【発明の詳細な説明】
本発明は高性能炭素繊維若しくは黒鉛繊維の製
造法に関するものであり、とくにアクリロニトリ
ル系合成繊維プレカーサーを用い軽く、高強度、
高弾性の炭素繊維若しくは黒鉛繊維を短時間で高
収率下に製造する方法にある。
アクリル系合成繊維プレカーサーを用いて炭素
繊維プレカーサーを製造する方法としては、ま
ず、プレカーサーを200〜250℃の酸化性雰囲気下
で0.01〜0.15ｇ／ｄなる範囲の張力をかけて、繊
維を伸長せしめながら予備酸化処理した後、250
〜1000℃以上の温度を温度勾配を有する非酸化性
雰囲気中で炭素化処理する方法が、特公昭44−
21175号公報明細書や特公昭45−12540号公報明細
書中に記載されている如く知られている。これら
の方法によつて作られた炭素繊維の性能のうち、
その弾性率は、ほぼ繊維の熱処理温度によつて一
義的に定めるものと考えられており、所望の弾性
率を有する炭素繊維を製造することは比較的容易
である。ところが、炭素繊維の強度及び密度と炭
素繊維の製造方法との関係については何等明確に
なされておらず、ただ単に炭素繊維中に形成され
た黒鉛結晶の大きさ、その配向度並びに炭素繊維
中に存在する微細なクラツクと強度との間に何等
かの関係がありそうだと推定されているにすぎな
い。
従来、開発されてきた炭素繊維の製法は、上述
の如くして製作した予備酸化処理した密度1.40未
満の繊維を250℃以上の温度で炭素化ないし黒鉛
化処理することによつて密度1.80以上の炭素繊維
を得ているのであるが、この従来法に於てはこの
炭素化ないし黒鉛化工程に於て繊維長は原料繊維
長に対し数％乃至20％の収縮をするものと言われ
ており、この収縮を低減するために糸に緊張を与
えながら焼成する方法の検討が加えているにもか
かわらず、耐炎繊維の炭素化工程において繊維に
伸張を与えることによつて高強度の炭素繊維を得
ようとする際には糸切れが生ずるようになるばか
りでなく、高強度の炭素繊維を得ることはできな
い。
本発明等は上述した如き現状に鑑み高強度の炭
素繊維を得ることを目的して検討し、繊維密度
1.42以下の耐炎化繊維を800℃以下の温度で25％
以下なる割合で延伸しながら前炭素化処理し、引
き続いて完全炭素化を行わしめることによつて、
その目的を達成しうることを見出し、先に特許出
願したが、更に強度、弾性率が高く、軽い炭素繊
維を得ることを目的として検討した結果本発明を
完成した。
本発明の要旨とするところはアクリロニトリル
系合成繊維よりつくられた繊維密度1.42ｇ／cm3を
越え1.50ｇ／cm3以下の耐炎化処理糸を、不活性雰
囲気中300〜800℃の温度領域に於て25％までの範
囲で伸長しながら炭素化処理し、引き続いて800
℃以上の温度で制限収縮下に熱処理しながら炭素
化処理を完結せしめることを特徴とする高性能炭
素繊維の製法にある。
本発明を実施するに際して用いる耐炎化処理糸
とは繊維密度1.42ｇ／cm3を越えるものであり、炭
素含量62〜68重量％程度のものならば、いかなる
耐炎化処理糸をも用い得るが、特に好ましいもの
はアクリロニトリルの重合量が85重量％以上であ
るポリアクリロニトリル又はアクリロニトリル系
重合体より作られた繊維を200℃以上400℃までの
温度範囲の酸化性雰囲気下で収縮せしめながら或
いは定長下に、更には延伸せしめながら酸化処理
することによつて作成したものであり、とくにア
クリル系繊維を酸化性雰囲気下で、ニトリル基の
約8.5〜12％の反応が終了するまで100〜150％な
る延伸を施し、次いで原繊維の長さに対し、耐炎
化糸の長さが負とならない条件下で繊維密度が
1.42ｇ／cm3以上となるようにしたものを用いるの
がよく、このような耐炎化糸を用いた場合に本発
明を最も効率よく発揮せしめることができる。
耐炎化処理糸の繊維密度は、乾燥除湿した耐炎
化処理糸の短片をキシロール／四塩化炭素系密度
勾配管にて測定したものである。この測定法は予
め試験繊維片をその繊維密度にほぼ等しい上記混
合溶媒中に浸漬し脱泡処理したものを密度勾配管
中に入れ、測定温度30℃、浸漬後測定時間までの
時間を３時間として測定したものである。
本発明の実施に際し繊維密度が1.42ｇ／cm3未満
である耐炎化処理糸を不活性雰囲気下で300〜800
℃の範囲で25％以下延伸し前炭素化し、次いで高
温処理すると、繊維密度が1.8ｇ／cm3以上の強度、
弾性率の優れた炭素繊維を作ることができるが、
このような密度の高いものは、炭素繊維の有力な
用途分野である航空機、自動車等の基礎資材とし
て用いる際には不足であり、出来るだけ密度が低
く、かつ高強度、高弾性率の開発が望まれている
と共に、それを高速生産し得る方法の検討も大き
な課題となつている。このような目的を達成し得
る繊維を作るには、これまで密度1.30〜1.42ｇ／
cm3の比較的繊維密度の低い耐炎化繊維を炭素化温
度以上の温度で熱処理する方法が望ましいとされ
てきたのであるが、本発明者等は種々の検討を加
えた結果、これらの予想に反し、1.42ｇ／cm3を越
え、とくに1.50ｇ／cm3以下なる範囲の高い繊維密
度を有する耐炎化繊維を300〜800℃の温度で25％
以内延伸して熱処理し、次いで800℃以上の温度
で熱処理することによつて、密度が1.7より大き
く1.78ｇ／cm3程度迄の低密度でしかも高強度、高
弾性率の炭素繊維を10分以内の熱処理時間でも作
り得る本発明を完成したのである。
耐炎化処理糸を作るに際して用いるアクリロニ
トリル系重合体はポリアクリロニトリル又は85重
量％以上のアクリロニトリルと他の共重合可能な
単量体、例えばアクリル酸、メタクリル酸、クロ
トン酸、イタコン酸等の不飽和カルボン酸類、こ
れら不飽和カルボン酸のメチル、エチル、ブチ
ル、プロピル、ヘキシル、２−エチルヘキシル、
ステアリルエステル類、アクリル酸アミド、メタ
クリル酸アミド及びこれら酸アミド類のメチロー
ル化物類、Ｎ−アルコキシメチル化物類、ジアセ
トンアクリルアミド、酢酸ビニル、プロピオン酸
ビニル、塩化ビニル、臭化ビニル、アリルスルホ
ン酸、メタリルスルホン酸、ビニルベンゼンスル
ホン酸、ナトリウム−Ｐ−スルホフエニルメタリ
ルエーテルなどを適宜共重合せしめた共重合体な
どである。
本発明は上述した特性を有する耐炎化処理糸を
300〜800℃の範囲の温度の不活性雰囲気下で25％
まで、好ましくは20％までの範囲の伸長を加えな
がら炭素化処理することが必要である。
かくの如き処理を施すことによつて得られる炭
素繊維の結晶配向度を従来法に比べて高めること
ができ、その結果高強度の炭素繊維を作ることに
成功したものである。本発明の800℃までの炭素
化処理工程に於ける繊維の伸長とは原料として用
いる耐炎化処理糸に対し、収縮を起させないこと
を意味し、好ましくは０〜20％なる範囲の伸長を
意味するものである。この工程に於ける繊維の伸
長を25％を越えて大きくする場合には繊維構造破
壊を招くようになり得られる炭素繊維の強度低下
を招くようになり一方、この工程に於て収縮が起
るような処理を加えると、得られる炭素繊維の結
晶配向度を実質的に高めることができず、従つて
最終的に得られる炭素繊維の強度を高めることが
できない。また、この処理工程に於ける処理時間
は好ましくは0.5〜40分程度とするのがよい。
上述の如くして得た伸長、炭素化処理した繊維
は、本発明に於ては800℃以上の温度の不活性雰
囲気中で、好ましくは耐炎化処理糸の原長に対し
負の長さとならないように炭素化を完了せしめ
る。この800℃以上の不活性雰囲気中での炭素化
処理を施さないものは高弾性、高強度の炭素繊維
とすることはできない。また、この工程で、出発
原料として用いた耐炎化処理糸の成長に対し、負
となるような収縮が起るような条件で炭素化を完
了する際には、得られる炭素繊維の結晶配向度を
高めることができないため、高強度の炭素繊維と
することはできないので、本発明においてはこの
工程に於ける炭素繊維の収縮は出発原料として用
いた耐炎性繊維の原長に対し負となるようにして
はならない。好ましくは前炭素化処理終了後の繊
維長に対し、後炭素化処理後の繊維の収縮率は10
％以下とするのがよい。
本発明の方法の実施に際し、800℃までの温度
範囲での不活性雰囲気下での前炭素化処理工程
と、800℃以上の不活性雰囲気下での後炭素化処
理工程とは連続的に温度勾配を有する連続炉や多
段昇温工程を取る多段炉を用いる方法、或いは前
炭素化処理工程で一度巻取つた後、後炭素化処理
炉で焼成する方法など種々の方法を取り得る。
本発明に於ては出発原料として用いる耐炎化処
理糸として繊維密度が1.42ｇ／cm3を越えるものを
用いること、前炭素化処理工程に於て０〜25％な
る範囲の伸長を施すこと、並びに後炭素化処理工
程を制限収縮下に行なうことによつて軽量にして
高強度の炭素繊維を得ることに成功したものであ
るが、もう一つの本発明の特徴は高強度、高弾性
の炭素繊維の短時間に製造しうる点である。この
目的を達成するためには、前炭素化処理時間を
0.5〜40分程度となし、移炭素化処理時間を前炭
素化処理時間の1/1〜1/15程度となすことによつ
て十分に性能の優れた炭素繊維を得ることができ
る。
本発明は従来の炭素繊維の製法に比べ、出発原
料として用いる耐炎化処理糸を特定化したこと、
炭素化工程を基本的に２分化し、その前炭素化工
程に於て25％、好ましくは20％までの伸長を加
え、後炭素化工程に於ては制限収縮下に炭素化を
完了せしめることによつて高強度、高弾性の炭素
繊維を短時間に製造し得た点に大きな特徴を有す
るものである。
以下実施例により本発明を更に詳細に説明する
が、強度、弾性率、Ｘ−線配向度、収率の測定は
次に示す方法に従つて求めたものである。
強度および弾性率
エポキシ樹脂（シエル化学社製：エピコート
828）を含浸硬化処理せしめた炭素繊維束を試長
200mm、変形速度５mm／minなる条件で引張り破
断試験法にて求めた。
Ｘ−線配向度
一方向に引き揃えた炭素繊維のＸ−線回折写真
において黒鉛結晶の（002）反射に基ずく赤道線
上に極大を有する回折パターンに注目してデイフ
ラクトメーター（理学電機製：Ｘ−線源Cu、
KCl）によつて方位角方向に測定し、得られた方
位角方向の強度分布曲線の半価中Ｈ（degree）を
求め、次式によつて微結晶のＸ−線配向度π
（002）を求めた。
π（002）＝（180−Ｈ）／180×100（％）
収 率
耐炎化処理糸および耐炎化処理糸を焼成して得
た炭素繊維の重量繊度を絶乾法で求めた値をそれ
ぞれDpおよびDcとする。一方、炭素化処理にお
ける伸長操作による耐炎化処理糸長さlpから炭素
繊維長さlcに至る変化、糸の移動速度を測定し次
式によつて算出した。
収縮＝Dc／Dp÷lc／lp×100（％）
実施例 １
アクリロニトリル／メチルアクリレート／メタ
クリル酸＝95／４／１なる共重合体を湿式法によ
り繊維化してフイラメント数3000本、単糸デニー
ル1.5d、引張強度6.2ｇ／ｄ、破断伸度15.4％のマ
ルチフイラメントを得た。この繊維束を230〜290
℃の温度勾配をもつた炉中を初期段階で３〜10％
延伸しながら通過せしめて耐炎化処理し、繊維密
度が第１表に示される如き値を有する耐炎化糸を
作り、次いで不活性雰囲気下600℃で、伸長率10
％で処理時間３分なる条件で前処理し、その後
1300℃で定長下で1.5分熱処理して炭素繊維を作
成した。得られた繊維の性能を第１表に示した。
【表】DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high-performance carbon fiber or graphite fiber, and in particular uses an acrylonitrile-based synthetic fiber precursor to produce lightweight, high-strength,
A method for producing highly elastic carbon fibers or graphite fibers in a short time and with high yield. As a method for producing a carbon fiber precursor using an acrylic synthetic fiber precursor, first, the fiber is elongated by applying a tension of 0.01 to 0.15 g/d to the precursor in an oxidizing atmosphere at 200 to 250°C. After pre-oxidation treatment, 250
A method of carbonization treatment in a non-oxidizing atmosphere with a temperature gradient of 1,000°C or higher was published in the Japanese Patent Publication No. 44-
It is known as described in the specification of Japanese Patent Publication No. 21175 and Japanese Patent Publication No. 12540/1983. Among the performance of carbon fiber made by these methods,
The modulus of elasticity is considered to be determined primarily by the heat treatment temperature of the fibers, and it is relatively easy to produce carbon fibers having a desired modulus of elasticity. However, the relationship between the strength and density of carbon fibers and the method of manufacturing carbon fibers has not been clarified in any way. It is only assumed that there is some kind of relationship between the minute cracks that exist and the strength. Conventionally, the method for manufacturing carbon fibers that has been developed involves carbonizing or graphitizing the pre-oxidized fibers with a density of less than 1.40 at a temperature of 250°C or higher to obtain a fiber with a density of 1.80 or more. Carbon fibers are obtained, but in this conventional method, the fiber length is said to shrink by several to 20% relative to the raw material fiber length during the carbonization or graphitization process. Despite the study of a method of firing the yarn while applying tension to reduce this shrinkage, it has not been possible to create high-strength carbon fibers by applying elongation to the fibers in the carbonization process of flame-resistant fibers. When attempting to obtain carbon fibers, not only yarn breakage occurs, but also high strength carbon fibers cannot be obtained. In view of the current situation as described above, the present invention was developed with the aim of obtaining high-strength carbon fibers, and
1.42 or less flame resistant fiber at a temperature of 800℃ or less by 25%
By performing pre-carbonization treatment while stretching at the following ratios, and then performing complete carbonization,
After discovering that the object could be achieved, we filed a patent application earlier, and as a result of our studies aimed at obtaining lighter carbon fibers with even higher strength and modulus, we completed the present invention. The gist of the present invention is to heat a flame-retardant yarn made from acrylonitrile-based synthetic fibers with a fiber density of more than 1.42 g/cm 3 and less than 1.50 g/cm 3 in an inert atmosphere in a temperature range of 300 to 800°C. Carbonization treatment is performed while elongating up to 25%, followed by 800%
The present invention provides a method for producing high-performance carbon fiber, which is characterized in that carbonization treatment is completed while heat treatment is performed under limited shrinkage at a temperature of 0.degree. C. or higher. The flame-resistant treated yarn used in carrying out the present invention has a fiber density exceeding 1.42 g/cm 3 and any flame-resistant treated yarn can be used as long as it has a carbon content of about 62 to 68% by weight. Particularly preferred are fibers made from polyacrylonitrile or acrylonitrile-based polymers in which the polymerization amount of acrylonitrile is 85% by weight or more, while shrinking or under constant length in an oxidizing atmosphere in a temperature range of 200°C to 400°C. It is made by oxidizing the acrylic fiber while stretching it, and in particular, it is made by oxidizing the acrylic fiber in an oxidizing atmosphere until the reaction of about 8.5 to 12% of the nitrile groups is completed. After stretching, the fiber density is increased under conditions where the length of the flame-resistant yarn is not negative with respect to the length of the original fiber.
It is preferable to use a flame-retardant yarn having a weight of 1.42 g/cm 3 or more, and the present invention can be exhibited most efficiently when such a flame-resistant yarn is used. The fiber density of the flame-resistant treated yarn is measured by measuring a short piece of the flame-resistant treated yarn that has been dried and dehumidified using a xylol/carbon tetrachloride density gradient tube. In this measurement method, a test fiber piece is immersed in advance in the above-mentioned mixed solvent whose density is approximately equal to the fiber density, and the sample is degassed and placed in a density gradient tube.The measurement temperature is 30℃, and the measurement time after immersion is 3 hours. It was measured as follows. In carrying out the present invention, a flame-retardant treated yarn having a fiber density of less than 1.42 g/cm 3 is heated under an inert atmosphere to
When pre-carbonized by stretching 25% or less in the range of ℃ and then treated at high temperature, the fiber density is 1.8 g/cm 3 or more,
Carbon fiber with excellent elastic modulus can be made, but
Such high-density materials are in short supply when used as basic materials for aircraft, automobiles, etc., which are important application fields for carbon fibers, and it is necessary to develop carbon fibers with as low a density as possible, as well as high strength and high modulus of elasticity. While this is desired, the study of methods that can produce it at high speed has also become a major issue. In order to make fibers that can achieve these purposes, it has been necessary to use a density of 1.30 to 1.42g/
It has been considered desirable to heat-treat flame-retardant fibers with a relatively low fiber density of cm 3 at a temperature higher than the carbonization temperature, but the inventors have conducted various studies and have confirmed that these predictions have not been met. On the other hand, flame-retardant fibers with a high fiber density of more than 1.42 g/cm 3 and especially less than 1.50 g/cm 3 are used at 25% at a temperature of 300 to 800°C.
By stretching and heat treating at a temperature of 800°C or higher, carbon fibers with low density, high strength, and high elastic modulus, with a density greater than 1.7 and up to about 1.78 g/ cm3 , can be made in 10 minutes. They have completed the present invention, which can be produced with a heat treatment time of less than 30 minutes. The acrylonitrile polymer used to make the flame-resistant yarn is polyacrylonitrile or 85% by weight or more of acrylonitrile and other copolymerizable monomers, such as unsaturated carboxylic acid such as acrylic acid, methacrylic acid, crotonic acid, and itaconic acid. Acids, methyl, ethyl, butyl, propyl, hexyl, 2-ethylhexyl of these unsaturated carboxylic acids,
Stearyl esters, acrylic acid amide, methacrylic acid amide and methylolated products of these acid amides, N-alkoxymethylated products, diacetone acrylamide, vinyl acetate, vinyl propionate, vinyl chloride, vinyl bromide, allyl sulfonic acid, These include copolymers obtained by appropriately copolymerizing methallyl sulfonic acid, vinylbenzenesulfonic acid, sodium-P-sulfophenyl methallyl ether, and the like. The present invention uses flame-resistant treated yarn having the above-mentioned characteristics.
25% under inert atmosphere at temperatures ranging from 300 to 800℃
It is necessary to carry out the carbonization treatment while adding elongation in the range of up to 20%, preferably up to 20%. By performing such a treatment, the degree of crystal orientation of the carbon fibers obtained can be increased compared to conventional methods, and as a result, it has been possible to successfully produce high-strength carbon fibers. The elongation of fibers in the carbonization process up to 800°C in the present invention means that the flame-retardant yarn used as a raw material does not shrink, preferably elongation in the range of 0 to 20%. It is something to do. If the elongation of the fibers in this process is increased by more than 25%, the fiber structure will be destroyed and the strength of the resulting carbon fibers will decrease, while shrinkage will occur in this process. If such a treatment is applied, the degree of crystal orientation of the obtained carbon fiber cannot be substantially increased, and therefore the strength of the ultimately obtained carbon fiber cannot be increased. Further, the treatment time in this treatment step is preferably about 0.5 to 40 minutes. In the present invention, the elongated and carbonized fibers obtained as described above preferably do not have a negative length relative to the original length of the flame-retardant yarn in an inert atmosphere at a temperature of 800°C or higher. Carbonization will be completed in this way. Unless this carbonization treatment is performed in an inert atmosphere at 800° C. or higher, carbon fibers with high elasticity and high strength cannot be obtained. In addition, in this process, when carbonization is completed under conditions that cause negative shrinkage with respect to the growth of the flame-resistant treated yarn used as the starting material, the degree of crystal orientation of the resulting carbon fiber is Therefore, in the present invention, the shrinkage of the carbon fiber in this process is negative with respect to the original length of the flame-resistant fiber used as the starting material. Do not do this. Preferably, the shrinkage rate of the fiber after the post-carbonization process is 10% relative to the fiber length after the pre-carbonization process.
% or less. When carrying out the method of the present invention, a pre-carbonization step under an inert atmosphere at a temperature range of up to 800°C and a post-carbonization step under an inert atmosphere at a temperature range of 800°C or higher are performed continuously at a temperature of up to 800°C. Various methods can be used, such as a method using a continuous furnace with a gradient, a multistage furnace with a multistage temperature raising process, or a method in which the material is wound once in a pre-carbonization process and then fired in a post-carbonization process furnace. In the present invention, the flame-retardant yarn used as the starting material has a fiber density exceeding 1.42 g/cm 3 , and is elongated in the range of 0 to 25% in the pre-carbonization process. In addition, by performing the post-carbonization process under limited shrinkage, we succeeded in obtaining lightweight and high-strength carbon fibers. Another feature of the present invention is that high-strength, high-elastic carbon fibers can be obtained. The advantage is that fibers can be produced in a short time. To achieve this objective, the pre-carbonization treatment time is
Carbon fibers with sufficiently excellent performance can be obtained by setting the carbonization treatment time to about 1/1 to 1/15 of the pre-carbonization treatment time. Compared to conventional carbon fiber manufacturing methods, the present invention specifies the flame-retardant yarn used as the starting material;
Basically, the carbonization process is divided into two parts, and in the pre-carbonization process, elongation is applied by 25%, preferably up to 20%, and in the post-carbonization process, carbonization is completed under limited contraction. The major feature of this method is that high-strength, high-elasticity carbon fibers can be produced in a short period of time. The present invention will be explained in more detail with reference to Examples below. Strength, elastic modulus, X-ray orientation, and yield were determined according to the following methods. Strength and elastic modulus Epoxy resin (manufactured by Ciel Chemical Co., Ltd.: Epicoat)
Test length of carbon fiber bundle impregnated and hardened with 828)
It was determined by a tensile fracture test method under the conditions of 200 mm and a deformation rate of 5 mm/min. X-ray orientation In an X-ray diffraction photograph of carbon fibers aligned in one direction, we focused on the diffraction pattern with a maximum on the equator line based on the (002) reflection of graphite crystals using a diffractometer (manufactured by Rigaku Denki: X-ray source Cu,
KCl) was measured in the azimuthal direction, and the half value H (degree) of the obtained intensity distribution curve in the azimuthal direction was determined, and the X-ray orientation degree π of the microcrystal was calculated using the following formula.
(002) was found. π (002) = (180-H) / 180 × 100 (%) Yield The weight fineness of the flame-retardant treated yarn and the carbon fiber obtained by firing the flame-retardant treated yarn is determined by the bone-dry method and is Dp. and Dc. On the other hand, the change from the flame-retardant yarn length lp to the carbon fiber length lc due to the elongation operation in the carbonization treatment and the yarn movement speed were measured and calculated using the following formula. Shrinkage = Dc/Dp÷lc/lp×100 (%) Example 1 A copolymer of acrylonitrile/methyl acrylate/methacrylic acid = 95/4/1 was made into fibers by a wet method, with a number of filaments of 3000 and a single yarn denier of 1.5. A multifilament with a tensile strength of 6.2 g/d and a breaking elongation of 15.4% was obtained. This fiber bundle is 230~290
3 to 10% in the initial stage in a furnace with a temperature gradient of ℃.
The flame resistant yarn is made by passing through it while being stretched to make it flame resistant, and the fiber density is as shown in Table 1.
% and treatment time is 3 minutes, and then
Carbon fibers were produced by heat treatment at 1300°C for 1.5 minutes at a constant length. The performance of the obtained fibers is shown in Table 1. 【table】