JP2004123774A - Polyimide resin composition, polyimide film, and polyimide tube - Google Patents

Abstract

[PROBLEMS] To easily adjust various medium resistance values that are stable from low temperature and low humidity to high temperature and high humidity, and there is little change in resistance value between samples, location, addition amount change, voltage change, and environmental change, and surface properties and mechanical properties. To obtain a polyimide resin composition, a polyimide film, a polyimide tubular article, and a tubular article for an electrophotographic apparatus, which are excellent in blackness and have high blackness.
SOLUTION: Based on 100 parts by weight of a polyimide resin, 20 to 200 parts by weight of a semiconductive filler and 0.01 to 20 parts by weight of carbon black having a volatilization amount of 2.0% or more and a pH of 5.0 or less are contained. A polyimide resin composition, a polyimide film, or a polyimide tubular material having a volume resistance value in the range of 1 × 10 ⁶ to 1 × 10 ¹⁵ Ω · cm and a black density of 1.0 or more.
[Selection diagram] None

Description

（式中、Ｘは同一または異なって、ハロゲン、−ＣＨ_３、−ＯＣＨ_３、−Ｏ（ＣＨ_２）_ｎＣＨ_３、−（ＣＨ_２）_ｎＣＨ_３、−ＣＦ_３、−ＯＣＦ_３からなる群から選ばれる少なくとも一種の基を表す。また、Ａは同一または異なって、Ｏ、Ｓ、Ｃ＝Ｏ、（ＣＨ_２）_ｎ、ＳＯ_２、Ｎ＝Ｎからなる群から選ばれる少なくとも一種の基を表す。ｍは１以上の整数。ｎは１以上の整数。）に示す種々のモノマーを用いる事ができる。
【００３８】
またテトラカルボン酸二無水物としては、
【００３９】
【化２】

（式中、ｎは１以上の整数。）
に示す種々のモノマーを用いる事ができる。
【００４０】
これらの組み合わせにより様々な特徴を出す事が可能であり、用途や加工法などの状況に応じて選択することができる。
【００４１】
例えば、屈曲鎖を多く（好ましくは一分子中に２つ以上）含む、および／またはアミノ基をメタ位に有する芳香族ジアミンを用い、２環以上のテトラカルボン酸二無水物を用いる事で、熱可塑性のポリイミドとすることができ、加熱溶融成型が可能なポリイミド樹脂組成物を提供可能である。例えば、２、２´−ビス（４−アミノフェノキシフェニル）プロパンと、オキシジフタル酸二無水物の組み合わせや、ビス（２−（４−アミノフェノキシ）エトキシ）エタンと３，３´，４，４´−ベンゾフェノンテトラカルボン酸二無水物の組み合わせ等を例示することができる。
【００４２】
また、ポリイミドはイミド基の存在により通常高吸水率であるが、特定のモノマーとの組み合わせにより比較的低吸水率の樹脂組成物とすることもできる。例として、テトラカルボン酸二無水物として２以上のエステル結合で複数のベンゼン核が結合された構造を持つモノマーを使用するポリイミドが挙げられる。具体的には、
【００４３】
【化３】

（式中、ｎは１以上の整数。）
【００４４】
【化４】

【００４５】
【化５】

に示されるような酸二無水物が挙げられる。
【００４６】
この場合に用いられるジアミン化合物としては、イミド基含有率を下げるために比較的長鎖のモノマーを用いることが好ましい。例えば、１，４−ビス（４−アミノフェノキシ）ベンゼンやその結合位置異性体、２，２´−ビス（４−アミノフェノキシフェニル）プロパン等を挙げることができる。
【００４７】
ただし、酸二無水物についてもジアミンについても、長鎖でかつ屈曲鎖を多数有する構造は、同時に前述の熱可塑性発現の条件でもあり、十分な耐熱性を要求する場合には不適当である。特に耐熱性と低吸水率の両方が求められる場合は長鎖でありかつ直線的構造を全体的または部分的に有するモノマーが適当である。例えばテトラカルボン酸二無水物としては、
【００４８】
【化６】

で示す構造のモノマー（以下、ＴＭＨＱ）が例として挙げられる。このモノマーは、屈曲鎖を含むものの全体としては概ね直線的なコンフォメーションを取りうる構造であり、その結合数の多さのわりには比較的剛直なポリイミドを形成する。この原料を用いれば、線膨張係数１５ｐｐｍ以下、吸水率１．５％以下、吸湿膨張係数１０ｐｐｍ以下であり、加熱や吸湿による寸法変化が少ないポリイミド樹脂を得ることも可能である。またジアミンとしても例えばビフェニル構造やナフタレン構造をエーテル結合でつなぐような構造が、長鎖でありながら比較的剛直な構造として選択できる。例えば４，４´−ビスアミノフェノキシビフェニルなどがあげられる。
【００４９】
これら酸二無水物とジアミンの組み合わせにより、比較的低吸水率であり、かつ顕著な熱軟化性を有さないポリイミドを得ることができる。またこれらモノマーのみでなく汎用のピロメリット酸二無水物、ベンゾフェノンテトラカルボン酸二無水物、パラフェニレンジアミン、４，４´−ジアミノジフェニルエーテル等を適宜共重合する事により、所望の特性のポリイミドを幅広く設計可能である。
【００５０】
また、ポリイミドは、銅のような金属に比べて線膨張係数が大きい。しかし、モノマーの種類や組成比が同じでも、モノマーの繋がりの組み合わせを制御（シーケンスコントロール）することにより比較的小さな線膨張係数を有するポリイミド樹脂とすることができる。例えば、４，４´−ジアミノジフェニルエーテル、パラフェニレンジアミン、ピロメリット酸二無水物をランダム共重合する場合に比べて、４，４´−ジアミノジフェニルエーテルとピロメリット酸二無水物を予め反応させておき、その後パラフェニレンジアミンを添加する手順を取ると規則的なモノマー配列のポリアミド酸が得られ、これをイミド化する事により低線膨張係数のポリイミド樹脂を得ることができる。
【００５１】
本発明では、ポリイミド樹脂に無機フィラーを配合するため、ポリイミド樹脂単体で用いる場合に比較して、ポリイミド樹脂に対し、より高い靭性が求められる。ポリイミド樹脂自身の靭性が十分でないと、無機フィラーの配合により必然的に靭性が低下するため、実用に供する事ができなくなる場合がある。その点から、ピロメリット酸二無水物と４，４´−ジアミノジフェニルエーテルから調製されるポリイミド樹脂であることが最も好ましい。本構造は、十分な耐熱性と高い靭性を兼ね備え、なおかつ広い範囲の加工条件でその特性を維持できるバランスの取れた構造である。
【００５２】
本発明に用いられる上記ポリイミド樹脂に配合される半導電性フィラーの体積抵抗値は、低抵抗値から中抵抗値のいずれであっても良いが、カーボンブラック、黒鉛、金属片といった低抵抗導電材料よりも高い１×１０^３〜１×１０^１０Ω・ｃｍが好ましく、より好ましくは１×１０^３〜１×１０^８Ω・ｃｍ、特に好ましくは１×１０^３〜１×１０^７である。一般に低抵抗値を有する導電材料は、樹脂に添加した場合、少量添加でも中間抵抗を実現できる。しかし、樹脂と導電材料では抵抗値の差が大きいため、添加部数のわずかなずれや分散の偏りにより、抵抗変動、又は電圧依存性が大きくなり、更に絶縁破壊電圧も低くなる。
【００５３】
半導電性フィラーを用いて安定的に中抵抗値を制御でき、配合部数、分散状態、サンプル間で抵抗のばらつきを小さくできる理由については、概ね以下のように考えている。半導電性フィラーは単体で１×１０^３〜１×１０^１０Ω・ｃｍ程度の抵抗値を有しており、カーボンブラック、導電性金属、あるいは金属セラミックス（１×１０^−５〜１×１０^３Ω・ｃｍ）とは異なり、その体積抵抗値が狙いの中抵抗値（１×１０^６〜１×１０^１３Ω・ｃｍ）に近い。その結果、過剰に添加したとしても、抵抗が低抵抗値まで下がりすぎることがなく、中抵抗値付近で飽和し、このため安定的に中抵抗値に制御することができると思われる。また、半導電性フィラーの添加された系は、カーボンブラックに見られるようなパーコレーションによる急激な抵抗の低下は見られず、抵抗は添加量に対してなだらかに変化する。その結果、半導電性フィラーを添加した系では、例えば、中抵抗領域に抵抗値を制御する添加部数に対して、添加量が５重量部程度変化したとしても抵抗値変化を３倍以下にすることもできる。また脱泡や分散過程でフィラーに凝集や偏りが生じたとしても抵抗値の大幅な変化は見られない。このような理由から、半導電性フィラーを用いた場合は、樹脂組成物中の添加量、分散状態がサンプル間でばらついたとしても、組成物の抵抗値の変化が少ないと思われる。一方、カーボンブラックを添加した系では、中抵抗領域に制御するために、樹脂１００重量部に対して１０〜２０重量部程度を添加するが、このような少ない添加部数に対して、添加部数が５重量部程度変化すると、抵抗はたちまち１０〜１００倍以上変化する。その結果、配合部数、分散状態、又はロット間のわずかな違いが、抵抗値へ大幅に影響する。
【００５４】
また、半導電性フィラーを用いることによって絶縁性が改善される理由は、概ね次のように考えている。ポリイミドと導電材からなるフィルムに電圧を印加すると、電圧はポリイミドと導電材に分圧され、電圧は導電材よりも高抵抗であるポリイミドの部分にかかると考えられる。特に、カーボンブラックや金属系材料のような低抵抗材料を添加した場合と、半導電性フィラーのような中抵抗材料を添加した場合とを比べると、ポリイミドにかかる電圧は中抵抗材料を添加したときのほうが小さいと考えられる。その結果、ポリイミドにおける絶縁破壊が低減されるものと考える。
【００５５】
さらに、半導電性フィラーを用いることにより抵抗の電圧依存性、環境依存性が改善される理由については、概ね次のように考えている。一般に樹脂に高電圧（例えば、厚み１００μｍに対して１ｋＶ以上の電圧を印加）を印加した場合、樹脂は絶縁破壊に近づき、抵抗値の電圧依存性は急激に悪化する。つまり、破壊直前には大電流が流れる。このことから抵抗値の電圧依存性は、樹脂に高電圧がかかることで樹脂が破壊に近づくために生じる現象と考えられる。しかし、半導電性フィラーのような中抵抗材料を添加した系では、カーボンブラックのような低抵抗材料を添加した場合に比べて、樹脂部分に局所的に高電圧がかかることを防ぐことができ、抵抗値の電圧依存性を改善できると考える。また、半導電性フィラーの多くは、表面に部分的に水酸基や活性な酸素等を有しているため、表面処理を行わずともイミド化の際に樹脂と強い相互作用を生じ、強固な複合材料となる。そして、これら強固な複合材料は高温高湿時の抵抗値低下と絶縁性悪化を防ぐことにも役立っていると考えられる。
【００５６】
以上の理由に基づくと考えられるが、半導電性フィラーを用いることで、次のような電気特性を実現することができる。まず、これらを適切に配合することで、ポリイミド樹脂組成物は、安定して体積抵抗値が１×１０^６〜１×１０^１５Ω・ｃｍ、好ましくは１×１０^９〜１×１０^１３Ω・ｃｍ、表面抵抗値が１０^６〜１０^１３Ω／□、好ましくは１×１０^９〜１×１０^１３Ω／□の範囲の中間的抵抗値を実現することができる。また、低温低湿時の抵抗値Ｒｌと高温高湿時の体積抵抗値Ｒｈとの比（Ｒｌ／Ｒｈ）を０．０１〜１００、さらに好ましくは０．３〜３０の範囲内に制御でき、環境安定性の優れた材料を調製することができる。また、１００Ｖ印加時の体積抵抗値Ｒ_１００Ｖと１０００Ｖ印加時の体積抵抗値Ｒ_{１０００Ｖ}との比（Ｒ_１００Ｖ／Ｒ_{１０００Ｖ}）を０．０１〜１００、さらに好ましくは０．３〜３０の範囲内に制御でき、電圧依存性の少ない材料を調製することができる。また前記抵抗値を実現する添加部数範囲内において、例えば、半導電性フィラーの添加部数が５重量部程度変化しても体積抵抗値の変動を３倍以下にすることも可能であり、添加部数依存性の少ない材料を調製することができる。また、例えば、サンプル間の抵抗値のバラツキを３倍以下に抑えることも可能であり、サンプル間バラツキの小さい材料を調製することができる。
【００５７】
また、本発明に用いられる半導電性フィラーとしては導電性物質で表面が被覆された無機フィラーも挙げられ、具体的には、炭素、黒鉛等の黒色導電性物質、インジウム−錫複合酸化物（以下、ＩＴＯとも言う。）、アンチモンドープ酸化錫（以下、ＡＴＯとも言う。）、ニオブドープ酸化錫（以下、ＮＴＯとも言う。）、タンタルドープ酸化錫（以下、ＴＴＯとも言う。）、フッ素化物ドープ酸化錫（以下、ＦＴＯとも言う。）、酸化錫（以下、ＴＯとも言う。）等の酸化錫系導電性物質で被覆された半導電性フィラーが挙げられる。これらのうち、黒色導電性物質や酸化錫系導電性物質で被覆された物質は、導電性物質の種類、量、形成方法によって様々な中抵抗へ調整することができるために好ましい。
【００５８】
例えば、炭素や黒鉛等の黒色導電性物質で抵抗を制御した材料では、表面に付着する黒色導電性物質の被覆量を調整することで抵抗値を制御することができる。また、一旦抵抗値の低い材料が得られたとしても、空気中で、５０〜７５０℃の温度で加熱すると、抵抗値が上がり、各種抵抗値を有する半導電性物質を容易に入手することができる。
【００５９】
また、酸化錫やドーピングを施した酸化錫で抵抗値を制御した材料では、ドーピングの量を変更することで、低抵抗値から高抵抗値まで幅広く制御することができる。また、芯材の表面に酸化錫またはドーピングされた酸化錫層を形成した後、加熱雰囲気を酸化性又は非酸化性のどちらかに選択することや加熱温度を変更することでも、抵抗値を制御することができる。このようにして、類似の形状からなる各種抵抗値を有する半導電性物質を容易に入手することができる。また、酸化錫系の材料は熱に強く、ポリイミドの製膜工程のような３００℃を越える過酷な成型においても物性劣化を引き起こすことがないために、使用の範囲も広くなる。また酸化錫系の材料は、無色に近く、芯材に無色のものを使用すると、無色の半導電性フィラーを得ることができる。その結果、黒色剤を併用することで、容易に黒色ポリイミド樹脂組成物を得ることができる。
【００６０】
また、上記のように表面被覆方法を制御することで、抵抗値を制御できる利点として次のようなことがある。例えば、チタン酸カリウム、酸化錫、酸化亜鉛等といった材料は、特定の抵抗値しか有しておらず、これらを用いて様々な抵抗値へ制御する場合、異なる抵抗値を有する２種以上のフィラーを混合したり、配合部数を変更する必要があった。また、各フィラーに応じた分散性の制御や配合調整に大変な労力を要し、配合量の変更により機械特性が異なり、また色も単一の色しかなく、各種色付けする際に、色変更の自由度が少なかった。しかし、本発明の導電性物質で被覆された材料を用いれば、各種抵抗を有する材料を単一材料で容易に作成することが可能となり、機械特性や分散性を変えることなく導電性の制御が可能となるため、配合量が全く同じで異なる抵抗値を有するポリイミド樹脂を作成することができる。また、半導電性無機物の機械特性、分散性といった基本特性は同一であるため、種類変更による洗浄作業や切り替え作業も非常に容易になる。また、表面の導電処理方法により、無色から黒色まで自在に選択することができ、着色も容易となる。
【００６１】
本発明に用いられる導電性物質で被覆された半導電性フィラーの芯材（無機材料）として、金属、金属酸化物、金属炭化物、金属窒化物といったセラミック材料や金属塩といったものが挙げられる。例えば、亜鉛、酸化亜鉛、アルミニウム、アルミナ、水酸化アルミニウム、カルシウム、炭酸カルシウム、銀、酸化クロム、ケイ素、ケイ酸塩、ケイ酸カルシウム、シリカ、ガラス、酸化チタン、チタン酸金属塩、ホウ酸アルミニウム、酸化錫、鉄、酸化鉄、銅、酸化銅、炭酸バリウム、硫酸バリウム、水酸化バリウム、マグネシウム、水酸化マグネシウム、炭化ケイ素、炭化タングステン、炭化チタン、窒化アルミニウム、窒化ケイ素、窒化ゲルマニウム、窒化タンタル、窒化チタン、窒化ホウ素、マイカ、タルク、ウォラストナイト、タルク、カオリン、粘土鉱物等が挙げられる。
【００６２】
このうち、ホウ酸アルミニウム、酸化錫、炭酸カルシウム、ケイ酸塩、ケイ酸カルシウム、硫酸バリウム、マイカは、屈折率が低く樹脂の屈折率に近似しているので、樹脂に混入しても透明性を損なうことが少なく、また着色することもない点から好ましい。またアルミナ、シリカ、ガラス、ウォラストナイト、タルク、カオリンも比較的屈折率が低く、樹脂に添加しても透明性が損なわれにくい点から好ましい。屈折率としては２．０以下、好ましくは１．８以下、さらに好ましくは１．７以下である。これらに黒色導電性物質を被覆すると黒色化された半導電性無機物を得ることができ、ポリイミドに配合する場合、黒色のポリイミド樹脂組成物を得やすいために好ましい。また、酸化錫系物質を被覆した際には、透明性に優れた半導電性フィラーを得ることができる点から好ましく、このフィラーを添加したポリイミド樹脂は、透明性を有する。さらに、他の着色剤を添加することで任意の色調を得ることができる点からも好ましい。
【００６３】
一方、芯材から遊離する金属成分は少ないほど良い。遊離金属成分量としては１００ｐｐｍ以下、好ましくは８０ｐｐｍ以下、さらに好ましくは５０ｐｐｍ以下であるとよい。上記範囲内では、遊離金属成分が少ないために、配合した樹脂の抵抗値の湿度依存性が小さくなるために好ましい。また、絶縁破壊電圧も小さくなるために好ましい。
【００６４】
また、単体で半導電性を有するフィラーとしては、酸化チタン、チタン酸金属塩、ホウ酸アルミニウム、酸化錫、炭化ケイ素等が挙げられる。
【００６５】
本発明においては、ポリイミド樹脂組成物に対して、前記半導電性フィラーの他に、導電性フィラーを加えることも可能である。導電性フィラーとしては、カーボンブラック、グラファイト、金属粉末、導電性セラミックス、導電処理された無機物、帯電防止剤等が挙げられる。
【００６６】
カーボンブラックとしては、導電性を有するものであれば種々のものを用いることができ、例えば、ファーネスブラック、アセチレンブラック、サーマルブラック、チャンネルブラック等があげられる。中でも、ファーネスブラックの１種であるが、特に比表面積が大きくケッチェンブラックと呼ばれるカーボンブラックを用いた場合、カーボンブラックの配合量が少なくても抵抗低減効果が高く、なおかつ他のカーボンブラックを使用した場合に比較して電圧依存性（電圧が変わると抵抗値が変わり、オームの法則に則った挙動を示さない性質）が少ないという利点を有する。この点から、ケッチェンブラックを用いることが特に好ましい。
【００６７】
金属粉末としては、銅、鉄、アルミニウム、ＳＵＳ等の粉末が挙げられ、導電性セラミックスとしてはドーピングされた酸化錫やＩＴＯ等が挙げられる。
【００６８】
導電化処理された無機物としては、酸化チタン、チタン酸金属塩、硫酸バリウム、マイカ等を黒色導電性物質、酸化錫系化合物等により、導電化処理した物が挙げられる。形成方法としては、前記に示した半導電性フィラーの導電性層の形成方法が利用できる。
【００６９】
本発明においては、ポリイミド樹脂組成物に対して、前記の半導電性フィラーの他に、絶縁性フィラーを加えることも可能である。絶縁性の無機物としては、例えばアルミナ、シリカ等の小径粒状物質、雲母、粘土鉱物等の板状・鱗片状物質、炭酸カルシウム等の短繊維状もしくはウィスカー状物質など多様な物が用いられる。絶縁性フィラーは、例えば弾性率等の特性をコントロールするために添加する場合もあるし、また導電性粉体の分散を補助し、導電体の凝集等を防止して安定した抵抗値を実現できる場合もある。
【００７０】
本発明に用いる半導電性フィラー、導電性フィラー、絶縁性フィラーの形状としては、粒状、針状、鱗片状等、特に限定されるものではないが、中でも針状が好ましい。針状フィラーを用いれば、絶縁性を保持したまま抵抗を低減でき、表面性に優れ、線膨張係数、吸湿膨張係数の小さい樹脂組成物を得ることができる。また、引き裂き等による断裂や張力による寸法変化を防ぎ、高耐久かつ高寸法安定性で長期の搬送特性が実現できる機械強度に優れたフィルムやベルトを得ることができる。
【００７１】
フィラーが粒状である場合、その粒径は１μｍ以下、好ましくは０．３μｍ以下、さらに好ましくは０．１μｍ以下である。１００μｍ以下といった厚みが薄い成形体においては、粒状フィラーが１μｍよりも大きい場合、分散不良による局部の凝集によって絶縁破壊が生じ、表面性も悪化する傾向がある。一方、フィラーの粒径が１μｍ以下であれば、多少の凝集であっても絶縁性、或いは表面性を悪化させないため、好ましい。しかしながら、逆に上記粒径が小さすぎると、ポリアミド酸溶液が増粘したり、嵩張りすぎて配合作業に支障をきたすおそれがある。このためフィラーの粒径は０．００５μｍ以上であることが好ましい。また、フィラーの体積抵抗値は、多少の凝集物が存在しても、厚み方向の絶縁破壊が発生しにくい点から、１×１０^３Ω・ｃｍ以上であるのが好ましい。
【００７２】
フィラーが針状や鱗片状である場合においても、上記と同様の理由により、その短軸径の上限は１μｍ、好ましくは０．３μｍ、さらに好ましくは０．１μｍであり、その下限は０．００５μｍであることが好ましい。
【００７３】
次にポリイミド樹脂に対する半導電性フィラーの配合量は、ポリイミド樹脂１００重量部に対し２０〜２００重量部、好ましく４０〜１８０重量部、さらに好ましくは５０〜１５０重量部である。上記配合部数よりも多いと、フィルムが脆くて成型が困難となり、また、黒色材料を添加しても黒濃度が０．９以上の組成物が作成困難となるために好ましくない。また、上記配合部数よりも少ないと、抵抗値が目的の範囲内まで下がりにくいため、好ましくない。
【００７４】
導電性フィラーを併用する場合においては、導電性フィラーは４０重量部以下、好ましくは２０重量部以下、さらに好ましくは１０重量部以下の部数で併用可能である。半導電性フィラーに加えて、４０重量部以上の導電性フィラーを添加すると抵抗値が低くなりすぎ、絶縁性も悪化する場合があるため好ましくない。
【００７５】
絶縁性フィラーを併用する場合においては、半導電性フィラーと絶縁性フィラーの総量が２０〜２００重量部、好ましく４０〜１８０重量部、さらに好ましくは５０〜１５０重量部であるように併用可能である。上記配合部数よりも多いと、フィルムが脆くて成型が困難となり、また、黒色材料を添加しても黒濃度が０．９以上の組成物が作成困難となる場合があるために好ましくない。
【００７６】
本発明に用いられる上記ポリイミド樹脂を黒色化するために配合される黒色剤としては、揮発量２．０％以上かつｐＨ５．０以下のカーボンブラックであることが好ましく、更には揮発量３．０％以上かつｐＨ４．０以下のカーボンブラックであることがより好ましい。ポリイミドの成型加工はモルフォロジー変化及び極性変化が激しいため、加工中に相分離するような形でカーボンブラックが凝集し、その結果としてポリイミドの黒濃度が低下する場合がある。しかし、上記特性のカーボンブラックを用いれば、加工中にカーボンブラックの凝集を抑制することができるため、特に、イミド化促進剤として酸無水物および／または三級アミンを用いてケミカルキュアする場合のようにモルフォロジーの変化が劇的に生じる場合でも、黒濃度の高いポリイミド樹脂組成物を得ることができる。さらに、本発明に用いられるカーボンブラックの一次粒径は、粒径が小さくなるほど、カーボンブラックの表面積が増え、光の吸収部分が増える点から、２０μｍ以下であることが好ましい。
【００７７】
なお、本発明において、黒濃度とはポリイミド表面の黒色度を意味し、マクベス反射濃度計（Ｍａｃｂｅｔｈ　　ＲＤ９１４）を用いて測定する値のことを言う。マクベス反射濃度計にて測定される黒濃度は、以下の点から、１．０以上、好ましくは１．１以上あることが好ましい。例えば、プリンターは光学機器を含み、光学処理及び光学色補整をする部分に使用される部品は過度に光を反射しないように有色、特に黒色であることが望まれる。特に、電子写真装置においては、マシン起動時や印刷中に、ベルトにパッチ像を転写し、光を反射させて画質の調整をおこなっている。この際、ベルトの色が明るい（例えば黄色）と光の反射が大きなり、画質の調整が難しくなるが、黒濃度が高いとこのような問題は発生することがない。
【００７８】
また本発明において、カーボンブラックのｐＨとは、ＪＩＳ　Ｋ　６２２０−１に従って測定する値、カーボンブラックの揮発量とは、ＪＩＳ　Ｋ　６２２０−１に従って測定する値、カーボンブラックの一次粒径とは、カーボンブラックをクロロホルムに投入し超音波を２０分間照射して分散させ、分散試料を支持膜に固定した後、透過型電子顕微鏡で写真撮影し、写真上の直径と写真の拡大倍率により計算して求める値のことを言う。
【００７９】
上記特性を有するカーボンブラックを用いることで黒濃度が高くなる理由については、概ね以下のように考えている。カーボンブラックは、揮発量が大きくなり、ｐＨが小さくなると、表面にＯＨ基やＣＯＯＨ基のような酸性官能基を有するようになる。このようなカーボンブラックは、アミノ基、カルボン酸基、カルボニル基を有するポリアミド酸或いはその溶媒に対し、親和性、及び分散性が高くなる傾向がある。また、上記カーボンブラックの官能基は、ポリアミド酸と反応を起こす場合があるため、分散が促進されることも考えられる。特に、イミド化促進剤を用いるケミカルキュア法においては、イミド化促進剤とカーボンブラックとの間で酸塩基反応や結合形成反応が起こり、また、ポリアミド酸とカーボンブラックとの間でも反応が起こりやすくなる。その結果、ポリイミド樹脂中におけるカーボンブラックの分散性が高まり、最終的に得られるポリイミドは黒濃度の高いものになると考えられる。
【００８０】
黒色用に添加するカーボンブラックの添加量としては、ポリイミド樹脂１００重量部に対し、０．０１〜２０重量部、好ましくは０．０５〜１０重量部、より好ましくは０．１〜５重量部、最も好ましくは０．５〜４重量部である。半導電性フィラーは無色から黒色まで幅広く選択することができるため、２０重量部以下という少量でも十分に着色が可能となる。２０重量部以上添加すると、機械特性、電気特性が悪化する場合がある。また、０．０１重量部よりも少ないと着色できないために好ましくない。
【００８１】
以上、半導電性フィラー単体及び半導電性フィラーと他のフィラーを適宜選択し、上記範囲内に調整することにより、高い絶縁性を保持して中抵抗値に制御でき、電圧依存性と環境依存性が少なく、添加部数、分散状態、サンプル間バラツキの小さい材料を調製することができる。また揮発量が多く、酸性度が高い、小粒径のカーボンブラックを添加することで、黒濃度の高いポリイミド樹脂組成物を得ることができる。
【００８２】
また、表面に水酸基や活性酸素等の官能基を多く含む半導電性フィラーは、分散性に優れ、ポリイミドと強固な結合を有するため、フィラー未添加品の機械強度に対して５０％以上の強度保持率を有するポリイミド樹脂組成物が得られやすく、特にピロメリット酸二無水物と４，４´−ジアミノジフェニルエーテルからなるポリイミド樹脂と組み合わせた場合には、引張り伸びは３５％以上、引き裂き伝播強度は２５０ｇ／ｍｍ以上のポリイミド樹脂組成物を得ることができるため好ましい。　また、半導電性フィラーを添加しても、例えば、吸水率を５％以下に保つように調整可能で、吸水率増加量はポリイミド元来の吸水率の２倍以下に抑えることもできる。
【００８３】
以上の組み合わせに加えて、フィラーとポリイミドの強固な結合を作る等の目的に応じて、フィラーの表面処理を行ってもよい。表面処理剤としては、例えば、シラン系カップリング剤、チタン系カップリング剤、アルミニウム系カップリング剤、アミノ酸系カップリング剤等を用いることができる。樹脂が反応硬化型の直鎖状ポリイミド樹脂の場合には、表面処理をすることで結合はより強固なものとなるが、処理を行わずとも十分な強度を得ることができる。
【００８４】
添加する半導電性フィラーや他のフィラー等をポリイミド樹脂に分散させるための方法としては、種々の方法がとられ得る。
【００８５】
ポリイミド樹脂が溶剤可溶性である場合、溶剤に溶解したポリイミド樹脂溶液と、予めフィラーを溶媒に予備分散した分散液を調製し、両者を攪拌翼や３本ロールなどの混練機によって混合、分散を進める方法がとられ得る。また、逆にフィラーを溶媒に予備分散した分散液に対し、溶剤可溶性のポリイミドの粉体またはペレット等を加えて良く混合するという方法も使用可能である。前記予備分散の方法としては、例えば、フィラーを溶剤に加えて超音波分散するといった方法が有効である。特に針状フィラーは過剰な剪断力を受けると形状が破壊される可能性があるため、超音波分散による方法が好ましい。
【００８６】
ポリイミド樹脂が溶剤不溶性の場合、ポリイミドの前駆体であるポリアミド酸の溶液に対し、前記の予備分散液を加えて、同様の方法で混合・混練等を行う方法も可能である。
【００８７】
ポリアミド酸とフィラーを混合する場合、以下のような方法を用い得る。例えば、ポリアミド酸を重合する溶媒に予めフィラーを添加してフィラーの分散溶液を調製しておき、その後ポリアミド酸の原料であるジアミンと酸二無水物を添加してポリアミド酸を重合する方法があげられる。別の方法としては、予め重合して得たポリアミド酸にフィラーの分散溶液を添加し混合する方法である。どちらの方法を用いるにしても、通常はフィラーの分散溶液を調製する必要がある。一般的にフィラーは樹脂より比重が大きく重いため、溶媒にフィラーを添加するとたちまち沈降してしまう。このような状態で、ポリアミド酸と混合すると、フィラーの凝集物ができ、ポリイミド成型体の表面に凹凸ができたり、局所的に抵抗値が異なったりするおそれがある。これを防止するために、フィラーの分散溶液を作成するに際し、分散剤を配合すると好ましい結果が得られる。分散剤としては、金属塩や界面活性剤といったものが挙げられる。特に分散性、耐熱性の点から金属塩が好ましく、Ｌｉ塩、Ｎａ塩、Ｋ塩、Ｒｂ塩、Ｃｓ塩、Ｂｅ塩、Ｍｇ塩、Ｃａ塩、Ｓｒ塩、Ｂａ塩からなる群より選択される１種または２種以上の組み合わせが良く、特に　Ｌｉ塩、Ｎａ塩、Ｋ塩が好ましい。Ｌｉ塩では格子エネルギーが１１００ｋＪｍｏｌ^−１以下のＬｉ塩が好ましく、具体的には　ＬｉＦ、ＬｉＣｌ、ＬｉＢｒ、ＬｉＩ、ＬｉＳＣＮ、ＬｉＣＦ_３ＳＯ_３といったものが挙げられる。Ｎａ塩では格子エネルギーが８００ｋＪｍｏｌ^−１以下のＮａ塩が好ましく、具体的にはＮａＦ、　ＮａＣｌ、　ＮａＢｒ、　ＮａＩ、　ＮａＳＣＮ、　ＮａＣＦ_３ＳＯ_３といったものが挙げられる。Ｋ塩では格子エネルギーが８００ｋＪｍｏｌ^−１以下のＫ塩が好ましく、具体的にはＫＦ、　ＫＣｌ、　ＫＢｒ、　ＫＩ、　ＫＳＣＮ、　ＫＣＦ_３ＳＯ_３といったものが挙げられる。これらの金属塩は、常温でイオンが解離しやすく、フィラーと相互作用が強くなるために好ましい。ただし、格子エネルギーが小さすぎると、添加量の影響が大きくなりすぎる場合がある。これら金属塩は有機物を含まないために、成型中の高温乾燥でも樹脂が焼け付くようなことはない。分散剤はポリイミド樹脂１００重量部に対して１重量部以下の所定量を配合すれば良く、０．０１〜０．１重量部程度でも十分効果はある。一般に電線被覆の用途では、金属塩が添加されると絶縁性が悪化し、誘電率が４以上の材料に添加した場合にはイオン伝導性が高まり、あまり好ましくないが、ポリイミド樹脂との組み合わせにおいては、ポリイミド樹脂が絶縁性に優れ、誘電率が４以下であるため、絶縁性や抵抗の電圧依存性の悪化を低減できる。
【００８８】
また、特に良好な分散性が得られる別の方法として、溶剤中に先にフィラーを加え、超音波分散機等により十分に分散させておき、これにポリイミド（ポリアミド酸）の原料であるジアミン化合物と酸二無水物化合物を加え重合反応を行うという方法がある。この方法によれば超音波分散などによりミクロなレベルでの分散が良好に保たれるのと同時に、初期のフィラー分散後から重合中にかけて常に攪拌がなされるために、マクロなレベルの分散性も非常に良好となる。
【００８９】
本発明におけるポリイミド樹脂組成物は、種々の目的、用途に応じて成型され、様々な形状で用いられるが、絶縁性を保持しながら抵抗値を一定レベルに保持することが特に難しくなるのは、厚みが薄い場合である。その意味で、フィルム状、シート状、ベルト状、チューブ状等の広義でのフィルム状形態において、特に厚みが１５０μｍ以下、好ましくは、１００μｍ以下の場合に、半導電性フィラー、その他導電性及び絶縁性フィラー、着色用カーボンブラックの混合による配合は特に有効となる。
【００９０】
以下、ポリイミド樹脂組成物の代表的な成型方法について説明する。
【００９１】
ポリイミド樹脂が溶剤可溶性の場合、ポリイミド樹脂溶液を調製し、これを任意の形状に加工した後、加熱、場合によっては減圧を併用することにより溶剤を揮発せしめ、ポリイミド成型体を得ることができる。
【００９２】
同様の方法が、ポリイミドの前駆体であるポリアミド酸の段階においても適用でき、この方法はポリイミド樹脂が溶剤可溶性でなくても適用可能である。この場合、加熱に先立ち、イミド化促進のため、脱水剤として無水酢酸などの酸無水物や触媒として三級アミンを単独または併用して用いる事ができる。ただし酸無水物はイミド化反応の促進だけでなく、ポリアミド酸の分子鎖主鎖の切断も引き起こし得るため、ポリイミドの機械的特性のためには、酸無水物と三級アミンの併用または三級アミンのみの添加がより好ましく、熱キュアのみのイミド化に比べて高い引き裂き伝播強度を有する物が得られる。具体的には、引き裂き伝播強度が２５０ｇ／ｍｍ以上、場合によっては５００ｇ／ｍｍ以上の物が得られる。また前記イミド化促進剤の添加は、加熱時間を減らすことができ、ポリイミド樹脂組成物の熱劣化を抑えることができるために非常に好ましい。特に、半導電性物質は、長時間の加熱によって導電性の変化を引き起こす場合があるため、加熱時間の短縮は非常に大切である。また、前記イミド化促進剤の添加による製法では、樹脂の面内方向への配向がより進みやすく、さらに針状や鱗片状の酸化錫を併用すると、フィラーは平面状に配向しやすくなる傾向がある。その結果、厚み方向に配向するフィラーが減り、電気絶縁性を改善でき、またフィラーの吸湿による厚み方向の電気特性劣化部分を減らすことができる。そして、抵抗の湿度依存性を減らすことができるために好ましい。また、成型時間が短くてすみ、生産性が飛躍的に向上し、製造中に強度が出やすく、製造中に脆くなることが防止できる。上記製法のこれらの利点は、厚みが１００μｍ以下といった薄いポリイミド成型体の場合、特に顕著である。
【００９３】
フィルムおよび管状物への具体的成型法の例として下記のような方法が挙げられる。フィラーを分散させたポリアミドまたはポリイミドの樹脂溶液をエンドレスベルト上に、Ｔダイ、コンマコーター、ドクターブレードなどを用いる事により厚み制御をした上で、塗布する。樹脂溶液を熱風などによって自己支持性が発現するまで加熱乾燥し、その後エンドレスベルトより引き剥がす。引き剥がした半乾燥のフィルムの幅両端をピンやクリップによって固定し、幅方向の長さを規制しながら順次高温の加熱炉内を通すことによって、フィルム状成型体を得ることができる。または金属などの連続したシート状の支持体上に同様の方法で塗布し、これを加熱炉内へ通過せしめることによってシート状に固定されたフィルムまたはシート形状のポリイミド成型体を得、その後これを支持体シートより引き剥がすかまたは支持体シートをエッチングなどの手段により除去する方法も取りうる。このようにして得たフィルムまたはシート状の成型体を所定の長さと幅に切り、つなぎ合わせてベルトまたはチューブ等の管状物を得る方法が最も容易である。つなぎ合わせには接着剤や接着テープ等を用いることができるが、この方法は不可避的につなぎ目で段差や切れ目が存在するため、用途によっては不都合が生じる場合がある。
【００９４】
前記管状物を得る方法としては、円筒状金型の内面または外面にポリアミドまたはポリイミドの樹脂溶液を塗布し、加熱乾燥あるいは減圧乾燥などにより溶媒を揮発させ、これをこのまま最終焼成温度まで加熱するか、あるいは一旦引き剥がして、最終的に内径を規定するための別金型の外周にはめ込み、最終焼成温度まで加熱するといった方法をとりうる。円筒状金型への樹脂溶液の塗布にあたっては、樹脂溶液の垂れによる厚みばらつきを緩和するため、金型を回転させることも有効である。最終焼成温度はポリイミドの構造や添加するカーボンの耐熱性により適宜選択する事が必要であるが、非熱可塑性ポリイミドにおいてポリアミド酸状態から加熱・焼成する場合は概ね３５０℃〜４５０℃の間、熱可塑性ポリイミドの場合はポリイミドのガラス転位温度に対し−１００℃〜−２０℃の間が好適な範囲である。
【００９５】
本発明のポリイミド成型体を電子写真装置の部材として用いる場合には、トナーの離型性や転写性、およびトナーのクリーニング性を改善するために、表面に導電性が制御されたフッ素樹脂最外層を形成するとよい。フッ素樹脂としては、ポリテトラフルオロエチレン（以下、ＰＴＦＥ）、テトラフルオロエチレン−パーフルオロアルキルビニルエーテルコポリマー（以下、ＰＦＡ）といったものが挙げられる。導電性制御用の添加剤としては、ポリイミドの導電性制御用添加剤として前述したもの等が使用されうる。最外層の形成方法は、塗布やフィルムの貼り合わせ等が考えられるが、これらの材料をディスパージョンとしてスプレー塗布する方法が一般的である。
【００９６】
本発明のポリイミド樹脂組成物を用いて調製されるポリイミドフィルム、ポリイミド管状物は、従来の半導電性のポリイミドフィルム、ポリイミド管状物に準じた各種の用途に用いうる。特に、機械特性や電気特性に優れることにより電子写真装置における像の転写及び中間転写用のベルト、その中間転写を兼ねた印刷シートの搬送用ベルト、定着用ベルトなどとして好ましく用いうる。ここで言う電子写真装置の種類としては、特に限定されず、複写機やレーザープリンタ、ビデオプリンタ、ファクシミリ、それらの複合機等の何れでもよい。また、その型式も、モノクロ画像、カラー画像、フルカラー画像など何れでもよく、トナーの種類、転写方式、記録媒体の種類なども特に限定されない。電子写真装置に用いられる場合、記録シートとしては紙やプラスチックシートなどの印刷用のシートを適宜用いることができる。また記録シートに像を形成する記録剤としても静電気を介し付着処理できるものを適宜用いうる。また、本発明のポリイミドフィルム及びポリイミド管状物は、体積抵抗値、表面抵抗値が中抵抗値に制御されており、ばらつきも非常に小さいため、カラー複写機の中間転写ベルトや転写搬送ベルトとして用いた場合、トナー像の変形や転写ムラがなく良好な画像を記録シートに転写でき、かつ搬送の記録シートを良好に分離できる性能を長期に持続することができる。また、定着ベルトとして用いた場合、半導電性を有するため、帯電を防止することができ、優れた定着性を実現することが可能となる。また、電子写真装置のような光学機器を含み、光学処理及び光学色補整をする部品に使用された場合、具体的には、マシン起動時や印刷中に、パッチ像を転写し、光を反射させて画質の調整をおこなっている転写または中間転写ベルトに用いられた場合、本発明のポリイミドフィルム及びポリイミド管状物は優れた黒色性を有するため、光の反射が一定と成り、画質の調整がしやすくなる。
【００９７】
【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よって限定されるものではない。
【００９８】
（物性評価方法）
次に、樹脂組成物の物性評価方法について説明する。なお、物性評価は管状物を成型した後、フィルム状のサンプルを切り出して行った。
【００９９】
フィルム状サンプルの黒濃度は、マクベス反射濃度計（Ｍａｃｂｅｔｈ　　ＲＤ９１４）を用いて測定を行った。
【０１００】
フィルム状サンプル、及びフィラーの抵抗値の測定は、次のように実施した。サンプルを、▲１▼温度１０℃・湿度１５％Ｒｈの環境（ＬＬ）、▲２▼温度２３℃・湿度５５％Ｒｈの環境（ＮＮ）、▲３▼温度３０℃・湿度８０％Ｒｈの環境（ＨＨ）に２４時間放置し、該環境下にてアドバンテスト（株）製デジタル超高抵抗／微小電流計Ｒ８３４０と三菱化学（株）製ＨＲプローブを用い１００Ｖにおける体積抵抗値と表面抵抗値を測定した。フィルム状サンプルでは、１０００Ｖでも測定を実施した。
【０１０１】
抵抗値の環境依存性とは、低温低湿時（ＬＬ）の体積抵抗値Ｒｌと高温高湿時（ＨＨ）の体積抵抗値Ｒｈとの比（Ｒｌ／Ｒｈ）の値を、抵抗値の電圧依存性とは、１００Ｖ印加時の体積抵抗値Ｒ_１００Ｖと１０００Ｖ印加時の体積抵抗値Ｒ_{１０００Ｖ}との比（Ｒ_１００Ｖ／Ｒ_{１０００Ｖ}）の値を意味する。これらの値が０．３〜３０の範囲にある場合は依存性が少ない材料（小）、０．０１〜０．３もしくは３０〜１００の範囲内にある場合は依存性が中程度ある材料（中）、０．０１以下もしくは１００以上の場合は依存性が悪い材料（大）とした。
【０１０２】
フィルム状サンプルの厚み方向の絶縁性測定は、次のように実施した。このフィルムを温度２３℃・湿度５５％Ｒｈの環境（ＮＮ）に２４時間放置し、該環境下にて安田精機製作所製のＹＳＳ式耐電破壊試験機における絶縁性を測定した。
【０１０３】
フィルム状サンプルの引張弾性率、引張伸びの測定は、ＡＳＴＭ　Ｄ８８２に準拠して実施した。フィルム状サンプルの引裂伝播強度測定は、ＡＳＴＭ　Ｄ１９３８に準拠して実施した。
【０１０４】
次に、実施例と比較例について説明する。
【０１０５】
（実施例１）
芳香族ジアミンとして４，４′−ジアミノジフェニルエーテルを、芳香族テトラカルボン酸二無水物としてピロメリット酸二無水物（以下、ＰＭＤＡ）を用いて得られたポリアミド酸のジメチルホルムアミド（以下、ＤＭＦ）溶液（固形分濃度１８．５％、溶液粘度３，０００ｐｏｉｓｅ）を７５ｇ準備した。次に、半導電性フィラーとしてカーボン被覆チタン酸カリウム（デントールＢＫ４００ＨＲ：大塚化学（株）：比重３．１５ｇ／ｃｍ^３、体積抵抗値５．０×１０^５Ω・ｃｍ、短軸径０．４５μｍ、長軸径１５μｍ、イオン溶出量５００〜１００００ｐｐｍ）を８．４２ｇ、カーボンブラックとして揮発分８．０％、ｐＨ３．０、一次粒子径１３ｎｍのカーボンブラック（三菱化学（株）：＃２６５０）を０．６７ｇ採取し、これら添加剤の総重量に対し８倍量のＤＭＦに分散させて添加剤分散溶液を調製した。
【０１０６】
前記のポリアミド酸溶液と添加剤分散液を添加し混練した。得られたドープを管状フィルム状にキャストする前に、無水酢酸／イソキノリン／ＤＭＦを９．０３ｇ／１１．４ｇ／１５．６ｇからなる溶液と混合し、次いでアルミ箔上にキャストした。１４０℃／６００秒、２７５℃／４０秒、４００℃／９３秒熱処理して約７５μｍのポリイミドフィルムを得た。なお、管状物として得る場合には、アルミ箔の代わりに鏡面を有する金属筒の内面もしくは外面に塗布することによって作成した。該管状物中の半導電性フィラー、カーボンブラックの配合量はポリイミド固形分１００重量部に対して、各々５０重量部と４重量部である。特性値を表２に示す。管状物の電気特性、機械特性等の物性はフィルムの物性と同じと考えてよい。アルミ箔および金属筒からのポリイミドの剥離は、１４０℃の加熱の後におこなった。
【０１０７】
上記と同様の方法にて重合したポリイミドフィルム単体（フィラーを含まない）の物性値を評価した結果、線膨張係数２１ｐｐｍ、吸湿膨張係数１６ｐｐｍ、引張弾性率２．９ＧＰａ、伸び７０％、引き裂き伝播強度４５０ｇ／ｍｍ、吸水率２．５％であった。
【０１０８】
（実施例２〜８）
カーボン被覆チタン酸カリウムの代わりに表１に示した配合部数で半導電性フィラー、およびカーボンブラックを配合した以外は、実施例１と同様にしてポリイミドフィルムを得た。特性値を表２に示す。
【０１０９】
なお、表１に記載のフィラーの詳細は次の通りである。酸化錫系被覆ホウ酸アルミニウムは三井金属（株）製のパストラン−ＴＹＰＥＶ−ＫＫ００６、カーボン被覆雲母は大塚化学（株）製ＢＫ４００Ｍ、酸化チタンは石原産業（株）製ＦＴＬ３００のことを指し、これらフィラーのイオン溶出量は、全て＜５０ｐｐｍであった。
【０１１０】
また、実施例１〜４、９および１０に使用したカーボンブラックは三菱化学（株）製＃２６５０、実施例５、６に使用したカーボンブラックは三菱化学（株）製＃１０００、実施例７、８に使用したカーボンブラックはデグッサジャパン（株）製ＦＷ２００、比較例２〜４に使用したカーボンブラックは三菱化学（株）製＃２６００である。
【０１１１】
（実施例９）
実施例１記載のポリアミド酸のＤＭＦ溶液を、芳香族ジアミンとして４，４′−ジアミノジフェニルエーテル３当量をＤＭＦに溶解し、次にＰＭＤＡ４当量を加え、さらに、パラフェニレンジアミン１当量を加えて重合したポリアミド酸のＤＭＦ溶液（固形分濃度１８．５％、溶液粘度３，０００ｐｏｉｓｅ）に変更した以外は実施例１と同様にしてポリイミドフィルムを得た。特性値を表２に示す。
【０１１２】
このようにして重合したポリイミドフィルム単体の物性値を評価した結果、線膨張係数８ｐｐｍ、吸湿膨張係数９ｐｐｍ、引張弾性率４ＧＰａ、伸び７０％、引き裂き伝播強度４５０ｇ／ｍｍ、吸水率２．１％であった。
【０１１３】
（実施例１０）
実施例１記載のポリアミド酸のＤＭＦ溶液を、芳香族ジアミンとして４，４′−ジアミノジフェニルエーテル１当量、パラフェニレンジアミン１当量をＤＭＦに溶解し、次にＴＭＨＱ１当量を加え、さらにＰＭＤＡ１当量を加えて重合したポリアミド酸のＤＭＦ溶液（固形分濃度１８．５％、溶液粘度３，０００ｐｏｉｓｅ）に変更した以外は実施例１と同様にしてポリイミドフィルムを得た。特性値を表２に示す。
【０１１４】
このようにして重合したポリイミドフィルム単体の物性値を評価した結果、線膨張係数９ｐｐｍ、吸湿膨張係数５ｐｐｍ、引張弾性率６ＧＰａ、伸び３０％、引き裂き伝播強度４５０ｇ／ｍｍ、吸水率１．２％であった。
【０１１５】
以上のようにして得られた実施例１〜１０のポリイミドフィルムの黒濃度を測定した結果、全て１．０以上あり、非常に黒色度に優れていた。また、前記ＮＮ条件での体積抵抗値は何れも１×１０^９〜１×１０^１３Ω・ｃｍと中抵抗領域に調整されており、絶縁性も全て１５ｋＶ／ｍｍ以上と優れていた。
【０１１６】
また前記ＬＬとＨＨ条件における体積抵抗値の比は何れも０．３〜３０の範囲にあり、体積抵抗値の環境依存性は小さかった。また、実施例３を除いた何れにおいても１００Ｖと１０００Ｖで測定した体積抵抗値の比は０．３〜３０の範囲にあり、体積抵抗値の電圧依存性も小さかった。但し、実施例３においても１００Ｖと１０００Ｖで測定した体積抵抗値の比は０．１〜１００の範囲にあり、体積抵抗値の電圧依存性は悪くなかった。また上記と同様の操作で作製した５点のサンプルについて、１００Ｖにおける体積抵抗値を測定した結果、最大値と最小値の差は３倍以下であり、サンプル間のばらつきも非常に小さかった。また同一サンプル内のばらつきも３倍以下と非常に小さかった。
【０１１７】
実施例１〜１０については、半導電性フィラーの添加部数の差（５重量部）による体積抵抗値の比は３倍以下であり、体積抵抗値の添加部数（配合）依存性は小さかった。
【０１１８】
フィルムの引張弾性率はフィラー未添加品に比べて優れており、伸びは何れも５０％以上を保持し、引裂伝播強度も５０％以上を保持していた。線膨張係数、吸湿膨張係数はフィラー未添加品よりも数ｐｐｍ低下していた。この結果は、半導電性フィラーの形状が針状であるためと考える。
【０１１９】
実施例１、実施例９、実施例１０の順に引張弾性率は増加していた。これは、ベース樹脂の引張弾性率がこの順に高くなっているためである。
【０１２０】
（比較例１）
カーボンブラックを使用せず、導電性酸化錫被覆針状酸化チタン（ＦＴ３０００：石原産業（株）：比重４．４ｇ／ｃｍ^３、体積抵抗値＜１０^３Ω・ｃｍ）２．７８ｇを分散させて分散液を調製したこと以外は、実施例１と同様にしてポリイミド管状物を得た。該管状物中のフィラー量はポリイミド固形分１００重量部に対して２０重量部である。特性値を表２に示す。
【０１２１】
（比較例２）
カーボンブラック（＃２６００：三菱化学（株）：揮発分１．８％、ｐＨ６．５、一次粒子径１３ｎｍ）０．６７ｇ、導電性酸化錫被覆針状酸化チタン（ＦＴ３０００：石原産業（株）：比重４．４ｇ／ｃｍ^３、体積抵抗値＜１０^３Ω・ｃｍ）２．７８ｇを分散させて分散液を調製した以外は、実施例１と同様にしてポリイミド管状物を得た。該管状物中のカーボンブラック、およびフィラーの配合量はポリイミド固形分１００重量部に対して４重量部と３０重量部である。特性値を表２に示す。
【０１２２】
（比較例３）
カーボンブラック（＃２６００：三菱化学（株）：揮発分１．８％、ｐＨ６．５、一次粒子径１３ｎｍ）０．６７ｇ、カーボン被覆チタン酸カリウム８．４２ｇを分散させて分散液を調製した以外は、実施例１と同様にしてポリイミド管状物を得た。該管状物中のカーボンブラック、およびフィラーの配合量はポリイミド固形分１００重量部に対して４重量部と５０重量部である。特性値を表２に示す。
【０１２３】
（比較例４）
半導電性フィラーを使用せず、カーボンブラック（＃２６００：三菱化学（株）：揮発分１．８％、ｐＨ６．５、一次粒子径１３ｎｍ）４．１７ｇを分散させて分散液を調製したこと以外は、実施例１と同様にしてポリイミド管状物を得た。該管状物中のカーボンブラックの配合量はポリイミド固形分１００重量部に対して３０重量部である。特性値を表２に示す。
【０１２４】
以上のようにして得られた比較例１〜３のポリイミド樹脂の黒濃度は１．０以下あり、実施例１〜１０と比較すると黒濃度で非常に劣っていた。また、比較例３と実施例１ではカーボンブラックの種類が異なっているだけであるが、低揮発分、高ｐＨのカーボンブラックに変更しただけで、黒濃度が０．３も大幅に低下した。
【０１２５】
比較例１、２、４のポリイミド樹脂におけるＮＮの体積抵抗値は狙い通りの中抵抗領域に調整されていたが、ＨＨで非常に抵抗値が低かった。またフィラーの添加部数の差（５重量部）による体積抵抗値の比は３倍以上あり、体積抵抗値の添加部数依存性は大きかった。またＬＬとＨＨの体積抵抗値の比は１０００倍以上であり、体積抵抗値の環境依存性は非常に大きかった。また、１００Ｖと１０００Ｖで測定した体積抵抗値の比は１００倍以上であり、体積抵抗値の電圧依存性は大きかった。また上記と同様の操作で作製した５点のサンプルについて、５００Ｖにおける体積抵抗値を測定した結果、最大値と最小値の差は３倍以上あり、サンプル間のばらつきも非常に大きかった。同一サンプル内のばらつきも３倍以上あり、非常に大きかった。
【０１２６】
また、本比較例と同じ配合処方で、ケミカルキュアではなく、熱キュア（１５０℃・３０分、２００℃・３０分、３００℃・３０分、４００℃・３０分）で作成したフィルムは、ケミカルキュアで作成したものに比べて非常に長時間の成型時間が必要であり、フィラーを多量に含むものにおいては、成型途中及び成型後のいずれにおいても非常に脆かった。
【０１２７】
【表１】

【０１２８】
【表２】

【０１２９】
【発明の効果】
本発明のポリイミド樹脂組成物、ポリイミドフィルム、ポリイミド管状物においては、黒濃度が高く、高絶縁性、中抵抗値を有し、添加部数、分散状態、サンプル間に基づくばらつきが小さく、抵抗値の環境依存性、電圧依存性が少なく、機械特性に優れ、搬送による帯電防止性や電子写真機での転写性・定着性に優れる。[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a polyimide resin composition, a polyimide film, and a polyimide tube having a high black concentration controlled to an intermediate resistance value without impairing excellent characteristics such as mechanical properties and heat resistance inherent to the polyimide resin. In addition, the present invention relates to a tubular member for an electrophotographic apparatus, such as a transfer belt, an intermediate transfer belt, a transfer-fixing belt, and a fixing belt using the same.
[0002]
[Prior art]
Polyimide resins are widely used in the form of films, tubes, belts, molded products, etc., utilizing their excellent properties such as heat resistance, chemical resistance, and electrical insulation. For example, as a film, a flexible printed wiring board (hereinafter, referred to as FPC) or TAB (Tape Automated Bonding) base material, an insulating film such as an electric wire, a tube, a part of an OA device such as a copying machine as a belt, and a molded body. It is used for various purposes such as a separation claw and a bearing of a copying machine. In recent years, it has been used as an adhesive, a protective film, and the like even in the vicinity of a semiconductor by utilizing its characteristics.
[0003]
However, polyimide resin has too high insulation properties, so that the resin is charged in the transport and winding steps in the manufacture of FPCs and semiconductor peripherals, and in recent high-density circuits, dielectric breakdown between wiring due to static electricity. Has become apparent. On the other hand, the resistance is so high that conduction does not occur, and excellent insulation must be maintained. In this case, the volume resistance is 10 ¹⁰ -10 ^Fifteen Ω · cm, more preferably 10 ¹⁰ -10 ^Thirteen Ω · cm is required.
[0004]
For transfer belts, intermediate transfer belts, and fixing belts in electrophotographic applications such as printers and copiers, having an intermediate resistance value as a function for transferring and fixing toner is an important quality issue. Is well known. In this case, the volume resistance is 10 ⁶ -10 ^Thirteen Ω · cm, preferably 10 ⁷ -10 ^Thirteen Ω · cm, more preferably 10 ⁹ -10 ^Thirteen Ω · cm is required. Further, it is desired that the resistance value be constant under any environment. Specifically, it is preferable that the ratio of the resistance value between low temperature and low humidity and high temperature and high humidity is 100 times or less, and more preferably 30 times or less. Further, it is necessary to control the voltage and the current in accordance with the type of the image and the environment. When the resistance value varies according to the voltage, the control becomes difficult. Therefore, the voltage dependence of the resistance value is preferably as small as possible. The ratio of the resistance value between 100 V and 1000 V is 100 times or less, more preferably 30 times or less. Further, it is desirable that the printer includes optical equipment and that parts used for optical processing and optical color correction be colored, particularly black, so as not to excessively reflect light.
[0005]
In view of such demands, various attempts have been made to lower the resistance value by adding various conductive substances to the polyimide resin, including an aromatic polyimide matrix and finely divided electrically conductive particle material, Are dispersed uniformly and 10 to 45% by weight of the entire product is disclosed (for example, see Patent Document 1). It also contains 5 to 20% by weight of carbon black and has a surface resistance (Ω / □) of 10%. ⁷ ≤Rs≤10 ^Fifteen (See, for example, Patent Document 2). An intermediate transfer member for an electrophotographic recording apparatus comprising an aromatic polyamide film or an aromatic polyimide film in the range of (1). Further, a film comprising a composition containing an aromatic polyimide and an inorganic filler having conductivity, wherein the film has a volume resistance of 10 ^-2 -10 ¹² A transparent conductive film characterized by having Ω · cm and a total light transmittance of 20% or more is disclosed (for example, see Patent Document 3).
[0006]
However, as described above, the method of mixing a filler having a conductive filler such as carbon black, graphite, metal particles, and indium oxide with polyimide is often poor in mechanical properties, and in these methods, The filler used has a very low volume resistance value (1.0 × 10 ³ Ω · cm or less), it was very difficult to control the resistance in the semiconductive region, particularly to improve the reproducibility of the resistance value and reduce the in-plane variation. In addition, only a large dependence of the resistance value on the measured voltage and the number of added parts can be obtained, and under high temperature and high humidity, water permeates the interface between the conductive material and the resin, and the electric resistance is greatly reduced. there were. Furthermore, when the base resin absorbs and expands by moisture, there is a problem that the dispersion state of the additive changes and the resistance value largely fluctuates. As described above, when a conductive filler such as carbon or metal is added, it is difficult to control the resistance value, and it is also difficult to optimize the addition amount.
[0007]
The main conductive filler has an average particle size of 1 to 50 μm and a volume resistance of 10 μm. ³ -10 ⁹ Ω · cm large-diameter high-resistance particles, and an auxiliary conductive filler having an average particle size of less than 0.1 μm and a volume resistance of 10 ² Ω · cm or smaller resistance particles are dispersed and have a volume resistance of 10 ⁵ -10 ⁹ A semiconductive resin composite material in the range of Ω · cm is disclosed (for example, see Patent Document 4).
[0008]
However, as described above, when large-diameter and high-resistance particles are added, the surface property may be deteriorated when a thin molded product having a thickness of about 100 μm typified by a film or a tube is obtained by extrusion molding or injection molding. In addition, when molding into the above-mentioned thin shape using a rubber material or a general-purpose resin by the above-described compounding, insulation properties and mechanical strength may be significantly inferior. There is a problem that the resistance value varies due to breakage of the high-resistance particles and the mechanical strength also decreases. In addition, the large-diameter high-resistance particles used in Patent Document 4 use an inorganic substance having a specific resistance value, and when a resin composite material having a desired resistance value is obtained, various resistance values are accordingly used. After searching for a filler having the following formula, it was necessary to perform an appropriate blending according to the resistance of the filler. However, such work requires a lot of work, and the type of filler is changed depending on the resistance value.Therefore, the mechanical properties may be extremely different, and there are various kinds of filler colors. Color control, especially blackening Was very difficult.
[0009]
[Patent Document 1]
JP-A-2-110138
[0010]
[Patent Document 2]
JP-A-63-31263
[0011]
[Patent Document 3]
Japanese Patent No. 2783537
[0012]
[Patent Document 4]
JP-A-4-133077
[0013]
[Problems to be solved by the invention]
Despite such various attempts, it is a very difficult task to control the polyimide resin composition to have a medium resistance and to achieve a high black density while maintaining high insulation properties.
[0014]
In particular, when carbon black is added to control the resistance value of the polyimide to blacken it, there are the following problems derived from a molding method unique to polyimide. Polyimide molding is not a simple molding by heat melting such as an extrusion method and a calendar molding, but is a very complicated one involving heating a precursor polyamic acid solution, drying the solvent and imidizing. During this drying and reaction, the morphology, polarity and solubility of the material change significantly. In particular, the change is even more dramatic in the method of imidization by chemical curing. Since carbon black is originally a material that easily agglomerates, carbon black added for resistance control causes agglomeration in the drying and reaction process, and even a slight change in molding conditions causes a large change in resistance, and the The settings were very tricky. In addition, since the chemical curing method easily causes agglomeration, the coloring effect of carbon black is greatly reduced, and it is very difficult to obtain a polyimide film having a high black concentration.
[0015]
In addition, polyimide resins, in particular, wholly aromatic polyimide resins have a volume resistivity of 10%. ¹⁶ Very high Ω · cm, requiring a large amount of conductive filler compared to resins with low volume resistance such as polyamide and polyvinyl chloride. Caused large variations in volume resistance.
[0016]
In addition, when controlling the resistance value by adding carbon black or conductive particles, since these materials have a low resistance value, the resistance value changes significantly due to a slight difference in the added amount or a difference in the dispersion state, There is a problem that the resistance value differs between batches even if the blends are exactly the same. Further, when the thickness of the molded body is small, such as a belt, the partial variation becomes large, which leads to a remarkable decrease in insulation reliability, so that resistance control becomes more difficult.
[0017]
In particular, when the resistance is controlled by using other inorganic conductive materials in addition to carbon black, the physical properties do not change under the molding conditions of the polyimide, and the conductive material for medium resistance control which does not cause the deterioration of the physical properties of the polyimide. Few are. Therefore, even if carbon black for coloring is used in combination for blackening, the resulting polyimide becomes gray or green, and it is difficult to obtain a film having a high black density.
[0018]
Naturally, it is conceivable to increase the blending amount of carbon black in order to increase the black density, but in that case, it becomes difficult to control the medium resistance value, and the insulating property is greatly deteriorated, so it is necessary to reduce the addition of carbon black as much as possible. Was.
[0019]
Thus, when molding a polyimide material comprising an inorganic conductive material and carbon black by chemical curing, particularly in a system containing a large amount of the inorganic conductive material, by adding a small amount of carbon black, it is possible to achieve a high black density. It was a very difficult task.
[0020]
[Means for Solving the Problems]
The present inventors have compared the effects of various inorganic fillers and carbon black in order to solve such problems, and as a result, in a polyimide resin composition comprising the inorganic filler and carbon black, a semiconductive filler and a specific pH. High carbon density, high insulation, medium resistance, small number of added parts, dispersion state, small variation between samples, and environmental dependence of resistance by using carbon black with high volatility and size The present inventors have found a polyimide resin composition having low voltage dependency, excellent mechanical properties, and excellent antistatic properties by transport and excellent transferability and fixability in an electrophotographic apparatus, and completed the present invention.
[0021]
That is, the first aspect of the present invention is that, based on 100 parts by weight of a polyimide resin, 20 to 200 parts by weight of a semiconductive filler, 2.0% or more of volatile matter, and 0.01 to 20 parts of carbon black having a pH of 5.0 or less. Parts by weight, volume resistance value is 1 × 10 ⁶ ~ 1 × 10 ^Fifteen The polyimide resin composition is in the range of Ω · cm and has a black density of 1.0 or more.
[0022]
It is preferable that the volatilization amount of the carbon black is 3.0% or more, the pH is 4.0 or less, the primary particle size is 20 nm or less, and the compounding amount is 0.1 to 5 parts by weight.
[0023]
Further, the compounding amount of the semiconductive filler is preferably 40 to 180 parts by weight.
[0024]
Further, the black density is preferably 1.1 or more.
[0025]
The semiconductive filler is preferably a semiconductive filler coated with a black conductive material.
[0026]
Further, the semiconductive filler is an indium-tin composite oxide, antimony-doped tin oxide, niobium-doped tin oxide, tantalum-doped tin oxide, fluoride-doped tin oxide, or a filler coated with a tin oxide-based material of tin oxide. Good to be.
[0027]
Further, the polyimide resin composition is characterized in that the semiconductive filler is titanium oxide, metal titanate, aluminum borate, tin oxide, or silicon carbide.
[0028]
The semiconductive filler has a volume resistance of 1 × 10 ³ ~ 1 × 10 ¹⁰ Ω · cm is preferable.
[0029]
In addition, the polyimide resin may be obtained by adding an acid anhydride and / or a tertiary amine as an imidization accelerator, followed by heating and baking.
[0030]
The second aspect of the present invention relates to a polyimide film prepared using the above-mentioned polyimide resin composition.
[0031]
The third aspect of the present invention relates to a polyimide tubular article prepared using the above-mentioned polyimide resin composition or film.
[0032]
One of the embodiments of the polyimide tubular article of the present invention is a polyimide tubular article used for any of a transfer belt, an intermediate transfer belt, a transfer fixing belt and a fixing belt of an electrophotographic apparatus.
[0033]
BEST MODE FOR CARRYING OUT THE INVENTION
The polyimide resin in the present invention means all resins having an imide bond in the structure thereof, including resins generally referred to as polyetherimide, polyesterimide, and polyamideimide, as well as copolymers and blends with other resins. It also includes things. In the case of a copolymer or a blend with another resin, the polyimide resin component may be contained in all the resins in an amount of 50% by weight or more, preferably 80% by weight or more. Among them, a reaction-curable linear polyimide resin which is strongly bonded to the inorganic filler and easily aligns the inorganic filler in the plane of the film is preferable. Here, the reaction-curable linear polyimide resin refers to a polyimide resin obtained by dehydrating and ring-closing an amide acid site via a linear polyamic acid as a precursor, for example, pyromellitic A typical example is a polyimide resin obtained by imidizing a linear polyamic acid obtained by a reaction between an acid dianhydride and 4,4'-diaminodiphenyl ether by heating, adding a catalyst, or the like. The reaction-curable linear polyamic acid has functional groups such as a carboxyl group and an amino group, and these functional groups strongly interact with the inorganic filler, and can form a strong bond with the inorganic filler. Are preferably used.
[0034]
Furthermore, when an acid anhydride and / or a tertiary amine is used as an imidization accelerator, a polyimide molded body having a high tear strength can be obtained during and after molding as compared with the case of heat curing, and the molding time is significantly longer. It is preferable because it is shortened. In addition, since imidization proceeds faster than heat curing, the resin is quickly rigidified and easily oriented in the in-plane direction.As a result, the added filler is also oriented in the in-plane direction, and surface resistance and surface roughness are reduced. A polyimide molded body which is small and has excellent insulation in the thickness direction can be obtained.
[0035]
Examples of the acid anhydride referred to herein include aliphatic acid anhydrides such as acetic anhydride, aromatic acid anhydrides such as phthalic anhydride and benzoic anhydride, and these may be used alone or in combination of two or more. Can be Examples of the tertiary amine include aliphatic tertiary amines such as triethylamine, aromatic tertiary amines such as N, N-dimethylaniline, and heterocyclic tertiary amines such as pyridine, picoline, isoquinoline, and quinoline. Examples thereof include amines, which are used alone or in combination of two or more.
[0036]
As a general raw material of polyimide, a diamine compound and a tetracarboxylic dianhydride are usually used as monomers. As the diamine compound, for example,
[0037]
Embedded image

(Wherein X is the same or different and is halogen, -CH ₃ , -OCH ₃ , -O (CH ₂ ) _n CH ₃ ,-(CH ₂ ) _n CH ₃ , -CF ₃ , -OCF ₃ Represents at least one group selected from the group consisting of A is the same or different and O, S, C = O, (CH ₂ ) _n , SO ₂ , N = N at least one group selected from the group consisting of m is an integer of 1 or more. n is an integer of 1 or more. ) Can be used.
[0038]
Also, as tetracarboxylic dianhydride,
[0039]
Embedded image

(In the formula, n is an integer of 1 or more.)
The following various monomers can be used.
[0040]
Various characteristics can be obtained by these combinations, and can be selected according to the situation such as the use and the processing method.
[0041]
For example, by using an aromatic diamine containing many bent chains (preferably two or more in one molecule) and / or having an amino group at a meta position, and using a tetracarboxylic dianhydride having two or more rings, It is possible to provide a polyimide resin composition which can be made of thermoplastic polyimide and can be melt-molded by heating. For example, a combination of 2,2'-bis (4-aminophenoxyphenyl) propane and oxydiphthalic dianhydride, or a mixture of bis (2- (4-aminophenoxy) ethoxy) ethane and 3,3 ', 4,4' -A combination of benzophenonetetracarboxylic dianhydride and the like can be exemplified.
[0042]
In addition, polyimide generally has a high water absorption due to the presence of an imide group, but a resin composition having a relatively low water absorption can be obtained by combination with a specific monomer. An example is a polyimide using a monomer having a structure in which a plurality of benzene nuclei are bonded by two or more ester bonds as tetracarboxylic dianhydride. In particular,
[0043]
Embedded image

(In the formula, n is an integer of 1 or more.)
[0044]
Embedded image

[0045]
Embedded image

And acid dianhydrides as shown in the above.
[0046]
As the diamine compound used in this case, it is preferable to use a relatively long-chain monomer in order to reduce the imide group content. For example, 1,4-bis (4-aminophenoxy) benzene, its bonding position isomer, 2,2′-bis (4-aminophenoxyphenyl) propane and the like can be mentioned.
[0047]
However, for both acid dianhydride and diamine, the structure having many long chains and bent chains is also a condition for the expression of thermoplasticity at the same time, and is not suitable when sufficient heat resistance is required. Particularly when both heat resistance and low water absorption are required, a monomer having a long chain and having a linear structure entirely or partially is suitable. For example, as tetracarboxylic dianhydride,
[0048]
Embedded image

A monomer having a structure represented by (hereinafter, TMHQ) is mentioned as an example. This monomer has a structure including a bent chain and can have a generally linear conformation as a whole, and forms a relatively rigid polyimide despite the large number of bonds. When this raw material is used, a polyimide resin having a linear expansion coefficient of 15 ppm or less, a water absorption of 1.5% or less, and a moisture expansion coefficient of 10 ppm or less, and a dimensional change due to heating or moisture absorption, which is small, can be obtained. As the diamine, for example, a structure in which a biphenyl structure or a naphthalene structure is connected by an ether bond can be selected as a relatively rigid structure having a long chain. For example, 4,4'-bisaminophenoxybiphenyl and the like can be mentioned.
[0049]
By the combination of these acid dianhydrides and diamines, it is possible to obtain a polyimide having a relatively low water absorption and having no remarkable heat softening property. In addition, not only these monomers but also general-purpose pyromellitic dianhydride, benzophenonetetracarboxylic dianhydride, paraphenylenediamine, 4,4′-diaminodiphenyl ether, and the like can be appropriately copolymerized to obtain polyimides having desired characteristics. Can be designed.
[0050]
In addition, polyimide has a higher linear expansion coefficient than metals such as copper. However, even when the types and composition ratios of the monomers are the same, a polyimide resin having a relatively small coefficient of linear expansion can be obtained by controlling the combination of the connection of the monomers (sequence control). For example, 4,4'-diaminodiphenyl ether, pyromellitic dianhydride are previously reacted with 4,4'-diaminodiphenyl ether and pyromellitic dianhydride as compared with a case where 4,4'-diaminodiphenyl ether, paraphenylenediamine, and pyromellitic dianhydride are randomly copolymerized. Then, by taking the procedure of adding paraphenylenediamine, a polyamic acid having a regular monomer sequence is obtained, and a polyimide resin having a low linear expansion coefficient can be obtained by imidizing the polyamic acid.
[0051]
In the present invention, since the inorganic filler is mixed with the polyimide resin, higher toughness is required for the polyimide resin as compared with the case where the polyimide resin is used alone. If the toughness of the polyimide resin itself is not sufficient, the toughness is inevitably reduced due to the addition of the inorganic filler, so that the polyimide resin may not be practically used in some cases. From that point, a polyimide resin prepared from pyromellitic dianhydride and 4,4'-diaminodiphenyl ether is most preferable. This structure is a balanced structure that has both sufficient heat resistance and high toughness, and can maintain its characteristics under a wide range of processing conditions.
[0052]
The volume resistivity of the semiconductive filler compounded in the polyimide resin used in the present invention may be any one of a low resistivity to a medium resistivity, but a low resistance conductive material such as carbon black, graphite, and metal fragments. 1 × 10 higher than ³ ~ 1 × 10 ¹⁰ Ω · cm is preferable, and more preferably 1 × 10 ³ ~ 1 × 10 ⁸ Ω · cm, particularly preferably 1 × 10 ³ ~ 1 × 10 ⁷ It is. In general, when a conductive material having a low resistance value is added to a resin, an intermediate resistance can be realized even by adding a small amount. However, since the difference in resistance between the resin and the conductive material is large, a slight shift in the number of added parts or a bias in dispersion increases resistance variation or voltage dependence, and further lowers a dielectric breakdown voltage.
[0053]
The reason why the medium resistance value can be stably controlled by using the semiconductive filler and the variation in the resistance between the number of components, the dispersion state, and the sample can be reduced is considered as follows. 1 × 10 semiconductive filler alone ³ ~ 1 × 10 ¹⁰ It has a resistance of about Ω · cm, and is made of carbon black, conductive metal, or metal ceramics (1 × 10 ^-5 ~ 1 × 10 ³ Ω · cm), the volume resistance of which is the target medium resistance (1 × 10 ⁶ ~ 1 × 10 ^Thirteen Ω · cm). As a result, even if it is excessively added, it is considered that the resistance does not drop too low to a low resistance value and saturates around the medium resistance value, so that the medium resistance value can be stably controlled. Further, in the system to which the semiconductive filler is added, a sharp decrease in resistance due to percolation as seen in carbon black is not observed, and the resistance changes gradually with the addition amount. As a result, in the system to which the semiconductive filler is added, for example, even if the addition amount changes by about 5 parts by weight with respect to the number of added parts for controlling the resistance value in the medium resistance region, the change in the resistance value is three times or less. You can also. Also, even if the filler is agglomerated or biased during the defoaming or dispersion process, no significant change in the resistance value is observed. For these reasons, when the semiconductive filler is used, it is considered that the change in the resistance value of the composition is small even if the amount of addition and the dispersion state in the resin composition vary between samples. On the other hand, in a system to which carbon black is added, about 10 to 20 parts by weight is added to 100 parts by weight of the resin in order to control the medium resistance region. When the amount changes by about 5 parts by weight, the resistance immediately changes 10 to 100 times or more. As a result, the number of blended parts, the state of dispersion, or slight differences between lots greatly affect the resistance value.
[0054]
The reason why the insulating property is improved by using a semiconductive filler is generally considered as follows. When a voltage is applied to a film made of polyimide and a conductive material, the voltage is divided into the polyimide and the conductive material, and the voltage is considered to be applied to a portion of the polyimide having higher resistance than the conductive material. In particular, when comparing the case where a low-resistance material such as carbon black or a metal-based material was added, and the case where a medium-resistance material such as a semiconductive filler was added, the voltage applied to the polyimide showed that the medium-resistance material was added. Time is thought to be smaller. As a result, it is considered that dielectric breakdown in the polyimide is reduced.
[0055]
Further, the reason why the voltage dependency and the environment dependency of resistance are improved by using a semiconductive filler is considered as follows. In general, when a high voltage is applied to a resin (for example, a voltage of 1 kV or more is applied to a thickness of 100 μm), the resin approaches dielectric breakdown, and the voltage dependence of the resistance value rapidly deteriorates. That is, a large current flows immediately before the breakdown. From this, it is considered that the voltage dependence of the resistance value is a phenomenon that occurs when a high voltage is applied to the resin and the resin approaches destruction. However, in a system to which a medium resistance material such as a semiconductive filler is added, it is possible to prevent a high voltage from being locally applied to the resin portion as compared with a case where a low resistance material such as carbon black is added. It is considered that the voltage dependence of the resistance value can be improved. In addition, most of the semiconductive fillers have a hydroxyl group or active oxygen on the surface partially, so that a strong interaction with the resin occurs at the time of imidization without performing a surface treatment, resulting in a strong composite. Material. And, it is considered that these strong composite materials are also useful for preventing a decrease in resistance value at the time of high temperature and high humidity and a deterioration in insulating property.
[0056]
Although it is thought to be based on the above reasons, the following electrical characteristics can be realized by using a semiconductive filler. First, by appropriately mixing these, the polyimide resin composition can stably have a volume resistance of 1 × 10 ⁶ ~ 1 × 10 ^Fifteen Ω · cm, preferably 1 × 10 ⁹ ~ 1 × 10 ^Thirteen Ω · cm, surface resistance value is 10 ⁶ -10 ^Thirteen Ω / □, preferably 1 × 10 ⁹ ~ 1 × 10 ^Thirteen Intermediate resistance values in the range Ω / □ can be realized. Further, the ratio (Rl / Rh) of the resistance value Rl at low temperature and low humidity to the volume resistance value Rh at high temperature and high humidity can be controlled in the range of 0.01 to 100, more preferably 0.3 to 30. A material having excellent stability can be prepared. Further, the volume resistance value R when 100 V is applied _100V And the volume resistance R when 1000 V is applied _1000V And the ratio (R _100V / R _1000V ) Can be controlled within the range of 0.01 to 100, more preferably 0.3 to 30, and a material having little voltage dependency can be prepared. Further, within the range of the number of added parts for realizing the resistance value, for example, even if the number of added parts of the semiconductive filler changes by about 5 parts by weight, it is possible to make the variation of the volume resistance value three times or less. Materials with little dependence can be prepared. Further, for example, it is possible to suppress the variation in the resistance value between the samples to three times or less, and it is possible to prepare a material having a small variation between the samples.
[0057]
Examples of the semiconductive filler used in the present invention also include inorganic fillers whose surfaces are coated with a conductive substance. Specifically, carbon, a black conductive substance such as graphite, indium-tin composite oxide ( Hereinafter, also referred to as ITO), antimony-doped tin oxide (hereinafter, also referred to as ATO), niobium-doped tin oxide (hereinafter, also referred to as NTO), tantalum-doped tin oxide (hereinafter, also referred to as TTO), and fluoride-doped oxidation. A semiconductive filler coated with a tin oxide-based conductive substance such as tin (hereinafter, also referred to as FTO) or tin oxide (hereinafter, also referred to as TO) is given. Of these, a substance coated with a black conductive substance or a tin oxide-based conductive substance is preferable because various medium resistances can be adjusted depending on the type, amount, and forming method of the conductive substance.
[0058]
For example, in the case of a material whose resistance is controlled by a black conductive substance such as carbon or graphite, the resistance value can be controlled by adjusting the coating amount of the black conductive substance attached to the surface. Further, even if a material having a low resistance value is once obtained, when the material is heated in air at a temperature of 50 to 750 ° C., the resistance value increases, and a semiconductive substance having various resistance values can be easily obtained. it can.
[0059]
In the case of a material whose resistance is controlled by tin oxide or doped tin oxide, the resistance can be controlled from a low resistance to a high resistance by changing the amount of doping. Also, after forming a tin oxide or doped tin oxide layer on the surface of the core material, the resistance value can also be controlled by selecting the heating atmosphere to be oxidizing or non-oxidizing or changing the heating temperature. can do. In this way, semiconductive substances having similar resistances and having various resistance values can be easily obtained. In addition, tin oxide-based materials are resistant to heat and do not cause deterioration in physical properties even in severe molding exceeding 300 ° C. in a polyimide film forming process, so that the range of use is widened. In addition, tin oxide-based materials are nearly colorless, and if a colorless core material is used, a colorless semiconductive filler can be obtained. As a result, a black polyimide resin composition can be easily obtained by using a black agent in combination.
[0060]
Further, by controlling the surface coating method as described above, there is an advantage that the resistance value can be controlled as follows. For example, materials such as potassium titanate, tin oxide, and zinc oxide have only specific resistance values, and when controlling to various resistance values using these materials, two or more fillers having different resistance values are used. And the number of parts to be mixed had to be changed. In addition, it takes a great deal of effort to control the dispersibility and adjust the blending according to each filler, the mechanical properties differ due to the change in the blending amount, and there is only a single color. There was little freedom. However, using a material coated with the conductive substance of the present invention makes it possible to easily create a material having various resistances from a single material, and to control conductivity without changing mechanical properties and dispersibility. As a result, polyimide resins having exactly the same amount but different resistance values can be produced. Further, since the semiconductive inorganic substance has the same basic properties such as mechanical properties and dispersibility, cleaning work and switching work by changing the type become very easy. In addition, the color can be freely selected from colorless to black depending on the surface conductive treatment method, and coloring becomes easy.
[0061]
Examples of the core material (inorganic material) of the semiconductive filler coated with the conductive material used in the present invention include ceramic materials such as metals, metal oxides, metal carbides, and metal nitrides, and metal salts. For example, zinc, zinc oxide, aluminum, alumina, aluminum hydroxide, calcium, calcium carbonate, silver, chromium oxide, silicon, silicate, calcium silicate, silica, glass, titanium oxide, metal titanate, aluminum borate , Tin oxide, iron, iron oxide, copper, copper oxide, barium carbonate, barium sulfate, barium hydroxide, magnesium, magnesium hydroxide, silicon carbide, tungsten carbide, titanium carbide, aluminum nitride, silicon nitride, germanium nitride, tantalum nitride , Titanium nitride, boron nitride, mica, talc, wollastonite, talc, kaolin, clay minerals and the like.
[0062]
Of these, aluminum borate, tin oxide, calcium carbonate, silicate, calcium silicate, barium sulfate, and mica have low refractive indices and are close to the refractive index of resin, so they are transparent even when mixed into resin. Is preferred because it does not impair the color and does not cause coloring. Alumina, silica, glass, wollastonite, talc, and kaolin are also preferable because they have relatively low refractive indices and their transparency is not easily impaired even when added to a resin. The refractive index is 2.0 or less, preferably 1.8 or less, and more preferably 1.7 or less. When these are coated with a black conductive substance, a blackened semiconductive inorganic substance can be obtained, and when blended with polyimide, it is preferable because a black polyimide resin composition is easily obtained. In addition, when coated with a tin oxide-based substance, a semiconductive filler having excellent transparency can be obtained, and the polyimide resin to which the filler is added has transparency. Further, it is preferable from the viewpoint that an arbitrary color tone can be obtained by adding another coloring agent.
[0063]
On the other hand, the smaller the metal component released from the core material, the better. The amount of the free metal component is 100 ppm or less, preferably 80 ppm or less, and more preferably 50 ppm or less. Within the above range, the amount of the free metal component is small, so that the humidity dependency of the resistance value of the compounded resin is reduced, which is preferable. Further, it is preferable because the dielectric breakdown voltage is reduced.
[0064]
In addition, examples of the filler having semiconductivity by itself include titanium oxide, metal titanate, aluminum borate, tin oxide, and silicon carbide.
[0065]
In the present invention, a conductive filler can be added to the polyimide resin composition in addition to the semiconductive filler. Examples of the conductive filler include carbon black, graphite, metal powder, conductive ceramics, conductive-treated inorganic substances, and antistatic agents.
[0066]
Various types of carbon black can be used as long as they have conductivity, and examples thereof include furnace black, acetylene black, thermal black, and channel black. Above all, it is a kind of furnace black. Particularly, when carbon black called Ketjen black having a large specific surface area is used, even if the amount of carbon black is small, the resistance reduction effect is high, and other carbon black is used. This method has an advantage that the voltage dependency (the property that the resistance value changes when the voltage changes and does not exhibit the behavior according to Ohm's law) is smaller than that in the case where the voltage is changed. From this point, it is particularly preferable to use Ketjen Black.
[0067]
Examples of the metal powder include powders of copper, iron, aluminum, and SUS, and examples of the conductive ceramic include doped tin oxide and ITO.
[0068]
Examples of the inorganic substance subjected to the conductivity treatment include substances obtained by subjecting titanium oxide, metal titanate, barium sulfate, mica, or the like to a conductivity treatment with a black conductive substance, a tin oxide-based compound, or the like. As a forming method, the above-described method for forming a conductive layer of a semiconductive filler can be used.
[0069]
In the present invention, an insulating filler can be added to the polyimide resin composition in addition to the semiconductive filler. As the insulating inorganic substance, various substances such as small-diameter granular substances such as alumina and silica, plate-like and flaky substances such as mica and clay minerals, and short-fiber or whisker-like substances such as calcium carbonate are used. Insulating fillers may be added, for example, to control properties such as elastic modulus, and also assist in dispersing the conductive powder, prevent aggregation of the conductor, etc., and realize a stable resistance value. In some cases.
[0070]
The shape of the semiconductive filler, the conductive filler, and the insulating filler used in the present invention is not particularly limited, such as a granular shape, a needle shape, and a flake shape, but among them, a needle shape is preferable. When the needle-like filler is used, the resistance can be reduced while maintaining the insulating property, and a resin composition having excellent surface properties and a small linear expansion coefficient and a small hygroscopic expansion coefficient can be obtained. Further, it is possible to obtain a film or belt excellent in mechanical strength capable of realizing long-term transport characteristics with high durability and high dimensional stability by preventing tearing and other dimensional changes due to tension.
[0071]
When the filler is granular, the particle size is 1 μm or less, preferably 0.3 μm or less, more preferably 0.1 μm or less. In a molded article having a small thickness of 100 μm or less, when the granular filler is larger than 1 μm, local breakdown due to poor dispersion causes dielectric breakdown, and the surface property tends to deteriorate. On the other hand, it is preferable that the particle size of the filler is 1 μm or less, because even a little aggregation does not deteriorate the insulating property or the surface property. However, if the particle size is too small, the polyamic acid solution may thicken or become too bulky, which may hinder the compounding operation. For this reason, the particle size of the filler is preferably 0.005 μm or more. In addition, the volume resistivity of the filler is 1 × 10 3 because dielectric breakdown in the thickness direction does not easily occur even if some aggregates are present. ³ It is preferably Ω · cm or more.
[0072]
Even when the filler is acicular or scaly, for the same reason as above, the upper limit of the minor axis diameter is 1 μm, preferably 0.3 μm, more preferably 0.1 μm, and the lower limit is 0.005 μm. It is preferable that
[0073]
Next, the compounding amount of the semiconductive filler with respect to the polyimide resin is 20 to 200 parts by weight, preferably 40 to 180 parts by weight, more preferably 50 to 150 parts by weight based on 100 parts by weight of the polyimide resin. If the number is more than the above, the film becomes brittle and molding becomes difficult, and addition of a black material makes it difficult to prepare a composition having a black concentration of 0.9 or more, which is not preferable. On the other hand, if the number is less than the above-mentioned number, the resistance value is not easily reduced to a target range, which is not preferable.
[0074]
When the conductive filler is used in combination, the conductive filler can be used in an amount of 40 parts by weight or less, preferably 20 parts by weight or less, more preferably 10 parts by weight or less. It is not preferable to add 40 parts by weight or more of the conductive filler in addition to the semiconductive filler, because the resistance value becomes too low and the insulating property may be deteriorated.
[0075]
When the insulating filler is used in combination, it can be used so that the total amount of the semiconductive filler and the insulating filler is 20 to 200 parts by weight, preferably 40 to 180 parts by weight, and more preferably 50 to 150 parts by weight. . If the number is more than the above, the film is brittle and molding is difficult, and even if a black material is added, it may be difficult to prepare a composition having a black density of 0.9 or more.
[0076]
The blackening agent blended for blackening the polyimide resin used in the present invention is preferably carbon black having a volatile amount of 2.0% or more and a pH of 5.0 or less, and more preferably a volatile amount of 3.0. % Or more and pH 4.0 or less is more preferable. Since the morphology change and polarity change of the polyimide molding process are severe, carbon black aggregates in such a manner that phase separation occurs during the processing, and as a result, the black concentration of the polyimide may decrease. However, if carbon black having the above characteristics is used, aggregation of carbon black can be suppressed during processing, and therefore, particularly when chemical curing is performed using an acid anhydride and / or a tertiary amine as an imidization accelerator. Even when the morphology changes dramatically, a polyimide resin composition having a high black concentration can be obtained. Further, the primary particle size of the carbon black used in the present invention is preferably 20 μm or less from the viewpoint that the smaller the particle size, the larger the surface area of the carbon black and the more the light absorbing portion.
[0077]
In the present invention, the black density means the degree of blackness of the polyimide surface, and means a value measured using a Macbeth reflection densitometer (Macbeth RD914). The black density measured by the Macbeth reflection densitometer is preferably 1.0 or more, more preferably 1.1 or more from the following points. For example, the printer includes optical equipment, and it is desired that components used for optical processing and optical color correction are colored, particularly black, so as not to excessively reflect light. Particularly, in an electrophotographic apparatus, a patch image is transferred to a belt during machine start-up or during printing, and light is reflected to adjust image quality. In this case, if the color of the belt is bright (for example, yellow), the reflection of light is large, and it is difficult to adjust the image quality. However, if the black density is high, such a problem does not occur.
[0078]
In the present invention, the pH of carbon black is a value measured according to JIS K 6220-1, the volatilization amount of carbon black is a value measured according to JIS K 6220-1, and the primary particle size of carbon black is The black is put in chloroform and irradiated with ultrasonic waves for 20 minutes to disperse it. After the dispersion sample is fixed on the supporting film, a photograph is taken with a transmission electron microscope, and the photograph is obtained by calculating the diameter on the photograph and the magnification of the photograph. Say value.
[0079]
The reason why the black density is increased by using the carbon black having the above characteristics is generally considered as follows. When the amount of volatilization increases and the pH decreases, carbon black comes to have acidic functional groups such as OH groups and COOH groups on the surface. Such a carbon black tends to have high affinity and dispersibility for a polyamic acid having an amino group, a carboxylic acid group, a carbonyl group or a solvent thereof. In addition, since the functional group of the carbon black may react with the polyamic acid, dispersion may be promoted. In particular, in the chemical cure method using an imidization accelerator, an acid-base reaction or a bond forming reaction occurs between the imidization accelerator and the carbon black, and a reaction easily occurs between the polyamic acid and the carbon black. Become. As a result, it is considered that the dispersibility of the carbon black in the polyimide resin is increased, and the polyimide finally obtained has a high black concentration.
[0080]
The amount of carbon black added for black is 0.01 to 20 parts by weight, preferably 0.05 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the polyimide resin. Most preferably, it is 0.5 to 4 parts by weight. Since the semiconductive filler can be widely selected from colorless to black, coloring can be sufficiently performed even in a small amount of 20 parts by weight or less. When added in an amount of 20 parts by weight or more, mechanical characteristics and electrical characteristics may be deteriorated. On the other hand, if the amount is less than 0.01 part by weight, it is not preferable because coloring cannot be performed.
[0081]
As described above, the semiconductive filler alone and the semiconductive filler and other fillers are appropriately selected and adjusted within the above range, whereby high insulation properties can be maintained and the medium resistance value can be controlled. It is possible to prepare a material having low addition properties, small number of added parts, dispersed state, and small variation between samples. Further, by adding carbon black having a large volatilization amount and a high acidity and a small particle diameter, a polyimide resin composition having a high black concentration can be obtained.
[0082]
In addition, a semiconductive filler having a large amount of functional groups such as hydroxyl groups and active oxygen on the surface is excellent in dispersibility and has a strong bond with polyimide. A polyimide resin composition having a retention ratio is easily obtained. Particularly, when the polyimide resin is composed of pyromellitic dianhydride and 4,4′-diaminodiphenyl ether, the tensile elongation is 35% or more, and the tear propagation strength is It is preferable because a polyimide resin composition of 250 g / mm or more can be obtained. Further, even if a semiconductive filler is added, for example, the water absorption can be adjusted so as to be maintained at 5% or less, and the increase in water absorption can be suppressed to twice or less the original water absorption of polyimide.
[0083]
In addition to the above combinations, the filler may be subjected to a surface treatment for the purpose of forming a strong bond between the filler and the polyimide. As the surface treatment agent, for example, a silane coupling agent, a titanium coupling agent, an aluminum coupling agent, an amino acid coupling agent, or the like can be used. In the case where the resin is a reaction-curable linear polyimide resin, the surface treatment is performed to make the bond stronger, but sufficient strength can be obtained without treatment.
[0084]
As a method for dispersing the semiconductive filler or other filler to be added to the polyimide resin, various methods can be adopted.
[0085]
When the polyimide resin is solvent-soluble, a polyimide resin solution dissolved in the solvent and a dispersion liquid in which the filler is preliminarily dispersed in the solvent are prepared, and the two are mixed and dispersed by a kneader such as a stirring blade or a three-roll. A method can be taken. Conversely, a method in which a powder or pellets of a solvent-soluble polyimide is added to a dispersion obtained by preliminarily dispersing a filler in a solvent and mixed well may be used. As a method of the preliminary dispersion, for example, a method of adding a filler to a solvent and performing ultrasonic dispersion is effective. In particular, since the shape of the acicular filler may be destroyed when it is subjected to excessive shearing force, a method using ultrasonic dispersion is preferable.
[0086]
When the polyimide resin is insoluble in a solvent, a method in which the above-mentioned preliminary dispersion liquid is added to a solution of a polyamic acid which is a precursor of the polyimide, and mixing and kneading are performed in the same manner, is also possible.
[0087]
When mixing a polyamic acid and a filler, the following method can be used. For example, a method in which a filler is added in advance to a solvent for polymerizing a polyamic acid to prepare a dispersion solution of the filler, and then a diamine and an acid dianhydride, which are raw materials of the polyamic acid, are added to polymerize the polyamic acid. Can be As another method, there is a method in which a dispersion solution of a filler is added to a polyamic acid obtained by polymerization in advance and mixed. Whichever method is used, it is usually necessary to prepare a dispersion solution of the filler. Generally, the filler has a higher specific gravity than the resin, so that when the filler is added to the solvent, the filler immediately precipitates. When mixed with the polyamic acid in such a state, aggregates of the filler are formed, and there is a possibility that unevenness may be formed on the surface of the polyimide molded body or the resistance value may be locally different. In order to prevent this, when a dispersion solution of the filler is prepared, a favorable result can be obtained by adding a dispersant. Examples of the dispersant include a metal salt and a surfactant. In particular, metal salts are preferred from the viewpoint of dispersibility and heat resistance, and are selected from the group consisting of Li salts, Na salts, K salts, Rb salts, Cs salts, Be salts, Mg salts, Ca salts, Sr salts, and Ba salts. One or a combination of two or more kinds is preferable, and a Li salt, a Na salt, and a K salt are particularly preferable. For Li salt, the lattice energy is 1100 kJmol ^-1 The following Li salts are preferable, and specifically, LiF, LiCl, LiBr, LiI, LiSCN, and LiCF ₃ SO ₃ And so on. In the case of Na salt, the lattice energy is 800 kJmol ^-1 The following Na salts are preferable, and specifically, NaF, NaCl, NaBr, NaI, NaSCN, NaCF ₃ SO ₃ And so on. The lattice energy of K salt is 800 kJmol ^-1 The following K salts are preferred, and specifically, KF, KCl, KBr, KI, KSCN, KCF ₃ SO ₃ And so on. These metal salts are preferable because ions are easily dissociated at room temperature and the interaction with the filler becomes strong. However, if the lattice energy is too small, the effect of the added amount may be too large. Since these metal salts do not contain organic matter, the resin does not burn even during high-temperature drying during molding. The dispersant may be blended in a predetermined amount of 1 part by weight or less with respect to 100 parts by weight of the polyimide resin, and a sufficient effect can be obtained with about 0.01 to 0.1 part by weight. In general, in wire coating applications, the addition of a metal salt deteriorates insulation, and the addition of a metal salt to a material having a dielectric constant of 4 or higher increases ionic conductivity. Since the polyimide resin has excellent insulating properties and a dielectric constant of 4 or less, it is possible to reduce the deterioration of the insulating properties and the voltage dependence of resistance.
[0088]
As another method for obtaining particularly good dispersibility, a filler is first added to a solvent and sufficiently dispersed by an ultrasonic disperser or the like, and a diamine compound as a raw material of polyimide (polyamic acid) is added thereto. And an acid dianhydride compound to carry out a polymerization reaction. According to this method, the dispersion at the micro level is favorably maintained by ultrasonic dispersion or the like, and at the same time, the stirring is always performed from the initial dispersion of the filler to the polymerization, so that the dispersibility at the macro level is also improved. Very good.
[0089]
The polyimide resin composition of the present invention is molded according to various purposes and applications, and is used in various shapes.However, it is particularly difficult to maintain a resistance value at a constant level while maintaining insulation. This is the case where the thickness is small. In that sense, in the form of a film in a broad sense such as a film, a sheet, a belt, and a tube, particularly when the thickness is 150 μm or less, preferably 100 μm or less, a semiconductive filler, other conductive and insulating materials The mixing by mixing the conductive filler and the coloring carbon black is particularly effective.
[0090]
Hereinafter, a typical molding method of the polyimide resin composition will be described.
[0091]
When the polyimide resin is solvent-soluble, a polyimide resin solution is prepared and processed into an arbitrary shape, and then the solvent is volatilized by heating and, in some cases, under reduced pressure, to obtain a polyimide molded body.
[0092]
A similar method can be applied to the stage of polyamic acid, which is a precursor of polyimide, and this method can be applied even if the polyimide resin is not solvent-soluble. In this case, prior to heating, an acid anhydride such as acetic anhydride or a tertiary amine can be used alone or in combination as a dehydrating agent or a catalyst to promote imidization. However, acid anhydrides can not only accelerate the imidation reaction but also cause the breaking of the main chain of the polyamic acid molecular chain.Therefore, for the mechanical properties of polyimide, the combined use of acid anhydrides and tertiary amines or tertiary amines The addition of only an amine is more preferable, and a product having a higher tear propagation strength than imidization using only heat cure can be obtained. Specifically, a product having a tear propagation strength of 250 g / mm or more, and in some cases, 500 g / mm or more is obtained. The addition of the imidization accelerator is very preferable because the heating time can be reduced and the thermal degradation of the polyimide resin composition can be suppressed. In particular, since the conductivity of a semiconductive substance may be changed by heating for a long time, shortening the heating time is very important. Further, in the production method by the addition of the imidization accelerator, the orientation of the resin in the in-plane direction is more likely to proceed, and when needle-shaped or flaky tin oxide is used in combination, the filler tends to be easily oriented in a plane. is there. As a result, the amount of fillers oriented in the thickness direction is reduced, and the electrical insulation properties can be improved. Further, the portion of the electric characteristics deteriorated in the thickness direction due to moisture absorption of the fillers can be reduced. This is preferable because the humidity dependency of the resistance can be reduced. In addition, the molding time can be shortened, productivity can be dramatically improved, strength can be easily obtained during manufacturing, and brittleness can be prevented during manufacturing. These advantages of the above manufacturing method are particularly remarkable in the case of a thin polyimide molded body having a thickness of 100 μm or less.
[0093]
The following method is mentioned as an example of a specific method of molding into a film and a tubular article. A polyamide or polyimide resin solution in which a filler is dispersed is applied on an endless belt after controlling the thickness by using a T-die, a comma coater, a doctor blade, or the like. The resin solution is heated and dried by hot air or the like until self-supporting properties are developed, and then peeled off from the endless belt. A film-like molded product can be obtained by fixing both ends of the peeled semi-dry film with pins and clips and passing the film through a high-temperature heating furnace sequentially while controlling the length in the width direction. Or it is applied on a continuous sheet-like support such as a metal in the same manner, and is passed through a heating furnace to obtain a film- or sheet-shaped polyimide molded body fixed in a sheet-like form. A method in which the support sheet is peeled off from the support sheet or the support sheet is removed by means such as etching may be employed. The easiest method is to cut the film or sheet-like molded body thus obtained into a predetermined length and width and join them to obtain a tubular material such as a belt or a tube. An adhesive, an adhesive tape, or the like can be used for joining. However, since this method inevitably has a step or a cut at the joint, inconvenience may occur depending on the application.
[0094]
As a method for obtaining the tubular material, a polyamide or polyimide resin solution is applied to the inner surface or the outer surface of the cylindrical mold, and the solvent is volatilized by heating or drying under reduced pressure. Alternatively, it may be peeled off once, fitted into the outer circumference of another mold for finally defining the inner diameter, and heated to the final firing temperature. In applying the resin solution to the cylindrical mold, it is also effective to rotate the mold in order to alleviate thickness variation due to dripping of the resin solution. The final baking temperature must be appropriately selected depending on the structure of the polyimide and the heat resistance of the carbon to be added. However, when heating and baking from a polyamic acid state in a non-thermoplastic polyimide, the temperature is generally about 350 ° C. to 450 ° C. In the case of a plastic polyimide, the preferred range is between -100 ° C and -20 ° C with respect to the glass transition temperature of the polyimide.
[0095]
When the polyimide molded article of the present invention is used as a member of an electrophotographic apparatus, in order to improve the toner releasability and transferability, and the cleaning property of the toner, a fluororesin outermost layer whose surface is controlled in conductivity is used. Should be formed. Examples of the fluororesin include polytetrafluoroethylene (hereinafter, PTFE) and tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (hereinafter, PFA). As the additive for controlling conductivity, those described above as the additive for controlling conductivity of polyimide can be used. The outermost layer may be formed by coating or laminating a film, for example, and a spray coating method using these materials as a dispersion is generally used.
[0096]
The polyimide film and the polyimide tubular article prepared using the polyimide resin composition of the present invention can be used for various applications according to the conventional semiconductive polyimide film and polyimide tubular article. In particular, because of its excellent mechanical properties and electrical properties, it can be preferably used as a belt for image transfer and intermediate transfer in an electrophotographic apparatus, a belt for conveying a printing sheet which also serves as the intermediate transfer, a belt for fixing and the like. The type of the electrophotographic apparatus mentioned here is not particularly limited, and may be any of a copier, a laser printer, a video printer, a facsimile, a multifunction machine thereof, and the like. Further, the model may be any of a monochrome image, a color image, a full-color image, and the like, and the type of the toner, the transfer method, the type of the recording medium, and the like are not particularly limited. When used in an electrophotographic apparatus, a printing sheet such as paper or a plastic sheet can be used as appropriate as the recording sheet. As a recording agent for forming an image on a recording sheet, a recording agent capable of performing an adhesion process via static electricity can be used as appropriate. In addition, the polyimide film and the polyimide tubular article of the present invention have a volume resistance value and a surface resistance value controlled to a medium resistance value, and have very small dispersion, so that they are used as an intermediate transfer belt or a transfer conveyance belt of a color copying machine. In such a case, it is possible to transfer a good image to a recording sheet without deformation and transfer unevenness of the toner image, and to maintain the performance of separating a conveyed recording sheet satisfactorily for a long period of time. Further, when used as a fixing belt, since it has semi-conductivity, charging can be prevented, and excellent fixing properties can be realized. In addition, when used for components for optical processing and optical color correction, including optical equipment such as electrophotographic devices, specifically, when a machine is started or during printing, a patch image is transferred and light is reflected. When used for a transfer or intermediate transfer belt in which the image quality is adjusted by adjusting the image quality, the polyimide film and the polyimide tubular article of the present invention have excellent blackness, so that the light reflection is constant and the image quality is adjusted. Easier to do.
[0097]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.
[0098]
(Physical property evaluation method)
Next, a method for evaluating the physical properties of the resin composition will be described. In addition, the evaluation of the physical properties was performed by cutting a film-shaped sample after molding the tubular article.
[0099]
The black density of the film sample was measured using a Macbeth reflection densitometer (Macbeth RD914).
[0100]
The measurement of the resistance values of the film sample and the filler was performed as follows. The sample was prepared in the following conditions: (1) an environment (LL) at a temperature of 10 ° C. and a humidity of 15% Rh, (2) an environment (NN) at a temperature of 23 ° C. and a humidity of 55% Rh, and (3) an environment at a temperature of 30 ° C. and a humidity of 80% Rh. (HH) for 24 hours, and measure the volume resistance and surface resistance at 100 V using the digital ultra-high resistance / micro ammeter R8340 manufactured by Advantest Corporation and the HR probe manufactured by Mitsubishi Chemical Corporation under the environment. did. For film samples, measurements were also performed at 1000V.
[0101]
The environmental dependence of the resistance value refers to the value of the ratio (R1 / Rh) of the volume resistance value Rl at low temperature and low humidity (LL) to the volume resistance value Rh at high temperature and high humidity (HH), and the voltage dependence of the resistance value. Is the volume resistance R when 100 V is applied. _100V And the volume resistance R when 1000 V is applied _1000V And the ratio (R _100V / R _1000V ) Means the value. When these values are in the range of 0.3 to 30, a material having small dependence (small), and when these values are in a range of 0.01 to 0.3 or 30 to 100, a material having medium dependence ( Medium), when the value was 0.01 or less or 100 or more, a material (large) having poor dependence was determined.
[0102]
The insulation measurement in the thickness direction of the film sample was performed as follows. The film was allowed to stand in an environment (NN) at a temperature of 23 ° C. and a humidity of 55% Rh for 24 hours, and the insulation was measured under a YSS-type electric breakdown tester manufactured by Yasuda Seiki Seisakusho under the environment.
[0103]
The measurement of the tensile elastic modulus and the tensile elongation of the film sample was performed in accordance with ASTM D882. The measurement of the tear propagation strength of the film sample was performed in accordance with ASTM D1938.
[0104]
Next, examples and comparative examples will be described.
[0105]
(Example 1)
Dimethylformamide (hereinafter, DMF) solution of polyamic acid obtained by using 4,4'-diaminodiphenyl ether as an aromatic diamine and pyromellitic dianhydride (hereinafter, PMDA) as an aromatic tetracarboxylic dianhydride 75 g (solid content concentration 18.5%, solution viscosity 3,000 poise) was prepared. Next, as a semiconductive filler, carbon-coated potassium titanate (Denthol BK400HR: Otsuka Chemical Co., Ltd .: specific gravity 3.15 g / cm) ³ , Volume resistance value 5.0 × 10 ⁵ 8.42 g of Ω · cm, minor axis diameter of 0.45 μm, major axis diameter of 15 μm, ion elution amount of 500 to 10,000 ppm), carbon black having a volatile content of 8.0%, pH 3.0, and a primary particle diameter of 13 nm (carbon black) 0.67 g of Mitsubishi Chemical Corporation: # 2650) was collected and dispersed in DMF in an amount 8 times the total weight of these additives to prepare an additive dispersion.
[0106]
The polyamic acid solution and the additive dispersion were added and kneaded. Before casting the obtained dope into a tubular film, acetic anhydride / isoquinoline / DMF was mixed with a solution consisting of 9.03 g / 11.4 g / 15.6 g, and then cast on an aluminum foil. Heat treatment was performed at 140 ° C./600 seconds, 275 ° C./40 seconds, and 400 ° C./93 seconds to obtain a polyimide film of about 75 μm. In the case of obtaining a tubular article, it was prepared by coating the inside or outside of a metal cylinder having a mirror surface instead of the aluminum foil. The amounts of the semiconductive filler and carbon black in the tubular material are 50 parts by weight and 4 parts by weight, respectively, based on 100 parts by weight of the solid content of the polyimide. Table 2 shows the characteristic values. Physical properties such as electrical properties and mechanical properties of the tubular article may be considered to be the same as those of the film. The polyimide was peeled off from the aluminum foil and the metal tube after heating at 140 ° C.
[0107]
As a result of evaluating the physical property values of the polyimide film alone (excluding the filler) polymerized by the same method as described above, the linear expansion coefficient was 21 ppm, the hygroscopic expansion coefficient was 16 ppm, the tensile modulus was 2.9 GPa, the elongation was 70%, and the tear propagation strength was measured. It was 450 g / mm and the water absorption was 2.5%.
[0108]
(Examples 2 to 8)
A polyimide film was obtained in the same manner as in Example 1, except that the semiconductive filler and the carbon black were compounded in the number of parts shown in Table 1 in place of the carbon-coated potassium titanate. Table 2 shows the characteristic values.
[0109]
The details of the filler described in Table 1 are as follows. Tin oxide-coated aluminum borate refers to Pastlan-TYPEV-KK006 manufactured by Mitsui Kinzoku Co., Ltd., carbon-coated mica refers to BK400M manufactured by Otsuka Chemical Co., Ltd., and titanium oxide refers to FTL300 manufactured by Ishihara Sangyo Co., Ltd. Were all <50 ppm.
[0110]
The carbon black used in Examples 1-4, 9 and 10 was # 2650 manufactured by Mitsubishi Chemical Corporation, and the carbon black used in Examples 5 and 6 was # 1000 manufactured by Mitsubishi Chemical Corporation, Example 7, The carbon black used for No. 8 was FW200 manufactured by Degussa Japan KK, and the carbon black used for Comparative Examples 2 to 4 was # 2600 manufactured by Mitsubishi Chemical Corporation.
[0111]
(Example 9)
The DMF solution of polyamic acid described in Example 1 was polymerized by dissolving 3 equivalents of 4,4'-diaminodiphenyl ether as an aromatic diamine in DMF, adding 4 equivalents of PMDA, and further adding 1 equivalent of paraphenylenediamine. A polyimide film was obtained in the same manner as in Example 1, except that the polyamic acid was changed to a DMF solution (solid content: 18.5%, solution viscosity: 3,000 poise). Table 2 shows the characteristic values.
[0112]
As a result of evaluating the physical properties of the polyimide film alone polymerized in this way, the linear expansion coefficient was 8 ppm, the hygroscopic expansion coefficient was 9 ppm, the tensile elasticity was 4 GPa, the elongation was 70%, the tear propagation strength was 450 g / mm, and the water absorption was 2.1%. there were.
[0113]
(Example 10)
The DMF solution of the polyamic acid described in Example 1 was dissolved in DMF by adding 1 equivalent of 4,4'-diaminodiphenyl ether and 1 equivalent of paraphenylenediamine as aromatic diamine, then adding 1 equivalent of TMHQ, and further adding 1 equivalent of PMDA. A polyimide film was obtained in the same manner as in Example 1 except that the DMF solution of the polymerized polyamic acid was changed to a DMF solution (solid content concentration: 18.5%, solution viscosity: 3,000 poise). Table 2 shows the characteristic values.
[0114]
As a result of evaluating the physical property values of the polyimide film alone polymerized in this way, the linear expansion coefficient was 9 ppm, the hygroscopic expansion coefficient was 5 ppm, the tensile elasticity was 6 GPa, the elongation was 30%, the tear propagation strength was 450 g / mm, and the water absorption was 1.2%. there were.
[0115]
As a result of measuring the black density of the polyimide films of Examples 1 to 10 obtained as described above, they were all 1.0 or more, and were extremely excellent in blackness. The volume resistance under the NN condition was 1 × 10 ⁹ ~ 1 × 10 ^Thirteen The resistance was adjusted to a medium resistance region of Ω · cm, and the insulating properties were all excellent at 15 kV / mm or more.
[0116]
Further, the ratio of the volume resistance under the LL and HH conditions was in the range of 0.3 to 30, and the environment dependence of the volume resistance was small. In all cases except Example 3, the ratio of the volume resistance measured at 100 V and 1000 V was in the range of 0.3 to 30, and the voltage dependence of the volume resistance was small. However, also in Example 3, the ratio of the volume resistance measured at 100 V and 1000 V was in the range of 0.1 to 100, and the voltage dependence of the volume resistance was not bad. Further, as a result of measuring the volume resistance value at 100 V of the five samples prepared by the same operation as above, the difference between the maximum value and the minimum value was three times or less, and the variation between the samples was very small. Also, the variation within the same sample was very small, not more than three times.
[0117]
In Examples 1 to 10, the ratio of the volume resistance value due to the difference (5 parts by weight) in the number of added semiconductive fillers was 3 times or less, and the dependence of the volume resistance value on the number of added portions (blending) was small.
[0118]
The tensile modulus of the film was superior to that of the product without the filler, the elongation was maintained at 50% or more, and the tear propagation strength was maintained at 50% or more. The coefficient of linear expansion and the coefficient of hygroscopic expansion were several ppm lower than those without filler. It is considered that this result is because the shape of the semiconductive filler is acicular.
[0119]
The tensile modulus increased in the order of Example 1, Example 9, and Example 10. This is because the tensile modulus of the base resin increases in this order.
[0120]
(Comparative Example 1)
Without using carbon black, conductive tin oxide-coated acicular titanium oxide (FT3000: Ishihara Sangyo Co., Ltd .: specific gravity 4.4 g / cm) ³ , Volume resistance <10 ³ Ω · cm) was obtained in the same manner as in Example 1 except that a dispersion was prepared by dispersing 2.78 g. The amount of the filler in the tubular material is 20 parts by weight based on 100 parts by weight of the solid content of the polyimide. Table 2 shows the characteristic values.
[0121]
(Comparative Example 2)
0.67 g of carbon black (# 2600: Mitsubishi Chemical Corporation: volatile matter 1.8%, pH 6.5, primary particle diameter 13 nm), conductive tin oxide-coated needle-like titanium oxide (FT3000: Ishihara Sangyo Co., Ltd.): Specific gravity 4.4 g / cm ³ , Volume resistance <10 ³ (Ω · cm) was obtained in the same manner as in Example 1 except that 2.78 g of a dispersion was prepared by dispersing the dispersion. The amounts of carbon black and filler in the tubular material are 4 parts by weight and 30 parts by weight based on 100 parts by weight of the solid content of polyimide. Table 2 shows the characteristic values.
[0122]
(Comparative Example 3)
Except that 0.67 g of carbon black (# 2600: Mitsubishi Chemical Corporation: volatile matter 1.8%, pH 6.5, primary particle diameter 13 nm) and 8.42 g of carbon-coated potassium titanate were dispersed to prepare a dispersion. In the same manner as in Example 1, a polyimide tubular article was obtained. The amounts of carbon black and filler in the tubular material are 4 parts by weight and 50 parts by weight based on 100 parts by weight of the solid content of polyimide. Table 2 shows the characteristic values.
[0123]
(Comparative Example 4)
A dispersion liquid was prepared by dispersing 4.17 g of carbon black (# 2600: Mitsubishi Chemical Corporation: volatile matter 1.8%, pH 6.5, primary particle diameter 13 nm) without using a semiconductive filler. Except for the above, a polyimide tubular article was obtained in the same manner as in Example 1. The blending amount of carbon black in the tubular material was 30 parts by weight based on 100 parts by weight of the solid content of polyimide. Table 2 shows the characteristic values.
[0124]
The black densities of the polyimide resins of Comparative Examples 1 to 3 obtained as described above were 1.0 or less, and the black densities were extremely inferior to those of Examples 1 to 10. Further, although only the type of carbon black is different between Comparative Example 3 and Example 1, the black density was significantly reduced by 0.3 only by changing to carbon black having a low volatile content and a high pH.
[0125]
The volume resistance value of NN in the polyimide resins of Comparative Examples 1, 2, and 4 was adjusted to the target medium resistance region, but the resistance value was extremely low at HH. Further, the ratio of the volume resistance value due to the difference in the number of added fillers (5 parts by weight) was three times or more, and the dependence of the volume resistance value on the number of added parts was large. Further, the ratio of the volume resistance values of LL and HH was 1000 times or more, and the environment dependence of the volume resistance value was very large. The ratio of the volume resistance measured at 100 V and 1000 V was 100 times or more, and the voltage dependence of the volume resistance was large. Further, as a result of measuring the volume resistance value at 500 V of the five samples manufactured by the same operation as above, the difference between the maximum value and the minimum value was three times or more, and the variation between the samples was very large. The variation within the same sample was three times or more, which was very large.
[0126]
In addition, a film prepared by the same formulation as in this comparative example but not by chemical curing but by heat curing (150 ° C./30 minutes, 200 ° C./30 minutes, 300 ° C./30 minutes, 400 ° C./30 minutes) An extremely long molding time was required as compared with those formed by curing, and those containing a large amount of filler were very brittle both during and after molding.
[0127]
[Table 1]

[0128]
[Table 2]

[0129]
【The invention's effect】
In the polyimide resin composition of the present invention, a polyimide film, and a polyimide tubular material, the black density is high, the insulating property is high, the medium resistance is high, the number of added parts, the dispersion state, the variation between samples is small, and the resistance value is small. It has little environmental dependence and voltage dependence, has excellent mechanical properties, and has excellent antistatic properties due to transport and transferability and fixing properties in electrophotographic machines.

Claims (14)

Based on 100 parts by weight of the polyimide resin, 20 to 200 parts by weight of a semiconductive filler, 0.01 to 20 parts by weight of carbon black having a volatilization amount of 2.0% or more and a pH of 5.0 or less, and a volume resistance value Is in the range of 1 × 10 ⁶ to 1 × 10 ¹⁵ Ω · cm, and the black density is 1.0 or more. The polyimide resin composition according to claim 1, wherein the carbon black has a volatilization amount of 3.0% or more and a pH of 4.0 or less. The polyimide resin composition according to any one of claims 1 to 2, wherein the carbon black has a primary particle size of 20 nm or less. The polyimide resin composition according to any one of claims 1 to 3, wherein an addition amount of the carbon black is 0.1 to 5 parts by weight. The polyimide resin composition according to any one of claims 1 to 4, wherein the amount of the semiconductive filler added is 40 to 180 parts by weight. The said black density is 1.1 or more, The polyimide resin composition in any one of Claims 1-5 characterized by the above-mentioned. The polyimide resin composition according to any one of claims 1 to 6, wherein the semiconductive filler is a semiconductive filler coated with a black conductive material. The semiconductive filler is indium-tin composite oxide, antimony-doped tin oxide, niobium-doped tin oxide, tantalum-doped tin oxide, fluoride-doped tin oxide, or a semiconductive filler coated with a tin oxide-based tin oxide material. The polyimide resin composition according to any one of claims 1 to 6, wherein The polyimide resin composition according to any one of claims 1 to 6, wherein the semiconductive filler is titanium oxide, metal titanate, aluminum borate, tin oxide, or silicon carbide. The polyimide resin composition according to claim 1, wherein the semiconductive filler has a volume resistance of 1 × 10 ³ to 1 × 10 ¹⁰ Ω · cm. The polyimide resin composition according to any one of claims 1 to 10, wherein the polyimide resin composition is obtained by adding an acid anhydride and / or a tertiary amine as an imidization accelerator, followed by heating and baking. A polyimide film prepared using the polyimide resin composition according to claim 1. A polyimide tubular article prepared using the polyimide resin composition or film according to claim 1. 14. The polyimide tubular article according to claim 13, which is used for any one of a transfer belt, an intermediate transfer belt, a transfer fixing belt, and a fixing belt of an electrophotographic apparatus.