【発明の詳細な説明】[Detailed description of the invention]
本発明は高強度かつ高弾性率の炭素繊維の製造
方法に関する。
現在、炭素繊維は主にポリアクリロニトリルを
原料として製造されている。しかしながらポリア
クリロニトリルを原料とした場合、原料が高価で
あり、また加熱炭化時において繊維状の原形がく
ずれ易く、さらに炭化収率も悪いという欠点があ
る。
近年、この点に着目して安価なピツチを原料と
して炭素繊維を製造する方法が数多く報告されて
いる。しかしながら、ピツチを原料として得られ
る炭素繊維は、ポリアクリロニトリル系炭素繊維
に比べ、強度が劣るという問題がある。
最近になつて、市販の石油ピツチを熱処理して
メソ相（mesophase）と呼ばれる光学的異方性の
液晶を40〜90重量％含有するピツチを得、このメ
ソ相を含有するピツチを溶融紡糸した後、不融化
し、次いで炭化あるいは更に黒鉛化することによ
り、弾性率および強度が向上した炭素繊維が得ら
れることが報告された（特開昭49−19127号）
しかしながら、メソ相を40重量％以上含有する
ピツチは軟化点および粘度がきわめて高いため、
溶融紡糸は通常350℃以上の高い温度で行うこと
が必要となる。このため、溶融紡糸の過程でピツ
チの熱分解が起こ易く、軽質ガスが発生するなど
の問題が生じ均一な紡糸は困難となる。
また軟化点および粘度を調整する目的で、メソ
相の含有量を低くおさえた場合には光学的に異方
性の領域と等方性の領域とが分離し、溶融特性が
著しく悪化する。すなわち、メソ相含量の低いピ
ツチを溶融紡糸したとしても、糸切れが頻発し、
はなはだしい場合には未溶解物粒子を連ねたよう
な繊維となり、さらにこの繊維の公知の方法で処
理して炭素繊維を製造したとしても、高強度、高
弾性率のものは得られない。
本発明者らは、低軟化点および低粘度の特性を
有するメソ相含有量の低いピツチについて鋭意検
討した結果、溶融特性を改善し、均一な紡糸を可
能とすることができ、さらに高強度かつ高弾性率
の炭素繊維を製造し得ることができたものであ
る。
すなわち、本発明は、光学的に異方性な領域を
５〜35重量％含有するピツチで酸化性ガスで接触
処理して得られるピツチを溶融紡糸した、不融化
処理および炭化処理あるいは更に黒鉛化処理して
炭素繊維を製造する方法を提供するものである。
このような本発明の製造方法により均一な紡糸が
可能となり、高強度かつ高弾性率の炭素繊維を製
造することができることは全く予期せざることで
あつた。
メソ相を５〜35重量％含有するピツチは、石炭
系ピツチ、石油系ピツチ等の炭素質ピツチを加熱
処理してメソ相化することにより得る。
メソ相化は、通常、常圧あるいは減圧下に温度
340〜450℃、好ましくは370〜420℃にて熱処理す
ることにより行われる。また、このときのメソ相
化に際し、窒素等の不活性ガスを通気しながら熱
処理することも好ましく用いられる。加熱処理時
間は温度、不活性ガスの通気量等の条件により任
意に変え得るものであるが、通常１分〜30時間、
好ましくは５分〜20時間で行う。不活性ガスの通
気量は0.7〜5.0scfh／1bピツチが好ましい。
メソ相化によりピツチ中のメソ相割合を５〜35
重量％の範囲内となるように調整する。この範囲
からはずれた場合には本発明の効果は期待できな
い。
次に、メソ相を５〜35重量％含有するピツチを
酸化性ガスで接触処理する。通常、常圧あるいは
加圧下に温度150〜400℃、好ましくは200〜350℃
で酸化性ガスをピツチに通気して処理する。処理
時間は温度、酸化性ガスの通気量等の条件により
任意に変え得るものではあるが、通常５分〜３時
間、好ましくは10分〜２時間にて行われる。酸化
性ガスの通気量は0.5〜5.0scfh／1bピツチ、好ま
しくは1.0〜3.5scfh／1bピツチである。酸化性ガ
スとしては空気、酸素、オゾン、窒素酸化物、亜
硫酸ガスおよびこれら２種以上の混合ガス等が用
いられる。
かくして調製されたピツチは、押出法、遠心
法、霧吹法等の公知の方法にて溶融紡糸が行われ
る。
溶融紡糸されて得られるピツチ繊維は、次に酸
化性ガス雰囲気下で不融化処理が施される。酸化
性ガスとしては、通常、酸素、オゾン、空気、窒
素酸化物、ハロゲン、亜硫酸ガス等の酸化性ガス
を１種あるいは２種以上用いる。この不融化処理
は、被処理体である溶融紡糸されたピツチ繊維が
軟化変形しない温度条件下で実施される。例えば
20〜360℃、好ましくは20〜300℃の温度が採用さ
れる。また処理時間は通常、５分〜10時間であ
る。
不融化処理されたピツチ繊維は、次に不活性ガ
ス雰囲気下で炭化あるいは更に黒鉛化を行い、炭
素繊維を得る。炭化は通常、温度800〜2500℃で
行う。一般には炭化に要する処理時間は0.5分〜
10時間である。さらに黒鉛化を行う場合には、温
度2500〜3500℃で、通常１秒〜１時間行う。
また、不融化、炭化あるいは黒鉛化処理の際、
必要であれば収縮や変形等を防止する目的で、被
処理体に若干の荷重あるいは張力をかけておくこ
ともできる。
以下に実施例および比較例をあげて本発明を具
体的に説明するが、本発明はこれらに制限される
ものではない。
実施例 １
ナフサ830℃で水蒸気分解した際に副生した沸
点200℃以上の重質油（性状を第１表に示す）を
温度400℃、圧力15Kg／cm3・Ｇにて３時間熱処理
した。この熱処理油を250℃／１mmＨｇにて蒸留
し、軽質分を留去させ、軟化点82℃の原料ピツチ
(A)を得た。この原料ピツチ(A)30ｇに対し、窒素を
600ml／分で通気しながら撹拌し、温度400℃で１
時間熱処理を行い、軟化点220℃、メソ相含有量
20重量％のピツチ(1)を得た。
次にこのピツチ(1)30ｇに対し、空気を600ml／
分で通気しながら撹拌し、300℃で90分間処理を
行い、軟化点260℃、メソ相含有量20重量％のピ
ツチ(2)を得た。
かく調製されてピツチ(2)をノズル径0.3mmφ、
Ｌ／Ｄ＝２の紡糸器を用い330℃で溶融紡糸し、
16〜19μのピツチ繊維をつくり、さらに下記に示
す条件にて不融化、炭化および黒鉛化処理して炭
素繊維を得た。
Γ不融化条件：空気雰囲気中で、200℃までは３
℃／分、300℃までは１℃／分の昇温速度で
加熱し、300℃で30分間保持。
Γ炭化条件：窒素雰囲気中で、５℃／分で昇温し
1000℃で30分間保持。
Γ黒鉛化条件：アルゴン気流中で、25℃／分の昇
温速度で、2500℃まで加熱処理。
得られた炭素繊維の引張強度は160Kg／mm2、ヤ
ング率は30ton／mm2であつた。
The present invention relates to a method for producing carbon fibers with high strength and high modulus of elasticity. Currently, carbon fiber is mainly manufactured using polyacrylonitrile as a raw material. However, when polyacrylonitrile is used as a raw material, there are disadvantages in that the raw material is expensive, the original fibrous shape is easily destroyed during heating and carbonization, and the carbonization yield is also poor. In recent years, focusing on this point, many methods have been reported for producing carbon fibers using inexpensive pitch as a raw material. However, carbon fibers obtained using pitch as a raw material have a problem in that their strength is inferior to that of polyacrylonitrile-based carbon fibers. Recently, commercially available petroleum pitch was heat-treated to obtain pitch containing 40 to 90% by weight of optically anisotropic liquid crystal called mesophase, and pitch containing this mesophase was melt-spun. It has been reported that carbon fibers with improved elastic modulus and strength can be obtained by making them infusible and then carbonizing or graphitizing them (Japanese Patent Application Laid-open No. 19127-1989). Pitch containing above has extremely high softening point and viscosity,
Melt spinning usually needs to be carried out at a high temperature of 350°C or higher. Therefore, thermal decomposition of the pitch tends to occur during the melt spinning process, causing problems such as the generation of light gas and making uniform spinning difficult. Furthermore, when the mesophase content is kept low for the purpose of adjusting the softening point and viscosity, the optically anisotropic region and the isotropic region are separated, and the melting properties are significantly deteriorated. In other words, even if pitch with a low mesophase content is melt-spun, thread breakage occurs frequently.
In extreme cases, the fiber becomes a string of undissolved particles, and even if this fiber is processed by a known method to produce carbon fiber, it will not be possible to obtain a carbon fiber with high strength and high modulus. As a result of intensive studies on pitches with low mesophase content that have the characteristics of low softening point and low viscosity, the present inventors have found that it is possible to improve melting characteristics and enable uniform spinning, as well as to achieve high strength and This made it possible to produce carbon fiber with a high modulus of elasticity. That is, the present invention involves melt-spinning pitch obtained by contact treatment with an oxidizing gas using pitch containing 5 to 35% by weight of an optically anisotropic region, infusible treatment and carbonization treatment, or further graphitization treatment. The present invention provides a method of processing carbon fibers to produce carbon fibers.
It was completely unexpected that the production method of the present invention enables uniform spinning and produces carbon fibers with high strength and high modulus of elasticity. Pitch containing 5 to 35% by weight of mesophase is obtained by heat-treating carbonaceous pitch such as coal-based pitch or petroleum-based pitch to convert it into a mesophase. Mesophase formation is usually carried out at normal pressure or reduced pressure.
This is carried out by heat treatment at 340-450°C, preferably 370-420°C. In addition, when forming the mesophase at this time, it is also preferable to perform heat treatment while passing an inert gas such as nitrogen. The heat treatment time can be changed arbitrarily depending on conditions such as temperature and amount of inert gas ventilation, but is usually 1 minute to 30 hours.
Preferably it is carried out for 5 minutes to 20 hours. The amount of inert gas ventilation is preferably 0.7 to 5.0 scfh/lb pitch. The meso phase ratio in pitch is increased from 5 to 35 by meso phase formation.
Adjust so that it is within the weight% range. If it deviates from this range, the effects of the present invention cannot be expected. Next, the pitch containing 5 to 35% by weight of mesophase is contacted with an oxidizing gas. Usually at normal pressure or under pressure at a temperature of 150 to 400℃, preferably 200 to 350℃
Process by venting oxidizing gas into the pit. Although the treatment time can be arbitrarily changed depending on conditions such as temperature and amount of oxidizing gas, it is usually carried out for 5 minutes to 3 hours, preferably 10 minutes to 2 hours. The amount of ventilation of the oxidizing gas is 0.5 to 5.0 scfh/lb pitch, preferably 1.0 to 3.5 scfh/lb pitch. As the oxidizing gas, air, oxygen, ozone, nitrogen oxides, sulfur dioxide gas, and a mixed gas of two or more of these gases are used. The pitch thus prepared is melt-spun by a known method such as an extrusion method, a centrifugation method, or an atomization method. The pitch fiber obtained by melt spinning is then subjected to an infusible treatment in an oxidizing gas atmosphere. As the oxidizing gas, one or more of oxidizing gases such as oxygen, ozone, air, nitrogen oxide, halogen, and sulfur dioxide gas are usually used. This infusibility treatment is carried out under temperature conditions that do not soften or deform the melt-spun pitch fibers to be treated. for example
Temperatures of 20-360°C, preferably 20-300°C are employed. Further, the treatment time is usually 5 minutes to 10 hours. The infusible pitch fibers are then carbonized or further graphitized in an inert gas atmosphere to obtain carbon fibers. Carbonization is usually carried out at a temperature of 800-2500°C. Generally, the processing time required for carbonization is 0.5 minutes ~
It is 10 hours. Further, when graphitizing is carried out, it is carried out at a temperature of 2500 to 3500°C, usually for 1 second to 1 hour. In addition, during infusibility, carbonization or graphitization treatment,
If necessary, a slight load or tension may be applied to the object to be processed in order to prevent shrinkage, deformation, etc. The present invention will be specifically explained below with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Example 1 Heavy oil with a boiling point of 200°C or higher (properties shown in Table 1), which was produced as a by-product when steam decomposing naphtha at 830°C, was heat-treated at a temperature of 400°C and a pressure of 15 kg/cm 3 G for 3 hours. . This heat-treated oil is distilled at 250℃/1mmHg to remove light components, and the raw material pitch with a softening point of 82℃ is distilled.
I got (A). Add nitrogen to 30g of this raw material pitch (A).
Stir with ventilation at 600 ml/min, 1 hour at 400°C.
After time heat treatment, softening point 220℃, mesophase content
20% by weight of pitch (1) was obtained. Next, add 600ml of air to 30g of this pitch (1).
The mixture was stirred with ventilation for 90 minutes and treated at 300°C for 90 minutes to obtain pitch (2) with a softening point of 260°C and a mesophase content of 20% by weight. The thus prepared pitch (2) was heated with a nozzle diameter of 0.3 mmφ.
Melt-spun at 330°C using a spinning machine with L/D = 2,
Pitch fibers with a diameter of 16 to 19μ were prepared, and further subjected to infusible, carbonized, and graphitized treatments under the conditions shown below to obtain carbon fibers. ΓInfusibility conditions: 3 in air atmosphere up to 200℃
℃/min, heat at a heating rate of 1℃/min up to 300℃, and hold at 300℃ for 30 minutes. Γ Carbonization conditions: In a nitrogen atmosphere, temperature was increased at 5°C/min.
Hold at 1000℃ for 30 minutes. Γ Graphitization conditions: Heat treatment in an argon stream at a heating rate of 25°C/min to 2500°C. The obtained carbon fiber had a tensile strength of 160 Kg/mm 2 and a Young's modulus of 30 ton/mm 2 .
【表】
比較例 １
実施例１で用いたピツチ(1)を酸化性ガスで処理
しないで、実施例１と同様の方法で溶融紡糸を行
つたところ、糸切れが頻発し連続的に紡糸するこ
とができなかつた。
実施例 ２
実施例１で用いた重質油を実施例１と同様の方
法で窒素を通気しながら撹拌し、400℃で２時間
熱処理し、軟化点230℃、メソ相含有量33重量％
のピツチを得た。
次に、このピツチを実施例１と同様の方法で空
気を通気しながら撹拌し、300℃で90分間処理を
行い、軟化点270℃、メソ相含有量33重量％のピ
ツチを得た。
かく調製されたピツチを実施例１で用いた紡糸
器を用い340℃で溶融紡糸した後、実施例１と同
様の方法で不融化、炭化および黒鉛化処理して炭
素繊維を得た。
得られた炭素繊維の引張強度は190Kg／mm2、ヤ
ング率は35ton／mm2であつた。
実施例 ３
実施例１で用いた重質油を実施例１と同様の方
法で窒素を通気しながら撹拌し、400℃で30分間
熱処理し、軟化点198℃、メソ相含有量８重量％
のピツチを得た。
次に、このピツチを実施例１と同様の方法で空
気を通気しながら撹拌し、300℃で90分間処理を
行い、軟化点243℃、メソ相含有量８重量％のピ
ツチを得た。
かく調製されたピツチを実施例１で用いた紡糸
器を用い315℃で溶融紡糸した後、実施例１と同
様の方法で不融化、炭化および黒鉛化処理して炭
素繊維を得た。
得られた炭素繊維の引張強度は150Kg／mm2、ヤ
ング率は27ton／mm2であつた。
実施例 ４
アラビア系原油の減圧軽油をシリカ・アルミナ
系触媒を用いて500℃にて接触分解して得られた
重質油（性状を第２表に示す）を温度430℃、圧
力15Kg／cm2．Ｇにて３時間熱処理した。この熱処
理油を250℃／１mmＨｇにて蒸留し、軽質分を留
去させ、軟化点85℃の原料ピツチ(B)を得た。この
原料ピツチ(B)を、実施例１と同様の方法で窒素を
通気しながら撹拌し、温度400℃で1.5時間熱処理
を行い、軟化点225℃、メソ相含有量32重量％の
ピツチ(3)を得た。
次に、このピツチ(3)を実施例１の同様の方法で
空気を通気しながら撹拌し、300℃で90分間処理
を行い軟化点260、メソ相含有量32重量％のピツ
チ(4)を得た。
かく調製されたピツチ(4)を実施例１で使用した
紡糸器を用い、330℃で溶融紡糸を行つた後、実
施例１と同様の方法で不融化、炭化および黒鉛化
処理して炭素繊維を得た。
得られた炭素繊維の引張速度は225Kg／mm2、ヤ
ング率は43ton／mm2であつた。[Table] Comparative Example 1 When Pitch (1) used in Example 1 was melt-spun in the same manner as in Example 1 without being treated with oxidizing gas, yarn breakage occurred frequently and the yarn was spun continuously. I couldn't do it. Example 2 The heavy oil used in Example 1 was stirred while bubbling nitrogen in the same manner as in Example 1, and heat-treated at 400°C for 2 hours, resulting in a softening point of 230°C and a mesophase content of 33% by weight.
I got the pitch. Next, this pitch was stirred while aerating air in the same manner as in Example 1, and treated at 300° C. for 90 minutes to obtain pitch with a softening point of 270° C. and a mesophase content of 33% by weight. The pitch thus prepared was melt-spun at 340° C. using the spinning machine used in Example 1, and then subjected to infusibility, carbonization and graphitization treatments in the same manner as in Example 1 to obtain carbon fibers. The obtained carbon fiber had a tensile strength of 190 Kg/mm 2 and a Young's modulus of 35 ton/mm 2 . Example 3 The heavy oil used in Example 1 was stirred while bubbling nitrogen in the same manner as in Example 1, and heat treated at 400°C for 30 minutes, resulting in a softening point of 198°C and a mesophase content of 8% by weight.
I got the pitch. Next, this pitch was stirred while aerating with air in the same manner as in Example 1, and treated at 300°C for 90 minutes to obtain pitch with a softening point of 243°C and a mesophase content of 8% by weight. The pitch thus prepared was melt-spun at 315° C. using the spinning machine used in Example 1, and then subjected to infusibility, carbonization and graphitization treatments in the same manner as in Example 1 to obtain carbon fibers. The obtained carbon fiber had a tensile strength of 150 Kg/mm 2 and a Young's modulus of 27 ton/mm 2 . Example 4 Heavy oil (properties shown in Table 2) obtained by catalytically cracking vacuum gas oil of Arabian crude oil at 500°C using a silica/alumina catalyst was heated at a temperature of 430°C and a pressure of 15 kg/cm. 2 . Heat treatment was performed at G for 3 hours. This heat-treated oil was distilled at 250°C/1 mmHg to remove light components to obtain raw material pitch (B) with a softening point of 85°C. This raw material pitch (B) was stirred while bubbling nitrogen in the same manner as in Example 1, and heat-treated at a temperature of 400°C for 1.5 hours. ) was obtained. Next, this pitch (3) was stirred while aerating air in the same manner as in Example 1, and treated at 300°C for 90 minutes to produce pitch (4) with a softening point of 260 and a mesophase content of 32% by weight. Obtained. Pitch (4) thus prepared was melt-spun at 330°C using the spinning machine used in Example 1, and then treated to be infusible, carbonized, and graphitized in the same manner as in Example 1 to obtain carbon fibers. I got it. The obtained carbon fiber had a tensile speed of 225 Kg/mm 2 and a Young's modulus of 43 ton/mm 2 .
【表】【table】
【表】
比較例 ２
実施例４で用いたピツチ(3)を酸化性ガスで処理
しないで、実施例１と同様な方法で溶融紡糸を行
つたところ、糸切れが頻発し連続的に紡糸するこ
とができなかつた。[Table] Comparative Example 2 When the pitch (3) used in Example 4 was melt-spun in the same manner as in Example 1 without being treated with oxidizing gas, yarn breakage occurred frequently and the yarn was spun continuously. I couldn't do it.