layer was within the field of view. At this time, the polished surface perpendicular to the longitudinal direction of the carbon fiber was selected for the photograph. An image analysis software was used to fit a perfect circle to the cross-section of the carbon fiber from the obtained image. The diameter of the fitted circle was obtained, and the average value of the diameters was taken as the diameter of the carbon fiber. This was done for each of 1000 arbitrarily selected carbon fibers.

[0110] The thickness of the interlayer resin layer used to define range b was determined as follows: Using the image of the interlayer resin layer obtained by the method described above, parallel lines were drawn at each interface between the interlayer resin layer and the adjacent carbon fiber layer. The distance between these parallel lines between adjacent carbon fiber layers was measured at 20 or more arbitrarily selected locations, and the average value was taken as the average thickness of the interlayer resin layer.

[0111] (10) Evaluation of the peak height ratio of conductive particles in CFRP From the particle size distribution obtained in (9), the peak height of CPspc (PTspc), which is the number-based frequency of CPspc, and the peak height of CPlpc (PTlpc), which is the number-based frequency of CPlpc, are calculated. The peak height ratio of conductive particles, PTlpc / PTspc, is calculated by dividing the obtained PTlpc by PTspc.

[0112] (11) Evaluation of the area ratio of conductive particles and thermoplastic particles in CFRP A cross-sectional image of the interlayer resin layer was obtained from the cross-sectional image of the CFRP obtained in (7), including the minimum range in which 1000 conductive particles exist and including the interface with the adjacent upper and lower carbon fiber layers. As in (9), circular fitting was performed on the conductive particles present in the interlayer resin layer, and the area of ​​each circle was calculated, and the sum of these was taken as the area of ​​the conductive particles (Acp). This was done for each of the 1000 arbitrarily selected particles. In addition, the thickness of the interlayer resin layer was obtained from the image used to calculate the area of ​​the conductive particles, as in (9), and the area of ​​the interlayer resin layer (Ar) was obtained by multiplying it by the distance in the image width direction. Acp / Ar was calculated by dividing the obtained Acp by Ar. In addition, the area of ​​thermoplastic particles (Atp) was calculated using the same method as when Acp was obtained, and Atp / Ar was calculated by dividing it by Ar.

[0113] (12) Evaluation of the distribution of conductive particles in CFRP Using image analysis software, the number of conductive particles present in the interlayer resin layer and the coordinates of the particle centers were determined from the cross-sectional image of the CFRP obtained in (7). This was done for each of 1000 arbitrarily selected particles. Next, a line parallel to the surface of the carbon fiber layer was drawn from the surface of the carbon fiber layer in the thickness direction at a depth of 25% of the average thickness of the interlayer resin layer. The total number of conductive particles whose center coordinates exist between the surface of the carbon fiber layer and the parallel line closest to it (Nc1) and the total number of conductive particles whose center coordinates exist throughout the entire thickness of the interlayer resin layer (Nc2) were determined. By dividing Nc1 by Nc2, the ratio of conductive particles present in a specific range near the inner surface of the interlayer resin layer was calculated, and this ratio is shown in the CFRP characteristics column of the table as the uneven distribution of component [C].

[0114] (Example 1) Using the primary resin composition shown in Table 1 and the resin compositions 2b and 2c shown in Tables 3 and 4, a thermosetting resin composition was prepared according to the methods of <Various Evaluation Methods> (2) and (4), and then a prepreg was produced. With respect to the obtained prepreg, according to <Various Evaluation Methods> (5), as a result of evaluating the distribution of the conductive particles present in the second layer, 78% of the number of conductive particles were present in the range of 25% or less near the inner surface in the second layer. According to the method of <Various Evaluation Methods> (6), as a result of evaluating the ratio of the peak heights of the conductive particles, PTlpp / PTspp was 0.14. Also, using the obtained prepreg, according to <Various Evaluation Methods> (7) and (8), as a result of evaluating the physical properties of the CFRP, the volume resistivity in the thickness direction was 20.0 Ωcm, and the CAI was 282 MPa, and a CFRP having excellent conductivity and impact resistance was obtained. According to <Various Evaluation Methods> (9) and (10), as a result of evaluating the particle size distribution of the conductive particles in the CFRP, they were conductive particles having one or more maxima in ranges a and b respectively, and the ratio of the peak heights (PTlpc / PTspc) was 0.12. According to <Various Evaluation Methods> (11), as a result of evaluating the area ratio of the conductive particles and the thermoplastic particles to the area of the interlayer resin layer, Acp / Ar was 0.16 and Atp / Ar was 0.23. According to <Various Evaluation Methods> (12), as a result of evaluating the distribution of the conductive particles present in the interlayer resin layer, 78% of the conductive particles were present in the range of 25% or less of the thickness of the interlayer resin layer from the surface of the carbon fiber layer.

[0115] (Examples 2 - 8) Except for changing the resin compositions 2b and 2c as shown in Tables 3 and 4, the preparation of the thermosetting resin composition and the production of the prepreg were carried out and evaluated in the same manner as in Example 1. The results of various measurements are as shown in Table 5. Even when the materials and content ratios were varied within a predetermined range as in Examples 2 - 8, there were no problems with the particle distribution of the conductive particles, the prepreg properties, and the CFRP properties, and a CFRP having excellent conductivity and impact resistance was obtained.

[0116] (Example 9) As shown in Tables 3 and 4, the resin compositions 2b and 2c were changed, and further the basis weight of the CF was 194 g / m ２Except for changing the Rc content to 34% by mass, the thermosetting resin composition was prepared and the prepreg was manufactured in the same manner as in Example 1, and then evaluated. The results of various measurements are shown in Table 5. As in Example 9, by changing the CF basis weight, a CFRP with excellent conductivity and impact resistance was obtained even when the thickness of the interlayer resin layer was varied within a predetermined range.

[0117] (Example 10) Except for changing the resin composition 2a as shown in Table 2 and following the method for preparing the prepreg in <Various Evaluation Methods> (3), the thermosetting resin composition was prepared and the prepreg was prepared and evaluated in the same manner as in Example 1. The results of the various measurements are shown in Table 5. A CFRP with excellent conductivity and impact resistance was obtained, but the conductivity was lower compared to Example 7, in which the total amount of conductive particles was the same and only the dispersibility of the conductive particles in the interlayer resin layer was different.

[0118] (Comparative Examples 1-6) Except for changing the secondary resin composition 2a as shown in Table 2, the thermosetting resin composition was prepared and the prepreg was made and evaluated in the same manner as in Example 10. The results of various measurements are shown in Table 6.

[0119] In Comparative Example 1, conductive particle D was used alone, and it was a conductive particle that showed only one maximum in the number-based particle size distribution. The obtained CFRP showed excellent impact resistance with a CAI of 275 MPa, but the volume resistivity in the thickness direction was 28.6 Ωcm, which was significantly lower than 67 Ωcm, and the conductivity in the thickness direction was remarkably low compared to Examples 1 to 10.

[0120] In Comparative Examples 2 and 3, the content of conductive particles D increased compared to Comparative Example 1, resulting in superior conductivity. However, the CAI of the resulting CFRP decreased significantly. Comparing Comparative Example 3 with Examples 1 to 3, it can be seen that even with approximately the same total amount of conductive particles, using conductive particles having one or more maxima in ranges a and b of the particle-based particle size distribution improved conductivity in the thickness direction while maintaining impact resistance.

[0121] In Comparative Example 4, conductive particles B with small particle sizes were used alone, and these conductive particles showed only one maximum in the number-based particle size distribution. The resulting CFRP showed excellent impact resistance with a CAI of 282 MPa, but the conductivity in the thickness direction was low.

[0122] Comparative Example 5 used conductive particles D and E in combination, resulting in conductive particles that showed two maxima in range b in the particle size distribution. The resulting CFRP had a volume resistivity in the thickness direction of 10.2 Ωcm, showing excellent conductivity, but the CAI was low. Comparing Comparative Example 5 with Examples 1 to 3, it can be seen that even with the same total amount of conductive particles, using conductive particles with one or more maxima in range b in the number-based particle size distribution improved conductivity in the thickness direction compared to using conductive particles with two or more maxima in range b.

[0123] Comparative Example 6 used conductive particles A and conductive particles B in combination, resulting in conductive particles that showed two maxima in range a in the particle number-based particle size distribution. It showed excellent impact resistance with a CAI of 282 MPa, but the conductivity in the thickness direction was low. Comparing Comparative Example 6 with Examples 1 to 3, it can be seen that even with the same total amount of conductive particles, using conductive particles that have one or more maxima in range a and range b respectively improved the conductivity in the thickness direction compared to using conductive particles that show two or more maxima in range a in the particle number-based particle size distribution.

[0124]

[0125]

[0126]

[0127]

[0128]

[0129]

[0130] The CFRP of the present invention is widely applicable to industrial fields where electrical conductivity is required for the material. In particular, when used in aircraft structural components, it can reduce the need for conventional lightning protection systems, static elimination systems, and electromagnetic shielding systems such as metal foil and metal mesh, making it suitable for use in such fields.

[0131] 1: Carbon fiber 2: Conductive particles 3: Thermoplastic particles 10: Carbon fiber layer 20: Interlaminar resin layer 21: Area from the surface of the carbon fiber layer to 25% or less of the thickness of the interlaminar resin layer 30: First layer 40: Second layer 41: Area from the surface of the first layer toward the surface of the prepreg to 25% or less of the thickness of the second layer 100: CFRP 110: Prepreg Scc1, Scc2: Surface of the carbon fiber layer Tpc1, Tpc2: Average thickness of the interlaminar resin layer Tpc11, Tpc21: Average thickness of 25% of the thickness of the interlaminar resin layer Sp1, Sp2: Surface of the prepreg Scp1, Scp2: Surface of the first layer Tpp1, Tpp2: Average thickness of the second layer Tpp11, Tpp21: Average thickness of 25% of the thickness of the second layer Pspc: Maximum of CPspc in the particle size distribution of conductive particles in CFRP Plpc: Maximum of CPlpc in the particle size distribution of conductive particles in CFRP PTspc: Peak height of CPspc in the particle size distribution of conductive particles in CFRP PTlpc: Peak height of CPlpc in the particle size distribution of conductive particles in CFRP Pspp: Maximum of CPspp in the particle size distribution of conductive particles in prepreg Plpp: Maximum of CPlpp in the particle size distribution of conductive particles in prepreg PTspp: Peak height of CPspp in the particle size distribution of conductive particles in prepreg PTlpp: Peak height of CPlpp in the particle size distribution of conductive particles in prepreg

Claims

1. A carbon fiber reinforced composite material comprising the following components [A], [B], and [C], wherein the structure consists of a plurality of carbon fiber layers comprising components [A] and [B], and an interlayer resin layer disposed between adjacent carbon fiber layers that does not contain component [A] but contains components [B] and [C], and the component [C] contained in the interlayer resin layer satisfies condition (Ic). [A]: carbon fiber [B]: matrix resin [C]: conductive particles (Ic): in the number-based particle size distribution of component [C] obtained from the cross-section of the carbon fiber reinforced composite material, there is one or more maxima in the ranges of (a) and (b), respectively. (a): Df × 1 / 6 ≤ Dsp ≤ Dlp × 2 / 3 (b): Tr × 1 / 5 ≤ Dlp ≤ Tr Dsp: Minimum number-based particle size [μm] showing the maximum Dlp: Maximum number-based particle size [μm] Df: Carbon fiber diameter [μm] Tr: Interlaminar thickness [μm] 2. The carbon fiber reinforced composite material according to claim 1, wherein in its cross-section, the ratio (Acp / Ar) of the area of ​​the component [C] (Acp) to the area of ​​the interlayer resin layer (Ar) is 0.05 or more and 0.30 or less.

3. The carbon fiber reinforced composite material according to claim 1 or 2, wherein, in the number-based particle size distribution of constituent element [C] obtained from the cross-section, the ratio (PTlpc / PTspc) of the peak height of the maximum number-based particle size (PTlpc) exhibiting the maximum to the peak height of the minimum number-based particle size (PTspc) exhibiting the maximum is 0.05 or more and 0.50 or less.

4. The carbon fiber reinforced composite material according to claim 1 or 2, wherein the component [B] is a cured product of a thermosetting resin.

5. The carbon fiber reinforced composite material according to claim 4, further comprising the component [D] in the interlayer resin layer. [D]: Thermoplastic particles 6. The carbon fiber reinforced composite material according to claim 5, wherein in its cross-section, the ratio (Atp / Ar) of the area of ​​the component [D] (Atp) to the area of ​​the interlayer resin layer (Ar) is 0.10 or more and 0.50 or less.

7. The carbon fiber reinforced composite material according to claim 1 or 2, wherein the component [C] is carbon particles.

8. The carbon fiber reinforced composite material according to claim 1 or 2, wherein in the interlayer resin layer within its cross-section, 50 to 80% of the constituent [C] are located within 25% of the average thickness of the interlayer resin layer in the thickness direction from the surface of the carbon fiber layer.

9. A structure obtained using the carbon fiber reinforced composite material described in claim 1 or 2, wherein the shape is selected from the group consisting of a flat plate structure, a cylindrical structure, a box-shaped structure, a C-shaped structure, an H-shaped structure, an L-shaped structure, a T-shaped structure, an I-shaped structure, a Z-shaped structure, and a hat-shaped structure.

10. A prepreg comprising a first layer containing the following components [A] and [B], and a second layer containing components [B] and [C] but not component [A], wherein the second layer is adjacent to one or both sides of the first layer, and the component [C] included in the second layer satisfies condition (Ip). [A]: carbon fiber [B]: matrix resin [C]: conductive particles (Ip): In the particle size distribution based on the number of components [C], there is one or more maxima in the range of 1.5 μm or more and less than 10 μm, and in the range of 10 μm or more and less than 100 μm.

11. The prepreg according to claim 10, wherein the component [C] satisfies condition (Ip) in addition to condition (IIp). (IIp): The number-based particle size distribution of component [C] has one or more maxima in the range of 3 μm or more and less than 8 μm, and in the range of 15 μm or more and less than 60 μm.

12. The prepreg according to claim 10, wherein, per 100 parts by mass of the total amount of matrix resin, the prepreg contains 1 to 15 parts by mass of conductive particles having a mode diameter in the range of 1.5 μm to less than 10 μm among the constituent [C], and 1 to 10 parts by mass of conductive particles having a mode diameter in the range of 10 μm to less than 100 μm.

13. The prepreg according to claim 10 or 11, wherein in component [C], the ratio (PTlpp / PTspp) of the peak height (PTlpp) of conductive particles having a mode diameter in the range of 10 μm or more and less than 100 μm to the peak height (PTspp) of conductive particles having a mode diameter in the range of 1.5 μm or more and less than 10 μm is 0.05 or more and 0.50 or less.

14. The prepreg according to claim 10 or 11, wherein the component [B] is a thermosetting resin.

15. The prepreg according to claim 14, further comprising a component [D] in the second layer. [D]: Thermoplastic particles 16. The prepreg according to claim 15, wherein component [D] is contained in the prepreg in an amount of 10 to 50 parts by mass per 100 parts by mass of thermosetting resin.

17. The prepreg according to claim 10 or 11, wherein the component [C] is a carbon particle.

18. The prepreg according to claim 10 or 11, wherein in the second layer, 50 to 80% of the number of constituent elements [C] are located within 25% of the average thickness of the second layer, from the surface of the first layer toward the surface of the prepreg.

19. A carbon fiber reinforced composite material obtained by laminating and molding the prepregs according to claim 10 or 11.

20. A structure obtained using the carbon fiber reinforced composite material described in claim 19, wherein the shape is selected from the group consisting of a flat plate structure, a cylindrical structure, a box-shaped structure, a C-shaped structure, an H-shaped structure, an L-shaped structure, a T-shaped structure, an I-shaped structure, a Z-shaped structure, and a hat-shaped structure.

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