JP2010229573A - Polyacrylonitrile-based carbon fiber strand and method for producing the same - Google Patents
Polyacrylonitrile-based carbon fiber strand and method for producing the same Download PDFInfo
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- 229920000049 Carbon (fiber) Polymers 0.000 title claims abstract description 91
- 239000004917 carbon fiber Substances 0.000 title claims abstract description 91
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims abstract description 82
- 229920002239 polyacrylonitrile Polymers 0.000 title claims description 18
- 238000004519 manufacturing process Methods 0.000 title abstract description 14
- 239000000835 fiber Substances 0.000 claims abstract description 90
- 238000000034 method Methods 0.000 claims abstract description 54
- 238000003763 carbonization Methods 0.000 claims description 51
- 238000011049 filling Methods 0.000 claims description 8
- 239000001307 helium Substances 0.000 claims description 8
- 229910052734 helium Inorganic materials 0.000 claims description 8
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 claims description 8
- 238000010298 pulverizing process Methods 0.000 claims description 6
- 239000002245 particle Substances 0.000 claims description 4
- 238000010000 carbonizing Methods 0.000 abstract description 5
- 239000000843 powder Substances 0.000 abstract description 4
- 239000006185 dispersion Substances 0.000 abstract 1
- 230000001105 regulatory effect Effects 0.000 abstract 1
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 12
- 230000000704 physical effect Effects 0.000 description 12
- 239000007789 gas Substances 0.000 description 7
- 238000005979 thermal decomposition reaction Methods 0.000 description 7
- 239000013078 crystal Substances 0.000 description 6
- 238000005259 measurement Methods 0.000 description 6
- 238000004513 sizing Methods 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 5
- 239000002131 composite material Substances 0.000 description 5
- 238000010304 firing Methods 0.000 description 5
- 229910052757 nitrogen Inorganic materials 0.000 description 5
- 230000007547 defect Effects 0.000 description 4
- 239000011800 void material Substances 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 239000002243 precursor Substances 0.000 description 3
- 229920005989 resin Polymers 0.000 description 3
- 239000011347 resin Substances 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- 238000004381 surface treatment Methods 0.000 description 3
- 238000010301 surface-oxidation reaction Methods 0.000 description 3
- NLHHRLWOUZZQLW-UHFFFAOYSA-N Acrylonitrile Chemical compound C=CC#N NLHHRLWOUZZQLW-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- BAPJBEWLBFYGME-UHFFFAOYSA-N Methyl acrylate Chemical compound COC(=O)C=C BAPJBEWLBFYGME-UHFFFAOYSA-N 0.000 description 2
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 2
- UIIMBOGNXHQVGW-UHFFFAOYSA-M Sodium bicarbonate Chemical compound [Na+].OC([O-])=O UIIMBOGNXHQVGW-UHFFFAOYSA-M 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 238000000498 ball milling Methods 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 239000000805 composite resin Substances 0.000 description 2
- 229910001873 dinitrogen Inorganic materials 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 239000007791 liquid phase Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000000178 monomer Substances 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 238000009987 spinning Methods 0.000 description 2
- 238000002411 thermogravimetry Methods 0.000 description 2
- SMZOUWXMTYCWNB-UHFFFAOYSA-N 2-(2-methoxy-5-methylphenyl)ethanamine Chemical compound COC1=CC=C(C)C=C1CCN SMZOUWXMTYCWNB-UHFFFAOYSA-N 0.000 description 1
- JAHNSTQSQJOJLO-UHFFFAOYSA-N 2-(3-fluorophenyl)-1h-imidazole Chemical compound FC1=CC=CC(C=2NC=CN=2)=C1 JAHNSTQSQJOJLO-UHFFFAOYSA-N 0.000 description 1
- NIXOWILDQLNWCW-UHFFFAOYSA-N 2-Propenoic acid Natural products OC(=O)C=C NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 description 1
- ZCYVEMRRCGMTRW-UHFFFAOYSA-N 7553-56-2 Chemical compound [I] ZCYVEMRRCGMTRW-UHFFFAOYSA-N 0.000 description 1
- 238000007088 Archimedes method Methods 0.000 description 1
- 239000004593 Epoxy Substances 0.000 description 1
- CERQOIWHTDAKMF-UHFFFAOYSA-N Methacrylic acid Chemical class CC(=C)C(O)=O CERQOIWHTDAKMF-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 238000002835 absorbance Methods 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- BFNBIHQBYMNNAN-UHFFFAOYSA-N ammonium sulfate Chemical compound N.N.OS(O)(=O)=O BFNBIHQBYMNNAN-UHFFFAOYSA-N 0.000 description 1
- 229910052921 ammonium sulfate Inorganic materials 0.000 description 1
- 235000011130 ammonium sulphate Nutrition 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
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- 238000004043 dyeing Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000001891 gel spinning Methods 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 229910001853 inorganic hydroxide Inorganic materials 0.000 description 1
- 229910052740 iodine Inorganic materials 0.000 description 1
- 239000011630 iodine Substances 0.000 description 1
- LVHBHZANLOWSRM-UHFFFAOYSA-N methylenebutanedioic acid Natural products OC(=O)CC(=C)C(O)=O LVHBHZANLOWSRM-UHFFFAOYSA-N 0.000 description 1
- 150000007522 mineralic acids Chemical class 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 238000010943 off-gassing Methods 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 230000000379 polymerizing effect Effects 0.000 description 1
- 238000004886 process control Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000000197 pyrolysis Methods 0.000 description 1
- 238000011002 quantification Methods 0.000 description 1
- 239000012783 reinforcing fiber Substances 0.000 description 1
- 238000007363 ring formation reaction Methods 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 229910000030 sodium bicarbonate Inorganic materials 0.000 description 1
- 235000017557 sodium bicarbonate Nutrition 0.000 description 1
- 229910000029 sodium carbonate Inorganic materials 0.000 description 1
- 235000017550 sodium carbonate Nutrition 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 238000003892 spreading Methods 0.000 description 1
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Abstract
Description
本発明は、ポリアクリロニトリル（以下、ＰＡＮとも表記する）系炭素繊維（以下、単に炭素繊維とも表記する）フィラメントの繊維内部のボイドが極めて少なく、複合材料用の炭素繊維として優れた物性を示す炭素繊維ストランド及びその製造方法に関する。 In the present invention, carbon inside the fiber of a polyacrylonitrile (hereinafter also referred to as “PAN”) type carbon fiber (hereinafter also simply referred to as “carbon fiber”) filament is extremely small and exhibits excellent physical properties as a carbon fiber for composite materials. The present invention relates to a fiber strand and a manufacturing method thereof.
炭素繊維は他の繊維と比較して優れた比強度及び比弾性率を有する。炭素繊維はその有する軽量性及び優れた機械的特性を利用して、樹脂と複合化する補強繊維として、広く工業的に利用されている。 Carbon fibers have superior specific strength and specific modulus compared to other fibers. Carbon fiber is widely used industrially as a reinforcing fiber to be combined with resin by utilizing its light weight and excellent mechanical properties.
近年、炭素繊維を利用する複合材料の工業的な用途は、多くの分野に広がりつつある。特にスポーツ・レジャー分野、航空宇宙分野においては、より高性能化（高強度化、高弾性率化）に向けた要求が強まっている。炭素繊維と樹脂との複合化において高性能化を追求するためには、樹脂の持つ物性だけでなく、炭素繊維そのものの物性を向上させることが不可欠である。 In recent years, industrial applications of composite materials using carbon fibers are spreading in many fields. Particularly in the sports / leisure field and the aerospace field, there is an increasing demand for higher performance (higher strength, higher elastic modulus). In order to pursue high performance in the composite of carbon fiber and resin, it is essential to improve not only the physical properties of the resin but also the physical properties of the carbon fiber itself.
通常、炭素繊維フィラメントは、その製造工程において発生する多数のボイド（空隙や欠陥）を繊維内部に含む。このボイドの量や大きさは炭素繊維フィラメント及び炭素繊維ストランドの強度等の物性を決する重要な要因である。そのため、炭素繊維の物性向上を図る上では、炭素繊維フィラメントの繊維内部ボイドの量や大きさを正確に把握し、これを低減するよう努めることが不可欠である。 Usually, the carbon fiber filament includes a large number of voids (voids and defects) generated in the manufacturing process inside the fiber. The amount and size of these voids are important factors that determine physical properties such as the strength of carbon fiber filaments and carbon fiber strands. Therefore, in order to improve the physical properties of carbon fibers, it is essential to accurately grasp the amount and size of the fiber internal voids of the carbon fiber filament and try to reduce them.
特許文献１には、炭素繊維前駆体繊維のボイドの量をヨウ素吸着による明度差を利用して測定する方法が開示されている。また、特許文献２には、広角Ｘ線測定で測定した面間隔と理論値との差から炭素繊維の空孔率を計算する方法が記載されている。特許文献３には、酸性可染染料の溶液に、凝固糸条を浸漬させて凝固糸条に染料を吸着させ、染色溶液の吸光度からボイドの量を見積る方法が記載されている。これらの方法によれば、繊維表面のボイドの総容積を見積ることが出来る。しかし、繊維内部のボイドを測定することは出来ない。この繊維内部ボイドは、炭素繊維の引張強度測定の際、破断開始点となる。この為、炭素繊維の引張強度を上げるには、ボイドを少なくする、即ち、繊維の緻密性を向上させることが必要である。繊維の緻密性を向上させることは、結晶構造の均質化を進めることを意味し、ひいては炭素繊維フィラメント間の緻密性の差を低減させることを意味する。炭素繊維フィラメント間の緻密性の差を低減させることが出来れば、炭素繊維ストランドの物性のばらつきを低減させることが可能となる。炭素繊維複合材料においては、最弱点から欠陥伸長が起こり破断に至る。そのため、炭素繊維フィラメントの緻密性を向上させて物性のばらつきを低減させれば、複合材料として炭素繊維が使用される際に、繊維の破断開始点となり得る部分を低減させることができ、複合材料としての物性を向上させることができる。 Patent Document 1 discloses a method for measuring the amount of voids in a carbon fiber precursor fiber by using a difference in brightness due to iodine adsorption. Patent Document 2 describes a method for calculating the porosity of carbon fiber from the difference between the interplanar spacing measured by wide-angle X-ray measurement and the theoretical value. Patent Document 3 describes a method of immersing a coagulated yarn in an acid dyeable dye solution to adsorb the dye to the coagulated yarn and estimating the amount of voids from the absorbance of the dyeing solution. According to these methods, the total volume of voids on the fiber surface can be estimated. However, voids inside the fiber cannot be measured. This fiber internal void serves as a break starting point when measuring the tensile strength of the carbon fiber. For this reason, in order to increase the tensile strength of the carbon fiber, it is necessary to reduce voids, that is, to improve the denseness of the fiber. Improving the denseness of the fiber means that the crystal structure is homogenized, and consequently, reducing the difference in denseness between the carbon fiber filaments. If the difference in denseness between the carbon fiber filaments can be reduced, variations in the physical properties of the carbon fiber strands can be reduced. In the carbon fiber composite material, defect elongation occurs from the weakest point and breaks. Therefore, if the density of the carbon fiber filaments is improved to reduce the variation in physical properties, when carbon fibers are used as the composite material, the portion that can be the break starting point of the fiber can be reduced. The physical properties as can be improved.
特許文献２には、不活性雰囲気中で、第一炭素化工程において、比重１．３〜１．４のＰＡＮ系耐炎化繊維を３００〜９００℃の温度範囲内で、１．０３〜１．０６の延伸倍率で一次延伸処理させ、次いで０．９〜１．０１の延伸倍率で二次延伸処理させた後、第二炭素化工程において８００〜１７００℃の温度範囲内で炭素化させる炭素繊維の製造方法が開示されている。係る方法によれば、繊維表面のボイドを減らすことが出来るが、繊維内部のボイド量を十分に減らすことは出来ない。 In Patent Document 2, in a first carbonization step, a PAN-based flameproof fiber having a specific gravity of 1.3 to 1.4 is added in a temperature range of 300 to 900 ° C. in an inert atmosphere at 1.03 to 1. Carbon fiber which is first stretched at a stretch ratio of 06 and then secondary stretched at a stretch ratio of 0.9 to 1.01, and then carbonized in a temperature range of 800 to 1700 ° C. in the second carbonization step. A manufacturing method is disclosed. According to such a method, voids on the fiber surface can be reduced, but the amount of voids inside the fiber cannot be reduced sufficiently.
本発明の目的は、従来と比較して、繊維内部ボイドが極めて少なく、高い強度を有する炭素繊維を提供することにある。また、フィラメントの強度のばらつきが小さい炭素繊維ストランドを提供することにある。さらに、本発明の他の目的は上記のような炭素繊維の製造方法を提供することにある。 An object of the present invention is to provide a carbon fiber having a high strength with very few internal voids in the fiber as compared with the prior art. Another object of the present invention is to provide a carbon fiber strand with a small variation in filament strength. Furthermore, the other object of this invention is to provide the manufacturing method of the above carbon fibers.
本発明者は、上記課題について検討した結果、繊維内部のボイドを、炭素繊維フィラメントの見かけ密度（Ａ）と粉末密度（Ｂ）を測定することにより定量することが可能となることを見出した。そして、ＡをＢで除した値が所定の値以上となる炭素繊維は高い引張強度を有することを見出した。このような炭素繊維は、耐炎化繊維を炭素化させて炭素繊維が製造される工程を二段階に分け、第一炭素化工程の最高温度を所定範囲とし、第二炭素化工程での工程張力を所定範囲とすることにより製造されることを見出し、本発明を完成するに至った。 As a result of examining the above problems, the present inventor has found that the voids inside the fiber can be quantified by measuring the apparent density (A) and the powder density (B) of the carbon fiber filament. And it discovered that the carbon fiber from which the value which remove | divided A by B becomes more than a predetermined value has high tensile strength. Such carbon fiber divides the process in which the carbon fiber is produced by carbonizing the flame-resistant fiber into two stages, the maximum temperature of the first carbonization process is within a predetermined range, and the process tension in the second carbonization process The present invention has been completed by finding out that it is produced by setting the value to a predetermined range.
上記目的を達成する本発明は、以下に記載のものである。
〔１〕樹脂含浸ストランドの引張弾性率が２９０ＧＰａ以上、且つ、引張強度６０００ＭＰａ以上のポリアクリロニトリル系炭素繊維ストランドであって、
フィラメントの状態で測定するヘリウム充填法による炭素繊維密度（Ａ）（単位はｇ／ｃｍ３）と、該フィラメントを体積平均粒子径０．２〜０．５μｍに粉砕した後に測定するヘリウム充填法による炭素繊維密度（Ｂ）（単位はｇ／ｃｍ３）とが下記不等式（１）
Ａ／Ｂ≧０．９０・・・（１）
を満たすことを特徴とするポリアクリロニトリル系炭素繊維ストランド。
〔２〕下記不等式（２）
配向度（％）／結晶子サイズ（ｎｍ）≧４０・・・（２）
を満たす〔１〕記載の炭素繊維ストランド。
〔３〕単糸径７〜１５μｍの耐炎化繊維を、最高温度が６００〜６４０℃の第一炭素化炉で工程張力を１〜２ｇ／ｔｅｘに保ちながら不活性雰囲気中で第一炭素化した後、前記第一炭素化炉の最高温度を超える入口温度に設定した第二炭素化炉で工程張力を２〜４ｇ／ｔｅｘに保ちながら不活性雰囲気中で前記第一炭素化繊維を第二炭素化する〔１〕に記載のポリアクリロニトリル系炭素繊維ストランドの製造方法。
The present invention for achieving the above object is as follows.
[1] A polyacrylonitrile-based carbon fiber strand having a tensile modulus of the resin-impregnated strand of 290 GPa or more and a tensile strength of 6000 MPa or more,
Carbon fiber density (A) (unit: g / cm 3 ) measured by helium filling method measured in the state of filaments, and helium filling method measured after pulverizing the filaments to a volume average particle diameter of 0.2 to 0.5 μm Carbon fiber density (B) (unit: g / cm 3 ) is the following inequality (1)
A / B ≧ 0.90 (1)
Polyacrylonitrile-based carbon fiber strands characterized by satisfying
[2] The following inequality (2)
Degree of orientation (%) / crystallite size (nm) ≧ 40 (2)
The carbon fiber strand according to [1], wherein
[3] Flame-resistant fibers having a single yarn diameter of 7 to 15 μm were first carbonized in an inert atmosphere while maintaining a process tension of 1 to 2 g / tex in a first carbonization furnace having a maximum temperature of 600 to 640 ° C. Thereafter, the first carbonized fiber is made to be a second carbon in an inert atmosphere while maintaining a process tension at 2 to 4 g / tex in a second carbonization furnace set to an inlet temperature exceeding the maximum temperature of the first carbonization furnace. The method for producing a polyacrylonitrile-based carbon fiber strand according to [1].
本発明による製造方法により得られる炭素繊維ストランドは、繊維内部及び繊維表面のボイドが極めて少ない。よって、この炭素繊維ストランドは高い強度を有し、樹脂複合材料用の炭素繊維ストランドとして優れた性質を有する。また、この炭素繊維ストランドはフィラメントの強度のばらつきが小さいため、樹脂複合材料用の炭素繊維ストランドとしての品質が安定する。 The carbon fiber strand obtained by the production method according to the present invention has very few voids inside and on the fiber surface. Therefore, this carbon fiber strand has high strength and has excellent properties as a carbon fiber strand for a resin composite material. In addition, since the carbon fiber strand has a small variation in the strength of the filament, the quality as the carbon fiber strand for the resin composite material is stabilized.
以下、本発明を詳細に説明する。 Hereinafter, the present invention will be described in detail.
〈繊維内部のボイドの定量〉
従来から、フィラメントの見かけ密度、即ち、フィラメントの状態で測定するアルキメデス法による炭素繊維密度を、炭化度を含むボイド量の指標としてきた。しかし、フィラメントの状態で測定した密度は、炭素繊維そのものの密度と、ボイド等の内部欠陥の要素を同時に含む。そのため、見かけ密度と炭素繊維強度とは必ずしも明確な相関関係を有しなかった。
<Quantification of voids inside fibers>
Conventionally, the apparent density of the filament, that is, the carbon fiber density measured by the Archimedes method measured in the state of the filament has been used as an index of the void amount including the degree of carbonization. However, the density measured in the filament state simultaneously includes the density of the carbon fiber itself and elements of internal defects such as voids. Therefore, the apparent density and the carbon fiber strength did not necessarily have a clear correlation.
本発明者は、上記事情に鑑み、フィラメントの見かけ密度（Ａ）と粉末密度（Ｂ）を測定した。即ち、炭素繊維のフィラメントを凍結粉砕して繊維内部のボイドを表面に露出させ、係る状態でヘリウム充填法による炭素繊維密度（Ｂ）を測定した。そして、同様のヘリウム充填法により測定したフィラメントの見かけ密度（Ａ）との比をとった密度比（Ａ／Ｂ）を炭素繊維内部のボイド量の尺度とする方法を採用した。 In view of the above circumstances, the present inventor measured the apparent density (A) and the powder density (B) of the filament. That is, the carbon fiber filaments were freeze-ground to expose the voids inside the fibers on the surface, and in this state, the carbon fiber density (B) was measured by the helium filling method. Then, a method was adopted in which a density ratio (A / B) obtained by taking a ratio with the apparent density (A) of the filament measured by the same helium filling method was used as a measure of the void amount inside the carbon fiber.
凍結粉砕は液体窒素中、ボールミル粉砕により行う。凍結粉砕は炭素繊維の体積平均粒子径が０．２〜０．５μｍとなるまで行う。０．５μｍを超える場合は、繊維内部のボイドが十分に露出しないからである。 Freeze pulverization is performed by ball milling in liquid nitrogen. Freeze pulverization is performed until the volume average particle diameter of the carbon fibers becomes 0.2 to 0.5 μm. This is because voids within the fiber are not sufficiently exposed when the thickness exceeds 0.5 μm.
本発明においては、密度比（Ａ／Ｂ）は０．９０以上である。０．９０未満では繊維内部のボイドが多いため、炭素繊維の強度が劣る。 In the present invention, the density ratio (A / B) is 0.90 or more. If it is less than 0.90, since there are many voids inside the fiber, the strength of the carbon fiber is inferior.
〈ボイドの発生要因〉
耐炎化繊維を炭素化し、その構造がグラファイト構造に変化する際には、窒素ガスを主とするガスが放出され、ボイドが形成されやすい。ボイドが多く含まれるフィラメントを強く引っ張る（工程張力を高くする）と、ボイド周辺に張力が集中してかかり、フィラメント全体にかかる張力が均等にならない。そのため、フィラメントの構造むらを生じさせ、繊維強度等の物性のばらつきを生じさせる。これを防ぐためには、耐炎化繊維の炭素化工程において、ガス放出量が多い温度帯においては、フィラメントの弾性率が低下しない程度に炭素化炉の工程張力を弛めることが有効である。
<Void generation factors>
When the flame resistant fiber is carbonized and its structure changes to a graphite structure, a gas mainly containing nitrogen gas is released and voids are easily formed. When a filament containing a large amount of voids is pulled strongly (the process tension is increased), the tension is concentrated around the voids, and the tension applied to the entire filament is not even. For this reason, the structure of the filament is uneven and the physical properties such as fiber strength are varied. In order to prevent this, it is effective to relax the process tension of the carbonization furnace to such an extent that the elastic modulus of the filament does not decrease in the temperature range where the amount of gas released is large in the carbonization process of the flame resistant fiber.
図１は耐炎化繊維の熱重量分析の分析結果を示すグラフである。耐炎化繊維の単位温度当りの質量減少量は、炭素化の進行に伴い増加を続ける。４２０℃付近で耐炎化繊維の単位温度当りの質量減少量は最大となる。その後は６４０℃付近まで耐炎化繊維の単位温度当りの質量減少量は減少を続ける。６４０℃付近では耐炎化繊維の単位温度当りの質量減少量が最小となる。その後は、再び耐炎化繊維の単位温度当りの質量減少量は徐々に増加している。 FIG. 1 is a graph showing the results of thermogravimetric analysis of flameproofed fibers. The amount of mass decrease per unit temperature of the flameproof fiber continues to increase as the carbonization progresses. Near 420 ° C., the mass loss per unit temperature of the flameproof fiber becomes maximum. Thereafter, the mass loss per unit temperature of the flameproof fiber continues to decrease until around 640 ° C. In the vicinity of 640 ° C., the mass loss per unit temperature of the flameproof fiber is minimized. Thereafter, the amount of mass reduction per unit temperature of the flameproof fiber gradually increases again.
耐炎化繊維の質量減少は、耐炎化繊維の熱分解によるガス放出によって生じる。図1の単位温度当りの質量減少量から、耐炎化繊維のガス放出の様子を見ると、４００℃付近での急激なガス発生量増加領域（第一の熱分解）と、６４０℃付近から開始する緩やかなガス発生量増加領域（第二の熱分解）とがある。よって、炭素化工程におけるこれら２つの温度帯では好ましい処理条件（温度勾配や工程張力等）は異なる。従来のように、耐炎化繊維を終始同一の温度勾配や工程張力で炭素化させたり、単に工程を分割したりするだけでは、上述のように、得られる炭素繊維にボイドを生じさせやすい。 The mass reduction of the flame resistant fiber is caused by outgassing due to thermal decomposition of the flame resistant fiber. From the mass loss per unit temperature shown in Fig. 1, the gas release of the flameproof fiber is seen from the region where the gas generation rate suddenly increases around 400 ° C (first pyrolysis) and from around 640 ° C. There is a gradual increase in the amount of gas generated (second thermal decomposition). Therefore, preferable processing conditions (temperature gradient, process tension, etc.) differ in these two temperature zones in the carbonization process. As described above, it is easy to cause voids in the obtained carbon fiber by simply carbonizing the flameproof fiber with the same temperature gradient and process tension from the beginning, or simply dividing the process.
そこで、耐炎化繊維から炭素繊維に至る３００〜１４００℃の炭素化工程を、耐炎化繊維の単位温度当りの質量減少量が最小になる６４０℃付近を基準に前後２つの工程に分ける。即ち、耐炎化繊維は、焼成開始から第一の熱分解を経て６４０℃付近までは第一炭素化炉において焼成され、第一炭素化繊維が製造される（第一炭素化工程）。第一炭素化炉で焼成された第一炭素化繊維は、第二の熱分解を経て炭素化終了までは第二炭素化炉で焼成される（第二炭素化工程）。これにより、炭素繊維の緻密性に関わる２つの熱分解領域において、それぞれに最適な温度勾配、工程張力に調節しながら耐炎化繊維の焼成を行うことが可能となる。 Therefore, the carbonization process at 300 to 1400 ° C. from the flame-resistant fiber to the carbon fiber is divided into two steps before and after the vicinity of 640 ° C. at which the mass reduction amount per unit temperature of the flame-resistant fiber is minimized. That is, the flame-resistant fiber is fired in the first carbonization furnace from the start of firing to the vicinity of 640 ° C. through the first thermal decomposition to produce the first carbonized fiber (first carbonization step). The first carbonized fiber fired in the first carbonization furnace is fired in the second carbonization furnace through the second thermal decomposition until the carbonization is completed (second carbonization step). Thereby, in the two thermal decomposition regions related to the denseness of the carbon fiber, it becomes possible to fire the flame resistant fiber while adjusting the temperature gradient and the process tension to be optimum for each.
〈炭素繊維の製造工程〉
上記のような炭素繊維の製造方法を以下に具体的に説明する。
<Manufacturing process of carbon fiber>
The method for producing the carbon fiber as described above will be specifically described below.
前駆体繊維であるＰＡＮ系繊維を、１０００〜２４０００本程度束ねた前駆体繊維ストランドに耐炎化処理がなされて、耐炎化繊維が製造される。その後、耐炎化繊維は６００〜６４０℃までは第一炭素化炉において所定の条件で炭素化され、第一炭素化繊維が製造される。次いで、第二炭素化炉において所定の条件で炭素化されて、炭素繊維ストランドとなる。その後、必要に応じて表面処理、サイジング処理がなされて、炭素繊維ストランドが得られる。なお、表面処理、サイジング処理の各工程は従来公知の方法を用いることが出来る。また、本発明の効果を妨げない限度において、各工程間に他の公知の工程が介在することを妨げない。 A precursor fiber strand in which about 1000 to 24,000 PAN fibers, which are precursor fibers, are bundled is subjected to flame resistance treatment to produce flame resistant fibers. Thereafter, the flame resistant fiber is carbonized under a predetermined condition in a first carbonization furnace up to 600 to 640 ° C. to produce a first carbonized fiber. Subsequently, it is carbonized under a predetermined condition in a second carbonization furnace to form a carbon fiber strand. Thereafter, surface treatment and sizing treatment are performed as necessary to obtain carbon fiber strands. In addition, a conventionally well-known method can be used for each process of a surface treatment and a sizing process. Moreover, it does not prevent that another well-known process intervenes between each process in the limit which does not prevent the effect of this invention.
〈原料繊維〉
アクリロニトリルを９０質量％以上、好ましくは９５質量％以上含有する単量体を重合して得られる紡糸溶液を、湿式又は乾湿式紡糸法において紡糸した後、水洗・乾燥・延伸して得られるＰＡＮ系繊維を用いることができる。必要によりアクリロニトリルと共重合する単量体としては、イタコン酸、アクリル酸、メチルアクリレート等の（メタ）アクリル酸エステル等が例示できる。
<Raw fiber>
A PAN system obtained by spinning a spinning solution obtained by polymerizing a monomer containing acrylonitrile at 90% by mass or more, preferably 95% by mass or more in a wet or dry wet spinning method, followed by washing, drying and stretching. Fibers can be used. Examples of the monomer copolymerized with acrylonitrile if necessary include (meth) acrylic acid esters such as itaconic acid, acrylic acid and methyl acrylate.
ＰＡＮ系繊維のフィラメント数は、製造効率の面では１０００フィラメント以上が好ましく、１００００フィラメント以上がより好ましい。 The number of filaments of the PAN-based fiber is preferably 1000 filaments or more, more preferably 10,000 filaments or more in terms of production efficiency.
〈耐炎化〉
ＰＡＮ系繊維を原料とする場合、ＰＡＮ系繊維は加熱空気中２３０〜２６０℃で３０〜１００分間耐炎化処理される。この耐炎化処理により、繊維に環化反応を生じさせ、酸素結合量が増加されて耐炎化繊維が得られる。この耐炎化処理は、一般的に、延伸倍率０．９５〜１．２０の範囲で延伸されることが好ましい。耐炎化時の張力は上記延伸倍率の範囲を超えない限り特に限定されない。ＰＡＮ系耐炎化繊維を原料とする場合には本工程は不要である。
<Flame resistance>
When using PAN-based fibers as a raw material, the PAN-based fibers are flameproofed at 230 to 260 ° C. in heated air for 30 to 100 minutes. By this flameproofing treatment, a cyclization reaction is caused in the fiber, the oxygen bond amount is increased, and a flameproofed fiber is obtained. In general, the flameproofing treatment is preferably performed at a draw ratio of 0.95 to 1.20. The tension at the time of flame resistance is not particularly limited as long as it does not exceed the range of the draw ratio. This step is not necessary when PAN-based flameproof fiber is used as a raw material.
耐炎化繊維の単糸径は７〜１５μｍである。１５μｍを超える場合は繊維内部のボイドを十分に除去することが出来ない。７μｍ未満の場合は繊維の毛羽立ちや切断を生じやすくなる。 The single yarn diameter of the flame resistant fiber is 7 to 15 μm. If it exceeds 15 μm, voids inside the fiber cannot be removed sufficiently. When the thickness is less than 7 μm, fiber fluffing or cutting tends to occur.
〈第一炭素化炉における焼成〉
ＰＡＮ系耐炎化繊維は、第一炭素化炉において窒素等の不活性雰囲気下、徐々に昇温され、耐炎化繊維の張力が制御されて焼成される。第一炭素化炉の開始温度は特に限定されないが１００〜３００℃である。温度勾配は４〜８℃／ｍｉｎ．が好ましい。また、第一炭素化炉の最高温度は６００〜６４０℃である。６００℃未満では耐炎化繊維の第一の熱分解が終了しない。６４０℃を超えると耐炎化繊維の第二の熱分解が開始されるため、繊維は延びやすくなり、ボイドを生じさせやすくなる。
<Firing in the first carbonization furnace>
The PAN-based flameproof fiber is gradually heated in an inert atmosphere such as nitrogen in the first carbonization furnace, and the tension of the flameproof fiber is controlled and fired. Although the starting temperature of a 1st carbonization furnace is not specifically limited, It is 100-300 degreeC. The temperature gradient is 4-8 ° C./min. Is preferred. Moreover, the maximum temperature of a 1st carbonization furnace is 600-640 degreeC. If it is less than 600 degreeC, the 1st thermal decomposition of a flame-resistant fiber will not complete | finish. When the temperature exceeds 640 ° C., the second thermal decomposition of the flameproof fiber is started, so that the fiber tends to be stretched and voids are likely to be generated.
第一炭素化炉の工程張力は１〜２ｇ／ｔｅｘであり、１〜１．５ｇ／ｔｅｘが好ましい。１ｇ／ｔｅｘ未満では繊維の延伸が十分に行われず、結晶配向度が低くなり、得られる炭素繊維の強度を低下させる。２ｇ／ｔｅｘを超えると繊維内部にボイドを発生させやすくなったり、繊維に切断を生じさせやすくなったりする。以上の第一炭素化工程により第一炭素化繊維が製造される。なお、このときの延伸倍率は１．２〜１．８倍となる。 The process tension of the first carbonization furnace is 1 to 2 g / tex, preferably 1 to 1.5 g / tex. If it is less than 1 g / tex, the fiber is not sufficiently stretched, the degree of crystal orientation is lowered, and the strength of the resulting carbon fiber is lowered. If it exceeds 2 g / tex, voids are likely to be generated inside the fibers, and the fibers are likely to be cut. A first carbonized fiber is produced by the above first carbonization step. In addition, the draw ratio at this time will be 1.2 to 1.8 times.
〈第二炭素化炉における焼成〉
第一炭素化炉で焼成されて得られる第一炭素化繊維は、第二炭素化炉で窒素等の不活性雰囲気下、徐々に昇温され、繊維の張力が制御されて焼成され、第二炭素化繊維が製造される。第二炭素化炉の開始温度は特に制限されないが、６００〜８００℃である。且つ、第一炭素化炉の最高温度よりも高くなる。６００℃未満では第一炭素化炉の最高温度を下回るため、製造効率を低下させる。８００℃を超えると第一炭素化炉の最高温度を大きく超え、温度勾配が大きくなり過ぎ、得られる炭素繊維の強度を低下させる。第二炭素化炉の最高温度は特に制限されないが、１３００〜２１００℃である。１３００℃未満では炭素繊維の炭素化率が低くなり、強度が十分でない。
<Baking in the second carbonization furnace>
The first carbonized fiber obtained by firing in the first carbonization furnace is gradually heated in an inert atmosphere such as nitrogen in the second carbonization furnace, fired while controlling the fiber tension, Carbonized fibers are produced. The starting temperature of the second carbonization furnace is not particularly limited, but is 600 to 800 ° C. And it becomes higher than the maximum temperature of the first carbonization furnace. If it is less than 600 ° C., it is lower than the maximum temperature of the first carbonization furnace, so that the production efficiency is lowered. When it exceeds 800 ° C., the maximum temperature of the first carbonization furnace is greatly exceeded, the temperature gradient becomes too large, and the strength of the obtained carbon fiber is lowered. The maximum temperature of the second carbonization furnace is not particularly limited, but is 1300 to 2100 ° C. If it is less than 1300 degreeC, the carbonization rate of carbon fiber will become low and intensity | strength is not enough.
第二炭素化炉の工程張力は２〜４ｇ／ｔｅｘである。２ｇ／ｔｅｘ未満では繊維の延伸が十分に行われず、結晶配向度が低くなり、得られる炭素繊維の強度を低下させる。４ｇ／ｔｅｘを超えると、繊維内部のボイドが多くなる。なお、このときの延伸倍率は０．９〜１．２倍となる。 The process tension of the second carbonization furnace is 2 to 4 g / tex. If it is less than 2 g / tex, the fiber is not sufficiently stretched, the degree of crystal orientation is lowered, and the strength of the resulting carbon fiber is lowered. When it exceeds 4 g / tex, voids inside the fiber increase. In addition, the draw ratio at this time becomes 0.9 to 1.2 times.
〈表面処理〉
上記第二炭素化処理後の第二炭素化繊維には、必要に応じて公知の表面酸化処理が施される。表面酸化処理には気相、液相処理が用いられるが、工程管理の簡便さと生産性を高める点から、液相での電解処理が好ましい。電解酸化処理に用いられる電解液としては、硫酸、硝酸、塩酸等の無機酸や、水酸化ナトリウム、水酸化カリウムなどの無機水酸化物、硫酸アンモニウム、炭酸ナトリウム、炭酸水素ナトリウム等の無機塩類などが挙げられる。
<surface treatment>
The second carbonized fiber after the second carbonization treatment is subjected to a known surface oxidation treatment as necessary. For the surface oxidation treatment, a gas phase or a liquid phase treatment is used, but an electrolytic treatment in a liquid phase is preferable from the viewpoint of easy process control and productivity. Examples of the electrolytic solution used for the electrolytic oxidation treatment include inorganic acids such as sulfuric acid, nitric acid, and hydrochloric acid, inorganic hydroxides such as sodium hydroxide and potassium hydroxide, and inorganic salts such as ammonium sulfate, sodium carbonate, and sodium bicarbonate. Can be mentioned.
〈サイジング処理〉
上記表面酸化処理後の炭素繊維には、必要に応じてサイジング処理が施される。サイジング方法は、従来の公知の方法で行うことができ、サイジング剤は、用途に即して適宜組成を変更して使用し、炭素繊維に均一付着させた後に、乾燥させることが好ましい。
<Sizing process>
The carbon fiber after the surface oxidation treatment is subjected to sizing treatment as necessary. The sizing method can be performed by a conventionally known method, and the sizing agent is preferably used by changing the composition as appropriate according to the application, and after uniformly adhering to the carbon fiber, it is preferably dried.
〈炭素繊維〉
上述の通り製造される炭素繊維は平均繊維直径が４．５〜７．５μｍで、４．５〜５．５μｍが好ましい。また、ボイドが少ないため、フィラメントにかかる張力は均等となりやすく、フィラメントの構造むらが少ない。よって、このフィラメントは、従来の製法によるものと比較して強度が高く、強度、弾性率ともに、フィラメント間でのばらつきが小さい。
<Carbon fiber>
The carbon fiber produced as described above has an average fiber diameter of 4.5 to 7.5 μm, preferably 4.5 to 5.5 μm. Moreover, since there are few voids, the tension | tensile_strength concerning a filament tends to become equal, and there is little structure irregularity of a filament. Therefore, this filament has higher strength than that obtained by the conventional manufacturing method, and variation between the filaments is small in both strength and elastic modulus.
例えば、炭素繊維の全フィラメント数の０．４％の単繊維引張強度を測定した場合、引張強度の平均値（Ｅ）と標準偏差（Ｆ）から下記式
ＣＶ値＝１００×Ｆ／Ｅ
により算出されるＣＶ値は２０以下である。
For example, when the single fiber tensile strength of 0.4% of the total number of filaments of carbon fiber is measured, the following formula CV value = 100 × F / E from the average value (E) and standard deviation (F) of the tensile strength.
The CV value calculated by is 20 or less.
また、炭素繊維の全フィラメント数の０．４％の単繊維引張強度を測定した場合、弾性率の平均値（Ｇ）と標準偏差（Ｈ）から下記式
ＣＶ値＝１００×Ｇ／Ｈ
により算出されるＣＶ値は１０以下である。
Moreover, when measuring the single fiber tensile strength of 0.4% of the total number of filaments of carbon fiber, the following formula CV value = 100 × G / H from the average value (G) and standard deviation (H) of the elastic modulus
The CV value calculated by is 10 or less.
また、本発明による炭素繊維は、炭素化時の工程張力が適切に制御されているので、緻密性が高い。そのため、密度比（Ａ／Ｂ）は０．９０以上と高いものとなる。 Further, the carbon fiber according to the present invention has high density because the process tension during carbonization is appropriately controlled. Therefore, the density ratio (A / B) is as high as 0.90 or more.
また、配向度（Ｉ）（単位は％）を結晶子サイズ（Ｊ）（単位はｎｍ）で除した値が下記不等式
Ｉ／Ｊ≧４０
を満たすことが好ましい。本発明の製造方法で製造される炭素繊維は通常、上記不等式を満たす。
Further, the value obtained by dividing the orientation degree (I) (unit:%) by the crystallite size (J) (unit: nm) is the following inequality I / J ≧ 40
It is preferable to satisfy. The carbon fiber produced by the production method of the present invention usually satisfies the above inequality.
４０未満であると、結晶配向度が低下していることとなる。 If it is less than 40, the degree of crystal orientation is reduced.
本発明により得られる炭素繊維は通常、樹脂含浸ストランドの弾性率が２９０ＧＰａ以上であって、且つ、引張強度が６０００ＭＰａ以上である。 The carbon fiber obtained by the present invention usually has a resin-impregnated strand with an elastic modulus of 290 GPa or more and a tensile strength of 6000 MPa or more.
以下、本発明を実施例及び比較例により具体的に説明する。また、各実施例及び比較例における繊維の物性についての評価方法は以下の方法により実施した。
［フィラメント密度］
島津製作所社製 ＳＨＩＭＡＤＺＵ ｍｉｃｒｏｍｅｔｒｉｃｓ ＡｃｃｕＰｙｃ １３３０を用い、ヘリウム充填法により測定した。測定セルは１０ｃｃのものを用い、サンプル約０．５ｇで測定した。
［粉末密度］
凍結粉砕は液体窒素中、ボールミル粉砕により行った。フィラメントを凍結粉砕後、ヘリウム充填法により測定した。凍結粉砕は体積平均粒子径が０．２〜０．５μｍとなるまで行った。
［結晶子サイズ、配向度］
Ｘ線回折装置：リガク社製ＲＩＮＴ２０００を使用し、透過法により面指数(００２)の回折ピークの半値幅βから、下式(１)
結晶子サイズＬｃ(ｎｍ) ＝ ０．９λ／βcosθ ・・・ (１)
λ：Ｘ線の波長、β：半値幅、θ：回折角
を用いて、結晶子サイズＬｃを算出した。また、この回折ピーク角度を円周方向にスキャンして得られる二つのピークの半値幅Ｈ１／２及びＨ'１／２(強度分布に由来)から下式(２)
結晶配向度(％) ＝ １００×[３６０−(Ｈ１／２−Ｈ'１／２)]／３６０ ・・・ (２)
Ｈ１／２及びＨ’１／２：半値幅
を用いて結晶配向度を算出した。
［ストランド強度、弾性率］
ＪＩＳ Ｒ−７６０１に準じてエポキシ樹脂含浸ストランドの強度を測定し、測定回数５回の平均値で示した。
［ＣＶ値］
各測定値の標準偏差をｓとし、平均値をａとして下記式
ＣＶ値（％）＝（ｓ／ａ）×１００
により計算した。
[熱重量分析]
理学サーモフレックスＰＴＣ−１０Ａ ＴＧ−ＤＴＡ ２０００S
白金パンに耐炎化繊維約０．３ｍｇを秤量して入れ、窒素中１０℃／ｍｉｎにて１０００℃まで昇温して測定した。
Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. Moreover, the evaluation method about the physical property of the fiber in each Example and a comparative example was implemented with the following method.
[Filament density]
Using SHIMADZU micrometrics AccuPyc 1330 manufactured by Shimadzu Corporation, measurement was performed by a helium filling method. A 10 cc measuring cell was used, and the measurement was performed with a sample of about 0.5 g.
[Powder density]
Freeze pulverization was performed by ball milling in liquid nitrogen. The filament was freeze-ground and measured by a helium filling method. The freeze pulverization was performed until the volume average particle size became 0.2 to 0.5 μm.
[Crystallite size, orientation]
X-ray diffractometer: RINT2000 manufactured by Rigaku Corporation is used, and from the half-value width β of the diffraction peak of the plane index (002) by the transmission method, the following formula (1)
Crystallite size Lc (nm) = 0.9λ / βcosθ (1)
The crystallite size Lc was calculated using λ: X-ray wavelength, β: half width, and θ: diffraction angle. Further, the following formula (2) is obtained from the half-value widths H 1/2 and H ′ 1/2 (derived from the intensity distribution) of two peaks obtained by scanning the diffraction peak angle in the circumferential direction.
Degree of crystal orientation (%) = 100 × [360− (H 1/2 −H ′ 1/2 )] / 360 (2)
H 1/2 and H ′ 1/2 : The degree of crystal orientation was calculated using the half width.
[Strand strength, elastic modulus]
The strength of the epoxy resin-impregnated strand was measured according to JIS R-7601, and indicated by an average value of 5 measurements.
[CV value]
The standard deviation of each measurement value is s, the average value is a, and the following formula CV value (%) = (s / a) × 100
Calculated by
[Thermogravimetric analysis]
Science Thermoflex PTC-10A TG-DTA 2000S
About 0.3 mg of flame-resistant fiber was weighed into a platinum pan, and the temperature was raised to 1000 ° C. at 10 ° C./min in nitrogen for measurement.
（実施例１）
ＰＡＮ系耐炎化繊維ストランド（単繊維繊度０．５〜０．７ｄｔｅｘ、繊維密度１．３４〜１．３８ｇ／ｃｍ３、フィラメント数２４０００、東邦テナックス（株）製）を第一炭素化炉において窒素ガス雰囲気下、開始温度３００℃、最高温度６４０℃、工程張力１．２５（ｇ／ｔｅｘ）で３分間、低温焼成させた。その後、第二炭素化炉において窒素ガス雰囲気下、開始温度６４０℃、最高温度１４２０℃、工程張力２．５０（ｇ／ｔｅｘ）で３分間焼成させることにより表１に示す物性の炭素繊維を得た。
Example 1
PAN-based flame-resistant fiber strand (single fiber fineness 0.5 to 0.7 dtex, fiber density 1.34 to 1.38 g / cm 3 , number of filaments 24,000, manufactured by Toho Tenax Co., Ltd.) in the first carbonization furnace Under a gas atmosphere, low temperature firing was performed for 3 minutes at a starting temperature of 300 ° C., a maximum temperature of 640 ° C., and a process tension of 1.25 (g / tex). Thereafter, carbon fibers having physical properties shown in Table 1 are obtained by firing for 3 minutes in a second carbonization furnace under a nitrogen gas atmosphere at a starting temperature of 640 ° C., a maximum temperature of 1420 ° C., and a process tension of 2.50 (g / tex). It was.
（実施例２、比較例１〜３）
実施例１における第一炭素化炉の最高温度と、第二炭素化炉の工程張力、最高温度を表１に示す通りに変更した以外は、実施例１と同様に処理を行い、表１に示す物性の炭素繊維を得た。
(Example 2, Comparative Examples 1-3)
Except that the maximum temperature of the first carbonization furnace, the process tension of the second carbonization furnace, and the maximum temperature in Example 1 were changed as shown in Table 1, the same treatment as in Example 1 was performed. Carbon fibers having the physical properties shown were obtained.
表１に示す通り、実施例１及び２の炭素繊維は密度比が大きく、強度、弾性率が優れる。また、これらのばらつきも小さい。一方、比較例１の炭素繊維は第一炭素化炉の最高温度が低いため、第二炭素化工程での張力は低いものの、糸にかかる張力が適切に制御されていない。そのため、特にフィラメント間の強度・弾性率のばらつきが大きい。また、比較例２及び３の炭素繊維は第二炭素化炉の工程張力が大きいため、密度比が小さい。即ち、炭素繊維内部のボイド、欠陥が多く、強度に劣る。 As shown in Table 1, the carbon fibers of Examples 1 and 2 have a large density ratio and are excellent in strength and elastic modulus. Also, these variations are small. On the other hand, since the maximum temperature of the first carbonization furnace is low in the carbon fiber of Comparative Example 1, the tension applied to the yarn is not properly controlled although the tension in the second carbonization process is low. For this reason, the variation in strength and elastic modulus among filaments is particularly large. Moreover, since the carbon fiber of Comparative Examples 2 and 3 has a large process tension of the second carbonization furnace, the density ratio is small. That is, there are many voids and defects inside the carbon fiber, and the strength is poor.
Claims (3)
フィラメントの状態で測定するヘリウム充填法による炭素繊維密度（Ａ）（単位はｇ／ｃｍ３）と、該フィラメントを体積平均粒子径０．２〜０．５μｍに粉砕した後に測定するヘリウム充填法による炭素繊維密度（Ｂ）（単位はｇ／ｃｍ３）とが下記不等式（１）
Ａ／Ｂ≧０．９０・・・（１）
を満たすことを特徴とするポリアクリロニトリル系炭素繊維ストランド。 A polyacrylonitrile-based carbon fiber strand having a tensile modulus of the resin-impregnated strand of 290 GPa or more and a tensile strength of 6000 MPa or more,
Carbon fiber density (A) (unit: g / cm 3 ) measured by helium filling method measured in the state of filaments, and helium filling method measured after pulverizing the filaments to a volume average particle diameter of 0.2 to 0.5 μm Carbon fiber density (B) (unit: g / cm 3 ) is the following inequality (1)
A / B ≧ 0.90 (1)
Polyacrylonitrile-based carbon fiber strands characterized by satisfying
配向度（％）／結晶子サイズ（ｎｍ）≧４０・・・（２）
を満たす請求項１記載の炭素繊維ストランド。 The following inequality (2)
Degree of orientation (%) / crystallite size (nm) ≧ 40 (2)
The carbon fiber strand of Claim 1 which satisfy | fills.
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