Carbon fiber reinforced composite materials

Abstract

[Problem] The present invention addresses the problem of controlling the CFRP structure to provide a low-edgeglow-risk CFRP without relying on costly electroconductive particles. In other words, the present invention addresses the problem of providing a CFRP in which the risk of edgeglow is greatly reduced even if electroconductive particles are used at an amount equal to or lower than that according to prior art. Furthermore, the present invention addresses the problem of providing a CFRP in which the risk of edgeglow is greatly reduced even if no electroconductive particles are used. [Solution] A carbon-fiber-reinforced composite material obtained by stacking, in multiple directions, carbon fiber sheets in which carbon fibers are oriented in one direction and impregnating and curing a matrix resin. When, in the carbon fiber sheets, a region in which the fiber orientation angle of the carbon fibers remains the same continuously in the thickness direction is deemed to be a layer, and in a case in which the layer comprises a plurality of regions that have a uniform thickness and between which the carbon fiber volume content (Vcf) differs, said regions having a uniform thickness are deemed to be sublayers, the carbon fiber sheets include a specific layer satisfying conditions (1) to (3), and the thickness of a resin portion between the specific layer and at least one layer adjacent to the specific layer is 5 μm or below. (1) The average value of Vcf of the layer (hereafter referred to as the layer Vcf average value) is 50% or above. (2) Sublayers having a Vcf whose ratio relative to the layer Vcf average value is 0.5 or higher (hereafter referred to as a high-Vcf sublayer) are disposed on the outermost parts on both sides of the layer, each having a Vcf average value higher than the layer Vcf average value. (3) A sublayer having a Vcf whose ratio relative to the layer Vcf average value is lower than 0.5 (hereafter referred to as a low-Vcf sublayer) is present between the high-Vcf sublayers on the outermost parts on both sides of the layer.

Description

[Technical Field]

[0001] This invention relates to a carbon fiber reinforced composite material that has excellent lightning resistance and is suitable for induction welding. [Background technology]

[0002] Fiber-reinforced composite materials (hereinafter sometimes abbreviated as FRP) are lightweight yet possess excellent mechanical properties such as strength and rigidity, as well as heat resistance and corrosion resistance, and have therefore been applied in numerous fields such as aerospace, automobiles, railway vehicles, ships, and sporting goods. In applications requiring 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 epoxy resin, which has excellent adhesion to CF, heat resistance, and elastic modulus, and has low curing shrinkage, is often used as the matrix resin. The proportion of carbon fiber reinforced composite materials (hereinafter sometimes abbreviated as CFRP) used in aircraft structural components has been increasing in recent years, and its usage is expected to continue to increase in the future. In recent years, due to expectations for high-rate production and fastenerless bonding, there has also been an increase in the use of thermoplastic resins as the matrix resin. Examples of CFRP include laminated CF sheets in which CF is aligned in one direction (UD), laminated CF fabric in which CF is arranged in multiple directions, and laminated sheets in which CF is randomly arranged. When prioritizing the mechanical properties of CFRP, unified CF sheets are used, while CF fabric tends to be used when fabricating complex-shaped CFRP. In aircraft structural applications, where mechanical properties are prioritized, unified CF sheets laminated in multiple directions are widely used.

[0003] CF is a conductor, while the matrix resin is generally an insulator. In CFRP, the conductivity is relatively high in the direction of the fiber axis (hereinafter referred to as the fiber direction) because the CF itself acts as a conductive path. On the other hand, in the direction perpendicular to the fiber axis (hereinafter referred to as the orthogonal direction), the conductivity is generally about 1 / 1000th lower than in the fiber direction because conductive paths are formed by contact between CF sheets. Even the conductivity in the fiber direction is generally about 1 / 1000th lower than that of metals such as aluminum. Thus, CFRP has inferior conductivity to metal materials and exhibits 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 in metal materials, and furthermore, in CFRP composed of multiple CF sheets with different fiber orientation angles, the current distribution becomes very complex.

[0004] Due to its complex electrical properties, aircraft made of CFRP (carbon fiber reinforced polymer) are susceptible to lightning damage. Because CFRP does not easily disperse lightning currents like metal materials, it is prone to problems such as damage caused by localized concentration of lightning currents and sparks generated by high-voltage applications. Therefore, to ensure safety, CFRP aircraft are equipped with lightning protection systems, such as metal meshes and sealant coatings for areas where sparks may occur. However, these lightning protection systems increase weight and cost. To reduce the need for these systems and further improve safety against lightning, it is necessary to enhance the electrical properties of CFRP itself.

[0005] One type of spark around fuel tanks is called edge glow. This refers to a light emission phenomenon (glow) at the edges of the components, and research is being conducted to elucidate its generation mechanism. Non-Patent Literature 1 compares the potential analysis of CFRP with experimental results of edge glow generation and discusses the mechanism in detail. Figure 8 of Non-Patent Literature 1 shows that in CFRP made by laminating CF sheets with various fiber orientation angles, the potential difference is particularly large between CF sheets with different fiber orientation angles. Furthermore, Figure 18 of Non-Patent Literature 1 shows that the generation of edge glow was experimentally confirmed in 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 with different fiber orientation angles is effective in suppressing edge glow.

[0006] To suppress edge glow, it is generally believed that increasing the conductivity in the thickness direction of CFRP is effective in reducing the potential difference between CF sheets with different fiber orientation angles. Therefore, many material designs have been proposed to improve the conductivity in the thickness direction of CFRP, and among them, the method of arranging conductive particles between CF sheets with different fiber orientation angles, as shown in Patent Documents 1 to 3, is particularly effective in improving the conductivity in the thickness direction of CFRP.

[0007] Patent Document 1 discloses a technique for arranging carbon particles between CF sheets with different fiber orientation angles. Patent Document 2 also discloses a technique for arranging carbon particles between CF sheets with different fiber orientation angles, and referring to its examples, it is shown that increasing the amount of carbon particles lowers the volume resistivity in the thickness direction of the CFRP and improves its conductivity. Patent Document 3 is a technique for arranging potato-shaped graphite between CF sheets with different fiber orientation angles, and referring to its examples, it is shown that increasing the amount of potato-shaped graphite improves the conductivity in the thickness direction of the CFRP. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] International Publication No. 2008 / 018421 [Patent Document 2] International Publication No. 2011 / 027160 [Patent Document 3] International Publication No. 2013 / 186389 [Non-patent literature]

[0009] [Non-Patent Document 1] RBGreegor 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 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] However, the conductivity required to suppress edge glow is high, and it was necessary to significantly improve conductivity. In Patent Document 1, the volume resistivity in the thickness direction of the CFRP shown in the example is 2.0 × 10⁻⁶. 3 The conductivity is not sufficient, being above Ωcm (conductivity of 0.05 S / m or less). Patent documents 2 and 3 show that increasing the amount of conductive particles placed between CF sheets is effective in improving conductivity, but the conductivity required to suppress edge glow is high, requiring the addition of a large amount of conductive particles. In addition, the conductive particles used in patent documents 1 to 3 are generally expensive, so it is preferable to reduce the amount added. Thus, reducing the amount of conductive particles added and reducing the risk of edge glow by improving conductivity are mutually exclusive.

[0011] An object of the present invention is to provide a CFRP in which the risk of edge glow is significantly reduced even when the same amount or a lower amount of conductive particles as in the prior art is used by controlling the CFRP structure. Furthermore, it is also possible to provide a CFRP in which the risk of edge glow is significantly reduced without using conductive particles.

Means for Solving the Problems

[0012] A first means for solving the problems of the present invention is that in a carbon fiber reinforced composite material in which carbon fiber sheets in which carbon fibers are arranged in one direction are laminated in multiple directions and impregnated with a matrix resin and cured, when the carbon fiber sheet has regions with the same fiber orientation angle of carbon fibers continuously in the thickness direction as layers, and when the layer consists of a plurality of constant-thickness regions with different carbon fiber volume contents (Vcf), and the constant-thickness regions are used as sub-layers, it includes a layer (such a layer is referred to as a "specific layer") that satisfies (1) to (3), and is a carbon fiber reinforced composite material in which the thickness of the resin portion between the specific layer and at least one adjacent layer is 5 μm or less. (1) The average value of Vcf in the layer (hereinafter referred to as the layer Vcf average value) is 50% or more. (2) Sub-layers (hereinafter referred to as high Vcf sub-layers) having a Vcf with a ratio to the layer Vcf average value of 0.5 or more are arranged on both outermost sides of the layer, and the average value of each Vcf is higher than the layer Vcf average value. (3) A sub-layer (hereinafter referred to as a low Vcf sub-layer) having a Vcf with a ratio to the layer Vcf average value of less than 0.5 exists between the high Vcf sub-layers on both outermost sides of the layer.

[0013] A second means for solving the problems of the present invention is that in a carbon fiber reinforced composite material in which carbon fiber sheets in which carbon fibers are arranged in one direction are laminated in multiple directions and impregnated with a matrix resin and cured, ​​​The carbon fiber sheet has regions in the thickness direction where the fiber orientation angle of the carbon fibers is the same, as layers. When the layer consists of multiple regions of constant thickness with different carbon fiber volume content (Vcf), and these regions of constant thickness are designated as sublayers, (1) to (3) includes a layer (such layer is referred to as a "specific layer"), This is a carbon fiber reinforced composite material in which a resin portion exists between the specific layer and the adjacent layer, and the resin portion contains conductive particles. (1) The average value of Vcf in the layer (hereinafter referred to as the average value of layer Vcf) is 50% or more. (2) Sublayers with Vcf ratios of 0.5 or higher to the average Vcf of the layer are placed on the outermost sides of the layer (hereinafter referred to as high Vcf sublayers), and the average Vcf of each is higher than the average Vcf of the layer. (3) Between the outermost high Vcf sublayers on both sides of the layer, there are sublayers with a Vcf ratio of less than 0.5 to the average layer Vcf (hereinafter referred to as low Vcf sublayers). [Effects of the Invention]

[0014] According to the CFRP of the present invention, a sufficient edge glow suppression effect can be obtained even with a reduction in the amount of expensive conductive particles used. Furthermore, an even greater edge glow suppression effect can be obtained compared to conventional techniques in which conductive particles are simply placed between CF sheets with different fiber orientation angles. By applying such CFRP to aircraft, the lightning protection system can be made more efficient overall. In addition, according to the present invention, there is also the advantage that the induction heating temperature can be increased in induction welding, which is used in CFRP mainly in which the matrix resin is made of thermoplastic resin. [Brief explanation of the drawing]

[0015] [Figure 1] Cross-sectional view showing one embodiment of the CFRP of the first invention. [Figure 2] Cross-sectional photograph of one embodiment of the CFRP of the first invention [Figure 3]Image 2 after being converted to binarized form. [Figure 4] Figure 3 shows the Z-direction distribution of Vcf in a cross-section and a magnified view of a portion of it. [Figure 5] Z-direction distribution of Vcf in layer L1, Figure 3. [Figure 6] Cross-sectional view showing another embodiment of the CFRP of the first invention. [Figure 7] Cross-sectional view showing another embodiment of the CFRP of the first invention. [Figure 8] Cross-sectional view showing a conventional form of CFRP. [Figure 9] Cross-sectional view showing one form of conventional interlayer-reinforced CFRP. [Figure 10] Cross-sectional photograph of a conventional interlayer-reinforced CFRP structure. [Figure 11] Image 10 after being binarized [Figure 12] Figure 11 shows the Z-direction distribution of Vcf in a cross-section and a magnified view of a portion of it. [Figure 13] Z-direction distribution of Vcf in layer L4 in Figure 11 [Figure 14] Cross-sectional view showing another form of conventional interlayer-reinforced CFRP. [Figure 15] Cross-sectional view showing one form of an intermediate substrate for obtaining CFRP of the first invention. [Figure 16] A cross-sectional view showing one form of a prepreg laminate for obtaining CFRP according to the first invention. [Figure 17] A cross-sectional view showing one form of a prepreg laminate for obtaining CFRP according to the first invention. [Figure 18] Top view of a CFRP panel [Figure 19] A graph showing the evaluation results of the embodiment of the first invention. [Figure 20] A graph showing the evaluation results of the embodiment of the first invention. [Figure 21] A graph showing the evaluation results of the embodiment of the first invention. [Figure 22] A cross-sectional view showing one form of a prepreg laminate for obtaining CFRP according to the second invention. [Figure 23]Cross-sectional photograph of one embodiment of CFRP having voids [Figure 24] Image obtained by binarizing Figure 23 [Figure 25] A graph showing the evaluation results of the embodiments of the present invention. [Figure 26] A graph showing the evaluation results of the embodiments of the present invention. [Modes for carrying out the invention]

[0016] The present invention will be described in more detail below.

[0017] <Carbon fiber sheets and CFRP> Carbon fiber (CF) is typically used as a "tow," which is a tape-like bundle of approximately 1,000 to 1,000,000 single fibers. The carbon fiber sheet used in this invention (hereinafter referred to as CF sheet) has the CF aligned in one direction, and preferably can be obtained by arranging these tows. Thus, a CF sheet arranged in one direction (UD: unidirectional) along the longitudinal direction of the CF, or a carbon fiber reinforced resin sheet impregnated with a matrix resin, is called a UD material. One form of UD material is Non Crimp Fabric (NCF), in which UD-arranged CF sheets are sewn together with stitching thread.

[0018] The CFRP according to the present invention can be obtained by impregnating the above-mentioned CF sheet with a matrix resin and then molding the resulting carbon fiber reinforced resin sheet, in which the matrix resin is impregnated into the laminated CF sheet and hardened. Alternatively, an intermediate substrate (prepreg) may be prepared by impregnating the CF sheet with a matrix resin, which may then be laminated and molded, or a resin infusion method may be used in which resin is injected into a laminate of unimpregnated CF sheets and then molded. In this CFRP, the UD material is laminated in multiple directions. "Laminated in multiple directions" refers to a state in which multiple UD materials are stacked and arranged with their fiber orientation angles changed. That is, in the CFRP according to the present invention, the CF is oriented in two or more different directions. When considering its use as a structural member of an aircraft, it is preferable to laminate and mold a unidirectional (UD) prepreg in multiple directions. Of course, a laminate in which UD material is laminated in multiple directions may be combined with a substrate other than UD material.

[0019] As described later, the present invention is characterized by having a structure in which a "specific layer" has high Vcf sublayers on both outermost sides and low Vcf sublayers between the high Vcf sublayers, and consists of two inventions, each characterized by the design of the interlayer resin layers, as described later. Note that the outermost sides on both sides are understood as the outermost parts in the thickness direction, given that the layers are layered.

[0020] <Outline of one embodiment of the first invention> The CFRP1000 shown in Figure 1 comprises a plurality of CF1 arranged in one direction and a matrix resin 2 impregnated into the CF sheet.

[0021] Herein, the present invention is not limited to this embodiment. Furthermore, in the present invention, not limited to this embodiment, a region of the CF sheet that includes a region in the thickness direction where the fiber orientation angle of the CF is the same is defined as a layer. Regions within the layer that do not contain fibers, and regions that use fibers other than CF, may exist as "sublayers" as described later.

[0022] The CFRP according to the present invention has multiple layers because CF sheets, in which CF is arranged in one direction, are laminated in multiple directions. Furthermore, when the above layers consist of multiple regions of constant thickness with different Vcf, these regions of constant thickness are designated as sublayers.

[0023] The present invention comprises multiple sublayers and includes at least one layer (specific layer) that satisfies the above conditions (1) to (3). A layer that does not satisfy the conditions of a "specific layer" is sometimes referred to as a normal layer. The above conditions (1) to (3) will be explained below using layer 100 as an example. In CFRP1000, layers 200 and 300, which have different fiber orientation angles from layer 100, are adjacent to the upper and lower sides of layer 100, respectively (hereinafter sometimes referred to as adjacent layers). Interlayer resin layers 20 and 30 exist between layer 100 and layers 200 and 300. The thicknesses of the respective interlayer resin layers are T20 and T30. However, in other embodiments of the present invention, the interlayer resin layers 20 and 30 may not be present. The average value of Vcf of layer 100 is 50% or more from the viewpoint of improving conductivity, as in condition (1). The average value of the Vcf is preferably 60% or more, while the upper limit is preferably 90%, and more preferably 80% in order to suppress the generation of voids.

[0024] Layer 100 contains sublayers with a Vcf ratio of 0.5 or higher to the average Vcf of the entire layer, and these are defined as high Vcf sublayers as described in condition (2). Furthermore, as described in condition (2), high Vcf sublayers are located on the outermost edges of both sides of layer 100, and the average value of the Vcf of each of these sublayers is higher than the average Vcf of the layer. High Vcf sublayers may exist in addition to those on the outermost edges of a particular layer 100, but from the viewpoint of conductivity, it is preferable that the average Vcf of each high Vcf sublayer located on the outermost edges is the first or second highest among the high Vcf sublayers present in that particular layer 100. If high Vcf sublayers exist in addition to those on the outermost edges, it is preferable that the individual Vcf values ​​of these sublayers are also 69% or higher, and it is more preferable that the average Vcf of all high Vcf sublayers combined with those on the outermost edges is 71% or higher, and even more preferable that it is 73% or higher.

[0025] On the other hand, layer 100 contains sublayers positioned between the outermost high Vcf sublayers on both sides of the layer, which have a Vcf ratio of less than 0.5 to the average value of the total Vcf of layer 100. As described in condition (3), these are defined as low Vcf sublayers. The low Vcf sublayer is preferably an insulating layer that does not contain CF. To make the low Vcf sublayer an insulating layer, it is also effective to insert glass fiber fabric or the like as a spacer, as described later.

[0026] In other words, in this invention, a layer that satisfies conditions (1) to (3), such as layer 100, is called a "specific layer." Furthermore, in this invention, in order to improve conductivity, at least one of the thicknesses of the resin portion between the "specific layer" and at least one adjacent layer (interlayer resin layer thicknesses T20, T30 in this embodiment) is 5 μm or less, and more preferably 2 μm or less. It is more preferable that both of these resin thicknesses (T20, T30 in this embodiment) are 5 μm or less, and even more preferable that both are 2 μm or less. The interlayer resin layer thickness may also be 0 μm. As shown in Figure 1, layers 200 and 300 are "specific layers" in this embodiment, just like layer 100, but they may also be ordinary layers.

[0027] To improve the conductivity of CFRP, increasing Vcf is effective. However, if the average Vcf of a certain layer is increased, the impregnation of the matrix resin into the CF sheet becomes insufficient, leading to a problem where voids are more likely to occur in the CFRP. On the other hand, in layer 100, which is a "specific layer," a low Vcf region exists, so it is possible to locally increase only the Vcf near adjacent layers (200, 300) while suppressing an excessively high average Vcf of the layer. If the vicinity of adjacent layers has a high Vcf, the CF of layer 100 and the CF of the adjacent layers will come into contact more easily, and the conductivity between layers can be greatly improved. In order to locally increase the Vcf near adjacent layers without excessively increasing the average Vcf of the layer, the average Vcf of the low Vcf sublayer is preferably 20% or less, and more preferably 10% or less. To further improve conductivity between adjacent layers, the ratio of the thickness of the low Vcf sublayer included in layer 100 (T110 in this embodiment) to the thickness of layer 100 (T100 in this embodiment) is preferably 5% or more, and more preferably 10% or more. Here, the thickness T100 of layer 100 is defined as the distance from the center point in the thickness direction of the lower interlayer resin layer 30 to the center point in the thickness direction of the upper interlayer resin layer 20. When the thickness of the “specific layer” is 350 μm or more, the ratio of the “specific layer” to the thickness direction of the CFRP increases, which is preferable from the viewpoint of the electrical properties of the CFRP. The thickness of the “specific layer” is more preferably 400 μm or more, and even more preferably 450 μm or more. There is no particular upper limit to the thickness of the “specific layer”, but it is generally 1000 μm or less. If the ratio of the thickness of the low Vcf sublayer is too large, the mechanical properties will become non-uniform in place, so it is preferably 30% or less. Furthermore, it is preferable for the low VCF layer to contain a breathable sheet-like substrate, from the viewpoint of stably forming the low VCF layer. A breathable sheet-like substrate is a sheet in which pores are continuous in three dimensions, capable of forming continuous airflow paths. Examples include woven or nonwoven fabrics made of glass fibers or organic fibers.Among these, glass fiber fabrics are preferred from the viewpoint of heat resistance and versatility, while woven or nonwoven fabrics made of polymer fibers are preferred from the viewpoint of improving the toughness of the resulting CFRP. Woven fabrics are preferred from the viewpoint of dimensional stability, while nonwoven fabrics are preferred from the viewpoint of thinness and cost. Of these, glass fiber fabrics are the most preferred because they offer a good balance for use in CFRP.

[0028] Furthermore, in order to further enhance conductivity between adjacent layers, the average Vcf value of the high Vcf sublayer in a "specific layer" is preferably 55% or higher, more preferably 65% ​​or higher. Even more preferably, it is 71% or higher, and most preferably 73% or higher. Also, from the viewpoint of enhancing conductivity between adjacent layers, it is preferable that the individual Vcf values ​​of the high Vcf sublayers at the outermost edges on both sides are 69% or higher. On the other hand, the upper limit of the average value of the Vcf of the high Vcf sublayer is preferably 90%, more preferably 80% or lower.

[0029] <Details of one embodiment of the first invention of this invention> The CFRP of the present invention will be described in more detail with reference to Figure 2. The CFRP shown in Figure 2 is one form of the CFRP of the present invention and includes layer L1, which is a "specific layer," and parts of the normal layers L2 and L3. The fiber orientation angles of L1 and CF are different in L2 and L3. As described above, in the present invention, although the orientation angles of CF in the layers are the same, it is not required that the orientation angles be completely identical, considering that CF may flow due to the effects of molding. In the present invention, it is possible to determine which layer each CF belongs to from the difference in the cross-sectional shape of the CF. Normally, the cross-sectional shape of CF is observed to be elliptical, but a region in which the length of the major axis of the ellipse is approximately the same and is continuous in the thickness direction is judged to be one layer. Also, if it is understood that the orientation angles of CF in a region continuous in the thickness direction are the same at the stage when the prepregs are laminated, it may be considered one layer. As shown in the figure, the rightward direction of the paper is the positive X-axis direction, and the upward direction of the paper is the positive Z-axis direction, and the origin O of the Z-axis is set at the lower end of the cross-sectional photograph.

[0030] In this invention, the boundary between a specific layer L1 and adjacent layers L2 and L3, as well as low Vcf sublayers and high Vcf sublayers, are determined from the Z-direction distribution of Vcf. The Z-direction distribution of Vcf can be determined as follows, and this will be explained using Figure 2 as an example. First, Figure 2 is binarized using image analysis software to distinguish between CF (black) and matrix resin (white) (Figure 3). At this time, the image shown in Figure 2 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. Image analysis software such as ImageJ (developed by Wayne Rasband, National Institutes of Health) can be used. Vcf can be calculated from the area ratio of the black area representing CF. Vcf is calculated using a rectangular region with a length of one pixel in the Z direction (0.2 μm here) and the total length of the X-axis in the image (W1) in the X direction (590 μm here) as the evaluation region. By calculating the Vcf of the evaluation area at intervals of 0.2 μm, which is the length of one pixel in the Z-axis direction from the Z-axis origin, the Z-direction distribution of Vcf can be obtained. The Z-direction distribution of Vcf obtained from Figure 3 is shown in Figure 4.

[0031] Next, in order to extract only the specific layer L1, the Z coordinates of the boundary with the adjacent layer (Z2 and Z3 in Figure 3) are determined. First, the median of Vcf is calculated from the Z-direction distribution of Vcf shown in Figure 4. This value corresponds to A1 in Figure 4 and is used as a representative value of Vcf including the specific layer L1 and layers L2 and L3 included in the cross-sectional photograph. The reason why the average value is not used as the representative value of Vcf here is that if the average value is used, the representative value of Vcf is likely 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 Figure 4) by 0.5 is used as the threshold for defining the interlayer resin layer between adjacent layers. This threshold corresponds to B1 in Figure 4. Near the boundary with the adjacent layer, the portion of Vcf that is less than or equal to the threshold B1 is defined as the interlayer resin layer. In the diagram above Figure 4, only the portion indicated by I1 is applicable, and I1 is considered to be the interlayer resin layer between layers L1 and L3. The thickness of the interlayer resin layer is defined as the length of the Z coordinate of the portion corresponding to the interlayer resin layer. In the lower left diagram of Figure 4, T30 corresponds to the thickness of the interlayer resin layer. The Z coordinate of the boundary with an adjacent layer is defined as the midpoint value of the Z coordinate of the portion corresponding to the interlayer resin layer. In Figure 4, Z3 corresponds to the Z coordinate of the boundary between layers L1 and L3. On the other hand, near the boundary between layers L1 and L2, there is no portion where Vcf is less than or equal to the threshold B1, so the interlayer resin layer is considered not to exist, and its thickness is 0. In this case, the Z coordinate of the boundary with an adjacent layer is defined as the Z coordinate of the point that shows the minimum value of Vcf near the boundary with the adjacent layer. In the lower right diagram of Figure 4, Z2 is the Z coordinate of the boundary between layers L1 and L2, which is the Z coordinate of point J1 that shows the minimum value of Vcf near the boundary between layers L1 and L2. The Z-direction region of a particular layer L1 is the range from Z3 to Z2, which is the Z coordinate of the boundary with the adjacent layer.

[0032] Next, focusing only on a specific layer L1, a new Z' axis parallel to the Z axis is defined with Z3 as the origin O', as shown in Figure 3. Figure 5 shows the Z' direction distribution of Vcf in a specific layer L1. The thickness T100 of a specific layer L1 is defined as the maximum value of the Z' coordinate, obtained by subtracting Z3 from Z2. The average value of Vcf in layer L1 is defined as the average value of the Z' direction distribution of Vcf. This value corresponds to C1 in Figure 5. A value of 0.5 times C1 is used as the threshold for defining a low Vcf sublayer. This threshold corresponds to D1 in Figure 5. Excluding the interlayer resin layers at the upper and lower ends of the layer, the portion where Vcf is less than D1 is defined as a low Vcf sublayer. This corresponds to the K1 portion in Figure 5. The thickness and average value of Vcf of the low Vcf sublayer are defined as the thickness and average value of Vcf in the portion where Vcf is less than D1. Conversely, the portion where Vcf is D1 or higher is defined as a high Vcf sublayer. The average Vcf value of the high Vcf sublayer is defined as the average Vcf value of the portion where Vcf is D1 or higher.

[0033] Layer L1 is determined to be a "specific layer" because its average VCF value across the entire layer is 50% or higher, high VCF sublayers are positioned on both sides of a low VCF sublayer, and the average VCF value of the high VCF sublayers is higher than the average VCF value of the entire layer.

[0034] Considering the mechanical properties of CFRP, it is preferable to reduce the number of voids in the CFRP. L. Liu et al. (Journal of Composite Structures, Vol. 73, pp. 303-309, 2006) reported that when the void ratio of CFRP exceeds 1.0%, the shear strength, bending strength, and tensile strength all decrease significantly. From the viewpoint of mechanical properties, in this invention, the void ratio of CFRP is 1.0% or less, preferably 0.5% or less.

[0035] In this invention, the void ratio of CFRP is calculated from the area ratio occupied by voids in the observation area of ​​the CFRP cross-section. Here, it is important that the observation area is the entire thickness of the CFRP and an area of ​​500 μm or more in the X-axis direction (Figure 23). Figure 23 is one form of CFRP according to the present invention, showing the entire thickness of the CFRP and an area of ​​590 μm in the X-axis direction. In addition to void V1, Figure 23 contains voids in multiple locations. Figure 23 is binarized using image analysis software to distinguish between voids (black) and other areas (white) (Figure 24). In Figure 24, the area ratio occupied by voids is defined as the void ratio of the CFRP. The CFRP in Figure 24 has a void ratio of 1.0% or less, and is therefore a desirable form of CFRP.

[0036] <Effect of suppressing edge glow> If the conductivity between layers is high, current flows in and out between layers more easily. In this case, even when lightning current flows into CFRP, it becomes easier to utilize multiple layers as current paths, thus preventing localized concentration of the lightning current and making it easier to distribute the current. If the current can be distributed across multiple layers, the electrical resistance between the inflow and outflow points of the lightning current decreases, and the potential difference becomes smaller. If the potential difference between the inflow and outflow points of the current becomes smaller, the overall potential difference generated within the CFRP also becomes smaller, and therefore the potential difference between adjacent layers also becomes smaller. By reducing the potential difference between adjacent layers, an edge glow suppression effect can be obtained. To further understand the potential difference between layers, the way current flows in CFRP is explained below.

[0037] As a representative example of aircraft structures, consider a multi-directional laminated CFRP structure with two metal bolts inserted, as shown in Figure 3 of the paper by I. Revel et al. (International Conference on Lightning Protection 2016, conference paper, 2016). A situation where edge glow is likely to occur is when lightning strikes one bolt, the lightning current flows in and flows through the CFRP structure, and the lightning current flows out from the other bolt.

[0038] Because CFRP has strong anisotropy in its conductivity, current tends to flow mainly in the CF direction within each layer. In a layer where 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 a layer where CF does not directly connect two bolts, the current needs to spread along the CF connected to the bolts and then flow orthogonally within the layer. Since the conductivity in the orthogonal direction is generally about 1,000 times lower 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.

[0039] In CFRP containing layers with different fiber orientation angles, current spreads along the fiber optics (CF) connected to the bolts in each layer. The current spreading along the CF can flow in a direction perpendicular to the CF within each layer, but it can also flow into adjacent layers with different fiber orientation angles and utilize the CF of those adjacent layers to flow. Within each layer, the electrical resistance between bolts is smaller if the current flows a short distance to adjacent layers with different fiber orientation angles and then flows a long distance in the direction of the highly conductive fibers in the adjacent layer, rather than flowing a long distance in the perpendicular direction with low conductivity. Since the current path is determined to minimize the electrical resistance between bolts, in CFRP with multiple layers with different fiber orientation angles, the current path becomes one in which current flows back and forth between those layers.

[0040] When current flows between layers, the conductivity between those layers determines the potential difference between them. If the conductivity between layers is high, current can easily flow between adjacent layers even if the potential difference between them is not large. In this case, the electrical resistance between the two voltages becomes small, and the potential difference becomes small.

[0041] Based on the above, in the case of CFRP containing multiple layers, improving the conductivity between adjacent layers can suppress the rise in the potential difference between two voltages even when large currents such as lightning currents flow, thereby reducing the voltage applied to the CFRP, especially the potential difference between adjacent layers. This reduces the risk of edge glow.

[0042] <Effect of improving induction heating temperature> High conductivity between adjacent layers yields desirable effects beyond edge glow suppression. For example, it enhances the effectiveness of induction welding, which is 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 that joins CFRP by melting the thermoplastic resin through induction heating and then applying separate pressure. Induction heating involves passing an alternating current through a coil placed on the outside of the CFRP, generating an induced current within the CFRP, and heating it through Joule heating caused by the induced current. In induction welding, it is desirable to increase the induction heating temperature with a small input energy.

[0043] To increase the induction heating temperature, it is important to improve Joule heating due to induced current, and therefore increasing the amount of induced current generated within the CFRP is effective. X.Xu et al. (Journal of NDT and E International, Vol. 94, pp. 79-91, 2018) numerically demonstrated that increasing the conductivity between layers with different fiber orientation angles increases the amount of induced current generated within the CFRP. In other words, the CFRP of the present invention generates a large amount of induced current, making it easier to raise the induction heating temperature, and thus achieving desirable effects in induction welding.

[0044] The amount of induced current generated within CFRP can be compared using eddy current testing. Eddy current testing is generally a test that detects cracks and other defects within CFRP by evaluating the induced current generated within it. In eddy current testing, a coil is placed near the CFRP, and the magnetic field generated by the induced current is evaluated from the change in the coil's impedance. According to the literature by K. Mizukami et al. (Journal of Polymer Testing, Vol. 69, pp. 320-324, 2018), the magnetic field generated by the induced current is evaluated from the change in the series resistance component of the coil. It has been shown that a larger change in the magnetic field, i.e., a larger amount of induced current, corresponds to a larger series resistance component of the coil.

[0045] <Another example of the first embodiment of the present invention> In the present invention, it is preferable that the layer satisfying the condition of being a "specific layer" is located within the second layer when counting the number of layers from the top or bottom surface of the CFRP. In this case, for example, in induction welding, the induced current can be concentrated and increased near the CFRP surface that becomes the welding surface, making it possible to heat efficiently. In the CFRP 1001 shown in Figure 6, which takes such an embodiment, the specific layer 101 is located as the second layer when counting the number of layers from the top surface of the CFRP 1001, and when the top surface is used as the welding surface, it is possible to efficiently induce heating the area near the top surface. Layers other than the specific layer 101 may satisfy the condition of being a "specific layer," or they may be ordinary layers.

[0046] Furthermore, a configuration in which two or more "specific layers" are stacked consecutively is preferable. The conductivity of the adjacent parts between the "specific layers" is greatly improved, further enhancing the effect of suppressing edge glow or improving the induction heating temperature. From the perspective of suppressing edge glow and improving the induction heating temperature alone, it is also preferable for all layers to be "specific layers".

[0047] Another embodiment of the CFRP of the present invention is shown in Figure 7. In layer 102, where the fiber direction is the same, low Vcf sublayers 112 and 122 are sandwiched between high Vcf sublayers 152, 162, and 172. Thus, in the CFRP of the present invention, even if there are multiple low Vcf sublayers, it is sufficient that high Vcf sublayers are placed on the outermost edges of both sides of the layer. In this case, it is preferable that the average Vcf value of the high Vcf sublayers 152 and 172 located on the outermost edges of both sides of layer 102 is higher than the average Vcf value of the high Vcf sublayer 162 located in the thickness direction. Note that in all embodiments, including this embodiment, when multiple low Vcf sublayers exist within a "specific layer", the characteristics of the low Vcf sublayer are defined as if all low Vcf sublayers within the layer were linked together. That is, as explained in Figure 7, 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. Furthermore, the average VCF value of the low VCF sublayer is the average VCF value of the concatenated low VCF sublayer 112 and low VCF sublayer 122.

[0048] <Examples of prior art forms> Figure 8 is a cross-sectional view showing a conventional (non-interlayer reinforced) CFRP, where the Vcf is almost uniform regardless of location within layers with the same fiber orientation angle. Furthermore, it does not have a structure in which high Vcf sublayers are placed on the outermost layers on both sides of the layer, with low Vcf sublayers in between. If the total thickness of the layers and the average value of the Vcf of the layers are the same, the present invention shown in Figures 1 and 7 will have higher Vcf near layers with different fiber orientation angles than the conventional technology shown in Figure 8, and can improve the conductivity between layers with different fiber orientation angles.

[0049] Figure 9 is a cross-sectional view showing a different form of conventional interlayer-reinforced CFRP than that shown in Figure 8. In the CFRP shown in Figure 9, in layers with the same fiber orientation angle, high Vcf sublayers are arranged on the outermost layers on both sides of the layer, and a low Vcf sublayer is not present in between. Instead, thick interlayer resin layers 24 and 34 exist between the layers. These interlayer resin layers 24 and 34 are mainly resin-rich layers for improving toughness and often contain thermoplastic resin particles, fibers, nonwoven fabrics, etc. If the layer thickness and the average value of Vcf are the same, the Vcf of the layers in conventional interlayer-reinforced CFRP and the Vcf of the high Vcf sublayer of the present invention may be approximately the same. However, in interlayer-reinforced CFRP, a certain thickness or more is often required for the interlayer resin layers 24 and 34, and in that case, the conductivity between layers is higher in the present invention.

[0050] Figure 10 shows a cross-sectional photograph of a conventional interlayer-reinforced CFRP, which will be explained in detail. Figure 10 shows layer L4 and parts of layers L5 and L6 of a CFRP consisting of layers L4, L5, and L6. To clarify the contrast between the resin and CF parts in Figure 10, the image is binarized to obtain Figure 11. Using Figure 11, the Z-direction distribution of Vcf is calculated in the same way as described above, resulting in the graph shown in Figure 12. Next, the boundaries between layers are determined in the same way as described above. In Figure 12, the median of Vcf is A1', which is taken as the representative value of Vcf for the regions of layers L4, L5, and L6 included in the cross-sectional photograph. Multiplying A1' by 0.5 gives B1' as a threshold for defining the interlayer resin layer. In Figure 12, there are parts I1' and J1' near the interlayer boundaries where the Vcf is lower than B1'. I1' and J1' are defined as interlayer resin layers, and their respective interlayer resin layer thicknesses T34 and T24 are defined by the Z-coordinate lengths of the parts corresponding to I1' and J1'. The midpoint values ​​of the Z-coordinates of the parts corresponding to I1' and J1' are the Z-coordinates of the boundaries between layers L4 and L6, or L4 and L5, respectively, which are Z6 and Z5. Next, focusing only on layer L4, and setting a new Z' axis as shown in Figure 11, the Z'-axis distribution of Vcf in layer L4 is obtained as shown in Figure 13. The thickness T104 of layer L4 is the value obtained by subtracting Z6 from Z5, and is defined as the maximum value of the Z' coordinate. The average value of Vcf in layer L4 is defined by the average value of the Z'-directional distribution of Vcf, which corresponds to C1' in Figure 13. A value 0.5 times C1' is a threshold for defining a low Vcf sublayer, which corresponds to D1'. Excluding the interlayer resin layers at the upper and lower ends of the layer, there are no portions where the Vcf is less than D1', so it is assumed that there are no low-Vcf sublayers. Layer L4 has an average Vcf of 50% or more overall, but it does not have a structure in which high-Vcf sublayers are arranged on the outermost layers on both sides of the layer, flanked by a low-Vcf sublayer, so it is not a "specific layer" and does not fall under the CFRP of the present invention.

[0051] Figure 14 is a cross-sectional view showing a different form of conventional interlayer-reinforced CFRP than that shown in Figure 9. In the CFRP shown in Figure 14, a low Vcf sublayer 115 is sandwiched between high Vcf sublayers 155 and 165 in layer 105, where the fiber orientation angles are the same. However, in conventional interlayer-reinforced CFRP, the interlayer resin layer thicknesses T25 and T35 are thicker, greater than 5 μm, between layers with different fiber orientation angles, thus clearly distinguishing it from the CFRP of the first invention. Furthermore, as can be understood from the fact that the interlayer resin layer does not contain conductive particles, the embodiment in Figure 14 is also clearly distinguishable from the CFRP of the second invention, which will be described later.

[0052] <Summary of one embodiment of the second invention of the present invention> The second invention of this invention replaces the statement in the first invention that "the thickness of the resin portion between a specific layer and at least one adjacent layer is 5 μm or less" with "a resin portion exists between a specific layer and an adjacent layer, and this resin portion contains conductive particles." The first invention focuses on thinning the interlayer resin layer and obtaining interlayer conductivity by CF, but the second invention improves interlayer conductivity by placing conductive particles in the interlayer resin layer. Generally, it is often formed as a resin-rich layer to improve toughness, and often contains thermoplastic resin particles, fibers, nonwoven fabrics, etc. inside. In this case, the interlayer resin layer that acts as an insulator tends to be thicker, so conductive particles are placed here.

[0053] <Conductive particles> The conductive particles used in this invention can be any particles that behave as good electrically conductive particles, and are not limited to those consisting solely of conductors. Preferably, they have a volume resistivity of 10 to 10. -9 It is Ωcm, and more preferably 10 -1 ~10 -9The particles have a density of Ωcm. Conductive particles can include, for example, metal particles, metal oxide particles, inorganic particles or organic polymer particles with metal coatings, and carbon particles. Among these, carbon particles are preferred because they do not pose a corrosion problem even when used in aircraft. Furthermore, using carbon particles with a (002) interplanar spacing of 3.4 to 3.7 angstroms is preferable because it is easier to improve conductivity. 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 described as nearly spherical carbon particles in Carbon, No. 168, 157-163 (1995). It is also described that these spherical carbon particles are very hard, are difficult to deform even when subjected to compression, and return to their original particle shape when the compression is removed.

[0054] The conductive particles used in this invention can be placed within layers or in interlayer resin layers with different fiber orientation angles. The size of the conductive particles is preferably larger than the thickness of the interlayer resin layer, specifically, an average particle size of 20 μm or more is preferred, and an average particle size of 30 μm or more is more preferred. If the average particle size of the conductive particles is too large, it will disrupt the structure of the resin layer between the CF sheets, so an average particle size of 60 μm or less is preferred. The average particle size of the conductive particles can be measured using the light scattering method, for example, with a Partica LA-950V2 from Horiba, Ltd., a Microtrac MT3300II from Microtrac, or a Shimadzu SALD series from Shimadzu Corporation.

[0055] <Matrix resin> The matrix resin used in the CFRP of the present invention preferably includes a thermosetting resin, a thermoplastic resin, and a curing agent, but may also consist only of a thermosetting resin and a curing agent, or only a thermoplastic resin. Epoxy resins are commonly used as thermosetting resins, but epoxy resins using amines, phenols, or compounds having carbon-carbon double bonds as precursors are particularly preferred. Specifically, examples of epoxy resins using amines as precursors include tetraglycidyldiaminodiphenylmethane, triglycidyl-p-aminophenol, triglycidyl-m-aminophenol, and various isomers of triglycidylaminocresol; examples of epoxy resins using phenols as precursors include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenol novolac type epoxy resin, and cresol novolac type epoxy resin; and examples of epoxy resins using compounds having carbon-carbon double bonds as precursors include alicyclic epoxy resins, but are not limited to these. Reducing the crosslinking density is effective in improving the tensile strength of CFRP, but this reduction leads to a decrease in heat resistance and elastic modulus. To address this issue, it is preferable to use dicyclopentadiene-type epoxy resins or pendant-type epoxy resins such as glycidylaniline-type epoxy resins, which have a rigid skeleton. Brominated epoxy resins, obtained by brominating these resins, can also be used. Epoxy resins that use aromatic amines as precursors, such as tetraglycidyldiaminodiphenylmethane, are suitable for the present invention because they have good heat resistance and good adhesion to CF.

[0056] Thermosetting resins are preferably used in combination with curing agents. For example, in the case of epoxy resins, any compound having an active group that can react with epoxy groups can be used as the curing agent. Preferably, compounds having amino groups, acid anhydride groups, or azide groups are suitable. Specifically, dicyandiamide, various isomers of diaminodiphenylsulfone, and aminobenzoic acid esters are suitable. To explain in more detail, dicyandiamide is preferred because it has excellent prepreg storage properties. Various isomers of diaminodiphenylsulfone are most suitable for the present invention because they give a cured product with good heat resistance. Among aminobenzoic acid esters, trimethylene glycol di-p-aminobenzoate and neopentyl glycol di-p-aminobenzoate are preferred. Although they have inferior heat resistance compared to diaminodiphenylsulfone, they have excellent tensile strength, so they are selected and used according to the application. Of course, it is also possible to use expensive catalysts as needed. Furthermore, in order to improve the pot life of the coating solution, it is also possible to use a complexing agent that can form a complex with the curing agent or curing catalyst in combination.

[0057] Furthermore, in the present invention, it is also preferable to use a mixture of a thermosetting resin and a thermoplastic resin as the matrix resin. A mixture of a thermosetting resin and a thermoplastic resin yields better results than when a thermosetting resin is used alone. This is because thermosetting resins generally have the disadvantage of being brittle but can be molded at low pressure by autoclaving, while thermoplastic resins generally have the advantage of being tough but are difficult to mold at low pressure by autoclaving. By mixing these, it is possible to balance the physical properties and moldability. When using a mixture, it is preferable to include more than 50% by mass of the thermosetting resin from the viewpoint of the mechanical properties of the CFRP obtained by curing the prepreg.

[0058] As thermoplastic resins, polymers having bonds selected from carbon-carbon bonds, amide bonds, imide bonds, ester bonds, ether bonds, carbonate bonds, urethane bonds, urea bonds, thioether bonds, sulfone bonds, imidazole bonds, and carbonyl bonds in the main chain can be used. Specifically, examples include 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), and polyamideimide (PAI). In fields requiring heat resistance, such as aircraft applications, PPS, PES, PI, PEI, PSU, PEEK, PEKK, and PAEK are preferred. On the other hand, for industrial and automotive applications, polyolefins such as polypropylene (PP), PA, polyester, and PPS are preferred to improve molding efficiency. These can be polymers, or oligomers or monomers may be used for low viscosity and low-temperature coating. Of course, these may be copolymerized depending on the purpose, or various types may be mixed and used as polymer blends or alloys.

[0059] Furthermore, when a thermoplastic resin is primarily used as the matrix resin, the term "curing" in this invention refers to the process of heat treatment after impregnation with the thermoplastic resin to create a prepreg. For example, heat treatment during molding falls under this category.

[0060] <Polymer particles> In the present invention, it is preferable to use polymer particles from the viewpoint of achieving both the formation of a low Vcf sublayer and improved toughness. As polymer particles, appropriate ones can be used by referring to the description in the WO2009 / 142231 pamphlet, etc. More specifically, particles made of polyamide resin or polyimide resin can be preferably used, with polyamide being the most preferred. As polyamides, nylon 12, nylon 11, nylon 6, nylon 66, nylon 6 / 12 copolymer, and nylon (semi-IPN nylon) semi-IPN (polymer interpenetrating network structure) with an epoxy compound as described in Example 1 of Japanese Patent Publication No. 01-104624 can be suitably used. The shape of these polymer particles is preferably spherical, especially perfectly spherical. More specifically, the sphericity of the polymer particles is preferably 85% or more, and more preferably 90% or more. Here, sphericity (unit: %) is determined by randomly selecting 30 particles from a cross-sectional photograph of the FRP and determining their short axis and long axis (unit: the same, typically μm) according to the following formula.

[0061]

number

[0062] Note that S represents sphericity, a represents the major axis, b represents the minor axis, and n represents the number of measurements (30).

[0063] Commercially available spherical polymer particles include, among others, polyamide-based products such as SP-500 and SP-10 (manufactured by Toray Industries, Inc.), polymethyl methacrylate-based products such as the MBX series including MBX-12 and the SSX series including SSX-115 (manufactured by Sekisui Chemical Co., Ltd.), polystyrene-based products such as the SBX series including SBX-12 (manufactured by Sekisui Chemical Co., Ltd.), and copolymers thereof such as MSX and SMX (manufactured by Sekisui Chemical Co., Ltd.), polyurethane-based products such as the Dymic Beads CM series, cellulose acetate-based products such as BELLOCEA (manufactured by Daicel Corporation), and phenolic resin-based products such as Marilyn (manufactured by Gun-ei Chemical Co., Ltd.). Furthermore, examples of spherical particles made of polyamides and their copolymers include the polyamide-based particles described in Example 1 of Japanese Patent Publication No. 1-104624 and the polyamide-based particles described in Brochure WO2018 / 207728. Furthermore, examples of polyethersulfone-based spherical particles include those described in Japanese Patent Publication No. 2017-197665. Among these, the polyamide-based particles described in Example 1 of Japanese Patent Publication No. 1-104624 are even more preferable due to their excellent resistance to humidity and heat, chemical resistance, etc. The particle size of the polymer particles added during the preparation of the intermediate substrate is preferably 5 μm to 45 μm in mode diameter determined by light scattering. A mode diameter of 10 to 20 μm is more preferable. Particle size measurement can be performed using light scattering, for example, with a Partica LA-950V2 from Horiba, Ltd., a Microtrac MT3300II, or a Shimadzu SALD series.

[0064] Next, the method for obtaining the CFRP of the present invention will be explained using a UD prepreg, which uses a matrix resin mainly composed of a thermosetting resin, as an example.

[0065] <Method for fabricating a prepreg laminate according to the present invention> There are no particular limitations on the method for obtaining the prepreg laminate as a precursor for the CFRP of the present invention, but for example, the following method can be used. First, a primary resin composition (hereinafter also referred to as "primary resin") is prepared by kneading using a combination of epoxy resin, aromatic amine-type curing agent, and thermoplastic resin, and then a primary resin film is made using a coater. After that, carbon fiber bundles are aligned to form a UD sheet, and the primary resin is impregnated to obtain a primary prepreg. At this time, it is preferable to increase the resin content of the primary prepreg and increase the degree of resin impregnation into the CF bundle (UD sheet) in order to produce a CFRP with few voids.

[0066] Next, in this example, a secondary resin composition (hereinafter also referred to as "secondary resin") is prepared by adding polymer particles to epoxy resin, aromatic amine-type curing agent, and thermoplastic resin, and a secondary resin film is produced using a coater.

[0067] Then, the secondary resin is applied to only one side of the primary prepreg, and after preheating, it is laminated by applying pressure with a nip roll. At this time, it is desirable to preheat sufficiently and ensure sufficient fluidity of the secondary resin. The prepreg obtained in this way, in which the secondary resin is applied to only one side, will be called a 1.5-grade prepreg. In the prepreg used in the present invention, by setting the resin content to 30-40 mass%, void generation during the molding process can be suppressed and the mechanical properties of the CFRP, especially toughness, can be further improved. The resin content of the prepreg is more preferably 32-36 mass%. Figure 15 is a cross-sectional view showing one form of a 1.5-grade prepreg. In the 1.5-grade prepreg 2000, the secondary resin 600 is applied to only one side of the primary prepreg 700.

[0068] Next, a prepreg laminate is fabricated by laminating 1.5th-order prepregs. During lamination, two 1.5th-order prepregs are considered as one set, and in each set, the fiber orientation angles of the 1.5th-order prepregs are set to the same direction, and the lamination is carried out so that the surfaces on which the secondary resin is applied are in contact with each other. In this way, the fiber orientation angle is unidirectional in each set, and a resin-rich, low-Vcf sublayer made of secondary resin is placed in the middle of the thickness direction of each set. By laminating sets of two 1.5th-order prepregs in multiple directions, a prepreg laminate for obtaining the CFRP of the present invention is obtained. Figure 16 is a cross-sectional view of the prepreg laminate obtained by the above method. Here, 1.5th-order prepregs 2001 and 2002 are one set (i.e., since the fibers are oriented in the same direction, 2001 and 2002 form one layer. The meaning of "set" is the same in this paragraph and below), and 1.5th-order prepregs 2003 and 2004 are another set.

[0069] In the case of the second invention, conductive particles are added to the secondary resin. In this example, a tertiary resin composition (hereinafter also referred to as "tertiary resin") is prepared by adding polymer particles to epoxy resin, aromatic amine-type curing agent, and thermoplastic resin, and a film made of the tertiary resin (tertiary resin film) is produced using a coater. Next, a prepreg laminate is produced by laminating the 1.5th prepreg and the tertiary resin film. During lamination, two 1.5th prepregs and one tertiary resin film are considered as one set, and in each set, the fiber orientation angle of the 1.5th prepregs is set to the same direction, and they are laminated so that the surfaces on which the secondary resin is not applied face each other, and the tertiary resin is sandwiched between them. In this way, the fiber orientation angle is unidirectional in each set, and a resin-rich, low-Vcf sublayer made of tertiary resin is placed in the middle of the thickness direction of each set. By laminating sets of two 1.5th-order prepregs and tertiary resin in multiple directions, a prepreg laminate for obtaining the CFRP of the present invention can be obtained. Figure 22 is a cross-sectional view of the prepreg laminate obtained by the above method. Here, 1.5th-order prepregs 2001 and 2002 and tertiary resin 611 constitute one set, and 1.5th-order prepregs 2003 and 2004 and tertiary resin 612 constitute another set.

[0070] Furthermore, as another method for producing the prepreg laminate according to the present invention, a primary prepreg can be used in combination with a sheet made of a breathable sheet-like substrate and resin. As mentioned above, a variety of materials can be used as the breathable sheet substrate, but an example using a glass fiber woven prepreg is described below. When laminating the prepregs, two primary prepregs and one glass fiber woven prepreg are considered as one set. In each set, the fiber orientation angles of the primary prepregs are set to the same direction, and the glass fiber woven prepreg is sandwiched between the two primary prepregs. In this way, the fiber orientation angle of the CF in each set is unidirectional, and a resin-rich low VCF sublayer made of glass fiber woven prepreg is placed in the middle of the thickness direction of each set. By laminating these sets in multiple directions, the prepreg laminate according to the present invention can be obtained. Figure 17 is a cross-sectional view showing one form of the prepreg laminate according to the present invention. Here, primary prepregs 705, 706 and glass fiber prepreg 605 constitute one set, while primary prepregs 707, 708 and glass fiber prepreg 607 constitute another set. Note that a resin film can be used instead of the sheet consisting of a breathable sheet-like substrate and resin.

[0071] Furthermore, a prepreg laminate can also be fabricated by laminating a primary prepreg with a breathable sheet-like substrate that is not impregnated with resin. By using a breathable sheet-like substrate, the matrix resin flows into it during heat molding, making it easier to increase the VCF in areas that become high VCF sublayers. During lamination, two primary prepregs and a breathable sheet-like substrate are considered as one set, and in each set, the fiber orientation angle of the primary prepregs is set to the same direction, and the breathable sheet-like substrate is sandwiched between the two primary prepregs. In this way, in each set, the fiber orientation angle is unidirectional, forming a single layer, and a low VCF sublayer made of the breathable sheet-like substrate is placed in the middle of the thickness direction of each layer. Then, the carbon fiber composite material obtained by curing forms the layer described above. The layer fabricated in this way can become the "specific layer" described above after curing. This makes it possible to obtain a CFRP as shown in Figure 17.

[0072] <Method for manufacturing CFRP according to the present invention> The prepreg laminate produced in this manner can be molded by a so-called heat-pressure molding method, in which the laminate is shaped by pressurizing and heating, and the resin is cured. In the case of a laminate consisting of the aforementioned specific laminate set, the resin composition contained in the primary prepreg is impregnated into the breathable sheet-like substrate during pressurizing and heating, and then molded. Whether the main component of the matrix resin is a thermosetting resin or a thermoplastic resin, the heat-pressure molding method can be appropriately selected from press molding, autoclave molding, vacuum pressure molding, or backing molding, etc.

[0073] When molding CFRP using epoxy resin, the temperature is typically in the range of 130°C to 220°C.

[0074] Autoclave molding is preferable when the main component of the matrix resin is a thermosetting resin, as it makes it easier to obtain molded products with fewer voids. The pressure used for molding in autoclave molding varies depending on the thickness of the prepreg and the volume content of CF, but it is usually between 0.1 MPa and 1.0 MPa. This makes it possible to obtain high-quality CFRP without defects such as voids.

[0075] The CFRP of the present invention can be suitably used in aircraft structures. Examples of 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, and hat-shaped structures. By combining these structures, aircraft components are constructed. For details, see, for example, "Structural Design of Aircraft," 5th edition, Torikai and Kuze, Japan Aeronautical Technology Association (2003). Such structures can be obtained by forming prepregs, for example, as described in paragraph

[0084] of International Publication No. 2017 / 110991. [Examples]

[0076] 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. Unless otherwise noted, the unit "parts" in composition ratios refers to parts by mass. Furthermore, unless otherwise noted, the measurements of various properties (physical properties) were performed under conditions of 23°C and 50% relative humidity.

[0077] <Raw materials used in the examples and comparative examples> (1) Carbon fiber For thermosetting CFRP, we used carbon fibers with 24,000 filaments, a tensile strength of 5.8 GPa, and a tensile modulus of 280 GPa.

[0078] For thermoplastic CFRP, we used carbon fibers with 12,000 filaments, a tensile strength of 4.5 GPa, and a tensile modulus of 230 GPa.

[0079] (2) Epoxy resin • "SumiEpoxy®" ELM434 (Tetraglycidyldiaminodiphenylmethane, manufactured by Sumitomo Chemical Co., Ltd.) • “EPICLON®” 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.).

[0080] (3) Hardener • "Seika Cure-S (registered trademark)" (4,4'-DDS, manufactured by Seika Co., Ltd.).

[0081] (4)Thermoplastic resin • "Sumika Excel (registered trademark)" 5003P (PES, manufactured by Sumitomo Chemical Co., Ltd.) • “Toray Cetex®” TC1000 (PEI, manufactured by Toray Advanced Composites).

[0082] (5) Polymer particles • Six perfectly spherical polyamide particles (mode system 15 μm, sphericity 96%, manufacturing method described below) Based on International Publication No. 2018 / 207728, 200g of ε-caprolactam (manufactured by Toray Industries, Inc.), 800g of polyethylene glycol (Wako Pure Chemical Industries, Ltd., Grade 1 polyethylene glycol 20,000, weight-average molecular weight 18,600) as the second polymer component, and 1,000g of water were added to a 3L autoclave equipped with a helical ribbon-type stirring blade. After forming a homogeneous solution, the autoclave was sealed and purged with nitrogen. Subsequently, the stirring speed was set to 100 rpm and the temperature was raised to 240°C. At this time, the system pressure was 10 kg / cm². 2 After reaching a certain pressure, the pressure becomes 10 kg / cm². 2 The pressure of the water vapor was controlled by slightly releasing it to maintain the desired temperature. After the temperature reached 240°C, 0.2 kg / cm³ was released. 2 The pressure was released at a rate of 1 minute. Then, the temperature was maintained for 1 hour while flowing nitrogen to complete polymerization, and the slurry was discharged into a 2,000 g water bath. After dissolving the dissolved material, the slurry was filtered, and 2,000 g of water was added to the filtrate and washed at 80°C. After removing the aggregates that had passed through a 200 μm sieve, the slurry liquid was filtered again to isolate the filtrate, and the resulting filtrate was dried at 80°C for 12 hours to prepare 140 g of polyamide 6 powder. The melting point of the obtained powder was 218°C, the same as polyamide 6, and the crystallization temperature was 170°C. The particle size was measured using a Microtrac MT3300II (light source 780 nm - 3 mW, wet cell (medium: water)).

[0083] (6) Conductive particles (carbon particles) • "Nikabeads (registered trademark)" ICB (average particle size (number basis): 27 μm, manufactured by Nippon Carbon Co., Ltd.).

[0084] <Various Evaluation Methods> (1) Preparation of epoxy resin composition Using the compositions shown in Table 1, epoxy resin and thermoplastic resin were kneaded together, the temperature was raised to over 150°C, and the mixture was stirred for 1 hour to dissolve the thermoplastic resin and obtain a transparent, viscous liquid. After the liquid was cooled while being kneaded, a curing agent was added and the mixture was kneaded further to obtain Resin-1 as a primary resin composition.

[0085] Also, with the composition shown in Table 1, an epoxy resin and a thermoplastic resin were kneaded, heated to 150°C or higher, and stirred for 1 hour as it was to dissolve the thermoplastic resin to obtain a transparent viscous liquid. After cooling this liquid while kneading, a curing agent, polymer particles, conductive particles, etc. were added and kneaded to obtain Resin-A to Resin-F, Resin-A2, and Resin-B2 as secondary resin compositions (hereinafter, they may be simply referred to as secondary resin A to secondary resin F, secondary resin A2, and secondary resin B2, respectively). Also, with the composition shown in Table 1, an epoxy resin and a thermoplastic resin were kneaded, heated to 150°C or higher, and stirred for 1 hour as it was to dissolve the thermoplastic resin to obtain a transparent viscous liquid. After cooling this liquid while kneading, a curing agent, polymer particles, etc. were added and kneaded to obtain Resin-3 as a tertiary resin composition.

[0086] The composition ratios of the resin compositions of each example and comparative example are shown in Table 1.

[0087] (2) Preparation of CF prepreg The following three types of CF prepregs were prepared.

[0088] A. Primary prepreg It was prepared using a one-stage impregnation method. On a release paper coated with silicone, the primary resin composition (Resin-1) prepared in (1) was uniformly coated using a coater to obtain a primary resin film. Carbon fibers uniformly aligned in one direction were sandwiched between two primary resin films, and heated and pressed using a press roll to obtain a primary prepreg in which the primary resin was sufficiently impregnated into the carbon fibers aligned in one direction. Unless otherwise specified, the basis weight of the carbon fibers of the primary prepreg is 268 g / m 2 , and the resin content is 20% by mass.

[0089] B. 1.5 - stage prepreg It was prepared using a two-stage impregnation method. First, according to (2)A, a primary prepreg was obtained (unless otherwise specified, the basis weight of the carbon fibers is 268 g / m 2The resin content was 20% by mass. Next, the primary or secondary resin composition prepared in (1) was uniformly applied to the silicone-coated release paper using a coater, corresponding to each example or comparative example, to form a secondary resin film. Next, the release paper was peeled off one side of the primary prepreg. One secondary resin film was attached to the surface of the primary prepreg on the side from which the release paper had been peeled off, and it was heated and pressurized using a press roll to obtain a 1.5-grade prepreg in which the secondary resin composition was applied to one side of the primary prepreg surface. Unless otherwise specified, the basis weight of the carbon fibers in the 1.5-grade prepreg was 268 g / m². 2 The resin content is 34% by mass.

[0090] C. Secondary prepreg It was prepared using a two-stage impregnation method. First, a primary prepreg was obtained according to (2)A (unless otherwise specified, the basis weight of the carbon fiber is 268 g / m²). 2 The resin content was 20% by mass. Next, the primary or secondary resin composition prepared in (1) was uniformly applied to the silicone-coated release paper using a coater, corresponding to each example or comparative example, to form a secondary resin film. Next, the release paper was peeled off both sides of the primary prepreg. Then, the primary prepreg was sandwiched between the secondary resin films and heated and pressed using a press roll to obtain a secondary prepreg in which the secondary resin composition was impregnated from both surfaces of the primary prepreg. The basis weight of the carbon fibers in the secondary prepreg was 268 g / m². 2 The resin content is 34% by mass.

[0091] (3) Preparation of glass fiber fabric prepregs The material was prepared using a one-stage impregnation method. The primary resin composition (Resin-1) prepared in (1) was uniformly applied to a silicone-coated release paper using a coater to form a primary resin film. A glass fiber woven sheet was prepared, with a glass fiber diameter of approximately 6 μm and a four-ply satin weave. The glass fiber woven sheet was then sandwiched between two primary resin films and heated and pressurized using a press roll to obtain a primary prepreg in which the primary resin composition was sufficiently impregnated into the glass fiber woven sheet (glass fiber woven fabric basis weight 104 g / m²). 2, resin content 39% by mass).

[0092] (4) Molding of CFRP Several different types of CFRP were fabricated, as described below. Unless otherwise specified, each CFRP consists of eight sets of fabricated layers [0 / 90]. 2S The layers were laminated in this configuration. Furthermore, the resin content of each CFRP layer was within the range of (resin content of the prepreg used - 0% by mass) to (resin content of the prepreg used - 1.5% by mass).

[0093] A. CFRP-A (corresponding to the layered structure shown in Figure 1) The 1.5th prepreg, prepared according to (2)B using the resin composition described in the examples below, was cut to 100 mm x 100 mm. Two cut 1.5th prepregs were considered as one set, and in each set, the fiber orientation angles of the prepregs were made the same, and the surfaces on which the secondary resin was applied were laminated together so that they were in contact (for convenience, this is referred to as "Layer A Precursor").

[0094] Each set has a fiber weight of 536g / m². 2 The resin content was 34% by mass. A total of 8 sets were laminated to create a prepreg orthogonal laminate. The prepreg orthogonal laminate was molded in an autoclave at 180°C for 2 hours at a pressure of 0.6 MPa and a heating rate of 1.5°C / min to produce CFRP-A. In CFRP-A, all layers are "specific layers".

[0095] B. CFRP-B (corresponding to the layered structure shown in Figure 6) As shown in Table 2, 1.5-order prepregs prepared according to (2)B using the primary and secondary resin compositions were cut to 100 mm x 100 mm. Two cut 1.5-order prepregs were considered as one set, and the fiber orientation angles of the prepregs were made the same so as the Layer A precursor, and they were laminated so that the surfaces on which the secondary resin was applied were in contact with each other. One such set was prepared.

[0096] Next, a secondary prepreg was prepared according to (2)C and cut to 100mm x 100mm. Two cut secondary prepregs were considered as one set, and in each set, the secondary prepregs were laminated so that the fiber orientation angles were in the same direction (for convenience, this is called the "Layer B Precursor"). Seven of these sets were prepared.

[0097] The fiber weight and resin content of each set were the same as those of CFRP-A. The above eight sets were combined, and the 1.5th-order prepreg set was laminated as the second layer from the top to create a prepreg orthogonal laminate. CFRP-B was produced by molding the prepreg orthogonal laminate under the same conditions as A. In CFRP-B, only the second layer from the top is a "specific layer".

[0098] C.CFRP-C (similar to the layered structure shown in Figure 6) The 1.5th and 2nd grade prepregs used in CFRP-B were prepared and cut to 100mm x 100mm. Two cut 1.5th grade prepregs were considered as one set and laminated in the same configuration as the Layer A precursor. One such set was prepared.

[0099] Next, two cut secondary prepreg sheets were considered as one set, and each set was laminated with the same configuration as the layer B precursor. Seven of these sets were prepared.

[0100] The fiber weight and resin content of each set were the same as those of CFRP-A. Combining the above eight sets, the 1.5th prepreg set was laminated as the fourth layer from the top to create a prepreg orthogonal laminate. The prepreg orthogonal laminate was molded under the same conditions as A to create CFRP-C. In CFRP-C, only the fourth layer from the top is a "specific layer".

[0101] D.CFRP-D (corresponding to the layered structure shown in Figure 1) The primary prepregs and glass fiber woven prepregs prepared according to 2(A) and 3 respectively were cut to 100mm x 100mm. Two cut primary prepregs and one glass fiber woven prepreg were considered as one set. In each set, the fiber orientation angles of the two primary prepregs were set to the same direction, and one glass fiber woven prepreg was sandwiched between the two primary prepregs and laminated. Eight of these sets were prepared.

[0102] Each set contains carbon fiber with a basis weight of 536g / m². 2 Considering the glass fibers as components of the matrix resin, the resin content was 36% by mass. A total of eight sets of each prepreg were laminated to create a prepreg orthogonal laminate. The prepreg orthogonal laminate was molded under the same conditions as A to produce CFRP-D. In CFRP-D, all layers are "specific layers".

[0103] E.CFRP-E (corresponding to the layered structure shown in Figure 9) Using the resin composition described in the comparative example below, the 1.5th prepreg prepared according to (2)B was cut to 100 mm x 100 mm. Two cut 1.5th prepregs were considered as one set, and each set was laminated with the fiber orientation angles of the 1.5th prepregs in the same direction, and the surfaces of the prepregs on the sides without secondary resin were in contact with each other. The resin-rich portion consisting of secondary resin was placed on both surfaces of each set, forming a thick interlayer resin layer after molding.

[0104] The fiber weight and resin content of each set were the same as those of CFRP-A. A total of eight sets of 1.5th-order prepregs were laminated to create a prepreg orthogonal laminate. The prepreg orthogonal laminate was molded under the same conditions as A to produce CFRP-E. CFRP-E does not contain a low-Vcf sublayer and therefore is not the CFRP of the present invention.

[0105] F.CFRP-F (corresponding to the layered structure shown in Figure 8) (2) A secondary prepreg was prepared by impregnating both surfaces of the primary prepreg prepared by the method described in A with Resin-1 (a resin composition having the same composition as the primary resin composition shown in Table 1). This secondary prepreg was cut to 100 mm x 100 mm. Two cut secondary prepregs were considered as one set, and each set was laminated so that it had the same configuration as the secondary prepreg of B, with the fiber orientation angles of the secondary prepregs being in the same direction. Before molding, a resin-rich portion made of primary resin exists in the center of the thickness direction of each set, but since no polymer particles or glass fiber fabrics that act as spacers are included, the CF flows during molding, and the resin-rich portion disappears after molding.

[0106] The fiber weight and resin content of each set were the same as those of CFRP-A. A total of eight sets of each secondary prepreg were laminated to create a prepreg orthogonal laminate. The prepreg orthogonal laminate was molded under the same conditions as A to produce CFRP-F. CFRP-F does not contain a low Vcf sublayer and therefore is not the CFRP of the present invention.

[0107] G.CFRP-G (corresponding to the layered structure shown in Figure 14) Secondary prepregs prepared using the resin compositions described in the comparative examples below were cut to 100 mm x 100 mm. Two cut secondary prepregs were considered as one set, and each set was laminated so that the fiber orientation angles of the secondary prepregs were in the same direction, resulting in the same configuration as F. A resin-rich portion made of secondary resin is located in the center of the thickness direction of each set, and at the same time, resin-rich portions made of secondary resin are also located on both side surfaces of each set, forming a thick interlayer resin layer after molding.

[0108] Each set has a fiber weight of 536g / m². 2 The resin content was 34% by mass. A total of eight sets of each secondary prepreg were laminated to create a prepreg orthogonal laminate. The prepreg orthogonal laminate was molded under the same conditions as A to produce CFRP-G. CFRP-G has a "specific layer," but because the interlayer resin layer is thick, it is not the CFRP of the first invention.

[0109] H.CFRP-H (corresponding to the layered structure shown in Figure 1) A 1.5-grade prepreg was prepared using the primary resin and secondary resin A compositions shown in Table 1. The basis weight of the secondary resin film was the same as that of CFRP-A, but the basis weight of the primary resin film was increased, thereby increasing the overall resin content of the 1.5-grade prepreg compared to CFRP-A. In other words, when preparing the primary prepreg, the basis weight of CF was 268 g / m². 2 The resin content is set to 29% by mass, and when preparing the 1.5th prepreg, the basis weight of the CF is 268 g / m². 2 The resin content was set to 40% by mass.

[0110] The above 1.5th-order prepreg was cut to 100mm x 100mm. Two cut 1.5th-order prepreg sheets were considered as one set, and each set was laminated so that it had the same configuration as A, with the fiber orientation angle of the prepreg being the same and the surfaces on which the secondary resin was applied in contact with each other.

[0111] Each set has a fiber weight of 536g / m². 2 The resin content was 40% by mass. A total of eight sets of 1.5th-order prepregs were laminated to create a prepreg orthogonal laminate. The prepreg orthogonal laminate was molded under the same conditions as A to produce CFRP-H. In CFRP-H, all layers are "specific layers".

[0112] I. CFRP-I (corresponding to the layered structure shown in Figure 9) The same 1.5th-order prepreg used in H was cut to 100mm x 100mm. Two cut 1.5th-order prepreg sheets were considered as one set, and the fiber orientation angles of the 1.5th-order prepregs were set to the same direction. They were then laminated so that the surfaces of the prepregs without secondary resin were in contact with each other. As a result, no resin-rich area was placed in the center of the thickness direction of each set. Instead, resin-rich areas consisting of secondary resin were placed on both sides of each set, forming a thick interlayer resin layer after molding.

[0113] Each set has a fiber weight of 536g / m². 2The resin content was 40% by mass. A total of eight sets of each 1.5th-order prepreg were laminated to create a prepreg orthogonal laminate. The prepreg orthogonal laminate was molded under the same conditions as A to produce CFRP-I. CFRP-I does not contain a low Vcf sublayer and is therefore not the CFRP of the present invention.

[0114] J.CFRP-J (corresponding to the layered structure shown in Figure 1) Thermoplastic UD prepreg (carbon fiber basis weight 142g / m²) 2 Using TC1000 (PEI) resin (33% by mass) and a thermoplastic resin film (TC1000 resin, 50 μm film thickness), each was cut to 100 mm x 100 mm. Two cut thermoplastic UD prepregs were made into a pair, and within each pair, the fiber orientation angles were aligned in the same direction. One thermoplastic resin film was placed between the two pairs to form one set.

[0115] Including the thermoplastic film sandwiched between each set, each set has a fiber basis weight of 568 g / m². 2 The resin content was 38% by mass. A total of eight sets of each UD prepreg were laminated to create a prepreg orthogonal laminate. The prepreg orthogonal laminate was molded in a press machine at a temperature of 340°C and a pressure of 3 MPa for 7 minutes to produce CFRP-J. In CFRP-J, all layers are "specific layers".

[0116] K.CFRP-K (corresponding to the layered structure shown in Figure 9) The same thermoplastic UD prepreg and thermoplastic resin film used in J were used and cut to 100mm x 100mm. Four cut thermoplastic UD prepreg sheets were made into one set, and within each set, they were laminated so that the fiber orientation angle was in the same direction. When laminating multiple sets, one thermoplastic resin film was sandwiched between each set. As a result, there is no resin-rich area in the center of the thickness direction of each set, and instead the resin-rich areas are located on both sides of each set, resulting in a thick interlayer resin layer after molding.

[0117] The fiber weight and resin content of each set were the same as those of CFRP-J. A total of eight sets of each UD prepreg were laminated to create a prepreg orthogonal laminate. The prepreg orthogonal laminate was molded under the same conditions as J to produce CFRP-K. CFRP-K does not contain a low Vcf sublayer and therefore is not the CFRP of the present invention.

[0118] L.CFRP-L (corresponding to the layered structure shown in Figure 7) The same thermoplastic UD prepreg used in J, and a thermoplastic UD prepreg with a higher resin content (carbon fiber basis weight 142g / m²). 2 A resin material (TC1000, resin content 40% by mass) was prepared. The former is called high VcfUD prepreg, and the latter is called medium VcfUD prepreg. In addition, the same thermoplastic resin film used in J was prepared. Each of the above was cut to 100 mm x 100 mm. Two pieces of each cut UD prepreg were considered as one pair, and three pairs were considered as one set. The fiber orientation angle of all UD prepregs constituting each set was set to the same direction, and one thermoplastic resin film was sandwiched between each pair. Of the three pairs, two pairs were made of high VcfUD prepreg, with one pair made of medium VcfUD prepreg sandwiched between them.

[0119] Each set has a fiber weight of 852g / m². 2 The resin content was 39% by mass. A total of eight sets of each UD prepreg were laminated to create a prepreg orthogonal laminate. The prepreg orthogonal laminate was molded under the same conditions as J to produce CFRP-L. In CFRP-L, all layers are "specific layers".

[0120] M.CFRP-M (corresponding to the layered structure shown in Figure 7) High VcfUD prepreg, medium VcfUD prepreg, and thermoplastic resin film, the same as those used in L, were prepared and cut to 100mm x 100mm. Two cut UD prepreg sheets were considered as one pair, and three pairs were considered as one set. The fiber orientation angle of all UD prepregs in each set was set to the same direction, and one thermoplastic resin film was sandwiched between each pair. Of the three pairs, two pairs were made of high VcfUD prepreg and one pair was made of medium VcfUD prepreg. In each set, one pair of high VcfUD prepreg was sandwiched between one pair of medium VcfUD prepreg and the other pair of high VcfUD prepreg.

[0121] The fiber weight and resin content of each set were the same as those of CFRP-L. A total of eight sets of each UD prepreg were laminated to create a prepreg orthogonal laminate. During lamination, one pair of medium VcfUD prepregs was placed on the top surface within each set. The prepreg orthogonal laminate was molded under the same conditions as J to produce CFRP-M. In CFRP-M, all layers are "specific layers". Unlike CFRP-L, among the three high Vcf sublayers present within the "specific layer", the one with the lowest average Vcf is positioned on the outermost side.

[0122] N.CFRP-N (corresponding to the layered structure shown in Figure 22) A 1.5-order prepreg A2 was prepared using the resin composition described in the examples below. Furthermore, the tertiary resin prepared in (1) using the tertiary resin composition shown in Table 1 was uniformly applied to a silicone-coated release paper using a coater to form a tertiary resin film (resin basis weight: 28 g / m²). 2 These were cut to 100mm x 100mm. Two cut 1.5th-order prepreg A2 sheets and one tertiary resin film sheet were considered as one set. In each set, the fiber orientation angles of the 1.5th-order prepreg A2 were made the same, and the surfaces on which the secondary resin was not applied faced each other, and the tertiary resin was laminated in between them.

[0123] Each set has a fiber weight of 536g / m². 2 The resin content was 34% by mass. Each set was [0 / 90] 2S A total of eight sets of prepreg orthogonal laminates were stacked to create a prepreg orthogonal laminate. The prepreg orthogonal laminate was molded in an autoclave at a temperature of 180°C for 2 hours at a pressure of 0.6 MPa and a heating rate of 1.5°C / min to produce CFRP-N. In CFRP-N, all layers are "specific layers".

[0124] O.CFRP-O A 1.5th prepreg B2 was prepared using the resin composition described in the comparative example below, and cut to 100 mm x 100 mm. Two cut 1.5th prepreg B2 pieces were considered as one set, and in each set, the fiber orientation angles of the 1.5th prepreg B2 were made the same, and the layers were laminated so that the surfaces on which the secondary resin was not applied were in contact with each other.

[0125] Each set has a fiber weight of 536g / m². 2 The resin content was 34% by mass. Each set was [0 / 90] 2S A total of eight sets were stacked to create a prepreg orthogonal laminate. The prepreg orthogonal laminate was molded in an autoclave under the same conditions as N to produce CFRP. CFRP-O does not have a low Vcf sublayer, and therefore does not have a "specific layer," and is not the CFRP of the present invention.

[0126] (5) Cross-sectional observation of CFRP Figure 18 shows a top view of the molded CFRP panel 3000. Samples of approximately 20mm x 20mm were cut from the panel, as indicated by the dashed line M1, to obtain observation samples. The observation samples were cut along the 30° or 120° direction, with the fiber direction of the outermost layer of the CFRP panel being defined as 0°. After embedding and curing with epoxy resin, the edges were polished. These polished surfaces were observed using a Keyence VHX-5000 digital microscope. A magnification of 500x was used as the base.

[0127] (6) Image analysis of CFRP cross-sections A. How to calculate Vcf The right direction of the paper was defined as the positive X-axis direction, and the upward direction as the positive Z-axis direction. The observation sample was set up so that the thickness direction of the CFRP coincided with the Z-axis direction. A stitched image was created in the Z-axis direction at 500x magnification so that any layer would fit into a single image. At this time, a portion of the adjacent layer was included both above and below. An example of a stitched image is shown in Figure 2 or Figure 10. The origin of the Z-axis was set at the bottom edge of the cross-sectional photograph.

[0128] First, the Z-direction distribution of Vcf was determined. The stitched images were binarized using ImageJ (Figure 3 or Figure 11) to distinguish between CF (black) and matrix resin (white). Vcf was calculated from the area ratio of the black areas. A rectangular region with a length of 0.2 μm in the Z direction and the entire length of the X-axis in the image in the X direction was defined as the evaluation range for Vcf, and Vcf was calculated. The Z-direction distribution of Vcf was obtained by calculating the Vcf within the evaluation range at 0.2 μm intervals in the Z-axis direction from the Z-axis origin.

[0129] B. Method for calculating the interlayer resin layer thickness between adjacent layers (6) For the Z-direction distribution of Vcf obtained in A, the median was used as the representative value of Vcf. The portion between adjacent layers where Vcf is 0.5 times or less of the representative value was defined as the interlayer resin layer. The thickness of the interlayer resin layer was defined as the Z-direction length of the portion corresponding to the interlayer resin layer. The Z-coordinate of the boundary between layers was defined as the midpoint of the Z-coordinate of the portion corresponding to the interlayer resin layer. If there was no portion between adjacent layers where Vcf was 0.5 times or less of the representative value, the interlayer resin layer was considered not to exist, and the thickness of the interlayer resin layer was set to 0. In this case, the Z-coordinate of the boundary between layers was defined as the Z-coordinate of the point in the vicinity of the layer where Vcf is at its minimum value.

[0130] C. Evaluation method for the entire layer (6) Using the Z coordinates of the boundaries between vertically adjacent layers obtained in B, the Z-direction distribution of Vcf for a single layer, excluding the vertically adjacent layers, was extracted. The average value of the extracted layer's Vcf was defined as the average value of the Z-direction distribution of Vcf for a single layer. The layer thickness was defined as the difference in Z coordinates of the boundaries between the vertically adjacent layers.

[0131] D. Evaluation method for low VCF sublayer (6) The Z-direction distribution of Vcf for one layer obtained in C was used. In layers where high Vcf sublayers exist on both outermost layers, excluding the interlayer resin layers at the upper and lower ends, the portion where the ratio of Vcf to the average Vcf of the layer is less than 0.5 was considered a low Vcf sublayer.

[0132] E. Evaluation method for high VCF sublayer (6) The Z-direction distribution of Vcf for one layer obtained in C was used. Sublayers where the ratio of Vcf to the average Vcf of the layer was 0.5 or greater were considered high Vcf sublayers. If there are three or more high VCF sublayers within a single layer, the average VCF value for each high VCF sublayer is calculated, and it is determined whether the high VCF sublayers located on the outermost sides of the layer have the first and second highest average VCF values ​​among all high VCF sublayers within the layer. F. Method for calculating the resin content of CFRP The resin content was calculated from the thickness of each Vcf and CFRP layer calculated in A above.

[0133] G. Method for calculating void fraction The right direction on the paper was defined as the positive X-axis, and the upward direction as the positive Z-axis. The observation sample was positioned so that the thickness direction of the CFRP coincided with the Z-axis direction. A stitched image was created in the Z-axis direction at 500x magnification so that the entire thickness of the CFRP would fit into a single image.

[0134] First, the CFRP region was cropped from the stitched image using ImageJ (Figure 23). Next, the cropped image was binarized using ImageJ (Figure 24) to distinguish between voids (black) and other areas (white). The void ratio was calculated from the percentage of the black area within the entire cropped image.

[0135] (7) Electrical conductivity in the thickness direction of CFRP From the molded CFRP panel, 40mm x 40mm samples were cut along the 0° and 90° directions. After polishing off approximately 50μm from both surfaces, Ag paste was uniformly applied to both sides using a spatula. The samples were then cured in a hot air oven set to 120°C for 1 hour to obtain samples for conductivity evaluation. The resistance in the thickness direction of the obtained samples was measured using an impedance analyzer (IM3570, HIOKI E.E. CORPORATION) under a DC current load condition of 5mA using the four-terminal method. Conductivity (S / m) was calculated from the measured resistance value and sample dimensions.

[0136] (8) Potential difference and conductivity in the longitudinal direction of CFRP From the molded CFRP panel, a 50mm x 5mm sample was cut out, with the 45° direction as the longitudinal direction and the -45° direction as the width direction. Ag paste was uniformly applied to both 5mm wide ends using a spatula, and cured in a hot air oven adjusted to 120°C for 1 hour to obtain a sample for conductivity evaluation. The potential difference and resistance in the longitudinal direction (45° direction) of the obtained sample were measured using an impedance analyzer (IM3570, HIOKI E.E. CORPORATION) under a DC current load condition of 5mA using the four-terminal method. The conductivity (S / m) in the longitudinal direction was calculated from the measured resistance value and the sample dimensions.

[0137] (9) Eddy current testing (evaluation of induced current) The series resistance component of a copper coil (inner diameter 10 mm, outer diameter 14 mm, height 3 mm, number of turns 60, with a PPS bobbin (ear thickness 1 mm), manufactured by Kitamoto Techno Co., Ltd.) was measured by the four-terminal method using an impedance analyzer (IM3570, manufactured by Hioki Electric Co., Ltd.) under a current load condition of 5 mA AC and a frequency of 300 kHz. In the first measurement, the measurement was carried out without placing any conductor near the coil. When a conductor is placed near the coil, the series resistance component of the coil changes. Therefore, no conductor was placed in the range where the series resistance component is affected. Next, the coil was installed so as to be in contact with the formed CFRP panel, and the series resistance component of the coil was measured by the same method. At this time, since the coil has a PPS bobbin, there is a 1 mm gap between the coil part and the CFRP panel. The resistance change of the coil was calculated by subtracting the result of the first measurement from the series resistance component when installed on the CFRP panel.

[0138] <Thermosetting CFRP with Vcf of about 60%> (Examples 1 to 7, Comparative Examples 1 to 4) In Examples 1 to 4, with each secondary resin as shown in Tables 1 and 2, using CFRP-A (all layers are "specific layers"), the thickness of the low-Vcf sublayer was changed. Examples 5 and 6 are in the form of CFRP-B or C, respectively, and in each, the "specific layer" exists only in the second layer from the top and only in the fourth layer. Example 7 used CFRP-D. This is because all layers are "specific layers" and the low-Vcf sublayer is formed of a glass fiber fabric.

[0139] In Comparative Examples 1 and 2, CFRP-E was produced. This does not contain the "specific layer" and there is a resin-rich layer between the layers. In Comparative Example 3, CFRP-F was used (all are normal layers). Comparative Example 4 used CFRP-G. This contains a low-Vcf sublayer, but the interlayer resin layer is thick. The results of various evaluations are shown in Table 2. In the comparative examples that do not contain the "specific layer", image analysis was performed on any layer (the same applies hereinafter).

[0140] First, to verify the edge glow suppression effect, Figure 19 shows a graph with the conductivity in the thickness direction of CFRP on the horizontal axis and the potential difference in the longitudinal direction on the vertical axis. In the comparative example related to the conventional technology, there is a tendency for the potential difference in the longitudinal direction to decrease as the conductivity in the thickness direction increases, but in the present invention, it was found that the potential difference in the longitudinal direction is suppressed to less than 20mV (the region represented by R1) regardless of the conductivity in the thickness direction. In particular, Example 7, which uses CFRP-D with a conductivity of 0 in the thickness direction, had the lowest potential difference in the longitudinal direction and was found to have a high edge glow suppression effect. CFRP-B or C shown in S1 (Example 5 or 6) is the same as CFRP-F shown in T1 (Comparative Example 3), but with only one layer replaced by a "specific layer", yet it was found that the reduction effect of the potential difference in the longitudinal direction was still significant.

[0141] Next, to verify the effect of improving the induction heating temperature, Figure 20 shows a graph in which the horizontal axis represents the conductivity in the thickness direction of the CFRP and the vertical axis represents the change in coil resistance in eddy current testing. In the CFRP of the present invention, regardless of the conductivity in the thickness direction, the change in coil resistance was greater than 2.8Ω (the region represented by R2), resulting in a larger induced current and, consequently, an improvement in the induction heating temperature. Among these, Example 7, which used CFRP-D with a conductivity of 0 in the thickness direction, showed the largest change in coil resistance and demonstrated a high improvement in induction heating temperature. Furthermore, in the comparison of Examples 5 and 6 shown in S1, Example 5 showed a slightly higher change in coil resistance. From this, it was found that placing the "specific layer" as the second layer from the outermost layer of the CFRP resulted in a greater improvement in induction heating temperature than placing it as the fourth layer.

[0142] To examine a more preferred embodiment of the present invention, a graph is shown in FIG. 21 in which the horizontal axis is (thickness of the low-Vcf sublayer) / (thickness of the layer) and the vertical axis is the longitudinal potential difference. Among the present inventions, in CFRP (other than the example shown in S1) where all layers are "specific layers", as (thickness of the low-Vcf sublayer) / (thickness of the layer) is higher, the longitudinal potential difference tends to decrease. From this, it was found that the greater the ratio of the thickness of the low-Vcf sublayer, the higher the effect of the present invention. Note that in Examples 5 and 6 shown in S1, since only one layer in the CFRP is the "specific layer", it is considered that they did not reach the effects of other examples where all layers are the "specific layer".

[0143] From the above, when targeting CFRP with the same fiber weight per unit area and substantially the same resin content rate, it was found that the present invention has a greater effect of suppressing edge glow and improving the induction heating temperature compared to the prior art. In particular, since the effect of Example 7 that does not use conductive particles is the highest, it was found that these effects can be obtained without using expensive conductive particles in the present invention.

[0144] In Comparative Example 3, both surfaces were resin-rich in the state of the secondary prepreg, but in the molded CFRP-F, almost no low-Vcf sublayer or interlayer resin layer existed. This is presumed that the CF moved during molding and the Vcf was made uniform throughout the layer. From this, it was suggested that in order to form a low-Vcf sublayer in CFRP, it is effective to arrange spacers such as polymer particles and glass fiber fabrics as in Examples 1 to 7.

[0145] <Thermosetting CFRP with Vcf of about 50%> (Examples 8, Comparative Example 5) In Example 8, CFRP-H was used. This is such that all layers are "specific layers", and the average value of Vcf of the entire layer is lower than that in Example 1. Comparative Example 5 produced CFRP-I. This does not include "specific layers", and the average value of Vcf of the entire layer is lower than that in Comparative Example 1. The results of various evaluations are shown in Table 3.

[0146] The potential difference in the in-plane longitudinal direction of CFRP was overwhelmingly lower in Example 8, being less than 100 mV. The resistance change of the coil was also larger in Example 8. From this, even when the average value of Vcf of the entire layer is as low as 50%, when targeting CFRP with the same fiber basis weight and the same resin content, it was found that the present invention has a greater edge glow suppression effect and an improvement effect on the induction heating temperature than the prior art. In Example 8, unlike Example 1 where the average value of Vcf was about 63% and higher, the potential difference in the in-plane longitudinal direction of CFRP was not low, and the value of the resistance change of the coil was not large.

[0147] <Thermoplastic CFRP with Vcf of about 50%> (Examples 9 to 11, Comparative Example 6) In Example 9, CFRP-J was used. This is such that all layers are "specific layers". Comparative Example 6 used CFRP-K. This does not include "specific layers", and there is a resin-rich layer between the layers. Example 10 used CFRP-L. This is such that all layers are "specific layers", and within the "specific layers", the average value of Vcf of the high-Vcf sub-layers at both outermost sides is the second highest. Example 11 used CFRP-M. This is such that all layers are "specific layers", and among the high-Vcf sub-layers within the "specific layers", the one with the lowest average value of Vcf is arranged in a form at one outermost side of the "specific layer". The results of various evaluations are shown in Table 4.

[0148] Comparing Example 9 and Comparative Example 6, which have the same fiber weight and resin content, it was found that Example 9 had a significantly lower potential difference in the longitudinal direction of the plane and a larger change in coil resistance. From this, it was found that even in thermoplastic CFRP, the present invention has a greater effect on suppressing edge glow and improving induction heating temperature compared to the conventional technology.

[0149] Comparing Examples 10 and 11, which have the same fiber weight and resin content, Example 10 showed a lower longitudinal potential difference and a larger change in coil resistance. This indicates that within a "specific layer," having the first and second highest average Vcf values ​​of the outermost high Vcf sublayers on both sides yields a greater effect in suppressing edge glow and improving induction heating temperature. Although a direct comparison is difficult between Examples 10 and 11 and Comparative Example 6 due to differences in fiber weight and resin content, Examples 10 and 11 showed a smaller longitudinal potential difference and a larger change in coil resistance than Comparative Example 7.

[0150] <Supplementary information on examples using conductive particles> (Examples 12-14, Comparative Examples 7, 8) In Example 12, the CFRP-G was prepared in the same manner as in Comparative Example 4, except that Resin-F was used as the secondary resin composition. Because conductive particles were placed in the interlayer resin layer, a high conductivity value was obtained in the thickness direction of the CFRP, as shown in Table 5. However, because the interlayer resin layer was thick, the change in coil resistance was small, and it was predicted that the induction heating effect would not be as good as in Examples 1 to 7.

[0151] In Examples 13 and 14, CFRP-N was fabricated as an embodiment of the present invention, with the secondary and tertiary resins having the compositions of Resin-A2 and Resin-B2 as shown in Table 1, respectively. In this case, all layers were "specific layers," and the amount of conductive particles between layers was varied. In Comparative Examples 7 and 8, CFRP-O was fabricated with the secondary and tertiary resins having the compositions of Resin-A2 and Resin-B2 as shown in Table 1, respectively. This did not include "specific layers" and is not the CFRP of the present invention. The amount of conductive particles between layers was the same for Example 13 and Comparative Example 7, and the same for Example 14 and Comparative Example 8. The results of various evaluations are shown in Table 5. In the comparative examples that did not include "specific layers," image analysis was performed on arbitrary layers.

[0152] First, to verify the edge glow suppression effect, Figure 24 shows a graph with the conductivity in the thickness direction of CFRP on the horizontal axis and the potential difference in the longitudinal direction on the vertical axis. In conventional technology, as the amount of conductive particles increases and the conductivity in the thickness direction increases, the potential difference in the longitudinal direction tends to decrease. However, in the present invention, it was found that even when the conductivity in the thickness direction is 0, the potential difference in the longitudinal direction is suppressed to less than 13mV (the region represented by R4). It was confirmed that the potential difference in the longitudinal direction was smaller in Example 13, which had a small amount of conductive particles, than in Comparative Example 7, which had a large amount of conductive particles. This shows that according to the present invention, even with a small amount of conductive particles, the effect of reducing the potential difference in the longitudinal direction is significant.

[0153] Next, to verify the effect of improving the induction heating temperature, Figure 25 shows a graph in which the horizontal axis represents the conductivity in the thickness direction of the CFRP and the vertical axis represents the change in coil resistance in the eddy current testing test. In this invention, even when the conductivity in the thickness direction is 0, the amount of induced current increases when the change in coil resistance is 3.2Ω or more (the region represented by R5), and consequently, the effect of improving the induction heating temperature is demonstrated.

[0154] <Supplementary information on an example where a breathable sheet is incorporated into the low VCF layer> (Examples 15, 16, Reference Example 1, Comparative Example 9) In these examples, the 1.5th prepreg was prepared according to (2)B above. However, the resin basis weight of the secondary resin film was 68 g / m². 2 The laminates P, Q, and R were fabricated as follows.

[0155] Laminate P: Primary prepregs and glass fiber fabrics (glass fiber diameter approximately 6 μm, 4-ply satin weave sheets) prepared to match the prepreg configurations shown in Table 6 were cut to 100 mm x 100 mm. Two cut primary prepregs and one glass fiber fabric were considered as one set. In each set, the fiber orientation angles of the two primary prepregs were set to the same direction, and one glass fiber fabric was sandwiched between the two primary prepregs before lamination. Each set is a specific lamination set. Eight of these specific lamination sets were prepared. Each specific lamination set had the CF basis weight and CF mass content shown in Table 6, and a total of eight of these specific lamination sets were laminated to produce a prepreg orthogonal laminate (laminated body P).

[0156] Laminate Q: A primary prepreg and a glass fiber woven prepreg, prepared with a resin mass content of 20%, were cut to 100mm x 100mm. Then, laminate Q was prepared using the same procedure as for laminate P.

[0157] Laminate R: As described above, a 1.5-order prepreg was prepared and cut to 100 mm x 100 mm. Two cut 1.5-order prepregs were considered as one set, and in each set, the fiber orientation angles of the 1.5-order prepregs were made the same, and the laminated layers were laid so that the surfaces without the secondary resin film faced each other. Then, laminate R was prepared using the same procedure as laminate P.

[0158] In Examples 15 and 16, laminates P were prepared by varying the resin mass content of the primary prepreg as shown in Table 6, and then molded to form CFRP-P.

[0159] Reference Example 1 involved fabricating a laminate Q and molding it to form CFRP-Q. Comparative Example 9 involved fabricating a laminate R and producing it in the form of CFRP-R, which does not include a "specific layer" and has resin-rich layers between the layers.

[0160] The void ratio was 1.0% or less in both Examples 15 and 16. In Example 16, the CF mass content was higher than in Example 15, and some voids were observed. In this invention, although the conductivity in the thickness direction of the CFRP was 0 S / m, the potential difference in the longitudinal direction was 1.6 mV or less in both cases, indicating a high effect in suppressing edge glow. In particular, in Example 16, the average Vcf value of the high Vcf sublayer was high at 73%, confirming a higher edge glow suppression effect compared to Example 15. In this invention, the resistance change of the coil was 4.3 Ω or more in both cases, indicating a larger induced current and, consequently, an improvement in induction heating temperature. It was found that Example 16, with its higher average Vcf value of the high Vcf sublayer, showed a greater improvement in induction heating temperature. In both Examples 15 and 16, the individual Vcf values ​​of the high Vcf sublayers at the outermost edges on both sides of the "specific layer" were 69% or higher.

[0161] In Reference Example 1, the CF mass content was the same as in Example 15, but the void ratio was very high at 3.1%. In particular, many voids were observed in areas where the CF was densely concentrated. In the present invention, represented by Examples 15 and 16, it was found that increasing the resin mass content of the primary prepreg during the lamination process and arranging a glass fiber fabric that is not impregnated with resin as a low VCF sublayer reduces the void ratio of the CFRP after molding. Note that in Reference Example 1, no further evaluations were performed due to the high void ratio.

[0162] Comparative Example 9 had fewer voids. Although Comparative Example 9 had the same CF mass content as Example 16, the longitudinal potential difference was overwhelmingly higher, and the change in coil resistance was overwhelmingly lower. It was found that the present invention, represented by Examples 15 and 16, has a greater effect on suppressing edge glow and improving induction heating temperature compared to the conventional technology.

[0163] [Table 1]

[0164] [Table 2]

[0165] [Table 3]

[0166] [Table 4]

[0167] [Table 5]

[0168] [Table 6] [Industrial applicability]

[0169] The CFRP of the present invention is widely applicable to fields requiring lightning protection and fields requiring induction welding. In particular, when used in aircraft structural members, it can reduce the need for conventional lightning protection systems such as metal mesh and sealants, making it suitable for use in such fields. This simplifies conventional lightning protection systems and contributes to aircraft weight reduction and cost reduction. [Explanation of symbols]

[0170] 1 Carbon fiber 2. Matrix resin impregnated into the carbon fiber layer 20, 21, 22, 23, 24, 25 Interlayer resin layer with upper adjacent layer 30, 31, 32, 33, 34, 35 Interlayer resin layer with the lower adjacent layer Layers with the same fiber orientation angle (specific layers): 100, 101, 102, 105 103, 104 Layers with the same fiber orientation angle 110, 111, 112, 115, 122, 210, 212, 222, 310 Low VCF sublayer 150, 151, 152, 155, 160, 161, 162, 165, 172 High VCF sublayer 200, 201, 202, 203, 204, 205 are adjacent layers located above. 300, 301, 302, 303, 304, 305 are adjacent layers located below. Layers 401 and 501 are located below. 600, 601, 602, 603, 604 Secondary resin 605, 607 Glass fiber fabric prepreg 611, 612 Tertiary resin 613 Conductive particles 700, 705, 706, 707, 708 Primary Prepreg 1000, 1001, 1002 One embodiment of CFRP of the present invention 1003 A conventional form of CFRP 1004 A form of conventional interlayer-reinforced CFRP 1005 A form of conventional interlayer-reinforced CFRP 2000, 2001, 2002, 2003, 2004 1.5th-order prepreg as a form of intermediate substrate Top view of 3000 CFRP panel Layers observed midway between L1 and L4 in the Z direction L2, L5 Adjacent layers observed on the upper side in the Z direction L3, L6 Adjacent layers observed on the lower side in the Z direction W1 Total length in the X-axis direction A1, A1' Representative value (median) of the Vcf for the entire three layers. Threshold of Vcf for defining the interlayer resin layer B1, B1' Average value of Vcf for the entire C1 and C1' layers D1, D1' VCF threshold for defining low VCF sublayers Relevant section of the K1 low VCF sublayer I1, I1' The corresponding area of ​​the interlayer resin layer between the lower adjacent layer. The point where Vcf is minimized near the boundary with the upper adjacent layer of J1. J1' The corresponding area of ​​the interlayer resin layer between 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 M1 Sample cut section for cross-sectional observation T1 Results from a conventional technique consisting of a normal layer (Comparative Example 3) S1 Results of the present invention (Examples 8, 9) where only one "specific layer" is included. R1 Desired region of potential difference in the longitudinal direction within the plane Desired range of resistance change for coil R2 Thickness of low VCF layers: T110, T112, T115, T122 T20, T22, T24, T25 Interlayer resin layer thickness between upper adjacent layers T30, T32, T34, T35 Interlayer resin layer thickness between lower adjacent layers Thickness of layers T100, T102, T104, T105

Claims

1. Carbon fiber sheets, in which carbon fibers are arranged in one direction, are laminated in multiple directions. In a carbon fiber reinforced composite material in which a matrix resin has been impregnated and cured, The carbon fiber sheet has regions in the thickness direction where the fiber orientation angle of the carbon fibers is the same, as layers. When the layer consists of multiple regions of constant thickness with different carbon fiber volume content (Vcf), and these regions of constant thickness are designated as sublayers, (1) to (3) includes a layer (such layer is referred to as a "specific layer"), A carbon fiber reinforced composite material in which the thickness of the resin portion between the specific layer and at least one adjacent layer is 5 μm or less. (1) The average value of Vcf in the layer (hereinafter referred to as the average value of layer Vcf) is 50% or more. (2) Sublayers having a Vcf ratio of 0.5 or higher to the average Vcf of the layer (hereinafter referred to as high Vcf sublayers) are placed on the outermost sides of both sides of the layer, and the average Vcf of each is higher than the average Vcf of the layer. (3) Between the outermost high Vcf sublayers on both sides of the layer, there are sublayers with a Vcf ratio of less than 0.5 to the average layer Vcf (hereinafter referred to as low Vcf sublayers).

2. Carbon fiber sheets, in which carbon fibers are arranged in one direction, are laminated in multiple directions. In a carbon fiber reinforced composite material in which a matrix resin has been impregnated and cured, The carbon fiber sheet has regions in the thickness direction where the fiber orientation angle of the carbon fibers is the same, as layers. When the layer consists of multiple regions of constant thickness with different carbon fiber volume content (Vcf), and these regions of constant thickness are designated as sublayers, (1) to (3) includes a layer (such layer is referred to as a "specific layer"), A carbon fiber reinforced composite material in which a resin portion exists between the specific layer and an adjacent layer, and the resin portion contains conductive particles. (1) The average value of Vcf in the layer (hereinafter referred to as the average value of layer Vcf) is 50% or more. (2) Sublayers having a Vcf ratio of 0.5 or higher to the average Vcf of the layer (hereinafter referred to as high Vcf sublayers) are placed on the outermost sides of both sides of the layer, and the average Vcf of each is higher than the average Vcf of the layer. (3) Between the outermost high Vcf sublayers on both sides of the layer, there are sublayers with a Vcf ratio of less than 0.5 to the average layer Vcf (hereinafter referred to as low Vcf sublayers).

3. The carbon fiber reinforced composite material according to claim 1 or 2, wherein the average value of the layer Vcf is 80% or less.

4. The carbon fiber reinforced composite material according to claim 1 or 2, wherein the high Vcf sublayers located on the outermost sides of the particular layer have the first or second highest average Vcf value among the high Vcf sublayers present in the particular layer.

5. The carbon fiber reinforced composite material according to claim 1 or 2, wherein at least one of the aforementioned specific layers is located within the second layer when counting the number of layers from the top or bottom surface of the carbon fiber reinforced composite material.

6. The carbon fiber reinforced composite material according to claim 1 or 2, wherein the average Vcf value of the low Vcf sublayer is 20% or less.

7. The carbon fiber reinforced composite material according to claim 1 or 2, wherein the ratio of the thickness of the low Vcf sublayer contained in the specific layer to the thickness of the specific layer is 5% to 30%.

8. The carbon fiber reinforced composite material according to claim 1 or 2, wherein the low Vcf sublayer is an insulating layer.

9. The carbon fiber reinforced composite material according to claim 1 or 2, wherein the average Vcf value of the high Vcf sublayer is 55% or more.

10. The carbon fiber reinforced composite material according to claim 1 or 2, wherein the average Vcf value of the high Vcf sublayer is 71% or more.

11. The carbon fiber reinforced composite material according to claim 1 or 2, wherein the resin content of the specific layer is 30 to 40% by mass.

12. The carbon fiber reinforced composite material according to claim 1 or 2, wherein the thickness of the specific layer is 350 μm or more.

13. A carbon fiber reinforced composite material according to claim 1 or 2, wherein the void ratio is 1.0% or less.

14. The carbon fiber reinforced composite material according to claim 1 or 2, wherein the low Vcf sublayer contains a breathable sheet-like substrate.

15. The carbon fiber reinforced composite material according to claim 14, wherein the breathable sheet-like base material is a woven or nonwoven fabric.

16. The carbon fiber reinforced composite material according to claim 1 or 2, wherein two or more of the aforementioned specific layers are laminated in a continuous manner.

17. A structure made of a carbon fiber reinforced composite material according to claim 1 or 2, A structure whose shape is selected from flat plate structures, cylindrical structures, box-shaped structures, C-shaped structures, H-shaped structures, L-shaped structures, T-shaped structures, I-shaped structures, Z-shaped structures, and hat-shaped structures.

Images