JP4039886B2 - Conductive molding - Google Patents

Description

ここで、
ｘ ；「微細炭素繊維ネットワークに囲まれた部分」の面積の平均値
ｘ_ｉ；「微細炭素繊維ネットワークに囲まれた部分」の個々の面積
Ｎ ；「微細炭素繊維ネットワークに囲まれた部分」の個数
【００１８】
▲７▼ 上記▲６▼を５つの視野に対して同様に行い、その平均値をとる。このようにして得られた平均値を本発明の「微細炭素繊維ネットワークに囲まれた部分の個数」及び「微細炭素繊維ネットワークに囲まれた部分の面積の平均値と標準偏差の積」と定義する。
【００１９】
以下に、このような本発明の微細炭素繊維ネットワークパラメータと、本発明の導電性発現効果との関係について、図４を参照して詳細に説明する。
【００２０】
図４の（Ａ）は、微細炭素繊維がお互いに絡み合うことなく均一に分散した状態を示す。本発明に係る上記画像処理により、微細炭素繊維ネットワークは均一かつ微細になり、その結果、微細炭素繊維ネットワークに囲まれた部分の個数（Ｎ）は多くなり、面積及びその平均値（ｘ（μｍ^２））は小さく、また面積の標準偏差（σ（μｍ^２））は小さくなる。従って、面積の平均値（ｘ（μｍ^２））と面積の標準偏差（σ（μｍ^２））の積も小さくなる。
かかる分散状態では、微細炭素繊維同士の電気的な接触が不十分となり、導電性は低下しやすくなる。即ち、所望の導電性を得るためには、多量の微細炭素繊維の添加を必要とする。
【００２１】
これに対して、図４の（Ｂ）のように、微細炭素繊維が適度に凝集かつ分散した状態になると、微細炭素繊維ネットワークに囲まれた部分の個数（Ｎ）は少なくなり、面積及びその平均値（ｘ（μｍ^２））は大きくなる。また、微細炭素繊維の粗密に起因して、面積の大小のばらつきも大きくなるために、面積の標準偏差（σ（μｍ^２））は大きくなる。従って、面積の平均値（ｘ（μｍ^２））と面積の標準偏差（σ（μｍ^２））の積も大きくなる。
このように微細炭素繊維がお互いに絡み合いながら適度に凝集した状態においては、優れた導電性が発現される。
【００２２】
なお、図４の（Ｃ）に示すように、微細炭素繊維の絡み合いが大きくなりすぎて塊状に凝集した場合、前述の画像処理を行っても微細炭素繊維ネットワークは形成されない。
【００２３】
本発明では、この微細炭素繊維ネットワークに囲まれた部分の個数（Ｎ）が１８０以下で、かつ囲まれた部分の面積の平均値（ｘ（μｍ^２））と標準偏差（σ（μｍ^２））の積が１２（μｍ^２）^２以上である。
これは、図４の（Ｂ）のように、微細炭素繊維が適度に絡み合いながら、比較的不均一に分散している状態を、定量的に表している。
【００２４】
なお、本発明に係る「微細炭素繊維ネットワークに囲まれた部分」の個数及び面積の平均値と標準偏差の積は、共に微細炭素繊維の分散の不均一性、即ち微細炭素繊維の凝集の度合いを表しているが、個数は微視的な凝集度合いを示しており、面積の平均値と標準偏差の積がそれよりも巨視的な凝集度合いを表している。
【００２５】
この微細炭素繊維ネットワークに囲まれた部分の個数の範囲は、望ましくは１７０以下、２０以上であり、また面積の平均値と標準偏差の積は望ましくは１５以上、２００以下である。
これよりも個数が多い、又は積が小さいと、本発明の微細炭素繊維の添加量の範囲では導電性が発現しない。
一方、これよりも個数が少ない、又は積が大きいものは、分散が不均一となりすぎるために、導電性が低下する。
【００２６】
ところで、ハードディスクなどの高密度デバイス用の帯電防止部品には、特に優れた静電気特性が要求される。即ち、帯電特性に優れること（帯電電荷を速やかに散逸すること）だけでなく、デバイス自体が帯電した際に、帯電したデバイスとの接触時に生じる接触電流が少ないことが要求される。
【００２７】
本発明では、特に、「微細炭素繊維ネットワークに囲まれた部分」の個数（Ｎ）が１８０以下、１２０以上、より望ましくは１７０以下、１２０以上、かつ面積の平均値（ｘ（μｍ^２））と標準偏差（σ（μｍ^２））の積が１２以上、２５以下、より望ましくは１５以上、２５以下であると、帯電防止性が良好となるだけでなく、電子デバイス等が接触した際に生じる接触電流が少ない点で望ましい。
【００２８】
これは、以下の理由による。
即ち、微細炭素繊維ネットワークに囲まれた部分の個数が１８０より多い、或いは面積と標準偏差の積が１２未満であると、微細炭素繊維のネットワークが均一に分散するため、微細炭素繊維同士の接触が不十分となり、その結果、帯電負荷の散逸が不十分となり、帯電が生じやすくなる。
一方、この個数が１２０未満、或いは面積と標準偏差の積が２５以上であると、ネットワークの粗密が大きくなり、ネットワークが密の部分の導電性が局部的に高くなる。その結果、接触電流を増大させる。
【００２９】
【発明の実施の形態】
以下に本発明の導電性成形品の実施の形態を詳細に説明する。
【００３０】
まず、本発明で用いる成形原料について説明する。
＜微細炭素繊維＞
本発明で使用される微細炭素繊維は、平均繊維径が１００ｎｍ以下の微細炭素繊維であり、一般的には気相成長法により製造される。例えば特表平８−５０８５３４号公報に記載されている炭素フィブリルを使用することができる。
該炭素フィブリルは、微細な管状の形態を有しており、壁厚み（管状体の壁厚）は、通常３．５〜７５ｎｍ程度である。これは、通常、炭素フィブリルの外径の約０．１〜０．４倍に相当する。
この、炭素フィブリルの繊維径は製法に依存し、ほぼ均一なものである。
【００３１】
本発明において、炭素フィブリル等の微細炭素繊維の平均繊維径が１００ｎｍより大きいと、樹脂中での微細炭素繊維同士の接触が不十分となり、導電性を十分に発現させることが困難となる上に、安定した導電性が得られ難い。従って、微細炭素繊維としては平均繊維径１００ｎｍ以下、好ましくは２０ｎｍ以下のものを用いる。
【００３２】
一方、微細炭素繊維の平均繊維径は、０．１ｎｍ以上、特に０．５ｎｍ以上であることが好ましい。繊維径がこれより小さいと、製造が著しく困難であり、製品のコストアップを招く。
【００３３】
また、微細炭素繊維は、長さと径の比（長さ／径比、即ちアスペクト比）が５０以上のもの、好ましくは１００以上のものを用いる。このような長さ／径比のものであれば、導電性ネットワークを形成しやすく、少量添加で優れた導電性を発現することができる。
【００３４】
なお、微細炭素繊維の繊維径、長さ（長さ／径比）は、例えば、得られた成形品の樹脂成分を溶媒やイオンスパッタリング等で除去して、微細炭素繊維を露出させて電子顕微鏡で観察するか、或いは成形品より切り出した超薄切片を電子顕微鏡観察することにより測定することができ、このような電子顕微鏡の観察において１０本の実測値の平均値で得られる。
【００３５】
微細炭素繊維はその少なくとも一部分が凝集体の形態である場合、原料となるマトリックス樹脂中に、面積ベースで測定して約５０μｍより大きい径を有する微細炭素繊維凝集体、望ましくは１０μｍよりも大きい径を有する微細炭素繊維凝集体を含有していないことが、所望の導電性を発現するための添加量が少なくてすみ、機械物性を低下させない点で望ましい。
【００３６】
本発明で使用する微細炭素繊維は、その屈曲度が１０°以上望ましくは２０°以上、更に望ましくは４０°以上のものが望ましい。屈曲度は微細炭素繊維同士の絡み易さの目安となる値であり、微細炭素繊維が絡み合いネットワークを形成することにより導電性ネットワークが形成されて導電性が発現することができる。
【００３７】
微細炭素繊維の屈曲度は、成形品の樹脂成分を溶媒やイオンスパッタリング等で除去して、微細炭素繊維を露出させるか、又は成形品より切り出した超薄切片を電子顕微鏡観察することによって測定する。屈曲度は図８に示すように、微細炭素繊維を顕微鏡で観察し、同一繊維上の、繊維径の５倍（繊維径（図８のｄ）を測定し、デバイダ等で繊維に沿って５回計る等の方法による）離れた任意の２点Ａ，Ｂを選び、それぞれの点に接線Ｌ_Ａ，Ｌ_Ｂを引いて、接線Ｌ_Ａ，Ｌ_Ｂの交差する点Ｑの外角（図８にαで示す）を測定する。１０点の平均値をとり、屈曲度とする。
即ち、繊維が直線的であればこの屈曲度は０°となり、半円で１８０°、円を描けば３６０°となる。
【００３８】
例えば従来の炭素繊維（ピッチ系、ＰＡＮ系）は、繊維直径が７〜１３μｍ程度の、剛直かつ直線的な繊維であり、屈曲度は１０°未満となる。かかる直線的な繊維では、お互いの絡み合いが生じることはなく、ネットワーク構造を本発明の範囲にコントロールすることは難しい。
【００３９】
このような微細炭素繊維は、市販品を使用することができ、例えば、ハイペリオンカタリシスインターナショナル社の「ＢＮ」が使用可能であるが、マスターバッチ等の成形条件、成形品の製造条件、特に混練の条件によって屈曲度が変化するので、条件を経験的に得ることが重要となる。
【００４０】
＜熱可塑性樹脂＞
本発明で使用する熱可塑性樹脂は、ポリカーボネートである。
【００４１】
ポリカーボネート樹脂は、寸法精度、耐熱性、機械物性などのバランスが良好である。
【００４２】
ポリカーボネート樹脂としては、例えば界面重合法、ピリジン法、クロロホーメート法などの溶液法により、二価フェノール系化合物を主成分とし、ホスゲンと反応させることによって製造される一般的なものを使用できる。
【００４３】
最終的な成形品中のポリカーボネートの重量平均分子量が、ポリスチレン換算値で３０，０００〜４５，０００、望ましくは３５，０００〜４３，０００となるように、予め原料のポリカーボネートの分子量や、製造条件を選ぶ。分子量がこの範囲内であると、得られる導電性成形品の微細炭素繊維ネットワークに囲まれた部分が、本発明の範囲内になりやすく、その結果、機械的強度を低下させることなく、導電性に優れたものとすることができる。
【００４４】
本発明の導電性成形品を構成するポリカーボネート樹脂組成物のメルトフローレート（ＭＦＲ）は、２８０℃、２．１６Ｋｇ荷重の測定において、２ｇ／１０分以上３０ｇ／１０分以下、特に４ｇ／１０分以上１５ｇ／１０分以下が望ましい。
【００４５】
本発明に好適な上記範囲の重量平均分子量を有するポリカーボネート樹脂成形品を得る方法としては、例えば予め本発明の範囲内、又はこれより大きめの分子量を有するポリカーボネート樹脂を用いて成形を行い、成形時の加工温度条件等を調整したり、成形を繰り返し行うなどによってポリカーボネートの分子量を適度に低下させる方法を採用することができる。
【００４６】
＜微細炭素繊維の割合＞
微細炭素繊維の配合割合は、上記熱可塑性樹脂と微細炭素繊維との合計に対して、０．１重量％以上、５．１重量％未満、好ましくは０．１〜４重量％、より好ましくは０．５〜３．５重量％とする。微細炭素繊維の配合量が上記範囲よりも少ないと十分な導電性が得られず、多いと得られる成形品の衝撃強度が低下したり、コストアップに繋がり、好ましくない。
【００４７】
＜添加成分＞
本発明においては、必要に応じて、本発明の目的を損なわない範囲で熱可塑性樹脂及び微細炭素繊維以外の任意の添加成分を配合することができる。
例えば、ガラス繊維、シリカ繊維、シリカ・アルミナ繊維、チタン酸カリウム繊維、ほう酸アルミニウム繊維等の無機繊維状強化材、アラミド繊維、ポリイミド繊維、フッ素樹脂繊維等の有機繊維状強化材、タルク、炭酸カルシウム、マイカ、ガラスビーズ、ガラスパウダー、ガラスバルーン等の無機充填材、各種カーボンブラック、フッ素樹脂パウダー、二硫化モリブデン等の固体潤滑剤、パラフィンオイル等の可塑剤、酸化防止剤、熱安定剤、光安定剤、紫外線吸収剤、中和剤、滑剤、相溶化剤、防曇剤、アンチブロッキング剤、スリップ剤、分散剤、着色剤、防菌剤、蛍光増白剤等といった各種添加剤を挙げることができる。
【００４８】
＜製造方法＞
本発明の導電性成形品は、例えば熱可塑性樹脂に微細炭素繊維を予め混合した後、バンバリーミキサー、ロール、ブラベンダー、単軸混練押し出し機、二軸混練押し出し機、ニーダーなどで溶融混練することによって導電性熱可塑性樹脂組成物を製造し、その後、射出成形することにより製造される。
【００４９】
射出成形方法としては、一般的な射出成形法のほかに、インサート射出成形法による金属部品その他の部品との一体成形や、二色射出成形法、コアバック射出成形法、サンドイッチ射出成形法、インジェクションプレス成形法等の各種成形法を用いることができる。
【００５０】
また、射出成形においては、樹脂温度、金型温度、成形圧力、射出速度によって製品中の微細炭素繊維ネットワークが変化し、その結果、得られる成形品の導電性が変化するので、適切な条件が設定されなければならない。
【００５１】
熱可塑性樹脂としてポリカーボネートを使用する場合の成形条件としては、射出成形による分子量の低下が２％以上、望ましくは２〜５％になるように成形条件を設定すると、得られる成形品の導電性が良好となる点で望ましい。
【００５２】
溶融成形後は、熱風や赤外線などの加熱処理を行って、微細炭素繊維の分散を調整しても良い。
【００５３】
【実施例】
以下に実施例及び比較例を挙げて本発明をより具体的に説明する。
【００５４】
なお、以下の実施例及び比較例で用いた原料成分は下記の通りである。
【００５５】
ポリカーボネート（ＰＣ）（Ｔｇ；１４５℃）：三菱エンジニアリングプラスチック社製「ユーピロン」
微細炭素繊維：ハイペリオンカタリシスインターナショナル社製「ハイペリオン ＢＮ」
【００５６】
実施例１〜５、比較例１，２
（１） 混練配合
ポリカーボネートと微細炭素繊維マスターバッチを、表１に示す配合で混合し、２軸押出機（池貝鉄鋼社製「ＰＣＭ４５」、Ｌ／Ｄ＝３２（Ｌ；スクリュー長、Ｄ；スクリュー径））を用いてバレル温度３００℃、スクリュ回転数１６０ｒｐｍにて溶融混練して、表１に示す微細炭素繊維含有量の樹脂組成物のペレットを得た。
なお、微細炭素繊維を配合する場合の配合混練は、予めマトリックス樹脂に微細炭素繊維を１５重量％添加したマスターバッチを製造し、これを希釈して所定の微細炭素繊維添加量とした。
【００５７】
（２） ペレット中のポリカーボネートの分子量の測定
（１）で得られた各組成物中のポリカーボネートの分子量を以下の要領で測定した。
組成物のクロロホルム溶液（２ｍｇ／ｍｌ）を調製し、これを０．２μｍフィルターにて濾過し、微細炭素繊維を分離してポリカーボネート溶液を得た。このポリカーボネート溶液を用いて、ＧＰＣにて重量平均分子量（Ｍｗ）を測定した。詳細な条件を以下に記す。
検出器：Ｗａｔｅｒｓ ＵＶ４９０（２５４ｎｍ）
カラム：Ｓｈｏｄｅｘ ＧＰＣ ＡＤ−８０６ＭＳ
カラム温度：３０℃
流量：１ｍｌ／ｍｉｎ
内標：トルエン
注入量 ：０．０５ｍｌ
各組成物のペレット中のポリカーボネートの重量平均分子量の測定結果を表１に示す。
なお、重量平均分子量は、ポリスチレン換算値である。
【００５８】
【表１】

【００５９】
（３） 測定用サンプルの成形
（１）で得られた各樹脂組成物のペレットを用いて、７５ＴＯＮ射出成形機にて１００ｍｍ×１００ｍｍ×２ｍｍ（厚さ）の抵抗値測定用シートを成形した。
成形温度を表２に示す。
金型温度は９０℃。射出率が１８〜２０ｃｃ／ｓｅｃ、但し、実施例２のみ９ｃｃ／ｓｅｃになるように、射出圧力と射出速度を調整して成形した。
【００６０】
（４） 成形品中のポリカーボネートの分子量の測定
（３）で得られたシートより分子量測定用サンプルをサンプリングし、（２）と同様にしてポリカーボネートの重量平均分子量（Ｍｗ）を測定し、結果を表２に示した。
【００６１】
（５） 表面抵抗値の測定
ダイヤインスツルメント社製ハイレスタＵＰを使用して、ＵＡプローブにて、（３）で得られたシートサンプルの中央部の表面抵抗値を測定し、結果を表２に示した。印加電圧は１０Ｖにて測定した。
【００６２】
（６） アイゾット衝撃強度の測定
ＡＳＴＭ Ｄ２５６に準拠した。結果を表２に示した。
【００６３】
（７） 微細炭素繊維の繊維径及び長さ／径比と屈曲度の測定
（３）で得たサンプルの中央部（抵抗測定部）の表面から０．１〜１０μｍの範囲で、流れ方向に沿って超薄切片を切り出した。同一条件で切り出した切片を、エポキシ樹脂に包埋した後、断面を切り出して切片の厚みを測定した結果、８５ｎｍであった。
この超薄切片について、前述の如く、微細炭素繊維上の５２．５ｎｍ（径１０．５ｎｍ×５）離れた２点の接線の角度を測定し（１０点）、屈曲度を測定した結果を表２に示した。
また、サンプルをクロロホルムに溶解した後濾過して、分離した微細炭素繊維を透過型電子顕微鏡にて１０点測定して、平均繊維径が１０．５ｎｍで、長さ／径比が５０以上であることを確認した。
【００６４】
（８） 微細炭素繊維ネットワークにより囲まれた部分の個数と面積の平均値と標準偏差の積の測定
（７）の超薄切片を透過型顕微鏡で４００００倍にて撮影した微細炭素繊維の分散画像について、以下の解析を行った。
解析には、アビオニクス社製画像解析装置（タイプ；スピカ２）を使用した。
先ず５μｍ×５μｍの範囲の画像を、ＣＣＤカメラを用いて積分入力（１６回）にてコンピュータに取り込み、９．７７ｎｍ×９．７７ｎｍ（５１２×５１２）の画素でデジタル画像とした（以下、前記の定義の通りの手順に従って微細炭素繊維が存在している画素がオン、存在していない画素がオフとする）。
微細炭素繊維ネットワークにより囲まれた部分の個数、及びこの囲まれた部分の面積の平均値と標準偏差の積を算出した。
測定結果を表２に示す。
また、微細炭素繊維ネットワークにより囲まれた部分の個数と表面抵抗値との関係、微細炭素繊維ネットワークにより囲まれた部分の面積の平均値と標準偏差の積と表面抵抗値との関係をそれぞれ図５，６に示す。
【００６５】
［静電気特性評価］
（３）で得られたサンプルの静電気特性として接触電流及び帯電電極を次の機器を用いて測定した。
チャージプレートモニター；ヒューグエレクトロニクス社製
表面電位計；モンローエレクトロニクス社製 ２４４Ａ
オシロスコープ；レクロイ社製 ＬＣ５８４Ａ
電流プローブ；テクトロニクス社製 ＣＴ１
【００６６】
１．接触電流
帯電したシートサンプルに、接地された電子部品が接触した場合に生じる接触電流について、電子部品を接地プローブで代用して以下の通り測定した。
▲１▼ チャージプレートモニター上に、シートサンプルを置いた。
▲２▼ チャージプレートモニターを使用して、プレート及びサンプルに１０００Ｖを３秒間充電させた後、接地から切り離して絶縁した。
▲３▼ ３秒後に接地プローブをサンプルに接触させて、プローブを流れる接触電流を測定した。測定はサンプル中央部（抵抗測定部）について行った。この場合、接触電流はナノ秒オーダーの交流電流が流れ、次第に減衰するので、最も高い電流値を接触電流とした。
▲４▼ 上記測定を３回繰り返して測定し、測定値を平均した。
【００６７】
２．帯電電位（帯電量）
帯電電位は次の通り測定した。
▲１▼ チャージプレートモニター上に、シートサンプルを置いた。
▲２▼ サンプル及びプレートが帯電ゼロで、かつ接地から絶縁された状態で、サンプルの上方よりコロナチャージによって、プレートモニターが１０００Ｖになるまで、帯電させた。
▲３▼ サンプルを載せているプレートを接地して、接地後３秒後のサンプル中央部（抵抗測定部）の表面電位を測定した。
▲４▼ 上記測定を３回繰り返して、測定値を平均した。
【００６８】
【表２】

【００６９】
この結果より、次の事項が認められる。
比較例１は分散パラメータが範囲外であるために、導電性が悪い（抵抗値が高い）。
比較例２のように、微細炭素繊維の添加量を増加すれば、パラメータが範囲外でも導電性は得られる。しかし、この方法では、コストアップと物性低下につながる。
【００７０】
実施例１〜５のように、分子量や成形条件を適正化することによって、コストアップや物性低下させずに、導電性が得られる。
中でも、実施例１〜４のように、成形後のポリカーボネートの重量平均分子量が４５０００以下であると、成形温度を大幅に上昇させずに優れた導電性が得られる。
なお、実施例５の成形温度３４０℃まで上げると、連続生産時のシリンダ内での樹脂劣化などを引き起こしやすい。
【００７１】
特に、分散パラメータとして、微細炭素繊維ネットワークにより囲まれた部分の個数が１８０以下、１２０以上で、面積と標準偏差の積が１２以上、２５以下であると、帯電特性に優れるだけでなく、ノイズ電流が低減される。
【００７２】
本実施例では示していないが、樹脂中の微細炭素繊維分散挙動と、導電性の発現メカニズムは、同様であるので、ポリカーボネート樹脂以外の熱可塑性樹脂であっても同様の結果となることが容易に予想される。
【００７３】
【発明の効果】
以上の通り、本発明によると、導電性に優れ、且つ衝撃強度が大きい導電性成形品が提供される。この導電性成形品は、微細炭素繊維の含有量が少ないので、安価である。
【図面の簡単な説明】
【図１】微細炭素繊維ネットワークに囲まれた部分の個数及び面積の平均値と標準偏差の積を求めるための画像処理方法を示す模式図である。
【図２】微細炭素繊維ネットワークに囲まれた部分の個数及び面積の平均値と標準偏差の積を求めるための画像処理方法を示す模式図である。
【図３】微細炭素繊維ネットワークに囲まれた部分の個数及び面積の平均値と標準偏差の積を求めるための画像処理方法を示す模式図である。
【図４】微細炭素繊維ネットワークの状態と本発明に係るパラメータとの関係を示す説明図である。
【図５】実施例１〜５及び比較例１，２の微細炭素繊維ネットワークにより囲まれた部分の個数と、表面抵抗値との関係を示すグラフである。
【図６】実施例１〜５及び比較例１，２の微細炭素繊維ネットワークにより囲まれた部分の面積の平均値と標準偏差の積と、表面抵抗値との関係を示すグラフである。
【図７】微細炭素繊維撮像のトレース図である。
【図８】微細炭素繊維の屈曲度の測定法を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a highly conductive molded article, and can be used particularly as an antistatic component in the electric and electronic fields and in the automobile field. For example, the manufacturing and transportation of an automobile fuel tank and surrounding antistatic components and semiconductor devices. The present invention relates to a conductive molded article suitable for a packaging member such as a tray, a case, and a package in a process, particularly a disk for a hard disk drive and an antistatic member for a magnetic head.
[0002]
[Prior art]
In recent years, with increasing information recording density and processing speed, semiconductor devices have become extremely vulnerable to static electricity, and antistatic measures such as cases and jigs have become important.
[0003]
Therefore, the antistatic products generally have 10 ¹² A surface resistance value (that is, conductivity) of Ω / □ or less is required.
[0004]
Conventionally, in order to prevent static electricity, for example, a method of blending and dispersing a conductivity-imparting component such as an antistatic agent, carbon black, or carbon fiber in a thermoplastic resin such as ABS, polycarbonate, or modified polyphenylene ether (PPE) has been applied. Yes.
[0005]
[Problems to be solved by the invention]
However, these methods have the following problems. That is, in the case of an antistatic agent, it is affected by environmental humidity due to the ionic conduction of the conductive mechanism, the antistatic agent flows out due to washing and long-term use, and the antistatic property decreases, When added in a large amount, heat resistance may be impaired. Although carbon black and carbon fiber are not affected by humidity, washing, etc., carbon particles and carbon fiber are likely to fall off, resulting in problems such as device damage.
[0006]
On the other hand, when carbon fibrils having a diameter of 100 nm or less are added as a conductivity-imparting component, it is effective because the falling off of the filler is reduced. However, there are problems below.
(1) By adding carbon fibrils, mechanical strength, particularly impact strength, is remarkably impaired, and cracks are likely to occur when dropped.
(2) Carbon fibrils are extremely expensive, leading to increased product costs.
The problems (1) and (2) can be solved to some extent by lowering the amount of carbon fibril added. However, if the amount of carbon fibril added is lowered, the conductivity of the molded article is significantly impaired.
[0007]
An object of this invention is to provide the electroconductive molded article which can obtain high electroconductivity even if the addition amount of a carbon fibril is decreased.
[0008]
[Means for Solving the Problems]
The conductive molded article of the present invention is A conductive molded article obtained by injection molding a resin composition comprising a thermoplastic resin comprising polycarbonate and fine carbon fibers, wherein the polycarbonate has a weight average molecular weight of 30,000 to 45,000, The average fiber diameter is 100 nm or less and the length / diameter ratio is 50 more than The injection molding temperature of the molded product is 300 to 340 ° C., the injection rate is 9 to 20 cc / sec, The content of the fine carbon fiber is 0.1% by weight or more and less than 5.1% by weight with respect to the total of the thermoplastic resin and the fine carbon fiber, and near the surface of the molded product (0.1 to 10 μm) 25μm ² The number of the parts surrounded by the fine carbon fiber network is 180 or less, and the average value of the area of the enclosed part (x (μm ² )) And standard deviation (σ (μm ² )) Product (x · σ) is 12 (μm) ² ) ² It is the above, It is characterized by the above.
[0009]
In such a conductive molded article, the fine carbon fibers are not uniformly dispersed, but are dispersed in the thermoplastic resin matrix in a state of being agglomerated or entangled to some extent to form a continuous network. High nature. That is, when the fine carbon fibers are uniformly dispersed, there is no conduction between the fine carbon fibers and the conductivity is low. On the other hand, when the fine carbon fibers are aggregated to contact or approach each other to form a network, conductivity is increased.
[0010]
In the present invention, since a sufficient amount of fine carbon fiber is added to develop sufficient conductivity, a decrease in impact strength due to the addition of fine carbon fiber is suppressed, and a highly conductive molded product with high impact strength. Can be provided. Moreover, since the amount of high-priced fine carbon fiber added is small, it is inexpensive.
[0011]
In the present invention, the number of parts surrounded by the fine carbon fiber network and the product of the average value and standard deviation of the area are defined as values measured by the following method.
[0012]
{Circle around (1)} An ultrathin section is cut out in a thickness of 70 to 100 nm in the range of 0.1 to 10 μm from the surface of the molded body.
[0013]
(2) The following analysis is performed on a dispersion image of fine carbon fibers obtained by photographing the ultrathin section of (1) with a transmission microscope (40,000 times).
First, an image in a range of 5 μm × 5 μm is converted into a digital image with 512 × 512 pixels having a pixel size of 9.77 nm × 9.77 nm. As a result, pixels in which fine carbon fibers are present are turned on, and pixels in which fine carbon fibers are not present are turned off, and binarization processing is performed. At this time, in order to perform the binarization process with higher accuracy and ease, an image obtained by previously tracing the original image on another paper may be digitized.
FIG. 7 shows an example of this trace diagram. In FIG. 7 (1), fine carbon fibers are relatively uniformly dispersed, and in FIG. 7 (2), they are aggregated to some extent.
[0014]
(3) Image processing (expansion processing) in which all nine pixels are on when one of 3 × 3 = 9 pixels adjacent to each other in the vertical and horizontal directions is on. Is applied over the entire image.
FIGS. 1A to 1D show the first expansion processing (image processing) when only one pixel is on. Specifically, as shown in FIG. 1 (a), when one ON point exists in a certain range, all 3 × 3 pixels are scanned, and if ON pixels are included in the pixel, All nine pixels are turned on {FIG. 1 (b), (c), (d)}. As a result, 5 × 5 pixels around one pixel that was on are turned on (FIG. 1D).
Further, as shown in FIGS. 1E and 1F, fine carbon fibers cut by the expansion treatment are bonded.
By one expansion process, the fine carbon fiber expands by 4 pixels in the vertical and horizontal directions.
By performing the image processing five times, a thick carbon fiber image that is close to or separated from each other in the initial imaging is connected.
[0015]
(4) Therefore, only the center pixel in the width direction (thickness direction) of the fine carbon fiber after the fifth treatment is left on, and the other pixels are turned off. That is, the center line of the image is replaced with a one-pixel continuum.
2A and 2B are schematic diagrams showing an example of this.
[0016]
(5) The same expansion process as in (3) above is repeated twice for the centerline image obtained in (4) above. The continuous line in the obtained image is defined as “fine carbon fiber network”.
FIG. 3 is a schematic diagram showing an example of an image having a fine carbon fiber network obtained in this way.
[0017]
(6) The number of closed regions surrounded by the fine carbon fiber network is defined as “a portion surrounded by the fine carbon fiber network”. Note that the area intersecting the edge of the field of view (image) is not subject to analysis.
The number (N) of the “parts surrounded by the fine carbon fiber network” and the individual areas of the “parts surrounded by the fine carbon fiber network” are measured. Next, the average value of the areas (x (μm ² )) And standard deviation of area (σ (μm ² )). After that, the average value (x (μm ² )) And standard deviation (σ (μm ² )) Product. The standard deviation (σ (μm ² )) Is calculated by the following equation.
[Expression 1]

here,
x: average value of the area of “the part surrounded by the fine carbon fiber network”
x _i Each area of “part surrounded by fine carbon fiber network”
N: Number of “parts surrounded by fine carbon fiber network”
[0018]
(7) The above (6) is similarly performed for the five visual fields, and the average value is obtained. The average value thus obtained is defined as “the number of the portions surrounded by the fine carbon fiber network” and “the product of the average value of the area surrounded by the fine carbon fiber network and the standard deviation” of the present invention. To do.
[0019]
Hereinafter, the relationship between the fine carbon fiber network parameter of the present invention and the conductivity development effect of the present invention will be described in detail with reference to FIG.
[0020]
FIG. 4A shows a state in which fine carbon fibers are uniformly dispersed without being entangled with each other. By the image processing according to the present invention, the fine carbon fiber network becomes uniform and fine. As a result, the number (N) of the portions surrounded by the fine carbon fiber network increases, and the area and its average value (x (μm ² )) Is small, and the standard deviation of the area (σ (μm ² )) Becomes smaller. Therefore, the average value of the area (x (μm ² )) And standard deviation of area (σ (μm ² )) Product is also smaller.
In such a dispersed state, the electrical contact between the fine carbon fibers becomes insufficient, and the conductivity tends to decrease. That is, in order to obtain desired conductivity, it is necessary to add a large amount of fine carbon fibers.
[0021]
On the other hand, when the fine carbon fibers are appropriately aggregated and dispersed as shown in FIG. 4B, the number (N) of the portions surrounded by the fine carbon fiber network is reduced, and the area and its Average value (x (μm ² )) Gets bigger. In addition, due to the density of the fine carbon fibers, the variation in the size of the area also increases, so the standard deviation of the area (σ (μm ² )) Gets bigger. Therefore, the average value of the area (x (μm ² )) And standard deviation of area (σ (μm ² )) Product also increases.
Thus, in a state where fine carbon fibers are appropriately aggregated while being entangled with each other, excellent conductivity is exhibited.
[0022]
As shown in FIG. 4C, when the entanglement of the fine carbon fibers becomes too large and agglomerates in a lump, a fine carbon fiber network is not formed even if the above-described image processing is performed.
[0023]
In the present invention, the number (N) of the portions surrounded by the fine carbon fiber network is 180 or less, and the average value of the area of the surrounded portions (x (μm ² )) And standard deviation (σ (μm ² )) Product is 12 (μm) ² ) ² That's it.
This quantitatively represents a state in which fine carbon fibers are relatively entangled and relatively non-uniformly dispersed as shown in FIG. 4B.
[0024]
Note that the product of the average value and the standard deviation of the number and area of the “parts surrounded by the fine carbon fiber network” according to the present invention is the non-uniformity of the fine carbon fiber dispersion, that is, the degree of aggregation of the fine carbon fibers. The number represents the degree of microscopic aggregation, and the product of the average value of the area and the standard deviation represents the degree of macroscopic aggregation.
[0025]
The range of the number of portions surrounded by the fine carbon fiber network is desirably 170 or less and 20 or more, and the product of the average value of the area and the standard deviation is desirably 15 or more and 200 or less.
When the number is larger or the product is smaller than this, conductivity is not exhibited within the range of the addition amount of the fine carbon fiber of the present invention.
On the other hand, when the number is smaller or the product is larger than this, the dispersion is too uneven, and the conductivity is lowered.
[0026]
By the way, antistatic parts for high-density devices such as hard disks are required to have particularly excellent electrostatic characteristics. That is, it is required not only to have excellent charging characteristics (to dissipate charged charges quickly), but also to reduce a contact current generated when contacting the charged device when the device itself is charged.
[0027]
In the present invention, in particular, the number (N) of “portions surrounded by the fine carbon fiber network” is 180 or less, 120 or more, more preferably 170 or less, 120 or more, and the average value of the areas (x (μm ² )) And standard deviation (σ (μm ² )) Is not less than 12 and not more than 25, more preferably not less than 15 and not more than 25, in addition to good antistatic properties, and is desirable in that the contact current generated when an electronic device or the like is brought into contact is small. .
[0028]
This is due to the following reason.
That is, when the number of parts surrounded by the fine carbon fiber network is more than 180, or the product of the area and the standard deviation is less than 12, the fine carbon fiber network is uniformly dispersed. As a result, the dissipation of the charging load becomes insufficient, and charging tends to occur.
On the other hand, if the number is less than 120, or the product of the area and the standard deviation is 25 or more, the density of the network becomes large, and the conductivity of the portion where the network is dense becomes locally high. As a result, the contact current is increased.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the conductive molded article of the present invention will be described in detail.
[0030]
First, the forming raw material used in the present invention will be described.
<Fine carbon fiber>
The fine carbon fiber used in the present invention is a fine carbon fiber having an average fiber diameter of 100 nm or less, and is generally produced by a vapor growth method. For example, carbon fibrils described in JP-T-8-508534 can be used.
The carbon fibril has a fine tubular form, and the wall thickness (wall thickness of the tubular body) is usually about 3.5 to 75 nm. This usually corresponds to about 0.1 to 0.4 times the outer diameter of the carbon fibrils.
The fiber diameter of the carbon fibril depends on the production method and is almost uniform.
[0031]
In the present invention, when the average fiber diameter of fine carbon fibers such as carbon fibrils is larger than 100 nm, the contact between the fine carbon fibers in the resin becomes insufficient, and it becomes difficult to sufficiently develop conductivity. It is difficult to obtain stable conductivity. Accordingly, fine carbon fibers having an average fiber diameter of 100 nm or less, preferably 20 nm or less are used.
[0032]
On the other hand, the average fiber diameter of the fine carbon fibers is preferably 0.1 nm or more, particularly preferably 0.5 nm or more. If the fiber diameter is smaller than this, the production is extremely difficult, resulting in an increase in the cost of the product.
[0033]
Fine carbon fibers have a ratio of length to diameter (length / diameter ratio, that is, aspect ratio). 50 More than Good Preferably, 100 or more are used. If it is such a length / diameter ratio, it is easy to form a conductive network, and excellent conductivity can be expressed by adding a small amount.
[0034]
The fine carbon fiber has a fiber diameter and length (length / diameter ratio) of, for example, an electron microscope in which the resin component of the obtained molded product is removed by a solvent or ion sputtering to expose the fine carbon fiber. Or by observing an ultrathin section cut out from the molded article with an electron microscope, and in such an observation with an electron microscope, an average value of ten actually measured values can be obtained.
[0035]
When the fine carbon fibers are at least partly in the form of aggregates, the fine carbon fiber aggregates having a diameter larger than about 50 μm, desirably larger than 10 μm, measured on an area basis in the matrix resin as a raw material. It is desirable that the fine carbon fiber agglomerates having no be added to reduce the amount of addition for expressing the desired conductivity and not to lower the mechanical properties.
[0036]
The fine carbon fiber used in the present invention has a bending degree of 10 ° or more, preferably 20 ° or more, more preferably 40 ° or more. The degree of bending is a value that is a measure of the ease with which the fine carbon fibers are entangled with each other, and when the fine carbon fibers are entangled to form a network, a conductive network is formed and conductivity can be expressed.
[0037]
The degree of bending of the fine carbon fiber is measured by removing the resin component of the molded product with a solvent, ion sputtering or the like to expose the fine carbon fiber, or by observing an ultrathin slice cut out from the molded product with an electron microscope. . As shown in FIG. 8, the degree of bending is observed by observing fine carbon fibers with a microscope, measuring 5 times the fiber diameter (fiber diameter (d in FIG. 8) on the same fiber, and 5 along the fibers with a divider or the like. Select two arbitrary points A and B that are separated (by a method such as turning) and tangent L to each point. _A , L _B Tangent L _A , L _B The outside angle (indicated by α in FIG. 8) of the point Q where the crossing points are measured. The average value of 10 points is taken as the degree of bending.
That is, if the fiber is straight, the degree of bending is 0 °, 180 ° in a semicircle, and 360 ° if a circle is drawn.
[0038]
For example, conventional carbon fibers (pitch-based and PAN-based) are rigid and linear fibers having a fiber diameter of about 7 to 13 μm, and the degree of bending is less than 10 °. Such straight fibers are not entangled with each other, and it is difficult to control the network structure within the scope of the present invention.
[0039]
As such fine carbon fibers, commercially available products can be used, for example, “BN” of Hyperion Catalysis International, Inc. can be used. However, molding conditions such as master batches, manufacturing conditions of molded products, particularly kneading Since the degree of flexion varies depending on the conditions, it is important to obtain the conditions empirically.
[0040]
<Thermoplastic resin>
The thermoplastic resin used in the present invention is The Recarbonate Is .
[0041]
Po Recarbonate resin Is Good balance of dimensional accuracy, heat resistance, mechanical properties, etc. Is .
[0042]
As the polycarbonate resin, a general resin produced by reacting phosgene with a dihydric phenol compound as a main component by a solution method such as an interfacial polymerization method, a pyridine method, or a chloroformate method can be used.
[0043]
The weight average molecular weight of the polycarbonate in the final molded product is the polystyrene equivalent value. 3 0.00 to 45,000 Hope The molecular weight of the raw material polycarbonate and the production conditions are selected in advance so that it is preferably 35,000 to 43,000. Huh. When the molecular weight is within this range, the portion surrounded by the fine carbon fiber network of the obtained conductive molded product is likely to be within the scope of the present invention, and as a result, the conductivity is reduced without reducing the mechanical strength. It can be made excellent.
[0044]
The melt flow rate (MFR) of the polycarbonate resin composition constituting the conductive molded article of the present invention is 2 g / 10 min or more and 30 g / 10 min or less, particularly 4 g / 10 min in the measurement of 280 ° C. and 2.16 kg load. The amount is preferably 15 g / 10 minutes or less.
[0045]
As a method for obtaining a polycarbonate resin molded article having a weight average molecular weight in the above range suitable for the present invention, for example, molding is performed in advance using a polycarbonate resin having a molecular weight larger than or within the scope of the present invention. It is possible to employ a method of appropriately reducing the molecular weight of the polycarbonate by adjusting the processing temperature conditions of the above, or by repeatedly performing the molding.
[0046]
<Ratio of fine carbon fiber>
The blending ratio of the fine carbon fiber is 0.1% by weight or more and less than 5.1% by weight, preferably 0.1 to 4% by weight, more preferably, with respect to the total of the thermoplastic resin and the fine carbon fiber. 0.5 to 3.5% by weight. When the blending amount of the fine carbon fiber is less than the above range, sufficient conductivity cannot be obtained, and when the blending amount is large, the impact strength of the obtained molded product is lowered or the cost is increased, which is not preferable.
[0047]
<Additive components>
In the present invention, if necessary, optional additive components other than the thermoplastic resin and fine carbon fibers can be blended within a range not impairing the object of the present invention.
For example, inorganic fiber reinforcement such as glass fiber, silica fiber, silica / alumina fiber, potassium titanate fiber, aluminum borate fiber, organic fiber reinforcement such as aramid fiber, polyimide fiber, fluororesin fiber, talc, calcium carbonate , Inorganic fillers such as mica, glass beads, glass powder, glass balloons, various carbon black, fluororesin powder, solid lubricants such as molybdenum disulfide, plasticizers such as paraffin oil, antioxidants, thermal stabilizers, light List various additives such as stabilizers, UV absorbers, neutralizers, lubricants, compatibilizers, anti-fogging agents, anti-blocking agents, slip agents, dispersants, colorants, antibacterial agents, fluorescent whitening agents, etc. Can do.
[0048]
<Manufacturing method>
The present invention Guidance Electrical molding Product is an example For example, after fine carbon fibers are premixed in a thermoplastic resin, the conductive thermoplastic resin composition is obtained by melt-kneading with a Banbury mixer, roll, Brabender, single-screw kneading extruder, twin-screw kneading extruder, kneader or the like. Manufactured and then , Cum Molding Manufactured by .
[0049]
In addition to general injection molding methods, injection molding methods include integral molding with metal parts and other parts by insert injection molding, two-color injection molding, core back injection molding, sandwich injection molding, and injection. Various molding methods such as a press molding method can be used.
[0050]
In injection molding, the fine carbon fiber network in the product changes depending on the resin temperature, mold temperature, molding pressure, and injection speed, and as a result, the conductivity of the resulting molded product changes. Must be set.
[0051]
When polycarbonate is used as the thermoplastic resin, the molding condition is set such that the decrease in molecular weight by injection molding is 2% or more, preferably 2 to 5%. Desirable in terms of improvement.
[0052]
After the melt molding, a heat treatment such as hot air or infrared rays may be performed to adjust the dispersion of the fine carbon fibers.
[0053]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
[0054]
In addition, the raw material components used in the following Examples and Comparative Examples are as follows.
[0055]
Polycarbonate (PC) (Tg; 145 ° C): "Iupilon" manufactured by Mitsubishi Engineering Plastics
Fine carbon fiber: Hyperion BN manufactured by Hyperion Catalysis International
[0056]
Examples 1 to 5, Comparative Examples 1 and 2
(1) Mixing and blending
Polycarbonate and fine carbon fiber masterbatch were mixed with the composition shown in Table 1, and using a twin screw extruder ("PCM45" manufactured by Ikekai Steel Co., Ltd., L / D = 32 (L: screw length, D: screw diameter)). Then, the mixture was melt-kneaded at a barrel temperature of 300 ° C. and a screw rotation speed of 160 rpm to obtain pellets of a resin composition having a fine carbon fiber content shown in Table 1.
In addition, the compounding kneading | mixing in the case of mix | blending a fine carbon fiber manufactured the masterbatch which added 15 weight% of fine carbon fibers to the matrix resin previously, and diluted this to make predetermined amount of fine carbon fiber addition.
[0057]
(2) Measurement of molecular weight of polycarbonate in pellets
The molecular weight of the polycarbonate in each composition obtained in (1) was measured as follows.
A chloroform solution (2 mg / ml) of the composition was prepared and filtered through a 0.2 μm filter to separate the fine carbon fibers to obtain a polycarbonate solution. Using this polycarbonate solution, the weight average molecular weight (Mw) was measured by GPC. Detailed conditions are described below.
Detector: Waters UV490 (254 nm)
Column: Shodex GPC AD-806MS
Column temperature: 30 ° C
Flow rate: 1 ml / min
Internal standard: Toluene
Injection volume: 0.05ml
Table 1 shows the measurement results of the weight average molecular weight of the polycarbonate in the pellets of each composition.
The weight average molecular weight is a polystyrene equivalent value.
[0058]
[Table 1]

[0059]
(3) Molding of measurement sample
Using the pellets of each resin composition obtained in (1), a sheet for resistance value measurement of 100 mm × 100 mm × 2 mm (thickness) was molded with a 75 TON injection molding machine.
Table 2 shows the molding temperature.
Mold temperature is 90 ° C. The injection rate and the injection speed were adjusted so that the injection rate was 18 to 20 cc / sec. However, only Example 2 was 9 cc / sec.
[0060]
(4) Measurement of molecular weight of polycarbonate in molded products
Samples for molecular weight measurement were sampled from the sheet obtained in (3), the weight average molecular weight (Mw) of the polycarbonate was measured in the same manner as (2), and the results are shown in Table 2.
[0061]
(5) Measurement of surface resistance
The surface resistance value at the center of the sheet sample obtained in (3) was measured with a UA probe using a Hiresta UP manufactured by Dia Instruments Co., Ltd., and the results are shown in Table 2. The applied voltage was measured at 10V.
[0062]
(6) Measurement of Izod impact strength
Conforms to ASTM D256. The results are shown in Table 2.
[0063]
(7) Measurement of fiber diameter and length / diameter ratio and bending degree of fine carbon fiber
An ultrathin section was cut out along the flow direction in the range of 0.1 to 10 μm from the surface of the central portion (resistance measuring portion) of the sample obtained in (3). The section cut out under the same conditions was embedded in an epoxy resin, and then the section was cut out and the thickness of the section was measured.
With respect to this ultrathin slice, as described above, the angle of two tangents separated by 52.5 nm (diameter 10.5 nm × 5) on the fine carbon fiber was measured (10 points), and the result of measuring the bending degree is shown. It was shown in 2.
The sample was dissolved in chloroform and then filtered, and the separated fine carbon fiber was measured at 10 points with a transmission electron microscope, the average fiber diameter was 10.5 nm, and the length / diameter ratio was 50 or more. It was confirmed.
[0064]
(8) Measurement of the product of the mean and standard deviation of the number and area of the parts surrounded by the fine carbon fiber network
The following analysis was performed on a dispersion image of fine carbon fibers obtained by photographing the ultrathin section of (7) with a transmission microscope at 40000 times.
For the analysis, an avionics image analyzer (type; Spica 2) was used.
First, an image in the range of 5 μm × 5 μm is taken into a computer by integration input (16 times) using a CCD camera and converted into a digital image with pixels of 9.77 nm × 9.77 nm (512 × 512) (hereinafter referred to as the above-mentioned). According to the procedure as defined in the above, the pixel where the fine carbon fiber is present is turned on, and the pixel where the fine carbon fiber is not present is turned off).
The product of the number of the parts surrounded by the fine carbon fiber network and the average value and the standard deviation of the area of the enclosed parts was calculated.
The measurement results are shown in Table 2.
In addition, the relationship between the number of the parts surrounded by the fine carbon fiber network and the surface resistance value, and the relation between the product of the average value and standard deviation of the area surrounded by the fine carbon fiber network and the surface resistance value are respectively shown. 5 and 6.
[0065]
[Static property evaluation]
As the electrostatic characteristics of the sample obtained in (3), the contact current and the charged electrode were measured using the following equipment.
Charge plate monitor; manufactured by Hugue Electronics
Surface potential meter; 244A manufactured by Monroe Electronics
Oscilloscope: LeCroy LC584A
Current probe: CT1 manufactured by Tektronix
[0066]
1. Contact current
The contact current generated when a grounded electronic component comes into contact with the charged sheet sample was measured as follows by substituting the grounded probe with the electronic component.
(1) A sheet sample was placed on the charge plate monitor.
(2) Using a charge plate monitor, the plate and the sample were charged with 1000 V for 3 seconds, and then insulated from the ground.
(3) After 3 seconds, the ground probe was brought into contact with the sample, and the contact current flowing through the probe was measured. The measurement was performed on the center part of the sample (resistance measurement part). In this case, an alternating current of nanosecond order flows and gradually attenuates, so the highest current value was determined as the contact current.
(4) The above measurement was repeated 3 times and the measured values were averaged.
[0067]
2. Charging potential (charge amount)
The charging potential was measured as follows.
(1) A sheet sample was placed on the charge plate monitor.
{Circle around (2)} The sample and the plate were charged to zero and charged from the top of the sample by corona charging until the plate monitor reached 1000V.
(3) The plate on which the sample was placed was grounded, and the surface potential at the center of the sample (resistance measurement unit) was measured 3 seconds after grounding.
(4) The above measurement was repeated three times, and the measured values were averaged.
[0068]
[Table 2]

[0069]
From this result, the following matters are recognized.
Comparative Example 1 has poor conductivity (high resistance value) because the dispersion parameter is out of range.
As in Comparative Example 2, if the amount of fine carbon fiber added is increased, conductivity can be obtained even if the parameter is out of range. However, this method leads to an increase in cost and a decrease in physical properties.
[0070]
As in Examples 1 to 5, by optimizing the molecular weight and molding conditions, conductivity can be obtained without increasing costs and reducing physical properties.
Among them, when the weight average molecular weight of the molded polycarbonate is 45000 or less as in Examples 1 to 4, excellent conductivity can be obtained without significantly increasing the molding temperature.
In addition, when the molding temperature of Example 5 is increased to 340 ° C., resin deterioration in the cylinder during continuous production tends to occur.
[0071]
In particular, when the number of parts surrounded by the fine carbon fiber network is 180 or less and 120 or more and the product of the area and the standard deviation is 12 or more and 25 or less as a dispersion parameter, not only excellent charging characteristics but also noise The current is reduced.
[0072]
Although not shown in this example, the fine carbon fiber dispersion behavior in the resin and the electrical conductivity expression mechanism are the same, so that the same result can be easily obtained even with a thermoplastic resin other than the polycarbonate resin. To be expected.
[0073]
【The invention's effect】
As described above, according to the present invention, a conductive molded article having excellent conductivity and high impact strength is provided. This conductive molded article is inexpensive because the content of fine carbon fibers is small.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an image processing method for obtaining a product of an average value of the number and area of a portion surrounded by a fine carbon fiber network and a standard deviation.
FIG. 2 is a schematic diagram showing an image processing method for obtaining a product of the average value of the number and area of portions surrounded by a fine carbon fiber network and a standard deviation.
FIG. 3 is a schematic diagram showing an image processing method for obtaining the product of the average value of the number and area of portions surrounded by a fine carbon fiber network and the standard deviation.
FIG. 4 is an explanatory diagram showing the relationship between the state of the fine carbon fiber network and the parameters according to the present invention.
FIG. 5 is a graph showing the relationship between the number of portions surrounded by the fine carbon fiber networks of Examples 1 to 5 and Comparative Examples 1 and 2 and the surface resistance value.
6 is a graph showing the relationship between the product of the average value and the standard deviation of the area surrounded by the fine carbon fiber networks of Examples 1 to 5 and Comparative Examples 1 and 2, and the surface resistance value. FIG.
FIG. 7 is a trace view of fine carbon fiber imaging.
FIG. 8 is a diagram showing a method for measuring the degree of bending of fine carbon fibers.

Claims (1)

A conductive molded article obtained by injection molding a resin composition comprising a thermoplastic resin made of polycarbonate and fine carbon fibers,
The polycarbonate has a weight average molecular weight of 30,000 to 45,000, an average fiber diameter of the fine carbon fibers of 100 nm or less, and a length / diameter ratio of 50 or more ,
The injection molding temperature of the molded product is 300 to 340 ° C., the injection rate is 9 to 20 cc / sec,
The content of the fine carbon fiber is 0.1 wt% or more and less than 5.1 wt% with respect to the total of the thermoplastic resin and the fine carbon fiber,
The number of the portions surrounded by the fine carbon fiber network per 25 μm ² near the surface (0.1 to 10 μm) of the molded product is 180 or less, and the average value of the area of the surrounded portions (x (μm ² )) ) And standard deviation (σ (μm ² )) (x · σ) is 12 (μm ² ) ² or more.

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