Carbon fiber sheet

Abstract

Provided is a carbon fiber sheet that is less susceptible to sheet breakage even in a wet state and impregnated with a resin component or the like, and in which cracks are unlikely to occur when wound around a core tube or the like having a high curvature. One embodiment of the present invention is a carbon fiber sheet containing carbon fibers and organic fibers. The organic fiber content based on the total mass of the carbon fiber sheet is 3 to 20 mass%. The organic fibers include one or more selected from the group consisting of cellulose fibers, acrylic fibers, polyamide fibers, polyester fibers, vinylon fibers, and polyurethane fibers. In the carbon fiber sheet, the ratio A / B is 0.033 to 0.125, where A% denotes the area percentage of organic-component-absent regions having an equivalent circle diameter of 1 to 4 μm, and B% denotes the area percentage of organic-component-absent regions having an equivalent circle diameter of 10 to 40 μm.

Description

carbon fiber sheet

[0001] This invention relates to a carbon fiber sheet.

[0002] Carbon fiber sheets are used in a variety of applications. A specific application of carbon fiber sheets is thermal insulation made by compounding carbon fiber sheets with resin components. More specifically, carbon fiber thermal insulation (molded thermal insulation) can be manufactured by impregnating carbon fiber sheets with resin components, then curing the resin components, and finally firing the material.

[0003] For example, Patent Document 1 discloses a molded thermal insulation material obtained by impregnating carbon fiber webs, carbon fiber felts, carbon fiber cloths, etc., with a thermosetting resin, molding them, and then subjecting them to carbonization or graphitization treatment, to which a graphite sheet is laminated via a carbonaceous adhesive. It is disclosed that such a molded thermal insulation material is suitable for use as thermal insulation material in high-temperature furnaces.

[0004] Japanese Patent Application Publication No. 06-190962

[0005] However, conventional carbon fiber sheets could tear during molding while impregnated with resin components. Furthermore, when carbon fiber sheets were wrapped around core tubes with high curvature, their flexibility was insufficient, potentially leading to cracking.

[0006] Therefore, the present invention aims to provide a carbon fiber sheet that is less prone to tearing even when impregnated with resin components, and less prone to cracking when wrapped around a core tube or the like with a high curvature.

[0007] The inventors have discovered that the above problems can be solved by a carbon fiber sheet having a specific structure, and have completed the present invention. That is, the present disclosure is as follows.

[0008] One embodiment of this disclosure is a carbon fiber sheet containing carbon fibers and organic fibers. The content of the organic fibers is 3 to 20% by mass, based on the total mass of the carbon fiber sheet. The organic fibers include one or more selected from the group consisting of cellulose fibers, acrylic fibers, polyamide fibers, polyester fibers, vinylon fibers, and polyurethane fibers. The carbon fiber sheet is analyzed under the following measurement conditions, and when the percentage of the area occupied by the portion without organic components with an equivalent circle diameter of 1 to 4 μm is A%, and the percentage of the area occupied by the portion without organic components with an equivalent circle diameter of 10 to 40 μm is B%, the ratio of A / B is 0.033 to 0.125. [Measurement conditions] A scanning electron microscope (product name: SU5000, manufactured by Hitachi High-Tech Corporation) and an EDS system (product name: Aztec, manufactured by Oxford Corporation) are used as the measuring devices. EDS analysis mapping is performed at a magnification of 200x with a field of view area of ​​1260 μm × 940 μm. Regions corresponding to organic components where "C" and "O" and / or "N" are detected are defined as organic regions, and regions other than organic regions are defined as regions without organic components. The images obtained by EDS detection are analyzed using the image analysis software "WinROOF" (manufactured by Mitani Shoji Co., Ltd.). For each region without organic components, the equivalent circle diameter is calculated from its area. The percentage of the area occupied by regions without organic components where the equivalent circle diameter is calculated to be in the range of 1 to 4 μm is defined as A%, and the percentage of the area occupied by regions without organic components where the equivalent circle diameter is calculated to be in the range of 10 to 40 μm is defined as B%.

[0009] The average fiber length of the carbon fibers is preferably 200 to 6000 μm. The average fiber diameter of the carbon fibers is preferably 5 to 20 μm. The density of the carbon fiber sheet is 0.18 to 0.30 g / cm³. ３ It is preferable that the coefficient of variation of the basis weight of the carbon fiber sheet measured by the following measurement conditions is 0.060 or less. [Measurement conditions] 4 cm x 4 cm test pieces are drawn from any 20 locations on the carbon fiber sheet. The basis weight of each drawn test piece is measured in an oven-dry state, and the coefficient of variation is calculated from the average and standard deviation of the basis weights. It is preferable that the carbon fiber sheet is for use as an insulating material.

[0010] Another embodiment of the present disclosure is a carbon fiber sheet containing carbon fibers and organic fibers. The content of the organic fibers is 3 to 20% by mass, based on the total mass of the carbon fiber sheet. The organic fibers include one or more selected from the group consisting of cellulose fibers, acrylic fibers, polyamide fibers, polyester fibers, vinylon fibers, and polyurethane fibers. The organic fibers include organic staple fibers with an average fiber length of 10 to 500 μm and organic filament fibers with an average fiber length of more than 500 μm and less than or equal to 10,000 μm. The ratio of the average fiber length of the organic filament fibers to the average fiber length of the organic staple fibers (organic filament fibers / organic staple fibers) is 2 to 200. The content of the organic staple fibers and the organic filament fibers is more than 1% by mass and less than 12% by mass, based on the total mass of the carbon fiber sheet.

[0011] According to the present invention, a carbon fiber sheet is provided that is less prone to tearing even when impregnated with resin components, and less prone to cracking when wrapped around a core tube or the like with a high curvature.

[0012] In the following, if the upper and lower limits are listed separately, it shall be assumed that a numerical range is substantially disclosed by combining any upper and lower limit.

[0013] In the following, unless otherwise specified, all measurements will be conducted at room temperature (23°C).

[0014] The composition, structure / properties, manufacturing method, and applications / usage methods of the carbon fiber sheets related to this disclosure will be described below, but the present invention is not limited to the following.

[0015] <<Composition>> The carbon fiber sheet relating to this disclosure includes carbon fibers and organic fibers. The carbon fiber sheet relating to this disclosure may also contain other components. Each component is described in detail below.

[0016] <Carbon Fibers> The average fiber length of the carbon fibers is preferably 20 μm or more, 50 μm or more, 100 μm or more, or 200 μm or more, and also preferably 20,000 μm or less, 10,000 μm or less, 8,000 μm or less, or 6,000 μm or less. By forming a carbon fiber sheet using such carbon fibers, a proper sheet texture is ensured, variations in strength and crack resistance in the sheet surface direction are reduced, sheet breakage is less likely to occur even in a wet state impregnated with resin components, etc., and cracks are less likely to occur even when the sheet is wrapped around a core tube with a high curvature. Furthermore, when the carbon fiber sheet is applied as an insulating material, variations in thermal insulation performance in the sheet surface direction are reduced, and an excellent thermal insulation effect is easily achieved.

[0017] The average fiber diameter of the carbon fibers is preferably 1 μm or more, or 5 μm or more, and preferably 50 μm or less, or 20 μm or less. By forming a carbon fiber sheet using such carbon fibers, sheet breakage becomes less likely even when the sheet is wet and impregnated with resin components, and cracks are less likely to occur even when the sheet is wrapped around a core tube or the like with a high curvature.

[0018] The average fiber length and average fiber diameter of the carbon fibers were calculated by measuring the fiber length and fiber diameter of 50 carbon fibers constituting a carbon fiber sheet using an optical microscope (or an electron microscope if necessary), and then averaging these values.

[0019] Furthermore, the aspect ratio (average fiber length / average fiber diameter) of the carbon fiber is preferably 3 or more, 5 or more, or 10 or more. The upper limit of the aspect ratio is not particularly limited, but for example, it is 2000, 1500, or 1000.

[0020] The carbon fiber content, based on the total mass of the carbon fiber sheet, is preferably 30% by mass or more, 40% by mass or more, or 50% by mass or more.

[0021] <Organic Fibers> The organic fibers preferably include one or more selected from the group consisting of cellulose fibers, acrylic fibers, polyamide fibers (including aramid fibers, etc.), polyester fibers (including fully aromatic polyester fibers, etc.), vinylon fibers, and polyurethane fibers. Hereinafter, these specific organic fibers may be simply referred to as organic fibers. The organic fibers more preferably include one or more selected from the group consisting of cellulose fibers, acrylic fibers, and aramid fibers. Carbon fiber sheets formed by combining such organic fibers with carbon fibers are less prone to tearing even in a wet state impregnated with resin components, and are less prone to cracking even when the sheet is wrapped around a core tube with a high curvature.

[0022] The average fiber length of the organic fibers is not particularly limited, but is preferably 10 μm or more, 50 μm or more, or 100 μm or more, and is also preferably 10,000 μm or less, 8,000 μm or less, or 5,000 μm or less.

[0023] The average fiber diameter of the organic fibers is not particularly limited, but is preferably 0.2 μm or more, 0.5 μm or more, or 1 μm or more, and is also preferably 200 μm or less, 100 μm or less, or 50 μm or less.

[0024] The average fiber length and average fiber diameter of the organic fibers were calculated by measuring the fiber length and fiber diameter of 50 organic fibers constituting the carbon fiber sheet using an optical microscope (and an electron microscope if necessary), and then averaging these values.

[0025] Furthermore, the aspect ratio (average fiber length / average fiber diameter) of the organic fiber is preferably 5 or more, 10 or more, or 50 or more. The upper limit of the aspect ratio is not particularly limited, but for example, it is 1000, 500, or 200.

[0026] Organic fibers are preferably fibrillated. Here, fibrillation of fibers refers to a process that involves fibrillating the fibers (a process that makes the fibers fluffy). Fibrillation of fibers can be carried out, for example, using a beating machine such as an SDR, DDR, or beater.

[0027] The organic fiber content, relative to the total mass of the carbon fiber sheet, is preferably 3 to 20% by mass. By setting the organic fiber content within this range, sheet breakage becomes less likely even when the sheet is wet and impregnated with resin components, cracks are less likely to occur when the sheet is wrapped around a core tube with a high curvature, and excellent heat insulation properties are easily achieved.

[0028] <<Other Ingredients>> Other ingredients include fillers (inorganic fillers, organic fillers), surfactants, dispersants, thickeners, defoamers, paper strength enhancers, inorganic binders, organic binders, flocculants, etc.

[0029] The other components preferably include organic fillers. Examples of organic fillers include resin particles such as phenolic resin, epoxy resin, melamine resin, silicone resin, acrylic resin, polyamide resin, and polyimide resin.

[0030] When other components include organic fillers, the content of organic fillers based on the total mass of the carbon fiber sheet is preferably, for example, 1% by mass or more, 5% by mass or more, or 10% by mass or more, and also preferably 40% by mass or less, 30% by mass or less, or 25% by mass or less.

[0031] Examples of inorganic fillers include carbon-based particles such as graphite particles and carbon black, and metal oxide-based particles such as silica and alumina.

[0032] When inorganic fillers are included as other components, the inorganic filler content, based on the total mass of the carbon fiber sheet, is preferably, for example, 1% by mass or more, 5% by mass or more, or 10% by mass or more, and also preferably 30% by mass or less, 25% by mass or less, or 20% by mass or less.

[0033] When other components include both organic and inorganic fillers, the ratio of the organic filler content to the inorganic filler content (organic filler / inorganic filler) is preferably 0.5 or higher, 0.8 or higher, or 1.0 or higher, and also preferably 5.0 or lower, 3.0 or lower, or 2.0 or lower.

[0034] The particle size (average particle size) of the organic or inorganic filler is preferably 1 μm or more, 5 μm or more, or 10 μm or more, and preferably 50 μm or less, 40 μm or less, or 30 μm or less. In this disclosure, the average particle size of the filler refers to the median diameter (D50) calculated by volume-based laser diffraction / scattering.

[0035] The content of other components based on the total mass of the carbon fiber sheet is, for example, 0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, 5% by mass or more, 10% by mass or more, or 15% by mass or more, and also 50% by mass or less, 40% by mass or less, 45% by mass or less, or 30% by mass or less.

[0036] Furthermore, the carbon fiber sheet may contain organic fibers other than those mentioned above (other organic fibers). In that case, the content of other organic fibers based on the total mass of the carbon fiber sheet is preferably, for example, 10% by mass or less, 5% by mass or less, 1% by mass or less, 0.1% by mass or less, or 0% by mass.

[0037] <<Structure / Physical Properties>> <Distribution of Equivalent Circle Diameter in Areas Without Organic Components (Pore Diameter Distribution)> When a carbon fiber sheet is analyzed under the following measurement conditions, and the area occupied by areas without organic components with an equivalent circle diameter of 1 to 4 μm is A%, and the area occupied by areas without organic components with an equivalent circle diameter of 10 to 40 μm is B%, it is preferable that the ratio of A / B is 0.033 to 0.125. [Measurement Conditions] A scanning electron microscope (product name: SU5000, manufactured by Hitachi High-Tech Corporation) and an EDS system (product name: Aztec, manufactured by Oxford Corporation) are used as the measuring devices. EDS analysis mapping processing is performed at a magnification of 200x with a field of view area of ​​1260 μm × 940 μm, and the region corresponding to the organic component in which "C" and "O" and / or "N" are detected is defined as the organic region, and the region other than the organic region is defined as the area without organic components. Images subjected to EDS detection are analyzed using the image analysis software "WinROOF" (manufactured by Mitani Corporation). For each area where no organic component is present, the equivalent circle diameter is calculated from its area. In the image (with the total image area being 100%), the percentage of the area occupied by areas where the equivalent circle diameter is calculated to be in the range of 1 to 4 μm is defined as A%, and the percentage of the area occupied by areas where the equivalent circle diameter is calculated to be in the range of 10 to 40 μm is defined as B%. In the above measurement method (EDS mapping), regions where "C" and "O" or "C" and "N" are detected (or regions where "C", "O", and "N" are detected) correspond to regions containing the specified organic component. In the above measurement method (EDS mapping), regions where the specified organic component is absent are defined as areas where no organic component is present. In this disclosure, these areas where no organic component is present may be conveniently referred to as "voids". Similarly, the equivalent circular diameter calculated from the area of ​​the organic component-free region is sometimes conveniently referred to as the "pore diameter" or "pore size." Alternatively, the equivalent circular diameter of the organic component-free region may be interpreted as the "diameter of the organic component-free region."

[0038] It has been confirmed that such a pore size distribution tends to improve the performance of the carbon fiber sheet. Although the details of the mechanism of action are unclear, when voids corresponding to microscopic pores of 1 to 4 µm and voids corresponding to macroscopic pores of 10 to 40 µm are arranged in a well-balanced manner (while a sheet skeleton is formed by carbon fibers and organic fibers, the dispersion state of organic components including organic fibers in the sheet becomes appropriate), it is expected that the impregnation property of resin components and the like into the carbon fiber sheet, the accompanying change in strength of the carbon fiber sheet, the flexibility of the carbon fiber sheet itself, and the like can be easily adjusted to appropriate levels.

[0039] Further, from the viewpoint of enhancing such effects, the proportion (A%) occupied by voids having a pore diameter of 1 to 4 µm is preferably 1.0% or more, 1.2% or more, or 1.6% or more, and is preferably 5.0% or less, 4.0% or less, or 3.0% or less. Further, the proportion (B%) occupied by voids having a pore diameter of 10 to 40 µm is preferably 20.0% or more, 25.0% or more, or 28.0% or more, and is preferably 60.0% or less, 55.0% or less, or 53.0% or less.

[0040] Here, when the fiber length distribution of organic fibers is measured, mixing two or more types of organic fibers having different fiber diameters and fiber lengths such that there are two or more peak positions is considered to enable control of the distribution of pores formed in the carbon fiber sheet. Furthermore, the A / B ratio can be controlled by adjusting the ratio between the fiber diameter and density of the first organic fiber and the fiber diameter and density of the second organic fiber, as well as the overall density of the carbon fiber sheet. In addition, increasing the proportion of organic fibers having a small fiber diameter tends to lower the A / B ratio. Further, the total of A and B (total void volume) can be controlled by changing the content of organic components other than organic fibers (for example, organic fillers).

[0041] As one example, the organic fibers preferably include organic short fibers having an average fiber length of 10 to 500 µm (preferably 20 to 300 µm or 50 to 200 µm), and organic long fibers having an average fiber length of more than 500 µm and 10000 µm or less (preferably 1000 to 8000 µm or 2000 to 6000 µm). In other words, the organic fibers are preferably a mixture of organic short fibers and organic long fibers. The ratio of the average fiber length of the organic long fibers to the average fiber length of the organic short fibers (organic long fibers / organic short fibers) is preferably 2 to 200, 5 to 150, 10 to 100, 15 to 80, or 20 to 60. When such a ratio is satisfied, the organic fibers have sufficiently separated peaks in the average fiber length distribution, and a carbon fiber sheet having excellent performance is easily formed. The average fiber diameter of the organic short fibers is preferably 0.2 to 10 µm, 0.5 to 5 µm, or 0.8 to 2 µm. The average fiber diameter of the organic long fibers is preferably more than 10 µm and 200 µm or less, 20 to 100 µm, or 30 to 80 µm. Based on the total amount of the carbon fiber sheet, the content of each of the organic short fibers and the organic long fibers is preferably more than 1% by mass, 2% by mass or more, 3% by mass or more, or 4% by mass or more, and is preferably less than 12% by mass, 11% by mass or less, 10% by mass or less, or 8% by mass or less. The ratio of the content of the organic long fibers to the content of the organic short fibers (organic long fibers / organic short fibers) is preferably 0.10 to 10.0, 0.20 to 5.0, 0.33 to 3.3, 0.50 to 2.0, 0.60 to 1.7, or 0.80 to 1.3.

[0042] <Basis Weight> The basis weight of the carbon fiber sheet can be appropriately changed depending on the application and the like, and is not particularly limited. From the viewpoint of processability and the like, the basis weight of the carbon fiber sheet is, for example, 50 g / m ２ or more, 100 g / m ２ or more, or 200 g / m ２ or more, and is 500 g / m ２ or less, 400 g / m ２ or less, or 300 g / m ２The following is preferable: (Method for measuring basis weight) A carbon fiber sheet cut to 125 mm x 400 mm is used as a measurement sample. The measurement sample is placed on an electronic balance and its mass is measured. The measured mass is divided by the sample size to obtain the basis weight of one sample. The basis weight is measured for five samples, and the average value is taken as the basis weight of the carbon fiber sheet.

[0043] <Coefficient of Variation of Basis Weight> The coefficient of variation of the basis weight of the carbon fiber sheet measured under the following measurement conditions is preferably 0.100 or less, 0.080 or less, or 0.060 or less. [Measurement Conditions] 4 cm x 4 cm test pieces are drawn from 20 arbitrary locations on the carbon fiber sheet. The basis weight of each drawn test piece is measured in an oven-dry state, and the coefficient of variation is calculated from the average value and standard deviation of the basis weight.

[0044] Because the coefficient of variation of the basis weight of the carbon fiber sheet is within this range, variations in strength and crack resistance in the direction of the sheet surface are reduced, making the sheet less prone to tearing even when wet with resin components, and less prone to cracking when the sheet is wrapped around a core pipe with a high curvature. Furthermore, when the carbon fiber sheet is applied as an insulating material, variations in thermal insulation performance in the direction of the sheet surface are reduced, making it easier to achieve excellent thermal insulation effects.

[0045] <Thickness> The thickness of the carbon fiber sheet is preferably 500 μm or more, 1000 μm or more, or 1200 μm or more, and preferably 2500 μm or less, 2000 μm or less, or 1500 μm or less. By setting the thickness of the carbon fiber sheet within this range, appropriate strength is achieved, resin components can be impregnated appropriately, and the sheet is less likely to tear even when wet with resin components. (Method of measuring thickness) A carbon fiber sheet cut to 125 mm x 400 mm is used as a measurement sample. The thickness of a total of 6 points is measured with a thickness gauge near the four corners of the measurement sample and at 2 points in the middle of the long side, and the average value is taken as the thickness of one sample. The thickness of 5 samples is measured and the average value is taken as the thickness of the carbon fiber sheet.

[0046] <Density> The density of the carbon fiber sheet is 0.10 g / cm³.３ or more, preferably 0.15 g / cm ３ or more, or 0.18 g / cm ３ or more, and 0.50 g / cm ３ or less, preferably 0.40 g / cm ３ or less, or 0.30 g / cm ３ or less. By setting the density of the carbon fiber sheet within this range, the sheet has appropriate strength, facilitates proper resin impregnation, and is less prone to sheet breakage during resin impregnation. The density is calculated from the thickness and mass measured by the method described above.

[0047] <<Manufacturing Method>> Hereinafter, an example of the method for manufacturing a carbon fiber sheet according to the present disclosure will be described.

[0048] The carbon fiber sheet according to the present disclosure can be manufactured by wet papermaking. More specifically, the carbon fiber sheet according to the present disclosure can be obtained by performing a raw material preparation step, a papermaking step, and a drying step. Each step will be described below.

[0049] <Raw Material Preparation Step> Each raw material (carbon fiber, organic fiber, other components, liquid medium, etc.) is uniformly dispersed to prepare a raw material slurry. The carbon fiber, organic fiber, other components and the like are as described above.

[0050] The liquid medium is usually water. The liquid medium may also be a liquid medium other than water that can be used for papermaking (for example, an aqueous medium such as alcohol), or a mixture of water and a liquid medium other than water. The solid content concentration in the raw material slurry may be appropriately set in consideration of manufacturing ease, manufacturing cost, etc., and is not particularly limited.

[0051] <Papermaking Step> The raw material slurry is papermaked with a known papermaking machine to form a moisture-containing fiber sheet (wet sheet).

[0052] As the papermaking machine used in the papermaking step, a papermaking machine applied to general papermaking technology can be applied, and is not particularly limited. Examples of papermaking machines include Fourdrinier papermaking machines, cylinder papermaking machines, inclined papermaking machines, twin-wire papermaking machines, and combination papermaking machines formed by combining same-type or different-type papermaking machines selected from the above.

[0053] Here, during the papermaking process, by controlling the flow (turbulence) during slurry supply, such as by changing the supply amount in the headbox, unevenness in concentration and pressure is eliminated, and structural variations in the carbon fiber sheet (coefficient of variation of basis weight of the carbon fiber sheet) are reduced.

[0054] <Drying Process> The moisture contained in the wet sheet is dried to form a carbon fiber sheet.

[0055] The drying equipment used in the drying process is not particularly limited and can be any equipment that is generally used for drying carbon fiber sheets. Examples of drying equipment include Yankee dryers, rotary dryers, hand dryers, air dryers, cylinder dryers, suction drum dryers, and infrared dryers.

[0056] The drying temperature is not particularly limited and can be 100 to 300°C, for example.

[0057] The drying time is not particularly limited and can be adjusted so that the moisture content in the wet sheet is sufficiently low.

[0058] <<Applications>> The carbon fiber sheet according to this disclosure has excellent performance and can be applied to a variety of applications. The carbon fiber sheet according to this disclosure is preferably used as a thermal insulation material. More specifically, it is preferably used as a carbon fiber molded thermal insulation material obtained by impregnating the carbon fiber sheet according to this disclosure with a resin component (curable resin component). The carbon fiber molded thermal insulation material may be a fired product obtained by high-temperature firing. Furthermore, since the carbon fiber sheet according to this disclosure is less prone to cracking even when wrapped around a core pipe or the like with a high curvature, it is preferably applied as a thermal insulation material to be placed in areas with complex shapes.

[0059] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following.

[0060] <<Example 1>> A raw material slurry was prepared by mixing carbon fibers, organic fibers, and other components so that the content of each component in the resulting carbon fiber sheet was as shown in Table 1, and then adding water.

[0061] Using an inclined paper machine, paper sheets were formed from raw material slurry so that the thickness, density, and basis weight of the resulting carbon fiber sheets were as shown in Table 1.

[0062] The papermaking sheet was dried using a Yankee dryer to obtain the carbon fiber sheet according to Example 1.

[0063] <<Example 2-19, Comparative Example 1-4>> Laminates according to Example 2-19 and Comparative Example 1-4 were obtained in the same manner as in Example 1, except that the raw materials used were changed to those shown in Table 1-2, and the thickness and density were changed.

[0064] For each example and comparative example of carbon fiber sheet, the distribution of pore size (diameter of the area without organic components) and the coefficient of variation of basis weight were measured according to the method described above. The measurement results are shown in Tables 1 and 2.

[0065] In Example 19, the amount of slurry deposited in the headbox during the papermaking process was set to 5 L, while in the other examples and comparative examples, the amount of slurry deposited in the headbox during the papermaking process was set to 20 L to control the variation in basis weight of the carbon fiber sheet.

[0066] Note that all organic fibers shown in Table 1-2 are fibrillated.

[0067] <<Measurement / Evaluation>> For each example and comparative example, the carbon fiber sheets were evaluated for wet tensile strength and winding performance according to the evaluation method described below. The evaluation results are shown in Tables 1 and 2.

[0068] <Wet Tensile Strength Evaluation> Carbon fiber sheets were cut to a width of 15 mm and a length of 150 mm, and then wet by immersion in methanol for 1 minute. Next, the wet carbon fiber sheets were placed in a Tensilon universal tester with a chuck distance of 100 mm, and the tensile strength was measured at a speed of 200 mm / min. Five samples were used, and the average tensile strength was calculated and evaluated based on the following criteria: A: 3.0 N / 15 mm or more B: 2.0 N / 15 mm or more and less than 3.0 N / 15 mm C: 1.0 N / 15 mm or more and less than 2.0 N / 15 mm D: Less than 1.0 N / 15 mm

[0069] <Wrapping Evaluation> A carbon fiber sheet was cut to a width of 30 mm and a length of 100 mm. The short side of the carbon fiber sheet was brought into contact with a cylinder, and the sample was wrapped around the cylinder once. Starting with a cylinder with an outer diameter of 30 mm, the carbon fiber sheet was wrapped around cylinders with an outer diameter of 20 mm and then 10 mm in order. The outer diameter of the cylinder around which the sheet could be wrapped without causing cracks was measured, and the following scores were given: 10 points: Can be wrapped around an outer diameter of 10 mm 7 points: Can be wrapped around an outer diameter of 20 mm 3 points: Can be wrapped around an outer diameter of 30 mm 0 points: Cannot be wrapped around an outer diameter of 30 mm Furthermore, the average score was calculated using five samples, and the results were evaluated based on the following criteria: A: 8.0 points or higher B: 6.0 points or higher but less than 8.0 points C: 3.0 points or higher but less than 6.0 points D: Less than 3.0 points

[0070]

[0071]

[0072] According to the present invention, a carbon fiber sheet can be obtained that is less prone to tearing even in a wet state and has appropriate flexibility. Such a carbon fiber sheet can be used without problems even when impregnated with resin components, and has excellent processability and moldability, making it preferably usable as an insulating material such as molded insulating material. Cross-reference of related applications

[0073] This application claims priority over Japanese Patent Application No. 2025-48786, filed with the Japan Patent Office on 24 March 2025, all of which disclosures are incorporated herein by reference in their entirety.

Claims

1. A carbon fiber sheet containing carbon fibers and organic fibers, wherein the content of the organic fibers is 3 to 20% by mass based on the total mass of the carbon fiber sheet, and the organic fibers include one or more selected from the group consisting of cellulose fibers, acrylic fibers, polyamide fibers, polyester fibers, vinylon fibers, and polyurethane fibers, and the carbon fiber sheet is analyzed according to the following measurement conditions, and when the percentage of the area occupied by the portion without organic components with an equivalent circle diameter of 1 to 4 μm is A%, and the percentage of the area occupied by the portion without organic components with an equivalent circle diameter of 10 to 40 μm is B%, the ratio of A / B is 0.033 to 0.

125. [Measurement conditions] A scanning electron microscope (product name: SU5000, manufactured by Hitachi High-Tech Corporation) and an EDS system (product name: Aztec, manufactured by Oxford Corporation) are used as the measuring devices. EDS analysis mapping is performed at a magnification of 200x with a field of view area of ​​1260 μm × 940 μm. Regions corresponding to organic components where "C" and "O" and / or "N" are detected are defined as organic regions, and regions other than organic regions are defined as regions without organic components. The images obtained by EDS detection are analyzed using the image analysis software "WinROOF" (manufactured by Mitani Shoji Co., Ltd.). For each region without organic components, the equivalent circle diameter is calculated from its area. The percentage of the area occupied by regions without organic components where the equivalent circle diameter is calculated to be in the range of 1 to 4 μm is defined as A%, and the percentage of the area occupied by regions without organic components where the equivalent circle diameter is calculated to be in the range of 10 to 40 μm is defined as B%.

2. The carbon fiber sheet according to claim 1, wherein the average fiber length of the carbon fibers is 200 to 6000 μm.

3. The carbon fiber sheet according to claim 1 or 2, wherein the average fiber diameter of the carbon fibers is 5 to 20 μm.

4. The density of the carbon fiber sheet is 0.18 to 0.30 g / cm³. ３ The carbon fiber sheet according to claim 1 or 2.

5. The carbon fiber sheet according to claim 1 or 2, wherein the coefficient of variation of the basis weight of the carbon fiber sheet measured by the following measurement conditions is 0.060 or less. [Measurement conditions] 4 cm x 4 cm test pieces are drawn from any 20 locations on the carbon fiber sheet. The basis weight of each drawn test piece is measured in an oven-dry state, and the coefficient of variation is calculated from the average value and standard deviation of the basis weights.

6. A carbon fiber sheet according to claim 1 or 2, for use as an insulating material.

7. A carbon fiber sheet comprising carbon fibers and organic fibers, wherein the content of the organic fibers is 3 to 20% by mass based on the total mass of the carbon fiber sheet, the organic fibers comprise one or more selected from the group consisting of cellulose fibers, acrylic fibers, polyamide fibers, polyester fibers, vinylon fibers, and polyurethane fibers, the organic fibers comprise organic staple fibers having an average fiber length of 10 to 500 μm and organic filament fibers having an average fiber length of more than 500 μm and 10,000 μm or less, the ratio of the average fiber length of the organic filament fibers to the average fiber length of the organic staple fibers (organic filament fibers / organic staple fibers) is 2 to 200, and the content of the organic staple fibers and the organic filament fibers is more than 1% by mass and less than 12% by mass, based on the total mass of the carbon fiber sheet.

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