JP2015180786A - carbon fiber - Google Patents

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JP2015180786A
JP2015180786A JP2015044434A JP2015044434A JP2015180786A JP 2015180786 A JP2015180786 A JP 2015180786A JP 2015044434 A JP2015044434 A JP 2015044434A JP 2015044434 A JP2015044434 A JP 2015044434A JP 2015180786 A JP2015180786 A JP 2015180786A
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fiber
carbon fiber
voids
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JP6432396B2 (en
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喬昭 山下
Takaaki Yamashita
喬昭 山下
潤 渡邉
Jun Watanabe
潤 渡邉
文彦 田中
Fumihiko Tanaka
文彦 田中
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Toray Industries Inc
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Abstract

PROBLEM TO BE SOLVED: To provide a carbon fiber with a narrow variation in monofilament strength and with excellent tensile strength, and enable excellent mechanical characteristics with a narrow variation in tensile strength to be expressed even in CFRP by using such a carbon fiber.SOLUTION: This invention provides a carbon fiber in which the Weibull shape modulus of monofilament strength in sample length 1 mm is 6.5 or more and 9.4 or less and the scale parameter is 280-350 mN.

Description

本発明は、航空機部材、宇宙機部材、自動車部材および船舶部材をはじめとして、ゴルフシャフトや釣竿等のスポーツ用途およびその他一般産業用途に好適に用いられる炭素繊維に関するものである。より詳しくは、本発明は炭素繊維内部に特定のボイドを有し、単繊維強度のバラツキが小さいために、高い複合材料引張強度と小さな強度バラツキを発現する炭素繊維に関する。   The present invention relates to a carbon fiber which is suitably used for sports applications such as golf shafts and fishing rods and other general industrial applications, including aircraft members, spacecraft members, automobile members, and ship members. More specifically, the present invention relates to a carbon fiber that has a specific void inside the carbon fiber and exhibits a high composite material tensile strength and a small strength variation because the single fiber strength variation is small.

炭素繊維は、低い比重を有するという特徴に加え、高い比強度および比弾性率を有するため、複合材料用補強繊維として、スポーツ用途、航空・宇宙用途、自動車、土木・建築、圧力容器および風車ブレードなどの一般産業用途に幅広く展開されつつある。さらに、炭素繊維に対して更なる高性能化による部材軽量化の要請が高い。特に、樹脂含浸ストランド（以下、単にストランドと述べる）強度を向上させるとともに、そのバラツキが小さくなる炭素繊維が求められている。ストランド強度とは、一種の複合材料引張強度であり、そのバラツキが小さくなることで、部材軽量化につながるのである。しかしながら、複合材料物性のバラツキを小さくする炭素繊維の特性については定量的には明らかにされてこなかった。   Carbon fiber has high specific strength and specific elastic modulus in addition to low specific gravity, so it can be used as a reinforcing fiber for composite materials in sports applications, aerospace applications, automobiles, civil engineering / architecture, pressure vessels and windmill blades. Widely deployed in general industrial applications such as Furthermore, there is a high demand for weight reduction of carbon fibers by further improving performance. In particular, there is a need for carbon fibers that improve the strength of resin-impregnated strands (hereinafter simply referred to as “strands”) and reduce variations. The strand strength is a kind of composite material tensile strength, and its variation is reduced, which leads to weight reduction of the member. However, the characteristics of carbon fibers that reduce the variation in composite material properties have not been clarified quantitatively.

一方、炭素繊維自体の引張強度バラツキについては過去いくつかの報告例がある（特許文献１〜４）。炭素繊維は、単繊維引張強度（以下、単に単繊維強度と述べる）試験を行った際の引張強度バラツキを通常ワイブル分布で表現し、ワイブル形状係数が大きいほど引張強度バラツキが小さいと知られている。ただし、炭素繊維引張強度のワイブル形状係数は３〜７と、引張強度バラツキが大きいと知られていた。また、試長が５ｍｍ未満で試験を行ったときにはクランプ効果により単繊維強度が正しく測定できないと知られていた（非特許文献１）ため、試長が５ｍｍ未満の単繊維強度分布については十分に議論されてこなかった。   On the other hand, there are some past reports on the tensile strength variation of the carbon fiber itself (Patent Documents 1 to 4). Carbon fiber is expressed as a normal Weibull distribution of tensile strength variation when a single fiber tensile strength (hereinafter simply referred to as single fiber strength) test is performed. It is known that the larger the Weibull shape factor, the smaller the tensile strength variation. Yes. However, it has been known that the Weibull shape factor of the carbon fiber tensile strength is 3 to 7, and the tensile strength variation is large. In addition, it was known that the single fiber strength could not be measured correctly due to the clamping effect when the test was conducted with a test length of less than 5 mm (Non-Patent Document 1). It has not been discussed.

炭素繊維は、一般的に脆性材料であることから欠陥サイズ分布により引張強度が支配される。ただし、欠陥先端の形状や欠陥位置、さらに構造に起因する破壊靱性値によっても引張強度は影響を受ける。炭素繊維の代表的な欠陥には、表面欠陥とボイドがあり、ボイドについて議論されている例がある（特許文献５〜８）。特許文献５および６では、炭素繊維の芯部に単一の中空部を有することで見かけ比重を低く制御した技術が提案されているが、非常に大きな中空部を有していることでストランド強度は十分なものではなかった。特許文献７では、炭素繊維内部に有するボイドの量を極めて少なくしてストランド強度の向上を図った技術が提案されているものの、ボイド分布についての制御は不十分であり、炭素繊維の単繊維強度分布を制御できるものではなかった。特許文献８では、炭素繊維内部のボイドを少なくすることで、ストランド強度の更なる向上を図った技術が提案されている。しかしながら、該技術による炭素繊維表層におけるボイド制御では、ボイド位置が炭素繊維表層から深すぎ、また炭素繊維単繊維内応力分布の制御ができていなかったために、単繊維間の強度バラツキおよび複合材料引張強度のバラツキを抑えるには不十分であった。   Since carbon fibers are generally brittle materials, the tensile strength is governed by the defect size distribution. However, the tensile strength is also affected by the shape of the defect tip, the position of the defect, and the fracture toughness value resulting from the structure. Typical defects of carbon fibers include surface defects and voids, and there are examples in which voids are discussed (Patent Documents 5 to 8). Patent Documents 5 and 6 propose a technique in which the apparent specific gravity is controlled to be low by having a single hollow portion in the core portion of the carbon fiber, but the strand strength by having a very large hollow portion. Was not enough. In Patent Document 7, although a technique for improving the strand strength by extremely reducing the amount of voids in the carbon fiber is proposed, the control on the void distribution is insufficient, and the single fiber strength of the carbon fiber The distribution could not be controlled. In patent document 8, the technique which aimed at the further improvement of strand strength by reducing the void inside carbon fiber is proposed. However, in the void control on the carbon fiber surface layer by this technique, the void position is too deep from the carbon fiber surface layer, and the stress distribution within the carbon fiber single fiber could not be controlled. It was insufficient to suppress the intensity variation.

特開２０１０−０１３７７２号公報JP 2010-013772 A 特開２００９−２５６８３３号公報JP 2009-256833 A 特開平４−２２２２２９号公報JP-A-4-222229 特開２００２−２６６１７３号公報JP 2002-266173 A 特開平３−２４１０１４号公報JP-A-3-241014 特開２００６−２８３２２６号公報JP 2006-283226 A 特開２０１０−２２９５７３号公報JP 2010-229573 A 国際公開第２０１０−１４３６８０号International Publication No. 2010-143680

ジャーナル・オブ・マテリアルス・サイエンス、１９９１年、２６、ｐ．３１０７Journal of Materials Science, 1991, 26, p. 3107

上述したように、炭素繊維内部に存在するボイドの量や大きさ、分布を特定の範囲に制御させて、機械的特性の向上を図った炭素繊維はなかった。本発明は、炭素繊維内部に特定のボイドを有することで、試長１ｍｍの単繊維強度のバラツキが小さく、かつ高い引張強度を達成する炭素繊維を提供することを目的とする。   As described above, there has been no carbon fiber whose mechanical properties are improved by controlling the amount, size, and distribution of voids present in the carbon fiber within a specific range. An object of the present invention is to provide a carbon fiber that has a specific void inside the carbon fiber, thereby achieving a small tensile strength variation of a single fiber having a test length of 1 mm and achieving a high tensile strength.

本発明者らは、炭素繊維表層付近に存在するボイドの量や大きさ、分布を特定の範囲に制御させることで、炭素繊維の短試長領域の強度分布を狭く制御して、ストランド強度のバラツキを抑制できることを見出した。   By controlling the amount, size, and distribution of voids existing in the vicinity of the carbon fiber surface layer to a specific range, the present inventors have narrowly controlled the strength distribution in the short test length region of the carbon fiber, and the strand strength. It has been found that variation can be suppressed.

上記目的を達成する本発明は次の構成を有する。すなわち本発明は、本明細書中で定義される方法で評価する、試長１ｍｍの単繊維強力のワイブル形状係数が６．５〜９．４、ワイブル尺度母数が２８０〜３５０ｍＮであることを特徴とする炭素繊維である。   The present invention for achieving the above object has the following configuration. That is, according to the present invention, the Weibull shape factor of a single fiber strength with a test length of 1 mm evaluated by the method defined in this specification is 6.5 to 9.4, and the Weibull scale parameter is 280 to 350 mN. It is a characteristic carbon fiber.

また、好ましい態様として、繊維径方向の断面の重心を含む繊維軸と垂直方向の断面においてボイドを０．００１〜０．０２面積％含有し、含有するボイドの繊維径方向の平均幅が３．０〜７．０ｎｍであり、本明細書中で定義されるボイドの局所集中率が２５面積％以上である単繊維を３３％以上含有すること、単繊維の繊維径方向の断面の単繊維表面から繊維径方向に５．０〜１６．０ｎｍの距離に断面内の全ボイドのうちの４５面積％以上のボイドを含む単繊維を５０％以上含有すること、単繊維の繊維径方向の断面の繊維の短径が６．０〜８．０μｍであること、本明細書中で定義される方法で評価する試長１０ｍｍの単繊維強力のワイブル形状係数が３．０〜６．０であること、表面積比が１．０２〜１．０８であること、単繊維断面の長径を４等分した点を垂直に交わる辺の最も短い辺から数えて１番目と３番目の比が１．０５〜１．２５となる卵形断面である単繊維を５０％以上含む炭素繊維である。   Further, as a preferred embodiment, 0.001 to 0.02 area% of voids are contained in the cross section perpendicular to the fiber axis including the center of gravity of the cross section in the fiber radial direction, and the average width of the contained voids in the fiber radial direction is 3. The surface of the single fiber having a cross section in the fiber radial direction of the single fiber, containing 0 to 7.0 nm and containing 33% or more of the single fiber having a local concentration ratio of voids as defined in this specification of 25 area% or more 50% or more of single fibers containing 45% by area or more of all voids in the cross section at a distance of 5.0 to 16.0 nm in the fiber diameter direction from the fiber diameter direction of the single fiber The short axis of the fiber is 6.0 to 8.0 μm, and the single fiber strength Weibull shape factor of 10 mm of the test length evaluated by the method defined in the present specification is 3.0 to 6.0. , Surface area ratio is 1.02-1.08, single fiber 50% or more of monofilaments having an oval cross section in which the first and third ratios are 1.05 to 1.25, counting from the shortest side of the side perpendicularly intersecting a point obtained by dividing the major axis of the surface into four equal parts Carbon fiber.

本発明は、紡糸段階での糸条の凝固状態を特定の状態に制御することにより、耐炎化、炭化工程を経て得られる炭素繊維表層に含まれるボイドの量や大きさ、分布を特定の範囲に制御することができ、炭素繊維の短試長領域の強度分布を狭く制御して、ストランド強度のバラツキを抑制できる。   The present invention controls the amount, size, and distribution of voids contained in the carbon fiber surface layer obtained through the flameproofing and carbonization processes by controlling the solidification state of the yarn at the spinning stage to a specific state. The strength distribution in the short test length region of the carbon fiber can be controlled to be narrow, and variations in strand strength can be suppressed.

図１は、炭素繊維の繊維径方向のＴＥＭ像を示す図である。FIG. 1 is a diagram showing a TEM image of carbon fibers in the fiber diameter direction.

本発明の炭素繊維は、炭素繊維表層付近の特定範囲にボイドを含有させることで短試長領域の引張強力分布を制御できるものである。具体的には、本発明の炭素繊維は、試長１ｍｍの単繊維強力のワイブル形状係数が６．５〜９．４、ワイブル尺度母数が２８０〜３５０ｍＮである。試長１ｍｍの単繊維強力は、単繊維コンポジット法（詳細は後述する）により評価する。単繊維強度を測定する手法に、単繊維を直接引っ張る単繊維引張試験があるが、クランプ効果により試長が５ｍｍ未満と短い場合には正しく評価ができない。そのため、単繊維コンポジットに応力を与えて、単繊維をコンポジット中で破断させた挙動を調べることによって試長１ｍｍ領域の強度分布を評価する方法がある。本発明では、単繊維コンポジットを４点曲げ試験して与えた歪みに対する破断数（個／１０ｍｍ）を評価する。その破断数７〜１５個の挙動を後述の式で解析することでワイブル形状係数と尺度母数を解析する。一般的な炭素繊維の長試長領域のワイブル形状係数は４〜６程度であるが、本手法で評価する短試長領域のワイブル形状係数は１０〜２０程度である。ワイブル形状係数は大きいほどバラツキが小さいことを示すが、複合材料引張強度を高く、そのバラツキを小さくするためには、長試長領域のワイブル形状係数を４〜６のままに、短試長領域のワイブル形状係数を本発明の範囲に制御することが重要である。試長１ｍｍの単繊維強力のワイブル形状係数が６．５未満の場合には、複合材料引張強度のばらつきが抑制できず、９．４を超えると複合材料引張強度が低下する。その強力分布をワイブル分布解析した形状係数は、好ましくは６．５〜８．５であり、より好ましくは７．０〜８．５である。ワイブル形状係数をかかる範囲に制御するためには、ボイドの大きさと分布、量、ボイド位置（繊維表面からの深さ）を制御する（詳細は後述）。また、単繊維強力の尺度母数は大きいほど短試長領域での炭素繊維の引張強度が高いことを示し、炭素繊維直径が大きくても複合材料引張強度の発現も大きくなる。炭素繊維は一般的に直径を大きくしていくと内層部分に引張強度の低い構造を有するため、直径を大きくしても強力が高まりにくいが、直径が大きいと生産性が高まるために大きな直径の炭素繊維を用いても複合材料引張強度を大きく発現することが好ましい。そこで、炭素繊維直径の効果も含んだ、単繊維当たりの最大荷重（単繊維強力）を本発明では用いている。かかる尺度母数は２８０ｍＮ以上であれば複合材料引張強度が高く、３５０ｍＮもあれば十分である。尺度母数をかかる範囲に制御することは、ボイドの大きさを小さくすることで達成できる。   The carbon fiber of the present invention can control the tensile strength distribution in the short test length region by containing a void in a specific range near the surface of the carbon fiber. Specifically, the carbon fiber of the present invention has a single fiber strength Weibull shape factor of 6.5 to 9.4 and a Weibull scale parameter of 280 to 350 mN. The single fiber strength of a test length of 1 mm is evaluated by a single fiber composite method (details will be described later). As a method for measuring the single fiber strength, there is a single fiber tensile test in which a single fiber is pulled directly. However, when the test length is as short as less than 5 mm due to a clamping effect, a correct evaluation cannot be performed. Therefore, there is a method for evaluating the strength distribution in the 1 mm test length region by applying a stress to the single fiber composite and examining the behavior of breaking the single fiber in the composite. In the present invention, the number of breaks (pieces / 10 mm) with respect to the strain applied to the single fiber composite by a 4-point bending test is evaluated. The Weibull shape factor and the scale parameter are analyzed by analyzing the behavior of the number of breaks of 7 to 15 using the following formula. The Weibull shape factor of the long test length region of a general carbon fiber is about 4 to 6, but the Weibull shape factor of the short sample length region evaluated by this method is about 10 to 20. The larger the Weibull shape factor is, the smaller the variation is. However, in order to increase the composite material tensile strength and reduce the variation, the Weibull shape factor in the long test length region is kept at 4 to 6, while the short test length region is kept. It is important to control the Weibull shape factor within the scope of the present invention. When the Weibull shape factor of the single fiber strength with a test length of 1 mm is less than 6.5, the dispersion of the composite material tensile strength cannot be suppressed, and when it exceeds 9.4, the composite material tensile strength decreases. The shape factor obtained by analyzing the strong distribution by Weibull distribution is preferably 6.5 to 8.5, and more preferably 7.0 to 8.5. In order to control the Weibull shape factor within such a range, the size, distribution, amount, and void position (depth from the fiber surface) of the void are controlled (details will be described later). Moreover, the larger the scale parameter of the single fiber strength, the higher the tensile strength of the carbon fiber in the short test length region, and the greater the expression of the composite material tensile strength even if the carbon fiber diameter is large. Carbon fibers generally have a structure with low tensile strength in the inner layer portion as the diameter increases, so it is difficult to increase the strength even if the diameter is increased. Even if carbon fiber is used, it is preferable that the composite material has a high tensile strength. Therefore, the maximum load per single fiber (single fiber strength) including the effect of the carbon fiber diameter is used in the present invention. If the scale parameter is 280 mN or more, the composite tensile strength is high, and 350 mN is sufficient. Controlling the scale parameter to such a range can be achieved by reducing the size of the void.

本発明の炭素繊維では、試長１０ｍｍの単繊維強力のワイブル形状係数が好ましくは３．０〜６．０である。試長１０ｍｍの単繊維強力は、単繊維コンポジット法（詳細は後述する）により評価する。本発明では、単繊維コンポジットを４点曲げ試験して与えた歪みに対する破断数（個／１０ｍｍ）を評価する。その破断数０．３〜２個の挙動を後述の式で解析することでワイブル形状係数を解析する。ワイブル形状係数は大きいほど単繊維強度のバラツキが小さいことを示すが、複合材料引張強度を高く、そのバラツキを小さくするためには、試長１０ｍｍ領域のワイブル形状係数を３．０〜６．０のままに、試長１ｍｍ領域のワイブル形状係数を６．５〜９．４の範囲に制御することが好ましい。試長１０ｍｍの単繊維強力のワイブル形状係数が３．０未満の場合は、単繊維の強度バラツキが大きくなるため、試長１ｍｍの単繊維強力のワイブル形状係数のみでの強度バラツキの抑制は難しくなりやすく、炭素繊維の強度バラツキが小さすぎる場合には逆に複合材料の強度バラツキがおおきくなりやすい。かかる範囲に制御するためには、ボイドの大きさと分布、量、ボイド位置（繊維表面からの深さ）を制御する（詳細は後述）。   In the carbon fiber of the present invention, the single fiber strong Weibull shape factor of a test length of 10 mm is preferably 3.0 to 6.0. The single fiber strength of a test length of 10 mm is evaluated by a single fiber composite method (details will be described later). In the present invention, the number of breaks (pieces / 10 mm) with respect to the strain applied to the single fiber composite by a 4-point bending test is evaluated. The Weibull shape factor is analyzed by analyzing the behavior of the number of breaks of 0.3 to 2 with the following formula. The larger the Weibull shape factor, the smaller the variation in single fiber strength. However, in order to increase the composite material tensile strength and reduce the variation, the Weibull shape factor in the 10 mm sample length region is set to 3.0 to 6.0. As it is, it is preferable to control the Weibull shape factor in the test length 1 mm region in the range of 6.5 to 9.4. When the Weibull shape factor of a single fiber strength with a test length of 10 mm is less than 3.0, the strength variation of the single fiber increases, so it is difficult to suppress the strength variation only with the Weibull shape factor of a single fiber strength of a test length of 1 mm. In contrast, when the strength variation of the carbon fiber is too small, the strength variation of the composite material tends to increase. In order to control within this range, the size and distribution of voids, the amount, and the void position (depth from the fiber surface) are controlled (details will be described later).

本発明の炭素繊維では、ボイドの繊維径方向の平均幅が好ましくは３．０〜７．０ｎｍである。なお、本発明において繊維径方向とは炭素繊維の繊維径の方向を、繊維軸方向とは炭素繊維の繊維軸の方向を表す。繊維径方向と繊維軸方向とは互いに直交する。炭素繊維の引張強度と、破断の開始点となる表面欠陥や表層ボイドといった欠陥サイズとの関係は、その破壊靱性値にも依存するが、引張強度８ＧＰａのときに欠陥サイズ３０ｎｍ程度であることが一般的である。単繊維強度は、ボイド以外の欠陥とボイドとが破断要因として競合するため、ボイドのサイズが単繊維強度と直接比例関係にある訳ではないが、単繊維横断面内の表面欠陥サイズの分布や単繊維の長手方向も含めたボイドサイズの分布を考慮して、ボイドの繊維径方向の平均幅を設定すればよい。炭素繊維内部に含まれるボイドの繊維径方向の平均幅が３．０ｎｍよりも小さい場合は、ボイドが炭素繊維内部にほとんど存在しない可能性が高いことを意味し、複合材料引張強度のバラツキの制御が困難となりやすい。一方、炭素繊維内部に含まれるボイドの繊維径方向の平均幅が７．０ｎｍよりも大きい場合は、短試長領域での炭素繊維破断の起点となる欠陥となりうる大きさのボイドが多数存在する可能性が高いため、複合材料引張強度が大幅に低下しやすい。かかるボイドの繊維径方向の平均幅はより好ましくは３．０〜６．５ｎｍであり、さらに好ましくは３．０〜５．５ｎｍである。炭素繊維内部に含まれるボイドの繊維径方向の平均幅は、以下のようにして求める。まず、炭素繊維の繊維軸と垂直方向に、集束イオンビーム（ＦＩＢ）により厚さ１００ｎｍの薄片を作製し、炭素繊維の繊維径方向の断面に対して透過型電子顕微鏡（ＴＥＭ）により１万倍で観察する。観察像で白い部分をボイドとし、ボイドの端から端の中で最も長くなる部分の長さをボイドの繊維径方向の幅とし、測定した全ボイドの算術平均値をボイドの繊維径方向の平均幅とする。なお、測定は炭素繊維の繊維径方向の断面全体に対して行い、３断面行う。かかるボイドの繊維径方向の平均幅は、主に炭素繊維前駆体繊維の凝固相分離単位を小さく制御することで制御できる。   In the carbon fiber of the present invention, the average width of voids in the fiber diameter direction is preferably 3.0 to 7.0 nm. In the present invention, the fiber diameter direction means the direction of the fiber diameter of the carbon fiber, and the fiber axis direction means the direction of the fiber axis of the carbon fiber. The fiber diameter direction and the fiber axis direction are orthogonal to each other. The relationship between the tensile strength of the carbon fiber and the defect size such as surface defects and surface voids that are the starting points of fracture depends on the fracture toughness value, but when the tensile strength is 8 GPa, the defect size may be about 30 nm. It is common. The single fiber strength is not directly proportional to the single fiber strength because the defects other than voids and voids compete as breakage factors, but the distribution of surface defect size within the single fiber cross section and The average width of the voids in the fiber diameter direction may be set in consideration of the void size distribution including the longitudinal direction of the single fibers. When the average width in the fiber diameter direction of voids contained in the carbon fiber is smaller than 3.0 nm, it means that there is a high possibility that voids are hardly present inside the carbon fiber, and control of variation in composite material tensile strength. Tends to be difficult. On the other hand, when the average width in the fiber radial direction of the voids contained in the carbon fiber is larger than 7.0 nm, there are many voids having a size that can become a defect that becomes the starting point of the carbon fiber breakage in the short test length region. Since the possibility is high, the composite material tensile strength tends to be greatly reduced. The average width of the voids in the fiber diameter direction is more preferably 3.0 to 6.5 nm, and still more preferably 3.0 to 5.5 nm. The average width in the fiber diameter direction of voids contained in the carbon fiber is determined as follows. First, a thin piece having a thickness of 100 nm is produced by a focused ion beam (FIB) in a direction perpendicular to the fiber axis of the carbon fiber, and 10,000 times by a transmission electron microscope (TEM) with respect to a cross section in the fiber diameter direction of the carbon fiber. Observe at. In the observation image, the white part is the void, the length of the longest part from the end of the void is the width in the fiber diameter direction of the void, and the arithmetic average value of all the measured voids is the average in the fiber diameter direction of the void Width. In addition, a measurement is performed with respect to the whole cross section of the fiber diameter direction of carbon fiber, and 3 cross sections are performed. The average width of the voids in the fiber diameter direction can be controlled mainly by controlling the solidified phase separation unit of the carbon fiber precursor fiber to be small.

本発明の炭素繊維は、繊維径方向の断面においてボイドを好ましくは０．００１〜０．０２面積％含有する。炭素繊維内部のボイド含有率が０．００１面積％未満である場合、炭素繊維短試長の単繊維強度にほとんど影響を与えないので、強度バラツキにつながることが多い。かかるボイド含有率が０．０２面積％を超える場合、強度バラツキは抑えられる一方で、炭素繊維内部に存在する平均ボイドサイズが大きくなってくることから、炭素繊維の単繊維強力が低下する。炭素繊維内部のボイド含有率は、以下のようにして求める。まず、炭素繊維の繊維径方向に、集束イオンビーム（ＦＩＢ）により厚さ１００ｎｍの薄片を作製し、炭素繊維の繊維径方向の断面に対して透過型電子顕微鏡（ＴＥＭ）により２千倍で観察する。ここで得られたＴＥＭ画像について、繊維径方向の断面積を計測する。次に、ＴＥＭにより炭素繊維の繊維径方向の断面を１万倍で、繊維断面全体の各要素について観察を行う。観察像で白い部分をボイドとし、ボイドの端から端の中で最も長くなる部分の長さについて、繊維径方向の長さをボイドの長径、ボイドの長径と垂直に交わるように、ボイドの端から端に直線を引いた最も長くなる部分の長さについてボイドの短径とする。なお、測定は炭素繊維の繊維径方向の断面全体に対して３断面行う。測定したボイドの形状を楕円と仮定し、各断面におけるボイド含有率を下記式で算出する。
ボイド含有率（面積％）＝Σ｛（各ボイドの長径（μｍ）／２×（各ボイドの短径（μｍ）／２×π｝／｛炭素繊維断面積（μｍ２）｝。 The carbon fiber of the present invention preferably contains 0.001 to 0.02 area% of voids in the cross section in the fiber radial direction. When the void content in the carbon fiber is less than 0.001 area%, the single fiber strength of the carbon fiber short test length is hardly affected, which often leads to variation in strength. When the void content exceeds 0.02 area%, the strength variation is suppressed, but the average void size existing inside the carbon fiber is increased, so that the single fiber strength of the carbon fiber is lowered. The void content inside the carbon fiber is determined as follows. First, a thin piece having a thickness of 100 nm is produced in the fiber diameter direction of the carbon fiber by a focused ion beam (FIB), and the cross section in the fiber diameter direction of the carbon fiber is observed by a transmission electron microscope (TEM) at a magnification of 2000 times. To do. About the TEM image obtained here, the cross-sectional area of a fiber radial direction is measured. Next, the cross section of the carbon fiber in the fiber radial direction is 10,000 times by TEM, and each element of the entire fiber cross section is observed. In the observation image, the white part is a void, and the length of the longest part from the end of the void to the end of the void is such that the length in the fiber diameter direction intersects the major axis of the void and the major axis of the void perpendicularly. The length of the longest part obtained by drawing a straight line from the end is defined as the minor diameter of the void. In addition, a measurement is performed 3 cross sections with respect to the whole cross section of the fiber diameter direction of carbon fiber. Assuming that the measured void shape is an ellipse, the void content in each cross section is calculated by the following equation.
Void content (area%) = Σ {(major diameter (μm) / 2 of each void / 2 × (minor diameter (μm) / 2 × π} of each void) / {carbon fiber cross-sectional area (μm 2 )}).

なお、求めた各断面のボイド含有率の算術平均値を炭素繊維束のボイド含有率として用いることとする。   In addition, suppose that the arithmetic mean value of the void content rate of each calculated | required cross section is used as the void content rate of a carbon fiber bundle.

本発明の炭素繊維は、本明細書中で定義されるボイドの局所集中率が２５面積％以上であることが好ましい。かかる局所集中率は高ければ高いほど、単繊維間での強度バラツキを抑制することができ、より好ましくは４０面積％以上である。局所集中率は繊維断面内において、特定部位におけるボイドの全ボイド面積に占める面積割合を示す。ボイドが特定部位に集中することにより、最大ボイドサイズの単繊維間における差を減らし、炭素繊維の強度バラツキを抑えることができる。ボイドの局所集中率は、以下のようにして求める。まず、炭素繊維の繊維径方向に、集束イオンビーム（ＦＩＢ）により厚さ１００ｎｍの薄片を作製し、炭素繊維の繊維径方向の断面に対して透過型電子顕微鏡（ＴＥＭ）により２千倍で観察する。ここで得られた断面ＴＥＭ写真に対して、炭素繊維表面の端から端へ最も長い直線を引き、単繊維の長径とする。長径により分割された半円それぞれを、長径の中点を原点として等角に８分割する。長軸と繊維表面の交点２つのうち、長径の中点から見て、より表面の曲率の大きい側の交点を卵形形状の尖頭とする。きわめて真円に近く長軸を決定できない場合は、円の中心と外周上の２点とを通る任意の線分を長軸と決める。このとき、卵形尖頭部から後方にかけて１から８まで順に番号を付す。繊維断面におけるボイドの８分割された繊維断面の各部位の局所集中率は以下の手順で求める。番号１（８）の部位については、半円それぞれの尖頭部に最も近い１の部位に存在するボイドを計測し、全ボイド面積に占める割合を求める。８の部位に関しても同様に求める。半円における他の番号を付された部位の局所集中率は次のようにして求める。番号２〜７においては、２以降の二連続した番号を組(すなわち、２と３、４と５、６と７)として、その部位に存在するボイドを計測し、半円それぞれに全ボイド面積に占める割合を求める。このようにして、８分割された繊維断面の部位（１〜８）について求めた局所集中率の中で最大の値をその単繊維の局所集中率とする。また、番号１の部位への局所集中率を尖頭集中率とする。このように分割し、計測することで、単繊維の周方向に対して繊維断面が８等分されているため、ボイドが均等に遍在している場合には繊維断面における各部位の局所集中率は最大１２．５％程度となる。この局所集中率は凝固状態を制御することによって、制御することが可能であり、略卵形状である場合には、その尖頭部分にボイドが凝集しやすく、尖頭集中率を高めることが容易である。なお、測定は炭素繊維の繊維径方向の断面全体に対して３断面行い、炭素繊維束の局所集中率には、得られた各局所集中率の算術平均値を用いる。ここにおいて各ボイド特性の評価を３断面分測定し、［Ａ］各断面におけるボイド含有率が０．００１〜０．０２面積％であり、かつ、［Ｂ］ボイドの繊維径方向の平均幅が３．０〜７．０ｎｍであり、かつ、［Ｃ］ボイドの局所集中率が２５％以上であることを満たす単繊維断面の測定した断面数に占める割合を、［Ａ］、［Ｂ］および［Ｃ］の条件を満たす単繊維の炭素繊維束内における含有率とする。   The carbon fiber of the present invention preferably has a local concentration rate of voids defined in the present specification of 25 area% or more. The higher the local concentration ratio, the more the strength variation between single fibers can be suppressed, and more preferably 40 area% or more. The local concentration ratio indicates the area ratio of the voids in the specific cross section to the total void area in the fiber cross section. By concentrating the void at a specific site, the difference between the single fibers having the maximum void size can be reduced, and the strength variation of the carbon fiber can be suppressed. The local concentration rate of voids is obtained as follows. First, a thin piece having a thickness of 100 nm is produced in the fiber diameter direction of the carbon fiber by a focused ion beam (FIB), and the cross section in the fiber diameter direction of the carbon fiber is observed by a transmission electron microscope (TEM) at a magnification of 2000 times. To do. With respect to the cross-sectional TEM photograph obtained here, the longest straight line is drawn from end to end on the surface of the carbon fiber to obtain the long diameter of the single fiber. Each semicircle divided by the major axis is divided into eight equiangular points with the midpoint of the major axis as the origin. Of the two intersections between the long axis and the fiber surface, the intersection on the side with the larger curvature of the surface as seen from the midpoint of the major axis is defined as an oval peak. If the long axis cannot be determined very close to a perfect circle, an arbitrary line segment passing through the center of the circle and two points on the outer periphery is determined as the long axis. At this time, numbers are assigned sequentially from 1 to 8 from the egg-shaped cusp to the rear. The local concentration rate of each part of the fiber cross section obtained by dividing the void in the fiber cross section into eight is obtained by the following procedure. For the part with number 1 (8), the void existing in one part closest to the cusp of each semicircle is measured, and the ratio to the total void area is obtained. The same applies to the 8 part. The local concentration ratio of the other numbered parts in the semicircle is obtained as follows. In numbers 2 to 7, two consecutive numbers after 2 are paired (that is, 2 and 3, 4 and 5, 6 and 7), and the voids existing in the part are measured, and the total void area is measured in each semicircle. Find the percentage of In this way, the maximum value among the local concentration ratios obtained for the parts (1 to 8) of the fiber cross section divided into eight is set as the local concentration ratio of the single fiber. Further, the local concentration rate on the part number 1 is defined as the peak concentration rate. By dividing and measuring in this way, the fiber cross section is divided into eight equal parts with respect to the circumferential direction of the single fiber, so that when the voids are evenly distributed, local concentration of each part in the fiber cross section The rate is about 12.5% at maximum. This local concentration rate can be controlled by controlling the coagulation state. If the shape is substantially egg-shaped, voids tend to aggregate at the peak, making it easy to increase the peak concentration rate. It is. In addition, the measurement is performed for three cross sections with respect to the entire cross section in the fiber diameter direction of the carbon fiber, and the arithmetic average value of each obtained local concentration ratio is used as the local concentration ratio of the carbon fiber bundle. Here, the evaluation of each void characteristic was measured for three cross sections, [A] the void content in each cross section was 0.001 to 0.02 area%, and [B] the average width of the voids in the fiber diameter direction was The ratio of the cross section of the single fiber satisfying that the local concentration ratio of [C] void is 25% or more in the range of 3.0 to 7.0 nm is measured by [A], [B] and It is set as the content rate in the carbon fiber bundle of the single fiber which satisfy | fills the condition of [C].

本発明において、長軸とは炭素繊維表面外周における最も離れた２点を通る線分のことを指し、短軸とは長軸の中点と外周上の２点を通り長軸に直交する線分のことを指す。きわめて真円に近く長軸を決定できない場合は、円の中心と外周上の２点とを通る任意の線分を長軸と決める。炭素繊維の繊維軸と垂直断面の短軸長さ（短径）は６．０〜８．０μｍであることが好ましく、より好ましくは６．４〜８．０μｍである。炭素繊維は一般的に繊維外側と中心で応力分布を持つことが多く、炭素繊維径が大きいほど応力分布の影響が大きいことがある。本発明では炭素繊維の短径を６．０μｍ以上とすることで外層部への応力集中を高め、表層付近のボイドで炭素繊維の単繊維強度を制御しやすくすることができる。一方、炭素繊維の短径が８．０μｍを超えると単繊維強度の平均値が低下しやすくなる。なお、炭素繊維の短径は、前駆体繊維の単繊維繊度を調整するとともに、断面円形度を調整するように凝固させれば制御することができる。   In the present invention, the long axis refers to a line segment passing through the two most distant points on the outer periphery of the carbon fiber surface, and the short axis is a line passing through the middle point of the long axis and two points on the outer periphery and orthogonal to the long axis. Refers to minutes. If the long axis cannot be determined very close to a perfect circle, an arbitrary line segment passing through the center of the circle and two points on the outer periphery is determined as the long axis. The minor axis length (minor axis) of the cross section perpendicular to the fiber axis of the carbon fiber is preferably 6.0 to 8.0 μm, more preferably 6.4 to 8.0 μm. In general, carbon fibers often have a stress distribution on the outside and center of the fiber, and the larger the carbon fiber diameter, the greater the influence of the stress distribution. In the present invention, by setting the minor axis of the carbon fiber to 6.0 μm or more, the stress concentration on the outer layer portion can be increased, and the single fiber strength of the carbon fiber can be easily controlled by the void near the surface layer. On the other hand, when the short axis of the carbon fiber exceeds 8.0 μm, the average value of the single fiber strength tends to decrease. The short diameter of the carbon fiber can be controlled by adjusting the single fiber fineness of the precursor fiber and coagulating so as to adjust the circularity of the cross section.

本発明の炭素繊維は、単繊維の繊維径方向の断面の単繊維表面から繊維径方向に５．０〜１６．０ｎｍの距離に断面内の全ボイドのうちの４５面積％以上のボイドを含む単繊維を５０％以上含有することが好ましい。ここで、単繊維表面からの距離はより好ましくは８．０〜１６．０ｎｍ、さらに好ましくは１０．０〜１６．０ｎｍである。通常炭素繊維は、繊維表層から重心方向にかけて弾性率分布を有するため、より表層に応力が集中することが知られている。このため、炭素繊維表層から５．０〜１６．０ｎｍの距離のボイドに応力が集中して欠陥として作用し、最大ボイド径に対応した引張強度で破断することとなる。かかる範囲に繊維束の５０％以上の単繊維において、繊維径方向の断面内の全ボイドのうちの４５面積％以上のボイドの位置を制御しておけば、単繊維強度のバラツキを抑えることができる。かかる位置にあるボイドの、断面内全ボイドに対する面積割合をボイドの表層存在率とする。ボイドの表層存在率が４５面積％未満である場合には、ボイド以外の破壊要因が競合し始めるため、単繊維強度のばらつきは大きくなり、かつ引張強度が落ちやすくなる。かかる単繊維が束内に一定以上存在していることが好ましく、かかる繊維束内に占める単繊維の割合は、６０％以上であることがさらに好ましい。かかる割合は高いほど好ましく、繊維束内に占める繊維の割合が大きくなると、強度制御が容易となり、強度のバラツキを抑えることができる。５０％に満たない場合には、ボイド以外の要因で破断する単繊維が増え始め、単繊維強度がばらつく原因となる。炭素繊維内部に含まれるボイドの繊維径方向に対する繊維表層からの距離は、以下のようにして求める。まず、炭素繊維の繊維軸と垂直方向に、集束イオンビーム（ＦＩＢ）により厚さ１００ｎｍの薄片を作製し、炭素繊維の繊維径方向の断面に対して透過型電子顕微鏡（ＴＥＭ）により１万倍で観察する。観察像で白い部分をボイドとし、ボイドにおける単繊維表面に近い側の端から繊維表面に垂線を垂らしたときに、最も短く引かれる線分を、炭素繊維内部に含まれるボイドの繊維径方向に対する表面からの距離とする。ボイドの表層存在率は、表面からの距離が特に５〜１６ｎｍであるボイドの端から端の中で最も長くなる部分の長さについて、繊維径方向の長さをボイドの長径、ボイドの長径と垂直に交わるように、ボイドの端から端に直線を引いた最も長くなる部分の長さについてボイドの短径とし、ボイドの形状を楕円と仮定して、下記式で算出する。
ボイド表層存在率（面積％）＝Σ｛（各ボイド(表面からの距離＝５〜１６ｎｍ)の長径（μｍ）／２×（各ボイド(表面からの距離＝５〜１６ｎｍ)の短径（μｍ）／２×π｝／｛断面内全ボイド面積（μｍ２）｝。 The carbon fiber of the present invention includes voids of 45% by area or more of all voids in the cross section at a distance of 5.0 to 16.0 nm in the fiber radial direction from the surface of the single fiber in the cross section in the fiber radial direction of the single fiber. It is preferable to contain 50% or more of single fibers. Here, the distance from the single fiber surface is more preferably 8.0 to 16.0 nm, and still more preferably 10.0 to 16.0 nm. Usually, carbon fiber has an elastic modulus distribution from the fiber surface layer to the center of gravity direction, and it is known that stress concentrates more on the surface layer. For this reason, stress concentrates on a void having a distance of 5.0 to 16.0 nm from the surface layer of the carbon fiber, acts as a defect, and breaks at a tensile strength corresponding to the maximum void diameter. In such a range, in a single fiber of 50% or more of the fiber bundle, by controlling the position of 45% by area or more of all voids in the cross section in the fiber radial direction, it is possible to suppress variations in single fiber strength. it can. The area ratio of the voids at such positions to the total voids in the cross section is the void surface layer abundance ratio. When the surface layer abundance ratio of voids is less than 45% by area, fracture factors other than voids start to compete, so the variation in single fiber strength increases and the tensile strength tends to decrease. The single fibers are preferably present in a certain amount or more in the bundle, and the ratio of the single fibers in the fiber bundle is more preferably 60% or more. Such a ratio is preferably as high as possible. When the ratio of the fibers in the fiber bundle is increased, the strength control is facilitated, and variations in strength can be suppressed. If it is less than 50%, the number of single fibers that breaks due to factors other than voids starts to increase, which causes the single fiber strength to vary. The distance from the fiber surface layer to the fiber diameter direction of voids contained in the carbon fiber is determined as follows. First, a thin piece having a thickness of 100 nm is produced by a focused ion beam (FIB) in a direction perpendicular to the fiber axis of the carbon fiber, and 10,000 times by a transmission electron microscope (TEM) with respect to a cross section in the fiber diameter direction of the carbon fiber. Observe at. In the observed image, the white part is a void, and when a perpendicular is suspended from the end of the void close to the single fiber surface to the fiber surface, the shortest line segment is drawn with respect to the fiber diameter direction of the void contained in the carbon fiber. The distance from the surface. The void surface layer abundance ratio is the length of the longest portion of the void from the end of the void, particularly the distance from the surface of 5 to 16 nm. Assuming that the length of the longest portion obtained by drawing a straight line from one end of the void to the other end is a short diameter of the void, and assuming that the shape of the void is an ellipse, the following equation is calculated.
Void surface layer existence ratio (area%) = Σ {(major diameter (μm) of each void (distance from surface = 5 to 16 nm) / 2 × (minor diameter (μm) from each void (distance from surface = 5 to 16 nm)) ) / 2 × π} / {total void area in cross section (μm 2 )}.

なお、測定は炭素繊維の繊維径方向の断面全てにわたって３断面行い、炭素繊維束のボイドの表層存在率には、各断面におけるボイド表層存在率の算術平均値を用いる。また、ボイドの表層存在率が４５面積％以上である単繊維断面の、測定した断面数に占める割合を炭素繊維束内における含有率とする。かかるボイドの位置は、主に炭素繊維前駆体繊維製造時にスキン層厚みを薄く制御することによって達成できる。   In addition, the measurement is performed in three cross sections over all the cross sections in the fiber diameter direction of the carbon fiber, and the arithmetic average value of the void surface layer existence ratio in each cross section is used as the void surface layer existence ratio of the carbon fiber bundle. Moreover, the ratio which occupies for the measured number of cross sections of the cross section of the single fiber whose surface layer existence rate of a void is 45 area% or more is made into the content rate in a carbon fiber bundle. Such void positions can be achieved mainly by controlling the skin layer thickness to be thin during the production of the carbon fiber precursor fiber.

本発明の炭素繊維は、単繊維の繊維径方向の断面の長径を４等分する３点のうち、長径の中点以外の２点をそれぞれ通って長径に直行する２つの線分の長さ（短い方の線分の長さをＬｃ、長い方の線分の長さをＬｄとする。）の比＜Ｌｄ／Ｌｃ＞が１．０５〜１．２５となる略卵形断面とする。また、本発明の炭素繊維において、略卵形断面の単繊維の割合が一定値以上存在していることが好ましい。かかる割合が低いと、単繊維の強度バラツキが大きくなることがある。略卵形断面の単繊維の含有率が５０％以上であれば、単繊維の強度バラツキと単繊維強力の範囲を満足する。かかる割合は高いほどよく、６０％以上がより好ましく、７０％以上がさらに好ましい。本発明において、＜Ｌｄ／Ｌｃ＞は、炭素繊維中のそれぞれの単繊維におけるＬｄ／Ｌｃの算術平均値である。断面形状のパラメーターＬｃ、Ｌｄは、単繊維の断面観察により評価する。引張破断面や研磨断面などを、光学顕微鏡やデジタルマイクロスコープ、走査型電子顕微鏡、透過型電子顕微鏡などで観察して評価することができる。本発明において、単繊維の外周に小さな窪みや欠けが存在する場合は、そのような窪みや欠けが存在しない場合に外周の他の部分の様子から想定される仮想の外周を描き込み、前記解析を行う。ただし、窪みや欠けの最も繊維中心に近い先端と、想定される仮想の外周との距離が、長軸の長さの１割を超える場合はかかる単繊維は炭素繊維束から無視するものとする。炭素繊維の単繊維断面形状は、口金孔配列および前駆体繊維の凝固条件によって制御され、単繊維表層に形成される緻密な層（スキン層）と凝固張力とに影響を受ける。ボイドは緻密な層に対しては形成されづらいため、炭素繊維の断面形状は、ボイドの繊維径方向の面内分布と相関を有する。単繊維断面をかかる略卵形形状に制御した場合、ボイドは卵形尖頭に凝集しやすく、炭素繊維の繊維径方向面内のボイド分布制御を容易とすることができる。   The carbon fiber of the present invention is the length of two line segments that go straight through the major axis through two points other than the midpoint of the major axis among the three points that divide the major axis of the cross section of the single fiber into four equal parts. It is assumed that the ratio <Ld / Lc> is 1.05 to 1.25 (Lc is the length of the shorter line segment and Ld is the length of the longer line segment). Further, in the carbon fiber of the present invention, it is preferable that the ratio of the single fiber having a substantially oval cross section is a certain value or more. When this ratio is low, the strength variation of single fibers may increase. If the content of single fibers having a substantially oval cross section is 50% or more, the range of single fiber strength variation and single fiber strength is satisfied. The higher the ratio, the better, 60% or more is more preferable, and 70% or more is more preferable. In the present invention, <Ld / Lc> is an arithmetic average value of Ld / Lc in each single fiber in the carbon fiber. The parameters Lc and Ld of the cross-sectional shape are evaluated by observing the cross section of the single fiber. A tensile fracture surface, a polished cross-section, and the like can be evaluated by observing with an optical microscope, a digital microscope, a scanning electron microscope, a transmission electron microscope, or the like. In the present invention, when a small dent or chip is present on the outer periphery of the single fiber, a virtual outer periphery assumed from the state of other parts of the outer periphery when such a dent or chip does not exist is drawn, and the analysis I do. However, if the distance between the tip closest to the fiber center of the depression or chip and the hypothetical outer circumference exceeds 10% of the length of the long axis, such single fiber shall be ignored from the carbon fiber bundle. . The single fiber cross-sectional shape of the carbon fiber is controlled by the die hole arrangement and the solidification conditions of the precursor fiber, and is affected by the dense layer (skin layer) formed on the single fiber surface layer and the solidification tension. Since voids are difficult to form in a dense layer, the cross-sectional shape of the carbon fiber has a correlation with the in-plane distribution of voids in the fiber radial direction. When the cross section of a single fiber is controlled to such an approximately oval shape, voids tend to aggregate at the oval peak, and void distribution control in the fiber radial direction plane of the carbon fiber can be facilitated.

また、本発明の炭素繊維は、原子間力顕微鏡を用いて後述する方法により測定される単繊維の表面積比が１．０２〜１．０８であることが好ましく、１．０２〜１．０６であることがより好ましい。上記の表面積比は、炭素繊維の表面の実表面積と投影面積との比で表され、表面の粗さの度合いを示している。表面積比が１に近付く程、平滑であることを意味し、炭素繊維の単繊維強度の向上に有利な傾向にあるものの、表面積比が１．０２以上であると単繊維の強度バラツキを抑制しやすく、１．０８以下であれば表面の皺形態による単繊維強度の低下は小さいため、１．０２〜１．０８の範囲に制御することが好ましい。上記の表面積比は、紡糸方法と凝固方法によって制御され、乾湿式紡糸では平滑な表面となる傾向があるが、凝固においては凝固速度を遅くする、例えば凝固浴中の溶媒濃度を高く設定するなどを行うことでスキン層が薄くなりフィブリルを表面に出し、また、凝固単位を大きくする、例えば凝固温度を高くすることでフィブリルを大きくし、凹凸のある表面とすることができる。ピッチ系炭素繊維ではこのようなフィブリルを反映した凹凸を有することは困難である。   The carbon fiber of the present invention preferably has a surface area ratio of single fibers measured by a method described later using an atomic force microscope of 1.02 to 1.08, and is 1.02 to 1.06. More preferably. The surface area ratio is represented by the ratio between the actual surface area of the carbon fiber surface and the projected area, and indicates the degree of surface roughness. The closer the surface area ratio is to 1, the smoother it is, and there is a tendency to improve the single fiber strength of the carbon fiber. However, when the surface area ratio is 1.02 or more, the strength variation of the single fiber is suppressed. If it is easy and 1.08 or less, since the fall of the single fiber strength by the surface wrinkle form is small, it is preferable to control to the range of 1.02-1.08. The above surface area ratio is controlled by the spinning method and the coagulation method, and there is a tendency for dry and wet spinning to have a smooth surface. However, in coagulation, the coagulation rate is slowed, for example, the solvent concentration in the coagulation bath is set high. By performing the above, the skin layer becomes thin and fibrils are brought out on the surface, and the fibrils can be enlarged by increasing the solidification unit, for example, by increasing the solidification temperature, so that an uneven surface can be obtained. It is difficult for pitch-based carbon fibers to have irregularities reflecting such fibrils.

次に、本発明の炭素繊維の製造方法を説明する。   Next, the manufacturing method of the carbon fiber of this invention is demonstrated.

炭素繊維のボイド量や大きさを制御するためには、炭素繊維前駆体繊維の時点でのボイドを制御する必要がある。焼成では一定サイズ以下のボイドを制御するのは困難であり、炭素繊維の単繊維強度を制御することまでは至らない。炭素繊維前駆体繊維のボイドを制御するためには、ポリアクリロニトリル系重合体溶液を凝固させる、すなわち該重合体と溶媒を相分離させるときの相分離単位の制御、およびその際のスキン層厚みの制御することにより達成される。通常、炭素繊維前駆体を製造する場合には、該相分離単位を小さく制御し、乾燥工程で溶媒（溶媒は水に置換されることが多い）を除去する際に溶媒を閉じ込めていた空間を潰してボイドを含まないようにする。そのため、本発明のような微細な表層ボイドを有する炭素繊維を製造するためには、凝固時の相分離単位を小さく制御して、薄いスキン層を通じてシリコーン油剤を導入し、シリコーン油剤が導入された部分を乾燥緻密化でも緻密化させないことが重要となる。また、凝固相分離時に張力を与えることでボイドが大きくなりやすく、凝固張力でもボイドサイズを調整可能である。   In order to control the void amount and size of the carbon fiber, it is necessary to control the void at the time of the carbon fiber precursor fiber. In firing, it is difficult to control voids of a certain size or less, and it is impossible to control the single fiber strength of carbon fibers. In order to control the voids of the carbon fiber precursor fiber, the polyacrylonitrile-based polymer solution is solidified, that is, the phase separation unit when the polymer and the solvent are phase-separated, and the thickness of the skin layer at that time is controlled. This is achieved by controlling. Usually, when producing a carbon fiber precursor, the phase separation unit is controlled to be small, and the space in which the solvent is confined when the solvent (the solvent is often replaced with water) is removed in the drying step. Crush it so that it does not contain voids. Therefore, in order to produce carbon fibers having fine surface layer voids as in the present invention, the silicone oil is introduced through the thin skin layer by controlling the phase separation unit during solidification to be small. It is important that the portion is not densified even by dry densification. In addition, voids tend to increase by applying tension during solidification phase separation, and the void size can be adjusted by solidification tension.

そのため、本発明において、凝固価を３０〜３４ｇと極めて狭い範囲に制御することが重要であり、好ましくは３１〜３３ｇである。本発明において凝固価とは、紡糸に用いる溶媒５０ｍｌに対して紡糸に用いる重合体を１質量％溶解した溶液に凝固浴液を徐々に滴下し、沈殿生成を開始して溶液が透明から白濁に変化する凝固浴液量（ｇ）と定義する。試験において温度は２５℃に調整する。凝固浴液そのものを滴下すると希釈されすぎて白濁が薄く、白濁開始点の判定が困難になることがあるので、凝固浴液中の凝固促進成分のみを滴下して求めた白濁点から、その必要凝固促進成分量を含む凝固浴液量に換算して凝固価とすることができる。両者の値が異なった場合は、後者を凝固価とする。凝固価は、重合体の分子量や共重合組成、重合体溶液の濃度、溶媒種類および凝固促進成分種類、溶媒濃度によっても変わり、紡糸条件に合わせてそれぞれ測定する必要があるが、特に凝固浴における溶媒の種類および溶媒濃度によって制御することが好ましい。溶媒濃度が高まるほど、凝固促進成分が減少するので凝固価が高まる。凝固価が３０ｇ以上であるとスキン層が薄く、凝固相分離単位が小さくなり、凝固価が３４ｇを超えると凝固が遅くなりすぎて凝固相分離単位が大きくなって結果的に炭素繊維のボイドが増加する。また、本範囲であれば、炭素繊維の断面形状は非円形となる。凝固価は、共重合成分や凝固促進成分とも関係するが、共重合成分を含まないＰＡＮを各種の溶媒に溶解し、水を凝固促進成分として調べると一般的な傾向としてジメチルアセトアミド＜ジメチルホルムアミド＜ジメチルスルホキシド＜塩化亜鉛水溶液＜チオ硫酸ナトリウム水溶液の順に凝固促進成分量を多く必要とする。共重合成分等によっても値は変化するが、ＡＮ１００％、Ｍｗ３２万のＰＡＮを用い、各種溶媒に溶解して、水を凝固促進成分とした場合、各種溶媒による凝固価はそれぞれ、ジメチルアセトアミド４ｇ、ジメチルスルホキシド５ｇ、塩化亜鉛水溶液（６０質量％水溶液）１０ｇ、チオ硫酸ナトリウム水溶液（５４質量％水溶液）２０ｇと異なる値を示す。   Therefore, in the present invention, it is important to control the coagulation value within a very narrow range of 30 to 34 g, preferably 31 to 33 g. In the present invention, the coagulation value means that a coagulation bath solution is gradually added dropwise to a solution in which 1% by mass of a polymer used for spinning is dissolved in 50 ml of a solvent used for spinning to start precipitation, and the solution turns from transparent to cloudy. It is defined as the amount of coagulation bath solution (g) that changes. In the test, the temperature is adjusted to 25 ° C. If the coagulation bath liquid itself is added dropwise, it may be too diluted and white turbidity may be difficult, and it may be difficult to determine the starting point of the white turbidity. It can be set as the coagulation value in terms of the amount of coagulation bath liquid containing the amount of coagulation promoting component. If the two values are different, the latter is regarded as the coagulation value. The coagulation value varies depending on the molecular weight and copolymer composition of the polymer, the concentration of the polymer solution, the type of solvent, the type of coagulation-promoting component, and the solvent concentration and must be measured according to the spinning conditions. It is preferable to control by the kind of solvent and solvent concentration. As the solvent concentration increases, the coagulation promoting component decreases, so the coagulation value increases. When the solidification value is 30 g or more, the skin layer is thin and the solidification phase separation unit is small, and when the solidification value exceeds 34 g, solidification is too slow and the solidification phase separation unit is large, resulting in voids in the carbon fiber. To increase. Moreover, if it is this range, the cross-sectional shape of carbon fiber will be non-circular. The coagulation value is related to the copolymerization component and the coagulation promoting component. When PAN containing no copolymerization component is dissolved in various solvents and water is examined as the coagulation promotion component, dimethylacetamide <dimethylformamide < The amount of coagulation-promoting components is increased in the order of dimethyl sulfoxide <zinc chloride aqueous solution <sodium thiosulfate aqueous solution. Although the value also varies depending on the copolymerization component, etc., when PAN with AN 100% and Mw 320,000 is dissolved in various solvents and water is used as the coagulation promoting component, the coagulation value with each solvent is 4 g of dimethylacetamide, The values are different from 5 g of dimethyl sulfoxide, 10 g of aqueous zinc chloride solution (60% by mass aqueous solution) and 20 g of sodium thiosulfate aqueous solution (54% by mass aqueous solution).

本発明において、凝固浴温度を−５〜１０℃とすることが好ましく、より好ましくは−５〜５℃である。凝固浴温度は溶媒の凝固浴中への拡散速度および凝固促進成分の紡糸溶液への拡散速度に影響を与え、その結果、凝固浴温度が低いほど凝固の相分離単位が緻密となり、ボイドが小さい炭素繊維が得られる。   In the present invention, the coagulation bath temperature is preferably −5 to 10 ° C., more preferably −5 to 5 ° C. The coagulation bath temperature affects the diffusion rate of the solvent into the coagulation bath and the diffusion rate of the coagulation promoting component into the spinning solution. As a result, the lower the coagulation bath temperature, the denser the phase separation unit of coagulation and the smaller the voids. Carbon fiber is obtained.

凝固時の相分離単位を制御するためには、凝固張力を制御することが重要である。凝固張力とは、凝固工程中の凝固浴出箇所で張力を２回測定し、その平均値を意味する。張力は、張力計により走行する糸条を挟み込んで荷重を測定し、その荷重を測定箇所の工程糸条の繊度（ｄｔｅｘ）で割って求めることができる。凝固張力は１．０〜２．５ｍＮ／ｄｔｅｘであり、より好ましくは１．５〜２．５ｍＮ/ｄｔｅｘであり、さらに好ましくは１．８〜２．２ｍＮ／ｄｔｅｘである。凝固張力が１．０ｍＮ／ｄｔｅｘよりも小さいと炭素繊維のボイド量が少なくなりすぎ、一方で、２．５ｍＮ／ｄｔｅｘよりも大きいと、炭素繊維のボイド量が多くなりすぎる。凝固張力は、適宜、凝固糸の走行方向変更角度、凝固浴中ガイドとの接触面積、凝固浴中ガイド表面処理による摩擦係数制御などにより設定することができる。張力を付与する方法を例示すると、下向きに吐出したＰＡＮ溶液を、凝固浴中ガイドを介して凝固糸走行方向を上向きに変更する際に凝固糸とガイドでの摩擦力を利用する方法がある。   In order to control the phase separation unit during solidification, it is important to control the solidification tension. The solidification tension means an average value obtained by measuring the tension twice at a solidification bath exit point during the solidification process. The tension can be obtained by measuring the load by inserting the yarn traveling with a tensiometer and dividing the load by the fineness (dtex) of the process yarn at the measurement location. The solidification tension is 1.0 to 2.5 mN / dtex, more preferably 1.5 to 2.5 mN / dtex, and still more preferably 1.8 to 2.2 mN / dtex. If the solidification tension is less than 1.0 mN / dtex, the amount of voids in the carbon fiber is too small. On the other hand, if the solidification tension is greater than 2.5 mN / dtex, the amount of voids in the carbon fiber is too large. The coagulation tension can be appropriately set by changing the traveling direction change angle of the coagulated yarn, the contact area with the guide in the coagulation bath, friction coefficient control by the guide surface treatment in the coagulation bath, and the like. As an example of a method for applying tension, there is a method of using the frictional force between the coagulated yarn and the guide when the PAN solution discharged downward is changed upward in the coagulating bath traveling direction via the guide in the coagulating bath.

本発明において、ポリアクリロニトリル系重合体とは、少なくともアクリロニトリルが重合体骨格の主構成成分となっているものをいい、主構成成分とは、通常、重合体骨格の８５〜１００ｍｏｌ％を占めることを言う。好ましく用いられるポリアクリロニトリル系重合体は、凝固時の相分離単位を制御する観点から、共重合成分を含む。好ましい共重合成分の量としては、０．５〜２質量％である。共重合成分としては、前記観点からカルボキシル基またはアミド基を一つ以上有するものが好ましく用いられる。例えば、アクリル酸、メタクリル酸、イタコン酸、クロトン酸、シトラコン酸、エタクリル酸、マレイン酸およびメサコン酸が好ましい。また、前記したポリアクリロニトリル系重合体を、ジメチルスルホキシド、ジメチルホルムアミドおよびジメチルアセトアミドなどのポリアクリロニトリル系重合体が可溶な溶媒に溶解して、重合体溶液として用いる。   In the present invention, the polyacrylonitrile-based polymer means that at least acrylonitrile is the main constituent of the polymer skeleton, and the main constituent usually occupies 85 to 100 mol% of the polymer skeleton. say. The polyacrylonitrile-based polymer preferably used includes a copolymer component from the viewpoint of controlling the phase separation unit during solidification. A preferable amount of the copolymer component is 0.5 to 2% by mass. As the copolymer component, those having at least one carboxyl group or amide group are preferably used from the above viewpoint. For example, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid and mesaconic acid are preferred. Further, the polyacrylonitrile polymer described above is dissolved in a solvent in which a polyacrylonitrile polymer such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide or the like is soluble, and used as a polymer solution.

本発明の炭素繊維の製造で好ましく用いられるポリアクリロニトリル系前駆体繊維の製造方法は、乾湿式紡糸法により紡糸口金から吐出させ紡糸する凝固工程と、該凝固工程で得られた繊維を水浴中で洗浄する水洗工程と、該水洗工程で得られた繊維を水浴中で延伸する水浴延伸工程と、該水浴延伸工程で得られた繊維を乾燥熱処理する乾燥熱処理工程からなり、必要に応じて、該乾燥熱処理工程で得られた繊維をスチーム延伸するスチーム延伸工程からなる。   The method for producing a polyacrylonitrile-based precursor fiber preferably used in the production of the carbon fiber of the present invention includes a coagulation step of spinning by spinning from a spinneret by a dry and wet spinning method, and a fiber obtained in the coagulation step in a water bath. A washing step for washing, a water bath drawing step for drawing the fibers obtained in the water washing step in a water bath, and a drying heat treatment step for drying and heat treating the fibers obtained in the water bath drawing step. It consists of the steam drawing process which carries out the steam drawing of the fiber obtained at the drying heat processing process.

本発明において、口金孔の形状を調整することで略卵形の断面形状を有する炭素繊維を得るのに好適な炭素繊維前駆体繊維を得ることができる。口金孔は、目的とする単繊維の断面形状と同じ略卵形とすることもできるが、製糸方法として乾湿式紡糸法を採用する場合、吐出ポリマーがエアギャップを通過する間に合一しやすいように２個以上の孔を近接して配置することも、加工コストの比較的安い円孔を組み合わせるだけで断面形状が略卵形に制御された単繊維を得られる点で好ましい。本発明における好ましい口金孔の形状は当業者が試行錯誤することによって最適化できる。しかしながら、口金孔の形状はこれらに限定して解釈されるべきではない。また、本発明において近接して配置させた２個以上の孔から１本の凝固糸単繊維を得る場合、かかる２個以上の孔をまとめて１つの口金孔と数える。口金孔は、その断面積を０．００２〜０．１ｍｍ２とすることが、機械的特性の発現に有利な単繊維繊度の小さな炭素繊維を得る上で好ましい。孔ピッチや、孔数、孔配置については当業者が容易に最適化できる。 In the present invention, a carbon fiber precursor fiber suitable for obtaining a carbon fiber having a substantially oval cross-sectional shape can be obtained by adjusting the shape of the die hole. The mouthpiece hole can also have an approximately oval shape that is the same as the cross-sectional shape of the target single fiber. However, when the dry and wet spinning method is adopted as the spinning method, the spouted polymer can easily be united while passing through the air gap. It is also preferable to arrange two or more holes close to each other in that a single fiber whose cross-sectional shape is controlled to be substantially oval can be obtained only by combining circular holes with relatively low processing costs. The shape of the preferable nozzle hole in the present invention can be optimized by a person skilled in the art through trial and error. However, the shape of the base hole should not be interpreted as being limited to these. In the present invention, when one coagulated yarn monofilament is obtained from two or more holes arranged close to each other, the two or more holes are collectively counted as one cap hole. The mouthpiece hole preferably has a cross-sectional area of 0.002 to 0.1 mm 2 in order to obtain a carbon fiber having a small single fiber fineness which is advantageous for the expression of mechanical properties. Those skilled in the art can easily optimize the hole pitch, the number of holes, and the hole arrangement.

水洗工程における水浴温度は２０〜１００℃の複数段からなる水洗浴を用い水洗することが好ましい。また、水浴延伸工程における延伸倍率は、２〜６倍であることが好ましい。   The water bath temperature in the water washing step is preferably 20 ° C. to 100 ° C. using a water bath having a plurality of stages. Moreover, it is preferable that the draw ratio in a water bath extending process is 2-6 times.

水浴延伸工程の後、単繊維同士の接着を防止し、炭素繊維の表層ボイドを制御する目的から、糸条にシリコーン油剤を付与することが好ましい。かかるシリコーン油剤は、変性されたシリコーンを用いることが好ましく、耐熱性の高いアミノ変性シリコーンを含有するものを用いることが好ましい。ポリアクリロニトリル前駆体繊維のＳｉ量が０．３〜２．０質量％となるように制御することが好ましい。Ｓｉ量が０．３質量％以上であれば、糸条中表層部分の相分離単位にシリコーン油剤が浸透し、炭素繊維においてボイドを生成することができ、Ｓｉ量が２．０質量％以下であれば、複合材料引張強度に悪影響を及ぼさないことが多い。かかるＳｉ量は、付与する際のシリコーン油剤濃度により調整することができる。   After the water bath drawing step, it is preferable to apply a silicone oil to the yarn for the purpose of preventing adhesion between single fibers and controlling the surface layer voids of the carbon fibers. As such a silicone oil agent, it is preferable to use a modified silicone, and it is preferable to use one containing an amino-modified silicone having high heat resistance. It is preferable to control the Si content of the polyacrylonitrile precursor fiber to be 0.3 to 2.0% by mass. If the amount of Si is 0.3% by mass or more, the silicone oil can penetrate into the phase separation unit of the surface layer portion in the yarn, and voids can be generated in the carbon fiber. The amount of Si is 2.0% by mass or less. If present, the composite tensile strength is often not adversely affected. Such Si amount can be adjusted with the silicone oil agent density | concentration at the time of providing.

前記した水洗工程、水浴延伸工程、油剤付与工程、公知の方法で行われた乾燥熱処理工程の後、スチーム延伸を行うことにより、炭素繊維の製造で好適に用いられるポリアクリロニトリル系前駆体繊維が得られる。本発明において、スチーム延伸は、加圧スチーム中において、少なくとも２倍以上延伸することがよい。   After the above-described water washing step, water bath stretching step, oil agent application step, and drying heat treatment step performed by a known method, by performing steam stretching, a polyacrylonitrile-based precursor fiber suitably used in the production of carbon fiber is obtained. It is done. In the present invention, the steam stretching is preferably performed at least twice or more in the pressurized steam.

以下、本発明の炭素繊維の機械的特性を満足させる方法について記載する。   Hereinafter, a method for satisfying the mechanical properties of the carbon fiber of the present invention will be described.

本発明の炭素繊維を好適に製造する方法において、前記したポリアクリロニトリル系前駆体繊維を耐炎化、予備炭素化、炭素化して、炭素繊維を得る。   In the method for suitably producing the carbon fiber of the present invention, the above-described polyacrylonitrile-based precursor fiber is flame-resistant, pre-carbonized, and carbonized to obtain a carbon fiber.

本発明において、ポリアクリロニトリル系前駆体繊維の耐炎化は暴走反応を生じない範囲でできるだけ高い温度で行うことが好ましく、具体的には２００〜３００℃の空気中において行うことが好ましい。本発明において、耐炎化の処理時間は、好適には１０〜１００分の範囲で適宜選択することができるが、得られる炭素繊維の力学的物性を向上させる目的から、得られる耐炎化繊維の比重が１．３〜１．４の範囲となるように設定することが好ましい。   In the present invention, the flame resistance of the polyacrylonitrile-based precursor fiber is preferably performed at as high a temperature as possible without causing a runaway reaction. Specifically, it is preferably performed in air at 200 to 300 ° C. In the present invention, the flameproofing treatment time can be suitably selected within a range of 10 to 100 minutes, but for the purpose of improving the mechanical properties of the obtained carbon fiber, the specific gravity of the obtained flameproof fiber. Is preferably set in a range of 1.3 to 1.4.

前記耐炎化に引き続いて、予備炭素化を行う。予備炭素化工程においては、得られた耐炎化繊維を、不活性雰囲気中、最高温度５００〜１２００℃において、比重１．５〜１．８になるまで熱処理することが好ましい。   Subsequent to the flame resistance, preliminary carbonization is performed. In the preliminary carbonization step, it is preferable that the obtained flame-resistant fiber is heat-treated in an inert atmosphere at a maximum temperature of 500 to 1200 ° C. until the specific gravity is 1.5 to 1.8.

前記予備炭素化に引き続いて、炭素化を行う。本発明では、炭素化工程において、得られた予備炭化繊維束を不活性雰囲気中、最高温度１２００〜３０００℃において製造することが好ましい。   Subsequent to the preliminary carbonization, carbonization is performed. In the present invention, in the carbonization step, the obtained pre-carbonized fiber bundle is preferably produced at a maximum temperature of 1200 to 3000 ° C. in an inert atmosphere.

炭素化工程の温度は、得られる炭素繊維のストランド弾性率を高める観点からは、高い方が好ましいが、高すぎると高強度領域の強度が低下する場合があり、両者を勘案して設定するのが良い。より好ましい温度範囲は１２００〜１８００℃であり、さらに好ましい温度範囲は、１２００〜１６００℃である。   The temperature of the carbonization step is preferably higher from the viewpoint of increasing the strand elastic modulus of the carbon fiber to be obtained, but if it is too high, the strength of the high strength region may decrease, and it is set in consideration of both. Is good. A more preferable temperature range is 1200 to 1800 ° C, and a more preferable temperature range is 1200 to 1600 ° C.

炭素化工程の後に、得られた炭素繊維束の表面改質のため、電解処理を施すこともできる。電解処理は公知の手法で行うことが好ましい。具体的には、電解処理に用いられる電解液には、硫酸、硝酸および塩酸等の酸性溶液や、水酸化ナトリウム、水酸化カリウム、テトラエチルアンモニウムヒドロキシド、炭酸アンモニウムおよび重炭酸アンモニウムのようなアルカリまたはそれらの塩を水溶液として使用することができる。ここで、電解処理に要する電気量は、適用する炭素繊維束の炭素化度に応じて適宜選択することができる。かかる電解処理により、得られる複合材料において炭素繊維とマトリックスとの接着性が適正化でき、接着が強すぎることによる複合材料のブリトルな破壊や、繊維方向の引張強度が低下する問題、繊維方向における引張強度は高いものの、樹脂との接着性に劣り、非繊維方向における強度特性が発現しないというような問題が解消され、得られる複合材料において、繊維方向と非繊維方向の両方向にバランスのとれた強度特性が発現されるようになる。   After the carbonization step, electrolytic treatment can be performed for surface modification of the obtained carbon fiber bundle. The electrolytic treatment is preferably performed by a known method. Specifically, the electrolytic solution used for the electrolytic treatment includes an acidic solution such as sulfuric acid, nitric acid and hydrochloric acid, an alkali such as sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, ammonium carbonate and ammonium bicarbonate, or These salts can be used as aqueous solutions. Here, the amount of electricity required for the electrolytic treatment can be appropriately selected according to the degree of carbonization of the carbon fiber bundle to be applied. By such electrolytic treatment, the adhesion between the carbon fiber and the matrix can be optimized in the obtained composite material, the brittle breakage of the composite material due to too strong adhesion, the problem of lowering the tensile strength in the fiber direction, in the fiber direction Although the tensile strength is high, the problem that the adhesive property with the resin is inferior and the strength property in the non-fiber direction is not expressed is solved, and the resulting composite material is balanced in both the fiber direction and the non-fiber direction. Strength characteristics are developed.

かかる電解処理の後、得られた炭素繊維束に集束性を付与するため、サイジング処理をすることもできる。サイジング処理は公知の手法で行うことが好ましい。サイジング剤には、複合材料に使用されるマトリックス樹脂の種類に応じて、マトリックス樹脂との相溶性の良いサイジング剤を適宜選択することができる。   After the electrolytic treatment, a sizing treatment can also be performed in order to impart a focusing property to the obtained carbon fiber bundle. The sizing process is preferably performed by a known method. As the sizing agent, a sizing agent having good compatibility with the matrix resin can be appropriately selected according to the type of the matrix resin used in the composite material.

本明細書に記載の各種物性値の測定方法は以下の通りである。   The measuring method of various physical property values described in this specification is as follows.

＜ボイド評価＞
炭素繊維内部に含まれるボイドの繊維径方向の平均幅は、以下のようにして求める。まず、炭素繊維の繊維軸と垂直方向に、集束イオンビーム（ＦＩＢ）により厚さ１００ｎｍの薄片を作製し、炭素繊維の繊維径方向の断面に対して透過型電子顕微鏡（ＴＥＭ）により１万倍で観察し、ＴＥＭ観察像に対して次の（イ）〜（ハ）の手順で画像処理を行う。
（イ）１万倍で観察したＴＥＭ観察像をさらに３４倍拡大し、ＪＴｒｉｍ（ジェイ・トリム）を用いて適用の強さを５０としてノイズ処理を行う。
（ロ）ＪＴｒｉｍ（ジェイ・トリム）を用いて、（イ）で得られた画像に対してノーマライズ処理を行う。
（ハ）ＪＴｒｉｍ（ジェイ・トリム）を用いて、（ロ）で得られた画像に対して境界の閾値を１３０〜１６０として２値化処理を行う。 <Void evaluation>
The average width in the fiber diameter direction of voids contained in the carbon fiber is determined as follows. First, a thin piece having a thickness of 100 nm is produced by a focused ion beam (FIB) in a direction perpendicular to the fiber axis of the carbon fiber, and 10,000 times by a transmission electron microscope (TEM) with respect to a cross section in the fiber diameter direction of the carbon fiber. The TEM observation image is subjected to image processing according to the following procedures (a) to (c).
(A) The TEM observation image observed at a magnification of 10,000 is further magnified by 34 times, and noise processing is performed using JTrim with an application strength of 50.
(B) A normalization process is performed on the image obtained in (a) using JTrim.
(C) Using JTrim, the binarization process is performed on the image obtained in (b) with a boundary threshold value of 130 to 160.

上記（イ）〜（ハ）の画像処理で得られた画像の白い部分をボイドとし、画像処理ソフトＩｍａｇｅＪ（イメージ・ジェイ）を用いて各ボイドの端から端の中で最も長くなる部分の長さを測定して各ボイドの繊維径方向の幅とし、測定した全ボイドの算術平均値をボイドの繊維径方向の平均幅とする。各ボイドの端から端の中で最も長くなる部分の長さの決定は目視で行い、連続して３回評価した結果の最も長くなる部分の長さを用いる。なお、測定する炭素繊維のサンプリングは炭素繊維束から無作為に行う。測定は炭素繊維の繊維径方向の断面全体に渡って行い、３断面行う。また、幅１ｎｍ未満のボイドは平均幅の計算には用いないものとする。ここで、サンプリングした炭素繊維の繊維軸方向と垂直方向の表面から表面に対して最も長い距離の直線を炭素繊維の繊維径方向の断面の長軸とする。長軸の決定は目視で行い、連続して３回評価した結果の最も長い距離の直線とする。ボイドの端から端の中で最も長くなる部分の長さについて、繊維軸と垂直方向の長さをボイドの径方向の幅とする。ボイドの端から端の中で最も長くなる部分の長さの決定は目視で行い、連続して３回評価した結果の最も長くなる部分の長さを用いる。   The white portion of the image obtained by the above image processing (a) to (c) is defined as a void, and the length of the longest portion of each void from the end to the end using image processing software ImageJ The width is measured as the width of each void in the fiber diameter direction, and the arithmetic average value of all the measured voids is defined as the average width of the voids in the fiber diameter direction. The length of the longest portion of each void is determined visually, and the length of the longest portion obtained as a result of three consecutive evaluations is used. In addition, sampling of the carbon fiber to measure is performed at random from a carbon fiber bundle. The measurement is performed over the entire cross section of the carbon fiber in the fiber diameter direction, and three cross sections are performed. In addition, voids having a width of less than 1 nm are not used for calculating the average width. Here, a straight line having the longest distance from the surface in the direction perpendicular to the fiber axis direction of the sampled carbon fiber is defined as the long axis of the cross section in the fiber diameter direction of the carbon fiber. The major axis is determined visually, and the longest straight line as a result of three consecutive evaluations is taken. About the length of the longest part from the end of the void, the length in the direction perpendicular to the fiber axis is defined as the radial width of the void. The length of the longest portion of the void is determined visually, and the length of the longest portion as a result of three consecutive evaluations is used.

炭素繊維内部のボイド含有率は、以下のようにして求める。まず、炭素繊維の繊維軸と垂直方向に集束イオンビーム（ＦＩＢ）により厚さ１００ｎｍの薄片を作製し、炭素繊維の繊維径方向の断面に対して透過型電子顕微鏡（ＴＥＭ）により１万倍で観察し、上記の（イ）〜（ハ）の手順で画像処理を行う。上記（イ）〜（ハ）の画像処理で得られた画像の白い部分をボイドとし、画像処理ソフトＩｍａｇｅＪ（イメージ・ジェイ）を用いて測定を行う。ボイドの端から端の中で最も長くなる部分の長さについて、繊維径方向の長さをボイドの長径、ボイドの長径と垂直に交わるように、ボイドの端から端に直線を引いた最も長くなる部分の長さについてボイドの短径とする。ボイドの端から端の中で最も長くなる部分の長さの決定は目視で行い、連続して３回評価した結果の最も長くなる部分の長さを用いる。ボイドの形状を楕円と仮定し、ボイド含有率を下記式で算出する。なお、測定する炭素繊維のサンプリングは炭素繊維束から無作為に行う。測定は炭素繊維の繊維径方向の断面全面に対して行い、３断面行う。
ボイド含有率（面積％）＝Σ｛（各ボイドの長径（μｍ）／２×（各ボイドの短径（μｍ）／２×π｝／｛炭素繊維断面積（μｍ２）｝。 The void content inside the carbon fiber is determined as follows. First, a thin piece having a thickness of 100 nm is prepared by a focused ion beam (FIB) in a direction perpendicular to the fiber axis of the carbon fiber, and the cross section in the fiber diameter direction of the carbon fiber is magnified 10,000 times by a transmission electron microscope (TEM). Observe and perform image processing according to the above procedures (a) to (c). A white portion of the image obtained by the image processing (a) to (c) above is used as a void, and measurement is performed using image processing software ImageJ. About the length of the longest part from the end of the void, the longest length in the fiber diameter direction is the longest length of the void, and the straight line from the end of the void is drawn so that it intersects the long axis of the void perpendicularly. The length of the part is the minor axis of the void. The length of the longest portion of the void is determined visually, and the length of the longest portion as a result of three consecutive evaluations is used. Assuming that the shape of the void is an ellipse, the void content is calculated by the following formula. In addition, sampling of the carbon fiber to measure is performed at random from a carbon fiber bundle. The measurement is performed on the entire cross section in the fiber diameter direction of the carbon fiber, and three cross sections are performed.
Void content (area%) = Σ {(major diameter (μm) / 2 of each void / 2 × (minor diameter (μm) / 2 × π} of each void) / {carbon fiber cross-sectional area (μm 2 )}).

炭素繊維内部に含まれるボイドの繊維径方向の断面における単繊維表面からの距離は、以下のようにして求める。まず、炭素繊維の繊維軸と垂直方向に、集束イオンビーム（ＦＩＢ）により厚さ１００ｎｍの薄片を作製し、炭素繊維の繊維径方向の断面に対して透過型電子顕微鏡（ＴＥＭ）により１万倍で観察し、上記の（イ）〜（ハ）の手順で画像処理を行う。上記（イ）〜（ハ）の画像処理で得られた画像の白い部分をボイドとし、画像処理ソフトＩｍａｇｅＪ（イメージ・ジェイ）を用いて測定を行う。ボイドにおける単繊維表面に近い側の端から繊維表面に垂線を垂らしたときに、最も短く引かれる線分を、炭素繊維内部に含まれるボイドの繊維径方向に対する単繊維表面からの距離とする。各ボイドの端から単繊維表面までの最も短くなる部分の長さの決定は目視で行い、連続して３回評価した結果の最も短くなる部分の長さを用いる。なお、測定は炭素繊維の繊維径方向の断面全てにわたって行い、３断面行う。なお、測定する炭素繊維のサンプリングは炭素繊維束から無作為に行う。   The distance from the surface of the single fiber in the cross section in the fiber radial direction of the void contained in the carbon fiber is determined as follows. First, a thin piece having a thickness of 100 nm is produced by a focused ion beam (FIB) in a direction perpendicular to the fiber axis of the carbon fiber, and 10,000 times by a transmission electron microscope (TEM) with respect to a cross section in the fiber diameter direction of the carbon fiber. And image processing is performed according to the above-mentioned procedures (a) to (c). A white portion of the image obtained by the image processing (a) to (c) above is used as a void, and measurement is performed using image processing software ImageJ. When a perpendicular is suspended from the end of the void close to the single fiber surface to the fiber surface, the shortest line segment is defined as the distance from the single fiber surface to the fiber radial direction of the void contained in the carbon fiber. The length of the shortest part from the end of each void to the surface of the single fiber is determined visually, and the length of the shortest part as a result of three consecutive evaluations is used. In addition, a measurement is performed over all the cross sections of the fiber diameter direction of carbon fiber, and 3 cross sections are performed. In addition, sampling of the carbon fiber to measure is performed at random from a carbon fiber bundle.

ボイド評価に用いた透過型電子顕微鏡（ＴＥＭ）の条件は以下の通りである。
・装置：日立製Ｈ−９０００ＵＨＲ
・加速電圧：３００ｋＶ
・観察倍率：１万倍。 The conditions of the transmission electron microscope (TEM) used for void evaluation are as follows.
・ Device: H-9000UHR made by Hitachi
・ Acceleration voltage: 300 kV
-Observation magnification: 10,000 times.

＜炭素繊維のストランド強度およびストランド弾性率＞
炭素繊維束のストランド強度は、ＪＩＳ−Ｒ−７６０８（２００４）の樹脂含浸ストランド試験法に準拠し、次の手順に従い求める。樹脂処方としては、“セロキサイド（登録商標）”２０２１Ｐ（ダイセル化学工業社製）／３フッ化ホウ素モノエチルアミン（東京化成工業（株）製）／アセトン＝１００／３／４（質量部）を用い、硬化条件としては、常圧、温度１２５℃、時間３０分を用いる。炭素繊維束のストランド１０本を測定し、その平均値をストランド引張強度およびストランド弾性率とする。 <Strand strength and strand modulus of carbon fiber>
The strand strength of the carbon fiber bundle is determined according to the following procedure in accordance with the resin impregnated strand test method of JIS-R-7608 (2004). As the resin formulation, “Celoxide (registered trademark)” 2021P (manufactured by Daicel Chemical Industries) / 3 boron trifluoride monoethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) / Acetone = 100/3/4 (part by mass) is used. As curing conditions, normal pressure, temperature of 125 ° C., and time of 30 minutes are used. Ten strands of the carbon fiber bundle are measured, and the average value is defined as the strand tensile strength and the strand elastic modulus.

＜炭素繊維の繊維径＞
測定する炭素繊維について、単位長さあたりの質量（ｇ／ｍ）を密度（ｇ／ｍ３）で除して、さらにフィラメント数で除して求められる単繊維断面積から、断面形状が真円と仮定して求める。 <Fiber diameter of carbon fiber>
For the carbon fiber to be measured, the cross-sectional shape is a perfect circle from the single fiber cross-sectional area obtained by dividing the mass per unit length (g / m) by the density (g / m 3 ) and further dividing by the number of filaments. Assuming that.

＜凝固張力＞
凝固工程中の凝固浴出箇所で張力を２回測定し、その平均値を意味する。張力は、張力計により走行する糸条を挟み込んで荷重を測定し、その荷重を測定箇所の工程糸条の繊度（ｄｔｅｘ）で割って求める。 <Coagulation tension>
The tension is measured twice at the coagulation bath exit point during the coagulation process, and means the average value. The tension is obtained by measuring the load by inserting the running yarn with a tensiometer and dividing the load by the fineness (dtex) of the process yarn at the measurement location.

＜炭素繊維の試長１ｍｍにおける単繊維強力＞
フラグメンテーション法による繊維破断数の測定は、次の（イ）〜（チ）の手順で行う。 <Single fiber strength at 1 mm test length of carbon fiber>
The measurement of the number of fiber breaks by the fragmentation method is performed according to the following procedures (a) to (h).

（イ）樹脂の調整
ビスフェノールＡ型エポキシ樹脂化合物“エポトート（登録商標）”ＹＤ−１２８（新日鐵化学（株）製）１９０質量部とジエチレントリアミン（和光純薬工業（株）製）２０．７質量部を容器に入れてスパチュラでかき混ぜ、自動真空脱泡装置を用いて脱泡する。 (A) Preparation of resin 190 parts by mass of bisphenol A type epoxy resin compound “Epototo (registered trademark)” YD-128 (manufactured by Nippon Steel Chemical Co., Ltd.) and diethylenetriamine (manufactured by Wako Pure Chemical Industries, Ltd.) 20.7 The mass part is put in a container, stirred with a spatula, and defoamed using an automatic vacuum defoamer.

（ロ）炭素繊維単繊維のサンプリングとモールドへの固定
２０ｃｍ程度の長さの炭素繊維束をほぼ４等分し、４つの束から順番に単繊維をサンプリングした。このとき、束全体からできるだけまんべんなくサンプリングする。次に、穴あき台紙の両端に両面テープを貼り、サンプリングした単繊維に一定張力を与えた状態で穴あき台紙に単繊維を固定する。次に、ポリエステルフィルム“ルミラー(登録商標)”（東レ（株）製）を貼り付けたガラス板を用意して、試験片の厚さを調整するための２ｍｍ厚のスペーサーをフィルム上に固定する。そのスペーサー上に単繊維を固定した穴あき台紙を置き、さらにその上に、同様にフィルムを貼り付けたガラス板をフィルムが貼り付いた面を下向きにセットする。このときに繊維の埋め込み深さを制御するために、厚み７０μｍ程度のテープをフィルムの両端に貼り付ける。 (B) Sampling of carbon fiber single fiber and fixing to mold A carbon fiber bundle having a length of about 20 cm was divided into approximately four equal parts, and single fibers were sampled in order from the four bundles. At this time, the entire bundle is sampled as evenly as possible. Next, a double-sided tape is applied to both ends of the perforated mount, and the single fibers are fixed to the perforated mount in a state where a constant tension is applied to the sampled single fibers. Next, a glass plate on which a polyester film “Lumirror (registered trademark)” (manufactured by Toray Industries, Inc.) is attached is prepared, and a 2 mm-thick spacer for adjusting the thickness of the test piece is fixed on the film. . A perforated mount with monofilaments fixed thereon is placed on the spacer, and a glass plate on which a film is similarly attached is set on the spacer with the surface on which the film is attached facing downward. At this time, in order to control the fiber embedding depth, a tape having a thickness of about 70 μm is attached to both ends of the film.

（ハ）樹脂の注型から硬化まで
上記（ロ）の手順のモールド内（スペーサーとフィルムに囲まれた空間）に上記（イ）の手順で調整した樹脂を流し込む。樹脂を流し込んだモールドを、あらかじめ５０℃に昇温させたオーブンを用いて５時間加熱後、降温速度２．５℃／分で３０℃の温度まで降温する。その後、脱型、カットをして２ｃｍ×７．５ｃｍ×０．２ｃｍの試験片を得る。このとき、試験片幅の中央０．５ｃｍ幅内に単繊維が位置するように試験片をカットする。 (C) From resin casting to curing The resin adjusted in the procedure (a) is poured into the mold (the space surrounded by the spacer and the film) in the procedure (b). The mold into which the resin has been poured is heated for 5 hours using an oven that has been heated to 50 ° C. in advance, and then the temperature is lowered to a temperature of 30 ° C. at a temperature lowering rate of 2.5 ° C./min. Thereafter, the mold is removed and cut to obtain a test piece of 2 cm × 7.5 cm × 0.2 cm. At this time, the test piece is cut so that the single fiber is located within the center 0.5 cm width of the test piece width.

（ニ）繊維埋め込み深さ測定
上記（ハ）の手順で得られた試験片に対して、レーザーラマン分光光度計（日本分光 ＮＲＳ−３０００）のレーザーと５３２ｎｍノッチフィルターを用いて繊維の埋め込み深さ測定を行う。まず、単繊維表面にレーザーを当て、レーザーのビーム径が最も小さくなるようにステージ高さを調整し、そのときの高さをＡ（μｍ）とする。次に試験片表面にレーザーを当て、レーザーのビーム径が最も小さくなるようにステージ高さを調整し、そのときの高さをＢ（μｍ）とする。繊維の埋め込み深さｄ（μｍ）は上記レーザーを使用して測定した樹脂の屈折率１．７３２を用いて、以下の式で計算する。 (D) Fiber Embedding Depth Measurement Fiber embedding depth for the test piece obtained by the procedure (c) above using a laser Raman spectrophotometer (JASCO NRS-3000) laser and a 532 nm notch filter. Measure. First, a laser is applied to the surface of the single fiber, the stage height is adjusted so that the beam diameter of the laser becomes the smallest, and the height at that time is defined as A (μm). Next, a laser is applied to the surface of the test piece, the stage height is adjusted so that the beam diameter of the laser becomes the smallest, and the height at that time is defined as B (μm). The fiber embedding depth d (μm) is calculated by the following formula using the refractive index of the resin 1.732 measured using the laser.

（ホ）４点曲げ試験
上記（ハ）の手順で得られた試験片に対して、外側圧子５０ｍｍ間隔、内側圧子２０ｍｍ間隔の治具を用いて４点曲げで引張り歪みを負荷する。ステップワイズに０．１％毎に歪みを与え、偏光顕微鏡により試験片を観察し、試験片長手方向の中心部１０ｍｍの破断数を測定する。測定した破断数を１０で除した値を繊維破断数（個/ｍｍ）とする。また、試験片の中心から幅方向に約５ｍｍ離れた位置に貼り付けた歪みゲージを用いて歪みε（％）を測定した。最終的な単繊維コンポジットの歪みεcは、歪みゲージのゲージファクターκ、上記（ニ）の手順で測定した繊維埋め込み深さｄ（μｍ）、残留歪み０．１５（％）を考慮して以下の式で計算する。なお、試験のｎ数は２５とする。 (E) Four-point bending test Tensile strain is applied to the test piece obtained in the procedure (c) by four-point bending using a jig having an outer indenter interval of 50 mm and an inner indenter interval of 20 mm. Stepwise is strained every 0.1%, the specimen is observed with a polarizing microscope, and the number of breaks at the center 10 mm in the longitudinal direction of the specimen is measured. A value obtained by dividing the measured number of breaks by 10 is defined as the number of fiber breaks (pieces / mm). Further, the strain ε (%) was measured using a strain gauge attached at a position about 5 mm away from the center of the test piece in the width direction. The strain ε c of the final single fiber composite is as follows in consideration of the gauge factor κ of the strain gauge, the fiber embedding depth d (μm) measured by the above procedure (d), and the residual strain of 0.15 (%). Calculate with the following formula. The n number of the test is 25.

（ヘ）試長１ｍｍの単繊維強度のワイブル尺度母数およびワイブル形状係数の算出
上記（ホ）の手順で行われた計算値について、繊維破断数が７〜１５個／ｍｍの範囲で以下の式を用いて最小二乗法によりフィッティングを行い、ワイブル尺度母数σ’０（ＧＰａ）およびワイブル形状係数ｍ’を求めた。ここで、繊維破断数Ｅ（Ｎｂ）（個／ｍｍ）、基準試長Ｌ０＝１０（ｍｍ）、負荷応力σ（ＧＰａ）、界面せん断強度τ＝７０（ＭＰａ）、炭素繊維の繊維径ｄ（μｍ）である。負荷応力は、上記（ホ）の手順で計算した単繊維コンポジットの歪みεc（％）にストランド弾性率（ＧＰａ）を乗じ、１００で除して算出する。 (F) Calculation of the Weibull scale parameter and the Weibull shape factor of single fiber strength of a test length of 1 mm About the calculated values obtained in the above procedure (e), the number of fiber breaks is in the range of 7 to 15 pieces / mm, and Fitting was performed by the least square method using the equation, and the Weibull scale parameter σ ′ 0 (GPa) and the Weibull shape factor m ′ were obtained. Here, the number of fiber breaks E (N b ) (pieces / mm), reference test length L 0 = 10 (mm), load stress σ (GPa), interfacial shear strength τ = 70 (MPa), fiber diameter of carbon fiber d (μm). The applied stress is calculated by multiplying the strain ε c (%) of the single fiber composite calculated in the above procedure (e) by the strand elastic modulus (GPa) and dividing by 100.

試長１ｍｍの単繊維強度のワイブル尺度母数を算出するため、上記で求めた試長１０ｍｍ相当の単繊維強度のワイブル尺度母数およびワイブル形状係数より、以下の式を用いて試長１ｍｍの単繊維強度のワイブル尺度母数σ’０（ＧＰａ）を算出する。なお、ワイブル形状係数ｍは試長１０ｍｍと同じとする。 In order to calculate the Weibull scale parameter of the single fiber strength of the test length of 1 mm, the Weibull scale parameter of the single fiber strength and the Weibull shape factor corresponding to the test length of 10 mm obtained above are used to calculate the test length of 1 mm using the following formula: A Weibull scale parameter σ ′ 0 (GPa) of single fiber strength is calculated. The Weibull shape factor m is the same as the test length of 10 mm.

（ト）単繊維強度から単繊維強力への変換
上記（ヘ）の手順で求めた試長１ｍｍの単繊維強度のワイブル尺度母数σ’０（ＧＰａ）を各水準における単繊維強度の代表値として用いる。各水準における単繊維の平均断面積をＳ（μｍ2）として、σ’’０＝σ’０Ｓから単繊維強力のワイブル尺度母数σ’’０（ｍＮ）を求める。 (G) Conversion from single fiber strength to single fiber strength The Weibull scale parameter σ ′ 0 (GPa) of the single fiber strength of the test length of 1 mm obtained by the above procedure (f) is a representative value of the single fiber strength at each level. Used as As S ([mu] m 2) the average cross-sectional area of single fiber at each level, σ '' 0 = σ ' 0 Weibull scale parameter number from S monofilament potent sigma''0 Request (mN).

（チ）試長１０ｍｍの単繊維強度のワイブル尺度母数およびワイブル形状係数の算出
上記（ホ）の手順で行われた計算値について、繊維破断数が０．３〜２個／ｍｍの範囲で式（３）〜（５）を用いて最小二乗法によりフィッティングを行い、ワイブル形状係数ｍを求めた。ここで、繊維破断数Ｅ（Ｎｂ）（個／ｍｍ）、基準試長Ｌ０＝１０（ｍｍ）、負荷応力σ（ＧＰａ）、界面せん断強度τ＝７０（ＭＰａ）、炭素繊維の繊維径ｄ（μｍ）である。負荷応力は、上記（ホ）の手順で計算した単繊維コンポジットの歪みεc（％）にストランド弾性率（ＧＰａ）を乗じ、１００で除して算出する。 (H) Calculation of the Weibull scale parameter and the Weibull shape factor of the single fiber strength of a test length of 10 mm With respect to the calculated values obtained in the above procedure (e), the number of fiber breaks is in the range of 0.3 to 2 pieces / mm. Fitting was performed by the method of least squares using equations (3) to (5), and the Weibull shape factor m was obtained. Here, the number of fiber breaks E (N b ) (pieces / mm), reference test length L 0 = 10 (mm), load stress σ (GPa), interfacial shear strength τ = 70 (MPa), fiber diameter of carbon fiber d (μm). The applied stress is calculated by multiplying the strain ε c (%) of the single fiber composite calculated in the above procedure (e) by the strand elastic modulus (GPa) and dividing by 100.

＜単繊維の断面形状（＜Ｌｄ／Ｌｃ＞）＞
炭素繊維束から単繊維を取り出し、繊維軸方向に引っ張ることで破断させる。破断により１本の繊維が２本になるが、片方は廃棄し、残った片方のみをＳＥＭ試料台にカーボンテープを用い、破断面が上を向くように貼り付ける。この操作を２５回繰り返し、２５本の破断面が貼り付けられたＳＥＭ試料台を作製する。株式会社日立ハイテクノロジーズ社製Ｓ−４８００走査型電子顕微鏡（ＳＥＭ）により、加速電圧５．０ｋＶ、作動距離８ｍｍの条件で観察して、次のようにして断面形状を計測する。 <Cross-sectional shape of single fiber (<Ld / Lc>)>
A single fiber is taken out from the carbon fiber bundle and is broken by pulling in the fiber axis direction. One fiber is broken by breaking, but one is discarded, and only the remaining one is attached to the SEM sample stage using carbon tape so that the fracture surface faces upward. This operation is repeated 25 times to produce an SEM sample table to which 25 fracture surfaces are attached. Using a S-4800 scanning electron microscope (SEM) manufactured by Hitachi High-Technologies Corporation, the cross-sectional shape is measured as follows under the conditions of an acceleration voltage of 5.0 kV and a working distance of 8 mm.

（イ）長軸の決定
破断面のＳＥＭ観察像から長軸を決定する。その際、破断面の外周上の任意の２点を通る直線であって、破断面がかかる直線で二分割されて生じる２つの領域の面積が互いに概ね等しくなるような直線のうち、最も長いものを長軸とする。かかる評価は目視で行うため、測定者により、また同一の測定者であっても評価時期により決定される長軸の角度が僅かに異なるが、かかる要因によるばらつきは最大でも±１０度程度と小さいことから、同一の測定者が連続して２回評価した結果の平均を採用する。 (A) Determination of long axis The long axis is determined from the SEM observation image of the fracture surface. At that time, the longest straight line passing through any two points on the outer periphery of the fractured surface, and the areas of the two regions generated by dividing the fractured surface into two by the straight line where the fractured surface is substantially equal to each other Is the long axis. Since this evaluation is performed visually, the angle of the major axis determined by the measurer and even by the same measurer is slightly different depending on the evaluation time, but the variation due to such factors is as small as ± 10 degrees at the maximum. Therefore, the average of the results of the same measurer evaluating twice in succession is adopted.

（ロ）Ｌｃ、Ｌｄの計測
計測にはオープンソースの画像解析ソフトウェア“ＩｍａｇｅＪ ｖｅｒ１．４７”を用いた。長軸の長さは、（イ）で決定した長軸の長さをピクセル単位で測定し、ＳＥＭ観察像に付されたスケールバーを用いて実長さ（単位はμｍ）に換算する。次に長軸を４等分するように３つの点をおき、それぞれの点と繊維外周上の２点とを通る長軸と垂直な線分を３本求める。これらのうち長軸の中点を通るものを短軸と定義し、短軸の長さを長軸と同じ方法で求めた。Ｌｃ・Ｌｄの長さを同様にして求め、短いものの長さをＬｃ、長いものの長さをＬｄとする。以上のようにして、単繊維２５本分のＬｄ／Ｌｃを計算する。 (B) Measurement of Lc and Ld Open source image analysis software “ImageJ ver 1.47” was used for measurement. For the length of the long axis, the length of the long axis determined in (a) is measured in pixel units, and converted to an actual length (unit: μm) using a scale bar attached to the SEM observation image. Next, three points are set so that the major axis is divided into four equal parts, and three line segments perpendicular to the major axis passing through each point and two points on the outer circumference of the fiber are obtained. Of these, the one passing through the midpoint of the major axis was defined as the minor axis, and the length of the minor axis was determined in the same manner as the major axis. The lengths of Lc and Ld are obtained in the same manner, and the length of the short one is Lc and the length of the long one is Ld. As described above, Ld / Lc for 25 single fibers is calculated.

（ハ）断面形状の平均値（＜Ｌｄ／Ｌｃ＞）
上記のように求めた単繊維２５本分のＬｄ／Ｌｃを、単純平均をとって＜Ｌｄ／Ｌｃ＞を計算する。また、２５本の単繊維の中で、Ｌｄ／Ｌｃ＝１．０５〜１．２５を満たす単繊維の割合を、炭素繊維束内における卵形断面単繊維の束内含有率とする。 (C) Average cross-sectional shape (<Ld / Lc>)
<Ld / Lc> is calculated by taking a simple average of Ld / Lc for 25 single fibers obtained as described above. Moreover, let the ratio of the single fiber which satisfy | fills Ld / Lc = 1.05-1.25 in 25 single fibers be the content rate in the bundle of the oval cross-section single fiber in a carbon fiber bundle.

＜炭素繊維束の単繊維の表面積比＞
評価すべき前駆体繊維単繊維を数本試料台にのせ、両端を接着液（例えば、文具の修正液）で固定したものをサンプルとし、原子間力顕微鏡（セイコーインスツルメンツ製、ＳＰＩ３８００Ｎ／ＳＰＡ−４００）を用い、下記条件にて３次元表面形状の像を得る。
・探針：シリコンカンチレバー（セイコーインスツルメンツ製、ＤＦ−２０）
・測定モード：ダイナミックフォースモード（ＤＦＭ）
・走査速度：１．５Ｈｚ
・走査範囲：３μｍ×３μ
・分解能：２５６ピクセル×２５６ピクセル。 <Surface area ratio of single fiber of carbon fiber bundle>
An atomic force microscope (SPI3800N / SPA-400, manufactured by Seiko Instruments Inc.) was prepared by placing several precursor single fibers to be evaluated on a sample stage and fixing both ends with an adhesive solution (for example, a stationery correction solution). ) To obtain an image of a three-dimensional surface shape under the following conditions.
Probe: Silicon cantilever (Seiko Instruments, DF-20)
Measurement mode: Dynamic force mode (DFM)
・ Scanning speed: 1.5Hz
・ Scanning range: 3μm × 3μ
-Resolution: 256 pixels x 256 pixels.

得られた測定画像は、繊維断面の曲率を考慮し、付属のソフトウェアにより、画像の全データから最小二乗法により１次平面を求めてフィッティングし、面内の傾きを補正する１次傾き補正を行い、続いて同様に２次曲線を補正する２次傾き補正を行った後、付属のソフトウェアにより表面粗さ解析を行い、表面積比を算出する。測定は、異なる単繊維３本をランダムにサンプリングし、単繊維１本につき、１回ずつ、計３回行い、その平均値を表面積比の値とする。   The obtained measurement image takes the curvature of the fiber cross-section into consideration and uses the attached software to obtain a first-order plane from the entire image data by the least-squares method and fit it, and to correct the in-plane inclination correction. Then, after performing quadratic inclination correction for correcting the quadratic curve in the same manner, surface roughness analysis is performed by the attached software to calculate the surface area ratio. In the measurement, three different single fibers are randomly sampled, and each single fiber is measured once, for a total of three times, and the average value is defined as the surface area ratio value.

本発明の炭素繊繊維の製造方法の一実施例を説明する。   An embodiment of the method for producing carbon fiber of the present invention will be described.

（実施例１）アクリロニトリル９９．５ｍｏｌ％とイタコン酸０．５ｍｏｌ％からなる共重合体を、ジメチルスルホキシドを溶媒とし、重合開始剤を用いて溶液重合法により重合させ、ポリアクリロニトリル系共重合体を製造した。製造されたポリアクリロニトリル系重合体に、アンモニアガスを用いてイタコン酸を中和しつつ、アンモニウム基をポリアクリロニトリル系共重合体に導入し、極限粘度が３．４である紡糸溶液を得た。   Example 1 A copolymer composed of 99.5 mol% acrylonitrile and 0.5 mol% itaconic acid was polymerized by a solution polymerization method using dimethyl sulfoxide as a solvent and a polymerization initiator to obtain a polyacrylonitrile copolymer. Manufactured. An ammonium group was introduced into the polyacrylonitrile copolymer while neutralizing itaconic acid using ammonia gas to the produced polyacrylonitrile polymer to obtain a spinning solution having an intrinsic viscosity of 3.4.

紡糸口金には、直径０．２ｍｍの円孔と直径０．０６ｍｍの円孔とが中心間距離０．１６ｍｍで穿孔された孔の組を有する紡糸口金を用いた。得られた紡糸溶液を一旦空気中に吐出し、５℃にコントロールした７７％ジメチルスルホキシドの水溶液からなる凝固浴に導入する乾湿式紡糸法により凝固糸条とした。このとき、凝固浴中の三角形断面（先端曲率半径５ｍｍ）折り返しガイドの頂点で凝固糸条が方向転換されながら凝固浴出側で凝固糸条が引き取られた。凝固張力は１．９ｍＮ／ｄｔｅｘであった。この凝固糸条を、常法により水洗した後、４槽の温水浴中で第１浴から１０℃ずつ昇温して、第４浴の温度を９５℃とした。またこのときトータルの延伸倍率は２．５倍とした。続いて、この水浴延伸後の繊維束に対して、アミノ変性シリコーン系シリコーン油剤を付与し、１６０℃の加熱ローラーを用いて、乾燥緻密化処理を行い、加圧スチーム中で３．７倍延伸することにより、製糸全延伸倍率を１３倍とし、単繊維繊度０．９ｄｔｅｘのポリアクリロニトリル系前駆体繊維を得た。次に、得られたポリアクリロニトリル系前駆体繊維を温度２５０〜２８０℃の空気中において、延伸比１．００で延伸しながらで耐炎化処理し、耐炎化繊維束を得た。得られた耐炎化繊維束を、温度３００〜８００℃の窒素雰囲気中において、延伸比１．１０で延伸しながら予備炭素化処理を行い、予備炭素化繊維束を得た。得られた予備炭素化繊維束を、窒素雰囲気中において、最高温度１５００℃で炭素化処理を行った。引き続いて硫酸水溶液を電解液として電解表面処理し、水洗、乾燥した後、サイジング剤を付与し、炭素繊維を得た。   As the spinneret, a spinneret having a set of holes in which a circular hole having a diameter of 0.2 mm and a circular hole having a diameter of 0.06 mm were drilled at a center-to-center distance of 0.16 mm was used. The obtained spinning solution was once discharged into the air, and a coagulated yarn was obtained by a dry and wet spinning method introduced into a coagulation bath composed of an aqueous solution of 77% dimethyl sulfoxide controlled at 5 ° C. At this time, the coagulated yarn was taken up on the exit side of the coagulation bath while the direction of the coagulated yarn was changed at the apex of the folded section of the triangular section (tip radius of curvature 5 mm) in the coagulation bath. The solidification tension was 1.9 mN / dtex. The coagulated yarn was washed with water by a conventional method, and then the temperature of the fourth bath was set to 95 ° C. by raising the temperature from the first bath by 10 ° C. in 4 warm water baths. At this time, the total draw ratio was 2.5 times. Subsequently, an amino-modified silicone-based silicone oil is applied to the fiber bundle after stretching in the water bath, dried and densified using a 160 ° C. heating roller, and stretched 3.7 times in pressurized steam. As a result, the total draw ratio for yarn production was 13 times, and a polyacrylonitrile-based precursor fiber having a single fiber fineness of 0.9 dtex was obtained. Next, the obtained polyacrylonitrile-based precursor fiber was subjected to flame resistance treatment in air at a temperature of 250 to 280 ° C. while being stretched at a stretch ratio of 1.00 to obtain a flame resistant fiber bundle. The obtained flame-resistant fiber bundle was subjected to a preliminary carbonization treatment while being stretched at a stretch ratio of 1.10 in a nitrogen atmosphere at a temperature of 300 to 800 ° C. to obtain a preliminary carbonized fiber bundle. The obtained pre-carbonized fiber bundle was carbonized at a maximum temperature of 1500 ° C. in a nitrogen atmosphere. Subsequently, an electrolytic surface treatment was performed using an aqueous sulfuric acid solution as an electrolytic solution, washing with water and drying, and then a sizing agent was applied to obtain a carbon fiber.

凝固条件、得られた炭素繊維内部に有するボイドの幅、繊維表面から内部ボイドまでの距離、含有（面積）率、炭素繊維物性を表１にまとめた。なお、表１に記載したボイドに関する各項目はＮ＝３の視野における平均値を示したものである（なお、以降の実施例、比較・参考例においても、表１に記載したボイドに関する各項目はＮ＝３の視野における全平均値を示したものである。）。   Table 1 summarizes the solidification conditions, the width of voids inside the obtained carbon fiber, the distance from the fiber surface to the internal void, the content (area) rate, and the carbon fiber properties. In addition, each item regarding the voids described in Table 1 shows an average value in the field of view of N = 3 (in the following Examples, Comparative / Reference Examples, each item regarding the voids described in Table 1) Indicates the total average value in the field of view of N = 3.)

（実施例２）凝固浴のジメチルスルホキシド濃度を７８％とした以外は、実施例１と同様に紡糸、炭化を行い、炭素繊維束を得た。凝固張力は２．０ｍＮ／ｄｔｅｘであった。凝固条件、得られた炭素繊維内部のボイドの特性値、炭素繊維物性を表１に示す。   (Example 2) A carbon fiber bundle was obtained by spinning and carbonizing in the same manner as in Example 1 except that the concentration of dimethyl sulfoxide in the coagulation bath was 78%. The solidification tension was 2.0 mN / dtex. Table 1 shows solidification conditions, characteristic values of voids inside the obtained carbon fiber, and physical properties of the carbon fiber.

（実施例３）凝固浴のジメチルスルホキシド濃度を７８％、凝固浴温度を１０℃とした以外は、実施例１と同様に紡糸、炭化を行い、炭素繊維束を得た。凝固張力は２．０ｍＮ／ｄｔｅｘであった。凝固条件、得られた炭素繊維内部のボイドの特性値、炭素繊維物性を表１に示す。   (Example 3) Spinning and carbonization were carried out in the same manner as in Example 1 except that the concentration of dimethyl sulfoxide in the coagulation bath was 78% and the temperature of the coagulation bath was 10 ° C to obtain a carbon fiber bundle. The solidification tension was 2.0 mN / dtex. Table 1 shows solidification conditions, characteristic values of voids inside the obtained carbon fiber, and physical properties of the carbon fiber.

（実施例４）凝固浴のジメチルスルホキシド濃度を７８％、凝固浴温度を−５℃とした以外は、実施例１と同様に紡糸、炭化を行い、炭素繊維束を得た。凝固張力は２．０ｍＮ／ｄｔｅｘであった。凝固条件、得られた炭素繊維内部のボイドの特性値、炭素繊維物性を表１に示す。   Example 4 Spinning and carbonization were carried out in the same manner as in Example 1 except that the dimethyl sulfoxide concentration in the coagulation bath was 78% and the coagulation bath temperature was −5 ° C. to obtain a carbon fiber bundle. The solidification tension was 2.0 mN / dtex. Table 1 shows solidification conditions, characteristic values of voids inside the obtained carbon fiber, and physical properties of the carbon fiber.

（比較例１)凝固浴のジメチルスルホキシド濃度を７５％とした以外は、実施例１と同様に紡糸、炭化を行い、炭素繊維束を得た。凝固張力は２．０ｍＮ／ｄｔｅｘであった。凝固条件、得られた炭素繊維内部のボイドの特性値、炭素繊維物性を表１に示す。   (Comparative Example 1) Spinning and carbonization were carried out in the same manner as in Example 1 except that the concentration of dimethyl sulfoxide in the coagulation bath was 75% to obtain a carbon fiber bundle. The solidification tension was 2.0 mN / dtex. Table 1 shows solidification conditions, characteristic values of voids inside the obtained carbon fiber, and physical properties of the carbon fiber.

（比較例２）凝固浴のジメチルスルホキシド濃度を７９％とした以外は、実施例１と同様に紡糸、炭化を行い、炭素繊維束を得た。凝固張力は２．２ｍＮ／ｄｔｅｘであった。凝固条件、得られた炭素繊維内部のボイドの特性値、炭素繊維物性を表１に示す。   (Comparative Example 2) Spinning and carbonization were performed in the same manner as in Example 1 except that the dimethyl sulfoxide concentration in the coagulation bath was 79% to obtain a carbon fiber bundle. The solidification tension was 2.2 mN / dtex. Table 1 shows solidification conditions, characteristic values of voids inside the obtained carbon fiber, and physical properties of the carbon fiber.

（比較例３）凝固浴のジメチルスルホキシド濃度を８０％とした以外は、実施例１と同様に紡糸、炭化を行い、炭素繊維束を得た。凝固張力は２．６ｍＮ／ｄｔｅｘであった。凝固条件、得られた炭素繊維内部のボイドの特性値、炭素繊維物性を表１に示す。   (Comparative Example 3) Spinning and carbonization were carried out in the same manner as in Example 1 except that the concentration of dimethyl sulfoxide in the coagulation bath was 80% to obtain a carbon fiber bundle. The solidification tension was 2.6 mN / dtex. Table 1 shows solidification conditions, characteristic values of voids inside the obtained carbon fiber, and physical properties of the carbon fiber.

（比較例４）凝固浴のジメチルスルホキシド濃度を８２％とした以外は、実施例１と同様に紡糸、炭化を行い、炭素繊維束を得た。凝固張力は２．３ｍＮ／ｄｔｅｘであった。凝固条件、得られた炭素繊維内部のボイドの特性値、炭素繊維物性を表１に示す。   (Comparative Example 4) Spinning and carbonization were carried out in the same manner as in Example 1 except that the concentration of dimethyl sulfoxide in the coagulation bath was 82% to obtain a carbon fiber bundle. The coagulation tension was 2.3 mN / dtex. Table 1 shows solidification conditions, characteristic values of voids inside the obtained carbon fiber, and physical properties of the carbon fiber.

（比較例５）凝固浴のジメチルスルホキシド濃度を２０％、凝固浴温度を３℃とした以外は、実施例１と同様に紡糸、炭化を行い、炭素繊維束を得た。凝固張力は３．５ｍＮ／ｄｔｅｘであった。凝固条件、得られた炭素繊維内部のボイドの特性値、炭素繊維物性を表１に示す。   (Comparative Example 5) Spinning and carbonization were carried out in the same manner as in Example 1 except that the concentration of dimethyl sulfoxide in the coagulation bath was 20% and the temperature of the coagulation bath was 3 ° C to obtain a carbon fiber bundle. The solidification tension was 3.5 mN / dtex. Table 1 shows solidification conditions, characteristic values of voids inside the obtained carbon fiber, and physical properties of the carbon fiber.

（比較例６）凝固浴のジメチルスルホキシド濃度を７７％、凝固浴温度を１０℃とした以外は、実施例１と同様に紡糸、炭化を行い、炭素繊維束を得た。凝固張力は１．９ｍＮ／ｄｔｅｘであった。凝固条件、炭素繊維物性を表１に示す。   (Comparative Example 6) Spinning and carbonization were carried out in the same manner as in Example 1 except that the dimethyl sulfoxide concentration in the coagulation bath was 77% and the coagulation bath temperature was 10 ° C to obtain a carbon fiber bundle. The solidification tension was 1.9 mN / dtex. Table 1 shows solidification conditions and carbon fiber properties.

（比較例７）凝固浴のジメチルスルホキシド濃度を７８％、凝固浴温度を１５℃とした以外は、実施例１と同様に紡糸、炭化を行い、炭素繊維束を得た。凝固張力は２．０ｍＮ／ｄｔｅｘであった。凝固条件、炭素繊維物性を表１に示す。   (Comparative Example 7) Spinning and carbonization were carried out in the same manner as in Example 1 except that the dimethyl sulfoxide concentration in the coagulation bath was 78% and the coagulation bath temperature was 15 ° C to obtain a carbon fiber bundle. The solidification tension was 2.0 mN / dtex. Table 1 shows solidification conditions and carbon fiber properties.

（比較例８）凝固浴のジメチルスルホキシド濃度を７７％、凝固浴温度を２０℃とした以外は、実施例１と同様に紡糸、炭化を行い、炭素繊維束を得た。凝固張力は１．９ｍＮ／ｄｔｅｘであった。凝固条件、炭素繊維物性を表１に示す。   Comparative Example 8 Spinning and carbonization were carried out in the same manner as in Example 1 except that the dimethyl sulfoxide concentration in the coagulation bath was 77% and the coagulation bath temperature was 20 ° C. to obtain a carbon fiber bundle. The solidification tension was 1.9 mN / dtex. Table 1 shows solidification conditions and carbon fiber properties.

（比較例９）凝固浴のジメチルスルホキシド濃度を７８％、凝固浴温度を２０℃とした以外は、実施例１と同様に紡糸、炭化を行い、炭素繊維束を得た。凝固張力は２．１ｍＮ／ｄｔｅｘであった。凝固条件、得られた炭素繊維内部のボイドの特性値、炭素繊維物性を表１に示す。   (Comparative Example 9) Spinning and carbonization were carried out in the same manner as in Example 1 except that the dimethyl sulfoxide concentration in the coagulation bath was 78% and the coagulation bath temperature was 20 ° C to obtain a carbon fiber bundle. The solidification tension was 2.1 mN / dtex. Table 1 shows solidification conditions, characteristic values of voids inside the obtained carbon fiber, and physical properties of the carbon fiber.

（比較例１０）直径０．１５ｍｍの円孔が１００個穿孔された口金を用いて、吐出量を調整して単繊維繊度を０．６ｄｔｅｘにした以外は、比較例８と同様に紡糸、炭化を行い、炭素繊維束を得た。凝固張力は２．４ｍＮ／ｄｔｅｘであった。凝固条件、得られた炭素繊維内部のボイドの特性値、炭素繊維物性を表１に示す。   (Comparative Example 10) Spinning and carbonization was performed in the same manner as in Comparative Example 8, except that a die having 100 circular holes with a diameter of 0.15 mm was used to adjust the discharge amount to a single fiber fineness of 0.6 dtex. To obtain a carbon fiber bundle. The solidification tension was 2.4 mN / dtex. Table 1 shows solidification conditions, characteristic values of voids inside the obtained carbon fiber, and physical properties of the carbon fiber.

（比較例１１）直径０．１５ｍｍの円孔が１００個穿孔された口金を用いて、吐出量を調整して単繊維繊度を０．６ｄｔｅｘにした以外は、比較例５と同様に紡糸、炭化を行い、炭素繊維束を得た。凝固張力は３．９ｍＮ／ｄｔｅｘであった。凝固条件、得られた炭素繊維内部のボイドの特性値、炭素繊維物性を表１に示す。   (Comparative Example 11) Spinning and carbonization was performed in the same manner as in Comparative Example 5, except that a die having 100 circular holes with a diameter of 0.15 mm was used to adjust the discharge amount to a single fiber fineness of 0.6 dtex. To obtain a carbon fiber bundle. The solidification tension was 3.9 mN / dtex. Table 1 shows solidification conditions, characteristic values of voids inside the obtained carbon fiber, and physical properties of the carbon fiber.

（比較例１２）直径０．１５ｍｍの円孔が１００個穿孔された口金を用いて、吐出量を調整して単繊維繊度を１．１ｄｔｅｘにした以外は、比較例６と同様に紡糸、炭化を行い、炭素繊維束を得た。凝固張力は１．９ｍＮ／ｄｔｅｘであった。凝固条件、得られた炭素繊維内部のボイドの特性値、炭素繊維物性を表１に示す。   (Comparative Example 12) Spinning and carbonization was performed in the same manner as in Comparative Example 6 except that a die having 100 circular holes having a diameter of 0.15 mm was used to adjust the discharge amount to set the single fiber fineness to 1.1 dtex. To obtain a carbon fiber bundle. The solidification tension was 1.9 mN / dtex. Table 1 shows solidification conditions, characteristic values of voids inside the obtained carbon fiber, and physical properties of the carbon fiber.

（参考例１）三菱レイヨン（株）製“パイロフィル（登録商標）”ＴＲＨ−５０についても、集束イオンビーム（ＦＩＢ）法により繊維軸方向の厚さ１００ｎｍの薄片を作製し、１万倍でＴＥＭ観察を行い、得られたＴＥＭ像からボイド評価を行った。評価により得られたボイドの特性値を表２に示す。   Reference Example 1 For “Pyrofil (registered trademark)” TRH-50 manufactured by Mitsubishi Rayon Co., Ltd., a thin piece having a thickness of 100 nm in the fiber axis direction was prepared by a focused ion beam (FIB) method, and TEM was magnified 10,000 times. Observation was performed, and void evaluation was performed from the obtained TEM image. Table 2 shows the characteristic values of the voids obtained by the evaluation.

（参考例２）東邦テナックス（株）製“テナックス（登録商標）”ＳＴＳ５６３１についても、集束イオンビーム（ＦＩＢ）法により繊維軸方向の厚さ１００ｎｍの薄片を作製し、１万倍でＴＥＭ観察を行い、得られたＴＥＭ像からボイド評価を行った。評価により得られたボイドの特性値を表２に示す。   (Reference Example 2) With respect to “TENAX (registered trademark)” STS5631 manufactured by Toho Tenax Co., Ltd., a thin piece having a thickness of 100 nm in the fiber axis direction was prepared by a focused ion beam (FIB) method, and TEM observation was performed at 10,000 times. And void evaluation was performed from the obtained TEM image. Table 2 shows the characteristic values of the voids obtained by the evaluation.

（参考例３）Ｚｏｌｔｅｋ社製“Ｐａｎｅｘ（登録商標）”Ｐａｎｅｘ３５についても、集束イオンビーム（ＦＩＢ）法により繊維軸方向の厚さ１００ｎｍの薄片を作製し、１万倍でＴＥＭ観察を行い、得られたＴＥＭ像からボイド評価を行った。評価により得られたボイドの特性値を表２に示す。   (Reference Example 3) For “Panex (registered trademark)” Panex 35 manufactured by Zoltek, a thin piece having a thickness of 100 nm in the fiber axis direction was prepared by a focused ion beam (FIB) method, and TEM observation was performed at a magnification of 10,000 times. Void evaluation was performed from the obtained TEM image. Table 2 shows the characteristic values of the voids obtained by the evaluation.

（参考例４）ＳＧＬ社製“ＳＩＧＲＡＦＩＬ（登録商標）”Ｃ３０Ｔ０５０についても、集束イオンビーム（ＦＩＢ）法により繊維軸方向の厚さ１００ｎｍの薄片を作製し、１万倍でＴＥＭ観察を行い、得られたＴＥＭ像からボイド評価を行った。評価により得られたボイドの特性値を表２に示す。   (Reference Example 4) For “SIGRAFIL (registered trademark)” C30T050 manufactured by SGL, a thin piece having a thickness of 100 nm in the fiber axis direction was prepared by a focused ion beam (FIB) method, and TEM observation was performed at 10,000 times. Void evaluation was performed from the obtained TEM image. Table 2 shows the characteristic values of the voids obtained by the evaluation.

（参考例５）Ｈｅｘｃｅｌ社製“Ｈｅｘｔｏｗ（登録商標）”ＩＭ−９についてフラグメンテーション法により曲げ試験を行うことにより、炭素繊維物性を得た。評価により得られた物性を表３に示す。   (Reference Example 5) Carbon fiber properties were obtained by performing a bending test by “fragmentation method” on “Hexto (registered trademark)” IM-9 manufactured by Hexcel. Table 3 shows the physical properties obtained by the evaluation.

（参考例６）Ｈｅｘｃｅｌ社製 ＩＭ−１０についてもフラグメンテーション法により、炭素繊維物性を得た。評価により得られた物性を表３に示す。   (Reference Example 6) Physical properties of carbon fiber were also obtained by the fragmentation method for IM-10 manufactured by Hexcel. Table 3 shows the physical properties obtained by the evaluation.

（参考例７）東邦テナックス社製 ＩＭ−６００についてもフラグメンテーション法により、炭素繊維物性を得た。評価により得られた物性を表３に示す。   Reference Example 7 Carbon fiber properties were also obtained by IM-600 manufactured by Toho Tenax Co., Ltd. by the fragmentation method. Table 3 shows the physical properties obtained by the evaluation.

Claims (7)

本明細書中で定義される方法で評価する、試長１ｍｍの単繊維強力のワイブル形状係数が６．５〜９．４、ワイブル尺度母数が２８０〜３５０ｍＮである炭素繊維。 A carbon fiber having a single fiber strength Weibull shape factor of 6.5 to 9.4 and a Weibull scale parameter of 280 to 350 mN, which is evaluated by the method defined in this specification. 下記[Ａ]、[Ｂ]および[Ｃ]の条件を満たす単繊維を３３％以上含有する請求項１に記載の炭素繊維。
［Ａ］単繊維の繊維径方向の断面においてボイドを０．００１〜０．０２面積％含有する
［Ｂ］ボイドの繊維径方向の平均幅が３．０〜７．０ｎｍである
［Ｃ］本明細書中で定義されるボイドの局所集中率が２５面積％以上である The carbon fiber according to claim 1, comprising 33% or more of single fibers satisfying the following conditions [A], [B] and [C].
[A] In the cross section in the fiber radial direction of the single fiber, 0.001 to 0.02 area% of voids are contained. [B] The average width in the fiber radial direction of voids is 3.0 to 7.0 nm. The local concentration rate of voids defined in the specification is 25 area% or more 単繊維の繊維径方向の断面の単繊維表面から繊維径方向に５．０〜１６．０ｎｍの距離に断面内の全ボイドのうちの４５面積％以上のボイドを含む単繊維を５０％以上含有する請求項１または２に記載の炭素繊維。 Containing 50% or more of single fibers containing 45% by area or more of all voids in the cross section at a distance of 5.0 to 16.0 nm in the fiber diameter direction from the surface of the single fiber in the cross section in the fiber diameter direction of the single fiber The carbon fiber according to claim 1 or 2. 単繊維の繊維径方向の断面の短径が６．０〜８．０μｍである、請求項１〜３のいずれかに記載の炭素繊維。 Carbon fiber in any one of Claims 1-3 whose minor axis of the cross section of the fiber diameter direction of a single fiber is 6.0-8.0 micrometers. 本明細書中で定義される方法で評価する、試長１０ｍｍの単繊維強力のワイブル形状係数が３．０〜６．０である請求項１〜４のいずれかに記載の炭素繊維。 The carbon fiber according to any one of claims 1 to 4, wherein a Weibull shape factor of a single fiber strength having a sample length of 10 mm, which is evaluated by a method defined in the present specification, is 3.0 to 6.0. 単繊維の表面の実表面積と投影面積との比で表される表面積比が１．０２〜１．０８である請求項１〜５のいずれかに記載の炭素繊維。 The carbon fiber according to any one of claims 1 to 5, wherein a surface area ratio represented by a ratio between an actual surface area of the surface of the single fiber and a projected area is 1.02 to 1.08. 単繊維の繊維径方向の断面の長径を４等分する３点のうち、長径の中点以外の２点をそれぞれ通って長径に直交する２つの線分の長さの比が１．０５〜１．２５となる断面形状が卵形である単繊維を５０％以上含有する請求項１〜６のいずれかに記載の炭素繊維。
Of the three points that divide the major axis of the cross section of the single fiber into four equal parts, the ratio of the lengths of two line segments that are perpendicular to the major axis through two points other than the middle point of the major axis is 1.05. Carbon fiber in any one of Claims 1-6 containing 50% or more of the single fiber whose cross-sectional shape used as 1.25 is oval.
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JP2009256833A (en) * 2008-04-18 2009-11-05 Toray Ind Inc Carbon fiber and reinforcing fabric
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JPH04222229A (en) * 1990-12-25 1992-08-12 Mitsubishi Rayon Co Ltd Production of graphite fiber
JPH11217734A (en) * 1997-11-21 1999-08-10 Toray Ind Inc Carbon fiber and its production
JP2002266173A (en) * 2001-03-09 2002-09-18 Mitsubishi Rayon Co Ltd Carbon fiber and carbon fiber-reinforced composite material
WO2009125832A1 (en) * 2008-04-11 2009-10-15 東レ株式会社 Carbon-fiber precursor fiber, carbon fiber, and processes for producing these
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