JP3875616B2 - Liquid crystal polymer - Google Patents

Description

（ただし、Ｒ^１は水素又はメチル基、ｍは１〜６の整数、Ｘ^１はＣＯ_２基又はＯＣＯ基であり、ｐ及びｑは１又は２で、かつｐ＋ｑ＝３を満足する。）
一般式（ｂ）：

（ただし、Ｒ^２は水素又はメチル基、ｎは１〜６の整数、Ｘ^２はＣＯ_２基又はＯＣＯ基、Ｘ^３は−ＣＯ−Ｒ^３又は−Ｒ^４であり、そのＲ^３は

Ｒ^４は

であり、Ｒ^５は下記のものである。）

【０００８】
【発明の効果】
前記の液晶ポリマーを用いて、良好なモノドメイン状態のグランジャン配向の膜を成膜性よく容易に形成でき、その配向処理も数分間等の短時間で達成できてガラス状態に安定して固定化でき、そのコレステリック相の螺旋ピッチも容易に制御できて可視光域で円偏光二色性を示す固化物も容易に形成でき、その固化物からなる薄くて軽く、耐久性や保存安定性に優れてピッチ等の配向状態が実用温度で変化しにくい円偏光二色性光学素子を効率よく形成することができる。
【０００９】
【発明の実施形態】
本発明の液晶ポリマーは、下記の一般式（ａ）で表わされるモノマー単位と、一般式（ｂ）で表わされるモノマー単位を含有する共重合体を成分とするものである。
【００１０】
一般式（ａ）：

（ただし、Ｒ^１は水素又はメチル基、ｍは１〜６の整数、Ｘ^１はＣＯ_２基又はＯＣＯ基であり、ｐ及びｑは１又は２で、かつｐ＋ｑ＝３を満足する。）
【００１１】
一般式（ｂ）：

（ただし、Ｒ^２は水素又はメチル基、ｎは１〜６の整数、Ｘ^２はＣＯ_２基又はＯＣＯ基、Ｘ^３は−ＣＯ−Ｒ^３又は−Ｒ^４であり、そのＲ^３は

Ｒ^４は

であり、Ｒ^５は下記のものである。）

【００１２】
前記の一般式（ａ）、一般式（ｂ）で表わされるモノマー単位を形成しうるアクリル系モノマーは、適宜な方法で合成することができる。ちなみに、式（ａ１）で表わされるアクリル系モノマーの合成例を下記に示した。
【００１３】

【００１４】
すなわち前記においては、先ずエチレンクロロヒドリンと４−ヒドロキシ安息香酸を、ヨウ化カリウムを触媒としてアルカリ水溶液中で加熱還流させてヒドロキシカルボン酸を得た後、それをアクリル酸又はメタクリル酸と脱水反応させて（メタ）アクリレートとし、その（メタ）アクリレートを４−シアノ−４'−ヒドロキシビフェニルでＤＣＣ（ジシクロヘキシルカルボジイミド）とＤＭＡＰ（ジメチルアミノピリジン）の存在下にエステル化することにより目的物の（ａ１）を得ることができる。
【００１５】
また、式（ｂ１）で表わされるアクリル系モノマーの合成例を下記に示した。

【００１６】
前記においては、先ずヒドロキシアルキルハライドと４−ヒドロキシ安息香酸を、ヨウ化カリウムを触媒としてアルカリ水溶液中で加熱還流させてヒドロキシカルボン酸を得た後、それをアクリル酸又はメタクリル酸と脱水反応させて（メタ）アクリレートとしその（メタ）アクリレートを、４位にＲ^３基含有のＣＯ基を有するフェノールでＤＣＣとＤＭＡＰの存在下にエステル化することにより目的物の（ｂ１）を得ることができる。
【００１７】
なお４位にＲ^３基含有のＣＯ基を有するフェノールは、例えば下記の如く、先ずクロロ蟻酸メチルと４−ヒドロキシ安息香酸をアルカリ水溶液中で反応させてカルボン酸とし、それをオキサリルクロリドで酸クロライドとした後、ピリジン／テトラヒドロフラン中でＨ−Ｒ^３と反応させてＲ^３基を導入し、ついでそれをアンモニア水で処理して保護基を除去することにより得ることができる。

【００１８】
上記した式（ｂ１）の合成において、最終工程で加える次の化合物

を、下記のものに代えることにより式（ｂ２）で表されるアクリル系モノマーを得ることができる。

【００１９】
すなわち、ヒドロキシカルボン酸を（メタ）アクリル酸と脱水反応させて（メタ）アクリレートとした後、その（メタ）アクリレートを４位に不斉炭素基を有するフェノールでＤＣＣとＤＭＡＰの存在下にエステル化することにより目的物の（ｂ２）を得ることができる。
【００２０】
なお４位に不斉炭素基を有するフェノールは、例えば下記の如く、４−ヒドロキシベンズアルデヒドと（Ｓ）−（−）−１−フェニルエチルアミンをトルエン中で共沸脱水することにより得ることができる。

【００２１】
従って一般式（ａ）、一般式（ｂ）で表わされるモノマー単位を形成しうる他のアクリル系モノマーも、目的の導入基を有する適宜な原料を用いて上記に準じて合成することができる。
【００２２】
光学素子の形成に用いうる液晶ポリマーは、上記した一般式（ａ）で表わされるモノマー単位の１種又は２種以上と、一般式（ｂ）で表わされるモノマー単位の１種又は２種以上とが共重合したものである。その共重合割合は、一般式（ｂ）で表わされるモノマー単位の含有率が過多では液晶性に乏しくなり、過少ではコレステリック液晶性に乏しくなることより、一般式（ａ）で表わされるモノマー単位６０〜９５重量％、一般式（ｂ）で表わされるモノマー単位４０〜５重量％が好ましい。
【００２３】
共重合体の分子量は、過少では成膜性に乏しくなり、過多では液晶としての配向性、モノドメイン化に乏しくなって均一な配向状態を形成しにくくなることより、重量平均分子量に基づき２千〜１０万、就中２．５千〜５万が好ましい。
【００２４】
共重合体の調製は、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、就中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。
【００２５】
共重合体は、その一般式（ｂ）で表わされるモノマー単位の含有率に基づいてコレステリック液晶のピッチが変化する。図１、図２に当該含有率と円偏光二色性を示す中心波長との関係を例示した。なお図１におけるグラフは、共重合体のモノマー成分に後記実施例における化学式で表わされる（ａ２）と（ｂ３）を、図２の場合は（ａ２）と（ｂ６）を用いたものである。円偏光二色性を示す波長は、当該ピッチで決定されることより、一般式（ｂ）で表わされるモノマー単位の含有率の制御で円偏光二色性を示す波長を調節することができる。従って後記する実施例の如く、可視光域の光に対して円偏光二色性を示す光学素子も容易に得ることができる。
【００２６】
共重合体は、その１種、又は２種以上を混合して光学素子の形成に用いることができる。円偏光二色性を示す波長域の異なる２種以上の共重合体を混合することによっても、円偏光二色性を示す波長域を調節することができる。本発明においては、得られる光学素子の耐久性や、ピッチ等の配向特性の実用時における温度変化等に対する安定性、ないし無変化性などの点よりガラス転移温度が８０℃以上の液晶ポリマーとしたものが光学素子の形成に好ましく用いうる。
【００２７】
なお本発明においては、上記した一般式（ａ）又は一般式（ｂ）で表わされるモノマー単位の１種又は２種以上からなる、その一般式に基づいたホモ型ポリマーを一般式（ａ）系のポリマーと一般式（ｂ）系のポリマーとの混合系の液晶ポリマーとして光学素子の形成に用いることもできる。その混合割合や分子量等については上記した共重合体に準じることができる。
【００２８】
円偏光二色性を示す光学素子の形成は、従来の配向処理に準じた方法で行いうる。ちなみにその例としては、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配向膜を形成してそれをレーヨン布等でラビング処理した後、その上に液晶ポリマーを展開してガラス転移温度以上、等方相転移温度未満に加熱し、液晶ポリマー分子がグランジャン配向した状態でガラス転移温度未満に冷却してガラス状態とし、当該配向が固定化された固化層を形成する方法などがあげられる。
【００２９】
前記の基板としては、例えばトリアセチルセルロースやポリビニルアルコール、ポリイミドやポリアリレート、ポリエステルやポリカーボネート、ポリスルホンやポリエーテルスルホン、エポキシ系樹脂の如きプラスチックからなるフイルム、あるいはガラス板などの適宜なものを用いうる。基板上に形成した液晶ポリマーの固化層は、基板との一体物としてそのまま光学素子に用いうるし、基板より剥離してフィルム等からなる光学素子として用いることもできる。
【００３０】
液晶ポリマーの展開は、加熱溶融方式によってもよいし、溶剤による溶液として展開することもできる。その溶剤としては、例えば塩化メチレンやシクロヘキサノン、トリクロロエチレンやテトラクロロエタン、Ｎ−メチルピロリドンやテトラヒドロフランなどの適宜なものを用いうる。展開は、バーコーターやスピナー、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。
【００３１】
形成する液晶ポリマーの固化層の厚さは、薄すぎると円偏光二色性を示しにくくなり、厚すぎると均一配向性に劣って円偏光二色性を示さなかったり、配向処理に長時間を要することなどより、０．５〜２０μm、就中１〜１０μmが好ましい。なお光学素子の形成に際しては、当該共重合体以外のポリマーや安定剤、可塑剤などの無機や有機、あるいは金属類などからなる種々の添加剤を必要に応じて配合することができる。
【００３２】
単層の液晶ポリマー固化層では通例、円偏光二色性を示す波長域に限界がある。その限界は通常、約１００nmの波長域に及ぶ広いものであるが、液晶表示装置等に適用する光学素子を得る場合には可視光の全域で円偏光二色性を示すことが望まれる。
【００３３】
前記の場合、異なる波長の光に対して円偏光二色性を示す液晶ポリマーの固化層を積層することで、円偏光二色性を示す波長域を拡大することができる。かかる積層化は、当該波長域の拡大のほか、斜め入射光の波長シフトに対処する点などにも有利である。積層化は、反射円偏光の中心波長が異なる組合せで２層以上積層することができる。積層に際しては、粘着剤などを用いて各界面での表面反射損の低減を図ることが好ましい。
【００３４】
ちなみに、反射円偏光の中心波長が３００〜９００nmの液晶ポリマー固化層を同じ方向の円偏光を反射する組合せで、かつ選択反射の中心波長が異なる、就中それぞれ５０nm以上異なる組合せで用いて、その２〜６種類を積層することで広い波長域で円偏光二色性を示す光学素子を形成することができる。なお同じ方向の円偏光を反射するものの組合せとする点は、各層で反射される円偏光の位相状態を揃えて各波長域で異なる偏光状態となることを防止し、反射層等を介して反射円偏光を再利用する場合にその効率の向上を目的とする。
【００３５】
光学素子は、その円偏光二色性に基づいて入射光を左右の円偏光に分離して透過光及び反射光として供給し、視野角の広さに優れ、視角変化に対する光学特性の変化が小さくて、斜め方向からも直接観察される直視型等の液晶表示装置などの種々の装置に好ましく適用することができる。特に反射層等を介して反射円偏光を再利用することで光の利用効率の向上を図ることができ、大面積化等も容易であることより液晶表示装置等におけるバックライトシステムなどとして好ましく用いうる。
【００３６】
【実施例】
実施例１

【００３７】
前記の化学式（ａ２）で表わしたモノマー３３．９重量部（８２ミリモル）と化学式（ｂ３）で表わしたモノマー９．１６重量部（１８ミリモル）をテトラヒドロフラン４３０mlに加熱溶解させ、５５〜６０℃に安定させて反応器内部を窒素ガスで置換し、酸素不存在下にアゾビスイソブチロニトリル０．５重量部を溶解したテトラヒドロフラン溶液５mlを滴下して６時間重合処理し、その反応液をジエチルエーテル３０００ml中に撹拌下に徐々に注いで白色ポリマーの沈殿物を得、それを遠心分離後乾燥してさらに２回、再沈精製し重量平均分子量７０００の共重合体を得た。この共重合体は、ガラス転移温度が８８℃で、等方相転移温度が２２５℃であり、その間の温度でコレステリック構造を示すものであった。
【００３８】
厚さ５０μmのトリアセチルセルロースフィルムに厚さ約０．１μmのポリビニルアルコール層を設け、それをレーヨン布でラビング処理し、その処理面に前記共重合体の１０重量％塩化メチレン溶液をバーコーターにて塗工し、乾燥後１４０℃で１５分間加熱配向処理して室温にて放冷して液晶ポリマーの配向をガラス状態に固定化した。この液晶ポリマーの厚さは２μmであり、トリアセチルセルロースフィルムとの一体物からなるフィルム状の光学素子は、鏡面的に青色光を反射する円偏光二色性を示し、その反射光は波長４１０〜４８５nmの左円偏光であった。なお当該光学素子の透過特性を図３に示した。
【００３９】
実施例２
化学式（ａ２）のモノマー３６．３重量部（８８ミリモル）、化学式（ｂ３）のモノマー６．１１重量部（１２ミリモル）の割合で用いたほかは実施例１に準じて重量平均分子量７５００の共重合体を得、光学素子を得た。この共重合体は、ガラス転移温度が９２℃で、等方相転移温度が２４０℃であり、その間の温度でコレステリック構造を示すものであった。また光学素子は、鏡面的に赤色光を反射する円偏光二色性を示し、その反射光は波長５８０〜６９５nmの左円偏光であった。なお当該光学素子の透過特性を図４に示した。
【００４０】
実施例３
実施例１及び実施例２に準じて得た共重合体を０．４７／０．５３（実施例１／実施例２）の比率で混合し、それを用いて実施例１に準じ光学素子を得た。この混合系の液晶ポリマーからなる光学素子は、鏡面的に緑色光を反射する円偏光二色性を示し、その反射光は波長４８０〜５８５nmの左円偏光であった。なお当該光学素子の透過特性を図５に示した。
【００４１】
実施例４

【００４２】
化学式（ａ２）のモノマー１６．５重量部（４０ミリモル）、前記の化学式（ａ３）のモノマー１７．１重量部（４０ミリモル）、及び（ｂ４）のモノマー９．１８重量部（２０ミリモル）の割合で用いたほかは実施例１に準じて重量平均分子量１１５００の共重合体を得た。この共重合体は、ガラス転移温度が１０５℃で、等方相転移温度が２３８℃であり、その間の温度でコレステリック構造を示すものであった。
【００４３】
一方、前記の共重合体を用いて実施例１に準じ１５０℃、１５分間の配向処理条件で厚さ３μmの液晶ポリマー固化層を形成して光学素子を得た。この光学素子は、鏡面的に赤黄色光を反射する円偏光二色性を示し、その反射光は波長５６５〜６７５nmの右円偏光であった。なお、当該光学素子の透過特性を図６に示した。
【００４４】
実施例５
下記の化学式（ａ４）のモノマー３６．３重量部（８５ミリモル）、及び（ｂ５）のモノマー９．０９重量部（１５ミリモル）の割合で用いたほかは実施例１に準じて重量平均分子量２１０００の共重合体を得た。この共重合体は、ガラス転移温度が９５℃で、等方相転移温度が２１５℃であり、その間の温度でコレステリック構造を示すものであった。
【００４５】

【００４６】
一方、前記の共重合体を用いて実施例１に準じ厚さ５μmの液晶ポリマー固化層を形成して光学素子を得た。この光学素子は、鏡面的に赤色光を反射する円偏光二色性を示し、その反射光は波長５９０〜６９５nmの右円偏光であった。なお、当該光学素子の透過特性を図７に示した。
【００４７】
実施例６
実施例１，２，３に準じて得た光学素子をアクリル系粘着層を介し積層して、波長４１０〜６９０nmの範囲で円偏光二色性を示す光学素子を得た。この光学素子の透過特性を図８に示した。
【００４８】
前記の光学素子に、ポリカーボネートからなる２枚の延伸フィルムの積層体からなる１／４波長板をアクリル系粘着層を介し積層し、それに自然光を入射させたところ、ＮＢＳ方式に基づく色変化△ａｂは３で、非常に小さいものであった。また、この１／４波長板付設の光学素子を８０℃、１０００時間の加熱試験、又は６０℃、９０％ＲＨ、１０００時間の湿熱試験に供したところ、いずれの試験においても光学特性や外観など変化が殆ど認められず、耐久性に優れるものであった。
【００４９】
実施例７

【００５０】
上記化学式（ａ２）で表わしたモノマー３１．８重量部（７７ミリモル）と前記の化学式（ｂ６）で表わしたモノマー１０．２重量部（２３ミリモル）をテトラヒドロフラン４１５mlに加熱溶解させたほかは実施例１に準じて、重量平均分子量７３００、ガラス転移温度８５℃、等方相転移温度２１５℃で、その間の温度でコレステリック構造を示す共重合体を得、それを用いて実施例１に準じ、１５０℃で５分間加熱配向処理する方式で、鏡面的に青色光を反射する円偏光二色性を示し、反射光の波長が４１０〜４８５nmの左円偏光である光学素子を得た。その光学素子の透過特性を図９に示した。
【００５１】
実施例８
化学式（ａ２）のモノマー３５．５重量部（８６ミリモル）、化学式（ｂ６）のモノマー６．２０重量部（１４ミリモル）の割合で用いたほかは実施例７に準じて重量平均分子量７１００の共重合体を得、光学素子を得た。この共重合体は、ガラス転移温度が８９℃で、等方相転移温度が２３０℃であり、その間の温度でコレステリック構造を示すものであった。また光学素子は、鏡面的に赤色光を反射する円偏光二色性を示し、その反射光は波長５８０〜６９５nmの左円偏光であった。その光学素子の透過特性を図１０に示した。
【００５２】
実施例９
実施例７及び実施例８に準じて得た共重合体を０．４７／０．５３（実施例７／実施例８）の比率で混合し、それを用いて実施例７に準じ光学素子を得た。この混合系の液晶ポリマーからなる光学素子は、鏡面的に緑色光を反射する円偏光二色性を示し、その反射光は波長４８０〜５８５nmの左円偏光であった。その光学素子の透過特性を図１１に示した。
【００５３】
実施例１０
実施例７，８，９に準じて得た光学素子をアクリル系粘着層を介し積層して、波長４１０〜６９０nmの範囲で円偏光二色性を示す光学素子を得た。この光学素子の透過特性を図１２に示した。
【００５４】
前記の光学素子に、ポリカーボネートからなる２枚の延伸フィルムの積層体からなる１／４波長板をアクリル系粘着層を介し積層し、それに自然光を入射させたところ、ＮＢＳ方式に基づく色変化△ａｂは３で、非常に小さいものであった。また、この１／４波長板付設の光学素子を８０℃、１０００時間の加熱試験、又は６０℃、９０％ＲＨ、１０００時間の湿熱試験に供したところ、いずれの試験においても光学特性や外観など変化が殆ど認められず、耐久性に優れるものであった。
【００５５】
比較例
下記の化学式（Ｃ）のモノマー３９．０重量部（８０ミリモル）、及び（Ｄ）のモノマー９．１４重量部（２０ミリモル）の割合で用いたほかは実施例１に準じて重量平均分子量１８０００の共重合体を得た。この共重合体は、ガラス転移温度が７１℃で、等方相転移温度が２０５℃であり、その間の温度でコレステリック構造を示すものであった。

【００５６】
一方、前記の共重合体を用いて実施例１に準じ液晶ポリマー固化層の形成を試みたが、均一配向物を得ることができず、厚さ３μmの液晶ポリマー層も鏡面的な反射は示さず、拡散反射を示して円偏光二色性は不充分なものであった。この光学素子の透過特性を図１３に示した。なお当該拡散反射は、均一なグランジャン配向が形成されていないためであると考えられる。
【図面の簡単な説明】
【図１】一般式（ｂ）のモノマー単位の含有率と円偏光二色性を示す中心波長との関係を示したグラフ
【図２】他の、一般式（ｂ）のモノマー単位の含有率と円偏光二色性を示す中心波長との関係を示したグラフ
【図３】透過特性を示したグラフ
【図４】他の透過特性を示したグラフ
【図５】さらに他の透過特性を示したグラフ
【図６】さらに他の透過特性を示したグラフ
【図７】さらに他の透過特性を示したグラフ
【図８】さらに他の透過特性を示したグラフ
【図９】さらに他の透過特性を示したグラフ
【図１０】さらに他の透過特性を示したグラフ
【図１１】さらに他の透過特性を示したグラフ
【図１２】さらに他の透過特性を示したグラフ
【図１３】さらに他の透過特性を示したグラフ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid crystal polymer suitable for forming a circular dichroic optical element.
[0002]
[Background]
Conventionally, there has been known a circular dichroic optical element in which a liquid cholesteric liquid crystal composed of a low molecular weight substance is sealed in an aligned state between substrates such as glass. This is a liquid crystal molecule in which the spiral axis of the liquid crystal molecules is aligned in the Grandjean direction perpendicular to the optical element, and light in a certain wavelength range is selected from natural light incident parallel to the spiral axis (incident angle of 0 degrees). Reflects as right (or left) circularly polarized light and transmits the rest as left (or right) circularly polarized light. The wavelength λ of the reflected light is determined by the formula: λ = n · p (where n is the average refractive index of the liquid crystal and p is the helical pitch of the cholesteric phase), and the left and right of the reflected circularly polarized light are the cholesteric phase It is determined by the spiral state and coincides with the spiral turning direction.
[0003]
The circular dichroic optical element described above may be able to use reflected light separated from transmitted light, and causes absorption loss by adsorbing a dichroic dye or the like to a stretched film such as polyvinyl alcohol. Expected to be an alternative to polarizing plates.
[0004]
However, since the conventional circular dichroic optical element needs to be used in combination with the substrate for sandwiching the liquid cholesteric liquid crystal as described above, it becomes thick and heavy, and the liquid crystal display device is light and thin. There was a problem that obstructed. There is also a problem that the orientation state of the cholesteric liquid crystal, for example, the pitch easily changes with temperature.
[0005]
On the other hand, although a cholesteric liquid crystal polymer is also known (Japanese Patent Laid-Open No. 55-21479, US Pat. No. 5,332,522), a solidified product such as a film having a good orientation state such as a low molecular weight substance is obtained. It takes a long time such as several hours for the alignment treatment, or the glass transition temperature is low and the durability is insufficient and the practicality is poor. It was difficult to obtain a circular dichroic optical element made of
[0006]
[Technical Problem of the Invention]
The present invention is excellent in film formability and can form a Grandjan orientation in a good monodomain state, and can achieve the orientation treatment in a short time such as several minutes, and can be stably fixed in a glass state, and can be durable. A liquid crystal capable of forming a circular dichroic optical element with excellent storage stability, easily controlling the helical pitch of the cholesteric phase, and forming a solidified product that is thin, light, and whose orientation state such as pitch is difficult to change at practical temperatures. An object is to obtain a polymer.
[0007]
[Means for solving problems]
The present invention provides a liquid crystal polymer comprising as a component a monomer unit represented by the following general formula (a) and a copolymer containing the monomer unit represented by the general formula (b). is there.
General formula (a):

(However, R ¹ is hydrogen or a methyl group, m is an integer of 1 to 6, X ¹ is a CO ₂ group or an OCO group, p and q are 1 or 2, and p + q = 3 is satisfied.)
General formula (b):

(Wherein, ^{R 2} is hydrogen or a methyl group, n represents an integer of 1 to 6, ^{X 2} is CO ₂ group or OCO group, ^{X 3} is ^{-CO-R 3} or -R ^4, the ^{R 3} is

R ⁴ is

And R ⁵ is: )

[0008]
【The invention's effect】
Using the above-mentioned liquid crystal polymer, it is possible to easily form a good monodomain Grandian alignment film with good film formability, and the alignment treatment can be achieved in a short time such as several minutes, and is stably fixed in the glass state. The helical pitch of the cholesteric phase can be easily controlled, and a solidified product exhibiting circular dichroism in the visible light region can be easily formed, and the thin and light product of the solidified product is durable and storage stable. It is possible to efficiently form a circular dichroic optical element in which the alignment state such as pitch is hardly changed at a practical temperature.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The liquid crystal polymer of the present invention comprises a copolymer containing a monomer unit represented by the following general formula (a) and a monomer unit represented by the general formula (b).
[0010]
General formula (a):

(However, R ¹ is hydrogen or a methyl group, m is an integer of 1 to 6, X ¹ is a CO ₂ group or an OCO group, p and q are 1 or 2, and p + q = 3 is satisfied.)
[0011]
General formula (b):

(Wherein, ^{R 2} is hydrogen or a methyl group, n represents an integer of 1 to 6, ^{X 2} is CO ₂ group or OCO group, ^{X 3} is ^{-CO-R 3} or -R ^4, the ^{R 3} is

R ⁴ is

And R ⁵ is: )

[0012]
The acrylic monomer capable of forming the monomer unit represented by the general formula (a) or the general formula (b) can be synthesized by an appropriate method. Incidentally, a synthesis example of an acrylic monomer represented by the formula (a1) is shown below.
[0013]

[0014]
That is, in the above, first, ethylene chlorohydrin and 4-hydroxybenzoic acid are heated to reflux in an alkaline aqueous solution using potassium iodide as a catalyst to obtain a hydroxycarboxylic acid, and then dehydrated with acrylic acid or methacrylic acid. (Meth) acrylate, and the (meth) acrylate is esterified with 4-cyano-4′-hydroxybiphenyl in the presence of DCC (dicyclohexylcarbodiimide) and DMAP (dimethylaminopyridine). ) Can be obtained.
[0015]
Moreover, the synthesis example of the acryl-type monomer represented by Formula (b1) was shown below.

[0016]
In the above, first, hydroxyalkyl halide and 4-hydroxybenzoic acid are heated and refluxed in an alkaline aqueous solution using potassium iodide as a catalyst to obtain hydroxycarboxylic acid, and then dehydrated with acrylic acid or methacrylic acid. The target product (b1) can be obtained by esterifying (meth) acrylate with phenol having an R ³ group-containing CO group at the 4-position in the presence of DCC and DMAP.
[0017]
For example, the phenol having an R ³ group-containing CO group at the 4-position is prepared by reacting methyl chloroformate and 4-hydroxybenzoic acid in an aqueous alkaline solution to form a carboxylic acid, which is then converted to acid chloride with oxalyl chloride. And then reacting with HR ³ in pyridine / tetrahydrofuran to introduce the R ³ group, which is then treated with aqueous ammonia to remove the protecting group.

[0018]
In the synthesis of the above formula (b1), the following compound added in the final step

Can be replaced with the following to obtain an acrylic monomer represented by the formula (b2).

[0019]
That is, after dehydration reaction of hydroxycarboxylic acid with (meth) acrylic acid to give (meth) acrylate, the (meth) acrylate is esterified with phenol having an asymmetric carbon group at the 4-position in the presence of DCC and DMAP. By doing so, the target product (b2) can be obtained.
[0020]
A phenol having an asymmetric carbon group at the 4-position can be obtained, for example, by azeotropic dehydration of 4-hydroxybenzaldehyde and (S)-(−)-1-phenylethylamine in toluene as described below.

[0021]
Accordingly, other acrylic monomers that can form the monomer units represented by the general formula (a) and the general formula (b) can also be synthesized according to the above using appropriate raw materials having a target introduction group.
[0022]
The liquid crystal polymer that can be used for forming the optical element includes one or more of the monomer units represented by the general formula (a) and one or more of the monomer units represented by the general formula (b). Are copolymerized. The copolymerization ratio is such that when the content of the monomer unit represented by the general formula (b) is excessive, the liquid crystallinity is poor, and when the content is too small, the cholesteric liquid crystallinity is poor, whereby the monomer unit 60 represented by the general formula (a) is obtained. The monomer unit represented by -95 wt% and the general formula (b) is preferably 40-5 wt%.
[0023]
If the molecular weight of the copolymer is too small, the film-forming property will be poor, and if it is too large, the orientation as a liquid crystal and monodomain formation will be poor, and it will be difficult to form a uniform alignment state. 100000 to 100,000, especially 25,000 to 50,000 are preferable.
[0024]
The copolymer can be prepared in accordance with a usual acrylic monomer polymerization method such as a radical polymerization method, a cationic polymerization method, or an anionic polymerization method. When applying the radical polymerization method, various polymerization initiators can be used. In particular, the decomposition temperature of azobisisobutyronitrile, benzoyl peroxide, etc. is not high and it is decomposed at an intermediate temperature that is not low. Those are preferably used.
[0025]
In the copolymer, the pitch of the cholesteric liquid crystal changes based on the content of the monomer unit represented by the general formula (b). FIG. 1 and FIG. 2 exemplify the relationship between the content rate and the center wavelength indicating circular dichroism. The graph in FIG. 1 is obtained by using (a2) and (b3) represented by the chemical formulas in Examples below as monomer components of the copolymer, and (a2) and (b6) in the case of FIG. Since the wavelength showing the circular dichroism is determined by the pitch, the wavelength showing the circular dichroism can be adjusted by controlling the content of the monomer unit represented by the general formula (b). Therefore, an optical element exhibiting circular dichroism with respect to light in the visible light range can be easily obtained as in the examples described later.
[0026]
The copolymer can be used for forming an optical element by mixing one or more of them. The wavelength region exhibiting circular dichroism can also be adjusted by mixing two or more copolymers having different wavelength regions exhibiting circular dichroism. In the present invention, the liquid crystal polymer has a glass transition temperature of 80 ° C. or higher in view of durability of the obtained optical element, stability of temperature and the like in practical use of orientation characteristics such as pitch, or no change. Can be preferably used to form an optical element.
[0027]
In the present invention, a homopolymer based on the general formula consisting of one or more of the monomer units represented by the general formula (a) or the general formula (b) is represented by the general formula (a) system. It can also be used for the formation of an optical element as a liquid crystal polymer of a mixed system of the above polymer and a polymer of the general formula (b). The mixing ratio, molecular weight, and the like can be based on the above-described copolymer.
[0028]
Formation of an optical element exhibiting circular dichroism can be performed by a method according to a conventional alignment treatment. As an example, an alignment film made of polyimide, polyvinyl alcohol, or the like is formed on a substrate, and it is rubbed with a rayon cloth. Examples of the method include heating to a temperature lower than the transition temperature, cooling to a temperature lower than the glass transition temperature in a state where the liquid crystal polymer molecules are aligned in the Grandjean state, and forming a solidified layer in which the alignment is fixed.
[0029]
As the substrate, for example, triacetylcellulose, polyvinyl alcohol, polyimide, polyarylate, polyester, polycarbonate, polysulfone, polyethersulfone, a film made of a plastic such as an epoxy resin, or an appropriate one such as a glass plate can be used. . The solidified layer of the liquid crystal polymer formed on the substrate can be used as it is for an optical element as an integral part of the substrate, or can be used as an optical element made of a film or the like by peeling off from the substrate.
[0030]
The liquid crystal polymer may be developed by a heat melting method or a solution using a solvent. As the solvent, for example, an appropriate solvent such as methylene chloride, cyclohexanone, trichloroethylene, tetrachloroethane, N-methylpyrrolidone, tetrahydrofuran or the like can be used. The development can be performed with an appropriate coating machine such as a bar coater, a spinner, or a roll coater.
[0031]
If the thickness of the solidified layer of the liquid crystal polymer to be formed is too thin, it will be difficult to exhibit circular dichroism, and if it is too thick, it will be inferior in uniform alignment and will not exhibit circular dichroism, or it may take a long time for the alignment treatment. In view of the necessity, 0.5 to 20 μm, especially 1 to 10 μm is preferable. In forming the optical element, various additives including polymers other than the copolymer, stabilizers, inorganics such as plasticizers, organics, and metals can be blended as necessary.
[0032]
In a single-layer liquid crystal polymer solidified layer, there is usually a limit in the wavelength region exhibiting circular dichroism. The limit is usually wide, covering a wavelength range of about 100 nm, but when obtaining an optical element applied to a liquid crystal display device or the like, it is desired to exhibit circular dichroism over the entire visible light range.
[0033]
In the above case, the wavelength region exhibiting circular dichroism can be expanded by laminating a solidified layer of a liquid crystal polymer exhibiting circular dichroism with respect to light of different wavelengths. Such layering is advantageous not only in expanding the wavelength range but also in dealing with the wavelength shift of obliquely incident light. In the lamination, two or more layers can be laminated in combinations with different center wavelengths of the reflected circularly polarized light. When laminating, it is preferable to reduce the surface reflection loss at each interface using an adhesive or the like.
[0034]
By the way, the liquid crystal polymer solidified layer having a central wavelength of reflected circularly polarized light of 300 to 900 nm is used in a combination that reflects circularly polarized light in the same direction, and the central wavelength of selective reflection is different. By laminating 2 to 6 types, an optical element exhibiting circular dichroism in a wide wavelength region can be formed. Note that the combination of those that reflect circularly polarized light in the same direction is that the phase state of circularly polarized light reflected by each layer is aligned to prevent different polarization states in each wavelength region, and reflected through a reflective layer, etc. The purpose is to improve the efficiency when circularly polarized light is reused.
[0035]
The optical element separates incident light into left and right circularly polarized light based on its circular dichroism and supplies it as transmitted light and reflected light, providing a wide viewing angle and small change in optical characteristics with respect to changes in viewing angle. Thus, the present invention can be preferably applied to various devices such as a direct-view type liquid crystal display device that can be directly observed from an oblique direction. In particular, it is possible to improve the light utilization efficiency by reusing the reflected circularly polarized light through the reflective layer, etc., and it is preferable to use it as a backlight system in a liquid crystal display device and the like because it is easy to increase the area. sell.
[0036]
【Example】
Example 1

[0037]
33.9 parts by weight (82 mmol) of the monomer represented by the chemical formula (a2) and 9.16 parts by weight (18 mmol) of the monomer represented by the chemical formula (b3) were dissolved by heating in 430 ml of tetrahydrofuran, and the temperature was increased to 55 to 60 ° C. The reactor was stabilized and the inside of the reactor was replaced with nitrogen gas. In the absence of oxygen, 5 ml of a tetrahydrofuran solution in which 0.5 part by weight of azobisisobutyronitrile was dissolved was added dropwise and polymerized for 6 hours. By gradually pouring the mixture into 3000 ml of ether with stirring, a white polymer precipitate was obtained, which was centrifuged and dried, and further purified by reprecipitation twice to obtain a copolymer having a weight average molecular weight of 7000. This copolymer had a glass transition temperature of 88 ° C. and an isotropic phase transition temperature of 225 ° C., and exhibited a cholesteric structure at temperatures in between.
[0038]
A polyvinyl alcohol layer having a thickness of about 0.1 μm is provided on a triacetyl cellulose film having a thickness of 50 μm, which is rubbed with a rayon cloth, and a 10 wt% methylene chloride solution of the copolymer is applied to the bar coater on the treated surface. After coating and drying, the film was heated at 140 ° C. for 15 minutes and allowed to cool at room temperature to fix the alignment of the liquid crystal polymer in the glass state. The liquid crystal polymer has a thickness of 2 μm, and the film-like optical element formed integrally with the triacetyl cellulose film exhibits circular dichroism that reflects blue light in a specular manner, and the reflected light has a wavelength of 410 Left circularly polarized light of ˜485 nm. The transmission characteristics of the optical element are shown in FIG.
[0039]
Example 2
Except for using 36.3 parts by weight (88 mmol) of the monomer of the chemical formula (a2) and 6.11 parts by weight (12 mmol) of the monomer of the chemical formula (b3), a common copolymer having a weight average molecular weight of 7500 was used. A polymer was obtained to obtain an optical element. This copolymer had a glass transition temperature of 92 ° C. and an isotropic phase transition temperature of 240 ° C., and exhibited a cholesteric structure at temperatures in between. The optical element exhibited circular dichroism that specularly reflects red light, and the reflected light was left circularly polarized light having a wavelength of 580 to 695 nm. The transmission characteristics of the optical element are shown in FIG.
[0040]
Example 3
The copolymer obtained according to Example 1 and Example 2 was mixed at a ratio of 0.47 / 0.53 (Example 1 / Example 2), and an optical element was prepared according to Example 1 using this. Obtained. The optical element made of this mixed liquid crystal polymer exhibited circular dichroism that specularly reflects green light, and the reflected light was left circularly polarized light having a wavelength of 480 to 585 nm. The transmission characteristics of the optical element are shown in FIG.
[0041]
Example 4

[0042]
16.5 parts by weight (40 mmol) of monomer of formula (a2), 17.1 parts by weight (40 mmol) of monomer of formula (a3) and 9.18 parts by weight (20 mmol) of monomer of (b4) A copolymer having a weight average molecular weight of 11,500 was obtained in the same manner as in Example 1 except that it was used in a proportion. This copolymer had a glass transition temperature of 105 ° C. and an isotropic phase transition temperature of 238 ° C., and exhibited a cholesteric structure at temperatures in between.
[0043]
On the other hand, a liquid crystal polymer solidified layer having a thickness of 3 μm was formed under the alignment treatment conditions at 150 ° C. for 15 minutes using the copolymer according to Example 1 to obtain an optical element. This optical element exhibited circular dichroism that specularly reflects red-yellow light, and the reflected light was right circularly polarized light having a wavelength of 565 to 675 nm. The transmission characteristics of the optical element are shown in FIG.
[0044]
Example 5
The weight average molecular weight of 21000 was the same as in Example 1 except that 36.3 parts by weight (85 mmol) of the monomer of the following chemical formula (a4) and 9.09 parts by weight (15 mmol) of the monomer of (b5) were used. The copolymer of was obtained. This copolymer had a glass transition temperature of 95 ° C. and an isotropic phase transition temperature of 215 ° C., and exhibited a cholesteric structure at temperatures in between.
[0045]

[0046]
On the other hand, a liquid crystal polymer solidified layer having a thickness of 5 μm was formed according to Example 1 using the above copolymer to obtain an optical element. This optical element exhibited circular dichroism that specularly reflects red light, and the reflected light was right circularly polarized light having a wavelength of 590 to 695 nm. The transmission characteristics of the optical element are shown in FIG.
[0047]
Example 6
Optical elements obtained according to Examples 1, 2, and 3 were laminated via an acrylic adhesive layer to obtain an optical element exhibiting circular dichroism in the wavelength range of 410 to 690 nm. The transmission characteristics of this optical element are shown in FIG.
[0048]
A quarter-wave plate made of a laminate of two stretched films made of polycarbonate was laminated on the optical element via an acrylic adhesive layer, and natural light was incident on it, resulting in a color change Δab based on the NBS method. Was 3, which was very small. Moreover, when this optical element with a quarter wavelength plate was subjected to a heating test at 80 ° C. for 1000 hours, or a wet heat test at 60 ° C., 90% RH, 1000 hours, the optical characteristics, appearance, etc. Almost no change was observed, and the durability was excellent.
[0049]
Example 7

[0050]
Except that 31.8 parts by weight (77 mmol) of the monomer represented by the above chemical formula (a2) and 10.2 parts by weight (23 mmol) of the monomer represented by the above chemical formula (b6) were heated and dissolved in 415 ml of tetrahydrofuran. According to 1, a copolymer having a weight average molecular weight of 7300, a glass transition temperature of 85 ° C. and an isotropic phase transition temperature of 215 ° C. and a temperature between them is obtained. An optical element having left circularly polarized light having a circular dichroism that reflects blue light in a specular manner and having a reflected light wavelength of 410 to 485 nm was obtained by heating and aligning at 5 ° C. for 5 minutes. The transmission characteristics of the optical element are shown in FIG.
[0051]
Example 8
A weight average molecular weight of 7100 was obtained in the same manner as in Example 7 except that the monomer was used in the ratio of 35.5 parts by weight (86 mmol) of the monomer of the chemical formula (a2) and 6.20 parts by weight (14 mmol) of the monomer of the chemical formula (b6). A polymer was obtained to obtain an optical element. This copolymer had a glass transition temperature of 89 ° C. and an isotropic phase transition temperature of 230 ° C., and exhibited a cholesteric structure at temperatures in between. The optical element exhibited circular dichroism that specularly reflects red light, and the reflected light was left circularly polarized light having a wavelength of 580 to 695 nm. The transmission characteristics of the optical element are shown in FIG.
[0052]
Example 9
The copolymer obtained in accordance with Example 7 and Example 8 was mixed at a ratio of 0.47 / 0.53 (Example 7 / Example 8), and an optical element was prepared in accordance with Example 7 using this. Obtained. The optical element made of this mixed liquid crystal polymer exhibited circular dichroism that specularly reflects green light, and the reflected light was left circularly polarized light having a wavelength of 480 to 585 nm. The transmission characteristics of the optical element are shown in FIG.
[0053]
Example 10
The optical elements obtained according to Examples 7, 8, and 9 were laminated via an acrylic adhesive layer to obtain an optical element exhibiting circular dichroism in the wavelength range of 410 to 690 nm. The transmission characteristics of this optical element are shown in FIG.
[0054]
When a quarter-wave plate made of a laminate of two stretched films made of polycarbonate was laminated on the optical element via an acrylic adhesive layer, and natural light was incident on it, the color change Δab based on the NBS method Was 3, which was very small. Moreover, when this optical element with a quarter wavelength plate was subjected to a heating test at 80 ° C. for 1000 hours, or a wet heat test at 60 ° C., 90% RH, 1000 hours, the optical characteristics, appearance, etc. Almost no change was observed, and the durability was excellent.
[0055]
Comparative Example A weight average according to Example 1 except that 39.0 parts by weight (80 mmol) of the monomer of the following chemical formula (C) and 9.14 parts by weight (20 mmol) of the monomer of (D) were used. A copolymer having a molecular weight of 18,000 was obtained. This copolymer had a glass transition temperature of 71 ° C. and an isotropic phase transition temperature of 205 ° C., and exhibited a cholesteric structure at temperatures in between.

[0056]
On the other hand, formation of a liquid crystal polymer solidified layer was attempted using the copolymer according to Example 1, but a uniform alignment product could not be obtained, and the liquid crystal polymer layer having a thickness of 3 μm also showed specular reflection. However, the circular dichroism was insufficient due to diffuse reflection. The transmission characteristics of this optical element are shown in FIG. The diffuse reflection is considered to be due to the fact that a uniform Grandjean orientation is not formed.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the content of monomer units of general formula (b) and the central wavelength indicating circular dichroism. FIG. 2 is the content of other monomer units of general formula (b). Graph showing the relationship between the center wavelength indicating circular dichroism and circular dichroism [FIG. 3] Graph showing transmission characteristics [FIG. 4] Graph showing other transmission characteristics [FIG. 5] Still showing other transmission characteristics Fig. 6 is a graph showing further transmission characteristics. Fig. 7 is a graph showing further transmission characteristics. Fig. 8 is a graph showing further transmission characteristics. Fig. 9 is another transmission characteristic. FIG. 10 is a graph showing other transmission characteristics. FIG. 11 is a graph showing other transmission characteristics. FIG. 12 is a graph showing other transmission characteristics. FIG. Graph showing transmission characteristics

Claims (4)

A liquid crystal polymer comprising, as components, a monomer unit represented by the following general formula (a) and a copolymer containing the monomer unit represented by the general formula (b).
General formula (a):

(However, R ¹ is hydrogen or a methyl group, m is an integer of 1 to 6, X ¹ is a CO ₂ group or an OCO group, p and q are 1 or 2, and p + q = 3 is satisfied.)
General formula (b):

(Wherein, ^{R 2} is hydrogen or a methyl group, n represents an integer of 1 to 6, ^{X 2} is CO ₂ group or OCO group, ^{X 3} is ^{-CO-R 3} or -R ^4, the ^{R 3} is

R ⁴ is

And R ⁵ is: )

2. The liquid crystal polymer according to claim 1, comprising as a component a copolymer composed of 60 to 95 wt% of the monomer unit represented by the general formula (a) and 40 to 5 wt% of the monomer unit represented by the general formula (b). 3. The liquid crystal polymer according to claim 1, wherein the liquid crystal polymer has a glass transition temperature of 80 ° C. or higher and exhibits a Grande-aligned cholesteric liquid crystal phase in a predetermined temperature range equal to or higher than the glass transition temperature. 4. The liquid crystal polymer according to claim 1 , wherein the liquid crystal polymer forms a solidified layer exhibiting circular dichroism with respect to light in a visible light region.

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