JP4251843B2 - Method for producing polyparaphenylene terephthalamide film - Google Patents

Description

【００１３】
本発明で用いるポリマーの重合度は、あまり低いと機械的性質の良好なフィルムが得られず、また、あまり高いと実用的でなくなるため、３．０〜８．５、好ましくは３．５〜７．５の対数粘度ηｉｎｈ（９８％硫酸１５０ｍｌにポリマー０．１ｇを溶解して３５℃で測定した値）を与える重合度のものが選ばれる。
本発明のＰＰＴＡフィルムを製造するためには、まずＰＰＴＡのドープを調整する必要がある。このドープを調整するのに適した溶媒は、９５重量％以上の濃硫酸である。９５重量％未満の硫酸ではポリマーの溶解が難しく、また溶解後のドープが異常に高粘度になる。硫酸は１００重量％以上のものも可能であるが、ポリマーの安定性や溶解性などの点から９８〜１００重量％濃度が好ましく用いられる。
【００１４】
本発明に用いられるドープ中のポリマーの濃度としては、常温（約２０〜３０℃）またはそれ以上の温度で光学異方性を示す濃度以上のものが好ましく用いられ、具体的には９．５重量％以上で用いられる。これに達しないポリマー濃度、すなわち常温またはそれ未満の温度で光学異方性を示さないポリマー濃度では、製造されたＰＰＴＡフィルムが好ましい機械的性質を持たなくなることが多い。ポリマー濃度の上限は特に限定されるものではないが、通常は２０重量％以下、特に高い対数粘度ηｉｎｈのポリマーに対しては１８重量％以下が好ましく用いられ、さらに好ましくは１６重量％以下である。
【００１５】
本発明のドープには普通の添加剤、例えば増量剤、除光沢剤、紫外線安定剤、帯電防止剤、熱安定剤、顔料、溶解助剤などを混入してもよい。また、フィルムとして滑り性や表面性の改良の為に、例えばＳｉＯ₂、ＴｉＯ₂、ＺｎＯ、Ａｌ₂Ｏ₃、ＣａＳＯ₄、ＢａＳＯ₄、ＣａＣＯ₃、カーボンブラック、ゼオライトなどの無機化合物の粒子のうちの1種又は2種以上を選択して用いる事ができる。
調整された光学異方性ドープ中には、凝固・乾燥に先立って可能な限り不溶性のゴミ、異物などや微細粒子の未分散物や再凝集物を濾過によって取り除いて置く事が好ましい。このときに用いるフィルターとしては５μｍの大きさを約８０％以上除去できるフィルター、より好ましくは３μｍの大きさの粒子を約８０％以上除去できるフィルターであり、このフィルターを２段以上で用いるのも有用な実施形態のひとつである。
【００１６】
このような高精度の濾過を行なうことは、フィルムの表面平滑性、特に粗大突起の生成を防止する上で効果的である。また、フィルムの表面性向上の為には、ドープ中のゴミや異物以外に、溶解中に発生または巻き込まれている空気などの微細な気泡を取り除いて置く事が好ましい。ドープ内の空気などの気体を取り除く方法としては、例えば一旦ドープを調整した後に真空（減圧）にして取り除く事も出来るし、原料の仕込みの段階から一貫して真空（減圧）下で行なうことによっても達成しうる。
【００１７】
調整後のドープが光学異方性か光学等方性であるかは、公知の方法、例えば特公昭５０−８４７４号公報記載の方法で調べることができるが、その臨界点は、溶媒の種類、温度、ポリマー濃度、ポリマーの重合度、非溶媒の含有量などに依存されるので、これらの関係を予め調べることによって、光学異方性を作り、光学等方性ドープとなる条件に変えることで、光学異方性から光学等方性に変えることができる。
【００１８】
このようにして調整された光学異方性ドープは、例えばスリットダイにより光学異方性を保ったまま支持面上に流延される。また、実験的にはドクターナイフ等で流延する事ができる。支持面としては、例えばガラス、ステンレス、タンタル、ハステロイ、フッ素樹脂等やこれらの材料に金、白金等の貴金属でコーティングされたドラム、ベルト、板状物等から選ぶ事ができる。
支持面上に流延されたドープは、次に光学異方性から光学等方性に転化させる必要がある。この光学等方性にドープを転化させる方法としては、効率が良くかつＰＰＴＡの分解をできるだけ少なくする為に、加熱加湿された空気を用いることが好ましい。この時使用する空気の露点について、本発明者らが研究したところ、低い露点にする方がカールをさらに小さくする事ができることがわかった。また、露点が低すぎるとドープの等方化に要する時間がかかりすぎて実用的ではなく、露点が高すぎるとドープ表面が過度の吸湿により凝固された時と同じような状態となり、フィルムの断面構造が非対称になりやすく、カールが増大する傾向があった。
【００１９】
よって、本発明の好ましい露点としては−３０〜３０℃の範囲である。露点を調整した空気は５０〜１８０℃、好ましくは７０〜１５０℃に加熱され、直接ドープに当てる事でドープを光学等方性に転化する。この時の空気の風速としては３〜２０ｍ／秒が好ましく、より好ましくは５〜１５ｍ／秒である。この風速を上げることにより、カールを小さくできる低い露点域の条件で生産性良く製造することができる。
【００２０】
光学等方化されたドープは次の凝固を行なう前に冷却することが本発明のフィルムのカールを殆ど完全になくす為に好ましい態様である。この凝固前にドープを冷却する事は、凝固液との温度差が小さくなり、凝固液と接触した時の急激な発熱が抑制される為に、ドープの厚み方向の構造が対称に近づくと考えられ、カールに対して有効な手段である。本発明の凝固前に冷却されたドープの温度としては、カールの状態や生産性の面から５〜８０℃が好ましく、より好ましくは５〜５０℃である。
【００２１】
このドープの温度を冷却する方法としては特に限定されないが、例えば直接的にドープの温度を下げる方法としては、支持面上に流延されているドープに冷却された空気などの気体を吹き付ける方法。間接的にドープの温度を下げる方法としては、支持面のドープが流延されていない面に液体や気体を吹き付ける方法や、温度コントロールされているロール等を接触させて下げる方法などがある。
支持面上で光学等方化された流延ドープは次に凝固させる必要がある。凝固する為の凝固液としては硫酸水溶液が好ましく、この硫酸水溶液の濃度と温度が本発明においてボイド数及びカールを少なくするのに非常に重要である。すなわち、本発明において凝固液濃度は、凝固液濃度Ｃ（重量％）が、凝固後の洗浄したフィルムの厚みをＴ（μｍ）とした時に、（１８ｌｏｇ_eＴ）−２０≧Ｃ≧（１８ｌｏｇ_eＴ）−５５であらわされる濃度であり、好ましくは（１８ｌｏｇ_eＴ）−３０≧Ｃ≧（１８ｌｏｇ_eＴ）−５５である。
【００２２】
ただし、この凝固液濃度の最低値は０％以下を含まない。凝固液濃度がこの範囲未満の場合には、発熱が生じて凝固速度が加速される為に、凝固液に接しているドープ面と支持面に固定されている面でそれぞれ生じる収縮に大きな差が発生する。この収縮差は、ボイドの生成を誘発すると共に、カール発生の構造の均一性を損なうと考えられる。また、この凝固液濃度の範囲を超えると、凝固液中の支持面上の光学等方化されたドープが、完全に凝固して支持面から容易に剥離出来るようになるまでに、非常に長時間を要することから生産性に欠け工業化を考えると難しい。
【００２３】
一方、凝固液温度については、本発明の凝固液濃度の範囲内でもドープが凝固する際には凝固液との接触によって当然発熱が生じるが、この凝固させる際の発熱をより良く抑制する為には、凝固液温度を限定する必要があることをつきとめた。よって、本発明の凝固液温度としては５〜３０℃とする事が必要であり、この温度範囲を下回ると、凝固速度が遅くなり過ぎて生産性の面で難しくなる。
このように調整された凝固液中でドープを凝固させるが、連続的にフィルムを製造する場合は濃度と温度が一定になるように凝固液槽内の凝固液を出し入れ（循環等により）させる必要がある。その際にドープが凝固液に突入する部分の凝固液の平均流速を制御する事が、本発明においてボイドをより抑制させるのに効果的である。この凝固液の流速が遅いと生産性の低下や、凝固斑によるフィルムの表面性の悪化につながり、流速が速いとボイドが生成しやすくなることをつきとめた。よって、ボイドの抑制が可能で生産性にも問題が生じさせない流速としては、ドープが突入する地点から２〜５ｃｍ以内の凝固液の平均流速が、０．０１〜０．５ｍ／秒とする事が好ましく、より好ましくは０．０１〜０．１ｍ／秒である。
【００２４】
凝固されたフィルムはそのままでは酸が含まれているため、加熱による機械的物性の低下の少ないフィルムを製造するには酸分の洗浄による除去をできるだけ行なう必要がある。酸分の除去は、具体的には約５００ｐｐｍ以下まで行なうことが望ましい。洗浄液としては通常水や必要に応じて温水が用いられるが、アルカリ水溶液で中和洗浄した後、水で洗浄しても良い。洗浄方法としては、例えば洗浄液中でフィルムを走行させる方法や、洗浄液を噴霧するなどの方法により行なわれる。このようにして洗浄されたフィルムは、次に乾燥されるが、もし望むならば、乾燥前の湿潤フィルムを１方向または２方向に１．０１から１.４倍程度延伸する事により、フィルムの機械的性質を向上させることができる。
【００２５】
洗浄されたフィルムの乾燥は、乾燥前後でのフィルムの厚み及び面寸法の変化が大きいので、高品質のフィルムを得るには乾燥時に注意が必要である。すなわち皺が生じないよう緊張下にフィルムの収縮を制限して行なう必要がある。ここでいう緊張下とは、定長下、皺が入らない程度に収縮させる、わずかに延伸させるという３つの態様が含まれる。また、乾燥中もしくは乾燥前後に延伸を加えることによって膜厚をより薄くすることも可能である。
【００２６】
もし、収縮を制限せずに乾燥した場合には、ミクロに不均一な構造形成（結晶化など）が起こるため、得られたフィルムの光線透過率が小さくなってしまう。また、フィルムの平面性が損なわれたり、カールしてしまうこともある。収縮を制限しつつ乾燥する方法としては、テンター乾燥機や金属枠に挟んで乾燥する方法がある。乾燥に係る他の条件としては特に制限されるものではなく、加熱方法としては加熱気体（空気、窒素、アルゴン等）や常温気体による方法、電気ヒーターや赤外線ランプなどの輻射熱を利用する方法、誘電加熱方法などの手段から自由に選ぶことが出来る。乾燥温度も特に制限されるものではないが、常温以上であれば良い。
【００２７】
ただし、機械的強度を大にする為には、高温の方が好ましく、１００℃以上、さらに好ましくは１５０℃以上が用いられる。乾燥の最高温度は、特に制限されるものではないが、乾燥エネルギーやポリマーの分解性を考慮すれば、５００℃以下が好ましい。この乾燥の後には、フィルムの弾性率や熱寸法安定性を向上させる為に熱処理を行なっても良い。この熱処理温度としては、３００〜５５０℃が好ましく、特に好ましくは３５０〜５００℃が用いられる。
【００２８】
この時の熱処理時間としては、０．５秒〜１０分が好ましく用いられる。熱処理時間が短すぎると、処理効果を充分に得る事ができず、また、長すぎるとポリマーの劣化が生じ、表面平滑性が失われ、フィルムの機械物性の低下が生じる。熱処理方法としては、接触式、非接触式いずれを用いても良く、例えば、温度コントロールしたロールに接触させる方法、赤外線加熱、板状ヒーター間で非接触で加熱する方法などがある。
【００２９】
本発明のフィルムには、フィルム表面と樹脂との親和性を向上する為に、フィルムの表面に改質処理を行なっても良い。表面改質処理としては、コロナ放電処理等が知られている。コロナ放電処理は、電極とロール間に高周波、高電圧を印加してコロナ放電を発生させ、この中をフィルムが通過することによって、フィルムの表面を処理するものである。
通常、ロールは金属性ロール上にハイポロンゴム、シリコンゴムなどの誘電体を被覆した誘電体ロールが用いられるが、場合によっては、誘電体を介さずに直接電極間で放電処理することもできる。放電周波数は通常１０ＫＨｚ程度であるが、特に限定されない。処理密度はフィルムの状態や必要な接着力等によって調整され、通常は１〜１０００Ｗ／ｍ²／分であり、好ましくは１０〜５００Ｗ／ｍ²／分の範囲が用いられる。処理密度が高すぎるとフィルムの物性の低下や、表面の平滑性が失われる。
【００３０】
本発明の方法によりフィルムを作製する上で、上記の工程はいずれも回分式に行なわれても連続的であってもよく、全工程を通して連続してフィルムを走行させつつ製造することも好ましい実施態様の1つである。また、本発明で製造したフィルムを、より高品位とするならば、ドープ中に異物やごみ混入させないこと以外に、吸湿用気体、加熱用気体、支持面体、凝固液、洗浄液、乾燥気体などに、ごみ等の含有量が可及的に少なくなることが好ましく、例えばいわゆるクリーンルームやクリーン水で本発明のフィルムを製造するのも好ましい実施態様の1つである。
【００３１】
【発明の実施の形態】
本発明について、以下に具体的に説明するが、本発明の物性値の測定方法は次の通りである。
（１）フィルムの厚み測定法
フィルムの厚みは、デジタル電子マイクロメータ（アンリツ株式会社製Ｋ３５１Ｃ型）により、直径２ｍｍの測定子を用いて異なる点５個所を測定し平均値で表す。
【００３２】
（２）ボイド数測定法
ボイド数の測定方法は、製造したフィルム片を直交偏光状態下で出来る限り広い面積を観察して、光学異常部を見つけ出してマーキングする。そのマーキングした部分を光学顕微鏡で１００倍から４００倍の範囲の倍率で観察し、ボイドとなっているものを選び出してボイド数を数え、フィルム１ｍｍ²当たりに換算してボイド数とした。
【００３３】
（３）カールの測定法
カールの測定方法は、製造したサンプルを２３℃５５％の環境下で６時間以上放置後、製造したフィルムのスリットダイから押し出す方向を長さ方向として５０ｍｍ、幅６．５ｍｍの試料片を５点切り出し、切り出した試験片の表面を除電し後に、除電したガラス板の上に置いて、測長顕微鏡を用いて図１に示すようにカールした状態での幅方向の直線距離を正確に測定する（測定値Ａ）。次に図２のように試料片の上にスライドガラスを乗せて、強制的にカールしていない状態としたときの幅方向の直線距離を正確に測定する（測定値Ｂ）。このようにして測定した値から、Ｃ＝１０×（１−（１．２×Ａ／Ｂ−０．２）^0.5）を求めて、カール値（ｍｍ）＝Ｂ×（ｔａｎ（（Ｃ）^0.5／２））／２を計算し、試験片５点の平均値をカール値とした。このカール値は、図１に示すように自由な状態でカールした時の、底面から一番高い所までの高さを示すものである。なお上記カール測定作業はすべて２３℃５５％の環境下で実施した。
【００３４】
（４）引っ張り物性測定法
フィルムの引っ張り物性は、定速伸長型強伸度測定機を用いて、測定長１００ｍｍ、測定フィルム幅１０ｍｍで測定できる試験片１０点を切り出し、引っ張り速度５０ｍｍ／分で測定する。
【００３５】
【実施例】
以下、本発明を実施例に基づいて説明する。
【００３６】
【実施例１】
６０℃の９９．８重量％の硫酸に、対数粘度ηｉｎｈが４．8のＰＰＴＡを１２．０重量％で溶解し、混入した空気を真空下において脱気して光学異方性ドープを得た。次にこのドープを０．１５ｍｍのスリットを有するダイから、１２０℃の鏡面に磨いたタンタル製のエンドレスベルト上にキャストし、１２０℃で露点１２℃の空気を７ｍ／秒の風速でドープに吹き付けて流延ドープを光学等方化させた。
【００３７】
この光学等方化させたドープを凝固させる前に、エンドレスベルトのドープがキャストされていない面に、凝固液と同じ１５℃の３０重量％硫酸水溶液のシャワーを行ない、ドープ全体の温度を４０℃に冷却させてから、１５℃の３０重量％の硫酸水溶液で、ドープ突入部分から２〜５ｃｍ以内の平均流速が０．０５ｍ／秒となっている凝固液中に導いて凝固させた。凝固させたフィルムは次に含まれている酸を除去する為に、３０℃の水槽中での洗浄、次に０．１％のカセイソウダ水溶液槽で中和し、さらにもう一度３０℃水槽中での水洗を実施した。この水洗を終えた時点でのフィルムの厚みを測ったところ７２μｍであった。
【００３８】
次に水槽から取り出した湿潤フィルムを長さ方向に１．１倍延伸した後クリップテンターにより１．１倍に横延伸し、ついで定長状態を保ちつつ１８０℃で熱風乾燥した後、４２０℃で緊張熱処理して、２００℃でフリー熱処理をしてロール状に巻き上げた。
このようにして得られたフィルムの厚みは約１２μｍで、ボイド数が３２×１０^-6個／ｍｍ²と非常に少なかった。また、フィルムのカールについても、試験片がカールした状態の幅（Ａ値）の平均値で６．５４７ｍｍ、スライドグラスを乗せてカールしていない状態での幅（Ｂ値）の平均値が６．５５２ｍｍとなり、計算するとカール値が０．１１１ｍｍとなり、殆どカールしていない状態に近いものであった。
【００３９】
【実施例２】
実施例１のドープの吐出量を調整して凝固後の洗浄したフィルムの厚みを１５０μｍとし、凝固液を１５℃の６０重量％硫酸水溶液をとした以外は全て実施例１と同様に行い、得られたフィルムの厚みは約２５μｍであった。このフィルムのボイド数は１６×１０^-6個／ｍｍ²で、カール値０．０６４ｍｍとなり、ハンドリング性が非常に良好であった。
【００４０】
【実施例３】
実施例１の凝固液としての硫酸水溶液の温度を２５℃とした以外は全て実施例１と同様に行い、約１２μｍの厚みのフィルムを得た。その結果、ボイド数２５×１０^-6個／ｍｍ²、カール値０．１２１ｍｍで実施例１同様非常に良好なフィルムが得られた。
【００４１】
【実施例４】
実施例１の凝固前のシャワーを実施せずに、ドープ温度８０℃で凝固液中に突入させた以外は全て実施例１と同様に行い、約１２μｍの厚みのフィルムを得た。そのフィルムを測定した結果、ボイド数は５６×１０^-6個／ｍｍ²で実施例１と同様良好な値となった。しかし、カールの方はカール値０．２２６ｍｍで実施例１に比べ大きい値のフィルムとなったが、ハンドリング性やロールとロールの間を連続走行させるのには全く問題のないレベルであった。
【００４２】
【実施例５】
実施例１の凝固液の流速を０．４ｍ／秒とした以外は全て実施例１と同様に行い、約１２μｍの厚みのフィルムを得た。その結果、カール値は０．１４２ｍｍで実施例１と殆ど変わらない程度だったが、ボイド数が１２１×１０^-6個／ｍｍ²となり、実施例１に比べ多くなった。しかし、このフィルムの引っ張り物性を調べてみたが、ばらつきは小さく実施例１のフィルムと殆ど変わらないものであった。
【００４３】
【比較例１】
実施例１の凝固液の硫酸水溶液濃度を２０重量％とした以外は、すべて実施例１と同様に行い約１２μｍのフィルムを得た。そのフィルムのボイド数は８９２×１０^-6個／ｍｍ²、カール値が０．５１３ｍｍとなり、この結果は、実施例１に比べてボイド数が３０倍近く、カールは５倍近い値であった。このサンプルの引っ張り物性を調べようとしたが、ボイドが多いために試験片によって伸度に大きなばらつきがあり、正確な測定ができなかった。
【００４４】
【比較例２】
実施例１の凝固液の硫酸水溶液温度を５０℃とした以外は、すべて実施例１と同様に実施して約１２μｍのフィルムを得た。そのフィルムのボイド数は、３６２×１０^-6個／ｍｍ²で実施例１の約１０倍、カール値の方は０．４６７ｍｍで実施例１の４倍程度の結果となり、比較例１同様引っ張り物性に大きなばらつきが生じた。
【００４５】
【比較例３】
実施例１のドープの吐出量を調整して凝固後の洗浄したフィルムの厚みが１５０μｍとなるようにし、凝固液の硫酸水溶液を−１０℃６０重量％とした以外は全て実施例１と同様に行ったが、凝固後に支持面であるタンタルベルトからフィルムが剥がれなかった。この為にスリットからの吐出量とベルト速度を実施例１の１／３にして、何とか厚みが約２５μｍのフィルムを得た。
【００４６】
【発明の効果】
本発明の方法は、実施例に示したようにボイド数が非常に少なく、カールが殆どないフィルムを得られるために、機械的性質や電気絶縁性などに高い信頼性を有し、フィルムを連続加工する時の安定走行性等に優れたフィルムが生産性良く提供される。
【図面の簡単な説明】
【図１】は、カールの測定法のカール値摸式図である。
【図２】は、カールの測定法のスライドグラス上のカールしていない状態模式図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a polyparaphenylene terephthalamide film. More specifically, the present invention relates to a polyparaphenylene terephthalamide film having excellent flatness with very few voids and almost no phenomenon that the film warps to one side (hereinafter referred to as curl). The present invention relates to a production method for obtaining an amide film.
[0002]
[Prior art]
A polyparaphenylene terephthalamide (hereinafter referred to as PPTA) film is a polymer material that is attracting attention because of its high heat resistance and high mechanical strength. In recent years, it has attracted attention as an electronic substrate material because of its high electrical insulation. In addition, PPTA film has superior mechanical properties such as rigidity and strength compared to other polymers, and is very advantageous for film thinning, so magnetic tape, photographic film, printer ink sheet, solar cell base film, print It is expected to be used as a material for wiring board films, electrical insulating films, capacitor films, and the like. A number of methods for producing this PPTA film have been disclosed so far, but it is insufficient to obtain a film having high mechanical properties and highly reliable electrical insulation, and the phenomenon that the film warps on one side, So-called curl has not been fully resolved.
[0003]
The reliability of PPTA film mechanical properties and electrical insulation depends on the presence of voids in the film. When this void exists, for example, in the tensile property of the film, the reliability of the mechanical property expected because the portion where the void exists starts as a starting point and easily breaks becomes low. In addition, in terms of electrical insulation in the thickness direction of the film, the portion where voids are present in the film has a small amount of polymer, so that the dielectric breakdown is likely to occur. As a method for suppressing the formation of voids that inhibit such mechanical properties and electrical insulation, for example, Japanese Patent Application Laid-Open No. 62-112629 discloses that the number of voids is 1 piece / mm. ² In order to make the following, the dope is sufficiently deaerated, and the coagulating liquid temperature is set to 5 ° C. or less.
[0004]
However, this 1 piece / mm ² Films with the following number of voids have a high frequency of occurrence of defects due to voids when they are used for applications with large areas and long lengths, and can satisfy industrially high reliability. It wasn't. Further, JP-A-63-99241, JP-A-62-104714, JP-A-62-116637, JP-A-62-119024, JP-A-1-207330, etc. By setting the liquid concentration to 10% by weight or 30% by weight and setting the coagulation liquid temperature to 10 ° C. or less, it is possible to produce a fill with excellent surface properties and flatness, and with less thickness unevenness, and lowering the coagulation liquid temperature. It is disclosed that the solidification rate tends to be small (slow), and voids generated in the film tend to decrease.
[0005]
However, when the film is manufactured by these methods, the productivity is very poor because the coagulation liquid concentration and / or coagulation liquid temperature makes the coagulation rate small (slow), and only a film with a large curl is obtained. I could not.
On the other hand, curling of the film, for example, when it is used for applications in which a resin or the like is continuously applied on both sides or one side of the manufactured film, the resin is bent at the end of the film by bending or bending of the end of the film due to the curling of the film. Since problems such as inability to paint and problems such as poor handling when handling a film are likely to occur, Japanese Patent Application Laid-Open No. 8-47978 discloses a solution. However, this method alone has not completely solved the curl problem.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. Sho 62-112629
[Patent Document 2]
JP-A-62-104714
[Patent Document 3]
JP-A-62-116637
[Patent Document 4]
JP-A-62-119024
[Patent Document 5]
JP-A-63-99241
[Patent Document 6]
JP-A-1-207330
[Patent Document 7]
Japanese Patent Laid-Open No. 8-47978
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for producing a PPTA film that has almost no voids and does not curl.
[0008]
[Means for Solving the Problems]
The inventors of the present invention have made extensive studies in order to obtain a PPTA film having good productivity with little or no voids that cause a decrease in mechanical properties and electrical insulation. As a result, in order to suppress the formation of voids, it is necessary to control the solidification rate when solidifying the dope that has been converted to optical isotropy and the heat generation and shrinkage accompanying solidification to allow uniform solidification, For this purpose, it has been found that a coagulating liquid having a coagulating liquid concentration changed depending on the thickness of the optical isotropic dope and a specific coagulating liquid temperature is necessary.
[0009]
However, since it is difficult to actually measure the dope thickness necessary for determining the concentration of the coagulating liquid, it is possible to obtain an appropriate coagulating liquid concentration by measuring the thickness of the washed film after coagulation. I found out that I could find the temperature. Surprisingly, it has also been discovered that the production of a film under this coagulation solution condition not only suppresses voids, but also reduces the curl of the film.
As a result of further research on the curl of the film, the occurrence of curl was found to be caused by an asymmetric cross-sectional structure of the film when the cross-sectional structure of the film with large curl was observed with an electron microscope. It was. In addition, the cross-sectional structure of this film is almost symmetrical by controlling the dew point of air used when optically isolating before solidification, the temperature of the dope immediately before solidification, and the coagulation liquid, and further curling is achieved. I found that I can suppress it.
[0010]
That is, the present invention
(1) An optically anisotropic dope comprising polyparaphenylene terephthalamide and sulfuric acid was cast on a support surface while maintaining optical anisotropy, and the dope was converted to optical isotropic by moisture absorption and heating. In the film production method, which is then coagulated, washed and dried, the coagulation liquid concentration C (wt%) is At the end of the water wash When the thickness of the film is T (μm), (18 log) _e T) -20 ≧ C ≧ (18 log _e A process for producing a polyparaphenylene terephthalamide film represented by T) -55 and having a coagulating liquid temperature of 5 to 30 ° C.
(2) The description of (1) above, wherein the average flow rate of the coagulating liquid in the dope entry portion when solidifying the dope after being converted to optical isotropic property is 0.01 to 0.5 m / sec. Of producing a polyparaphenylene terephthalamide film.
(3) The dope converted to optical isotropy is cooled to 5 to 80 ° C. before contacting the coagulation liquid (1) Or (2) In The manufacturing method of the polyparaphenylene terephthalamide film of description.
[0011]
(4) The above-mentioned (1) to (3), wherein the dew point of air used for conversion to optical isotropy by moisture absorption and heating is −30 to 30 ° C. Either The manufacturing method of the polyparaphenylene terephthalamide film of description.
Related to.
The present invention is described in detail below. PPTA used in the present invention is a polymer represented by Chemical Formula 1, and is conveniently produced from paraphenylenediamine and terephthaloyl chloride by a low temperature solution polymerization method.
[0012]
[Chemical 1]

[0013]
If the degree of polymerization of the polymer used in the present invention is too low, a film having good mechanical properties cannot be obtained, and if it is too high, it becomes impractical, so 3.0 to 8.5, preferably 3.5 to A degree of polymerization giving a logarithmic viscosity ηinh of 7.5 (value measured at 35 ° C. by dissolving 0.1 g of polymer in 150 ml of 98% sulfuric acid) is selected.
In order to produce the PPTA film of the present invention, it is first necessary to adjust the PPTA dope. A suitable solvent for adjusting the dope is 95% or more concentrated sulfuric acid. When sulfuric acid is less than 95% by weight, it is difficult to dissolve the polymer, and the dope after dissolution becomes abnormally high in viscosity. Although sulfuric acid having a concentration of 100% by weight or more is possible, a concentration of 98 to 100% by weight is preferably used from the viewpoint of the stability and solubility of the polymer.
[0014]
As the concentration of the polymer in the dope used in the present invention, a polymer having a concentration higher than that exhibiting optical anisotropy at room temperature (about 20 to 30 ° C.) or higher is preferably used, specifically 9.5. Used in weight percent or more. At polymer concentrations that do not reach this point, i.e., polymer concentrations that do not exhibit optical anisotropy at room temperature or below, the PPTA films produced often do not have favorable mechanical properties. The upper limit of the polymer concentration is not particularly limited, but is usually 20% by weight or less, preferably 18% by weight or less, and more preferably 16% by weight or less, particularly for a polymer having a high logarithmic viscosity ηinh. .
[0015]
The dope of the present invention may contain ordinary additives such as extenders, delustering agents, UV stabilizers, antistatic agents, heat stabilizers, pigments, dissolution aids and the like. In addition, for improving slipperiness and surface property as a film, for example, SiO ₂ TiO ₂ , ZnO, Al ₂ O _Three , CaSO _Four , BaSO _Four , CaCO _Three In addition, one or more kinds of particles of inorganic compounds such as carbon black and zeolite can be selected and used.
In the adjusted optically anisotropic dope, it is preferable to remove insoluble dust, foreign substances, etc., undispersed fine particles and re-aggregates by filtration before solidification and drying as much as possible. The filter used at this time is a filter capable of removing about 80% or more of a size of 5 μm, more preferably a filter capable of removing about 80% or more of particles having a size of 3 μm, and this filter can be used in two or more stages. This is one useful embodiment.
[0016]
Performing such highly accurate filtration is effective in preventing the surface smoothness of the film, particularly the formation of coarse protrusions. Further, in order to improve the surface properties of the film, it is preferable to remove fine bubbles such as air generated or entrained during dissolution in addition to dust and foreign matters in the dope. As a method of removing gas such as air in the dope, for example, after adjusting the dope, it can be removed by vacuum (reduced pressure), or by performing under vacuum (reduced pressure) consistently from the stage of raw material charging. Can also be achieved.
[0017]
Whether the dope after adjustment is optically anisotropic or optically isotropic can be examined by a known method, for example, the method described in Japanese Patent Publication No. 50-8474, the critical point is the type of solvent, Since it depends on temperature, polymer concentration, polymer polymerization degree, non-solvent content, etc., by examining these relationships in advance, optical anisotropy can be created and changed to conditions that become optically isotropic dope. The optical anisotropy can be changed to the optical isotropy.
[0018]
The optically anisotropic dope thus adjusted is cast on the support surface while maintaining the optical anisotropy by, for example, a slit die. Experimentally, it can be cast with a doctor knife or the like. The supporting surface can be selected from, for example, glass, stainless steel, tantalum, hastelloy, fluororesin, and the like, drums coated with noble metals such as gold and platinum, belts, plates, and the like.
The dope cast on the support surface must then be converted from optical anisotropy to optical isotropic. As a method of converting the dope into this optical isotropy, it is preferable to use heat-humidified air in order to reduce the decomposition of PPTA as much as possible. The present inventors have studied the dew point of the air used at this time, and found that the curl can be further reduced by lowering the dew point. Also, if the dew point is too low, it takes too much time for isotropic isotropic, and it is not practical.If the dew point is too high, the dope surface is solidified due to excessive moisture absorption, and the cross section of the film The structure tends to be asymmetric and the curl tends to increase.
[0019]
Therefore, the preferable dew point of the present invention is in the range of -30 to 30 ° C. The air whose dew point is adjusted is heated to 50 to 180 ° C., preferably 70 to 150 ° C., and is directly applied to the dope to convert the dope into optical isotropic. The wind speed of the air at this time is preferably 3 to 20 m / second, more preferably 5 to 15 m / second. By increasing the wind speed, it is possible to manufacture with high productivity under conditions of a low dew point region where the curl can be reduced.
[0020]
Cooling the optically isotropic dope before subsequent solidification is a preferred embodiment in order to almost completely eliminate curl of the film of the present invention. The cooling of the dope before this solidification is thought to reduce the temperature difference from the coagulation liquid and suppress rapid heat generation when in contact with the coagulation liquid, so that the structure in the thickness direction of the dope approaches symmetry. It is an effective means against curling. The temperature of the dope cooled before solidification according to the present invention is preferably 5 to 80 ° C., more preferably 5 to 50 ° C. in terms of curl state and productivity.
[0021]
The method for cooling the temperature of the dope is not particularly limited. For example, as a method for directly reducing the temperature of the dope, a method of blowing a gas such as cooled air to the dope cast on the support surface. As a method for indirectly lowering the temperature of the dope, there are a method of spraying a liquid or a gas on the surface of the support surface where the dope is not cast, a method of bringing a temperature-controlled roll or the like into contact, and the like.
The cast dope optically isotropic on the support surface must then be solidified. As the coagulation liquid for coagulation, an aqueous sulfuric acid solution is preferable, and the concentration and temperature of the aqueous sulfuric acid solution are very important for reducing the number of voids and curl in the present invention. That is, in the present invention, the concentration of the coagulation liquid is (18 log) when the coagulation liquid concentration C (% by weight) is T (μm) after the thickness of the washed film after coagulation. _e T) -20 ≧ C ≧ (18 log _e T) -55 concentration, preferably (18 log) _e T) -30 ≧ C ≧ (18 log _e T) -55.
[0022]
However, the minimum value of the coagulation liquid concentration does not include 0% or less. When the concentration of the coagulation liquid is less than this range, heat generation occurs and the coagulation speed is accelerated. Therefore, there is a large difference in contraction caused between the dope surface in contact with the coagulation liquid and the surface fixed to the support surface. appear. This shrinkage difference is thought to induce void formation and impair the uniformity of the structure of curling. In addition, if the concentration of the coagulation liquid is exceeded, the optically isotropic dope on the support surface in the coagulation liquid is very long before it completely solidifies and can be easily separated from the support surface. Since it takes time, it is difficult to consider industrialization due to lack of productivity.
[0023]
On the other hand, regarding the coagulation liquid temperature, when the dope coagulates even within the range of the coagulation liquid concentration of the present invention, naturally heat is generated due to contact with the coagulation liquid. In order to better suppress the heat generation during the coagulation. Found that it was necessary to limit the coagulation liquid temperature. Therefore, it is necessary to set the coagulation liquid temperature of the present invention to 5 to 30 ° C. If the temperature falls below this temperature range, the coagulation rate becomes too slow and it becomes difficult in terms of productivity.
The dope is coagulated in the coagulation liquid adjusted as described above. However, when continuously producing a film, the coagulation liquid in the coagulation liquid tank needs to be taken in and out (by circulation etc.) so that the concentration and temperature are constant. There is. In this case, controlling the average flow rate of the coagulating liquid in the portion where the dope enters the coagulating liquid is effective in suppressing voids in the present invention. It has been found that if the flow rate of the coagulation liquid is low, productivity is lowered and the surface property of the film is deteriorated due to coagulation spots, and voids are easily generated when the flow rate is high. Therefore, as a flow rate at which voids can be suppressed and productivity does not cause a problem, the average flow rate of the coagulating liquid within 2 to 5 cm from the point where the dope enters is set to 0.01 to 0.5 m / second. Is more preferable, and 0.01 to 0.1 m / second is more preferable.
[0024]
Since the solidified film contains an acid as it is, it is necessary to remove the acid content by washing as much as possible in order to produce a film with little deterioration in mechanical properties due to heating. Specifically, it is desirable to remove the acid content up to about 500 ppm or less. As the cleaning liquid, usually water or hot water as necessary is used, but it may be washed with water after neutralizing and cleaning with an alkaline aqueous solution. As the cleaning method, for example, a method of running the film in the cleaning liquid or a method of spraying the cleaning liquid is performed. The film washed in this way is then dried. If desired, the wet film before drying can be stretched by 1.01 to 1.4 times in one direction or two directions to obtain the film. Mechanical properties can be improved.
[0025]
Since drying of the washed film has a large change in film thickness and surface dimensions before and after drying, care must be taken during drying to obtain a high-quality film. That is, it is necessary to limit the shrinkage of the film under tension so as not to cause wrinkles. The term “under tension” as used herein includes three modes of contracting to a certain length and not causing wrinkles and slightly stretching. It is also possible to make the film thickness thinner by applying stretching before or after drying.
[0026]
If the film is dried without restricting the shrinkage, micro-inhomogeneous structure formation (crystallization, etc.) occurs, so that the light transmittance of the obtained film becomes small. Moreover, the flatness of the film may be impaired or curled. As a method of drying while restricting shrinkage, there is a method of drying by sandwiching between a tenter dryer and a metal frame. Other conditions related to drying are not particularly limited, and heating methods include a method using a heated gas (air, nitrogen, argon, etc.) or room temperature gas, a method using radiant heat such as an electric heater or an infrared lamp, and a dielectric. You can choose freely from means such as heating method. The drying temperature is not particularly limited, but may be any room temperature or higher.
[0027]
However, in order to increase the mechanical strength, a higher temperature is preferable, and 100 ° C. or higher, more preferably 150 ° C. or higher is used. The maximum drying temperature is not particularly limited, but is preferably 500 ° C. or lower in consideration of drying energy and polymer decomposability. After this drying, heat treatment may be performed to improve the elastic modulus and thermal dimensional stability of the film. As this heat processing temperature, 300-550 degreeC is preferable, Most preferably, 350-500 degreeC is used.
[0028]
The heat treatment time at this time is preferably 0.5 seconds to 10 minutes. If the heat treatment time is too short, the treatment effect cannot be sufficiently obtained, and if it is too long, the polymer is deteriorated, the surface smoothness is lost, and the mechanical properties of the film are lowered. As the heat treatment method, either a contact type or a non-contact type may be used. For example, there are a method of contacting a temperature-controlled roll, infrared heating, a method of heating non-contact between plate heaters, and the like.
[0029]
In order to improve the affinity between the film surface and the resin, the film of the present invention may be subjected to a modification treatment. Corona discharge treatment and the like are known as surface modification treatment. In the corona discharge treatment, high frequency and high voltage are applied between an electrode and a roll to generate a corona discharge, and the film passes through this to treat the surface of the film.
Usually, a dielectric roll in which a dielectric material such as hypolon rubber or silicon rubber is coated on a metallic roll is used as the roll. However, in some cases, the discharge treatment can be performed directly between the electrodes without using a dielectric. The discharge frequency is usually about 10 KHz, but is not particularly limited. The treatment density is adjusted depending on the state of the film and the necessary adhesive force, etc., and usually 1-1000 W / m. ² / Min, preferably 10 to 500 W / m ² A range of / min is used. When the treatment density is too high, the physical properties of the film are deteriorated and the surface smoothness is lost.
[0030]
In producing a film by the method of the present invention, any of the above steps may be carried out batchwise or continuously, and it is also preferable that the film is produced while continuously running through all the steps. One of the embodiments. In addition, if the film produced by the present invention is of higher quality, in addition to not allowing foreign matter and dust to be mixed in the dope, it can be used for moisture absorption gas, heating gas, support surface body, coagulating liquid, cleaning liquid, dry gas, etc. In addition, it is preferable that the content of dust or the like is as small as possible. For example, the production of the film of the present invention in a so-called clean room or clean water is one of the preferred embodiments.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below. The method for measuring physical properties of the present invention is as follows.
(1) Film thickness measurement method
The thickness of the film is expressed as an average value by measuring five different points with a digital electronic micrometer (K351C type, manufactured by Anritsu Corporation) using a probe having a diameter of 2 mm.
[0032]
(2) Void number measurement method
In the method for measuring the number of voids, the manufactured film piece is observed as wide as possible under the orthogonal polarization state, and an optically abnormal part is found and marked. The marked part is observed with an optical microscope at a magnification in the range of 100 to 400 times, the voids are selected, the number of voids is counted, and the film is 1 mm. ² The number of voids was converted to a hit.
[0033]
(3) Curl measurement method
The curl is measured by leaving the manufactured sample in a 23 ° C. and 55% environment for 6 hours or longer, and then extruding it from the slit die of the manufactured film in a length direction of 50 mm and a width of 6.5 mm. After cutting out and removing the surface of the cut specimen, it is placed on a glass plate that has been discharged, and the linear distance in the width direction in the curled state is accurately measured using a length measuring microscope as shown in FIG. (Measured value A). Next, as shown in FIG. 2, a slide glass is placed on the sample piece, and the linear distance in the width direction is measured accurately when it is not forcedly curled (measured value B). From the values measured in this way, C = 10 × (1− (1.2 × A / B−0.2) ^0.5 ) To obtain the curl value (mm) = B × (tan ((C) ^0.5 / 2)) / 2 was calculated, and the average value of 5 test pieces was defined as the curl value. This curl value indicates the height from the bottom surface to the highest place when curled in a free state as shown in FIG. All the curl measurement operations were performed in an environment of 23 ° C. and 55%.
[0034]
(4) Tensile property measurement method
Tensile properties of the film are measured at a tensile speed of 50 mm / min by cutting out 10 test pieces that can be measured at a measurement length of 100 mm and a measurement film width of 10 mm using a constant speed stretch type high elongation measuring machine.
[0035]
【Example】
Hereinafter, the present invention will be described based on examples.
[0036]
[Example 1]
PPTA having a logarithmic viscosity ηinh of 4.8 was dissolved at 12.0% by weight in 99.8% by weight sulfuric acid at 60 ° C., and the mixed air was deaerated under vacuum to obtain an optically anisotropic dope. . Next, this dope was cast from a die having a slit of 0.15 mm onto a tantalum endless belt polished to a mirror surface of 120 ° C., and air with a dew point of 12 ° C. was blown onto the dope at a wind speed of 7 m / second at 120 ° C. The casting dope was optically isotropic.
[0037]
Before solidifying the optically isotropic dope, the surface of the endless belt on which the dope is not cast is showered with a 30 wt% aqueous sulfuric acid solution at 15 ° C., which is the same as the coagulation solution, and the temperature of the entire dope is 40 ° C. Then, the mixture was introduced into a coagulation solution having an average flow velocity within 2 to 5 cm from the dope entry portion with a 30 wt% aqueous sulfuric acid solution at 15 ° C. and coagulated. The coagulated film is then washed in a 30 ° C. water bath, then neutralized with a 0.1% aqueous solution of sodium isotope, and then again in a 30 ° C. water bath to remove the acid contained therein. Washed with water. When the thickness of the film at the time of finishing this water washing was measured, it was 72 μm.
[0038]
Next, the wet film taken out from the water tank was stretched 1.1 times in the length direction, then stretched 1.1 times by a clip tenter, and then hot-air dried at 180 ° C. while maintaining a constant length state, then at 420 ° C. It was subjected to tension heat treatment, and was subjected to free heat treatment at 200 ° C. to be rolled up.
The thickness of the film thus obtained was about 12 μm and the number of voids was 32 × 10. ^-6 Piece / mm ² And very few. As for the curl of the film, the average value of the width (A value) when the test piece is curled is 6.547 mm, and the average value of the width (B value) when the slide glass is not curled is 6 As a result, the curl value was 0.111 mm, which was almost the same as the curled state.
[0039]
[Example 2]
The same procedure as in Example 1 was carried out except that the thickness of the washed film after coagulation was adjusted to 150 μm by adjusting the discharge amount of the dope of Example 1 and the coagulating liquid was 60% by weight sulfuric acid aqueous solution at 15 ° C. The resulting film thickness was about 25 μm. The number of voids in this film is 16 × 10 ^-6 Piece / mm ² Thus, the curl value was 0.064 mm, and the handling property was very good.
[0040]
[Example 3]
A film having a thickness of about 12 μm was obtained in the same manner as in Example 1 except that the temperature of the sulfuric acid aqueous solution as the coagulating liquid in Example 1 was 25 ° C. As a result, the number of voids 25 × 10 ^-6 Piece / mm ² A very good film was obtained with a curl value of 0.121 mm as in Example 1.
[0041]
[Example 4]
A film having a thickness of about 12 μm was obtained in the same manner as in Example 1 except that the pre-solidification shower in Example 1 was not carried out and the film was rushed into the coagulation liquid at a dope temperature of 80 ° C. As a result of measuring the film, the number of voids was 56 × 10. ^-6 Piece / mm ² As in Example 1, the values were good. However, the curl film had a curl value of 0.226 mm and a value larger than that of Example 1. However, the curl was at a level that had no problem at all for handling and continuous running between rolls.
[0042]
[Example 5]
A film having a thickness of about 12 μm was obtained in the same manner as in Example 1 except that the flow rate of the coagulation liquid in Example 1 was 0.4 m / sec. As a result, the curl value was 0.142 mm, which was almost the same as Example 1, but the number of voids was 121 × 10 ^-6 Piece / mm ² Thus, the number was larger than that in Example 1. However, when the tensile properties of this film were examined, the variation was small and almost the same as the film of Example 1.
[0043]
[Comparative Example 1]
A film having a thickness of about 12 μm was obtained in the same manner as in Example 1 except that the concentration of the aqueous sulfuric acid solution in the coagulation liquid in Example 1 was 20% by weight. The number of voids in the film is 892 × 10 ^-6 Piece / mm ² The curl value was 0.513 mm. As a result, the number of voids was nearly 30 times that of Example 1, and the curl value was nearly 5 times. An attempt was made to examine the tensile properties of this sample. However, due to the large number of voids, there was a large variation in elongation depending on the test piece, and accurate measurement could not be performed.
[0044]
[Comparative Example 2]
A film of about 12 μm was obtained in the same manner as in Example 1 except that the sulfuric acid aqueous solution temperature of the coagulation liquid in Example 1 was 50 ° C. The number of voids in the film is 362 × 10 ^-6 Piece / mm ² Thus, the result was about 10 times that of Example 1 and the curl value was 0.467 mm, which was about 4 times that of Example 1. As in Comparative Example 1, there was a large variation in tensile physical properties.
[0045]
[Comparative Example 3]
Except for adjusting the discharge amount of the dope of Example 1 so that the thickness of the washed film after coagulation becomes 150 μm and changing the sulfuric acid aqueous solution of the coagulation liquid to −10 ° C. 60% by weight, everything is the same as Example 1. The film was not peeled off from the tantalum belt as the support surface after solidification. For this purpose, the discharge amount from the slit and the belt speed were set to 1/3 of Example 1, and a film with a thickness of about 25 μm was obtained.
[0046]
【The invention's effect】
As shown in the examples, the method of the present invention can provide a film having a very small number of voids and almost no curling. Therefore, the method has high reliability in mechanical properties and electrical insulation, and the film is continuously formed. A film excellent in stable running property during processing is provided with high productivity.
[Brief description of the drawings]
FIG. 1 is a curl value schematic diagram of a curl measurement method;
FIG. 2 is a schematic view of a curled state of the curled state on the slide glass.

Claims (4)

An optically anisotropic dope composed of polyparaphenylene terephthalamide and sulfuric acid is cast on a supporting surface while maintaining optical anisotropy, and the dope is converted to optical isotropic by moisture absorption and heating, and then solidified. , washed, in the preparation process of the film to be dried, when the coagulation solution concentration C (wt%) is, the washing after solidification, the thickness of the film at the End of washing was _{T (μm), (18log e} T ) −20 ≧ C ≧ (18 log _e T) −55, and the coagulating liquid temperature is 5 to 30 ° C.   2. The polyparaphenylene according to claim 1, wherein the average flow rate of the coagulating liquid in the dope entry portion when the dope is converted to optical isotropic and then solidified is 0.01 to 0.5 m / sec. A method for producing a terephthalamide film. The method for producing a polyparaphenylene terephthalamide film according to claim 1 or 2, wherein the dope converted to optical isotropy is cooled to 5 to 80 ° C before contacting the coagulation liquid. The polyparaphenylene terephthalamide film according to any one of claims 1 to 3, wherein a dew point of air used for conversion to optical isotropy by moisture absorption and heating is -30 to 30 ° C. Production method.

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