JP2004131659A - Polyimide resin composition and molded polyimide article made thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyimide resin composition keeping various excellent properties of polyimide resins, especially electrical insulation and capable of controlling the volume resistivity to an intermediate level by using carbon black and provide a molded polyimide article produced by using the composition. <P>SOLUTION: The polyimide resin composition and the molded polyimide article are produced by compounding a polyimide resin with at least a high-resistance carbon black. The volume resistivity of the composition is 1×10<SP>6</SP>to 1×10<SP>16</SP>Ωcm. The high-resistance carbon black has a volume resistivity of 1×10<SP>2</SP>to 1×10<SP>10</SP>Ωcm measured on a specimen compressed at 490 N/cm<SP>2</SP>and is compounded in an amount of 20-100 pts. wt. based on 100 pts. wt. of the polyimide resin. <P>COPYRIGHT: (C)2004,JPO

Description

【００５７】
なお、群（２）中、Ｘは、それぞれ独立して、ハロゲン原子、または、−ＣＨ_３、−ＯＣＨ_３、−Ｏ（ＣＨ_２）_ｎＣＨ_３、−（ＣＨ_２）_ｎＣＨ_３、−ＣＦ_３、−ＯＣＦ_３からなる群から選択される少なくとも一種の１価の有機基を示す。また、Ａは、それぞれ独立して、−Ｏ−、−Ｓ−、−ＣＯ−、−（ＣＨ_２）_ｎ−、−ＳＯ_２−、−Ｎ＝Ｎ−からなる群から選択される少なくとも一種の２価の基を示す。また、ｎは１以上の整数を示し、ｍは１〜５の何れかの整数を示す。また、これら芳香族系ジアミン化合物は、単独で用いても良いし、２種以上を組み合わせて用いてもよい。
【００５８】
上記ポリアミド酸の合成に用いられるテトラカルボン酸二無水物（以下、説明の便宜上、酸二無水物と略す）は、特に限定されるものではないが、例えば、次に示す式（３）で表される酸二無水物、すなわち１分子中に芳香環を１個以上有する芳香族系酸二無水物を挙げることができる。
【００５９】
【化２】

【００６０】
ただし、上記式（３）中、Ｒ^２は、次に示す群（４）から選択される、芳香環を含む４価の有機基を示す。
【００６１】
【化３】

【００６２】
なお、群（４）中、ｎは１以上の整数を示す。また、これら芳香族系酸二無水物は、単独で用いても良いし、２種以上を組み合わせて用いてもよい。
【００６３】
また、後述するように、上記ジアミン化合物および酸二無水物を適宜選択して組み合わせることにより、得られる反応硬化型直鎖状ポリイミド樹脂に、様々な特性を付与することが可能となる。それゆえ、本発明にかかるポリイミド樹脂組成物またはポリイミド成形物の用途や加工法等に応じて、上記各モノマー成分を選択して、所望の物性を有するポリイミド樹脂を合成すればよい。
【００６４】
＜モノマー成分の組み合わせの具体例＞
モノマー成分の組み合わせの例としては、特に限定されるものでは無いが、本実施の形態では、次に示す（１）〜（３）の例を挙げることにより、本発明をより詳細に説明する。
【００６５】
まず、モノマー成分の組み合わせの一例として、（１）熱可塑性のポリイミド樹脂を合成できる組み合わせを挙げることができる。この例では、ジアミン化合物として、屈曲鎖を多く（好ましくは２つ以上）含む条件か、アミノ基をメタ位に有する条件の少なくとも一方の条件を満たす芳香族ジアミンを用い、酸二無水物として、１分子内に芳香環を２つ以上含む芳香族系酸二無水物を用いる。これにより、熱可塑性のポリイミド樹脂を得ることができる。このような熱可塑性のポリイミド樹脂を用いれば、加熱溶融による成形が可能なポリイミド樹脂組成物を得ることが可能となる。
【００６６】
この（１）の例における各モノマー成分の組み合わせとしては、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挙げることができる。
【００６７】
また、モノマー成分の組み合わせの他の例としては、（２）吸水率が比較的低い（低吸水性の）ポリイミド樹脂を合成できる組み合わせを挙げることができる。この例では、酸二無水物として、２つ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有する芳香族系化合物を用いる。具体的には、次に示す式（５）、式（６）または式（７）
【００６８】
【化４】

【００６９】
（式中、ｎは１以上の整数を示す。）
【００７０】
【化５】

【００７１】
【化６】

【００７２】
で表される芳香族系酸二無水物の少なくとも何れかを用いればよい。また、この例で用いるジアミン化合物としては、イミド基の含有率を下げるために、比較的長鎖の化合物を用いることが好ましい。具体的には、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。
【００７３】
一般に、ポリイミド樹脂は、イミド基を有することにより吸水率は比較的高いが、上記各モノマー成分を用いて得られるポリイミド樹脂は、低吸水性となる。そのため、得られるポリイミド樹脂組成物およびポリイミド成形物も低吸水性とすることができる。
【００７４】
ただし、ジアミン化合物についても酸二無水物についても、長鎖かつ屈曲鎖を多数有する構造は、前記（１）で述べたように、ポリイミド樹脂に熱可塑性を発現する条件でもある。それゆえ、ポリイミド樹脂に十分な耐熱性を与えたい場合には好ましくないこともあり得る。
【００７５】
そこで、モノマー成分の組み合わせのさらに他の例として、（３）熱可塑性および低吸水性の少なくとも一方と、ある程度の耐熱性との双方を実現したポリイミド樹脂を得たい場合には、長鎖かつ直線的構造を全体的または部分的に有する化合物を上記各モノマー成分の少なくとも何れかとして用いることが適当である。例えば、このような酸二無水物としては、次に示す式（８）で表される構造を有する芳香族系酸二無水物、すなわちｐ−フェニレンビス（トリメリット酸モノエステル酸無水物）（ＴＭＨＱ）を挙げることができる。
【００７６】
【化７】

【００７７】
上記ＴＭＨＱは、屈曲鎖を含むものの全体は概ね直線的な構造となっており、その結合数が多いにも関わらず、比較的剛直なポリイミド樹脂を形成することが可能となっている。このＴＭＨＱを酸二無水物として用いてポリイミド樹脂を合成すれば、加熱や吸湿による寸法変化の少ない、すなわち良好な耐熱性と良好な低吸水性との双方を満たすポリイミド樹脂を得ることができる。例えば、上記ＴＭＨＱを用いて合成されたポリイミド樹脂の一例では、線膨張係数１５ｐｐｍ以下、吸水率１．５％以下、吸湿膨張係数１０ｐｐｍ以下の物性を実現することができる。
【００７８】
同様に、長鎖かつ比較的剛直な構造を有するジアミン化合物としては、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いだ構造を有する化合物を好ましく挙げることができ、より具体的には、例えば、４，４’−ビスアミノフェノキシビフェニルを挙げることができる。
【００７９】
このように、酸二無水物およびジアミン化合物の少なくとも一方として、長鎖かつ直線的構造を全体的または部分的に有し、比較的剛直な構造を有する化合物を選択して組み合わせることにより、吸水率を比較的低く抑えることができ、かつ、顕著な熱軟化性の発現も抑えることのできるポリイミド樹脂を得ることができる。
【００８０】
もちろん、上述した特定の構造を有する化合物のみでなく、汎用の化合物、例えば、ジアミン化合物であれば、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や、酸二無水物であれば、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等を適宜選択して、上記特定の構造を有する化合物と共重合することにより、得られるポリイミド樹脂の特性を適宜設計することが可能となる。
【００８１】
＜モノマー成分のシーケンスコントロール＞
また、所望の物性を有するポリイミド樹脂を合成する手法としては、上述したモノマー成分の組み合わせる手法以外にも、シーケンスコントロールによる手法が挙げられる。この手法では、各モノマー成分（ジアミン化合物および酸二無水物）の種類や各モノマー成分の組成比（重合比）が同じであっても、重合後のポリイミド樹脂において、各モノマー成分由来の構造の配列（シーケンス）を制御（シーケンスコントロール）する。
【００８２】
一般に、ポリイミド樹脂の線膨張係数は、銅等の金属に比べて大きくなる。そこで、上記シーケンスコントロールにより、比較的小さな線膨張係数を有するポリイミド樹脂を合成することができ、得られるポリイミド樹脂組成物やポリイミド成形物の線膨張係数も小さくすることができる。
【００８３】
具体的には、例えば、ジアミン化合物として、４，４’−ジアミノジフェニルエーテルおよびパラフェニレンジアミンを用い、酸二無水物として、ピロメリット酸二無水物を用いるとする。ここで、ポリイミド樹脂を合成する手順として、これら３種のモノマー成分を混合して反応させ、ランダムに共重合する手順と、先に、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と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して反応させる手順とを実施したとする。この場合、前者のランダムな共重合手順に比べて、後者のシーケンスコントロールした手順の方が、線膨張係数を小さくしたポリイミド樹脂を得ることができる。
【００８４】
このように、本発明で好ましく用いられる反応硬化型直鎖状ポリイミド樹脂では、２種類のモノマー成分として、種々の化合物を適宜選択して組み合わせて用いたり、シーケンスコントロールしたりすることで、所望の物性を有するポリイミド樹脂を合成することができる。
【００８５】
中でも、本発明では、後述するように、高抵抗カーボンブラックをポリイミド樹脂に配合する。そのため、本発明で用いられるポリイミド樹脂は、ポリイミド樹脂単体で用いる場合に比較してより高い靭性を有することが非常に好ましい。ポリイミド樹脂そのものの靭性が十分でないと、無機物（高抵抗カーボンブラック等）の配合により必然的に靭性が低下するため、実用に供することができなくなる可能性が生じる。
【００８６】
上記靭性を向上した反応硬化型直鎖状ポリイミド樹脂としては、特に好ましい一例として、４，４’−ジアミノジフェニルエーテルおよびピロメリット酸二無水物の組み合わせを用いて合成されるポリイミド樹脂を挙げることができる。このポリイミド樹脂は、十分な耐熱性と高い靭性を兼ね備えており、さらに広い範囲の加工条件でその特性を維持することができるという優れた特性を有する。
【００８７】
＜ポリアミド酸の合成＞
上記各モノマー成分を用いたポリアミド酸の重合方法（合成方法）は特に限定されるものではないが、例えば、アルゴン、窒素等の不活性雰囲気中において、ジアミン化合物を有機溶媒中に溶解またはスラリー状に分散（懸濁）させた後に、酸二無水物を添加して各モノマーを反応させる方法を好ましく用いることができる。この重合方法では、上記酸二無水物の添加は固体状態で直接添加してもよいし、酸二無水物を有機溶媒に溶解した酸二無水物溶液、または酸二無水物を有機溶媒に分散（懸濁）させてスラリー状とした酸二無水物分散液（懸濁液）として添加してもよい。この重合方法では、重合されたポリアミド酸が有機溶媒に溶解されてなるポリアミド酸溶液が得られる。
【００８８】
上記の製造方法では、ジアミン化合物と酸二無水物とを実質的に当モルに調節すれば、酸成分対ジアミン成分が１：１のポリアミド酸とすることができる。このとき、酸二無水物およびジアミン化合物の何れも１種類のみ用いても良いし、任意の２種類以上を適宜組み合わせて用いてもよい。酸二無水物およびジアミン化合物の何れも１種類のみでそれぞれが実質的に当モルの場合、酸成分１種・ジアミン成分１種のポリアミド酸とすることができる。一方、酸二無水物およびジアミン化合物の少なくとも一方が２種類以上であり、それぞれが実質的に当モルの場合、酸成分およびジアミン成分の少なくとも一方が２種以上のポリアミド酸共重合体を得ることができる。
【００８９】
上記ポリアミド酸の重合方法に用いられる有機溶媒は、有機極性溶媒であってポリアミド酸を溶解可能とするものであれば特に限定されるものではない。具体的には、例えば、Ｎ，Ｎ−ジメチルホルムアミド、Ｎ，Ｎ−ジエチルホルムアミドなどのホルムアミド系溶媒；Ｎ，Ｎ−ジメチルアセトアミド、Ｎ，Ｎ−ジエチルアセトアミドなどのアセトアミド系溶媒；Ｎ−メチル−２−ピロリドン、Ｎ−ビニル−２−ピロリドンなどのピロリドン系溶媒；テトラヒドロフラン、ジオキサン、ジオキソラン等のエーテル系溶媒；等を挙げることができる。
【００９０】
これら有機極性溶媒は単独で用いても良いし、２種類以上を適宜混合した混合溶媒として用いてもよい。さらに、ポリアミド酸からポリイミド樹脂を合成する後段の工程を効率的に進める関係上、ポリアミド酸を良好に溶解し、かつ、なるべく沸点の低い溶媒を選択すると有利である。
【００９１】
上記ポリアミド酸の重合方法における反応条件は特に限定されるものではないが、ジアミン化合物と酸二無水物との反応温度は８０℃以下であればよく、０℃〜５０℃の範囲内であることが好ましい。また、ジアミン化合物と酸二無水物との反応時間は特に限定されるものではなく、下限３０分から上限５０時間の範囲内で任意に設定することができる。重合反応が進行するにつれてポリアミド酸が生成するため、反応液の温度および粘度が上昇する。それゆえ、反応温度の上昇に合わせて反応容器を冷却したり、粘度の上昇に合わせて撹拌速度を遅くしたりして上記反応条件を適宜変化させてもよい。
【００９２】
＜ポリアミド酸のイミド化＞
本発明で好ましく用いられる反応硬化型直鎖状ポリイミド樹脂は、上記ポリアミド酸のアミド部位を脱水閉環する（イミド化する）ことで合成される。このイミド化の方法は特に限定されるものではなく、熱的な方法を用いても良いし化学的な方法を用いても良い。
【００９３】
熱的に脱水閉環する方法（熱キュア法）は、ポリアミド酸に熱を加えて脱水閉環を生じさせる方法であれば特に限定されるものではない。例えば、上記の重合方法により得られたポリアミド酸溶液を８０℃〜３００℃の範囲内で加熱してもよいし、上記ポリアミド酸溶液をフィルム状支持体に流延または塗布し、８０℃〜３００℃で熱処理してもよい。上記フィルム状支持体としては、例えば、ガラス板、金属板、ＰＥＴ（ポリエチレンテレフタレート）製板等を用いることができる。
【００９４】
さらに、フッ素樹脂コート等の離型処理を施した容器に、直接ポリアミド酸溶液を入れ、減圧下で加熱乾燥させることで反応硬化型直鎖状ポリイミド樹脂を得ることもできる。このときの加熱条件としては、加熱温度は８０℃〜３００℃の範囲内であることが好ましく、１００℃〜２５０℃の範囲内がより好ましく、１５０℃〜２５０℃の範囲内がさらに好ましい。加熱時間は処理量や加熱温度により異なるが、一般には最高温度に達してから１分〜５時間の範囲が好ましい。
【００９５】
化学的に脱水閉環する方法（化学キュア法）では、上記ポリアミド酸溶液に、所定量のイミド化促進剤を加え、熱キュア法と同様に加熱処理すればよい。上記イミド化促進剤としては、酸無水物および三級アミンの少なくとも一方を挙げることができる。
【００９６】
上記酸無水物としては、無水酢酸、無水プロピオン酸などを用いることができるが特に限定されるものではない。上記三級アミンとしては、ピリジン、イソキノリン、トリエチルアミン、トリメチルアミン、イミダゾール、ピコリン等を用いることができるが特に限定されるものではない。これらイミド化促進剤の添加量は特に限定されるものではなく、イミド化を促進できる量であればよい。
【００９７】
本発明にかかるポリイミド樹脂組成物では、後述する高抵抗カーボンブラックを用いることにより、化学キュア法のような変化の激しい環境下でも、反応硬化型直鎖状ポリイミド樹脂と親和性を維持することができる。そのため、ポリイミド樹脂組成物中での高抵抗カーボンブラックの凝集は有効に抑制または回避され、得られるポリイミド樹脂組成物やポリイミド成形物の物性を向上させることができる。
【００９８】
しかも、化学キュア法では、熱キュア法に比べて、ポリアミド酸に対する加熱時間を減らすことができる。そのため、後述する高抵抗カーボンブラックをポリアミド酸に添加してからイミド化する場合でも、当該高抵抗カーボンブラックが過剰に熱せられて劣化することを抑制することができるために非常に好ましい。
【００９９】
特に、高抵抗カーボンブラックとして、後述するグラフト化カーボンブラック等を用いる場合、導電性を有する被膜が長時間の加熱によって導電性の変化を引き起こす。そのため、化学キュアのように加熱時間を短縮できることは、得られるポリイミド樹脂組成物またはポリイミド成形物の体積抵抗値を安定化させる点からも非常に重要となる。また、化学キュア法では、加熱時間が短いために、ポリイミド樹脂（またはポリアミド酸）そのものの熱劣化や、ポリイミド樹脂（またはポリアミド酸）と高抵抗カーボンブラックとの反応による劣化を抑制することができるために好ましい。
【０１００】
このように、化学キュア法によりポリアミド酸のイミド化を進めることで、機械特性に優れたポリイミド樹脂を得ることができる。具体的には、ポリイミド樹脂の引き裂き伝播強度を向上させることができる。このとき実現可能な引き裂き伝播強度としては、少なくとも２．４５Ｎ／ｍｍ（２５０ｇｆ／ｍｍ）以上を実現することができ、好ましくは４．９０Ｎ／ｍｍ（５００ｇｆ／ｍｍ）以上を実現することができる。
【０１０１】
なお、上記酸無水物は、イミド化の促進だけでなく、ポリアミド酸の分子鎖主鎖の切断を引き起こす可能性がある。それゆえ、得られるポリイミド樹脂の機械的特性を向上させるためには、酸無水物と三級アミンとを併用するか、三級アミンのみを用いることがより好ましい。
【０１０２】
本発明にかかるポリイミド樹脂組成物は、このようにして得られたポリイミド樹脂に、少なくとも、後述する高抵抗カーボンブラックを特定量配合するか、前駆体であるポリアミド酸に高抵抗カーボンブラックを特定量配合することによって得られる。また、本発明にかかるポリイミド成形物は、このポリイミド樹脂組成物を用いて成形される。なお、ポリイミド成形物に関しては後述する。
【０１０３】
＜ポリイミド樹脂の他の合成方法＞
また、本発明では、酸二無水物とジイソシアナートとを反応させる合成することで、ポリアミド酸を経由せずに直接ポリイミドを重合してもよい。この方法で用いられる酸二無水物は上記ポリアミド酸を経由する合成方法と同様であり、特に限定されるものではない。ジイソシアナートとしては、特に限定されるものではない。また、酸二無水物とジイソシアナートとの反応条件についても特に限定されるものではない。
【０１０４】
＜高抵抗カーボンブラック＞
本発明にかかるポリイミド樹脂組成物には、高抵抗カーボンブラックが含まれている。この高抵抗カーボンブラックとは、本発明では、４９０Ｎ／ｃｍ^２（５０ｋｇｆ／ｃｍ^２）で圧縮した状態の試料を用いて測定され、その体積抵抗値が１×１０^２〜１×１０^１０Ω・ｃｍの範囲内、好ましくは体積抵抗値が１×１０^３〜１×１０^８Ω・ｃｍの範囲内にあるカーボンブラックが用いられる。
【０１０５】
上記高抵抗カーボンブラックとしては、上記条件で測定した上記範囲内の体積抵抗値を有するものであれば特に限定されるものではないが、具体的には、例えば、カーボンブラックの表面にポリマーをグラフトしたり、他の方法で絶縁材を被覆したりしたカーボンブラック（説明の便宜上、表面修飾型カーボンブラックと称する）等を挙げることができる。また、これら表面修飾型カーボンブラックにおいては、その体積抵抗値は、グラフトするポリマーの種類やグラフト量、または、被覆する絶縁材の種類や量を変えたり、あるいはカーボンブラックそのものの種類等を適宜選択したりすることによって調整することができる。
【０１０６】
なお、本発明で用いる高抵抗カーボンブラックは、１種類のみであってもよいし、２種類以上であってもよい。
【０１０７】
カーボンブラックとしては、酸性度、揮発分量、構造の違い等により様々な種類が知られている。ここで、カーボンブラックの体積抵抗値は、通常、１×１０^２Ω・ｃｍ以下と非常に低く、カーボンブラックの酸性度、揮発分量、構造等を変更するだけでは、体積抵抗値の高いカーボンブラックを得ることは難しい。また、カーボンブラックは、その種類によって分散性が大きく異なる。そのため、ポリイミド樹脂組成物に添加して体積抵抗値を制御するような用途に用いる場合には、ポリイミド樹脂中での分散の制御や、その配合を調整することに大変な労力を要する。
【０１０８】
これに対して、グラフト化カーボンブラックのように、表面修飾型カーボンブラックを用いれば、所望の体積抵抗値を有するカーボンブラックを容易に作製することが可能となる。そのため、ポリイミド樹脂中での分散性を変えることなく導電性を制御することが可能となり、カーボンブラックの配合量が全く同じであっても、異なる体積抵抗値を有するポリイミド樹脂組成物を容易に得ることができる。
【０１０９】
特に、表面処理型カーボンブラックでは、当該カーボンブラックを分散する対象となるポリイミド樹脂との親和性の高いポリマーや絶縁材を選択することができる。そのため、表面処理の程度（グラフトしたポリマーや被覆した絶縁材の量）を大きくするほど、対象となるポリイミド樹脂への分散性を向上することができる。そのため、ポリイミド樹脂組成物またはポリイミド成形物において、部分的な体積抵抗値のばらつきの発生を回避することができる。
【０１１０】
また、本発明で用いられる高抵抗カーボンブラックは、従来の導電性カーボンブラックや、黒鉛、金属等といった各種導電性材料よりも抵抗が高い。すなわち、その体積抵抗値は、本発明で求められる所望の体積抵抗値、すなわち前記中間抵抗値（１０^６〜１０^１５Ω・ｃｍの範囲内）に近いものとなっている。そのため、ポリイミド樹脂に添加した量に対する、体積抵抗値の変動を少ない幅に抑えることができる。
【０１１１】
さらに、上記高抵抗カーボンブラックは、導電性カーボンブラックや金属等よりもポリイミド樹脂に体積抵抗値が近いものとなっている。そのため、複合材料となるポリイミド樹脂組成物またはポリイミド成形物中に、電圧の局所的な偏りが発生することを抑えることが可能となる。その結果、体積抵抗値の電圧依存性を小さくすることができる。
【０１１２】
＜グラフト化カーボンブラック＞
本発明では、上記表面修飾型カーボンブラックの中でも、付与できる半導電性が安定していることから、カーボンブラックの表面にポリマーをグラフトしたカーボンブラック（説明の便宜上、グラフト化カーボンブラックと称する）が好ましく用いられる。
【０１１３】
特に、本発明で好適に用いられるグラフト化カーボンブラックでは、その表面にグラフトするポリマーとしては、カーボンブラック表面の官能基と反応し得る反応性基を有し、当該カーボンブラック表面との親和性が良好なセグメントと、その他のセグメントとを有する共重合体を選択することが好ましい。このような共重合体をグラフトしたグラフト化カーボンブラックについては、例えば、特開平１０−１２０９３５号公報に記載されている技術により得ることができる。
【０１１４】
また、カーボンブラックの表面にグラフトされるポリマーは、ポリイミド樹脂中に混合して均一に分散させる点から、親水性ポリマーを選択することがより好ましい。
【０１１５】
このような親水性ポリマーとしては、特に限定されるものではないが、例えば、ポリアミド、ポリアミド酸、ポリイミド、ポリビニルピロリドン（ポリ（Ｎ−ビニル−２−ピロリドン）等）、ポリ（Ｎ，Ｎ’−ジエチルアクリルアジド）、ポリ（Ｎ−ビニルホルムアミド）、ポリ（Ｎ−ビニルアセトアミド）、ポリ（Ｎ−ビニルフタルアミド）、ポリ（Ｎ−ビニルコハク酸アミド）、ポリ（Ｎ−ビニル尿素）、ポリ（Ｎ−ビニルピペリドン）、ポリ（Ｎ−ビニルカプロラクタム）、ポリ（Ｎ−ビニルオキサゾリドン）等を挙げることができる。また、これら親水性ポリマーは、カーボンブラック表面との親和性が良好なセグメントを介在させたブロック共重合体であってもよい。このようなブロック共重合体であれば、これら親水性ポリマーをカーボンブラックにグラフトさせ易くなる。
【０１１６】
なお、上記カーボンブラック表面との親和性が良好なセグメントとしては、特に限定されるものではなく、カーボンブラックの種類に応じて、適宜好ましい構造を選択すればよい。
【０１１７】
このようなグラフト化カーボンブラックを用いた場合、当該グラフト化カーボンブラックはポリイミド樹脂と強固な結合を有するため、ポリイミド樹脂組成物の物性、特に機械特性（特に、機械強度や寸法安定性）を向上させることができる。具体的には、得られるポリイミド樹脂組成物の引張伸びは３５％、引き裂き伝播強度は２．４５Ｎ／ｍｍ（２５０ｇｆ／ｍｍ）以上にすることができ、カーボンブラックを添加していないポリイミド樹脂（組成物）に対して、５０％以上の保持率を実現することができる。
【０１１８】
また、本発明におけるグラフト化カーボンブラック、あるいは表面修飾型カーボンブラックに用いられる母材としてのカーボンブラックは、上述したように、最終的に得られるポリイミド樹脂組成物またはポリイミド成形物の用途や種類等に応じて、従来公知のカーボンブラックを適宜選択して用いることができる。
【０１１９】
ここで、上記カーボンブラックの平均粒径については、一次粒子に基づく平均粒径が１μｍ以下であることが好ましく、特に、同平均粒径が０．００１〜０．５μｍの範囲内にあるカーボンブラックが好ましい。このような平均粒径を満たすカーボンブラックを用いることで、カーボンブラックの偏在による、ポリイミド樹脂組成物またはポリイミド成形物の体積抵抗値にばらつきが発生することを抑制または回避することができる。
【０１２０】
＜高抵抗カーボンブラックの配合量＞
本発明にかかるポリイミド樹脂組成物またはポリイミド成形物においては、上記高抵抗カーボンブラックの配合量（配合率）は、ポリイミド樹脂１００重量部に対して、２０〜１００重量部の範囲内であればよく、２０〜８０重量部の範囲内が好ましく、２０〜６０重量部の範囲内がより好ましい。
【０１２１】
上記高抵抗カーボンブラックの配合量が２０重量部未満であれば、得られるポリイミド樹脂組成物またはポリイミド成形物の体積抵抗値が、中間抵抗値よりも高くなる。そのため、例えば、ポリイミド成形物を電子写真装置の中間転写ベルト等に用いると、トナー像の転写時に中間転写ベルトが著しく帯電する。その結果、中間転写ベルトが像担持体から離れる際に剥離放電が生じ、中間転写ベルトの表面に転写されたトナー像が飛散するという問題が生じる。
【０１２２】
一方、上記高抵抗カーボンブラックの配合量が１００重量部を超えれば、得られるポリイミド樹脂組成物またはポリイミド成形物の体積抵抗値が、中間抵抗値よりも低くなる。そのため、上記と同様に、ポリイミド成形物を中間転写ベルト等に用いると、中間転写ベルトと像担持体との間に過大な電流が流れる。そのため、中間転写ベルトの表面に転写されたトナー像が像担持体に戻る現象が生じ易いという問題が生じる。また、ポリイミド成形体そのものの機械特性も低下して脆い材料となってしまうので好ましくない。
【０１２３】
これに対して、上記高抵抗カーボンブラックの配合量を上記の範囲内に設定すれば、例えば５重量部程度の配合量のばらつきがあったとしても、体積抵抗値の変化は３倍以下に抑えることができる。そのため、得られるポリイミド成形物において、大幅な体積抵抗値の変化を引き起こすことなく、中間抵抗値に制御することが可能となる。
【０１２４】
なお、本発明では、上記高抵抗カーボンブラックの配合量は、従来公知の各種用途（例えば、着色、抵抗の制御、機械強度の改善等）にて用いられるカーボンブラックの配合量に比較すると非常に多くなっている。しかしながら、本発明では、このようなカーボンブラックの多量の添加にもかかわらず、ポリイミド樹脂組成物またはポリイミド成形物の機械特性や電気絶縁性は低下しない。その理由については、後述の＜高抵抗カーボンブラックの配合による作用＞の項で説明する。
【０１２５】
＜高抵抗カーボンブラックの配合による諸物性の制御＞
本発明にかかるポリイミド樹脂組成物またはポリイミド成形物では、少なくとも、上記高抵抗カーボンブラックをポリイミド樹脂に配合することで、次の（１）〜（５）に示す諸物性の良好な制御を実現することができる。
【０１２６】
（１）ポリイミド樹脂組成物またはポリイミド成形物の体積抵抗値を１×１０^６〜１×１０^１５Ω・ｃｍの範囲内に、その表面抵抗値を１０^６〜１０^１５Ω／□の範囲内、すなわち中間抵抗値に制御することができる。そのため、体積抵抗値を過剰に高めることなく優れた電気絶縁性を実現することができる。
【０１２７】
（２）ポリイミド樹脂組成物またはポリイミド成形物における常温常湿時の体積抵抗値をＲｎとし、同じく高温高湿の体積抵抗値をＲｈとした場合、これら体積抵抗値の比（Ｒｎ／Ｒｈ）を、０．０３〜３０の範囲内、好ましくは０．１〜１０の範囲内に制御することができる。そのため、周囲の環境によっても体積抵抗値の変動の幅が小さく、抵抗値の環境に対する安定性に優れたポリイミド系材料を提供することができる。
【０１２８】
（３）ポリイミド樹脂組成物またはポリイミド成形物における１００Ｖ印加時の体積抵抗値をＲ_１００Ｖとし、同じく１０００Ｖ印加時の体積抵抗値をＲ_{１０００Ｖ}とした場合、これら体積抵抗値の比（Ｒ_１００Ｖ／Ｒ_{１０００Ｖ}）を、０．０３〜３０の範囲内に制御することができる。そのため、印加する電圧によっても体積抵抗値の変動の幅が小さく、抵抗値の電圧に対する依存性が小さいポリイミド系材料を提供することができる。
【０１２９】
（４）ポリイミド樹脂に対して、前述した配合量の範囲内で高抵抗カーボンブラックを添加した場合、添加量が５重量部変化しても、体積抵抗値の変動を３倍以下に抑えることができる。そのため、添加する高抵抗カーボンブラックの量によっても体積抵抗値の変動の幅が小さく、抵抗値の添加量に対する依存性が小さいポリイミド系材料を提供することができる。しかも、サンプル間の体積抵抗値のばらつきも３倍以下に抑えることができるので、サンプル間の抵抗値のばらつきが小さいポリイミド系材料を提供することができる。
【０１３０】
（５）特に、高抵抗カーボンブラックとして、グラフト化カーボンブラック等を用いることで、ポリイミド樹脂との間に強固な結合を形成することができる。そのため、ポリイミド樹脂組成物の機械特性（特に、機械強度や寸法安定性）を向上させることができる。しかも、グラフト化カーボンブラックはポリイミド樹脂に対する分散性に優れているので、カーボンブラックの偏在による体積抵抗値のばらつきを抑制または回避することができる。
【０１３１】
＜高抵抗カーボンブラックの配合による作用＞
このように、本発明では、ポリイミド樹脂に高抵抗カーボンブラックを配合することにより、従来では困難であった上記（１）〜（５）の諸物性の制御を容易に実現することができる。その結果、本発明にかかるポリイミド樹脂組成物およびポリイミド成形物は、例えば、電子写真装置の転写ベルト、中間転写ベルト、転写定着ベルト、および定着ベルト等の部材として有効に用いることができる。
【０１３２】
ここで、本発明において、ポリイミド樹脂（好ましくは、反応硬化型直鎖状ポリイミド樹脂）に高抵抗カーボンブラックを添加することで、上記（１）〜（５）の諸物性を容易に制御できる理由（本発明の作用）について説明する。
【０１３３】
高抵抗カーボンブラックは、単体で１×１０^３〜１×１０^１０Ω・ｃｍの範囲内の体積抵抗値を有しており、通常用いられるカーボンブラック、金属、金属セラミックス（体積抵抗値：１×１０^−５〜１×１０^３Ω・ｃｍ）等とは異なり、体積抵抗値がポリイミド樹脂の体積抵抗値：１×１０^１６Ω・ｃｍに近い。そのため、高抵抗カーボンブラックを添加したポリイミド樹脂組成物またはポリイミド成形物では、通常のカーボンブラックの添加に見られるようなパーコレーションによる急激な体積抵抗値の低下は見られず、体積抵抗値は添加量に応じて緩やかに変化する。
【０１３４】
通常のカーボンブラックでは、中間抵抗値を実現するために、樹脂１００重量部に対して１０〜２０重量部の範囲内となるようにカーボンブラックを添加する。しかしながら、このような添加量であれば、当該添加量が５重量部程度変化するだけでも体積抵抗値は１００倍以上低下してしまう。
【０１３５】
これに対して、本発明のように、高抵抗カーボンブラックを添加する場合、前述した中間抵抗値を実現するための範囲内であれば、添加量が５重量部程度変化したとしても体積抵抗値は３倍も変化しない。また、ポリイミド樹脂組成物における脱泡過程やカーボンブラックの分散過程にて、カーボンブラック等の導電性フィラー（導電性充填材）に凝集や偏りが生じても、体積抵抗値の大幅な変化は見られない。そのため、本発明で用いる高抵抗カーボンブラックは、添加量にばらつきが生じても、体積抵抗値の変化が少ない材料ということができる。
【０１３６】
また、本発明で用いる高抵抗カーボンブラックは、それ自体の体積抵抗値が高いため、得られるポリイミド樹脂組成物やポリイミド成形物における電気絶縁性の改善や体積抵抗値の電圧依存性の低減にも大きな役割を果たすと考えられる。
【０１３７】
具体的には、例えば、ポリイミド樹脂と他の導電性充填材からなるフィルムの体積抵抗値を測定するために、当該フィルムに電圧を印加すると、電圧はポリイミド樹脂と導電性充填材とに分圧される。そのため、電圧は、低抵抗の導電性充填材よりも高抵抗であるポリイミド樹脂にかかると考えられる。特に、導電性充填材として、導電性カーボンブラックや金属系材料のような低抵抗の材料と、高抵抗カーボンブラックのような中抵抗の材料とを添加した場合を比較すれば、ポリイミド樹脂にかかる電圧は中抵抗の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、ポリイミド樹脂にかかる電圧が小さくなるために、ポリイミド樹脂組成物やポリイミド成形物における絶縁破壊が低減されるものと考えられる。
【０１３８】
一般に、樹脂に対して、高電圧（例えば、厚み１００μｍに対して１ｋＶ以上の電圧）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とになる。それゆえ、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。
【０１３９】
これに対して、本発明では、ポリイミド樹脂に高抵抗カーボンブラックのような中抵抗材料を添加する。そのため、導電性カーボンブラックのような低抵抗の材料を添加した場合に比べて、ポリイミド樹脂に局所的に高電圧がかかることを防ぐことができる。その結果、抵抗値の電圧依存性を改善することができると考えられる。
【０１４０】
また、高抵抗カーボンブラックは、その表面に、水酸基や活性な酸素を部分的に有する場合がある。そのため、表面処理を実施しなくてもイミド化の際にポリイミド樹脂と強い相互作用を起こす。それゆえ、得られるポリイミド樹脂組成物またはポリイミド成形物は、強固な複合材料となる。
【０１４１】
そのため、本発明にかかるポリイミド樹脂組成物またはポリイミド成形物は、当該分野で知られている従来のポリイミド系材料に比べて、強い引き裂き伝播強度と伸びを実現することができる。従来公知の各種用途（例えば、着色、抵抗の制御、機械強度の改善等）で配合されるカーボンブラックの配合量は、通常、樹脂１００重量部に対して５重量部程度であるが、本発明では、これよりも多く添加しても、十分な機械特性や電気絶縁性を保持することができる。
【０１４２】
さらに、本発明にかかるポリイミド樹脂組成物やポリイミド成形物は、高温高湿であっても体積抵抗値や電気絶縁性が低下しない。その理由は、本発明にかかるポリイミド樹脂組成物やポリイミド成形物が、ポリイミド樹脂および高抵抗カーボンブラックが互いに強固に結合してなる強固な複合材料となっているからであると考えられる。
【０１４３】
すなわち、導電性充填材を配合してなるポリイミド系複合材料においては、吸湿時に電気特性が悪化する原因は、吸湿によってポリイミド樹脂と導電性充填材との界面に、水からなるスキン層が形成され、その結果、複合材料中に電気の流れ易い流路が形成されるためだと考えられる。そこで、吸湿時における電気特性の悪化を改善するために、一般的には、導電性充填材（フィラーやカーボンブラック）の表面処理が行われる。
【０１４４】
これに対して、本発明では、高抵抗カーボンブラックとポリイミド樹脂、特に、反応硬化型直鎖状ポリイミド樹脂との間には、強固な結合が形成される。そのため、上記一般的なポリイミド系複合材料のようなスキン層が形成されず、その結果、吸湿しても、体積抵抗値や電気絶縁性に大幅な変化が生じないと考えられる。
【０１４５】
このように、本発明では、カーボンブラックとして、高抵抗カーボンブラックを用いることにより、当該分野の従来技術よりも非常に優れた作用・効果を発揮し得る。その結果、本発明にかかるポリイミド樹脂組成物およびポリイミド成形物は、従来よりも優れた特性を実現することができる。
【０１４６】
＜高抵抗カーボンブラックの混合方法＞
本発明において、ポリイミド樹脂に上記高抵抗カーボンブラックを混合する具体的な手法は特に限定されるものではない。しかしながら、本発明では、ポリイミド樹脂として、ポリアミド酸を経由して合成される、反応硬化型直鎖状ポリイミド樹脂を用いることが好ましいため、高抵抗カーボンブラックは、前駆体であるポリアミド酸に添加してから、当該ポリアミド酸をイミド化することがより好ましい。
【０１４７】
ポリアミド酸に高抵抗カーボンブラックを添加して混合する具体的な手法としては、次に示す（１）・（２）の２つの手法を挙げることができる。
【０１４８】
（１）ポリアミド酸の重合に用いる溶媒に、高抵抗カーボンブラックを添加することによって、高抵抗カーボンブラックの分散溶液を予め調製しておく。そして、この分散溶液に、ジアミン化合物と酸二無水物とを添加してポリアミド酸を重合する。
【０１４９】
（２）ジアミン化合物と酸二無水物とからポリアミド酸を予め重合して、ポリアミド酸溶液を調製しておき、同じく予め調製しておいた高抵抗カーボンブラックの分散溶液を、ポリアミド酸溶液に混合する。
【０１５０】
上記（１）・（２）の何れの方法を用いるにしても、高抵抗カーボンブラックの分散溶液を調製する必要がある。ここで、高抵抗カーボンブラックは比重が樹脂よりも大きく非常に重いため、溶媒に高抵抗カーボンブラックを添加してしばらくすると沈降してしまう。このように沈降した状態で高抵抗カーボンブラックをポリアミド酸溶液に添加して混合すると、高抵抗カーボンブラックの凝集物が生じる。その結果、最終的に得られるポリイミド樹脂組成物またはポリイミド成形物の表面に凹凸が生じたり、体積抵抗値が局所的に異なったりする。
【０１５１】
そこで、高抵抗カーボンブラックの分散溶液を調製する場合には、溶媒に分散剤を配合して、高抵抗カーボンブラックの沈降を抑制または回避することが好ましい。
【０１５２】
＜分散剤＞
上記分散剤としては、溶媒中で高抵抗カーボンブラックの沈降を抑制または回避することができるものであれば特に限定されるものではないが、例えば、各種金属塩や、界面活性剤等を挙げることができる。中でも金属塩が好ましい。
【０１５３】
上記金属塩としては、具体的には特に限定されるものではないが、高抵抗カーボンブラックの分散性を向上させる点から、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種類または２種類以上の組み合わせが好ましく、特に、Ｌｉ塩、Ｎａ塩、Ｋ塩がより好ましい。
【０１５４】
上記Ｌｉ塩としては、格子エネルギーが１１００ｋＪ／ｍｏｌ　以下のＬｉ塩が好ましく用いられ、具体的には、ＬｉＦ、ＬｉＣｌ、ＬｉＢｒ、ＬｉＩ、ＬｉＳＣＮ、ＬｉＣＦ_３ＳＯ_３等の化合物を好ましく挙げることができる。また、Ｎａ塩としては、格子エネルギーが８００ｋＪ／ｍｏｌ　以下のＮａ塩が好ましく用いられ、具体的には、ＮａＦ、ＮａＣｌ、ＮａＢｒ、ＮａＩ、ＮａＳＣＮ、ＮａＣＦ_３ＳＯ_３等の化合物を好ましく挙げることができる。さらに、Ｋ塩としては、格子エネルギーが８００ｋＪ／ｍｏｌ　以下のＫ塩が好ましく用いられ、具体的には、ＫＦ、ＫＣｌ、ＫＢｒ、ＫＩ、ＫＳＣＮ、ＫＣＦ_３ＳＯ_３等の化合物を好ましく挙げることができる。
【０１５５】
上記各金属塩は、常温でイオンが解離し易く、高抵抗カーボンブラックと相互作用が強くなるため、分散剤として好ましく用いられる。ただし、格子エネルギーが小さすぎると、分散剤の添加量による影響が大きくなり過ぎるため、上述したように格子エネルギーが大きい金属塩であることが好ましい。なお、これら金属塩は有機物を含まないため、ポリイミド樹脂組成物を成形する際の高温乾燥でも、ポリイミド樹脂が焼け付くような事態の発生を回避することができる。
【０１５６】
上記分散剤の配合量は、高抵抗カーボンブラックを分散できる程度の量であれば特に限定されるものではないが、一般的には、最終的に得られるポリイミド樹脂１００重量部に対して、１重量部以下となるように配合すればよく、０．０１〜０．１重量部の範囲内またはそれ以下でも、高抵抗カーボンブラックを十分に分散させることができる。
【０１５７】
一般に、電線を被覆する用途では、樹脂に金属塩が添加されると電気絶縁性が悪化する。特に、誘電率が４以上の樹脂に金属塩を添加すると、イオン伝導性が高まるため特に好ましくない。しかしながら、本発明では、ポリイミド樹脂が電気絶縁性に優れ、誘電率が４以下であるため、上述した範囲内で金属塩を配合しても、電気絶縁性や体積抵抗値の電圧依存性等は顕著な低下を有効に回避することができる。
【０１５８】
＜その他の充填材＞
本発明にかかるポリイミド樹脂組成物またはポリイミド成形物には、前述した高抵抗カーボンブラック以外にも、各種導電性または半導電性を有する充填材（フィラー）を加えても良い。他の充填材としては、導電性または半導電性を有するものであればよく、例えば、導電性カーボンブラック、グラファイト、金属粉末、金属酸化物粉末、導電処理された金属酸化物、帯電防止剤、芯材を表面被覆してなる半導電性フィラー等を挙げることができる。これら他の充填材は１種類のみを用いてもよいし、２種類以上を組み合わせて用いてもよい。
【０１５９】
＜カーボンブラック＞
本発明で、ポリイミド樹脂に配合することのできる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特に限定されるものではなく、従来公知の各種カーボンブラックを好適に用いることができる。
【０１６０】
具体的には、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を挙げることができる。中でも、ファーネスブラックの一種である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ることが好ましい。
【０１６１】
このケッチェンブラックは、比表面積が大きいため、カーボンブラックの配合量が少なくても効果が高く、さらに、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しめさない性質）が少ないため好ましい。
【０１６２】
＜金属粉末・金属酸化物粉末・導電処理された金属酸化物＞
本発明で、ポリイミド樹脂に配合することのできる金属粉末、金属酸化物粉末、導電処理された金属酸化物としては、導電性を有するものであれば特に限定されるものではなく、従来公知のものを好適に用いることができる。
【０１６３】
具体的には、例えば、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る。また、金属酸化物粉末としては、導電性半導体セラミックスの粉末が挙げられる。さらに、導電処理された金属酸化物としては、酸化チタン、チタン酸カリウム、硫酸バリウム、マイカ等を導電化処理したものが挙げられる。
【０１６４】
＜帯電防止剤＞
本発明で、ポリイミド樹脂に配合することのできる帯電防止剤としては、特に限定されるものではなく、従来公知の帯電防止剤を好適に用いることができる。具体的には、例えば、アニオン系、カチオン系、非イオン系、両性系の各種界面活性剤を挙げることができる。
【０１６５】
＜半導電性フィラー＞
本発明で、ポリイミド樹脂に配合することのできる半導電性充填材とは、半導電性を有する充填材であれば特に限定されるものではない。なお、ここでいう半導電性とは、ほぼ無荷重の圧力で圧縮した試料を用いて測定する、体積抵抗値が１×１０^３〜１０^１０Ω・ｃｍの範囲内、好ましくは１×１０^４〜１０^９Ω・ｃｍの範囲内であることを示すものとする。
【０１６６】
半導電性充填材としては、例えば、導電性物質で芯材の表面を被覆した無機充填材を挙げることができる。具体的には、次に示す２種類の半導電性フィラーを挙げることができる。
【０１６７】
（１）炭素、黒鉛等の黒色導電性物質で芯材の表面を被覆してなる黒色系フィラー。
【０１６８】
（２）ＩＴＯ（インジウム−錫複合酸化物）、ＡＴＯ（アンチモンドープ酸化錫）、ＮＴＯ（ニオブドープ酸化錫）、ＴＴＯ（タンタルドープ酸化錫）、ＦＴＯ（フッ素化物ドープ酸化錫）、ＴＯ（酸化錫）等の酸化錫系導電性物質で芯材を被覆してなる酸化錫系フィラー。
【０１６９】
これら（１）黒色系フィラーや（２）酸化錫系フィラーでは、上記各導電性物質の種類、量、形成方法によって、その抵抗値を中間抵抗値に調整することができるために好ましい。
【０１７０】
例えば、（１）黒色系フィラーでは、表面に付着する黒色導電物質の被覆量を調整することでその抵抗値を制御することができる。また、得られた半導電性フィラーの抵抗値が低かったとしても、空気中で５０〜７５０℃の範囲内の温度で加熱すると、抵抗値を上昇させることができるため、所望の抵抗値を有する半導電性フィラーを容易に入手することができる。
【０１７１】
また、（２）酸化錫系フィラーでは、酸化錫にドーピングする元素の量を変更することで、抵抗値を低い値から高い値まで幅広く制御することができる。また、芯材の表面に、酸化錫系導電性物質の層を形成した後、加熱雰囲気を酸化性や非酸化性の何れ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。したがって、酸化錫系フィラーでは、類似の形状からなり、様々な抵抗値を有する半導電性フィラーを容易に入手することができる。
【０１７２】
また、酸化錫系の材料は熱に強く、ポリイミド樹脂組成物を成形する際、例えば、ポリイミドフィルムを製膜する工程のように、３００℃を越える過酷な条件での成形においても、物性の劣化を引き起こすことがない。そのため、酸化錫系フィラーは使用できる範囲が広くなり好ましい。また、また酸化錫系の材料は無色に近いため、例えば、芯材に無色の材質を用いると、無色の半導電性フィラーを得ることができる。その結果、黒色の着色剤を併用すれば、黒色ポリイミド樹脂組成物を容易に得ることができる。このような黒色ポリイミド樹脂組成物およびこれを用いたポリイミド成形物は、電子写真装置の転写ベルト等に好適に用いることができる。
【０１７３】
ここで、半導電性充填材として、上述したように芯材の表面を被覆することで抵抗値を制御してなるフィラーを用いることの利点について説明する。
【０１７４】
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からなるフィラーは、特定の抵抗値しか有していない。そのため、これらを用いてポリイミド樹脂組成物またはポリイミド成形物の体積抵抗値を所望の範囲に制御する場合、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、配合する量を変更したりする必要があり、体積抵抗値の制御が煩雑になるという問題が生じていた。
【０１７５】
また、各フィラーに応じて分散性が異なるため、配合時の分散の制御や、上述した配合量の調整に大変な労力を要し、ポリイミド樹脂組成物の製造そのものが煩雑化するという問題も生じていた。さらに、配合量を変更すると、得られるポリイミド樹脂組成物またはポリイミド成形物の機械特性が異なり、製品の物性が安定しないという問題もあった。しかも、色も単一の色しかないため、ポリイミド成形物を着色する際に、色変更の自由度も小さいという問題があった。
【０１７６】
これに対して、本発明では、高抵抗カーボンブラックに併用する導電性物質として、上記芯材の表面を被覆することで抵抗値を制御してなるフィラーを用いれば、様々な体積抵抗値を、単一材料からなる半導電性フィラーにより実現することができたり、その機械特性や分散性を変えることなく導電性を制御したりすることができる。そのため、配合量が全く同じでも、異なる体積抵抗値を有するポリイミド樹脂組成物またはポリイミド成形物を製造することができる。
【０１７７】
また、半導電性フィラーの機械特性や分散性といった基本的な物性は同一であるため、体積抵抗値を制御するために半導電性フィラーの種類を変更しても、製造過程での洗浄作業や切り替え作業が非常に容易になり、製造過程の煩雑化を回避することができる。また、芯材の表面の被覆するため、得られる半導電性フィラーの色を、無色から黒色まで自由に選択することが可能となる。その結果、着色も容易となる。
【０１７８】
＜半導電性フィラーの芯材＞
上記半導電性フィラーの芯材（無機材料）としては、無機系の材料であれば特に限定されるものではないが、一般的には、各種の金属、あるいは金属酸化物、金属炭化物、金属窒化物等のセラミック材料、あるいは金属塩等を挙げることができる。
【０１７９】
具体的には、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、粘土鉱物等を挙げることができる。
【０１８０】
これらの中でも屈折率が低い無機材料が好ましい。具体的には、（１）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、マイカから選択される少なくとも１種の材料がより好ましく用いられる。あるいは、（２）アルミナ、シリカ、ガラス、ウォラストナイト、タルク、カオリンから選択される少なくとも１種の材料であってもよい。
【０１８１】
上記（１）の無機材料は、酸化チタンやチタン酸金属塩等とは異なり屈折率が小さく、ポリイミド樹脂を含む各種樹脂の屈折率に近似している。そのため、樹脂に混入して透明性を損なうことが少なく、樹脂を着色することも回避できるという利点がある。また、上記（２）の無機材料は、（１）の無機材料ほどでは無いが比較的屈折率が低い。そのため、ポリイミド樹脂に添加しても透明性が損なわれ難いため好ましく用いることができる。
【０１８２】
なお、半導電性フィラーの芯材として用いることのできる無機材料の屈折率としては、通常は、２．０以下であればよく、好ましくは１．８以下、より好ましくは１．７以下であればよい。
【０１８３】
このような芯材に黒色導電性物質を被覆した前記（１）黒色系フィラーでは、ポリイミド樹脂に配合した後、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。一方、上記芯材に酸化錫系物質を被覆した前記（２）酸化錫系フィラーは透明性に優れているので、このフィラーを添加したポリイミド樹脂組成物またはポリイミド成形物では透明性を実現することが可能となる。また、他の着色剤を併用すれば自由に着色することが可能となる。
【０１８４】
なお、上記芯材においては、当該芯材から遊離する金属成分は少ないほど好ましい。具体的には、遊離金属成分量としては１００ｐｐｍ以下であればよく、８０ｐｐｍ以下が好ましく、５０ｐｐｍ以下がより好ましい。遊離金属成分量が上記上限以下であれば、遊離金属成分が少ないために、これら芯材を用いてなる半導電性フィラーを配合したポリイミド樹脂組成物またはポリイミド成形物において、その体積抵抗値の湿度依存性が小さくなるために好ましい。また、遊離金属成分が少ないと、これら芯材を用いてなる半導電性フィラーを配合したポリイミド樹脂組成物またはポリイミド成形物において、絶縁破壊電圧も小さくなるために好ましい。
【０１８５】
また、本発明では、上述した表面を被覆してなる複合材料としての半導電性フィラー以外に、１種類の材料からなる半導電性フィラーであってもよい。このような半導電性フィラーとしては、酸化チタン、チタン酸金属塩、ホウ酸アルミニウム、酸化錫、炭化ケイ素等を挙げることができる。
【０１８６】
＜導電性充填材の配合量＞
本発明にかかるポリイミド樹脂組成物またはポリイミド成形物においては、上記導電性充填材および／または半導電性充填材の配合量（配合率）は、ポリイミド樹脂１００重量部に対して、１００重量部の範囲内であればよく、特に導電性充填材の場合には、導電性２０〜８０重量部の範囲内が好ましく、２０〜６０重量部の範囲内がより好ましい。
【０１８７】
上記充填材の配合量が１００重量部を超えると、得られるポリイミド樹脂組成物またはポリイミド成形物の体積抵抗値の電圧依存性や電気絶縁性が悪化するため好ましくない。また、上記充填材の配合量が少なすぎるとこれらの導電性物質を用いた効果が発揮され難くなるので好ましくない。一般的には、上記充填材の配合量の下限値は、０．０１重量部以上であることが好ましく、０．１重量部以上であることがより好ましく、１重量部以上であることがさらに好ましく、５重量部以上であることが特に好ましい。
【０１８８】
＜非導電性充填材＞
本発明にかかるポリイミド樹脂組成物またはポリイミド成形物には、前述した高抵抗カーボンブラックおよび上述した導電性または半導電性充填材以外にも、非導電性充填材を加えても良い。非導電性充填材としては、例えば、各種非導電性の無機粉体を挙げることができる。
【０１８９】
具体的には、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；チタン酸バリウム、チタン酸カリウム等の短繊維状またはウィスカー状物質；等を挙げることができるが、特に限定されるものではない。
【０１９０】
この非導電性充填材の添加により、例えば、ポリイミド樹脂組成物またはポリイミド成形物における弾性率等の各種物性を制御することが可能となる。また、非導電性充填材は、前記高抵抗カーボンブラック、導電性または半導電性充填材等、導電性を有する粒子の分散を適度に補助することも可能になる。そのため、非導電性充填材の添加により、これら導電性を有する粒子の凝集等を防止して安定した体積抵抗値を実現できる場合がある。
【０１９１】
このように、前述した高抵抗カーボンブラックに加えて、導電性または半導電性充填材や非導電性充填材を適宜選択してポリイミド樹脂に配合することによって、前記＜高抵抗カーボンブラックの配合による諸物性の制御＞の項で説明したような諸物性の良好な制御をより良好に実現することができる。
【０１９２】
＜充填材等の分散方法＞
上記高抵抗カーボンブラック、導電性または半導電性充填材、および非導電性充填材等（説明の便宜上、まとめて粉体類と称する）をポリイミド樹脂に混合して分散させる方法としては、特に限定されるものではなく、種々の方法を用いることができる。具体的には、ポリイミド樹脂組成物に含まれるポリイミド樹脂が溶媒に可溶性であるか否かで、次に示すように、大きく２つの手法に分けることができる。
【０１９３】
（１）ポリイミド樹脂が溶媒に可溶性である場合
溶媒に溶解したポリイミド樹脂組成物中に上記粉体を直接加えるか、上記粉体類を溶媒に分散させた粉体類分散液を予め調製してこれを加える。そして、攪拌翼での混合や、３本ロール等を備える混練機による混合によって、これら粉体類を分散させることができる。あるいは、上記粉体類を溶媒に分散させた粉体類分散液を予め調製しておき、これに対して、ポリイミド樹脂組成物の粉体またはペレット等を加えて混合してもよい。
【０１９４】
なお、上記粉体類に例えば針状のものが含まれる場合、混合によって過剰な剪断力を受けると、その針状の形状が破壊される可能性がある。そこで、球形または略球形以外の形状、例えば上記針状のように、外力によってその形状が破壊され易い粉体類を含んでいる場合には、３本ロール等を備える混練機を使用しないことが好ましい。
【０１９５】
（２）ポリイミド樹脂が溶媒に不溶性の場合
前記＜高抵抗カーボンブラックの混合方法＞の項で述べたように、ポリイミド樹脂の前駆体であるポリアミド酸の溶液に対し、上記粉体類分散液を加えて、上記（１）と同様の方法で混合・混練等を実施すればよい。
【０１９６】
＜粉体類分散液の調製＞
ここで、上記粉体類分散液の調製方法としては、粉体類を溶媒に加えて超音波分散機による超音波の照射により、粉体類を十分に分散させておく手法が有効である。また、このとき、前記＜分散剤＞の項でも述べたように、粉体類の分散性を補助するために前記分散剤を併用してもよい。これら分散剤は、ポリイミド樹脂組成物の特性を顕著に劣化させない範囲内で用いればよい。
【０１９７】
特に、粉体類分散剤として、前述した金属塩を添加した場合には、分散状態が非常に均一となるため、超音波分散機を用いなくても手による攪拌で十分均一な分散状態を実現することができる。
【０１９８】
さらに、上記（２）ポリイミド樹脂が溶媒に不溶性の場合に、粉体類分散液とポリアミド酸溶液とを混合する手法としては、特に限定されるものではないが、粉体分散液に対して、ポリアミド酸溶液を少量ずつ攪拌しながら添加していく方が、その逆の手順よりも粉体類の分散性が向上するため好ましい。
【０１９９】
さらに、粉体類の特に良好な分散性が得られる方法としては、上記粉体分散液を調製して、超音波分散機等により十分に分散させておき、これに、ジアミン化合物と酸二無水物を加えてポリアミド酸の重合反応を行う方法を挙げることができる。この方法では、超音波分散等によりミクロなレベルでの分散性が良好に保持されるとともに、粉体類が分散している初期状態から重合中にかけて、常に攪拌されることになるために、マクロなレベルの分散性も非常に良好となる。
【０２００】
なお、前述した各説明および後述の説明中において、「溶媒」とは、特に断りのない限り、前記＜ポリアミド酸の合成＞で説明したポリアミド酸合成用の有機溶媒、好ましくは極性有機溶媒を指すものとする。
【０２０１】
＜ポリイミド樹脂組成物の成形＞
上述した、本発明にかかるポリイミド樹脂組成物は様々な形状に成形加工することで用いることができる。本発明にかかるポリイミド樹脂組成物の成形加工、すなわち本発明にかかるポリイミド成形物の製造方法は、特に限定されるものではないが、具体的には、前記＜充填材等の分散方法＞の項と同様に、ポリイミド樹脂組成物に含まれるポリイミド樹脂が溶媒に可溶性であるか否かで、次に示すような２つの手法に分けることができる。
【０２０２】
（１）ポリイミド樹脂が溶媒に可溶性である場合
ポリイミド樹脂組成物を溶媒に溶解してポリイミド溶液を調製し、これに高抵抗カーボンブラック等の粉体類を混合・分散させる。そして、このポリイミド溶液を、成形型等を用いて任意の形状に加工した後、加熱あるいは加熱と減圧との併用により溶媒を揮発させる。これによって、本発明にかかるポリイミド成形物を得ることができる。
【０２０３】
（２）ポリイミド樹脂が溶媒に不溶性の場合
前駆体であるポリアミド酸を溶媒に溶解してポリアミド酸溶液を調製し、これに高抵抗カーボンブラック等の粉体類を混合・分散させる。そして、好ましくは化学キュア法によりイミド化を進めた後には、上記（１）と同様の工程を実施することにより、本発明にかかるポリイミド成形物を得ることができる。
【０２０４】
ここで、一般に、ポリイミド系材料を成形加工する場合、成形物の厚みが薄いと、電気絶縁性を保持しながら、体積抵抗値を一定に保持することが特に難しくなる。特に、フィルム状（シート状）または管状（ベルト状およびチューブ状を含む）等、広義の「フィルム状形態」を有する成形物では、特に、その厚みが１５０μｍ以下となると、電気絶縁性と体積抵抗値との双方を良好な値に維持することが非常に困難となる。
【０２０５】
これに対して、本発明にかかるポリイミド樹脂組成物およびポリイミド成形物は、成形物の厚みが薄くても、電気絶縁性と体積抵抗値との双方を良好な値に保持することが可能となる。その結果、本発明にかかるポリイミド成形物は、フィルム状（シート状）、管状（ベルト状またはチューブ状）等、広義の「フィルム状形態」を有する成形物として好適に用いることができる。なお、上記ベルト状とは、管状のうち、比較的大口径の形状を指し、上記チューブ状は、管状のうち、比較的小口径の形状を指す。
【０２０６】
＜ポリイミド樹脂組成物の成形例＞
本発明にかかるポリイミド成形物のうち、特に、フィルム状（シート状）成形物と、管状（ベルト状）成形物を製造する具体的な方法としては、次に示す方法を好ましい一例として挙げることができる。
【０２０７】
まず、フィルム状成形物を製造する方法としては、次に示す２つの例を挙げることができる。
【０２０８】
（１）前記粉体類を分散させたポリイミド溶液（本発明にかかる溶液状のポリイミド樹脂組成物）を調製し、これをエンドレスベルト上に、その厚み制御をした上で塗布する。このとき用いられる塗布手段としては、Ｔダイ、コンマコーター、ドクターブレード等を挙げることができるが特に限定されるものではない。
【０２０９】
次に、上記ポリイミド溶液を、熱風などによって自己支持性を有するまで加熱乾燥し、その後、エンドレスベルトから引き剥がす。これによって半乾燥状態のポリイミドフィルムが得られる。この半乾燥状態のポリイミドフィルムの幅両端を、ピンやクリップ等により固定し、幅方向の長さを規制しながら順次高温の加熱炉内を通過させる。これによって、フィルム状成形物を得ることができる。
【０２１０】
あるいは、（２）例えば金属製の連続したシート状の支持体上に、上記（１）と同様の方法でポリイミド溶液を塗布する。そして、この支持体とともに塗布されたポリイミド溶液を加熱炉内へ通過させる。その後、支持体からフィルム状成形物を剥離するか、支持体をエッチング等により除去する。これによって、フィルム状成形物を得ることができる。
【０２１１】
次に、管状（ベルト状）成形物を製造する方法としては、次に示す２つの例を挙げることができる。
【０２１２】
（３）上記（１）または（２）の方法で得られたフィルム状（シート状）成形物を、所定の長さおよび幅となるように切断し、ベルトまたはチューブ状につなぎ合わせる。これによって、管状成形物（ベルト状成形物またはチューブ状成形物）を容易に得ることができる。ただし、フィルムまたはシート状成形物をつなぎ合わせるには、従来公知の各種接着剤や接着テープ等を用いるが、この方法では、つなぎ目で段差や切れ目が存在することが避けられないため、ポリイミド成形物の用途によっては不都合が生じる場合がある。
【０２１３】
そこで、（４）例えば、管状成形物を得る場合には、円筒状金型の内面または外面にポリイミド溶液を塗布し、加熱乾燥または減圧乾燥等により溶媒を揮発させる。この状態では、円筒状金型の内面または外面に半乾燥状態のポリイミド成形物が存在している。そして、これをこのまま最終焼成温度まで加熱するか、あるいは、半乾燥状態のポリイミド成形物を一旦引き剥がして、最終的な内径を規定するために、別の金型の外周にはめ込み、最終焼成温度まで加熱する。これによって、管状成形物を容易に得ることができる。
【０２１４】
なお、円筒状金型へのポリイミド溶液の塗布に際しては、ポリイミド溶液の垂れによる厚みのばらつきを緩和するため、円筒状金型を回転させることも有効である。
【０２１５】
また、最終焼成温度はポリイミド樹脂の構造や、添加する高抵抗カーボンブラックの耐熱性に基づいて、適切な温度を適宜設定すればよい。一般的には、ポリイミド樹脂が、非熱可塑ポリイミドであって、前駆体のポリアミド酸から加熱・焼成する場合には、概ね３５０℃〜４５０℃の範囲内であればよい。また、熱可塑ポリイミドの場合には、ポリイミド樹脂のガラス転位点温度に対し−２０℃〜＋１００℃の範囲内となる温度範囲がより好ましい。
【０２１６】
＜ポリイミド成形物の用途の一例＞
本発明にかかるポリイミド成形物の用途としては、その特性を活かすことができる用途であれば特に限定されるものではないが、特に、各種電子機器の部品等として非常に好適に用いることができる。
【０２１７】
上記電子部品の例としては、具体的には、フレキシブルプリント配線板（ＦＰＣ）やＴＡＢ（Ｔａｐｅ　Ａｕｔｏｍａｔｅｄ　Ｂｏｎｄｉｎｇ）等のベース基材、電線等の絶縁被膜、複写機等の各種ＯＡ機器の部品（例えば、分離爪やベアリング等の成形物）、半導体用の接着剤や絶縁膜等が挙げられる。
【０２１８】
中でも、本発明にかかるポリイミド成形物は、各種コピー機やプリンター等の電子写真装置の部品である、転写ベルト、中間転写ベルト、転写定着ベルト等として非常に好適に用いることができる。
【０２１９】
具体的には、まず、上記転写ベルトや中間転写ベルト等では、トナーを良好に転写するために、体積抵抗値を中間抵抗値に制御することが重要となる。さらに、これら転写ベルトや中間転写ベルト等では、体積抵抗値は、どのような環境下でもほぼ一定であることが好ましい。具体的には、特に、常温常湿時と高温高湿時とにおける体積抵抗値の比が１００倍以下であることが好ましく、３０倍以下であることがより好ましい。
【０２２０】
しかも、ポリイミド樹脂は吸湿性を有することから、特に、カーボンブラックやその他の導電性充填剤を添加すると、高温高湿下では、導電性充填材とポリイミド樹脂との界面に水が浸透し、体積抵抗値が大幅に低下する。また、ベースとなるポリイミド樹脂が吸湿して膨張すると、上記カーボンブラックや添加剤等の分散状態が変化し、体積抵抗値が大幅に変動する。
【０２２１】
また、これら転写ベルトや中間転写ベルト等では、電子写真装置で形成する画像の種類や、電子写真装置の使用環境に応じて、電圧や電流を制御する必要がある。そのため、転写ベルトや中間転写ベルト等において、電圧に応じて体積抵抗値が変動すると電圧や電流の制御が困難となるので、体積抵抗値の電圧依存性も小さいほど好ましい。具体的には、１００Ｖおよび１０００Ｖにおける体積抵抗値の比が１００倍以下であることが好ましく、３０倍以下であることがより好ましい。
【０２２２】
さらに、転写ベルトや中間転写ベルト等は、電子写真装置内において、光学処理部の近傍に設けられる。そのため、その色は黒色であることが望まれる。しかしながら、一般的なカーボンブラックを添加したポリイミド系材料で作製されるベルト（管状成形物）は、体積抵抗値の制御が難しいため、着色料でもあるカーボンブラックの添加量を最適化することが難しく、黒色を良好に実現し難い場合がある。
【０２２３】
上記のような物性を全て満たすことは、従来のポリイミド系材料では非常に困難であった。しかしながら、本発明にかかるポリイミド樹脂組成物およびポリイミド成形物は、前記＜高抵抗カーボンブラックの配合による諸物性の制御＞で説明した（１）〜（５）の諸物性の制御を容易に実現することができる。その結果、本発明にかかるポリイミド成形物は、特に、ベルト状（管状）に成形されている場合、電子写真装置の転写ベルト、中間転写ベルト、および転写定着ベルトの少なくとも何れかとして非常に好適に用いることができる。
【０２２４】
なお、本発明にかかるポリイミド成形物を、上記転写ベルトや中間転写ベルトとして用いる場合、当該ポリイミド成形物の表面には導電性制御されたフッ素樹脂製の最外層を形成するとよい。これによって、転写ベルトまたは中間転写ベルトからのトナーの離型性や、トナーの転写性、あるいはトナーのクリーニング性を改善することができる。
【０２２５】
上記フッ素樹脂としては、ＰＴＦＥ（ポリテトラフルオロエチレン）やＰＦＡ（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）等が挙げられるが特に限定されるものではない。また、フッ素樹脂の導電性を制御するための添加剤としては、前述した導電性または半導電性充填剤を用いることが可能である。上記最外層の形成方法は、フッ素樹脂溶液の塗布や、フッ素樹脂フィルムの貼り合わせ等が挙げられるが、これら材料を溶媒に分散してスプレー塗布する方法が一般的である。
【０２２６】
【実施例】
以下、実施例および比較例により、本発明をさらに詳細に説明するが、本発明はこれに限定されるものではない。なお、各実施例および比較例におけるポリイミド成形物の物性の評価は、次に示すようにして実施した。
【０２２７】
〔ポリイミド成形物の物性評価方法〕
＜抵抗値の測定と評価＞
各実施例または比較例で得られた管状のポリイミド成形物からフィルム状のサンプルを切り出した。また、カーボンブラックおよび充填剤については、ベークライト製の円筒状容器にそれぞれ約０．２５ｇ充填し、カーボンブラックの場合は約４９０Ｎ／ｃｍ^２（５０ｋｇｆ／ｃｍ^２）の圧力で、その他充填剤の場合は無荷重で圧縮することで、高さが約１０ｍｍの円筒状サンプルを作製した。
【０２２８】
上記フィルム状サンプル、あるいは、カーボンブラックまたは充填剤の円筒状サンプルを次の３つの条件下で２４時間放置した。
【０２２９】
▲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）
そして、当該環境下にて、アドバンテスト（株）製デジタル超高抵抗／微小電流計Ｒ８３４０および三菱化学（株）製ＨＲプローブを用いて、１００Ｖにおける体積抵抗値と表面抵抗値を測定した。また、フィルム状サンプルでは、１０００Ｖでも測定を実施した。
【０２３０】
なお、抵抗値の環境依存性とは、上記ＬＬ（低温低湿時）の体積抵抗値Ｒｌと、上記ＨＨ（高温高湿時）の体積抵抗値Ｒｈとの比（Ｒｌ／Ｒｈ）を指し、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}の比（Ｒ_１００Ｖ／Ｒ_{１０００Ｖ}）を指す。これらの値が０．３〜３０の範囲内にある場合には、何れも依存性が少ないと判断し、前者が０．０１〜０．３の範囲内で後者が３０〜１００の範囲内にある場合には、何れも依存性が中程度あると判断し、前者が０．０１以下であり、後者が１００以上である場合には、何れも依存性が悪い材料とした。
【０２３１】
＜電気絶縁性の測定と評価＞
フィルム状サンプルを、上記▲２▼（ＮＮ）の環境に２４時間放置し、該環境下にて安田精機製作所製のＹＳＳ式耐電破壊試験機を用いて電気絶縁性を測定した。絶縁破壊電圧が１５ｋＶ／ｍｍ以上であれば電気絶縁性が高いと判断し、１０ｋＶ／ｍｍ以上であれば電気絶縁性が中程度であると判断し、１０ｋＶ／ｍｍ以下であれば電気絶縁性が低いと判断した。
【０２３２】
＜引張弾性率、引張伸び、および引裂伝播強度の測定＞
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。また、フィルム状サンプルの引裂伝播強度の測定は、ＡＳＴＭ　Ｄ１９３８に準拠して実施した。
【０２３３】
〔実施例１〕
芳香族系ジアミン化合物として、４，４’−ジアミノジフェニルエーテルを用い、芳香族系酸二無水物として、ピロメリット酸二無水物（ＰＭＤＡ）を用いてポリアミド酸を合成し、ポリアミド酸のジメチルホルムアミド（ＤＭＦ）溶液（固形分濃度１８．５％、溶液粘度３，０００　ｐｏｉｓｅ）を７５ｇ調製した。
【０２３４】
また、高抵抗カーボンブラック（カーボンブラックの表面に、ポリビニルピロリドンをグラフトしたもの、体積抵抗値：９００Ω・ｃｍ）４．１７ｇを、当該高抵抗カーボンブラック量の８倍量のＤＭＦに分散させて分散液を調製した。
【０２３５】
上記ポリアミド酸溶液に高抵抗カーボンブラックの分散液を添加し混合した。さらに、この混合物に対して、無水酢酸／イソキノリン／ＤＭＦ＝９．０３ｇ／１１．４ｇ／１５．６ｇの配合比からなるイミド化促進剤溶液を添加して混合した。その後、ＳＵＳ製の円筒状金型にキャストし、１４０℃／２４０秒、２７５℃／４０秒、および４００℃／９３秒の条件で熱処理した。
【０２３６】
これにより、約５０μｍの厚みを有する管状のポリイミド成形物を得た。得られたポリイミド成形物の配合を表１に、物性の評価結果のうち、電気特性を表２に、依存性・機械特性を表３に示す。なお、このポリイミド成形物に含まれる高抵抗カーボンブラックの量は、ポリイミド固形分１００重量部に対して３０重量部である。
【０２３７】
また、このようにして得られたフィルム状成形物（ポリイミドフィルム）単体の線膨張係数は２１ｐｐｍであり、吸湿膨張係数は１６ｐｐｍであり、引張弾性率は２．９ＧＰａであり、引張伸びは７０％であり、引き裂き伝播強度は４．４１Ｎ／ｍｍ（４５０ｇｆ／ｍｍ）であり、吸水率は２．５％であった。
【０２３８】
〔実施例２〕
高抵抗カーボンブラックとして、ポリビニルピロリドンをグラフトしたもので、体積抵抗値：２０，０００Ω・ｃｍのもの６．９５ｇを、当該高抵抗カーボンブラック量の８倍量のＤＭＦに分散させて分散液を調製した以外は、前記実施例１と同様にして、管状のポリイミド成形物を得た。
【０２３９】
得られたポリイミド成形物の配合を表１に、物性の評価結果のうち、電気特性を表２に、依存性・機械特性を表３に示す。なお、このポリイミド成形物に含まれる高抵抗カーボンブラックの量は、ポリイミド固形分１００重量部に対して５０重量部である。
【０２４０】
〔実施例３〕
高抵抗カーボンブラックに加えて、黒色系フィラーとして、カーボン被覆フィラー（カーボン被覆チタン酸カリウムウィスカー：デントールＢＫ４００ＨＲ：Ｌｏｔ．９Ｃ００：大塚化学（株）製：比重３．１５ｇ／ｃｍ^３、体積抵抗値５×１０^５〜５×１０^６Ω・ｃｍ、イオン溶出量５００〜１００００ｐｐｍ、短軸０．３〜０．６μｍ、長軸１０〜２０μｍ）を添加した以外は、前記実施例１と同様にして、管状のポリイミド成形物を得た。
【０２４１】
得られたポリイミド成形物の配合を表１に、物性の評価結果のうち、電気特性を表２に、依存性・機械特性を表３に示す。なお、このポリイミド成形物に含まれる高抵抗カーボンブラックおよびカーボン被覆フィラーの量は、ポリイミド固形分１００重量部に対して４０重量部である。
【０２４２】
〔実施例４〕
高抵抗カーボンブラックに加えて、酸化錫系フィラー（酸化錫系被覆ホウ酸アルミニウムウィスカー：パストラン−タイプＩＶ−ＫＫ００７：三井金属（株）製：比重３ｇ／ｃｍ^３、体積抵抗値１×１０^７Ω・ｃｍ、イオン溶出量＜５０ｐｐｍ、短軸１μｍ、長軸１０μｍ）を添加した以外は、前記実施例１と同様にして、管状のポリイミド成形物を得た。
【０２４３】
得られたポリイミド成形物の配合を表１に、物性の評価結果のうち、電気特性を表２に、依存性・機械特性を表３に示す。なお、このポリイミド成形物に含まれる高抵抗カーボンブラックおよびカーボン被覆フィラーの量は、ポリイミド固形分１００重量部に対して４０重量部である。
【０２４４】
〔実施例５〕
芳香族系ジアミン化合物として、４，４’−ジアミノジフェニルエーテル５当量、およびパラフェニレンジアミン５当量を用い、これらをＤＭＦに溶解し、次に、芳香族系酸二無水物としてｐ−フェニレンビス（トリメリット酸モノエステル酸無水物）（ＴＭＨＱ）５当量を加え、さらに、芳香族系酸二無水物としてＰＭＤＡ５当量を加えてポリアミド酸を重合した。このようにして得られたポリアミド酸のＤＭＦ溶液（固形分濃度１８．５％、溶液粘度３，０００　ｐｏｉｓｅ）を用いた以外は、前記実施例１と同様にして、管状のポリイミド成形物を得た。得られたポリイミド成形物の配合を表１に、物性の評価結果のうち、電気特性を表２に、依存性・機械特性を表３に示す。
【０２４５】
また、このようにして得られたフィルム状成形物（ポリイミドフィルム）単体の線膨張係数は９ｐｐｍであり、吸湿膨張係数は５ｐｐｍであり、引張弾性率は６ＧＰａであり、引張伸びは４０％であり、引き裂き伝播強度は４．４１Ｎ／ｍｍ（４５０ｇｆ／ｍｍ）であり、吸水率は１．２％であった。
【０２４６】
〔実施例６〕
芳香族ジアミン化合物として４，４’−ジアミノジフェニルエーテル５当量、およびパラフェニレンジアミン５当量を用い、これらをＤＭＦに溶解し、次に、芳香族系酸二無水物としてＴＭＨＱ５当量加え、さらに、芳香族系酸二無水物としてＰＭＤＡ５当量を加えてポリアミド酸を重合した。このようにして得られたポリアミド酸のＤＭＦ溶液（固形分濃度１８．５％、溶液粘度３，０００　ｐｏｉｓｅ）を用いたい以外は、前記実施例２と同様にして、管状のポリイミド成形物を得た。得られたポリイミド成形物の配合を表１に、物性の評価結果のうち、電気特性を表２に、依存性・機械特性を表３に示す。
【０２４７】
〔比較例１〕
カーボンブラックとして、ポリビニルピロリドンをグラフトしたもの、体積抵抗値１０Ω・ｃｍもの２．７８ｇを、当該カーボンブラック量の８倍量のＤＭＦに分散させて分散液を調製した以外は、前記実施例１と同様にして、管状のポリイミド成形物を得た。なお、このポリイミド成形物に含まれるカーボンブラックの量は、ポリイミド固形分１００重量部に対して２０重量部である。得られたポリイミド成形物の配合を表１に、物性の評価結果のうち、電気特性を表２に、依存性・機械特性を表３に示す。
【０２４８】
〔比較例２〕
ＤＭＦ２１ｇに、カーボンブラック（＃３０３０Ｂ：三菱化学（株）：＜１．０Ｅ＋１Ω・ｃｍ）４．１７ｇを分散させて分散液を調製した以外は、前記実施例１と同様にして、管状のポリイミド成形物を得た。なお、このポリイミド成形物に含まれるカーボンブラックの量は、ポリイミド固形分１００重量部に対して３０重量部である。得られたポリイミド成形物の配合を表１に、物性の評価結果のうち、電気特性を表２に、依存性・機械特性を表３に示す。
【０２４９】
【表１】

【０２５０】
【表２】

【０２５１】
【表３】

【０２５２】
上記実施例１〜６のポリイミド成形物においては、その物性は次のようになった。
【０２５３】
（１）上記▲２▼ＮＮおよび▲３▼ＨＨの環境下における体積抵抗値は１×１０^８〜１×１０^１３Ω・ｃｍの範囲内となっており、中間抵抗値の範囲内に制御されていた。また、電気絶縁性も１０ｋＶ／ｍｍ以上と優れていた。
【０２５４】
（２）高抵抗カーボンブラックの配合量の差（５重量部）による体積抵抗値の比は３倍以下であり、体積抵抗値の配合量に対する依存性は小さかった。また、上記▲２▼ＮＮおよび▲３▼ＨＨの環境下における体積抵抗値の比は３０倍以下であり、体積抵抗値の環境依存性は小さかった。
【０２５５】
（３）１００Ｖと１０００Ｖで測定した体積抵抗値の比は３０倍以下であり、体積抵抗値の電圧依存性は小さかった。
【０２５６】
（４）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倍以下であり、非常に小さかった。
【０２５７】
（５）フィルム状サンプルにおける引張弾性率は、フィラー未配合のものに比べて優れており、引張伸びは５０％以上、引裂伝播強度は５０％以上を保持していた。また、線膨張係数、吸湿膨張係数も、フィラー未配合のものよりも数ｐｐｍ低下していた。なお、引張弾性率は、実施例１〜４、実施例５、実施例６の順に増加していた。これは、ベースとなるポリイミド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。
【０２５８】
これに対して、上記比較例１・２のポリイミド成形物においては、その物性は次のようになった。
【０２５９】
（１）比較例１〜２のポリイミド樹脂では、何れも上記▲２▼ＮＮの環境下における体積抵抗値は、所望の中間抵抗値に制御されていたが、▲３▼ＨＨの環境下では非常に抵抗値が低かった。
【０２６０】
（２）カーボンブラックの配合量の差（５重量部）による体積抵抗値の比は３倍以上あり、体積抵抗値の配合量に対する依存性は大きかった。
【０２６１】
（３）上記▲２▼ＮＮおよび▲３▼ＨＨの環境下における体積抵抗値の比は１００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。
【０２６２】
（４）１００Ｖと１０００Ｖで測定した体積抵抗値の比は１００倍以上あり、体積抵抗値の電圧依存性は大きかった。
【０２６３】
（５）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測定を行った結果、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。また、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。
【０２６４】
以上より、本発明にかかるポリイミド樹脂組成物およびポリイミド成形物が非常に優れた物性を有することがわかる。
【０２６５】
【発明の効果】
このように、本発明にかかるポリイミド樹脂組成物およびポリイミド成形物においては、少なくとも上記高抵抗カーボンブラックを添加することにより、従来では困難であった、前記＜高抵抗カーボンブラックの配合による諸物性の制御＞の項で説明した（１）〜（５）の諸物性の制御を容易に実現することができる。
【０２６６】
その結果、体積抵抗値を過剰に高めることなく優れた電気絶縁性を実現することができるとともに、抵抗値の環境依存性、高抵抗カーボンブラックの配合量に対する依存性、電圧依存性、サンプル間でのばらつき、同一成形物における偏り、イミド化による影響等が小さく、安定した特性を実現することができる。
【０２６７】
それゆえ、本発明にかかるポリイミド樹脂組成物およびポリイミド成形物は、特に、ＦＰＣやＴＡＢ、あるいは電子写真装置の部品等のような各種電子機器の部品の用途等に好適に用いることができる。例えば、ＦＰＣ等では、搬送や巻取時の帯電防止性を優れたものとすることができる。また、電子写真装置の部品として用いる場合、トナー像の転写性を優れたものとすることができる。
【０２６８】
したがって、本発明は、ＦＰＣやＴＡＢ等の高密度実装材料や配線材料を製造する産業、例えば電子部品用の樹脂材料を製造する樹脂産業分野に好適に用いることができるだけでなく、半導体関連の分野、電子写真装置に代表される各種電子機器の部品に関連する分野、さらにはこのような電子部品を用いる電子機器の産業分野に好適に用いることができるという効果を奏する。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a polyimide resin composition and a polyimide molded product using the same, and more particularly, to controlling the volume resistivity within a moderate range while maintaining various excellent properties of the polyimide resin. The present invention relates to a polyimide resin composition that can be used and a polyimide molded product using the same.
[0002]
[Prior art]
Polyimide resin has excellent properties such as heat resistance, chemical resistance, and electrical insulation. Therefore, it has been widely used in various fields, and is particularly preferably used for, for example, parts of various electronic devices. Specific examples of electronic device components include, specifically, base materials such as a flexible printed wiring board (FPC) and TAB (Tape Automated Bonding), insulating films such as electric wires, and various OA device components such as copiers. For example, molded articles such as separation claws and bearings) are exemplified.
[0003]
Products made of polyimide resin (polyimide products) can be used as the above-mentioned parts as films, tubes (including tubes and belts), or molded products of polyimide resin molded into other specific shapes. Used. In recent years, it has also been used for semiconductors, and for example, has been used as an adhesive for semiconductors, etc., utilizing its characteristics.
[0004]
By the way, characteristics possessed by the polyimide resin, particularly, its excellent electrical insulation properties, may not be preferable depending on applications. For example, in the production of FPCs and semiconductors, when a polyimide product is transported or a film-like polyimide product is wound, the polyimide resin is easily charged due to its excellent electrical insulation. For this reason, in particular, in a high-density integrated circuit or the like, a problem that dielectric breakdown occurs between wirings has become apparent.
[0005]
On the other hand, in the production of FPCs and semiconductors, it is also required that the polyimide resin maintain a high resistance value so that conduction does not occur and maintain excellent electrical insulation. That is, in a component or the like of an electronic device, a resistance value that does not easily charge the polyimide resin and that can exhibit excellent electrical insulation properties is required. The specific resistance value required in this case is generally 10 ¹⁰ -10 ^Fifteen Ω · cm, and 10 ¹⁰ -10 ^Thirteen The range of Ω · cm is more preferable.
[0006]
Further, in electrophotographic apparatuses such as various copiers and printers, as described above, various molded products using a polyimide resin are used as parts, for example, a transfer belt, an intermediate transfer belt, or a transfer fixing belt. Can be mentioned. Here, it is well known that for a transfer belt, an intermediate transfer belt, or the like, controlling the volume resistance within a medium range is an important quality issue in order to transfer toner satisfactorily. The specific volume resistance value required in this case is generally 10 ⁶ -10 ^Thirteen Within the range of Ω · cm.
[0007]
As described above, it is strongly required that the resistance value of the polyimide resin be controlled to be in a middle range so as to maintain preferable electric insulation in various fields. In consideration of the above-mentioned respective uses, the range of the medium range is generally 10%. ⁶ -10 ^Fifteen It is particularly preferred that it is within the range of Ω · cm. In the following description, a resistance value within this range is referred to as an intermediate resistance value for convenience of description.
[0008]
Therefore, conventionally, a technique has been developed in which various conductive substances are added to a polyimide resin to control its resistance value.
[0009]
<Filling material mixing technology>
Specifically, first, a technique of mixing a conductive filler such as carbon black, graphite, metal particles, and indium oxide with a polyimide resin (hereinafter, referred to as a filler mixing technique for convenience of description) is known. ing. For example, Patent Literature 1 discloses a semiconductive resin composite material containing an aromatic polyimide and a finely divided electrically conductive particle material, in which the particle material is uniformly dispersed and present in an amount of 10 to 45% by weight of the entirety. The developing roll used is disclosed. Patent Document 2 discloses that a carbon black is contained in an amount of 5 to 20% by weight and a surface resistance Rs (Ω / □) is 10%. ⁷ ≤Rs≤10 ^Fifteen An intermediate transfer member for an electrophotographic recording apparatus comprising an aromatic polyamide film or an aromatic polyimide film in the range described above is disclosed. Further, Patent Document 3 discloses a composition comprising an aromatic polyimide and a conductive inorganic filler, and having a volume resistivity of 10%. ^-2 -10 ¹² A transparent conductive film having a range of Ω · cm and a total light transmittance of 20% or more is disclosed.
[0010]
<Technology using two types of conductive fillers>
Patent Literature 4 discloses a technique using two types of conductive fillers, a main conductive filler and a supplemental conductive filler. The main conductive filler has an average particle diameter of 1 to 50 μm and a volume resistivity of 10 ³ -10 ⁹ High resistance particles having a large diameter of Ω · cm are used, and the auxiliary conductive filler has an average particle diameter smaller than 0.1 μm and a volume resistivity of 10 μm. ² Resistive particles having a small particle size of Ω · cm or less are used. In this technique, these are dispersed in a resin, so that the volume resistivity is 10%. ⁵ -10 ⁹ A semiconductive resin composite material controlled to a range of Ω · cm is realized.
[0011]
<Carbon black technology>
Furthermore, recently, a technique of using carbon black as a conductive filler and attempting to realize the above-described intermediate resistance value (hereinafter, referred to as a carbon black-based technique for convenience of description) has also been proposed. For example, Patent Literature 5 discloses a technique in which carbon black and a plate-like or column-like conductive powder are added to a polyimide resin in a predetermined compounding amount. Patent Document 6 discloses a technique of using conductive carbon black containing an acidic volatile component in aromatic polyimide, and Patent Document 7 discloses a conductive carbon black having specific surface characteristics. The technology used is disclosed. Further, Patent Document 8 discloses a technique of adding carbon black having an electric resistance value in a range of 1 to 100 Ω · cm. Particularly, in Patent Document 8, a grafted carbon black obtained by grafting a hydrophilic polymer is preferably used.
[0012]
<Polymer blend technology>
Alternatively, Patent Literatures 9 and 10 disclose a technology for imparting conductivity by polymer blending a polyaniline resin and a polyimide resin (hereinafter, described as a technology for improving the problems of the technology for adding the various conductive materials described above). For convenience, referred to as polymer blending technology).
[0013]
[Patent Document 1]
JP-A-2-110138 (Published date: April 23, 1990)
[0014]
[Patent Document 2]
JP-A-63-31263 (publication date: December 10, 1988)
[0015]
[Patent Document 3]
Japanese Patent No. 2783537 (Registration date: May 22, 1998, published patent: JP-A-63-241804, published date: October 7, 1988)
[0016]
[Patent Document 4]
Japanese Patent Application Laid-Open No. 4-133077 (published on May 7, 1992)
[0017]
[Patent Document 5]
JP 2000-88242 A (publication date: March 27, 2000)
[0018]
[Patent Document 6]
JP 2001-47451 A (publication date: February 20, 2001)
[0019]
[Patent Document 7]
JP-A-2002-132061 (publication date: May 9, 2002)
[0020]
[Patent Document 8]
JP 2000-355432 A (publication date: December 26, 2000)
[0021]
[Patent Document 9]
JP-A-8-259810 (publication date: October 8, 1996)
[0022]
[Patent Document 10]
JP-A-8-259709 (publication date: October 8, 1996)
[0023]
[Problems to be solved by the invention]
However, in each of the above-mentioned conventional techniques, it is difficult to control the resistance value to an intermediate resistance value while maintaining excellent characteristics such as the electrical insulation property of the polyimide resin.
[0024]
<Problems of filler mixing technology>
First, in the above-mentioned filler mixing technique, the mechanical properties of the obtained polyimide resin and its molded product often deteriorate. The conductive filler used in this technique has a resistivity of 1.0 × 10 ³ Since the resistance is very low at Ω · cm or less, it is very difficult to control the resistance value in the semiconductive region.
[0025]
In particular, in the above-described filler mixing technique, it is difficult to obtain (1) a polyimide resin or a polyimide molded product having a certain range of resistance value (especially, an intermediate resistance value) with good reproducibility. (3) The resistance value of the polyimide molded product greatly depends on the measured voltage and the amount of the conductive filler added.
[0026]
<Problems of technology using two types of conductive fillers>
In addition, in the technique using the above two types of conductive fillers, the main conductive filler is a large-diameter, high-resistance particle. Therefore, when such a conductive filler is added, it has an effect on obtaining a molded article having a small thickness. Occurs. For example, a molded product such as a film or a tube has a thickness of about 100 μm. However, if the large-sized high-resistance particles as described above are added to such a thin molded product, a dielectric breakdown occurs or a voltage of a resistance value is generated. It is not preferable because dependency is increased.
[0027]
<Problems of polymer blend technology>
Furthermore, since the polyaniline resin used in the polymer blend technique has ionic conductivity, its resistance value is highly environmentally dependent. In addition, the polyaniline resin has a problem that it is very expensive to use as a polymer blend because no industrial production technology has been established.
[0028]
<Problems of carbon black technology>
Further, as in the above carbon black-based technology, when carbon black is added as a conductive filler to control the resistance value of a polyimide resin or a polyimide molded product, the volume resistance value is increased due to a problem specific to the polyimide resin. The problem arises that the variation in the size tends to increase.
[0029]
Specifically, (1) the molding of polyimide is not a simple molding by heat melting, but a very complicated one involving heating a precursor polyamic acid solution and involving solvent drying and imidization reaction. Therefore, the morphology, polarity, and solubility of the material change significantly during drying and during the reaction. As a result, the added carbon black causes agglomeration during the drying and reaction processes, and the dispersion of the volume resistance value tends to increase.
[0030]
(2) In particular, a polyimide resin containing an aromatic, especially a polyimide resin containing an aromatic in both the diamine structure and the acid dianhydride structure, has a volume resistance of 10%. ¹⁶ Very high Ω · cm. Therefore, it is necessary to add a large amount of carbon black as compared with a resin having a low volume resistance such as a polyamide resin or a polyvinyl chloride resin. When the amount of addition is large as described above, the dispersion of the volume resistance value due to insufficient mixing / dispersion tends to increase.
[0031]
Furthermore, (3) since the conductive filler such as carbon black has a low resistance value, the resistance value may significantly change due to a slight difference in the amount of addition or a difference in the dispersion state, or even if the composition is exactly the same, the inter-sample In this case, there is a problem that the resistance value differs.
[0032]
In addition, as described above, the main applications of the polyimide resin and the polyimide molded product having an intermediate resistance value include a transfer belt and an intermediate transfer belt of an electrophotographic apparatus. Here, since the thickness of these belt-shaped molded products is small, the partial variation of the volume resistance value is likely to be large. This partial variation in the volume resistance value leads to a significant decrease in the reliability of the electrical insulation, so that it is more difficult to control the volume resistance value.
[0033]
Moreover, in the transfer belt and the intermediate transfer belt, it is preferable that the volume resistance is constant under any environment. However, in the case of a resin material to which carbon black or the like is added, the interface between the conductive material and the resin is high under high temperature and high humidity. However, there is a problem that water penetrates into the air and the electric resistance is greatly reduced. Further, when the resin absorbs and expands by moisture, the dispersion state of carbon black and the like also changes, so that there is a problem that the volume resistance value largely fluctuates.
[0034]
In the case of using imidization by heating (thermal curing method) in molding a polyimide resin, it is possible to control the volume resistance value even with a carbon black-based technique. However, when imidization (chemical curing method) in which an imidization accelerator is added is used, the morphology, polarity, and solubility of the material change dramatically. Therefore, there is a problem that the carbon black easily aggregates in the polyimide resin, and therefore, the obtained polyimide molded article is very liable to vary in volume resistance value.
[0035]
The present invention has been made in view of the above problems, and while maintaining various excellent properties of the polyimide resin, particularly the electrical insulation, by using carbon black, the volume resistance value to an intermediate resistance value. An object of the present invention is to provide a polyimide resin composition which can be controlled well and a polyimide molded product using the same.
[0036]
[Means for Solving the Problems]
The present inventors have conducted intensive studies in view of the above problems, and as a result, by adding a specific amount of a high-resistance carbon black having a specific volume resistance to a polyimide resin and mixing and dispersing the same, an intermediate resistance value can be realized. The present inventors have found that stable electrical insulation can be realized, and in particular, a variation in volume resistance value can be reduced, and the present invention has been completed.
[0037]
That is, in order to solve the above problems, the polyimide resin composition according to the present invention contains at least a polyimide resin and carbon black, and has a volume resistance of 1 × 10 ⁶ ~ 1 × 10 ¹⁶ A polyimide resin composition in the range of Ω · cm, wherein the carbon black is 490 N / cm ² The volume resistance measured using the sample compressed in ² ~ 1 × 10 ¹⁰ High resistance carbon black in the range of Ω · cm is used, and the carbon black is contained in the range of 20 to 100 parts by weight with respect to 100 parts by weight of the polyimide resin.
[0038]
In the polyimide resin composition, it is preferable that a grafted carbon black obtained by grafting a hydrophilic polymer onto the surface of carbon black is used as the high resistance carbon black.
[0039]
The polyimide resin composition further contains a conductive or semiconductive filler, and the filler is 0.01 to 100 parts by weight based on 100 parts by weight of the polyimide resin. It is preferable that it is contained within the range.
[0040]
Further, in the polyimide resin composition, a reaction-curable linear polyimide resin is preferably used as the polyimide resin, and the polyimide resin is obtained by adding an acid anhydride and a tricarboxylic acid to a polyamic acid as an imidization accelerator. More preferably, it is obtained by heating after adding at least one of the secondary amines.
[0041]
Moreover, in order to solve the above-mentioned problems, a polyimide molded product according to the present invention is characterized by comprising a polyimide resin composition having the above-described configuration.
[0042]
In the above-mentioned polyimide molded product, it is preferable that the molded product is formed into a film or a tube. More preferably, it is used.
[0043]
According to the above configuration, an intermediate resistance value can be easily realized by using the high resistance carbon black. As a result, excellent electrical insulation can be realized without excessively increasing the volume resistance value. In addition, even under an environment of rapid change such as a chemical curing method, the affinity with the polyimide resin can be maintained. Therefore, aggregation in the polyimide resin composition can be effectively suppressed or avoided, and a situation in which a partial bias occurs in the volume resistance value can be avoided, and a stable resistance value can be realized. . Furthermore, if a grafted carbon black having a high affinity with the polyimide resin is used, its mechanical properties (particularly, mechanical strength, dimensional stability, etc.) can be improved.
[0044]
Moreover, according to the above configuration, even under conditions such as high temperature and high humidity, there is little change in both the volume resistance value and the electrical insulation, so that the environment dependency is small. In addition, the voltage dependency of the volume resistance value is small, and the dependency on the amount of the high-resistance carbon black added is small. Further, variation in the volume resistance value between samples can be reduced. Therefore, the polyimide resin and the polyimide molded product according to the present invention can realize stable electric insulation and volume resistance.
[0045]
As a result, the polyimide resin composition and the polyimide molded product according to the present invention can be suitably used, in particular, for applications such as FPC, TAB, and components of various electronic devices such as components of an electrophotographic apparatus. For example, in an FPC or the like, an excellent antistatic property at the time of conveyance or winding can be obtained. Further, when used as a component of an electrophotographic apparatus, the transferability of a toner image can be improved.
[0046]
BEST MODE FOR CARRYING OUT THE INVENTION
The following will describe one embodiment of the present invention. Note that the present invention is not limited to this.
[0047]
The polyimide resin composition according to the present invention is obtained by adding at least a specific amount of high-resistance carbon black to a polyimide resin and mixing and dispersing the same. ⁶ ~ 1 × 10 ¹⁶ It is within the range of Ω · cm. Further, the polyimide molded article according to the present invention is molded using this polyimide resin composition.
[0048]
<Polyimide resin>
The polyimide resin contained in the polyimide resin composition according to the present invention is not particularly limited as long as it has an imide bond in its structure. Specifically, for example, polyether imide, polyester imide, polyamide imide and the like can be mentioned. These may be used alone or in combination. In addition, the polyimide resin in the present invention may be a copolymer containing a structure derived from a monomer component used in another resin as long as the polyimide resin has an imide bond.
[0049]
Therefore, the polyimide resin in the present invention may be the above-mentioned various polyimide resins alone, a polyimide copolymer, or a blend of a plurality of polyimide resins. Further, a resin other than the polyimide resin may be used to such an extent that desired physical properties of the obtained polyimide resin composition or polyimide molded product are not affected.
[0050]
The method for producing the polyimide resin is not particularly limited. And the like.
[0051]
<Reaction-curable linear polyimide resin>
Here, the polyimide resin in the present invention can be particularly preferably used. Among them, a polyimide resin obtained by a method of synthesizing a polyamic acid and dehydrating and ring-closing (imidizing) an amide moiety is preferably used. This polyimide resin is referred to as a reaction-curable linear polyimide resin for convenience of explanation.
[0052]
The linear polyamic acid as a precursor has a functional group such as a carboxyl group or an amino group. These functional groups interact strongly with the high-resistance carbon black (particularly, grafted carbon black) described below, and can form a strong bond or have a strong affinity with the high-resistance carbon black. Therefore, if the reaction-curable linear polyimide resin is used, the aggregation of the high-resistance carbon black in the polyimide resin composition is more effectively suppressed or avoided, and the physical properties of the obtained polyimide resin composition or polyimide molded product Can be further improved.
[0053]
<Monomer component used for synthesis of polyamic acid>
Polyamic acid, which is a precursor of the reaction-curable linear polyimide resin, can be obtained by using a diamine compound and a tetracarboxylic dianhydride as monomer components and reacting them in an organic solvent.
[0054]
The diamine compound used for synthesizing the above polyamic acid is not particularly limited. For example, a diamine represented by the following formula (1), that is, an aromatic compound having one or more aromatic rings in one molecule. A system diamine can be mentioned.
[0055]
H ₂ NR ¹ -NH ₂ ... (1)
However, in the above formula (1), R ¹ Represents a divalent organic group containing an aromatic ring selected from the following group (2).
[0056]
Embedded image

[0057]
In the group (2), X is each independently a halogen atom or -CH ₃ , -OCH ₃ , -O (CH ₂ ) _n CH ₃ ,-(CH ₂ ) _n CH ₃ , -CF ₃ , -OCF ₃ And at least one monovalent organic group selected from the group consisting of A is each independently -O-, -S-, -CO-,-(CH ₂ ) _n -, -SO ₂ And at least one divalent group selected from the group consisting of-, -N = N-. Further, n represents an integer of 1 or more, and m represents any integer of 1 to 5. Further, these aromatic diamine compounds may be used alone or in combination of two or more.
[0058]
The tetracarboxylic dianhydride (hereinafter, abbreviated as acid dianhydride for convenience of description) used in the synthesis of the polyamic acid is not particularly limited, but may be, for example, a compound represented by the following formula (3). Acid dianhydrides, ie, aromatic acid dianhydrides having one or more aromatic rings in one molecule.
[0059]
Embedded image

[0060]
However, in the above formula (3), R ² Represents a tetravalent organic group containing an aromatic ring selected from the following group (4).
[0061]
Embedded image

[0062]
In addition, in group (4), n shows the integer of 1 or more. These aromatic acid dianhydrides may be used alone or in combination of two or more.
[0063]
Further, as described later, by appropriately selecting and combining the diamine compound and the acid dianhydride, it becomes possible to impart various properties to the obtained reaction-curable linear polyimide resin. Therefore, the above-mentioned respective monomer components may be selected according to the use or processing method of the polyimide resin composition or the polyimide molded product according to the present invention, and a polyimide resin having desired physical properties may be synthesized.
[0064]
<Specific examples of combinations of monomer components>
Examples of the combination of the monomer components are not particularly limited, but in the present embodiment, the present invention will be described in more detail by giving the following examples (1) to (3).
[0065]
First, as an example of a combination of monomer components, (1) a combination capable of synthesizing a thermoplastic polyimide resin can be mentioned. In this example, as the diamine compound, an aromatic diamine which satisfies at least one of the conditions including a large number of bent chains (preferably two or more) or the condition having an amino group at the meta position is used, and as an acid dianhydride, An aromatic acid dianhydride containing two or more aromatic rings in one molecule is used. Thereby, a thermoplastic polyimide resin can be obtained. If such a thermoplastic polyimide resin is used, it is possible to obtain a polyimide resin composition that can be molded by heating and melting.
[0066]
Examples of the combination of the monomer components in the example of (1) include a combination of 2,2′-bis (4-aminophenoxyphenyl) propane and oxydiphthalic dianhydride, and a combination of bis (2- (4-amino A combination of phenoxy) ethoxy) ethane with 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride can be mentioned.
[0067]
As another example of the combination of the monomer components, (2) a combination capable of synthesizing a polyimide resin having a relatively low water absorption (low water absorption) can be exemplified. In this example, an aromatic compound having a structure in which a plurality of benzene nuclei are bonded by two or more ester bonds is used as the acid dianhydride. Specifically, the following equation (5), equation (6) or equation (7)
[0068]
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[0069]
(In the formula, n represents an integer of 1 or more.)
[0070]
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[0071]
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[0072]
At least one of the aromatic acid dianhydrides represented by As the diamine compound used in this example, it is preferable to use a relatively long-chain compound in order to reduce the content of the imide group. Specifically, for example, 1,4-bis (4-aminophenoxy) benzene and its bonding position isomer, 2,2′-bis (4-aminophenoxyphenyl) propane and the like can be mentioned.
[0073]
In general, a polyimide resin has a relatively high water absorption due to having an imide group, but a polyimide resin obtained using each of the above monomer components has low water absorption. Therefore, the obtained polyimide resin composition and polyimide molded product can also have low water absorption.
[0074]
However, for both the diamine compound and the acid dianhydride, the structure having many long chains and bent chains is also a condition for exhibiting thermoplasticity in the polyimide resin as described in (1) above. Therefore, it may not be preferable to give sufficient heat resistance to the polyimide resin.
[0075]
Therefore, as still another example of the combination of the monomer components, (3) when it is desired to obtain a polyimide resin realizing at least one of thermoplasticity and low water absorption and a certain degree of heat resistance, a long chain and linear It is appropriate to use a compound having a general structure partially or entirely as at least one of the above monomer components. For example, as such an acid dianhydride, an aromatic acid dianhydride having a structure represented by the following formula (8), that is, p-phenylenebis (trimellitic acid monoester acid anhydride) ( TMHQ).
[0076]
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[0077]
The above-mentioned TMHQ, which includes a bent chain, has a substantially linear structure as a whole, and is capable of forming a relatively rigid polyimide resin despite its large number of bonds. By synthesizing a polyimide resin using this TMHQ as an acid dianhydride, it is possible to obtain a polyimide resin having little dimensional change due to heating or moisture absorption, that is, satisfying both good heat resistance and good low water absorption. For example, in an example of a polyimide resin synthesized using the above-described TMHQ, physical properties of 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 can be realized.
[0078]
Similarly, as the diamine compound having a long-chain and relatively rigid structure, for example, a compound having a structure in which a biphenyl structure or a naphthalene structure is connected by an ether bond can be preferably mentioned, and more specifically, for example, 4,4'-bisaminophenoxybiphenyl can be mentioned.
[0079]
As described above, as at least one of the acid dianhydride and the diamine compound, a compound having a long-chain and linear structure is wholly or partially and has a relatively rigid structure is selected and combined, so that the water absorption rate is increased. Can be suppressed to a relatively low level, and a polyimide resin that can also suppress the development of remarkable heat softening property can be obtained.
[0080]
Of course, not only the compound having the specific structure described above, but also a general-purpose compound, for example, a diamine compound, such as paraphenylenediamine, 4,4′-diaminodiphenyl ether, and an acid dianhydride, pyromellitic. By appropriately selecting an acid dianhydride, benzophenonetetracarboxylic dianhydride, and the like, and copolymerizing with a compound having the above specific structure, it is possible to appropriately design the characteristics of the obtained polyimide resin.
[0081]
<Sequence control of monomer components>
In addition, as a method for synthesizing a polyimide resin having desired physical properties, there is a method based on sequence control other than the method for combining the above-mentioned monomer components. In this method, even if the type of each monomer component (diamine compound and acid dianhydride) and the composition ratio (polymerization ratio) of each monomer component are the same, the polyimide resin after polymerization has a structure derived from each monomer component. Controls the sequence (sequence).
[0082]
Generally, the linear expansion coefficient of a polyimide resin is larger than that of a metal such as copper. Thus, by the above sequence control, a polyimide resin having a relatively small coefficient of linear expansion can be synthesized, and the coefficient of linear expansion of the obtained polyimide resin composition or polyimide molded product can be reduced.
[0083]
Specifically, for example, 4,4′-diaminodiphenyl ether and paraphenylenediamine are used as the diamine compound, and pyromellitic dianhydride is used as the acid dianhydride. Here, as a procedure for synthesizing a polyimide resin, a procedure of mixing and reacting these three types of monomer components and randomly copolymerizing them, and a step of previously mixing 4,4′-diaminodiphenyl ether and pyromellitic dianhydride Was reacted in advance, and then the reaction was performed by adding paraphenylenediamine. In this case, compared to the former random copolymerization procedure, the latter sequence-controlled procedure can obtain a polyimide resin having a smaller linear expansion coefficient.
[0084]
As described above, in the reaction-curable linear polyimide resin preferably used in the present invention, as the two types of monomer components, various compounds are appropriately selected and used in combination, or the sequence control is performed to obtain a desired compound. A polyimide resin having physical properties can be synthesized.
[0085]
Among them, in the present invention, as described later, high-resistance carbon black is blended with a polyimide resin. Therefore, it is very preferable that the polyimide resin used in the present invention has higher toughness 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 incorporation of an inorganic substance (such as high-resistance carbon black), so that the polyimide resin may not be practically usable.
[0086]
As a particularly preferred example of the reaction-curable linear polyimide resin having improved toughness, a polyimide resin synthesized using a combination of 4,4′-diaminodiphenyl ether and pyromellitic dianhydride can be given. . This polyimide resin has both sufficient heat resistance and high toughness, and has excellent characteristics that its characteristics can be maintained under a wider range of processing conditions.
[0087]
<Synthesis of polyamic acid>
The polymerization method (synthesis method) of the polyamic acid using each of the above monomer components is not particularly limited. For example, a diamine compound is dissolved in an organic solvent or slurry in an inert atmosphere such as argon or nitrogen. After the dispersion (suspension), the method of reacting each monomer by adding an acid dianhydride can be preferably used. In this polymerization method, the acid dianhydride may be added directly in a solid state, or may be added as an acid dianhydride solution in which the acid dianhydride is dissolved in an organic solvent, or the acid dianhydride may be dispersed in the organic solvent. The acid dianhydride dispersion (suspension) may be added (suspended) to form a slurry. In this polymerization method, a polyamic acid solution obtained by dissolving the polymerized polyamic acid in an organic solvent is obtained.
[0088]
In the above production method, if the diamine compound and the acid dianhydride are adjusted to substantially equimolar, a polyamic acid having a 1: 1 ratio of the acid component to the diamine component can be obtained. At this time, either one of the acid dianhydride and the diamine compound may be used alone, or two or more of them may be used in appropriate combination. When only one kind of the acid dianhydride and the diamine compound is used and each is substantially equimolar, a polyamic acid having one kind of acid component and one kind of diamine component can be obtained. On the other hand, when at least one of the acid dianhydride and the diamine compound is two or more types and each is substantially equimolar, at least one of the acid component and the diamine component obtains a polyamic acid copolymer of two or more types. Can be.
[0089]
The organic solvent used in the above polyamic acid polymerization method is not particularly limited as long as it is an organic polar solvent and can dissolve the polyamic acid. Specifically, for example, formamide solvents such as N, N-dimethylformamide and N, N-diethylformamide; acetamido solvents such as N, N-dimethylacetamide and N, N-diethylacetamide; N-methyl-2 Pyrrolidone solvents such as -pyrrolidone and N-vinyl-2-pyrrolidone; ether solvents such as tetrahydrofuran, dioxane and dioxolane;
[0090]
These organic polar solvents may be used alone or as a mixed solvent obtained by appropriately mixing two or more kinds. Further, from the viewpoint of efficiently performing the subsequent step of synthesizing the polyimide resin from the polyamic acid, it is advantageous to select a solvent that dissolves the polyamic acid well and has a boiling point as low as possible.
[0091]
The reaction conditions in the above polyamic acid polymerization method are not particularly limited, but the reaction temperature between the diamine compound and the acid dianhydride may be 80 ° C or less, and is in the range of 0 ° C to 50 ° C. Is preferred. The reaction time between the diamine compound and the acid dianhydride is not particularly limited, and can be arbitrarily set within a range from a lower limit of 30 minutes to an upper limit of 50 hours. Since the polyamic acid is generated as the polymerization reaction proceeds, the temperature and the viscosity of the reaction solution increase. Therefore, the above reaction conditions may be appropriately changed by cooling the reaction vessel in accordance with the rise in the reaction temperature or decreasing the stirring speed in accordance with the rise in the viscosity.
[0092]
<Imidation of polyamic acid>
The reaction-curable linear polyimide resin preferably used in the present invention is synthesized by dehydrating and ring-closing (imidizing) the amide moiety of the polyamic acid. The imidation method is not particularly limited, and a thermal method or a chemical method may be used.
[0093]
The method of thermally dehydrating ring closure (thermal curing method) is not particularly limited as long as it is a method of applying heat to polyamic acid to cause dehydration ring closure. For example, the polyamic acid solution obtained by the above polymerization method may be heated in the range of 80 ° C to 300 ° C, or the polyamic acid solution is cast or coated on a film-like support, Heat treatment may be performed at ℃. As the film-like support, for example, a glass plate, a metal plate, a PET (polyethylene terephthalate) plate, or the like can be used.
[0094]
Furthermore, a reaction-curable linear polyimide resin can also be obtained by directly putting a polyamic acid solution into a container that has been subjected to a release treatment such as a fluororesin coat, and drying by heating under reduced pressure. As heating conditions at this time, the heating temperature is preferably in the range of 80 ° C to 300 ° C, more preferably in the range of 100 ° C to 250 ° C, and even more preferably in the range of 150 ° C to 250 ° C. The heating time varies depending on the treatment amount and the heating temperature, but is generally preferably in the range of 1 minute to 5 hours after reaching the maximum temperature.
[0095]
In the method of chemically dehydrating and cyclizing the ring (chemical curing method), a predetermined amount of an imidization accelerator is added to the polyamic acid solution, and heat treatment may be performed in the same manner as in the heat curing method. Examples of the imidization accelerator include at least one of an acid anhydride and a tertiary amine.
[0096]
Acetic anhydride, propionic anhydride, and the like can be used as the acid anhydride, but are not particularly limited. As the tertiary amine, pyridine, isoquinoline, triethylamine, trimethylamine, imidazole, picoline and the like can be used, but are not particularly limited. The amount of addition of these imidization accelerators is not particularly limited as long as the amount can promote imidization.
[0097]
In the polyimide resin composition according to the present invention, by using a high-resistance carbon black described below, even under an environment of intense change such as a chemical curing method, it is possible to maintain affinity with the reaction-curable linear polyimide resin. it can. Therefore, aggregation of the high-resistance carbon black in the polyimide resin composition can be effectively suppressed or avoided, and the physical properties of the obtained polyimide resin composition and polyimide molded product can be improved.
[0098]
Moreover, in the chemical curing method, the heating time for the polyamic acid can be reduced as compared with the heat curing method. Therefore, even when the high-resistance carbon black described below is added to the polyamic acid and then imidized, the high-resistance carbon black can be suppressed from being excessively heated and deteriorated, which is very preferable.
[0099]
In particular, when a grafted carbon black or the like described later is used as the high-resistance carbon black, the conductive coating causes a change in conductivity due to long-term heating. Therefore, shortening the heating time as in the case of chemical curing is very important from the viewpoint of stabilizing the volume resistivity of the obtained polyimide resin composition or polyimide molded product. In the chemical curing method, since the heating time is short, thermal degradation of the polyimide resin (or polyamic acid) itself and degradation due to the reaction between the polyimide resin (or polyamic acid) and the high-resistance carbon black can be suppressed. Preferred for.
[0100]
As described above, a polyimide resin having excellent mechanical properties can be obtained by advancing the imidization of the polyamic acid by the chemical curing method. Specifically, the tear propagation strength of the polyimide resin can be improved. At this time, the achievable tear propagation strength can be at least 2.45 N / mm (250 gf / mm) or more, and preferably 4.90 N / mm (500 gf / mm) or more.
[0101]
In addition, the above-mentioned acid anhydride may cause not only the promotion of imidization but also the cleavage of the main chain of the molecular chain of the polyamic acid. Therefore, in order to improve the mechanical properties of the obtained polyimide resin, it is more preferable to use an acid anhydride and a tertiary amine together or to use only a tertiary amine.
[0102]
The polyimide resin composition according to the present invention, the polyimide resin obtained in this way, at least, a specific amount of high-resistance carbon black described later is blended, or a specific amount of high-resistance carbon black to the precursor polyamic acid Obtained by blending. Further, the polyimide molded product according to the present invention is molded using this polyimide resin composition. The polyimide molding will be described later.
[0103]
<Other synthesis method of polyimide resin>
Further, in the present invention, the polyimide may be directly polymerized without going through the polyamic acid by performing synthesis by reacting the acid dianhydride with the diisocyanate. The acid dianhydride used in this method is the same as the synthesis method via the above-mentioned polyamic acid, and is not particularly limited. The diisocyanate is not particularly limited. Further, the reaction conditions of the acid dianhydride and the diisocyanate are not particularly limited.
[0104]
<High resistance carbon black>
The polyimide resin composition according to the present invention contains high-resistance carbon black. In the present invention, this high-resistance carbon black is 490 N / cm ² (50kgf / cm ² ) Is measured using a sample in a compressed state, and its volume resistance value is 1 × 10 ² ~ 1 × 10 ¹⁰ Ω · cm, preferably 1 × 10 ³ ~ 1 × 10 ⁸ Carbon black in the range of Ω · cm is used.
[0105]
The high-resistance carbon black is not particularly limited as long as it has a volume resistivity within the above range measured under the above conditions. Specifically, for example, a polymer is grafted on the surface of carbon black. And carbon black coated with an insulating material by another method (for convenience of description, referred to as surface-modified carbon black). In these surface-modified carbon blacks, the volume resistance value can be changed by changing the type and amount of the grafted polymer, the type and amount of the insulating material to be coated, or the type of the carbon black itself. Can be adjusted.
[0106]
The high resistance carbon black used in the present invention may be only one type or two or more types.
[0107]
Various types of carbon black are known depending on the acidity, the volatile content, the difference in structure, and the like. Here, the volume resistance of carbon black is usually 1 × 10 ² It is very low at Ω · cm or less, and it is difficult to obtain a carbon black having a high volume resistance value only by changing the acidity, volatile content, structure, etc. of the carbon black. The dispersibility of carbon black varies greatly depending on the type. Therefore, when it is used for applications in which the volume resistance value is controlled by adding it to the polyimide resin composition, great effort is required to control the dispersion in the polyimide resin and to adjust the composition.
[0108]
On the other hand, if a surface-modified carbon black is used like a grafted carbon black, it is possible to easily produce a carbon black having a desired volume resistance value. Therefore, it is possible to control the conductivity without changing the dispersibility in the polyimide resin, and even if the compounding amount of the carbon black is exactly the same, it is easy to obtain a polyimide resin composition having a different volume resistance value. be able to.
[0109]
In particular, in the case of the surface-treated carbon black, a polymer or an insulating material having a high affinity for the polyimide resin to be dispersed in the carbon black can be selected. Therefore, the greater the degree of the surface treatment (the amount of the grafted polymer or the coated insulating material), the more the dispersibility in the target polyimide resin can be improved. Therefore, in the polyimide resin composition or the polyimide molded product, it is possible to avoid the occurrence of partial variation in the volume resistance value.
[0110]
The high-resistance carbon black used in the present invention has higher resistance than various types of conductive materials such as conventional conductive carbon black, graphite, and metals. That is, the volume resistance value is the desired volume resistance value required in the present invention, that is, the intermediate resistance value (10 ⁶ -10 ^Fifteen (In the range of Ω · cm). Therefore, the fluctuation of the volume resistance value with respect to the amount added to the polyimide resin can be suppressed to a small width.
[0111]
Further, the high-resistance carbon black has a volume resistance closer to that of the polyimide resin than conductive carbon black or metal. For this reason, it is possible to suppress the occurrence of local bias in the voltage in the polyimide resin composition or the polyimide molded product to be a composite material. As a result, the voltage dependence of the volume resistance can be reduced.
[0112]
<Grafted carbon black>
In the present invention, among the above-mentioned surface-modified carbon blacks, carbon black obtained by grafting a polymer onto the surface of carbon black (referred to as grafted carbon black for convenience of explanation) is used because the semiconductivity that can be imparted is stable. It is preferably used.
[0113]
In particular, in the grafted carbon black suitably used in the present invention, the polymer to be grafted on the surface has a reactive group capable of reacting with a functional group on the surface of the carbon black, and has an affinity for the surface of the carbon black. It is preferable to select a copolymer having good segments and other segments. The grafted carbon black obtained by grafting such a copolymer can be obtained, for example, by the technique described in JP-A-10-120935.
[0114]
Further, it is more preferable to select a hydrophilic polymer from the viewpoint that the polymer grafted on the surface of the carbon black is mixed and uniformly dispersed in the polyimide resin.
[0115]
Examples of such a hydrophilic polymer include, but are not particularly limited to, polyamide, polyamic acid, polyimide, polyvinylpyrrolidone (such as poly (N-vinyl-2-pyrrolidone)), and poly (N, N′-). Diethylacrylazide), poly (N-vinylformamide), poly (N-vinylacetamide), poly (N-vinylphthalamide), poly (N-vinylsuccinamide), poly (N-vinylurea), poly (N-vinylurea) -Vinylpiperidone), poly (N-vinylcaprolactam), poly (N-vinyloxazolidone) and the like. Further, these hydrophilic polymers may be block copolymers having segments having good affinity with the carbon black surface. With such a block copolymer, it becomes easy to graft these hydrophilic polymers to carbon black.
[0116]
The segment having good affinity with the carbon black surface is not particularly limited, and a suitable structure may be appropriately selected according to the type of the carbon black.
[0117]
When such a grafted carbon black is used, since the grafted carbon black has a strong bond with the polyimide resin, the physical properties of the polyimide resin composition, particularly the mechanical properties (particularly, mechanical strength and dimensional stability) are improved. Can be done. Specifically, the resulting polyimide resin composition can have a tensile elongation of 35%, a tear propagation strength of 2.45 N / mm (250 gf / mm) or more, and a polyimide resin without carbon black (composition Object), a retention rate of 50% or more can be realized.
[0118]
Further, as described above, the grafted carbon black in the present invention, or carbon black as a base material used for the surface-modified carbon black, as described above, the use and type of the polyimide resin composition or polyimide molded product finally obtained According to the above, conventionally known carbon black can be appropriately selected and used.
[0119]
Here, as for the average particle size of the carbon black, the average particle size based on the primary particles is preferably 1 μm or less, and particularly, the carbon black having the average particle size in the range of 0.001 to 0.5 μm. Is preferred. By using carbon black that satisfies such an average particle size, it is possible to suppress or avoid occurrence of variation in the volume resistance value of the polyimide resin composition or the polyimide molded product due to uneven distribution of carbon black.
[0120]
<Blending amount of high resistance carbon black>
In the polyimide resin composition or the polyimide molded product according to the present invention, the compounding amount (mixing ratio) of the high-resistance carbon black may be within a range of 20 to 100 parts by weight with respect to 100 parts by weight of the polyimide resin. The range is preferably from 20 to 80 parts by weight, more preferably from 20 to 60 parts by weight.
[0121]
When the amount of the high-resistance carbon black is less than 20 parts by weight, the volume resistance value of the obtained polyimide resin composition or polyimide molded product is higher than the intermediate resistance value. Therefore, for example, when a polyimide molded article is used for an intermediate transfer belt of an electrophotographic apparatus, the intermediate transfer belt is significantly charged during transfer of a toner image. As a result, when the intermediate transfer belt separates from the image carrier, a peeling discharge occurs, causing a problem that the toner image transferred to the surface of the intermediate transfer belt is scattered.
[0122]
On the other hand, if the amount of the high-resistance carbon black exceeds 100 parts by weight, the volume resistance value of the obtained polyimide resin composition or polyimide molded product will be lower than the intermediate resistance value. Therefore, as described above, when a polyimide molded product is used for an intermediate transfer belt or the like, an excessive current flows between the intermediate transfer belt and the image carrier. Therefore, there is a problem that the phenomenon that the toner image transferred to the surface of the intermediate transfer belt returns to the image carrier easily occurs. In addition, the mechanical properties of the polyimide molded article itself are also deteriorated, resulting in a brittle material, which is not preferable.
[0123]
On the other hand, if the blending amount of the high-resistance carbon black is set within the above range, even if there is a variation in the blending amount of, for example, about 5 parts by weight, the change in the volume resistivity is suppressed to three times or less. be able to. Therefore, in the obtained polyimide molded article, it is possible to control the intermediate resistance value without causing a significant change in the volume resistance value.
[0124]
In the present invention, the compounding amount of the high-resistance carbon black is much higher than the compounding amount of the carbon black used in various conventionally known applications (for example, coloring, controlling resistance, improving mechanical strength, etc.). More. However, in the present invention, the mechanical properties and electrical insulation properties of the polyimide resin composition or the polyimide molded product do not decrease even though such a large amount of carbon black is added. The reason for this will be described later in the section <Effects of Mixing High Resistance Carbon Black>.
[0125]
<Control of various physical properties by blending high resistance carbon black>
In the polyimide resin composition or the polyimide molded product according to the present invention, good control of various physical properties shown in the following (1) to (5) is realized by blending at least the high-resistance carbon black into the polyimide resin. be able to.
[0126]
(1) The volume resistivity of the polyimide resin composition or the polyimide molded product is 1 × 10 ⁶ ~ 1 × 10 ^Fifteen Within the range of Ω · cm, the surface resistance is set to 10 ⁶ -10 ^Fifteen It can be controlled within the range of Ω / □, that is, an intermediate resistance value. Therefore, excellent electrical insulation can be realized without excessively increasing the volume resistance value.
[0127]
(2) When the volume resistance of a polyimide resin composition or a polyimide molded product at normal temperature and normal humidity is Rn, and the volume resistance of high temperature and high humidity is Rh, the ratio of these volume resistance values (Rn / Rh) is calculated as follows. , 0.03 to 30, preferably 0.1 to 10. Therefore, it is possible to provide a polyimide-based material which has a small fluctuation range of the volume resistance value even depending on the surrounding environment and has excellent resistance value environment stability.
[0128]
(3) The volume resistance of the polyimide resin composition or the polyimide molded product when 100 V is applied is represented by R _100V And the volume resistance value when 1000 V is applied is R _1000V , The ratio of these volume resistance values (R _100V / R _1000V ) Can be controlled in the range of 0.03 to 30. Therefore, it is possible to provide a polyimide-based material in which the variation of the volume resistance value is small depending on the applied voltage and the resistance value has little dependence on the voltage.
[0129]
(4) When high resistance carbon black is added to the polyimide resin within the above-mentioned range, the variation in volume resistance can be suppressed to three times or less even if the addition amount changes by 5 parts by weight. it can. Therefore, it is possible to provide a polyimide-based material in which the range of change in the volume resistance value is small even depending on the amount of the high-resistance carbon black to be added, and the dependency of the resistance value on the added amount is small. In addition, since the variation in the volume resistance value between samples can be suppressed to three times or less, it is possible to provide a polyimide-based material in which the variation in the resistance value between samples is small.
[0130]
(5) Particularly, by using a grafted carbon black or the like as the high resistance carbon black, a strong bond can be formed with the polyimide resin. Therefore, the mechanical properties (particularly, mechanical strength and dimensional stability) of the polyimide resin composition can be improved. Moreover, since the grafted carbon black is excellent in dispersibility in the polyimide resin, it is possible to suppress or avoid the variation in the volume resistance value due to the uneven distribution of the carbon black.
[0131]
<Action by blending high resistance carbon black>
As described above, in the present invention, by blending the high resistance carbon black with the polyimide resin, it is possible to easily control the various physical properties (1) to (5), which have been difficult in the related art. As a result, the polyimide resin composition and the polyimide molded product according to the present invention can be effectively used as members such as a transfer belt, an intermediate transfer belt, a transfer fixing belt, and a fixing belt of an electrophotographic apparatus.
[0132]
Here, in the present invention, the reason that the various physical properties (1) to (5) can be easily controlled by adding a high-resistance carbon black to a polyimide resin (preferably, a reaction-curable linear polyimide resin). (Operation of the present invention) will be described.
[0133]
High resistance carbon black is 1 × 10 ³ ~ 1 × 10 ¹⁰ It has a volume resistivity in the range of Ω · cm, and is generally used for carbon black, metal, and metal ceramics (volume resistivity: 1 × 10 ^-5 ~ 1 × 10 ³ Ω · cm) and the like, the volume resistivity of the polyimide resin is 1 × 10 ¹⁶ It is close to Ω · cm. Therefore, in a polyimide resin composition or a polyimide molded product to which high-resistance carbon black is added, a sharp drop in volume resistance due to percolation as seen in ordinary addition of carbon black is not seen, and the volume resistance is determined by the amount of addition. It changes slowly according to.
[0134]
In the case of ordinary carbon black, carbon black is added in an amount of 10 to 20 parts by weight with respect to 100 parts by weight of the resin in order to realize an intermediate resistance value. However, with such an addition amount, even if the addition amount changes by only about 5 parts by weight, the volume resistance value is reduced by 100 times or more.
[0135]
On the other hand, when the high-resistance carbon black is added as in the present invention, the volume resistance value is within the range for realizing the above-mentioned intermediate resistance value even if the addition amount is changed by about 5 parts by weight. Does not change by a factor of three. Also, even if the conductive filler (conductive filler) such as carbon black is agglomerated or biased in the defoaming process or the carbon black dispersing process in the polyimide resin composition, a significant change in the volume resistance value is not observed. I can't. Therefore, it can be said that the high-resistance carbon black used in the present invention has a small change in volume resistance value even when the amount of addition varies.
[0136]
Further, since the high-resistance carbon black used in the present invention has a high volume resistance value, the resulting polyimide resin composition and the polyimide molded product also have improved electrical insulation properties and reduced voltage dependence of the volume resistance value. It is thought to play a major role.
[0137]
Specifically, for example, when a voltage is applied to the film made of a polyimide resin and another conductive filler to measure a volume resistance value, the voltage is divided between the polyimide resin and the conductive filler. Is done. Therefore, it is considered that the voltage is applied to the polyimide resin having higher resistance than the conductive filler having low resistance. In particular, when comparing the case where a low-resistance material such as conductive carbon black or a metal-based material and a medium-resistance material such as high-resistance carbon black are added as a conductive filler, polyimide resin It is considered that the voltage is lower when the medium resistance material is added. As a result, since the voltage applied to the polyimide resin is reduced, it is considered that dielectric breakdown in the polyimide resin composition or the polyimide molded product is reduced.
[0138]
Generally, when a high voltage (for example, a voltage of 1 kV or more for a thickness of 100 μm) is applied to the resin, 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. Therefore, the voltage dependence of the resistance value is considered to be a phenomenon that occurs when a high voltage is applied to the resin and the resin approaches breakage.
[0139]
On the other hand, in the present invention, a medium resistance material such as high resistance carbon black is added to the polyimide resin. Therefore, it is possible to prevent a high voltage from being locally applied to the polyimide resin as compared with a case where a low-resistance material such as conductive carbon black is added. As a result, it is considered that the voltage dependency of the resistance value can be improved.
[0140]
Further, the high-resistance carbon black may partially have a hydroxyl group or active oxygen on its surface. For this reason, a strong interaction with the polyimide resin occurs at the time of imidization without performing the surface treatment. Therefore, the obtained polyimide resin composition or polyimide molded product becomes a strong composite material.
[0141]
Therefore, the polyimide resin composition or the polyimide molded product according to the present invention can realize higher tear propagation strength and elongation than conventional polyimide materials known in the art. The amount of carbon black compounded for conventionally known various uses (for example, coloring, control of resistance, improvement of mechanical strength, etc.) is usually about 5 parts by weight with respect to 100 parts by weight of the resin. Then, even if it is added in a larger amount, sufficient mechanical properties and electrical insulation can be maintained.
[0142]
Further, the polyimide resin composition and the polyimide molded product according to the present invention do not decrease in volume resistance value and electrical insulation even at high temperature and high humidity. It is considered that the reason is that the polyimide resin composition or the polyimide molded product according to the present invention is a strong composite material in which the polyimide resin and the high-resistance carbon black are firmly bonded to each other.
[0143]
That is, in a polyimide-based composite material containing a conductive filler, the cause of the deterioration of the electrical properties when moisture is absorbed is that a skin layer made of water is formed at the interface between the polyimide resin and the conductive filler due to moisture absorption. As a result, it is considered that a flow path through which electricity easily flows is formed in the composite material. Therefore, in order to improve the deterioration of the electric characteristics at the time of moisture absorption, a surface treatment of a conductive filler (filler or carbon black) is generally performed.
[0144]
On the other hand, in the present invention, a strong bond is formed between the high-resistance carbon black and the polyimide resin, particularly, the reaction-curable linear polyimide resin. Therefore, a skin layer such as the general polyimide-based composite material described above is not formed, and as a result, even if moisture is absorbed, it is considered that a significant change does not occur in the volume resistance value and the electrical insulation.
[0145]
As described above, in the present invention, by using a high-resistance carbon black as the carbon black, it is possible to exhibit a function and an effect which are much superior to those of the related art in the field. As a result, the polyimide resin composition and the polyimide molded product according to the present invention can realize characteristics superior to those of the related art.
[0146]
<Method of mixing high resistance carbon black>
In the present invention, a specific method of mixing the high-resistance carbon black with the polyimide resin is not particularly limited. However, in the present invention, it is preferable to use a reaction-curable linear polyimide resin that is synthesized via a polyamic acid as the polyimide resin, and thus the high-resistance carbon black is added to the precursor polyamic acid. After that, it is more preferable to imidize the polyamic acid.
[0147]
Specific methods for adding and mixing high-resistance carbon black to polyamic acid include the following two methods (1) and (2).
[0148]
(1) A high-resistance carbon black dispersion solution is prepared in advance by adding high-resistance carbon black to a solvent used for the polymerization of polyamic acid. Then, a diamine compound and an acid dianhydride are added to the dispersion solution to polymerize the polyamic acid.
[0149]
(2) Polyamic acid is preliminarily polymerized from a diamine compound and an acid dianhydride to prepare a polyamic acid solution, and the previously prepared dispersion solution of high-resistance carbon black is mixed with the polyamic acid solution. I do.
[0150]
Regardless of which of the above methods (1) and (2) is used, it is necessary to prepare a dispersion solution of high resistance carbon black. Here, since the high-resistance carbon black has a specific gravity larger than that of the resin and is very heavy, the high-resistance carbon black precipitates a while after being added to the solvent. When the high-resistance carbon black is added to the polyamic acid solution and mixed in the state of the sedimentation, aggregates of the high-resistance carbon black are generated. As a result, unevenness occurs on the surface of the polyimide resin composition or the polyimide molded product finally obtained, or the volume resistance value varies locally.
[0151]
Therefore, when preparing a dispersion solution of the high-resistance carbon black, it is preferable to mix or disperse a dispersant with the solvent to suppress or avoid the sedimentation of the high-resistance carbon black.
[0152]
<Dispersant>
The dispersant is not particularly limited as long as it can suppress or avoid the sedimentation of the high-resistance carbon black in a solvent, and includes, for example, various metal salts and a surfactant. Can be. Among them, metal salts are preferred.
[0153]
The metal salt is not particularly limited, but is preferably a Li salt, a Na salt, a K salt, an Rb salt, a Cs salt, a Be salt, from the viewpoint of improving the dispersibility of the high-resistance carbon black. One or a combination of two or more selected from the group consisting of Mg salt, Ca salt, Sr salt and Ba salt is preferable, and Li salt, Na salt and K salt are more preferable.
[0154]
As the Li salt, a Li salt having a lattice energy of 1100 kJ / mol or less is preferably used. Specifically, LiF, LiCl, LiBr, LiI, LiSCN, LiCF ₃ SO ₃ And the like. As the Na salt, a Na salt having a lattice energy of 800 kJ / mol or less is preferably used. Specifically, NaF, NaCl, NaBr, NaI, NaSCN, NaCF ₃ SO ₃ And the like. Further, as the K salt, a K salt having a lattice energy of 800 kJ / mol or less is preferably used, and specifically, KF, KCl, KBr, KI, KSCN, KCF ₃ SO ₃ And the like.
[0155]
Each of the above metal salts is preferably used as a dispersant because ions are easily dissociated at room temperature and the interaction with high-resistance carbon black becomes strong. However, if the lattice energy is too small, the effect of the added amount of the dispersant becomes too large, and therefore, as described above, a metal salt having a large lattice energy is preferable. In addition, since these metal salts do not contain an organic substance, even when the polyimide resin composition is dried at a high temperature at the time of molding, it is possible to avoid a situation in which the polyimide resin is burned.
[0156]
The amount of the dispersant is not particularly limited as long as the amount of the high-resistance carbon black can be dispersed, but generally, 1 part by weight based on 100 parts by weight of the finally obtained polyimide resin. It may be blended so as to be not more than part by weight, and even in the range of 0.01 to 0.1 part by weight or less, the high resistance carbon black can be sufficiently dispersed.
[0157]
In general, in applications for covering electric wires, when a metal salt is added to a resin, electrical insulation deteriorates. In particular, when a metal salt is added to a resin having a dielectric constant of 4 or more, ionic conductivity increases, which is not particularly preferable. However, in the present invention, since the polyimide resin is excellent in electrical insulation and has a dielectric constant of 4 or less, even if a metal salt is blended within the above-described range, the electrical insulation and the voltage dependency of the volume resistance value are not improved. Significant reduction can be effectively avoided.
[0158]
<Other fillers>
The polyimide resin composition or the polyimide molded product according to the present invention may contain various conductive or semiconductive fillers in addition to the above-described high-resistance carbon black. As the other filler, any material having conductivity or semi-conductivity may be used.For example, conductive carbon black, graphite, metal powder, metal oxide powder, conductive-treated metal oxide, antistatic agent, A semiconductive filler formed by coating the surface of a core material can be used. One of these other fillers may be used alone, or two or more may be used in combination.
[0159]
<Carbon black>
In the present invention, the carbon black that can be blended with the polyimide resin is not particularly limited as long as it has conductivity, and conventionally known various carbon blacks can be suitably used.
[0160]
Specific examples include furnace black, acetylene black, thermal black, and channel black. Among them, it is preferable to use carbon black called Ketjen black, which is a kind of furnace black.
[0161]
Since Ketjen Black has a large specific surface area, its effect is high even if the amount of carbon black is small, and its voltage dependency (resistance changes when the voltage changes) is higher than when other carbon blacks are used. Is changed, and the property that does not behave in accordance with Ohm's law is small.
[0162]
<Metal powders, metal oxide powders, and conductive metal oxides>
In the present invention, the metal powder that can be blended with the polyimide resin, the metal oxide powder, and the metal oxide that has been subjected to the conductive treatment are not particularly limited as long as they have conductivity, and are conventionally known. Can be suitably used.
[0163]
Specifically, for example, as the metal powder, a powder of copper, iron, aluminum, SUS or the like can be used. Examples of the metal oxide powder include conductive semiconductor ceramic powder. Examples of the metal oxide subjected to the conductivity treatment include those obtained by subjecting titanium oxide, potassium titanate, barium sulfate, mica, and the like to a conductivity treatment.
[0164]
<Antistatic agent>
In the present invention, the antistatic agent that can be blended with the polyimide resin is not particularly limited, and a conventionally known antistatic agent can be suitably used. Specifically, for example, various anionic, cationic, nonionic and amphoteric surfactants can be mentioned.
[0165]
<Semiconductive filler>
In the present invention, the semiconductive filler that can be blended with the polyimide resin is not particularly limited as long as it is a semiconductive filler. Here, the semiconductivity means that a volume resistance value measured by using a sample compressed under almost no load pressure is 1 × 10 5 ³ -10 ¹⁰ Within the range of Ω · cm, preferably 1 × 10 ⁴ -10 ⁹ Ω · cm.
[0166]
Examples of the semiconductive filler include an inorganic filler in which the surface of a core is coated with a conductive substance. Specifically, the following two types of semiconductive fillers can be mentioned.
[0167]
(1) A black filler obtained by coating the surface of a core material with a black conductive material such as carbon or graphite.
[0168]
(2) ITO (indium-tin composite oxide), ATO (antimony-doped tin oxide), NTO (niobium-doped tin oxide), TTO (tantalum-doped tin oxide), FTO (fluoride-doped tin oxide), TO (tin oxide) A tin oxide-based filler obtained by coating a core material with a tin oxide-based conductive material such as.
[0169]
These (1) black fillers and (2) tin oxide fillers are preferable because their resistance can be adjusted to an intermediate resistance depending on the type, amount, and formation method of each of the conductive substances.
[0170]
For example, (1) the resistance value of the black filler can be controlled by adjusting the coating amount of the black conductive substance attached to the surface. In addition, even if the obtained semiconductive filler has a low resistance value, when heated at a temperature in the range of 50 to 750 ° C. in air, the resistance value can be increased, so that the desired resistance value is obtained. A semiconductive filler can be easily obtained.
[0171]
In the case of (2) the tin oxide-based filler, the resistance value can be widely controlled from a low value to a high value by changing the amount of the element doped into the tin oxide. Also, after forming a layer of a tin oxide conductive material on the surface of the core material, the resistance value can be controlled by selecting a heating atmosphere to be either oxidizing or non-oxidizing or by changing the heating temperature. can do. Therefore, in the case of the tin oxide-based filler, semiconductive fillers having similar shapes and having various resistance values can be easily obtained.
[0172]
In addition, tin oxide-based materials are resistant to heat, and when molding a polyimide resin composition, for example, as in the process of forming a polyimide film, even in molding under severe conditions exceeding 300 ° C., physical properties deteriorate. Will not cause. Therefore, the tin oxide-based filler is preferable because the usable range is widened. Further, since tin oxide-based materials are almost colorless, for example, if a colorless material is used for the core material, a colorless semiconductive filler can be obtained. As a result, when a black colorant is used in combination, a black polyimide resin composition can be easily obtained. Such a black polyimide resin composition and a polyimide molded article using the same can be suitably used for a transfer belt of an electrophotographic apparatus.
[0173]
Here, the advantage of using a filler whose resistance value is controlled by coating the surface of the core material as described above will be described as the semiconductive filler.
[0174]
For example, a filler made of a material such as potassium titanate, tin oxide, zinc oxide, or the like has only a specific resistance value. Therefore, when using these to control the volume resistance value of the polyimide resin composition or the polyimide molded product to a desired range, two or more fillers having different resistance values are mixed or the amount to be mixed is changed. This necessitates a problem that control of the volume resistance value becomes complicated.
[0175]
In addition, since the dispersibility varies depending on each filler, control of dispersion at the time of blending and adjustment of the blending amount described above require a great deal of labor, and the production of the polyimide resin composition itself becomes complicated. I was Further, when the amount is changed, the mechanical properties of the obtained polyimide resin composition or polyimide molded product are different, and there is a problem that the physical properties of the product are not stable. Moreover, since there is only a single color, there is a problem that the degree of freedom of color change is small when coloring the polyimide molded product.
[0176]
On the other hand, in the present invention, as a conductive substance used in combination with the high-resistance carbon black, if a filler whose resistance value is controlled by coating the surface of the core material is used, various volume resistance values can be obtained. It can be realized by a semiconductive filler made of a single material, or the conductivity can be controlled without changing its mechanical properties and dispersibility. Therefore, it is possible to produce a polyimide resin composition or a polyimide molded product having different volume resistance values even if the compounding amounts are exactly the same.
[0177]
In addition, since the basic physical properties such as the mechanical properties and dispersibility of the semiconductive filler are the same, even if the type of the semiconductive filler is changed to control the volume resistance value, even if the type of the semiconductive filler is changed, the cleaning work during the manufacturing process or the like. The switching operation becomes very easy, and the complication of the manufacturing process can be avoided. In addition, since the surface of the core material is covered, the color of the obtained semiconductive filler can be freely selected from colorless to black. As a result, coloring becomes easy.
[0178]
<Semiconductive filler core material>
The core material (inorganic material) of the semiconductive filler is not particularly limited as long as it is an inorganic material. Generally, various metals, metal oxides, metal carbides, and metal nitrides are used. Ceramic materials such as materials, metal salts, and the like.
[0179]
Specifically, 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 Salt, 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, Examples thereof include germanium nitride, tantalum nitride, titanium nitride, boron nitride, mica, talc, wollastonite, talc, kaolin, and clay minerals.
[0180]
Among these, an inorganic material having a low refractive index is preferable. Specifically, (1) at least one material selected from aluminum borate, tin oxide, calcium carbonate, silicate, calcium silicate, barium sulfate, and mica is more preferably used. Alternatively, (2) at least one material selected from alumina, silica, glass, wollastonite, talc, and kaolin may be used.
[0181]
The inorganic material of the above (1) has a small refractive index unlike titanium oxide and metal titanate, and is close to the refractive index of various resins including polyimide resin. Therefore, there is an advantage that the transparency is hardly impaired by being mixed into the resin, and that the resin can be prevented from being colored. Further, the inorganic material of (2) has a relatively low refractive index, though not as much as the inorganic material of (1). Therefore, even if it is added to the polyimide resin, the transparency is hardly impaired, so that it can be preferably used.
[0182]
The refractive index of the inorganic material that can be used as the core material of the semiconductive filler is usually 2.0 or less, preferably 1.8 or less, and more preferably 1.7 or less. Just fine.
[0183]
The black filler (1) in which such a core material is coated with a black conductive material is preferable because a black polyimide resin composition is easily obtained after being mixed with the polyimide resin. On the other hand, since the tin oxide-based filler (2) in which the core material is coated with a tin oxide-based material is excellent in transparency, the polyimide resin composition or the polyimide molded product to which the filler is added should realize transparency. Becomes possible. If another coloring agent is used in combination, coloring can be freely performed.
[0184]
In addition, in the above-mentioned core material, the smaller the metal component released from the core material, the better. Specifically, the amount of the free metal component may be 100 ppm or less, preferably 80 ppm or less, more preferably 50 ppm or less. If the amount of the free metal component is equal to or less than the above upper limit, the amount of the free metal component is small, and therefore, in a polyimide resin composition or a polyimide molded product containing a semiconductive filler formed using these core materials, the humidity of the volume resistance value is reduced. This is preferable because dependency is reduced. In addition, it is preferable that the amount of the free metal component is small because the dielectric breakdown voltage of a polyimide resin composition or a polyimide molded product containing a semiconductive filler using these core materials is reduced.
[0185]
Further, in the present invention, a semiconductive filler made of one kind of material may be used in addition to the semiconductive filler as a composite material whose surface is covered. Examples of such a semiconductive filler include titanium oxide, metal titanate, aluminum borate, tin oxide, and silicon carbide.
[0186]
<Amount of conductive filler>
In the polyimide resin composition or the polyimide molded product according to the present invention, the amount of the conductive filler and / or the semiconductive filler is 100 parts by weight with respect to 100 parts by weight of the polyimide resin. It is sufficient if it is within the range, and particularly in the case of the conductive filler, the conductivity is preferably in the range of 20 to 80 parts by weight, more preferably 20 to 60 parts by weight.
[0187]
If the amount of the filler is more than 100 parts by weight, the resulting polyimide resin composition or polyimide molded product is not preferable because the voltage dependency of the volume resistance value and the electrical insulation are deteriorated. On the other hand, if the amount of the filler is too small, the effect of using these conductive substances is not easily exerted, which is not preferable. Generally, the lower limit of the amount of the filler is preferably 0.01 part by weight or more, more preferably 0.1 part by weight or more, and further preferably 1 part by weight or more. Preferably, the amount is at least 5 parts by weight.
[0188]
<Non-conductive filler>
A non-conductive filler may be added to the polyimide resin composition or the polyimide molded product according to the present invention, in addition to the above-described high-resistance carbon black and the above-mentioned conductive or semi-conductive filler. Examples of the non-conductive filler include various non-conductive inorganic powders.
[0189]
Specifically, for example, small-diameter granular substances such as alumina and silica; plate-like and scale-like substances such as mica and clay mineral; short-fiber or whisker-like substances such as barium titanate and potassium titanate; , But is not particularly limited.
[0190]
By the addition of the non-conductive filler, for example, various physical properties such as an elastic modulus of the polyimide resin composition or the polyimide molded product can be controlled. In addition, the non-conductive filler can appropriately assist the dispersion of the conductive particles such as the high-resistance carbon black, the conductive or semi-conductive filler, and the like. For this reason, the addition of the non-conductive filler may prevent aggregation of the conductive particles and achieve a stable volume resistance value in some cases.
[0191]
As described above, in addition to the above-described high-resistance carbon black, by appropriately selecting a conductive or semiconductive filler or a non-conductive filler and blending the same into the polyimide resin, Control of Various Physical Properties> Good control of various physical properties as described in the section <1.
[0192]
<Dispersion method of filler etc.>
The method of mixing and dispersing the above-mentioned high-resistance carbon black, conductive or semiconductive filler, non-conductive filler and the like (collectively referred to as powders for convenience of explanation) in a polyimide resin is not particularly limited. Instead, various methods can be used. Specifically, as shown below, it can be roughly divided into two methods depending on whether the polyimide resin contained in the polyimide resin composition is soluble in a solvent.
[0193]
(1) When the polyimide resin is soluble in the solvent
The powder is directly added to the polyimide resin composition dissolved in the solvent, or a powder dispersion prepared by dispersing the powder in a solvent is prepared in advance and added. These powders can be dispersed by mixing with a stirring blade or mixing with a kneader having three rolls or the like. Alternatively, a powder dispersion in which the above powders are dispersed in a solvent may be prepared in advance, and a powder or pellets of the polyimide resin composition may be added thereto and mixed.
[0194]
In the case where the powders include, for example, a needle-like material, if an excessive shearing force is applied by mixing, the needle-like shape may be broken. Therefore, when a shape other than a spherical shape or a substantially spherical shape, for example, the above-mentioned needle-like shape contains powders whose shape is easily broken by an external force, it is necessary not to use a kneader equipped with three rolls or the like. preferable.
[0195]
(2) When the polyimide resin is insoluble in the solvent
As described in the above section <Method of mixing high-resistance carbon black>, the above-mentioned powder dispersion is added to a solution of polyamic acid which is a precursor of a polyimide resin, and the same method as in the above (1) is performed. May be used for mixing and kneading.
[0196]
<Preparation of powder dispersion>
Here, as a method of preparing the powder dispersion liquid, a method of adding the powders to a solvent and irradiating ultrasonic waves with an ultrasonic disperser to sufficiently disperse the powders is effective. At this time, as described in the above <Dispersant>, the dispersant may be used in combination to assist the dispersibility of the powders. These dispersants may be used within a range that does not significantly deteriorate the characteristics of the polyimide resin composition.
[0197]
In particular, when the above-mentioned metal salt is added as a powder dispersing agent, the dispersion state is very uniform, so that a sufficiently uniform dispersion state can be achieved by manual stirring without using an ultrasonic disperser. can do.
[0198]
Further, the method of mixing the powder dispersion and the polyamic acid solution when the polyimide resin (2) is insoluble in the solvent is not particularly limited, It is preferable to add the polyamic acid solution little by little while stirring, since the dispersibility of the powders is improved as compared with the reverse procedure.
[0199]
Further, as a method for obtaining particularly good dispersibility of the powders, the above-mentioned powder dispersion is prepared and sufficiently dispersed by an ultrasonic disperser or the like, and the diamine compound and the acid dianhydride are added thereto. And a method of performing a polymerization reaction of a polyamic acid by adding a substance. In this method, the dispersibility at the micro level is favorably maintained by ultrasonic dispersion or the like, and the powder is constantly stirred from the initial state in which the powder is dispersed to during the polymerization. A very good level of dispersibility is also obtained.
[0200]
In each of the above description and the following description, “solvent” refers to the organic solvent for synthesizing polyamic acid described in the above <Synthesis of polyamic acid>, preferably a polar organic solvent, unless otherwise specified. Shall be.
[0201]
<Molding of polyimide resin composition>
The above-described polyimide resin composition according to the present invention can be used by molding into various shapes. The molding process of the polyimide resin composition according to the present invention, that is, the method for producing the polyimide molded product according to the present invention is not particularly limited, but specifically, the section <dispersion method of filler and the like>. Similarly to the above, it can be divided into the following two methods depending on whether the polyimide resin contained in the polyimide resin composition is soluble in a solvent.
[0202]
(1) When the polyimide resin is soluble in the solvent
A polyimide solution is prepared by dissolving the polyimide resin composition in a solvent, and powders such as high-resistance carbon black are mixed and dispersed therein. Then, after processing the polyimide solution into an arbitrary shape using a molding die or the like, the solvent is volatilized by heating or a combination of heating and reduced pressure. Thereby, the polyimide molding according to the present invention can be obtained.
[0203]
(2) When the polyimide resin is insoluble in the solvent
A polyamic acid as a precursor is dissolved in a solvent to prepare a polyamic acid solution, and powders such as high-resistance carbon black are mixed and dispersed therein. Then, preferably after the imidization is advanced by the chemical curing method, the polyimide molded article according to the present invention can be obtained by performing the same steps as in the above (1).
[0204]
Here, in general, when molding a polyimide material, if the thickness of the molded product is small, it is particularly difficult to maintain a constant volume resistance value while maintaining electrical insulation. In particular, in the case of a molded product having a broadly defined "film-like form" such as a film-like (sheet-like) or tubular (including a belt-like and tubular-like), particularly when the thickness becomes 150 μm or less, the electrical insulation and the volume resistance are reduced. It is very difficult to maintain both of these values at good values.
[0205]
On the other hand, the polyimide resin composition and the polyimide molded product according to the present invention can maintain both the electrical insulation property and the volume resistance value at favorable values even when the thickness of the molded product is small. . As a result, the polyimide molded article according to the present invention can be suitably used as a molded article having a broadly defined “film-like form” such as a film-like (sheet-like) or tubular (belt-like or tube-like) form. In addition, the above-mentioned belt shape refers to a relatively large-diameter shape among tubular shapes, and the above-described tubular shape refers to a relatively small-diameter shape among tubular shapes.
[0206]
<Molding example of polyimide resin composition>
Among the polyimide molded products according to the present invention, in particular, as a specific method for producing a film-shaped (sheet-shaped) molded product and a tubular (belt-shaped) molded product, the following method may be mentioned as a preferred example. it can.
[0207]
First, the following two examples can be given as a method for producing a film-shaped molded product.
[0208]
(1) A polyimide solution in which the above-mentioned powders are dispersed (a polyimide resin composition in the form of a solution according to the present invention) is prepared, and is applied onto an endless belt after controlling the thickness thereof. Examples of the coating means used at this time include a T-die, a comma coater, a doctor blade, and the like, but are not particularly limited.
[0209]
Next, the polyimide solution is heated and dried by hot air or the like until it has a self-supporting property, and then peeled off from the endless belt. Thereby, a semi-dried polyimide film is obtained. Both ends of the width of the semi-dried polyimide film are fixed by pins, clips, or the like, and the polyimide film is sequentially passed through a high-temperature heating furnace while regulating the length in the width direction. Thereby, a film-shaped molded product can be obtained.
[0210]
Alternatively, (2) a polyimide solution is applied on a continuous sheet-like support made of metal, for example, in the same manner as in (1) above. Then, the applied polyimide solution together with the support is passed into a heating furnace. Thereafter, the film-shaped molded product is peeled from the support or the support is removed by etching or the like. Thereby, a film-shaped molded product can be obtained.
[0211]
Next, as a method for producing a tubular (belt-like) molded product, the following two examples can be given.
[0212]
(3) The film-shaped (sheet-shaped) molded product obtained by the above method (1) or (2) is cut into a predetermined length and width, and joined into a belt or a tube. Thereby, a tubular molded product (a belt-shaped molded product or a tubular molded product) can be easily obtained. However, in order to join the film or sheet-like molded product, conventionally known various adhesives and adhesive tapes are used, but in this method, since it is inevitable that a step or a cut is present at the joint, a polyimide molded product is used. In some cases, inconveniences may occur depending on the application.
[0213]
Therefore, (4) For example, when obtaining a tubular molded product, a polyimide 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. In this state, a semi-dried polyimide molding exists on the inner surface or outer surface of the cylindrical mold. Then, this is heated to the final firing temperature as it is, or the polyimide molded product in a semi-dried state is once peeled off and fitted to the outer periphery of another mold in order to define the final inner diameter, and the final firing temperature is set. Heat until Thereby, a tubular molded product can be easily obtained.
[0214]
In applying the polyimide solution to the cylindrical mold, it is also effective to rotate the cylindrical mold in order to reduce the variation in thickness due to the dripping of the polyimide solution.
[0215]
The final firing temperature may be appropriately set based on the structure of the polyimide resin and the heat resistance of the high-resistance carbon black to be added. In general, when the polyimide resin is a non-thermoplastic polyimide and is heated and baked from the precursor polyamic acid, the temperature may be approximately in the range of 350 ° C to 450 ° C. In the case of thermoplastic polyimide, the temperature range is more preferably in the range of −20 ° C. to + 100 ° C. with respect to the glass transition temperature of the polyimide resin.
[0216]
<Example of use of polyimide molding>
The use of the polyimide molded article according to the present invention is not particularly limited as long as it can make use of its characteristics, but it can be used very suitably as a part of various electronic devices.
[0217]
Specific examples of the electronic components include base materials such as a flexible printed wiring board (FPC) and TAB (Tape Automated Bonding), insulating coatings such as electric wires, and various OA equipment components such as copying machines (for example, Molded products such as separation claws and bearings), semiconductor adhesives and insulating films.
[0218]
Above all, the polyimide molded product according to the present invention can be very suitably used as a transfer belt, an intermediate transfer belt, a transfer fixing belt, and the like, which are parts of electrophotographic devices such as various copying machines and printers.
[0219]
Specifically, first, in the transfer belt and the intermediate transfer belt, it is important to control the volume resistance value to the intermediate resistance value in order to transfer the toner satisfactorily. Further, in these transfer belts, intermediate transfer belts and the like, it is preferable that the volume resistance value is substantially constant under any environment. Specifically, the ratio of the volume resistivity between normal temperature and normal humidity and high temperature and high humidity is preferably 100 times or less, and more preferably 30 times or less.
[0220]
Moreover, since the polyimide resin has a hygroscopic property, especially when carbon black or other conductive filler is added, under high temperature and high humidity, water permeates the interface between the conductive filler and the polyimide resin, and The resistance value drops significantly. In addition, when the polyimide resin serving as the base absorbs moisture and expands, the dispersion state of the carbon black, the additives, and the like changes, and the volume resistance value greatly changes.
[0221]
In these transfer belts, intermediate transfer belts, and the like, it is necessary to control the voltage and current according to the type of image formed by the electrophotographic apparatus and the use environment of the electrophotographic apparatus. Therefore, in a transfer belt, an intermediate transfer belt, or the like, if the volume resistance varies according to the voltage, it becomes difficult to control the voltage and the current. Specifically, the ratio of the volume resistance values at 100 V and 1000 V is preferably 100 times or less, and more preferably 30 times or less.
[0222]
Further, a transfer belt, an intermediate transfer belt, and the like are provided near the optical processing unit in the electrophotographic apparatus. Therefore, the color is desired to be black. However, it is difficult to control the volume resistance value of a belt (tubular molded product) made of a general polyimide-based material to which carbon black is added, so that it is difficult to optimize the amount of carbon black that is also a coloring agent. In some cases, it is difficult to achieve good black color.
[0223]
Satisfying all of the above physical properties has been extremely difficult with conventional polyimide-based materials. However, the polyimide resin composition and the polyimide molded product according to the present invention easily realize the control of various physical properties (1) to (5) described in the above <Control of various physical properties by blending high-resistance carbon black>. be able to. As a result, when the polyimide molded product according to the present invention is formed into a belt shape (tubular shape), it is very suitable as at least one of a transfer belt, an intermediate transfer belt, and a transfer fixing belt of an electrophotographic apparatus. Can be used.
[0224]
When the polyimide molded product according to the present invention is used as the transfer belt or the intermediate transfer belt, it is preferable to form an outermost layer made of a fluororesin whose conductivity is controlled on the surface of the polyimide molded product. Thereby, the releasability of the toner from the transfer belt or the intermediate transfer belt, the transferability of the toner, or the cleaning property of the toner can be improved.
[0225]
Examples of the fluororesin include PTFE (polytetrafluoroethylene) and PFA (tetrafluoroethylene-perfluoroalkylvinyl ether copolymer), but are not particularly limited. Further, as the additive for controlling the conductivity of the fluororesin, the above-mentioned conductive or semiconductive filler can be used. Examples of the method of forming the outermost layer include application of a fluororesin solution, lamination of a fluororesin film, and the like, and a method of dispersing these materials in a solvent and spraying is generally used.
[0226]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In addition, the evaluation of the physical properties of the polyimide molded product in each of the examples and comparative examples was performed as follows.
[0227]
(Physical properties evaluation method of polyimide molded product)
<Measurement and evaluation of resistance value>
A film-like sample was cut out from the tubular polyimide molded product obtained in each of the examples or comparative examples. In addition, about 0.25 g of carbon black and a filler were filled in a cylindrical container made of Bakelite, respectively, and about 490 N / cm in the case of carbon black. ² (50kgf / cm ² At the pressure of (2), the other fillers were compressed under no load to produce a cylindrical sample having a height of about 10 mm.
[0228]
The film sample or the cylindrical sample of carbon black or filler was left for 24 hours under the following three conditions.
[0229]
(1) Environment (LL) with temperature of 10 ° C and humidity of 15% Rh
(2) Environment of 23 ° C and 55% RH (NN)
(3) Environment (HH) with a temperature of 30 ° C and a humidity of 80% Rh
Then, in this environment, the volume resistance and the surface resistance at 100 V were measured using a digital ultra-high resistance / microammeter R8340 manufactured by Advantest Corporation and an HR probe manufactured by Mitsubishi Chemical Corporation. In the case of a film sample, the measurement was performed at 1000 V.
[0230]
The environmental dependency of the resistance value refers to the ratio (R1 / Rh) between the volume resistance value Rl of the LL (low temperature and low humidity) and the volume resistance value Rh of the HH (high temperature and high humidity). Is the volume resistance value R when 100 V is applied. _100V And the volume resistance R when 1000 V is applied _1000V Ratio (R _100V / R _1000V ). When these values are in the range of 0.3 to 30, it is determined that there is little dependence, and the former is in the range of 0.01 to 0.3 and the latter is in the range of 30 to 100. In some cases, it was determined that the dependency was moderate, and when the former was 0.01 or less and the latter was 100 or more, all of the materials were poorly dependent.
[0231]
<Measurement and evaluation of electrical insulation>
The film sample was left in the environment of the above (2) (NN) for 24 hours, and the electrical insulation was measured under the environment using a YSS-type electric breakdown tester manufactured by Yasuda Seiki Seisakusho. If the dielectric breakdown voltage is 15 kV / mm or more, it is determined that the electrical insulation is high. If it is 10 kV / mm or more, it is determined that the electrical insulation is moderate. If it is 10 kV / mm or less, the electrical insulation is poor. Judged low.
[0232]
<Measurement of tensile modulus, tensile elongation, and tear propagation strength>
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.
[0233]
[Example 1]
Polyamide acid is synthesized using 4,4′-diaminodiphenyl ether as an aromatic diamine compound and pyromellitic dianhydride (PMDA) as an aromatic dianhydride, and dimethylformamide of polyamic acid is synthesized. 75 g of a DMF) solution (solid content concentration 18.5%, solution viscosity 3,000 poise) was prepared.
[0234]
4.17 g of high-resistance carbon black (a carbon black surface grafted with polyvinylpyrrolidone, volume resistance value: 900 Ω · cm) is dispersed and dispersed in DMF eight times the amount of the high-resistance carbon black. A liquid was prepared.
[0235]
A dispersion of high resistance carbon black was added to the polyamic acid solution and mixed. Further, to this mixture, an imidization accelerator solution having a mixing ratio of acetic anhydride / isoquinoline / DMF = 9.03 g / 11.4 g / 15.6 g was added and mixed. Thereafter, it was cast on a SUS cylindrical mold and heat-treated under the conditions of 140 ° C./240 seconds, 275 ° C./40 seconds, and 400 ° C./93 seconds.
[0236]
Thus, a tubular polyimide molded product having a thickness of about 50 μm was obtained. Table 1 shows the composition of the obtained polyimide molded product, and Table 2 shows the electrical properties and Table 3 shows the dependence and mechanical properties among the evaluation results of the physical properties. The amount of the high-resistance carbon black contained in the polyimide molded product was 30 parts by weight based on 100 parts by weight of the solid content of the polyimide.
[0237]
The linear expansion coefficient of the thus obtained film-shaped molded product (polyimide film) alone was 21 ppm, the coefficient of hygroscopic expansion was 16 ppm, the tensile modulus was 2.9 GPa, and the tensile elongation was 70%. The tear propagation strength was 4.41 N / mm (450 gf / mm), and the water absorption was 2.5%.
[0238]
[Example 2]
A dispersion liquid is prepared by dispersing 6.95 g of a high-resistance carbon black grafted with polyvinylpyrrolidone having a volume resistance value of 20,000 Ω · cm in 8 times the amount of the high-resistance carbon black. A tubular polyimide molded product was obtained in the same manner as in Example 1 except for the above.
[0239]
Table 1 shows the composition of the obtained polyimide molded product, and Table 2 shows the electrical properties and Table 3 shows the dependence and mechanical properties among the evaluation results of the physical properties. The amount of the high-resistance carbon black contained in the polyimide molded product was 50 parts by weight based on 100 parts by weight of the solid content of the polyimide.
[0240]
[Example 3]
In addition to the high resistance carbon black, as a black filler, a carbon-coated filler (carbon-coated potassium titanate whisker: Dentol BK400HR: Lot. 9C00: manufactured by Otsuka Chemical Co., Ltd .: specific gravity 3.15 g / cm) ³ , Volume resistance value 5 × 10 ⁵ ~ 5 × 10 ⁶ Ω · cm, ion elution amount 500 to 10000 ppm, short axis 0.3 to 0.6 μm, long axis 10 to 20 μm), and a tubular polyimide molded article was obtained in the same manner as in Example 1 above. .
[0241]
Table 1 shows the composition of the obtained polyimide molded product, and Table 2 shows the electrical properties and Table 3 shows the dependence and mechanical properties among the evaluation results of the physical properties. The amount of the high-resistance carbon black and the carbon-coated filler contained in the polyimide molded product was 40 parts by weight based on 100 parts by weight of the solid content of the polyimide.
[0242]
[Example 4]
In addition to the high-resistance carbon black, tin oxide-based filler (tin oxide-coated aluminum borate whisker: Pastoran-type IV-KK007: manufactured by Mitsui Kinzoku Co., Ltd .: specific gravity 3 g / cm) ³ , Volume resistance value 1 × 10 ⁷ Ω · cm, ion elution <50 ppm, short axis 1 μm, long axis 10 μm) in the same manner as in Example 1 except that a tubular polyimide molded article was obtained.
[0243]
Table 1 shows the composition of the obtained polyimide molded product, and Table 2 shows the electrical properties and Table 3 shows the dependence and mechanical properties among the evaluation results of the physical properties. The amount of the high-resistance carbon black and the carbon-coated filler contained in the polyimide molded product was 40 parts by weight based on 100 parts by weight of the solid content of the polyimide.
[0244]
[Example 5]
As an aromatic diamine compound, 5 equivalents of 4,4′-diaminodiphenyl ether and 5 equivalents of paraphenylenediamine are dissolved in DMF, and then p-phenylenebis (tri-) is used as an aromatic dianhydride. The polyamic acid was polymerized by adding 5 equivalents of meric acid monoester acid anhydride (TMHQ) and 5 equivalents of PMDA as an aromatic acid dianhydride. A tubular polyimide molded product was obtained in the same manner as in Example 1 except that the thus obtained DMF solution of polyamic acid (solid content concentration: 18.5%, solution viscosity: 3,000 poise) was used. Was. Table 1 shows the composition of the obtained polyimide molded product, and Table 2 shows the electrical properties and Table 3 shows the dependence and mechanical properties among the evaluation results of the physical properties.
[0245]
The linear expansion coefficient of the thus obtained film-shaped molded product (polyimide film) alone was 9 ppm, the coefficient of hygroscopic expansion was 5 ppm, the tensile modulus was 6 GPa, and the tensile elongation was 40%. The tear propagation strength was 4.41 N / mm (450 gf / mm), and the water absorption was 1.2%.
[0246]
[Example 6]
Using 5 equivalents of 4,4′-diaminodiphenyl ether and 5 equivalents of paraphenylenediamine as the aromatic diamine compound, dissolving them in DMF, then adding 5 equivalents of TMHQ as an aromatic acid dianhydride, Polyamide acid was polymerized by adding 5 equivalents of PMDA as a system dianhydride. A tubular polyimide molded product was obtained in the same manner as in Example 2 except that the thus obtained DMF solution of polyamic acid (solid content: 18.5%, solution viscosity: 3,000 poise) was used. Was. Table 1 shows the composition of the obtained polyimide molded product, and Table 2 shows the electrical properties and Table 3 shows the dependence and mechanical properties among the evaluation results of the physical properties.
[0247]
[Comparative Example 1]
The same procedures as in Example 1 were carried out except that a dispersion was prepared by dispersing 2.78 g of a carbon black grafted with polyvinylpyrrolidone and a volume resistance value of 10 Ω · cm in DMF eight times the amount of the carbon black. Similarly, a tubular polyimide molded product was obtained. The amount of carbon black contained in the polyimide molded product was 20 parts by weight based on 100 parts by weight of the solid content of the polyimide. Table 1 shows the composition of the obtained polyimide molded product, and Table 2 shows the electrical properties and Table 3 shows the dependence and mechanical properties among the evaluation results of the physical properties.
[0248]
[Comparative Example 2]
Tubular polyimide molding was performed in the same manner as in Example 1 except that 4.17 g of carbon black (# 3030B: Mitsubishi Chemical Corporation: <1.0E + 1 Ω · cm) was dispersed in 21 g of DMF. I got something. The amount of carbon black contained in the polyimide molded product was 30 parts by weight based on 100 parts by weight of the solid content of the polyimide. Table 1 shows the composition of the obtained polyimide molded product, and Table 2 shows the electrical properties and Table 3 shows the dependence and mechanical properties among the evaluation results of the physical properties.
[0249]
[Table 1]

[0250]
[Table 2]

[0251]
[Table 3]

[0252]
The physical properties of the polyimide molded products of Examples 1 to 6 were as follows.
[0253]
(1) The volume resistance under the environment of (2) NN and (3) HH is 1 × 10 ⁸ ~ 1 × 10 ^Thirteen It was within the range of Ω · cm, and was controlled within the range of the intermediate resistance value. In addition, the electrical insulation was as excellent as 10 kV / mm or more.
[0254]
(2) The ratio of the volume resistance value due to the difference (5 parts by weight) in the amount of the high resistance carbon black was not more than three times, and the dependence of the volume resistance value on the amount was small. Further, the ratio of the volume resistance under the environment of (2) NN and (3) HH was not more than 30 times, and the environment dependence of the volume resistance was small.
[0255]
(3) The ratio of the volume resistance measured at 100 V and 1000 V was 30 times or less, and the voltage dependence of the volume resistance was small.
[0256]
(4) As a result of measuring the volume resistance value at 500 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. . Further, the variation within the same sample was 3 times or less, which was very small.
[0257]
(5) The tensile modulus of the film sample was superior to that of the sample without filler, and the tensile elongation was maintained at 50% or more and the tear propagation strength was maintained at 50% or more. Further, the linear expansion coefficient and the hygroscopic expansion coefficient were also lower by several ppm than those without filler. The tensile modulus increased in the order of Examples 1-4, Example 5, and Example 6. This is because the tensile modulus of the polyimide resin as the base increases in this order.
[0258]
On the other hand, the physical properties of the polyimide molded products of Comparative Examples 1 and 2 were as follows.
[0259]
(1) In each of the polyimide resins of Comparative Examples 1 and 2, the volume resistance value in the above-mentioned (2) NN environment was controlled to a desired intermediate resistance value, but in the (3) HH environment, the volume resistance was extremely low. The resistance was low.
[0260]
(2) The ratio of the volume resistivity due to the difference (5 parts by weight) in the blending amount of carbon black was 3 times or more, and the dependence of the volume resistivity on the blending amount was large.
[0261]
(3) The ratio of the volume resistance under the environment of (2) NN and (3) HH was 100 times or more, and the environment dependence of the volume resistance was extremely large.
[0262]
(4) 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.
[0263]
(5) As a result of measuring the volume resistance at 500 V for five samples prepared 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. . In addition, the variation within the same sample was three times or more, which was very large.
[0264]
From the above, it can be seen that the polyimide resin composition and the polyimide molded product according to the present invention have extremely excellent physical properties.
[0265]
【The invention's effect】
As described above, in the polyimide resin composition and the polyimide molded product according to the present invention, by adding at least the high-resistance carbon black, various physical properties due to the blending of the <high-resistance carbon black, which have been difficult in the related art, were obtained. Control> The control of various physical properties (1) to (5) described in the section above can be easily realized.
[0266]
As a result, excellent electrical insulation can be achieved without excessively increasing the volume resistance value, and the environmental dependence of the resistance value, the dependence on the compounding amount of the high-resistance carbon black, the voltage dependence, and the And the influence of imidization on the same molded product is small, and stable characteristics can be realized.
[0267]
Therefore, the polyimide resin composition and the polyimide molded product according to the present invention can be suitably used particularly for applications of various electronic devices such as FPC, TAB, and components of electrophotographic devices. For example, in an FPC or the like, an excellent antistatic property at the time of conveyance or winding can be obtained. Further, when used as a component of an electrophotographic apparatus, the transferability of a toner image can be improved.
[0268]
Therefore, the present invention can be suitably used not only in the industry for manufacturing high-density packaging materials such as FPC and TAB and wiring materials, for example, in the resin industry for manufacturing resin materials for electronic components, but also in the semiconductor-related field. The present invention is advantageous in that it can be suitably used in a field related to components of various electronic devices represented by an electrophotographic apparatus, and furthermore, in an industrial field of electronic devices using such electronic components.

Claims (8)

A polyimide resin composition containing at least a polyimide resin and carbon black, and having a volume resistance value within a range of 1 × 10 ⁶ to 1 × 10 ¹⁶ Ω · cm,
As the carbon black, a high-resistance carbon black having a volume resistance value of 1 × 10 ² to 1 × 10 ¹⁰ Ω · cm measured using a sample compressed at 490 N / cm ² is used. ,
A polyimide resin composition comprising the carbon black in an amount of 20 to 100 parts by weight based on 100 parts by weight of the polyimide resin. The polyimide resin composition according to claim 1, wherein a grafted carbon black obtained by grafting a hydrophilic polymer on the surface of carbon black is used as the high-resistance carbon black. Further, it contains a conductive or semiconductive filler, and the filler is contained in the range of 0.01 to 100 parts by weight with respect to 100 parts by weight of the polyimide resin. The polyimide resin composition according to claim 1 or 2, wherein 4. The polyimide resin composition according to claim 1, wherein a reaction-curable linear polyimide resin is used as the polyimide resin. 5. The polyimide resin composition according to claim 5, wherein the polyimide resin is obtained by adding at least one of an acid anhydride and a tertiary amine as an imidization accelerator to the polyamic acid, and then heating. . A polyimide molded article comprising the polyimide resin composition according to any one of claims 1 to 4. The polyimide molded product according to claim 6, wherein the polyimide molded product is formed into a film or a tube. The polyimide molded product according to claim 7, which is used as at least one of a transfer belt, an intermediate transfer belt, and a transfer / fixing belt of an electrophotographic apparatus when formed into a tubular shape.