JP4351341B2 - Biaxially oriented polyester film for capacitors - Google Patents

Description

【００４０】
【化３】

【００４１】
本発明において球状シリカ粒子の含有量は、ＰＥＮに対して、０．０１重量％以上１重量％以下とするのが好ましく、さらに好ましくは０．０２重量％以上０．７重量％以下である。
【００４２】
多孔質シリカ微粒子と球状シリカ粒子のＰＥＮヘの添加時期は、ＰＥＮの重合完了前であることが好ましく、エステル交換反応の終了前に（好ましくはグリコールスラリーとして）反応系中に添加することが好ましい。また、多孔質シリカ微粒子、球状シリカ粒子を個々に含有するＰＥＮを製造し、これらをブレンドして所定の含有量とすることもできる。
【００４３】
本発明の二軸配向ポリエステルフィルムは、該フィルム中に存在する４０μｍを超える粗大粒子の個数が１０個／ｍ²以下であることを要する。この数が１０個／ｍ²を超えると、フィルム生産時の破断頻度の増加による生産性の低下や、コンデンサの絶縁欠陥の多発を招き、好ましくない。
【００４４】
粗大粒子の個数を上記範囲にするには、製膜時のフィルターとして線径１５μｍ以下のステンレス鋼細線よりなる平均目開き１０〜３５μｍの不織布型フィルターを用いて濾過することが好ましい。
【００４５】
［交流体積抵抗率］
本発明の二軸配向ポリエステルフィルムは、溶融フィルムの３００℃での交流体積抵抗率の値が２×１０ ⁸ Ωｃｍ以上８×１０ ⁸ Ωｃｍ以下であることを要する。この交流体積抵抗率の値が２×１０ ⁸ Ωｃｍより小さい５×１０⁷Ωｃｍ未満であると、７０℃以上の比較的高温域で絶縁特性が低下し、誘電正接が大きくなり、コンデンサ特性が悪化する。一方、８×１０ ⁸ Ωｃｍより大きい１×１０⁹Ωｃｍを超えると、製膜時の破断が頻繁に発生し、生産性が著しく低下する。
【００４６】
この体積抵抗率を上記範囲に制御する方法は、ポリマー中にエステル形成官能基を有するスルホン酸４級ホスホニウム塩を含有させる方法を挙げることができる。該スルホン酸４級ホスホニウム塩の含有量は、ポリマーを構成する全酸成分に対して０．１ｍｍｏｌ％以上２ｍｍｏ１％以下とする。更には、エステル形成性官能基を有するスルホン酸４級ホスホニウム塩が下記式で表わされる化合物であることがより好ましい。
【００４７】
【化４】

（ここで、Ａはｎ＋２価の炭素数２〜１８の脂肪族基又は芳香族基であり、Ｘ₁およびＸ₂は、同一もしくは異なり、水素原子又はエステル形成性官能基であり、ｎは１又は２であり、そして、Ｒ₁、Ｒ₂、Ｒ₃、およびＲ₄は、同一もしくは異なり、炭素数１〜１８のアルキル基、ベンジル基又は炭素数６〜１２のアリール基である。但し、Ｘ₁およびＸ₂が同時に水素であることはない。）
【００４８】
上記スルホン酸４級ホスホニウム塩の好ましい具体例としては、３，５−ジカルボキシベンゼンスルホン酸テトラブチルホスホニウム塩、３，５−ジカルボキシベンゼンスルホン酸エチルトリブチルホスホニウム塩、３，５−ジカルボキシベンゼンスルホン酸ベンジルトリブチルホスホニウム塩、３，５−ジカルボキシベンゼンスルホン酸フェニルトリブチルホスホニウム塩、３，５−ジカルボキシベンゼンスルホン酸テトラフェニルホスホニウム塩、３，５−ジカルボキシベンゼンスルホン酸エチルトリフェニルホスホニウム塩、３，５−ジカルボキシベンゼンスルホン酸ブチルトリフェニルホスホニウム塩、３，５−ジカルボキシベンゼンスルホン酸ベンジルトリフェニルホスホニウム塩、３，５−ジカルボメトキシベンゼンスルホン酸テトラブチルホスホニウム塩、３，５−ジカルボメトキシベンゼンスルホン酸エチルトリブチルホスホニウム塩、３，５−ジカルボメトキシベンゼンスルホン酸ベンジルトリブチルホスホニウム塩、３，５−ジカルボメトキシベンゼンスルホン酸フェニルトリブチルホスホニウム塩、３，５−ジカルボメトキシベンゼンスルホン酸テトラフェニルホスホニウム塩、３，５−ジカルボメトキシベンゼンスルホン酸エチルトリフェニルホスホニウム塩、３，５−ジカルボメトキシベンゼンスルホン酸ブチルトリフェニルホスホニウム塩、３，５−ジカルボメトキシベンゼンスルホン酸ベンジルトリフェニルホスホニウム塩、３−カルボキシベンゼンスルホン酸テトラブチルホスホニウム塩、３−カルボキシベンゼンスルホン酸テトラフェニルホスホニウム塩、３−カルボメトキシベンゼンスルホン酸テトラブチルホスホニウム塩、３−カルボメトキシベンゼンスルホン酸テトラフェニルホスホニウム塩、３，５−ジ（β−ヒドロキシエトキシカルボニル）ベンゼンスルホン酸テトラブチルホスホニウム塩、３，５−ジ（β−ヒドロキシエトキシカルボニル）ベンゼンスルホン酸テトラフェニルホスホニウム塩、３−（β−ヒドロキシエトキシカルボニル）ベンゼンスルホン酸テトラブチルホスホニウム塩、３−（β−ヒドロキシエトキシカルボニル）ベンゼンスルホン酸テトラフェニルホスホニウム塩、４−ヒドロキシエトキシベンゼンスルホン酸テトラブチルホスホニウム塩、ビスフェノールＡ−３，３’−ジ（スルホン酸テトラブチルホスホニウム塩）、２，６−ジカルボキシナフタレン−４−スルホン酸テトラブチルホスホニウム塩、α−テトラブチルホスホニウムスルホコハク酸等をあげることができる。上記スルホン酸４級ホスホニウム塩は１種のみを単独で用いても２種以上併用してもよい。
【００４９】
前記スルホン酸４級ホスホニウム塩は、一般に、対応するスルホン酸とホスフィン類とのそれ自体公知の反応、又は対応するスルホン酸金属塩と４級ホスホニウムハライド類とのそれ自体公知の反応に容易に製造することができる。
【００５０】
本発明におけるポリエチレン−２，６−ナフターレートは、上記の如きスルホン酸4級ホスホニウム塩を、ポリエステルの全酸成分に対し、０．１ｍｍｏｌ％以上２ｍｍｏｌ％以下含有し、さらには０．２ｍｍｏｌ％以上２ｍｍｏｌ％以下で含有することが好ましい。この量が０．１ｍｍｏｌ％未満では３００℃における交流体積抵抗率の値を１０⁹Ωｃｍ以下にできない。一方含有量が２ｍｍｏｌ％より多い１０ｍｍｏｌ％を超えると、高温域（７０℃以上）での絶縁特性の低下や誘電正接の増加が生ずることがあり、好ましくない。
【００５１】
本発明において、ポリエチレン−２，６−ナフタレジカルボキシレートにスルホン酸４級ホスホニウム塩を含有させる方法としては、公知の任意の方法を用いることができる。例えば、ポリエチレン−２，６−ナフタレジカルボキシレートの重合時に前記化合物を添加し共重合する方法、フィルム製膜前に該化合物をポリマーに添加する方法、該化合物を高濃度含むポリマー組成物（マスターチップ）を作成し、ポリマーを溶融する前に所定量混合する方法などが挙げられる。いずれの方法によってもスルホン酸４級ホスホニウム塩を最終的にポリエチレン−２，６−ナフタレジカルボキシレートフィルムに所定量含有させれば、効果は発現する。
【００５２】
［表面粗さ］
本発明の二軸配向ポリエステルフィルムは、フィルム表面の中心線平均表面粗さ（Ｒａ）が４０ｎｍ以上９０ｎｍ以下であることを要する。この粗さ（Ｒａ）が４０ｎｍ未満では、フィルム生産時およびコンデンサ製造工程での作業性が悪く、特に極薄フィルムでは安定した生産が困難である。一方、９０ｎｍを超えるとコンデンサ素子のスペースファクタが大きく、容量不足や用途によってはコロナ放電による雑音や素子の劣化を生じることがある。
【００５３】
また、フィルム表面の１０点平均粗さ（Ｒｚ）は１０００ｎｍ以上１８００ｎｍ以下であることを要する。この粗さ（Ｒｚ）が１０００ｎｍ未満であると、フィルムの滑り性やエア抜け性が悪く、極薄品生産時にフィルムをロールに巻き取ることが困難となる。一方、１８００ｎｍを超えると、極薄品生産時に破断頻度が増加し、生産性が著しく低下する。
【００５４】
［熱収縮率］
本発明の二軸配向ポリエステルフィルムは、２００℃で１０分間処理した後の熱収縮率が縦方向（ＭＤ）で０．９％以上３．０％以下、さらには１．０％以上２．８％以下、横方向（ＴＤ）で２．０％以上５．０％以下、さらには２．２以上４．８％以下であることが好ましい。フィルムの熱収縮率が高すぎると、蒸着工程においてフィルムが収縮し、皺が入ることがあり、素子端面へのメタリコン処理ができないことがあり、好ましくない。一方、熱収縮率が低すぎると、蒸着工程で熱負けが発生することがあり、好ましくない。
【００５５】
［フィルムの厚み］
本発明の二軸配向ポリエステルフィルムは、厚みが０．５μｍ以上２０μｍ以下、さらに０．５μｍ以上１６μｍ以下であることが好ましい。この厚みが０．５μｍ未満では製膜生産性が低く、コンデンサの製造における作業性が悪い。一方、２０μｍを超えるとコンデンサの小型化が図りにくい。
【００５６】
０．５μｍ以上７μｍ以下の厚みのフィルムは、主として電子回路用に用いられ、本発明のフィルムの効果が最も発揮される。７μｍ以上２０μｍ以下の厚みのフィルムは、高圧または交流電源回路に主として用いられる。２０μｍを超える厚みのフィルムは、誘電体としても用いられるが主としてコンデンサの外装（上巻き）に用いられる。
【００５７】
［フィルムの密度］
本発明の二軸配向ポリエステルフィルムは、密度が１．３３８ｇ／ｃｍ³以上１．３６１ｇ／ｃｍ³以下であることが好ましい。さらに好ましくは１．３４０ｇ／ｃｍ³以上１．３５８ｇ／ｃｍ³以下、特に好ましくは１．３４３ｇ／ｃｍ³以上１．３５６ｇ／ｃｍ³以下である。フィルム密度が１．３３８ｇ／ｃｍ³未満であると、コンデンサ性能のバラツキの原因になり、加工歩留まりの低下の原因となるため好ましくない。一方、１．３６１ｇ／ｃｍ³を超えると、フィルムの結晶化度が高くなりすぎてフィルムの靭性が失われるため、フィルム搬送時、特にスリットを伴う工程で破断頻度が増加するようになる。
【００５８】
［その他特性］
本発明の二軸配向ポリエステルフィルムは、スペースファクタが１０〜３３％であることが好ましい。なお、スペースファクタとは、試料フィルム１００ｃｍ²の重量ｗ（ｇ）と、密度ｄ（ｇ／ｃｍ³）から求めた重量法厚みをｔ₁（μｍ）、１０ｃｍ角の試料フィルムを１０枚重ね、マイクロメーターを用いて求めた試料フィルム１枚分の厚みをｔ₂（μｍ）としたとき、下記式より算出される値である。
【００５９】
【数１】
スペースファクタＦ（％）＝１００− ｔ₁／ ｔ₂×１００
【００６０】
このスペースファクタが１０％未満では、フィルムの滑り性、作業性（ハンドリング性）が不充分であり、一方、３３％を超えると、体積当りのコンデンサ容量が低くコンデンサの小型大容量化に不適であるため好ましくない。
【００６１】
さらには電気絶縁材料であるという観点から絶縁破壊電圧（ＢＤＶ）は、２００V／μｍ以上（ＪＩＳ Ｃ ２３１８に示す方法に従って測定し、ｎ=１００の平均値）であることが好ましい。
【００６２】
また、本発明の二軸配向ポリエステルフィルムは、ピンホール、すなわちフィルムを感熱紙上に密着させ、試薬特級エタノールで１０倍に希釈したマジックインキ溶液を試料フィルム上に滴下し、エアーブラシで全体に広げた後に感熱紙側に転写して観測されるピンホールの数が、０．１個／ｃｍ²以下であることが好ましい。
【００６３】
さらに、本発明の二軸配向ポリエステルフィルムは、１００℃、１ｋＨｚの条件下で測定したＣＲ値が８００ΩＦより大きい９２０ΩＦ以上であることが好ましい。１００℃、１ｋＨｚにおけるＣＲ値が９２０ΩＦより小さい８００ΩＦ未満では、フィルムの絶縁抵抗が不足し、電気絶縁材料として不適となることがある。
【００６４】
［製膜法］
本発明の二軸配向ポリエステルフィルムは、二軸方向（例えば縦及び横方向）にそれぞれ延伸倍率２．５倍以上５．０倍以下で延伸されているのが好ましい。二軸方向の延伸倍率は等しくても、等しくなくてもよい。また、該フィルムは単一膜であっても、積層フィルムであってもよい。
【００６５】
本発明の二軸配向ポリエステルフィルムは、その製造法によって制限を受けるものではないが、下記の方法で製造するのが好ましい。
【００６６】
所定の不活性微粒子、好ましくはさらに所定量のエステル形成性官能基を有するスルホン酸４級ホスホニウム塩を含有するポリエチレン−２，６−ナフタレンジカルボキシレートを所定のフィルターで濾過した後、例えば通常の押出温度、すなわち融点（以下Ｔｍと表わす）以上（Ｔｍ＋７０℃）以下の温度で溶融押出し、押出されたフィルム状溶融物をピンニングワイヤー（ステンレス鋼線（０．０５〜０．６０ｍｍφ、印加電圧：直流０．５〜１５ｋＶ）により回転冷却ドラムの表面に密着させて急冷して固有粘度が０．４０〜０．９０ｄｌ／ｇの未延伸フィルムを得、続いてこの未延伸フィルムを１２０〜１８０℃、より好ましくは１３０〜１６０℃の温度で縦方向に２．５倍以上５．０倍以下の延伸倍率で延伸し、次いで横方向に１２０〜１５０℃の温度で２．５倍以上５．０倍以下の延伸倍率で延伸し、次いで得られた二軸延伸フィルムを２１０〜２４０℃の温度で０．３〜２０秒間熱固定する。その後、熱収縮率を低下させる必要があれば、縦方向および／または横方向に弛緩率０．３〜１５％の範囲で熱弛緩処理を行う。これらの延伸には複数段階に分割する多段延伸法を用いてもよい。
【００６７】
【実施例】
以下に実施例を挙げて本発明をさらに詳細に説明する。なお、実施例における各特性値は下記の方法で測定、評価した。
【００６８】
１．微粒子の平均粒径
（１−１）粉体の平均粒径
島津製作所製ＣＰ５０型セントリフュグル パーティクル サイズ アナライザー（Ｃｅｎｔｒｉｆｕｇａｌ Ｐａｒｔｉｃｌｅ Ｓｉｚｅ Ａｎａｌｙｓｅｒ）を用いて測定した。得られた遠心沈降曲線を基に算出した各粒径の粒子とその存在量との累積曲線から、５０マスパーセント（ｍａｓｓ ｐｅｒｃｅｎｔ）に相当する粒径を読み取り、この値を平均粒径とする。（「粒度測定技術」、日刊工業新聞社発行、１９７５年、ｐ．２４２−２４７参照）
【００６９】
（１−２）フィルム中の微粒子の粒径および粒径比
試料フィルム小片を走査型電子顕微鏡用試料台に固定し、日本電子（株）製スパッタリング装置（ＪＩＳ−１１００型イオンスパッタリング装置）を用いてフィルム表面に、０．１３Ｐａの真空下で０．２５ｋV、１．２５ｍＡの条件でイオンエッチング処理を１０分間施す。さらに、同じ装置で金スパッターを施し、走査型電子顕微鏡を用いて１万〜３万倍で観測し、日本レギュレーター（株）製ルーゼックス５００にて、少なくとも１００個の粒子の長径（Ｄｌｉ）、短径（Ｄｓｉ）及び面積相当粒径（Ｄｉ）を求める。下式で表わされる面積相当粒径（Ｄｉ）の数平均値を平均粒径（Ｄ）とする。
【００７０】
【数２】

【００７１】
上記長径の平均値をＤｌ、短径の平均値をＤｓとし、粒径比はＤｌ／Ｄｓとして算出する。
【００７２】
（１−３）粗大粒子
フィルム面を万能投影機を用いて、透過照明にて５０倍に拡大して測定面積１ｍ²を観察し、フィルム中に存在する粒子のうち最大径が４０μｍを超える粒子の数を数える。
【００７３】
２．交流体積抵抗率
図１に示す装置を用いて測定する。測定サンプルは厚さが約１５０μｍになるようにフィルムを重ねる。直径２０ｃｍの円柱状下部電極２の上面に、１５０μｍの平行な間隙が保持出来る直径５．６ｃｍ、厚さ０．２ｃｍの上部電極３を配し、この間に測定サンプル１が電極と密着するようにして挿入する。
【００７４】
下部電極２は加熱装置４と温度検出端５を内蔵し、下部電極２の表面温度の測定面におけるバラツキが１℃以内、検出端部分との温度差が昇温速度８℃／分において２℃以内となるように構成する。なお、検出温度は読取温度計７で測定する。電極の全体は保温箱１１中に配置する。電圧調整器６を調整して昇温速度を調整する。
【００７５】
電源８はその発生電圧を標準抵抗９を介して両電極間に印加するが、該電源は１００ｖ、５０Ｈｚを発生する電源である。この回路に流れる電流は、標準抵抗９の両端に発生する電圧を内部インピーダンスが１００ＭΩ以上のエレクトロンメーター１０で読取ることで求める。
【００７６】
本発明におけるフィルムの溶融時の交流体積抵抗率の測定は上記装置により、下部電極の昇温速度８℃／分、測定温度３００℃にて行い、交流体積抵抗率Ｚは、印加電圧Ｅ、電流Ｉ、電極面積Ｓ、電極間隔ｄより、次式で求められる。
【００７７】
【数３】
Ｚ＝（Ｅ／Ｉ）×（Ｓ／ｄ）
【００７８】
３．表面粗さ
（３−１）中心線表面粗さ（Ｒａ）
非接触式三次元粗さ計（小坂研究所製、ＥＴ−３０ＨＫ）を用いて波長７８０ｎｍの半導体レーザー、ビーム径１．６μｍの光触針で測定長（Ｌｘ）１ｍｍ、サンプリングピッチ２μｍ、カットオフ０．２５ｍｍ、厚み方向拡大倍率１万倍、横方向拡大倍率２００倍、走査線数１００本（従って、Ｙ方向の測定長Ｌｙ＝０．２ｍｍ）の条件にてフィルム表面の突起プロファイルを測定する。その粗さ曲面をＺ＝Ｆ（ｘ，ｙ）で表わしたとき、次の式で得られる値（Ｒａ、単位ｎｍ）をフィルムの表面粗さとして定義する。
【００７９】
【数４】

【００８０】
（３−２）１０点平均粗さ（Ｒｚ）
ピーク（ＨＰ）の高い方から５点と谷（Ｈｖ）の低い方から５点をとり、その平均粗さをＲｚとする。
【００８１】
【数５】

【００８２】
４．熱収縮率
試料フィルムに３０ｃｍ間隔で標線を入れ、加熱オーブン中で張力フリーの状態で一定時間熱処理（２００℃、１０分間）後の試料長の変化から下記式により求める。
【００８３】
【数６】
熱収縮率（％）＝（熱処理前の長さ−熱処理後の長さ）／熱処理前の長さ×１００
【００８４】
５．フィルムの厚み
試料フィルムの幅をＷ（ｃｍ）、長さをｌ（ｃｍ）、重量をＧ（ｇ）、密度をｄ（ｇ／ｃｍ³）としたとき、フィルム厚みｔ（μｍ）を下記式で算出する。
【００８５】
【数７】
ｔ＝Ｇ／（Ｗ×ｌ×ｄ）×１００００
【００８６】
６．フィルムの密度
硝酸カルシウム水溶液を溶媒として用いた密度勾配管中、２５℃で浮沈法により測定した値である。
【００８７】
７．固有粘度（ＩＶ）
ο−クロロフェノールを溶媒として用い、２５℃で測定する。
【００８８】
８．ポリエチレン−２，６−ナフタレンジカルボキシレートの成分量（主成分モル比、共重合成分モル比）
フィルムサンプルを測定溶媒（ＣＤＣｌ３： ＣＦ３ＣＯＯＤ＝１：１）に溶解後、¹Ｈ−ＮＭＲ測定を行い、得られた各シグナルの積分比をもって算出する。
【００８９】
９．ＣＲ値
ＪＩＳ Ｃ ２３１８に示す方法に準じて、１２ｍｍ幅にスリットしたフィルムサンプルと厚み７μｍ、幅１４ｍｍのアルミニウム箔を片側のマージン幅として２．５ｍｍを維持しながら重ね合わせた状態のものを２組用意し、各々のマージンが試料の両端になるように配置して有効面積が１００００ｍｍ²となるように巻取り試料を作成する。試料を１２０℃の温度下で５分間２ＭＰａの圧力でプレスする。この試料を（株）カトー製 サーモキーパー（ＴＨＫ−２１−１）で１００℃に保ち、試料の両端を安藤電気（株）製 ＬＣＲメーター（ＡＧ−４３０１）と接続し、印加電圧１００Ｖで絶縁抵抗値（Ω）を測定し、その後１ｋＨｚにおける静電容量（ｎＦ）を測定する。得られた絶縁抵抗値および静電容量からＣＲ値を下記式により算出する。
【００９０】
【数８】
ＣＲ値＝絶縁抵抗値×静電容量
【００９１】
１０．フィルムの製膜性
フィルムの製膜性を下記の基準で評価する。
ランクＡ：破断は起こらず、極めて安定な製膜が可能。生産性が極めて良い。
ランクＢ：破断はほとんど起こらず、安定な製膜が可能。生産性が良い。
ランクＣ：時々破断が起こり、製膜が不安定。生産性が悪い。
ランクＤ：破断が頻繁に発生し、製膜が極めて不安定。生産性が極めて悪い。
ランクＡおよびＢを合格とする。
【００９２】
１１．フィルムロールの巻き姿
幅５５０ｍｍ、長さ１００００ｍのフィルムをロールに巻き取った後の巻き姿を製膜工程のスリット時および蒸着後について各々肉眼で観察し、下記の基準で評価する。
◎：スリット時および蒸着後に表面のシワ、巻きズレ等がなく、巻き姿が良好
○：スリット後わずかにシワが認められたが、蒸着後のシワはなく、実用上問題無い
×：蒸着後表面のシワおよび／または巻きズレが確認され、巻き姿が不良
【００９３】
［実施例１〜４および比較例６］
２，６−ナフタレンジカルボン酸ジメチル１００部（実施例３では、全酸成分の５モル％量をイソフタル酸ジメチルで置換する）とエチレングリコール６０部の混合物に、酢酸マンガン・４水塩０．０３部を添加し、１５０℃から２４０℃に徐々に昇温しながらエステル交換反応を行った。途中反応温度が１７０℃に達した時点で三酸化アンチモン０．０２４部を添加し、さらに表１記載の粒径を有する多孔質シリカ微粒子及び球状シリカ粒子を表１記載の量添加して、次いで２２０℃に達した時点で３，５−ジカルボキシベンゼンスルホン酸テトラブチルホスホニウム塩０．０４２部（２ｍｍｏｌ％に相当）を添加した。引き続いてエステル交換反応を行い、エステル交換反応終了後燐酸トリメチル０．０２３部を添加した。その後反応生成物を重合反応器に移し、２９０℃まで昇温し、３０Ｐａ以下の高真空下にて重縮合反応を行って２５℃のｏ−クロロフェノール溶液で測定した固有粘度が０．６１ｄｌ／ｇであるポリエチレン−２，６−ナフタレンジカルボキシレート（ポリマー）を得た。
【００９４】
このポリマーを１７０℃において６時間乾燥させた後、押出機に供給し、溶融温度３１０℃で溶融し、スリット状ダイを通して押出し、表面仕上げ０．３Ｓの回転ドラム上にピンニングワイヤー（ＳＵＳ線（０．１ｍｍφ）、印加電圧：直流３ｋＶ）により密着固化させ未延伸フィルムを得た。
【００９５】
こうして得られた未延伸フィルムを１４０℃で縦方向に３．６倍に延伸し、次いで１４０℃で横方向に３．９倍延伸し、さらに２３０℃で５秒間熱固定処理し、表１に示す厚みの二軸配向（共重合）ポリエチレン−２，６−ナフタレンジカルボキシレートフィルムを得た。これら実施例１〜５のフィルムの組成および特性、添加物の内容を表１に示す。
なお、これらのフィルムのスペースファクタは１６〜２１％で問題はない。
【００９６】
［比較例１］
４級ホスホニウム塩を含有しない以外は実施例１と同様にして厚み２．５μｍの二軸配向ポリエチレン−２，６−ナフタレンジカルボキシレートフィルムを得た。このフィルムの特性を表１に示す。フィルムの物性は良好であるが、製膜性が不満足であった。
【００９７】
［比較例２］
４級ホスホニウム塩を５０ｍｍｏｌ％添加する以外は実施例１と同様にして厚み２．５μｍの二軸配向ポリエチレン−２，６−ナフタレンジカルボキシレートフィルムを得た。このフィルムの特性を表１に示す。 製膜性は良好であったが、交流体積抵抗率が低く、コンデンサの絶縁特性が不満足であった。
【００９８】
［比較例３］
平均粒径の大きい多孔質シリカ微粒子を用いる以外は実施例１と同様にして厚み２．５μｍの二軸配向ポリエチレン−２，６−ナフタレンジカルボキシレートフィルムを得た。このフィルムの特性を表１に示す。製膜時の切断が多かった。また、スペースファクタが３６％であり過大であった。
【００９９】
［比較例４］
球状シリカ粒子を用いず、平均粒径が小さい多孔質シリカ微粒子のみを添加する以外は実施例１と同様にして厚み２．５μｍの二軸配向ポリエチレン−２，６−ナフタレンジカルボキシレートフィルムを得た。このフィルムの特性を表１に示す。フィルムの物性は良好であったが、巻き姿が非常に悪く、製品として不合格であった。
【０１００】
［比較例５］
イソフタル酸を２０ｍｏｌ％共重合する以外は実施例１と同様にして厚み２．５μｍの二軸配向共重合ポリエチレン−２，６−ナフタレンジカルボキシレートフィルムを得た。このフィルムの特性を表１に示す。生産性が悪く、コンデンサの絶縁特性に問題があった。
【０１０１】
【表１】

【０１０２】
【発明の効果】
本発明の二軸配向ポリエステルフィルムは、次のような優れた特性を持ち、コンデンサ用フィルムとして好適に用いられる。
（１）製膜時の生産性が優れ、特に極薄フィルムの製膜に有効である。
（２）フィルム表面が適度に粗面化されており、フィルムの滑り性が良好で、製膜時、加工時の作業性に優れる。
（３）ポリエチレン−２，６−ナフタレンジカルボキシレートの持つ耐熱性や絶縁性が生かされており、絶縁抵抗が高く、ＣＲ特性が優れる。
【図面の簡単な説明】
【図１】図１は交流体積抵抗率を測定する装置の概略図である。
【符号の説明】
１：測定サンプル
２：下部電極
３：上部電極
４：加熱装置
５：温度検出端
６：電圧調整器
７：読取温度計
８：電源
９：標準抵抗
１０：エレクトロンメーター
１１：保温箱[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a biaxially oriented polyester film for capacitors. More specifically, the polymer constituting the film is polyethylene-2,6-naphthalenedicarboxylate, and the capacitor has excellent productivity, workability, space factor, etc. The present invention relates to an axially oriented polyester film.
[0002]
[Prior art]
Biaxially oriented polyethylene-2,6-naphthalene dicarboxylate film is used as a film for capacitors because of its excellent mechanical properties, thermal properties and heat resistance, and its amount is increasing.
[0003]
By the way, in recent years, with the miniaturization of electric or electronic circuits, it has become necessary to reduce the size and capacity of capacitors, and it has become a quality condition. Is underway. In the film capacitor, the reason why the film as the dielectric material is made thin is that (a) the capacitance of the capacitor is proportional to the dielectric constant and electrode area of the dielectric material, and (b) is inversely proportional to the film thickness, In other words, the capacitance per unit volume of the dielectric material is inversely proportional to the square of the film thickness and proportional to the dielectric constant. Therefore, the dielectric material with the same dielectric constant is used to reduce the size or increase the capacity of the capacitor. This is because it is essential to reduce the thickness of the film.
[0004]
As described above, although the effect of thinning the film is clear, a new problem arises by simply reducing the thickness of the conventional biaxially oriented film, for example, when an electrode is deposited on the film as the film becomes thinner. In addition, there is a problem that workability in processes such as slitting and element winding deteriorates.
[0005]
This workability is related to the slipperiness of the film. As a method for improving the slipperiness, a method of giving fine irregularities to the film surface is known and used in the polyester film. In this method, inert inorganic fine particles are added at the time of polymerization of polyester as a raw material of the film, or after polymerization (external particle addition method), or a part or all of the catalyst used at the time of polymerization of polyester is polymerized in the reaction step. A technique for precipitation inside (internal particle precipitation method) is known.
[0006]
However, in the production of an ultrathin film, the number of inert inorganic fine particles per unit area of the ultrathin film can be obtained by using a polymer containing inert inorganic fine particles at the same concentration as the raw material polymer. , The spacing between the fine particles on the film surface is widened, the film surface is flattened, and the slipperiness is lowered. In addition, the ultrathin film has low waist (rigidity), and the films can be easily brought into close contact with each other, which causes a decrease in slipperiness. Therefore, in order to compensate for the decrease in slipperiness accompanying the reduction in film thickness, the thinner the film thickness, the higher the concentration of the inert inorganic fine particles to be contained or the larger the particle size.
[0007]
In this case, at the time of melt extrusion with a high draft ratio or at the time of stretching, voids are likely to occur around the inert inorganic fine particles due to poor affinity between the inert inorganic fine particles and the polyester, and This frequency also increases. For this reason, not only the mechanical properties (for example, breaking strength and breaking elongation) and electrical properties (for example, insulation defects) of the obtained film are deteriorated, but also breakage is likely to occur at the time of film production. The problem that it falls and the stability of manufacturing conditions is lacking arises.
[0008]
Japanese Patent Publication No. 7-47645 discloses a porous inert inorganic particle having a porosity of 50 to 95% and an average particle diameter of 0.05 to 5 μm as a film in which void generation is suppressed. 3% by weight and 0.005 to 1% by weight of spherical silica particles having an average particle size larger than the thickness of the film and 0.2 to 4 μm are contained, so that workability (handling property), film forming property (non-breaking) A thin thermoplastic film having an improved thickness of 4 μm or less is disclosed.
[0009]
However, in the case of a polyethylene-2,6-naphthalenedicarboxylate film, in the study of the present inventors, the film has no mechanical properties, excellent electrical insulation and heat resistance, and has advantages such as few voids. However, it has been revealed that there is still a problem that film productivity is impaired due to many breaks during film formation.
[0010]
The polyethylene-2,6-naphthalene dicarboxylate film has a property that is inferior in tear resistance as compared with, for example, a polyethylene terephthalate film, and this property is a factor that increases the trouble of fracture during film formation. For this reason, it is estimated that the factor which did not become a problem in a polyethylene terephthalate film may cause a fracture in a polyethylene-2,6-naphthalene dicarboxylate film.
[0011]
In addition, the polyethylene-2,6-naphthalene dicarboxylate film has a thick air layer generated when the films are stacked by surface protrusions, and the insulation characteristics and space factor cannot be said to be sufficient. It became clear that compatibility of workability, workability and space factor still remains as a solution.
[0012]
[Problems to be solved by the invention]
The object of the present invention is to maintain the heat resistance, insulation, and possibility of thinning of polyethylene-2,6-naphthalenedicarboxylate, achieve both workability, space factor, and insulation characteristics, and remarkably improve productivity. Another object of the present invention is to provide a biaxially oriented polyester film for a capacitor.
[0013]
[Means for Solving the Problems]
The present inventor makes the film breakage without impairing other characteristics (for example, electrical insulation characteristics) by setting the electrical characteristics at the time of melting polyethylene-2,6-naphthalenedicarboxylate, that is, the AC volume resistivity within a specific range. It is possible to improve productivity, and to limit the number of large particles in the film and adjust the surface roughness to a specific range, so that both electrical insulation characteristics, space factor and workability can be achieved. The present invention has been found.
[0014]
  That is, in the present invention, the polymer component constituting the biaxially oriented film is composed of polyethylene-2,6-naphthalenedicarboxylate,Containing 0.1 mmol% or more and 2 mmol or less of 1 mmol% or less of a sulfonic acid quaternary phosphonium salt having an ester-forming functional group with respect to the total acid component of the polymer;The center line average surface roughness (Ra) of the film is 40 nm or more and 90 nm or less, the 10-point average roughness (Rz) is 1000 nm or more and 1800 nm or less, and the number of coarse particles exceeding 40 μm present in the film is 10 Pieces / m²And the value of the AC volume resistivity when the film is melted (300 ° C.) is2 × 10 ⁸ Ωcm or more8 × 10 ⁸ It is a biaxially oriented polyester film for capacitors, characterized in that it is Ωcm or less.
[0015]
[Polyethylene-2,6-naphthalenedicarboxylate]
In the biaxially oriented polyester film in the present invention, the polymer component is made of polyethylene-2,6-naphthalenedicarboxylate.
[0016]
This polyethylene-2,6-naphthalene dicarboxylate is a polymer in which the main acid component is 2,6-naphthalenedicarboxylic acid and the main glycol component is ethylene glycol. Here, the “principal” means that it is at least 90 mol%, preferably 95 mol% or more, respectively, with respect to the total acid component and total glycol component constituting the polymer.
[0017]
The polyethylene-2,6-naphthalene dicarboxylate in the present invention can be a copolymer, but this copolymer does not extremely lose the original properties of the polyethylene-2,6-naphthalene dicarboxylate (homopolymer) film. Those that can ensure insulation properties, mechanical properties and thermal dimensional stability are preferred. Furthermore, a copolymer capable of forming a film having excellent fracture resistance and slitting properties is preferred.
[0018]
In the case of a copolymer, a compound having two ester-forming functional groups in the molecule can be used as the copolymer component other than 2,6-naphthalenedicarboxylic acid and ethylene glycol component. Examples of such compounds include oxalic acid, adipic acid, phthalic acid, sebacic acid, dodecanedicarboxylic acid, isophthalic acid, terephthalic acid, 1,4-cyclohexanedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, phenylindandicarboxylic acid, 2, Dicarboxylic acids such as 7-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, tetralin dicarboxylic acid, decalin dicarboxylic acid, diphenyl ether dicarboxylic acid; oxycarboxylic acids such as p-oxybenzoic acid, p-oxyethoxybenzoic acid; Or propylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, cyclohexanemethylene glycol, neopentyl glycol, ethylene oxide adduct of bisphenolsulfone, bis Ethylene oxide adducts of phenol A, diethylene glycol, can be exemplified preferably a dihydric alcohol such as polyethylene oxide glycol and the like.
[0019]
These compounds can be used alone or in combination of two or more. Of these, more preferred are isophthalic acid, terephthalic acid, 4,4′-diphenyldicarboxylic acid, 2,7-naphthalenedicarboxylic acid, p-oxybenzoic acid as the acid component, and triglyceride as the glycol component. Ethylene oxide adducts of methylene glycol, hexamethylene glycol, neopentyl glycol, and bisphenol sulfone.
[0020]
Further, polyethylene-2,6-naphthalene dicarboxylate may be one in which part or all of the terminal hydroxyl groups and / or carboxyl groups are blocked with a monofunctional compound such as benzoic acid or methoxypolyalkylene glycol. Alternatively, for example, it may be copolymerized with a very small amount of trifunctional or higher ester-forming compound such as glycerin and pentaerythritol within a range where a substantially linear polymer is obtained.
[0021]
The polyethylene-2,6-naphthalene dicarboxylate of the present invention may also be a composition in which a small proportion of other organic polymers are mixed.
[0022]
Examples of the organic polymer include polyethylene terephthalate, polyethylene isophthalate, polytrimethylene terephthalate, polyethylene-4,4′-tetramethylene diphenyldicarboxylate, polyethylene-2,7-naphthalenedicarboxylate, polyethylene-1,5-naphthalene. Dicarboxylate, polytrimethylene-2,6-naphthalene dicarboxylate, polyneopentylene-2,6-naphthalene dicarboxylate, poly (bis (4-ethyleneoxyphenyl) sulfone) -2,6-naphthalene Examples include carboxylate. Among these, polyethylene isophthalate, polytrimethylene terephthalate, polytrimethylene-2,6-naphthalene dicarboxylate, and poly (bis (4-ethyleneoxyphenyl) sulfone) -2,6-naphthalene dicarboxylate are preferable. .
[0023]
These organic polymers may be used not only in one type but also in two or more types, up to 10 mol%, preferably up to 5 mol%, in terms of the repeating units of the organic polymer, with respect to all repeating units of the polymer constituting the composition. preferable. This composition may be a composition comprising a homopolymer or copolymer of polyethylene-2,6-naphthalene dicarboxylate and another organic polymer, and a homopolymer of polyethylene-2,6-naphthalene dicarboxylate and A composition comprising a copolymer and another organic polymer may be used.
[0024]
This composition is a polymer composition in which at least 90 mol%, preferably 95 mol% or more of all polymer repeating units constituting the composition are composed of ethylene-2,6-naphthalenedicarboxylate units.
[0025]
Polyethylene-2,6-naphthalene dicarboxylate can be produced by a generally known polyester production method.
[0026]
For example, polyethylene-2,6-naphthalene dicarboxylate is obtained by reacting 2,6-naphthalenedicarboxylic acid and ethylene glycol (esterification reaction), or by lower alkyl ester of 2,6-naphthalenedicarboxylic acid and ethylene glycol. It can be produced by reacting in the presence of a transesterification catalyst (transesterification reaction) and then polymerizing the reaction product to the desired molecular weight in the presence of a polymerization catalyst. Examples of the transesterification catalyst include known transesterification catalysts such as a compound containing sodium, potassium, magnesium, calcium, zinc, strontium, titanium, zirconium, manganese, or cobalt. These can use 1 type (s) or 2 or more types. The polymerization catalyst includes antimony compounds such as antimony trioxide and antimony pentoxide, germanium compounds represented by germanium dioxide, tetraethyl titanate, tetrapropyl titanate, tetraphenyl titanate or partial hydrolysates thereof, and oxalic acid. Preferable examples include titanium compounds such as titanyl ammonium, potassium titanyl oxalate, and titanium trisacetylacetonate. The amount of catalyst used may be selected from a conventionally known amount range.
[0027]
When performing polymerization via a transesterification reaction, a phosphorus compound such as trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, or normal phosphoric acid is added for the purpose of deactivating the transesterification catalyst before the polymerization reaction. Is preferred. The content of polyethylene-2,6-naphthalenedicarboxylate as the phosphorus element is preferably 20 to 100 ppm from the viewpoint of the thermal stability of the polymer.
[0028]
Polyethylene-2,6-naphthalenedicarboxylate can be converted into chips after melt polymerization and solid-phase polymerization can be performed under heating under reduced pressure or in an inert gas stream such as nitrogen.
[0029]
The intrinsic viscosity (orthochlorophenol, 25 ° C.) of the polymer is preferably 0.40 dl / g or more, and more preferably 0.40 dl / g or more and 0.90 dl / g or less. When the intrinsic viscosity is less than 0.40 dl / g, process cutting may occur frequently. On the other hand, if it is higher than 0.90 dl / g, melt extrusion becomes difficult because the melt viscosity of the polymer is high, and the polymerization time is long and uneconomical.
[0030]
[Additive]
The biaxially oriented polyester film of the present invention has a large number of fine protrusions on the film surface. The many fine protrusions are derived from many inert fine particles dispersed and contained in polyethylene-2,6-naphthalene dicarboxylate (hereinafter sometimes abbreviated as PEN). The inert fine particles can be arbitrarily used as long as they meet the object of the present invention, but it is particularly preferable that the following conditions are satisfied.
[0031]
That is, the porous silica particles (A) having an average particle size of 0.5 μm or more and 5 μm or less are contained in the range of 0.05% by weight or more and 2% by weight or less (relative to the polymer), and at the same time, the average particle size is 0.00. It is preferable to contain spherical silica particles (B) having a thickness of not less than 05 μm and not more than 1.5 μm and less than the film thickness in a range of not less than 0.01 wt% and not more than 1 wt% (relative to the polymer).
[0032]
Here, the “average particle diameter” means the “equivalent spherical diameter” of the particles at the point of 50% by weight of the measured total particles. “Equivalent spherical diameter” means the diameter of an imaginary sphere (ideal sphere) having the same volume as the particle, and can be calculated from an electron micrograph of the particle or measurement by a conventional sedimentation method.
[0033]
If the average particle size of the porous silica fine particles is less than 0.5 μm, the air squeeze property is poor when the film is wound into a roll such as a master roll or a product roll, and wrinkles are likely to occur. In addition, the slipperiness (slip property) is insufficient and the workability in the processing step is lowered, which is not preferable. On the other hand, if the average particle diameter exceeds 5 μm, the film surface is too rough, which causes a decrease in dielectric breakdown voltage, an increase in insulation defects, and the like, which is not preferable. The average particle diameter of the porous silica fine particles may be larger than the film thickness. This is because the porous silica fine particles have a high affinity for PEN.
[0034]
The content of the porous silica fine particles is preferably 0.05% by weight or more and 2% by weight or less in PEN, more preferably 0.1% by weight or more and 1% by weight or less, and particularly preferably 0.1% by weight. % To 0.7% by weight. If the content of the porous silica fine particles is less than 0.05% by weight, the air squeezing property at the time of winding the film becomes poor. On the other hand, if the content exceeds 2% by weight, the film surface becomes too rough, resulting in a decrease in capacity and dielectric breakdown voltage. This is not preferable.
[0035]
In the present invention, it is preferable to disperse and contain spherical silica particles together with the porous silica fine particles in PEN, particularly for ultra-thin film applications. The spherical silica particles have an average particle size not larger than the film thickness and 0.05 μm or more and 1.5 μm or less, and preferably have a particle size ratio (major axis / minor axis) of 1.0 or more and 1.2 or less. is there. The spherical silica particles have a spherical shape in which the shape of each fine particle is extremely close to a true sphere, and the silica particles conventionally known as a lubricant are ultrafine bulk particles of about 10 nm, or they are aggregated to give an O.D. This is remarkably different from those forming aggregates (aggregated particles) of about 5 μm.
[0036]
The average particle size of the spherical silica particles needs to be smaller than the film thickness. However, if the average particle size is larger than the film thickness, the film around the projections due to the spherical silica fine particles is cracked, and the film is stretched, heat fixed, etc. This is not preferable because breakage occurs frequently. Accordingly, the average particle size of the spherical silica fine particles is preferably 90% or less of the film thickness, and more preferably 80% or less of the film thickness.
[0037]
Further, the average particle diameter of the spherical silica fine particles is more preferably 0.1 μm or more and 1 μm or less, and particularly preferably 0.2 μm or more and 0.8 μm or less within a range not exceeding the thickness of the film. If the average particle size is less than 0.05 μm, the slipperiness of the film is insufficient, and workability in the processing step is lowered, which is not preferable. On the other hand, if the average particle size exceeds 1.5 μm, the film surface becomes too rough, which causes a decrease in dielectric breakdown voltage, an increase in insulation defects, and the like, which is not preferable. The particle size ratio (major axis / minor axis) of the spherical silica particles is preferably 1.0 or more and 1.2 or less, more preferably 1.0 or more and 1.15 or less, and particularly preferably 1.0 or more and 1.1 or less. It is.
[0038]
The spherical silica particles are not limited to the production method and others as long as the above-described conditions are satisfied. For example, spherical silica fine particles form hydrous silica [Si (OH)] monodisperse spheres from hydrolysis of ethyl orthosilicate [Si (OCH)], and the hydrous silica monodisperse spheres are dehydrated to form the following silica bonds: Can be produced by growing them three-dimensionally (The Chemical Society of Japan, '81, No. 9, P. 1503).
[0039]
[Chemical formula 2]

[0040]
[Chemical 3]

[0041]
In the present invention, the content of the spherical silica particles is preferably 0.01% by weight or more and 1% by weight or less, more preferably 0.02% by weight or more and 0.7% by weight or less with respect to PEN.
[0042]
The addition timing of the porous silica particles and the spherical silica particles to the PEN is preferably before the completion of the polymerization of the PEN, and is preferably added to the reaction system before the end of the transesterification reaction (preferably as a glycol slurry). . Alternatively, PEN containing individual porous silica particles and spherical silica particles can be produced, and these can be blended to obtain a predetermined content.
[0043]
In the biaxially oriented polyester film of the present invention, the number of coarse particles exceeding 40 μm present in the film is 10 / m.²The following is required. This number is 10 / m²Exceeding this is undesirable because it causes a decrease in productivity due to an increase in the frequency of breakage during film production and frequent occurrence of insulation defects in capacitors.
[0044]
In order to make the number of coarse particles in the above range, it is preferable to filter using a nonwoven fabric type filter having an average opening of 10 to 35 μm made of stainless steel fine wire having a wire diameter of 15 μm or less as a filter during film formation.
[0045]
    [AC volume resistivity]
  The biaxially oriented polyester film of the present invention has a value of AC volume resistivity at 300 ° C. of the molten film.2 × 10 ⁸ Ωcm or more8 × 10 ⁸ It needs to be Ωcm or less. The value of this AC volume resistivity is2 × 10 ⁸ Less than Ωcm5 × 10⁷If it is less than Ωcm, the insulation characteristics deteriorate at a relatively high temperature range of 70 ° C. or higher, the dielectric loss tangent increases, and the capacitor characteristics deteriorate. on the other hand,8 × 10 ⁸ Greater than Ωcm1 × 10⁹When it exceeds Ωcm, breakage during film formation frequently occurs, and productivity is significantly reduced.
[0046]
  The method of controlling this volume resistivity within the above range isTheExamples thereof include a method in which a sulfonic acid quaternary phosphonium salt having an ester-forming functional group is contained in the remer. The content of the sulfonic acid quaternary phosphonium salt is 0.1 mmol% or more with respect to the total acid components constituting the polymer.2mmo 1% or lessTheFurthermore, the sulfonic acid quaternary phosphonium salt having an ester-forming functional group is more preferably a compound represented by the following formula.
[0047]
[Formula 4]

(Here, A is an n + divalent aliphatic group having 2 to 18 carbon atoms or an aromatic group, and X₁And X₂Are the same or different and are hydrogen atoms or ester-forming functional groups, n is 1 or 2, and R₁, R₂, R_Three, And R_FourAre the same or different and are a C1-C18 alkyl group, a benzyl group, or a C6-C12 aryl group. However, X₁And X₂Are not simultaneously hydrogen. )
[0048]
Preferred examples of the sulfonic acid quaternary phosphonium salt include tetrabutylphosphonium salt of 3,5-dicarboxybenzenesulfonic acid, ethyltributylphosphonium salt of 3,5-dicarboxybenzenesulfonic acid, and 3,5-dicarboxybenzenesulfone. Acid benzyltributylphosphonium salt, 3,5-dicarboxybenzenesulfonic acid phenyltributylphosphonium salt, 3,5-dicarboxybenzenesulfonic acid tetraphenylphosphonium salt, 3,5-dicarboxybenzenesulfonic acid ethyltriphenylphosphonium salt, 3 , 5-Dicarboxybenzenesulfonic acid butyltriphenylphosphonium salt, 3,5-dicarboxybenzenesulfonic acid benzyltriphenylphosphonium salt, 3,5-dicarbomethoxybenzenesulfonic acid Trabutylphosphonium salt, 3,5-dicarbomethoxybenzenesulfonic acid ethyl tributylphosphonium salt, 3,5-dicarbomethoxybenzenesulfonic acid benzyltributylphosphonium salt, 3,5-dicarbomethoxybenzenesulfonic acid phenyltributylphosphonium salt, 3,5-dicarbomethoxybenzenesulfonic acid tetraphenylphosphonium salt, 3,5-dicarbomethoxybenzenesulfonic acid ethyltriphenylphosphonium salt, 3,5-dicarbomethoxybenzenesulfonic acid butyltriphenylphosphonium salt, 3,5 -Dicarbomethoxybenzenesulfonic acid benzyltriphenylphosphonium salt, 3-carboxybenzenesulfonic acid tetrabutylphosphonium salt, 3-carboxybenzenesulfonic acid tetraphenylphosphine Nium salt, 3-carbomethoxybenzenesulfonic acid tetrabutylphosphonium salt, 3-carbomethoxybenzenesulfonic acid tetraphenylphosphonium salt, 3,5-di (β-hydroxyethoxycarbonyl) benzenesulfonic acid tetrabutylphosphonium salt, 3,5 -Di (β-hydroxyethoxycarbonyl) benzenesulfonic acid tetraphenylphosphonium salt, 3- (β-hydroxyethoxycarbonyl) benzenesulfonic acid tetrabutylphosphonium salt, 3- (β-hydroxyethoxycarbonyl) benzenesulfonic acid tetraphenylphosphonium salt 4-hydroxyethoxybenzenesulfonic acid tetrabutylphosphonium salt, bisphenol A-3,3′-di (sulfonic acid tetrabutylphosphonium salt), 2,6-dicarboxynaphthalene 4-sulfonic acid tetrabutylphosphonium salt, alpha-tetrabutylphosphonium sulfosuccinate and the like. The sulfonic acid quaternary phosphonium salts may be used alone or in combination of two or more.
[0049]
The sulfonic acid quaternary phosphonium salt is generally easily produced by a reaction known per se between a corresponding sulfonic acid and a phosphine, or a reaction known per se between a corresponding sulfonic acid metal salt and a quaternary phosphonium halide. can do.
[0050]
  Polyethylene-2,6-naphthalate in the present invention is a sulfonic acid quaternary phosphonium salt as described above, 0.1 mmol% or more based on the total acid component of the polyester.2mmol% or lessContainsAnd more than 0.2mmol%2It is preferable to contain in less than mmol%. When this amount is less than 0.1 mmol%, the value of the AC volume resistivity at 300 ° C. is 10⁹Cannot be less than Ωcm. On the other hand, the content isMore than 2mmol%If it exceeds 10 mmol%, the insulation characteristics may be lowered and the dielectric loss tangent may be increased in a high temperature range (70 ° C. or higher), which is not preferable.
[0051]
In the present invention, any known method can be used as a method for incorporating a sulfonic acid quaternary phosphonium salt into polyethylene-2,6-naphthalenedicarboxylate. For example, a method in which the above compound is added and copolymerized at the time of polymerization of polyethylene-2,6-naphthalenedicarboxylate, a method in which the compound is added to a polymer before film formation, and a polymer composition containing a high concentration of the compound (master Chip) and a method of mixing a predetermined amount before melting the polymer. In any method, when a predetermined amount of the sulfonic acid quaternary phosphonium salt is finally contained in the polyethylene-2,6-naphthalenedicarboxylate film, the effect is exhibited.
[0052]
[Surface roughness]
The biaxially oriented polyester film of the present invention requires that the center line average surface roughness (Ra) of the film surface is 40 nm or more and 90 nm or less. When the roughness (Ra) is less than 40 nm, the workability during film production and the capacitor manufacturing process is poor, and stable production is particularly difficult with an extremely thin film. On the other hand, when the thickness exceeds 90 nm, the space factor of the capacitor element is large, and noise and element deterioration due to corona discharge may occur depending on the capacity shortage and application.
[0053]
Moreover, 10-point average roughness (Rz) of the film surface needs to be 1000 nm or more and 1800 nm or less. When the roughness (Rz) is less than 1000 nm, the slipping property and air release property of the film are poor, and it is difficult to wind the film on a roll during the production of an extremely thin product. On the other hand, if it exceeds 1800 nm, the frequency of fracture increases during production of ultra-thin products, and the productivity is significantly reduced.
[0054]
[Heat shrinkage]
The biaxially oriented polyester film of the present invention has a heat shrinkage ratio of 0.9% or more and 3.0% or less in the machine direction (MD) after treatment at 200 ° C. for 10 minutes, and further 1.0% or more and 2.8. % Or less, 2.0 to 5.0% in the transverse direction (TD), and preferably 2.2 to 4.8%. If the film has a too high thermal shrinkage rate, the film shrinks in the vapor deposition step, and wrinkles may occur, which may not allow the metallicon treatment to the element end face, which is not preferable. On the other hand, if the thermal contraction rate is too low, heat loss may occur in the vapor deposition step, which is not preferable.
[0055]
[Film thickness]
The biaxially oriented polyester film of the present invention preferably has a thickness of 0.5 μm to 20 μm, and more preferably 0.5 μm to 16 μm. When the thickness is less than 0.5 μm, the film forming productivity is low, and the workability in manufacturing the capacitor is poor. On the other hand, if it exceeds 20 μm, it is difficult to reduce the size of the capacitor.
[0056]
A film having a thickness of 0.5 μm or more and 7 μm or less is mainly used for electronic circuits, and the effect of the film of the present invention is most exhibited. A film having a thickness of 7 μm or more and 20 μm or less is mainly used for a high voltage or AC power supply circuit. A film having a thickness exceeding 20 μm is also used as a dielectric, but is mainly used for the exterior (upper winding) of a capacitor.
[0057]
[Film density]
The biaxially oriented polyester film of the present invention has a density of 1.338 g / cm.^Three1.361 g / cm^ThreeThe following is preferable. More preferably 1.340 g / cm^Three1.358 g / cm^ThreeBelow, particularly preferably 1.343 g / cm^Three1.356 g / cm^ThreeIt is as follows. Film density is 1.338 g / cm^ThreeIf it is less than the range, it will cause variation in capacitor performance and decrease in processing yield, which is not preferable. Meanwhile, 1.361 g / cm^ThreeIf it exceeds 1, the crystallinity of the film becomes too high and the toughness of the film is lost. Therefore, the frequency of breakage increases at the time of film conveyance, particularly in the process involving slitting.
[0058]
[Other characteristics]
The biaxially oriented polyester film of the present invention preferably has a space factor of 10 to 33%. The space factor is 100 cm of sample film.²Weight w (g) and density d (g / cm^Three) To determine the thickness by weight method t₁(Μm) Ten sample films of 10 cm square are stacked, and the thickness of one sample film obtained using a micrometer is t.₂(Μm) is a value calculated from the following formula.
[0059]
[Expression 1]
Space factor F (%) = 100−t₁/ T₂× 100
[0060]
If the space factor is less than 10%, the slipperiness and workability (handleability) of the film are insufficient. On the other hand, if the space factor exceeds 33%, the capacitor capacity per volume is low and it is not suitable for reducing the size and capacity of the capacitor. This is not preferable.
[0061]
Furthermore, from the viewpoint of being an electrically insulating material, the dielectric breakdown voltage (BDV) is preferably 200 V / μm or more (measured according to the method shown in JIS C 2318, and an average value of n = 100).
[0062]
In addition, the biaxially oriented polyester film of the present invention is a pinhole, that is, the film is closely attached to the thermal paper, and a magic ink solution diluted 10 times with reagent-grade ethanol is dropped on the sample film and spread over the whole with an air brush. The number of pinholes observed after being transferred to the thermal paper side is 0.1 / cm²The following is preferable.
[0063]
  Furthermore, the biaxially oriented polyester film of the present invention has a CR value measured at 100 ° C. and 1 kHz of 800ΩF.Greater than 920ΩFThe above is preferable. The CR value at 100 ° C and 1 kHz isLess than 920ΩFIf it is less than 800ΩF, the insulation resistance of the film is insufficient, and it may be unsuitable as an electrical insulating material.
[0064]
[Film forming method]
The biaxially oriented polyester film of the present invention is preferably stretched in a biaxial direction (for example, longitudinal and lateral directions) at a stretching ratio of 2.5 to 5.0 times. The biaxial stretching ratios may or may not be equal. The film may be a single film or a laminated film.
[0065]
The biaxially oriented polyester film of the present invention is not limited by the production method, but is preferably produced by the following method.
[0066]
After filtering a predetermined inert fine particle, preferably polyethylene-2,6-naphthalenedicarboxylate containing a sulfonic acid quaternary phosphonium salt having a predetermined amount of an ester-forming functional group with a predetermined filter, for example Extrusion temperature, that is, melt extrusion at a temperature not lower than the melting point (hereinafter referred to as Tm) and not higher than (Tm + 70 ° C.), and the extruded film-like melt is subjected to pinning wire (stainless steel wire (0.05 to 0.60 mmφ, applied voltage: direct current) 0.5 to 15 kV) is brought into close contact with the surface of the rotary cooling drum and rapidly cooled to obtain an unstretched film having an intrinsic viscosity of 0.40 to 0.90 dl / g. More preferably, the film is stretched at a stretching ratio of 2.5 to 5.0 times in the machine direction at a temperature of 130 to 160 ° C., and then 1 in the transverse direction. The film is stretched at a stretching ratio of 2.5 to 5.0 times at a temperature of 0 to 150 ° C., and then the obtained biaxially stretched film is heat-set at a temperature of 210 to 240 ° C. for 0.3 to 20 seconds. Thereafter, if it is necessary to reduce the thermal shrinkage rate, a thermal relaxation treatment is performed in the longitudinal and / or lateral direction within a range of relaxation rate of 0.3 to 15%. The method may be used.
[0067]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. In addition, each characteristic value in an Example was measured and evaluated by the following method.
[0068]
1. Average particle size of fine particles
(1-1) Average particle diameter of powder
It measured using the Shimadzu Corporation CP50 type centrifugul particle size analyzer (Centrifugal Particle Size Analyzer). The particle size corresponding to 50 mass percent is read from the cumulative curve of the particles of each particle size calculated based on the obtained centrifugal sedimentation curve and the abundance thereof, and this value is taken as the average particle size. (See “Particle Size Measurement Technology”, published by Nikkan Kogyo Shimbun, 1975, p. 242-247)
[0069]
(1-2) Particle size and particle size ratio of fine particles in the film
A sample film piece is fixed to a sample stage for a scanning electron microscope, and 0.25 kV under a vacuum of 0.13 Pa on the film surface using a sputtering apparatus (JIS-1100 type ion sputtering apparatus) manufactured by JEOL Ltd. Ion etching treatment is performed for 10 minutes under the condition of 1.25 mA. Furthermore, gold sputtering was performed with the same apparatus, and observation was performed at 10,000 to 30,000 times using a scanning electron microscope, and a major diameter (Dli) and a short diameter of at least 100 particles were measured with a Luzex 500 manufactured by Japan Regulator Co., Ltd. The diameter (Dsi) and the area equivalent particle diameter (Di) are obtained. The number average value of the area equivalent particle diameter (Di) represented by the following formula is defined as the average particle diameter (D).
[0070]
[Expression 2]

[0071]
The average value of the major axis is Dl, the average value of the minor axis is Ds, and the particle size ratio is calculated as Dl / Ds.
[0072]
(1-3) Coarse particles
Using a universal projector, the film surface is magnified 50 times with transmitted illumination, and the measurement area is 1 m.²And the number of particles having a maximum diameter exceeding 40 μm is counted among the particles present in the film.
[0073]
2. AC volume resistivity
Measurement is performed using the apparatus shown in FIG. The film is overlaid so that the measurement sample has a thickness of about 150 μm. An upper electrode 3 having a diameter of 5.6 cm and a thickness of 0.2 cm capable of holding a parallel gap of 150 μm is disposed on the upper surface of the cylindrical lower electrode 2 having a diameter of 20 cm, and the measurement sample 1 is in close contact with the electrode in the meantime. Insert.
[0074]
The lower electrode 2 incorporates a heating device 4 and a temperature detection end 5, the variation in the surface temperature measurement surface of the lower electrode 2 is within 1 ° C., and the temperature difference from the detection end portion is 2 ° C. at a heating rate of 8 ° C./min. Configure to be within. The detected temperature is measured with a reading thermometer 7. The entire electrode is placed in the heat insulating box 11.The temperature regulator is adjusted by adjusting the voltage regulator 6.
[0075]
The power supply 8 applies the generated voltage between the two electrodes through the standard resistor 9, and the power supply is a power supply that generates 100 V and 50 Hz. Current flowing in this circuitIsVoltage generated across standard resistor 9WithinReading with an electron meter 10 with a partial impedance of 100 MΩ or moreAsk by.
[0076]
In the present invention, the measurement of the AC volume resistivity at the time of melting of the film is carried out by the above-mentioned apparatus using the temperature rise rate of the lower electrode.Degree 8 ℃/ Min, at a measurement temperature of 300 ° C., and the AC volume resistivity Z is obtained from the applied voltage E, current I, electrode area S, and electrode interval d by the following equation.
[0077]
[Equation 3]
Z = (E / I) × (S / d)
[0078]
3. Surface roughness
(3-1) Centerline surface roughness (Ra)
Measurement length (Lx) 1 mm, sampling pitch 2 μm, cut-off using a non-contact type three-dimensional roughness meter (Kosaka Laboratories, ET-30HK) with a semiconductor laser with a wavelength of 780 nm and an optical stylus with a beam diameter of 1.6 μm The protrusion profile on the film surface is measured under the conditions of 0.25 mm, thickness direction enlargement magnification of 10,000 times, lateral direction enlargement magnification of 200 times, and the number of scanning lines of 100 (thus, the measurement length Ly in the Y direction is 0.2 mm). . When the roughness curved surface is represented by Z = F (x, y), a value (Ra, unit nm) obtained by the following formula is defined as the surface roughness of the film.
[0079]
[Expression 4]

[0080]
(3-2) 10-point average roughness (Rz)
Take 5 points from the higher peak (HP) and 5 points from the lower valley (Hv), and let Rz be the average roughness.
[0081]
[Equation 5]

[0082]
4). Heat shrinkage
Marks are placed on the sample film at intervals of 30 cm, and the following formula is obtained from the change in the sample length after heat treatment (200 ° C., 10 minutes) for a certain period of time in a heating oven in a tension-free state.
[0083]
[Formula 6]
Thermal contraction rate (%) = (length before heat treatment−length after heat treatment) / length before heat treatment × 100
[0084]
5). Film thickness
The width of the sample film is W (cm), the length is l (cm), the weight is G (g), and the density is d (g / cm^Three), The film thickness t (μm) is calculated by the following formula.
[0085]
[Expression 7]
t = G / (W × l × d) × 10000
[0086]
6). Film density
This is a value measured by a floatation method at 25 ° C. in a density gradient tube using a calcium nitrate aqueous solution as a solvent.
[0087]
7. Intrinsic viscosity (IV)
Measured at 25 ° C. using o-chlorophenol as solvent.
[0088]
8). Component amount of polyethylene-2,6-naphthalenedicarboxylate (molar ratio of main component, molar ratio of copolymer component)
After dissolving the film sample in the measurement solvent (CDCl3: CF3COOD = 1: 1),¹An H-NMR measurement is performed, and calculation is performed with the integration ratio of each obtained signal.
[0089]
9. CR value
In accordance with the method shown in JIS C 2318, two sets of film samples slitted to a width of 12 mm and an aluminum foil having a thickness of 7 μm and a width of 14 mm are superposed while maintaining 2.5 mm as a margin width on one side are prepared. , The effective area is 10000mm by placing each margin at the both ends of the sample²A winding sample is prepared so that The sample is pressed at a pressure of 2 MPa at a temperature of 120 ° C. for 5 minutes. This sample was kept at 100 ° C. by a thermo-keeper (THK-21-1) manufactured by Kato Co., Ltd., and both ends of the sample were connected to an LCR meter (AG-4301) manufactured by Ando Electric Co., Ltd. The value (Ω) is measured, and then the capacitance (nF) at 1 kHz is measured. The CR value is calculated by the following formula from the obtained insulation resistance value and capacitance.
[0090]
[Equation 8]
CR value = insulation resistance value × capacitance
[0091]
10. Film formability
The film formability is evaluated according to the following criteria.
Rank A: Breakage does not occur and extremely stable film formation is possible. Productivity is extremely good.
Rank B: Breakage hardly occurs and stable film formation is possible. Productivity is good.
Rank C: Breaking sometimes occurs, and film formation is unstable. Productivity is poor.
Rank D: Breaking frequently occurs and film formation is extremely unstable. Productivity is extremely poor.
Ranks A and B are accepted.
[0092]
11. Rolled film roll
The wound form after winding a film having a width of 550 mm and a length of 10,000 m on a roll is observed with the naked eye at the time of slitting and after vapor deposition in the film forming process, and evaluated according to the following criteria.
A: There is no surface wrinkle or winding deviation at the time of slitting and after vapor deposition, and the winding shape is good.
○: Slight wrinkles were observed after slitting, but there were no wrinkles after vapor deposition and there was no practical problem.
X: Wrinkles and / or winding deviations on the surface after deposition were confirmed, and the winding shape was poor
[0093]
    [Examples 1 to4 and Comparative Example 6]
  100 parts of dimethyl 2,6-naphthalenedicarboxylate (Example)3Then, 5 mol% of the total acid component is replaced with dimethyl isophthalate) and 0.03 part of manganese acetate tetrahydrate is added to a mixture of 60 parts of ethylene glycol, and the temperature is gradually raised from 150 ° C to 240 ° C. The ester exchange reaction was carried out while warming. When the reaction temperature reached 170 ° C. during the process, 0.024 part of antimony trioxide was added, and porous silica particles and spherical silica particles having the particle diameters shown in Table 1 were added in the amounts shown in Table 1, and then When the temperature reached 220 ° C., 0.042 part of 3,5-dicarboxybenzenesulfonic acid tetrabutylphosphonium salt (corresponding to 2 mmol%) was added. Subsequently, a transesterification reaction was performed, and 0.023 part of trimethyl phosphate was added after the transesterification reaction. Thereafter, the reaction product was transferred to a polymerization reactor, heated to 290 ° C., subjected to a polycondensation reaction under a high vacuum of 30 Pa or less, and an intrinsic viscosity measured with an o-chlorophenol solution at 25 ° C. was 0.61 dl / Polyethylene-2,6-naphthalenedicarboxylate (polymer) as g was obtained.
[0094]
The polymer was dried at 170 ° C. for 6 hours, then fed to an extruder, melted at a melting temperature of 310 ° C., extruded through a slit die, and a pinning wire (SUS wire (0 0.1 mmφ) and applied voltage: direct current 3 kV) to solidify and obtain an unstretched film.
[0095]
The unstretched film thus obtained was stretched 3.6 times in the longitudinal direction at 140 ° C., then stretched 3.9 times in the transverse direction at 140 ° C., and further heat-set at 230 ° C. for 5 seconds. A biaxially oriented (copolymerized) polyethylene-2,6-naphthalenedicarboxylate film with the indicated thickness was obtained. Table 1 shows the composition and characteristics of the films of Examples 1 to 5 and the contents of the additives.
In addition, the space factor of these films is 16 to 21%, and there is no problem.
[0096]
[Comparative Example 1]
A biaxially oriented polyethylene-2,6-naphthalenedicarboxylate film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that it did not contain a quaternary phosphonium salt. The properties of this film are shown in Table 1. Although the physical properties of the film were good, the film forming property was unsatisfactory.
[0097]
[Comparative Example 2]
A biaxially oriented polyethylene-2,6-naphthalenedicarboxylate film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that 50 mmol% of the quaternary phosphonium salt was added. The properties of this film are shown in Table 1. The film-forming property was good, but the AC volume resistivity was low, and the insulating properties of the capacitor were unsatisfactory.
[0098]
[Comparative Example 3]
A biaxially oriented polyethylene-2,6-naphthalenedicarboxylate film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that porous silica fine particles having a large average particle diameter were used. The properties of this film are shown in Table 1. There were many cuts during film formation. The space factor was 36%, which was excessive.
[0099]
[Comparative Example 4]
A biaxially oriented polyethylene-2,6-naphthalenedicarboxylate film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that spherical silica particles were not used and only porous silica fine particles having a small average particle diameter were added. It was. The properties of this film are shown in Table 1. Although the physical properties of the film were good, the rolled shape was very poor and the product was rejected.
[0100]
[Comparative Example 5]
A biaxially oriented copolymer polyethylene-2,6-naphthalenedicarboxylate film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that 20 mol% of isophthalic acid was copolymerized. The properties of this film are shown in Table 1. Productivity was poor and there was a problem with the insulation characteristics of the capacitor.
[0101]
[Table 1]

[0102]
【The invention's effect】
The biaxially oriented polyester film of the present invention has the following excellent characteristics and is suitably used as a capacitor film.
(1) Productivity at the time of film formation is excellent, and is particularly effective for forming an ultrathin film.
(2) The film surface is moderately roughened, the film has good sliding properties, and is excellent in workability during film formation and processing.
(3) Heat resistance and insulation properties of polyethylene-2,6-naphthalenedicarboxylate are utilized, insulation resistance is high, and CR characteristics are excellent.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an apparatus for measuring AC volume resistivity.
[Explanation of symbols]
1: Measurement sample
2: Lower electrode
3: Upper electrode
4: Heating device
5: Temperature detection end
6:Voltage regulator
7: Reading thermometer
8: Power supply
9: Standard resistance
10: Electron meter
11: Thermal insulation box

Claims (5)

The polymer component constituting the biaxially oriented film is made of polyethylene-2,6-naphthalenedicarboxylate, and 0.1 mmol% of sulfonic acid quaternary phosphonium salt having an ester-forming functional group with respect to the total acid component of the polymer. The film has a center line average surface roughness (Ra) of 40 nm or more and 90 nm or less, a 10-point average roughness (Rz) of 1000 nm or more and 1800 nm or less, and 40 μm existing in the film. The number of coarse particles exceeding 10 particles / m ² or less, and the value of the AC volume resistivity when the film is melted (300 ° C.) is 2 × 10 ⁸ Ωcm or more and 8 × 10 ⁸ Ωcm or less. A biaxially oriented polyester film for capacitors. After the film is treated at 200 ° C. for 10 minutes, the longitudinal direction (MD) thermal contraction rate is 0.9% to 3.0%, and the lateral direction (TD) thermal contraction rate is 2.0% to 5.0%. The biaxially oriented polyester film for capacitors according to claim 1, which is not more than%. The film thickness is 0.5 μm or more and 20 μm or less, the density is 1.338 g / cm ³ or more and 1.361 g / cm ³ or less, and the intrinsic viscosity of the polymer constituting the film is 0.40 dl / g or more and 0.90 dl. The biaxially oriented polyester film for a capacitor according to claim 1 or 2 , which is / g or less. The film contains 0.05% by weight or more and 2% by weight or less of porous silica particles (A) having an average particle size of 0.5 μm or more and 5 μm or less, and at the same time the average particle size is 0.05 μm or more and 1.5 μm or less, and The biaxially oriented polyester film for a capacitor according to any one of claims 1 to 3 , comprising spherical silica particles (B) having a thickness less than the film thickness of 0.01 wt% or more and 1 wt% or less. The sulfonic acid quaternary phosphonium salt having an ester-forming functional group contained in the polymer constituting the film has the following formula:

(Wherein A is an n + divalent aliphatic group having 2 to 18 carbon atoms or an aromatic group, X ₁ and X ₂ are the same or different and are a hydrogen atom or an ester-forming functional group, and n is 1 or 2, and, R _1, R _2, R _3, and R ₄ are the same or different, is an alkyl group, a benzyl group or an aryl group having 6 to 12 carbon atoms having 1 to 18 carbon atoms. However, X ₁ and X ₂ are not hydrogen at the same time.)
The biaxially oriented polyester film for capacitors according to any one of claims 1 to 4 , which is a compound represented by the formula:

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