JP3651621B2 - Method for producing polybenzazole fiber - Google Patents

Description

【００１０】
【化２】

【００１１】
ＰＢＺポリマーのドープを形成するための好適な酸性溶媒としては、クレゾールやそのポリマーを溶解し得る非酸化性の酸が含まれる。好適な酸溶媒の例としては、ポリリン酸、メタンスルホン酸および高濃度の硫酸あるいはそれらの混合物が挙げられる。更に適する溶媒は溶解度の高いポリリン酸およびメタンスルホン酸である。また最も適する溶媒は、ポリリン酸である。
【００１２】
溶液のポリマー濃度は好ましくは少なくとも約７重量％であり、更に好ましくは、少なくとも約１０重量％、最も好ましくは少なくとも１４重量％である。最大濃度は、例えばポリマーの溶解性やドープ粘度といった実際上の取扱性により限定される。それらの限界要因の為に、ポリマー濃度は通常では２０重量％を越える事はない。
【００１３】
好適なポリマーやコポリマーあるいはドープは公知の手法により合成される。例えば、Wolfe らのU.S.Patent 4,533,693(August 6,1985) 、SybertらのU.S.Patent 4,772,678(September 20,1988) 、HarrisのU.S.Patent 4,847,350(July 11,1989)に見られる。ＰＢＺポリマーは、Gregory らのU.S.Patent 5,089,591(February 18,1992)によると、脱水性の酸溶媒中での比較的高温、高せん断条件下において高反応速度での高分子量化が可能である。
【００１４】
ドープは公知の乾湿式紡糸法により製糸される。すなわちドープを口金から吐出した繊維状のドープは気体中を通過して、ポリマーを溶解しない程度の薄い溶媒（非溶解性溶液）に接触させて（凝固）製糸される。凝固後繊維中の残留酸溶媒は洗浄される。洗浄後の繊維は通常、２５重量％から２００重量％の残存液体分率を有している。洗浄に用いる流体は水蒸気のような気体であってもよいが、好ましくは液体が良く最も好ましくは水溶液が良い。繊維は液体の浴中で接触させても、スプレーで接触させてもよい。
【００１５】
液浴は、特開昭63-12710号公報；特開昭51-35716号公報、及び；特公昭44-22204号公報等に記載の様々な形式のものを用いることができる。また、例えばGuertin のU.S.P.5,034,250(July 23,1991) に記載されているような２つのローラーに繊維を走行させる間にスプレーする方法を組み合わせて用いてもよい。洗浄された繊維は溶媒との相互拡散により約３０重量％以上の非溶解性液体を含んでおりこのまま、もしくは繊維表面に付着た非溶解性液体を取り除き、塩基性溶液と接触させ繊維中の残留酸溶媒と中和させる。塩基性液体は水蒸気のような気体であってもよいが、好ましくは取り扱いの簡単な液体が良く更に好ましくは水溶液が良い。
【００１６】
ここで塩基性溶液とは水酸化ナトリウム、水酸化カルシウム、アンモニア、炭酸ナトリウム、炭酸カルシウム、などを水又はメタノール、エタノール、アセトン等有機溶媒に溶解し塩基性を示すことが肝要であるがここに挙げた塩基性溶液に限定されるものではない。塩基性溶液の濃度は好ましくは０．００１Ｎ以上、更に好ましくは０．０１Ｎ以上、望ましくは０．１Ｎ以上、そして３．０Ｎは越えない範囲が望ましい。接触時間は好ましくは０．１秒以上、更に好ましくは１秒以上、望ましくは３秒以上で１２０秒は越えない範囲である。接触時間は濃度が濃いほど一定の時間迄短く出来る。
【００１７】
また塩基性溶液への接触方法は上記に記載された液体と浴の中で接触させてもスプレーでもよく、２つのローラーに繊維を走行させる間にスプレーする方法を組み合わせて用いてもよいを組み合わせた方法であってもよい。なお、上述の凝固、洗浄過程で塩基性溶液で洗浄してもよいが、経済的観点から糸中残留酸溶媒濃度ができるだけ低い段階で塩基性溶液と接触させて糸中残留酸を中和させることが好ましい。溶媒残留率は好ましくは１００００ｐｐｍ以下、更に好ましくは５０００ｐｐｍ以下である。ここで中和後の繊維内部の塩基／酸のモル比は少なくとも０．５、より好ましくは０．７５以上で１．５は越えない範囲が望ましい。より好ましくは１．２５で最も好ましいのは１．０から１．３の間である。１．０以上では糸中残留酸は完全に中和されていると考えられる。例えば水酸化ナトリウムを使用した場合のリン：ナトリウム比は蛍光Ｘ線分析装置等の適切な分析装置によって測定できる。
【００１８】
中和を行った目的は（１）繊維内部の残留酸溶媒は、乾燥や熱処理の段階での加熱や光照射による加水分解を引き起こす触媒の働きをするが、これを抑制すること、（２）残留洗浄液の表面張力を小さくすることにより、ボイドの発生を抑制することである。図１に各残留非溶解性液体の含有率に基づいて決定される繊維に欠陥が生じない最高温度を特願平5-304111号に掲載されている技術と比較して示す。残留非溶解性液体の性質を変えることで乾燥工程中での繊維の強力低下をもたらすボイド欠陥の発生が従来の工程に比べ発生しにくくなっていた。
【００１９】
塩基性溶液との接触の後、この塩基性溶液を除去するために塩基性溶液を溶解しうる流体で洗浄を行なう。この流体は水蒸気のような気体であってもよいが好ましくは取り扱いの簡単な液体がよい。溶媒の洗浄に用いる流体は、ポリマー溶媒が易溶性であり、フィラメント中に拡散したものが後で取り除く事ができる事が肝要である。好ましくは水溶液がよい。洗浄に使用する液の酸性度はおよそｐＨ６〜１１がよい。
【００２０】
凝固・洗浄され、塩基性溶液と接触、洗浄された繊維は通常約２５％以上の残存液体を含んでいる。次いで塩基性溶液に接触させ、洗浄された繊維を加熱帯を通し乾燥する。加熱帯は電気炉もしくは加熱ローラーもしくは加熱空気または加熱不活性ガス、もしくは衝撃波、もしくは過熱水蒸気、もしくはオイル等の熱媒等が使用できる。高温に保持して一部マイクロ波等の電磁場を併用してもよい。またこれらの組み合わせで使用してもよい。当該繊維をすばやく昇温できることが肝要である。
【００２１】
乾燥工程では加熱帯を通し繊維内部の上記残存液体をおよそ４％以下迄乾燥させる。これはパッケージに捲いた後の糸の半径方向の収縮でチーズのす抜けや耳落ちが生じるためその許容範囲の非溶媒含有率である４％迄乾燥させる必要がある。
例えば２段の加熱帯を使用する場合、図１に示すように洗浄上がりのおよそ３８重量％の非溶媒含有率の繊維を１段目の加熱体で２２０℃以下の温度で１０重量％まで乾燥された繊維は２段目加熱体で２４０℃以下の温度で３重量％まで乾燥される。
図１に示される繊維に欠陥が生じない領域にしたがって加熱される時間は工業的要請から３分以下が好ましい。更に好ましくは１２０秒以下、最も好ましくは９０秒以下である。
【００２２】
加熱帯の雰囲気は空気もしくはヘリウム、アルゴン等の不活性ガス、二酸化炭素等のガス分率が高くてもよい。加熱帯の雰囲気は大気圧で使用するのが好ましいが圧力を変化させてもよい。また加熱帯内の風速を上げることは繊維表面からの物質移動を促し好適である。
【００２３】
繊維の平均引っ張り強度は単位デニール当りの破断強力（ｇ／ｄ）で表され、好ましくは少なくとも７．３ｇ／ｄ，更に好ましくは少なくとも１２．７ｇ／ｄ、より好ましくは少なくとも２０ｇ／ｄ、さらにより好ましくは少なくとも２９．８ｇ／ｄ、最も好ましくは少なくとも４５ｇ／ｄである。また繊維内に光学顕微鏡で観察されるボイドを写真に示す。このボイドが多く発生することで繊維の引っ張り強度は強力保持率で約９５％以下まで減少する。
また繊維の平均引張弾性率は単位デニール当りの初期引張抵抗度（ｇ／ｄ）で表され、好ましくは少なくとも１１００ｇ／ｄ、さらに好ましくは１６００ｇ／ｄである。この繊維は必要に応じて引張弾性率を上げる為に熱処理をする事ができる。適正な紡糸油剤を付与してパッケージに捲き取る。熱処理はオンラインで行っても、一旦捲き上げて行ってもよい。
【００２４】
塩基性溶液に接触させることによる耐ボイド発現性改善のメカニズムはよく分かっていないが繊維内のおよそ３０オングストローム以下の空隙にトラップされている非溶媒の表面張力特性が変化し乾燥によって液がぬけた後の残存応力が低下するためでないかと考えている。そのため図１で点線で示す繊維に欠陥が発生しない温度が実線で示す従来の技術より広くなる。乾燥温度を高くしても良好なポリベンザゾール繊維が得られるので短時間で乾燥できる。また塩基性溶液に接触させることにより繊維の乾燥、熱処理による引張強度の保持率を向上させる効果もある。
【００２５】
【実施例】
以下の実施例は説明だけの目的であり、これらにより本発明はこの実施例により制約を受けるものではない。断りがない場合には分量およびパーセンテージはすべて重量で示す。
残存非溶媒含有率の測定法は次に示すとおりである。約１.０ｇの繊維を秤量（Ｗ１）し、その繊維を静置乾燥機で２３０℃、３０分乾燥させ、再び秤量（Ｗ０）し、次式で算出する。
残存非溶媒含有率（％）＝｛（Ｗ１−Ｗ０）／Ｗ０｝×１００
繊維の欠陥の発生量と分散状態は、約４ｃｍにカットした繊維片をスライドグラスに載せ、光学顕微鏡を使用して２００倍で観察した。
欠陥は繊維軸に沿った黒い筋（ボイド）として観察され、繊維軸方向に角度を持った筋（キンク）とは本発明で区別する。写真にボイドの例を示す。
欠陥のランクは、１６６フィラメント、１８ｍｍ当たりの欠陥の数を光学顕微鏡で測定し、無し（０個）、非常にわずか（１〜２個）、非常にわずか〜わずか（３〜４個）、僅か（５〜１０個）、僅か〜多い（１１〜１５個）、非常に多い（１６個以上）、と６ランクに判別を行った。
【００２６】
実施例１
極限粘度数３０ｄＬ／ｇのシス−ポリベンズオキサゾールポリマーを１４重量％溶かしたポリ燐酸溶液を、１６０℃に保たれた紡糸口金より押し出した。押し出されたフィラメントを室温のイオン交換水で凝固させこの糸を洗浄過程に導き水洗した。中和工程では塩基性溶液としてＮａＯＨの０．１Ｎ溶液を使用した。その後水洗工程を経てエアー・ナイフで水を切った糸を温度が２２０℃の加熱ロ−ラーに６０秒間通し、さらに２２５℃の過熱ローラーに通し残存液体分率が５．７％になるまで乾燥し、さらに２５５℃の加熱ローラーにて乾燥を行った。表１に乾燥状況、繊維の物理特性を示す。表１から図１の欠陥の生じない乾燥温度条件（乾燥前残存液体分率３８％、加熱帯温度２２０℃）では欠陥は生じていない。また乾燥時間が従来の約４分と比較して飛躍的に早くなっている。
【００２７】
比較例１、２
実施例１と同様に凝固、洗浄を行った後、中和を行わずにエアナイフで水を切った糸の乾燥を行った。表１に乾燥状況、繊維の物理特性を示す。中和を行わない場合、繊維に欠陥を生じさせないで乾燥を行う場合には洗浄上りの残存液体分率３８％の糸を乾燥させるために最初に適用できる温度は１９０℃以下までしか使用できないために本発明に比べ非常に長い時間を必要とする（比較例１）。また実施例１と同様の乾燥条件で乾燥すると塩基性溶液と接触させていないため繊維に欠陥を発生させる温度での乾燥となり欠陥の発生の為に繊維の引張強度が低下する（比較例２）。
【００２８】
比較例３
実施例１と同様に凝固、洗浄、塩基性溶液と接触、洗浄後、エアナイフで水を切った糸の乾燥を行った。表１に乾燥状況、繊維の物理特性を示す。図１の欠陥を生じない乾燥温度条件をはずれるような場合においては繊維中に欠陥が非常に多く発生し繊維の強度が著しく低下する。
【００２９】
【表１】

【００３０】
実施例２
実施例１と同様紡糸、洗浄、乾燥を行ったが中和工程においてＮａＯＨの溶液濃度を０．００１Ｎへ変更した。表２に乾燥状況、繊維の物理特性を示す。表２から図１の欠陥の生じない乾燥温度条件内のような本発明の請求の範囲条件の場合において塩基性溶液を変更しても実施例１と比べも同程度の水分率迄乾燥させる事ができる。また塩基性溶液が変化することでの乾燥状況、繊維の物理特性には大きな影響は認められない。
【００３１】
実施例３
実施例１と同様紡糸、洗浄、乾燥を行ったが紡糸速度を６００ｍ／分へ変更した。表２に乾燥状況、繊維の物理特性を示す。表２から紡糸速度が上がってもボイドが発生することなくすばやく乾燥させる事ができる。
【００３２】
【表２】

【００３３】
実施例４、５
実施例１と同様紡糸、洗浄、乾燥を行ったが乾燥工程において乾燥装置の変更を行った。表３に乾燥状況、繊維の物理特性を示す。表３から図１の欠陥の生じない乾燥温度条件内のような本発明の請求の範囲条件の場合では乾燥オーブンおよび過熱水蒸気と乾燥ローラーの組合せで乾燥を行っても乾燥は同程度の時間ですばやく乾燥することができた。また乾燥装置を変更した場合でも加熱帯の温度をコントロールすることで乾燥状況を良好にすることができる。
【００３４】
【表３】

【００３５】
【発明の効果】
本発明により繊維中のボイド欠陥を発生させる事なく従来技術の乾燥方法より飛躍的に乾燥時間を短縮したポリベンザゾール繊維の乾燥をすることが可能となった。
【図面の簡単な説明】
【図１】本発明で使用するポリベンザゾール繊維の非溶媒含有率と乾燥温度の関係を従来技術と比較した図。
【符号の説明】
１：塩基性溶液を接触させない場合のボイド発生限界上限温度。
２：塩基性溶液を接触させた場合のボイド発生限界上限温度。
３：本発明の初期乾燥条件（斜線部分）[0001]
[Industrial application fields]
The present invention relates to a method for obtaining a high-quality fiber excellent in strength and elastic modulus composed of a polybenzazole polymer such as polybenzoxazole or polybenzthiazole.
[0002]
[Prior art]
Lyotropic liquid crystalline polybenzoxazole and polybenzthiazole polymers do not exhibit thermoplasticity. These are fiberized by a dry jet wet spinning method. That is, a dope containing a polybenzazole polymer and an acid solvent is extruded from a spinneret and stretched by an air gap. Thereafter, coagulation is carried out by contacting with a non-solvent that does not dissolve the polymer, and the solvent is similarly diluted, desolvated and dried.
[0003]
In order to improve productivity, it is preferable to dry many filaments at high speed in a short time. However, the polybenzazole fiber after desolvation contains a large amount of non-solvent of 25% by weight or more, and a volume change occurs when it is dried. When the filament is dried at a high speed in a short time, if it suddenly passes through a high temperature heating zone from a state containing a large amount of non-solvent, a defect occurs in the drying process. This defect is not preferable because it causes a reduction in the strength of the yarn. By drying in a low-temperature heating zone, the occurrence of this defect can be prevented. However, when drying is performed at a low temperature, there is a problem in productivity because much time is required for drying.
[0004]
Therefore, as described in Japanese Patent Application No. 5-304111 as a conventional method, a polybenzazole fiber containing 25% by weight or more of a non-solvent is used at 170 ° C. for 84.3 seconds, 200 ° C. for 84.3 seconds, 240 ° C. A high-speed drying method is exemplified in which the content of non-solvent is reduced to 1.5% by weight without causing defects, and the drying time is reduced to about 4 minutes.
However, the drying after the desolvation step by this conventional method still requires a long time. In order to shorten the time required for drying, it is necessary to increase the diffusion coefficient of the non-solvent inside the polybenzazole fiber. As a result of examining various methods for increasing the diffusion coefficient of the non-solvent inside the polybenzazole fiber, it was the drying temperature that was most effective. That is, since the drying time cannot be shortened sufficiently at the drying temperature that can be used in the conventional method, it is desired to develop a high-speed drying technique by increasing the limit temperature that does not generate voids.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for producing a high-quality polybenzazole fiber having no defects in fibers and excellent in strength and elastic modulus in an extremely short drying time.
[0006]
[Means for Solving the Problems]
That is, in a method in which a filament is spun from a dope comprising a polybenzazole polymer and an acidic solvent and coagulated, washed and dried, the spun dope filament is coagulated, brought into contact with a basic solution, and then subjected to a drying process. It is the manufacturing method of the polybenzazole fiber characterized by drying at the temperature set in relation to the residual liquid fraction in the inside.
[0007]
Polybenzazole fiber refers to a fiber made of a polybenzazole (PBZ) polymer. Polybenzazole (PBZ) refers to polybenzoxazole (PBO) homopolymer, polybenzothiazole (PBT) homopolymer, and random, sequential or block copolymer of PBO and PBT. Here, polybenzoxazole, polybenzothiazole and their random, sequential or block copolymer polymers are described in, for example, Wolfe et al. `` Liquid Crystalline Polymer Compositions, Process and Products '' US Patent 4,703,103 (October 27,1987), `` Liquid Crystalline Polymer Compositions , Process and Products '' US Patent 4,533,692 (August 6,1985), `` Liquid Crystalline Poly (2,6-Benzothiazole) Compositions, Process and Products '' USPatent 4,533,724 (August 6,1985), `` Liquid Crystalline Polymer Compositions, Process and Products '' USPatent 4,533,693 (August 6,1985), Evers' `` Thermooxdatively Stable Articulated p-Benzobisoxazole p-Benzobisthiazole Polymers''USPatent 4,359,567 (November 16,1982), Tsai et al. `` Method for Making Heterocyclic Block Copolymer Compositions, Process and Products'' USPatent 4,578,432 (March 25, 1986).
[0008]
The structural unit contained in the PBZ polymer is preferably selected from lyotropic liquid crystal polymers. Monomer units are described in structural formulas (a)-(h). The polymer preferably consists essentially of rigid monomer units of the molecular chain itself selected from structural formulas (a)-(h), more preferably selected from structural formulas (a)-(c). Monomer unit.
[0009]
[Chemical 1]

[0010]
[Chemical formula 2]

[0011]
Suitable acidic solvents for forming the PBZ polymer dope include cresol and non-oxidizing acids that can dissolve the polymer. Examples of suitable acid solvents include polyphosphoric acid, methanesulfonic acid and high concentrations of sulfuric acid or mixtures thereof. Further suitable solvents are highly soluble polyphosphoric acid and methanesulfonic acid. The most suitable solvent is polyphosphoric acid.
[0012]
The polymer concentration of the solution is preferably at least about 7% by weight, more preferably at least about 10% by weight, and most preferably at least 14% by weight. The maximum concentration is limited by practical handling properties such as polymer solubility and dope viscosity. Because of these limiting factors, the polymer concentration usually does not exceed 20% by weight.
[0013]
Suitable polymers, copolymers or dopes are synthesized by known techniques. For example, US Patent 4,533,693 (August 6,1985) by Wolfe et al., US Patent 4,772,678 (September 20,1988) by Sybert et al., USPatent 4,847,350 (July 11,1989) by Harris. According to US Patent 5,089,591 (February 18,1992) by Gregory et al., PBZ polymers can be made to have a high molecular weight at a high reaction rate under relatively high temperature and high shear conditions in a dehydrating acid solvent.
[0014]
The dope is produced by a known dry and wet spinning method. That is, the fibrous dope discharged from the die is passed through the gas and brought into contact with a thin solvent (insoluble solution) that does not dissolve the polymer (coagulation) to produce a yarn. The residual acid solvent in the fiber after coagulation is washed. The washed fibers usually have a residual liquid fraction of 25% to 200% by weight. The fluid used for cleaning may be a gas such as water vapor, but is preferably a liquid and most preferably an aqueous solution. The fibers may be contacted in a liquid bath or by spraying.
[0015]
Various types of liquid baths described in JP-A-63-12710; JP-A-51-35716; and JP-B-44-22204 can be used. Also, for example, a combination of spraying methods while the fibers are running on two rollers as described in Guertin USP 5,034,250 (July 23,1991) may be used. The washed fiber contains about 30% by weight or more of an insoluble liquid due to mutual diffusion with the solvent, or the non-soluble liquid adhering to the fiber surface is removed and contacted with a basic solution to remain in the fiber. Neutralize with acid solvent. The basic liquid may be a gas such as water vapor, preferably a liquid that is easy to handle, and more preferably an aqueous solution.
[0016]
Here, the basic solution is essential to show basicity by dissolving sodium hydroxide, calcium hydroxide, ammonia, sodium carbonate, calcium carbonate, etc. in water or an organic solvent such as methanol, ethanol, acetone, etc. It is not limited to the basic solution mentioned. The concentration of the basic solution is preferably 0.001 N or more, more preferably 0.01 N or more, desirably 0.1 N or more, and a range not exceeding 3.0 N is desirable. The contact time is preferably 0.1 seconds or longer, more preferably 1 second or longer, desirably 3 seconds or longer and not exceeding 120 seconds. The contact time can be shortened to a certain time as the concentration increases.
[0017]
In addition, the contact method with the basic solution may be a spray or contact with the liquid described above, or may be used in combination with a method of spraying while running the fiber on two rollers. May be used. In addition, although it may be washed with a basic solution in the above-described coagulation and washing processes, from the economical viewpoint, the residual acid solvent concentration in the yarn is brought into contact with the basic solution at a stage where the concentration is as low as possible to neutralize the residual acid in the yarn. It is preferable. The solvent residual ratio is preferably 10,000 ppm or less, more preferably 5000 ppm or less. Here, the molar ratio of the base / acid in the fiber after neutralization is preferably at least 0.5, more preferably 0.75 or more and 1.5 or less. More preferred is 1.25 and most preferred is between 1.0 and 1.3. If it is 1.0 or more, the residual acid in the yarn is considered to be completely neutralized. For example, the phosphorus: sodium ratio when sodium hydroxide is used can be measured by an appropriate analyzer such as a fluorescent X-ray analyzer.
[0018]
The purpose of neutralization is as follows: (1) Residual acid solvent inside the fiber acts as a catalyst that causes hydrolysis by heating or light irradiation in the stage of drying or heat treatment, and (2) The generation of voids is suppressed by reducing the surface tension of the residual cleaning liquid. FIG. 1 shows the maximum temperature at which no defect occurs in the fiber, which is determined based on the content of each residual insoluble liquid, in comparison with the technique disclosed in Japanese Patent Application No. 5-304111. By changing the properties of the residual non-dissolvable liquid, generation of void defects that cause a decrease in fiber strength during the drying process is less likely to occur than in the conventional process.
[0019]
After contact with the basic solution, washing is performed with a fluid that can dissolve the basic solution in order to remove the basic solution. This fluid may be a gas such as water vapor, but is preferably a liquid that is easy to handle. It is important that the fluid used for washing the solvent is easily soluble in the polymer solvent and that the matter diffused in the filament can be removed later. An aqueous solution is preferable. The acidity of the liquid used for washing is preferably about pH 6-11.
[0020]
Fibers that have been coagulated and washed, contacted with a basic solution, and washed typically contain more than about 25% residual liquid. It is then contacted with a basic solution and the washed fibers are dried through a heating zone. As the heating zone, an electric furnace, a heating roller, heated air, a heated inert gas, a shock wave, superheated steam, or a heat medium such as oil can be used. An electromagnetic field such as a microwave may be used in combination while maintaining a high temperature. Further, these combinations may be used. It is important that the temperature of the fiber can be raised quickly.
[0021]
In the drying step, the residual liquid inside the fiber is dried to about 4% or less through a heating zone. This is because the shrinkage in the radial direction of the yarn after being sown in the package causes the cheese to slip through and the ear drop, so it is necessary to dry it to 4% which is the allowable non-solvent content.
For example, when a two-stage heating zone is used, as shown in FIG. 1, a non-solvent content fiber of about 38% by weight after washing is dried to 10% by weight at a temperature of 220 ° C. or less with a first-stage heating element. The resulting fibers are dried to 3% by weight at a temperature of 240 ° C. or less in a second stage heating element.
The heating time according to the region where no defect occurs in the fiber shown in FIG. 1 is preferably 3 minutes or less in view of industrial requirements. More preferably, it is 120 seconds or less, and most preferably 90 seconds or less.
[0022]
The atmosphere in the heating zone may have a high gas fraction such as air, an inert gas such as helium or argon, or carbon dioxide. The atmosphere in the heating zone is preferably used at atmospheric pressure, but the pressure may be changed. Increasing the wind speed in the heating zone is preferable because it promotes mass transfer from the fiber surface.
[0023]
The average tensile strength of the fiber is expressed in terms of breaking strength per unit denier (g / d), preferably at least 7.3 g / d, more preferably at least 12.7 g / d, more preferably at least 20 g / d, even more Preferably it is at least 29.8 g / d, most preferably at least 45 g / d. Moreover, the void observed with an optical microscope in the fiber is shown in the photograph. When many voids are generated, the tensile strength of the fiber is reduced to about 95% or less in terms of strength retention.
The average tensile elastic modulus of the fiber is expressed as an initial tensile resistance per unit denier (g / d), preferably at least 1100 g / d, more preferably 1600 g / d. This fiber can be heat-treated as necessary to increase the tensile modulus. Appropriate spinning oil is applied to the package. The heat treatment may be performed online or may be performed once.
[0024]
Although the mechanism of improving the void resistance by contacting with a basic solution is not well understood, the surface tension characteristics of the non-solvent trapped in the voids of about 30 angstroms or less in the fiber changed and the liquid was removed by drying. I think this is because the residual stress later decreases. Therefore, the temperature at which no defect occurs in the fiber indicated by the dotted line in FIG. 1 becomes wider than the conventional technique indicated by the solid line. Even if the drying temperature is raised, a good polybenzazole fiber can be obtained, so that it can be dried in a short time. Moreover, there is also an effect of improving the retention of tensile strength by drying and heat treatment of fibers by contacting with a basic solution.
[0025]
【Example】
The following examples are for illustrative purposes only, and the present invention is not limited by these examples. Unless otherwise noted, all quantities and percentages are given by weight.
The method for measuring the residual non-solvent content is as follows. About 1.0 g of fiber is weighed (W1), the fiber is dried at 230 ° C. for 30 minutes with a stationary dryer, weighed again (W0), and calculated by the following formula.
Residual non-solvent content (%) = {(W1-W0) / W0} × 100
The amount of fiber defects and the dispersion state were observed at 200 times using an optical microscope by placing a fiber piece cut to about 4 cm on a slide glass.
The defect is observed as a black streak (void) along the fiber axis, and is distinguished from a streak (kink) having an angle in the fiber axis direction in the present invention. An example of a void is shown in the photograph.
The rank of defects is 166 filaments, the number of defects per 18 mm is measured with an optical microscope, none (0), very few (1-2), very few to few (3-4), slightly The determination was made into 6 ranks: (5 to 10), slightly to many (11 to 15), and very many (16 or more).
[0026]
Example 1
A polyphosphoric acid solution in which 14% by weight of a cis-polybenzoxazole polymer having an intrinsic viscosity of 30 dL / g was dissolved was extruded from a spinneret maintained at 160 ° C. The extruded filament was coagulated with room temperature ion-exchanged water, and this yarn was guided to the washing process and washed with water. In the neutralization step, a 0.1N solution of NaOH was used as the basic solution. Then, after passing through a water washing process, the yarn cut with an air knife is passed through a heating roller with a temperature of 220 ° C. for 60 seconds, and further passed through a superheated roller with a temperature of 225 ° C. until the residual liquid fraction becomes 5.7%. Further, drying was performed with a 255 ° C. heating roller. Table 1 shows the drying conditions and the physical properties of the fibers. From Table 1, no defect occurs under the drying temperature conditions (the residual liquid fraction before drying is 38% before heating and the heating zone temperature is 220 ° C.) where no defects occur. Also, the drying time is dramatically faster than the conventional 4 minutes.
[0027]
Comparative Examples 1 and 2
After coagulation and washing in the same manner as in Example 1, the yarn that had been drained with an air knife was dried without neutralization. Table 1 shows the drying conditions and the physical properties of the fibers. When neutralization is not performed, when drying is performed without causing defects in the fiber, the temperature that can be initially applied to dry the yarn having a residual liquid fraction of 38% after washing can be used only up to 190 ° C. or less. Therefore, a very long time is required as compared with the present invention (Comparative Example 1). Further, when dried under the same drying conditions as in Example 1, since it is not in contact with the basic solution, it is dried at a temperature at which defects are generated in the fibers, and the tensile strength of the fibers decreases due to the generation of defects (Comparative Example 2). .
[0028]
Comparative Example 3
In the same manner as in Example 1, coagulation, washing, contact with a basic solution, washing, and drying of the thread from which water had been cut with an air knife were performed. Table 1 shows the drying conditions and the physical properties of the fibers. In the case where the drying temperature condition that does not cause the defect shown in FIG.
[0029]
[Table 1]

[0030]
Example 2
Spinning, washing and drying were performed in the same manner as in Example 1, but the NaOH solution concentration was changed to 0.001 N in the neutralization step. Table 2 shows the drying conditions and the physical properties of the fibers. From Table 2, in the case of the claimed conditions of the present invention, such as within the drying temperature condition in which defects do not occur, even if the basic solution is changed, the moisture content can be dried to the same level as in Example 1. Can do. In addition, there is no significant effect on the drying condition and the physical properties of the fiber due to the change in the basic solution.
[0031]
Example 3
Spinning, washing and drying were performed in the same manner as in Example 1, but the spinning speed was changed to 600 m / min. Table 2 shows the drying conditions and the physical properties of the fibers. From Table 2, even if the spinning speed is increased, it can be quickly dried without generating voids.
[0032]
[Table 2]

[0033]
Examples 4 and 5
Spinning, washing and drying were performed in the same manner as in Example 1, but the drying apparatus was changed in the drying process. Table 3 shows the drying conditions and the physical properties of the fibers. In the case of the claimed conditions of the present invention such as those within the drying temperature conditions in FIG. 1 where no defects occur, drying takes about the same time even if drying is performed using a drying oven and a combination of superheated steam and a drying roller. We were able to dry quickly. Even when the drying apparatus is changed, the drying condition can be improved by controlling the temperature of the heating zone.
[0034]
[Table 3]

[0035]
【The invention's effect】
According to the present invention, it is possible to dry a polybenzazole fiber whose drying time is drastically shortened compared to the conventional drying method without generating void defects in the fiber.
[Brief description of the drawings]
FIG. 1 is a graph comparing the relationship between the non-solvent content of a polybenzazole fiber used in the present invention and the drying temperature with the prior art.
[Explanation of symbols]
1: Upper limit of void generation limit when a basic solution is not contacted.
2: Upper limit of void generation limit when a basic solution is contacted.
3: Initial drying conditions of the present invention (shaded area)

Claims (3)

In a method in which a filament is spun from a dope comprising a polybenzazole polymer and an acidic solvent and coagulated, washed and dried, the spun dope filament is solidified and then contacted with a basic solution, and then subjected to a drying step. A method for producing polybenzazole fibers, wherein the drying introduction temperature is 190 to 220 ° C when the residual liquid fraction is 25% or more .  The method for producing a polybenzazole fiber according to claim 1, wherein drying is performed until the residual moisture content in the filament after drying is 6% or less.  3. The method for producing polybenzazole fiber according to claim 1, wherein the drying time is 3 minutes or less.

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