JP2004170595A - Manufacture method of retardation film and the retardation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a retardation film having an excellent optical compensation effect, and to provide a manufacture method thereof. <P>SOLUTION: In the manufacture method, the retardation film is manufactured by the process comprising an operation of subjecting the birefringence inducing material to photoirradiation and heating/cooling: wherein, the birefringence inducing material is a material which induces the birefringence by virtue of the molecular motion due to the photoirradiation and heating and the molecular orientation based on the molecular motion. Further, the energy transfer material is added to the birefringence inducing material: wherein, the energy transfer material is a material which has a light absorption at a wavelength different from the light absorption wavelength of the birefringence inducing material and is capable of transferring the energy excited by light absorption to the birefringence inducing material. <P>COPYRIGHT: (C)2004,JPO

Description

【化１３】

【化１４】

【化１５】

【化１６】

【化１７】

【化１８】

【化１９】

【化２０】

但し、−Ｒ_１〜−Ｒ_１１＝−Ｈ、ハロゲン基、−ＣＮ、アルキル基またはメトキシ基などのアルキルオキシ基、またはそれらを弗化した基、−Ｒ_１２＝メチル基、エチル基などのアルキル基、またはそれらを弗化した基であり、ｘ：ｙ＝１００〜０：０〜１００、ｎ＝１〜１２、ｍ＝１〜１２、ｊ＝１〜１２、Ｘ，Ｙ，＝ｎｏｎｅ、−ＣＯＯ、−ＯＣＯ−、−Ｎ＝Ｎ−、−Ｃ＝Ｃ−ｏｒ−Ｃ_６Ｈ_４−、Ｗ_１，Ｗ_２＝化学式１または化学式２または化学式３または化学式４または化学式５または化学式６または化学式７または化学式８で表される構造である。
また、メソゲン成分として多用されているビフェニル、ターフェニル、フェニルベンゾエート、アゾベンゼンなどの置換基を有する結晶性または、液晶性を有する化学式１０ないしは化学式１１に示す低分子化合物を混合することもできる。混合する低分子化合物は、単一の化合物のみとは限らず複数種の化合物を混合することも可能である。
【化２１】

【化２２】

但し、ｏ＝０〜１２、ｐ＝０〜１２、ｑ＝０〜１２、Ｘ，Ｙ＝ｎｏｎｅ、−ＣＯＯ、−ＯＣＯ−、−Ｎ＝Ｎ−、−Ｃ＝Ｃ−ｏｒ−Ｃ_６Ｈ_４−、Ｗ_３，Ｗ_４，Ｗ_５，Ｗ_６＝化学式１または化学式２または化学式３または化学式４または化学式５または化学式６または化学式７または化学式８で表される構造またはメタクリロイル基、アクリロイル基、クロトニル基などである。
更には、液晶性を損なわない程度に配向性を向上させるための配向助剤や耐熱性を向上させるための架橋剤を添加することや、液晶性を損なうことなく液晶性を示さない単量体を感光性の重合体に共重合してもかまわない。
本発明で複屈折誘起材料に添加するエネルギ転移材料の特性と、その機能について図３、図４を参照して説明する。
図３は、横軸に照射光の波長をとり縦軸には照射光の波長別の相対分光強度をとった照射光スペクトルを細線で示すととともに、この照射光に対する複屈折誘起材料およびエネルギ転移材料の吸収強度をそれぞれ、一点鎖線および太実線で示し例示したものである。この例では、複屈折誘起材料の光吸収強度が波長ｈν１をピークとしているのに対して、エネルギ転移材料では、より長波長のｈν２に光吸収強度のピークを有する材料が用いられる。
図４に、複屈折誘起材料とエネルギ転移材料のエネルギ準位を並べ示し、エネルギ転移材料から複屈折誘起材料へのエネルギ転移を模式的に説明する。
光吸収により、複屈折誘起材料およびエネルギ転移材料は、それぞれ基底状態Ｓ_０、Ｓ´_０から異なるエネルギ準位の励起一重項状態Ｓ_１、Ｓ´_１に励起する。複屈折材料の励起一重項状態Ｓ_１のエネルギ準位は大きく照射光のｈν１の波長域にのみ光吸収を有し、より長波長の光は吸収されない。これに対し、エネルギ転移材料の光吸収による励起一重項状態Ｓ´_１のエネルギは、複屈折誘起材料の励起一重項状態Ｓ_１より小さく複屈折誘起材料に吸収されない長波長ｈν２の光を吸収することができる。
エネルギ転移材料の分子内では、光吸収により生じた励起一重項状態がよりエネルギ準位の低い励起三重項状態Ｔ´_１へ移る傾向が生じ、この励起三重項状態Ｔ´_１が複屈折誘起材料の励起三重項状態Ｔ_１とエネルギ準位が略等しい材料の場合、効果的にエネルギ転移材料から複屈折誘起材料へのエネルギ移動が起こる。このような経路のエネルギ移動によって、複屈折誘起材料はそれ自身が光吸収を有さない波長の光でも反応を進行するようになる。
このようなエネルギ転移材料は、フォトレジストなどに使われてきたような感光性基に対して光反応の増感作用を有するものが挙げられる。複屈折誘起材料の感光性基としてシンナモイル基を用い、照射する光源に高圧水銀灯を用いた場合は、シンナモイル基が吸収を有さない波長３６５ｎｍ付近に吸収を有する４，４’−ビス（ジエチルアミノ）ベンゾフェノン、ミヒラーズケトンなどを適宜使用することができる。これら化合物を添加する手段として、複屈折誘起材料に混合し相溶、分散させることや、複屈折誘起材料を重合する際にこれら化合物と同一もしくは類似した構造を含有した重合性の化合物を共重合させる方法が挙げられる。添加される化合物は、シンナモイル基に由来する光吸収波長より長波長側に吸収を有し、フィルム表面より入射した照射光のうちシンナモイル基に吸収されずにフィルム深部で到達する照射光のより長波長の光を吸収し、該光吸収により励起したエネルギを複屈折誘起材料の感光性基であるシンナモイル基へ転移し光反応を促進することができる。光反応の増感作用を有する化合物のエネルギ転移は、光反応の増感作用を有する化合物の励起三重項状態から複屈折誘起材料の感光性基の励起三重項状態へのエネルギ転移であり、電子交換相互作用を必要するため化合物同士の電子雲の重なりができる程度に近接した分子にのみエネルギ転移（デクスター転移）する。このため、偏光した光を照射したときに誘起する光吸収による励起エネルギは、その異方性を保ったまま複屈折誘起材料にエネルギ転移すると考えられる。このため、照射した偏光の電界振動方向でのみ増感され、光反応の異方性を乱すことなく促進することができる。このことにより、増感作用を有する化合物用いてもフィルム深部での分子の配向を増強させ位相差の増強とヘイズの低減を実現できる。
【０００６】
このように、エネルギ転移材料を添加することによりフィルム深部での分子の配向を増強させ位相差の増強とヘイズの低減を実現できる。フィルム深部まで光反応を促進するためには、添加する化合物の濃度を調節する必要があり、これらは分子−分子間のエネルギ転移が起こるための分子間距離が近くなるように勘案して添加されおり、その量は一般に１０重量％以上である。それにたいして本発明では請求項１または請求項２または請求項３の位相差フィルムおよびその製造法では、５％以下の添加量で充分な光増感反応が得られることを見出した。これは、本発明における、複屈折フィルムの作製が光増感反応と、分子運動に基づく配向の双方が関連しているためであると思われる。また、本発明の位相フィルムまたはその製造法では、エネルギ転移材料の過剰な添加は、フィルム深部までの照射光の到達を妨げ該部分で未反応となるため位相差の増強やヘイズの低減を実現できなくなるうえ、材料自体の液晶性を損ない分子配向を妨げ位相差の低下につながる原因となる。このことから、添加されるエネルギ転移材料の添加量は、添加する化合物の種類やその吸光係数にもよるが０．０５ｗｔ％以上、５ｗｔ％以下が好ましく、更には、０．０５ｗｔ％以上、３ｗｔ％以下が好ましい。
【０００７】
本発明の位相フィルムの製造例としては、照射する光の偏光度や照射角度によって複屈折性を調整された、光学的に１軸性の異方性を有するフィルム、光学的に２軸性の異方性を有するフィルム、それら屈折率楕円体がフィルム面に対して傾斜した配置にあるフィルム、本発明者が提案した特願平２００２−１１４４９０号に記載されているような、Ｘ軸、Ｙ軸、Ｚ軸方向に主屈折率ｎｘ、ｎｙ、ｎｚを有する２軸性の屈折率楕円体を想定し、該屈折率楕円体をＹ軸を回転軸として回転させ、更にＸ軸を回転軸として回転させた複屈折性を有する位相差フィルム、または、本発明者が提案した特願平２００２−１１４４９１号に記載されているような、Ｘ軸とＹ軸の成す面をフィルム面内としＺ軸を厚さ方向とした場合に、Ｘ軸方向に主屈折率ｎｘ、Ｙ軸方向に主屈折率ｎｙ、Ｚ軸方向に主屈折率ｎｚを有する第１の屈折率楕円体（ここで第１の屈折率楕円体の主屈折率の関係は、ｎｘ＞ｎｙ≧ｎｚである）と、第１の屈折率楕円体をＹ軸を回転軸として回転させ、更にＺ軸を回転軸として回転させた方向に主屈折率ｎｘ´ｎｙ´ｎｚ´を有する第２の屈折率楕円体（ここで第２の屈折率楕円体の主屈折率の関係は、ｎｘ´＞ｎｙ´≧ｎｚ´である）とを併せてなる複屈折性を有していることを特徴とする位相差フィルムを挙げることができる。但し、これに限定されるものではない。
本発明の位相差フィルムの実施例において用いた感光性重合体の原料化合物および低分子化合物に関する合成方法を以下に示す。
【０００８】
（単量体１）
４，４’−ビフェニルジオールと２−クロロエタノールを、アルカリ条件下で加熱することにより、４−ヒドロキシ−４’−ヒドロキシエトキシビフェニルを合成した。この生成物に、アルカリ条件下で１，６−ジブロモヘキサンを反応させ、４−（６−ブロモヘキシルオキシ）−４’−ヒドロキシエトキシビフェニルを合成した。次いで、リチウムメタクリレートを反応させ、４−ヒドロキシエトキシ−４’−（６−メタクリロイルヘキシルオキシ）ビフェニルを合成した。最後に、塩基性の条件下において、塩化シンナモイルを加え、化学式１２に示される単量体１を合成した。
【化２３】

【０００９】
（単量体２）
４，４’−ビフェニルジオールと１，６−ジブロモヘキサンを、アルカリ条件下で加熱することにより、４−ヒドロキシ−４’−（６−ブロモヘキシルオキシ）ビフェニルを合成した。この生成物に、リチウムメタクリレートを反応させ、４−ヒドロキシ−４’−（６−メタクリロイルヘキシルオキシ）ビフェニルを合成した。次いで、４−ヒドロキシエトキシ−４’−（６−メタクリロイルヘキシルオキシ）ビフェニルを合成した。最後に、塩基性の条件下において、ｐ−メトキシ桂皮酸クロライドを加え、化学式１３に示される単量体２を合成した。
【化２４】

【００１０】
（重合体１）
単量体１をテトラヒドロフラン中に溶解し、反応開始剤としてＡＩＢＮ（アゾビスイソブチロニトリル）を添加して重合することにより感光性の重合体１を得た。この重合体１は、４７−７５℃の温度領域において、液晶性を呈した。
【００１１】
（重合体２）
単量体１をテトラヒドロフラン中に溶解し、反応開始剤としてＡＩＢＮ（アゾビスイソブチロニトリル）を添加して重合することにより感光性の重合体２を得た。この重合体２も液晶性を呈した。
【００１２】
（低分子化合物１）
４，４’−ビフェニルジオールと６−ブロモヘキサノールを、アルカリ条件下で反応させ、４，４’− ビス（６−ブロモヘキシルオキシ）ビフェニルを合成した。次いで、塩基性の条件下において、メタクリル酸クロライドを加え反応させ、生成物を再結晶することにより化学式１４に示される低分子化合物１を合成した。
【化２５】

【００１３】
図１には、本発明の位相差フィルムの製造方法（装置）を、例を挙げて示す。紫外線ランプ（１２）、集光鏡（１３）、平面鏡（１４、１４´）、インテグレータレンズ（１５）、コリメーターレンズ（１６）などから構成されている通常用いられている光照射装置の光路中ないしは光照射装置と被照射サンプル（１１）の間に、非偏光性の紫外線を所望の偏光度に変換する素子（１７）を介して被照射サンプルに任意の方法で照射する。
実施例１から実施例３は、本発明の製造方法により光軸の傾いた位相差フィルムまたは異方性を有するフィルムを作製した実施例である。
【００１４】
（実施例１） ４．６８重量％の重合体１、１．２重量％の低分子化合物１および０．１２重量％（重合体１と低分子化合物の総重量に対し２重量％）の市販（東京化成）の４、４’−ビス（ジエチルアミノ）ベンゾフェノンをシクロヘキサノンに溶解し塗布溶液を調製した。該溶液をケン化処理したＴＡＣ基材（支持体）上に塗布し、約１．５μｍの厚さの塗布膜を作製した。
該基材を水平面に対して５５度傾け、塗布面が照射面となるように配置し、完全偏光成分と非偏光成分からなる偏光度（ここで、偏光度は、完全偏光成分／（完全偏光成分＋非偏光成分）×１００％である。）が６３．５％の紫外線を、完全偏光成分の電界振動方向が照射面の傾斜軸に対して４５°回転させて水平面に対し垂直方向から室温で２００ｍＪ／ｃｍ^２照射し、続いて、１００℃に加熱した後、室温まで冷却した。更に、配向を固定するために５００ｍＪ／ｃｍ^２の非偏光性の紫外光を照射した。このように作製した位相差フィルムのフィルム法線方向から見た場合のリタデーションは、６３３ｎｍの測定波長に対して９０ｎｍであった。また、目視によるヘイズは目立たず実用に耐え得るものであった。
【００１５】
（実施例２） ４．６８重量％の重合体１、１．２重量％の低分子化合物１および０．１２重量％（重合体１と低分子化合物の総重量に対し２重量％）の市販（東京化成）のミヒラーケトンをシクロヘキサノンに溶解し塗布溶液を調製した。該溶液をケン化処理したＴＡＣ基材（支持体）上に塗布し、約１．５μｍの厚さの塗布膜を作製した。
該基材を水平面に対して５５度傾け、塗布面が照射面となるように配置し、完全偏光成分と非偏光成分からなる偏光度が６３．５％の紫外線を、完全偏光成分の電界振動方向が照射面の傾斜軸に対して４５°回転させて水平面に対し垂直方向から室温で２００ｍＪ／ｃｍ^２照射し、続いて、１００℃に加熱した後、室温まで冷却した。このように作製した位相差フィルムのフィルム法線方向から見た場合のリタデーションは、６３３ｎｍの測定波長に対して９６ｎｍであった。また、目視によるヘイズは目立たず実用に耐え得るものであった。
【００１６】
（実施例３） ９．８重量％の重合体２と０．２重量％の市販（東京化成）の４、４’−ビス（ジエチルアミノ）ベンゾフェノンをジクロロエタンに溶解し塗布溶液を調製した。該溶液をガラス基板上にスピンコーターを用いて塗布し、約３００ｎｍの厚さの塗布膜を作製した。
該基材の塗布面側から、直線偏光性の紫外線を室温で５０ｍＪ／ｃｍ^２照射し、続いて、１００℃に加熱した後、室温まで冷却した。このように作製した塗布膜の配向度Ｓ（配向度Ｓは、Ｓ＝（Ａ／／−Ａ⊥）／（Ａ／／＋２×Ａ⊥）であり、ここで、Ａ／／は、波長３２０ｎｍにおける照射した直線偏光性の紫外線の電界振動方向と平行方向の吸光度、Ａ⊥は、波長３２０ｎｍにおける照射した直線偏光性の紫外線の電界振動方向と垂直方向の吸光度である。）は、０．８０であった。
【００１７】
実施例１または実施例２で作製した位相差フィルムを、カシオ製液晶カラーテレビＥＶ−５１０の偏光シートを剥がし、液晶セルの上下面に１枚ずつ貼り合わせ、次いで、偏光シート（日東電工製 ＨＥＧ１４２５ＤＵ）を上下１枚ずつ貼り合わせた。各光学素子の軸配置は、図２のようにした。
図２において、２１、２１´は本発明の位相差フィルムであり、ａ、ａ´はその位相鎖フィルムを正面から見たときの遅相軸の方向を示し、２２は液晶セルであり、ｂ、ｂ´がプレチルト方向を示し、２３、２３´は偏光シートであり、ｃ、ｃ´がそれぞれの光透過軸方向を示している。
このような構成で液晶カラーテレビを駆動したところ、実施例１および実施例２の両方のフィルムとも左右方向で黄色味を呈することなく、大幅に視野角特性が改善され、更に、上下方向でも視野角拡大効果が確認された。
【００１８】
（比較例１） 実施例１と同様に、４．６８重量％の重合体１および１．２重量％の低分子化合物１をシクロヘキサノンに溶解し塗布溶液を調製し、ケン化処理したＴＡＣ基材（支持体）（支持体）上に約１．５μｍの厚さで塗布した。
実施例１と同様の方法で、完全偏光成分と非偏光成分からなる偏光度が６３．５％の紫外線を６００ｍＪ／ｃｍ^２照射し、続いて、１００℃に加熱した後、室温まで冷却した。このように作製した位相差フィルムのフィルム法線方向から見た場合のリタデーションは、６３３ｎｍの測定波長に対して４３ｎｍであった。また、ヘイズの発生も顕著であった。
【００１９】
（比較例２） 実施例３と同様に、９．８重量％の重合体２をジクロロエタンに溶解し塗布溶液を調製した。該溶液をガラス基板上にスピンコーターを用いて塗布し、約３００ｎｍの厚さの塗布膜を作製した。
該基材の塗布面側から、直線偏光性の紫外線を室温で４０００ｍＪ／ｃｍ^２照射し、続いて、１００℃に加熱した後、室温まで冷却した。このように作製した塗布膜の配向度Ｓは、０．７５であった。
【００２０】
実施例１と実施例２から、複屈折誘起材料に光照射と加熱冷却する操作を含む工程によって作製される位相差フィルムの製造法において、複屈折誘起材料にエネルギ転移材料を添加することによって従来課題を解決した位相差フィルムおよびその製造法が得られることが立証された。更には、実施例１と比較例１、実施例３と比較例２の比較によると、エネルギ転移材料を添加することにより製造工程における光の照射量をも削減でき、製造コストを低減できることも判明した。
【００２１】
【発明の効果】
従来技術の位相差フィルムでは製造装置および工程が煩雑になるなどの問題があったが、本発明の、光照射と加熱による分子運動とそれに基づく分子配向により複屈折を誘起する材料（＝複屈折誘起材料）に光照射と加熱冷却する操作を含む工程によって作製される位相差フィルムの製造法において、複屈折誘起材料の光吸収波長と異なる波長に光吸収を有しかつ複屈折誘起材料に光吸収により励起したエネルギを転移可能な材料（＝エネルギ転移材料）を複屈折誘起材料に添加することによって従来技術の問題点を解決した液晶表示装置の視野角拡大に有効な位相差フィルムおよびその製造法を提供できる。更には、製造工程における光の照射量をも削減でき製造コストを低減できる。
【００２２】
【図面の簡単な説明】
【図１】本発明の位相差フィルムの製造方法を示す概念図
【図２】視野角特性評価時の光学系
【図３】照射光の相対分光強度スペクトルと、この照射光に対する複屈折誘起材料およびエネルギ転移材料の吸収強度を示す。
【図４】エネルギ転移材料から複屈折誘起材料へのエネルギ転移を模式的に示す。
【符号の説明】
１０・・・本発明に適した位相差フィルムの製造装置を示す。
１１・・・被照射材料（複屈折誘起材料）
１２・・・紫外線ランプ
２０・・・実施例評価用の光学系を示す。
２１、２１’・・・位相差フィルム
ａ、ａ’・・・遅相軸の方向を示す。
２２・・・液晶セル
ｂ、ｂ’・・・プレチルト方向を示す。
２３、２３’・・・偏光シート
ｃ、ｃ’・・・光透過軸方向を示す。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a retardation film used for improving viewing angle characteristics of a polarizing plate in a liquid crystal display device or the like.
[0002]
[Prior art]
The retardation film is a film having birefringence that transmits linearly polarized components that vibrate in directions of principal axes perpendicular to each other and gives a necessary retardation between the two components. Such a retardation film has been utilized in the field of liquid crystal display, and in particular, a retardation film in which a liquid crystalline material having a negative birefringence is inclined or bend-aligned is effective in expanding the viewing angle of a liquid crystal display device. It has been used as an optical compensation film. Although such a retardation film provides a significant viewing angle widening effect, depending on the direction in which the liquid crystal display device is viewed, an optical compensation effect cannot be obtained sufficiently and cannot be used as a substitute for a CRT. is there.
Further, such a retardation film can be used for rubbing, SiO oblique deposition, light irradiation, etc., as described in JP-A-7-287119, JP-A-7-287120, and JP-A-10-278123. A liquid crystal material that is a negative refractive index ellipsoid such as a discotic liquid crystal is arranged on an alignment film that has been subjected to alignment treatment by the method. This discotic liquid crystal has a structure like a triphenylene skeleton, and because of its large wavelength dispersion, when mounted on a liquid crystal display device, the display becomes yellowish in the left-right direction at the viewing angle, and the image quality deteriorates. is there. In addition, such a method using an alignment film requires steps such as an alignment material coating and drying process, an alignment film alignment process, an alignment liquid crystal material coating and drying process, and a liquid crystal material alignment process. There are also problems such as becoming.
As a method for solving such a complicated process, there is a method for expressing a phase difference by light irradiation. As such a method, a retardation film having a negative uniaxial property in which the optical axis is inclined by irradiating a polymer sheet containing an azobenzene portion photoisomerized in JP-A-7-168020 and JP-A-7-207037. However, it is considered that this film lacks practicality in terms of heat resistance and the like because it uses photoisomerization of azobenzene. Japanese Patent Application Laid-Open No. 11-160708 also mentions a method of irradiating a two-color photoisomerization-reactive liquid crystalline alignment material substituted with an azobenzene derivative, but only for confirming the expression of birefringence by light irradiation. There is no mention of practicality. Further, in JP-A-11-183722, a film of a liquid crystalline material having a photoreactive substituent is irradiated with light, and the direction of fast axis in the film plane of the film or the slow axis direction in which the projection direction to the irradiation direction of irradiation light is obtained. There is described a retardation film that coincides with the phase axis direction, and that the inclination angle dependency of the retardation value when the fast axis or the slow axis is the tilt axis is asymmetric with respect to the normal direction. However, when the inclination angle dependency of the retardation value when the fast axis or the slow axis is the tilt axis is only asymmetric with respect to the normal direction, the viewing angle when mounted on the liquid crystal display device There is a problem in that the image quality is degraded, for example, the display is yellowish in the left-right direction, and the optical compensation effect is not sufficient. In contrast to these prior arts, the present inventors disclosed in Japanese Patent Application Nos. 2002-114490 and 2002-114491 that light irradiation, light irradiation and heating / cooling induce light irradiation or light irradiation and heating. A retardation film produced by a process including a cooling operation and a method for producing the same were proposed. However, in these methods, if the film thickness is increased in order to obtain a large phase difference, the light absorption of the material itself is strong, so that the irradiated light does not reach the inside of the film or the opposite surface, and the orientation in the part is sufficiently induced. However, when it is used as an optical compensation film used for a liquid crystal display device or the like, there is a problem that a decrease in contrast is caused. Moreover, as a method for solving this, a method of applying light to a light-transmitting base material described in JP-A-2002-90539 and irradiating light from the coated surface side and the back surface side of the base material can be used. Since the light is irradiated from the direction, there is a problem that the manufacturing apparatus and the process become complicated.
[Patent Document 1]
JP-A-7-168020 [Patent Document 2]
JP-A-7-207037 [Patent Document 3]
JP-A-11-160708 [Patent Document 4]
JP-A-11-183722 [Patent Document 5]
Japanese Patent Laid-Open No. 11-189665
[Problems to be solved by the invention]
The present invention provides a retardation film that improves the viewing angle characteristics of a TN liquid crystal display device, that is, reduces coloring phenomenon and gradation inversion, and an industrial production method of the retardation film.
[0004]
[Means for Solving the Problems]
The inventors of a retardation film produced by a process including light irradiation, heating and cooling operations on a material that induces birefringence by molecular movement based on light irradiation and heating and molecular orientation based on the movement (= birefringence inducing material). In the manufacturing method, birefringence induction is performed on a material that has light absorption in a wavelength region different from the light absorption wavelength of the birefringence inducing material and can transfer energy excited by light absorption to the birefringence inducing material (= energy transfer material). The inventors have found that the above-mentioned problems can be solved by adding to the material, and have come to the invention.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Details of the present invention will be described below.
The present invention is characterized in that an energy transfer material is added to a birefringence inducing material in a method for producing a retardation film produced by a process including an operation of irradiating light and heating and cooling the birefringence inducing material.
As a method for producing the retardation film of the present invention, the present inventor uses a material that causes birefringence by light irradiation and heating and cooling as described in Japanese Patent Application Laid-Open No. 11-189665 and Japanese Patent Application No. 2000-400356. Can be used. These materials include photosensitive groups such as cinnamoyl group, chalcone group, cinnamylidene group, β- (2-furyl) acryloyl group (or their derivatives) as shown in Chemical Formula 1 to Chemical Formula 8, and high liquid crystallinity. It has a side chain that includes a structure in which substituents such as biphenyl, terphenyl, phenylbenzoate, and azobenzene, which are frequently used as mesogenic components of the molecule, and has a structure such as hydrocarbon, acrylate, methacrylate, and siloxane as the main chain. Examples thereof include a polymer represented by the following chemical formula 9. The polymer may be a single polymer composed of the same repeating unit or a copolymer of units having side chains with different structures, or a unit having side chains not containing a photosensitive group can be copolymerized. .
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However, -R ₁ to -R ₁₁ = -H, a halogen group, -CN, an alkyloxy group such as an alkyl group or a methoxy group, or a group obtained by fluorination thereof, -R ₁₂ = an alkyl such as a methyl group or an ethyl group Group, or a group obtained by fluorinating them, x: y = 100 to 0: 0 to 100, n = 1 to 12, m = 1 to 12, j = 1 to 12, X, Y, = none, − COO, —OCO—, —N═N—, —C═C—or—C ₆ H ₄ —, W ₁ , W ₂ = Chemical Formula 1 or Chemical Formula 2 or Chemical Formula 3 or Chemical Formula 4 or Chemical Formula 5 or Chemical Formula 6 or Chemical Formula 7 or a structure represented by Chemical Formula 8.
In addition, low molecular weight compounds represented by Chemical Formula 10 or Chemical Formula 11 having crystallinity or liquid crystallinity having substituents such as biphenyl, terphenyl, phenylbenzoate, and azobenzene, which are frequently used as mesogenic components, can also be mixed. The low molecular compound to be mixed is not limited to a single compound, and a plurality of types of compounds can be mixed.
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However, o = 0~12, p = 0~12 , q = 0~12, X, Y = none, -COO, -OCO -, - N = N -, - C = C-or-C 6 H 4 -, W ₃ , W ₄ , W ₅ , W ₆ = Chemical Formula 1 or Chemical Formula 2 or Chemical Formula 3 or Chemical Formula 4 or Chemical Formula 5 or Chemical Formula 6 or Chemical Formula 7 or Chemical Formula 8 or a Methacryloyl Group, Acryloyl Group, Crotonyl Group.
Furthermore, a monomer which does not exhibit liquid crystallinity without adding an alignment aid for improving alignment to the extent that liquid crystallinity is not impaired or a crosslinking agent for improving heat resistance, or without impairing liquid crystallinity. May be copolymerized with a photosensitive polymer.
The characteristics and functions of the energy transfer material added to the birefringence inducing material in the present invention will be described with reference to FIGS.
FIG. 3 shows the irradiation light spectrum in which the horizontal axis represents the wavelength of the irradiation light and the vertical axis represents the relative spectral intensity for each wavelength of the irradiation light, and the birefringence inducing material and energy transfer for the irradiation light. The absorption strength of the material is illustrated by a dashed line and a thick solid line, respectively. In this example, the light absorption intensity of the birefringence inducing material has a peak at the wavelength hν1, whereas the energy transfer material uses a material having a light absorption intensity peak at a longer wavelength hν2.
FIG. 4 shows the energy levels of the birefringence inducing material and the energy transfer material, and the energy transfer from the energy transfer material to the birefringence inducing material is schematically described.
By light absorption, the birefringence inducing material and the energy transfer material are excited from ground states S ₀ and S ′ ₀ to excited singlet states S ₁ and S ′ ₁ having different energy levels, respectively. Energy level of the excited singlet state S ₁ of the birefringent material has a light absorption only in a wavelength range of hν1 of large irradiation light, more light of a longer wavelength is not absorbed. On the other hand, the energy of the excited singlet state S ′ ₁ due to light absorption of the energy transfer material is smaller than the excited singlet state S _{1 of the} birefringence inducing material and absorbs light having a long wavelength hν 2 that is not absorbed by the birefringence inducing material. be able to.
Within the molecule of the energy transfer material, the excited singlet state generated by light absorption tends to shift to an excited triplet state T ′ _{1 having} a lower energy level, and this excited triplet state T ′ ₁ is birefringence inducing material. In the case of a material having substantially the same energy level as that of the excited triplet state T ₁ , energy transfer from the energy transfer material to the birefringence inducing material effectively occurs. Due to the energy transfer of such a path, the birefringence inducing material proceeds to react even with light having a wavelength that does not absorb light.
Examples of such energy transfer materials include those having a photoreaction sensitizing action on photosensitive groups such as those used in photoresists. When a cinnamoyl group is used as the photosensitive group of the birefringence inducing material and a high-pressure mercury lamp is used as the light source for irradiation, 4,4′-bis (diethylamino) having an absorption at a wavelength of about 365 nm where the cinnamoyl group has no absorption. Benzophenone, Michler's ketone, etc. can be used as appropriate. As a means of adding these compounds, they are mixed with a birefringence inducing material, mixed and dispersed, and when a birefringence inducing material is polymerized, a polymerizable compound containing the same or similar structure as these compounds is copolymerized. The method of letting it be mentioned. The added compound has absorption on the longer wavelength side than the light absorption wavelength derived from the cinnamoyl group, and is longer than the irradiation light that reaches the deep part of the film without being absorbed by the cinnamoyl group out of the irradiation light incident from the film surface. Light of a wavelength is absorbed, and energy excited by the light absorption can be transferred to a cinnamoyl group that is a photosensitive group of the birefringence inducing material to promote a photoreaction. The energy transfer of a compound having a photoreaction sensitizing action is an energy transfer from the excited triplet state of the photoreactive sensitizing compound to the excited triplet state of the photoreactive group of the birefringence inducing material. Since exchange interaction is required, energy transfer (Dexter transition) occurs only in molecules close enough to allow overlapping of electron clouds between compounds. For this reason, it is considered that the excitation energy due to light absorption induced when irradiated with polarized light is transferred to the birefringence inducing material while maintaining its anisotropy. For this reason, it is sensitized only in the electric field vibration direction of the irradiated polarized light, and can be promoted without disturbing the anisotropy of the photoreaction. Accordingly, even when a compound having a sensitizing action is used, the molecular orientation in the deep part of the film can be enhanced, and the retardation can be enhanced and the haze can be reduced.
[0006]
As described above, by adding the energy transfer material, it is possible to enhance the molecular orientation in the deep part of the film, thereby enhancing the retardation and reducing the haze. In order to promote the photoreaction to the deep part of the film, it is necessary to adjust the concentration of the compound to be added. These are added considering the intermolecular distance for the energy transfer between molecules to be close. The amount is generally 10% by weight or more. On the other hand, in the present invention, it has been found that the retardation film of claim 1 or claim 2 or claim 3 and the production method thereof can obtain a sufficient photosensitizing reaction with an addition amount of 5% or less. This seems to be because the production of a birefringent film in the present invention involves both photosensitization reaction and orientation based on molecular motion. In addition, in the phase film of the present invention or the manufacturing method thereof, excessive addition of the energy transfer material prevents the irradiation light from reaching the deep part of the film and becomes unreacted at the part, thereby realizing an increase in phase difference and a reduction in haze. In addition, the liquid crystallinity of the material itself is impaired and molecular orientation is hindered, leading to a decrease in retardation. Accordingly, the amount of energy transfer material added is preferably 0.05 wt% or more and 5 wt% or less, although it depends on the type of compound to be added and its extinction coefficient, and more preferably 0.05 wt% or more and 3 wt%. % Or less is preferable.
[0007]
Examples of the production of the phase film of the present invention include an optically uniaxial anisotropy film whose birefringence is adjusted by the degree of polarization and the irradiation angle of the irradiated light, and an optically biaxial film. Films having anisotropy, films in which the refractive index ellipsoids are inclined with respect to the film surface, X axis, Y as described in Japanese Patent Application No. 2002-114490 proposed by the present inventor Assuming a biaxial refractive index ellipsoid having principal refractive indexes nx, ny, and nz in the axis and Z axis directions, rotating the refractive index ellipsoid around the Y axis as the rotation axis, and further using the X axis as the rotation axis A rotated retardation film, or a surface formed by the X-axis and the Y-axis, as described in Japanese Patent Application No. 2002-114491 proposed by the present inventor, is in-plane with the Z-axis. Is the main refraction in the X-axis direction. nx, a first refractive index ellipsoid having a main refractive index ny in the Y-axis direction and a main refractive index nz in the Z-axis direction (where the relationship of the main refractive index of the first refractive index ellipsoid is nx> ny ≧ nz), the second refractive index having the main refractive index nx'ny'nz 'in the direction rotated about the Y-axis as the rotation axis and further rotated around the Z-axis as the rotation axis. And a birefringence of the second refractive index ellipsoid (the relationship of the main refractive index of the second refractive index ellipsoid is nx ′> ny ′ ≧ nz ′). A retardation film can be mentioned. However, it is not limited to this.
The synthesis method regarding the raw material compound and low molecular weight compound of the photosensitive polymer used in the examples of the retardation film of the present invention is shown below.
[0008]
(Monomer 1)
4-Hydroxy-4'-hydroxyethoxybiphenyl was synthesized by heating 4,4'-biphenyldiol and 2-chloroethanol under alkaline conditions. This product was reacted with 1,6-dibromohexane under alkaline conditions to synthesize 4- (6-bromohexyloxy) -4′-hydroxyethoxybiphenyl. Subsequently, lithium methacrylate was reacted to synthesize 4-hydroxyethoxy-4 ′-(6-methacryloylhexyloxy) biphenyl. Finally, cinnamoyl chloride was added under basic conditions to synthesize monomer 1 represented by Chemical Formula 12.
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[0009]
(Monomer 2)
4-Hydroxy-4 ′-(6-bromohexyloxy) biphenyl was synthesized by heating 4,4′-biphenyldiol and 1,6-dibromohexane under alkaline conditions. This product was reacted with lithium methacrylate to synthesize 4-hydroxy-4 ′-(6-methacryloylhexyloxy) biphenyl. Next, 4-hydroxyethoxy-4 ′-(6-methacryloylhexyloxy) biphenyl was synthesized. Finally, p-methoxycinnamic acid chloride was added under basic conditions to synthesize monomer 2 represented by chemical formula 13.
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[0010]
(Polymer 1)
Monomer 1 was dissolved in tetrahydrofuran, and AIBN (azobisisobutyronitrile) was added as a reaction initiator for polymerization to obtain photosensitive polymer 1. The polymer 1 exhibited liquid crystallinity in a temperature range of 47 to 75 ° C.
[0011]
(Polymer 2)
The monomer 1 was dissolved in tetrahydrofuran, and AIBN (azobisisobutyronitrile) was added as a reaction initiator for polymerization to obtain a photosensitive polymer 2. This polymer 2 also exhibited liquid crystallinity.
[0012]
(Low molecular compound 1)
4,4′-biphenyldiol and 6-bromohexanol were reacted under alkaline conditions to synthesize 4,4′-bis (6-bromohexyloxy) biphenyl. Next, methacrylic acid chloride was added and reacted under basic conditions, and the product was recrystallized to synthesize a low molecular compound 1 represented by Chemical Formula 14.
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[0013]
In FIG. 1, the manufacturing method (apparatus) of the retardation film of this invention is shown as an example. In the optical path of a commonly used light irradiation device composed of an ultraviolet lamp (12), a condenser mirror (13), a plane mirror (14, 14 '), an integrator lens (15), a collimator lens (16), etc. Alternatively, the irradiated sample is irradiated by an arbitrary method between the light irradiation device and the irradiated sample (11) via an element (17) that converts non-polarizing ultraviolet light into a desired degree of polarization.
Examples 1 to 3 are examples in which a retardation film having an inclined optical axis or a film having anisotropy was produced by the production method of the present invention.
[0014]
Example 1 4.68% by weight of polymer 1, 1.2% by weight of low molecular weight compound 1 and 0.12% by weight (2% by weight based on the total weight of polymer 1 and the low molecular weight compound) A coating solution was prepared by dissolving 4,4′-bis (diethylamino) benzophenone (Tokyo Kasei) in cyclohexanone. The solution was applied on a saponified TAC substrate (support) to prepare a coating film having a thickness of about 1.5 μm.
The substrate is tilted by 55 degrees with respect to the horizontal plane, and the coating surface is arranged to be the irradiation surface, and the degree of polarization composed of a completely polarized component and a non-polarized component (where the degree of polarization is a completely polarized component / (completely polarized component) Component + non-polarized component) × 100%)) of 63.5% ultraviolet light, the electric field oscillation direction of the completely polarized component is rotated 45 ° with respect to the tilt axis of the irradiated surface, and the room temperature is perpendicular to the horizontal plane. Was irradiated with 200 mJ / cm ² , followed by heating to 100 ° C. and then cooling to room temperature. Furthermore, in order to fix the orientation, non-polarizing ultraviolet light of 500 mJ / cm ² was irradiated. The retardation of the retardation film produced in this manner when viewed from the film normal direction was 90 nm with respect to the measurement wavelength of 633 nm. Further, visual haze was inconspicuous and could withstand practical use.
[0015]
Example 2 4.68% by weight of polymer 1, 1.2% by weight of low molecular weight compound 1 and 0.12% by weight (2% by weight based on the total weight of polymer 1 and the low molecular weight compound) (Tokyo Kasei) Michler's ketone was dissolved in cyclohexanone to prepare a coating solution. The solution was applied on a saponified TAC substrate (support) to prepare a coating film having a thickness of about 1.5 μm.
The base material is tilted 55 degrees with respect to the horizontal plane, and the coating surface is arranged to be the irradiation surface. The direction was rotated by 45 ° with respect to the tilt axis of the irradiated surface, and 200 mJ / cm ^{2 was} irradiated from the direction perpendicular to the horizontal plane at room temperature, followed by heating to 100 ° C. and then cooling to room temperature. The retardation of the retardation film produced as described above when viewed from the film normal direction was 96 nm with respect to the measurement wavelength of 633 nm. Further, visual haze was inconspicuous and could withstand practical use.
[0016]
Example 3 A coating solution was prepared by dissolving 9.8% by weight of Polymer 2 and 0.2% by weight of commercially available (4,4'-bis (diethylamino) benzophenone in Tokyo Kasei) in dichloroethane. The solution was applied on a glass substrate using a spin coater to prepare a coating film having a thickness of about 300 nm.
From the coated surface side of the substrate, linearly polarized ultraviolet light was irradiated at 50 mJ / cm ² at room temperature, subsequently heated to 100 ° C., and then cooled to room temperature. The orientation degree S (orientation degree S of the coating film thus produced is S = (A // − A⊥) / (A // + 2 × A⊥), where A // is a wavelength of 320 nm. The absorbance in the direction parallel to the electric field vibration direction of the linearly polarized ultraviolet light irradiated at A and A⊥ is the absorbance in the direction perpendicular to the electric field vibration direction of the linearly polarized ultraviolet light irradiated at a wavelength of 320 nm. Met.
[0017]
The retardation film produced in Example 1 or Example 2 is peeled off the polarizing sheet of the Casio liquid crystal color television EV-510, and bonded to the upper and lower surfaces of the liquid crystal cell one by one. ) Were attached one above the other. The axial arrangement of each optical element was as shown in FIG.
In FIG. 2, 21 and 21 ′ are retardation films of the present invention, a and a ′ indicate the direction of the slow axis when the phase chain film is viewed from the front, 22 is a liquid crystal cell, and b B ′ indicate the pretilt direction, 23 and 23 ′ indicate polarizing sheets, and c and c ′ indicate the respective light transmission axis directions.
When the liquid crystal color television was driven in such a configuration, both the films of Example 1 and Example 2 did not exhibit yellowishness in the left-right direction, and the viewing angle characteristics were greatly improved. A corner enlargement effect was confirmed.
[0018]
(Comparative Example 1) In the same manner as in Example 1, 4.68% by weight of polymer 1 and 1.2% by weight of low molecular weight compound 1 were dissolved in cyclohexanone to prepare a coating solution, and saponified TAC substrate (Support) The film was applied on the (support) to a thickness of about 1.5 μm.
In the same manner as in Example 1, 600 mJ / cm ² of ultraviolet light having a polarization degree of 63.5% composed of a completely polarized component and a non-polarized component was irradiated, followed by heating to 100 ° C. and then cooling to room temperature. The retardation of the retardation film produced in this way when viewed from the film normal direction was 43 nm with respect to the measurement wavelength of 633 nm. Moreover, the occurrence of haze was also remarkable.
[0019]
(Comparative Example 2) In the same manner as in Example 3, 9.8% by weight of the polymer 2 was dissolved in dichloroethane to prepare a coating solution. The solution was applied on a glass substrate using a spin coater to prepare a coating film having a thickness of about 300 nm.
From the coated surface side of the substrate, linearly polarized ultraviolet light was irradiated at 4000 mJ / cm ² at room temperature, subsequently heated to 100 ° C., and then cooled to room temperature. The orientation degree S of the coating film thus produced was 0.75.
[0020]
From Example 1 and Example 2, in the manufacturing method of the retardation film produced by the process including the operation of irradiating the light to the birefringence inducing material and heating and cooling, it is conventional by adding the energy transfer material to the birefringence inducing material. It was proved that a retardation film and a method for producing the same were obtained. Furthermore, according to the comparison between Example 1 and Comparative Example 1 and Example 3 and Comparative Example 2, it was found that the amount of light irradiation in the manufacturing process can be reduced by adding the energy transfer material, and the manufacturing cost can be reduced. did.
[0021]
【The invention's effect】
The conventional retardation film has problems such as complicated manufacturing equipment and processes, but the material of the present invention that induces birefringence by molecular movement by light irradiation and heating and molecular orientation based on it (= birefringence) In the method for producing a retardation film produced by a process including irradiation with light and heating and cooling to the inducing material), the inducing material has light absorption at a wavelength different from the light absorption wavelength of the birefringence inducing material and Retardation film effective for widening the viewing angle of liquid crystal display device which solved the problems of the prior art by adding a material capable of transferring energy excited by absorption (= energy transfer material) to birefringence inducing material and its manufacture Can provide law. Furthermore, the amount of light irradiation in the manufacturing process can be reduced, and the manufacturing cost can be reduced.
[0022]
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing a method for producing a retardation film of the present invention. FIG. 2 is an optical system for viewing angle characteristic evaluation. FIG. 3 is a relative spectral intensity spectrum of irradiated light and a birefringence inducing material for the irradiated light. And the absorption strength of the energy transfer material.
FIG. 4 schematically shows energy transfer from an energy transfer material to a birefringence inducing material.
[Explanation of symbols]
10: An apparatus for producing a retardation film suitable for the present invention is shown.
11 ... Irradiated material (birefringence inducing material)
12... UV lamp 20... An optical system for evaluating the examples.
21, 21 '... retardation film a, a' ... shows the direction of the slow axis.
22... Liquid crystal cells b, b ′... Pretilt direction.
23, 23 '... polarizing sheets c, c' ... light transmission axis directions.

Claims (5)

A method for producing a retardation film, which is produced by adding a light irradiation operation and a heating / cooling operation to a birefringence inducing material which generates molecular motion by light irradiation or heating and induces birefringence by molecular orientation based on the movement,
An energy transfer material having a light absorption property at least in a wavelength region different from the light absorption wavelength region of the birefringence inducing material and capable of transferring energy excited by light absorption to the birefringence inducing material is previously introduced into the birefringence inducing material. A method for producing a retardation film, comprising adding to a material. A method for producing a retardation film, wherein a three-dimensional molecular orientation is induced in the retardation film produced in claim 1. 3. The birefringence inducing material according to claim 1, wherein the birefringence inducing material is a compound having a structure represented by chemical formula 9, or a material in which the compound is mixed with a compound represented by chemical formula 10 and / or chemical formula 11. A method for producing a retardation film.

However, x: y = 100-0: 0-0, n = 1-12, m = 1-12, j = 1-12, X, Y = none, -COO, -OCO-, -N = N- _{, -C = C-or-C} 6 H 4 -, is a structure represented by W 1, _{W 2} = formula 1 or formula 2 or 3 or formula 4 or formula 5 or chemical formula 6 or formula 7 or formula 8 .

However, -R ₁ to -R ₁₁ = -H, a halogen group, -CN, an alkyloxy group such as an alkyl group or a methoxy group, or a group obtained by fluorination thereof, -R ₁₂ = an alkyl such as a methyl group or an ethyl group A group, or a group obtained by fluorination thereof.

However, o = 0~12, p = 0~12 , q = 0~12, X, Y = none, -COO, -OCO -, - N = N -, - C = C-or-C 6 H 4 -, W ₃ , W ₄ , W ₅ , W ₆ = Chemical Formula 1 or Chemical Formula 2 or Chemical Formula 3 or Chemical Formula 4 or Chemical Formula 5 or Chemical Formula 6 or Chemical Formula 7 or Chemical Formula 8 or a Methacryloyl Group, Acryloyl Group, Crotonyl Group. 4. The method for producing a retardation film according to claim 1, wherein an addition amount of the energy transfer material is 0.05 wt% or more and 5 wt% or less with respect to the birefringence inducing material. A method for producing a retardation film. A retardation film obtained by the method for producing a retardation film according to claim 1.

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