JP2004212911A - Method of manufacturing wide band cholesteric liquid crystal film, circular polarizing plate, linear polarizer, lighting device and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a wide band cholesteric liquid crystal film easily and inexpensively with the thickness of a liquid crystal layer reduced. <P>SOLUTION: The method of manufacturing the wide band cholesteric liquid crystal film has a process for applying a solution prepared by dissolving a cholesteric liquid crystal polymer in a solvent on an alignment base material, a process for aligning the cholesteric spiral axis of the cholesteric liquid crystal polymer to be perpendicular to the alignment base material surface and a process for drying and film forming while keeping the liquid crystal state formed by the orientation. As the cholesteric liquid crystal polymer, a mixture of ≥2 kinds of cholesteric liquid crystal polymers non-compatible with each other and having twist pitch length different each is used. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

（式中、Ｒ^１ は水素原子またはメチル基を、ｍは１〜６の整数を、Ｘ^１ は−ＣＯ_２ −基、−ＯＣＯ−基、−ＣＯ−、−ＣＨ＝ＣＨ−または−Ｃ≡Ｃ−を、Ｒ^２ は炭素数１〜６のアルコキシ基、シアノ基、フルオロ基または炭素数１〜６のアルキル基を、ｐおよびｑは１または２を示す。）で表されるアクリル酸エステル誘導体があげられる。
【００４０】
一般式（ａ）で表されるアクリル酸エステル誘導体において、ｐ＝１が好ましく、ｑ＝２が好ましく、Ｒ^１ としては水素原子が好ましく、Ｒ^２ としてはシアノ基が好ましく、Ｘ^１ としては−ＣＯＯ−基が好ましい。一般式（ａ）で表されるアクリル酸エステル誘導体の具体例としては、たとえば、４−（４−シアノビフェニルオキシカルボニル）フェノキシエチルアクリレート、４−（４−シアノビフェニルオキシカルボニル）フェノキシプロピルアクリレート、４−（４−シアノビフェニルオキシカルボニル）フェノキシブチルアクリレート、４−（４−シアノビフェニルオキシカルボニル）フェノキシペンチルアクリレート、４−（４−シアノビフェニルオキシカルボニル）フェノキシヘキシルアクリレート等があげられる。これらは単独でまたは混合して用いることができる。
【００４１】
重合性カイラル剤（ｂ）は、重合性官能基を少なくとも１つ有し、かつ光学活性基を有し、重合性ネマティック剤（ａ）の配向を乱さないものであれば特に制限されない。重合性官能基としては、アクリロイル基、メタクリロイル基、エポキシ基、ビニルエーテル基等があげられるが、これらのなかでアクリロイル基、メタクリロイル基が好適である。重合性カイラル剤（ｂ）は、液晶性を有していてもよく液晶性を有しなくてもよいが、コレステリック液晶性を示すものを好ましく使用できる。また重合性カイラル剤（ｂ）は、重合性官能基を２つ以上有するものを用いることができる。
【００４２】
重合性カイラル剤（ｂ）としては、たとえば、一般式（ｂ）：
【化２】

（式中、Ｒ^３ は水素原子またはメチル基を、ｎは１〜６の整数を、Ｘ^２ は−ＣＯ_２ −基、−ＯＣＯ−基、−ＣＯ−、−ＣＨ＝ＣＨ−または−Ｃ≡Ｃ−を、Ｒ^４ は一般式（ｃ）：
【化３】

（各式中、Ｒ^５ は、フェニル基、１−ナフチル基、２−ナフチル基またはビフェニル基を、Ｒ^６ は、メチル基、フェニル基またはカルボキシメチル基を、Ｒ^７ はメチル基、ベンジル基またはｔ−ブチル基を示す。＊は不斉炭素原子を示す。）で表される置換基を示す。） で表される光学活性基を有するアクリル酸エステル誘導体があげられる。
【００４３】
一般式（ｂ）で表されるアクリル酸エステル誘導体において、Ｒ^５ としては水素原子が好ましく、Ｒ^６ としてはシッフ塩基構造を有するもの（特にＲ^７ がフェニル基のもの）が好ましく、Ｘ^２ としては−ＣＯＯ−基が好ましい。一般式（ｂ）で表される光学活性基を有するアクリル酸エステル誘導体の具体例としては、たとえば、（（３−フェニル−３−メチル−２−アザプロペニルフェニル）オキシカルボニル）フェノキシエチルアクリレート、（（３−フェニル−３−メチル−２−アザプロペニルフェニル）オキシカルボニル）フェノキシプロピルアクリレート、（（３−フェニル−３−メチル−２−アザプロペニルフェニル）オキシカルボニル）フェノキシブチルアクリレート、（（３−フェニル−３−メチル−２−アザプロぺニルフェニル）オキシカルボニル）フェノキシベンチルアクリレート、（（３−フェニル−３−メチル−２−アザプロペニルフェニル）オキシカルボニル）フェノキシヘキシルアクリレート等があげられる。これらは単独でまたは混合して用いることができる。
【００４４】
重合性カイラル剤（ｂ）の配合量は、その配合量により選択反射波長を決定する捻れピッチが変化することから前記配合量の制御で選択反射波長を調節することができる。したがって、捻れピッチ長が異なる２種以上のコレステリック液晶ポリマーは、重合性カイラル剤（ｂ）の配合量を制御して、重合性ネマチック剤（ａ）と重合性カイラル剤（ｂ）の組成比が異なるものから調製することができる。重合性カイラル剤（ｂ）の配合量は、重合性ネマチック剤（ａ）１００重量部に対し１〜３０重量部程度の範囲内で、コレステリック液晶ポリマーの捻れピッチ長が異なるように制御するのが好ましい。
【００４５】
コレステリック液晶ポリマーの調製は、例えばラジカル重合方式、カチオン重合方式、アニオン重合方式などの通例のアクリル系モノマーの重合方式に準じて行うことができる。なお、ラジカル重合方式を適用する場合、各種の重合開始剤を用いうるが、そのうちアゾビスイソブチロニトリルや過酸化ベンゾイルなどの分解温度が高くもなく、かつ低くもない中間的温度で分解するものが好ましく用いられる。コレステリック液晶ポリマーの数平均分子量は、２千〜１０万程度であるのが好ましい。好ましくは５千〜５万程度である。
【００４６】
前記コレステリック液晶ポリマーとして、非相溶性の２種以上のものを調製する方法は特に制限されない。たとえば、前記重合性ネマチック剤（ａ）および重合性カイラル剤（ｂ）として、非相溶性のコレステリック液晶ポリマーを形成するもの適宜に選択することにより行うことができる。
【００４７】
またコレステリック液晶ポリマーの少なくとも１つに、結晶性成分をブロック体として導入することにより、２種以上のコレステリック液晶ポリマーを非相溶性とすることができる。結晶性成分をブロック体として導入したコレステリック液晶ポリマーは、重合性ネマチック剤（ａ）および重合性カイラル剤（ｂ）が同一のもの、または相溶性のコレステリック液晶ポリマーに対しても非相溶性となりうる。
【００４８】
結晶性成分をブロック体として導入したコレステリック液晶ポリマーを作製する方法は特に制限されない。たとえば、重合性ネマチック剤（ａ）および重合性カイラル剤（ｂ）から得られたポリマーと、結晶性成分のブロックポリマーを、任意の重合法によって別々に重合し、これらポリマーを混合することで得られる。ブロックポリマーを作成する方法としてはリビングラジカル重合法を用いるのが特に好ましい。このリビングラジカル重合法の参考文献として、例えば、Ｐａｔｔｅｎらによる報告、”Ｒａｄｉｃａｌ Ｐｏｌｙｍｅｒｉｚａｔｉｏｎ Ｙｉｅｌｄｉｎｇ Ｐｏｌｙｍｅｒｓ ｗｉｔｈ Ｍｗ／Ｍｎ 〜１．０５ ｂｙＨｏｍｏｇｅｎｅｏｕｓ Ａｔｏｍ Ｔｒａｎｓｆｅｒ Ｒａｄｉｃａｌ Ｐｏｌｙｍｅｒｉｚａｔｉｏｎ’’Ｐｏｌｙｍｅｒ Ｐｒｅｐｒｉｎｔｅｄ，ｐｐ５７５−６，Ｎｏ３７（Ｍａｒｃｈ １９９６）；あるいは、Ｍａｔｙｊａｓｅｗｓｋｉ らによる報告、”Ｃｏｎｔｏｒｏｌｌｅｄ／Ｌｉｖｉｎｇ Ｒａｄｉｃａｌ Ｐｏｌｉｍｅｒｉｚａｔｉｏｎ． Ｈａｌｏｇｅｎ Ａｔｏｍ Ｔｒａｎｓｆｅｒ Ｒａｄｉｃａｌ Ｐｏｌｙｍｅｒｉｚａｔｉｏｎ Ｐｒｏｍｏｔｅｄ ｂｙ ａ Ｃｕ（Ｉ）／Ｃｕ（ＩＩ） Ｒｅｄｏｘ Ｐｒｏｃｅｓｓ’’，Ｍａｃｒｏｍｏｌｅｃｕｌｅｓ ｌ９９５，２８，７９０１−１０（Ｏｃｔｏｂｅｒ １５，１９９５）；あるいは 同著ＰＣＴ／ＵＳ９６／０３３０２，Ｉｎｔｅｒｎａｔｉｏｎａｌ Ｐｕｂｌｉｃａｔｉｏｎ Ｎｏ．ＷＯ９６／３０４２１（Ｏｃｔｏｂｅｒ３，１９９６）；あるいはＭ．Ｓａｗａｍｏｔｏらの報告，’’Ｒｕｔｈｕｎｉｕｍ−ｍｅｄｉａｔｅｄ Ｌｉｖｉｎｇ Ｒａｄｉｃａｌ Ｐｏｌｉｍｅｒｉｚａｔｉｏｎ ｏｆ Ｍｅｔｈｙｌ Ｍｅｔｈａｃｒｙｌａｔｅ Ｍａｃｒｏｍｏｌｅｃｕｌｅｓ，１９９６，２９，１０７０．などが知られている。
【００４９】
たとえば、重合性ネマチック剤（ａ）と重合性カイラル剤（ｂ）とをリビング重合したポリマー（ブロック体ａｂ）に、結晶性成分としてモノマー（ｃ）を加えて、ａｂ（ブロック体）からなるポリマーの重合末端にモノマー（ｃ）が順々に付加していくことにより、第２次ブロック、結晶性成分（ブロック体ｃ）が導入されて、ａｂ−ｃの形態のジブロックポリマーにすることができる。また、重合性カイラル剤（ｂ）をリビング重合した末端（ブロック体ｂ）に、重合性ネマチック剤（ａ）をリビング重合して付加させ（ブロック体ａ）、その後さらにその末端に結晶性成分（ブロック体ｃ）を導入して、ｂ−ａ−ｃのトリブロックポリマーとしてもよい。一方、結晶性成分（ブロック体ｃ）をリビング重合した後に、重合性ネマチック剤（ａ）と重合性カイラル剤（ｂ）を重合して、ｃ−ｂ−ａのトリブロックの形態にしてもよい。また、ｂ−ｃ−ａの形態なども可能である。重合性ネマチック剤（ａ）と重合性カイラル剤（ｂ）は、同時に添加して、ｃ−ａｂの形態とすることができる。
【００５０】
リビング重合したポリマーに、途中から添加するモノマーは、重合されているポリマーの重合率が少なくとも６０重量％を超えたとき、好ましくは８０重量％を超えたとき、さらには９０重量％を超えたときとするのが好ましい。重合率は、（残存モノマー／重合前の仕込みモノマー量）×１００（％）で定義され、加熱してモノマー成分を揮発除去したり、ゲルパーミエーションクロマトグラフィーやガスクロマトグラフィー、液体クロマトグラフィーにより測定することができる。
【００５１】
結晶性成分となるモノマー（ｃ）は、重合性ネマチック剤（ａ）、重合性カイラル剤（ｂ）と相溶性の悪いものであれば液晶性成分でも、非液晶性成分でもよい。前記モノマー（ｃ）としては、例えば、側鎖に長鎖アルキル基を有するアクリル系モノマーがあげられる。長鎖アルキル基を有するアクリル系モノマーではオクタデシル（メタ）アクリレート、ラウリル（メタ）アクリレート、ミスチリル（メタ）アクリレート、パルミチル（メタ）アクリレート、ステアリル（メタ）アクリレートなどの炭素数１２〜２８アルキル基を持つものがあげられる。
【００５２】
また、モノマー（ｃ）として、２個以上の重合性官能基を有するものを用いることもでき、これを用いれば３次元架橋により、より強固な膜質を得ることができる。また、モノマー（ｃ）としては、１種を単独で、または２種以上を用いてもよい。
【００５３】
結晶性成分（モノマー（ｃ））の割合は、得られるコレステリック液晶ポリマーの５〜４０重量％程度、好ましくは１０〜３０重量％である。４０重量％を超えると、光学特性に悪影響を与える。
【００５４】
前記リビングラジカル重合の際には、モノマー中の溶存酸素を取り除く必要がある。溶存酸素濃度を下げる方法としては、窒素やアルゴンなどの不活性ガスを吹き込みながら撹拌を行う方法、不活性ガスをモノマー中にバブリングする方法、減圧脱気する方法、加熱して脱気する方法などがある。これらの方法は併用してもよい。
【００５５】
重合開始剤としては、臭素もしくは塩素をα位に有するエステルまたはスチレンの誘導体が好適である。好ましくは２−ブロモ（もしくはクロロ）プロピオン酸誘導体もしくは塩化（もしくは臭化）１−フェニル誘導体があげられる。その中でも特に好ましくは２−ブロモ（もしくはクロロ）プロピオン酸メチル、２−ブロモ（もしくはクロロ）プロピオン酸エチル、２−ブロモ（もしくはクロロ）−２−プロピオン酸メチル、２−ブロモ（もしくはクロロ）−２−プロピオン酸エチル、塩化（もしくは臭化）１−フェニルエチル、２−ブロモイソ酪酸エチルから選ばれるハロゲン系化合物を用いることができる。水酸基を有する開始剤として、例えば、２−ブロモ−２−メチルプロピオン酸−２−ヒドロキシエチルなどを用いることもできる。２官能の開始剤も用いることができる。具体的にはエチレンビス（２−ブロモ−２−メチルプロピオネート）などがあげられる。
【００５６】
前記重合では得られるブロック共重合体の数平均分子量を意図的に制御する事が可能である。かかる重合法においては、開始剤のほかの触媒として遷移金属および配位子を用いる。
【００５７】
遷移金属としては、Ｃｕ，Ｒｕ，Ｆｅ，Ｒｈ，Ｖ，Ｎｉの金属種及びこれらの金属塩や金属錯体を用いることができる。また、配位子としては、とくに限定されるものではないが、例えば、ビピリジル誘導体、アミン誘導体、メルカプタン誘導体、トリフルオレート誘導体などを用いることができる。これらの中でも、Ｃｕ（Ｉ）と２，２′−ビピリジル錯体を用いることが、重合の安定性・速度から特に好ましい。
【００５８】
重合開始剤は、重合性モノマー全体に対し、通常０．０５〜３０モル％、好ましくは０．１〜１０モル％の割合で用いられる。また、遷移金属の使用量は、ハロゲン化物などの形態として、上記重合開始剤１モル部に対して、通常０．０１〜３モル部、好ましくは０．１〜１モル部の割合で用いられる。さらに、その配位子は、上記遷移金属（ハロゲン化物などの形態）１モル部に対して、通常０．５〜５モル部、好ましくは１〜３モル部の割合で用いられる。重合開始剤と活性化剤とをこのような使用割合にすると、リビングラジカル重合の反応性、生成ポリマーの分子量などに好結果が得られる。
【００５９】
ブロック共重合体は、前記重合法を用いて得られるが、モノマー成分が重合温度下で液状であるものは溶剤を用いても、また無溶剤でも製造することが可能である。液晶モノマーは通常液状ではないため、溶剤に溶解して重合する。溶剤は液晶モノマーを溶解するものであればよい。使用できる溶剤の例として、テトラヒドロフラン、アニソール、ジメチルアセトアミド、シクロヘキサノン．シクロペンタノンなどを用いることができる。通常、モノマー濃度が１０〜３０重量％程度で重合を行なう。
【００６０】
上記のようにして、非相溶性であり、かつ捻れピッチ長が異なる、２種以上のコレステリック液晶ポリマーが調製される。これらコレステリック液晶ポリマーの混合物は、溶媒に溶解した溶液として用いられる。２種以上のコレステリック液晶ポリマーの混合物における、各ポリマーの割合は特に制限されないが、たとえば、前記ａｂ共重合体から得られるとコレステリック液晶ポリマーと、これにブロック体ｃを付加したブロックポリマーを用いる場合には、前者：後者（重量比）＝１０／９０〜９０／１０、とするのが好ましい。より好ましくは、前者：後者（重量比）＝２０／８０〜８０／２０である。
【００６１】
前記２種以上のコレステリック液晶ポリマー混合物を溶解する溶媒としては、たとえば、クロロホルム、ジクロロメタン、ジクロロエタン、テトラクロロエタン、トリクロロエチレン、テトラクロロエチレン、クロロベンゼンなど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などのフェノール類、ベンゼン、トルエン、キシレン、メトキシベンゼン、１，２−ジメトキベンゼンなどの芳香族炭化水素類、その他、アセトン、酢酸エチル、ｔｅｒｔ−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、エチレンブ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、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、テトラヒドロフラン、ジメチルホルムアミド、ジメチルアセトアミド、ジメチルスルホキシド、アセトニトリル、ブチロニトリル、二硫化炭素、メチルエチルケトン、シクロヘキサノン、シクロペンタノン等が好ましい。溶液の濃度は、通常３〜５０重量％程度である。
【００６２】
前記コレステリック液晶ポリマー混合物の溶液は、配向基材上に塗布する工程、当該コレステリック液晶ポリマーのコレステリック螺旋軸が前記配向基材面に対し垂直方向になるように配向させる工程、前記配向による液晶状態を維持しながら乾燥成膜する工程を施す。
【００６３】
上記溶液の、配向基材上への塗布方法は特に限定されず、バーコーター、スピナー、ロールコーターなどの適宜な塗工機にて行うことができるが、キャスト法が成膜面の品質から好適である。
【００６４】
配向基材としては、従来知られているものを採用できる。たとえば、基板上にポリイミドやポリビニルアルコール等からなる薄膜を形成して、それをレーヨン布等でラビング処理したラビング膜、斜方蒸着膜、シンナメートやアゾベンゼンなど光架橋基を有するポリマーあるいはポリイミドに偏光紫外線を照射した光配向膜、延伸フィルムなどが用いられる。その他、磁場、電場配向、ずり応力操作により配向させることもできる。
【００６５】
なお、前記基板としては、ポリエチレンテレフタレート、トリアセチルセルロース、ノルボルネン樹脂、ポリビニルアルコール、ポリイミド、ポリアリレート、ポリカーボネート、ポリスルホンやポリエーテルスルホン等のプラスチックからなるフィルム、ガラス板、石英シートが用いられる。
【００６６】
前記配向は、コレステリック液晶ポリマーの液晶転移温度以上で行う。配向温度、時間はコレステリック液晶ポリマーの種類に応じて適宜に決定される。
【００６７】
前記コレステリック液晶ポリマーは、配向による液晶状態を維持しながら乾燥成膜する。乾燥温度としては、溶媒の沸点以上の温度であればよい。乾燥成膜は前記配向工程とともに、行うことができる。乾燥成膜を前記配向工程とともに、行う場合には、溶媒およびコレステリック液晶ポリマーの種類に応じて温度を設定する。
【００６８】
広帯域コレステリック液晶フィルムの製造方法（２）では、重合性ネマチック剤（ａ）および重合性カイラル剤（ｂ）を含む液晶組成物を用いる。当該液晶組成物は、少なくとも１種の重合性ネマチック剤（ａ）および少なくとも２種の重合性カイラル剤（ｂ）を含有する液晶組成物、または、少なくとも２種の重合性ネマチック剤（ａ）および少なくとも１種の重合性カイラル剤（ｂ）を含有する液晶組成物であり、かつ、前記液晶組成物は、配向時において、非相溶性であり、かつ捻れピッチ長の異なる２成分以上の液晶組成物となるものである。
【００６９】
重合性ネマチック剤（ａ）および重合性カイラル剤（ｂ）は前記と同様のものを使用できる。液晶組成物は、これら成分の種類等を適宜に変えることにより、非相溶性とすることができる。また、重合性カイラル剤（ｂ）の使用量により、捻れピッチ長を異なるものとすることができる。重合性カイラル剤（ｂ）の使用量は前記と同様の範囲で調整される。
【００７０】
前記液晶組成物には、配向基材上に塗布する工程、液晶組成物のコレステリック螺旋軸が前記配向基材面に対し垂直方向になるように配向させる工程、前記配向による液晶状態を維持しながら光または熱重合により硬化成膜する工程を施す。配向基材上への塗布方法、配向方法は、製造方法（１）と同様の方法を採用することができる。
【００７１】
光または熱重合により硬化成膜する工程は、従来各種方法により行うことができる。光重合硬化は、配向基材上に塗布、配向した液晶組成物に紫外線等の放射線を照射することにより行う。前記液晶組成物を紫外線硬化する場合には光重合開始剤が含まれる。光重合開始剤は各種のものを特に制限なく使用できる。光重合開始剤としては、たとえば、チバスペシャルティケミカルズ社製のイルガキュア（Ｉｒｇａｃｕｒｅ）９０７，同１８４、同６５１、同３６９などを例示できる。また、熱重合硬化は、配向基材上に塗布、配向した液晶組成物に加熱処理を施すことにより行う。熱硬化する前記液晶組成物には、通常、熱重合開始剤が含まれる。
【００７２】
本発明のコレステリック液晶フィルム（溶液の場合は溶媒乾燥後の塗布厚み）の厚みは特に規定する物ではないが、通常０．５〜２０μｍ、望ましくは１〜１０μｍである。塗布厚が薄いと光学的効果が少なく、また塗布厚が厚いと配向しにくくなるためである。
【００７３】
本発明で得られるコレステリック液晶フィルムは、各々のコレステリック液晶ポリマー（製造方法（２）では、液晶組成物から得られた硬化物）が相分離構造を形成して広帯域化しており、捻れピッチ長の異なる微小領域を各々固定化している。したがって、コレステリック液晶フィルムの相分離構造として、厚み方向に２種以上の捻れピッチを持つ層が存在する場合には、１層のコレステリック液晶フィルムで十分な偏光度を得ることができる。かかるコレステリック液晶フィルムは、多層積層品と等価であるからである。
【００７４】
一方、コレステリック液晶フィルムの相分離構造として、厚み方向に１種の捻れピッチしか存在せず、異なるピッチは隣接する横方向にのみ存在する場合には、かかる１層のコレステリック液晶フィルムの相分離構造として、厚み方向に２種以上の捻れピッチを持つ層を１回透過／反射するだけでは十分な偏光度を得ることはできない。１回の透過／反射では１ピッチ分の影響しか受けず、その選択反射域外の光線は偏光分離を受けていないからである。このような場合には２層以上の積層を行うことで偏光度の向上を得ることができる。積層品は同一品の積層でも、各々異なる組成の成分で作製したコレステリック液晶フィルムの積層でも良い。同一品であっても相分離構造が全く同一形状を再現することはないので積層品の厚み方向に同一ピッチの構造が連続して重なり続ける可能性は低いからである。
【００７５】
また、３層積層する場合でも同一材料の個別積層が可能である。そのため、捻れピッチの異なる組成の材料を複数準備する、従来の特許文献４のような手法は必要ではなく、同一組成のコレステリック液晶フィルムを個別に積層することで偏光度を向上させることができる。
【００７６】
なお、コレステリック液晶フィルムの積層は、積層数が多くなると、厚みが大きくなることから、２層以上６層以下とするのが好ましい。特に、２層以上４層以下が好ましい。積層厚みは１０μｍ以下、さらには８μｍ以下となる範囲に制御するのが好ましい。
【００７７】
コレステリック液晶フィルムの積層手段は特に制限されない。たとえば、接着剤により行うことができる。また、下層となるコレステリック液晶フィルムに、上記製造方法（１）または（２）により広帯域コレステリック液晶フィルムを上層として積層することができる。この場合には、捻れピッチの同一の相分離構造が厚み方向に連続して存在することのないように、下層となるコレステリック液晶フィルムの表面に下地処理を行った後、上層となるコレステリック液晶フィルムを積層することが好ましい。直接、上塗り塗工を行う場合には、相分離するお互いが、濡れ性の悪さから自己の硬化物の上に選択的に凝集析出する可能性があるため、上層の塗工前に下地処理を適時行うことが好ましい。下地処理は、例えば、ポリビニルアルコールに代表される配向膜を形成することで下層の表面状態の影響を排除する方法、またはコロナ処理やケン化処理のような表面性の改質手法で下層の表面状態の影響を排除する方法があげられる。
【００７８】
こうして得られるコレステリック液晶フィルムは、基材から剥離することなく用いられる他、基材から剥離して用いてもよい。
【００７９】
本発明の広帯域コレステリック液晶フィルムは円偏光板として用いられる。本発明で得られる広帯域選択反射機能を有するコレステリック液晶積層体は正面方向は円偏光反射／透過機能を有するが、これを広帯域円偏光として液晶表示装置に用いることができる。この場合には円偏光モードの液晶セル、例えばマルチドメインを有する透過型ＶＡモード液晶セルの光源側に配置することで円偏光板として用いることができる。
【００８０】
円偏光板には、λ／４板を積層して直線偏光子とすることができる。λ／４板としては、ポリカーボネート、ノルボルネン系樹脂、ポリビニルアルコール、ポリスチレン、ポリメチルメタクリレート、ポリプロピレンやその他のポリオレフィン、ポリアリレート、ポリアミド、ポリエチレンテレフタレート、ポリスルホンの如き適宜なポリマーからなるフィルムを延伸処理してなる複屈折性フィルムや液晶ポリマーなどの液晶材料からなる配向フィルム、液晶材料の配向層をフィルムにて支持したものなどがあげられる。λ／４波長板の厚さは、通常、０．５〜２００μｍであることが好ましく、特に１〜１００μｍであることが好ましい。
【００８１】
λ／４板は単一材料による単層では特定の波長に対してのみ良好に機能するが、その他の波長に対しては波長分散特性上λ／４板として機能が低下する問題がある。そこでλ／２板と軸角度を規定して積層すれば可視光全域で実用上差し支えない程度の範囲で機能する広帯域λ／４板として用いることができる。この場合の各λ／４板、λ／２板は同一材料でも良いし上記記述のλ／４板と同様の手法で得られる別個の材料によって作製した物を組み合わせても良い。
【００８２】
例えば広帯域円偏光板にλ／４板（１４０ｎｍ）を積層し、この軸角度に対して１１７．５度でλ／２板（２７０ｎｍ）を配置する。この場合の透過偏光軸はλ／４板の軸に対して１０度となる。この貼り合わせ角度は各位相差板の位相差値により変動するので上記の貼り合わせ角度に限定するものではない。
【００８３】
また本発明によるコレステリック液晶層は広帯域の円偏光反射特性を有する他に、相分離構造から生じる散乱特性を有する。このため本発明による円偏光板は反射板としても好適に用いるいることができる。
【００８４】
前記直線偏光子の透過軸には、吸収型偏光子をその透過軸方向を合わせて貼り合わせて用いられる。
【００８５】
偏光子は、特に制限されず、各種のものを使用できる。偏光子としては、たとえば、ポリビニルアルコール系フィルム、部分ホルマール化ポリビニルアルコール系フィルム、エチレン・酢酸ビニル共重合体系部分ケン化フィルム等の親水性高分子フィルムに、ヨウ素や二色性染料等の二色性物質を吸着させて一軸延伸したもの、ポリビニルアルコールの脱水処理物やポリ塩化ビニルの脱塩酸処理物等ポリエン系配向フィルム等があげられる。これらのなかでもポリビニルアルコール系フィルムとヨウ素などの二色性物質からなる偏光子が好適である。これら偏光子の厚さは特に制限されないが、一般的に、５〜８０μｍ程度である。
【００８６】
ポリビニルアルコール系フィルムをヨウ素で染色し一軸延伸した偏光子は、たとえば、ポリビニルアルコールをヨウ素の水溶液に浸漬することによって染色し、元長の３〜７倍に延伸することで作製することができる。必要に応じてホウ酸やヨウ化カリウムなどの水溶液に浸漬することもできる。さらに必要に応じて染色の前にポリビニルアルコール系フィルムを水に浸漬して水洗してもよい。ポリビニルアルコール系フィルムを水洗することでポリビニルアルコール系フィルム表面の汚れやブロッキング防止剤を洗浄することができるほかに、ポリビニルアルコール系フィルムを膨潤させることで染色のムラなどの不均一を防止する効果もある。延伸はヨウ素で染色した後に行っても良いし、染色しながら延伸してもよし、また延伸してからヨウ素で染色してもよい。ホウ酸やヨウ化カリウムなどの水溶液中や水浴中でも延伸することができる。
【００８７】
前記偏光子は、通常、片側または両側に透明保護フィルムが設けられ偏光板として用いられる。透明保護フィルムは透明性、機械的強度、熱安定性、水分遮蔽性、等方性などに優れるものが好ましい。透明保護フィルムとしては、例えばポリエチレンテレフタレート、ポリエチレンナフタレート等のポリエステル系ポリマー、ジアセチルセルロース、トリアセチルセルロース等のセルロース系ポリマー、ポリカーボネート系ポリマー、ポリメチルメタクリレート等のアクリル系ポリマー等の透明ポリマーからなるフィルムがあげられる。またポリスチレン、アクリロニトリル・スチレン共重合体等のスチレン系ポリマー、ポリエチレン、ポリプロピレン、環状ないしノルボルネン構造を有するポリオレフィン、エチレン・プロピレン共重合体等のオレフィン系ポリマー、塩化ビニル系ポリマー、ナイロンや芳香族ポリアミド等のアミド系ポリマー等の透明ポリマーからなるフィルムもあげられる。さらにイミド系ポリマー、スルホン系ポリマー、ポリエーテルスルホン系ポリマー、ポリエーテルエーテルケトン系ポリマー、ポリフェニレンスルフィド系ポリマー、ビニルアルコール系ポリマー、塩化ビニリデン系ポリマー、ビニルブチラール系ポリマー、アリレート系ポリマー、ポリオキシメチレン系ポリマー、エポキシ系ポリマーや前記ポリマーのブレンド物等の透明ポリマーからなるフィルムなどもあげられる。特に光学的に複屈折の少ないものが好適に用いられる。偏光板の保護フィルムの観点よりは、トリアセチルセルロース、ポリカーボネート、アクリル系ポリマー、シクロオレフィン系樹脂、ノルボルネン構造を有するポリオレフィンなどが好適である。本発明は、トリアセチルセルロースのように、高い温度での焼成が難しい透明基材について好適である。なお、トリアセチルセルロースは、１３０℃以上ではフィルム中の可塑剤が揮発し特性が著しく低下する。
【００８８】
また、特開２００１−３４３５２９号公報（ＷＯ０１／３７００７）に記載のポリマーフィルム、たとえば、（Ａ）側鎖に置換および／または非置換イミド基を有する熱可塑性樹脂と、（Ｂ）側鎖に置換および／非置換フェニルならびにニトリル基を有する熱可塑性樹脂を含有する樹脂組成物があげられる。具体例としてはイソブチレンとＮ−メチルマレイミドからなる交互共重合体とアクリロニトリル・スチレン共重合体とを含有する樹脂組成物のフィルムがあげられる。フィルムは樹脂組成物の混合押出品などからなるフィルムを用いることができる。
【００８９】
偏光特性や耐久性などの点より、特に好ましく用いることができる透明基板は、表面をアルカリなどでケン化処理したトリアセチルセルロースフィルムである。透明基板１の厚さは、適宜に決定しうるが、一般には強度や取扱性等の作業性、薄層性などの点より１０〜５００μｍ程度である。特に２０〜３００μｍが好ましく、３０〜２００μｍがより好ましい。
【００９０】
また、透明保護フィルムは、できるだけ色付きがないことが好ましい。したがって、Ｒｔｈ＝［（ｎｘ＋ｎｙ）／２−ｎｚ］・ｄ（ただし、ｎｘ、ｎｙはフィルム平面内の主屈折率、ｎｚはフィルム厚方向の屈折率、ｄはフィルム厚みである）で表されるフィルム厚み方向の位相差値が−９０ｎｍ〜＋７５ｎｍである保護フィルムが好ましく用いられる。かかる厚み方向の位相差値（Ｒｔｈ）が−９０ｎｍ〜＋７５ｎｍのものを使用することにより、保護フィルムに起因する偏光板の着色（光学的な着色）をほぼ解消することができる。厚み方向位相差値（Ｒｔｈ）は、さらに好ましくは−８０ｎｍ〜＋６０ｎｍ、特に−７０ｎｍ〜＋４５ｎｍが好ましい。
【００９１】
前記透明保護フィルムは、表裏で同じポリマー材料からなる透明保護フィルムを用いてもよく、異なるポリマー材料等からなる透明保護フィルムを用いてもよい。
【００９２】
前記透明保護フィルムの偏光子を接着させない面には、ハードコート層や反射防止処理、スティッキング防止や、拡散ないしアンチグレアを目的とした処理を施したものであってもよい。
【００９３】
ハードコート処理は偏光板表面の傷付き防止などを目的に施されるものであり、例えばアクリル系、シリコーン系などの適宜な紫外線硬化型樹脂による硬度や滑り特性等に優れる硬化皮膜を透明保護フィルムの表面に付加する方式などにて形成することができる。反射防止処理は偏光板表面での外光の反射防止を目的に施されるものであり、従来に準じた反射防止膜などの形成により達成することができる。また、スティッキング防止処理は隣接層との密着防止を目的に施される。
【００９４】
またアンチグレア処理は偏光板の表面で外光が反射して偏光板透過光の視認を阻害することの防止等を目的に施されるものであり、例えばサンドブラスト方式やエンボス加工方式による粗面化方式や透明微粒子の配合方式などの適宜な方式にて透明保護フィルムの表面に微細凹凸構造を付与することにより形成することができる。前記表面微細凹凸構造の形成に含有させる微粒子としては、例えば平均粒径が０．５〜５０μｍのシリカ、アルミナ、チタニア、ジルコニア、酸化錫、酸化インジウム、酸化カドミウム、酸化アンチモン等からなる導電性のこともある無機系微粒子、架橋又は未架橋のポリマー等からなる有機系微粒子などの透明微粒子が用いられる。表面微細凹凸構造を形成する場合、微粒子の使用量は、表面微細凹凸構造を形成する透明樹脂１００重量部に対して一般的に２〜５０重量部程度であり、５〜２５重量部が好ましい。アンチグレア層は、偏光板透過光を拡散して視角などを拡大するための拡散層（視角拡大機能など）を兼ねるものであってもよい。
【００９５】
なお、前記反射防止層、スティッキング防止層、拡散層やアンチグレア層等は、透明保護フィルムそのものに設けることができるほか、別途光学層として透明保護層とは別体のものとして設けることもできる。
【００９６】
前記直線偏光子の積層、さらには各種光学層の積層は、液晶表示装置等の製造過程で順次別個に積層する方式にても行うことができるが、これらを予め積層したのものは、品質の安定性や組立作業等に優れていて液晶表示装置などの製造工程を向上させうる利点がある。積層には粘着層等の適宜な接着手段を用いうる。前記接着に際し、それらの光学軸は目的とする位相差特性などに応じて適宜な配置角度とすることができる。
【００９７】
前述した直線偏光子には、液晶セル等の他部材と接着するための粘着層を設けることもできる。粘着層を形成する粘着剤は特に制限されないが、例えばアクリル系重合体、シリコーン系ポリマー、ポリエステル、ポリウレタン、ポリアミド、ポリエーテル、フッ素系やゴム系などのポリマーをベースポリマーとするものを適宜に選択して用いることができる。特に、アクリル系粘着剤の如く光学的透明性に優れ、適度な濡れ性と凝集性と接着性の粘着特性を示して、耐候性や耐熱性などに優れるものが好ましく用いうる。
【００９８】
また上記に加えて、吸湿による発泡現象や剥がれ現象の防止、熱膨張差等による光学特性の低下や液晶セルの反り防止、ひいては高品質で耐久性に優れる液晶表示装置の形成性などの点より、吸湿率が低くて耐熱性に優れる粘着層が好ましい。
【００９９】
粘着層は、例えば天然物や合成物の樹脂類、特に、粘着性付与樹脂や、ガラス繊維、ガラスビーズ、金属粉、その他の無機粉末等からなる充填剤や顔料、着色剤、酸化防止剤などの粘着層に添加されることの添加剤を含有していてもよい。また微粒子を含有して光拡散性を示す粘着層などであってもよい。
【０１００】
粘着層の付設は、適宜な方式で行いうる。その例としては、例えばトルエンや酢酸エチル等の適宜な溶剤の単独物又は混合物からなる溶媒にベースポリマーまたはその組成物を溶解又は分散させた１０〜４０重量％程度の粘着剤溶液を調製し、それを流延方式や塗工方式等の適宜な展開方式で前記偏光子上に直接付設する方式、あるいは前記に準じセパレータ上に粘着層を形成してそれを光学素子上に移着する方式などがあげられる。粘着層は、各層で異なる組成又は種類等のものの重畳層として設けることもできる。粘着層の厚さは、使用目的や接着力などに応じて適宜に決定でき、一般には１〜５００μｍであり、５〜２００μｍが好ましく、特に１０〜１００μｍが好ましい。
【０１０１】
粘着層の露出面に対しては、実用に供するまでの間、その汚染防止等を目的にセパレータが仮着されてカバーされる。これにより、通例の取扱状態で粘着層に接触することを防止できる。セパレータとしては、上記厚さ条件を除き、例えばプラスチックフィルム、ゴムシート、紙、布、不織布、ネット、発泡シートや金属箔、それらのラミネート体等の適宜な薄葉体を、必要に応じシリコーン系や長鎖アルキル系、フッ素系や硫化モリブデン等の適宜な剥離剤でコート処理したものなどの、従来に準じた適宜なものを用いうる。
【０１０２】
なお、粘着層などの各層には、例えばサリチル酸エステル系化合物やべンゾフェノール系化合物、ベンゾトリアゾール系化合物やシアノアクリレート系化合物、ニッケル錯塩系化合物等の紫外線吸収剤で処理する方式などの方式により紫外線吸収能をもたせたものなどであってもよい。
【０１０３】
本発明の直線偏光子は液晶表示装置等の各種装置の形成などに好ましく用いることができる。液晶表示装置の形成は、従来に準じて行いうる。すなわち液晶表示装置は一般に、液晶セルと光学素子、及び必要に応じての照明システム等の構成部品を適宜に組立てて駆動回路を組込むことなどにより形成されるが、本発明の直線偏光子を用いる点を除いて特に限定はなく、従来に準じうる。液晶セルについても、例えばＴＮ型やＳＴＮ型、π型などの任意なタイプのものを用いうる。
【０１０４】
液晶セルの片側又は両側に前記直線偏光子を配置した液晶表示装置や、照明システムにバックライトあるいは反射板を用いたものなどの適宜な液晶表示装置を形成することができる。その場合、本発明による直線偏光子は液晶セルの片側又は両側に設置することができる。両側に直線偏光子を設ける場合、それらは同じものであってもよいし、異なるものであってもよい。さらに、液晶表示装置の形成に際しては、例えば拡散板、アンチグレア層、反射防止膜、保護板、プリズムアレイ、レンズアレイシート、光拡散板、バックライトなどの適宜な部品を適宜な位置に１層又は２層以上配置することができる。
【０１０５】
【実施例】
以下、実施例、比較例をあげて本発明を説明するが、本発明はこれらの実施例に限定されるものではない。
【０１０６】
製造例１
メカニカルスターラー、窒素導入管、冷却管およびラバーセプタムを備えた４つ口フラスコに、下式化４：
【化４】

のネマチック液晶モノマー（３７ｇ）と、下式化５：
【化５】

のカイラル性モノマー（１３ｇ）の液晶モノマー混合物（モノマーのモル比，化４：化５＝７５：２５）およびアニソール（２８３ｇ）を加え、液晶モノマー混合物を溶解した後、系内に２時間窒素を流し置換した。これに窒素気流下、開始剤としてアゾビスイソブチロニトリル（０．５ｇ）を加えて、７０℃で８時間重合した。これにメタノールを加えて２度再沈精製を行なってコレステリック液晶ポリマー（液晶転移温度８４℃）を得た。液晶転移温度は、ホットステージＦＰ８２ＨＴ（メトラートレド社製）で、１℃／ｍｉｎで昇温しながら偏光顕微鏡（５０倍）で観察して測定した。
【０１０７】
製造例２
製造例１において、ネマチック液晶モノマー（４２ｇ）とカイラル性モノマー（８ｇ）の液晶モノマー混合物（モノマーのモル比，化４：化５＝８５：１５）を用いたこと以外は製造例１と同様にしてコレステリック液晶ポリマー（液晶転移温度８８℃）を得た。
【０１０８】
製造例３
メカニカルスターラー、窒素導入管、冷却管およびラバーセプタムを備えた４つ口にオクタデシアクリレート（１０ｇ）、ジメチルアセトアミド（５６ｇ）を加え、これに２，２′−ビピリジン（２．６ｇ）を加え、系内に２時間窒素を流し置換した。これに窒素気流下、臭化鋼（０．８０ｇ）、１官能開始剤（２−ブロモ−イソ酪酸エチル，１．０８ｇ）を加え重合を開始し、窒素気流下で、８０℃で２時間重合した。
【０１０９】
別途、ジメチルアセトアミド（２２７ｇ）に前記化４で示すネマチック液晶モノマー（３０ｇ）と化５で示すカイラル性モノマー（１０ｇ）の液晶モノマー混合物（モノマーのモル比，化４：化５＝７５：２５）を加熱溶解した後、窒素を２時間パブリングして濃度１５％の液晶モノマー混合物溶液を作成しておく。
【０１１０】
オクタデシアクリレートの重合率が８０重量％以上であることを確認した後、用意しておいた液晶モノマー混合物溶液をシリンジでラバーセプタムから添加し、８０℃で３時間、さらに９０℃で３０時間重合した。これにメタノールを加えて２度再沈精製を行なってコレステリック液晶ポリマー（液晶転移温度７５℃）を得た。
【０１１１】
製造例４
製造例３において、オクタデシアクリレートの代わりに、オクタデシルメタクリレートを用い、化４で示すネマチック液晶モノマー（３４ｇ）と化５で示すカイラル性モノマー（６ｇ）の液晶モノマー混合物（モノマーのモル比，化４：化５＝８５：１５）を用いたこと以外は製造例３と同様にしてコレステリック液晶ポリマー（液晶転移温度７６℃）を得た。
【０１１２】
実施例１
（１）コレステリック液晶フィルムの作製
製造例１で得られたコレステリック液晶ポリマーと、製造例４で得られたコレステリック液晶ポリマーを重量比で５０：５０で混合し、シクロヘキサノンに溶解して２０重量％溶液を作成した。ガラス板にポリビニルアルコール水溶液をスピンコートして配向膜を形成し表面をラビング処理した上に、前記コレステリック液晶ポリマー溶液を、塗布厚（乾燥厚）１．５μｍになるようにスピンコートで塗布し、常温、常湿にて３０分間放置して風乾したあと、１６０℃で４分間加熱して配向させて、コレステリック液晶フィルムを得た。
【０１１３】
得られたコレステリック液晶フィルムの偏光顕微鏡写真（５０倍）を、図１に示す。偏光板を回転させて観察したところ、連続相、分離層がそれぞれ均一に一様に変化しており、相分離構造を確認した。
【０１１４】
コレステリック液晶フィルムは捻れピッチ長の異なる微小領域を有しており、連続相の捻れピッチ長は３７０ｎｍ、分離層の捻れピッチ長は２８０ｎｍであった。なお、捻れピッチ長はＴＥＭ（透過型電子顕微鏡）にて断面撮像により測定される。
【０１１５】
また、選択反射帯域は、４００〜６６０ｎｍであった。なお、反射帯域巾は、広帯域コレステリック液晶フィルムの反射スペクトルを分光光度計（大塚電子株式会社製、瞬間マルチ測光システム ＭＣＰＤ−２０００）にて測定し、最大反射率の半分の反射率を有する反射帯域とした。
【０１１６】
（２）直線偏光子等の作製
上記（１）で得られたコレステリック液晶フィルム３枚をイソシアネート系接着剤（厚み２μｍ）を用いて積層した。得られた積層フィルムの反射率は８％向上した。
【０１１７】
また、この積層フィルムに日東電工製のλ／４板（ポリカーボネート製）を粘着剤（２５μｍ）にて積層し、直線偏光子（反射偏光子）とした。この直線偏光子に透過軸を合わせて日東電工製の偏光板（ＴＥＧ１４６５ＤＵ）を積層し、反射偏光子付き偏光板を得た。これを液晶表示装置の下側偏光板として配置し、バックライト点灯時の輝度を計測した。未加工部分と比較して約１．２倍の輝度上昇を確認した。なお、輝度の測定は、ＥＬＤＩＭ社製Ｅｚ−Ｃｏｎｔｒａｓｔにより行った。
【０１１８】
実施例２
（１）コレステリック液晶フィルムの作製
製造例２で得られたコレステリック液晶ポリマーと、製造例３で得られたコレステリック液晶ポリマーを重量比で５０：５０で混合し、シクロヘキサノンに溶解して２０重量％溶液を作成した。２軸延伸ポリエチレンテレフタレートフィルム（東レ製，ルミナー３８μｍ厚）表面をラビング処理した上に、前記コレステリック液晶ポリマー溶液を、塗布厚（乾燥厚）２μｍになるようにワイヤーバーで塗布し、常温、常湿にて３０分間放置して風乾したあと、１６０℃で４分間加熱して配向させて、コレステリック液晶フィルムを得た。
【０１１９】
得られたコレステリック液晶フィルムの偏光顕微鏡写真（５０倍）は、図１と同様であった。偏光板を回転させて観察したところ、連続相、分離層がそれぞれ均一に一様に変化しており、相分離構造を確認した。
【０１２０】
コレステリック液晶フィルムは捻れピッチ長の異なる微小領域を有しており、連続相の捻れピッチ長は３６０ｎｍ、分離層の捻れピッチ長は２６０ｎｍであった。選択反射帯域は、４００〜６６０ｎｍであった。
【０１２１】
（２）直線偏光子等の作製
上記（１）で得られたコレステリック液晶フィルムと、実施例１（１）で得られたコレステリック液晶フィルムをイソシアネート系接着剤（厚み２μｍ）を用いて積層した。得られた積層フィルムの反射率は６％向上した。
【０１２２】
また、この積層フィルムに日東電工製のλ／４板（ポリカーボネート製）を粘着剤（２５μｍ）にて積層し、直線偏光子（反射偏光子）とした。この直線偏光子に透過軸を合わせて日東電工製の偏光板（ＴＥＧ１４６５ＤＵ）を積層し、反射偏光子付き偏光板を得た。得られた反射偏光子付き偏光板を反射液晶表示装置の下板に用いると本発明によるコレステテリック液晶フィルム（積層フィルム）は肌理の細かい拡散反射板として機能した。相分離構造によるランダム構造から反射板と液晶画素の干渉やぎらつき、モアレなどの欠陥は生じなかった。
【０１２３】
比較例１
製造例１で得られたコレステリック液晶ポリマーを、シクロヘキサノンに溶解して２０重量％溶液を作成した。この溶液を用いたこと以外は実施例１と同様にしてコレステリック液晶フィルムを得た。得られたコレステリック液晶フィルムには、相分離構造が確認できなかった。選択反射帯域は、４００〜４８０ｎｍであった。
【０１２４】
比較例２
製造例１で得られたコレステリック液晶ポリマーと、製造例２で得られたコレステリック液晶ポリマーを重量比で５０：５０で混合し、シクロヘキサノンに溶解して２０重量％溶液を作成した。この溶液を用いたこと以外は実施例１と同様にしてコレステリック液晶フィルムを得た。得られたコレステリック液晶フィルムには、相分離構造が確認できなかった。選択反射帯域は、４３０〜５３０ｎｍであった。
【図面の簡単な説明】
【図１】実施例の顕微鏡写真である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a broadband cholesteric liquid crystal film and a method for producing the same. The broadband cholesteric liquid crystal film of the present invention is useful as a circularly polarizing plate (reflection type polarizer). The present invention also relates to a linear polarizer using the circularly polarizing plate, a lighting device, and a liquid crystal display device.
[0002]
[Prior art]
Generally, a liquid crystal display has a structure in which liquid crystal is injected between glass plates on which transparent electrodes are formed, and polarizers are arranged before and after the glass plates. A polarizer used for such a liquid crystal display is manufactured by adsorbing iodine, a dichroic dye, or the like on a polyvinyl alcohol film and stretching the same in a certain direction. The polarizer thus manufactured per se absorbs light oscillating in one direction and passes only light oscillating in the other direction to produce linearly polarized light. Therefore, the efficiency of the polarizer cannot theoretically exceed 50%, which is the largest factor that lowers the efficiency of the liquid crystal display. Also, due to this absorbed light, if the output of the light source is increased to a certain degree or more, the liquid crystal display device will break down the polarizer due to the heat generated by the heat conversion of the absorbed light, or display the liquid crystal layer inside the cell due to the thermal effect This has caused adverse effects such as deterioration of quality.
[0003]
A cholesteric liquid crystal having a function of separating circularly polarized light has a selective reflection characteristic in which the direction of rotation of the liquid crystal helix coincides with the direction of circular polarization, and reflects only circularly polarized light whose wavelength is the helical pitch of the liquid crystal. By using this selective reflection characteristic, only specific circularly polarized light of natural light in a certain wavelength band is transmitted and separated, and the rest is reflected and reused, whereby a highly efficient polarizing film can be manufactured. At this time, the transmitted circularly polarized light is converted into linearly polarized light by passing through a λ / 4 wavelength plate, and the direction of the linearly polarized light is aligned with the transmission direction of the absorption polarizer used in the liquid crystal display, thereby achieving high transmittance. A liquid crystal display device can be obtained. That is, when a cholesteric liquid crystal film is used as a linear polarizer in combination with a λ / 4 wavelength plate, there is theoretically no loss of light. Therefore, when a conventional absorption polarizer that absorbs 50% of light is used alone, In comparison, a two-fold improvement in brightness can be obtained in theory.
[0004]
However, the selective reflection characteristic of the cholesteric liquid crystal is limited to only a specific wavelength band, and it has been difficult to cover the entire visible light range. The selective reflection wavelength range width △ λ of cholesteric liquid crystal is
Δλ = 2λ · (ne−no) / (ne + no)
no: Refractive index of cholesteric liquid crystal molecules to normal light ne: Refractive index of cholesteric liquid crystal molecules to extraordinary light λ: Center wavelength of selective reflection, which depends on the molecular structure of cholesteric liquid crystal itself. From the above equation, if the value of ne-no is increased, the width of the selective reflection wavelength region Δλ can be increased, but the value of ne-no is usually 0.3 or less. When this value is increased, other functions (alignment characteristics, liquid crystal temperature, etc.) of the liquid crystal become insufficient, and practical use has been difficult. Accordingly, in practice, the selective reflection wavelength region width Δλ is at most about 150 nm. Most of practically usable cholesteric liquid crystals have a thickness of only about 30 to 100 nm.
[0005]
The selective reflection center wavelength λ is
λ = (ne + no) P / 2
P: It is represented by the helical pitch length required for one turn of the cholesteric liquid crystal, and if the pitch is constant, it depends on the average refractive index of the liquid crystal molecules and the pitch length.
[0006]
Therefore, in order to cover the entire visible light region, a plurality of layers having different selective reflection center wavelengths are laminated, or the pitch length is continuously changed in the thickness direction to form the existence distribution of the selective reflection center wavelength itself. Was.
[0007]
For example, there is a method of continuously changing the pitch length in the thickness direction (for example, see Patent Literature 1, Patent Literature 2, and Patent Literature 3). In this method, when the cholesteric liquid crystal composition is cured by ultraviolet light exposure, the difference in the exposure intensity between the exposed surface side and the outgoing surface side, and the difference in the polymerization rate, the composition ratio of the liquid crystal compositions with different reaction rates. The change is provided in the thickness direction.
[0008]
The point of this method is to take a large difference in exposure intensity between the exposure surface side and the emission surface side. Therefore, in many cases of the above-mentioned prior art examples, a method of mixing an ultraviolet absorber into a liquid crystal composition, generating absorption in a thickness direction, and amplifying a difference in exposure amount due to an optical path length has been adopted. .
[0009]
However, in the method of continuously changing the pitch length as in Patent Document 1, the thickness of the liquid crystal layer required to exhibit the function needs to be about 15 to 20 μm. For this reason, in addition to the problem of precise coating of the liquid crystal layer, a large amount of expensive liquid crystal is required, so that an increase in cost cannot be avoided. Further, the exposure time required was about 1 to 60 minutes, and a long production line having an exposure line length of 10 to 600 m was required to obtain a line speed of 10 m / min. On the other hand, if the line speed is reduced, the line length can be reduced, but a reduction in the production speed is inevitable.
[0010]
This is because, as described in Patent Document 1, to change the pitch length in the thickness direction, the cholesteric pitch is changed by a composition ratio change due to a difference in ultraviolet exposure intensity in the thickness direction and a mass transfer caused by a difference in polymerization rate. This is because it is difficult to form a quick pitch change due to a theoretical problem of controlling the pitch. In Patent Document 1, since the pitch length differs by about 100 nm between the short pitch side and the long pitch side, it is necessary to greatly change the composition ratio. To achieve this, a considerable liquid crystal thickness, weak ultraviolet irradiation and a long exposure time are required. is necessary.
[0011]
In Patent Literature 2, the temperature conditions for the primary exposure and the secondary exposure are changed, and the time required for the composition ratio to change in the thickness direction is separately provided in a dark place. However, the waiting time for mass transfer due to this temperature change needs to be about 10 to 30 minutes.
[0012]
In Patent Document 3, since the mobility of the substance that changes the pitch is better than the material example used in Patent Document 1, the film is formed with an exposure amount of about 1 minute. However, even in this case, a thickness of 15 μm is required.
[0013]
Also in Patent Documents 2 and 3, the liquid crystal coating thickness is about 15 μm, and when viewed in conjunction with Patent Document 1 which requires a thickness of about 20 μm, visible in the liquid crystal layer due to a pitch change due to a composition ratio change in the thickness direction. It can be seen that many cholesteric liquid crystal thicknesses and mass transfer times are required to cover the entire light range.
[0014]
On the other hand, it is necessary to laminate at least three layers to cover the entire visible light region with the cholesteric liquid crystal described in Patent Document 4, and it is necessary to cover the long wavelength side in order to improve the viewing angle characteristics. Further, when countermeasures against oblique incident light rays are required, the required number of stacked layers is as large as 4 to 5 layers, and it is inevitable that the production process becomes complicated and the yield decreases due to an increase in the number of processes. Further, since it is necessary to change the selective reflection wavelength for each layer, it is necessary to change the composition of the coating liquid.
[0015]
[Patent Document 1]
JP-A-6-281814
[Patent Document 2]
Patent No. 3272668 Specification
[Patent Document 3]
JP-A-11-248943
[Patent Document 4]
Japanese Patent Application Laid-Open No. 9-189811
[Problems to be solved by the invention]
An object of the present invention is to provide a method for manufacturing a broadband cholesteric liquid crystal film simply and at low cost by reducing the thickness of a liquid crystal layer. Still another object is to provide a broadband cholesteric liquid crystal film obtained by the manufacturing method.
[0020]
Another object of the present invention is to provide a circularly polarizing plate using the broadband cholesteric liquid crystal film, and further to provide a linear polarizer, a lighting device, and a liquid crystal display using the circularly polarizing plate.
[0021]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above problems, and as a result, have found that the above object can be achieved by the following method for producing a broadband cholesteric liquid crystal film, and have completed the present invention. That is, the present invention is as follows.
[0022]
1. A step of applying a solution obtained by dissolving a cholesteric liquid crystal polymer in a solvent on an alignment substrate,
A step of aligning the cholesteric liquid crystal polymer such that the cholesteric spiral axis is perpendicular to the alignment substrate surface, and
A method for producing a cholesteric liquid crystal film having a step of drying and forming a film while maintaining a liquid crystal state by the alignment,
A method (1) for producing a broadband cholesteric liquid crystal film, characterized in that a mixture of two or more cholesteric liquid crystal polymers which are incompatible in the absence of a solvent and have different twist pitch lengths is used as the cholesteric liquid crystal polymer.
[0023]
2. Two or more cholesteric liquid crystal polymers are polymers obtained from a liquid crystal composition containing a polymerizable nematic agent (a) and a polymerizable chiral agent (b),
Each cholesteric liquid crystal polymer has a different composition ratio of the polymerizable nematic agent (a) and the polymerizable chiral agent (b),
2. The method (1) for producing a broadband cholesteric liquid crystal film according to the above item 1, wherein a crystalline component is introduced as a block into at least one of the cholesteric liquid crystal polymers.
[0024]
3. A broadband cholesteric liquid crystal film obtained by the production method (1) according to the above 1 or 2, wherein the cholesteric liquid crystal film is
Since the mixture of the cholesteric liquid crystal polymer is incompatible in the absence of a solvent as the cholesteric liquid crystal polymer, and the twist pitch length is different from two or more cholesteric liquid crystal polymers,
A broadband cholesteric liquid crystal film, wherein each cholesteric liquid crystal polymer forms a phase-separated structure, and immobilizes minute regions having different twist pitch lengths.
[0025]
4. Applying a liquid crystal composition containing a polymerizable nematic agent (a) and a polymerizable chiral agent (b) onto an alignment substrate,
A step of aligning the cholesteric spiral axis of the liquid crystal composition so as to be perpendicular to the alignment substrate surface, and
A method for producing a cholesteric liquid crystal film having a step of forming a cured film by light or thermal polymerization while maintaining the liquid crystal state by the alignment,
A liquid crystal composition containing at least one polymerizable nematic agent (a) and at least two polymerizable chiral agents (b); or
A liquid crystal composition comprising at least two polymerizable nematic agents (a) and at least one polymerizable chiral agent (b),
The method for producing a broadband cholesteric liquid crystal film (2) is characterized in that the liquid crystal composition is incompatible at the time of orientation and becomes a liquid crystal composition of two or more components having different twist pitch lengths. ).
[0026]
5. A broadband cholesteric liquid crystal film obtained by the production method (2) according to the above item 4, wherein the cholesteric liquid crystal film is
Since the liquid crystal composition is incompatible at the time of alignment, and becomes a liquid crystal composition of two or more components having different twist pitch lengths,
A cholesteric liquid crystal film having a wide band, wherein a cholesteric liquid crystal polymer obtained from each of the liquid crystal compositions forms a phase-separated structure, and immobilizes minute regions having different twist pitch lengths.
[0027]
6. 6. A broadband cholesteric liquid crystal film, wherein the wideband cholesteric liquid crystal film according to the above item 3 or 5 is laminated in two to six layers.
[0028]
7. The broadband cholesteric liquid crystal film as the upper layer is laminated on the lower layer of the broadband cholesteric liquid crystal film of the above item 3 or 5, by the production method (1) of the above item 1 or 2 or the production method (2) of the above item 4 to form an upper layer. In producing the broadband cholesteric liquid crystal film of
A method for producing a broadband cholesteric liquid crystal film, comprising: performing a base treatment on a surface of a cholesteric liquid crystal film as a lower layer, and then laminating a cholesteric liquid crystal film as an upper layer.
[0029]
8. 7. A circularly polarizing plate using the broadband cholesteric liquid crystal film of the above item 3, 5 or 6.
[0030]
9. 9. A linear polarizer obtained by laminating a λ / 4 plate on the circularly polarizing plate described in 8 above, and capable of obtaining linearly polarized light by transmission.
[0031]
10. 10. A linear polarizer obtained by adhering an absorption type polarizer to the transmission axis of the linear polarizer according to the above item 9, with its transmission axis direction aligned.
[0032]
11. A lighting device, comprising: the surface light source having a reflective layer on the back side; and the circular polarizer described in the above item 8 and the linear polarizer described in the item 9 or 10 on the surface side.
[0033]
12. 12. A liquid crystal display device comprising a liquid crystal cell on the light emission side of the lighting device according to the above item 11.
[0034]
(Effect)
As described above, the method for producing a cholesteric liquid crystal film of the present invention comprises, as a cholesteric liquid crystal polymer or a polymerizable liquid crystal composition forming a cholesteric liquid crystal polymer, two or more types that are incompatible and have different twist pitch lengths. By using these, a cholesteric liquid crystal layer is formed in which these form a phase-separated structure when the solvent evaporates or cures, and immobilizes minute regions having different twist pitch lengths. As described above, the cholesteric liquid crystal film of the present invention has poor compatibility of the material forming the cholesteric liquid crystal layer, the liquid crystal layer has a phase separation structure, and the twist pitch length of each phase is different. Broadband having different selective reflection center wavelengths is realized. According to such a method, the thickness of the cholesteric liquid crystal layer can be reduced as compared with the conventional method. Further, since the number of manufacturing steps can be reduced and the number of laminated layers can be reduced, a cholesteric liquid crystal film can be manufactured simply and at low cost, and the production speed can be improved by improving the line speed.
[0035]
The obtained cholesteric liquid crystal film has a selective reflection function of circularly polarized light over a wide band, and is useful as a circularly polarizing plate. The broadband circularly polarizing plate is combined with a λ / 4 plate or an absorption polarizer to obtain a broadband linear light. A polarizer can be obtained.
[0036]
BEST MODE FOR CARRYING OUT THE INVENTION
In the method (1) for producing a broadband cholesteric liquid crystal film of the present invention, a solution in which a cholesteric liquid crystal polymer is dissolved in a solvent is used as a material for forming the cholesteric liquid crystal film. As the cholesteric liquid crystal polymer, two or more kinds that are incompatible in the absence of a solvent are used. "Incompatible" is one that forms a phase-separated structure without mixing in a solvent-free environment. The incompatible cholesteric liquid crystal polymer can be made incompatible by, for example, appropriately changing the type of a monomer forming the cholesteric liquid crystal polymer. Further, as the cholesteric liquid crystal polymer, two or more kinds having different twist pitch lengths are used. The twist pitch length is appropriately adjusted depending on the content of the chiral component introduced into the cholesteric liquid crystal polymer.
[0037]
The cholesteric liquid crystal polymer is obtained, for example, by polymerizing a liquid crystal composition containing a polymerizable nematic agent (a) and a polymerizable chiral agent (b).
[0038]
Examples of the polymerizable nematic agent (a) include those having at least one polymerizable functional group and having a mesogen group comprising a cyclic unit or the like. Examples of the polymerizable functional group include an acryloyl group, a methacryloyl group, an epoxy group, and a vinyl ether group, and among these, an acryloyl group and a methacryloyl group are preferable. In addition, by using a compound having two or more polymerizable functional groups, a crosslinked structure can be introduced to improve the durability. Examples of the cyclic unit to be a mesogen group include biphenyl, phenylbenzoate, phenylcyclohexane, azoxybenzene, azomethine, azobenzene, phenylpyrimidine, diphenylacetylene, diphenylbenzoate, bicyclohexane, and the like. And cyclohexylbenzenes, terphenyls and the like. In addition, the terminal of these cyclic units may have a substituent such as a cyano group, an alkyl group, an alkoxy group, and a halogen group. The mesogen group may be bonded via a spacer that imparts flexibility. Examples of the spacer portion include a polymethylene chain and a polyoxymethylene chain. The number of repeating structural units forming the spacer portion is appropriately determined depending on the chemical structure of the mesogen portion, but the number of repeating units of the polymethylene chain is 0 to 20, preferably 2 to 12, and the number of repeating units of the polyoxymethylene chain is 0 to 10. 10, preferably 1-3.
[0039]
As the polymerizable nematic agent (a), for example, the following general formula (a):
Embedded image

(Wherein, R ¹ is a hydrogen atom or a methyl group, m is an integer of 1 to 6, X ¹ is a —CO ₂ — group, —OCO— group, —CO—, —CH ＝ CH— or —C}. C-, and R ² represents an alkoxy group having 1 to 6 carbon atoms, a cyano group, a fluoro group or an alkyl group having 1 to 6 carbon atoms, and p and q each represent 1 or 2.) Derivatives.
[0040]
In the acrylate derivative represented by the general formula (a), p = 1 is preferable, q = 2 is preferable, R ¹ is preferably a hydrogen atom, R ² is preferably a cyano group, and X ¹ is-. COO- groups are preferred. Specific examples of the acrylate derivative represented by the general formula (a) include, for example, 4- (4-cyanobiphenyloxycarbonyl) phenoxyethyl acrylate, 4- (4-cyanobiphenyloxycarbonyl) phenoxypropyl acrylate, -(4-cyanobiphenyloxycarbonyl) phenoxybutyl acrylate, 4- (4-cyanobiphenyloxycarbonyl) phenoxypentyl acrylate, 4- (4-cyanobiphenyloxycarbonyl) phenoxyhexyl acrylate, and the like. These can be used alone or as a mixture.
[0041]
The polymerizable chiral agent (b) is not particularly limited as long as it has at least one polymerizable functional group, has an optically active group, and does not disturb the orientation of the polymerizable nematic agent (a). Examples of the polymerizable functional group include an acryloyl group, a methacryloyl group, an epoxy group, and a vinyl ether group, and among these, an acryloyl group and a methacryloyl group are preferable. The polymerizable chiral agent (b) may or may not have liquid crystallinity, but those having cholesteric liquid crystallinity can be preferably used. Further, as the polymerizable chiral agent (b), those having two or more polymerizable functional groups can be used.
[0042]
As the polymerizable chiral agent (b), for example, a compound represented by the general formula (b):
Embedded image

(Wherein, R ³ is a hydrogen atom or a methyl group, n is an integer of 1 to 6, X ² is a —CO ₂ — group, —OCO— group, —CO—, —CH ＝ CH— or —C}. C- and R ⁴ represent the general formula (c):
Embedded image

(In each formula, R ⁵ is a phenyl group, 1-naphthyl group, 2-naphthyl group or biphenyl group, R ⁶ is a methyl group, a phenyl group or a carboxymethyl group, R ⁷ is a methyl group, a benzyl group or represents a t-butyl group, and * represents an asymmetric carbon atom.) Acrylic ester derivatives having an optically active group represented by:
[0043]
In the acrylate derivative represented by the general formula (b), R ⁵ is preferably a hydrogen atom, R ⁶ is preferably a compound having a Schiff base structure (particularly, R ⁷ is a phenyl group), and X ² is Is preferably a -COO- group. Specific examples of the acrylate derivative having an optically active group represented by the general formula (b) include, for example, ((3-phenyl-3-methyl-2-azapropenylphenyl) oxycarbonyl) phenoxyethyl acrylate, ( (3-phenyl-3-methyl-2-azapropenylphenyl) oxycarbonyl) phenoxypropyl acrylate, ((3-phenyl-3-methyl-2-azapropenylphenyl) oxycarbonyl) phenoxybutyl acrylate, ((3-phenyl -3-methyl-2-azapropenylphenyl) oxycarbonyl) phenoxybentyl acrylate, ((3-phenyl-3-methyl-2-azapropenylphenyl) oxycarbonyl) phenoxyhexyl acrylate, and the like. These can be used alone or as a mixture.
[0044]
The amount of the polymerizable chiral agent (b) varies the twist pitch, which determines the selective reflection wavelength, depending on the amount of the polymerizable chiral agent. Therefore, the selective reflection wavelength can be adjusted by controlling the amount of the polymerizable chiral agent (b). Therefore, the composition ratio of the polymerizable nematic agent (a) and the polymerizable chiral agent (b) is controlled by controlling the amount of the polymerizable chiral agent (b) in two or more cholesteric liquid crystal polymers having different twist pitch lengths. It can be prepared from different ones. The blending amount of the polymerizable chiral agent (b) is controlled so that the twist pitch length of the cholesteric liquid crystal polymer is different within a range of about 1 to 30 parts by weight based on 100 parts by weight of the polymerizable nematic agent (a). preferable.
[0045]
The cholesteric liquid crystal polymer can be prepared according to a conventional polymerization method of an acrylic monomer such as a radical polymerization method, a cation polymerization method, or an anion polymerization method. When the radical polymerization method is applied, various polymerization initiators can be used, but the decomposition temperature of azobisisobutyronitrile or benzoyl peroxide is not high, and decomposes at an intermediate temperature that is not low. Are preferably used. The number average molecular weight of the cholesteric liquid crystal polymer is preferably about 2,000 to 100,000. Preferably it is about 5,000 to 50,000.
[0046]
The method of preparing two or more incompatible cholesteric liquid crystal polymers is not particularly limited. For example, it can be carried out by appropriately selecting the polymerizable nematic agent (a) and the polymerizable chiral agent (b) that form an incompatible cholesteric liquid crystal polymer.
[0047]
Further, by introducing a crystalline component as a block into at least one of the cholesteric liquid crystal polymers, two or more cholesteric liquid crystal polymers can be made incompatible. A cholesteric liquid crystal polymer in which a crystalline component is introduced as a block may be incompatible with the same polymerizable nematic agent (a) and polymerizable chiral agent (b), or with a compatible cholesteric liquid crystal polymer. .
[0048]
A method for producing a cholesteric liquid crystal polymer in which a crystalline component is introduced as a block body is not particularly limited. For example, a polymer obtained from the polymerizable nematic agent (a) and the polymerizable chiral agent (b) and a block polymer of a crystalline component are separately polymerized by an arbitrary polymerization method, and the polymer is mixed. Can be As a method for producing a block polymer, it is particularly preferable to use a living radical polymerization method. As a reference of this living radical polymerization method, for example, a report by Patten et al., “Radical Polymerization Yielding Polymers with Mw / Mn １．０1.05 by Homogeneous Atom Transfer Radical Polymerization, Polymer. Alternatively, a report by Matyjasewski et al., "Controlled / Living Radical Polymerization. Halogen Atom Transfer Radical Polymerization Promoted by a Cu (I) / Cu (II) Redox Process ", Macromolecules 1995, 28, 7901-10 (October 15, 1995); or PCT / U.Nation. WO 96/30421 (October 3, 1996); Sawamoto et al., "Ruthium-mediated Living Radical Polymerization of Methyl Methylate Macromolecules, 1996, 29, 1070. Etc. are known.
[0049]
For example, a polymer (block) is obtained by adding a monomer (c) as a crystalline component to a polymer (block ab) obtained by living polymerization of a polymerizable nematic agent (a) and a polymerizable chiral agent (b). By sequentially adding the monomer (c) to the polymerization terminal of the above, a secondary block and a crystalline component (block c) are introduced to form a diblock polymer in ab-c form. it can. In addition, a polymerizable nematic agent (a) is added by living polymerization to a terminal (block body b) where the polymerizable chiral agent (b) is subjected to living polymerization (block body b), and then a crystalline component ( Block c) may be introduced to form a bac triblock polymer. On the other hand, after the crystalline component (block c) is subjected to living polymerization, the polymerizable nematic agent (a) and the polymerizable chiral agent (b) may be polymerized to form a c-ba triblock. . Further, the form of bca is also possible. The polymerizable nematic agent (a) and the polymerizable chiral agent (b) can be added simultaneously to form c-ab.
[0050]
Monomers to be added to the living polymerized polymer in the middle are when the polymerization rate of the polymer being polymerized exceeds at least 60% by weight, preferably when it exceeds 80% by weight, and further when it exceeds 90% by weight. It is preferred that The polymerization rate is defined as (residual monomer / amount of charged monomer before polymerization) × 100 (%), and is measured by heating to volatilize and remove the monomer component, or by gel permeation chromatography, gas chromatography, or liquid chromatography. can do.
[0051]
The monomer (c) to be a crystalline component may be a liquid crystalline component or a non-liquid crystalline component as long as it has poor compatibility with the polymerizable nematic agent (a) and the polymerizable chiral agent (b). Examples of the monomer (c) include an acrylic monomer having a long-chain alkyl group in a side chain. An acrylic monomer having a long-chain alkyl group has an alkyl group having 12 to 28 carbon atoms such as octadecyl (meth) acrylate, lauryl (meth) acrylate, mystyryl (meth) acrylate, palmityl (meth) acrylate, and stearyl (meth) acrylate. Things are raised.
[0052]
In addition, a monomer having two or more polymerizable functional groups can be used as the monomer (c). If this is used, stronger film quality can be obtained by three-dimensional crosslinking. As the monomer (c), one type may be used alone, or two or more types may be used.
[0053]
The proportion of the crystalline component (monomer (c)) is about 5 to 40% by weight, preferably 10 to 30% by weight of the obtained cholesteric liquid crystal polymer. If it exceeds 40% by weight, the optical properties are adversely affected.
[0054]
In the case of the living radical polymerization, it is necessary to remove dissolved oxygen in the monomer. As a method of lowering the dissolved oxygen concentration, a method of stirring while blowing an inert gas such as nitrogen or argon, a method of bubbling the inert gas into the monomer, a method of degassing under reduced pressure, a method of degassing by heating, etc. There is. These methods may be used in combination.
[0055]
As the polymerization initiator, an ester having bromine or chlorine at the α-position or a derivative of styrene is preferable. Preferably, a 2-bromo (or chloro) propionic acid derivative or a 1-phenyl chloride (or bromide) derivative is used. Among them, particularly preferred are methyl 2-bromo (or chloro) propionate, ethyl 2-bromo (or chloro) propionate, methyl 2-bromo (or chloro) -2-propionate, and 2-bromo (or chloro) -2. -A halogen compound selected from ethyl propionate, 1-phenylethyl chloride (or bromide) and ethyl 2-bromoisobutyrate can be used. As the initiator having a hydroxyl group, for example, 2-hydroxyethyl 2-bromo-2-methylpropionate and the like can also be used. Bifunctional initiators can also be used. Specific examples include ethylene bis (2-bromo-2-methylpropionate).
[0056]
In the above polymerization, the number average molecular weight of the obtained block copolymer can be controlled intentionally. In such a polymerization method, a transition metal and a ligand are used as a catalyst other than the initiator.
[0057]
As the transition metal, metal species of Cu, Ru, Fe, Rh, V, and Ni, and their metal salts and metal complexes can be used. The ligand is not particularly limited, but for example, a bipyridyl derivative, an amine derivative, a mercaptan derivative, a trifluorate derivative and the like can be used. Among these, it is particularly preferable to use Cu (I) and a 2,2'-bipyridyl complex from the viewpoint of stability and rate of polymerization.
[0058]
The polymerization initiator is used in a proportion of usually 0.05 to 30 mol%, preferably 0.1 to 10 mol%, based on the entire polymerizable monomer. The transition metal is used in an amount of usually 0.01 to 3 parts by mol, preferably 0.1 to 1 part by mol, based on 1 part by mol of the polymerization initiator, in the form of a halide or the like. . Further, the ligand is used in a proportion of usually 0.5 to 5 parts by mol, preferably 1 to 3 parts by mol, per 1 part by mol of the above-mentioned transition metal (form of halide or the like). When the polymerization initiator and the activator are used in such a ratio, good results can be obtained in the reactivity of living radical polymerization, the molecular weight of the produced polymer, and the like.
[0059]
The block copolymer is obtained by using the above-mentioned polymerization method. If the monomer component is liquid at the polymerization temperature, it can be produced using a solvent or without a solvent. Since liquid crystal monomers are not usually liquid, they are dissolved in a solvent and polymerized. The solvent only needs to dissolve the liquid crystal monomer. Examples of solvents that can be used include tetrahydrofuran, anisole, dimethylacetamide, cyclohexanone. Cyclopentanone or the like can be used. Usually, polymerization is carried out at a monomer concentration of about 10 to 30% by weight.
[0060]
As described above, two or more cholesteric liquid crystal polymers that are incompatible and have different twist pitch lengths are prepared. A mixture of these cholesteric liquid crystal polymers is used as a solution dissolved in a solvent. The ratio of each polymer in the mixture of two or more cholesteric liquid crystal polymers is not particularly limited. For example, when a cholesteric liquid crystal polymer obtained from the ab copolymer and a block polymer obtained by adding a block c thereto are used. It is preferable that the former: the latter (weight ratio) = 10/90 to 90/10. More preferably, the former: the latter (weight ratio) = 20/80 to 80/20.
[0061]
Examples of the solvent for dissolving the mixture of two or more cholesteric liquid crystal polymers include, for example, halogenated hydrocarbons such as chloroform, dichloromethane, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, and chlorobenzene; phenols; phenols such as parachlorophenol; Aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene, 1,2-dimethoxybenzene, etc., acetone, ethyl acetate, tert-butyl alcohol, glycerin, ethylene glycol, triethylene glycol, ethylene bricol monomethyl ether , Diethylene glycol dimethyl ether, ethyl cellosolve, butyl cellosolve, 2-pyrrolidone, N-methyl-2-pyrrolidone, pyridine, triethyl Amines, tetrahydrofuran, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, acetonitrile, butyronitrile, carbon disulfide, methyl ethyl ketone, cyclohexanone, cyclopentanone and the like are preferable. The concentration of the solution is usually about 3 to 50% by weight.
[0062]
A solution of the cholesteric liquid crystal polymer mixture is coated on an alignment substrate, a step of aligning the cholesteric liquid crystal polymer such that a cholesteric spiral axis of the cholesteric liquid crystal polymer is perpendicular to the alignment substrate surface, and changing the liquid crystal state by the alignment. A process of forming a dry film while maintaining the film is performed.
[0063]
The method of applying the above solution to the alignment substrate is not particularly limited, and the coating can be performed with an appropriate coating machine such as a bar coater, a spinner, and a roll coater. It is.
[0064]
As the alignment base material, a conventionally known one can be used. For example, a thin film made of polyimide or polyvinyl alcohol is formed on a substrate, and the thin film is rubbed with rayon cloth or the like. A photo-alignment film, a stretched film, or the like irradiated with is used. In addition, the orientation can be performed by a magnetic field, an electric field orientation, and a shear stress operation.
[0065]
As the substrate, a film, a glass plate, and a quartz sheet made of polyethylene terephthalate, triacetyl cellulose, norbornene resin, polyvinyl alcohol, polyimide, polyarylate, polycarbonate, polysulfone, polyethersulfone, and other plastics are used.
[0066]
The alignment is performed at a temperature equal to or higher than the liquid crystal transition temperature of the cholesteric liquid crystal polymer. The alignment temperature and time are appropriately determined according to the type of the cholesteric liquid crystal polymer.
[0067]
The cholesteric liquid crystal polymer is formed into a dry film while maintaining a liquid crystal state by alignment. The drying temperature may be a temperature not lower than the boiling point of the solvent. Dry film formation can be performed together with the orientation step. When dry film formation is performed together with the alignment step, the temperature is set according to the type of the solvent and the cholesteric liquid crystal polymer.
[0068]
In the method (2) for producing a broadband cholesteric liquid crystal film, a liquid crystal composition containing a polymerizable nematic agent (a) and a polymerizable chiral agent (b) is used. The liquid crystal composition contains at least one polymerizable nematic agent (a) and at least two polymerizable chiral agents (b), or at least two polymerizable nematic agents (a) and A liquid crystal composition containing at least one polymerizable chiral agent (b), wherein the liquid crystal composition is incompatible at the time of alignment and has two or more components having different twist pitch lengths. It is a thing.
[0069]
As the polymerizable nematic agent (a) and the polymerizable chiral agent (b), those described above can be used. The liquid crystal composition can be made incompatible by appropriately changing the types and the like of these components. Further, the twist pitch length can be varied depending on the amount of the polymerizable chiral agent (b) used. The amount of the polymerizable chiral agent (b) used is adjusted within the same range as described above.
[0070]
In the liquid crystal composition, a step of applying the liquid crystal composition on an alignment substrate, a step of aligning the cholesteric spiral axis of the liquid crystal composition in a direction perpendicular to the alignment substrate surface, while maintaining a liquid crystal state due to the alignment. A step of forming a film by curing by light or thermal polymerization is performed. The same method as the production method (1) can be adopted as a method of applying the composition on the orientation base material and an orientation method.
[0071]
The step of forming a cured film by light or thermal polymerization can be performed by various conventional methods. The photopolymerization curing is performed by irradiating the liquid crystal composition applied and aligned on the alignment substrate with radiation such as ultraviolet rays. When the liquid crystal composition is cured by ultraviolet light, a photopolymerization initiator is included. Various photopolymerization initiators can be used without particular limitation. Examples of the photopolymerization initiator include Irgacure 907, 184, 651, and 369 manufactured by Ciba Specialty Chemicals. The thermal polymerization curing is performed by subjecting the liquid crystal composition applied and aligned on the alignment substrate to a heat treatment. The thermosetting liquid crystal composition generally contains a thermal polymerization initiator.
[0072]
The thickness of the cholesteric liquid crystal film of the present invention (the coating thickness after drying the solvent in the case of a solution) is not particularly limited, but is usually 0.5 to 20 μm, preferably 1 to 10 μm. This is because, when the coating thickness is small, the optical effect is small, and when the coating thickness is large, orientation becomes difficult.
[0073]
In the cholesteric liquid crystal film obtained in the present invention, each cholesteric liquid crystal polymer (in the production method (2), a cured product obtained from a liquid crystal composition) forms a phase-separated structure to broaden the band, and has a twist pitch length. Different minute regions are respectively fixed. Therefore, when there is a layer having two or more kinds of twist pitches in the thickness direction as a phase separation structure of the cholesteric liquid crystal film, a sufficient degree of polarization can be obtained with one layer of the cholesteric liquid crystal film. This is because such a cholesteric liquid crystal film is equivalent to a multilayer laminated product.
[0074]
On the other hand, as a phase separation structure of the cholesteric liquid crystal film, when only one kind of twist pitch exists in the thickness direction and different pitches exist only in the adjacent horizontal direction, the phase separation structure of the one-layer cholesteric liquid crystal film is used. As described above, a single degree of transmission / reflection of a layer having two or more kinds of twist pitches in the thickness direction cannot provide a sufficient degree of polarization. This is because one transmission / reflection is affected only by one pitch, and rays outside the selective reflection area are not subjected to polarization separation. In such a case, the degree of polarization can be improved by laminating two or more layers. The laminate may be a laminate of the same product or a cholesteric liquid crystal film made of components having different compositions. This is because, even for the same product, the phase separation structure does not reproduce exactly the same shape, so that it is unlikely that the structures with the same pitch continue to overlap in the thickness direction of the laminated product.
[0075]
Even when three layers are stacked, the same material can be individually stacked. Therefore, there is no need for a method of preparing a plurality of materials having compositions having different twist pitches as in the conventional Patent Document 4, and the degree of polarization can be improved by separately laminating cholesteric liquid crystal films having the same composition.
[0076]
Note that the cholesteric liquid crystal film is preferably stacked with two or more and six or less layers because the number of layers increases as the number of layers increases. In particular, two or more and four or less layers are preferable. It is preferable to control the lamination thickness to a range of 10 μm or less, more preferably 8 μm or less.
[0077]
The means for laminating the cholesteric liquid crystal film is not particularly limited. For example, it can be performed with an adhesive. In addition, a broadband cholesteric liquid crystal film can be laminated as an upper layer on the lower cholesteric liquid crystal film by the above-mentioned production method (1) or (2). In this case, the lower layer of the cholesteric liquid crystal film is subjected to a base treatment, and then the upper layer of the cholesteric liquid crystal film is formed so that the phase separation structure having the same twist pitch does not exist continuously in the thickness direction. Are preferably laminated. When direct overcoating is applied, each phase-separated layer may selectively coagulate and precipitate on its own cured product due to poor wettability. It is preferable to perform it at appropriate times. The underlayer treatment is, for example, a method of eliminating the influence of the surface state of the lower layer by forming an alignment film typified by polyvinyl alcohol, or a method of modifying the surface property such as a corona treatment or a saponification treatment. There is a method to eliminate the influence of the state.
[0078]
The cholesteric liquid crystal film thus obtained is used without being separated from the substrate, or may be used after being separated from the substrate.
[0079]
The broadband cholesteric liquid crystal film of the present invention is used as a circularly polarizing plate. The cholesteric liquid crystal laminate having a wideband selective reflection function obtained in the present invention has a circularly polarized light reflection / transmission function in the front direction, and this can be used as a broadband circularly polarized light in a liquid crystal display device. In this case, it can be used as a circularly polarizing plate by arranging it on the light source side of a circularly polarized mode liquid crystal cell, for example, a transmissive VA mode liquid crystal cell having a multi-domain.
[0080]
A linear polarizer can be formed by laminating a λ / 4 plate on the circularly polarizing plate. As a λ / 4 plate, a film made of an appropriate polymer such as polycarbonate, norbornene-based resin, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene or other polyolefin, polyarylate, polyamide, polyethylene terephthalate, or polysulfone is stretched. And an alignment film made of a liquid crystal material such as a liquid crystal polymer, and an alignment layer of a liquid crystal material supported by a film. Usually, the thickness of the λ / 4 wavelength plate is preferably 0.5 to 200 μm, and particularly preferably 1 to 100 μm.
[0081]
The λ / 4 plate functions well only for a specific wavelength with a single layer made of a single material, but there is a problem that the function of the λ / 4 plate is reduced for other wavelengths due to wavelength dispersion characteristics. Therefore, if the λ / 2 plate and the λ / 2 plate are laminated while defining the axis angle, the λ / 2 plate can be used as a broadband λ / 4 plate that functions within a practically acceptable range over the entire visible light range. In this case, each of the λ / 4 plate and the λ / 2 plate may be the same material, or may be a combination of those made of different materials obtained by the same method as the λ / 4 plate described above.
[0082]
For example, a λ / 4 plate (140 nm) is laminated on a broadband circularly polarizing plate, and a λ / 2 plate (270 nm) is arranged at 117.5 degrees with respect to this axis angle. In this case, the transmission polarization axis is 10 degrees with respect to the axis of the λ / 4 plate. Since the bonding angle varies depending on the phase difference value of each retardation plate, the bonding angle is not limited to the above bonding angle.
[0083]
In addition, the cholesteric liquid crystal layer according to the present invention has a broadband circularly polarized light reflection characteristic and a scattering characteristic resulting from a phase separation structure. Therefore, the circularly polarizing plate according to the present invention can be suitably used as a reflecting plate.
[0084]
An absorption type polarizer is attached to the transmission axis of the linear polarizer with its transmission axis direction aligned.
[0085]
The polarizer is not particularly limited, and various types can be used. Examples of the polarizer include a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, an ethylene-vinyl acetate copolymer-based partially saponified film, and a dichromatic dye such as iodine or a dichroic dye. And uniaxially stretched by adsorbing a hydrophilic substance, or a polyene-based oriented film such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride. Among these, a polarizer composed of a polyvinyl alcohol-based film and a dichroic substance such as iodine is preferable. The thickness of these polarizers is not particularly limited, but is generally about 5 to 80 μm.
[0086]
A polarizer obtained by dyeing a polyvinyl alcohol-based film with iodine and uniaxially stretching can be produced by, for example, dyeing polyvinyl alcohol by immersing it in an aqueous solution of iodine, and stretching the film to 3 to 7 times its original length. If necessary, it can be immersed in an aqueous solution of boric acid or potassium iodide. Further, if necessary, the polyvinyl alcohol-based film may be immersed in water and washed with water before dyeing. By washing the polyvinyl alcohol-based film with water, dirt on the surface of the polyvinyl alcohol-based film and an anti-blocking agent can be washed, and by swelling the polyvinyl alcohol-based film, the effect of preventing unevenness such as uneven dyeing can be obtained. is there. Stretching may be performed after dyeing with iodine, may be performed while dyeing, or may be dyed with iodine after stretching. Stretching can be performed in an aqueous solution of boric acid or potassium iodide or in a water bath.
[0087]
The polarizer is usually provided with a transparent protective film on one or both sides and used as a polarizing plate. The transparent protective film preferably has excellent transparency, mechanical strength, thermal stability, moisture shielding property, isotropy and the like. Examples of the transparent protective film include films made of transparent polymers such as polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, polycarbonate polymers, and acrylic polymers such as polymethyl methacrylate. Is raised. Styrene polymers such as polystyrene and acrylonitrile / styrene copolymer; polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure; olefin polymers such as ethylene / propylene copolymer; vinyl chloride polymers; nylon and aromatic polyamides And a film made of a transparent polymer such as an amide-based polymer. Furthermore, imide-based polymers, sulfone-based polymers, polyethersulfone-based polymers, polyetheretherketone-based polymers, polyphenylene sulfide-based polymers, vinyl alcohol-based polymers, vinylidene chloride-based polymers, vinylbutyral-based polymers, arylate-based polymers, and polyoxymethylene-based polymers Films made of transparent polymers such as polymers, epoxy polymers and blends of the above polymers are also included. In particular, those having low optical birefringence are preferably used. From the viewpoint of a protective film for a polarizing plate, triacetyl cellulose, polycarbonate, an acrylic polymer, a cycloolefin resin, a polyolefin having a norbornene structure, and the like are preferable. The present invention is suitable for a transparent substrate, such as triacetyl cellulose, which is difficult to bake at a high temperature. At 130 ° C. or higher, the plasticizer in the film volatilizes at a temperature of 130 ° C. or more, and the properties of triacetyl cellulose are significantly reduced.
[0088]
Further, polymer films described in JP-A-2001-343529 (WO 01/37007), for example, (A) a thermoplastic resin having a substituted and / or unsubstituted imide group in the side chain, and (B) a thermoplastic resin having a side chain And / or an unsubstituted phenyl and a resin composition containing a thermoplastic resin having a nitrile group. A specific example is a film of a resin composition containing an alternating copolymer of isobutylene and N-methylmaleimide and an acrylonitrile / styrene copolymer. As the film, a film composed of a mixed extruded product of a resin composition or the like can be used.
[0089]
A transparent substrate that can be particularly preferably used in view of polarization characteristics and durability is a triacetyl cellulose film whose surface has been saponified with an alkali or the like. Although the thickness of the transparent substrate 1 can be determined as appropriate, it is generally about 10 to 500 μm in view of strength, workability such as handleability, and thin layer property. In particular, 20 to 300 μm is preferable, and 30 to 200 μm is more preferable.
[0090]
Further, it is preferable that the transparent protective film has as little coloring as possible. Therefore, Rth = [(nx + ny) / 2−nz] · d (where nx and ny are the main refractive indices in the film plane, nz is the refractive index in the film thickness direction, and d is the film thickness). A protective film having a retardation value in the film thickness direction of -90 nm to +75 nm is preferably used. By using a film having a retardation value (Rth) in the thickness direction of -90 nm to +75 nm, coloring (optical coloring) of the polarizing plate caused by the protective film can be almost eliminated. The thickness direction retardation value (Rth) is more preferably -80 nm to +60 nm, and particularly preferably -70 nm to +45 nm.
[0091]
As the transparent protective film, a transparent protective film made of the same polymer material on both sides may be used, or a transparent protective film made of a different polymer material or the like may be used.
[0092]
The surface of the transparent protective film on which the polarizer is not adhered may be subjected to a hard coat layer, an antireflection treatment, a treatment for preventing sticking, and a treatment for diffusion or antiglare.
[0093]
The hard coat treatment is performed for the purpose of preventing scratches on the surface of the polarizing plate, for example, by applying a suitable ultraviolet-curable resin such as an acrylic resin or a silicone resin to a cured film having excellent hardness and sliding properties, etc., as a transparent protective film. It can be formed by a method of adding to the surface of. The anti-reflection treatment is performed for the purpose of preventing reflection of external light on the polarizing plate surface, and can be achieved by forming an anti-reflection film or the like according to the related art. In addition, the anti-sticking treatment is performed for the purpose of preventing adhesion to an adjacent layer.
[0094]
The anti-glare treatment is performed for the purpose of preventing external light from being reflected on the surface of the polarizing plate and hindering the visibility of light transmitted through the polarizing plate, and is, for example, a roughening method using a sand blast method or an embossing method. The transparent protective film can be formed by giving a fine uneven structure to the surface of the transparent protective film by an appropriate method such as a method of mixing transparent fine particles or the like. As the fine particles to be contained in the formation of the surface fine uneven structure, for example, a conductive material composed of silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide and the like having an average particle size of 0.5 to 50 μm. Transparent fine particles such as inorganic fine particles that may be used and organic fine particles made of a crosslinked or uncrosslinked polymer or the like are used. When forming the fine surface unevenness structure, the amount of the fine particles to be used is generally about 2 to 50 parts by weight, preferably 5 to 25 parts by weight, per 100 parts by weight of the transparent resin forming the fine surface unevenness structure. The anti-glare layer may also serve as a diffusion layer (such as a viewing angle expanding function) for diffusing light transmitted through the polarizing plate to increase the viewing angle or the like.
[0095]
The anti-reflection layer, anti-sticking layer, diffusion layer, anti-glare layer and the like can be provided on the transparent protective film itself, or can be provided as an optical layer separately from the transparent protective layer.
[0096]
The lamination of the linear polarizer, and further the lamination of various optical layers, can be performed by a method of sequentially laminating sequentially in a manufacturing process of a liquid crystal display device or the like. It is excellent in stability and assembling work, and has an advantage that a manufacturing process of a liquid crystal display device or the like can be improved. Appropriate bonding means such as an adhesive layer can be used for lamination. At the time of the bonding, the optical axes thereof can be set at an appropriate arrangement angle depending on the target retardation characteristic or the like.
[0097]
The above-described linear polarizer may be provided with an adhesive layer for bonding to another member such as a liquid crystal cell. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is not particularly limited, and for example, an acrylic polymer, a silicone-based polymer, a polyester, a polyurethane, a polyamide, a polyether, and a polymer having a fluorine-based or rubber-based polymer as a base polymer are appropriately selected. Can be used. In particular, an acrylic adhesive having excellent optical transparency, exhibiting appropriate wettability, cohesiveness and adhesive adhesive properties and having excellent weather resistance and heat resistance can be preferably used.
[0098]
In addition to the above, prevention of foaming and peeling phenomena due to moisture absorption, reduction of optical characteristics due to thermal expansion difference and the like, prevention of warpage of the liquid crystal cell, and, in view of the formability of a liquid crystal display device having high quality and excellent durability, etc. An adhesive layer having low moisture absorption and excellent heat resistance is preferred.
[0099]
The adhesive layer is, for example, a natural or synthetic resin, in particular, a tackifier resin, or a filler, a pigment, a colorant, an antioxidant, or the like made of glass fiber, glass beads, metal powder, other inorganic powder, and the like. May be added to the pressure-sensitive adhesive layer. In addition, an adhesive layer containing fine particles and exhibiting light diffusibility may be used.
[0100]
The attachment of the adhesive layer can be performed by an appropriate method. As an example thereof, for example, an adhesive solution of about 10 to 40% by weight is prepared by dissolving or dispersing a base polymer or a composition thereof in a solvent composed of a single solvent or a mixture of appropriate solvents such as toluene and ethyl acetate, A method in which it is directly attached on the polarizer by an appropriate developing method such as a casting method or a coating method, or a method in which an adhesive layer is formed on a separator according to the above and transferred to an optical element. Is raised. The pressure-sensitive adhesive layer can be provided as a superposed layer of different compositions or types of layers. The thickness of the pressure-sensitive adhesive layer can be appropriately determined depending on the purpose of use, adhesive strength, and the like, and is generally 1 to 500 µm, preferably 5 to 200 µm, particularly preferably 10 to 100 µm.
[0101]
A separator is temporarily attached to the exposed surface of the adhesive layer for the purpose of preventing contamination and the like until the adhesive layer is put to practical use and covered. This can prevent the adhesive layer from coming into contact with the adhesive layer in a normal handling state. Except for the above thickness conditions, the separator may be, for example, a plastic film, a rubber sheet, paper, cloth, a nonwoven fabric, a net, a foamed sheet or a metal foil, a suitable thin sheet such as a laminate thereof, or a silicone-based material as necessary. Appropriate conventional ones, such as those coated with an appropriate release agent such as a long-chain alkyl-based, fluorine-based, or molybdenum sulfide, may be used.
[0102]
Each layer such as an adhesive layer may be subjected to ultraviolet absorption by a method such as a method of treating with an ultraviolet absorber such as a salicylic acid ester compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, or a nickel complex compound. It may have a function.
[0103]
The linear polarizer of the present invention can be preferably used for forming various devices such as a liquid crystal display device. The formation of the liquid crystal display device can be performed according to a conventional method. That is, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell and an optical element, and an illumination system as necessary, and incorporating a drive circuit, and uses the linear polarizer of the present invention. There is no particular limitation except for the point, and it can be in accordance with the related art. As for the liquid crystal cell, any type such as TN type, STN type and π type can be used.
[0104]
Appropriate liquid crystal display devices such as a liquid crystal display device in which the linear polarizer is arranged on one or both sides of a liquid crystal cell, and a lighting system using a backlight or a reflector can be formed. In that case, the linear polarizer according to the present invention can be installed on one side or both sides of the liquid crystal cell. When linear polarizers are provided on both sides, they may be the same or different. Further, when forming the liquid crystal display device, for example, a suitable component such as a diffusion plate, an anti-glare layer, an antireflection film, a protection plate, a prism array, a lens array sheet, a light diffusion plate, a backlight, etc. Two or more layers can be arranged.
[0105]
【Example】
Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.
[0106]
Production Example 1
In a four-necked flask equipped with a mechanical stirrer, a nitrogen inlet tube, a cooling tube and a rubber septum, the following formula 4:
Embedded image

Of a nematic liquid crystal monomer (37 g) of the following formula:
Embedded image

Of a chiral monomer (13 g) (molar ratio of monomer, chemical formula 4: chemical formula 5 = 75: 25) and anisole (283 g) were dissolved to dissolve the liquid crystal monomer mixture, and then nitrogen was added to the system for 2 hours. The sink was replaced. To the mixture was added azobisisobutyronitrile (0.5 g) as an initiator under a nitrogen stream, followed by polymerization at 70 ° C. for 8 hours. Methanol was added to the mixture, followed by reprecipitation purification twice to obtain a cholesteric liquid crystal polymer (liquid crystal transition temperature: 84 ° C.). The liquid crystal transition temperature was measured using a hot stage FP82HT (manufactured by METTLER TOLEDO) while observing with a polarizing microscope (× 50) while heating at a rate of 1 ° C./min.
[0107]
Production Example 2
Production Example 1 is the same as Production Example 1 except that a liquid crystal monomer mixture (monomer molar ratio, chemical formula 4: chemical formula 5 = 85:15) of a nematic liquid crystal monomer (42 g) and a chiral monomer (8 g) was used. As a result, a cholesteric liquid crystal polymer (liquid crystal transition temperature: 88 ° C.) was obtained.
[0108]
Production Example 3
Octadecyl acrylate (10 g) and dimethylacetamide (56 g) were added to a four-necked port equipped with a mechanical stirrer, a nitrogen inlet tube, a cooling tube and a rubber septum, and 2,2'-bipyridine (2.6 g) was added thereto. Nitrogen was passed through the system for 2 hours to replace the system. Under a nitrogen stream, bromide steel (0.80 g) and a monofunctional initiator (ethyl 2-bromo-isobutyrate, 1.08 g) were added to initiate polymerization, and polymerization was performed at 80 ° C. for 2 hours under a nitrogen stream. did.
[0109]
Separately, a liquid crystal monomer mixture of a nematic liquid crystal monomer (30 g) shown in Chemical Formula 4 and a chiral monomer (10 g) shown in Chemical Formula 5 in 227 g of dimethylacetamide (molar ratio of monomers, Chemical Formula 4: Chemical Formula 5 = 75: 25) Is heated and dissolved, and nitrogen is bubbled for 2 hours to prepare a liquid crystal monomer mixture solution having a concentration of 15%.
[0110]
After confirming that the polymerization rate of octadecyl acrylate is 80% by weight or more, the prepared liquid crystal monomer mixture solution was added from a rubber septum with a syringe, and polymerized at 80 ° C. for 3 hours and further at 90 ° C. for 30 hours. did. Methanol was added to the mixture, followed by reprecipitation purification twice to obtain a cholesteric liquid crystal polymer (liquid crystal transition temperature: 75 ° C.).
[0111]
Production Example 4
In Production Example 3, octadecyl methacrylate was used in place of octadecyl acrylate, and a liquid crystal monomer mixture (molar ratio of monomer, 4 g) of a nematic liquid crystal monomer (34 g) represented by Chemical Formula 4 and a chiral monomer (6 g) represented by Chemical Formula 5 was used. Cholesteric liquid crystal polymer (liquid crystal transition temperature: 76 ° C.) was obtained in the same manner as in Production Example 3 except that Compound No. 5 = 85: 15) was used.
[0112]
Example 1
(1) Preparation of Cholesteric Liquid Crystal Film The cholesteric liquid crystal polymer obtained in Production Example 1 and the cholesteric liquid crystal polymer obtained in Production Example 4 were mixed at a weight ratio of 50:50, and dissolved in cyclohexanone to obtain a 20% by weight solution. It was created. A glass plate is spin-coated with an aqueous solution of polyvinyl alcohol to form an alignment film, and the surface is rubbed. Then, the cholesteric liquid crystal polymer solution is spin-coated to a coating thickness (dry thickness) of 1.5 μm, After leaving it to stand at room temperature and room humidity for 30 minutes and air-drying, it was heated at 160 ° C. for 4 minutes for orientation to obtain a cholesteric liquid crystal film.
[0113]
FIG. 1 shows a polarizing microscope photograph (× 50) of the obtained cholesteric liquid crystal film. When the polarizing plate was rotated and observed, the continuous phase and the separation layer were changed uniformly and uniformly, and the phase separation structure was confirmed.
[0114]
The cholesteric liquid crystal film had minute regions with different twist pitch lengths, the continuous phase twist pitch length was 370 nm, and the separation layer twist pitch length was 280 nm. The twist pitch length is measured by cross-sectional imaging using a TEM (transmission electron microscope).
[0115]
The selective reflection band was 400 to 660 nm. The reflection bandwidth is obtained by measuring the reflection spectrum of a broadband cholesteric liquid crystal film with a spectrophotometer (manufactured by Otsuka Electronics Co., Ltd., instantaneous multi-photometry system MCPD-2000), and has a reflection band having half the maximum reflectance. And
[0116]
(2) Production of Linear Polarizer, etc. Three cholesteric liquid crystal films obtained in the above (1) were laminated using an isocyanate-based adhesive (2 μm in thickness). The reflectance of the obtained laminated film was improved by 8%.
[0117]
In addition, a Nitto Denko λ / 4 plate (made of polycarbonate) was laminated on this laminated film with an adhesive (25 μm) to obtain a linear polarizer (reflective polarizer). A polarizing plate (TEG1465DU) manufactured by Nitto Denko was laminated with the transmission axis aligned with this linear polarizer to obtain a polarizing plate with a reflective polarizer. This was arranged as a lower polarizing plate of a liquid crystal display device, and the luminance when the backlight was turned on was measured. It was confirmed that the brightness increased about 1.2 times as compared with the unprocessed portion. The measurement of the luminance was performed by Ez-Contrast manufactured by ELDIM.
[0118]
Example 2
(1) Preparation of Cholesteric Liquid Crystal Film The cholesteric liquid crystal polymer obtained in Production Example 2 and the cholesteric liquid crystal polymer obtained in Production Example 3 were mixed at a weight ratio of 50:50, and dissolved in cyclohexanone to obtain a 20% by weight solution. It was created. After rubbing the surface of a biaxially stretched polyethylene terephthalate film (manufactured by Toray Co., Ltd., having a thickness of 38 μm), the cholesteric liquid crystal polymer solution is applied with a wire bar to a coating thickness (dry thickness) of 2 μm. , And air-dried at 160 ° C. for 4 minutes to obtain a cholesteric liquid crystal film.
[0119]
A polarizing microscope photograph (× 50) of the obtained cholesteric liquid crystal film was similar to FIG. When the polarizing plate was rotated and observed, the continuous phase and the separation layer were changed uniformly and uniformly, and the phase separation structure was confirmed.
[0120]
The cholesteric liquid crystal film had minute regions with different twist pitch lengths, the continuous phase twist pitch length was 360 nm, and the separation layer twist pitch length was 260 nm. The selective reflection band was 400-660 nm.
[0121]
(2) Production of Linear Polarizer, etc. The cholesteric liquid crystal film obtained in (1) above and the cholesteric liquid crystal film obtained in Example 1 (1) were laminated using an isocyanate-based adhesive (2 μm in thickness). The reflectance of the obtained laminated film was improved by 6%.
[0122]
In addition, a Nitto Denko λ / 4 plate (made of polycarbonate) was laminated on this laminated film with an adhesive (25 μm) to obtain a linear polarizer (reflective polarizer). A polarizing plate (TEG1465DU) manufactured by Nitto Denko was laminated with the transmission axis aligned with this linear polarizer to obtain a polarizing plate with a reflective polarizer. When the obtained polarizing plate with a reflective polarizer was used as a lower plate of a reflective liquid crystal display device, the cholesteric liquid crystal film (laminated film) according to the present invention functioned as a diffuse reflector having a fine texture. No defects such as interference, glare, and moire between the reflector and the liquid crystal pixel were generated due to the random structure by the phase separation structure.
[0123]
Comparative Example 1
The cholesteric liquid crystal polymer obtained in Production Example 1 was dissolved in cyclohexanone to prepare a 20% by weight solution. A cholesteric liquid crystal film was obtained in the same manner as in Example 1 except that this solution was used. No phase separation structure was observed in the obtained cholesteric liquid crystal film. The selective reflection band was 400-480 nm.
[0124]
Comparative Example 2
The cholesteric liquid crystal polymer obtained in Production Example 1 and the cholesteric liquid crystal polymer obtained in Production Example 2 were mixed at a weight ratio of 50:50, and dissolved in cyclohexanone to prepare a 20% by weight solution. A cholesteric liquid crystal film was obtained in the same manner as in Example 1 except that this solution was used. No phase-separated structure was observed in the obtained cholesteric liquid crystal film. The selective reflection band was 430 to 530 nm.
[Brief description of the drawings]
FIG. 1 is a micrograph of an example.

Claims (12)

A step of applying a solution obtained by dissolving a cholesteric liquid crystal polymer in a solvent on an alignment substrate,
A step of aligning the cholesteric liquid crystal polymer such that the cholesteric spiral axis is perpendicular to the alignment substrate surface, and
A method for producing a cholesteric liquid crystal film having a step of drying and forming a film while maintaining a liquid crystal state by the alignment,
A method for producing a broadband cholesteric liquid crystal film, characterized by using, as the cholesteric liquid crystal polymer, a mixture of two or more cholesteric liquid crystal polymers that are incompatible in the absence of a solvent and have different twist pitch lengths. Two or more cholesteric liquid crystal polymers, each of which is a polymer obtained from a liquid crystal composition containing a polymerizable nematic agent (a) and a polymerizable chiral agent (b),
Each cholesteric liquid crystal polymer has a different composition ratio of the polymerizable nematic agent (a) and the polymerizable chiral agent (b),
The method for producing a broadband cholesteric liquid crystal film according to claim 1, wherein a crystalline component is introduced as a block body into at least one of the cholesteric liquid crystal polymers. A broadband cholesteric liquid crystal film obtained by the production method according to claim 1 or 2, wherein the cholesteric liquid crystal film is:
Since the mixture of the cholesteric liquid crystal polymer is incompatible in the absence of a solvent as the cholesteric liquid crystal polymer, and the twist pitch length is different from two or more cholesteric liquid crystal polymers,
A broadband cholesteric liquid crystal film, wherein each cholesteric liquid crystal polymer forms a phase-separated structure, and immobilizes minute regions having different twist pitch lengths. A step of applying a liquid crystal composition containing a polymerizable nematic agent (a) and a polymerizable chiral agent (b) on an alignment substrate. The cholesteric spiral axis of the liquid crystal composition is perpendicular to the alignment substrate surface. Orienting to, and
A method for producing a cholesteric liquid crystal film having a step of forming a cured film by light or thermal polymerization while maintaining the liquid crystal state by the alignment,
A liquid crystal composition containing at least one polymerizable nematic agent (a) and at least two polymerizable chiral agents (b); or
A liquid crystal composition comprising at least two polymerizable nematic agents (a) and at least one polymerizable chiral agent (b),
A method for producing a broadband cholesteric liquid crystal film, wherein the liquid crystal composition is incompatible at the time of alignment and becomes a liquid crystal composition of two or more components having different twist pitch lengths. A broadband cholesteric liquid crystal film obtained by the production method according to claim 4, wherein the cholesteric liquid crystal film is:
Since the liquid crystal composition is incompatible at the time of alignment, and becomes a liquid crystal composition of two or more components having different twist pitch lengths,
A cholesteric liquid crystal film having a wide band, wherein a cholesteric liquid crystal polymer obtained from each of the liquid crystal compositions forms a phase-separated structure, and immobilizes minute regions having different twist pitch lengths. 6. A broadband cholesteric liquid crystal film according to claim 3, wherein the wideband cholesteric liquid crystal film according to claim 3 or 5 is laminated in two to six layers. The broadband cholesteric liquid crystal film according to claim 6 is manufactured by laminating the broadband cholesteric liquid crystal film as an upper layer on the broadband cholesteric liquid crystal film according to claim 3 or 5, which is a lower layer, by the manufacturing method according to claim 1, 2, or 4. In how to
A method for producing a broadband cholesteric liquid crystal film, comprising: performing a base treatment on a surface of a cholesteric liquid crystal film as a lower layer, and then laminating a cholesteric liquid crystal film as an upper layer. A circularly polarizing plate using the broadband cholesteric liquid crystal film according to claim 3. A linear polarizer that is obtained by laminating a λ / 4 plate on the circularly polarizing plate according to claim 8 and that can obtain linearly polarized light by transmission. A linear polarizer obtained by attaching an absorption polarizer to the transmission axis of the linear polarizer according to claim 9 so that the transmission axis direction thereof is aligned. An illumination device comprising a circular polarizer according to claim 8 and a linear polarizer according to claim 9 on the front side of a surface light source having a reflective layer on the back side. A liquid crystal display device comprising a liquid crystal cell on the light emitting side of the lighting device according to claim 11.

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