JP4033716B2 - Aromatic polyimide foam and method for producing the same - Google Patents

Description

[上記式においてＲ_１およびＲ_２は芳香族基を表す。]
【００１２】
で表される繰り返し単位からなる芳香族ポリイミド構造で構成されるのが好ましく、かつ芳香族ポリイミド発泡体は独立気泡を有する。
【００１３】
また本発明の非熱可塑性芳香族ポリイミドはその一部に、その芳香族ポリイミド構造の異性体であるイソイミド構造を有していてもよく、該イソイミド構造を含有する事により独立気泡を有する芳香族ポリイミド発泡体を好ましく製造する事ができる。
【００１４】
また本発明の芳香族ポリイミド発泡体を構成する非熱可塑性芳香族ポリイミドとは高いガラス転移温度を有し、融点以上では分解をともなう線状芳香族ポリイミドの事を指す。中でもガラス転移温度（Ｔｇ）が２５０℃以上であることが好ましく、３００℃以上であることがより好ましい。
【００１５】
上記式（３）および該イソイミド構造において、Ｒ₁は芳香族テトラカルボン酸にかかわる芳香族残基であり、Ｒ₂は芳香族ジアミン成分にかかわる芳香族残基である。さらに詳細にはＲ₁はビフェニル残基、ベンゾフェノン残基、ジフェニルメタン残基、ジフェニルスルホン酸基、ジフェニルエーテル残基、ジフェニルチオエーテル残基、芳香環などが好ましく挙げられる。またＲ₂はジフェニルエーテル残基、ジフェニルチオエーテル残基、ベンゾフェノン残基、ジフェニルメタン残基、ジフェニルプロパン残基、ジフェニルスルホキシド残基、ジフェニルスルホン酸基、ビフェニル残基、ピリジン残基、芳香環等を好ましく挙げることができる。なおイソイミド構造についても上述のＲ₁およびＲ₂と同様の芳香族残基を好ましく用いることができる。
【００１６】
本発明の非熱可塑性芳香族ポリイミドを製造するには芳香族テトラカルボン酸および／またはその誘導体、並びに芳香族ジアミンおよび／またはその誘導体から製造することができる。本発明の非熱可塑性芳香族ポリイミドを製造する芳香族テトラカルボン酸として具体的には例えば３，３’，４，４’−ビフェニルテトラカルボン酸、２，３，３’，４’−ビフェニルテトラカルボン酸、３，３’，４，４’−ベンゾフェノンテトラカルボン酸、２，３，３’，４’−ベンゾフェノンテトラカルボン酸、２，２−ビス（３，４−ジカルボキシフェニル）プロパン、ビス（３，４−ジカルボキシフェニル）メタン、ビス（３，４−ジカルボキシフェニル）スルホン、ビス（３，４−ジカルボキシフェニル）エーテル、ビス（３，４−ジカルボキシフェニル）チオエーテル、ピロメリット酸、あるいはそれらの水和物などを挙げることができる。これらのうちビフェニルテトラカルボン酸、ピロメリット酸等が好ましく使用しうる。またこれらは単独で使用してもよく、２種以上混合して使用してもよい。また必要に応じてこれら芳香族テトラカルボン酸の誘導体、例えば酸無水物（その水和物を含む）、酸ハロゲン化物、脂肪族エステル、芳香族エステル等を用いても良い。
【００１７】
また本発明の非熱可塑性芳香族ポリイミドを製造する芳香族ジアミンとしては、４，４’−ジアミノジフェニルエーテル、３，３’−ジメチル−４，４’−ジアミノジフェニルエーテル、３，３’−ジメトキシ−４，４’−ジアミノジフェニルエーテル、３，３’−ジアミノジフェニルエーテル、３，４’−ジアミノジフェニルエーテルなどのジフェニルエーテル系ジアミン；４，４’−ジアミノジフェニルチオエーテル、３，３’−ジメチル−４，４’−ジアミノジフェニルチオエーテル、３，３’−ジメトキシ−４，４’−ジアミノチオエーテル、３，３’−ジアミノジフェニルチオエーテルなどのジフェニルチオエーテル系ジアミン；４，４’−アミノベンゾフェノン、３，３’−ジメチル−４，４’−ジアミノベンゾフェノン、３，３’−ジアミノベンゾフェノンなどのベンゾフェノン系ジアミン；３，３’−ジアミノジフェニルメタン、４，４’−ジアミノジフェニルメタン、３，３’−ジメトキシ−４，４’−ジアミノジフェニルメタン、３，３’−ジメチル−４，４’−ジアミノジフェニルメタンなどのジフェニルメタン系ジアミン；２，２−ビス（４−アミノフェノール）プロパン、２，２−ビス（３−アミノフェニル）プロパンなどのビスフェニルプロパン系ジアミン；４，４’−ジアミノジフェニルスルホキシド、３，３’−ジアミノジフェニルスルホキシドなどのジフェニルスルホキシド系ジアミン；４，４’−ジアミノジフェニルスルホン、３，３’−ジアミノジフェニルスルホンなどのジフェニルスルホン系アミン；ベンチジン、３，３’−ジメチルベンチジン、３，３’−ジメトキシベンチジン、３，３’−ジアミノビフェニルなどのビフェニル系ジアミン；２，６−ジアミノピリジン、３，６−ジアミノピリジン、２，５−ジアミノピリジン、３，４−ジアミノピリジンなどのピリジン系ジアミン；オルトジアミノベンゼン、メタジアミノベンゼン、パラジアミノベンゼン等のベンゼン系ジアミンを挙げる事ができる。これらのうちベンゼン系ジアミン、ジフェニルエーテル系ジアミンなどが好ましく使用しうる。またこれらは単独で使用してもよく、２種以上混合して使用してもよい。また必要に応じてこれら芳香族ジアミンの誘導体、例えばアセチル化物等を用いても良い。
【００１８】
これらの芳香族テトラカルボン酸および／またはその誘導体、並びに芳香族ジアミンおよび／またはその誘導体から通常行われている溶液重合法、界面重合法、溶融重合法等の公知の方法で本発明に好適な非熱可塑性芳香族ポリイミドを製造することができる。
【００１９】
更に、該非熱可塑性芳香族ポリイミドは、物性を損なわない程度（例えば３０モル％以下）で、共重合成分を有していてもよい。この場合例えば芳香族テトラカルボン酸の代わりにトリカルボン酸もしくはジカルボン酸等を使用すればポリマー中にアミド結合が導入され、芳香族ジアミンの代わりにジヒドロキシ化合物等を使用すればエステル結合を導入する事ができる。
【００２０】
また、該非熱可塑性芳香族ポリイミドは、物性を損なわない程度（例えば全体の３０重量％以下の割合）で、他の高分子量体をブレンドされていてもよい。ブレンドできる該他の高分子量体としては、例えば芳香族ポリエステル、芳香族ポリアミド、脂肪族ポリアミド、脂肪族ポリエステル等が挙げられる。これらの共重合成分およびブレンド成分は非熱可塑性に限らず、熱可塑性であっても良い。
【００２１】
本発明の芳香族ポリイミド発泡体は独立気泡を有するが、該独立気泡の大きさは０．０１〜１００マイクロメートルである。また本発明における独立気泡の形状は通常はほぼ球形であり、断面形状は円形になる。その場合の独立気泡大きさとは円の直径を表す。この値が１００マイクロメートルより大きいと発泡体の力学強度が低下し好ましくなく、０．０１マイクロメートル未満の大きさでは有効な発泡体とは言えない。実際上は、０．５〜５０マイクロメートルの大きさの独立気泡が好ましい。しかし時には独立気泡の形状が楕円体となり、断面が楕円形になることもありうる。この場合の独立気泡の大きさとは、該楕円形の長軸方向の長さと短軸方向の長さの平均をその楕円体形状の独立気泡の大きさと推定する。また断面が円形でも楕円形でもない時には円、または楕円に近似して独立気泡の大きさを算出する。
【００２２】
該独立気泡の断面における占有面積は３０〜９５％である。３０％より小さいと発泡体としての軽量性がなくなり、９５％より多いと発泡体の強度が低下するので好ましくない。実質的には４０〜９０％の範囲であることが好ましい。
【００２３】
また本発明の芳香族ポリイミド発泡体中の有機溶剤含有量は５重量％以下が好ましい。より好ましくは１重量％以下、特に好ましくは０．１重量％以下である。５重量％を越えると該芳香族ポリイミド発泡体の強度等が低下するので好ましくない。
【００２４】
また本発明の芳香族ポリイミド成形前駆体は、主に非熱可塑性芳香族ポリイミドからなり、圧力５〜５０ＭＰａかつ温度１００〜４００℃の条件下で有機溶剤および炭酸ガスの存在下膨潤状態にある。好ましくは炭酸ガスが超臨界状態である条件下である。ここで述べる「膨潤状態」とは、非熱可塑性芳香族ポリイミドに有機溶剤、および炭酸ガスが溶け込むか、もしくは非熱可塑性芳香族ポリイミドが有機溶剤、および炭酸ガスに部分溶解し、完全均一溶液状態にいたらないものの、初期形態が有機溶剤、炭酸ガスを吸収した分だけ膨らんだゲル状態になっていることを指す。本発明の芳香族ポリイミド成形前駆体を構成する非熱可塑性芳香族ポリイミドは、上述の芳香族ポリイミド発泡体を構成する非熱可塑性芳香族ポリイミドと同様に、好ましくは主に上記式（３）の繰り返し単位で表される構造および／または該イソイミド構造のものを用いることができる。またイソイミド構造を含むことは赤外赤外分光計を用いて９２０ｃｍ^-1のピークの有無にて評価することができる。なお該非熱可塑性芳香族ポリイミドはガラス転移温度（Ｔｇ）が２５０℃以上であることが好ましく、３００℃以上であることがより好ましい。
【００２５】
本発明の芳香族ポリイミド成形前駆体を得る為には、該非熱可塑性芳香族ポリイミドを圧力５〜５０ＭＰａかつ温度１００〜４００℃の条件下、有機溶剤の存在下で炭酸ガスに接触させる必要がある。該炭酸ガスは超臨界状態であることが好ましい。
【００２６】
ここで述べる超臨界状態にある炭酸ガスとは、炭酸ガスを物理化学的に、圧力７.４８ＭＰａ以上、温度３１．１℃以上の条件にすることにより達成することができる状態を示し、液体でも気体でもない様相を示す超臨界状態をなす炭酸ガスを意味する。圧力が５ＭＰａ未満では非熱可塑性芳香族ポリイミドが可塑性を有することができないため芳香族ポリイミド発泡体を製造することができず、また５０ＭＰａを超える圧力で接触させることは超高耐圧の圧力容器が必要であり、実質的に困難である。また温度が１００℃未満では、圧力が５ＭＰａ未満の時と同様に非熱可塑性芳香族ポリイミドが可塑性を有することができない。また４００℃を超える温度では有機溶剤もしくは非熱可塑性芳香族ポリイミド、特に有機溶剤の分解反応が起こりやすく、目的とする芳香族ポリイミド発泡体を得ることができない。
【００２７】
上記のような条件下に、有機溶剤の存在下で非熱可塑性芳香族ポリイミドを炭酸ガスに接触せしめることにより、非熱可塑性芳香族ポリイミドが可塑性を有するようになる。
【００２８】
また接触せしめる炭酸ガスを非熱可塑性芳香族ポリイミドの重量に対して１〜１０⁶倍量仕込むのが好ましく、より好ましくは１０〜１０⁵倍量である。炭酸ガスの仕込み量が非熱可塑性芳香族ポリイミドの重量に対して１倍量未満であると芳香族ポリイミドが可塑性を有することができず芳香族ポリイミド発泡体が得られない可能性があり、１０⁶倍量を超えると非熱可塑性芳香族ポリイミドの可塑性が顕著となり、良好な芳香族ポリイミド発泡体を得ることができない可能性がある。
【００２９】
またこの際に有機溶剤は非熱可塑性芳香族ポリイミドとの合計重量に対して０．０５〜１００重量％仕込むことも好ましい。０．０５重量％未満であると芳香族ポリイミド発泡体が得られず、１００重量％を超えると非熱可塑性芳香族ポリイミドの可塑化が顕著となり、良好な芳香族ポリイミド発泡体を得ることができない。好ましくは０．１〜５０重量％、より好ましくは０．５〜２０重量％である。
【００３０】
上記のような圧力、温度、仕込み条件下で、有機溶剤の存在下で非熱可塑性芳香族ポリイミドを炭酸ガスに接触せしめることにより、膨潤状態にある芳香族ポリイミド成形前駆体を製造することができる。この状態下で芳香族ポリイミド成形前駆体は、好ましくは炭酸ガスを芳香族ポリイミド成形前駆体の重量に対して０.０１〜５重量％を含有することが好ましい。炭酸ガスの含有量が０．０１重量％未満であると芳香族ポリイミド発泡体が得られない可能性があり、５重量％を超えると非熱可塑性芳香族ポリイミドの可塑化が顕著となり、良好な芳香族ポリイミド発泡体を得ることができない可能性がある。好ましくは０．１〜５重量％、より好ましくは０．５〜５重量％である。
【００３１】
また、この状態において有機溶剤は芳香族ポリイミド成形前駆体の重量に対して０．０１〜２０重量％を含有することも好ましい。この範囲外の場合は良好な芳香族ポリイミド発泡体を得ることができなくなる可能性がある。好ましくは０．１〜１５重量％、より好ましくは０．５〜１０重量％である。
【００３２】
この有機溶剤を非熱可塑性芳香族ポリイミドに対して特定量用いることが、本発明の大きな特長である。学術的には、「エントレーナ」と称される役割を担う。従来は圧力５ＭＰａ以上７．４８ＭＰａ未満の超臨界状態でない炭酸ガスに対してはもちろんのこと、超臨界状態の炭酸ガスに対しても可塑性を示さなかった非熱可塑性芳香族ポリイミドに対して、有機溶剤を添加することにより、驚くべきことに非熱可塑性芳香族ポリイミドが５ＭＰａ以上、かつ温度１００〜４００℃の条件下で炭酸ガスに可塑性を示し芳香族ポリイミド発泡体を製造することができることを見出したのである。
【００３３】
用いる該有機溶剤としては、用いる非熱可塑性芳香族ポリイミドの繰り返し単位の化学構造にもよるが、極性溶媒から選ばれる化合物であることが好ましく、さらに非プロトン性の極性溶媒から選ばれる化合物であることがより好ましい。具体的には、下記（１）
［Ｎ−メチルピロリドン，ジメチルアセトアミド，ジメチルホルムアミド，ジメチルスルホキシド，スルホラン，テトラヒドロフラン，エタノール，メタノール，塩化メチレン，クロロホルム，四塩化炭素、ジグライム、トリグライム、炭素数１〜１０の芳香族炭化水素化合物および下記式（２）
【００３４】
【化３】

【００３５】
｛上記式（２）中、ｍは０〜５の整数であり、Ｘはハロゲン原子、炭素数１〜１０のアルキルオキシ基、およびアルキル基、並びに炭素数６〜１０のアリール基、およびアリールオキシ基から選ばれる少なくとも１つの基である。ｍが２以上の時、複数のＸは同じ置換基であっても異なる置換基であってもよい。｝
で表される化合物］ （１）
よりなる群から少なくとも１種選択された有機溶剤が好ましく挙げられる。なかでもＮ−メチルピロリドン，ジメチルアセトアミド，ジメチルホルムアミド，ジメチルスルホキシド，スルホラン，テトラヒドロフランがより好ましく、Ｎ−メチルピロリドンが最も好ましい。
【００３６】
該有機溶剤はあらかじめ非熱可塑性ポリイミドに含有されていても良く、該有機溶剤を含んだ非熱可塑性芳香族ポリイミドを用いて芳香族ポリイミド発泡体を製造する事も本発明の範囲となろう。
【００３７】
上記（１）より選択された有機溶剤を使用し、非熱可塑性芳香族ポリイミドを前述の圧力および温度条件下で炭酸ガスに接触せしめ芳香族ポリイミド成形前駆体を好ましく製造することができる。この様にして得られる芳香族ポリイミド成形前駆体の形状は、チップ状、フィブリル状、フィルム状またはシート状等、適宜必要に応じて選択することができる。
【００３８】
さらに本発明の芳香族ポリイミド発泡体を製造するには、芳香族ポリイミド成形前駆体を製造した条件の状態から有機溶剤の抽出処理を行いながら炭酸ガスを除去する必要がある。その工程は芳香族ポリイミド成形前駆体が製造された状態から常圧、常温の状態に戻すことで達成することができる。常温常圧に戻す方法には特に限定はないが、通常は以下の手法を好ましく挙げることができる。すなわちまず温度を常温近くまで降下させ、それに伴い圧力も低下する。最後に常温下で圧力を開放し、常圧とする方法である。さらに好ましくはその温度降下速度を１００℃／ｈｒを超える速度で降下させることである。
【００３９】
最終的には上記の手法等にて常温常圧にした後、炭酸ガスを系内から放出する。その際には、エントレーナとして役割を担っていた有機溶剤も炭酸ガスと同時に若しくは炭酸ガス排出の後で系外へ排出され目的となる芳香族ポリイミド発泡体を得ることができる。このようにして得られた芳香族ポリイミド発泡体中の有機溶剤含有量は５重量％以下が好ましい。より好ましくは１重量％以下、特に好ましくは０．１重量％以下である。５重量％をこえると上述したように該芳香族ポリイミド発泡体の強度が低下するので好ましくない。
【００４０】
以下に、より具体的な処理装置やプロセスについて述べる。これら一連の方法としては、オートクレーブなどの密閉式の耐圧容器や、連続式の反応容器、エクストルーダーなどの押出機を用いることができる。
【００４１】
これらを一般的に公知に用いられる装置、例えば一軸スクリュー型押し出し機、二軸スクリュー型押し出し機、ピストン型押し出し機、モーノポンプ型押し出し機などに供し、特定の圧力で押し出されたとき、ある程度の流動性と成形性を有する効果が発揮されて、目的の芳香族ポリイミド発泡体を作ることが可能となる。さらにこの様な状態から目的に応じて、特定の断面形状をしたスリットを通して押出し処理をして、様々な形状の芳香族ポリイミド発泡体を得ることができる。
【００４２】
この様にして得られた、具体的な芳香族ポリイミド発泡体の形状としては、チップ状、フィブリル状、フィルム状、またはシート状を適宜必要に応じて選択することができる。また、所望の形状の芳香族ポリイミド発泡体を得るために本発明の芳香族ポリイミド成形前駆体を成形型に投入することもある。
【００４３】
これらの処理装置および成形型は、０〜４００℃の範囲で温度調節機能を有するものが好ましいが、成形型が該機能を有しなくても、あらかじめ成形型の出し入れができる該温度調整が可能なオーブンとを共用してもなんら差し支えない。また、成形型にガス抜き機構を備えてあると、高圧の炭酸ガスを開放する操作がスムーズに行われるため、好ましく用いることができる。
【００４４】
【発明の効果】
本発明によれば機械物性等の芳香族ポリイミドが従来から有する特性が良好で、従来より軽量、即ち見かけ密度の小さい芳香族ポリイミド発泡体を提供することができる。
【００４５】
【実施例】
以下に本発明の実施例を述べる。尚、以下に記載される内容により本発明が限定されるものではない。
【００４６】
≪独立気泡の大きさ・独立気泡の占有面積の測定方法≫
２０００倍で撮影されたＳＥＭ写真を画像処理し、面積比で算出した。画像処理システムは粒子解析ｖｅｒ．２．０（住友金属テクノロジー（株））を用いた。写真の濃淡から空孔は黒く、ポリマー部分は白く撮影されており、空孔部分にカーソルを合わせることでその独立気泡の半径（または長軸と短軸の長さ）と独立気泡の断面積を計算することできる。これを画面上の全ての独立気泡について実施し、独立気泡の平均面積、平均半径、空隙率、空孔占有面積が算出できる。
【００４７】
≪見かけ密度の測定方法≫
ＭｉＲＡＧＥ製ＥＬＥＣＴＲＯＮＩＣ ＤＥＮＳＩＭＥＴＥＲ ＥＤ−１２０Ｔを用いて測定した。
【００４８】
≪残留有機溶媒量の測定方法≫
常法に従い熱分解ガスクロマトグラフにて測定を行なった。
【００４９】
≪ガラス転移温度（Ｔｇ）の測定方法≫
ＴＡインストルメンツ社製示差走査熱量計を用い、窒素ガス気流下１０℃／分の速度で昇温して測定を実施した。
【００５０】
≪イソイミド構造の確認≫
フーリエ変換赤外分光計（Ｎｉｃｏｌｅｔ Ｍａｇｎａ ７５０）を用いてイソイミド構造に起因する９２０ｃｍ^-1のピークの有無により確認した。
【００５１】
[参考例１：芳香族ポリイミドの製造］
反応容器に脱水ＮＭＰ（Ｎ−メチル−２−ピロリドン）１リットルを入れ、パラジアミノベンゼン２０ｇを溶解したのち０℃へ冷却した。これに無水ピロメリット酸二水和物４０ｇを添加し１時間反応させ、さらに室温下２時間反応後アニリン０．０１ｇを添加し３０分反応させ粘ちょう溶液を得た。この溶液からガラス板上に厚み約１．５ｍｍのフィルムを作成し、ジシクロヘキシルカルボジイミド（ＤＣＣ）２８ｗｔ％含有ＮＭＰ溶液へ導入しゲル状フィルムを得た。これをＮＭＰ溶媒へ浸漬した後、２．３倍の倍率で同時二軸延伸し、枠固定した後２５０℃で乾燥し、芳香族ポリイミドフィルムを得た。
【００５２】
フィルムの厚みを測定すると測定点１０箇所で平均０．０５mmであった。また残留するＮＭＰは０．５重量％、またガラス転移温度は２７０℃であった。またフーリエ変換赤外分光計を用いて９２０ｃｍ^-1のピークの有無を調べ、イソイミド構造の存在を確認した。
【００５３】
［実施例１］
上記方法で得られた芳香族ポリイミドフィルム１００重量部とＮ−メチルピロリドン１．５重量部をＣＯ₂光散乱セル中に挿入し、炭酸ガス４４００００重量部を注入して１６ＭＰａまで加圧した。その後、ＣＯ₂光散乱セルの入ったオートクレーブを２５０℃に上げその様子をデジタル顕微鏡で観察した。この時点でフィルムが膨潤した状態でフィルム状の芳香族ポリイミド成形前駆体を形成されていることを確認した。その後２００℃／ｈｒの速度で温度を降下させ常温、常圧にしたのち得られたフィルム状の芳香族ポリイミド発泡体サンプルをＳＥＭで観察し、各物性の測定を行なった。表１に得られたフィルム状の芳香族ポリアミド発泡体の物性値を製造条件とともにまとめた。
【００５４】
［実施例２］
参考例１で得られた芳香族ポリイミドフィルム１００重量部をＣＯ_２光散乱セルに入れる際に、Ｎ−メチルピロリドンを１．５重量部入れるかわりにＮ−メチルピロリドンを５．０重量部入れた以外は、実施例１と同様な処理を行った。表１に得られたフィルム状の芳香族ポリイミド発泡体の物性値をまとめた。
【００５５】
［比較例１］
参考例１で得られた芳香族ポリイミドフィルムを更に熱風乾燥機中で乾燥熱処理し、熱分解ガスクロマトグラフで測定した残留ＮＭＰの量を０．１重量％以下にし実質的にＮＭＰが存在しないフィルムを得た。このフィルム１００重量部を、芳香族ポリイミドフィルム１００重量部の代わりに用いる以外は、実施例１と同様な処理を行った。
【００５６】
その結果芳香族ポリイミドフィルムは膨潤せず、芳香族ポリイミド成形前駆体の生成を確認することはできなかった。
【００５７】
得られたサンプルの物性測定の結果を表１に示した。
【００５８】
【表１】

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an aromatic polyimide foam having closed cells and a method for producing the same.
[0002]
[Prior art]
Aromatic polyimide is a high molecular weight material with excellent heat resistance and mechanical properties, but due to its high heat resistance, the moldability is remarkably limited. It is limited to liquid crystal molding, film by wet molding, and the like. Other molding methods include molding obtained by press-molding powdered aromatic polyimide at a high pressure equal to or higher than the glass transition temperature.
[0003]
However, with this method, only a high-density aromatic polyimide molded body can be obtained, and the lightness required for a conventional plastic molded body is insufficient.
[0004]
As a generally known method, there is a method of obtaining a foam having closed cells by heat-treating a thermoplastic resin under a specific condition in which the resin exhibits plasticity using a specific organic foaming agent. However, even if the above method is used, there is no organic foaming agent that can function at a temperature at which the aromatic polyimide exhibits fluidity, and it cannot be applied. There have been problems such as unfavorable effects on physical properties and the occurrence of undesired gas in the human body.
[0005]
In addition, a light-weight aromatic polyimide foam having a smaller apparent specific gravity is demanded in the market, and the present situation is that it is not possible to satisfy this requirement satisfactorily.
[0006]
On the other hand, in recent years, a technique for forming a plastic foam using supercritical carbon dioxide gas has attracted attention, and is introduced in US4473664, US5159586, WO92 / 17533. These methods are techniques in which carbon dioxide gas in a supercritical state is dissolved in a thermoplastic resin to improve fluidity and plasticity, and extrusion is performed under atmospheric pressure. By doing so, it is a technique in which minute cavities are formed in the molded product and a lightweight foam is obtained.
[0007]
However, at present, aromatic polyimide, particularly non-thermoplastic aromatic polyimide, has not realized an aromatic polyimide foam that can withstand practical use even if this method is used.
[0008]
[Problems to be solved by the invention]
It is an object of the present invention to provide a lightweight aromatic polyimide foam by introducing a foam structure while taking advantage of the characteristics of a conventionally known aromatic polyimide, and to provide a decomposed product or undesirable gas of the aromatic polyimide foam. An object of the present invention is to provide a production method that does not use an organic foaming agent that is accompanied by the generation of the above.
[0009]
[Means for Solving the Problems]
The present invention is as follows.
1. Aromatic polyimide foam mainly composed of non-thermoplastic aromatic polyimide, having closed cells, the size of the closed cells is 0.01 to 100 micrometers, and the occupied area of the closed cells in the cross section is 30 to 95%. body.
2. An aromatic polyimide molding precursor mainly composed of non-thermoplastic aromatic polyimide and in a swollen state in the presence of an organic solvent and carbon dioxide under conditions of a pressure of 5 to 50 MPa and a temperature of 100 to 400 ° C.
3. After a polymer mainly composed of non-thermoplastic aromatic polyimide is brought into contact with carbon dioxide in the presence of an organic solvent under the conditions of a pressure of 5 to 50 MPa and a temperature of 100 to 400 ° C. to produce an aromatic polyimide molding precursor, A method for producing an aromatic polyimide foam in which carbon dioxide gas is removed while performing an organic solvent extraction treatment.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The non-thermoplastic aromatic polyimide constituting the aromatic polyimide foam of the present invention is mainly represented by the following formula (3).
[0011]
[Chemical 2]

[In the above formula, R ₁ and R ₂ represent an aromatic group. ]
[0012]
It is preferable to be comprised by the aromatic polyimide structure which consists of a repeating unit represented by these, and an aromatic polyimide foam has a closed cell.
[0013]
In addition, the non-thermoplastic aromatic polyimide of the present invention may have an isoimide structure which is an isomer of the aromatic polyimide structure in a part thereof, and an aromatic having closed cells by containing the isoimide structure. A polyimide foam can be preferably manufactured.
[0014]
Further, the non-thermoplastic aromatic polyimide constituting the aromatic polyimide foam of the present invention refers to a linear aromatic polyimide having a high glass transition temperature and being decomposed at a melting point or higher. Among these, the glass transition temperature (Tg) is preferably 250 ° C. or higher, and more preferably 300 ° C. or higher.
[0015]
In the above formula (3) and the isoimide structure, R ₁ is an aromatic residue related to an aromatic tetracarboxylic acid, and R ₂ is an aromatic residue related to an aromatic diamine component. More specifically, R ₁ is preferably a biphenyl residue, a benzophenone residue, a diphenylmethane residue, a diphenylsulfonic acid group, a diphenyl ether residue, a diphenylthioether residue, an aromatic ring, or the like. R ₂ preferably includes diphenyl ether residue, diphenyl thioether residue, benzophenone residue, diphenylmethane residue, diphenylpropane residue, diphenyl sulfoxide residue, diphenyl sulfonic acid group, biphenyl residue, pyridine residue, aromatic ring and the like. be able to. For the isoimide structure, the same aromatic residues as those for R ₁ and R ₂ described above can be preferably used.
[0016]
The non-thermoplastic aromatic polyimide of the present invention can be produced from an aromatic tetracarboxylic acid and / or a derivative thereof, and an aromatic diamine and / or a derivative thereof. Specific examples of the aromatic tetracarboxylic acid for producing the non-thermoplastic aromatic polyimide of the present invention include 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 2,3,3 ′, 4′-biphenyltetra Carboxylic acid, 3,3 ′, 4,4′-benzophenone tetracarboxylic acid, 2,3,3 ′, 4′-benzophenone tetracarboxylic acid, 2,2-bis (3,4-dicarboxyphenyl) propane, bis (3,4-dicarboxyphenyl) methane, bis (3,4-dicarboxyphenyl) sulfone, bis (3,4-dicarboxyphenyl) ether, bis (3,4-dicarboxyphenyl) thioether, pyromellitic acid Or hydrates thereof. Of these, biphenyltetracarboxylic acid, pyromellitic acid and the like can be preferably used. Moreover, these may be used independently and may be used in mixture of 2 or more types. If necessary, derivatives of these aromatic tetracarboxylic acids such as acid anhydrides (including hydrates), acid halides, aliphatic esters, aromatic esters and the like may be used.
[0017]
The aromatic diamine for producing the non-thermoplastic aromatic polyimide of the present invention includes 4,4′-diaminodiphenyl ether, 3,3′-dimethyl-4,4′-diaminodiphenyl ether, and 3,3′-dimethoxy-4. Diphenyl ether diamines such as 4,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether; 4,4′-diaminodiphenyl thioether, 3,3′-dimethyl-4,4′-diamino Diphenylthioether diamines such as diphenylthioether, 3,3′-dimethoxy-4,4′-diaminothioether, 3,3′-diaminodiphenylthioether; 4,4′-aminobenzophenone, 3,3′-dimethyl-4, 4'-diaminobenzophenone, 3,3'-diaminobenzof Benzophenone-based diamines such as non; 3,3′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane, 3,3′-dimethoxy-4,4′-diaminodiphenylmethane, 3,3′-dimethyl-4,4′- Diphenylmethane-based diamines such as diaminodiphenylmethane; bisphenylpropane-based diamines such as 2,2-bis (4-aminophenol) propane and 2,2-bis (3-aminophenyl) propane; 4,4′-diaminodiphenyl sulfoxide; Diphenyl sulfoxide-based diamines such as 3,3′-diaminodiphenyl sulfoxide; diphenyl sulfone-based amines such as 4,4′-diaminodiphenyl sulfone and 3,3′-diaminodiphenyl sulfone; benzidine, 3,3′-dimethyl benzidine, 3,3'-dimethoxybenzidine Biphenyl diamines such as 3,3′-diaminobiphenyl; Pyridine diamines such as 2,6-diaminopyridine, 3,6-diaminopyridine, 2,5-diaminopyridine, and 3,4-diaminopyridine; Orthodiaminobenzene And benzene-based diamines such as metadiaminobenzene and paradiaminobenzene. Of these, benzene-based diamine, diphenyl ether-based diamine and the like can be preferably used. Moreover, these may be used independently and may be used in mixture of 2 or more types. If necessary, derivatives of these aromatic diamines such as acetylated compounds may be used.
[0018]
These aromatic tetracarboxylic acids and / or derivatives thereof, and aromatic diamines and / or derivatives thereof are suitable for the present invention by known methods such as solution polymerization, interfacial polymerization, and melt polymerization that are usually performed. Non-thermoplastic aromatic polyimides can be produced.
[0019]
Further, the non-thermoplastic aromatic polyimide may have a copolymer component in such an extent that physical properties are not impaired (for example, 30 mol% or less). In this case, for example, if tricarboxylic acid or dicarboxylic acid is used instead of aromatic tetracarboxylic acid, an amide bond is introduced into the polymer, and if a dihydroxy compound is used instead of aromatic diamine, an ester bond may be introduced. it can.
[0020]
In addition, the non-thermoplastic aromatic polyimide may be blended with other high molecular weight substances so as not to impair physical properties (for example, a ratio of 30% by weight or less of the whole). Examples of other high molecular weight materials that can be blended include aromatic polyesters, aromatic polyamides, aliphatic polyamides, and aliphatic polyesters. These copolymer components and blend components are not limited to non-thermoplastic, and may be thermoplastic.
[0021]
The aromatic polyimide foam of the present invention has closed cells, and the size of the closed cells is 0.01 to 100 micrometers. In addition, the shape of the closed cell in the present invention is usually almost spherical, and the cross-sectional shape is circular. The closed cell size in this case represents the diameter of the circle. If this value is larger than 100 micrometers, the mechanical strength of the foam is lowered, which is not preferable, and if it is less than 0.01 micrometers, it cannot be said to be an effective foam. In practice, closed cells with a size of 0.5 to 50 micrometers are preferred. However, sometimes the shape of the closed cell becomes an ellipsoid and the cross section becomes an ellipse. The size of the closed cell in this case is the average of the length of the ellipse in the major axis direction and the length in the minor axis direction is estimated as the size of the ellipsoidal closed cell. When the cross section is neither circular nor elliptical, the size of the closed cell is calculated by approximating a circle or an ellipse.
[0022]
The occupied area in the cross section of the closed cell is 30 to 95%. If it is less than 30%, the lightweight property as a foam is lost, and if it exceeds 95%, the strength of the foam is lowered, which is not preferable. It is preferably substantially in the range of 40 to 90%.
[0023]
The organic solvent content in the aromatic polyimide foam of the present invention is preferably 5% by weight or less. More preferably, it is 1 weight% or less, Most preferably, it is 0.1 weight% or less. If it exceeds 5% by weight, the strength and the like of the aromatic polyimide foam deteriorate, which is not preferable.
[0024]
The aromatic polyimide molding precursor of the present invention is mainly composed of a non-thermoplastic aromatic polyimide and is in a swollen state in the presence of an organic solvent and carbon dioxide under conditions of a pressure of 5 to 50 MPa and a temperature of 100 to 400 ° C. Preferably, the carbon dioxide gas is in a supercritical state. The “swelled state” described here is a completely homogeneous solution state in which an organic solvent and carbon dioxide gas dissolve in non-thermoplastic aromatic polyimide, or non-thermoplastic aromatic polyimide partially dissolves in organic solvent and carbon dioxide gas. Although it is not necessary, it indicates that the initial form is in a gel state swollen by the absorption of the organic solvent and carbon dioxide. The non-thermoplastic aromatic polyimide constituting the aromatic polyimide molding precursor of the present invention is preferably mainly of the above formula (3), similarly to the non-thermoplastic aromatic polyimide constituting the above-mentioned aromatic polyimide foam. A structure represented by a repeating unit and / or an isoimide structure can be used. The inclusion of an isoimide structure can be evaluated by the presence or absence of a peak at 920 cm ⁻¹ using an infrared infrared spectrometer. The non-thermoplastic aromatic polyimide preferably has a glass transition temperature (Tg) of 250 ° C. or higher, and more preferably 300 ° C. or higher.
[0025]
In order to obtain the aromatic polyimide molding precursor of the present invention, it is necessary to contact the non-thermoplastic aromatic polyimide with carbon dioxide gas in the presence of an organic solvent under conditions of a pressure of 5 to 50 MPa and a temperature of 100 to 400 ° C. . The carbon dioxide gas is preferably in a supercritical state.
[0026]
The carbon dioxide gas in the supercritical state described here indicates a state that can be achieved by making the carbon dioxide gas physicochemically at a pressure of 7.48 MPa or more and a temperature of 31.1 ° C. or more. It means carbon dioxide gas in a supercritical state showing an aspect that is not a gas. If the pressure is less than 5 MPa, the non-thermoplastic aromatic polyimide cannot have plasticity, so an aromatic polyimide foam cannot be produced, and contact with pressure exceeding 50 MPa requires an ultra-high pressure container. And practically difficult. Further, when the temperature is less than 100 ° C., the non-thermoplastic aromatic polyimide cannot have plasticity as in the case where the pressure is less than 5 MPa. Moreover, when the temperature exceeds 400 ° C., the organic solvent or non-thermoplastic aromatic polyimide, particularly the organic solvent is likely to be decomposed, and the desired aromatic polyimide foam cannot be obtained.
[0027]
By bringing the non-thermoplastic aromatic polyimide into contact with carbon dioxide gas in the presence of an organic solvent under the above conditions, the non-thermoplastic aromatic polyimide comes to have plasticity.
[0028]
Further, the carbon dioxide gas to be brought into contact is preferably charged in an amount of 1 to 10 ⁶ times, more preferably 10 to 10 ⁵ times the weight of the non-thermoplastic aromatic polyimide. If the amount of carbon dioxide charged is less than 1 times the weight of the non-thermoplastic aromatic polyimide, the aromatic polyimide may not have plasticity and an aromatic polyimide foam may not be obtained. ^{When the} amount exceeds ⁶ times, the plasticity of the non-thermoplastic aromatic polyimide becomes remarkable, and a good aromatic polyimide foam may not be obtained.
[0029]
In this case, the organic solvent is also preferably added in an amount of 0.05 to 100% by weight based on the total weight of the non-thermoplastic aromatic polyimide. If it is less than 0.05% by weight, an aromatic polyimide foam cannot be obtained, and if it exceeds 100% by weight, plasticization of the non-thermoplastic aromatic polyimide becomes significant and a good aromatic polyimide foam cannot be obtained. . Preferably it is 0.1 to 50 weight%, More preferably, it is 0.5 to 20 weight%.
[0030]
By bringing non-thermoplastic aromatic polyimide into contact with carbon dioxide in the presence of an organic solvent under the above pressure, temperature, and charging conditions, an aromatic polyimide molding precursor in a swollen state can be produced. . Under this condition, the aromatic polyimide molding precursor preferably contains 0.01 to 5% by weight of carbon dioxide gas based on the weight of the aromatic polyimide molding precursor. If the carbon dioxide content is less than 0.01% by weight, an aromatic polyimide foam may not be obtained. If it exceeds 5% by weight, plasticization of the non-thermoplastic aromatic polyimide becomes remarkable and good. An aromatic polyimide foam may not be obtained. Preferably it is 0.1 to 5 weight%, More preferably, it is 0.5 to 5 weight%.
[0031]
In this state, the organic solvent preferably contains 0.01 to 20% by weight based on the weight of the aromatic polyimide molding precursor. If it is outside this range, there is a possibility that a good aromatic polyimide foam cannot be obtained. Preferably it is 0.1 to 15 weight%, More preferably, it is 0.5 to 10 weight%.
[0032]
The use of a specific amount of this organic solvent with respect to the non-thermoplastic aromatic polyimide is a great feature of the present invention. Academically, it plays a role called “Entrainer”. Conventionally, not only for non-supercritical carbon dioxide with a pressure of 5 MPa or more and less than 7.48 MPa, but also for non-thermoplastic aromatic polyimides that did not exhibit plasticity against supercritical carbon dioxide. Surprisingly, it has been found that by adding a solvent, a non-thermoplastic aromatic polyimide can produce an aromatic polyimide foam exhibiting plasticity to carbon dioxide gas under conditions of 5 MPa or more and a temperature of 100 to 400 ° C. It was.
[0033]
The organic solvent to be used is preferably a compound selected from polar solvents, more preferably a compound selected from aprotic polar solvents, although it depends on the chemical structure of the repeating unit of the non-thermoplastic aromatic polyimide used. It is more preferable. Specifically, the following (1)
[N-methylpyrrolidone, dimethylacetamide, dimethylformamide, dimethylsulfoxide, sulfolane, tetrahydrofuran, ethanol, methanol, methylene chloride, chloroform, carbon tetrachloride, diglyme, triglyme, C1-C10 aromatic hydrocarbon compound and the following formula (2)
[0034]
[Chemical 3]

[0035]
{In the above formula (2), m is an integer of 0 to 5, X is a halogen atom, an alkyloxy group having 1 to 10 carbon atoms, and an alkyl group, and an aryl group having 6 to 10 carbon atoms, and aryloxy] It is at least one group selected from the group. When m is 2 or more, the plurality of Xs may be the same or different substituents. }
Compound represented by (1)
Preferred is an organic solvent selected from at least one selected from the group consisting of: Of these, N-methylpyrrolidone, dimethylacetamide, dimethylformamide, dimethylsulfoxide, sulfolane, and tetrahydrofuran are more preferable, and N-methylpyrrolidone is most preferable.
[0036]
The organic solvent may be previously contained in the non-thermoplastic polyimide, and it would be within the scope of the present invention to produce an aromatic polyimide foam using a non-thermoplastic aromatic polyimide containing the organic solvent.
[0037]
Using the organic solvent selected from (1) above, the non-thermoplastic aromatic polyimide can be brought into contact with carbon dioxide under the aforementioned pressure and temperature conditions to preferably produce an aromatic polyimide molding precursor. The shape of the aromatic polyimide molding precursor thus obtained can be appropriately selected as needed, such as a chip shape, a fibril shape, a film shape or a sheet shape.
[0038]
Furthermore, in order to produce the aromatic polyimide foam of the present invention, it is necessary to remove the carbon dioxide gas while performing an organic solvent extraction treatment from the condition under which the aromatic polyimide molding precursor was produced. The process can be achieved by returning the state of the aromatic polyimide molding precursor from normal to normal temperature. There is no particular limitation on the method for returning to room temperature and normal pressure, but the following methods are usually preferred. That is, the temperature is first lowered to near normal temperature, and the pressure is also lowered accordingly. Finally, the pressure is released at room temperature to normal pressure. More preferably, the temperature drop rate is lowered at a rate exceeding 100 ° C./hr.
[0039]
Finally, after the temperature is set to normal temperature and normal pressure by the above-described method, carbon dioxide gas is released from the system. At that time, the organic solvent that has played a role as an entrainer is also discharged out of the system simultaneously with the carbon dioxide gas or after the carbon dioxide gas is discharged, and the desired aromatic polyimide foam can be obtained. The organic solvent content in the aromatic polyimide foam thus obtained is preferably 5% by weight or less. More preferably, it is 1 weight% or less, Most preferably, it is 0.1 weight% or less. If it exceeds 5% by weight, the strength of the aromatic polyimide foam decreases as described above, which is not preferable.
[0040]
Hereinafter, more specific processing apparatuses and processes will be described. As a series of these methods, a closed pressure vessel such as an autoclave, an extruder such as a continuous reaction vessel or an extruder can be used.
[0041]
When these are used in a generally known device, such as a single screw extruder, a twin screw extruder, a piston extruder, a monopump extruder, etc., a certain amount of fluid flows when extruded at a specific pressure. The effect which has a property and a moldability is exhibited, and it becomes possible to make the target aromatic polyimide foam. Furthermore, from such a state, an aromatic polyimide foam having various shapes can be obtained by extrusion through a slit having a specific cross-sectional shape according to the purpose.
[0042]
As a specific shape of the aromatic polyimide foam thus obtained, a chip shape, a fibril shape, a film shape, or a sheet shape can be appropriately selected as necessary. In addition, the aromatic polyimide molding precursor of the present invention may be put into a molding die in order to obtain an aromatic polyimide foam having a desired shape.
[0043]
These processing devices and molds preferably have a temperature adjustment function in the range of 0 to 400 ° C., but the temperature can be adjusted in advance so that the mold can be taken in and out even if the mold does not have this function. You can share it with other ovens. In addition, if the mold is provided with a gas venting mechanism, the operation of releasing the high-pressure carbon dioxide gas can be performed smoothly, so that it can be preferably used.
[0044]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the characteristic which an aromatic polyimide, such as a mechanical property conventionally has favorable, is lighter than before, ie, an aromatic polyimide foam with a small apparent density can be provided.
[0045]
【Example】
Examples of the present invention will be described below. In addition, this invention is not limited by the content described below.
[0046]
≪Measurement method of closed cell size and closed cell area≫
An SEM photograph taken at a magnification of 2000 was subjected to image processing, and the area ratio was calculated. The image processing system is based on particle analysis ver. 2.0 (Sumitomo Metal Technology Co., Ltd.) was used. From the light and shade of the photograph, the pores are black and the polymer part is photographed white. By placing the cursor on the pores, the radius of the closed cell (or the length of the major and minor axes) and the cross-sectional area of the closed cell are determined. Can be calculated. This is performed for all the closed cells on the screen, and the average area, average radius, porosity, and occupied area of the closed cells can be calculated.
[0047]
≪Measurement method of apparent density≫
It measured using ELECTRONIC DENSIMETER ED-120T made from MiRAGE.
[0048]
≪Measurement method of residual organic solvent amount≫
Measurement was carried out by a pyrolysis gas chromatograph according to a conventional method.
[0049]
≪Measurement method of glass transition temperature (Tg) ≫
Using a differential scanning calorimeter manufactured by TA Instruments, the temperature was increased at a rate of 10 ° C./min under a nitrogen gas stream, and measurement was performed.
[0050]
≪Confirmation of isoimide structure≫
It confirmed with the presence or absence of the peak of 920 cm < ^-1 > resulting from an isoimide structure using the Fourier-transform infrared spectrometer (Nicolet Magna 750).
[0051]
[Reference Example 1: Production of aromatic polyimide]
1 liter of dehydrated NMP (N-methyl-2-pyrrolidone) was placed in the reaction vessel, and 20 g of paradiaminobenzene was dissolved and cooled to 0 ° C. To this was added 40 g of pyromellitic anhydride dihydrate and allowed to react for 1 hour. After reacting for 2 hours at room temperature, 0.01 g of aniline was added and reacted for 30 minutes to obtain a viscous solution. From this solution, a film having a thickness of about 1.5 mm was formed on a glass plate and introduced into an NMP solution containing 28 wt% of dicyclohexylcarbodiimide (DCC) to obtain a gel film. This was immersed in an NMP solvent, biaxially stretched at a magnification of 2.3 times, fixed in a frame, and then dried at 250 ° C. to obtain an aromatic polyimide film.
[0052]
When the thickness of the film was measured, the average was 0.05 mm at 10 measurement points. The remaining NMP was 0.5% by weight, and the glass transition temperature was 270 ° C. Further, the presence of an isoimide structure was confirmed by examining the presence or absence of a peak at 920 cm ⁻¹ using a Fourier transform infrared spectrometer.
[0053]
[Example 1]
100 parts by weight of the aromatic polyimide film obtained by the above method and 1.5 parts by weight of N-methylpyrrolidone were inserted into a CO ₂ light scattering cell, 444,000 parts by weight of carbon dioxide gas was injected, and the pressure was increased to 16 MPa. Thereafter, the autoclave containing the CO ₂ light scattering cell was raised to 250 ° C., and the state was observed with a digital microscope. At this time, it was confirmed that a film-like aromatic polyimide molding precursor was formed with the film swollen. Thereafter, the film-like aromatic polyimide foam sample obtained after lowering the temperature at a rate of 200 ° C./hr to normal temperature and normal pressure was observed with an SEM, and each physical property was measured. Table 1 summarizes the physical properties of the film-like aromatic polyamide foam obtained together with the production conditions.
[0054]
[Example 2]
When 100 parts by weight of the aromatic polyimide film obtained in Reference Example 1 was placed in a CO ₂ light scattering cell, 5.0 parts by weight of N-methylpyrrolidone was added instead of 1.5 parts by weight of N-methylpyrrolidone. Except for this, the same processing as in Example 1 was performed. Table 1 summarizes the physical properties of the obtained film-like aromatic polyimide foam.
[0055]
[Comparative Example 1]
The aromatic polyimide film obtained in Reference Example 1 was further dried and heat-treated in a hot air dryer, and the amount of residual NMP measured by pyrolysis gas chromatograph was reduced to 0.1% by weight or less to produce a film substantially free of NMP. Obtained. The same treatment as in Example 1 was performed except that 100 parts by weight of this film was used instead of 100 parts by weight of the aromatic polyimide film.
[0056]
As a result, the aromatic polyimide film did not swell, and the production of an aromatic polyimide molding precursor could not be confirmed.
[0057]
The results of measuring the physical properties of the obtained samples are shown in Table 1.
[0058]
[Table 1]

Claims (10)

  An aromatic polyimide molding precursor mainly composed of non-thermoplastic aromatic polyimide and in a swollen state in the presence of an organic solvent and carbon dioxide under conditions of a pressure of 5 to 50 MPa and a temperature of 100 to 400 ° C.   The aromatic polyimide molding precursor according to claim 1, wherein the non-thermoplastic aromatic polyimide has a glass transition temperature (Tg) of 250 ° C or higher.   The aromatic polyimide molding precursor according to claim 1 or 2, wherein the carbon dioxide gas is in a supercritical state. A polymer composed mainly of non-thermoplastic aromatic polyimide is brought into contact with carbon dioxide in the presence of an organic solvent under conditions of a pressure of 5 to 50 MPa and a temperature of 100 to 400 ° C. to form an aromatic polyimide molding precursor in a swollen state. After manufacturing, the manufacturing method of the aromatic polyimide foam which removes a carbon dioxide gas, performing the extraction process of an organic solvent.   The manufacturing method according to claim 4, wherein the glass transition temperature (Tg) of the aromatic polyimide foam is 250 ° C or higher.   The method according to claim 4 or 5, wherein the content of the organic solvent in the non-thermoplastic aromatic polyimide foam is 5% by weight or less.   The manufacturing method according to any one of claims 4 to 6, wherein the carbon dioxide gas is in a supercritical state. The organic solvent is the following (1)
[N-methylpyrrolidone, dimethylacetamide, dimethylformamide, dimethylsulfoxide, sulfolane, tetrahydrofuran, ethanol, methanol, methylene chloride, chloroform, carbon tetrachloride, diglyme, triglyme, C1-C10 aromatic hydrocarbon compound and the following formula (2)

{In the above formula (2), m is an integer of 0 to 5, X is a halogen atom, an alkyloxy group having 1 to 10 carbon atoms, and an alkyl group, and an aryl group having 6 to 10 carbon atoms, and aryloxy] It is at least one group selected from the group. When m is 2 or more, the plurality of Xs may be the same or different substituents. } (1)
The production method according to claim 4, wherein the organic solvent is at least one selected from the group consisting of:   The manufacturing method according to any one of claims 4 to 8, wherein the aromatic polyimide molding precursor has a chip shape, a fibril shape, a film shape, or a sheet shape.   The manufacturing method according to any one of claims 4 to 9, wherein the aromatic polyimide foam has a chip shape, a fibril shape, a film shape, or a sheet shape.