JP4078630B2 - Carbon film manufacturing method and carbon film obtained thereby - Google Patents

Description

但し、α・・・未延伸フィルムのＣＴＥave
β・・・二軸延伸フィルムのＣＴＥave
（γ²−δ²）／（γ²＋δ²）×２００＝面内異方性指数（ＡＩ値）・・・(iv)
但し、γ・・・最大配向角方向の音波伝播速度
δ・・・最小配向角方向の音波伝播速度
以上のように製造された延伸ポリイミドフィルムまたは炭素化前のポリイミドフィルムのヤング率は４（GPa）以上である。このポリイミドフィルムを５００℃以上で不活性ガス又は真空中で炭素化する。
【００５７】
一旦５００〜８００℃の間で前処理焼成を行い、８００℃以上で後処理焼成を行う方法が好ましい。５００〜８００℃の前処理工程で脱水反応が進行する。この脱水反応は５００℃以下で行われるイミド化による脱水とは異なり、解重合に起因する脱水素反応に伴う脱水である。従ってこの工程は解重合が伴うためボイド生成を抑制するように管理することが重要である。この前工程では好ましくは比重を１．１以上、更に好ましくは１．３以上、最も好ましくは１．５以上に保つように管理することである。この工程で比重が１．１未満のフィルムは、後述する後焼成工程で脆くなりフィルム割れなどが生じる場合がある。
【００５８】
炭素フィルム強度を向上させるため、前焼成処理工程の後または後焼成工程の後にプレスまたはロールなどで圧延し中に含まれるボイドまたは空隙を除くことも好ましい。
【００５９】
前処理工程のみでは焼成時間が十分でない場合グラファイト構造が十分成長化されないため、柔軟性が乏しく脆くなる。後処理焼成温度の好ましい範囲は１０００℃以上３５００℃以下、更に好ましくは２０００℃以上３４００℃以下である。後処理焼成の温度にて長時間保持し黒鉛結晶構造を再配列成長させることも好ましい。３５００℃を超えると炭素の昇華が起こり炭素収率が低くなるので好ましくない。
【００６０】
以上の工程を経て得られた炭素フィルムは、比重が２．０以下、熱伝導率が６００［Ｗｍ^-1Ｋ^-1］以上である。
【００６１】
比重は低い程良いが、具体的な好ましい比重は１．８以下、更には１．７５以下、最も好ましくは１．７以下である。比重が２．０を超えると、放熱シートとして組み込まれた場合、軽量化と高性能化が両立しにくい。
【００６２】
好ましい引張り弾性率は２０［ＧＰａ］以上、更には３５［ＧＰａ］以上、最も好ましくは４０［ＧＰａ］以上である。弾性率が２０［ＧＰａ］未満では、炭素分子の配向が不十分であるか、炭素からなる結晶が十分に成長していない為、強靱性が劣る物となる。
【００６３】
好ましい熱伝導率は７５０［Ｗｍ^-1Ｋ^-1］以上、更には９００［Ｗｍ^-1Ｋ^-1］以上である。熱伝導率が６００［Ｗｍ^-1Ｋ^-1］未満では携帯型電子機器の放熱シートとして性能が不十分である。
本発明の炭素フィルムにより、可撓性の熱放熱シートを実現することができる。
【００６４】
具体的に、テトラカルボン酸二無水物成分としてピロメリット酸二無水物（ＰＭＤＡ）、ジアミン成分として、３，４’−オキシジアニリン（３４’ＯＤＡ）と４，４’−オキシジアニリン（４４’ＯＤＡ）を使用し、ＰＭＤＡと３４’ＯＤＡとからなるブロック成分または混交ポリマー成分を含有するポリイミドフィルムを経由した炭素フィルムの製造例を以下に説明する。
【００６５】
まず、有機溶剤としてのジメチルアセトアミド（ＤＭＡｃ）に、３４’ＯＤＡを溶解し、ＰＭＤＡを加え、第一段目のブロック成分または混交ポリマー成分の反応を完了させる。
【００６６】
次いで、溶液に４４’ＯＤＡを加え溶解した後、溶液にＰＭＤＡを加えて反応させることにより、３４’ＯＤＡとＰＭＤＡとのブロック成分または混交ポリマー成分を含有するポリアミド酸溶液が得られる。
【００６７】
この場合に、最初に供給するＰＭＤＡに微量の４４’ＯＤＡを添加したり、最初に反応させる３４’ＯＤＡとＰＭＤＡとのモル比を非等量にし、過剰量のジアミン成分と十分に反応させる量の末端封止剤を添加することにより、混交ポリマー成分の大きさを制御することも可能である。この様に混交ポリマー成分の効果を有効にするためには、３４’ＯＤＡとＰＭＤＡとのモル比を実質的に等量とするまたは酸無水物／ジアミンのモル比を非等量にし、過剰量のジアミン成分と十分に反応させる量の末端封止剤で末端封鎖された混交ポリマーとすることが好ましい。
【００６８】
この時用いる末端封止剤は無水ジカルボン酸、シリル化剤などの末端封止剤を固形分（ポリマー濃度）に対して０．００１〜２％の範囲で添加することも好ましい。この無水ジカルボン酸として無水酢酸または無水フタル酸、シリル化剤として非ハロゲン系であるヘキサメチルジシラザン、Ｎ，Ｏ−（ビストリメチルシリル）アセトアミド、Ｎ，Ｎ−ビス（トリメチルシリル）ウレアが特に好ましく用いられる。
【００６９】
ポリアミド酸の製造は、その溶液のポリアミド酸濃度と溶液の粘度とでその終了点を決定される。終了点の溶液の粘度を精度良く決定するためには、最後に供給する成分の一部を、反応に使用する有機溶剤の溶液として添加することは有効であるが、ポリアミド酸濃度をあまり低下させないような調節が必要である。
【００７０】
溶液中のポリアミド酸濃度は、５ないし４０重量％、好ましくは１０ないし３０重量％である。
【００７１】
上記有機溶剤としては、それぞれの成分および重合生成物であるポリアミド酸と非反応性であり、成分の１つから全てを溶解でき、ポリアミド酸を溶解するものから選択するのが好ましい。
【００７２】
望ましい有機溶剤としては、Ｎ，Ｎ−ジメチルアセトアミド、Ｎ，Ｎ−ジエチルアセトアミド、Ｎ，Ｎ−ジメチルホルムアミド、Ｎ，Ｎ−ジエチルホルムアミド、Ｎ−メチル−２−ピロリドン等が挙げられ、これらは単独でまたは混合使用することができ、場合によってはベンゼン等の貧溶媒と併用することも可能である。
【００７３】
本発明の炭素フィルムの前駆体であるポリイミドフィルムを製造するに際しては、かくして得られたポリアミド酸溶液を押出機やギヤポンプで加圧して、ポリアミド酸フィルムの製造工程に送液する。
【００７４】
ポリアミド酸溶液は、原料に混入していたり、重合工程で生成した異物、固形物及び高粘度の不純物等を除去するためにフィルターされ、フィルム成形用の口金やコーチングヘッドを通してフィルム状に成形され、回転または移動する支持体上に押出され、支持体から加熱されて、ポリアミド酸が一部イミド転化したポリアミド酸−ポリイミドゲルフィルムが生成され、このゲルフィルムが自己支持性となり、支持体から剥離可能となった時に支持体から剥離され、乾燥機に導入され、乾燥機で加熱されて、溶剤を乾燥し、イミド転化を完了することにより、ポリイミドフィルムが製造される。
【００７５】
このとき、金属焼結フィルターを用いることは、途中で生成されたゲル物の除去に効果的である。好ましくは金属繊維焼結フィルターである。具体的には２０μｍカットの金属焼結フィルターであり、更に好ましくは１０μｍカットの金属焼結フィルターであり、最も好ましくは５μｍカットの金属焼結フィルターである。
【００７６】
ポリアミド酸のイミド転化の方法は、加熱のみによる熱転化法と、イミド転化薬剤を混合したポリアミド酸を加熱処理したり、またはポリアミド酸をイミド転化薬剤の浴に浸漬する化学転化法のいずれも採用することができるが、本発明においては、化学転化法が熱転化法に比べて、可撓性の炭素フィルムが、高弾性率、平面性および製膜性を均衡して高度に実現するのに好適である。
【００７７】
しかも、化学転化法によってポリアミド酸にイミド転化薬剤を混合し、フィルム状に成形後加熱処理する方法は、イミド転化に要する時間が短く、均一にイミド転化が行える等の利点に加え、支持体からの剥離が容易であり、さらには、臭気が強く、隔離を必要とするイミド転化用薬剤を密閉系で取り扱える等の利点を有することから、ポリアミド酸フィルム成形後に転化用薬剤や脱水剤の浴に浸漬する方法に比べて好ましく採用される。
【００７８】
本発明においては、イミド転化用薬剤として、イミド転化を促進する３級アミン類と、イミド転化で生成する水分を吸収する脱水剤とを併用する。３級アミン類は、ポリアミド酸とほぼ等モルないしやや過剰に添加混合され、脱水剤は、ポリアミド酸の約２倍モル量ないしやや過剰に添加されるが、支持体からの剥離点を調整するために適当に調整される。
【００７９】
そして、イミド転化用薬剤は、ポリアミド酸を重合完了した時点から、ポリアミド酸溶液がフィルム成形用口金やコーチングヘッドに達するいかなる時点で添加してもよいが、送液途中におけるイミド転化を防止する意味では、フィルム成形用口金またはコーチングヘッドに到達する少し前に添加し、混合機で混合するのが好ましい。
【００８０】
３級アミンとしては、ピリジンまたはβ−ピコリンが好適であるが、α−ピコリン、４−メチルピリジン、イソキノリン、トリエチルアミン等も使用することができる。使用量は、それぞれの活性によって調整する。
【００８１】
脱水剤としては、無水酢酸が最も一般的に使用されるが、プロピオン酸無水物、酪酸無水物、安息香酸、蟻酸無水物等も使用することができる。
【００８２】
イミド転化薬剤を含有するポリアミド酸フィルムは、支持体上で支持体および反対面空間から受ける熱により、イミド転化が進み、一部イミド転化したポリアミド酸−ポリイミドゲルフィルムとなり、支持体から剥離される。
【００８３】
この場合に、支持体および反対面空間から与える熱量は多いほどイミド転化が促進されて、速く剥離するが、熱量が多すぎると支持体とゲルフィルムの間の有機溶剤のガスがゲルフィルムを変形させ、フィルムの欠点となるので、剥離点の位置とフィルム欠点を勘案して、熱量を決定することが望ましい。
【００８４】
支持体から剥離されたゲルフィルムは、乾燥機に導入され、溶剤の乾燥およびイミド転化の完了がなされる。
【００８５】
このゲルフィルムは、多量の有機溶剤を含有しており、その乾燥過程において体積が大幅に減少する。したがって、この体積減少による寸法収縮を厚さ方向に集中させるために、ゲルフィルムの両端をテンタークリップで把持し、このテンタークリップの移動によりゲルフィルムを乾燥機（テンター）に導入し、テンター内で加熱して、溶剤の乾燥とイミド転化とを一貫して実施するのが一般的である。このゲルフィルムを、回転ロールにより走行速度を規制しながら走行方向に１．１〜２倍延伸し、この延伸されたゲルフィルムの端部をテンタクリップにより把持し、このゲルフィルムを幅方向に走行方向の延伸倍率の０．８〜１．３倍の倍率で延伸する。なお、テンター内において、フィルム両端のテンタークリップの距離を拡大または縮小して、延伸またはリラックスをおこなうことができる。
特に幅方向の延伸操作においてイミド化率、雰囲気温度または溶媒含有量が異なる状態で２段階以上に分割されて延伸操作が施されることは、フィルム破断を生じさせずに高延伸倍率が得られるので好ましい。
【００８６】
熱収縮率を低くするためには、高温領域での冷却は低張力で徐冷することが好ましい。徐冷条件は５０〜３００℃の温度範囲の冷却速度が５００℃／分以下、好ましくは１００℃／分以下で冷却することが好ましい。
【００８７】
この乾燥及びイミド転化は、５０ないし５００℃の温度で行われる。乾燥温度とイミド転化温度は同一温度でもよいし、異なる温度でもよいが、溶剤を大量に乾燥する段階では、低めの温度、具体的には５０〜２００℃で、として溶剤の突沸を防ぎ、溶剤の突沸のおそれがなくなったら、高温にして、具体的には２００〜５００℃で、イミド転化を促進するように、段階的に高温にすることが好ましい。
【００８８】
好ましくはブロック成分または混交ポリマー成分を含有し、化学転化法によりイミド転化して得られるカットシート状のポリイミドフィルムは、上記のように製造した連続したフィルムから切り取って製造することができるが、少量のフィルムを製造するには、後述の実施例で示しているように、樹脂製やガラス製のフラスコ内で、好ましくはブロック成分または混交ポリマー成分を含有するポリアミド酸を製造し、このポリアミド酸溶液に化学転化薬剤を混合して得られる混合溶液を、ガラス板等の支持体上にキャストし、加熱して、一部イミド転化した自己支持性のポリアミド酸−ポリイミドゲルフィルムとして、支持体から剥離し、金属製の固定枠等に固定して寸法変化を防止しながら加熱して、溶剤の乾燥およびイミド転化する方法により製造することができる。
【００８９】
このようにして、化学転化法によりイミド転化して得られる本発明のポリイミドフィルムは、熱転化法により得られるポリイミドフィルムに比しても、炭素フィルム用の原料に適用した場合に、高弾性率かつ熱伝導率に優れた炭素素材を提供できる。
【００９０】
以上のような方法で得られた延伸ポリイミドフィルムは、ヤング率が４［ＧＰａ］以上で、好ましくは５［ＧＰａ］以上のポリイミドフィルムである。
【００９１】
引き続き、炭素化工程を行う。上記で得られたポリイミドフィルムを黒鉛板に挟み、窒素ガス雰囲気中、１〜５０℃／分の昇温速度で５００〜８００℃まで昇温し前焼成を行う（前焼成工程）。このときフィルムの比重は１．１以上に管理することが好ましい。一旦室温まで冷却し、前焼成したフィルムを炭素繊維織布に挟み、アルゴンガス雰囲気中で室温から１０〜５００℃／分の昇温速度で８００〜３５００℃まで昇温する（後焼成工程）。この焼成工程において、積層炭素フィルムを得るため、ポリイミドフィルムを重ね合わせて行っても良い。または前焼成工程で得られたフィルムを重ね合わせ後焼成工程を行っても良い。
【００９２】
以上の製造方法により、本発明の比重が２．０以下、熱伝導率が６００［Ｗｍ^-1Ｋ^-1］以上の炭素フィルムを得ることが出来る。
【００９３】
更にこの炭素フィルムはこの優れた特性により、電極、発熱体、構造体、ガスケット、断熱体、耐食性シール材、電機用ブラシ、Ｘ線または中性子線モノクロメータ、原子炉用減速材、電池用セパレータなどに用いられる。特に、携帯型コンピューターなどの電気回路に起因する発熱を放熱するための軽量でかつ高性能の放熱シートが得られる。
【００９４】
【実施例】
以下、実施例により、本発明を具体的に説明するが、本発明は、これら実施例に限定されるものではない。なお各フィルム特性値は、下記の方法で測定したものである。
【００９５】
また、下記の実施例中で、略号ＤＭＡｃはジメチルアセトアミドを、ＰＭＤＡはピロメリット酸二無水物を、３４’ＯＤＡは３，４’−オキシジアニリンを、また、４４’ＯＤＡは４，４’−オキシジアニリンを示す略記である。
（１）弾性率および破断伸度
弾性率は、ＪＩＳＫ７１１３に準じて、室温でＯＲＩＥＮＲＥＣ社製のテンシロン型引張試験器により、引張速度３００ｍｍ／分にて得られる張力−歪み曲線の初期立ち上がり部の勾配から求めた。
【００９６】
破断伸度は試料が破断するときの伸度を取った。
（２）ガラス転移温度（Ｔｇ）
装置は理学電機（株）社製 微少定荷重熱膨張計で、窒素気流中にて測定
Ａ．ガラス転移温度（Ｔｇ）
１０ｍｍ長さ×約１５ｍｍ幅の切片を切り出し、これを円筒状にして１０ｍｍの長さ方向に圧縮モードで測定する。０．５ｇの付加荷重で行った。
【００９７】
２℃／分の昇温速度で、室温から４００℃までの１回目の昇温で測定した。寸法変化試料長Ｌ0とその長さの変化量ΔＬから、長さ変化率ΔＬ／Ｌ0とする。ΔＬは１０℃毎に読みとり、横軸に温度、縦軸に長さ変化率ΔＬ／Ｌ0を取り、２００〜４００℃で観測される屈曲温度をＴｇとした。
【００９８】
３５０℃未満のＴｇのものは、炭素化工程で皺が発生したり、配向緩和が生じ本発明の主用途には不適である。
（３）製膜性
用意したフィルムを研究用高分子フィルム二軸延伸装置（ＢＩＸ−７０３、（株）岩本製作所社製）により、４００℃で両軸当速度同時二軸延伸方式により延伸させフィルム破断面積を求めた。予熱時間６０秒、片側延伸速度１０ｃｍ／min、
◎；極めて良好 破断延伸面倍率が２倍を超える。
【００９９】
○；良好 破断延伸面倍率が１．５倍〜２倍。
【０１００】
△；実用上問題ない 破断延伸面倍率が１．１倍〜１．５倍。
【０１０１】
×；製膜困難 破断延伸面倍率が１．１倍未満。
（４）面内異方性指数
野村商事社製 Sonic Sheet Tester ＳＳＴ−２５０型を用いた。サンプルは２５μｍフィルムについて６枚重ねとして、ＭＤ方向２５０ｍｍ、ＴＤ方向１７０ｍｍの大きさに正確に切断しサンプルとした。中央部は、幅方向の中央部から、端部はフィルムの端から１００ｍｍの位置を中心とする位置からサンプリングした。中央部は、幅方向の中央部から、端部はフィルムの端から１００ｍｍの位置を中心とする位置からサンプリングした。測定結果からフィルム中の音波の伝播速度が１０°間隔に測定でき、測定データを２次曲線で相関させ、円周全方向にわたる配向分布を求め、最大配向角、最小配向角および最大配向角と最小配向角における音波の伝播速度を求めた。
【０１０２】
面内異方性指数（ＡＩ値）は、最大配向角の音波伝播速度Peak Value MAX. と最小配向角の音波伝播速度Peak Value MIN. から上述した式(iv)より計算される。
（５）面配向係数
メトリコン コーポレーション社製のメトリコンＰＣ−２０１０を用い、波長0.633μｍの光線により測定した。サンプルは３ｃｍ×３ｃｍに切り取り、メトリコンＰＣ−２０１０にセットされて面内最大屈折率、面内最小屈折率および厚さ方向屈折率を測定し、上述した(i)式により面配向係数を求めた。
（６）比重
フィルムより４ｃｍ×４ｃｍの試料片を切り出し、アルキメデス法により測定した。測定温度は２５℃。浸漬液は水。
【０１０３】
重量ｍ（ｋｇ）の試料が、密度ρw（ｋｇ／ｃｍ³）の水に浸かったときに受ける浮力をＦ（ｋｇ）とすると、試料の密度ρ（ｋｇ／ｃｍ³）は次式により算出される。
【０１０４】
ρ＝（ｍ×ρw）／Ｆ
ここで浮力Ｆは、細線により天秤に試料をつるし、試料を水につけ、浸漬前後の天秤の読みの差から求めることが出来る。
【０１０５】
測定装置：重量・・・島津製作所製 電子分析天秤 ＡＥＬ−２００
（７）熱伝導率
面方向の熱伝導率λ（Ｗ/ｍＫ）は、熱拡散率αおよび熱容量ρＣｐ（Ｊ/ｍ³Ｋ）の積として算出した。
【０１０６】
λ＝αρＣｐ
比熱はＤＳＣ（示差走査熱量計）法により求めた。
【０１０７】
熱拡散率は光交流法により求めた。測定条件は以下の通り。
【０１０８】
測定装置：真空理工（株）製熱定量測定装置ＰＩＴ−１
測定温度：１７０℃
照射光 ：ハロゲンランプ光
雰囲気 ：真空中
（８）非融着性
ポリイミドフィルムを３枚重ね炭素繊維織布に挟み、加熱炉内に入れる。窒素雰囲気にした後、室温より８００℃まで５℃／分で昇温し、引き続き１２００℃まで１０℃／分で昇温し１時間保持した。冷却は室温まで５℃／分で行う。
【０１０９】
炉内よりフィルムを取り出し得られた炭素フィルムの融着状態を観察する。
【０１１０】
△以上が一度に炭素フィルムを得ることが出来実用レベルである。
【０１１１】
○・・・融着していない。３枚同時に炭素フィルムが得られる。
【０１１２】
△・・・わずかに融着しているが手で簡単に剥がすことが出来る
×・・・融着して剥がすことが出来ない。
【０１１３】
［実施例１］
５００ｃｃのガラス製フラスコに、ＤＭＡｃ１５０ｍｌおよび気相法炭素繊維（昭和電工（株）社製、ＶＧＣＦ）０．３ｇを入れ、３４’ＯＤＡをＤＭＡｃ中に供給して溶解させ、続いて４４’ＯＤＡ及びＰＭＤＡを順次供給し、室温で、約１時間攪拌する。最終的にテトラカルボン酸二無水物成分とジアミン成分が約１００モル％化学量論で表１に示す組成の成分からなるポリアミド酸濃度２０重量％の溶液を調製した。
【０１１４】
このポリアミド酸溶液３０ｇを、１２．７ｍｌのＤＭＡｃ、３．６ｍｌの無水酢酸及び３．６ｍｌのβ−ピコリンと混合した混合溶液を調製し、この混合溶液をガラス板上にキャストした後１５０℃に加熱したホットプレート上で約４分間加熱して、自己支持性のポリアミド酸−ポリイミドゲルフィルムを形成し、これをガラス板から剥離した。
【０１１５】
このゲルフィルムを、多数のピンを備えた金属製の固定枠に固定し、２５０℃から３３０℃に昇温しながら３０分間加熱した。さらに４５０℃で１分熱処理後徐冷し厚さ約２５μｍのポリイミドフィルムを得た。
【０１１６】
この得られたフィルムを研究用高分子フィルム二軸延伸装置（ＢＩＸ−７０３、（株）岩本製作所社製）により、４００℃で両軸当速度二軸延伸方式により延伸させフィルム破断面積を求めた。破断面倍率は約２．３倍であった。予熱時間６０秒、片側延伸速度１０ｃｍ／min。
【０１１７】
同様の条件で、ＭＤおよびＴＤ方向に同時２軸に１．４倍ずつ延伸した。更にこのフィルムを４５０℃で１分熱処理し徐冷を行った。
【０１１８】
得られたポリイミドフィルムの特性値評価結果を表１に示した。
【０１１９】
これらのポリイミドフィルムを３枚重ね炭素繊維織布に挟み、加熱炉内に入れた。窒素雰囲気にした後、室温より８００℃まで５℃／分で昇温し、引き続き１２００℃まで１０℃／分で昇温し１時間保持した。冷却は室温まで５℃／分で行った。
【０１２０】
炉内よりフィルムを取り出したところ、フィルムは金属光沢の炭素フィルムが得られた。炭素フィルムはわずかに融着していたが簡単に剥がすことが出来、３枚の面状フィルムが得られた。この炭素フィルムは折り曲げても割れないものであった。得られた炭素フィルムの特性値評価結果を表１に示した。
【０１２１】
［実施例２］
５００ｃｃのガラス製フラスコに、ＤＭＡｃ１５０ｍｌを入れ、３４’ＯＤＡをＤＭＡｃ中に供給して溶解させ、続いてＰＭＤＡを供給し、室温で約１時間攪拌した。このポリアミド酸溶液に４４’ＯＤＡを供給し、完全に溶解させた後室温で約１時間攪拌した。引き続きジアミン成分に対して０．５モル％の無水酢酸を添加し更に約１時間攪拌し、テトラカルボン酸二無水物成分とジアミン成分が約１００モル％化学量論で表１に示す組成の成分からなるポリアミド酸濃度２０重量％の溶液を調製した。
【０１２２】
このポリアミド酸濃度２０重量％の溶液を実施例１と同じ方法で処理して、厚さ約２５μｍのポリイミドフィルムを得た。
【０１２３】
この得られたフィルムを研究用高分子フィルム二軸延伸装置（ＢＩＸ−７０３、（株）岩本製作所社製）により、４００℃で両軸当速度二軸延伸方式により延伸させフィルム破断面積を求めた。破断面倍率は約１．７倍であった。予熱時間６０秒、片側延伸速度１０ｃｍ／min。
【０１２４】
同様の条件で、ＭＤおよびＴＤ方向に同時２軸に１．２倍ずつ延伸した。更にこのフィルムを４５０℃で１分熱処理し徐冷を行った。
【０１２５】
得られたポリイミドフィルムの特性値評価結果を表１に併せて示した。
【０１２６】
炭素化処理は実施例１と同様に行った。
【０１２７】
得られた炭素フィルムの特性値評価結果を表１に併せて示した。
［比較例１］
５００ｃｃのガラス製フラスコに、ＤＭＡｃ１５０ｍｌを入れ、３４’ＯＤＡをＤＭＡｃ中に供給して溶解させ、ＰＭＤＡを溶解させ、室温で、約１時間攪拌し、テトラカルボン酸二無水物成分とジアミン成分が約１００モル％化学量論で表１に示す組成の成分からなるポリアミド酸濃度２０重量％の溶液を調製した。
【０１２８】
このポリアミド酸溶液を、実施例１と同じ方法で処理して、厚さ約２５μｍのポリイミドフィルムを得た。
【０１２９】
得られたポリイミドフィルムの特性値評価結果を表２に示した。得られたフィルムのＴｇが約３２０℃付近に観察された。
【０１３０】
得られたポリイミドフィルムを３枚重ね炭素繊維織布に挟み、加熱炉内に入れた。窒素雰囲気にした後、室温より８００℃まで５℃／分で昇温し、引き続き１２００℃まで１０℃／分で昇温し１時間保持した。冷却は室温まで５℃／分で行った。
【０１３１】
炉内よりフィルムを取り出したところ、フィルムは金属光沢の炭素フィルムが得られたが融着しており簡単に剥がすことが出来なかった。
【０１３２】
そこでポリイミドフィルム１枚を炭素繊維織布に挟み、加熱炉内に入れた。窒素雰囲気にした後、室温より８００℃まで５℃／分で昇温し、引き続き１２００℃まで１０℃／分で昇温し１時間保持した。冷却は室温まで５℃／分で行った。炉内よりフィルムを取り出したところ、フィルムはややくすんだ金属光沢の炭素フィルムが得られ、若干波打ったフィルムが得られた。
【０１３３】
得られた炭素フィルムの特性値評価結果を表２に併せて示した。
【０１３４】
［比較例２］
５００ｃｃのガラス製フラスコに、ＤＭＡｃ１５０ｍｌを入れ、３４’ＯＤＡをＤＭＡｃ中に供給して溶解させ、続いてＰＭＤＡを供給し、室温で約１時間攪拌した。このポリアミド酸溶液に４４’ＯＤＡを供給し、完全に溶解させた後室温で約１時間攪拌した。引き続きジアミン成分に対して１モル％の無水酢酸を添加し更に約１時間攪拌し、テトラカルボン酸二無水物成分とジアミン成分が約１００モル％化学量論で表１に示す組成の成分からなるポリアミド酸濃度２０重量％の溶液を調製した。
【０１３５】
このポリアミド酸濃度２０重量％の溶液を実施例１と同じ方法で処理して、厚さ約２５μｍのポリイミドフィルムを得た。得られたフィルムのＴｇが約３４０℃付近に観察された。
【０１３６】
得られたポリイミドフィルムを３枚重ね炭素繊維織布に挟み、加熱炉内に入れた。窒素雰囲気にした後、室温より８００℃まで５℃／分で昇温し、引き続き１２００℃まで１０℃／分で昇温し１時間保持した。冷却は室温まで５℃／分で行った。
炉内よりフィルムを取り出したところ、フィルムは金属光沢の炭素フィルムが得られたが融着しており簡単に剥がすことが出来なかった。
【０１３７】
そこでポリイミドフィルム１枚を炭素繊維織布に挟み、加熱炉内に入れた。窒素雰囲気にした後、室温より８００℃まで５℃／分で昇温し、引き続き１２００℃まで１０℃／分で昇温し１時間保持した。冷却は室温まで５℃／分で行った。炉内よりフィルムを取り出したところ、フィルムはややくすんだ金属光沢の炭素フィルムが得られ、若干波打ったフィルムが得られた。
【０１３８】
得られた炭素フィルムの特性値評価結果を表２に併せて示した。
【０１３９】
［比較例３，実施例３、４］混交ポリイミド
乾燥窒素で常時パージされる容器に、ＤＭＡｃ１９０．６ｋｇを入れ、３４’ＯＤＡ（２９．８モル％）をＤＭＡｃ中に供給し、溶解させ、続いてＰＭＤＡ（３０モル％）を供給し、室温で、約１時間攪拌した。引き続きジアミン成分に対して０．５モル％の無水酢酸を添加し更に約１時間攪拌し、このポリアミド酸溶液に４４’ＯＤＡ（７０モル％）を供給し、完全に溶解させた後、ＰＭＤＡ（７０モル％）を供給し、室温で約１時間攪拌し、テトラカルボン酸二無水物成分とジアミン成分が約１００モル％化学量論で表１に示す組成の成分からなるポリアミド酸濃度２３重量％の溶液を調製した。この溶液は２０℃で４０００ポイズの粘度であった。このポリアミド酸溶液に、無水酢酸をポリアミド酸単位に対して２．５モル、ピリジンをポリアミド酸単位に対して２．０モルを冷却しながら混合し、ポリアミド酸の有機溶媒溶液を得た。このポリアミド酸の有機溶媒溶液をスリット付金属に定量供給し、９０℃の金属ドラム上に流延し、自己支持性のあるゲルフィルムを得た。得られたゲルフィルムの固形分は１８重量％であった。
（比較例３）
このゲルフィルムの一部を、多数のピンを備えた金属製の固定枠に固定し、２５０℃から３３０℃に昇温しながら３０分間加熱し、さらに４５０℃で１分熱処理後徐冷し厚さ約２５μｍのポリイミドフィルムを得た（比較例３用のポリイミドフィルム）。得られたポリイミドフィルムの特性値評価結果を表２に示した。
【０１４０】
炭素化処理は実施例１と同様に行った。
【０１４１】
得られた炭素フィルムの特性値評価結果を表２に示した。
（実施例３）
この得られたフィルムを研究用高分子フィルム二軸延伸装置（ＢＩＸ−７０３、（株）岩本製作所社製）により、４００℃で両軸当速度二軸延伸方式により延伸させフィルム破断面積を求めた。破断面倍率は約１．７倍であった。予熱時間６０秒、片側延伸速度１０ｃｍ／min。
【０１４２】
同様の条件で、ＭＤおよびＴＤ方向に同時２軸に１．２倍ずつ延伸した。更にこのフィルムを４５０℃で１分熱処理し徐冷を行った（実施例３用のポリイミドフィルム）。
【０１４３】
得られたポリイミドフィルムの特性値評価結果を表１に併せて示した。炭素化処理は実施例１と同様に行った。
【０１４４】
得られた炭素フィルムの特性値評価結果を表１に示した。
（実施例４）このゲルフィルムを金属ドラムから剥離し、金属ロールとシリコーンゴムロールからなる２組のニップロールで温度６３℃で走行方向（ＭＤ）に延伸し次いでテンタに導入した。走行方向の延伸倍率、すなわち金属ドラムと各ニップロールおよびテンタとの速度比は、１．１２、２組目のニップロールのそれは１．２４、テンタのそれは１．４０に調整した。テンタで２００℃の温度で幅方向（ＴＤ）に１．５倍延伸し、次いで４００℃で１．１倍延伸し、引き続き４５０℃で１分間熱処理し、徐冷却ゾーンで約５％幅方向リラックスさせながら３０秒間冷却し、フィルムをエッジカットし、幅２ｍ、厚さ２５μｍの二軸延伸ポリイミドフィルムを得た。得られたポリイミドフィルムの面配向係数は０．１６であった。またその面内異方性指数の平均値は１１であった。その他の特性値評価結果は表１に示した。
【０１４５】
炭素化処理は実施例１と同様に行った。
【０１４６】
得られた炭素フィルムの特性値評価結果を表１に併せて示した。
【０１４７】
［比較例４］
５００ｃｃのガラス製フラスコに、ＤＭＡｃ１５０ｍｌを入れ、４４’ＯＤＡをＤＭＡｃ中に供給して溶解させ、ＰＭＤＡを溶解させ、室温で、約１時間攪拌し、テトラカルボン酸二無水物成分とジアミン成分が約１００モル％化学量論で表１に示す組成の成分からなるポリアミド酸濃度２０重量％の溶液を調製した。
【０１４８】
このポリアミド酸溶液を、実施例１と同じ方法で処理して、厚さ約２５μｍのポリイミドフィルムを得た。
【０１４９】
得られたポリイミドフィルムの特性値評価結果を表２に示した。
【０１５０】
炭素化処理は実施例１と同様に行った。
【０１５１】
得られた炭素フィルムの特性値評価結果を表２に併せて示した。
［実施例５］
５００ｃｃのガラス製フラスコに、ＤＭＡｃ１５０ｍｌを入れ、３４’ＯＤＡをＤＭＡｃ中に供給して溶解させ、続いてＰＭＤＡを供給し、室温で約１時間攪拌した。このポリアミド酸溶液に４４’ＯＤＡを供給し、完全に溶解させた後室温で約１時間攪拌した。引き続きジアミン成分に対して０．５モル％の無水酢酸を添加し更に約１時間攪拌し、テトラカルボン酸二無水物成分とジアミン成分が約１００モル％化学量論で表１に示す組成の成分からなるポリアミド酸濃度２０重量％の溶液を調製した。
【０１５２】
この得られたフィルムを研究用高分子フィルム二軸延伸装置（ＢＩＸ−７０３、（株）岩本製作所社製）により、４００℃で両軸当速度二軸延伸方式により延伸させフィルム破断面積を求めた。破断面倍率は約１．３倍であった。予熱時間６０秒、片側延伸速度１０ｃｍ／min。
【０１５３】
同様の条件で、ＭＤおよびＴＤ方向に同時２軸に１．１倍ずつ延伸した。更にこのフィルムを４５０℃で両軸共に５％リラックスを掛けて１分熱処理し徐冷を行った。
【０１５４】
得られたポリイミドフィルムの特性値評価結果を表１に併せて示した。炭素化処理は実施例１と同様に行った。得られた炭素フィルムの特性値評価結果を表１に併せて示した。
【０１５５】
表１〜表２に記載された結果から明らかなように、ＰＭＤＡ、３４’ＯＤＡおよび４４’ＯＤＡからなる化学転化法で得られた本発明のランダムポリイミドフィルムおよびブロックポリイミドフィルム、または混交ポリマーより製造されたポリイミドフィルムを前駆体として用いて製造された炭素フィルムは、従来の炭素フィルムに比較して、高熱伝導率、高弾性率および可とう性を同時に満足しており、携帯型コンピューターの放熱拡散シートとしての好適な性能を有するものである。
【０１５６】
【表１】

【０１５７】
【表２】

【０１５８】
【発明の効果】
以上説明したように、本発明の炭素フィルムは、ピロメリット酸無水物および４，４’−オキシジアニリンにより得られる炭素ポリイミドフィルムに比しても、可撓性を有し、高弾性率および優れた平面性、製膜性を有するものである。
【０１５９】
したがって、本発明の炭素フィルムを用い、高熱伝導率、高弾性率および可とう性を同時に満足しており、携帯型コンピューターの放熱拡散シートとしての好適な性能を有するものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an insoluble, insoluble, high rigidity and high thermal conductivity carbon film obtained by carbonizing a polyimide film at a high temperature and the carbon film.
[0002]
This carbon film is preferably used for electrodes, heating elements, structures, gaskets, heat insulators, corrosion-resistant sealing materials, electric brushes, X-ray or neutron monochromators, nuclear moderators, battery separators, and the like.
[0003]
[Prior art]
The metal plate used for the heat radiating plate has a high specific gravity, insufficient heat conductivity, and insufficient flexibility.
[0004]
For example, aluminum has a specific gravity of about 2.7 and a thermal conductivity of 200 [Wm. ^-1 K ^-1 It was easy to break by bending. Therefore, it is possible to calcinate the polymer at a high temperature and carbonize it as described in JP-B No. 64-12305, JP-A-1-105199, JP-A-4-31069, JP-A-4-21508, and JP-A-3. JP-A-75211, JP-A-62-91414, JP-A-53-139676, JP-A-60-11215, and the like have been proposed. Japanese Patent Publication No. 1-408204 discloses a method of performing a carbonization treatment after stretching a vinylene-based polymer film. In the baking of the polymer films used in these, the carbon yield is low, so there is a problem of flatness and strength due to severe shrinkage.
[0005]
A method of obtaining a carbon film by using an aromatic polyimide film having a high carbon yield and thermally decomposing it by high-temperature heat treatment is disclosed in JP-A-5-43213 and JP-B-64-12305. . In Japanese Patent Laid-Open Nos. 4-149012 and 4-149013, in order to improve brittleness after firing, a binder is impregnated or rolled to improve strength. These methods are troublesome and have a problem that the thermal conductivity is not sufficient.
[0006]
In order to omit the process such as rolling, Japanese Patent Nos. 3152316 and 30612247 disclose a method of obtaining a carbon film by thermally decomposing a polyimide film using paraphenylenediamine (hereinafter abbreviated as PPD) by high temperature heat treatment. However, PPD is designated as a non-medicinal deleterious substance, and is a substance that has been confirmed to be mutagenic by a notification from the Ministry of Labor (H7. Basic No. 348-2). Moreover, since the boiling point is 267 ° C. at 1 atm, there is a concern that the PPD component is released by high-temperature heat treatment during the carbon film manufacturing process. As shown in these specific examples, PPD polyimide itself has a high Young's modulus and a high glass transition temperature. In particular, a copolymer of pyromellitic acid and PPD has a problem that it is difficult to stretch. For this reason, it was difficult to perform the orientation treatment by stretching before carbonization. In Japanese Patent No. 3152316, polyvalent amines are copolymerized. However, these are also toxic and difficult to handle.
[0007]
Therefore, the raw material used for the carbon film has been desired to have a handling risk that is lower than that of PPD or polyvalent amine and can impart high stretchability. In particular, there has been a demand for a carbon film starting from a copolymer of diaminodiphenyl ether and pyromellitic anhydride, which are used in large quantities in polyimide films and are known for handling.
[0008]
That is, in the comparative example of Japanese Patent No. 3061247, a graphite film can be obtained from a copolymer of 4,4′-oxydianiline (same substance as 4,4′-diaminodiphenyl ether) and pyromellitic anhydride. It has been shown that cracks occur intermittently.
[0009]
In order to solve these problems, the present inventors reduced the glass transition temperature by copolymerizing pyromellitic anhydride, 3,4′-oxydianiline and 4,4′-oxydianiline, By increasing the degree of freedom of molecular orientation, the above problems have been solved.
[0010]
As shown by the fact that the melting point of 4,4′-oxydianiline is 191 ° C., whereas the melting point of 3,4′-oxydianiline is 78 ° C., The molecular skeleton has a higher degree of freedom in molecular orientation and flexibility, that is, higher molecular mobility. By copolymerizing 3,4′-oxydianiline with pyromellitic acid and 4,4′-oxydianiline, the glass transition temperature of the polyimide film comprising pyromellitic acid and 4,4′-oxydianiline is reduced. It has been clarified by the present inventor that the temperature becomes lower than the glass transition temperature and, consequently, the stretch orientation is improved, which makes it suitable as a carbon film having high thermal conductivity and high rigidity.
[0011]
However, when 3,4'-oxydianiline is copolymerized at a high concentration, the glass transition temperature becomes too low, so that it is easy to relax or soften / fuse when it is fired or carbonized at high temperature. There was a problem of strength reduction, flatness deterioration, or fusion of the carbon film later. Specifically, the glass transition temperature (Tg) of a polyimide film composed of pyromellitic acid and 4,4′-oxydianiline is 400 ° C. or higher, and heat resistance at high temperature is good, but stretchability is poor, and after firing. There was a problem of insufficient strength and rigidity of the carbon film. On the other hand, the glass transition temperature (Tg) of the polyimide film composed of pyromellitic acid and 3,4′-oxydianiline is 320 ° C. and the stretchability is good, but the thermal dimensional stability at high temperature is poor, There was a problem of carbon film strength reduction, flatness deterioration, or fusion / softening.
[0012]
Conventionally, aluminum (Al) or copper (Cu) has been used as a heat diffusion plate. Each thermal conductivity is about 200 [W / (m / K)] or about 350 [W / (m / K)].
[0013]
Each specific gravity is 2.7 or 8.9. There has been no material that is lightweight and has a high thermal conductivity characteristic suitable for portable computers in recent years.
[0014]
For this reason, a high-rigidity polyimide film is prepared by optimizing the copolymerization ratio with 4,4'-oxydianiline and 3,4'-oxydianiline and oriented by stretching, and then fired under special conditions. By carbonizing, the inventors have reached an invention for obtaining a suitable carbon film.
[0015]
[Problems to be solved by the invention]
The present invention has been achieved as a result of studying the solution of the above-described problems in the prior art as a subject, and a suitable carbon film is obtained through two steps. (1) a step of providing a film having a desired Young's modulus with a film composition capable of high-magnification drawing because Young's modulus, flatness and isotropy are improved by stretching at a low temperature; An object of the present invention is to provide a carbon film having a high rigidity, a light weight, and a high thermal conductivity, and a method for producing the same, through a step of carbonizing in a non-oxidizing atmosphere at a high temperature.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, the carbon film of the present invention undergoes at least the following two steps.
(1) Pyromellitic dianhydride, and 5 to 80 mol% of 3,4′-oxydianiline and 20 to 95 mol% of 4,4′-oxydianiline based on diamine A film is formed from a polyamic acid solution synthesized from a diamine comprising, and then stretched at an area magnification of 1.1 to 4 times at a temperature of 500 ° C. or lower to obtain a stretched polyimide film having a Young's modulus of 4 [GPa] or more. Process,
Furthermore, 3,4′-oxydianiline may be 20 mol% or more and 60 mol% or less based on diamine, and 4,4′-oxydianiline may be 40 mol% or more and less than 80 mol%. It is a manufacturing method of the polyimide film for obtaining a preferable carbon film.
[0017]
Moreover, the manufacturing method of the carbon film which includes the manufacturing process of the stretched polyimide film which performs a process (A)-(E) sequentially in this (1) process, and has a block component or a mixed polymer component.
[0018]
(A) pyromellitic dianhydride, 3,4'-oxydianiline and 4,4'-oxydianiline are mixed with 3,4'-oxydianiline and pyromellitic dianhydride in an inert solvent. A step of reacting at least 1 to 99% by weight of pyromellitic dianhydride or diamine so as to form a polyamic acid having a block component or a mixed polymer component with the product,
(B) a step of additionally using the remaining raw materials for the polyamic acid polymer from the step (A) and finally reacting using the total amount of the total amount used;
(C) The process of mixing the conversion agent which can convert a polyamic acid into a polyimide in the polyamic acid solution from the said process (B),
(D) casting or extruding the mixture from step (C) onto a smooth surface to form a polyamic acid-polyimide gel film; and
(E) The gel film from the step (D) is stretched 1.1 to 2 times in the traveling direction while regulating the traveling speed with a rotating roll, and the end of the stretched gel film is gripped with a tenter clip. The step of stretching the gel film in the width direction at a stretching ratio of 0.8 to 1.3 times the stretching ratio in the running direction, and the stretching operation in this step are divided and stretched at least twice at different temperatures.
[0019]
(F) The process of converting a polyamic acid into a polyimide by heating at the temperature of 200-500 degreeC.
(2) The polyimide film is carbonized in an inert gas or vacuum to have a specific gravity of 2.0 or less and a thermal conductivity of 600 [Wm. ^-1 K ^-1 A step of forming the above carbon film,
In the carbonization step (2), the polyimide film is infusibilized in advance at a temperature of 500 to 800 ° C. in an inert gas or vacuum, and then 800 to 3500 ° C. or more in an inert gas or vacuum. It is also preferable to heat at a temperature.
[0020]
Further, the above-described polyimide film was used as a raw material, the tensile elastic modulus was 35 [GPa] or more, and the thermal conductivity was 800 [Wm. ^-1 K ^-1 ] The above carbon film.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the configuration and effects of the present invention will be described in detail.
[0022]
The method for producing a carbon film of the present invention and the carbon film obtained therefrom are composed of pyromellitic dianhydride, 5 mol% or more and less than 80 mol% of 3,4'-oxydianiline and 20 mol% or more based on diamine. It is produced via a polyamic acid solution consisting of less than 95 mol% of 4,4′-oxydianiline. Preferably, 3,4′-oxydianiline is 20 mol% or more and 60 mol% or less based on diamine, and 4,4′-oxydianiline is 40 mol% or more and less than 80 mol%.
[0023]
In the case of adding inorganic particles, addition of a small amount is preferable, but addition of particles that can become a graphite crystal nucleating agent during the sintering process is particularly preferable. For example, there are graphite particles such as pulverized graphite particles, carbon nanotubes, and carbon nanohorns, and fine particles having different shapes of graphite. Since the long axis of the flat or fibrous particles is oriented in the in-plane direction during stretching, fine flat particles or fibrous particles having an average short axis diameter of 1 μm or less are preferable. A preferable addition amount is 20% by weight or less, more preferably 5% by weight or less. The addition can be carried out by mixing with the polymer solution before or after polymer polymerization, during transfer in piping or immediately before extrusion casting.
[0024]
The amount of particles having no graphite crystal nucleating agent capacity is preferably 1% by weight or less.
[0025]
A film is formed from this polyamic acid solution, and then stretched at an area magnification of 1.1 to 4 times in biaxial directions perpendicular to each other at a temperature of 500 ° C. or lower, preferably 300 to 500 ° C. It is manufactured via a process of obtaining a stretched polyimide film of 4 [GPa] or more.
[0026]
The diamines used in the present invention are mainly 3,4′-oxydianiline and 4,4′-oxydianiline. Other diamines can be used in combination within a range of addition amounts that do not impair the object of the present invention. In the present invention, 3,4'-oxydianiline lowers the glass transition point (Tg) and at the same time improves the elongation and stretchability of the film and increases the rigidity of the polyimide film before carbonization. 4,4′-oxydianiline acts to increase Tg and impart flexibility. The polyimide is 5 mol% or more and less than 80 mol%, preferably 20 mol% to 60 mol% of 3,4'-oxydianiline and 20 mol% or more and less than 95 mol%, preferably 40 mol%, based on the total molar amount of diamine. The polyamic acid obtained by using 4,4′-oxydianiline in an amount of not less than 80 mol% and not more than 80 mol% is produced by imide conversion. Accordingly, by copolymerizing 5% by mole or more of 3,4′-oxydianiline based on diamine with a composition comprising pyromellitic dianhydride and 4,4′-oxydianiline, a glass transition temperature is obtained. However, there exists an effect which can be made lower than the polyimide film which consists of pyromellitic dianhydride and 4,4'- oxydianiline.
[0027]
The diamines used in the present invention are 3,4′-oxydianiline and 4,4′-oxydianiline, but other diamines can be used in combination as long as the effects of these two diamine systems are not impaired. Particularly preferred is a diamine having two or more benzene rings. For example, bisaminophenoxyphenylpropane, bisaminophenoxybenzene, bisaminophenoxybiphenyl, methylene dianiline, diaminodiphenyl sulfide, diaminodiphenyl sulfone and the like can be added in less than 30 mol%.
[0028]
If 3,4'-oxydianiline is less than 5 mol%, the stretchability of the film is insufficient, and the carbon film after firing becomes insufficient in strength or rigidity, resulting in cracks and lack of flexibility, resulting in a brittle carbon film.
[0029]
Also, if 3,4'-oxydianiline is 80 mol% or more, Tg is 350 ° C. or less, orientation relaxation occurs during firing at high temperature, and the elastic modulus of the carbon film is lowered or the thermal conductivity is sufficient. It will not be high. In addition, the flatness is poor and it is fused.
[0030]
Moreover, since 3,4'-oxydianiline has a low melting point, it is difficult to dry industrially, and there is a problem that it becomes difficult to handle rapidly when the copolymerization ratio increases. In addition, when the amount of copolymerization increases, there is a problem that the polymerization is delayed or does not proceed due to moisture. Furthermore, there is a serious industrial meaning that it is possible to supply an inexpensive film without increasing the polymerization reaction time by reducing the copolymerization amount of expensive 3,4′-oxydianiline due to the above reasons. .
[0031]
The tetracarboxylic dianhydride used in the present invention is pyromellitic dianhydride, but tetracarboxylic dianhydride and the like can be used in combination within a range of addition amounts that do not impair the object of the present invention. For example, biphenyl tetracarboxylic dianhydride or benzophenone tetracarboxylic dianhydride can be added in less than 50 mol%.
The resulting polyamic acid is produced by imide conversion.
[0032]
The elastic modulus of the polyimide film can be adjusted by the use ratio of 3,4'-oxydianiline in the diamine component used for producing the polyamic acid and the film stretching ratio. When a large amount of 3,4′-oxydianiline is used, the high elastic modulus and dimensional stability are improved, but Tg is lowered, and there is a drawback that orientation relaxation or fusion occurs during firing.
[0033]
By stretching and orienting before carbonization, the crystal structure of the carbonized film, particularly the orientation of the graphite crystal structure, is accelerated to form a dense structure, which tends to improve rigidity and strength. In this case, if the rigidity of the polyimide film is high, it can not be said that the rigidity of the carbon film is high, but it is related to the glass transition temperature and the relative relationship with the pre-baking process conditions described later. In order to balance, the molar ratio of each component must be carefully prepared.
[0034]
The polyamic acid of the present invention has a molar ratio of the tetracarboxylic dianhydride component and the diamine component of about 0.90 to 1.10, preferably 0.95 at a temperature of 175 ° C. or lower, preferably 90 ° C. or lower. From 1.08 to 1.05, more preferably from 0.98 to 1.02, by reacting each component in a non-reactive organic solvent. For the above reasons, a method for producing a polyimide film having a high glass transition temperature and high rigidity is preferred, and therefore a block polymerization method or a mixed polymer polymerization method described later is preferred.
[0035]
Each of the above components may be separately supplied to the organic solvent one after another, or may be simultaneously supplied, or the organic solvent may be supplied to the mixed components, in order to perform a uniform reaction. It is preferable to sequentially add each component to the organic solvent.
[0036]
When supplying each component sequentially, it is preferable to supply the diamine component and the tetracarboxylic dianhydride component preferentially as the block component or the mixed polymer component. That is, in order to produce a polyamic acid containing a block component or a mixed polymer component, the reaction is divided and carried out at least twice, and first a polyamic acid containing a block component or a mixed polymer component is obtained. Is converted into an imide, whereby a block component or a mixed polymer component is incorporated into the obtained polyimide.
[0037]
The step (1) further includes the step of producing a stretched polyimide film having a block component or a mixed polymer component, wherein the steps (A) to (E) are sequentially performed. Production method.
[0038]
(A) pyromellitic dianhydride, 3,4'-oxydianiline and 4,4'-oxydianiline are mixed with 3,4'-oxydianiline and pyromellitic dianhydride in an inert solvent. A step of reacting at least 1 to 99% by weight of pyromellitic dianhydride or diamine so as to form a polyamic acid having a block component or a mixed polymer component with the product,
(B) a step of additionally using the remaining raw materials for the polyamic acid polymer from the step (A) and finally reacting using the total amount of the total amount used;
(C) The process of mixing the conversion agent which can convert a polyamic acid into a polyimide in the polyamic acid solution from the said process (B),
(D) casting or extruding the mixture from step (C) onto a smooth surface to form a polyamic acid-polyimide gel film; and
(E) The gel film from the step (D) is stretched 1.1 to 2 times in the traveling direction while regulating the traveling speed with a rotating roll, and the end of the stretched gel film is gripped with a tenter clip. The process of extending | stretching this gel film by the magnification of 0.8-1.3 times of the draw ratio of a running direction to the width direction.
[0039]
(F) The process of converting a polyamic acid into a polyimide by heating at the temperature of 500 degrees C or less.
[0040]
Imidization is sequentially performed in the steps (C) to (E), and the imidization step can be completed in the step (F). Condensed water is sequentially released by this imidization.
[0041]
And each said characteristic can be made into a more preferable range by incorporating a block component or a mixed polymer component further into extending | stretching operation and / or a polyimide polymer. Particularly preferred block components or mixed polymer components in this case are those obtained by reaction with 3,4'-oxydianiline and pyromellitic dianhydride.
[0042]
The time required to produce the block component or mixed polymer component of the polyamic acid may be determined by the reaction temperature and the ratio of the block component or mixed polymer component in the polyamic acid, but empirically, from about 1 minute to about 20 Time is appropriate.
[0043]
At this time, as will be described later, in order to form a polymer containing a block component, the diamine component to be reacted in the reaction step (A) and the tetracarboxylic dianhydride component are substantially non-equal moles.
[0044]
In order to form a mixed polymer component, (A) the diamine component and tetracarboxylic dianhydride component in the reaction step are substantially equimolar, or if the reaction step is excessive with diamine, dicarboxylic acid is used. It is preferable to block the end with an acid anhydride. The fact that the diamine component and the tetracarboxylic dianhydride component are substantially equimolar, or that the ends are blocked with a dicarboxylic anhydride in the reaction step with excess diamine, is a mixed polymer formed in these reaction steps. It means that the component is chemically inert and not incorporated at the end of the polyimide polymer formed in the subsequent reaction. However, the reaction of the mixed polymer component and the subsequent reaction to form the polyimide are carried out in the same reaction tank, so that a molecular composite (complex of different molecules) is easily formed, and the characteristics of the mixed polymer component are more manifested. It can be done.
[0045]
The gel film produced from the polyamic acid obtained from these has good stretchability when biaxially stretched, and can therefore be biaxially stretched at a high magnification. The imidization includes a chemical ring closure method in which heating is performed using a ring closure catalyst, and a thermal ring closure method in which the ring is closed only by heating without using a ring closure catalyst. This chemical ring closure method is preferable because stable stretching is possible. The gel film is cast from a slit base on a heated support and molded on the film, and the polyamic acid undergoes a ring-closing reaction on the support to form a self-supporting gel film from the support. It is peeled off. The support may be a metal rotating drum or an endless belt, and its temperature is controlled by radiant heat from a heat medium or an electric heater.
[0046]
At the time of producing a conventional polyimide film, a stretching operation by self-shrinkage at the time of solvent drying was mainly performed, but in the present invention, stretching is performed at an area stretching ratio of 1.1 times or more.
As described above, by setting the area magnification to 1.1 times or more, the rigidity / strength and flexibility of the carbonized film can be improved.
[0047]
That is, the gel film is then stretched at an area magnification of 1.1 to 4 times at a temperature of 500 ° C. or lower, and the stretched state is either a polyamic acid gel film, a polyamic acid / polyimide coexisting gel film or a polyimide film, or The stretching may be performed by combining two or more steps.
[0048]
The higher the imidization rate or the lower the solvent content, the higher the orientation effect by stretching, but conversely the film breaks easily, so it is divided into two or more stages in processes where the imidization rate or solvent content is different. The stretching operation is performed. Of course, simultaneous stretching in the biaxial state in the state of a polyamic acid gel film, a polyamic acid / polyimide coexisting gel film or a polyimide film, particularly in the state of a polyimide film, is preferably performed in combination with other steps.
[0049]
In the case of stretching by combining two or more steps, stretching is performed in biaxial directions perpendicular to each other, but stretching at different temperatures is also preferably used.
[0050]
The gel film is heated to 30 ° C. to 200 ° C., preferably 40 ° C. to 150 ° C. by receiving heat from the support or receiving heat from the outside, such as hot air or an electric heater. It becomes self-supporting by drying and peels from the support. When a polyamic acid film that has not undergone a ring-closure reaction is heated rapidly, a gel film with a smooth surface cannot be obtained, and the heating temperature must be appropriately controlled.
[0051]
As a preferred method, the gel film peeled from the support is stretched in the running direction (MD) while regulating the running speed with a rotating roll. Stretching is performed at a temperature of 50 to 200 ° C. at a magnification of 1.1 to 2 times, preferably 1.1 to 1.6 times. The rotating roll requires a necessary gripping force to regulate the traveling speed of the gel film, and a nip roll or a vacuum suction type suction roll formed by combining a metal roll and a rubber roll is used. If the draw ratio of the gel film in the MD direction is less than 1.1 times, the stretching effect is small and the strength increase may be insufficient. As the draw ratio increases, the effect of improving the mechanical properties and dimensional stability in the MD direction increases, but the gel film tends to break, and the subsequent selection range in the width direction becomes narrow. For this reason, MD draw ratio is 1.1 to 1.9 times, preferably 1.1 to 1.6 times.
[0052]
The gel film stretched in the running direction is introduced into a tenter device, and both ends in the width direction are gripped by the tenter clip, and both ends in the width direction are gripped by the tenter clip, and travels with the tenter clip in the width direction (TD). The volatile component such as an organic solvent is dried and then heat treated to form a biaxially oriented polyimide film. Stretching in the width direction is 500 ° C. or less, preferably 450 ° C. or less, and the draw ratio ratio defined by the following formula (i) is 0.9 to 1.3, preferably 1.0 to 1.3. It implements by the draw ratio of the width direction which becomes.
[0053]
(Stretch ratio in TD direction) / (Stretch ratio in MD direction) = Stretch ratio ratio (i)
The draw ratio is important for improving high rigidity and in-plane isotropy, which is one of the objects of the present invention. If the draw ratio is less than 0.9, the orientation effect in the MD direction becomes strong, and the orientation effect in the TD direction exceeding 1.3 times becomes strong, so that the flatness or in-plane isotropy is outside the preferred range. May end up. Moreover, before the gel film is introduced into the drying oven, the stretching in the width direction is preferably performed at 50% or more of the stretching ratio. The gel film may be stretched in the MD direction and TD direction sequentially in this order or in the reverse order, or simultaneously.
[0054]
The stretchability of the gel film is affected by its solid content concentration. When the gel film is dried and the solid content concentration reaches 60% by weight, stretching becomes difficult, and the gel film may break during high-speed stretching. Therefore, the solid content concentration of the gel film molded and peeled off from the support is preferably 50% by weight or less. In order to maintain the self-supporting property of the gel film, the solid content concentration is 5% by weight or more.
[0055]
The drying and heat treatment of the gel film in the tenter oven is carried out using hot air or radiant heat from an electric heater or the like, and the drying temperature is 200 to 400 ° C. and the heat treatment temperature is 350 to 500 ° C. There is a method of controlling the heating method because voids are generated by foaming of the contained volatile components.
The biaxially oriented polyimide film thus produced has a plane orientation coefficient defined by the following formula (ii) that indicates the degree of orientation in the plane direction of the molecular chain, in which the molecular chain is oriented in the film plane direction. The average in-plane coefficient of thermal expansion (CTEave), which is a representative value of dimensional stability, is 0.11 or more, and is at least 10% smaller than the unstretched film calculated by the following formula (iii). It has a mechanical property with an in-plane anisotropy index defined by the following formula (iv) showing 20 or less, excellent in-plane isotropy, and further improved dimensional stability. The biaxially stretched polyimide film is preferable.
[0056]

Where α ... CTEave of unstretched film
β ・ ・ ・ CTEave of biaxially stretched film
(Γ ² −δ ² ) / (Γ ² + Δ ² ) × 200 = In-plane anisotropy index (AI value) (iv)
However, γ ... Sound propagation velocity in the maximum orientation angle direction
δ ・ ・ ・ Sound propagation velocity in the minimum orientation angle direction
The Young's modulus of the stretched polyimide film produced as described above or the polyimide film before carbonization is 4 (GPa) or more. This polyimide film is carbonized at 500 ° C. or higher in an inert gas or vacuum.
[0057]
A method in which pretreatment baking is once performed between 500 to 800 ° C. and posttreatment baking is performed at 800 ° C. or higher is preferable. The dehydration reaction proceeds in the pretreatment step at 500 to 800 ° C. This dehydration reaction is different from dehydration by imidization performed at 500 ° C. or less, and is dehydration accompanying dehydrogenation reaction caused by depolymerization. Therefore, since this process involves depolymerization, it is important to manage so as to suppress void formation. In this pre-process, the specific gravity is preferably controlled to be 1.1 or more, more preferably 1.3 or more, and most preferably 1.5 or more. In this step, the film having a specific gravity of less than 1.1 may become brittle in the post-baking step described later, resulting in film cracking.
[0058]
In order to improve the strength of the carbon film, it is also preferable to remove voids or voids contained during rolling by a press or a roll after the pre-baking treatment step or after the post-baking step.
[0059]
If the firing time is not sufficient only by the pretreatment step, the graphite structure is not sufficiently grown, so that the flexibility is poor and the brittleness becomes brittle. The preferable range of the post-treatment firing temperature is 1000 ° C. or higher and 3500 ° C. or lower, more preferably 2000 ° C. or higher and 3400 ° C. or lower. It is also preferable that the graphite crystal structure is rearranged and grown for a long time at the post-treatment firing temperature. If it exceeds 3500 ° C., carbon sublimation occurs and the carbon yield decreases, which is not preferable.
[0060]
The carbon film obtained through the above steps has a specific gravity of 2.0 or less and a thermal conductivity of 600 [Wm. ^-1 K ^-1 That's it.
[0061]
The specific gravity is preferably as low as possible, but the specific preferred specific gravity is 1.8 or less, further 1.75 or less, and most preferably 1.7 or less. When the specific gravity exceeds 2.0, it is difficult to achieve both weight reduction and high performance when incorporated as a heat dissipation sheet.
[0062]
A preferable tensile elastic modulus is 20 [GPa] or more, further 35 [GPa] or more, and most preferably 40 [GPa] or more. If the elastic modulus is less than 20 [GPa], the orientation of the carbon molecules is insufficient, or the crystals made of carbon are not sufficiently grown, so that the toughness is inferior.
[0063]
The preferred thermal conductivity is 750 [Wm ^-1 K ^-1 ] Further, 900 [Wm ^-1 K ^-1 That's it. Thermal conductivity is 600 [Wm ^-1 K ^-1 ] Is insufficient as a heat dissipation sheet for portable electronic devices.
A flexible thermal radiation sheet can be realized by the carbon film of the present invention.
[0064]
Specifically, pyromellitic dianhydride (PMDA) as the tetracarboxylic dianhydride component, and 3,4′-oxydianiline (34′ODA) and 4,4′-oxydianiline (44) as the diamine component. A production example of a carbon film using a polyimide film containing a block component or a mixed polymer component composed of PMDA and 34′ODA using “ODA” will be described below.
[0065]
First, 34′ODA is dissolved in dimethylacetamide (DMAc) as an organic solvent, and PMDA is added to complete the reaction of the block component or mixed polymer component in the first stage.
[0066]
Next, after 44'ODA is added to the solution and dissolved, PMDA is added to the solution and reacted to obtain a polyamic acid solution containing a block component or mixed polymer component of 34'ODA and PMDA.
[0067]
In this case, a small amount of 44 'ODA is added to the PMDA supplied first, or the molar ratio of 34' ODA to PMDA to be reacted first is made unequal to sufficiently react with an excess amount of the diamine component. It is also possible to control the size of the mixed polymer component by adding the end-capping agent. Thus, in order to make the effect of the mixed polymer component effective, the molar ratio of 34′ODA to PMDA is made substantially equal or the molar ratio of acid anhydride / diamine is made unequal, It is preferable to use a mixed polymer end-capped with an end-capping agent in an amount sufficient to react with the diamine component.
[0068]
It is also preferred that the end-capping agent used at this time is a terminal capping agent such as dicarboxylic anhydride or silylating agent added in a range of 0.001 to 2% with respect to the solid content (polymer concentration). As the dicarboxylic anhydride, acetic anhydride or phthalic anhydride, non-halogen hexamethyldisilazane, N, O- (bistrimethylsilyl) acetamide, N, N-bis (trimethylsilyl) urea are particularly preferably used as the silylating agent. .
[0069]
The production end of the polyamic acid is determined by the polyamic acid concentration of the solution and the viscosity of the solution. In order to accurately determine the viscosity of the solution at the end point, it is effective to add a part of the last component to be supplied as a solution of the organic solvent used for the reaction, but the polyamic acid concentration is not lowered so much. Such adjustment is necessary.
[0070]
The polyamic acid concentration in the solution is 5 to 40% by weight, preferably 10 to 30% by weight.
[0071]
The organic solvent is preferably selected from those that are non-reactive with each component and the polyamic acid that is the polymerization product, can dissolve all of the components, and dissolve the polyamic acid.
[0072]
Desirable organic solvents include N, N-dimethylacetamide, N, N-diethylacetamide, N, N-dimethylformamide, N, N-diethylformamide, N-methyl-2-pyrrolidone, and the like. Alternatively, they can be mixed and used in some cases together with a poor solvent such as benzene.
[0073]
When manufacturing the polyimide film which is the precursor of the carbon film of the present invention, the polyamic acid solution thus obtained is pressurized with an extruder or a gear pump and fed to the polyamic acid film manufacturing process.
[0074]
The polyamic acid solution is mixed to the raw material, filtered to remove foreign matters, solids and high-viscosity impurities generated in the polymerization process, and formed into a film shape through a film forming die or a coating head, Extruded onto a rotating or moving support and heated from the support to produce a polyamic acid-polyimide gel film in which the polyamic acid is partially imide converted. This gel film becomes self-supporting and can be peeled off from the support. When it becomes, it peels from a support body, is introduce | transduced into a dryer, is heated with a dryer, a solvent is dried, A polyimide film is manufactured by completing imide conversion.
[0075]
At this time, the use of a sintered metal filter is effective for removal of the gel product generated during the process. A metal fiber sintered filter is preferable. Specifically, it is a 20 μm cut metal sintered filter, more preferably a 10 μm cut metal sintered filter, and most preferably a 5 μm cut metal sintered filter.
[0076]
The method of imide conversion of polyamic acid employs either a thermal conversion method by heating alone, a chemical conversion method in which the polyamic acid mixed with the imide conversion agent is heat-treated, or the polyamic acid is immersed in a bath of the imide conversion agent. However, in the present invention, the flexible carbon film achieves a high degree of balance between high elastic modulus, flatness, and film-forming property compared with the thermal conversion method in the chemical conversion method. Is preferred.
[0077]
In addition, the method of mixing the imide conversion agent with the polyamic acid by the chemical conversion method, and heat-treating after forming into a film form has the advantage that the time required for imide conversion is short and the imide conversion can be performed uniformly. Is easy to peel off, and also has the advantage of being able to handle imide conversion chemicals that have strong odor and need to be sequestered in a closed system, so that it can be used as a bath for conversion chemicals and dehydrating agents after forming a polyamic acid film. It is preferably employed as compared with the dipping method.
[0078]
In the present invention, as the imide conversion agent, a tertiary amine that promotes imide conversion and a dehydrating agent that absorbs moisture generated by imide conversion are used in combination. Tertiary amines are added and mixed with polyamic acid in substantially equimolar or slightly excessive amount, and the dehydrating agent is added in about twice the molar amount or slightly excessive amount of polyamic acid, but adjusts the peeling point from the support. Is adjusted appropriately.
[0079]
The imide conversion agent may be added at any time when the polyamic acid solution reaches the film forming die or the coating head from the time when the polyamic acid is completely polymerized. Then, it is preferable to add a little before reaching the film forming die or the coaching head and to mix with a mixer.
[0080]
As the tertiary amine, pyridine or β-picoline is suitable, but α-picoline, 4-methylpyridine, isoquinoline, triethylamine and the like can also be used. The amount used is adjusted according to each activity.
[0081]
Acetic anhydride is most commonly used as the dehydrating agent, but propionic anhydride, butyric anhydride, benzoic acid, formic anhydride, and the like can also be used.
[0082]
The polyamic acid film containing the imide conversion agent is subjected to imide conversion by heat received from the support and the opposite surface space on the support, and becomes a partially polyimide-converted polyamic acid-polyimide gel film, which is peeled off from the support. .
[0083]
In this case, as the amount of heat applied from the support and the opposite surface space increases, imide conversion is promoted and peels faster, but if the amount of heat is excessive, the gas of the organic solvent between the support and the gel film deforms the gel film. Therefore, it is desirable to determine the amount of heat in consideration of the position of the peeling point and the film defect.
[0084]
The gel film peeled from the support is introduced into a dryer, and the drying of the solvent and the imide conversion are completed.
[0085]
This gel film contains a large amount of organic solvent, and its volume is greatly reduced during the drying process. Therefore, in order to concentrate the dimensional shrinkage due to the volume reduction in the thickness direction, the both ends of the gel film are gripped by the tenter clip, and the gel film is introduced into the dryer (tenter) by the movement of the tenter clip. In general, the drying of the solvent and the imide conversion are performed consistently by heating. The gel film is stretched 1.1 to 2 times in the running direction while regulating the running speed with a rotating roll, the end of the stretched gel film is gripped by a tenter clip, and the gel film is run in the width direction. The film is stretched at a magnification of 0.8 to 1.3 times the stretching ratio in the direction. In the tenter, the distance between the tenter clips at both ends of the film can be expanded or reduced to stretch or relax.
In particular, in the stretching operation in the width direction, when the imidation ratio, the atmospheric temperature, or the solvent content is different, the stretching operation is performed by being divided into two or more stages, so that a high stretching ratio can be obtained without causing film breakage. Therefore, it is preferable.
[0086]
In order to reduce the heat shrinkage rate, it is preferable that the cooling in the high temperature region is gradually cooled with a low tension. As for the slow cooling conditions, it is preferable that the cooling rate in the temperature range of 50 to 300 ° C. is 500 ° C./min or less, preferably 100 ° C./min or less.
[0087]
This drying and imide conversion is carried out at a temperature of 50 to 500 ° C. The drying temperature and the imide conversion temperature may be the same temperature or different temperatures, but at the stage of drying a large amount of the solvent, a lower temperature, specifically 50 to 200 ° C. When there is no risk of bumping, it is preferable to raise the temperature stepwise, specifically at 200 to 500 ° C., so as to promote imide conversion.
[0088]
A cut sheet-like polyimide film preferably containing a block component or a mixed polymer component and obtained by imide conversion by a chemical conversion method can be produced by cutting from a continuous film produced as described above. In order to produce the film, a polyamic acid preferably containing a block component or a mixed polymer component is produced in a resin or glass flask as shown in the examples described later, and this polyamic acid solution is produced. A mixed solution obtained by mixing a chemical conversion agent with a glass plate is cast on a support such as a glass plate, and heated to release a partially supported imide-converted self-supporting polyamic acid-polyimide gel film from the support. And drying the solvent and imide conversion by fixing to a metal fixed frame etc. and heating while preventing dimensional change It is possible to more production.
[0089]
Thus, the polyimide film of the present invention obtained by imide conversion by the chemical conversion method has a high modulus of elasticity when applied to the raw material for the carbon film, even compared to the polyimide film obtained by the thermal conversion method. In addition, a carbon material excellent in thermal conductivity can be provided.
[0090]
The stretched polyimide film obtained by the above method is a polyimide film having a Young's modulus of 4 [GPa] or more, preferably 5 [GPa] or more.
[0091]
Subsequently, a carbonization process is performed. The polyimide film obtained above is sandwiched between graphite plates, and pre-baked by raising the temperature to 500-800 ° C. at a heating rate of 1-50 ° C./min in a nitrogen gas atmosphere (pre-baking step). At this time, the specific gravity of the film is preferably controlled to 1.1 or more. Once cooled to room temperature, the pre-baked film is sandwiched between carbon fiber woven fabrics, and heated from room temperature to 800 to 3500 ° C. at a heating rate of 10 to 500 ° C./min in an argon gas atmosphere (post-baking step). In this baking process, in order to obtain a laminated carbon film, you may superimpose a polyimide film. Or you may perform a baking process after superimposing the film obtained at the prebaking process.
[0092]
With the above manufacturing method, the specific gravity of the present invention is 2.0 or less and the thermal conductivity is 600 [Wm. ^-1 K ^-1 The above carbon film can be obtained.
[0093]
Furthermore, this carbon film has the excellent characteristics, and therefore, an electrode, a heating element, a structure, a gasket, a heat insulator, a corrosion-resistant sealing material, an electric brush, an X-ray or neutron monochromator, a reactor moderator, a battery separator, etc. Used for. In particular, a lightweight and high-performance heat-dissipating sheet for dissipating heat generated by an electric circuit such as a portable computer can be obtained.
[0094]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples. Each film characteristic value is measured by the following method.
[0095]
In the following examples, the abbreviation DMAc is dimethylacetamide, PMDA is pyromellitic dianhydride, 34′ODA is 3,4′-oxydianiline, and 44′ODA is 4,4 ′. -Abbreviation for oxydianiline.
(1) Elastic modulus and elongation at break
The elastic modulus was determined from the slope of the initial rising portion of the tension-strain curve obtained at a tensile speed of 300 mm / min with a Tensilon type tensile tester manufactured by ORIENREC at room temperature according to JISK7113.
[0096]
The elongation at break was taken when the sample broke.
(2) Glass transition temperature (Tg)
The instrument is a small constant load thermal dilatometer manufactured by Rigaku Corporation and measured in a nitrogen stream.
A. Glass transition temperature (Tg)
A section of 10 mm length × about 15 mm width is cut out, made into a cylindrical shape, and measured in a compression mode in a length direction of 10 mm. It was carried out with an additional load of 0.5 g.
[0097]
The measurement was performed at the first temperature increase from room temperature to 400 ° C. at a temperature increase rate of 2 ° C./min. From the dimensional change sample length L0 and the change amount ΔL of the length, the length change rate ΔL / L0 is obtained. ΔL was read every 10 ° C., the temperature was plotted on the horizontal axis, the length change rate ΔL / L 0 was plotted on the vertical axis, and the bending temperature observed at 200 to 400 ° C. was defined as Tg.
[0098]
Those having a Tg of less than 350 ° C. are unsuitable for the main application of the present invention because wrinkles are generated in the carbonization process or orientation relaxation occurs.
(3) Film forming properties
The prepared film was stretched at 400 ° C. by a biaxial stretching method using a biaxial stretching method at 400 ° C. using a research polymer film biaxial stretching apparatus (BIX-703, manufactured by Iwamoto Seisakusho Co., Ltd.) to determine the film break area. A preheating time of 60 seconds, a one-side stretching speed of 10 cm / min,
A: Very good The ratio of the stretched stretched surface exceeds 2 times.
[0099]
○: Good The ratio of the stretched stretched surface is 1.5 to 2 times.
[0100]
Δ: No problem in practical use The ratio of the stretched stretched surface is 1.1 times to 1.5 times.
[0101]
X: Difficult to form film The ratio of the stretched stretched surface is less than 1.1.
(4) In-plane anisotropy index
Sonic Sheet Tester SST-250 manufactured by Nomura Corporation was used. Samples were stacked on 6 sheets of 25 μm film, and cut accurately to a size of 250 mm in the MD direction and 170 mm in the TD direction to prepare a sample. The central part was sampled from the central part in the width direction, and the end part was sampled from a position centered at a position 100 mm from the end of the film. The central part was sampled from the central part in the width direction, and the end part was sampled from a position centered at a position 100 mm from the end of the film. From the measurement results, the propagation speed of sound waves in the film can be measured at intervals of 10 °, and the measurement data is correlated with a quadratic curve to obtain the orientation distribution in all directions of the circumference, and the maximum orientation angle, the minimum orientation angle, the maximum orientation angle and the minimum The propagation speed of the sound wave at the orientation angle was obtained.
[0102]
The in-plane anisotropy index (AI value) is calculated from the above equation (iv) from the sound propagation velocity Peak Value MAX. At the maximum orientation angle and the sound propagation velocity Peak Value MIN. At the minimum orientation angle.
(5) Plane orientation coefficient
Measurement was performed using a Metricon PC-2010 manufactured by Metricon Corporation with a light beam having a wavelength of 0.633 μm. The sample was cut to 3 cm × 3 cm, set on a Metricon PC-2010, and measured for the in-plane maximum refractive index, the in-plane minimum refractive index and the thickness direction refractive index, and obtained the plane orientation coefficient by the above-described equation (i). .
(6) Specific gravity
A 4 cm × 4 cm sample piece was cut out from the film and measured by the Archimedes method. The measurement temperature is 25 ° C. The immersion liquid is water.
[0103]
A sample of weight m (kg) has a density ρw (kg / cm ^Three ) If the buoyancy received when immersed in water is F (kg), the sample density ρ (kg / cm ^Three ) Is calculated by the following equation.
[0104]
ρ = (m × ρw) / F
Here, the buoyancy F can be obtained from the difference in reading of the balance before and after immersion by suspending the sample on a balance with a thin wire, placing the sample in water.
[0105]
Measuring device: Weight: Electronic analysis balance AEL-200 manufactured by Shimadzu Corporation
(7) Thermal conductivity
The thermal conductivity λ (W / mK) in the plane direction is expressed by the thermal diffusivity α and the heat capacity ρCp (J / m ^Three Calculated as the product of K).
[0106]
λ = αρCp
Specific heat was determined by the DSC (Differential Scanning Calorimeter) method.
[0107]
The thermal diffusivity was determined by the optical alternating current method. The measurement conditions are as follows.
[0108]
Measuring device: Thermoquantitative measuring device PIT-1 manufactured by Vacuum Riko Co., Ltd.
Measurement temperature: 170 ° C
Irradiation light: Halogen lamp light
Atmosphere: In vacuum
(8) Non-fusibility
3 layers of polyimide films are sandwiched between carbon fiber woven fabrics and placed in a heating furnace. After changing to a nitrogen atmosphere, the temperature was raised from room temperature to 800 ° C. at 5 ° C./min, and subsequently to 1200 ° C. at 10 ° C./min and held for 1 hour. Cooling is performed at room temperature at 5 ° C / min.
[0109]
The film is taken out from the furnace and the carbon film obtained is observed for fusion.
[0110]
Above Δ is a practical level because a carbon film can be obtained at a time.
[0111]
○ ... not fused. Three carbon films can be obtained simultaneously.
[0112]
△ ・ ・ ・ Slightly fused but can be easily removed by hand
X: Cannot be fused and peeled off.
[0113]
[Example 1]
In a 500 cc glass flask, 150 ml of DMAc and 0.3 g of vapor-grown carbon fiber (manufactured by Showa Denko KK, VGCF) are placed, and 34′ODA is supplied and dissolved in DMAc, followed by 44′ODA and PMDA is sequentially supplied and stirred at room temperature for about 1 hour. Finally, a solution with a polyamic acid concentration of 20% by weight was prepared, in which the tetracarboxylic dianhydride component and the diamine component consisted of components having the composition shown in Table 1 at about 100 mol% stoichiometry.
[0114]
A mixed solution was prepared by mixing 30 g of this polyamic acid solution with 12.7 ml of DMAc, 3.6 ml of acetic anhydride and 3.6 ml of β-picoline, and the mixed solution was cast on a glass plate and then heated to 150 ° C. The mixture was heated on a heated hot plate for about 4 minutes to form a self-supporting polyamic acid-polyimide gel film, which was peeled from the glass plate.
[0115]
This gel film was fixed to a metal fixed frame provided with a large number of pins, and heated for 30 minutes while raising the temperature from 250 ° C to 330 ° C. Further, after heat treatment at 450 ° C. for 1 minute, it was gradually cooled to obtain a polyimide film having a thickness of about 25 μm.
[0116]
The obtained film was stretched by a biaxial stretching method at 400 ° C. using a biaxial stretching method at 400 ° C. with a research polymer film biaxial stretching apparatus (BIX-703, manufactured by Iwamoto Seisakusho Co., Ltd.) to determine the film breaking area. . The fracture surface magnification was about 2.3 times. Preheating time 60 seconds, one-side stretching speed 10 cm / min.
[0117]
Under the same conditions, the film was stretched 1.4 times in two directions in the MD and TD directions simultaneously. Further, this film was heat-treated at 450 ° C. for 1 minute and gradually cooled.
[0118]
Table 1 shows the evaluation results of the characteristic values of the obtained polyimide film.
[0119]
Three of these polyimide films were sandwiched between carbon fiber woven fabrics and placed in a heating furnace. After changing to a nitrogen atmosphere, the temperature was raised from room temperature to 800 ° C. at 5 ° C./min. Cooling was performed at 5 ° C./min to room temperature.
[0120]
When the film was taken out from the furnace, a metallic glossy carbon film was obtained. The carbon film was slightly fused, but could be easily peeled off, and three planar films were obtained. This carbon film was not broken even when bent. Table 1 shows the evaluation results of the characteristic values of the obtained carbon film.
[0121]
[Example 2]
In a 500 cc glass flask, 150 ml of DMAc was placed, 34′ODA was fed into DMAc to dissolve, and then PMDA was fed, followed by stirring at room temperature for about 1 hour. 44′ODA was supplied to this polyamic acid solution, and after complete dissolution, the solution was stirred at room temperature for about 1 hour. Subsequently, 0.5 mol% of acetic anhydride is added to the diamine component, and the mixture is further stirred for about 1 hour. The tetracarboxylic dianhydride component and the diamine component are components having the composition shown in Table 1 at about 100 mol% stoichiometry. A solution having a polyamic acid concentration of 20% by weight was prepared.
[0122]
This solution having a polyamic acid concentration of 20% by weight was treated in the same manner as in Example 1 to obtain a polyimide film having a thickness of about 25 μm.
[0123]
The obtained film was stretched at 400 ° C. by a biaxial stretching method using a biaxial stretching method at 400 ° C. using a research polymer film biaxial stretching apparatus (BIX-703, manufactured by Iwamoto Seisakusho Co., Ltd.) to determine the film breaking area. . The fracture surface magnification was about 1.7 times. Preheating time 60 seconds, one-side stretching speed 10 cm / min.
[0124]
Under the same conditions, the film was stretched 1.2 times in two directions in the MD and TD directions simultaneously. Further, this film was heat-treated at 450 ° C. for 1 minute and gradually cooled.
[0125]
The evaluation results of the characteristic values of the obtained polyimide film are also shown in Table 1.
[0126]
Carbonization treatment was performed in the same manner as in Example 1.
[0127]
The evaluation results of the characteristic values of the obtained carbon film are also shown in Table 1.
[Comparative Example 1]
In a 500 cc glass flask, 150 ml of DMAc is added, 34′ODA is fed into DMAc and dissolved, PMDA is dissolved, and stirred at room temperature for about 1 hour. The tetracarboxylic dianhydride component and diamine component are about A solution having a polyamic acid concentration of 20% by weight comprising the components shown in Table 1 at 100 mol% stoichiometry was prepared.
[0128]
This polyamic acid solution was treated in the same manner as in Example 1 to obtain a polyimide film having a thickness of about 25 μm.
[0129]
The evaluation results of the characteristic values of the obtained polyimide film are shown in Table 2. Tg of the obtained film was observed around 320 ° C.
[0130]
Three sheets of the obtained polyimide film were sandwiched between carbon fiber woven fabrics and placed in a heating furnace. After changing to a nitrogen atmosphere, the temperature was raised from room temperature to 800 ° C. at 5 ° C./min, and subsequently to 1200 ° C. at 10 ° C./min and held for 1 hour. Cooling was performed at 5 ° C./min to room temperature.
[0131]
When the film was taken out from the furnace, a metallic glossy carbon film was obtained, but it was fused and could not be easily removed.
[0132]
Therefore, one polyimide film was sandwiched between carbon fiber woven fabrics and placed in a heating furnace. After changing to a nitrogen atmosphere, the temperature was raised from room temperature to 800 ° C. at 5 ° C./min, and subsequently to 1200 ° C. at 10 ° C./min and held for 1 hour. Cooling was performed at 5 ° C./min to room temperature. When the film was taken out from the furnace, a slightly dull metallic luster carbon film was obtained, and a slightly wavy film was obtained.
[0133]
The characteristic value evaluation results of the obtained carbon film are also shown in Table 2.
[0134]
[Comparative Example 2]
In a 500 cc glass flask, 150 ml of DMAc was placed, 34′ODA was fed into DMAc to dissolve, and then PMDA was fed, followed by stirring at room temperature for about 1 hour. 44′ODA was supplied to this polyamic acid solution, and after complete dissolution, the solution was stirred at room temperature for about 1 hour. Subsequently, 1 mol% of acetic anhydride is added to the diamine component, and the mixture is further stirred for about 1 hour, and the tetracarboxylic dianhydride component and the diamine component are composed of components having the composition shown in Table 1 at about 100 mol% stoichiometry. A solution having a polyamic acid concentration of 20% by weight was prepared.
[0135]
This solution having a polyamic acid concentration of 20% by weight was treated in the same manner as in Example 1 to obtain a polyimide film having a thickness of about 25 μm. Tg of the obtained film was observed around about 340 ° C.
[0136]
Three sheets of the obtained polyimide film were sandwiched between carbon fiber woven fabrics and placed in a heating furnace. After changing to a nitrogen atmosphere, the temperature was raised from room temperature to 800 ° C. at 5 ° C./min. Cooling was performed at 5 ° C./min to room temperature.
When the film was taken out from the furnace, a metallic glossy carbon film was obtained, but it was fused and could not be easily removed.
[0137]
Therefore, one polyimide film was sandwiched between carbon fiber woven fabrics and placed in a heating furnace. After changing to a nitrogen atmosphere, the temperature was raised from room temperature to 800 ° C. at 5 ° C./min. Cooling was performed at 5 ° C./min to room temperature. When the film was taken out from the furnace, a slightly dull metallic luster carbon film was obtained, and a slightly wavy film was obtained.
[0138]
The characteristic value evaluation results of the obtained carbon film are also shown in Table 2.
[0139]
[Comparative Example 3, Examples 3 and 4] Mixed polyimide
In a container that is constantly purged with dry nitrogen, 190.6 kg of DMAc is placed, 34′ODA (29.8 mol%) is fed into DMAc, dissolved, and then PMDA (30 mol%) is fed at room temperature. , Stirred for about 1 hour. Subsequently, 0.5 mol% of acetic anhydride was added to the diamine component, and the mixture was further stirred for about 1 hour, and 44′ODA (70 mol%) was supplied to this polyamic acid solution and completely dissolved. 70 mol%) and stirred at room temperature for about 1 hour. The polycarboxylic acid concentration of the tetracarboxylic dianhydride component and the diamine component is about 100 mol% stoichiometric and consists of the components shown in Table 1 at a concentration of 23% by weight. A solution of was prepared. This solution had a viscosity of 4000 poise at 20 ° C. The polyamic acid solution was mixed while cooling 2.5 mol of acetic anhydride with respect to the polyamic acid unit and 2.0 mol of pyridine with respect to the polyamic acid unit to obtain an organic solvent solution of the polyamic acid. This polyamic acid organic solvent solution was quantitatively supplied to a metal with slits and cast on a metal drum at 90 ° C. to obtain a self-supporting gel film. The obtained gel film had a solid content of 18% by weight.
(Comparative Example 3)
A part of this gel film is fixed to a metal fixing frame having a large number of pins, heated for 30 minutes while being heated from 250 ° C. to 330 ° C., further heat-treated at 450 ° C. for 1 minute, and then gradually cooled. A polyimide film having a thickness of about 25 μm was obtained (polyimide film for Comparative Example 3). The evaluation results of the characteristic values of the obtained polyimide film are shown in Table 2.
[0140]
Carbonization treatment was performed in the same manner as in Example 1.
[0141]
Table 2 shows the evaluation results of the characteristic values of the obtained carbon film.
(Example 3)
The obtained film was stretched at 400 ° C. by a biaxial stretching method using a biaxial stretching method at 400 ° C. using a research polymer film biaxial stretching apparatus (BIX-703, manufactured by Iwamoto Seisakusho Co., Ltd.) to determine the film breaking area. . The fracture surface magnification was about 1.7 times. Preheating time 60 seconds, one-side stretching speed 10 cm / min.
[0142]
Under the same conditions, the film was stretched 1.2 times in two directions in the MD and TD directions simultaneously. Furthermore, this film was heat-treated at 450 ° C. for 1 minute and then slowly cooled (polyimide film for Example 3).
[0143]
The evaluation results of the characteristic values of the obtained polyimide film are also shown in Table 1. Carbonization treatment was performed in the same manner as in Example 1.
[0144]
Table 1 shows the evaluation results of the characteristic values of the obtained carbon film.
(Example 4) This gel film was peeled off from a metal drum, stretched in the running direction (MD) at a temperature of 63 ° C with two sets of nip rolls composed of a metal roll and a silicone rubber roll, and then introduced into a tenter. The draw ratio in the running direction, that is, the speed ratio between the metal drum and each nip roll and tenter was adjusted to 1.12, that of the second set of nip rolls was 1.24, and that of the tenter was 1.40. Stretched 1.5 times in the width direction (TD) at a temperature of 200 ° C with a tenter, then stretched 1.1 times at 400 ° C, followed by heat treatment at 450 ° C for 1 minute, relaxing about 5% in the width direction in the slow cooling zone Then, the film was cooled for 30 seconds, and the film was edge-cut to obtain a biaxially stretched polyimide film having a width of 2 m and a thickness of 25 μm. The plane orientation coefficient of the obtained polyimide film was 0.16. The average value of the in-plane anisotropy index was 11. The other characteristic value evaluation results are shown in Table 1.
[0145]
Carbonization treatment was performed in the same manner as in Example 1.
[0146]
The evaluation results of the characteristic values of the obtained carbon film are also shown in Table 1.
[0147]
[Comparative Example 4]
In a 500 cc glass flask, 150 ml of DMAc is added, 44′ODA is fed into DMAc and dissolved, PMDA is dissolved, and stirred at room temperature for about 1 hour. A solution having a polyamic acid concentration of 20% by weight comprising the components shown in Table 1 at 100 mol% stoichiometry was prepared.
[0148]
This polyamic acid solution was treated in the same manner as in Example 1 to obtain a polyimide film having a thickness of about 25 μm.
[0149]
The evaluation results of the characteristic values of the obtained polyimide film are shown in Table 2.
[0150]
Carbonization treatment was performed in the same manner as in Example 1.
[0151]
The characteristic value evaluation results of the obtained carbon film are also shown in Table 2.
[Example 5]
In a 500 cc glass flask, 150 ml of DMAc was placed, 34′ODA was fed into DMAc to dissolve, and then PMDA was fed, followed by stirring at room temperature for about 1 hour. 44′ODA was supplied to this polyamic acid solution, and after complete dissolution, the solution was stirred at room temperature for about 1 hour. Subsequently, 0.5 mol% of acetic anhydride is added to the diamine component, and the mixture is further stirred for about 1 hour. The tetracarboxylic dianhydride component and the diamine component are components having the composition shown in Table 1 at about 100 mol% stoichiometry. A solution having a polyamic acid concentration of 20% by weight was prepared.
[0152]
The obtained film was stretched at 400 ° C. by a biaxial stretching method using a biaxial stretching method at 400 ° C. using a research polymer film biaxial stretching apparatus (BIX-703, manufactured by Iwamoto Seisakusho Co., Ltd.) to determine the film breaking area. . The fracture surface magnification was about 1.3 times. Preheating time 60 seconds, one-side stretching speed 10 cm / min.
[0153]
Under the same conditions, the film was stretched 1.1 times in two directions simultaneously in the MD and TD directions. Further, this film was heat-treated at 450 ° C. with 5% relaxation on both axes for 1 minute and gradually cooled.
[0154]
The evaluation results of the characteristic values of the obtained polyimide film are also shown in Table 1. Carbonization treatment was performed in the same manner as in Example 1. The evaluation results of the characteristic values of the obtained carbon film are also shown in Table 1.
[0155]
As apparent from the results described in Tables 1 and 2, produced from the random polyimide film and block polyimide film of the present invention obtained by the chemical conversion method comprising PMDA, 34′ODA and 44′ODA, or a mixed polymer. Carbon film manufactured using the prepared polyimide film as a precursor satisfies high thermal conductivity, high elastic modulus and flexibility at the same time, compared with conventional carbon film. It has a suitable performance as a sheet.
[0156]
[Table 1]

[0157]
[Table 2]

[0158]
【The invention's effect】
As described above, the carbon film of the present invention has flexibility even when compared with the carbon polyimide film obtained from pyromellitic anhydride and 4,4′-oxydianiline, and has a high elastic modulus and It has excellent flatness and film forming properties.
[0159]
Therefore, the carbon film of the present invention is used, and simultaneously satisfies high thermal conductivity, high elastic modulus, and flexibility, and has suitable performance as a heat radiating diffusion sheet for portable computers.

Claims (5)

(1) Pyromellitic dianhydride, and 5 to 80 mol% of 3,4′-oxydianiline and 20 to 95 mol% of 4,4′-oxydianiline based on diamine A film is formed from a polyamic acid solution synthesized from a diamine comprising, and then stretched at an area magnification of 1.1 to 4 times at a temperature of 500 ° C. or lower to obtain a stretched polyimide film having a Young's modulus of 4 [GPa] or more. Process,
(2) The polyimide film is carbonized in an inert gas or vacuum at a temperature of 500 ° C. or more to form a carbon film having a specific gravity of 2.0 or less and a thermal conductivity of 600 [Wm ⁻¹ K ⁻¹ ] or more. Process,
The manufacturing method of the carbon film characterized by including. In the step (1), a step of producing a stretched polyimide film having a block component or a mixed polymer component that is divided and stretched at least twice at different temperatures by sequentially performing the following steps (A) to (E). The method for producing a carbon film according to claim 1, comprising:
(A) pyromellitic dianhydride, 3,4'-oxydianiline and 4,4'-oxydianiline are mixed with 3,4'-oxydianiline and pyromellitic dianhydride in an inert solvent. A step of reacting at least 1 to 99% by weight of pyromellitic dianhydride or diamine so as to form a polyamic acid having a block component or a mixed polymer component with the product,
(B) a step of additionally using the remaining raw materials for the polyamic acid polymer from the step (A) and finally reacting using the total amount of the total amount used;
(C) The process of mixing the conversion agent which can convert a polyamic acid into a polyimide in the polyamic acid solution from the said process (B),
(D) Cast or extrude the mixture from the step (C) on a smooth surface to form a polyamic acid-polyimide gel film, and (E) the gel film from the step (D) with a rotating roll. Stretching 1.1 to 2 times in the running direction while regulating the running speed, the end of the stretched gel film is gripped with a tenter clip, and the gel film is stretched in the width direction to a draw ratio of 0.8 in the running direction. The process of extending | stretching by the magnification of -1.3 times.
(F) The process of converting a polyamic acid into a polyimide by heating at the temperature of 500 degrees C or less. 3,4′-oxydianiline is 20 mol% or more and 60 mol% or less based on diamine, and 4,4′-oxydianiline is 40 mol% or more and less than 80 mol%. The manufacturing method of the carbon film of Claim 1 or 2. In the carbonization step of (2), the polyimide film is previously infusibilized at a temperature of 500 to 800 ° C. in an inert gas or vacuum, and then at a temperature of 800 to 3500 ° C. in an inert gas or vacuum. 4. The method for producing a carbon film according to claim 1, wherein the carbon film is carbonized by heating. A carbon film produced by the method according to claim 1, having a tensile elastic modulus of 35 [GPa] and a thermal conductivity of 800 [Wm ⁻¹ K ⁻¹ ] or more.