JP3876509B2 - Polyester film and method for producing the same - Google Patents

Description

（但し式中のＲ１は、
【化５】

を示し、Ｒ２は
【化６】

から選ばれた一種以上の基を示し、Ｒ３は、
【化７】

から選ばれた一種以上の基を示す。また、式中Ｘは水素原子または塩素原子を示し、構造単位［（（II）＋（III ）］と構造単位（IV）は実質的に等モルである。）
上記構造単位（Ｉ）はｐーヒドロキシ安息香酸および／または６ーヒドロキシー２ーナフトエ酸から生成したポリエステルの構造単位を、構造単位（II）は、４、４´ージヒドロキシビフェニル、３、３´、５、５´ーテトラメチルー４、４´ージヒドロキシビフェニル、ハイドロキノン、ｔーブチルハイドロキノン、フェニルハイドロキノン、２、６ージヒドキシナフタレン、２、７ージヒドキシナフタレン、２、２´ービス（４ーヒドロキシフェニル）プロパンおよび４、４´ージヒドロキシジフェニルエーテルから選ばれた芳香族ジヒドロキシ化合物から生成した構造単位を、構造単位（III ）はエチレングリコールから生成した構造単位を、構造単位（IV）は、テレフタル酸、イソフタル酸、４、４´ージフェニルジカルボン酸、２、６ーナフタレンジカルボン酸、１、２ービス（フェノキシ）エタンー４、４´ージカルボン酸、１、２ービス（２ークロルフェノキシ）エタンー４、４´ージカルボン酸および４、４´ージフェニルエーテルジカルボン酸から選ばれた芳香族ジカルボン酸から生成した構造単位を各々示す。
【００１４】
また、上記構造単位（Ｉ）、（II）および（IV）からなる共重合ポリエステルの場合は、Ｒ１が
【化８】

であり、Ｒ２が
【化９】

から選ばれた一種以上であり、Ｒ３が
【化１０】

から選ばれた一種以上であるものが好ましい。
【００１５】
また、上記構造単位（Ｉ）、（III ）および（IV）からなる共重合ポリエステルの場合は、Ｒ１が
【化１１】

であり、Ｒ３が
【化１２】

であるものが特に好ましい。
【００１６】
また、上記構造単位（Ｉ）、（II）、（III ）および（IV）からなる共重合ポリエステルの場合は、Ｒ１が
【化１３】

であり、Ｒ２が
【化１４】

であり、Ｒ３が
【化１５】

であるものが特に好ましい。
【００１７】
本発明では、共重合量を、ポリマーを形成し得る繰返し構造単位のモル比から計算し、モル％で表す。上記好ましい共重合ポリエステルの場合には、構造単位（Ｉ）、構造単位（II）＋（IV）、構造単位（III ）＋（IV）がポリマーを形成し得る繰返し構造単位であり、これらの共重合モル比から共重合量が計算できる。
【００１８】
構造単位（Ｉ）、（II）＋（IV）、（III ）＋（IV）の共重合モル比は任意であるが、非液晶性ポリエステル中での微分散性、分散ドメインの制御、ヤング率の向上の点から、メソゲン基の共重合量は、５〜９５モル％であり、好ましくは２０〜８０モル％である。メソゲン基である構造単位（Ｉ）、（II）＋（IV）の共重合量が５モル％よりも低くなると、ヤング率の向上効果、押出工程での剪断発熱抑制効果が得られにくく、また９５モル％よりも高くなると分散性が低下し、ポリエステルフィルム表面の荒れが激しくなるので好ましくない。
【００１９】
上記構造単位（Ｉ）、（II）、（III ）および（IV）からなる共重合ポリエステルの場合は、上記構造単位［（Ｉ）＋（II）＋（III ）］に対する［（Ｉ）＋（II）］のモル分率は５〜９５モル％であり、２０〜８０％がより好ましく、４０〜７５モル％が最も好ましい。また、構造単位［（Ｉ）＋（II）＋（III ）］に対する（III ）のモル分率は９５〜５モル％であり、８０〜２０モル％がより好ましく、６０〜２５モル％が最も好ましい。また、構造単位（Ｉ）／（II）のモル比は流動性の点から、好ましくは７５／２５〜９５／５であり、より好ましくは７８／２２〜９３／７である。また、構造単位（IV）のモル数は構造単位［（II）＋（III ）］のトータルモル数と実質的に等しい。
【００２０】
また、上記構造単位（Ｉ）、（III ）および（IV）からなる共重合ポリエステルの場合は、上記構造単位（Ｉ）は［（Ｉ）＋（III ）］の５〜９５モル％が好ましく、２０〜８０モル％がより好ましく、４０〜７５モル％が最も好ましい。構造単位（IV）は構造単位（III ）と実質的に等モルである。
【００２１】
さらに上記構造単位（Ｉ）、（II）および（IV）からなる共重合ポリエステルの場合は、単独ではなく、構造単位（Ｉ）、（II）、（III ）および（IV）からなる共重合ポリエステルまたは／および構造単位（Ｉ）、（III ）および（IV）からなる共重合ポリエステルのブレンドポリマーとして用いることが好ましい。このブレンドポリマーの場合においても、前記同様に、構造単位［（Ｉ）＋（II）＋（III ）］に対する［（Ｉ）＋（II）］のモル分率は５〜９５モル％が好ましく、２０〜８０％がより好ましく、４０〜７５モル％が最も好ましい。
【００２２】
以上述べた説明中の「実質的に」とは、必要に応じてポリエステルの末端基をカルボキシル基末端あるいはヒドロキシル末端基のいずれかを多くすることができることを意味し、このような場合には構造単位（IV）のモル数は構造単位［（II）＋（III ）］のトータルモル数と完全には等しくない。
【００２３】
上記好ましい共重合ポリエステルを重縮合する際には、上記構造単位（Ｉ）〜（IV）を構成する成分以外に、３、３´ージフェニルジカルボン酸、２、２´ージフェニルジカルボン酸などの芳香族ジカルボン酸、アジピン酸、アゼライン酸、セバシン酸、ドデカンジオン酸などの脂肪族ジカルボン酸、ヘキサヒドロテレフタル酸などの脂環式ジカルボン酸、クロルハイドロキノン、メチルハイドロキノン、４、４´ージヒドロキシジフェニルスルフォン、４、４´ージヒドロキシジフェニルスルフィド、４、４´ージヒドロキシベンゾフェノンなどの芳香族ジオール、１、４ーブタンジオール、１、６ーヘキサンジオール、ネオペンチルグリコール、１、４ーシクロヘキサンジオール、１、４ーシクロヘキサンジメタノール等の脂肪族、脂環式ジオールおよびｍーヒドロキシ安息香酸、２、６ーヒドロキシナフトエ酸などの芳香族ヒドロキシカルボン酸およびｐーアミノフェノール、ｐーアミノ安息香酸などを本発明の目的を損なわない程度の少割合の範囲でさらに共重合せしめることができる。
【００２４】
本発明における共重合ポリエステルの製造方法は、特に制限がなく、公知のポリエステルの重縮合法に準じて製造できる。
【００２５】
例えば、上記の好ましく用いられる共重合ポリエステルの製造法において、上記構造単位（III ）を含まない場合は下記（１）および（２）、構造単位（III ）を含む場合は下記（３）の製造方法が好ましい。
【００２６】
（１）ｐーアセトキシ安息香酸および４、４´ージアセトキシビフェニル、４、４´ージアセトキシベンゼンなどの芳香族ジヒドロキシ化合物のジアシル化物とテレフタル酸などの芳香族ジカルボン酸から脱酢酸重縮合反応によって製造する方法。
【００２７】
（２）ｐーヒドロキシ安息香酸および４、４´ージヒドロキシビフェニル、ハイドロキノンなどの芳香族ジヒドロキシ化合物、テレフタル酸などの芳香族ジカルボン酸に無水酢酸を反応させて、フェノール性水酸基をアシル化した後、脱酢酸重縮合反応によって製造する方法。
【００２８】
（３）ポリエチレンテレフタレートなどのポリエステルのポリマ、オリゴマまたはビス（βーヒドロキシエチル）テレフタレートなどの芳香族ジカルボン酸のビス（βーヒドロキシエチル）エステルの存在下で（１）または（２）の方法により製造する方法。
【００２９】
これらの重縮合反応は無触媒でも進行するが、酢酸第一錫、テトラブチルチタネート、酢酸カリウムおよび酢酸ナトリウム、三酸化アンチモン、金属マグネシウムなどの金属化合物を添加した方が好ましい場合もある。
【００３０】
本発明では、低粘度のポリマー（Ｂ）、すなわち、溶融粘度比（非液晶性ポリエステル（Ａ）の溶融粘度（ηＡ ）／非液晶性ポリエステル（Ａ）とブレンドした時に相分離構造を形成するポリマー（Ｂ）の溶融粘度（ηＢ ））を大きくするポリマー（Ｂ）が好ましい。本発明の目的は、非液晶性ポリエステルに低粘度のポリマーを添加した場合ほど効果的に達成できるからである。この溶融粘度比は、少なくとも５以上であることが望ましく、さらには、好ましくは１０以上、より好ましくは５０以上、特に好ましくは２００以上である。本発明者らの知見によれば、２００以上、１０万以下が最も好ましい。従って、ポリマー（Ｂ）の溶融粘度は、使用する非液晶性ポリエステルの溶融粘度にもよるが、マトリックスを構成する非液晶性ポリエステルの融点＋１５℃、剪断速度１００秒ー１の条件下で、１００Ｐａ・秒程度以下であることが望ましく、好ましくは１０Ｐａ・秒以下、さらに好ましくは１Ｐａ・秒以下である。このような低い溶融粘度を有し、本発明の目的を達成する上で特に好適に用いることのできる共重合ポリエステルは、上記構造単位（Ｉ）、（II）、（III ）および（IV）からなる共重合ポリエステルである。この共重合ポリエステルは、その分散ドメインのアスペクト比の比率Ｑｃ／Ｑｓが大きくなり易いため、ポリエステルフィルムの品質を高める上で特に有効である。
【００３１】
該ポリマー（Ｂ）の添加量は、本発明の目的を達成できる適量であれば特に限定されないが、全ポリマーの０．０１〜４０重量％、好ましくは０．０５〜２０重量％、さらに好ましくは０．１〜５重量％の範囲が良い。添加量が０．０１重量％未満であったり、逆に４０重量％を超えると本発明の効果を得ることが難しくなるので好ましくない。
【００３２】
本発明でいうフィルムの表層とは、図１に示すように、厚みＴのポリエステルフィルムにおいてフィルム表面からＴ／８の深さの部分であり、フィルムの中央層とは厚みがＴ／２の中央部分である。非液晶性ポリエステル（Ａ）中において、ポリマー（Ｂ）の個々の分散ドメインは、球型、偏球型、繊維型、小判型などの形をとるが、フィルム全体の構造から判断される分散ドメインの形状は、表層部では小判状、偏球状、または球状、中央層では小判状、繊維状または層状であることが好ましい。ポリマー（Ｂ）の分散ドメインの表層と中央層におけるアスペクト比の比率Ｑｃ／Ｑｓは２以上、３００以下であることが好ましく、さらに好ましくは５以上、１５０以下、最も好ましくは１０以上、１００以下である。ポリマー（Ｂ）の分散ドメインのアスペクト比の比率Ｑｃ／Ｑｓが２未満であったり、 Ｑｃ／Ｑｓが３００を越えると、高ヤング率と表面易滑性、耐磨耗性を両立することが難しくなる。
【００３３】
ポリマー（Ｂ）の分散ドメインのＬ／Ｄは、フィルム全体の構造から判断されるものであり、フィルム表層または中央層の各層に含まれているポリマー（Ｂ）の分散ドメインの平均的な形状を示す幾何学的指数である。尚、本発明でいう平均長径Ｌおよび平均短径Ｄは下記（１）および（２）式から求めることができる。
【００３４】
Ｌ＝ｍａｘ［Ｉ、Ｊ、Ｋ］ ・・・・（１）
Ｄ＝（Ｉ＋Ｊ＋Ｋ−Ｌ）／２ ・・・・（２）
ここで、Ｉ、Ｊ、Ｋは、ポリマー（Ｂ）のドメインのフィルムの長手方向、幅方向、および厚み方向の最大長さの平均値に対応する。ｍａｘ［Ｉ、Ｊ、Ｋ］はＩ、Ｊ、Ｋの長さを比較して、最も大きな値を選択する関数である。尚、Ｉ，Ｊ，Ｋは、後述するように透過型電子顕微鏡を用いて測定し、１００個の分散ドメインを用いて算出する。また、本発明では、Ｉ，Ｊ，Ｋの平均値をポリマー（Ｂ）からなるドメインの平均分散径という。尚、Ｉ，Ｊ，Ｋは、後述するように、透過型電子顕微鏡を用いて測定し、表層と中央層で各々１００個の分散ドメインを無作為に用いて算出する。
【００３５】
本発明でいう小判状とは、ポリマー（Ｂ）からなる複数の分散ドメインから算出される上記形状指数Ｉ，Ｊ，Ｋが下記（３）および（４）の関係を満足する形状である。
【００３６】
０．０２＜（Ｉ／Ｊ）＜５０ ・・・・（３）
Ｋ＜（１／２）・Ｓ［Ｉ、Ｊ］ ・・・・（４）
ここで、ＳはＩとＪの長さを比較して、短い方の値を選択する関数であり、Ｉ＞Ｊの場合はＳ［Ｉ、Ｊ］はＪであり、Ｉ＜Ｊの場合はＳ［Ｉ、Ｊ］はＩである。また、Ｉ，Ｊ，Ｋが（３）、（４）式の範囲から外れる場合、本発明では、フィルム中に存在している分散ドメインの形状を下記のように表現する。
【００３７】
球状 ：Ｉ＝Ｊ＝Ｋ
偏球状：Ｉ／Ｊが１／３以上、３未満であり、（４）式を満足しない。
【００３８】
繊維状：Ｉ／Ｊが１／３未満または３以上であり、（４）式を満足しない。
【００３９】
層状 ：（３）式を満足しないが、（４）式を満足する。
【００４０】
また、本発明では、個々の分散ドメインの形についても、上記と同様に表現し、（５）、（６）式を満足するドメインの形を小判型という。尚、本発明では、フィルム面と平行な切断面に現れる分散ドメインが円、楕円またはこれらが一部変形した形の板型または薄片型の分散ドメインも小判型ドメインに含まれる。ドメインの形が（５）、（６）式の範囲から外れる場合は、上記ドメイン形状に関する判断基準と同様の基準をもとに、本発明ではドメインの形を球型、偏球型、繊維型、層型と表現する。
【００４１】
０．０２＜（ｉ／ｊ）＜５０ ・・・・（５）
ｋ＜（１／２）・Ｓ［ｉ、ｊ］ ・・・・（６）
ここで、ｉ、ｊ、ｋはポリマー（Ｂ）からなる個々の分散ドメインのフィルムの長手方向、幅方向、および厚み方向の最大長さである。
【００４２】
また、本発明では、ポリマー（Ｂ）の分散ドメインのフィルム表層部におけるアスペクト比Ｑｓは１〜２０であることが好ましく、さらに好ましくは１〜１０、最も好ましくは１〜３である。また、フィルム表層部におけるポリマー（Ｂ）の分散ドメインの平均長径Ｌは、０．０１〜３μｍであることが好ましく、さらに好ましくは０．０１〜１．０μｍ、最も好ましくは０．０２〜０．５μｍである。フィルム表層部のアスペクト比Ｑｓが２０を越えたり、分散ドメインの平均長径Ｌが３μｍを越えるとフィルムの表面特性が悪化するので好ましくない。
【００４３】
本発明では、フィルムの長手方向（ＭＤ）のヤング率（ＹＭＤ）と幅方向（ＴＤ）のヤング率（ＹＴＤ）幅方向の和、すなわちトータルヤング率は、ポリマー（Ｂ）の剛直性、添加量にもよるが、８〜３０ＧＰａである。トータルヤング率のより好ましい範囲は１０〜２５ＧＰａであり、特に好ましい範囲は１２〜２０ＧＰａである。トータルヤング率が８ＧＰａ未満ではフィルムとしての実用性に乏しく、また、３０ＧＰａを越えると、フィルムの表面特性が悪化し易いので好ましくない。
【００４４】
本発明のフィルムの表面粗さＲａは０．５〜１００ｎｍであり、動摩擦係数μｋは０．３０以下である。表面粗さＲａの好ましい範囲は０．５〜３０ｎｍであり、より好ましくは１〜１０ｎｍであり、特に好ましい範囲は２〜７である。ポリマー（Ｂ）の添加量を０．１〜５重量％とし、ポリマー（Ｂ）を平均分散径１μｍ未満のサイズで前記（３）式を満足する形状に微分散させると、磁気テープ用途、特にメタル・蒸着テープ用ベースフィルムの必須要件とされている、表面粗さＲａが１〜１０ｎｍのフィルムを得ることが容易となるので好ましい。表面粗さＲａが０．５ｎｍ未満であるとフィルムの滑りが悪いため、フィルムの巻取工程でトラブルが生じ易く、また、これとは逆に表面粗さＲａが１００ｎｍを越えると各種フィルム用途に展開する際に問題が生じることが多いので好ましくない。
【００４５】
本発明で開示するポリマー（Ｂ）の分散ドメインの形は溶融押出時に使用するスクリューによって変化する。本発明では、スクリューはフルフライト、バリアフライト等、いかなる形状のスクリューを使用してもよいが、ポリマー（Ｂ）の微分散化を促進し、フィルムの表面易滑性および耐磨耗性を向上させるためには、スクリューの長さと直径の比が２０以上の各種ミキシング型スクリューを使用することが好ましい。ミキシング型スクリューとは、スクリュー圧縮部、計量部またはこれらの中間の位置にミキシング部を有するスクリューであり、例えばフルーテッドバリア、ダルメージ、ユニメルト、多条ピン等を有したスクリューが挙げられる。
【００４６】
本発明のポリエステルフィルム中における非液晶性ポリエステル（Ａ）の環状三量体の含有率は、本発明のポリマー（Ｂ）を特定量添加することにより、０．１〜１．０重量％に低減することができる。ポリエステルフィルム中の非液晶性ポリエステル（Ａ）の環状三量体の含有率は、ポリエステルフィルムを製造する際に用いる非液晶性ポリエステル（Ａ）にもよるが、固相重合を施した固有粘度の高い非液晶性ポリエステル（Ａ）に前記溶融粘度比（ηＡ／ηＢ）が５以上のポリマー（Ｂ）を適量添加すると、溶融押出時のオリゴマー増量が激減し、その結果、環状三量体の含有率の低いポリエステルフィルムが得られる。このオリゴマー量の低減では、上述した主鎖にメソゲン基を有する共重合ポリエステル、共重合ポリエステルアミド、共重合ポリエステルイミド、数平均分子量が１５００〜１００００の低分子量の熱可塑性ポリイミドがポリマー（Ｂ）として特に好ましい。環状三量体の含有率のより好ましい範囲は、０．１〜０．６重量％であり、さらに好ましくは０．１〜０．４重量％である。ポリエステルフィルム中の環状三量体の含有率を０．１重量％未満にすることは、非液晶性ポリエステル（Ａ）の原料チップ中の環状３量体が通常０．１重量％以上であるため、非常に難しい。
【００４７】
また、環状三量体の含有率が１．０重量％より大きいと、製膜時のオリゴマー汚れが顕著となり、フィルム品質や工程管理上の問題となるので好ましくない。尚、本発明のポリエステルフィルム中には、非液晶性ポリエステル（Ａ）と共重合ポリエステル（Ｂ）以外に本発明の効果を阻害しない範囲であれば、非液晶性ポリエステル（Ａ）と共重合ポリエステル（Ｂ）の相溶化剤、可塑剤、耐候剤、酸化防止剤、熱安定剤、滑剤、帯電防止剤、増白剤、着色剤、導電剤などを添加してもかまわない。相溶化剤については、平均屈折率が前記非液晶性ポリエステル（Ａ）とポリマー（Ｂ）の中間の値である相溶化剤がポリエステルフィルムの機械特性および表面特性の向上の点で好ましい。
【００４８】
また、本発明のポリエステルフィルムは単膜でもよいが、片面に他のポリマー層、例えばポリエステル、ポリオレフィン、ポリアミド、ポリ塩化ビニリデン、アクリル系ポリマーなどを積層してもよい。また、易接着性、帯電防止性を付与するために、少なくとも片面にコーティング層を設けることも好ましく行うことができる。
【００４９】
本発明のポリエステルフィルムは、未延伸、未配向フィルムでもよいが、公知の方法により一軸あるいは二軸延伸、熱固定した配向フィルムとすることが好ましい。フィルムのヤング率、表面易滑性、耐磨耗性、透明性、電気特性などがより顕著に向上するからである。尚、本発明で対象とするフィルムの厚みは０．５〜３００μｍであるが、好ましくは１〜１００μｍ、さらに好ましくは２〜３０μｍであり、特に磁気テープ用途では２〜１０μｍが好ましい。
【００５０】
ポリマー（Ｂ）の分散ドメインのＱｓをＱｃよりも小さくするには、非液晶性ポリエステル（Ａ）とポリマー（Ｂ）からなる樹脂組成物を、下記(1) 、(2) 、(3) を満足する条件で溶融押出成形した後、長手方向に３〜１０倍、幅方向に３〜１０倍の倍率で延伸し、かかる後に１５０℃以上、該非液晶性ポリエステル（Ａ）の融点未満の温度で熱固定することが好ましい。本発明では、少なくとも(1) を満足する条件で押出成形する必要があり、(2) 、(3) の条件を組み合わせると、本発明で目的とするポリエステルフィルムがさらに得られ易くなるので好ましい。
【００５１】
(1) 押出成形温度を、該非液晶性ポリエステル（Ａ）の降温時の結晶化開始温度以上、融点以下に設定。
【００５２】
(2) キャスト時のドラフト比を３〜５０に設定する。
【００５３】
(3) ランド部の長さが１０〜７０ｍｍの口金を使用。
【００５４】
押出成形温度は、非液晶性ポリエステル（Ａ）の（降温時の結晶化開始温度＋２℃）以上、（融点−２℃）以下がより好ましく、（降温時の結晶化開始温度＋５℃）以上、（融点−５℃）以下がさらに好ましい。溶融成形温度が非液晶性ポリエステル（Ａ）の融点を越えると、ＱｓがＱｃよりも小さいフィルムが得られにく、また、溶融成形温度が非液晶性ポリエステル（Ａ）の降温時の結晶化開始温度未満ではポリマーの固化によりトラブルが生じるので好ましくない。尚、本発明でいう押出成形温度とは、Ｔダイ内部の中央部のポリマー温度である。
【００５５】
Ｔダイによりシート状に押出す時のドラフト比は、５〜３０がより好ましく、最も好ましくは７〜２０である。ドラフト比が３未満であると、共重合ポリエステルの分散ドメインが、表層と中央層で共に球状、偏球状となり、フィルム表層部と中央層部のアスペクト比が同等になるので好ましくない。一方、ドラフト比が５０を越えると、表層と中央層で共に繊維状または層状になって、フィルム表層部と中央層部のアスペクト比の比率Ｑｃ／Ｑｓが小さくなるので好ましくない。Ｔダイの口金ランド部の長さは１５〜５０ｍｍにすることがより好ましく、２０〜４０ｍｍがさらに好ましい。口金ランド部の長さが１０ｍｍ未満では、本発明で目的とする、ＱｓがＱｃよりも小さいフィルムが得られにくいので好ましくない。また、口金ランド部の長さが７０ｍｍを越えると、厚み調整が困難になってフィルムの品質が低下するばかりでなく、薄物のフィルムではフィルム破れも多発し易いので好ましくない。尚、ポリマー（Ｂ）からなる分散ドメインのＱｃおよびＱｓの大小関係は、溶融ポリマーの冷却速度にも影響を受けるので、これらを後述する好ましい条件に設定しておくことが重要である。
【００５６】
次に、本発明のポリエステルフィルムを製造する方法について説明するが、本発明がかかる例に限定されないことは無論である。
【００５７】
ここでは非液晶性ポリエステル（Ａ）としてポリエチレンテレフタレート、該非液晶性ポリエステル（Ａ）と相分離構造を形成するポリマー（Ｂ）としてｐーヒドロキシ安息香酸６０モル％とポリエチレンテレフタレート４０モル％の共重合ポリエステルを用いた例を示すが、使用するポリエステルにより製造条件は異なる。常法に従って、テレフタル酸とエチレングリコールからエステル化し、または、テレフタル酸ジメチルとエチレングリコールをエステル交換により、ビス−β−ヒドロキシエチルテレフタレート（ＢＨＴ）を得る。次にこのＢＨＴを重合槽に移行しながら、真空下で２８０℃に加熱して重合反応を進める。ここで、固有粘度が０．５程度のポリエステルを得る。得られたポリエステルをペレット状で減圧下において固相重合する。固相重合する場合は、あらかじめ１８０℃以下の温度で予備結晶化させた後、１９０〜２５０℃で１ｍｍＨｇ程度の減圧下、１０〜５０時間固相重合し、使用する共重合ポリエステルの溶融粘度の５倍以上になるように重合度を上昇させる。
【００５８】
次に、該高粘度のポリエチレンテレフタレートと共重合ポリエステルをドライブレンドした原料や、これらを一旦溶融・混練し共重合ポリエステルを微分散化させたマスター原料、さらには本発明のフィルムの回収原料を単独、または適度に上記２〜３種類の原料を混合した原料を、１８０℃で３時間以上真空乾燥したのち、固有粘度が低下しないように窒素気流下、あるいは真空下で２８０℃に加熱された単軸または二軸押出機に供給し、各種の方法により製膜する。この時、押出機のスクリュー剪断速度（＝πＤＮ／ｈ、Ｄ：スクリュー直径、Ｎ：スクリュー回転数、ｈ：スクリュー計量部の溝深さ）は２０秒ー１以上とする。スクリュー剪断速度は、５０秒ー１以上がより好ましいが、３００秒ー１以上に大きくすると、剪断発熱によってポリマーが熱分解ゲル化したり、オリゴマー量が増加するので好ましくない。口金内部のポリマー温度、ドラフト比、口金のランド長は、前記(1) 〜(3) で示した条件に設定すると、共重合ポリエステルの分散ドメインのＬ／Ｄが、中央層部よりも表層部で小さくなり易いので好ましい。ここで、キャスト時のポリマーの冷却速度は、１５０℃／秒以上の冷却速度が好ましく、エアーや水でフィルムを直接冷却し、フィルムの冷却速度をコントロールすることも好適に行うことができる。フィルム中央層よりもフィルム表層を早く冷却すると、共重合ポリエステルの分散ドメインのＱｃ／Ｑｓが大きくなるので好ましい。
【００５９】
また、溶融押出では異物を除去するために、各種のフィルター、例えば焼結金属、多孔性セラミックス、サンド、金網などを用いることが好ましい。この時、フィルター通過時の剪断速度は１０秒ー１以下の低いものであり、固有粘度の高い非液晶性ポリエステル（Ａ）のみでは濾過通過時の圧力が高くなるが、本発明で開示する共重合ポリエステルを添加することにより、濾過時の圧力を実用範囲まで低下させ易くなる。共重合ポリエステルの添加のみでは濾過時の圧力が充分に低下しない場合は、公知の低圧損タイプのフィルターを用いることが好ましい。
【００６０】
その後、シート状のキャストフィルムを８０〜１８０℃の加熱ロール群で加熱し、縦方向に３〜１０倍に１段もしくは２段以上の多段で延伸し、２０〜５０℃の冷却ロール群で冷却する。続いて、公知のテンターに導いて、該フィルムの両端をクリップで把持しながら、８０〜１８０℃に加熱された熱風雰囲気中で加熱し、横方向に３〜１０倍に１段もしくは２段以上の多段で延伸する。続いて、該フィルムに１５０℃以上、ポリエチレンテレフタレートの融点未満の温度で熱固定を施す。熱固定は緊張下または１．０５〜１．５の微延伸下で行ってもよく、また熱寸法安定性をさらに向上させるために、縦または／および幅方向に弛緩することも好ましく行なわれる。また、必要に応じ、熱固定を行う前に、再縦延伸および／または再横延伸を行うこともできる。
【００６１】
【物性の測定方法ならびに効果の評価方法】
（１）固有粘度
２５℃で、オルトクロロフェノール中０．１ｇ／ｍｌ濃度で測定した値である。単位は［ｄｌ／ｇ］で示す。
【００６２】
（２）溶融粘度
高下式フローテスターを用いて、２８０℃、剪断速度１００秒−１の時の値を測定した。単位は［Ｐａ・秒］で表す。
【００６３】
（３）融点、降温結晶化開始温度
パーキンエルマー社製のＤＳＣ（示差走査熱量計）ＩＩ型を用いて測定した。試料１０ｍｇをＤＳＣ装置にセットし、３００℃の温度で５分間溶融した後、液体窒素中で急冷する。この試料を１０℃／分で昇温し、ガラス転移点、冷結晶化温度を検知した後、さらに昇温を続け、結晶融解に基づく吸熱ピーク温度を融点Ｔｍとした。また、３００℃の溶融状態から１０℃／分で降温し、結晶化が始まり発熱が生じる温度を降温結晶化開始温度Ｔｍｃｓ、結晶化発熱ピーク温度を降温結晶化温度Ｔｍｃとした。
【００６４】
（４）ビカット軟化温度
ＪＩＳ−Ｋ７２０６記載の方法に従って、ビカット軟化温度を測定した。
【００６５】
（５）ヤング率
テンシロン型引張試験（オリエンテック社製）に幅１０ｍｍ、チャック間長さ１００ｍｍになるようにサンプルをセットし、２３℃、６５％ＲＨの雰囲気下で引張速度２００ｍｍ／分で引張試験を行い求めた。
【００６６】
（６）表面粗さＲａ
小坂研究所製の高精度薄膜段差測定器ＥＴ−１０を用いて、表面粗さＲａを測定した。条件は下記のとおりであり、フィルム幅方向に走査して２０回測定した時の平均値をもって値とした。
【００６７】
・触針先端半径：０．５μｍ
・触針荷重 ：５ｍｇ
・測定長 ：１ｍｍ
・カットオフ値：０．０８ｍｍ
尚、Ｒａの定義は、例えば、奈良治郎著「表面粗さの測定・評価法」（総合技術センター、１９８３）に示されているものである。
【００６８】
（７）耐磨耗性、動摩擦係数
フィルムを幅１／２インチのテープ状にスリットしたものをテープ走行試験機を用いてステンレス製ガイドピン（表面粗度：Ｒａで１００ｎｍ）上を走行させる（走行速度２５０ｍ／分、巻き付け角６０゜、出側張力９０ｇ、走行回数１回）。この時、フィルムに入った傷を顕微鏡で観察し、幅２．５μｍ以上の傷がテープ幅あたり２本未満は優、２本以上１０本未満は良、１０本以上は不良と判定した。この耐磨耗性は優が望ましいが、良でも実用的には使用可能である。
【００６９】
また、この時、初期のμｋを下記の式により求めた。
【００７０】
μｋ＝２．２０ｌｏｇ（９０／Ｔ）
ここで、Ｔは入側の張力である。このμｋが０．３０以下だと滑り性良好、０．３０を越えると滑り性不良と判断した。このμｋ値０．３０は、印刷工程など加工工程で滑り性不良によるトラブルが発生するか否かの臨界点である。
【００７１】
（８）ポリマー（Ｂ）の分散ドメインの形状指数Ｉ，Ｊ，Ｋ、平均長径Ｌ、平均短径Ｄ、アスペクト比Ｑｓ、Ｑｃ
ポリエステルフィルムを(1) 長手方向に平行かつフィルム面に垂直な方向、(2) 幅方向に平行かつフィルム面に垂直な方向、(3) フィルム面に対して平行な方向に切断し、その切断面を透過型電子顕微鏡（ＴＥＭ）で観察する。(1) の切断面に現れるポリマー（Ｂ）のドメインのフィルムの厚み方向の最大長さ（ｌａ）と長手方向の最大長さ（ｌｂ）、(2) の切断面に現れるポリマー（Ｂ）のドメインのフィルムの厚み方向の最大長さ（ｌｃ）と幅方向の最大長さ（ｌｄ）、および(3) の切断面に現れるポリマー（Ｂ）のドメインの長手方向の最大長さ（ｌｅ）と幅方向の最大長さ（ｌｆ）を、直接観察または顕微鏡写真により、フィルムの表層と中央層に対して各々求める。尚、これらｌａ、ｌｂ、ｌｃ、ｌｄ、ｌｅ、ｌｆは、各切断面の表層および中央層の各層に分布する分散ドメインを無作為に用い、１００個のドメインに対して求めた（図１、２）。相分離構造を形成するドメインと非液晶性ポリエステルの境界は、ＴＥＭ画像の濃淡により判断し、境界部分が幅を有すると認められる場合には非液晶性ポリエステルまたはポリマー（Ｂ）と判断できる２点の中心の位置を境界とした（図２）。また、ポリマー（Ｂ）のドメイン内部にも、ミクロ相分離構造などにより濃淡が認められる場合には、非液晶性ポリエステルに対するポリマー（Ｂ）の全体の輪郭部を境界部として境界を決めた。
【００７２】
次いで、ポリマー（Ｂ）の分散ドメインの形状指数Ｉ，Ｊ，Ｋを求める。Ｉは（ｌｂの平均値＋ｌｅの平均値）／２、Ｊは（ｌｄの平均値＋ｌｆの平均値）／２、Ｋは（ｌａの平均値＋ｌｃの平均値）／２とした。平均長径Ｌと平均短径Ｄは、上記Ｉ，Ｊ，Ｋと前記（１）式および（２）式により決定し、その比率Ｌ／Ｄをアスペクト比とした。また、フィルム表層部のアスペクト比Ｑｓと中央層でのアスペクト比Ｑｃの比率Ｑｃ／Ｑｓは、フィルムの表裏で２つある表層部のＱｓを比較して、小さい方のＬ／ＤをＱｓとして採用し求めた。
【００７３】
尚、分散ドメインがポリマーであるか否かは、フィルムと本フィルムを再度、溶融押出して得られるキャストフィルムの分散ドメインの形状指数の比較により行う。本発明では、上記形状指数の少なくとも一つが１０％以上変化する時に、分散ドメインがポリマーであると判断する。
【００７４】
【実施例】
本発明を実施例、比較例に基づいて説明する。
【００７５】
実施例１（表１〜３）
非晶性ポリエステル（Ａ）として、固有粘度０．６３（ｄｌ／ｇ）の無粒子系のポリエチレンテレフタレート原料（融点２５８℃、降温結晶化開始温度２３０℃）を用いた。ポリマー（Ｂ）としては、下記原料から重縮合した共重合ポリエステルＡ（融点２５０℃、ビカット軟化点１６５℃、液晶開始温度２１５℃、溶融粘度１０Ｐａ・秒）を用いた。
【００７６】

該ポリエチレンテレフタレート８０重量％、共重合ポリエステルＡ２０．０重量％を乾燥した後、二軸混練機で溶融混練し、共重合ポリエステルＡを約１μｍのサイズに微分散させたマスターチップを作成した。次いで該ポリエチレンテレフタレート５０．０重量％、上記共重合ポリエステルＡの２０％マスターチップ５０．０重量％を乾燥し、該混合体を長さと直径の比が２８のバリアフライトスクリューを備えた１５０ｍｍ単軸押出機に供給し、２８５℃にて、スクリュー剪断速度１００秒ー１で溶融混合計量させた後、繊維焼結ステンレス金属フィルター（５μｍカット）内を剪断速度１０秒ー１で通過させた後、Ｔダイ内部のポリマー温度を２４０℃に設定して、口金ランド長が３０ｍｍのＴダイを用いて、ドラフト比１０でシート状に押出成形し、２５℃に保たれた冷却ドラムに静電荷を印加させながら密着冷却固化した。尚、この時のポリマーの冷却速度はエアーチャンバーを使用して３００℃／秒にコントロールした。続いて、該キャストフィルムを長手方向にロール式延伸機にて９５℃で４倍延伸した後、テンターに導入し、９５℃で４倍延伸後、一旦６０℃に冷却した後、２３０℃で熱固定して、厚さ２５μｍの二軸配向ポリエステルフィルムを得た。かくして得られたフィル中での共重合ポリエステルＡのモルフォロジーを表２に、フィルム特性を表３に示す。共重合ポリエステルの個々の分散ドメインは、表層部で球型または小判型、中央層部で繊維または小判型であり、分散ドメイン全体の形状は、表層で偏球状、中央層で小判状であった。フィルムのＱｃ／Ｑｓは１０であり、高ヤング率を有し、かつ表面易滑性、耐磨耗性に優れた高品質のポリエステルフィルムが得られた。
【００７７】
【表１】

【表２】

【表３】

実施例２〜７、比較例１〜３（表１〜３）
ＰＥＴの固有粘度、共重合ポリエステルＡの添加量、溶融粘度およびキャスト条件（口金内部のポリマー温度、ドラフト比）を変更し、実施例１と同様に製膜し、ポリエステルフィルムを得た。本実施例および比較例では、長手方向の延伸温度、倍率を１１５℃、４．５倍、幅方向の延伸温度・倍率を１３０℃、５．０倍とした。
【００７８】
ＰＥＴの固有粘度を高くすると、中央層でのドメイン配向が高まってＱｃ／Ｑｓの値が大きくなり、実施例１よりも高ヤング率のポリエステルフィルムが得られた（実施例２、３）。また、添加量、共重合ポリエステルＡの溶融粘度、溶融押出温度を変更した場合においても、ＰＥＴの融点以下、降温結晶化開始温度以上で溶融押出を行うと、共重合ポリエステルＡのＱｃ／Ｑｓの値が大きくなり、高ヤング率かつ表面特性に優れたポリエステルフィルムが得られた（実施例４〜７）。
【００７９】
これに対して、ＰＥＴの溶融押出を２９０℃、すなわち通常の押出温度であるＰＥＴの融点以上の温度で行うと、Ｑｃ／Ｑｓが１になり、所望のポリエステルフィルムが得られなかった。キャスト時のドラフト比が小さいと、フィルム表層と中央層共に、共重合ポリエステルＡの分散ドメインが偏球状となり、低いヤング率のフィルムしか得られなかった（比較例１）。また、ＰＥＴの融点以上のポリマー温度でドラフト比を大きくしてキャストすると、共重合ポリエステルＡは、フィルム表層と中央層で共に繊維状の分散ドメインを形成し、フィルムの表面特性が悪化した（比較例２、３）。
【００８０】
実施例８（表１〜３）
非晶性ポリエステル（Ａ）として、固有粘度０．６３（ｄｌ／ｇ）の無粒子系のポリエチレンテレフタレート原料を用いた。ポリマー（Ｂ）としては、下記原料から重縮合した共重合ポリエステルＢ（融点２１０℃、ビカット軟化点１４０℃、液晶開始温度１８５℃、溶融粘度３Ｐａ・秒）を用いた。
【００８１】

該ポリエチレンテレフタレート９８．０重量％、共重合ポリエステルＢ２．０重量％を乾燥し、該混合体を長さと直径の比が２８、スクリュー先端にミキシング部を有するバリアフライトスクリューを備えた１５０ｍｍ単軸押出機に供給し、２８５℃にて、スクリュー剪断速度１００秒ー１で溶融混合計量させた後、繊維焼結ステンレス金属フィルター（１μｍカット）内を剪断速度１０秒ー１で通過させた後、ランド長３０ｍｍのＴダイを用いて、ポリマー温度２４０℃、ドラフト比１０でシート状に押出成形し、２５℃に保たれた冷却ドラムに静電荷を印加させながら密着冷却固化した。尚、この時のポリマーの冷却速度はエアーチャンバーを使用して３００℃／秒にコントロールした。その後、実施例１同様に、逐次二軸延伸および熱処理を施して、二軸配向ポリエステルフィルムを得た。共重合ポリエステルＢは前記実施例で使用した共重合ポリエステルＡよりも微分散性が良好であり、かくして得られたフィルムは、高ヤング率でかつ表面易滑性と耐磨耗性を有した高品質のポリエステルフィルムであった。
【００８２】
実施例９〜１１、比較例４、５（表１、３）
ＰＥＴの固有粘度、共重合ポリエステルＢの添加量、押出キャスト条件（ポリマー温度、ドラフト比）を変更し、実施例８と同様に製膜して、ポリエステルフィルムを得た。本実施例および比較例では、長手方向の延伸温度、倍率を１１５℃、４．５倍、幅方向の延伸温度・倍率を１３０℃、５．０倍とした。実施例１〜３で見られた高分子量化による傾向は、共重合ポリエステルＢを用いた場合においても同様であった。固有粘度が１．０および１．４という、より高い固有粘度のＰＥＴを使用すると、共重合ポリエステルＢの分散ドメインはより小さくなり、ポリエステルフィルムのヤング率が向上した（実施例９、１０）。また、共重合ポリエステルＢの添加量を０．５重量％に少なくすると、フィルムのヤング率は幾分小さくなったが、この場合においても、表面特性に優れた高品質のポリエステルフィルムが得られた（実施例１１）。
【００８３】
一方、溶融押出時のポリマー温度をＰＥＴの融点以上に設定すると、共重合ポリエステルＢのアスペクト比の比率Ｑｃ／Ｑｓが１となり、本発明のフィルムが得られなかった。分散性良好な共重合ポリエステルＢを使用しているため、表面粗さの小さいフィルムが得られたが、ヤング率が小さく、表面特性も不良であった（比較例４、５）。
【００８４】
実施例１２、１３
非液晶性ポリエステル（Ａ）として、固有粘度０．６２のポリエチレンー２、６ーナフタレート（ＰＥＮ：融点２６２℃）を使用して、実施例１または８と同様の方法で製膜し二軸延伸ポリエステルフィルムを得た。本実施例では、長手方向の延伸温度、倍率を１３５℃、５．０倍、幅方向の延伸温度・倍率を１４０℃、５．０倍とした。かくして得られたフィルムでは、共重合ポリエステルＡまたはＢの分散ドメインが実施例１、８のＰＥＴフィルムよりも小さくなった。また、フィルム表層と中央層における分散ドメインのアスペクト比の比率Ｑｃ／Ｑｓが大きくなり、高ヤング率でかつ優れた表面特性を有するポリエステルフィルムが得られた。
【００８５】
【発明の効果】
本発明は、非液晶性ポリエステル（Ａ）と該非液晶性ポリエステル（Ａ）と相分離構造を形成するポリマー（Ｂ）からなるポリエステルフィルムにおいて、フィルム表層と中央層における該ポリマー（Ｂ）の分散ドメインの形状を制御し、フィルムの剛性、表面易滑性、耐磨耗性を改良して品質向上を図るものであり、磁気記録用、電気絶縁用、感熱転写リボン用、感熱孔版印刷用、包装用など各種フィルム用途に広く活用が可能である。
【図面の簡単な説明】
【図１】フィルム断面のＴＥＭ写真の模式図であり、ポリマー（Ｂ）の各ドメインに濃淡があり、個々の分散ドメインの形にもむらがある場合を例示した。非液晶性ポリエステル（Ａ）は図中の白色部、ポリマー（Ｂ）は相分離している分散ドメインに対応する。
【図２】フィルム面に平行な切断面に現れるポリマー（Ｂ）の分散ドメインの模式図であり、非液晶性ポリエステル（Ａ）との境界が幅を有すると認められる場合を例示した。
【符号の説明】
Ｌｓ‥‥境界の幅の半分の長さ
ｌｅ‥‥分散ドメインのフィルムの長手方向の最大長さ
ｌｆ‥‥分散ドメインのフィルムの幅方向の最大長さ[0001]
BACKGROUND OF THE INVENTION
The present invention is a polyester film that has greatly improved the physical properties and quality of a conventional polyester film, specifically excellent in rigidity, toughness, slipperiness, abrasion resistance, transparency, electrical properties, and the like. The present invention relates to a polyester film having a low oligomer content and a pyrolytic gelled product content and a method for producing the same.
[0002]
[Prior art]
In recent years, a method of polymer blending has been frequently studied as a method for improving the quality and physical properties of a polyester film. In particular, studies on blends of liquid crystalline polyesters and non-liquid crystalline polyesters are active worldwide, including Japanese Patent Publication No. 3-45104, International Publication No. WO87-05919, Japanese Publication No. 7-37577, Many inventions represented by Japanese Utility Model Publication No. 57-25354 have been made. Since the liquid crystalline polyester generally has a high Young's modulus, the polyester film can be reinforced and strengthened by being finely dispersed in the polyester film. As another utilization method, there is a method utilizing the high fluidity of liquid crystalline polyester. The liquid crystalline polyester has the effect of improving the fluidity of the polymer and suppressing the shearing heat generated in the extrusion process, so it is possible to improve the quality of the polyester film by reducing the pyrolysis gel and oligomers in the polyester film. It is effective in.
[0003]
It has been reported in Japanese Patent Publication No. 7-37577 that the Young's modulus is remarkably improved if the liquid crystalline polyester is present in a fibrous form. However, when the liquid crystalline polyester has a fiber form in the film as described above, the Young's modulus in the orientation direction of the fiber is improved, but surface characteristics such as surface slipperiness and wear resistance are deteriorated. There was a problem. In addition, when a conventional liquid crystalline polyester is added to and blended with a non-liquid crystalline polyester, the dispersion diameter of the liquid crystalline polyester in the polyester film is as large as or larger than the wavelength of visible light (400 to 900 nm). There was a problem that the transparency of the film deteriorated. In particular, when the average dispersion diameter of the liquid crystalline polyester is large and is 1 μm or more, the shape of each dispersion domain of the liquid crystalline polymer is any of spherical, oblate, fiber, layer, oval, etc. Even so, the surface characteristics and transparency of the film were significantly reduced.
[0004]
Of course, the above-mentioned problems of deterioration of the surface properties and transparency are more pronounced when the content of liquid crystalline polyester in the polyester film is increased for the purpose of enhancing the Young's modulus and other qualities. A polyester film satisfying both the rate and the surface characteristics could not be obtained. When developing into applications where surface characteristics are a problem, such as applications for base films for magnetic tapes, a polymer layer having excellent surface characteristics had to be laminated on a polyester film containing liquid crystalline polyester.
[0005]
In the above description, an example in which a liquid crystalline polyester is used as a polymer blended with the non-liquid crystalline polyester has been described, but a phase separation structure is formed with the non-liquid crystalline polyester such as polyolefin, polystyrene, and polycarbonate. Even when other polymers are blended, it seems that there is a similar problem in terms of a change in required characteristics due to the shape of the dispersion domain. In order to obtain a high-quality polyester film by a polymer blending technique, further improvement techniques are currently required.
[0006]
[Problems to be solved by the invention]
The object of the present invention is to solve the above-mentioned problems of the prior art, high quality polyester film with excellent mechanical properties, surface slipperiness, abrasion resistance, transparency, electrical properties and few surface defects / oligomers And to obtain a manufacturing method thereof.
[0007]
[Means for Solving the Problems]
In the polyester film comprising the non-liquid crystalline polyester (A) and the polymer (B) forming a phase separation structure in the non-liquid crystalline polyester (A), the polymer (B ) Was studied intensively for controlling the domain shape of the polyester film and improving the physical properties and quality of the polyester film. As a result, in the non-liquid crystalline polyester (A), the aspect ratio L / D (= Qs) of the average major axis L and the average minor axis D of the dispersion domain in the film surface layer part of the polymer (B) is set to L in the film central layer part. It has been found that by making it smaller than / D (= Qc), a film having a high Young's modulus and excellent in surface slipperiness and abrasion resistance can be obtained.
[0008]
Further, as a method for producing the film, in order to make Qs of the dispersion domain of the polymer (B) smaller than Qc, a resin composition comprising the non-liquid crystalline polyester (A) and the polymer (B) is used. (A) After melt extrusion molding under a temperature condition not lower than the melting point and not higher than the crystallization start temperature at the time of temperature decrease, the film is stretched at a magnification of 3 to 10 times in the longitudinal direction and 3 to 10 times in the width direction, and then 150 ° C. As described above, the present inventors have found that a method of heat-setting at a temperature lower than the melting point of the non-liquid crystalline polyester (A) is effective, and have completed the present invention. That is, the present invention is characterized in that "the aspect ratio L / D of the dispersion domain of the polymer (B) forming a phase separation structure in the non-liquid crystalline polyester (A) is smaller in the surface layer than in the film central layer. "The polyester film and its manufacturing method".
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Representative examples of the non-liquid crystalline polyester (A) used in the present invention include polyethylene terephthalate, polybutylene terephthalate, polyhexamethylene terephthalate, polyethylene naphthalate, polycyclohexanedimethylene terephthalate, and copolymers thereof. Can be mentioned. Of course, a polyester having an ether component in the main chain, for example, a copolymer of diethylene glycol, triethylene glycol, polyethylene glycol, polytetramethylene glycol, or the like may be used. In the present invention, polyethylene terephthalate and polyethylene naphthalate having an intrinsic viscosity of 0.6 or more, preferably 0.8 or more, and more preferably 1.0 or more are preferable. When the intrinsic viscosity of the non-liquid crystalline polyester (A) is large, (1) the polymer (B) that forms a phase separation structure in the liquid crystalline polyester is finely dispersed to a size below the wavelength of visible light (400 to 900 nm). It is easy to obtain a surface with excellent slipperiness and wear resistance. (2) The L / D of the dispersion domain of the polymer (B) tends to be larger in the center layer than in the surface layer, the Young's modulus of the polyester film, It is preferable because toughness is easily improved. As a means for obtaining such a non-liquid crystalline polyester having a high intrinsic viscosity, a solid phase polymerization method is most preferably used. The melting point of the non-liquid crystalline polyester (A) is equal to or higher than that of the polymer (B), and the dispersion domain L / D of the polymer (B) in the non-liquid crystalline polyester (A) is higher than that of the surface layer. The center layer is preferable because it tends to be large.
[0010]
In general, a polymer is a molecule having a very large molecular weight, and the molecular weight of a polymer that is usually handled is 10,000 to several million. However, in the present invention, the molecular weight is not limited to this range. Small molecules having a molecular weight of 10,000 or less are also included in the range of the polymer (B) of the present invention. In the present invention, since a melt-formable polymer is handled, whether or not the dispersion domain that is phase-separated in the non-liquid crystalline polyester is a polymer is determined in the state of the cast film obtained by remelting the film and the film. If the shape changes, it can be determined to be a polymer. The polymer (B) used in the present invention may be a homopolymer or a copolymer as long as it is melt moldable and forms a phase separation structure in the non-liquid crystalline polyester (A). The copolymer can be any polymer of alternating, block, random copolymer and mixtures thereof. Polyester, polyimide, polyesterimide, polyesteramide, polyarylate, polycarbonate, polystyrene, polyolefin, and polyvinyl polymers generally used in polyester polymer blends can be suitably used. .
[0011]
In the present invention, a polymer having a Vicat softening temperature (TB) that is at least 20 ° C. lower than the melting point of the non-liquid crystalline polyester (A) is preferable. Such a polymer tends to increase the aspect ratio Qc / Qs of the dispersed domains in the film surface layer and the center layer, and is suitable for obtaining the polyester film disclosed in the present invention. More preferably, the range of TB of the polymer (B) is a melting point of the non-liquid crystalline polyester (A) of −30 ° C. or lower, a melting point of −200 ° C. or higher, particularly preferably a melting point of the non-liquid crystalline polyester (A) of −40 ° C. or lower. The melting point is -120 ° C or higher. Non-liquid crystalline polyester (A) having a melting point of less than -200 ° C, the polymer has a large dispersion domain L / D even on the surface of the film, leading to deterioration of the surface properties of the film, and sticking with an extrusion hopper, etc. It is not preferable because of the handling problem.
[0012]
The polymer (B) of the present invention is preferably a polymer having a rigid site in the main chain, such as a copolymer polyester, a copolymer polyester amide, or a polyester imide containing a mesogenic group (liquid crystalline structural unit) in the main chain. A polymer containing an imide ring in the main chain is preferred. The mesogenic group-containing copolymer polyester and copolymer polyester amide may be liquid crystalline or non-liquid crystalline. In the present invention, a polymer having a domain structure due to density unevenness inside the polymer, for example, a copolymer having a microphase separation structure, such as an AB alternating layer, is particularly preferable as the polymer (B). The polymer (B) having such a microphase-separated structure is preferable because it is easily finely dispersed in the non-liquid crystalline polyester and the ratio Qc / Qs of the aspect ratio of the dispersed domain tends to increase. Specific examples of the copolyester and polyesteramide include JP-A-3-47861. Specific examples of the polymer or oligomer having an imide ring in the main chain include JP-A-8-157642, JP-A-8-157596, JP-A-8-225741, and JP-A-2558339. . The most preferred polymer (B) is a copolyester comprising a structural unit selected from an aromatic oxycarbonyl unit, an aromatic dioxy unit, an aromatic dicarbonyl unit, an alkylenedioxy unit, and the like. (I), (II), (III) and a copolymerized polyester comprising the structural units of (IV), (I), (III) and a copolymerized polyester comprising the structural units of (IV), (I), ( Examples thereof include one or more selected from polyesters comprising the structural units of II) and (IV).
[0013]
[Formula 4]

(However, R1 in the formula is
[Chemical formula 5]

R2 is
[Chemical 6]

One or more groups selected from R3,
[Chemical 7]

One or more groups selected from In the formula, X represents a hydrogen atom or a chlorine atom, and the structural unit [((II) + (III)] and the structural unit (IV) are substantially equimolar.)
The structural unit (I) is a polyester structural unit formed from p-hydroxybenzoic acid and / or 6-hydroxy-2-naphthoic acid, and the structural unit (II) is 4,4′-dihydroxybiphenyl, 3,3 ′, 5'-tetramethyl-4,4'-dihydroxybiphenyl, hydroquinone, t-butylhydroquinone, phenylhydroquinone, 2,6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, 2,2'-bis (4-hydroxyphenyl) A structural unit generated from an aromatic dihydroxy compound selected from propane and 4,4′-dihydroxydiphenyl ether, a structural unit (III) is a structural unit generated from ethylene glycol, and a structural unit (IV) is terephthalic acid, isophthalic acid. Acid, 4,4'-diphenyldicarboxylic acid, 2,6-na Selected from phthalenedicarboxylic acid, 1,2-bis (phenoxy) ethane-4,4'-dicarboxylic acid, 1,2-bis (2-chlorophenoxy) ethane-4,4'-dicarboxylic acid and 4,4'-diphenyl ether dicarboxylic acid Each structural unit generated from an aromatic dicarboxylic acid is shown.
[0014]
In the case of the copolyester comprising the structural units (I), (II) and (IV), R1 is
[Chemical 8]

And R2 is
[Chemical 9]

One or more selected from R3 is
[Chemical Formula 10]

One or more selected from the above is preferred.
[0015]
In the case of a copolyester comprising the structural units (I), (III) and (IV), R1 is
Embedded image

And R3 is
Embedded image

Are particularly preferred.
[0016]
In the case of the copolymer polyester comprising the structural units (I), (II), (III) and (IV), R1 is
Embedded image

And R2 is
Embedded image

And R3 is
Embedded image

Are particularly preferred.
[0017]
In the present invention, the copolymerization amount is calculated from the molar ratio of repeating structural units capable of forming a polymer, and is expressed in mol%. In the case of the above preferred copolyester, the structural unit (I), the structural unit (II) + (IV), and the structural unit (III) + (IV) are repeating structural units capable of forming a polymer. The amount of copolymerization can be calculated from the polymerization molar ratio.
[0018]
Copolymerization molar ratio of structural units (I), (II) + (IV), (III) + (IV) is arbitrary, but fine dispersion in non-liquid crystalline polyester, control of dispersion domain, Young's modulus From the point of improvement of this, the copolymerization amount of a mesogen group is 5-95 mol%, Preferably it is 20-80 mol%. When the copolymerization amount of structural units (I) and (II) + (IV) that are mesogenic groups is lower than 5 mol%, it is difficult to obtain an effect of improving Young's modulus and an effect of suppressing shearing heat generation in the extrusion process. If it is higher than 95 mol%, the dispersibility is lowered, and the surface of the polyester film becomes very rough.
[0019]
In the case of a copolyester comprising the structural units (I), (II), (III) and (IV), [(I) + () with respect to the structural units [(I) + (II) + (III)] II)] is 5 to 95 mol%, more preferably 20 to 80%, and most preferably 40 to 75 mol%. Moreover, the molar fraction of (III) with respect to structural unit [(I) + (II) + (III)] is 95-5 mol%, 80-20 mol% is more preferable, 60-25 mol% is the most. preferable. The molar ratio of the structural units (I) / (II) is preferably 75/25 to 95/5, more preferably 78/22 to 93/7, from the viewpoint of fluidity. The number of moles of the structural unit (IV) is substantially equal to the total number of moles of the structural unit [(II) + (III)].
[0020]
In the case of a copolymer polyester comprising the structural units (I), (III) and (IV), the structural unit (I) is preferably 5 to 95 mol% of [(I) + (III)] 20-80 mol% is more preferable, and 40-75 mol% is the most preferable. The structural unit (IV) is substantially equimolar with the structural unit (III).
[0021]
Further, in the case of the copolymer polyester comprising the structural units (I), (II) and (IV), the copolymer polyester comprising the structural units (I), (II), (III) and (IV), not a single unit. Or / and it is preferably used as a blend polymer of a copolyester comprising the structural units (I), (III) and (IV). Also in the case of this blend polymer, the molar fraction of [(I) + (II)] relative to the structural unit [(I) + (II) + (III)] is preferably 5 to 95 mol%, as described above. 20 to 80% is more preferable, and 40 to 75 mol% is most preferable.
[0022]
The term “substantially” in the above description means that the terminal group of the polyester can be increased in either the carboxyl group terminal or the hydroxyl terminal group as required. The number of moles of the unit (IV) is not completely equal to the total number of moles of the structural unit [(II) + (III)].
[0023]
In the polycondensation of the above preferred copolyester, in addition to the components constituting the structural units (I) to (IV), a fragrance such as 3,3′-diphenyldicarboxylic acid, 2,2′-diphenyldicarboxylic acid, etc. Aliphatic dicarboxylic acids such as aliphatic dicarboxylic acids, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, alicyclic dicarboxylic acids such as hexahydroterephthalic acid, chlorohydroquinone, methylhydroquinone, 4,4′-dihydroxydiphenylsulfone, Aromatic diols such as 4,4'-dihydroxydiphenyl sulfide, 4,4'-dihydroxybenzophenone, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanediol, 1,4-cyclohexane Aliphatic and alicyclic dimers such as dimethanol And hydroxyhydroxy acids such as 2,6-hydroxynaphthoic acid and p-aminophenol, p-aminobenzoic acid and the like are further added in a small proportion within a range not impairing the object of the present invention. It can be polymerized.
[0024]
The method for producing the copolyester in the present invention is not particularly limited, and can be produced according to a known polyester polycondensation method.
[0025]
For example, in the above-mentioned method for producing a copolyester that is preferably used, when the structural unit (III) is not included, the following (1) and (2) are produced, and when the structural unit (III) is contained, the production of the following (3) is produced. The method is preferred.
[0026]
(1) Deacetic acid polycondensation reaction from p-acetoxybenzoic acid and diacylated products of aromatic dihydroxy compounds such as 4,4'-diacetoxybiphenyl and 4,4'-diacetoxybenzene and aromatic dicarboxylic acids such as terephthalic acid How to manufacture.
[0027]
(2) Acetic anhydride is reacted with p-hydroxybenzoic acid, aromatic dihydroxy compounds such as 4,4′-dihydroxybiphenyl and hydroquinone, and aromatic dicarboxylic acids such as terephthalic acid to acylate the phenolic hydroxyl group, and then dehydrated. A method of producing by an acetic acid polycondensation reaction.
[0028]
(3) In the presence of a polyester polymer such as polyethylene terephthalate, an oligomer, or a bis (β-hydroxyethyl) ester of an aromatic dicarboxylic acid such as bis (β-hydroxyethyl) terephthalate, by the method of (1) or (2) How to manufacture.
[0029]
Although these polycondensation reactions proceed even without a catalyst, it may be preferable to add a metal compound such as stannous acetate, tetrabutyl titanate, potassium acetate and sodium acetate, antimony trioxide, and metal magnesium.
[0030]
In the present invention, the low viscosity polymer (B), that is, a polymer that forms a phase separation structure when blended with the melt viscosity ratio (melt viscosity (ηA) of non-liquid crystalline polyester (A) / non-liquid crystalline polyester (A)). A polymer (B) that increases the melt viscosity (ηB) of (B) is preferred. This is because the object of the present invention can be achieved more effectively as the low viscosity polymer is added to the non-liquid crystalline polyester. The melt viscosity ratio is desirably at least 5 or more, more preferably 10 or more, more preferably 50 or more, and particularly preferably 200 or more. According to the knowledge of the present inventors, 200 to 100,000 is most preferable. Therefore, the melt viscosity of the polymer (B) depends on the melt viscosity of the non-liquid crystalline polyester used, but is 100 Pa under the conditions of the melting point of the non-liquid crystalline polyester constituting the matrix + 15 ° C. and the shear rate of 100 seconds−1. It is desirable that it is about 2 seconds or less, preferably 10 Pa · second or less, more preferably 1 Pa · second or less. Copolyesters having such a low melt viscosity and particularly suitable for achieving the object of the present invention are the structural units (I), (II), (III) and (IV) described above. Is a copolyester. This copolyester is particularly effective in improving the quality of the polyester film because the ratio Qc / Qs of the aspect ratio of the dispersion domain tends to increase.
[0031]
The addition amount of the polymer (B) is not particularly limited as long as it is an appropriate amount that can achieve the object of the present invention, but is 0.01 to 40% by weight of the total polymer, preferably 0.05 to 20% by weight, more preferably A range of 0.1 to 5% by weight is preferable. If the addition amount is less than 0.01% by weight, or conversely exceeds 40% by weight, it is difficult to obtain the effects of the present invention, which is not preferable.
[0032]
As shown in FIG. 1, the surface layer of the film in the present invention is a portion having a depth of T / 8 from the film surface in a polyester film having a thickness T, and the central layer of the film is a center having a thickness of T / 2. Part. In the non-liquid crystalline polyester (A), the individual dispersion domains of the polymer (B) are spherical, oblate, fiber, oval, etc., but are determined from the structure of the entire film. The surface layer portion is preferably oval, oblate, or spherical, and the center layer is preferably oval, fibrous, or layered. The aspect ratio Qc / Qs between the surface layer and the central layer of the dispersion domain of the polymer (B) is preferably 2 or more and 300 or less, more preferably 5 or more and 150 or less, and most preferably 10 or more and 100 or less. is there. If the aspect ratio Qc / Qs of the dispersion domain of the polymer (B) is less than 2 or if Qc / Qs exceeds 300, it is difficult to achieve both high Young's modulus, surface slipperiness and wear resistance. Become.
[0033]
The L / D of the dispersion domain of the polymer (B) is determined from the structure of the entire film, and the average shape of the dispersion domain of the polymer (B) contained in each layer of the film surface layer or the central layer is The geometric index shown. The average major axis L and the average minor axis D in the present invention can be obtained from the following formulas (1) and (2).
[0034]
L = max [I, J, K] (1)
D = (I + J + KL) / 2 (2)
Here, I, J, and K correspond to the average value of the maximum length in the longitudinal direction, the width direction, and the thickness direction of the film of the domain of the polymer (B). max [I, J, K] is a function that compares the lengths of I, J, and K and selects the largest value. In addition, I, J, and K are measured using a transmission electron microscope as described later, and are calculated using 100 dispersion domains. Moreover, in this invention, the average value of I, J, and K is called the average dispersion diameter of the domain which consists of a polymer (B). As will be described later, I, J, and K are measured using a transmission electron microscope, and are calculated by randomly using 100 dispersed domains in the surface layer and the central layer.
[0035]
The oval shape referred to in the present invention is a shape in which the shape indexes I, J, and K calculated from a plurality of dispersion domains made of the polymer (B) satisfy the following relationships (3) and (4).
[0036]
0.02 <(I / J) <50 (3)
K <(1/2) · S [I, J] (4)
Here, S is a function that compares the lengths of I and J and selects the shorter value. When I> J, S [I, J] is J, and when I <J S [I, J] is I. Further, when I, J, and K are out of the ranges of the formulas (3) and (4), in the present invention, the shape of the dispersion domain existing in the film is expressed as follows.
[0037]
Sphere: I = J = K
Ovality: I / J is 1/3 or more and less than 3, and does not satisfy the formula (4).
[0038]
Fibrous: I / J is less than 1/3 or 3 or more and does not satisfy the formula (4).
[0039]
Layered: Does not satisfy formula (3), but satisfies formula (4).
[0040]
In the present invention, the shape of each distributed domain is also expressed in the same manner as described above, and the shape of a domain that satisfies the expressions (5) and (6) is called an oval type. In the present invention, a plate-type or thin-plate-type dispersion domain in which the dispersion domain appearing on the cut surface parallel to the film surface is a circle, an ellipse, or a part thereof is also included in the oval domain. When the domain shape deviates from the range of the formulas (5) and (6), the domain shape is changed to a spherical, oblate, or fiber type according to the present invention based on the same criteria as the criteria for determining the domain shape. It is expressed as a layer type.
[0041]
0.02 <(i / j) <50 (5)
k <(1/2) · S [i, j] (6)
Here, i, j, and k are the maximum lengths in the longitudinal direction, the width direction, and the thickness direction of the film of each dispersed domain made of the polymer (B).
[0042]
Moreover, in this invention, it is preferable that the aspect ratio Qs in the film surface layer part of the dispersion domain of a polymer (B) is 1-20, More preferably, it is 1-10, Most preferably, it is 1-3. Moreover, it is preferable that the average major axis L of the dispersion domain of the polymer (B) in a film surface layer part is 0.01-3 micrometers, More preferably, it is 0.01-1.0 micrometer, Most preferably, it is 0.02-0. 5 μm. If the aspect ratio Qs of the film surface layer exceeds 20 or the average major axis L of the dispersion domain exceeds 3 μm, the surface characteristics of the film deteriorate, which is not preferable.
[0043]
In the present invention, the sum of the Young's modulus (YMD) in the longitudinal direction (MD) of the film and the Young's modulus (YTD) in the width direction (TD), that is, the total Young's modulus is the rigidity of the polymer (B) and the amount added. Although it depends, it is 8-30 GPa. A more preferable range of the total Young's modulus is 10 to 25 GPa, and a particularly preferable range is 12 to 20 GPa. If the total Young's modulus is less than 8 GPa, the practicality as a film is poor, and if it exceeds 30 GPa, the surface properties of the film tend to deteriorate, which is not preferable.
[0044]
The film according to the present invention has a surface roughness Ra of 0.5 to 100 nm and a dynamic friction coefficient μk of 0.30 or less. A preferable range of the surface roughness Ra is 0.5 to 30 nm, more preferably 1 to 10 nm, and a particularly preferable range is 2 to 7. When the addition amount of the polymer (B) is 0.1 to 5% by weight, and the polymer (B) is finely dispersed in a shape satisfying the above-mentioned formula (3) with a size of an average dispersion diameter of less than 1 μm, particularly for magnetic tape use. It is preferable because it becomes easy to obtain a film having a surface roughness Ra of 1 to 10 nm, which is an essential requirement for a base film for metal / deposition tape. If the surface roughness Ra is less than 0.5 nm, the film slips poorly, so troubles are likely to occur in the film winding process. Conversely, if the surface roughness Ra exceeds 100 nm, the film is used for various films. It is not preferable because problems often occur during deployment.
[0045]
The shape of the dispersed domain of the polymer (B) disclosed in the present invention varies depending on the screw used during melt extrusion. In the present invention, the screw of any shape such as full flight or barrier flight may be used as the screw, but the fine dispersion of the polymer (B) is promoted, and the surface smoothness and abrasion resistance of the film are improved. In order to achieve this, it is preferable to use various mixing-type screws having a screw length / diameter ratio of 20 or more. A mixing type screw is a screw which has a mixing part in a screw compression part, a measurement part, or these intermediate positions, for example, a screw which has a fluidized barrier, a dull image, a unimelt, a multi-row pin etc. is mentioned.
[0046]
The content of the cyclic trimer of the non-liquid crystalline polyester (A) in the polyester film of the present invention is reduced to 0.1 to 1.0% by weight by adding a specific amount of the polymer (B) of the present invention. can do. The content of the cyclic trimer of the non-liquid crystalline polyester (A) in the polyester film depends on the non-liquid crystalline polyester (A) used when producing the polyester film, but the intrinsic viscosity subjected to solid phase polymerization. When an appropriate amount of the polymer (B) having a melt viscosity ratio (ηA / ηB) of 5 or more is added to the high non-liquid crystalline polyester (A), the amount of oligomer increase at the time of melt extrusion is drastically reduced. As a result, the cyclic trimer is contained. A low rate polyester film is obtained. In the reduction of the oligomer amount, the above-described copolymer polyester having a mesogen group in the main chain, copolymer polyester amide, copolymer polyester imide, and low molecular weight thermoplastic polyimide having a number average molecular weight of 1500 to 10,000 are used as the polymer (B). Particularly preferred. A more preferable range of the content of the cyclic trimer is 0.1 to 0.6% by weight, and further preferably 0.1 to 0.4% by weight. The content of the cyclic trimer in the polyester film is less than 0.1% by weight because the cyclic trimer in the raw material chip of the non-liquid crystalline polyester (A) is usually 0.1% by weight or more. ,very difficult.
[0047]
On the other hand, when the content of the cyclic trimer is larger than 1.0% by weight, oligomer contamination during film formation becomes remarkable, which causes problems in film quality and process control. In addition, in the polyester film of this invention, if it is a range which does not inhibit the effect of this invention other than non-liquid crystalline polyester (A) and copolymer polyester (B), non-liquid crystalline polyester (A) and copolymer polyester A compatibilizer, a plasticizer, a weathering agent, an antioxidant, a heat stabilizer, a lubricant, an antistatic agent, a whitening agent, a coloring agent, a conductive agent, etc. may be added. As for the compatibilizer, a compatibilizer having an average refractive index that is an intermediate value between the non-liquid crystalline polyester (A) and the polymer (B) is preferable from the viewpoint of improving the mechanical properties and surface properties of the polyester film.
[0048]
The polyester film of the present invention may be a single film, but may be laminated with another polymer layer such as polyester, polyolefin, polyamide, polyvinylidene chloride, acrylic polymer, etc. on one side. In order to impart easy adhesion and antistatic properties, it is also preferable to provide a coating layer on at least one side.
[0049]
The polyester film of the present invention may be an unstretched or unoriented film, but is preferably a uniaxial or biaxially stretched and heat-set oriented film by a known method. This is because the Young's modulus, surface slipperiness, abrasion resistance, transparency, electrical properties, and the like of the film are significantly improved. In addition, although the thickness of the film made into object by this invention is 0.5-300 micrometers, Preferably it is 1-100 micrometers, More preferably, it is 2-30 micrometers, and 2-10 micrometers is especially preferable for a magnetic tape use.
[0050]
In order to make Qs of the dispersion domain of the polymer (B) smaller than Qc, the resin composition comprising the non-liquid crystalline polyester (A) and the polymer (B) is changed to the following (1), (2), (3) After melt extrusion molding under satisfying conditions, the film is stretched at a magnification of 3 to 10 times in the longitudinal direction and 3 to 10 times in the width direction, and after that, at a temperature of 150 ° C. or higher and lower than the melting point of the non-liquid crystalline polyester (A). It is preferable to heat-set. In the present invention, it is necessary to perform extrusion molding under conditions satisfying at least (1), and it is preferable to combine the conditions (2) and (3) because the target polyester film of the present invention can be obtained more easily.
[0051]
(1) The extrusion molding temperature is set to be not less than the crystallization start temperature when the non-liquid crystalline polyester (A) is cooled and not more than the melting point.
[0052]
(2) Set the draft ratio at casting to 3-50.
[0053]
(3) Use a base with a land part length of 10 to 70 mm.
[0054]
The extrusion temperature is more preferably (non-liquid crystalline polyester (A) (crystallization start temperature at the time of cooling + 2 ° C) or more, (melting point -2 ° C) or less, (crystallization start temperature at the time of cooling + 5 ° C) or more, More preferably (melting point−5 ° C.) or less. When the melt molding temperature exceeds the melting point of the non-liquid crystalline polyester (A), it is difficult to obtain a film having a Qs smaller than Qc, and the crystallization starts when the melt molding temperature is lowered. If the temperature is lower than the temperature, troubles occur due to solidification of the polymer, which is not preferable. In addition, the extrusion molding temperature as used in the field of this invention is the polymer temperature of the center part inside T-die.
[0055]
The draft ratio when extruding into a sheet with a T-die is more preferably 5 to 30, and most preferably 7 to 20. When the draft ratio is less than 3, the copolymerized polyester dispersion domains are both spherical and oblate in the surface layer and the central layer, and the aspect ratios of the film surface layer portion and the central layer portion are not preferable. On the other hand, if the draft ratio exceeds 50, both the surface layer and the central layer are in the form of fibers or layers, and the aspect ratio ratio Qc / Qs between the film surface layer portion and the central layer portion is not preferable. The length of the die land portion of the T die is more preferably 15 to 50 mm, and further preferably 20 to 40 mm. If the length of the base land portion is less than 10 mm, it is difficult to obtain a film having a Qs smaller than Qc, which is an object of the present invention. Further, if the length of the base land portion exceeds 70 mm, it is not preferable because not only the thickness adjustment becomes difficult and the quality of the film is deteriorated, but also a thin film is likely to be broken. The magnitude relationship between the Qc and Qs of the dispersion domain made of the polymer (B) is also affected by the cooling rate of the molten polymer, so it is important to set these to preferable conditions described later.
[0056]
Next, although the method for producing the polyester film of the present invention will be described, it goes without saying that the present invention is not limited to such examples.
[0057]
Here, polyethylene terephthalate is used as the non-liquid crystalline polyester (A), and a copolymer polyester of 60 mol% p-hydroxybenzoic acid and 40 mol% polyethylene terephthalate is used as the polymer (B) that forms a phase separation structure with the non-liquid crystalline polyester (A). Although the used example is shown, manufacturing conditions differ with polyester to be used. Bis-β-hydroxyethyl terephthalate (BHT) is obtained by esterification from terephthalic acid and ethylene glycol or transesterification of dimethyl terephthalate and ethylene glycol according to a conventional method. Next, while transferring this BHT to the polymerization tank, the polymerization reaction is advanced by heating to 280 ° C. under vacuum. Here, a polyester having an intrinsic viscosity of about 0.5 is obtained. The obtained polyester is solid-state polymerized in a pellet form under reduced pressure. In the case of solid-phase polymerization, after preliminarily crystallizing at a temperature of 180 ° C. or less in advance, solid-phase polymerization is performed at 190 to 250 ° C. under a reduced pressure of about 1 mmHg for 10 to 50 hours. The degree of polymerization is increased so as to be 5 times or more.
[0058]
Next, a raw material obtained by dry blending the high-viscosity polyethylene terephthalate and the copolyester, a master raw material obtained by once melting and kneading these to finely disperse the copolyester, and further, a recovered raw material for the film of the present invention alone. Alternatively, the raw material obtained by appropriately mixing the above two or three kinds of raw materials is vacuum-dried at 180 ° C. for 3 hours or more, and then heated to 280 ° C. in a nitrogen stream or under vacuum so that the intrinsic viscosity does not decrease. The film is supplied to a screw or twin screw extruder and formed into a film by various methods. At this time, the screw shear rate (= πDN / h, D: screw diameter, N: screw rotation speed, h: groove depth of screw metering section) of the extruder is set to 20 seconds-1 or more. The screw shear rate is more preferably 50 seconds-1 or more. However, if the screw shear rate is increased to 300 seconds-1 or more, the polymer is pyrolytically gelled or the amount of oligomers is increased by shearing heat generation, which is not preferable. When the polymer temperature inside the die, draft ratio, and land length of the die are set to the conditions shown in the above (1) to (3), the L / D of the dispersed domain of the copolyester is larger than the central layer portion. It is preferable because it tends to be small. Here, the cooling rate of the polymer at the time of casting is preferably a cooling rate of 150 ° C./second or more, and the film can be directly cooled with air or water to control the cooling rate of the film suitably. Cooling the film surface layer earlier than the film center layer is preferable because Qc / Qs of the dispersion domain of the copolyester increases.
[0059]
In the melt extrusion, it is preferable to use various types of filters such as sintered metal, porous ceramics, sand, and wire mesh in order to remove foreign substances. At this time, the shear rate at the time of passing through the filter is as low as 10 seconds-1 or less, and the pressure at the time of passing through the filtration increases only with the non-liquid crystalline polyester (A) having a high intrinsic viscosity. By adding the polymerized polyester, the pressure during filtration is easily lowered to a practical range. When the pressure at the time of filtration is not sufficiently reduced only by the addition of the copolyester, it is preferable to use a known low-pressure loss type filter.
[0060]
Thereafter, the sheet-like cast film is heated with a heating roll group of 80 to 180 ° C., stretched in the vertical direction 3 to 10 times in one or more stages, and cooled with a cooling roll group of 20 to 50 ° C. To do. Subsequently, the film was guided to a known tenter and heated in a hot air atmosphere heated to 80 to 180 ° C. while holding both ends of the film with clips, and 1 or 2 or more stages in the horizontal direction 3 to 10 times. Stretch in multiple stages. Subsequently, the film is heat-set at a temperature of 150 ° C. or higher and lower than the melting point of polyethylene terephthalate. The heat setting may be performed under tension or under a fine stretch of 1.05 to 1.5, and in order to further improve the thermal dimensional stability, relaxation in the longitudinal or / and width direction is also preferably performed. Further, if necessary, before the heat setting, re-longitudinal stretching and / or re-lateral stretching can be performed.
[0061]
[Methods for measuring physical properties and methods for evaluating effects]
(1) Intrinsic viscosity
It is a value measured at a concentration of 0.1 g / ml in orthochlorophenol at 25 ° C. The unit is indicated by [dl / g].
[0062]
(2) Melt viscosity
Using a high and low flow tester, the value was measured at 280 ° C. and a shear rate of 100 seconds−1. The unit is represented by [Pa · second].
[0063]
(3) Melting point, temperature drop crystallization start temperature
It was measured using DSC (differential scanning calorimeter) type II manufactured by PerkinElmer. 10 mg of a sample is set in a DSC apparatus, melted at a temperature of 300 ° C. for 5 minutes, and then rapidly cooled in liquid nitrogen. The sample was heated at 10 ° C./min, and after detecting the glass transition point and the cold crystallization temperature, the temperature was further increased and the endothermic peak temperature based on crystal melting was defined as the melting point Tm. In addition, the temperature was lowered at a rate of 10 ° C./min from the 300 ° C. melt state, the temperature at which crystallization started and heat generation occurred was defined as the temperature drop crystallization start temperature Tmcs, and the crystallization exothermic peak temperature was taken as the temperature drop crystallization temperature Tmc.
[0064]
(4) Vicat softening temperature
The Vicat softening temperature was measured according to the method described in JIS-K7206.
[0065]
(5) Young's modulus
A sample was set in a Tensilon-type tensile test (Orientec Co., Ltd.) so that the width was 10 mm and the length between chucks was 100 mm, and a tensile test was performed at a tensile rate of 200 mm / min in an atmosphere of 23 ° C. and 65% RH. .
[0066]
(6) Surface roughness Ra
The surface roughness Ra was measured using a high-precision thin film level difference measuring instrument ET-10 manufactured by Kosaka Laboratory. The conditions were as follows, and the value was defined as the average value when measured 20 times by scanning in the film width direction.
[0067]
・ Tip tip radius: 0.5μm
-Stylus load: 5mg
・ Measurement length: 1mm
・ Cutoff value: 0.08mm
The definition of Ra is shown in, for example, Jiro Nara “Measurement / Evaluation Method of Surface Roughness” (General Technology Center, 1983).
[0068]
(7) Abrasion resistance, dynamic friction coefficient
A film slit into a 1/2 inch wide tape is run on a stainless steel guide pin (surface roughness: 100 nm Ra) using a tape running tester (running speed 250 m / min, winding angle 60 °). , Exit side tension 90g, number of travels once). At this time, scratches entering the film were observed with a microscope, and it was determined that scratches with a width of 2.5 μm or more were excellent when less than 2 per tape width, good when 2 or more and less than 10 were good, and poor when 10 or more. This wear resistance is preferably excellent, but it can be used practically even if it is good.
[0069]
At this time, the initial μk was determined by the following equation.
[0070]
μk = 2.20 log (90 / T)
Here, T is the tension on the entry side. When this μk was 0.30 or less, it was judged that the slipperiness was good, and when it exceeded 0.30, the slipperiness was poor. This μk value of 0.30 is a critical point as to whether or not troubles due to slipperiness occur in a processing process such as a printing process.
[0071]
(8) Shape index I, J, K of dispersion domain of polymer (B), average major axis L, average minor axis D, aspect ratio Qs, Qc
Cut the polyester film in (1) a direction parallel to the longitudinal direction and perpendicular to the film surface, (2) a direction parallel to the width direction and perpendicular to the film surface, and (3) a direction parallel to the film surface. The surface is observed with a transmission electron microscope (TEM). The maximum length (la) and the maximum length (lb) in the thickness direction of the domain film of the polymer (B) appearing on the cut surface of (1), and the maximum length (lb) of the polymer (B) appearing on the cut surface of (2) The maximum length (lc) in the thickness direction of the film of the domain, the maximum length (ld) in the width direction, and the maximum length (le) in the longitudinal direction of the domain of the polymer (B) appearing on the cut surface of (3) The maximum length (lf) in the width direction is determined for each of the surface layer and the center layer of the film by direct observation or micrograph. These la, lb, lc, ld, le, and lf were obtained for 100 domains by randomly using distributed domains distributed on the surface layer and the central layer of each cut surface (FIG. 1, FIG. 1). 2). The boundary between the domain forming the phase separation structure and the non-liquid crystalline polyester is determined by the density of the TEM image, and when the boundary portion is recognized to have a width, it can be determined as the non-liquid crystalline polyester or polymer (B). The center position was taken as the boundary (FIG. 2). In addition, when the inside of the domain of the polymer (B) was also shaded due to the microphase separation structure or the like, the boundary was determined with the entire contour of the polymer (B) with respect to the non-liquid crystalline polyester as the boundary.
[0072]
Next, the shape index I, J, K of the dispersion domain of the polymer (B) is obtained. I is (average value of lb + average value of le) / 2, J is (average value of ld + average value of lf) / 2, and K is (average value of la + average value of lc) / 2. The average major axis L and the average minor axis D were determined by the above I, J, K and the above formulas (1) and (2), and the ratio L / D was defined as the aspect ratio. Moreover, the ratio Qc / Qs of the aspect ratio Qs of the film surface layer part and the aspect ratio Qc in the center layer is compared with the Qs of the two surface layer parts on the front and back of the film, and the smaller L / D is adopted as Qs. I asked.
[0073]
Whether or not the dispersion domain is a polymer is determined by comparing the shape index of the dispersion domain of the cast film obtained by melt-extruding the film and the present film again. In the present invention, the dispersion domain is determined to be a polymer when at least one of the shape indices changes by 10% or more.
[0074]
【Example】
The present invention will be described based on examples and comparative examples.
[0075]
Example 1 (Tables 1-3)
As the amorphous polyester (A), a particle-free polyethylene terephthalate raw material having an intrinsic viscosity of 0.63 (dl / g) (melting point: 258 ° C., temperature drop crystallization start temperature: 230 ° C.) was used. As the polymer (B), copolymerized polyester A (melting point: 250 ° C., Vicat softening point: 165 ° C., liquid crystal starting temperature: 215 ° C., melt viscosity: 10 Pa · second) obtained from the following raw materials was used.
[0076]

The polyethylene terephthalate 80% by weight and the copolymerized polyester A 20.0% by weight were dried and then melt-kneaded with a biaxial kneader to prepare a master chip in which the copolymerized polyester A was finely dispersed to a size of about 1 μm. Next, 50.0% by weight of the polyethylene terephthalate, 50.0% by weight of the 20% master chip of the copolyester A were dried, and the mixture was uniaxially provided with a barrier flight screw having a length to diameter ratio of 28. After being fed to an extruder and melt-mixed and metered at 285 ° C. at a screw shear rate of 100 seconds-1 and then passed through a fiber sintered stainless steel filter (5 μm cut) at a shear rate of 10 seconds-1, The polymer temperature inside the T-die is set to 240 ° C, and a die with a die land length of 30mm is used to extrude into a sheet with a draft ratio of 10, and an electrostatic charge is applied to the cooling drum maintained at 25 ° C. The solution was solidified by cooling. The cooling rate of the polymer at this time was controlled to 300 ° C./second using an air chamber. Subsequently, the cast film was stretched 4 times at 95 ° C. in the longitudinal direction by a roll type stretching machine, then introduced into a tenter, stretched 4 times at 95 ° C., once cooled to 60 ° C., and then heated at 230 ° C. The biaxially oriented polyester film having a thickness of 25 μm was obtained by fixing. Table 2 shows the morphology of the copolyester A in the film thus obtained, and Table 3 shows the film properties. The individual dispersion domains of the copolyester were spherical or oval at the surface layer, fiber or oval at the center layer, and the shape of the entire dispersion domain was oblate at the surface and oval at the center layer. . The film had a Qc / Qs of 10, and a high-quality polyester film having a high Young's modulus and excellent surface slipperiness and wear resistance was obtained.
[0077]
[Table 1]

[Table 2]

[Table 3]

Examples 2-7, Comparative Examples 1-3 (Tables 1-3)
The intrinsic viscosity of PET, the addition amount of copolymer polyester A, the melt viscosity, and the casting conditions (polymer temperature inside the die, draft ratio) were changed, and a film was formed in the same manner as in Example 1 to obtain a polyester film. In this example and comparative example, the stretching temperature and magnification in the longitudinal direction were 115 ° C. and 4.5 times, and the stretching temperature and magnification in the width direction were 130 ° C. and 5.0 times.
[0078]
When the intrinsic viscosity of PET was increased, the domain orientation in the central layer was increased and the value of Qc / Qs was increased, and a polyester film having a higher Young's modulus than Example 1 was obtained (Examples 2 and 3). In addition, even when the addition amount, the melt viscosity of the copolyester A, and the melt extrusion temperature are changed, if melt extrusion is performed at a temperature lower than the melting point of PET and at a temperature lowering the crystallization start temperature, the Qc / Qs of the copolyester A The value was increased, and polyester films having high Young's modulus and excellent surface characteristics were obtained (Examples 4 to 7).
[0079]
On the other hand, when melt extrusion of PET was performed at 290 ° C., that is, at a temperature equal to or higher than the melting point of PET, which is a normal extrusion temperature, Qc / Qs was 1, and a desired polyester film could not be obtained. When the draft ratio at the time of casting was small, the dispersion domain of the copolyester A became oblate in both the film surface layer and the center layer, and only a film having a low Young's modulus was obtained (Comparative Example 1). Moreover, when the draft ratio was increased at a polymer temperature equal to or higher than the melting point of PET, the copolyester A formed a fibrous dispersion domain in both the film surface layer and the center layer, and the surface characteristics of the film deteriorated (comparison) Example 2, 3).
[0080]
Example 8 (Tables 1-3)
As the amorphous polyester (A), a particle-free polyethylene terephthalate raw material having an intrinsic viscosity of 0.63 (dl / g) was used. As the polymer (B), copolymerized polyester B (melting point: 210 ° C., Vicat softening point: 140 ° C., liquid crystal starting temperature: 185 ° C., melt viscosity: 3 Pa · second) obtained from the following raw materials was used.
[0081]

The polyethylene terephthalate 98.0% by weight and the copolyester B 2.0% by weight are dried, and the mixture has a length-to-diameter ratio of 28 and a 150 mm single screw extrusion equipped with a barrier flight screw having a mixing part at the screw tip. After being melt-mixed and metered at a screw shear rate of 100 seconds-1 at 285 ° C., it was passed through a fiber sintered stainless steel filter (1 μm cut) at a shear rate of 10 seconds-1 and then landed. Using a T-die having a length of 30 mm, it was extruded into a sheet shape at a polymer temperature of 240 ° C. and a draft ratio of 10, and was closely cooled and solidified while applying an electrostatic charge to a cooling drum maintained at 25 ° C. The cooling rate of the polymer at this time was controlled to 300 ° C./second using an air chamber. Thereafter, as in Example 1, biaxial stretching and heat treatment were sequentially performed to obtain a biaxially oriented polyester film. Copolyester B has better fine dispersion than the copolyester A used in the above examples, and the film thus obtained has a high Young's modulus, high surface slipperiness and wear resistance. It was a quality polyester film.
[0082]
Examples 9 to 11, Comparative Examples 4 and 5 (Tables 1 and 3)
A polyester film was obtained by changing the intrinsic viscosity of PET, the amount of copolymerized polyester B added, and extrusion casting conditions (polymer temperature, draft ratio), and in the same manner as in Example 8. In this example and comparative example, the stretching temperature and magnification in the longitudinal direction were 115 ° C. and 4.5 times, and the stretching temperature and magnification in the width direction were 130 ° C. and 5.0 times. The tendency by high molecular weight seen in Examples 1-3 was the same also when the copolyester B was used. When higher intrinsic viscosity PET with intrinsic viscosity of 1.0 and 1.4 was used, the dispersion domain of copolymer polyester B became smaller and the Young's modulus of the polyester film was improved (Examples 9 and 10). Further, when the addition amount of the copolyester B was reduced to 0.5% by weight, the Young's modulus of the film was somewhat reduced, but even in this case, a high-quality polyester film having excellent surface characteristics was obtained. (Example 11).
[0083]
On the other hand, when the polymer temperature at the time of melt extrusion was set to be equal to or higher than the melting point of PET, the aspect ratio Qc / Qs of the copolyester B was 1, and the film of the present invention could not be obtained. Since copolyester B having good dispersibility was used, a film having a small surface roughness was obtained, but the Young's modulus was small and the surface characteristics were poor (Comparative Examples 4 and 5).
[0084]
Examples 12 and 13
Biaxially stretched polyester film formed by the same method as in Example 1 or 8 using polyethylene-2,6-naphthalate (PEN: melting point 262 ° C.) having an intrinsic viscosity of 0.62 as the non-liquid crystalline polyester (A). A film was obtained. In this example, the stretching temperature and magnification in the longitudinal direction were 135 ° C. and 5.0 times, and the stretching temperature and magnification in the width direction were 140 ° C. and 5.0 times. In the film thus obtained, the dispersion domain of the copolyester A or B was smaller than that of the PET films of Examples 1 and 8. Moreover, the ratio Qc / Qs of the aspect ratio of the dispersed domains in the film surface layer and the central layer was increased, and a polyester film having a high Young's modulus and excellent surface characteristics was obtained.
[0085]
【The invention's effect】
The present invention relates to a polyester film comprising a non-liquid crystalline polyester (A) and a polymer (B) that forms a phase separation structure with the non-liquid crystalline polyester (A), and the dispersion domain of the polymer (B) in the film surface layer and the central layer The quality of the film is controlled by improving the rigidity, surface slipperiness and abrasion resistance of the film, for magnetic recording, for electrical insulation, for thermal transfer ribbons, for thermal stencil printing, and for packaging It can be widely used for various film applications.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a TEM photograph of a film cross section, illustrating the case where each domain of polymer (B) is shaded and the shape of individual dispersed domains is uneven. The non-liquid crystalline polyester (A) corresponds to the white part in the figure, and the polymer (B) corresponds to the dispersed domains that are phase-separated.
FIG. 2 is a schematic diagram of a dispersion domain of a polymer (B) appearing on a cut surface parallel to a film surface, and illustrates a case where a boundary with a non-liquid crystalline polyester (A) is recognized to have a width.
[Explanation of symbols]
Ls ... half the width of the boundary
le ...... Maximum length in the longitudinal direction of the film of the dispersion domain
lf ... The maximum length in the width direction of the film of the dispersion domain

Claims (2)

A resin composition comprising a non-liquid crystalline polyester (A) and a polymer (B) that forms a phase-separated structure when blended with the non-liquid crystalline polyester (A) is used to initiate temperature-fall crystallization of the non-liquid crystalline polyester (A). After melt extrusion molding under temperature conditions not lower than the melting point and lower than the melting point, the film is stretched at a magnification of 3 to 10 times in the longitudinal direction and 3 to 10 times in the width direction, and then 150 ° C. or higher and the non-liquid crystalline polyester (A). A method for producing a polyester film, comprising heat-setting at a temperature lower than the melting point. Process for producing a polyester film according to claim 1, wherein the length of the land portion is used a die of 10 to 70 mm, the draft ratio during casting and 3-50.

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