JP2023106337A - Prepreg, prepreg roll, prepreg tape, prepreg laminate, carbon fiber-reinforced composite material, and structure - Google Patents

Abstract

To provide a novel prepreg which can obtain CFRP of low risk to an edge glow by controlling a prepreg structure, with no need of depending exclusively on expensive conductive particles.SOLUTION: In a prepreg, a carbon fiber sheet is impregnate with a matrix resin 2, and carbon fiber sub-layers 4 and 5 having carbon fibers 1 and a matrix resin 2 are arranged respectively on an upper surface and a lower surface of the prepreg. The prepreg has a sandwich structure where a resin sub-layer 6 is arranged between the two carbon fiber sub-layers 4 and 5. In the prepreg, fiber orientation angles of the carbon fibers 1 of the carbon fiber sub-layers 4 and 5 are the same, and an amount of insoluble particles existing on surfaces of the upper surface and/or lower surface is 0.1 g/m2 or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a prepreg, a prepreg roll, a prepreg tape, a prepreg laminate, a carbon fiber reinforced composite material, and a structure that can be suitably used for carbon fiber reinforced composite materials that are excellent in lightning resistance and suitable for induction welding.

Fiber reinforced composite materials (hereinafter abbreviated as FRP) are lightweight, yet have excellent mechanical properties such as strength and rigidity, heat resistance, and corrosion resistance. It has been applied in many fields such as In applications that require high mechanical properties, carbon fiber (hereinafter sometimes abbreviated as CF), which has excellent specific strength and inelastic modulus, is used as the reinforcing fiber, and adhesion with CF is used as the matrix resin. Epoxy resins are widely used because they have excellent properties, heat resistance, elastic modulus, and low cure shrinkage. The proportion of carbon fiber reinforced composite materials (hereinafter abbreviated as CFRP) used for aircraft structural members has been increasing in recent years, and it is expected that the proportion of their use will continue to increase in the future. In recent years, the use of thermoplastic resins as matrix resins has been increasing due to expectations for high-rate production and fastener-less joining. CFRP can be obtained by molding after impregnating a CF sheet formed by arranging CFs into a sheet with a matrix resin. Examples of the CF sheet include a UD sheet in which CFs are arranged in a unidirectional (UD) plane, a CF fabric in which CFs are arranged in multiple directions, and a CF fabric in which CFs are randomly arranged and formed into a sheet. UD sheets tend to be used when the mechanical properties of CFRP are prioritized, and CF fabrics tend to be used when fabricating CFRPs with complex shapes, but they are sometimes mixed and used. In applications for aircraft structural materials, mechanical properties are given priority, so CFRP is widely used by laminating prepregs (CFRP precursors) containing UD sheets in multiple directions and molding them.

CF is a conductor, and the matrix resin is generally an insulator in many cases. In the fiber axis direction of CFRP (hereinafter abbreviated as fiber direction), the CF itself serves as a conductive path, so the electrical conductivity is relatively high. On the other hand, in the direction orthogonal to the fiber axis of CFRP (hereinafter abbreviated as orthogonal direction), a conductive path is formed by contact between CFs, but the conductivity is generally about 1,000 times lower than that in the fiber direction. Even the conductivity of CFRP in the fiber direction is generally about 1,000 times lower than that of metals such as aluminum. Thus, CFRP is inferior to metal materials in conductivity and has anisotropy in conductivity in the direction perpendicular to the fiber direction. Therefore, when a certain current flows into CFRP, a higher voltage is applied than that of a metal material, and furthermore, the current distribution becomes very complicated in CFRP consisting of a plurality of CF sheets with different fiber orientation angles. .

Due to such complicated electrical characteristics, aircraft using CFRP are concerned about damage due to lightning. Unlike metal materials, it is difficult to disperse lightning current in CFRP, so problems such as damage due to local concentration of lightning current and sparks due to high voltage application tend to occur. For this reason, aircraft using CFRP are provided with a lightning protection system to ensure safety, such as adding a metal mesh or covering a place where sparks can occur with a sealant. However, these lightning protection systems have the problem of increased weight and cost. In order to reduce the number of lightning protection systems and further improve safety against lightning, it is required to enhance the electrical properties of CFRP itself.

One form of spark around the fuel tank is called edge glow. This refers to the phenomenon of light emission (glow) at the edge of a member, and research is being conducted to clarify the mechanism of this phenomenon. Non-Patent Document 1 compares the potential analysis of CFRP with experimental results of edge glow generation, and discusses the mechanism in detail. According to FIG. 8 of Non-Patent Document 1, in CFRP in which CF sheets with various fiber orientation angles are laminated, the potential difference is particularly large between CF sheets with different fiber orientation angles. Furthermore, according to FIG. 18 of Non-Patent Document 1, occurrence of edge glow was experimentally confirmed at locations where the potential difference between CF sheets with different fiber orientation angles was large. Therefore, it is considered that reducing the potential difference between CF sheets having different fiber orientation angles is effective in suppressing edge glow.

It is generally considered effective to increase the electrical conductivity in the thickness direction of CFRP in order to reduce the potential difference between CF sheets with different fiber orientation angles in order to suppress edge glow. Therefore, many material designs have been proposed to improve the conductivity in the thickness direction of CFRP. Among them, as shown in Patent Documents 1 to 3, conductive particles are arranged between CF sheets with different fiber orientation angles. This method has a great effect of improving the conductivity of CFRP in the thickness direction.

Patent Document 1 discloses a technique of arranging carbon particles between CF sheets having different fiber orientation angles. Patent Document 2 also discloses a technique of arranging carbon particles between CF sheets with different fiber orientation angles. The resistance value is lowered and the conductivity is improved. Patent Document 3 is a technique of arranging potato-shaped graphite between CF sheets with different fiber orientation angles. rate improves.

R. B. Greegor et al. "Finite Element Simulation and Experimental Analysis of Edge Glow for a Generic, 16-Ply Carbon Fiber Reinforced Plastic Composite Laminate" ICOLSE15 Paper 2015

WO2008/018421 WO2011/027160 WO2013/186389

However, there is a high demand for electrical conductivity necessary for suppressing edge glow, and it has been necessary to greatly improve electrical conductivity. In Patent Document 1, the volume resistivity in the thickness direction of CFRP shown in Examples is 2.0×10 ³ Ωcm or more (conductivity of 0.05 S/m or less), and sufficient conductivity is obtained. do not have. Patent Documents 2 and 3 show that it is effective to increase the amount of conductive particles arranged between CF sheets in order to improve conductivity, but the conductivity required for suppressing edge glow is highly demanded, and it has been necessary to add a large amount of conductive particles. In addition, the conductive particles used in Patent Documents 1 to 3 are generally expensive, and it is preferable to reduce the amount added. Thus, reducing the amount of conductive particles to be added and reducing the risk of edge glow by improving conductivity are contradictory.

An object of the present invention is to provide a prepreg from which CFRP with a low risk of edge glow can be obtained without relying only on expensive conductive particles. In other words, the present invention provides a prepreg for obtaining CFRP with greatly reduced risk of edge glow even when using the same amount of conductive particles as in the prior art or a lower amount.

In order to solve the above-described problems, the present invention provides a prepreg in which a carbon fiber sheet is impregnated with a matrix resin, wherein carbon fiber sublayers having carbon fibers and a matrix resin are arranged on the upper surface and the lower surface, and the two A resin sublayer is arranged between the carbon fiber sublayers to form a sandwich structure, the fiber orientation angles of the carbon fibers in the upper and lower carbon fiber sublayers in the prepreg are the same, and the upper and/or lower surfaces have A prepreg construction is taken in which the amount of insoluble particles present is less than or equal to 0.1 g/m ² .

By using the prepreg of the present invention, it is possible to obtain CFRP that can be expected to have a sufficient effect of suppressing edge glow without depending on expensive conductive particles. Furthermore, it is also possible to obtain CFRP that can be expected to have a higher edge glow suppressing effect than the conventional technique in which conductive particles are arranged between CF sheets having different fiber orientation angles. By applying such CFRP to an aircraft, it is possible to improve the efficiency of the lightning protection system as a whole. In addition, the CFRP using the prepreg of the present invention has the advantage of being able to improve the induction heating temperature in induction welding, which is mainly used for CFRP in which the matrix resin is a thermoplastic resin.

1 is a cross-sectional view showing one embodiment of a prepreg of the present invention; FIG. 1 is a photograph showing an example of a slit prepreg tape. 1 is a cross-sectional view showing one embodiment of CFRP obtained from the prepreg of the present invention; FIG. 1 is a cross-sectional photograph of one embodiment of CFRP obtained from the prepreg of the present invention. 5 is an image obtained by binarizing FIG. 4. FIG. 6 shows the Z-direction distribution of the carbon fiber volume content ratio (Vcf) obtained from FIG. It is the Z' direction distribution of Vcf in the layer L1. FIG. 4 is a cross-sectional view showing another embodiment of CFRP obtained from the sandwich structure prepreg of the present invention; FIG. 4 is a cross-sectional view showing another embodiment of CFRP obtained from the sandwich structure prepreg of the present invention; FIG. 2 is a cross-sectional view showing one form of CFRP obtained from a conventional prepreg. FIG. 2 is a cross-sectional view showing one form of an interlayer reinforced CFRP obtained from a conventional prepreg. 1 is a cross-sectional photograph of a form of an interlayer reinforced CFRP according to a conventional technique; It is an image obtained by binarizing FIG. 12 . 14 is the Z-direction distribution of Vcf obtained from FIG. 13; It is the Z' direction distribution of Vcf in the layer L4. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an example of a prepreg manufacturing apparatus of the present invention; FIG. 3 is a schematic diagram showing another example of the prepreg manufacturing apparatus of the present invention.

<Outline of the prepreg of the present invention>
The prepreg of the present invention has a sandwich structure of several sublayers. Explain the term "sublayer". First, when prepregs are laminated and molded to form a CFRP, a CF sheet continues in the thickness direction and includes a region having the same CF fiber orientation angle as a “layer”. A layer indicates one unit of lamination when prepreg is laminated or molded to CFRP, and is sometimes called Ply in the industry. When a layer is composed of a plurality of constant-thickness regions with different Vcf, the constant-thickness regions are called sublayers. In the present invention, one sheet of prepreg usually constitutes one layer, so the term "sublayer" is also used as a term indicating a constant-thickness region that constitutes the prepreg in the present invention. That is, the CF sublayer in the prepreg of the present invention is a part of layers in CFRP.

A cross-sectional view showing one embodiment of the present invention is shown in FIG. The prepreg 3 of the present invention has a plurality of sublayers, and carbon fiber sublayers (CF sublayers) 4 and 5 are arranged on its upper and lower surfaces. Hereinafter, the upper and lower CF sublayers 4 and 5 may be referred to as "upper and lower CF sublayers". Here, the CF sublayer contains at least CF and matrix resin. The matrix resin is composed of a thermosetting resin, a thermoplastic resin, or the like, and may contain various additives in addition to a curing agent and a catalyst, if necessary. As will be described later, in the present invention, in order to suppress the edge glow of CFRP and improve the induction heating temperature in induction welding, when prepregs are laminated and molded to form CFRP, a layer derived from the prepreg of the present invention and an adjacent layer It is important to increase the conductivity between From this point of view, the volume ratio (Vcf) of CF in the CF sublayers above and below the prepreg of the present invention is preferably as high as 60% or higher, more preferably 65% or higher, and even more preferably 69% or higher. Improving the Vcf of these upper and lower CF sublayers significantly increases the number of CF contacts between adjacent CF layers when forming a laminate, so the conductivity between adjacent CF layers increases dramatically. improve to On the other hand, the upper limit of the CF volume ratio in the upper and lower CF sublayers is that the Vcf of the CF sublayer is 90% or less in order to suppress the deterioration of the slit workability of the prepreg and the generation of voids when converted to CFRP. preferably 80% or less, even more preferably 75% or less. A prepreg in which a resin is further laminated on the surface of the prepreg has a resin layer on the surface side of the CF sublayer, and is different from the prepreg of the present invention. Also, a prepreg with a large amount of resin remaining on the prepreg surface, such as when the impregnation of the resin is insufficient, is also different from the prepreg of the present invention. Specifically, the thickness of the resin on the surface of the prepreg is preferably 10 μm or less. The thickness of the resin on the surface of the prepreg can be measured, for example, by the method described in Examples.

In the prepreg shown in FIG. 1, the CF fiber orientation angles in the upper and lower CF sublayers 4 and 5 are arranged to be the same. Here, the same fiber orientation angle of the CF means that the arrangement direction of the CF in the CF sublayers 4 and 5 is the same. It refers to the state obtained by laminating such layers. In many cases, different fiber orientation angles on both sides of the resin sublayer, which is effectively an insulator, increases the potential gradient between them and increases the risk of edge glow, so the fiber orientation angle should be the same. . Even if more than two CF sublayers are included in the prepreg, their fiber orientation angles are all the same. As the CF base material constituting the CF sublayer, it is preferable to use a UD sheet in which CF long fibers are aligned in one direction from the viewpoint of improving the mechanical properties of CFRP.

In the prepreg of the present invention, resin sublayers 6 exist between the upper and lower CF sublayers to form a sandwich structure. Since the resin sublayer remains in the CFRP after molding, the matrix resin content rate (hereinafter sometimes referred to as Rc) of the entire prepreg is set to a certain level or more, and carbon fibers are concentrated in the upper and lower CF sublayers. and a high Vcf, which enhances the conductivity between layers in CFRP. On the other hand, as in the case of insufficient impregnation in a normal prepreg, when the resin that reaches the inside of the prepreg is insufficient and a space different from the CF sublayer can be seen in the prepreg thickness direction, the space is the resin It is not considered to form a sublayer.

The amount of insoluble particles present on the upper and lower surfaces of the prepreg 3 of the present invention is 0.1 g/m ² or less. Here, the insoluble particles refer to particles that are sparingly soluble or insoluble in the matrix resin of the CF sublayer and that do not dissolve or melt during the prepreg molding process. Specifically, it is a standard that 25% or more of the particle volume is retained after molding, or that the melting point is higher than the molding temperature. is. Molding conditions vary depending on the molding method and application, but general ranges are described later. In particular, for aircraft primary structural material applications using the autoclave method, general conditions include a molding temperature of 180° C., a molding time of 2 hours, and a molding pressure of 0.59 MPa. If there are many insoluble particles on the surface of the prepreg, when the prepreg is laminated, molded, and converted to CFRP, the insoluble particles play an undesirable role as a spacer, forming a so-called interleaf structure CF interlayer resin layer, and the upper and lower CF layers. increases the potential gradient between and increases the risk of edge glow. Here, the upper and lower surfaces of the prepreg will be described with reference to FIG. Become. In the case of prepregs that are arranged on the upper and lower surfaces of the laminate when the prepregs are laminated, the surface of the upper surface or the lower surface that is in contact with the other prepreg may satisfy the condition for the amount of insoluble particles described above. In the case of the prepreg arranged in the middle part of the , both the upper surface and the lower surface preferably satisfy the condition of the amount of insoluble particles described above. Since a large amount of prepreg is generally placed in the middle part of the laminate, in the prepreg of the present invention, the amount of insoluble particles present on both the upper and lower surfaces is 0.1 g/m ² or less. Preferably.

In addition, the CF mass per unit area of the prepreg in the CF sublayer (hereinafter sometimes referred to as FAW) is preferably large from the viewpoint of lamination efficiency, specifically 190 g / m ² or more, and more It is preferably 260 g/m ² or more. On the other hand, it is preferably 600 g/m ² or less from the viewpoint of handleability of the prepreg. The matrix resin content (hereinafter sometimes referred to as Rc) in the prepreg is preferably 30% or more from the viewpoint of suppressing the generation of voids, and more preferably 32% or more. On the other hand, it is preferably 36% or less from the viewpoint of the mechanical properties of the resulting CFRP. Here, Rc is the ratio of the resin content including the resin composition of the resin sublayer in the entire prepreg. In general, when the FAW is 190-280 g/m ² and the Rc is 32%-36%, the thickness of the prepreg is preferably 180-300 μm.

The present invention will be described in more detail below.

<Carbon fiber sublayer (CF sublayer)>
The CF sublayer used in the present invention contains at least CF and a matrix resin. Examples of CF include polyacrylonitrile (PAN), pitch, etc. For aircraft materials, PAN with high tensile strength is preferred. It is preferably used. A CF sheet obtained by forming CF into a sheet and impregnated with a matrix resin is preferably used as the CF sublayer. The CF sheet generally refers to a state in which resins other than the sizing agent attached to the surface of the CF are not substantially contained in order to improve handling properties. Specifically, the CF sheet is a resin other than the sizing agent. The content is preferably 1% by mass or less. This differs from conventional prepregs in which a plurality of aligned CFs are already impregnated with resin. When the average fiber diameter of CF is 3 μm or more, sufficient mechanical properties can be obtained as CFRP for structural materials. 5 μm or more is common for aircraft structural material applications. Furthermore, when the thickness is 6 μm or more and 9 μm or less, impregnation of the matrix resin into the CF sheet in the prepreg manufacturing process is facilitated, and the non-impregnated area in the CF sublayer can be reduced. As a result, in the process of transporting the prepreg with a slitting device or an automatic laminating (AFP, ATL) device, it is possible to suppress the occurrence of fluff due to CF in the non-impregnated region. In addition, due to the flow of the matrix resin during prepreg molding, the fluidity of the matrix resin can be increased even in the process of impregnating the non-impregnated region of the prepreg with CF, and the risk of void generation in the CFRP can be reduced. Furthermore, when the ratio of the number of atoms of all carbon atoms to all oxygen atoms measured by X-ray photoelectron spectroscopy, that is, the CF surface oxygen concentration [O / C] is 0.12 or less, the mechanical properties and conductivity of CFRP Gender balanced and desirable. [O/C] is more preferably 0.10 or less. Paragraph [0126] of JP-A-2013-067750 describes that [O/C] can be set to 0.10 by electrical treatment with an aqueous sulfuric acid solution. As the CF sheet, a UD sheet in which the CF is aligned in one direction is preferably used, but a so-called non-crimp fabric (NCF) in which the UD sheet is bound with stitch yarns can also be used.

As described above, the volume content ratio (Vcf) of CF in the CF sublayer is preferably high. As a result, when the prepreg is laminated and molded to form CFRP, the conductivity between the prepreg of the present invention and the adjacent layer can be increased, edge glow can be suppressed, and the induction heating temperature in induction welding can be improved. Although the preferred CF sublayer Vcf is as described above, such Vcf can be obtained, for example, by the following procedure.
Procedure 1: Calculate the volume fraction of the CF sublayer from the cross-sectional photograph of the prepreg.
Procedure 2: Cut the prepreg into a size of 10 cm square.
Procedure 3: Measure the mass of the cut prepreg.
Step 4: The matrix resin in the cut prepreg is eluted with a solvent or the like, and the CF contained in the prepreg is collected.
Step 5: Measure the mass of the collected CF.
Step 6: Calculate the mass fraction of CF relative to the prepreg.
Procedure 7: Calculate Vcf of the entire prepreg from CF density and matrix resin density.
Step 8: Obtain Vcf in the CF sublayer from the Vcf of the entire prepreg and the volume fraction of the CF sublayer.

The matrix resin used in the prepreg of the present invention preferably contains a thermosetting resin and a curing agent. Alternatively, a thermoplastic resin may be used alone as the main component. Alternatively, as will be described later, a thermosetting resin may be mixed with a thermoplastic resin that dissolves therein and used together with a curing agent. From the viewpoint of ease of impregnation of the matrix resin into the CF sheet, it is preferable that the thermosetting resin is contained in an amount of more than 50% by mass in the matrix resin. Epoxy resins are generally used as thermosetting resins, and epoxy resins whose precursors are amines, phenols, and compounds having a carbon-carbon double bond are particularly preferred. Specifically, as epoxy resins having amines as precursors, tetraglycidyldiaminodiphenylmethane, triglycidyl-p-aminophenol, triglycidyl-m-aminophenol, various isomers of triglycidylaminocresol, and phenols are used as precursors. Epoxy resins used as the body include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenol novolak type epoxy resin, cresol novolak type epoxy resin, and a compound having a carbon-carbon double bond as a precursor. Examples of the epoxy resin to be used include, but are not limited to, alicyclic epoxy resins and the like. In order to improve the tensile strength of CFRP, it is effective to reduce the crosslink density of the matrix resin. To solve this problem, it is also preferable to use a dicyclopentadiene type epoxy resin having a rigid skeleton or a glycidylaniline type epoxy resin which is a pendant type epoxy resin. A brominated epoxy resin obtained by bromating these is also used. Epoxy resins whose precursors are aromatic amines represented by tetraglycidyldiaminodiphenylmethane are suitable for the present invention because they have good heat resistance and good adhesiveness to CF.

A thermosetting resin is preferably used in combination with a curing agent. For example, in the case of epoxy resin, a compound having an active group capable of reacting with an epoxy group can be used as a curing agent. Compounds having an amino group, an acid anhydride group, or an azide group are preferred. Specifically, dicyandiamide, various isomers of diaminodiphenylsulfone, and aminobenzoic acid esters are suitable. Specifically, dicyandiamide is preferably used because it is excellent in preservability of the prepreg. Further, various isomers of diaminodiphenylsulfone are most suitable for the present invention since they give a cured product having good heat resistance. As aminobenzoic acid esters, trimethylene glycol di-p-aminobenzoate and neopentyl glycol di-p-aminobenzoate are preferably used. Because it is excellent, it is selected and used according to the application. Expensive catalysts can also be used if necessary. Moreover, from the viewpoint of improving the pot life of the matrix resin, it is also possible to use a complexing agent capable of forming a complex with a curing agent or a curing catalyst.

In the present invention, it is also preferable to use a mixture of a thermosetting resin and a thermoplastic resin as the matrix resin. The thermoplastic resin used here is preferably one that is soluble at 150° C. in other components of the matrix resin including the thermosetting resin. Mixtures of thermosets and thermoplastics give better results than thermosets alone. This is because thermosetting resins generally have the disadvantage of being brittle but can be molded at low pressure using an autoclave, whereas thermoplastic resins generally have the advantage of being tough but are difficult to mold at low pressure using an autoclave. This is because the physical properties and moldability can be balanced by mixing them. When mixed and used, the matrix resin preferably contains more than 50% by mass of the thermosetting resin from the viewpoint of the mechanical properties of the CFRP obtained by curing the prepreg. In addition to the viewpoint of good mechanical properties of the obtained CFRP, from the viewpoint of ease of impregnation of the matrix resin into the CF sheet, when the total matrix resin constituting the resin sublayer is 100 parts by mass, heat The total mass of the curable resin and the curing agent is preferably 60 parts by mass or more, more preferably 70 parts by mass or more, and even more preferably 80 parts by mass or more. The thermoplastic resin preferably contains 1 part by mass or more and 40 parts by mass or less, more preferably 3 parts by mass or more and 30 parts by mass or less, and even more preferably 5 parts by mass or more and 20 parts by mass or less. . In the present invention, the entire matrix resin constituting the resin sublayer refers to the resin other than the carbon fiber sheets on the upper and lower surfaces constituting the prepreg.

The thermoplastic resin has a main chain 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. Polymers with bonds can be used. Specifically, polyacrylate, polyolefin, polyamide (PA), aramid, polyester, polycarbonate (PC), polyphenylene sulfide (PPS), polybenzimidazole (PBI), polyimide (PI), polyetherimide (PEI), polysulfone (PSU), polyethersulfone (PES), polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyaryletherketone (PAEK), polyamideimide (PAI), etc. can. PPS, PES, PI, PEI, PSU, PEEK, PEKK, PAEK and the like are suitable for fields such as aircraft applications where heat resistance is required. On the other hand, for industrial applications and automotive applications, polyolefins such as polypropylene (PP), PA, polyester, PPS, etc. are suitable in order to increase molding efficiency. These may be polymers, or may be oligomers or monomers for low viscosity and low temperature application. Depending on the purpose, these may be copolymerized, or various types may be mixed and used as a polymer blend alloy.

In addition, the CF sublayer preferably contains a conductive substance from the viewpoint of further improving conductivity. For example, metal particles, metal-coated particles, carbon particles, nanocarbon (carbon nanotubes, carbon black, etc.), etc., which will be described later, can be exemplified. Nano-substances such as nanocarbon can also serve as a conductive aid, which will be described later. However, it should be noted that the amount of insoluble particles present on the upper surface of the CF sublayer forming the upper surface and the lower surface of the CF sublayer forming the lower surface should be 0.1 g/m ² or less.

<Resin sublayer>
Since the resin sublayer remains in the CFRP after molding, Vcf in the CF sublayer can be increased even if the matrix resin content (Rc) of the prepreg as a whole is kept within a desired range. As a result, the electrical conductivity between adjacent CF sublayers (between prepreg plies) in the prepreg laminate of the present invention is dramatically improved. In addition, since the resin sublayer that can be deformed against impact remains in the CFRP, the impact resistance is improved when compared to a prepreg that does not form a resin sublayer and has the same resin content. is also obtained. From this point of view, the thickness of the resin sublayer is preferably 1 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. More preferably, it is 30 μm or more. On the other hand, the thickness of the resin sublayer is preferably 100 μm or less, and more preferably 70 μm or less, in order to reduce the thickness of the prepreg as a whole and improve the handleability of the prepreg tape. Further, when a conductive spacer is used for the resin sublayer, the thickness of the resin sublayer is preferably 70 μm or less, more preferably 55 μm or less, and more preferably 50 μm or less. preferable. When the upper limit of the thickness of the resin sublayer is within the above range, the ratio of conductive spacers present in the resin sublayer to function as conductive paths between adjacent CF sublayers increases, so adjacent fibers in CFRP In addition to improving the conductivity between CF layers having different directions, it is also expected to improve the conductivity of CFRP. In the molding process, the resin sublayer preferably contains a spacer in order to ensure the distance between the upper and lower CF sublayers, that is, the thickness of the resin sublayer, at a certain level or more. Here, the molding conditions are appropriately selected depending on the purpose, and for example, the conditions described in the examples of the present specification can be exemplified. Further, the spacer is a matrix resin that has the function of holding the shape of the resin sublayer between the CF sublayers by physical action in the prepreg and the CFRP manufacturing method obtained by molding the same, which will be described later. It is a solid substance contained in the matrix resin and a substance that is sparingly soluble or insoluble in the resin composition of the resin sublayer. Specifically, it is preferable to retain 25% or more of the volume of the spacer before molding after molding, or to have a melting point equal to or higher than the molding temperature. In addition, the spacer has at least one side of the spacer, such as a long diameter when the spacer is in the form of particles, a cross-sectional diameter when the spacer is in the form of fibers, and a fiber length, so that mixing of the spacer into the CF sublayer is suppressed during the molding process. A material having a size larger than the fiber diameter of the carbon fibers is often sought.

Examples of the form include particles, fibrous materials, aggregates thereof, and the like, and a preferred example is the form of particles. From the viewpoint of controlling the resin sublayer thickness as described above, the mode diameter or average particle diameter of the particles is preferably 10 μm or more, more preferably 15 μm or more, and still more preferably 20 μm or more. On the other hand, the upper limit is 100 μm or less, more preferably 50 μm or less, still more preferably 40 μm or less. The particle shape may be a true sphere or any other shape. It is preferable from the viewpoint of improving the mechanical properties after making it into CFRP. Here, the sphericity is obtained by extracting particles from the prepreg or resin sublayer using a solvent or the like, randomly selecting 30 particles from the micrograph, and calculating the minor axis and major axis according to the following formula. be able to. If extraction is difficult, the cross section and surface of the prepreg or resin sublayer can be observed under a microscope to obtain the minor axis and diameter.

In the above formula, S: sphericity, a: major axis, b: minor axis, n: 30 measurements.

In thermosetting prepregs, polymer particles such as polyamide, polyetherimide, polyamideimide, and polyphenylene ether are generally used as particulate spacers to improve CF interlayer toughness and impact resistance. Polyamide 12, polyamide 11, polyamide 6, polyamide 66 or polyamide 6/12 copolymer, polyamide semi-IPN (polymer interpenetrating network structure) in the epoxy compound described in Example 1 of JP-A-1-104624 (semi-IPN polyamide) and the like can be suitably used. Commercially available spherical polymer particles include polyamide-based SP-500 and SP-10 (manufactured by Toray Industries, Inc.), and polymethylmethacrylate-based MBX series such as MBX-12 and SSX series such as SSX-115. (manufactured by Sekisui Plastics Co., Ltd.), SBX series such as SBX-12 as polystyrene (manufactured by Sekisui Plastics Co., Ltd.), and MSX and SMX (manufactured by Sekisui Plastics Co., Ltd.) as their copolymers (manufactured by Gunei Chemical Co., Ltd.), Dymic Beads CM series as polyurethane type, BELLOCEA (manufactured by Daicel Corporation) as cellulose acetate type, and Marilyn (manufactured by Gun Ei Kagaku Co., Ltd.) as phenolic resin type. Although not spherical, "Orgasol (registered trademark)" 1002D, 2001UD, 2001EXD, 2002D, 3202D, 3501D, 3502D (manufactured by Arkema Co., Ltd.), "Grilamid (registered trademark)" TR90 (Mzawerke) Co., Ltd.), "TROGAMID (registered trademark)" CX7323, CX9701, CX9704 (Degussa Co., Ltd.) and the like can also be used. These particles may be used singly or in combination. Commercially available polyetherimide products include "Ultem (registered trademark)" 1000, "Ultem (registered trademark)" 1010, and "Ultem (registered trademark)" 1040 (manufactured by SABIC Innovative Plastics). Inorganic particles, which are not polymer particles, can also be used as spacers, such as metal oxide particles, metal particles, and carbon particles. For metal oxide particles, the use of glass particles, particularly hollow glass particles, can further reduce the weight of CFRP. Further, the conductivity of CFRP can be further improved by using metal particles, carbon particles, polymer particles, or glass particles coated with metal or carbon. Carbon particles having a (002) interplanar spacing of 3.4 to 3.7 angstroms are preferable because the conductivity is easily improved. For example, as an example of carbon particles, ICB manufactured by Nippon Carbon Co., Ltd. has a (002) interplanar spacing of 3.53 angstroms, and is a substantially spherical carbon particle. 168, 157-163 (1995). It is described in. It is also described that the perfectly spherical carbon particles are very hard and hardly deform even when compressive deformation is applied, and that the particle shape returns to its original shape when the compression is removed. When CFRP is used as a structural material for an aircraft, the structural material is deformed as typified by the bending of the main wing during flight, but in FRP containing spherical carbon particles, the spherical carbon particles are irreversible Since it is difficult to have significant deformation, it is expected to exhibit stable conductivity.

Moreover, a fiber base material can also be used as a spacer. Here, the fiber substrate refers to a structure formed by combining fibers, and examples thereof include a two-dimensional sheet-like structure and a three-dimensional braid-like structure. In this case, the resin sublayer contains fibers. Among them, it is preferable to use a sheet-like fiber base material as a spacer and use FRP impregnated with a resin as a resin sublayer. Examples of sheet-like fiber substrates include unidirectional materials as well as fabrics such as woven fabrics, knitted fabrics, non-woven fabrics, and paper. Inorganic fibers, such as glass fibers (GF), are preferred as the fibers because they preferably retain their fiber shape during the prepreg molding process. On the other hand, from the viewpoint of improving the toughness of CFRP, polymer fibers are preferable, and in this case, fibers made of highly heat-resistant polymers having a glass transition temperature, softening point, flow initiation temperature, melting point, etc. higher than the molding temperature are preferable. For example, polyamide (PA)-based, polyester-based, polyetherketone-based (PEK, PEEK, PEKK, PAEK, etc.) having a melting point of 180 ° C. or higher, polyimide-based (PI, PEI, PAI, etc.), aromatic polyamide-based, poly Ethersulfone-based (PES, etc.), polysulfone-based (PS, etc.), polyphenylene sulfide (PPS)-based, and fibers made of copolymers based on them can be exemplified. It is preferable to use GFRP or polyamide FRP from the results of application to CFRP. A thermosetting resin, a thermoplastic resin, or the like can be used as the resin forming the resin sublayer, but it is preferable to use the same matrix resin as the CF sublayer from the viewpoint of consistency. In addition, the use of the above-mentioned highly heat-resistant polymer makes it possible to maintain the thickness of the resin sublayer after molding without including a spacer in the resin sublayer. For example, if the matrix resin is composed of an epoxy resin and an amine-based curing agent and the prepreg is molded at 180° C., it is possible to use polyamide 6 with a melting point of 225° C. as the resin sublayer. In this case, the resin sublayer can be used in the form of a resin film, and can substantially retain the film form during the prepreg molding process. In aircraft applications, PES and PA are often used to improve toughness, and in this case also, it can be in the form of a film, and it is preferable to use these films. In recent years, PPS, PEEK, PEKK, PAEK, and copolymers thereof have been used in thermoplastic CFRP.

<Amount of insoluble particles present on the upper surface and/or lower surface of the prepreg>
In the present invention, it is important that the amount of insoluble particles present on the upper surface and/or the lower surface of the prepreg is small from the viewpoint of improving the conductivity between layers in CFRP obtained by laminating prepregs. As described above, the insoluble particles are sparingly soluble or insoluble in the resin composition of the matrix resin, and do not dissolve or melt during the molding process of the prepreg. If the amount is reduced, the amount of the substance functioning as a spacer between layers when prepregs are laminated is reduced, and as a result, the conductivity between layers in CFRP can be improved. It is important that the amount of insoluble particles present on the upper surface and/or the lower surface of the prepreg is 0.1 g/m ² or less, preferably 0.05 g/m ² or less.

The amount of insoluble particles present on the upper surface and/or the lower surface of the prepreg can be obtained, for example, as follows. That is, only the resin on the surface of the prepreg is carefully collected using a spatula or the like from the surface (one side) of the prepreg cut out as a sample. After dissolving the collected resin in a solvent, it is filtered to separate the particles. Then, the mass of the filtered particles is measured and divided by the sample area of the prepreg to obtain the amount of insoluble particles (g/m ² ). If the amount of resin on the prepreg surface is too small to collect a sample, the prepreg surface is observed with a microscope or the like. If the presence of particles cannot be confirmed, the amount of insoluble particles can be considered to be 0.05 g/m ² or less. . Here, as the solvent, it is important to select a solvent that dissolves the matrix resin but does not dissolve the insoluble particles. For example, N-methylpyrrolidone (NMP) or the like can be used for a matrix resin based on epoxy resin + aromatic amine curing agent + polyethersulfone (PES) containing polyamide particles. can be done. For filtration, use a filter with an appropriate pore size that allows particle trapping.

<Prepreg roll>
The prepreg of the present invention is preferably in the form of a roll formed by winding the prepreg from the viewpoint of ease of transportation. At this time, if the fiber orientation direction of the carbon fibers of the carbon fiber sublayers on the upper and lower surfaces is the same as the longitudinal direction of the prepreg roll, the 0° direction with high tensile and compressive properties can be long when the prepreg is cut and laminated. Therefore, it is preferable. In particular, it is important when slitting the prepreg to form a tape for automatic lamination, which will be described later.

<Prepreg tape>
In recent years, automatic lamination of prepreg tapes called Automated Fiber Placement (AFP) or Automated Tape Lay-up (ATL) has become common in order to improve prepreg lamination efficiency. The prepreg of the present invention can be made into a tape by slitting the wide prepreg in the longitudinal direction.

In the slitting process, CF, matrix resin, or a mixture thereof may adhere, accumulate, or wrap around the slitting blade. Also in the automatic lamination process, the same problem may occur in the running route of the prepreg tape in the automatic lamination machine. From this point of view, it is preferable to reduce the tackiness of the prepreg surface. Moreover, it is preferable to reduce the existence ratio of dry CF as much as possible. Here, the dry CF refers to a state in which the matrix resin is not attached to the CF, and since the CFs are not restrained by the matrix resin, they are characterized by being easily released from the prepreg during slitting. Therefore, it is preferable to reduce the amount of matrix resin on the surface of the prepreg by increasing the degree of impregnation of the prepreg with the matrix resin and to reduce the existence ratio of dry CF as much as possible. The degree of resin impregnation of the prepreg can be evaluated by the water absorption rate of the prepreg (hereinafter sometimes referred to as WPU), and the WPU is preferably 7% or less, more preferably 3% or less, and still more preferably 2% or less. Note that WPU can be measured as follows. That is, from the prepreg, a test piece having a size of 100 mm square in the length in the longitudinal direction of the fiber and the length in the width direction (direction orthogonal to the fiber direction) is cut. When the width of the prepreg is less than 100 mm, the width in the width direction of the prepreg may be less than 100 mm, but the length in the fiber direction shall be 100 mm. Next, after measuring the mass W1 of the obtained test piece, one side of the test piece is arranged so that the fiber direction of the test piece is perpendicular to the water surface, and the range of 5 mm from the end of the test piece (ie 100 mm x 5 mm) are immersed in water for 5 minutes. The test piece immersed for 5 minutes is removed from the water, and after wiping off moisture adhering to the surface of the test piece with a waste cloth or the like while being careful not to touch the immersed surface, the mass W2 of the test piece is measured. WPU (%)=((W2−W1)/W1)×100(%), indicating that the smaller the WPU, the higher the degree of impregnation.

On the other hand, in the automatic lamination process, by increasing the sticking property of the prepreg tape, the lamination speed can be increased and the production efficiency can be improved. From this point of view, it is preferable that the prepreg has a high tack, but considering the above-described problems in the slitting process and the running path of the automatic lamination machine, there is an appropriate tack force range. Specifically, when the tack force at 22° C. measured by the probe tack method is 0.0059 MPa or more and 0.025 MPa or less, it is preferable that the sticking property is good and the lamination trouble can be easily repaired. Such tack force can be measured, for example, as follows. As a tack tester, PICMA Tack Tester II: manufactured by Toyo Seiki Co., Ltd. can be used. First, in an atmosphere of 22 ° C., a prepreg to be measured was placed on a tack tester, and a stainless steel plate (SUS304) to which a 18 mm square glass plate was attached was lowered from the top of the prepreg at a speed of 10 mm / min, and immediately after contacting the prepreg. Second, the stainless steel plate is lifted at a speed of 10 mm/min to measure the peel load when it is peeled off from the prepreg. The tack force can be obtained by dividing the maximum load at this time by the contact area. For example, if the measured load is 2.06 N, it is divided by the contact area (18 mm square) to give about 0.0064 MPa.

Moreover, in the slitting step, it is preferable to lengthen the length of the prepreg tape to be wound as much as possible by splicing the prepreg. At this time, it is preferable that the strength of the splice portion for splicing the prepregs in the longitudinal direction is high for winding the prepreg tape and high-speed conveyance in an automatic laminating machine. Splice strength is affected not only by the adhesive strength between prepregs but also by the easiness of deformation of the prepregs in the out-of-plane direction, that is, the drape property. The drape property of the prepreg of the present invention can be evaluated as follows. That is, the produced prepreg is cut into a length of 25 mm in the width direction and a length of 300 mm in the fiber direction. A portion of 25 mm in the width direction and 100 mm in the fiber direction length at one end of the cut prepreg is brought into close contact with the base and fixed, and the remaining portion of the prepreg, that is, a portion of 25 mm in the width direction and 200 mm in the fiber direction length. is a cantilever projecting from the side of the pedestal. After standing in this state for 10 minutes, the horizontal distance A from the side of the pedestal to the unfixed end of the prepreg, and the vertical height B from the surface of the prepreg fixed to the pedestal to the unfixed end of the prepreg. is measured, and the drape angle θ (PP) is calculated from the tangent values of the two sides. That is, the relationship is tan θ(PP)=B/A. The greater the drape angle θ(PP), the higher the shape followability. That is, the larger the drape angle θ(PP), the better the drapeability. In the present invention, by setting the drape angle θ (PP) to 7° or more, the prepreg can be easily deformed in the out-of-plane direction and the splice strength can be increased. On the other hand, by setting the drape angle θ (PP) to 17° or less, it is possible to suppress the prepreg tape from being folded during automatic lamination, thereby improving the automatic lamination efficiency.

In the prepreg tape of the present invention, the presence frequency of CF-containing fluff having a length of 1 cm or more, which is present on the side surface of the tape, is 1/10 m or less. It is preferable from the viewpoint of improving the quality of. More preferably, the existence frequency is 0.2 pieces/10 m or less. Here, the tape sides refer to the right side and left side of each slit tape shown in FIG. 2, for example. In addition, fluff containing CF means dry CF itself, or a fibrous material composed of a mixture of CF and constituents of a matrix resin, and aggregates thereof. Then, fluff with a length of 1 cm or more in the longitudinal direction is evaluated. An example of target fluff is shown in a portion surrounded by a white ellipse in FIG. 2 (FIG. 2 shows an example of long fluff and frequent fluff in order to show fluff in an easy-to-understand manner).

The prepreg of the present invention can be made into a prepreg laminate in which a plurality of sheets are laminated in a desired direction, and then molded into CFRP. By including at least one layer of the prepreg of the present invention in the prepreg laminate, edge glow of CFRP can be suppressed and the induction heating temperature can be improved. The ratio of the prepreg of the present invention used in the prepreg laminate is preferably 50% or more in terms of the number of laminates. Further, if necessary, a woven prepreg or surface protective material (Surfacing Material) can be placed on the surface of the prepreg laminate or CFRP. The term "molding" as used herein refers to curing after shaping the prepreg laminate as necessary.

The prepreg of the present invention can be manufactured by, for example, a so-called heat and pressure molding method in which prepregs are laminated in a predetermined form, shaped by applying pressure and heat, and the resin is cured. As the heat pressure molding method, a press molding method, an autoclave molding method, a bagging molding method, a wrapping tape method, an internal pressure molding method, or the like can be used. The molding temperature usually varies depending on the type of curing agent, but is generally 130°C to 220°C. Sufficient curability can be obtained by setting the molding temperature within the above range. The molding pressure in the autoclave molding method varies depending on the thickness of the prepreg and the volume content of carbon fibers, but is generally 0.1 to 1 MPa. By setting the molding pressure within the above range, it is possible to obtain a CFRP that is free from defects such as voids and has little dimensional variation such as warpage. In particular, when CFRP is applied to an aircraft structure, an aromatic amine-based curing agent is often used as the main curing agent. After reaching the temperature, the molding pressure is generally about 0.59 MPa for about 2 hours.

The CFRP obtained by the present invention can be suitably used for aircraft structures. Aircraft structures include 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, It is selected from hat-shaped structures and the like. Aircraft parts are constructed by combining these structures. Details are described, for example, in "Airplane Structural Design" 5th Edition, Torikai and Kuze, Japan Aeronautical Engineering Association (2003). Such a structure is formed by forming a prepreg, for example, as described in WO2017/110991 [0084], WO2016/043156 [0073], and WO2019/0314078 [0088]. can be obtained. Also, a structure having a desired shape can be obtained by automatically laminating a prepreg tape on a mold having the desired shape and then curing the same.

In manufacturing an aircraft, a fuselage, a main wing, a center wing, a tail wing, etc. are formed by a joint structure in which a plurality of the above structures are joined. As means for joining structures, so-called fasteners such as bolts and rivets, adhesive films, and the like are used. Furthermore, a co-curing method can also be used in which uncured or semi-cured prepreg laminates are bonded and then cured.

<Method for producing prepreg of the present invention>
Although there is no particular limitation on the method for producing the sandwich structure prepreg of the present invention, some examples are given below.

<Manufacturing method 1>
First, a resin sheet is prepared. The resin sheet refers to a sheet in which resin is held in a thinly spread form. Examples thereof include a resin film containing a thermoplastic resin as a main component, and a resin in which a thermosetting resin composition is applied on release paper. Examples include films and sheet-like fiber substrates impregnated with matrix resin. The resin sheet is sandwiched between two prepregs to form a prepreg/resin sheet/prepreg sandwich structure, and if necessary, the prepreg of the present invention is obtained by heating and/or pressurizing to integrate. can be done. At this time, the two prepregs are laminated such that the fiber directions of the two prepregs are the same. A simplified diagram of this manufacturing method is shown in FIG. 16. The prepreg longitudinal direction and the CF longitudinal direction are made to coincide with each other. Regarding the positional relationship of the resin sheet 11 with respect to the lower prepreg 10, it is important that the resin sheet is arranged on the lower prepreg, so the lower prepreg does not necessarily need to be arranged in the horizontal direction. Alternatively, the prepreg may be arranged with an arbitrary angle of inclination with respect to the resin sheet. A desired prepreg roll can be obtained by winding this. The content of insoluble particles in the matrix resin on the surface of the prepreg should be 0.1 g/m ² or less. Furthermore, a resin sheet that does not dissolve in the matrix resin of the upper and lower prepregs or a resin sheet that contains a spacer is selected. By using such a resin sheet, the shape of the resin sheet can be maintained during the integration process and the subsequent molding process, and the function of forming a resin sublayer between the upper and lower CF sublayers in the prepreg is achieved. Furthermore, when spacers are contained in the resin sheet, the content of the spacers is preferably 3% by mass or more, more preferably 5% by mass or more, relative to the entire resin sheet. It is preferable from the viewpoint of maintaining the shape of the resin sheet during the molding process and forming a resin sublayer with a preferable thickness.

More specific examples for obtaining the prepreg of the present invention are described below. Two prepregs (CF sublayers) containing a matrix resin made of epoxy resin, diaminodiphenylsulfone-based curing agent, polyethersulfone, and CF aligned in one direction are placed so that the fiber direction is the same. A prepreg is obtained by arranging, sandwiching from above and below a resin film (which becomes a resin sublayer) made of polyamide 6, and applying heat and pressure to integrate them. As another example, instead of the resin film made of polyamide 6, GF fabric or GFRP can be used as the resin sheet. As another example, two prepregs made of CF aligned in one direction are arranged so that the fiber direction is the same, and a resin film made of copolymerized PAEK is sandwiched from above and below and heated. The prepreg is obtained by applying pressure while unifying them. At this time, the copolymerized PAEK can contain carbon particles having an average diameter of about 20 μm as a spacer.

<Manufacturing method 2>
Manufacturing method 2 exemplifies a manufacturing method that is more efficient than manufacturing method 1 .

A plurality of CFs are aligned to form two CF sheets having the same fiber direction, and a matrix resin containing spacers is applied to one of the CF sheets. After that, another CF sheet is covered thereon to form a sandwich structure (corresponding to using the CF sheet instead of the prepreg in <manufacturing method 1>). Thereafter, this sandwich structure is heated and pressurized to impregnate the CF sheet with the matrix resin to obtain the prepreg of the present invention. A simplified diagram of this manufacturing method is shown in FIG. 17. The prepreg longitudinal direction is aligned with the CF longitudinal direction. Regarding the positional relationship of the resin applying device 15 with respect to the lower CF sheet 14, it is important that the resin applying device is arranged above the lower CF sheet. The CF sheet may be arranged at an arbitrary angle of inclination with respect to the resin coating direction. A desired prepreg roll can be obtained by winding this. The matrix resin may be applied by direct coating using a T-die, spray coating, or the like, or by laminating separately prepared resin sheets containing the matrix resin. As the form of the resin sheet, one shown in <Manufacturing method 1> is used. Also, the resin may be applied in a form containing a carrier base material as a spacer, such as GF prepreg. The spacer may be contained in the resin when the resin is applied, or only the spacer may be added after the resin is applied. Specific examples of the latter method include a method in which spacer particles are added to the surface of the resin applied to the CF sheet, and a method in which a GF fabric or the like is laminated as a sheet-like material. In addition, International Publication No. 2018/173618 etc. can be referred for the method of film-forming resins, such as T-die, and providing. Also, by pressing a T-die against the CF sheet or passing it through a die, the resin can be applied without once forming a film. In addition, International Publication No. 2018/173619 and the like can be referred to for the method of spray coating. Also at this time, the content of the spacer is preferably 3% by mass or more and 40% by mass or less, more preferably 5% by mass or more and 20% by mass or less, and still more preferably 7% by mass or more, relative to the entire matrix resin constituting the sublayer. The content of 16% by mass or less is preferable from the viewpoint of maintaining the shape of the resin sheet during the integration process and the subsequent molding process. The entire matrix resin constituting the sublayer refers to the resin other than the carbon fiber sheets of the upper and lower surfaces constituting the prepreg. When the content of the spacer is 3% by mass or more and 40% by mass or less, it is effective for forming the resin sublayer with the preferable thickness described above during prepreg molding, and in addition, it causes deterioration of the slit workability of the prepreg. It is possible to suppress the occurrence of resin non-impregnated areas in the CF sublayer. Furthermore, it is effective in forming CF sublayers that have a Vcf that is preferable for exhibiting excellent conductivity between adjacent CF layers in the prepreg laminate described above.

More specific examples are described below. A resin composition is prepared by adding polyamide-based particles (spacer particles) to a matrix resin composed of an epoxy resin, a diaminodiphenylmethane-based curing agent, and polyethersulfone. This is applied to a CF sheet using a T-die, followed by stacking another CF sheet, and then applying pressure while heating to impregnate the CF sheet with the matrix resin. As another example, after applying the matrix resin described above to the surface of the CF sheet using a spray coater, the polyamide-based particles are dispersed, and then another CF sheet is laminated, followed by heating and pressing to form the matrix. The resin is impregnated into the CF sheet.

<Details of CFRP obtained by the present invention>
Next, the CFRP obtained by the present invention will be described in further detail.

<Characteristics of CFRP obtained by the present invention>
A cross-sectional view of an example of CFRP (1000) obtained by the present invention is shown in FIG. Here, a portion (100, 200, 300) in which three layers are laminated in the prepreg laminate of the present invention is shown.

In this example, a layer derived from one prepreg is a layer. A layer derived from the prepreg of the present invention is called a "specific layer". In general, CFRP is designed to have anisotropic mechanical properties by laminating CF sheets in which CF is arranged in one direction in multiple directions. Therefore, although the fiber orientation angle of CF is the same in each of 100, 200 and 300, the fiber orientation angles of 100 and 200 and 300 differ by 90°.

The features of the layer 100, which is a specific layer, will be described below as an example. In the CFRP 1000, layers 200 and 300 having different fiber orientation angles from the layer 100 are adjacent to the upper side and the lower side of the layer 100 (hereinafter sometimes referred to as adjacent layers). Between layer 100 and layers 200 and 300 are inter-layer resin layers 20 and 30, respectively. The thickness of each inter-layer resin layer is T20 and T30. However, depending on conditions, the inter-layer resin layers 20 and 30 may not exist. Layer 100 is formed with high Vcf sublayers derived from CF sublayers on both outermost sides of the layer, and low Vcf sublayers 110 derived from resin sublayers formed therebetween. Since the low Vcf sublayer is derived from the resin sublayer of the prepreg of the present invention, it is a layer that does not substantially contain CF, but the possibility of CF entering from above and below during molding is not zero, so CFRP will be explained When we do, we use the term low Vcf sublayer. Also, a region derived from the CF sublayer in the prepreg is called a high Vcf sublayer in CFRP. If the resin sublayer of the prepreg does not contain CF, the average Vcf in the low Vcf sublayer can be 20% or less. However, according to the definition of the low Vcf sublayer boundary in CFRP, Vcf may be relatively high in the high Vcf sublayer/low Vcf sublayer boundary region, as described below. The presence of the low Vcf sublayers in the CFRP allows the Vcf of the high Vcf sublayers 150, 160 to be sufficiently high to improve conductivity while maintaining the matrix resin content of the entire CFRP. Although the low Vcf sublayer is called "low Vcf", its Vcf is substantially almost zero, so if the resin sublayer of the prepreg does not contain other conductive materials (such as conductive particles) of CF is almost an insulating layer. In the CFRP obtained by the present invention (that is, the carbon fiber reinforced composite material of the present invention formed by molding the prepreg laminate of the present invention), a specific layer and at least one At least one of the thicknesses of the resin portions between adjacent layers (interlayer resin layer thicknesses T20 and T30 in this embodiment) is preferably 10 μm or less, more preferably 5 μm or less (further preferably 2 μm or less). The prepreg is preferably designed for This improves the conductivity between adjacent layers and reduces the risk of edge glow. Therefore, it is more preferable to design the prepreg so that both T20 and T30 are thin. The thickness of the resin layer between layers may be 0 μm.

In general, to improve the conductivity of CFRP, it is effective to improve Vcf. However, when the Vcf of the entire CFRP is increased, Rc is lowered, resulting in insufficient impregnation of the CF sheet with the matrix resin. There is a problem that voids are likely to occur in CFRP. On the other hand, in the layer 100, which is a specific layer, there is a low Vcf region derived from the resin sublayer of the prepreg. ) Only the nearby Vcf can be boosted locally. A high Vcf in the vicinity of the adjacent layer facilitates contact between the CF of the layer 100 and the CF of the adjacent layer, thereby greatly improving the conductivity between the layers. Therefore, the thickness of the resin sublayer in the prepreg is designed such that the ratio of the thickness (T110) of the low-Vcf sublayer to the thickness (T100) of the layer 100 is preferably 5% or more, more preferably 10% or more. be. Here, the thickness T100 of the layer 100 is defined as the distance from the center point in the thickness direction of the lower inter-layer resin layer 30 to the center point in the thickness direction of the upper inter-layer resin layer 20. do. If the ratio of the thickness of the low-Vcf sublayer to the layer is too large, the mechanical properties become uneven depending on the location. be.

<Details of one embodiment of CFRP obtained by the present invention>
CFRP obtained by the present invention will be described in more detail with reference to FIG. The CFRP shown in FIG. 4 is one of the forms of CFRP obtained by the present invention, and includes a specific layer, layer L1, and portions of ordinary layers L2 and L3. The fiber orientation angles of L1 and CF are different between L2 and L3. In CFRP, it is possible to determine which layer each CF belongs to from the difference in CF cross-sectional shape. The cross-sectional shape of the CF is generally observed to be elliptical. A region in which the length of the long axis of the ellipse is substantially the same and which is continuous in the thickness direction is determined to be one layer. Further, if it is understood that the orientation angles of the CF are the same in the continuous regions in the thickness direction at the stage of laminating the prepregs, the prepregs may be formed as one layer. The positive direction of the X-axis is defined as the rightward direction on the paper surface, and the positive direction of the Z-axis is defined as the upward direction on the paper surface.

A photograph for CFRP cross-sectional observation can be obtained, for example, by the following method. First, a sample of about 20 mm square is cut from the CFRP panel. Next, after embedding and curing this with epoxy resin, the edge portion is polished. After that, the polished surface is observed with a digital microscope VHX-5000 manufactured by Keyence Corporation. The observation magnification may be appropriately selected, but in many cases, it is easy to see at about 500 times. In addition, the observation sample may be cut in a direction according to the purpose. Easy to observe direction.

In the present invention, the boundary between adjacent layers L2 and L3 in a particular layer L1, the low Vcf sublayer and the high Vcf sublayer are determined from the Z-direction distribution of Vcf. The Z-direction distribution of Vcf can be obtained as follows. First, image analysis software is used to binarize FIG. 4 to discriminate between CF (black) and matrix resin (white) (FIG. 5). At this time, the image shown in FIG. 4 must have a resolution such that the length of one side of one pixel is 0.3 μm or less, and the range in the X-axis direction must be 500 μm or more. For image analysis software, for example, ImageJ (developer: Wayne Rasband, National Institutes of Health) or the like can be used. Vcf can be calculated from the area ratio of the black portion representing CF. Vcf is calculated using a rectangular area (here, 590 μm) with a length of one pixel in the Z direction (here, 0.2 μm) and a whole X-axis length (W1) in the image in the X direction as an evaluation area. The Vcf distribution in the Z direction can be obtained by calculating the Vcf of the evaluation region for each 0.2 μm length, which is the length of one pixel in the Z-axis direction, from the origin of the Z-axis. The Z-direction distribution of Vcf obtained from FIG. 5 is shown in FIG.

Next, in order to extract only a specific layer L1, the Z coordinates (Z2, Z3 in FIG. 5) of the boundary with adjacent layers are determined. First, the median of Vcf is calculated from the Z-direction distribution of Vcf shown in FIG. This value corresponds to A1 in FIG. 6 and is a representative value of Vcf including a specific layer L1 included in the cross-sectional photograph and layers L2 and L3. The reason why the average value is not used as the representative value of Vcf is that if the average value is used, the representative value of Vcf tends to change depending on the range of the Z-direction observation area of the cross-sectional photograph. A value obtained by multiplying the representative value of Vcf (A1 in FIG. 6) by 0.5 is used as a threshold for defining an inter-layer resin layer between adjacent layers. This threshold corresponds to B1 in FIG. In the vicinity of the boundary with the adjacent layer, a portion where Vcf is equal to or less than the threshold value B1 is defined as an inter-layer resin layer. In the upper diagram of FIG. 6, only the portion indicated by I1 corresponds, and I1 is regarded as an inter-layer resin layer between layers L1 and L3. The inter-layer resin layer thickness is defined as the length of the Z-coordinate of the portion corresponding to the inter-layer resin layer. In the lower left diagram of FIG. 6, T30 corresponds to the thickness of the inter-layer resin layer. The Z-coordinate of the boundary with the adjacent layer is defined as the central value of the Z-coordinate of the portion corresponding to the inter-layer resin layer. In FIG. 6, Z3 corresponds to the Z coordinate of the boundary between layers L1 and L3. On the other hand, in the vicinity of the boundary between the layers L1 and L2, there is no portion where Vcf is equal to or less than the threshold value B1. In this case, the Z-coordinate of the boundary with the adjacent layer is defined as the Z-coordinate of the point showing the minimum value of Vcf in the vicinity of the boundary with the adjacent layer. In the lower right diagram of FIG. 6, Z2 is the Z coordinate of the boundary between layers L1 and L2, which is the Z coordinate of point J1 showing the minimum value of Vcf near the boundary between layers L1 and L2. The Z-direction area of the specific layer L1 is the range from Z3 to Z2, which is the Z-coordinate of the boundary with the adjacent layer.

Next, focusing only on a specific layer L1, as shown in FIG. 5, a Z'-axis parallel to the Z-axis is newly defined with Z3 as the origin O'. FIG. 7 shows the Z' distribution of Vcf in a particular layer L1. The thickness T100 of a particular layer L1 is defined as the maximum value of the Z' coordinate, which is Z2 minus Z3. The average value of Vcf in layer L1 is defined by the average value of the Z' direction distribution of Vcf. This value corresponds to C1 in FIG. A value of 0.5 times C1 is taken as the threshold for defining the low Vcf sublayer. This threshold corresponds to D1 in FIG. A low Vcf sublayer is defined as a portion where Vcf is less than D1, except for the inter-layer resin layer at the top and bottom of the layer. This corresponds to the portion K1 in FIG. The average value of Vcf, the thickness of the low Vcf sublayer, is defined by the average value of Vcf, the thickness of the portion where Vcf is less than D1. Conversely, the portion where Vcf is greater than or equal to D1 is defined as the high Vcf sublayer. The average value of Vcf in the high Vcf sublayer is defined as the average value of Vcf in the portion where Vcf is greater than or equal to D1.

In layer L1, the average Vcf of the entire CFRP is 50% or more, the high Vcf sublayer is arranged on both sides of the low Vcf sublayer, and the average Vcf of the high Vcf sublayer is the average Vcf of the entire CFRP. get higher.

<Effect of suppressing edge glow>
High conductivity between layers facilitates the flow of current in and out of the layers. In this case, even when a lightning current flows into the CFRP, it becomes easier to utilize a plurality of layers as a current path, so local concentration of the lightning current can be prevented and the current can be easily dispersed. If the current can be distributed over multiple layers, the electrical resistance between the inflow and outflow of the lightning current will decrease, and the potential difference will decrease. If the potential difference between the current inflow portion and the current outflow portion is reduced, the potential difference generated in the CFRP as a whole is also reduced, so that the potential difference between adjacent layers is also reduced. The effect of suppressing edge glow is obtained by reducing the potential difference between adjacent layers. To better understand the potential difference between layers, the following describes how current flows in CFRP.

As a representative example of an aircraft structure, I. Consider a multi-directional laminated CFRP structure with two metal bolts inserted as shown in FIG. 3 of Revel et al. As a situation in which edge glow is likely to occur, consider a situation in which lightning strikes a bolt on one side, causing an inflow of lightning current, a lightning current flowing through the CFRP structure, and an outflow of lightning current from the other bolt.

Since CFRP has strong anisotropy in conductivity, current tends to flow mainly only in the CF direction within each layer. In the layer where the CF directly connects two bolts, the current concentrates in the CF connecting the bolts. Since the conductivity in the fiber direction is relatively high, in this case the electrical resistance between the two bolts is low and the potential difference between the bolts is small. On the other hand, in layers where the CF does not connect directly between two bolts, the current must flow in the orthogonal direction within the layer after spreading along the CF connected to the bolt. Since the conductivity in the orthogonal direction is generally about 1,000 times smaller than the conductivity in the fiber direction, in this case the electrical resistance between the two bolts is high and the potential difference between the bolts is large.

For CFRPs containing layers with different fiber orientation angles, each layer spreads the current along the CF connected to the bolt. The current spread along the CF can flow in the direction perpendicular to the CF within each layer, or it can flow into adjacent layers with different fiber orientation angles and utilize the CF of the adjacent layers. Within each layer, flow a short distance to an adjacent layer with a different fiber orientation angle, then flow a long distance in the direction of the high-conductivity fibers of the adjacent layer, rather than a long distance in the orthogonal direction of low conductivity. However, the electrical resistance between the bolts becomes smaller. Since the current path is determined so as to minimize the electrical resistance between bolts, in CFRP having a plurality of layers with different fiber orientation angles, current flows between the layers.

The conductivity between the layers determines the potential difference between the layers when current flows between the layers. If the conductivity between layers is high, current can flow easily between adjacent layers even if the potential difference between adjacent layers is not large. In this case, the electrical resistance between the two bolts becomes small and the potential difference becomes small.

From the above, in the case of CFRP including multiple layers, by improving the conductivity between adjacent layers, even if a large current such as a lightning current flows, the increase in the potential difference between the two bolts can be suppressed. It is possible to reduce the voltage applied to the CFRP, particularly the potential difference between adjacent layers. Thereby, the risk of occurrence of edge glow can be reduced.

<Effect of improving induction heating temperature>
High conductivity between adjacent layers has desirable effects other than edge glow suppression. For example, it is advantageous for induction welding used in CFRP with a thermoplastic resin as the matrix resin. Induction welding technology has been partially put into practical use for aircraft structures made of CFRP. Induction welding is a technique of joining by melting the thermoplastic resin of CFRP by induction heating and applying pressure separately. Induction heating is to generate an induced current in the CFRP by passing an alternating current through a coil installed outside the CFRP, and heat the CFRP by Joule heat generated by the induced current. In induction welding, it is desired to raise the induction heating temperature with less input energy.

In order to raise the induction heating temperature, it is important to improve the Joule heat generated by the induced current, so it is effective to increase the amount of the induced current generated in the CFRP. X. In Xu et al. (Journal of NDT and E International, Vol. 94, p.79-91, 2018), by increasing the conductivity between layers with different fiber orientation angles, the amount of induced current generated in CFRP Numerical analysis shows that That is, in the CFRP of the present invention, a large amount of induced current is generated, the induction heating temperature tends to be high, and desirable effects can be obtained even in induction welding.

A comparison of the amount of induced current generated in CFRP is possible by eddy current testing. Eddy current testing is generally a test for detecting cracks and the like in CFRP through evaluation of induced current generated in CFRP. In the eddy current testing, a coil is installed near the CFRP, and the magnetic field generated by the induced current is evaluated from the impedance change of the coil. K. According to Mizukami et al. (Journal of Polymer Testing, Vol. 69, p. 320-324, 2018), the magnetic field generated by the induced current is evaluated from changes in the series resistance component of the coil. It is shown that the greater the change in the magnetic field, that is, the greater the amount of induced current, the greater the series resistance component of the coil.

<Another example of CFRP obtained by the present invention>
In the CFRP obtained by the present invention, it is preferable that the layer that satisfies the conditions as a specific layer is arranged within the second layer counted from the upper surface or the lower surface of the CFRP. In this case, for example, in induction welding, the induced current can be increased intensively in the vicinity of the CFRP surface, which serves as the welding surface, and heating can be efficiently performed. In the CFRP 1001 shown in FIG. 8 that takes such a form, the specific layer 101 is arranged second when counting the number of layers from the upper surface of the CFRP 1001, and when the upper surface is the welding surface, the vicinity of the upper surface can be efficiently Induction heating is possible. Layers other than the specific layer 101 may satisfy the conditions of the specific layer, or may be normal layers.

Moreover, the form in which two or more specific layers are continuously laminated is preferable. The conductivity of the portion where these are adjacent between the specific layers is greatly improved, and the effect of suppressing the edge glow or improving the induction heating temperature is further enhanced. It is also preferable that all layers are specific layers only from the viewpoint of suppressing edge glow and improving induction heating temperature.

Another form is shown in FIG. In the layer 102 with the same fiber direction, there are low Vcf sublayers 112,122 sandwiched between high Vcf sublayers 152,162,172. Thus, even if there are a plurality of low Vcf sublayers, it is sufficient that the high Vcf sublayers are arranged at the outermost sides of the layer. In this case, in the layer 102, it is preferable that the average Vcf of the high Vcf sublayers 152 and 172 existing on both sides is higher than the average Vcf of the high Vcf sublayer 162 existing inside in the thickness direction. . In addition, in all aspects including this aspect, when a plurality of low Vcf sublayers exist in a specific layer, the characteristic of the low Vcf sublayer is that all the low Vcf sublayers existing in the layer are connected. defined as 9, the thickness of the low Vcf sublayer is defined as the sum of the thickness T112 of the low Vcf sublayer 112 and the thickness T122 of the low Vcf sublayer 122. FIG. Also, the average Vcf of the low Vcf sublayer is the average Vcf of the concatenated low Vcf sublayer 112 and low Vcf sublayer 122 . Such a CFRP can be obtained by using a prepreg having a sandwich structure in which two resin sublayers are sandwiched between three CF sublayers, as in the form of the layer 102 .

<Example of conventional CFRP form>
FIG. 10 is a cross-sectional view showing one form of ordinary (non-interlayer reinforced) CFRP according to the prior art. It is not a structure in which high Vcf sublayers are arranged in the outermost layers on both sides of the layer and low Vcf sublayers are present therebetween. If the total thickness of the layers and the average Vcf of the layers are the same, the CFRP using the prepreg of the present invention (see FIGS. 3 and 9) has a higher fiber orientation angle than the conventional technology shown in FIG. The Vcf near different layers can be higher and the conductivity between layers with different fiber orientation angles can be improved.

FIG. 11 is a cross-sectional view showing one form of an interlayer reinforced CFRP according to the prior art. In the CFRP shown in FIG. 11, in the layer 104 with the same fiber orientation angle, high Vcf sublayers are arranged in the outermost layers on both sides of the layer, there is no structure in which a low Vcf sublayer exists in between, and there is no structure in which a low Vcf sublayer exists between layers. Resin layers 24, 34 are present. The inter-layer resin layers 24 and 34 are mainly resin-rich layers for improving toughness, and often contain thermoplastic resin particles, fibers, non-woven fabric, and the like. If the layer thickness, the thickness of the resin layer between layers, and the average value of Vcf of the entire CFRP are the same, the Vcf of the layer of the conventional interlayer reinforced CFRP and the Vcf of the high Vcf sublayer of the present invention are approximately the same. However, in the interlayer-reinforced CFRP, the interlayer resin layers 24 and 34 often need to have a certain thickness or more. is higher.

FIG. 12 shows a photograph of a cross section of one form of conventional interlayer reinforced CFRP, and will be described in detail. FIG. 12 shows part of layer L4 and layers L5 and L6 of the CFRP consisting of layers L4, L5 and L6. By binarizing FIG. 12, FIG. 13 is obtained. When the Z-direction distribution of Vcf is calculated using FIG. 13 in the same manner as described above, the graph shown in FIG. 14 is obtained. First, the boundaries between layers are determined in the same manner as described above. In FIG. 14, the median of Vcf is A1', which is the representative value of Vcf in the regions of layers L4, L5 and L6 included in the cross-sectional photograph. Multiplying A1' by 0.5 gives B1' as the threshold for defining the inter-layer resin layer. In FIG. 14, near the boundary between layers, there are I1' and J1' where Vcf is lower than B1'. I1' and J1' are defined as inter-layer resin layers, and respective inter-layer resin layer thicknesses T34 and T24 are defined by the length of the Z coordinate of the portions corresponding to I1' and J1'. The central values of the Z coordinates of the portions corresponding to I1' and J1' are the Z coordinates of the boundaries of the layers L4 and L6, or the layers L4 and L5, respectively, and are Z6 and Z5, respectively. Next, focusing only on the layer L4 and newly setting the Z'-axis shown in FIG. 13, the Z'-axis direction distribution of Vcf in the layer L4 is obtained as shown in FIG. The thickness T104 of the layer L4 is defined as the maximum value of the Z' coordinate, which is the value obtained by subtracting Z6 from Z5. The average value of Vcf in layer L4 is defined by the average value of the Z' direction distribution of Vcf, and corresponds to C1' in FIG. A value of 0.5 times C1' is the threshold for defining the low Vcf sublayer and corresponds to D1'. Except for the inter-layer resin layer at the top and bottom of the layer, there is no part where Vcf is less than D1', so it is considered that there is no low Vcf sublayer. Layer L4 is not a specific layer because it does not have a structure in which high Vcf sublayers are arranged in the outermost layers on both sides of a low Vcf sublayer, even if the average Vcf of the entire CFRP is 50% or more. , CFRP obtained using the prepreg of the present invention.

EXAMPLES The present invention will be described in detail below with reference to examples. However, the scope of the present invention is not limited to these examples. In addition, the unit "part" of a composition ratio means a mass part unless there is a comment in particular. In addition, measurements of various properties (physical properties) were performed under an environment of 23° C. temperature and 50% relative humidity unless otherwise noted.

<Raw materials>
(A) Carbon fibers with an average fiber diameter of 7 μm, which are electrically treated so that the number of carbon fiber filaments is 24,000, the tensile strength is 5.8 GPa, the tensile modulus is 280 GPa, and the [O/C] is 0.10 or less. used.

(B) Thermosetting resin (epoxy resin)
・ “Sumiepoxy (registered trademark)” ELM434 (tetraglycidyldiaminodiphenylmethane, manufactured by Sumitomo Chemical Co., Ltd.)
・"EPICLON (registered trademark)" 830 (bisphenol F type epoxy resin, manufactured by DIC Corporation)
- "TOREP (registered trademark)" A-204E (N,N-diglycidyl-p-phenoxyaniline, manufactured by Toray Fine Chemicals Co., Ltd.).

(C) Curing agent "Seika Cure-S (registered trademark)"(4,4'-DDS, manufactured by Seika Co., Ltd.).

(D) Thermoplastic resin "Sumika Excel (registered trademark)" 5003P (PES, manufactured by Sumitomo Chemical Co., Ltd.).

(E) Polymer particles / spherical polyamide 6 particles (PA6, mode system 15 μm, sphericity 96%, manufacturing method described below)
With reference to International Publication No. 2018/207728, 200 g of ε-caprolactam (manufactured by Toray Industries, Inc.) and polyethylene glycol (Wako Pure Chemical Industries, Ltd.) as the second component polymer are added to an autoclave equipped with a 3 L helical ribbon stirring blade. 800 g of primary polyethylene glycol 20,000, weight average molecular weight 18,600, and 1,000 g of water were added to form a homogeneous solution, which was then sealed and purged with nitrogen. The stirring speed was then set to 100 rpm and the temperature was raised to 240°C. At this time, after the pressure of the system reached 0.98 MPa, the pressure was controlled while slightly releasing the steam so as to maintain the pressure at 0.98 MPa. After the temperature reached 240° C., the pressure was released at a rate of 0.02 MPa/min. Thereafter, the temperature was maintained for 1 hour while flowing nitrogen to complete the polymerization, and the mixture was discharged into a water bath of 2,000 g to obtain a slurry. After dissolving the dissolved material, filtration was performed, and 2,000 g of water was added to the filtrate and washed at 80°C. After that, the slurry was passed through a 200 μm sieve to remove agglomerates, filtered again, and the isolated filtrate was dried at 80° C. for 12 hours to prepare 140 g of polyamide 6 powder. The powder thus obtained had a melting point of 218° C., which is the same as that of polyamide 6, and a crystallization temperature of 170° C. The particle size was measured by a laser diffraction/scattering method using Microtrac MT3300II (light source 780 nm-3 mW, wet cell (medium: water)). The polymer particles are insoluble in the epoxy resin, and function as spacers in the resin and resin composition of this example. In addition, they can be the insoluble particles referred to in the present invention.

(F) Conductive particles/carbon particles: “Nikabeads (registered trademark)” ICB (average particle size (number base): 27 μm, manufactured by Nippon Carbon Co., Ltd.)
・ Nanocarbon: conductive carbon black # 3230B (primary particle diameter 23 nm (arithmetic mean diameter obtained by observing carbon black particles with an electron microscope), manufactured by Mitsubishi Chemical Corporation) This particle is a carbon particle ( ICB) was used as a conductive aid for assisting the action of ICB).

<Prepreg, CFRP production method and various measurement methods>
(1) Preparation of epoxy resin composition (matrix resin) The epoxy resin and thermoplastic resin described in <Raw materials> are kneaded, heated to 150°C or higher, and stirred for 1 hour to dissolve the thermoplastic resin. A clear viscous liquid was obtained. After cooling the liquid while kneading, a curing agent was added and further kneaded to obtain a resin. In addition, polymer particles, conductive particles and the like were added as necessary.

Table 1 shows the composition ratio of the resin composition of each example and comparative example. The numbers in Table 1 are parts by mass unless otherwise specified.

(2) Fabrication of prepreg Prepreg of sandwich structure As shown in FIG. 17, prepare two CF sheets 14 in which CF is evenly aligned in one direction, arrange them one above the other, and run them to become the lower side. A release paper 12 was inserted under the CF sheet 14 . On the upper surface of the lower CF sheet 14, using a resin application device 15 (T die), the matrix resin containing the polymer particles as spacers prepared in (1) is applied, then the upper CF sheet 14, and then separated. The pattern paper 12 was laminated. This was passed through an impregnating device 13 (press rolls) while being heated and pressurized to be impregnated with a matrix resin to obtain a prepreg having a sandwich structure. Then, this prepreg was wound up as a roll. In this prepreg roll, the fiber orientation direction of the carbon fibers of the carbon fiber sublayers on the upper and lower surfaces was the same as the longitudinal direction of the prepreg roll. Conditions were adjusted so that the CF mass (FAW) per unit area of the prepreg was 268 g/m ² and Rc was 34%. The thickness of the prepreg was in the range of 230-270 μm.

As the resin application device 15, the device described in International Publication No. 2018/173618 FIG. The air pressure was 0.2 MPa. Also, the running speed of the prepreg was 10 m/min.

- A prepreg having a structure according to the prior art A resin film was produced by uniformly coating an epoxy resin composition on release paper. Then, a CF sheet that is evenly aligned in one direction is sandwiched between two resin films, and passed through an impregnation device (press roll) while being heated and pressed to be impregnated with a matrix resin. Got the prepreg. Conditions were adjusted so that the CF mass (FAW) per unit area of the prepreg was 268 g/m ² and Rc was 34%.

In the case of performing two-stage impregnation, a primary resin film for the first-stage impregnation and a secondary resin film for the second-stage impregnation are prepared, and only the second-stage secondary resin film is prepared. , containing particles as described above. In addition, the resin basis weight of the primary resin film on the first stage and the secondary resin film on the second stage were the same.

(3) Amount of insoluble particles present on the upper surface and/or lower surface of the prepreg Select an arbitrary portion from the prepreg and cut a 5 cm square 25 cm ² as a sample. was taken. After dissolving the collected resin in NMP, it was filtered to separate the particles. The mass of the filtered particles was measured and divided by the sample area of 25 cm ² (0.0025 m ² ) to obtain the amount of insoluble particles (g/m ² ). In addition, the prepreg surface is observed with a microscope (Keyence Digital Microscope VHX-5000), and if the resin coating amount is 80% or less, if the presence of particles cannot be confirmed, the amount of insoluble particles is 0.05 g. /m ² or less.

(4) Amount of resin coating on prepreg surface The entire surface of the prepreg was observed and photographed with a digital microscope VHX-5000 manufactured by Keyence Corporation, and the amount of resin coating was determined from image analysis.
Amount of resin coating (%)=(area occupied by resin/area of entire prep surface)×100(%).

(5) Cross section observation of prepreg and resin thickness on prepreg surface A prepreg frozen at −15° C. or lower was taken out, and a sample of approximately 20 mm square was quickly cut using a single-edged razor to obtain a sample for cross section observation. This was observed with a digital microscope VHX-5000 manufactured by Keyence Corporation. The magnification was basically 500 times, and an appropriate magnification was selected for observation.

Among the cross-sectional observation images obtained above, the one in which the 0 ° direction of the CF is the cross section (the cross section of the CF is visible as shown in FIG. 1) is used, and the CF located on the most surface side in the prepreg thickness direction and The distance between the outermost resin surfaces of the prepreg was measured. This was measured in an observation range of 10 mm or more at a pitch of 20 μm or less in the horizontal direction (in-plane direction) of the prepreg, and the average value was obtained as the resin thickness of the prepreg surface. At this time, in order to set the observation range to 10 mm or more, a plurality of cross-sectional observation images were used. The thickness of the resin on the prepreg surface was set to zero at points where the CF was exposed on the prepreg surface.

(6) CF volume ratio Vcf in the sublayer
Vcf in the CF sublayer was obtained by the following procedure.

First, the volume fraction of the CF sublayer was obtained from a cross-sectional photograph of the prepreg. Next, the prepreg was cut into a size of 10 cm square, and its mass (W _P ) was measured. Then, the matrix resin in the prepreg was eluted with NMP, and the residue was separated by filtration. After drying the residue, the mass (W _R ) was measured to obtain the mass fraction (R _R ) of the residue.
R _R (%) = (W _R /W _P ) x 100 (%)
After that, the mass fraction (R _CF ) of CF relative to the entire prepreg is calculated from the mass fraction (R R ) of the residue, the input amount of components insoluble in NMP (PA6 particles, carbon particles, carbon black), and the input amount of _CF. rice field. Then, the Vcf of the entire prepreg was calculated from the CF density and the matrix resin density. Finally, the Vcf in the CF sublayer was obtained from the Vcf of the entire prepreg and the volume fraction of the CF sublayer.

(7) WPU, an index of impregnation degree of prepreg
A test piece having a size of 100 mm square in which the length in the longitudinal direction of the fiber×the width direction (the direction perpendicular to the fiber direction) is cut from the prepreg. Next, after measuring the mass W1 of the obtained test piece, one side of the test piece is arranged so that the fiber direction of the test piece is perpendicular to the water surface, and the range of 5 mm from the end of the test piece (ie 100 mm x 5 mm) were immersed in water for 5 minutes. After immersing the test piece for 5 minutes, remove it from the water, wipe off the water adhering to the surface of the test piece with a rag or the like while being careful not to touch the immersed surface, measure the mass W2 of the test piece, and measure WPU. asked.
WPU (%)=((W2−W1)/W1)×100(%).

(8) Tack force of prepreg It was measured using the probe tack method. As a tack tester, PICMA tack tester II (manufactured by Toyo Seiki Co., Ltd.) was used. First, a prepreg to be measured was placed on a tack tester, and a stainless steel plate (SUS304) with a 18 mm square glass plate was lowered from above the prepreg at a speed of 10 mm / min. to measure the peel load when peeling from the prepreg. The tack force can be obtained by dividing the maximum load at this time by the contact area. The measurement temperature was 22°C.

(9) Drapability of prepreg A prepreg was cut to a length of 25 mm in the width direction and 300 mm in the fiber direction, and the portion of one end of the length with a width direction length of 25 mm and a fiber direction length of 100 mm was brought into close contact with the pedestal. fixed. Then, the remaining portion of the prepreg, that is, the portion having a width of 25 mm and a length of 200 mm in the fiber direction, was formed into a cantilever beam projecting from the side surface of the pedestal. After standing in this state for 10 minutes, measure the horizontal distance A from the side of the pedestal to the unfixed end of the prepreg and the vertical height B from the surface of the prepreg fixed to the pedestal to the unfixed end of the prepreg. Then, the drape angle θ (PP) was calculated from the tangent values of these two sides. The measurement temperature was 22°C.
tan θ(PP)=B/A.

(10) Prepreg slitting test Using Gerber Technology's GERBERcutter (R) DSC as an automatic cutting machine and a 28 mm circular blade made by Olfa (RB28) as a 28 mm circular blade, the prepreg is cut into fibers against the fixed circular blade. Slitting was performed by moving along the direction at 18 m/min. Slitting is performed for a processing length of 100 m or more, and the number of fluffs containing carbon fibers with a length of 1 cm or more is counted on the side surface of the slit prepreg, and divided by the processing length. The frequency of occurrence of fluff (pieces/10m) containing was determined.

(11) Molding of CFRP Laminate 8 sets of each layer in a [0/90] _2S configuration, and autoclave at a temperature of 180 ° C for 2 hours, a pressure of 0.59 MPa, and a heating rate of 1.5 ° C/min. A CFRP panel (flat plate structure) was produced by curing the resin.

(12) Observation of Cross Section of CFRP A sample of about 20 mm square was cut from the CFRP panel obtained in (11). Next, after embedding and curing this with epoxy resin, the edge portion was polished. After that, the polished surface was observed with a digital microscope VHX-5000 manufactured by Keyence Corporation.

(13) Conductivity of CFRP in thickness direction From the CFRP panel obtained in (11), with the angle of the CF on the outermost layer of the panel set to 0°, cut out a 40 mm square sample along the 0° and 90° directions, After removing about 50 μm from both surfaces by polishing, Ag paste was evenly applied to both surfaces using a spatula. The Ag paste was cured over 1 hour in a hot air oven adjusted to a temperature of 120° C. to obtain a sample for conductivity evaluation. The resistance in the thickness direction of the obtained sample was measured by the four-probe method using an impedance analyzer (IM3570, manufactured by Hioki Electric Co., Ltd.) under a DC current load condition of 5 mA. Conductivity (S/m) was calculated from the measured resistance value and sample dimensions.

(14) Eddy current testing (induced current evaluation)
The series resistance component of a copper coil (inner diameter 10 mm, outer diameter 14 mm, height 3 mm, number of turns 60, with PPS bobbin (thickness of ear 1 mm), manufactured by Kitamoto Tech) was measured using an impedance analyzer (IM3570, Hioki Electric Co., Ltd.). (manufactured by the same company) under current load conditions of 5 mA AC and 300 kHz frequency, and measured by the four-probe method. In the first measurement, no conductor was placed near the coil. If a conductor is placed near the coil, the series resistance component of the coil changes. Next, the coil was placed in contact with the molded CFRP panel, and the series resistance component of the coil was measured in the same manner. At this time, since the PPS bobbin is attached to the coil, there is a distance of 1 mm between the coil portion and the CFRP panel. The resistance change of the coil was calculated by subtracting the first measurement result from the series resistance component when installed on the CFRP panel.

(Example 1) Conductive Particle Containing Resin 1 containing polymer particles and conductive particles was used as the matrix resin, and a sandwich structure prepreg was produced by the method shown in (2) above using the apparatus shown in FIG. Observation of the cross section of the prepreg confirmed that it had a sandwich structure of CF sublayer/resin sublayer/CF sublayer. The WPU of this prepreg was sufficiently impregnated with 2% or less. In addition, since the particles contained in the matrix resin have a particle diameter sufficiently larger than the diameter of the CF, they function as spacers. was shown to form. The thickness of the resin sublayer was 30 to 50 μm, which was a preferable range. Further, as shown in Table 2, the CF sublayer had a sufficiently high Vcf of 69%, and the insoluble particle content on the prepreg surface (both sides) was 0.05 g/m ² or less. This prepreg had a tack force of 0.0059 MPa or more and 0.025 MPa or less, and a drape angle (θ) of 7 to 17°, both of which were within preferable ranges. Moreover, the surface resin thickness of the prepreg was 10 μm or less, and the resin coating amount on the prepreg surface was 80% or less.

This prepreg was laminated and molded by the method (11) to obtain a CFRP panel. Observation of the CFRP cross-section confirmed the structure of specific layers derived from the prepreg of the present invention, as exemplified in FIG. Also, the resin layer between layers was very thin or at a level that could be regarded as having zero thickness. The thickness direction conductivity of this is 9 S / m, which is higher than Comparative Example 1 (two-stage impregnated prepreg according to the prior art containing the same amount of conductive particles as in Example 1), and the edge glow suppressing effect is sufficient. It was at the expected level. Furthermore, the resistance value change by the eddy current flaw detection test was 3.8 Ω, which is clearly higher than 2.5 Ω of Comparative Example 1, and an increase in the induced current can be expected. Thus, by using the prepreg of the present invention, a CFRP having better conductivity than the prepreg of the prior art containing the same amount of conductive particles was obtained.

(Comparative Example 1) Two-stage impregnated prepreg (contains conductive particles) according to conventional technology
A prepreg was produced by a two-step impregnation method using resin 2-1 as a matrix resin as a primary resin (prepreg inner layer side) and resin 2-2 containing polymer particles and conductive particles as a secondary resin (prepreg outer layer side). . From observation of the cross section of the prepreg, it was confirmed that a resin sublayer sandwiched between CF sublayers was not formed.

This prepreg was laminated and molded by the method (11) above to obtain a CFRP panel. Observation of the CFRP cross section revealed that no low Vcf sublayer was formed within the layer, and a thick interlayer resin layer was formed between adjacent layers, as illustrated in FIG. The conductivity in the thickness direction of this was 8 S/m, and the resistance value change in the eddy current flaw detection test was 2.5Ω, which were smaller than those of Example 1.

(Example 2) Containing Conductive Aid A sandwich structure prepreg was produced in the same manner as in Example 1, using resin 3 containing polymer particles, conductive particles, and a conductive aid as the matrix resin. Observation of the cross section of the prepreg confirmed that it had a sandwich structure of CF sublayer/resin sublayer/CF sublayer. Although the WPU of this prepreg was 2% or less, for the same reason as in Example 1, it was shown that a resin sublayer sandwiched between the upper and lower CF sublayers was formed even if the resin impregnation progressed sufficiently. was done. The thickness of the resin sublayer was in the range of 30-50 μm. Further, as shown in Table 2, the CF sublayer had a sufficiently high Vcf of 69%, and the insoluble particle content on the prepreg surface (both sides) was 0.05 g/m ² or less. This prepreg had a tack force in the range of 0.0059 MPa to 0.025 MPa and a drape angle (θ) in the range of 7 to 17°. Moreover, the surface resin thickness of the prepreg was 10 μm or less, and the resin coating amount on the prepreg surface was 80% or less.

This prepreg was laminated and molded by the method (11) to obtain a CFRP panel. Observation of the CFRP cross-section confirmed the structure of specific layers derived from the prepreg of the present invention, as illustrated in FIG. Also, the resin layer between layers was very thin or at a level that could be regarded as having zero thickness. The conductivity in the thickness direction of this was 12 S/m, and the change in resistance value by the eddy current flaw detection test was 4.2 Ω, which were higher than those of Example 1.

Example 3 No Conductive Particles Resin 4 containing polymer particles as spacers (no conductive particles) was used as the matrix resin, and a sandwich structure prepreg was produced using the apparatus shown in FIG. Observation of the cross section of the prepreg confirmed that it had a sandwich structure of CF sublayer/resin sublayer/CF sublayer. In this prepreg, for the same reason as in Example 1, it was shown that resin sublayers sandwiched between upper and lower CF sublayers were formed even when resin impregnation progressed. The thickness of the resin sublayer was 30 to 50 μm, which was a preferable range. Further, as shown in Table 3, the CF sublayer had a sufficiently high Vcf of 69%, and the insoluble particle content on the prepreg surface (both sides) was 0.05 g/m ² or less. This sandwich-structure prepreg had a WPU content of 2% or less and was sufficiently impregnated, had a tack force in the range of 0.0059 MPa or more and 0.025 MPa or less, and had a drape angle (θ) in the range of 7 to 17°. Moreover, the surface resin thickness of the prepreg was 10 μm or less, and the resin coating amount on the prepreg surface was 80% or less.

This prepreg was laminated and molded by the method (11) to obtain a CFRP panel. Observation of the CFRP cross-section confirmed the structure of specific layers derived from the sandwich structure prepreg of the present invention, as illustrated in FIG. Also, the resin layer between layers was very thin or at a level that could be regarded as having zero thickness. The eddy current flaw detection test showed a change in resistance value of 1.5 Ω, which is higher than 1.0 Ω in Comparative Example 2, and an increase in the induced current can be expected. By increasing the induced current, not only the efficiency of induction heating can be improved, but also the effect of reducing the potential difference between adjacent layers can be expected.

(Comparative Example 2) Two-stage impregnated prepreg according to conventional technology (without conductive particles)
By using resin 2-1 as a matrix resin as a primary resin (prepreg inner layer side) and resin 2-3 containing polymer particles (not containing conductive particles) as a secondary resin (prepreg outer layer side), a two-step impregnation method is performed. A prepreg according to the prior art was produced. From observation of the cross section of the prepreg, it was confirmed that the prepreg did not have a sandwich structure, and no resin sublayers sandwiched between CF sublayers were formed.

This prepreg was laminated and molded by the method (11) above to obtain a CFRP panel. When the CFRP cross section was observed, as illustrated in FIG. 11, no low Vcf sublayer was formed within the layer, and a thick interlayer resin layer was formed between adjacent layers. The change in resistance value by the eddy current flaw detection test was 1.0Ω or less, which is smaller than that of Example 3.

(Example 4) Prepreg tape The prepreg obtained in Example 1 was slit to obtain a prepreg tape with a width of 1.3 cm (1/2 inch). Observation of the side surface of this prepreg tape revealed that the WPU was sufficiently impregnated to 2% or less, so the frequency of presence of CF-containing fluff of 1 cm or more was as low as 0.2 fluff/10 m or less.

(Example 5) Conductive Particle Containing Resin 5 containing polymer particles and conductive particles was used as the matrix resin, and a prepreg having a sandwich structure was produced by the method shown in (2) above using the apparatus shown in FIG. 17 . Observation of the cross section of the prepreg confirmed that it had a sandwich structure of CF sublayer/resin sublayer/CF sublayer. The WPU of this prepreg was sufficiently impregnated with 2% or less. In addition, since the particles contained in the matrix resin have a particle diameter sufficiently larger than the diameter of the CF, they function as spacers. It has been shown that sublayers are formed. The thickness of the resin sublayer was 10 to 19 μm, which was a preferable range. Further, as shown in Table 4, the CF sublayer had a high Vcf of 61%, and the insoluble particle content on the prepreg surface (both sides) was 0.05 g/m ² or less. This prepreg had a tack force of 0.0059 MPa or more and 0.025 MPa or less, and a drape angle (θ) of 7 to 17°, both of which were within preferable ranges. Moreover, the surface resin thickness of the prepreg was 10 μm or less, and the resin coating amount on the prepreg surface was 80% or less.

This prepreg was laminated and molded by the method (11) to obtain a CFRP panel. Observation of the CFRP cross-section revealed a specific layer structure derived from the prepreg of the present invention, as exemplified in FIG. Also, the resin layer between layers was very thin or at a level that could be regarded as having zero thickness. The conductivity in the thickness direction was 9 S/m, which was at a level at which the effect of suppressing edge glow could be fully expected. Furthermore, the resistance value change by the eddy current flaw detection test was 2.8 Ω, which is clearly higher than 2.5 Ω of Comparative Example 1, and an increase in the induced current can be expected.

(Example 6) Conductive Particle Containing Resin 6 containing polymer particles and conductive particles was used as the matrix resin, and a prepreg having a sandwich structure was produced by the method shown in (2) above using the apparatus shown in FIG. 17 . Observation of the cross section of the prepreg confirmed that it had a sandwich structure of CF sublayer/resin sublayer/CF sublayer. The WPU of this prepreg was sufficiently impregnated with 2% or less. In addition, since the particles contained in the matrix resin have a particle diameter sufficiently larger than the diameter of the CF, they function as spacers. It has been shown that sublayers are formed. The thickness of the resin sublayer was 20 to 29 μm, which was a preferable range. Further, as shown in Table 4, the CF sublayer had a high Vcf of 65%, and the insoluble particle content on the prepreg surface (both sides) was 0.05 g/m ² or less. This prepreg had a tack force of 0.0059 MPa or more and 0.025 MPa or less, and a drape angle (θ) of 7 to 17°, both of which were within preferable ranges. Moreover, the surface resin thickness of the prepreg was 10 μm or less, and the resin coating amount on the prepreg surface was 80% or less.

This prepreg was laminated and molded by the method (11) to obtain a CFRP panel. Observation of the CFRP cross-section revealed a specific layer structure derived from the prepreg of the present invention, as exemplified in FIG. Also, the resin layer between layers was very thin or at a level that could be regarded as having zero thickness. The conductivity in the thickness direction was 9 S/m, which was at a level at which the effect of suppressing edge glow could be fully expected. Furthermore, the resistance value change by the eddy current flaw detection test was 3.4 Ω, which is clearly higher than 2.5 Ω in Comparative Example 1, and an increase in the induced current can be expected.

(Example 7) Conductive Particle Containing Resin 7 containing polymer particles and conductive particles was used as the matrix resin, and a prepreg having a sandwich structure was produced by the method shown in (2) above using the apparatus shown in FIG. 17 . Observation of the cross section of the prepreg confirmed that it had a sandwich structure of CF sublayer/resin sublayer/CF sublayer. The WPU of this prepreg was sufficiently impregnated with 2% or less. In addition, since the particles contained in the matrix resin have a particle diameter sufficiently larger than the diameter of the CF, they function as spacers. It has been shown that sublayers are formed. The thickness of the resin sublayer was 30 to 55 μm, which was considered a preferable range. Further, as shown in Table 4, the CF sublayer had a high Vcf of 72%, and the insoluble particle content on the prepreg surface (both sides) was 0.05 g/m ² or less. This prepreg had a tack force of 0.0059 MPa or more and 0.025 MPa or less, and a drape angle (θ) of 7 to 17°, both of which were within preferable ranges. Moreover, the surface resin thickness of the prepreg was 10 μm or less, and the resin coating amount on the prepreg surface was 80% or less.

This prepreg was laminated and molded by the method (11) to obtain a CFRP panel. Observation of the CFRP cross-section revealed a specific layer structure derived from the prepreg of the present invention, as exemplified in FIG. Also, the resin layer between layers was very thin or at a level that could be regarded as having zero thickness. The conductivity in the thickness direction was 17 S/m, which was at a level at which the effect of suppressing edge glow could be fully expected. Furthermore, the resistance value change by the eddy current flaw detection test was 4.9 Ω, which is clearly higher than 2.5 Ω of Comparative Example 1, and an increase in the induced current can be expected.

(Example 8) Conductive Particle Containing Resin 8 containing polymer particles and conductive particles was used as the matrix resin, and a prepreg having a sandwich structure was produced by the method shown in (2) above using the apparatus shown in FIG. Observation of the cross section of the prepreg confirmed that it had a sandwich structure of CF sublayer/resin sublayer/CF sublayer. The WPU of this prepreg was 6%. In addition, since the particles contained in the matrix resin have a particle diameter sufficiently larger than the diameter of the CF, they function as spacers. It has been shown that sublayers are formed. The thickness of the resin sublayer was 56 to 70 μm, which was a preferable range. Further, as shown in Table 4, the CF sublayer had a high Vcf of 76%, and the insoluble particle content on the prepreg surface (both sides) was 0.05 g/m ² or less. This prepreg had a tack force of 0.0059 MPa or more and 0.025 MPa or less, and a drape angle (θ) of 7 to 17°, both of which were within preferable ranges. Moreover, the surface resin thickness of the prepreg was 10 μm or less, and the resin coating amount on the prepreg surface was 80% or less.

This prepreg was laminated and molded by the method (11) to obtain a CFRP panel. Observation of the CFRP cross-section revealed a specific layer structure derived from the prepreg of the present invention, as exemplified in FIG. Also, the resin layer between layers was very thin or at a level that could be regarded as having zero thickness. The conductivity in the thickness direction was 15 S/m, which was at a level at which the effect of suppressing edge glow could be fully expected. Example Further, the resistance value change by the eddy current flaw detection test was 5.7Ω, which is clearly higher than 2.5Ω of Comparative Example 1, and an increase in induced current can be expected.

The prepreg of the present invention is widely applicable to fields requiring lightning resistance and fields requiring induction welding. In particular, when used for aircraft structural members, it can reduce the need for conventional lightning protection systems such as metal mesh and sealant, so it can be suitably used in this field, simplifying conventional lightning protection systems, reducing weight and cost of aircraft. can contribute to

1 carbon fiber 2 matrix resin 3 sandwich structure prepreg 4, 5 carbon fiber sublayer 6 resin sublayer 10 prepreg 11 resin sheet 12 release sheet 13 impregnation device 14 carbon fiber sheet 15 resin application device 16 rollers 20, 21, 22, 23 , 24 Layer-to-layer resin layers 30, 31, 32, 33, 34 Layer-to-layer resin layers to upper adjacent layers Layer-to-layer resin layers 100, 101, 102 to Lower-side adjacent layers Specific layers 103, 104 Layers 110, 111, 112, 122, 210, 212, 222, 310 Low Vcf sublayers 150, 151, 152, 160, 161, 162, 172 High Vcf sublayers 200, 201, 202, 203, 204 Overlying adjacent layers 300, 301, 302, 303 , 304 Underlying adjacent layers 401, 501 Underlying layers 1000, 1001, 1002 One embodiment of CFRP obtained with the prepreg of the present invention 1003 One form of CFRP obtained with the prepreg according to the prior art 1004 Conventional One form of interlayer reinforced CFRP obtained with the prepreg according to the technology L1, L4 Layers L2 and L5 observed in the middle of the Z direction Adjacent layers L3 and L6 observed on the upper side in the Z direction L3 and L6 Observed on the lower side in the Z direction adjacent layer W1 X-axis direction total length A1, A1′ representative value (median) of Vcf of all three layers
B1, B1′ Vcf thresholds C1, C1′ for defining resin layers between layers Average Vcf values for all layers D1, D1′ Vcf threshold values for defining low Vcf sublayers K1 Applicability of low Vcf sublayers Locations I1, I1' Corresponding location J1 of the inter-layer resin layer with the lower adjacent layer Point J1' near the boundary with the upper adjacent layer where Vcf takes the minimum value Corresponding location of the inter-layer resin layer with the upper adjacent layer Z3, Z6 Z coordinates at the boundary between layers with the lower adjacent layer Z2, Z5 Z coordinates at the boundary between layers with the upper adjacent layer T110, T112, T122 Thickness of the low Vcf sublayer T20, T22, T24 Upper adjacent layer Layer-to-layer resin layer thicknesses T30, T32, T34 Layer-to-layer resin layer thicknesses to the lower adjacent layer T100, T102, T104 Layer thickness

Claims (17)

A prepreg in which a carbon fiber sheet is impregnated with a matrix resin, wherein carbon fiber sublayers having carbon fibers and a matrix resin are arranged on upper and lower surfaces, and a resin sublayer is arranged between the two carbon fiber sublayers. The fiber orientation angle of the carbon fibers in the top and bottom carbon fiber sublayers in the prepreg is the same, and the amount of insoluble particles present on the top and/or bottom surfaces is 0.1 g/m2. ² or less, prepreg. The prepreg according to claim 1, wherein the resin sublayer has a thickness of 1 to 100 µm. The prepreg according to claim 1, wherein the resin sublayer contains spacers. The prepreg according to claim 1, wherein a thermosetting resin, a curing agent, and a thermoplastic resin are included in the matrix resin that constitutes the carbon fiber sublayers on the upper and lower surfaces and the resin sublayer. The prepreg according to claim 3, wherein particles are contained as said spacers. The prepreg according to claim 3, which contains a fiber base material as the spacer. 4. The prepreg according to claim 3, wherein the spacer content is 3% by mass or more and 40% by mass or less when the entire matrix resin constituting the resin sublayer is taken as 100% by mass. The prepreg according to claim 1, wherein the carbon fibers are arranged in one direction in the carbon fiber sheet. The prepreg according to claim 1, wherein the resin sublayer has the form of a resin film, and the resin film can substantially retain the film form during the prepreg molding process. The prepreg according to claim 1, wherein the carbon fiber volume fraction (Vcf) of the top and bottom carbon fiber sublayers are both 60% to 90%. The prepreg according to claim 1, wherein the tack force measured by a probe tack method is 0.0059 MPa or more and 0.025 MPa or less. The prepreg according to claim 1, wherein the drape angle θ (PP) of the prepreg is 7° or more and 17° or less. A prepreg roll obtained by winding the prepreg according to claim 1,
A prepreg roll, wherein the fiber orientation directions of the carbon fibers of the carbon fiber sublayers on the upper surface and the lower surface are both the same as the longitudinal direction of the prepreg roll. A tape made of the prepreg according to claim 1,
The fiber orientation direction of the carbon fibers of the carbon fiber sublayers on the upper surface and the lower surface is the same as the longitudinal direction of the tape, and the frequency of occurrence of fluff containing carbon fibers and having a length of 1 cm or more, which is present on the side surface of the tape, is 1/10 m. Prepreg tape, which is: A prepreg laminate containing at least one layer of the prepreg according to claim 1, the prepreg cut from the prepreg roll according to claim 13, or the prepreg tape according to claim 14. A carbon fiber reinforced composite material obtained by molding the prepreg laminate according to claim 15. A structure comprising the carbon fiber reinforced composite material of claim 16, the shape of which is selected from:
Planar structures, cylindrical structures, box structures, C-shaped structures, H-shaped structures, L-shaped structures, T-shaped structures, I-shaped structures, Z-shaped structures and hat-shaped structures.

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