JP4107741B2 - Optical film manufacturing method, optical film and liquid crystal display device - Google Patents

Description

【００２６】
式中Ｘ及びＲ¹は、任意の残基であって、少なくとも一方が芳香環を含む基である。
【００２７】
前記Ｘは、
【００２８】
【化２】

【００２９】
等の基であることが好ましく、Ｒ¹は、
【００３０】
【化３】

【００３１】
【化４】

【００３２】
等の基であることが好ましい。但し式中ｒは２〜１２の数を示し、ｓは１〜５００の数を示し、ｔは０〜５００の数を示す。
【００３３】
前記ポリアミドとしては、より具体的には、下記式（２）で表わされるポリマー、
【００３４】
【化５】

【００３５】
式（３）で表わされるポリマー、
【００３６】
【化６】

【００３７】
式（４）で表わされるポリマー、
【００３８】
【化７】

【００３９】
並びに式（５）で表わされるポリマー等を挙げることができる。
【００４０】
【化８】

【００４１】
但しｕは０．５≦ｕ≦９．５の数を示す。
【００４２】
前記ポリイミドとしては、例えば下記式（６）で示されるポリマー：
【００４３】
【化９】

【００４４】
（式中ｍは平均重合度である。またＹは、
【００４５】
【化１０】

【００４６】
等の基を示し、Ｒ²は、
【００４７】
【化１１】

【００４８】
等の基を示す。）を挙げることができ、より具体的には、下記式（７）〜（９）で示されるポリマーを挙げることができる。
【００４９】
【化１２】

【００５０】
前記ポリアミック酸としては、例えば下記式（１０）〜（１２）で示されるポリマーを挙げることができる。
【００５１】
【化１３】

【００５２】
（式中ｎは２〜４００の数を示す。）
なお、前記ポリアミック酸を用いる場合、溶液塗布、乾燥した後、そのまま第２工程を行うこともできるが、熱処理によりイミド化した後、第２工程に供することもできる。
【００５３】
前記成膜材料溶液中の前記成膜材料の濃度は、通常０．５重量％以上４０重量％以下、好ましくは１重量％以上３０重量％以下、さらに好ましくは２重量％以上２０重量％以下とすることができる。
【００５４】
前記成膜材料溶液において、前記成膜材料を溶解させる溶媒としては、前記成膜材料を溶解でき、かつ基板フィルムを極度には浸食しないものであればよく、使用する成膜材料及び基板に応じ適宜選択することができる。具体的には例えば、クロロホルム、ジクロロメタン、四塩化炭素、ジクロロエタン、テトラクロロエタン、トリトリクロロエチレン、テトラクロロエチレン、クロロベンゼン、オルソジクロロベンゼン等のハロゲン化炭化水素類、フェノール、パラクロロフェノール等のフェノール類、ベンゼン、トルエン、キシレン、メトキシベンゼン、１，２−ジメトキシベンゼン等の芳香族炭化水素類、アセトン、酢酸エチル、ｔ−ブチルアルコール、グリセリン、エチレングリコール、トリエチレングリコール、エチレングリコールモノメチルエーテル、ジエチレングリコールジメチルエーテル、プロピレングリコール、ジプロピレングリコール、２−メチル−２，４−ペンタンジオール、エチルセルソルブ、ブチルセルソルブ、２−ピロリドン、Ｎ−メチル−２−ピロリドン、ピリジン、トリエチルアミン、ジメチルホルムアミド、ジメチルアセトアミド、アセトニトリル、ブチロニトリル、二硫化炭素等及びこれらの混合溶媒等が用いられる。また、用いる成膜材料によっては硫酸も使用できる。
【００５５】
前記成膜材料溶液は、前記成膜材料及び溶媒に加えて、目的に応じ界面活性剤等の他の添加物を加えても良い。
【００５６】
前記第１工程において、前記成膜材料溶液を前記基板上に配する方法は、特に限定されず、スピンコート法、ロールコート法、ダイコート法等により行うことができる。これらの方法により前記成膜材料溶液を、得られるフィルムが所望の膜厚になるように基板上に配した後、乾燥させることにより負の一軸性フィルムを得ることができる。乾燥温度は溶媒の種類等に応じて適宜選択することができるが、通常４０℃以上２５０℃以下、好ましくは５０℃以上２００℃以下とすることができる。乾燥は一定温度下で行っても良いし段階的に温度を上昇させて行っても良い。乾燥時間は通常１０秒間以上３０分間以下、好ましくは３０秒間以上２０分間以下、さらに好ましくは２分間以上１５分間以下とすることができる。
【００５７】
前記成膜材料として前記各種のポリマーを用いた場合、成膜材料溶液を基板上に配し、乾燥させることでポリマーが面配向（乾燥時に溶剤を含む塗膜が膜厚方向に収縮するため分子配向に異方性が生じる現象）した負の一軸性フィルムとすることができるが、前記成膜材料として重合可能な低分子化合物を用いた場合は、成膜材料溶液を基板上に配し、乾燥させて低分子化合物の面配向物を得た後、必要に応じ熱や光により架橋することにより、負の一軸性フィルムとすることができる。
【００５８】
前記負の一軸性フィルムとは、主屈折率ｎｘ及びｎｙがほぼ同一であり、且つｎｚより大きい関係を満たすフィルムをいう。具体的にはｎｘとｎｙとの差は０．００１以下程度であれば、負の一軸性を有するものとして用いることができる。
【００５９】
主屈折率ｎｘ、ｎｙ及びｎｚの値は、前記第１工程に従ってフィルムを作成した場合、通常用いる材料及び作製する条件に依存してはぼ決まってくる値であり、目的に応じて膜厚を選択して、光学的に重要なパラメータである面内と厚み方向のリターデーション値（（ｎｘ−ｎｚ）と膜厚ｄの積で得られる値）を制御することができる。
【００６０】
前記負の一軸性フィルムにおいては、面内方向の屈折率と厚み方向の屈折率との差、すなわちｎｘ−ｎｚは、ある程度大きいことが好ましく、通常０．００２以上、好ましくは０．００５以上、さらに好ましくは０．０１以上、特に好ましくは０．０２以上とすることが望ましい。該屈折率差が小さい場合は、面内と厚み方向に関する所望のリターデーションを得るために、フィルムの膜厚を厚くしなければならない。後で述べるように該膜厚が厚すぎる場合は延伸工程において均一な構造が得られにくくなるため、ｎｘ−ｎｚの値は０．００２以上であることが好ましい。
【００６１】
前記負の一軸性フィルムの厚み方向のリターデーション値、即ち（ｎｘ−ｎｚ）×ｄで与えられる値は通常２０ｎｍ以上２０００ｎｍ以下、より好ましくは５０ｎｍ以上１０００ｎｍ以下、さらに好ましくは１００ｎｍ以上６００ｎｍ以下とすることができる。２０ｎｍ未満の場合はリターデーション値が小さすぎて、光学素子としての機能に欠けるおそれがあるため好ましくない。２０００ｎｍを超える場合は塗布や乾燥時にむらができ不均一なフィルムを与えるおそれがあるのであまり好ましくない。また、前記負の一軸性フィルムの膜厚は、通常０．２μｍ以上１００μｍ以下、好ましくは０．５μｍ以上５０μｍ以下、さらに好ましくは１μｍ以上２０μｍ以下とすることができる。０．２μｍ未満の場合は、フィルムの複屈折値（ｎｘ−ｎｚ）にもよるが、概してリターデーション値が小さくなるため、光学素子としての機能に欠けるおそれがあるため好ましくない。１００μｍを超える場合は塗布や乾燥時にむらができ不均一なフィルムを与えるおそれがあるため好ましくない。
【００６２】
また、前記負の一軸性フィルムの膜厚は、後の第２工程において前記負の一軸性フィルムを前記基板と共に延伸する場合、前記基板の膜厚よりも小さいことが好ましく、前記基板の膜厚の半分よりも小さいことがさらに好ましい。前記基板の膜厚に対して前記負の一軸性フィルムの膜厚を相対的に小さくすることにより、これらを共に延伸した際に均一な延伸を行うことができる。
【００６３】
本発明の方法は、前記第１工程に続いて、前記負の一軸性フィルムを延伸して二軸性フィルムとする第２工程を含む。
【００６４】
前記延伸は、前記基板としてガラス板又は金属板を用いた場合、第１工程により得られた負の一軸性フィルムを基板から剥離してから行うことができる。一方、前記基板として適当な厚みを有するプラスチックフィルム等の延伸フィルムを用いた場合、前記負の一軸性フィルムを、基板から剥離することなく、基板と共に延伸することができる。
【００６５】
前記負の一軸性フィルムを前記延伸フィルムと共に延伸すると、前記基板に張力が課せられ、前記基板が均一に延伸し、この均一な延伸に伴い前記負の一軸性フィルムが間接的に延伸されるので、前記負の一軸性フィルムを単独で延伸した場合等に比べて均一な延伸を行うことができるので好ましい。特に、前記基板の膜厚に対して前記負の一軸性フィルムの膜厚を相対的に小さくしてこれらを共に延伸すると、前記基板に主に張力が課せられ、均一な延伸が可能となるため特に好ましい。
【００６６】
前記延伸は、前記負の一軸性フィルムを、基板としての前記延伸フィルムと共に、加熱しつつ行うこが好ましい。加熱温度は、基枚のガラス転移点以上、融点以下とすることができ、基板の種類や延伸倍率等により適宜選択することができる。通常４０℃以上２５０℃以下、好ましくは８０℃以上２２０℃以下、さらに好ましくは１００℃以上２００℃以下とすることができる。ガラス転移点温度未満であると延仲を行うのに膨大な張力を必要とし、また融点を超えた温度だと、基板により大きな張力を課し、前記負の一軸性フィルムの延伸を制御できなくなるので好ましくない。
【００６７】
前記延伸は、一方向に張力をかける一軸延伸操作、又は互いに直交する二方向に張力をかける二軸延伸操作等により行うことができる。ただし本発明の方法においては、前記第１工程で既に負の一軸性の異方性が得られているので、二軸性フィルムを得るためには一軸延伸操作で十分である。また、操作が簡便であり、装置が単純であり、また均一な屈折率分布を得るという観点からも一軸延伸操作の方が二軸延伸操作よりも好ましい。
【００６８】
前記一軸延伸を行う場合、延伸倍率は通常１．０１倍以上２．０倍以下、好ましくは１．０３倍以上１．５倍以下、さらに好ましくは１．０５倍以上１．３倍以下とすることができる。延伸倍率が１．０１倍未満であると延伸による効果が十分でなくフィルムが負の一軸性に近い構造にしかならないおそれがあるため好ましくない。延伸倍率が２．０倍より大きい時は、延伸むらのためにフィルムが不均一な屈折率構造となってしまうおそれがある。
【００６９】
二軸延伸を行う場合は、直交する２方向の延伸方向のうちより大きい張力をかける方向の張力をＴｙ、それに直交する方向にかける張力をＴｘとしたとき、ＴｙをＴｘに比べ十分に大きくすることにより、具体的にはＴｙ／Ｔｘ＞３、より好ましくはＴｙ／Ｔｘ＞５、さらに好ましくはＴｙ／Ｔｘ＞１０であるような条件とすることにより、ある程度屈折率分布の少ない二軸性フィルムを得ることができる。Ｔｙ／Ｔｘ比は極力大きい方が屈折率分布の少ない二軸性フィルムを得る上で有利であり、Ｔｘ＝０の場合は一軸延伸に相当し最も好ましい。より大きい張力をかける方向の延伸倍率は通常１．０１倍以上２．０倍以下、好ましくは１．０３倍以上１．５倍以下、さらに好ましくは１．０５倍以上１．３倍以下とすることができる。
【００７０】
前記延伸を行うことにより、３つの主屈折率のうちｎｘ及びｎｚを大きく変化させることなくｎｙだけを大きく変化させ、ｎｙ＞ｎｘ＞ｎｚの二軸構造を得ることができる。そのため、前記負の一軸性フィルムにおける（ｎｘ−ｎｚ）×ｄの値を大きく変化させることなく、もう一つの重要なパラメーターである面内のリターデーション値（（ｎｙ−ｎｘ）×ｄ）を延伸段階で制御することができる。なお、前記一軸延伸を行った場合は、通常、延伸方向を前記ｙ方向、即ち３方向の主屈折率のうち最大の屈折率を有する方向とすることができ、前記二軸延伸を行った場合、前記Ｔｙの張力をかけた延伸方向を前記ｙ方向とすることができる。
【００７１】
本発明の方法を工業的に行う場合、前記第１工程において負の一軸性フィルムをロール状の基板上に形成し、さらに連続的に前記延伸を行うことが好ましい。この場合、延伸として一軸延伸を行う場合の延伸方向は、ロールの長手方向（この場合縦延伸）あるいは幅方向（この場合横延伸）とすることができる。工業的な観点からは縦延伸の方が容易で、より好ましい。前記縦延伸を行った場合、得られる二軸フィルムの前記ｙ方向は通常ロール長手方向とすることができる。一方前記横延伸を行った場合は、通常ロール幅方向が前記ｙ方向になり縦延伸時とその方向は９０度異なる。横延伸は縦延伸に比べると延伸のための装置が複雑になるという欠点があるが、得られる光学フィルムの用途によっては行う価値がある。例えば、本発明の方法によって得られるロール状二軸性のフィルムと他のロール状の光学フィルムを連続的に貼合する場合、二軸性のフィルムの最大屈折率方向の向きによって貼合物の光学性能は異なるので、光学性能の点で横延伸により製造された二軸性のフィルムの方が、より容易に連続的な貼り合わせが達成でき、好ましい場合もありうる。なお、横延伸する場合、フィルムの搬送のためにある程度の張力が長手方向にも必要になる場合もあるが、この場合の長手方向の張力に対し幅方向の延伸の張力を十分に大きくすることにより、実質的な幅方向の一軸延伸を行うことができる。
【００７２】
前記延伸終了後、得られた前記二軸性フィルムは、必要に応じて室温まで冷却される。冷却速度や手段は特に制限はない。ただし、冷却前に急激に延伸時の張力を解放すると得られたフィルムにしわが入りやすいので、冷却工程の一部又は全部を、前記延伸においてかけた張力の解放の前に行うことが好ましい。
【００７３】
前記負の一軸性フィルムを前記延伸フィルムと共に延伸した場合、必要に応じて基板である前記延伸フィルムを延伸工程後に除去することができ、あるいは製品を使用する上で問題なければ残しておくこともできる。
【００７４】
以上の工程により得られる二軸性フィルムは、そのまま製品である本発明の光学フィルムとすることも可能であるが、通常は比較的薄い膜であるので、前記第１工程で用いたものとは別の他の基板（以下、第１工程で用いた前記基板と区別して「第２の基板」という。）に転写して本発明の光学フィルムとすることがより好ましい。前記転写は、例えば、前記基板上の二軸性フィルムと第２の基板とを接着剤又は粘着剤を用いて貼り合わせ、次いで前記基板のみを、前記二軸性フィルムとの界面で剥離して除去することにより行うことができる。
【００７５】
転写に用いられる第２の基板としては、適度な平面性を有するものであれば特に限定されないが、ガラスや、透明で光学的等方性を有するプラスチックフィルム等が好ましい。かかるプラスチックフィルムの例としては、ポリメタクリレート、ポリスチレン、ポリカーボネート、ポリエーテルスルフォン、ポリフェニレンサルファイド、ポリアリレート、アモルファスポリオレフイン、トリアセチルセルロースあるいはエポキシ樹脂等のフィルムをあげることができる。なかでもポリメチルメタクリレート、ポリカーボネート、ポリアリレート、トリアセチルセルロース、ポリエーテルスルフォン等が好ましく用いられる。また、光学的に異方性な基板も、目的とする用途にとって必要な部材である場合には第２の基板として使用することができる。このような光学的に異方性の第２の基板の例としては、ポリカーボネートやポリスチレン等のプラスチックフィルムを延伸して得られる位相差フィルム、偏光フィルム等が挙げられる。
【００７６】
転写に用いられる第２の基板と二軸性フィルムとを貼り合わせる接着剤又は粘着剤は、光学グレードのものであれば特に制限はないが、アクリル系、エポキシ系、ウレタン系等のものを用いることができる。
【００７７】
前記剥離の方法は、ロール等を用いて機械的に剥離する方法、貼り合わせられた構造体の材料すべてに対する貧溶媒に浸漬したのち機械的に剥離する方法、前記貧溶媒中で超音波をあてて剥離する方法、前記基板と前記二軸性フィルムとの熱膨張係数の差を利用して温度変化を与えて剥離する方法等を例示することができる。剥離性は、二軸性フィルムに用いた材料と前記基板との密着性によって異なるため、その系に最も適した方法を採用することができる。
【００７８】
また、得られた二軸フィルムの表面はそのままでも製品である本発明の光学フィルムとすることができるが、必要に応じて表面に保護層を設けたり、粘着加工を行ったり、表面加工を行ったりして製品とすることもできる。
【００７９】
前記二軸性フィルム又は前記二軸性フィルムと第2の基板とを組み合わせたものは、そのまま、又は必要に応じて他の光学用フィルム、例えば他の屈折率構造を有する位相差フィルムや偏光板等と組み合わせ、製品である本発明の光学フィルムとすることができる。具体的には例えば、工業的に一般に製造されている形式の、ヨウ素を含潰したポリビニルアルコール膜を２枚の基板フィルムで保護した形の偏光板の中に、前記二軸性フィルムを組み込んで一体化し、製品である本発明の光学フィルムとすることもできる。
【００８０】
本発明の製造法は、均一性が高い本発明の光学フィルムを製造することができ、屈折率構造の制御が容易であるため、品質の高い、優れた機能を発揮する光学フィルムを製造することができる。とりわけ液晶ディスプレーの分野は、視覚に訴える用途であるため、使用する光学部材の均一性やパラメーターの妥当性が非常に厳しく評価されるが、本発明の製造法によれば、そのような要求にも十分応えることができる光学フィルムを製造できる。
【００８１】
本発明の光学フィルムは、光軸をフィルム面に投影したとき、その分布は、成膜材料溶液の塗工端を除けば、通常±５度以内とすることができる。基板として前記延伸フィルムを用い、前記負の一軸性フィルムを共に延伸する方法を採用すれば、通常±３度以内の分布を得ることができ、延伸温度の均一性及び延伸張力の均一性が高い条件に制御すれば±２度の制御も可能である。さらに一軸延伸の場合に限定すれば、通常±２度以内、条件を制御すれば±１度、最高±０．５度の制御が達成できる。
【００８２】
本発明の光学フィルムの用途は、特に限定されないが、位相差フィルム、偏光板と組み合わせた楕円偏光板等として用いることが出来る。
【００８３】
本発明の液晶表示装置は、前記本発明の光学フィルムを含む。
【００８４】
本発明の液晶表示装置の形式は、特に限定されず、例えばＳＴＮ（ＳｕｐｅｒＴｗｉｓｔｅｄ Ｎｅｍａｔｉｃ）セル、ＴＮ（Ｔｗｉｓｔｅｄ Ｎｅｎａｔｉｃ）セル、ＶＡ（Ｖｅｒｔｉｃａｌ Ａｌｉｇｎｅｄ）セル、ＯＣＢ（Ｏｐｔｉｃａｌｌｙ Ｃｏｎｔｒｏｌｅｄ Ｂｉｒｅｆｒｉｎｇｅｎｃｅ）セル、ＨＡＮ（Ｈｙｂｒｉｄ Ａｌｉｇｎｅｄ Ｎｅｍａｔｉｃ）セル、及びこれらに規則正しい配向分割を施したもの、ランダムな配向分割を行ったもの等の、各種のセルを含むものとすることができ、また、単純マトリックス方式、ＴＦＴ（Ｔｈｉｎ Ｆｉｌｍ Ｔｒａｎｓｉｓｔｏｒ）電極やＭＩＭ（Ｍｅｔａｌ Ｉｎｓｕｌａｔｏｒ Ｍｅｔａｌ）電極等を用いたアクティブマトリックス方式、セルの面内方向に駆動電圧を印加するＩＰＳ（Ｉｎ−Ｐｌａｎｅ Ｓｗｉｔｃｈｉｎｇ）方式、プラズマアドレッシング方式等の各種の駆動方式を採るものとすることができる。また、バックライトシステムを備えた透過型のもの、あるいは反射板を供えた反射型のもの、さらには投射型のものとすることもできる。
【００８５】
本発明の液晶表示における、前記光学フィルムを備える態様は、特に限定されないが、通常、偏光板と駆動セルとの間であって、駆動セルの上側及び／又は下側の位置に、１枚若しくは複数枚前記光学フィルムを配置する態様を挙げることができる。なかでも駆動セルの上側と下側に当該フィルムを１枚ずつ配置する態様が好ましい。またさらに別の光学用フィルム、例えば本発明の光学フィルムとは異なる屈折率構造を有する位相差フィルム、散乱フィルム、レンズシート等と組み合わせた態様とすることもできる。
【００８６】
【発明の効果】
本発明の光学フィルムの製造法は、特定の負の一軸性フィルムを得る工程とそれを延伸する工程とを含むことにより、屈折率分布の制御が容易でかつ均一性の高い光学フィルムを製造することができる。
【００８７】
本発明の光学フィルムは、前記製造法により得られる光学フィルムであるので、容易に製造することができ、屈折率分布が正確に所望の値に制御され、均一性が高く、位相差フィルム及び楕円偏光板等として有用である。
【００８８】
本発明の液晶表示装置は、前記本発明の光学フィルムを含むので、透過光の屈折率が正確に制御され、性能が高く、容易に製造しうる液晶表示装置として有用である。
【００８９】
【実施例】
以下に実施例を述べるが、本発明はこれらに限定されるものではない。
なお実施例で用いた各分析法は以下の通りである。
（化学構造決定）
４００ＭＨｚの¹Ｈ−ＮＭＲ（日本電子製 ＪＮＭ−ＧＸ４００）で測定した。
（偏光解析）
（株）溝尻光学工業所製エリプソメーター ＤＶＡ−３６ＶＷＬＤを用いて行った。
（屈折率測定）
アタゴ（株）製アッベ屈折計Ｔｙｐｅ−４Ｔを用いて行った。
（膜厚測定）
（株）小坂研究所製高精度薄膜段差測定器ＥＴ−１０を主に用いた。
【００９０】
また、干渉波測定（日本分光 紫外・可視・近赤外分光光度計Ｖ−５７０）と屈折率のデーターから膜厚を求める方法も併用した。
（実施例１）
成膜材料として、式（１３）で表わされるポリアミドを合成した。
【００９１】
【化１４】

【００９２】
このポリアミドの固有粘度は１．６ｄｌ／ｇであった（３０℃、０．５ｇ／ｄｌのＮ−メチル−２−ピロリドン（ＮＭＰ）溶液）。このポリアミドをＮＭＰに溶解させ６重量％の成膜材料溶液を調製した。この成膜材料溶液を厚さ８０μｍ、長さ３０ｃｍ、幅２０ｃｍのポリエチレンナフタレートフィルム（帝人（株）製）にスピンコート法を用いて塗布し、８０℃のオーブン中で１時間乾燥処理を行い、積層フィルムを得た。この積層フィルムを数枚調製した。次いで、１５０℃のオーブン中でそれぞれの積層フィルムを一定速度（１０ｍｍ／ｍｉｎ）で、表１に示す様々な延伸倍率で一軸延伸した。延伸は前記積層フィルムの長さ方向に行った。延伸後のそれぞれの積層フィルムの一部を切りだし、ポリアミド膜を剥離し、これらを試料とし、屈折率測定及び膜厚測定を行った。結果を表１に示す。
【００９３】
【表１】

【００９４】
３方向の屈折率から、延伸していないポリアミド膜（試料番号１）はｎｙ＝ｎｘ＞ｎｚの負の一軸性構造を有する一方、延伸したポリアミド膜（試料番号２〜４）はｎｙ＞ｎｘ＞ｎｚの二軸性構造を有することが分かった。ここで最大屈折率方向ｙは延伸した方向であった。
【００９５】
剥離ポリアミド膜自身は薄膜であり自己支持性に乏しかったため、 前記積層フィルムの、前記測定に用いなかった残りの部分を用い、ポリアミド膜の他の透明基板への転写を行った。表面に粘着剤を塗布した透明なソーダガラス板（厚さ１．１ｍｍ）を調製し、その上に前記積層フィルムを、粘着剤とポリアミド膜が接するように貼り合わせ、次いでポリエチレンナフタレートフィルムを剥離した。このようにして二軸性屈折率構造を有するポリアミド膜を表面に備えた、積層ガラスを得ることができた。得られた積層ガラスを２枚のクロスニコル下の偏光板に挟んでむらの様子を観察したところ、均一なポリマーの膜が得られていることが分かった。
（実施例２）
成膜材料として、式（１４）で表わされるポリマーを合成した。
【００９６】
【化１５】

【００９７】
このポリマーの固有粘度は１．５ｄｌ／ｇであった（３０℃、０．５ｇ／ｄｌのＮＭＰ溶液）。このポリマーをＮＭＰに溶解し、ポリマー濃度４重量％の成膜材料溶液を調製した。
【００９８】
この成膜材料溶液を、幅４０ｃｍ、長さ５００ｍ、厚さ８０μｍのポリエチレンテレフタレートフィルムの上にロールコーターを用いて連続的に塗布し、１００℃で乾燥処理し、積層フィルムを得た。この積層フィルムを１５０℃に加熱しつつ、長手方向に５５Ｋｇｆの張力をかけて延伸を行った。延伸後の積層フィルムは、長手方向は１．０９倍に伸び、幅方向は約０．９５倍に収縮していた。延伸後の積層フィルム上のポリマー層の膜厚は１０μｍであった。
【００９９】
ポリエチレンテレフタレートフィルムが、面内で均一性の低い複屈折性をもっており、光学的性質を測定する上で望ましくないため、次の剥離転写操作を行った。
【０１００】
まず、延伸した積層フィルム上のポリマー層の上に紫外線硬化型接着剤を塗布し、その上にトリアセチルセルロースフィルム（長さ ５００ｍ、幡４０ｃｍ、厚み８０μｍ、富士写真フィルム社製）をラミネートした。紫外線を照射して接着剤を硬化させた後、ポリエチレンテレフタレートをポリマー層から剥離し、トリアセチルセルロースフィルムとポリマー層との積層物を得た。
【０１０１】
得られた積層物を偏光解析した。光軸は２本あり、光軸が積層物の法線となす角はいずれも３８度であった。また光軸を積層物の面に投影した方向は、積層物の長手方向と一致した。
【０１０２】
また、この積層物を１ｍ切り出し、長手方向、幅方向に関し１ｃｍおきに面内のリターデーシヨンを測定して分布を調べた（ただしポリマー層が積層された部分の幅方向の両端５ｃｍを除く）。その結果、リターデーション値は２１３ｎｍ±２ｎｍの範囲にあり、±１％以内の精度で複屈折性が制御できていることがわかった。従って、得られた積層物は、均一な二軸性のフィルムであることがわかった。
（実施例３）
実施例２と同じ成膜材料溶液及びポリエチレンテレフタレートフィルムを用い、同様に塗布及び乾燥を行い、積層フィルムを調製した。この積層フィルムを、１８０℃に加熱しつつテンターを用いて横延伸した。横方向の張力は長さ１ｃｍあたり０．９Ｋｇｆとし、長手方向には搬送のため３Ｋｇｆの張力（１ｃｍあたり０．０７Ｋｇｆ）をかけた。延伸によりフィルム幅は約６％増加した。延伸後、実施例２と同様にトリアセチルセルロースフィルムにポリマー層を転写し、トリアセチルセルロースフィルムとポリマー層との積層物を得た。
【０１０３】
得られた積層物を偏光解析した。光軸は２本あり、光軸が積層物の法線となす角はいずれも２４度であった。また光軸を積層物の面に投影した方向は、積層物の幅方向とほぼ一致し、積層物の面内の場所による分布は±１度であった。また面内のリターデーションの分布は±２％以内であった。従って、得られた積層物は、均一な二軸性フィルムであることがわかった。
（実施例４）
本発明の光学フィルムの態様の一つとしての、偏光素子と二軸性フィルムとを一体化した光学素子を作製した。
【０１０４】
延伸したポリビニルアルコール膜にヨウ素を含浸させ、これを熱硬化型接着剤を用いてトリアセチルセルロースフィルム上に接着し、ポリビニルアルコール−トリアセチルセルロース積層物を得た。次に実施例３で得られたトリアセチルセルロースフィルムとポリマー層との積層物上のポリマー層上に熱硬化型接着剤を塗布し、前記ポリビニルアルコール−トリアセチルセルロース積層物のポリビニルアルコール膜側と貼り合わせ、熱をかけて接着剤を硬化させた。なお貼り合わせ方向は、ポリビニルアルコール膜の延伸方向と実施例３の積層物のロール長手方向とが平行になるようにした。このようにして、二枚のトリアセチルセルロースフィルムの間に偏光層及び複屈折層を有する光学素子を作製することができた。
（実施例５）
式（１５）の化合物を合成した。
【０１０５】
【化１６】

【０１０６】
（式中Ｒ³は
【０１０７】
【化１７】

【０１０８】
で表わされる基を示し、Ｒ⁴は
【０１０９】
【化１８】

【０１１０】
で表わされる基を示す。）
また式（１６）及び式（１７）の化合物を入手した（それぞれ東亜合成（株）製アロニックスＭ−１１７及びＭ−２１０）。
【０１１１】
【化１９】

【０１１２】
（式中ｐ及びｑは平均の重合度であり、それぞれ約４、約２である。）
これらの化合物を、式（１５）の化合物：式（１６）の化合物：式（１７）の化合物＝５０：４５：５の重量比で混合し、ポリマーフィルムのための出発原料とした。なお、式（１５）の化合物は単独ではディスコチック液晶相を有する化合物であるが、前記出発原料は液晶性を示さず、室温下では粘ちゆうな液体であった。
【０１１３】
光開始剤イルガキュアー９０７（Ｃｉｂａ−Ｇｅｉｇｙ社製）を前記出発原料に対し１．５重量％加え、成膜材料組成物とした。これにジエチレングリコールジメチルエーテル溶媒を加えて、成膜材料組成物濃度１５重量％の溶液を調製した。
【０１１４】
この溶液を、厚さ５０μｍ、長さ３０ｃｍ、幅２０ｃｍのポリフェニレンサルフアイドフィルム（東レ（株）製）にスピンコート法を用いて塗布し、８０℃のオーブン中で１０分間乾燥処理を行ない、さらに温度を６０℃に保ちつつ、高圧水銀灯ランプにより塗布面に紫外線照射を行い、成膜材料組成物を光硬化させてポリマー化させ、ポリマー層を有する積層フィルムを得た。得られた積層フィルム上のポリマー層の屈折率を測定したところ、負の一軸性構造を有しており、面内の屈折率は一定で１．５９、膜厚方向の屈折率は１．５６であることがわかった。
【０１１５】
次に、２００℃のオーブン中で前記積層フィルムを一定速度（１０ｍｍ／ｍｉｎ）で、長手方向に１．１倍に一軸延伸した。延伸後のフィルムの屈折率は、ｎｙ＝１．６１、ｎｘ＝１．５８、ｎｚ＝１．５６であった。得られた積層フィルム上のポリマー層を、実施例１と同様に、ガラス基板上へ転写した。偏光下で観察を行い、その結果、ガラス基板上のポリマー層はむらのない均質な二軸性構造を有していることが分かった。
（実施例６）
成膜材料として、式（１８）で表わされるポリマーを合成した。
【０１１６】
【化２０】

【０１１７】
このポリマーの固有粘度は０．６５ｄｌ／ｇであった（３０℃、０．５ｇ／ｄｌのＮＭＰ溶液）。この成膜材料をＮＭＰに溶解させ４重量％の成膜材料溶液を調製し、２０ｃｍ角のアルミ板に塗布し、８０℃のオーブン中で乾燥させ、積層板を得た。この積層板上のポリマー層の膜厚は４５μｍであった。次いで、ポリマー層を注意深くアルミ板から剥がしとりポリマー膜を得、これを１４０℃で１．０５倍に延伸した。延伸後のポリマー膜は透明で二軸性を有していた。偏光解析により、（ｎｘ−ｎｚ）と膜厚の積であるリターデーションを求めたところ、１００ｎｍであった。また、（ｎｙ−ｎｚ）と膜厚である面内のリターデーションは約３９０ｎｍであった。光軸のポリマー膜の面への投影方向を、ポリマー膜中心部の１０ｃｍ角の範囲について調べたところ、ポリマー膜の延伸方向を中心に±４度の分布があった。また面内のリターデーションの分布は３９０ｎｍ±１８ｎｍであった。[0001]
BACKGROUND OF THE INVENTION
The present invention is a biaxial film suitable as various optical films such as a retardation film and a polarizing film. For liquid crystal display The present invention relates to an optical film, a manufacturing method thereof, and a liquid crystal display device including the optical film.
[0002]
[Prior art]
A biaxial film with a controlled three-dimensional refractive index is useful in the optical field using polarized light. In particular, in the field of liquid crystal displays, such a film capable of finely controlling the polarization is highly important.
[0003]
Many of the birefringent optical films currently available industrially have a uniaxial refractive index structure. There are those having positive or negative axiality, those having the optical axis in the film plane, those having the normal direction of the film, and the like. For example, a color compensation film used in a STN (Super Twisted Nematic) liquid crystal display is a positive uniaxial film having an optical axis in the plane. Moreover, for example, Harris et al. Obtains a negative uniaxial structure having an optical axis in the film normal direction by drying a solution of a specific polymer on a substrate and orienting the polymer in a plane direction (US Pat. No. 5,344,916). 6480964 and 5580950). This production method is notable as a simple production method for optical films. However, the uniaxial optical film having high symmetry naturally has a limit in the effect of controlling the polarization.
[0004]
On the other hand, a biaxial film can be produced by biaxial stretching of a polymer film, and there are many reports on this. However, there is a problem with the quality of the film obtained. That is, the refractive index control is difficult because the refractive index structure in the three directions is controlled by the balance of stretching in the two directions, and the obtained film is easy to distribute the refractive index structure in the plane, and it is difficult to obtain a uniform film.
[0005]
As described above, the biaxial film remains a big problem in industrial production.
[0006]
[Problems to be solved by the invention]
The object of the present invention is to easily control the refractive index distribution and to provide highly uniform biaxiality. For liquid crystal display It is in providing the method of manufacturing an optical film.
[0007]
Another object of the present invention is that it can be easily manufactured, the refractive index distribution is accurately controlled to a desired value, and has high uniformity. For liquid crystal display It is to provide an optical film.
[0008]
Another object of the present invention is to provide a liquid crystal display device in which the refractive index of transmitted light is accurately controlled, has high performance, and can be easily manufactured.
[0009]
[Means for Solving the Problems]
As a method of obtaining a biaxial structure, the present inventors considered using two different methods step by step without relying only on stretching, and as a result of conducting a thorough examination based thereon, finally reached the present invention. .
[0010]
That is, according to the present invention, a film forming material solution is disposed on a substrate and dried to obtain a surface-oriented optically negative uniaxial film, and the negative uniaxial film is stretched. It has a refractive index structure of ny>nx> nz Including a step of forming a biaxial film For liquid crystal display A method of manufacturing an optical film is provided.
[0011]
Moreover, according to this invention, the said board | substrate is a stretched film, The manufacturing method of the said optical film characterized by the above-mentioned is provided.
[0012]
Furthermore, according to the present invention, in the step of stretching the negative uniaxial film, the method for producing the optical film is characterized in that the negative uniaxial film is stretched while being heated together with the stretched film. Is done.
[0013]
Furthermore, according to the present invention, it is obtained by the production method. For liquid crystal display An optical film is provided.
[0014]
Furthermore, according to the present invention, there is provided the optical film, wherein the distribution of the projection direction of the film optical axis onto the film surface is within ± 2 °.
[0015]
Furthermore, according to this invention, the liquid crystal display element characterized by including the said optical film is provided.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The method of the present invention is a method for producing an optical film, particularly a method for producing a biaxial optical film having a refractive index structure of ny>nx> nz. In the present specification, nx, ny and nz are the main refractive indexes in the three directions of the x direction, the y direction and the z direction, respectively, and the x direction and the y direction are directions in the film plane perpendicular to each other The z direction is the film thickness direction.
[0017]
In the method of the present invention, a two-stage process for forming a film while controlling the refractive index, that is, a film forming material solution is placed on a substrate and dried to obtain a surface-oriented optically negative uniaxial film. A step (hereinafter referred to as the first step) and a step of stretching the negative uniaxial film to form a biaxial film (hereinafter referred to as the second step).
[0018]
The substrate used in the first step is not particularly limited, and a plastic substrate such as a plastic film, a glass plate or a metal plate can be used. It is particularly preferable to use a stretched film such as a plastic film having an appropriate thickness as the substrate because the negative uniaxial film and the substrate can be stretched together in the second step.
[0019]
Examples of the plastic film include a film made by a casting method, a film formed through a molten state of a polymer, and then subjected to a stretching operation. The latter is particularly preferable. This is because the latter film can deform the negative uniaxial film more precisely because the substrate exhibits a certain level of strength in the second stretching step.
[0020]
Examples of the plastic film include polyolefins such as polyethylene and polypropylene, polyimide, polyamideimide, polyamide, polyetherimide, polyetheretherketone, polyetherketone, polyketonesulfide, polyethersulfone, polysulfone, polyphenylenesulfide, polyphenyleneoxide, Examples include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyacetal, polycarbonate, polyarylate, acrylic resin, polyvinyl alcohol, polypropylene, cellulosic plastics, epoxy resin, and phenol resin. Among these, polyethylene, polypropylene, polyethylene terephthalate, polyethylene naphthalate, cellulosic plastic, and the like are particularly preferable. Moreover, what gave surface treatments, such as a hydrophilic treatment and a hydrophobic treatment, to these plastic films can also be used.
[0021]
The thickness of the plastic film can usually be 20 μm or more and 200 μm or less, preferably 30 μm or more and 150 μm or more, and particularly preferably 60 μm or more and 100 μm or less. When the thickness is less than 20 μm, the strength of the film is weak, and thus stretching unevenness may occur when stretching with the negative uniaxial film in the second step. In the case of 200 μm or more, the tension necessary for stretching becomes too large, which is not suitable for industrial production.
[0022]
As the film forming material solution, a solution containing film forming materials such as various polymers and polymerizable low molecular weight compounds can be used. In order to obtain sufficiently large birefringence, that is, in order to obtain a negative uniaxial film having a sufficiently large nx-nz, it is preferable to include a film forming material having at least one kind of aromatic ring.
[0023]
As the film forming material, specifically, for example, various polymers such as polyamide, polyimide, polyamic acid, polyester or polyesteramide having at least one aromatic ring, or polymerizable capable of giving these polymers is possible. A low molecular compound can be mentioned. These may be used alone or in combination.
[0024]
As said polyamide, the polymer containing the polymer unit represented by following formula (1) is mentioned, for example.
[0025]
[Chemical 1]

[0026]
Where X and R ¹ Is an arbitrary residue, at least one of which is a group containing an aromatic ring.
[0027]
X is
[0028]
[Chemical 2]

[0029]
Is preferably a group such as R ¹ Is
[0030]
[Chemical 3]

[0031]
[Formula 4]

[0032]
And the like. In the formula, r represents a number of 2 to 12, s represents a number of 1 to 500, and t represents a number of 0 to 500.
[0033]
More specifically, as the polyamide, a polymer represented by the following formula (2),
[0034]
[Chemical formula 5]

[0035]
A polymer represented by formula (3),
[0036]
[Chemical 6]

[0037]
A polymer represented by formula (4),
[0038]
[Chemical 7]

[0039]
Moreover, the polymer etc. which are represented by Formula (5) can be mentioned.
[0040]
[Chemical 8]

[0041]
However, u shows the number of 0.5 <= u <= 9.5.
[0042]
Examples of the polyimide include a polymer represented by the following formula (6):
[0043]
[Chemical 9]

[0044]
(Where m is the average degree of polymerization and Y is
[0045]
[Chemical Formula 10]

[0046]
Etc., R ² Is
[0047]
Embedded image

[0048]
Etc. are shown. More specifically, polymers represented by the following formulas (7) to (9) can be mentioned.
[0049]
Embedded image

[0050]
Examples of the polyamic acid include polymers represented by the following formulas (10) to (12).
[0051]
Embedded image

[0052]
(In the formula, n represents a number of 2 to 400.)
In addition, when using the said polyamic acid, after solution application | coating and drying, the 2nd process can also be performed as it is, but after imidation by heat processing, it can also use for a 2nd process.
[0053]
The concentration of the film forming material in the film forming material solution is usually 0.5% by weight to 40% by weight, preferably 1% by weight to 30% by weight, and more preferably 2% by weight to 20% by weight. can do.
[0054]
In the film forming material solution, the solvent for dissolving the film forming material may be any solvent that can dissolve the film forming material and does not extremely erode the substrate film, depending on the film forming material and the substrate to be used. It can be selected appropriately. Specifically, for example, halogenated hydrocarbons such as chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, tritrichloroethylene, tetrachloroethylene, chlorobenzene, orthodichlorobenzene, phenols such as phenol and parachlorophenol, benzene, toluene, Aromatic hydrocarbons such as xylene, methoxybenzene, 1,2-dimethoxybenzene, acetone, ethyl acetate, t-butyl alcohol, glycerin, ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, di Propylene glycol, 2-methyl-2,4-pentanediol, ethyl cellosolve, butyl cellosolve, 2-pyrrolidone, N Methyl-2-pyrrolidone, pyridine, triethylamine, dimethylformamide, dimethylacetamide, acetonitrile, butyronitrile, carbon disulfide etc., and mixed solvents thereof and the like can be used. Further, depending on the film forming material used, sulfuric acid can also be used.
[0055]
In addition to the film forming material and the solvent, the film forming material solution may contain other additives such as a surfactant depending on the purpose.
[0056]
In the first step, the method of disposing the film forming material solution on the substrate is not particularly limited, and can be performed by a spin coat method, a roll coat method, a die coat method, or the like. A negative uniaxial film can be obtained by arranging the film-forming material solution on the substrate so that the resulting film has a desired film thickness by these methods and then drying the solution. Although a drying temperature can be suitably selected according to the kind of solvent etc., it is 40 degreeC or more and 250 degrees C or less normally, Preferably it can be 50 degreeC or more and 200 degrees C or less. Drying may be performed at a constant temperature or may be performed by increasing the temperature stepwise. The drying time is usually 10 seconds to 30 minutes, preferably 30 seconds to 20 minutes, and more preferably 2 minutes to 15 minutes.
[0057]
When the above-mentioned various polymers are used as the film-forming material, the film-forming material solution is placed on the substrate and dried, so that the polymer is oriented in the plane (the film containing the solvent shrinks in the film thickness direction during drying). A phenomenon in which anisotropy occurs in the orientation) can be a negative uniaxial film, but when a polymerizable low molecular compound is used as the film forming material, a film forming material solution is disposed on the substrate, After obtaining a plane alignment product of a low molecular compound by drying, a negative uniaxial film can be obtained by crosslinking with heat or light as necessary.
[0058]
The negative uniaxial film refers to a film in which the main refractive indexes nx and ny are substantially the same and satisfy a relationship larger than nz. Specifically, if the difference between nx and ny is about 0.001 or less, it can be used as having negative uniaxiality.
[0059]
The values of the main refractive indexes nx, ny and nz are values that are determined depending on the materials used and the conditions under which the film is produced in accordance with the first step. The retardation value in the in-plane and thickness direction (value obtained by the product of (nx−nz) and the film thickness d), which is an optically important parameter, can be selected.
[0060]
In the negative uniaxial film, the difference between the refractive index in the in-plane direction and the refractive index in the thickness direction, that is, nx-nz is preferably large to some extent, usually 0.002 or more, preferably 0.005 or more, More preferably, it is 0.01 or more, and particularly preferably 0.02 or more. When the refractive index difference is small, the film thickness must be increased in order to obtain the desired retardation in the in-plane and thickness direction. As will be described later, when the film thickness is too thick, it is difficult to obtain a uniform structure in the stretching step. Therefore, the value of nx-nz is preferably 0.002 or more.
[0061]
The retardation value in the thickness direction of the negative uniaxial film, that is, the value given by (nx−nz) × d is usually 20 nm to 2000 nm, more preferably 50 nm to 1000 nm, and still more preferably 100 nm to 600 nm. be able to. If the thickness is less than 20 nm, the retardation value is too small, and the function as an optical element may be lacking. If it exceeds 2000 nm, it is not preferred because it may cause unevenness during coating or drying, resulting in a non-uniform film. The film thickness of the negative uniaxial film is usually 0.2 μm or more and 100 μm or less, preferably 0.5 μm or more and 50 μm or less, and more preferably 1 μm or more and 20 μm or less. When the thickness is less than 0.2 μm, although depending on the birefringence value (nx−nz) of the film, the retardation value is generally small, so that the function as an optical element may be lacking. A thickness exceeding 100 μm is not preferable because it may cause unevenness during coating or drying and may give a non-uniform film.
[0062]
The film thickness of the negative uniaxial film is preferably smaller than the film thickness of the substrate when the negative uniaxial film is stretched together with the substrate in the second step. More preferably, it is smaller than half of the above. By making the film thickness of the negative uniaxial film relatively small with respect to the film thickness of the substrate, uniform stretching can be performed when they are stretched together.
[0063]
Following the first step, the method of the present invention includes a second step of stretching the negative uniaxial film to form a biaxial film.
[0064]
When the glass plate or the metal plate is used as the substrate, the stretching can be performed after the negative uniaxial film obtained in the first step is peeled off from the substrate. On the other hand, when a stretched film such as a plastic film having an appropriate thickness is used as the substrate, the negative uniaxial film can be stretched together with the substrate without peeling from the substrate.
[0065]
When the negative uniaxial film is stretched together with the stretched film, tension is imposed on the substrate, the substrate is stretched uniformly, and the negative uniaxial film is indirectly stretched along with the uniform stretching. The negative uniaxial film is preferable because it can be stretched more uniformly than when stretched alone. In particular, when the film thickness of the negative uniaxial film is made relatively small with respect to the film thickness of the substrate and these are stretched together, tension is mainly applied to the substrate, and uniform stretching becomes possible. Particularly preferred.
[0066]
The stretching is preferably performed while heating the negative uniaxial film together with the stretched film as a substrate. The heating temperature can be not lower than the glass transition point of the base sheet and not higher than the melting point, and can be appropriately selected depending on the type of substrate and the draw ratio. Usually, it can be set to 40 ° C. or higher and 250 ° C. or lower, preferably 80 ° C. or higher and 220 ° C. or lower, more preferably 100 ° C. or higher and 200 ° C. or lower. If the temperature is lower than the glass transition temperature, enormous tension is required to carry out elongation, and if the temperature exceeds the melting point, a large tension is imposed on the substrate and the stretching of the negative uniaxial film cannot be controlled. Therefore, it is not preferable.
[0067]
The stretching can be performed by a uniaxial stretching operation in which tension is applied in one direction, a biaxial stretching operation in which tension is applied in two directions orthogonal to each other, or the like. However, in the method of the present invention, since a negative uniaxial anisotropy has already been obtained in the first step, a uniaxial stretching operation is sufficient to obtain a biaxial film. In addition, the uniaxial stretching operation is preferable to the biaxial stretching operation from the viewpoint of simple operation, simple apparatus, and uniform refractive index distribution.
[0068]
When the uniaxial stretching is performed, the stretching ratio is usually 1.01 to 2.0 times, preferably 1.03 to 1.5 times, more preferably 1.05 to 1.3 times. be able to. If the draw ratio is less than 1.01, the effect of stretching is not sufficient, and the film may become only a negative uniaxial structure, which is not preferable. When the draw ratio is greater than 2.0 times, the film may have a non-uniform refractive index structure due to uneven drawing.
[0069]
When performing biaxial stretching, Ty is sufficiently larger than Tx, where Ty is the tension in the direction in which the larger tension is applied, and Tx is the tension applied in the direction perpendicular thereto. In particular, by setting the conditions such that Ty / Tx> 3, more preferably Ty / Tx> 5, and even more preferably Ty / Tx> 10, a biaxial film having a small refractive index distribution to some extent. Can be obtained. A larger Ty / Tx ratio is advantageous for obtaining a biaxial film having a small refractive index distribution. When Tx = 0, it corresponds to uniaxial stretching and is most preferable. The draw ratio in the direction of applying a larger tension is usually 1.01 to 2.0 times, preferably 1.03 to 1.5 times, more preferably 1.05 to 1.3 times. be able to.
[0070]
By performing the stretching, it is possible to greatly change only ny without greatly changing nx and nz among the three main refractive indexes, and to obtain a biaxial structure of ny>nx> nz. Therefore, the in-plane retardation value ((ny−nx) × d), which is another important parameter, is stretched without greatly changing the value of (nx−nz) × d in the negative uniaxial film. Can be controlled in stages. In addition, when the uniaxial stretching is performed, the stretching direction can be normally set to the y direction, that is, the direction having the maximum refractive index among the three main refractive indexes, and the biaxial stretching is performed. The stretching direction to which the tension of Ty is applied can be the y direction.
[0071]
When performing the method of this invention industrially, it is preferable to form a negative uniaxial film on a roll-shaped board | substrate in the said 1st process, and to perform the said extending | stretching continuously. In this case, the stretching direction when performing uniaxial stretching as stretching can be the longitudinal direction of the roll (longitudinal stretching in this case) or the width direction (transverse stretching in this case). From an industrial viewpoint, longitudinal stretching is easier and more preferable. When the longitudinal stretching is performed, the y direction of the obtained biaxial film can be usually set to the roll longitudinal direction. On the other hand, when the transverse stretching is performed, the roll width direction is usually the y direction, and the direction is 90 degrees different from that during longitudinal stretching. Transverse stretching has the disadvantage that the apparatus for stretching becomes more complicated than longitudinal stretching, but it is worth performing depending on the use of the resulting optical film. For example, when continuously laminating a roll-shaped biaxial film obtained by the method of the present invention and another roll-shaped optical film, depending on the direction of the maximum refractive index direction of the biaxial film, Since the optical performance is different, a biaxial film produced by transverse stretching in terms of optical performance can achieve continuous bonding more easily and may be preferable. In the case of transverse stretching, a certain amount of tension may be required in the longitudinal direction for film transport. In this case, the stretching tension in the width direction must be sufficiently larger than the tension in the longitudinal direction. Thus, uniaxial stretching in the substantial width direction can be performed.
[0072]
After completion of the stretching, the obtained biaxial film is cooled to room temperature as necessary. There is no particular limitation on the cooling rate and means. However, if the tension at the time of stretching is suddenly released before cooling, the resulting film is likely to wrinkle. Therefore, it is preferable to perform part or all of the cooling step before releasing the tension applied in the stretching.
[0073]
When the negative uniaxial film is stretched together with the stretched film, the stretched film, which is a substrate, can be removed after the stretching step as needed, or may be left if there is no problem in using the product. it can.
[0074]
Although the biaxial film obtained by the above steps can be used as it is as the optical film of the present invention as it is, it is usually a relatively thin film, so what is used in the first step More preferably, it is transferred to another substrate (hereinafter referred to as “second substrate” in distinction from the substrate used in the first step) to obtain the optical film of the present invention. In the transfer, for example, the biaxial film on the substrate and the second substrate are bonded together using an adhesive or an adhesive, and then only the substrate is peeled off at the interface with the biaxial film. This can be done by removing.
[0075]
The second substrate used for the transfer is not particularly limited as long as it has an appropriate flatness, but glass, a transparent plastic film having optical isotropy, and the like are preferable. Examples of such plastic films include films of polymethacrylate, polystyrene, polycarbonate, polyether sulfone, polyphenylene sulfide, polyarylate, amorphous polyolefin, triacetyl cellulose, or epoxy resin. Of these, polymethyl methacrylate, polycarbonate, polyarylate, triacetyl cellulose, polyether sulfone and the like are preferably used. An optically anisotropic substrate can also be used as the second substrate if it is a member necessary for the intended application. Examples of such an optically anisotropic second substrate include a retardation film and a polarizing film obtained by stretching a plastic film such as polycarbonate or polystyrene.
[0076]
The adhesive or pressure-sensitive adhesive that bonds the second substrate and the biaxial film used for transfer is not particularly limited as long as it is optical grade, but acrylic, epoxy, urethane, or the like is used. be able to.
[0077]
The peeling method is a method of mechanically peeling using a roll or the like, a method of mechanically peeling after dipping in a poor solvent for all materials of the bonded structure, and applying ultrasonic waves in the poor solvent. And a method of peeling by applying a temperature change using a difference in thermal expansion coefficient between the substrate and the biaxial film. Since the peelability varies depending on the adhesion between the material used for the biaxial film and the substrate, a method most suitable for the system can be adopted.
[0078]
In addition, the surface of the obtained biaxial film can be used as it is as the optical film of the present invention, but if necessary, a protective layer is provided on the surface, adhesive processing is performed, or surface processing is performed. It can also be made into a product.
[0079]
The biaxial film or the combination of the biaxial film and the second substrate is used as it is, or as necessary, for other optical films, for example, a retardation film or a polarizing plate having another refractive index structure. It can be set as the optical film of this invention which is a product combining with these. Specifically, for example, the biaxial film is incorporated into a polarizing plate in a form in which a polyvinyl alcohol film containing iodine is protected with two substrate films, in a form generally produced industrially. The optical film of the present invention, which is a product, can be integrated.
[0080]
The production method of the present invention is capable of producing the optical film of the present invention with high uniformity, and is easy to control the refractive index structure, so that an optical film with high quality and excellent functions is produced. Can do. In particular, the field of liquid crystal displays is an application that appeals to the eye, so the uniformity of optical members used and the validity of parameters are evaluated very strictly. According to the manufacturing method of the present invention, such demands are met. Can be produced.
[0081]
In the optical film of the present invention, when the optical axis is projected onto the film surface, the distribution can usually be within ± 5 degrees except for the coating end of the film forming material solution. If the stretched film is used as a substrate and the negative uniaxial film is stretched together, a distribution within ± 3 degrees can be usually obtained, and the uniformity of stretching temperature and the uniformity of stretching tension are high. If controlled to the condition, control of ± 2 degrees is also possible. Further, if it is limited to the case of uniaxial stretching, it is usually within ± 2 degrees, and by controlling the conditions, ± 1 degree and a maximum of ± 0.5 degrees can be achieved.
[0082]
Although the use of the optical film of the present invention is not particularly limited, it can be used as a retardation film, an elliptically polarizing plate combined with a polarizing plate, or the like.
[0083]
The liquid crystal display device of the present invention includes the optical film of the present invention.
[0084]
The type of the liquid crystal display device of the present invention is not particularly limited, and for example, a STN (Super Twisted Nematic) cell, a TN (Twisted Nematic) cell, a VA (Vertical Controlled BirefringenceN cell), an OCB (Optically Controlled BirefringenceH cell). ) Cells and various cells such as those obtained by regular alignment division and those obtained by random alignment division may be included, and a simple matrix type, TFT (Thin Film Transistor) electrode, MIM (Metal Insulator Metal) An active matrix system using electrodes and the like, IPS (I -Plane Switching) scheme, can be assumed to take various driving methods such as a plasma addressing scheme. Further, it can be of a transmissive type provided with a backlight system, a reflective type provided with a reflecting plate, or a projection type.
[0085]
Although the aspect provided with the said optical film in the liquid crystal display of this invention is not specifically limited, Usually, it is between a polarizing plate and a drive cell, Comprising: One sheet or the position below a drive cell, or An embodiment in which a plurality of the optical films are arranged can be exemplified. In particular, a mode in which the films are arranged one by one on the upper side and the lower side of the driving cell is preferable. Moreover, it can also be set as the aspect combined with another optical film, for example, the phase difference film which has a refractive index structure different from the optical film of this invention, a scattering film, a lens sheet, etc.
[0086]
【The invention's effect】
The method for producing an optical film of the present invention comprises a step of obtaining a specific negative uniaxial film and a step of stretching the same, thereby producing an optical film with easy control of the refractive index distribution and high uniformity. be able to.
[0087]
Since the optical film of the present invention is an optical film obtained by the above-described manufacturing method, it can be easily manufactured, the refractive index distribution is accurately controlled to a desired value, the uniformity is high, the retardation film and the elliptical film. It is useful as a polarizing plate.
[0088]
Since the liquid crystal display device of the present invention includes the optical film of the present invention, the refractive index of transmitted light is accurately controlled, the performance is high, and it is useful as a liquid crystal display device that can be easily manufactured.
[0089]
【Example】
Examples will be described below, but the present invention is not limited thereto.
The analytical methods used in the examples are as follows.
(Chemical structure determination)
400MHz ¹ It was measured by H-NMR (JNM-GX400 manufactured by JEOL Ltd.).
(Polarization analysis)
This was carried out using an ellipsometer DVA-36VWLD manufactured by Mizoji Optical Co., Ltd.
(Refractive index measurement)
An Abbe refractometer Type-4T manufactured by Atago Co., Ltd. was used.
(Film thickness measurement)
A high precision thin film level difference measuring device ET-10 manufactured by Kosaka Laboratory Ltd. was mainly used.
[0090]
In addition, a method for determining the film thickness from interference wave measurement (JASCO UV / VIS / NIR spectrophotometer V-570) and refractive index data was also used.
(Example 1)
A polyamide represented by the formula (13) was synthesized as a film forming material.
[0091]
Embedded image

[0092]
The intrinsic viscosity of this polyamide was 1.6 dl / g (30 ° C., 0.5 g / dl N-methyl-2-pyrrolidone (NMP) solution). This polyamide was dissolved in NMP to prepare a 6 wt% film forming material solution. This film forming material solution was applied to a polyethylene naphthalate film (manufactured by Teijin Limited) having a thickness of 80 μm, a length of 30 cm, and a width of 20 cm using a spin coating method, followed by drying in an oven at 80 ° C. for 1 hour. A laminated film was obtained. Several sheets of this laminated film were prepared. Next, each laminated film was uniaxially stretched at various speeds shown in Table 1 at a constant speed (10 mm / min) in an oven at 150 ° C. Stretching was performed in the length direction of the laminated film. A part of each laminated film after stretching was cut out, the polyamide film was peeled off, and these were used as samples to perform refractive index measurement and film thickness measurement. The results are shown in Table 1.
[0093]
[Table 1]

[0094]
From the three-direction refractive index, the unstretched polyamide film (sample number 1) has a negative uniaxial structure of ny = nx> nz, while the stretched polyamide film (sample numbers 2 to 4) has ny>nx>. It was found to have a nz biaxial structure. Here, the maximum refractive index direction y was a stretched direction.
[0095]
Since the peeled polyamide film itself was a thin film and had poor self-supporting properties, the remaining part of the laminated film that was not used for the measurement was used to transfer the polyamide film to another transparent substrate. A transparent soda glass plate (thickness: 1.1 mm) with an adhesive applied to the surface is prepared, and the laminated film is laminated on the adhesive so that the adhesive and the polyamide film are in contact, and then the polyethylene naphthalate film is peeled off. did. In this way, a laminated glass having a polyamide film having a biaxial refractive index structure on the surface could be obtained. When the obtained laminated glass was sandwiched between two polarizing plates under crossed Nicols and the state of unevenness was observed, it was found that a uniform polymer film was obtained.
(Example 2)
A polymer represented by the formula (14) was synthesized as a film forming material.
[0096]
Embedded image

[0097]
The intrinsic viscosity of this polymer was 1.5 dl / g (30 ° C., 0.5 g / dl NMP solution). This polymer was dissolved in NMP to prepare a film forming material solution having a polymer concentration of 4% by weight.
[0098]
This film forming material solution was continuously applied onto a polyethylene terephthalate film having a width of 40 cm, a length of 500 m, and a thickness of 80 μm using a roll coater, and dried at 100 ° C. to obtain a laminated film. While this laminated film was heated to 150 ° C., it was stretched by applying a tension of 55 kgf in the longitudinal direction. The stretched laminated film had a lengthwise direction of 1.09 times and a width direction of about 0.95 times. The film thickness of the polymer layer on the laminated film after stretching was 10 μm.
[0099]
Since the polyethylene terephthalate film has birefringence with low uniformity in the plane and is not desirable for measuring the optical properties, the following peeling transfer operation was performed.
[0100]
First, an ultraviolet curable adhesive was applied on the polymer layer on the stretched laminated film, and a triacetyl cellulose film (length 500 m, 幡 40 cm, thickness 80 μm, manufactured by Fuji Photo Film Co., Ltd.) was laminated thereon. After irradiating ultraviolet rays to cure the adhesive, the polyethylene terephthalate was peeled from the polymer layer to obtain a laminate of the triacetyl cellulose film and the polymer layer.
[0101]
The obtained laminate was subjected to polarization analysis. There were two optical axes, and the angle between the optical axis and the normal of the laminate was 38 degrees. The direction in which the optical axis was projected on the surface of the laminate coincided with the longitudinal direction of the laminate.
[0102]
Further, this laminate was cut out by 1 m, and the distribution was examined by measuring in-plane retardation every 1 cm in the longitudinal direction and the width direction (except for 5 cm at both ends in the width direction of the portion where the polymer layer was laminated). . As a result, it was found that the retardation value was in the range of 213 nm ± 2 nm, and the birefringence could be controlled with an accuracy within ± 1%. Therefore, it was found that the obtained laminate was a uniform biaxial film.
(Example 3)
Using the same film forming material solution and polyethylene terephthalate film as in Example 2, coating and drying were performed in the same manner to prepare a laminated film. This laminated film was horizontally stretched using a tenter while being heated to 180 ° C. The lateral tension was 0.9 kgf per 1 cm length, and 3 kgf tension (0.07 kgf per cm) was applied in the longitudinal direction for conveyance. Stretching increased the film width by about 6%. After stretching, the polymer layer was transferred to the triacetyl cellulose film in the same manner as in Example 2 to obtain a laminate of the triacetyl cellulose film and the polymer layer.
[0103]
The obtained laminate was subjected to polarization analysis. There were two optical axes, and the angle between the optical axis and the normal of the laminate was 24 degrees. Further, the direction in which the optical axis was projected onto the surface of the laminate substantially coincided with the width direction of the laminate, and the distribution depending on the location in the plane of the laminate was ± 1 degree. The distribution of retardation in the plane was within ± 2%. Therefore, it was found that the obtained laminate was a uniform biaxial film.
Example 4
As one aspect of the optical film of the present invention, an optical element in which a polarizing element and a biaxial film were integrated was produced.
[0104]
The stretched polyvinyl alcohol film was impregnated with iodine and adhered to a triacetyl cellulose film using a thermosetting adhesive to obtain a polyvinyl alcohol-triacetyl cellulose laminate. Next, a thermosetting adhesive was applied on the polymer layer on the laminate of the triacetyl cellulose film and the polymer layer obtained in Example 3, and the polyvinyl alcohol film side of the polyvinyl alcohol-triacetyl cellulose laminate was The adhesive was cured by laminating and applying heat. The bonding direction was such that the stretching direction of the polyvinyl alcohol film and the roll longitudinal direction of the laminate of Example 3 were parallel. In this manner, an optical element having a polarizing layer and a birefringent layer between two triacetyl cellulose films could be produced.
(Example 5)
A compound of formula (15) was synthesized.
[0105]
Embedded image

[0106]
(Where R ^Three Is
[0107]
Embedded image

[0108]
R represents a group represented by R ^Four Is
[0109]
Embedded image

[0110]
The group represented by is shown. )
Moreover, the compound of Formula (16) and Formula (17) was obtained (Aronix M-117 and M-210 by Toa Gosei Co., Ltd. respectively).
[0111]
Embedded image

[0112]
(Wherein p and q are average degrees of polymerization, which are about 4 and about 2, respectively)
These compounds were mixed in a weight ratio of the compound of formula (15): the compound of formula (16): the compound of formula (17) = 50: 45: 5, and used as starting materials for the polymer film. In addition, although the compound of Formula (15) is a compound which has a discotic liquid crystal phase independently, the said starting material did not show liquid crystallinity, and was a viscous liquid at room temperature.
[0113]
Photoinitiator Irgacure 907 (manufactured by Ciba-Geigy) was added in an amount of 1.5% by weight to the starting material to obtain a film forming material composition. Diethylene glycol dimethyl ether solvent was added thereto to prepare a solution having a film forming material composition concentration of 15% by weight.
[0114]
This solution was applied to a polyphenylene sulfide film (manufactured by Toray Industries, Inc.) having a thickness of 50 μm, a length of 30 cm, and a width of 20 cm using a spin coating method, followed by drying in an oven at 80 ° C. for 10 minutes. While maintaining the temperature at 60 ° C., the coated surface was irradiated with ultraviolet rays using a high-pressure mercury lamp lamp, and the film-forming material composition was photocured and polymerized to obtain a laminated film having a polymer layer. When the refractive index of the polymer layer on the obtained laminated film was measured, it had a negative uniaxial structure, the in-plane refractive index was constant 1.59, and the refractive index in the film thickness direction was 1.56. I found out that
[0115]
Next, the laminated film was uniaxially stretched 1.1 times in the longitudinal direction at a constant speed (10 mm / min) in an oven at 200 ° C. The refractive index of the film after stretching was ny = 1.61, nx = 1.58, and nz = 1.56. The polymer layer on the obtained laminated film was transferred onto a glass substrate in the same manner as in Example 1. Observation was performed under polarized light, and as a result, it was found that the polymer layer on the glass substrate had a uniform biaxial structure without unevenness.
(Example 6)
A polymer represented by the formula (18) was synthesized as a film forming material.
[0116]
Embedded image

[0117]
The inherent viscosity of this polymer was 0.65 dl / g (30 ° C., 0.5 g / dl NMP solution). This film forming material was dissolved in NMP to prepare a 4 wt% film forming material solution, applied to a 20 cm square aluminum plate, and dried in an oven at 80 ° C. to obtain a laminated plate. The film thickness of the polymer layer on this laminate was 45 μm. Next, the polymer layer was carefully peeled from the aluminum plate to obtain a polymer film, which was stretched 1.05 times at 140 ° C. The polymer film after stretching was transparent and biaxial. It was 100 nm when the retardation which is a product of (nx-nz) and a film thickness was calculated | required by ellipsometry. Moreover, the in-plane retardation which is (ny-nz) and a film thickness was about 390 nm. When the projection direction of the optical axis onto the surface of the polymer film was examined in the range of 10 cm square at the center of the polymer film, a distribution of ± 4 degrees centered on the stretching direction of the polymer film was found. The in-plane retardation distribution was 390 nm ± 18 nm.

Claims (6)

Disposing a film forming material solution on a substrate and drying to obtain a surface-oriented optically negative uniaxial film, and stretching the negative uniaxial film, and having a refractive index structure of ny>nx> nz The manufacturing method of the optical film for liquid crystal display devices characterized by including the process made into the biaxial film which has this . The method for producing an optical film for a liquid crystal display device according to claim 1, wherein the substrate is a stretched film. 3. The method for producing an optical film for a liquid crystal display device according to claim 2, wherein in the step of stretching the negative uniaxial film, the negative uniaxial film is stretched while being heated together with the stretched film. The optical film for liquid crystal display devices obtained by the manufacturing method of any one of Claims 1-3. 5. The optical film for a liquid crystal display device according to claim 4, wherein the distribution of the projection direction of the film optical axis onto the film surface is within ± 2 °. A liquid crystal display element comprising the optical film for a liquid crystal display device according to claim 4.